Ultra Low Sulfur Diesel 2010

Transcription

1 Ultra Low Sulfur Diesel 21

2 Advanced Refining Technologies - Hydroprocessing Catalysts from Chevron and Grace Davison Advanced Refining Technologies (ART), is the joint venture of Chevron Products Company and W. R. Grace & Co. s Grace Davison catalysts business unit, created to develop, market and sell a comprehensive line of state-of-the-art hydroprocessing catalysts. Since our formation in March 21, we have firmly established ourselves as a leading supplier of premium hydroprocessing catalysts and technical service to the petroleum refining industry worldwide. ART brings new standards of product innovation and customer service to the global refining industry by harnessing the technical expertise of both Chevron and Grace Davison in catalyst development and their broad experience in supporting refiners. With the combination of Grace Davison s material science, manufacturing, marketing and sales strength, and Chevron s extensive experience from operating its own refineries and leadership in design and process licensing, ART offers refiners one-stop access to hydroprocessing knowledge and technical service unparalleled in the industry. Product Overview Chart Crude Tower Naphtha Kerosene & Jet ART offers refiners the unique synergies derived from our parent joint venture partners being leaders in hydroprocessing catalyst technologies. Chevron, and now Chevron Lummus Global (CLG) represent over 35 years of experience designing and licensing RDS and VRDS units, as well as operating resid hydroprocessing and distillate hydrotreating units at Chevron refineries. Grace Davison has over 5 years of experience in extruding hydroprocessing catalysts. Leveraging the refining and hydroprocessing experience of Chevron with Grace Davison s expertise in specialty materials and catalyst technologies makes ART uniquely equipped to quickly commercialize and deliver innovative products to the dynamic hydroprocessing marketplace. To keep pace with the high demand for ART catalysts driven by heavy resid hydroprocessing applications and more stringent clean fuels standards, ART has expanded manufacturing capacity at its existing North American plants. ART acquired Orient Catalyst Company s (OCC) hydroprocessing catalyst technologies, and the HOP catalyst product line in 22; and obtained an ownership position in Kuwait Catalyst Company (KCC) which has manufactured HOP resid hydroprocessing catalysts under license since 21. ART s comprehensive line of hydroprocessing catalysts deliver maximum sulfur removal and upgrading for a wide range of feedstocks. ART offers hydroprocessing catalysts for the resid segment of the hydroprocessing market, including the fixed-bed Onstream Catalyst Replacement (OCR) resid process and ebullating bed applications, as well as a complete product line of premium catalysts for distillate hydrotreating of heavy VGO/DAO, diesel, kerosene and light naphtha applications. Diesel Hydrocracker Pretreat Vacuum Tower Coker Naphtha AT TM Series AT TM Series DX TM Series AT TM Series DX TM Series ICR Series FCC Pretreat ICR Series HOP Series GR Series LS TM Series HSLS TM Series StART TM Catalyst System AT Series SmART Catalyst System DX Series ApART TM Catalyst System AT, DX Series Fixed Bed Resid Fixed Bed Resid Ebullating Bed Resid for LC-Fining and H-Oil processes

3 Contents Understanding Ultra Low Sulfur Diesel By Gerianne D Angelo and Charles Olsen This article discusses the importance of feedstock properties and operating conditions to successfully producing ultra low sulfur diesel. The SmART Catalyst System : Meeting the Challenges of Ultra Low Sulfur Diesel By Charles Olsen A disucssion of the various components of the SmART catalyst system and the factors that go into designing customized systems to meet a variety of ULSD processing needs. No Need to Trade ULSD Catalyst Performance for Hydrogen Limits: SmART Approaches By Charles Olsen and Geri D Angelo The SmART Catalyst System provides the optimum balance between activity and hydrogen consumption. This article discusses the chemistry and kinetics involved in designing a system, and reviews the commercial performance observed in several ULSD applications ART Excels In ULSD Service: Update on Sulfur minimization By ART By Greg Rosinski, Dave Krenzke, and Charles Olsen ULSD production with the first SmART Catalyst System Series began early in 24 at a North American refinery processing a feed containing 4% of a high endpoint LCO. Since that time DX Platform Catalysts have been selected for over 7 ULSD applications as either stand-alone catalysts or as components in SmART System. The technology has been a great success since its introduction with millions of pounds installed in commercial units around the world. 23 Distillate Pool Maximization by Exploiting the use of Opportunity Feedstocks Such as LCO and Syncrude By Brian Watkins and Charles Olsen The use of opportunity feeds such as FCC LCGO, diesel streams from other hydroprocessing units and feeds from synthetic crude sources has helped refiners to maximize their diesel pool. In this article we highlight differences in feed reactivity for various feed components and explore the impact of various Hydrotreating Catalysts and operating conditions on diesel production. Cetane Improvement In Diesel Hydrotreating by Greg Rosinski and Charles Olsen This article discusses the importance of cetane in ULSD. The SmART Catalyst System, which utilizes both the CoMo and NiMo catalyst, results in a cetane uplift which is nearly two numbers higher than an all-como system with only a small increase in hydrogen consumption. For H 2 constrained refiners this is an ideal solution for improving the product cetane Factors Influencing ULSD Product Color By Greg Rosinski, Charles Olsen and Brian Watkins Product Color of petroleum products such as kerosene, jet fuel, diesel fuel and lube oils is a concern. Unit cycle length can be shortened due to product color degradation. In this paper we identify components that contribute to color degradation and report on the effects of feedstocks and operating conditions on ULSD color. 43 1

4 Understanding Ultra Low Sulfur Diesel Charles Olsen New Product Development Manager Gerianne D Angelo Senior Technical Services Engineer ADVANCED REFINING TECHNOLOGIES Chicago, IL USA Very tight specifications on sulfur content in diesel fuel have recently been announced by the European Union, the U.S. EPA and others. Refiners will be required to produce transportation diesel fuel with sulfur levels below ten ppm (Ultra Low Sulfur Diesel or ULSD). These new specifications will place a severe burden on diesel hydrotreaters as refiners struggle to keep up with diesel fuel demand and quality. As the diesel sulfur specification drops to the low ppm range, it is important to look at the types of sulfur compounds that need to be removed in order to meet the lower sulfur levels. The sulfur compounds can be classified into different groups commonly termed easy and hard sulfur, based on the ease of sulfur removal. The easy sulfur compounds are represented by dibenzothiophenes (DBT) and lighter. The hard sulfur species include multi-substituted dibenzothiophenes commonly represented by 4,6 dimethyl-dibenzothiophene (DMDBT), and these compounds are extremely difficult to desulfurize. The reason for the reactivity differences can be explained by the different reaction pathways for sulfur removal from DBT s and substituted DBT s. DBT s are more effectively desulfurized via a direct sulfur abstraction route, and it is the generally accepted reaction pathway for HDS of diesel to 5 ppm sulfur. Substituted DBT s, on the other hand, are not effectively desulfurized via direct abstraction because the methyl group(s) adjacent to the sulfur atom effectively shield the sulfur from the catalyst active sites. However, hydrogenation of an aromatic ring allows the molecule to flex enabling access to the sulfur atom, and C-S bond scission readily follows. Direct abstraction is catalyzed more effectively by CoMo catalysts, while the hydrogenation-abstraction route is typically more facile over NiMo catalysts. This forms the basis for ART s 2

5 Figure 22 Fraction Hard Sulfur Correlates with Feed End Point Fraction Hard Sulfur Feed D86 9% Point, C SR LCGO LCO SmART Catalyst System which is tailored to optimize both reaction pathways. The relative amounts of easy and hard sulfur in a feed are critical parameters to consider when choosing a catalyst and operating conditions for production of ULSD. Their concentration can vary significantly from feed to feed depending on crude source, the boiling range, and the treatment the feed has been subjected to whether it be thermal (coker) or catalytic treating (cycle oil). Analysis of a wide array of diesel feeds shows that the fraction of hard sulfur correlates quite well with the end point of the feed. Figure 22 shows the fraction of hard sulfur as a function of D86 9% point for a variety of feeds. The figure clearly shows a strong correlation with the 9% point of the feed. The fraction of hard sulfur increases rapidly for feed T9 between about 316 C and 343 C. Interestingly, the fraction of hard sulfur does not correlate strongly with feed type; whether it is straight run, light cycle oil, or light coker gas oil the fraction of hard sulfur is largely determined by the feed endpoint. The amount of nitrogen in the feedstock is another critical parameter that must be considered. Figure 23 demonstrates the detrimental effects nitrogen has on the removal of hard sulfur. The relative rate constant for hard sulfur removal decreases significantly in going from a feedstock containing 5 ppm nitrogen to a feedstock containing 15 ppm nitrogen. The relative rate constant continues to decrease as nitrogen content increases beyond 15 ppm, but the decrease is at a somewhat slower rate. This inhibiting effect of nitrogen is a result of poisoning of the acid sites needed for aromatic ring saturation, and as discussed above, the saturation-abstraction route is the preferred reaction pathway for hard sulfur removal. Thermodynamic equilibrium is another issue related to poly nuclear aromatic (PNA) saturation which must be taken into account. The saturation of PNA s does reach a thermodynamic constraint on conversion at high enough temperatures. Figure 24 shows the expected PNA conversion as a function of temperature for a variety of LHSV s. The equilibrium constraint is readily apparent for the higher temperatures in the chart. Decreasing the LHSV serves to increase conversion in the kinetically controlled region (i.e. low temperatures), but has no effect on conversion in the thermodynamically controlled regime (i.e. high temperatures). This suggests that adding catalyst volume will help in the removal of hard sulfur, but a point is reached where decreases in sulfur do not occur due to unfavorable thermodynamic equilibrium at those conditions. This raises the potential for situations where significant increases in temperature will not result in appreciable decreases in product sulfur at very low levels. reprinted from Catalagram

6 Figure 23 Nitrogen Inhibits Hard Sulfur Removal A number of operating parameters take on greater importance in ultra low diesel HDS due to the issues raised above. ART has conducted extensive pilot plant work to define appropriate operating conditions for ULSD and to define the influence of cracked stocks. One study utilized a straight run feed and a 2% LCO blend with the same straight run component, and selected properties of the two feeds are shown in Table X. The operating conditions used in the work are representative of the pressure and H 2 /oil ranges typically found in diesel hydrotreaters. Figure 25 summarizes the influence of H 2 /oil ratio on ULSD production. It is a plot of the relative HDS rate constant as a function of the relative excess hydrogen (H 2 /oil ratio divided by the hydrogen consumption). Data for both high and low pressure operation are shown for each feed. For the high pressure operation, it is apparent that increasing H 2 /oil is beneficial for both feeds up to a certain point. The reactivity of the straight run feed increases from about 6 at low H 2 /oil (i.e. 6% of the highest activity achievable for that feed) to nearly 1 at a H 2 /oil ratio / H 2 consumption ratio of about five. Further increases in H 2 beyond that provide little additional benefit. Similarly, the 2% LCO feed shows a reactivity of about 2 at low hydrogen rate, and steadily increases towards 1 near a H 2 /oil ratio / H 2 consumption ratio of about six. Further increases in hydrogen rate again do not add much additional benefit. These data suggest that for high pressure more excess hydrogen is required for ULSD compared to conventional diesel hydrotreating (i.e. 5 ppm sulfur) where H 2 /oil ratio consumption ratios of between three and four are generally recommended. Table X Feed Properties Straight Run 2% LCO/Straight Run Specific Gravity Sulfur, wt.% Nitrogen, ppm 95 2 D86 Dist., C, IP/5/FP 212/288/354 28/286/

7 Figure 24 Thermodynamic Equilibrium Can Limit Conversion The effect of H 2 /oil ratio at lower pressure is quite different. In this case, the relative HDS rate constant for both feeds shows a steady increase with increasing hydrogen rate. Note that the activity is relative to the straight run feed at high pressure and high H 2 rate. The benefit of increasing H 2 /oil never reaches a plateau as observed in the high pressure case, suggesting that more hydrogen is always better at low pressure. The effect of hydrogen pressure is also readily apparent in Figure 25. At relative excess hydro- Figure 25 Excess Hydrogen Improves Reactivity reprinted from Catalagram

8 Figure 26 H 2 S is Detrimental to Hard Sulfur Removal gen values around three to four, the straight run feed at low pressure has a relative rate constant of about 2 compared to the high pressure case, and the difference for the LCO feed is even greater. Figure 26 summarizes these data in another way. This chart shows the relative activity plotted as a function of H 2 S partial pressure at reactor outlet conditions. Again, quite different behavior is observed for the low and high pressure cases. At high pressure, the data suggest some tolerance for low H 2 S pressure and a steady decline in activity as H 2 S pressure increases beyond that. The straight run feed also appears more forgiving, as it has a slower activity decline compared to the LCO containing feed. Looking at the low pressure data, it is apparent that even a small amount of H 2 S is detrimental to activity. There is a rapid initial decrease in activity with the first increments of H 2 S, and thereafter a slow steady drop-off in activity as H 2 S level increases further. These data are from the pilot plant where there is no H 2 S in the treat gas to the unit. A hydrogen stream containing H 2 S will exacerbate the activity loss due to H 2 S especially at low pressure. This study also investigated the effects of adding catalyst volume and the potential tradeoffs between catalyst volume, operating pressure and H 2 /oil ratio. Figure 27 summarizes the relationship between 1/LHSV or residence time (i.e. catalyst volume), H 2 /oil ratio and hydrogen pressure at 1 ppm product sulfur for the straight run feed. Not surprisingly, there is a significant difference in required catalyst volume between high and low pressure operation at constant H 2 /oil ratio. The catalyst volume at low pressure is nearly three times higher than required for the high pressure operation at typical H 2 rates. Figure 28 is a similar plot, but in this case it is comparing the performance of the straight run feed with the 2% LCO blend at an intermediate pressure. The intermediate pressure is the practical lower limit for ULSD production for the 2% LCO feed. Lower pressures required unreasonably high gas rates and or long residence times (very large reactors). This chart clearly shows the difficulty in treating cracked stocks relative to a straight run feed. At high H 2 rates, 1.5 times higher catalyst volume is required for the LCO, and this increases to nearly two times higher at the low H 2 rate. Of course, increasing the pressure helps somewhat, but even at high pressure the LCO case requires times higher catalyst volume depending upon the H 2 rate. 6

9 Figure 27 Trade-offs Between Pressure, H 2 /Oil and LHSV In summary, it is possible in some cases to trade off pressure, H 2 /oil and catalyst volume, when designing for ULSD production. However, there is a limit which depends strongly upon the feedstock. For example, cracked stocks require higher pressure and higher H 2 /oil ratio compared to a straight run feed. To learn more about producing ULSD at your refinery, contact your ART technical or sales representative. Figure 28 Cracked Stocks Change The Rules reprinted from Catalagram

10 The SmART Catalyst System TM : Meeting the Challenges of Ultra Low Sulfur Diesel Charles Olsen New Product Development Manager ADVANCED REFINING TECHNOLOGIES Chicago, IL USA In 21, ART introduced the SmART Catalyst System TM to help refiners deal with the severe demands of ultra low sulfur diesel (ULSD). The SmART Catalyst System utilizes state-of-the-art catalyst technology which is staged in the proper proportions to provide the best performance while at the same time meeting individual refiner requirements. The catalyst staging is designed to take advantage of the different reaction mechanisms for sulfur removal; ART CDX, a high activity CoMo catalyst, efficiently removes the unhindered, easy sulfur via the direct abstraction route and ART CDY, a high activity NiMo catalyst, then attacks the remaining sterically hindered, hard sulfur. Pilot plant work has proven that the properly configured SmART Catalyst System provides higher activity than either the CoMo or NiMo catalyst alone. ART CDX and ART CDY, individually or as part of a SmART Catalyst System, were selected for 14 diesel units in 24, and most of these applications aim to evaluate ULSD capability and/or produce ultra low sulfur fuels in advance of the regulations for economic benefit. Optimizing the SmART Catalyst System An important aspect of the SmART Catalyst System is determination of the optimum proportions of the CoMo and NiMo catalysts that will deliver the best performance. This is dependent upon a number of factors, including the refiners requirements, and selected feed properties and operating conditions as discussed in detail previously in Catalagram No. 95 (March 24). One clearly important parameter which must be considered is the boiling range of the feedstock. Sulfur speciation on a wide variety of feedstocks has shown that there is a strong correlation between the fraction of multi-substituted dibenzothiophenes (hard sulfur) and the feed endpoint. Once the D86 endpoint increases beyond about 329 C there is a rapid increase in the fraction of hard sulfur contained in the feed. This has a large impact on catalyst activity as shown in Figure 21. The figure shows pilot plant data comparing results from treating two feeds with different endpoints over the same catalyst under identical conditions. At ultra low sulfur levels there is about 17 C difference in reactivity of the two feeds with the lower endpoint feed more reactive. Clearly, feed endpoint and the amount of hard sulfur are critical parameters that influence the optimum SmART configuration. Another critical feed property that must be accounted for is the nitrogen content. It is generally accepted that nitrogen inhibits aromatic saturation reactions through poisoning of acidic sites on the catalyst. Recall that the primary reaction pathway for removal of hard sulfur is via hydrogenation of an aromatic ring, and it is not surprising that feed nitrogen content has a serious, negative impact on HDS activity. The magnitude of the impact can be seen in Figure 22 which summarizes data for NiMo and CoMo catalyst activity on an SR feed 8

11 Figure 21 Feed Endpoint Impacts HDS Activity 357 C D86 EP 39 C D86 EP Temperature, C 17 C 31 F 1 C Product Sulfur, ppm before and after selectively removing the nitrogen via an adsorption process. The difference in activity on the two feeds is quite large. Increasing the nitrogen content from 25 to 16 ppm results in a loss in HDS activity of C for both catalysts. Comparing the catalysts on the low nitrogen feed shows that the NiMo catalyst has about 8 C higher activity relative to the CoMo, and that decreases to an advantage of about 3 C or less on the higher nitrogen feed. This suggests the impact of nitrogen is different for NiMo and CoMo catalysts with the CoMo catalyst more tolerant of nitrogen. This is another important consideration when designing the optimum SmART Catalyst System. Hydrogen availability, in terms of hydrogen pressure and hydrogen circulation, also takes on greater importance in ULSD. Figure 23 is a chart showing how the relative HDS rate constant changes as a function of the excess hydrogen (H 2 /Oil ratio divided by the hydrogen consumption) for both high and low pressure operation. Note the range in operating pressure from low to high represents that typically encountered in diesel Figure 22 Nitrogen Impacts Catalysts Differently 28 Increase in required Temperature, C Base 16 ppm Nitrogen 25 ppm Nitrogen NiMo CoMo reprinted from Catalagram

12 Figure 23 Hydrogen Availability is Critical hydrotreating. At high pressure, increasing the H 2 /Oil is beneficial for both SR and 2% LCO feeds up to a point, after which further increases in H 2 rate provide little additional benefit. At low pressure, the effect of H 2 /Oil ratio is quite different. In that case, the relative rate constant for both feeds shows a steady increase with increasing hydrogen rate. The benefit of increasing H 2 /Oil never reaches a plateau as observed in the high pressure case indicating that more hydrogen is always better at low pressure. The effect of pressure is also readily apparent in the figure. Comparing the relative rate constant for high and low pressure at a typical H 2 /Oil ratio reveals that the activity at low pressure is only 1-2% of that at high pressure for 2% LCO and SR feed respectively. Controlling Hydrogen Consumption One of the key advantages of the SmART Catalyst System is the efficient use of Hydrogen. Figure 24 illustrates how the system can be tailored to provide the best balance of high HDS activity while minimizing H 2 consumption. The figure shows that as NiMo catalyst is added to the system there is a large increase in HDS activity relative to the all CoMo reference, and eventually, a minimum in the product sulfur curve is reached (i.e. maximum HDS activity). The position and magnitude of this minimum varies with feed and operating conditions such as those discussed above. The figure also shows the relative H 2 consumption, and again, as the percentage of the NiMo component increases, the H 2 consumption relative to the base CoMo system increases. In the region where the system shows the best activity, the hydrogen consumption is only slightly greater than that for the all CoMo system, and well below that for the all NiMo catalyst. This is a result of the different kinetics for sulfur and aromatics removal and is a critical consideration when customizing a SmART Catalyst System. To help understand the differences in kinetics it is useful to compare the performance of CoMo and NiMo catalysts alone. Figure 25 shows a comparison of the hydrogen consumption over a NiMo and CoMo catalyst for a straight run feed at ULSD conditions. The amount of hydrogen consumed by sulfur, nitrogen and olefins removal is essentially the same for each catalyst and is not shown. What separates the two catalysts is the amount of aromatics saturation which occurs, and in particular, the amount of mono ringed aromatics which are hydrogenated. In this case, an additional 12 Nm 3 /m 3 of hydrogen is consumed with the NiMo catalyst due to mono ringed aromatics saturation. This represents excess hydrogen consumption above that required for the removal of sulfur. Figure 26 is a similar chart for LCGO feed. In this example, the NiMo catalyst hydrogenates more PNA (2 rings and greater) and mono ringed aromatics compared to the CoMo catalyst accounting for an additional 19 Nm 3 /m 3 of hydrogen consumption above that required for sulfur, nitrogen and olefins removal. Clearly, in cases where hydrogen consumption needs 1

13 Figure 24 Optimizing HDS and H 2 Consumption Figure 25 Excess H 2 Consumption with SR Feed in ULSD NiMo CoMo HDS HDN Olefins HDS HDN Olefins 28 Nm 3 /m 3 32 Nm 3 /m 3 28 Nm 3 /m 3 2 Nm 3 /m 3 Poly aromatics Mono aromatics Poly aromatics Mono aromatics to be minimized, a NiMo catalyst for ULSD is the wrong choice. Unfortunately, in many of these cases a CoMo catalyst does not provide the best activity for ULSD, and it is precisely these units where the SmART Catalyst System is ideal as it offers the highest activity and is more efficient with hydrogen compared to an all NiMo system. It perhaps appears contradictory that a NiMo catalyst is included in the SmART Catalyst System due to its high hydrogenation activity making it preferred for hard sulfur removal, and yet, under some conditions the hydrogenation activity is too high and excess aromatics saturation occurs. This highlights one of the keys to designing the proper system. The design involves increasing the hydrogenation selectivity of the system to provide highest HDS activity, while at the same time minimizing hydrogen consumption (i.e. minimizing excess aromatics saturation). Figure 27 shows a schematic of the reaction pathway for poly aromatics saturation. Naphthalene, a two ringed aromatic molecule, is featured at the top of the figure. The reaction begins with the hydrogenation of one of the aromatic rings to form tetralin, a mono ring aromatic. The next reaction in the sequence is hydrogenation of the remaining aromatic ring to produce decalin, a fully saturated molecule. Each step is reversible and subject to equilibrium constraints. The slowest reaction in the sequence is the saturation of the mono ring aromatic. The reaction sequence for a substituted biphenyl is also shown at the bottom of the figure. The sequence is essentially the same. In both examples the hydrogenation of the mono aromatic is reprinted from Catalagram

14 Figure 26 Excess H 2 Consumption with LCGO Feed in ULSD NiMo CoMo HDS HDN HDS HDN Olefins Olefins 46 Nm 3 /m 3 22 Nm 3 /m 3 42 Nm 3 /m 3 8. Nm 3 /m 3 Poly aromatics Mono aromatics Poly aromatics Mono aromatics the slowest step and also consumes more hydrogen compared to the other hydrogenation reactions shown; three moles of hydrogen per mole of aromatic are consumed by the saturation of the mono ring aromatic compared with two moles of hydrogen/mole for the multi ringed aromatics. The reaction sequences shown in Figure 27 can be treated as a series of first order reversible reactions where the intermediate (the mono ring aromatic) is the desired product. For these sorts of reaction systems the intermediate often tends to be favored at shorter contact times (see Chemical Reaction Engineering by Octave Levenspiel [Wiley, 1998], for example), and it this tendency which is exploited when customizing a SmART Catalyst System. The effective residence time in both the CoMo and NiMo beds of a system is short compared to the overall reactor residence time, and this helps minimize the hydrogenation of the mono ring aromatic (i.e. minimize hydrogen consumption). Figure 28 shows the effect of residence time, as indicated by 1/LHSV, on aromatics saturation. For PNA saturation, the two ringed aromatic going to the mono ring aromatic, there is a fairly steep curve for conversion as a function of residence time below about 1 hr. Above that point, which represents space velocities of 1 hr -1 or less there is very little change due to equilibrium constraints. For mono ring aromatic saturation there is a steady increase in conversion as the residence time is increased indicating more and more saturation as the residence time is increased (i.e., LHSV is decreased). Both sets of curves suggest aromatic saturation can be limited by appropriate choice of LHSV, or in the case of a SmART Catalyst System, by adjusting the relative quantities of CoMo and NiMo catalyst. SmART Catalyst System Experience The SmART Catalyst System is the culmination of an extensive effort put towards understanding the chemistry and process conditions required for ultra low sulfur fuels. In addition, properly designed high activity Figure 27 Reaction Sequence for Poly Aromatics Hydrogenation 12

15 Figure 28 Limiting Aromatics Saturation Table VII Commercial Experience with ART CDX, CDY and the SmART Catalyst System Refiner Pilot Testing Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Startup Date 4Q4 4Q4 4Q4 2Q5 2Q4 3Q4 1Q Catalysts CDX CDX CDX CDX CDX CDX CDX CDX CDX CDX CDX CDX CDX CDY CDY CDY CDY CDY CDY CDY CDY CDY CDY Feedstock: % cracked stock Sp Gravity Sulfur, wt.% EP D86 Dist, C Product : Sulfur, ppm Conditions LHSV Inlet P, BARG reprinted from Catalagram

16 catalysts must be used in order to take full advantage of the SmART System concept. ART has devoted significant resources to designing the best ULSD catalysts for use in the SmART Catalyst System, and this effort has lead to the commercialization in 24 of a new CoMo catalyst CDX, and a new NiMo catalyst CDY. These new technologies benefit from the optimization of the alumina chemistry to give the right surface area and pore size distribution, as well as providing the right surface chemistry (i.e., acidity). ULSD production with the CDX/CDY SmART System began early in 24, in a North American refinery processing a feed containing 2-4% of a high endpoint LCO. Since that time, ART CDX and ART CDY have been selected for 14 different diesel applications either as components in SmART Systems or as a complete charge. A list of commercial applications of CDX, CDY and SmART Catalyst Systems is shown in Table VII. It is apparent from the table that the SmART catalyst technology has been successfully applied to a wide range of feeds and conditions. In most cases it has been selected based on the high activity demonstrated in pilot plant testing. As these and other recent successes demonstrate, Advanced Refining Technologies has developed stateof-the-art technologies aimed at helping refiners meet the challenges of clean fuels. These successes are the result of harnessing the unique heritage of ART which includes a collective expertise in material science, catalyst formulation, and manufacturing knowhow. The science of designing specific catalyst components to operate in an optimum system is a fundamental part of ART's catalyst technology. With the advent of clean fuels, ART seized the opportunity to extrapolate their catalyst system expertise from resid to lighter feedstocks. As a result, ART has been able to deliver high performance technologies ranging from StART Catalyst Systems for Si tolerance in coker naphtha applications, SmART Catalyst Systems for ULSD, and ApART Catalyst Systems for cat feed hydrotreating. ART strives to continuously improve the performance of its catalysts, and the current focus of that effort is on maximizing the effectiveness of the catalytic metals. As described in Catalagram No. 96 (October 24), ART's new CoMo catalyst, CDX, benefits from improved metals utilization through the application of novel metals chemistry and a unique impregnation technique. These same techniques have been successfully applied to a new NiMo catalyst called ART NDXi. As shown in Figure 26, this catalyst has significantly higher activity for ULSD than ART CDY and the conventional reference NiMo catalyst. ART NDXi will be commercialized in early 25 and is slated to become the latest NiMo catalyst component of the SmART Catalyst System. Figure 29 ART NDXi has Step Out Activity 14

17 No Need to Trade ULSD Catalyst Performance for Hydrogen Limits: SmART Approaches Charles Olsen New Product Development Manager Gerianne D Angelo Senior Technical Services Engineer ADVANCED REFINING TECHNOLOGIES Chicago, IL USA I t has been widely discussed that desulfurization of dibenzothiophene and substituted dibenzothiophenes occurs through two reaction pathways, the direct sulfur abstraction route and the hydrogenation-abstraction route. The former involves adsorption of the molecule on the catalyst surface via the sulfur atom followed by C-S bond scission. This is the primary pathway over cobaltmolybdenum (CoMo) based hydrotreating catalysts. The second pathway involves saturation of one aromatic ring of the dibenzothiophene species followed by the extraction of the sulfur atom. Nickel-molybdenum (NiMo) catalysts have a higher activity for desulfurization via this route. It has become a fairly common practice to model ULSD applications by lumping the various sulfur species into easy sulfur and hard sulfur. The so-called easy sulfur reprinted from Catalagram

18 Figure 9 Optimizing HDS and Hydrogen Consumption Product Sulfur, ppm All CoMo Reference is made up of compounds which are readily desulfurized via direct abstraction and boil below about 363 CF whereas hard sulfur is made up of compounds which are more readily removed via hydrogenation followed by abstraction. These compounds include 4,6 dimethyl-dibenzothiophene and other di- and tri-substituted dibenzothiophenes. The relative amounts of easy and hard sulfur in a feed are a critical property to consider since the concentration of each can vary significantly from feed to feed depending on crude source, boiling range and the prior thermal or catalytic treatment of the feedstock. ART first introduced the SmART Catalyst System in 21 (1,2) in anticipation of the stringent new demands required for ULSD. The SmART system concept is based on a staged catalyst approach designed to exploit the fact that there are two reaction pathways for desulfurization. The system utilizes a high activity CoMo catalyst like ART CDXi for efficient removal of sulfur via the direct abstraction route and a high activity NiMo catalyst like ART NDXi which effectively removes the multisubstituted dibenzothiophenes via the hydrogenation route. Product Sulfur H 2 Consumption SmART Systems All NiMo Reference 1.15 Relative H 2 Consumption 1. A number of factors need to be considered when designing the optimum SmART system for a given application. These have been reviewed in detail previously (3, 4), and include feed endpoint (amount of hard sulfur), feed nitrogen and H 2 availability. One of the big advantages of the SmART System is illustrated in Figure 9. The figure shows that as NiMo catalyst is added to the SmART system there is a large increase in HDS activity relative to the all CoMo reference, and eventually, a maximum in HDS activity is reached. The position and magnitude of this maximum varies with feed and operating conditions, especially H 2 partial pressure. The figure also includes the relative H 2 consumption, and again, as the percentage of the NiMo component increases, the H 2 consumption relative to the base CoMo system increases. Notice, however, that in this case the relationship between H 2 consumption and the fraction of NiMo catalyst is nonlinear. In the region where the system shows the highest activity the hydrogen consumption is only slightly greater than that for the all CoMo system, and well below that for the all NiMo catalyst. Again, the nature of this relationship varies with feed and operating conditions, with a strong correlation to hydrogen availability. It is this ability to balance HDS activity and H 2 consumption to meet individual refiner requirements that sets SmART apart. The balancing of hydrogen consumption and HDS activity is possible because of the different kinetics and reaction pathways for sulfur removal and aromatic hydrogenation. The reaction pathways for sulfur removal were discussed above with the main point being the hydrogenation pathway is critical for ULSD production. The multisubstituted dibenzothiophenes (hard sulfur) are polynuclear aromatic species containing two aromatic rings, one of which must be hydrogenated for efficient removal of the sulfur atom. Thus, the catalyst system needs good hydrogenation activity and selectivity in order to minimize the use of hydrogen. To more fully understand how this works, it is useful to review polynuclear aromatic hydrogenation in general. To begin with, hydrogenation of aromatics is reversible, and equilibrium conversion is less than 1% under practical hydrotreating conditions. The equilibrium conversion decreases with increasing temperature, and therefore, increasing temperature to get higher hydrogenation rates may ultimately result in lower conversion. These reactions are also exothermic which can have an impact on conversion in adiabatic systems. The hydrogenation of a number of poly aromatic species such as naphthalene and biphenyl have been studied by a number of investigators (5) and the work has lead to the reaction networks presented in Figure 1. In the case of naphthalene, the reaction begins with the hydrogenation of one of the aromatic rings to form tetralin, a mono ring aromatic. The next reaction is hydrogenation of the remaining aromatic ring to produce decalin, the fully saturated species. As indicated in the figure, the reactions proceed sequentially with the rate of hydro- 16

19 genation of the final aromatic ring (tetralin) at least an order of magnitude lower than saturation of the first aromatic ring (naphthalene). Interestingly, the rate of tetralin hydrogenation is about the same as that observed for benzene hydrogenation. A variety of substituted naphthalene s have also been shown to follow a similar reaction network with the rate of hydrogenation of the first aromatic ring roughly the same as that observed for naphthalene. Figure 1 Reaction Pathways for Poly Aromatics Hydrogenation naphthalene tetralin decalin k1 biphenyl cyclohexylbenzene bicyclohexyl k3 k2 k4 The hydrogenation of biphenyl proceeds similarly. The hydrogenation is a stepwise reaction with the rate of hydrogenation of the first aromatic ring about an order of magnitude faster than that of the mono ring compound. An important difference is that the rate of the first hydrogenation reaction in naphthalene is about and an order of magnitude faster than the rate of hydrogenation of the first ring in biphenyl. Thus, there is a significant difference between the hydrogenation of an aromatic with two fused rings compared to a two ring aromatic where the rings are not fused. This is an important difference when considering hard sulfur removal since these species do not contain two fused aromatic rings and as such, can be expected to behave more like a biphenyl species. Concentration The challenge when designing a SmART system is to provide enough hydrogenation activity to efficiently saturate the first ring on the two ring aromatic (biphenyl type, sulfur containing) molecule, but not so much as to catalyze the final hydrogenation step in the reaction pathway discussed above. The poly aromatic hydrogenation reaction networks shown in Figure 1 can be modeled as first order reversible reactions in series. Figure 11 shows the species concentration profiles as a function of residence time for a hydrogenation reaction sequence such as that for naphthalene. In the example shown, the rate Figure 11 First Order Reversible Reactions in Series: Concentration Profile mono di Sat d Contact time k1=1*k2 k1>k2, k3>k4, and k1>k3 of the first hydrogenation reaction in the series is an order of magnitude faster then the rate of the second hydrogenation reaction. There is a rapid decrease in the concentration of the two ringed aromatic at short times, and a corresponding increase in the mono ringed species. As time increases however, the mono ring aromatic concentration begins to decrease and the fully saturated species begin to build up. This type of concentration profile suggests that there is a window of residence times corresponding to a maximum in the mono ringed aromatic concentration. The way to minimize hydrogen consumption is by avoiding saturation of the mono ringed compounds. This can be accomplished by adjusting the residence time in the CoMo and NiMo beds of a SmART system through varying the amounts of each catalyst. This effectively tunes the hydrogenation activity of the overall catalyst bed to maximize hydrogenation of the poly aromatics and minimize hydrogenation of the mono ringed species. This is explored further on a diesel feed comparing a CoMo and NiMo catalyst in a pilot plant test. Figure 12 compares the HDS activity of the two catalysts as a function of residence time at constant reactor temperature. It is apparent that the NiMo catalyst is more active than the CoMo catalyst at the indicated reprinted from Catalagram

20 Figure 12 HDS Activity Comparison at High Pressure 5 Product Sulfur, ppm CoMo NiMo /LHSV, hrs 4 Figure 13 Aromatics Concentration Profile for CoMo Catalyst at High Pressure Concentration, % Mono's Sat'd Poly's Concentration, % /LHSV, hrs Figure 14 Aromatics Concentration Profile for NiMo Catalyst at High Pressure Mono's Sat'd Poly's /LHSV, hrs 18

21 Cetane Index Increase Product Sulfur, ppm CoMo NiMo Relative H 2 Consumption Figure 16 HDS Activity Comparison at Moderate Pressure 1 9 CoMo 8 NiMo Concentration, % Figure 15 Cetane Index Increase with H 2 Consumption /LHSV, hrs Figure 17 Aromatics Concentration Profile for CoMo Catalyst at Moderate Pressure 4 Mono's Poly's Sat'd /LHSV, hrs conditions, although both catalysts are able to achieve <1 ppm product sulfur if the residence time is long enough. Figures 13 and 14 compare the concentration profiles for poly aromatics, mono ringed aromatics and the saturates as a function of residence time for the CoMo and NiMo catalyst respectively. Both charts show the same concentration trends as shown in Figure 11. There is a rapid decrease in poly aromatics concentration and a corresponding increase in mono ringed aromatics for both catalysts. Clearly, however, the NiMo catalyst is much more efficient at hydrogenating the final aromatic ring as evidenced by a lower maximum mono ringed aromatic concentration and a faster increase in saturates with increasing residence time compared to the CoMo catalyst. At the longest residence time (lowest LHSV), the NiMo catalyst has about 15 numbers (absolute) higher saturate concentration (and about 15 numbers lower mono ringed aromatic concentration) than the CoMo catalyst. That translates to about 53 Nm 3 /m 3 higher hydrogen consumption compared to the CoMo catalyst. This difference decreases rapidly as the residence time decreases. Of course, if there is sufficient H 2 available, the incremental increase in aromatics saturation and the correspondingly higher hydrogen consumption can offer some benefits such as cetane improvement. Figure 15 summarizes the cetane index increase observed for this example. The cetane index increases linearly with increasing H 2 consumption, and ultimately, a cetane index improvement of six numbers was achieved by the high activity NiMo catalyst. Not surprisingly, pressure has a dramatic effect on the performance of NiMo and CoMo catalysts in ULSD. Figure 16 compares the HDS activity of the NiMo and CoMo catalyst for the same feed and conditions as above, but at lower pressure. At reprinted from Catalagram

22 these conditions the CoMo catalyst is more active at the higher LHSV s (shorter residence times), while at the lower LHSV s the catalysts have essentially the same activity. A comparison of the aromatic species concentration profiles is shown in Figures 17 and 18. In this case, the difference between the catalysts is much less than observed for the higher pressure case, and the degree of saturation achieved by either catalyst is lower. For the CoMo catalyst in Figure 17, the concentration of Mono ringed aromatics never begins to decrease, and the concentration of saturates remains very low. The NiMo catalyst data shown in Figure 18 looks similar, although at long residence time there is a decrease in mono ringed aromatics, the poly aromatic level is lower and the saturates concentration is higher than for the CoMo catalyst case. These data are a good example of the flexibility of the SmART system. In applications where there is sufficient H 2 partial pressure, a NiMo catalyst is likely the most active system for HDS. However, it will consume significantly more hydrogen due to its efficiency at catalyzing hydrogenation reactions. If the incremental hydrogen consumption cannot be tolerated, a SmART system can be designed which will deliver high HDS activity and minimize hydrogen consumption. In cases where the hydrogen pressure is lower, the SmART system is often more active than either component alone without increasing the H 2 consumption significantly over the all CoMo system. SmART Performance Since introducing the SmART system for ULSD, ART has conducted a significant amount pilot work to demonstrate both the activity and stability of these systems. Figure 19 summarizes some of that work comparing ART CDXi and a SmART system consisting of CDXi and NDXi. This particular study 2 Temperature, C Concentration, % Product Aromatics, vol.% Figure 18 Aromatics Concentration Profile for NiMo Catalyst at Moderate Pressure Mono's Poly's Sat'd /LHSV, hrs Figure 19 Pilot Plant Aging of a SmART System Normalized to 1.25 LHSV and 55 BARG 1.26 wt.% feed sulfur and 1 ppm product sulfur LHSV and 55 BARG Hours on Stream CDXi SmART Figure 2 Pilot Plant Aging of a SmART System Aromatics Hydrogenation Hours on Stream CDXi SmART

23 spanned about 2 hours at the conditions shown in the chart processing a straight run feed from the West Coast. The H 2 partial pressure is quite good in this example which explains the large activity advantage for the SmART system relative to the all CoMo system. Notice that the slopes of the lines through each data set are essentially the same indicating the ART CDXi and a SmART system of CDXi/NDXi have the same relative stability when producing ULSD. Figure 2 shows how the aromatic saturation activity changed over the course of the 2 hour run. The total aromatics saturation stayed essentially constant for the SmART system throughout the run, while for CDXi there is a suggestion of some slight loss in saturation activity at the end of the run. Although not shown in the chart, the PNA content in the product was also analyzed, and the data tell the same story. Another thing to note is the similarity in aromatics (and PNA) conversion between the SmART system and CDXi. This is an indication that the hydrogen consumption is similar for both systems, even though the SmART system has a substantial activity advantage. The SmART catalyst system or its components have been selected for over 2 applications since being introduced to the market. The technology has been successfully applied to a wide range of feeds Temperature, C % LCO blend with C end point and conditions, and in most cases has been chosen based on the high activity demonstrated in pilot plant testing, both in ART labs and refiner testing facilities. A few of these applications are discussed in the paragraphs that follow. ULSD production with the SmART System began early in 24 in a North American refinery processing a feed containing 3-5% of a refractory, high endpoint LCO. The LCO end point can gat as high as 391 C, and sulfur speciation indicates that the concentration of hard sulfur often exceeds 4 ppm. The performance of the SmART system is shown in Figure 12. Despite processing a feed which was more difficult than anticipated, the SmART system provided excellent performance. The typical deactivation period following start up was exacerbated by the fact that the Table V Commercial ULSD Performance for Refiner A Months on stream 1.5 LHSV H 2 /Oil, Nm3/m Inlet pressure, BARG WABT, C Figure 21 Commercial SmART System Performance Days on Stream 18 refiner had to run off a tank of LCO which had built up during the unit turnaround. Even when processing a blend of 5-6% LCO at SOR, the SmART system had no problems making the <1 ppm sulfur target. Once the feed and operating conditions lined out the operation was very stable with essentially no deactivation apparent over the last several months. In another example, Refiner A conducted in-house testing for their ULSD catalyst selection. ART proposed a SmART catalyst system which ultimately tested substantially more active than other catalysts in the program including one from the perceived market leader. As a result, this refiner selected a CDX/CDY SmART system for their ULSD unit. The commercial unit began operation in the fourth quarter of 24, and a snapshot of the performance thus far is shown in Table V. The feed is a blend of up to 4% LCO and light coker gas oil with a sulfur content of about 1.3 wt.%. The unit has decent pressure, but the H 2 /Oil ratio is lower than optimum especially given that the H 2 consumption is typically around 98 Nm 3 /m 3. The performance of the SmART system has met the high expectations set by the pilot plant testing. Product sulfur reprinted from Catalagram

24 Reactor Train 1 Months on stream 1 9 LHSV H 2 /Oil, Nm3/m3 Inlet pressure, BARG WABT, C Table VI SmART System Performance for Refiner C Product sulfur, ppm ART and Refiner B worked together to generate data for a planned ULSD unit revamp. The feedstock had a very high endpoint of 396 C which corresponded to over 6 ppm of hard sulfur. ART proposed a SmART system consisting of its new high activity catalysts ART CDX and CDY. This system was designed to provide high HDS activity and minimize hydrogen consumption in order to stay within the refiners hydrogen availability limits. The refiner conducted pilot plant testing on a variety of proposed catalysts, and found that the SmART system easily met the targets and outperformed the other vendors in the program. Temperature, C As a result of this work, Refiner B selected the SmART system for the first cycle in the ULSD unit. The unit started up in the second quarter of 25, and has been online for about nine months. The performance of the SmART system is shown in Figure 22. This refiner conducted a ULSD test run early in the cycle, and the performance met all expectations and in fact, closely matched the pilot plant results. The unit was then operated to produce 2 ppm sulfur for several months before pushing again to make ULSD. The hydrogen consumption increased from about 55 Nm 3 /m 3 to 62 Nm 3 /m 3 when they went from 2 ppm sulfur to 1 ppm sulfur. As the Figure 22 SmART System Performance for Refiner B.72 LHSV and 43 BARG H 2 Pressure, 1.24 wt.% feed sulfur 1 ppm sulfur 2 ppm sulfur 2 9 chart shows, the SmART system has experienced essentially no deactivation since start up. In the final example, Refiner C wanted to produce <5 ppm sulfur diesel in an existing reactor. ART optimized a SmART loading based on the product sulfur requirement while at the same time staying within the constraints of the refinery s hydrogen system. The unit started up with the SmART system in the second quarter of 25, and has been producing <5 ppm sulfur diesel for about 9 months. A summary of the performance is shown in Table VI. The performance of the SmART system has been excellent even with the high LHSV and low hydrogen partial pressure. The required temperature is within a few degrees of the predicted performance, and the catalyst deactivation observed to date is minimal. Hydrogen consumption has also been within expectations at Nm 3 /m 3. Refiner C is extremely pleased, and is now working with ART on a unit revamp which will allow production of <1 ppm sulfur diesel. References 1. Olsen, C., Krenzke, L.D., Watkins, B., AICHE Spring National Meeting, New Orleans, March Krenzke, D., Armstrong, M., 21 ERTC Meeting, Madrid, Spain. 3. D Angelo, G., Olsen, C., Davison Catalagram 95, March, 24, pp Olsen, C., Krenzke, L.D. 25 NPRA Annual Meeting, Paper AM Girgis, M.J., Gates, B.C., Ind. Eng. Chem. Res., 3, 1991, p Days on Stream 22

25 ART Excels In ULSD Service: Update on Sulfur minimization by ART Greg Rosinski Technical Service Engineer Dave Krenzke Regional Technical Services Manager Charles Olsen Worldwide Technical Services Manager ADVANCED REFINING TECHNOLOGIES Chicago, IL USA A RT first introduced the SmART Catalyst System Series for ultra-low sulfur diesel (ULSD) in 21. Since that time the technology has been widely accepted by the refining industry as top tier for ULSD. As detailed previously (Catalagram 99, 26), the SmART System is a staged catalyst system customized to meet individual refiners objectives with the performance of the system driven by ART s DX TM Catalyst Platform. ULSD production with the first SmART System began early in 24 at a North American refinery processing a feed containing 4% of a high endpoint Light Cycle Oil (LCO). Since that time DX Catalyst Platform has been selected for over 35 ULSD applications as either stand-alone catalysts or as components in SmART System. The technology has been a great success since its introduction with millions of pounds installed in commercial units around the world. Several of the first refiners to utilize a SmART System are still enjoying benefits today, or have reloaded another SmART System based on the exceptional first cycle they received from the technology. This article contains several case studies highlighting the performance of ART catalysts in a variety of ULSD units around the world. These are summarized in Table I. Refiner A is an initial user of a SmART System in Asia Pacific. This refiner conducted in-house testing for their ULSD catalyst selection. reprinted from Catalagram 14 SE 28 23

26 Region A AP B AP C AP D AP E NA F NA G NA H NA WABT, C Table I Summary of ULSD Case Studies Feed 4% cracked stock Straight Run Straight Run Straight Run 4% coker/lco 5% LCO 7% LCO 45% LCO/LCGO Inlet Pressure BARG N/A 86 9 Figure 1 Asia Pacific Refiner A LHSV % CoMo/ % NiMo 7/3 9/1 55/45 3/7 35/65 7/3 + Dewax 35/65 25/75 5 ppm product sulfur They requested catalyst samples from ART and a market leading domestic supplier. The DX TM Catalyst Platform tested as a substantially more active catalyst than the others in the program. As a result, ART was selected as the catalyst supplier for their unit, which started up in the last half of 24. This refiner was completing a revamp, which involved the addition of a new reactor in front of an existing reactor. They decided to use fresh catalyst in the new lead reactor while keeping used ART catalyst in the lag reactor. The unit conditions are characterized by an inlet pressure of 64 BARG and a LHSV of.7 hr -1. The feed contains up to 4% cracked stocks, and the product sulfur has averaged 5 ppm. The unit ran for three years before the refiner decided to change out the used catalyst in the lag reactor with fresh catalyst from ART. The performance of the unit is summarized in Figure 1 and, as the figure depicts, stability has been exceptional. WABT, C 293 Actual Normalized Days on Stream Low severity mode Product Sulfur: 15% <8ppm Figure 2 Asia Pacific Refiner B High severity mode Product Sulfur: 85% <8ppm Return to low severity mode: WABT dropped about 8 C Days on Stream Actual Normalized to 1 ppm Figure 2 shows data for Refiner B. This was another major Asia Pacific refiner using a SmART System. This refiner needed to produce 1 ppm sulfur diesel for two years in a newly revamped unit. The operating conditions for this unit are 53 BARG inlet pressure with an LHSV around.7 hr -1. The feed was a high end point, straight run diesel with typical sulfur content of 1.25 wt.%. This refiner was concerned with minimizing hydrogen consumption as hydrogen availability was limited at the refinery. This was a situation well suited for the flexibility of the SmART System to tune the hydrogen consumption/activity relationship. The optimum loading for this unit was 9% cobalt-molybdenum (CoMo) and 1% nickel-molybdenum (NiMo) catalyst. This design was expected to be significantly more active than an all CoMo loading and would consume the same amount of hydrogen as an all CoMo loading. The final selection of the SmART System was based on competitive pilot plant testing by the refiner. 24

27 About eight months into the ULSD portion of the cycle, the refiner significantly increased the operating severity and began producing very low sulfur diesel. Typically, 8 ppm is the recommended product sulfur target when producing <1 ppm ULSD. In the higher severity mode, the product sulfur was well below 8 ppm 85% of the time, whereas in the lower severity mode the product sulfur was below 8 ppm only 15% of the time. The higher severity led to a much higher deactivation rate and potentially jeopardized the two year cycle length. After discussions with the refiner, the severity was reduced and the two year cycle length was achieved. WABT, C Figure 3 Asia Pacific Refiner C Days on Stream Actual Normalized to 8 ppm 3 ART was chosen for the second cycle which again was based on competitive testing and the outstanding performance demonstrated in the first cycle. The current system is performing very well. Refiner C, another Asia Pacific refiner, selected ART catalysts for their ULSD unit based on the strong reference from the refiners mentioned above. This refiner needed to produce 8 ppm sulfur diesel for two years and hydrogen availability was not a constraint. The operating conditions included an inlet pressure of 59 BARG and LHSV of 1.2 hr -1. The feed was also a high endpoint, straight run diesel with a sulfur content of 1.8 wt.%. This was a more WABT, C demanding operation than those discussed previously, and a required system designed for maximum activity. The catalyst loading in this case was 55% CoMo and 45% NiMo. The performance is summarized in Figure 3. This unit met all performance targets during the two year cycle and has just been reloaded with a new SmART System. Figure 4 Asia Pacific Refiner D Days on Stream Actual Normalized to 8 ppm Operating data for Refiner D is shown in Figure 4. This is a grass roots ULSD unit in Asia Pacific. ART was chosen to participate in this project because of the excellent performance of the SmART System from previous references in the region. ART worked closely with the refiner and engineering construction firm on the design basis for this project. A 3% CoMo and 7% NiMo SmART System was designed for this unit in order to deliver maximum activity. The operating conditions for this unit included an inlet pressure of 78 BARG and LHSV of 1.1 hr -1. This unit also processes a straight run feed which has a relatively high level of nitrogen and an endpoint of 388 C (by D86). The unit is running well and meeting all performance expectations with a somewhat lower than estimated deactivation rate, and is well on track to meet the targeted threeyear cycle length. Refiner E is another grassroots ULSD unit, which started up in the second quarter of 26 in North America. ART worked with the licensor on the unit design and proposed a SmART System loading consisting of about 65% NiMo. This loading was designed for maximum activity as the design feed contained a high percentage of cracked stocks. The conditions of the unit included an inlet pressure of 74 BARG with an LHSV of 1.25 hr -1. This refinery processes mostly sweet crudes, and the feed to the unit typically contains about 4% FCC LCO and coker LGO. The activity of the system has been extremely high, allowing this refiner to operate at 2% over design charge rate. Figure 5 shows the reprinted from Catalagram 14 SE 28 25

28 performance for the cycle thus far, and it is evident from the figure that the catalyst stability has been excellent. In fact, the unit was designed for a 24-month cycle, but 48 months appears possible even at higher than design feed rates. This unit also typically processes 1% kerosene with occasional increases to as much as 3%. As can be seen in Figure 5, the addition of kerosene to the feed has no negative impact on the activity of the system, and may even improve the performance. Notice how the WABT decreases when processing higher amounts of kerosene. This suggests that the increase in feed vaporization (decrease in H 2 pressure) is offset by the decrease in hard to treat, substituted dibenzothiophene sulfur species. Figure 6 summarizes data from Refiner F in North America. This refiner had completed a project to revamp an existing hydrocracker to ULSD service. The objectives were to increase feed capacity from 477 to 7155 MTD, while ensuring the capability to process 5% or more LCO, as well as provide for cold flow improvement during the winter months. This refiner also wanted to minimize the hydrogen consumption so that feed rate could be maximized within make-up hydrogen constraints. Along with Süd Chemie, ART designed a dewaxing/ulsd catalyst system meeting the unit objectives. The unit started up successfully in the 2nd quarter of 26 and processes both sweet and sour crude derived feeds in block operation. The feed is also comprised of 4-5 vol.% of a high endpoint LCO. The performance of the unit is summarized in Figure 6. The unit came on stream with higher than expected activity, and is well on its way to exceeding the target three year cycle length. Additional details on this unit can be found in Catalagram 13, Spring 28. Refiner G is another grassroots unit which started up in the fourth quar- WABT, C Normalized WABT, C Normalized WABT, C Figure 5 North American Refiner E Days on Stream WABT Kerosene Figure 6 North American Refiner F Days on Stream Figure 7 North American Refiner G 5 ppm average product sulfur Days on Stream Kerosene, vol.% 26

29 Inlet Pressure, BARG Figure 8 North American Refiner G Hydrogen Availability 1 2 ter of 26. The performance of this unit is summarized in Figure 7. ART again worked closely with the licensor on the new unit design and proposed a SmART System loading using 65% NiMo catalyst for maximum activity. The unit typically processes >7% LCO, including both LCO produced within the refinery and purchased externally. The initial deactivation rate of the unit was significantly higher than expected, and it was determined that this was due to lower H 2 partial pressure than design combined with lower H 2 /Oil ratio. This can be seen in Figure 8 which shows the trend of reactor inlet pressure and the recycle hydrogen purity. Early in the cycle there were control issues and the inlet pressure showed a steady decline. The recycle hydrogen purity also decreased steadily and had periods where it fell dramatically. Once the H 2 partial pressure concerns were addressed, combined with better bed temperature management, the deactivation rate decreased significantly. The operation became much more consistent, and since that time the deactivation rate indicates that the unit will easily meet the expected 24-month cycle length. Finally for Refiner H, Figure 9 summarizes the performance of a Days on Stream Pressure Recycle H 2 WABT, C Recycle H 2 Purity, vol.% SmART System at a U.S. Gulf Coast refinery. This was another grassroots unit that started up in the Fall of 26. SOR activity met expectations, and since that time the unit operating severity has steadily increased. The current feedrate is 22% over design and the feedstock endpoint has increased by C. Typical unit conditions include.8 hr -1 LHSV and 9 BARG inlet pressure, and, on average, the unit processes a feed containing 15% FCC LCO, 3% LCGO and 5% coker naphtha. At times the unit has processed as much as 8% cracked stocks in the feed, and still the product sulfur has averaged less than 6 ppm for the cycle. The target cycle length was 24 months, and the unit is currently on track for a 36- Figure 9 North American Refiner H Days on Stream month cycle. Also shown in Figure 9 is the API uplift from the unit. From the chart, the API typically increases 6-1 numbers depending on the feedstock. As this sampling of case studies demonstrates, the SmART System has been employed in a wide variety of ULSD applications around the world. The technology has been successfully operating over a broad range of operating conditions from low to high pressure with feeds ranging from straight run to 8% cracked stocks. In each application, all expectations have been met or exceeded, and in a number of cases ART catalyst has been selected for the second cycle based on the excellent performance. ADVANCED REFINING TECHNOLOGIES continues to develop higher performance products for ULSD as evidenced by the recent introduction of the newest DX TM Catalyst Platform, 42DX. The addition of this catalyst to the ULSD portfolio is an example of the commitment that ART will continue to deliver state-of-the-art technology for ULSD API Gravity Increase WABT API Uplift reprinted from Catalagram 14 SE 28 27

30 Editor s Note: A lot has changed since ART first introduced the SmART Catalyst System series for ULSD in 21. Many ULSD units have been built or retrofitted and are now into their second or third cycles. Most countries in the world are either mandating ULSD from their refineries, or in the process of doing so. ART has made many improvements in its offerings for making ULSD as a result of extensive investment in the research and development of new and improved catalysts for expanding performance and flexibility. Since the introduction of CDY and CDX, ART is already on its third generation of catalysts. The premier catalysts used in today s SmART system are 42DX and NDXi. The table below shows the commercial experience of the SmART System. There are many repeat users among the more than 7 unit start-ups that have occurred using the SmART catalyst system. A wide variety of feedstocks and operating conditions are represented from units all over the world. SmART Catalyst System Users List Country/Region Start-up Date % Cracked Stock Product Sulfur (ppm) Pressure BARG % NiMo Catalyst Mid Continent, USA % Japan % Japan % Japan % Mid Continent, USA % Mid Continent, USA % Japan 25 1% Japan % Korea % Russia % South Africa % West Coast 26 1% Mid Continent, USA % Eastern Canada % South America % Korea % Russia % Mid Continent, USA % Mid Continent, USA % Gulf Coast, USA % Gulf Coast, USA % Gulf Coast, USA % Western Canada % 28

31 Country/Region Start-up Date % Cracked Stock Product Sulfur (ppm) Pressure BARG % NiMo Catalyst Gulf Coast % United Kingdom v Mid Continent, USA % Taiwan % Korea % Japan % South America % South America % Korea % Korea % Korea % Singapore % Russia % Russia % Russia % Thailand % Thailand % Russia % South Africa % Gulf Coast, USA % India % India % Thailand % Korea % Korea % Gulf Coast, USA % Russia % Australia % United Kingdom % Gulf Coast, USA % Chile % Gulf Coast, USA % Japan 29 % Poland % Singapore % Singapore % East Coast, USA % Russia % Taiwan % Taiwan % Mid Continent, USA % reprinted from Catalagram 14 SE 28 29

32 Distillate Pool Maximization by Exploiting the Use of Opportunity Feedstocks Such as LCO and Syncrude Brian Watkins Hydrotreating Technical Services Engineer Charles Olsen Worldwide Technical Services Manager ADVANCED REFINING TECHNOLOGIES Chicago, IL USA A s the distillate market demand has increased over the last few years, the production of ultra low sulfur diesel (ULSD) has prompted refiners to look for ways to maximize their diesel pool. One way to accomplish this has been to increase the use of opportunity feedstocks such as additional LCO, diesel streams from other hydroprocessing units, and feeds from various synthetic crudes. Some of these opportunity feedstocks, having already been processed through conventional refinery processes, may pose unexpected challenges to refiners wishing to incorporate them into the distillate pool. Some of these streams have proven to be significantly more difficult to process, underscoring the fact that it is important to understand the poten- tial impact of processing new feed streams in order to avoid unpleasant surprises. This paper highlights a few examples demonstrating significant differences in feed reactivity for a variety of different feed components which are not necessarily anticipated from the usual bulk feed analyses. FCC LCO and coker diesels have long been used as feed components combined with a straight run (SR) feed source to produce ULSD products. The quality of the LCO varies with distillation range, and depends on the severity of the pretreatment of the FCC feed as well as on the conditions in the FCC and the FCC catalyst employed. A common element in LCO is a very high 3

33 Table I Diesel Feedstock Analysis Light SR Gas Oil LCO EB Diesel Synthetic Diesel FB Diesel Sulfur, wt.% Nitrogen, wppm Specific Gravity Aromatics, vol.% Total Mono Poly Distillation, D2887, C Thiophenes 8 Benzothiophenes (BT) 2 69 Substituted BT s Di Benzothiophene (DBT) C 2 -DBT s ,6 DiMethyl DBT C 3 -DBT s concentration of polynuclear aromatic compounds relative to other feeds. Synthetic diesel material is often initially processed by either a coker or ebullating bed residue hydrocracking unit, and then processed through a hydrotreater or hydrotreater/hydrocracker combination. These hydrocracking units tend to operate at severe conditions in conjunction with high hydrogen partial pressures. At these conditions, the removal of all the easy, less refractory sulfur is readily achieved, and the majority of the multi-ring aromatics are saturated. This leaves a product which is relatively low in sulfur and PNA s and, when added to the feed to a ULSD unit, gives rise to a surprisingly difficult feedstock to process. Likewise, the use of diesel range products from an H-Oil, LC-FIN- ING TM unit or fixed bed resid desulfurizer can also have a significant impact on downstream diesel catalyst activity for similar reasons. The general properties of these types of diesel feeds often indicate that they may be relatively easy to hydrotreat due to their low sulfur content and API gravity which is often similar to SR materials. Table I lists the properties for several diesel feeds including the diesel product fractions from an ebullating bed resid (EB) unit, a fixed bed resid (FB) unit, and a diesel fraction from a Canadian synthetic crude. ART conducted pilot plant testing to investigate the impact of various diesel feed components on catalyst activity. The pilot work utilized the SR diesel shown in Table I as the base case feed. The other components shown in Table I were blended into the base feed at 2% by volume to show the effects on catalyst performance. The pilot plant work involved several tailored catalyst systems as well as changes to operating pressure and hydrogen rate in order to cover a broad range of operation. The base case testing was done at a hydrogen pressure of about 48 BAR, a LHSV of.7 and 232 Nm 3 /m 3 hydrogen/oil ratio. The catalyst system was a stacked system of high activity CoMo and NiMo catalysts containing >8% CoMo catalyst. This system was chosen due to limited hydrogen availability and a desire to minimize hydrogen consumption Additional information on the theory, design and use of this type of staged catalyst loading can be found in references 1-5. Table II shows the analysis of the different feed blends. The 2% LCO has 16 ppm lower sulfur, a one number lower API, and 2 ppm higher nitrogen content compared to the SR feed. The total aromatic content in the blend is also higher by 1 volume percent absolute. Compare this to the feed blends containing the EB diesel, FB diesel, or the synthetic diesel where all three have even lower sulfur com- reprinted from Catalagram

34 Table II Blended Diesel Feedstock Analysis Light SR 2% 2% Gas Oil 2% LCO EB Diesel 2% Syncrude FB Diesel Sulfur, wt.% Nitrogen, wppm Specific Gravity Aromatics, vol.% Total Mono Poly Distillation, D2887, C Thiophenes Benzothiophenes (BT) Substituted BT s Di Benzothiophene (DBT) C 2 -DBT s ,6 DM-DBT C 3 -DBT s pared to the SR, and slightly higher API gravities, despite having a higher total aromatic content. Other changes to note are the fact the feed nitrogen content stays fairly constant, and the mono aromatic content is higher and PNA content lower for these blends compared to the SR feed. Figure 1 summarizes some of the pilot plant data comparing the SR and LCO feed blends. It shows that the SR diesel requires a 23 C increase in temperature to go from about 1 ppm sulfur down to 1 ppm sulfur at base LHSV and pressure. The LCO blend requires almost 11 C higher temperature to achieve the same product sulfur relative to the SR feed. The product from the LCO blend has a two to three number lower API compared to the SR product, and hydrogen consumption increases significantly for the LCO blend due to saturation of additional polyaromatic compounds found in the LCO. These lat- Required Temperature Increase, C Figure 1 Activity Comparison on SR and Blended SR/LCO Product Sulfur, ppm LCO SR 32

35 ter consequences set limits on the amount of LCO which can be processed and still meet product cetane specifications and hydrogen availability constraints. Results indicate that both feeds have similar API number upgrades (i.e. product feed) as the reactor increases in temperature; however, the actual product API is different at equal product sulfur. Even though the LCO blended feedstock requires a higher temperature to achieve the same product sulfur, the product API is still about a full number lower as shown in Figure 2. Figure 2 Comparison of Product Gravity for the SR and LCO Blend LCO SR Specific Gravity The LCO also has the additional issue of increasing hydrogen consumption when added to the ULSD operation. Figure 3 compares the aromatic saturation achieved on the blended LCO feedstock as compared to the SR. The majority of the aromatic saturation occurs with the poly aromatic compounds and, as shown in Table II, the LCO blend contains significantly more PNA s compared to the SR feed. The hydrogen consumption is estimated to be Nm 3 /m 3 higher for the LCO blend at 1 ppm product sulfur. The figure above shows that processing LCO is significantly more difficult than processing the SR feed. One option to gain back some of the lost activity is to change the Increasing WABT, C end point of the LCO in the feed. ART completed pilot plant testing on an LCO stock as received and the same LCO with a 22 C end point reduction to simulate how this can affect catalyst performance. Table III lists the major component analysis of the two LCO feeds. The decrease in endpoint lowers the total sulfur by almost 1 ppm and total nitrogen decreases by 129 ppm. The impact this degree of LCO endpoint reduction has on ULSD performance is over 17 C difference in activity which corresponds to additional life in Figure 3 Comparison of Aromatic Saturation Increasing WABT, C LCO SR Change in Total Aromatics, vol.% the hydrotreater. A comparison of the two LCO feeds blended at 3% into SR feed is shown in Figure 4. The addition of LCO has a major impact on activity for both the low and high endpoint LCO materials. The required temperature increase for ULSD in going from to 3% LCO for the lower endpoint material is about.7 C per percent LCO. Processing the higher endpoint LCO increases the required temperature to about.8 C per percent LCO. Figure 5 demonstrates this more clearly in the form of a plot of the required temperature increase as a function of LCO content. Notice from the chart that the activity effects are not exactly linear with increasing LCO content. The first 15% LCO has a larger impact on activity than the next 15%. The diesel products from an EB unit, a FB unit and the synthetic crude diesel provide very different sulfur distribution patterns compared to the SR feed and LCO shown in Table I. Almost all of the sulfur species in those feeds are multisubstituted dibenzothiophenes, the so-called hard sulfur species. The species groupings from sulfur speciation using a GC-AED technique, however, indicate little about what the actual molecular structure is reprinted from Catalagram

36 Required Temperature Increase, C Required Temperature Increase, C Table III Impact of End Point Reduction on FCC LCO Type Specific Gravity Sulfur, wt.% Nitrogen, ppm Aromatics, lv.% Mono-, lv.% Poly-, lv.% Dist., D2887, C IBP 1% 5% 7% 9% FBP LCO (Low FBP) LCO (High FBP) Figure 4 Impact of LCO Endpoint Reduction on Hydrotreating Performance SR Product Sulfur, ppm 3% Hi FBP LCO 3% Lo FBP LCO Figure 5 Activity Comparisons at Different LCO FBP and Concentration Hi EP LCO Lo EP LCO since the basic technique separates out the sulfur based on boiling point distribution. The sulfur molecules left in these previously treated feeds have already been processed once in a high temperature, high pressure hydrotreating application. Those conditions easily remove the majority of sulfur molecules and leave only those sulfur species that are multi-ring, sterically hindered molecules and other aromatic nitrogen compounds. It is these species that require a greater level of saturation or ring opening before the nitrogen or sulfur can be removed. It is likely for there to be very low concentrations of multiple-ring, partially saturated compounds that need to be more fully saturated in order to remove the sulfur. This is enough to make it more difficult to produce 1 ppm sulfur product from such feeds. An understanding of the upstream processing is important when considering the use of synthetic crudes. Production of synthetic fuels involves a combination of several processes in order to accommodate downstream processing. These upstream processes include coking or an ebullating bed resid operation, followed by a hydrotreating or hydrocracking operation in order to produce a lighter grade material. These products are then blended in with other heavier materials as a diluting or cutting stock and sent downstream as synthetic crude. The synthetic diesel used in this work is taken from a product diesel cut from a synthetic VGO hydrocracker. Figure 6 shows the activity difference between the SR and the blended SR/synthetic diesel. Note that at higher product sulfur, the two feedstocks respond fairly similarly to each other. As the application becomes more demanding, the required reactor temperature increases dramatically for the synthetic diesel feed as compared to the SR feed. The blended feed requires more than 14 C higher temperature relative to the SR to achieve ULSD sulfur levels. % LCO 34

37 Figure 6 Activity Comparison of the SR and Synthetic Diesel Blend Required Temperature Increase, C Product Sulfur, ppm SR Synthetic Figure 7 Activity Comparison of Previously Hydrotreated Streams Required Temperature Increase, C Product Sulfur, ppm Synthetic FB EB Figure 8 Comparison in Specific Gravity Syn Diesel SR Increasing WABT, C Specific Gravity It is reasonable to expect that the upstream hydroprocessing of the synthetic diesel material results in a feed which behaves similarly to other previously hydrotreated feedstocks like those from the EB and FB resid applications. Two feedstocks from these sources are shown in Figure 7. These two feedstocks have a remarkably similar response as that observed for the synthetic diesel feedstock. The fixed bed diesel fraction, which has significantly lower sulfur and nitrogen than the other two feedstocks, shows over 22 C higher SOR than either the EB or synthetic diesels at 1 ppm sulfur. These data show that upstream processing prior to treating in a ULSD unit can have a dramatic effect on the activity of the unit and consequently decrease cycle length. Figure 8 examines how the product API is changed during processing for the synthetic diesel blend. As can be seen, there is only a one number increase in product API over an almost 56 C WABT change compared to greater than two number increase for the SR feed over a similar temperature span. Aromatic saturation in the ULSD unit is also a concern in order to meet required cetane and aromatic targets. The higher temperature required to process these previously processed streams may make it difficult to achieve much aromatics saturation because of the approach to the thermodynamic equilibrium limit for aromatic saturation. Figure 9 compares the aromatic saturation achieved for the SR diesel and the synthetic diesel blend. The synthetic diesel has a low level of poly aromatic compounds, and the blend actually has a slightly lower concentration of PNA s compared to the SR feed. Less saturation is achieved on the synthetic blend, probably a reflection of the fact that mono aromatic molecules are the predominant species, and these are quite difficult to saturate. The equilibrium limit on conversion is readily apparent in the figure. The synthetic reprinted from Catalagram

38 diesel provides a two number decrease in total aromatics while the SR diesel has an almost 1 number decrease. This can be problematic if trying to meet an aromatic target in the diesel pool. When evaluating opportunities to hydrotreat previously treated streams for ULSD, the need to examine the catalytic effects of these feeds is important. ART completed a series of pilot tests using the synthetic diesel feed blend covering a wide range in operating conditions. Figure 1 summarizes some of the results for one of ART s high activity CoMo catalysts. The base case condition was again 48 BAR, 232 Nm 3 /m 3 hydrogen/oil ratio and.7 LHSV. As you can see from the figure, the base case conditions result in the highest start of run temperature for ULSD. Increasing the H 2 /Oil ratio to 463 Nm3/m3 results in a decrease in the SOR WABT of over 8 C. The third data set shows results for higher hydrogen partial pressure, 9 BAR, and 463 Nm 3 /m 3 hydrogen to oil ratio. This results in a gain of 14 C lower SOR compared to the base case conditions or an incremental 6 C lower temperature due to the increase in hydrogen pressure. Finally, increasing the hydrogen rate to 712 Nm 3 /m 3 at high pressure provides over 17 C lower SOR as compared to the base case system, but only an additional 3 C relative to the high pressure lower gas rate case. These data clearly demonstrate the significant benefits of increasing hydrogen partial pressure when treating these types of difficult feeds. Making the switch to using a NiMo catalyst in this application has much more significant effect on unit performance. In Figure 11 the base case conditions of low pressure and low hydrogen/oil ratio actually result in activity which is similar to what was observed at these conditions for the CoMo catalyst. After increasing the hydrogen rate at low pressure, the all NiMo system gains over 14 C relative to the base condi Figure 9 Change in Total Aromatics on SR and Synthetic Diesel Required Temperature Increase, C Syn Diesel SR Increasing WABT, C Figure 1 CoMo Catalyst Activity on Synthetic Diesel Required Temperature Increase, C Product Sulfur, ppm 48 BAR & 232 H 2/Oil 48 BAR & 463 H 2/Oil 9 BAR & 463 H 2/Oil 9 BAR & 712 H 2/Oil Figure 11 NiMo Catalyst Activity on Synthetic Diesel Product Sulfur, ppm 49 BAR & 232 H 2/Oil 48 BAR & 463 H 2/Oil 9 BAR & 463 H 2/Oil 9 BAR & 712 H 2/Oil Total Aromatics, vol.%

39 tions, a larger activity gain than observed for the CoMo catalyst. The activity benefit increases to over 22 C lower required temperature at 13 psia, and increasing the hydrogen rate to 712 Nm 3 /m 3 results in over 28 C lower temperature compared to the base conditions. The NiMo catalyst is at least 11 C more active than the CoMo catalyst at this last set of conditions. Clearly there is a need to maximize saturation when treating these preprocessed types of feeds. Any increase in hydrogen partial pressure helps this and, as the data just discussed indicates, the catalyst selection has a significant impact. High activity NiMo catalysts are better saturation catalysts compared to high activity CoMo catalysts, and this appears critical to removing the harder sulfur species present in these preprocessed feeds. In units that are constrained by limited hydrogen or lower hydrogen pressures, the use of even a small amount of NiMo catalyst will prove to be beneficial in order to remove the remaining difficult sulfurs. Advanced Refining Technologies can work closely with refining technical staff to help plan for processing opportunity feeds such as those discussed above. One of the keys is being aware of the potential impact processing certain feeds will have on unit performance. Feeds which have been previously processed present unique challenges and ART is well positioned with its experience at providing customized catalyst systems for ULSD applications. Opportunity feeds provide yet another objective to consider when designing the appropriate catalyst system to maximize unit performance. References 1. Olsen, C., Krenzke, L.D., Watkins, B., AICHE Spring National Meeting, New Orleans, March Krenzke, D., Armstrong, M., 21 ERTC Meeting, Madrid, Spain. 3. Olsen, C., Krenzke, L.D., 25 NPRA Annual Meeting, Paper AM Olsen, C., D Angelo, G., 26 NPRA Annual Meeting, Paper AM Olsen, C., Watkins, B., Shiflett, W., ERTC Meeting, Barcelona, Spain, November 27 reprinted from Catalagram

40 Cetane Improvement In Diesel Hydrotreating Greg Rosinski Technical Services Engineer Charles Olsen Worldwide Technical Services Manager ADVANCED REFINING TECHNOLOGIES Chicago, IL USA D emand for higher performance in diesel engines has resulted in an increase in minimum cetane numbers for diesel fuel. It is expected that the desire for higher cetane will continue as indicated by the recommendations of the World Wide Fuels Charter. Thus, it is important for refiners to understand the effects of both feedstock and processing parameters on the cetane of diesel fuel to enable them to more effectively manage their distillate hydrotreating units to meet ever more stringent fuels specifications. While some diesel is produced in hydrocrackers, the vast majority of diesel is processed in diesel hydrotreaters (DHT s) which usually co-process streams such as FCC LCO, LCGO, SR diesel, and Kerosene. The units processing significant amounts of cracked stocks need special attention in order to meet product cetane requirements. To understand why this is so it is necessary to know what cetane is, and how the different molecular species influence it. The cetane number is a measure of the ignition quality of diesel fuel and is based upon the compound cetane or hexadecane which is assigned a cetane number of 1. It is analogous to the octane number in gasoline. Gasoline octane increases with olefin, aromatic, and iso-paraffin contents, whereas cetane number increases with paraffin and naphthene contents. 38

41 Table I Cetane Number of Pure Compunds Paraffins Isoparaffins Naphthenes Aromatics Compound Formula Cetane Number n-decane C1H22 76 n-pentadecane C15H32 95 n-eicosane C2H Ethyldecane C12H ,5-Diethyloctane C12H26 2 Heptamethylnonane C16H Propylpentadecane C18H ,8-Diethyltetradecane C18H ,1-Dimethyloctadecane C2H42 59 Decalin C1H Cyclohexylhexane C12H Methyl-3-cyclohexylnonane C16H Cyclohexyltetradecane C2H Methylnaphthalene C11H1 n-pentylbenzene C11H16 8 Biphenyl C12H Butylnaphthalene C14H16 6 n-nonylbenzene C15H Octylnaphthalene C18H24 18 n-tetradecylbenzene C2H34 72 Thus, a fuel with a high cetane value has low octane and visa versa. Table 1 lists some pure compounds and their corresponding cetane number. As can be seen, paraffins, particularly normal paraffins, have very high cetane numbers while aromatics, especially naphthalene type aromatics, have very low cetane numbers. Certain distillate range materials like FCC LCO are high in naphthalenes which explains the low cetane number of LCO feedstocks. The actual cetane number is rarely analyzed in refineries since it requires a specialized motor for its determination. Most refiners use cetane index, typically, ASTM D-976 and ASTM D D976 uses the API gravity and the 5% distillation point, whereas D4737 uses the gravity with the 1%, 5% and 9% distillation points. The two equations are shown below. ASTM D-976 cetane index = *API *API*(log(T5)) *log (T5).189 *T5 2 Where T5 is the D86 5% point in degrees F ASTM D-4737 Cetane index= *( T1-215)+[ * B]*[T5-26] + [ (. 4 2 ) * ( B ) ] [ T 9-31]+[.49]*[(T1-215) 2 (T9-31) 2 ] + (17)*(B) + (6)*B 2 Where: B = Exp[-3.5*(sp. gr..85)] 1 and the D86 temperatures are in C Figure 1 compares the cetane index (D976) for a number of different distillate feed sources. It is readily apparent that FCC LCO s have the lowest cetane while straight run (SR) materials have the highest cetane. Distillate feeds derived from coking operations tend to have a cetane similar to SR material, while kerosene tends to have somewhat lower cetane owing to the lower boiling point. For the diesel range materials, the feeds with lower API gravity (LCO) have lower cetane index demonstrating that within a given boiling range the API is a reasonable tool for estimating the cetane index. Figure 2 shows the cetane index as a function of poly aromatics content for a variety of distillate feeds. The LCO s clearly have the highest concentration of poly aromatics and correspondingly lower cetane index. The SR, LCGO and vacuum bottom gas oil (VBGO) all have considerably lower PNA content with higher cetane index values compared to the LCO s. Kerosenes have very low polynuclear aromatics (PNA) content, but because of the lower molecular weight (kerosene generally has compounds containing less than 16 carbon atoms) the cetane index is slightly lower than for SR diesel material. The figures make it clear that when it comes to cetane, LCO is a problem due to the high PNA content. reprinted from Catalagram 16 SE 29 39

42 Treating feedstocks that contain LCO will become more challenging as LCO yields increase and cetane requirements become more stringent. With this in mind, it is useful to survey the level of performance currently being achieved in commercial diesel hydrotreating units today. This will help to define what the reasonable level of cetane uplift that can be expected is, and if there is a practical maximum uplift that can be achieved via hydrotreating. It is also useful to ascertain whether current operations indicate if cetane changes (decreases) during the cycle. All of these are important questions for refiners interested in increasing diesel yields from lower quality feedstocks. There are a number of parameters which influence cetane improvement in the diesel hydrotreater. Hydrogen partial pressure and LHSV are key operating conditions which effect the product cetane. Catalyst selection also plays an important role since at higher pressures NiMo catalysts have a higher PNA saturation activity compared to CoMo catalysts. Figures 3 shows the level of cetane increase (measured by delta cetane index) that has been achieved commercially as a function of unit LHSV. Generally speaking, as LHSV decreases the potential cetane improvement increases. At a LHSV around 1 hr-1 or less, cetane index increases of 1 or more numbers are achievable (provided the H 2 pressure is high enough), while at a LHSV greater than about 1.7 hr-1 the cetane improvement is about 4 numbers or less. Figure 4 summarizes the cetane increase as a function of unit pressure. Not surprisingly, higher pressure units tend to achieve much larger cetane increases. In these examples, the cetane uplift is typically less than 6 numbers when the unit pressure is less than 69 BARG. Cetane uplift increases to 8-1 numbers as pressure increases beyond 69 BARG. The data in Figures 3 and 4 also suggest there might be a 4 Cetane Index (D976) Figure 1 Cetane Index of Various Distillate Feeds LCO Feed Specific Gravity LCGO/VBGO Straight Run Kerosene Figure 2 Cetane Index and Polynuclear Aromatics (PNA s) Feed Cetane Index (D976) Feed PNA s, vol.% LCO LCGO/VBGO Straight Run Kerosene Figure 3 Effect of LHSV on Cetane in a Variety of Commercial Units Delta Cetane Index LHSV Refiner A Refiner B Refiner C Refiner D Refiner E Refiner F

43 Delta Cetane Index Figure 4 Effect of Unit Pressure on Product Cetane Reactor Inlet Pressure, BARG Refiner A Refiner B Refiner C Refiner D Refiner E Refiner F Figure 5 Feed Gravity Has a Significant Impact on Cetane Uplift Delta Cetane Index Delta Cetane Index Feed Specific Gravity Refiner A Refiner B Refiner D Refiner E Refiner F Figure 6 API Uplift and Cetane Increase for Several Commercial Units Delta, API Refiner A Refiner B Refiner D Refiner E Refiner F practical limit to cetane improvement achieved from typical hydrotreating. Comparing the cetane uplift achieve by Refiners A and C shows about 8-1 number improvement for both units despite the difference in operating pressure at similar LHSV. Figure 5 summarizes the commercial data in another way. It shows how the cetane increase correlates with the API gravity of the feed. In general, the cetane uplift increases as the feed API decreases. Figure 6 shows how the observed API increase correlates with the cetane index increase. This data shows that the API uplift is a reasonable predictor for the cetane increase. The hydrogen consumption is another important consideration when discussing cetane improvement. There is a general rule of thumb that says the hydrogen consumption is roughly equal to (1* API Uplift) or (1* Cetane uplift). Averaging the H 2 consumption required for the observed cetane increase with the units discussed here indicates that the H 2 consumption varies from about (8*Cetane uplift) at low pressure (Refiner D) to (15-175* Cetane uplift) for the high pressure units (Refiners A & C). The data suggests the rule of thumb is a reasonable estimate for H 2 consumption for units operating below about 69 BARG. These data demonstrate that as the unit conditions (LHSV and pressure) get more favorable for PNA saturation, the cetane uplift increases. However, is cetane uplift constant during an entire cycle? Figure 7 summarizes the observed cetane from three ULSD units currently using SmART systems. Refiner A is a high pressure unit with a LHSV around 1. The feed to this unit contains 4-5 vol.% LCO. This unit has not experienced a significant decline in cetane uplift during the cycle. Refiner B is a higher LHSV unit, with a lower pressure than Refiner A, but the feed is rela- reprinted from Catalagram 16 SE 29 41

44 tively light with about 35-4 vol.% LCO and LCGO. Despite the lower pressure and higher LHSV, this refiner also did not see an appreciable decline in cetane uplift during the cycle. Refiner C is a higher pressure unit with a lower LHSV compared to Refiner B. The feed is high in sulfur with large (>8 vol.%) amounts of cracked stock, especially LCO. This unit does show a slow, steady decline in cetane uplift; the cetane uplift is 2-3 numbers lower after more than two years on stream. This suggests that units with difficult feeds containing high fractions of LCO and other cracked stocks, or units without sufficient hydrogen, will experience decreasing cetane uplift during the cycle. As mentioned previously, the catalyst system will also have an impact on the degree of cetane uplift achieved in a hydrotreater. It is common knowledge that NiMo catalysts have a higher saturation activity than CoMo catalysts, and therefore a NiMo catalyst is expected to deliver greater cetane uplift. Figure 8 summarizes pilot plant data which demonstrates this. These data were generated using a 5% LCO containing feed, and shows that the NiMo catalyst results in almost twice the cetane uplift compared to the CoMo catalyst. The SmART Catalyst System, which utilizes both the CoMo and NiMo catalyst, results in a cetane uplift which is nearly 2 numbers higher than the all CoMo system with only a small increase in hydrogen consumption. For H 2 constrained refiners this is an ideal solution for improving the product cetane. Delta Cetane Index Figure 7 Variation in Cetane Uplift During a Cycle Days on Stream Refiner A Refiner B Refiner C Figure 8 The Catalyst System Has a Large Impact on Cetane Uplift Cetane Index Increase Temperature, C NiMo CoMo SmART 42

45 Factors Influencing ULSD Product Color Greg Rosinski Technical Services Engineer Brian Watkins Technical Services Engineer Charles Olsen Worldwide Technical Services Manager ADVANCED REFINING TECHNOLOGIES Chicago, IL USA P roduct color is a common concern for refiners with a number of petroleum products including kerosene, jet fuel, diesel fuel and lube base oils. With the introduction of ultra low sulfur diesel (ULSD) the issue of diesel product color has become more of an issue as the typical ULSD unit cycle length may now be limited by color degradation of the product. Refiners have been uncertain about end of run (EOR) reactor outlet temperatures with expectations in the range of C. The typical ULSD unit has a deactivation rate in the range of C/month so an increase in EOR temperature of 6-11 C has a significant impact on a refiner s planning and economics. Figure 1 summarizes data from a commercial ULSD unit using ART catalysts. The data shows that in this case the product color exceeded 2.5 ASTM, the pipeline color specification for diesel, at a reactor outlet temperature above 388 C. The feed to this unit contained 3% LCO and it was operated at 1. LHSV and 59 BARG inlet pressure. It is well known that the color of distillate products is affected by the reaction conditions in the hydrotreater, especially temperature and hydrogen partial pressure. As (outlet) temperature increases and/or hydrogen partial pressure decreases, the product color degrades. It is also generally accepted that the species responsible for color formation in distillates are polynuclear aromatic (PNA) molecules. Some of these PNA s are green/blue and fluorescent in color which is apparent even at very low concentrations of these species. Certain nitrogen (and other polar) reprinted from Catalagram

46 Product Color (ASTM) Figure 1 ULSD Product Color Using a SmART Catalyst System TM compounds have also been implicated as problems for distillate product color and product instability. These species can polymerize to form condensed aromatic structures which tend to be green to yellow/brown in color and can also form sediment via oxidation and free radical reactions. (1) Work conducted by Ma et.al. (2) concluded that the specific species responsible for color degradation are anthracene, fluoranthene and their alkylated derivatives. These are both three ringed aromatic structures and are shown in Figure 2. Reactor Outlet Temperature C PNA s such as these are readily saturated to one and two ringed aromatics under typical diesel hydrotreating conditions at start of run (SOR), but as the temperature of the reactor increases towards EOR, an equilibrium constraint may be reached whereby the reverse dehydrogenation reaction becomes more favorable. At some combination of low hydrogen partial pressure and high temperature the dehydrogenation reaction predominates and PNA s begin to form resulting in a degradation of the color of the diesel product. Other work completed by Takatsuka et.al. (3,4) showed that the color bodies responsible for diesel product color degradation were concentrated in the higher boiling points in the diesel (>25 C). This suggests that color can be improved by adjusting the diesel endpoint. They also suggest that the color bodies responsible for color formation in desulfurized diesel are newly formed PNA structures from desulfurized aromatic compounds. To learn more about color degradation in ULSD, ART completed a pilot plant study which investigated diesel product color over a wide range of operating conditions. The study utilized spent ART CDXi, a premium high activity CoMo catalyst for ULSD. The sample of spent catalyst had been in commercial diesel service for well over a year and had a carbon content of 1.9 wt.%. The testing program included straight run (SR) diesels, a 3 vol.% LCO blend and a 3 vol.% light coker gas oil (LCGO) blend. The properties of all the feeds are listed in Table I. The test was designed to examine the effects of H 2 partial pressure, H 2 /Oil ratio and temperature on ULSD product color. H 2 partial pressure varied from 2-8 BAR and the H 2 /Oil ratio covered the range of Nm 3 /m 3. Figure 3 shows how the diesel product color changes with temperature and pressure for the straight run feed (SR #1). Not surprisingly, pressure clearly has a significant impact. At the lowest operating pressure, which corresponds to BAR H 2 pressure, the product color exceeds 2.5 ASTM at a temperature greater than C. Doubling the unit pressure to 55 BARG allows the temperature to increase to 416 C before the product color reaches 2.5 ASTM, and at even higher pressures the product color is well below 2.5 ASTM for all practical temperatures encountered in ULSD processing. At these con- Figure 2 Primary Fluorescence Species in Hydrotreated Diesel (Ref 2) anthracene fluoranthene 44

47 Table I Feedstock Properties Specific Gravity Sulfur, wt.% Nitrogen, wppm Total Aromatics, vol.% PNA s (2-ring+), vol.% ASTM Color Distillation (D2887), C IBP 1% 5% 9% FBP SR # L SR #1/LCO L SR # L SR #2/LCGO L ASTM Color Figure 3 Product Color Improves with Pressure Straight Run 28 BARG 55 BARG 83 BARG Temperature, C Figure 4 Product Color Improvement with Increased H 2 /Oil Ratio ASTM Color Straight Run 125 Nm 3 /m 3 H Nm 3 /m 3 H Temperature, C ditions the H 2 partial pressure increases by a factor of about 3.4 going from 28 BARG up to 83 BARG total pressure for temperatures around 4 C. The data in Figure 3 were generated at the low end of H 2 /Oil ratios investigated. Figure 4 shows the effect of increasing the H 2 /Oil ratio at 28 BARG on the SR #1 feed. At this low pressure, the H 2 /Oil ratio has a significant impact on product color. The data show that the temperature can be increased from 396 C to well above 44 C before product color exceeds 2.5 ASTM. AT 28 BARG total pressure and 44 C, changing the H 2 /Oil ratio from Nm 3 /m 3 results in a 1% increase in H 2 partial pressure which appears to be enough to keep the reaction environment on the favorable side of the hydrogenation-dehydrogenation equilibrium curve. At higher operating pressures the impact of increasing the H 2 /Oil ratio is reduced when processing the SR feed, but still has a positive effect on suppressing product color. As might be expected, adding LCO to the ULSD unit feed makes the product color situation worse. Figure 5 compares the product color for the SR feed and the 3% LCO feed at 375 Nm3/m3 H 2 /Oil ratio and two pressures. The SR feed results in acceptable color reprinted from Catalagram

48 over the wide range of temperatures for both pressures shown. This compares with the 3% LCO feed which goes off color at about C at 55 BARG; and at 83 BARG the temperature can exceed 44 C before reaching 2.5 ASTM color. This data demonstrates the significant impact that pressure has on diesel product color when processing feeds that contain LCO. Figure 6 demonstrates the effects of the H 2 /Oil ratio on product color when processing the 3% LCO feed. It shows the temperature at which the color reaches 2.5 ASTM as a function of H 2 /Oil ratio for both 55 and 83 BARG total pressure. The temperature increases by about 14 C when the H 2 /Oil ratio is increased from 125 to 375 Nm 3 /m 3. That range of H 2 rates corresponds to an increase in hydrogen partial pressure of 5-1% The pilot plant program also investigated the effects of a coker derived material on ULSD product color. Figure 7 compares the product color for the second SR feed and a 3% LCGO/7% SR #2 blend at 55 BARG. The data indicates that the feed containing LCGO behaves similarly to the SR feed. In both cases the outlet temperature can exceed 416 C before product color approaches the ASTM 2.5 level. This is not surprising when comparing the properties of the two feeds. The aromatics level, and in particular the PNA concentrations, are essentially the same for the SR and the coker blend. Compare this with the LCO blend shown in Table I where the PNA s are twice that of the SR or LCGO feeds. Figure 5 Comparison of Product Color for SR and 3% LCO ASTM Color Temperature for 2.5 ASTM Color, C SR LCO BARG 55 BARG Temperature, C 55 BARG 83 BARG H 2 /Oil Ratio, Nm3/m3 83 BARG 55 BARG Figure 6 Effects of H 2 /Oil Ratio on Product Color for 3% LCO Figure 7 Product Color Comparison for LCGO and SR SR #2 LCGO As mentioned previously, it is generally accepted that product color is related to PNA s, and earlier work has concluded that specific threeringed aromatics are responsible for color degradation in diesel. Figure 8 shows a comparison of the product PNA s (three-ring aromatics) and diesel product color 46 ASTM Color Temperature, C

49 for all the feeds and conditions of the study. It is readily apparent that the PNA s correlate reasonably well with product color.. Figure 8 3+ Ring Aromatics Correlate with Diesel Product Color 4. From these data it is clear that hydrogenation of PNA s is key to maintaining acceptable product color in ULSD. This suggests a couple of approaches that allow an increase in EOR outlet temperatures and thereby increase the ULSD unit cycle length. ASTM Color SR LCO LCGO One approach which has been put to commercial practice is to increase quench to the bottom bed of the hydrotreater. This accomplishes two things which are important to maintaining a good environment for hydrogenation of PNA s. It reduces the outlet temperature and helps to increase the outlet hydrogen partial pressure relative to no or lower amounts of quench. This, of course, requires that the upper beds of the hydrotreater be run at higher WABT s in order to maintain the required HDS conversion. This means that the furnace must have sufficient capacity to achieve the higher inlet temperatures. Operating in this manner offers the potential to add an additional 6-11 C on to the cycle length depending on the unit capabilities (furnace, quench capacity) Product PNAs (3 rings+), vol.% Another approach, which may be implemented with the one just discussed, involves adjusting the feed to the unit. The data from this work shows the significant impact LCO has on diesel product color. Reducing (or eliminating) the amount of LCO in the feed will help to suppress product color degradation as the unit approaches EOR. There is also data showing that the color bodies that cause problems for ULSD tend to be concentrated at the higher boiling points of the distillation on the feed/product. Reducing the endpoint of the LCO reduces the concentration of these species which will help maintain acceptable product color as the unit moves towards EOR. References 1. J. Pedley et.al, ACS Division of Fuel Chemistry, 35 (4), (199). 2. X. Ma et. al., Energy and Fuels, 1, pp (1996). 3. T. Takatsuka et.al., 1991 NPRA Annual Meeting, Paper AM T. Takatsuka et.al., Journal of the Japan Petroleum Institute, Vol. 23, No. 2, pp , reprinted from Catalagram

50 Hydroprocessing Catalysts from Chevron and Grace ART delivers innovative and economic hydroprocessing catalyst solutions worldwide, helping refiners on their never-ending quest to upgrade difficult petroleum feedstocks into clean fuels and other valuable products. Supported by cutting edge research and development and world class technical service, the joint venture between Chevron and Grace combines over 6 years of material science expertise and catalyst formulation experience with over 3,3 unit-years operating experience. In addition, our partner affiliate licenses exceed 26 units across the globe. Let ART be part of your solution. For more information on our products, contact us. Advanced Refining Technologies 75 Grace Drive Columbia, MD 2144 USA V F E artcatalysts.com

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52 Advanced Refining Technologies Columbia, Maryland USA Fax Houston, Texas USA Fax Singapore Fax Richmond, California USA Fax Worms, Germany Fax Toda, Japan Fax Advanced Refining Technologies 21 The information presented herein is derived from our testing and experience. It is offered, free of charge, for your consideration, investigation and verification. Since operating conditions vary significantly, and since they are not under our control, we disclaim any and all warranties on the results which might be obtained from the use of our products. You should make no assumption that all safety or environmental protection measures are indicated or that other measures may not be required. GRACE, GRACE DAVISON, GR, and SmART Catalyst System are trademarks, registered in the United States and/or other countries, of W. R. Grace & Co.-Conn. H-OIL is a registered trademark of Axens North America, Inc. CHEVRON, ICR, LC-FINING is a trademark of Chevron Lummus Global. OCR is a registered trademark of Chevron Intellectual Property LLC. HOP is a registered trademark of Japan Energy Corporation licensed to Advanced Refining Technologies LLC. This presentation is an independent publication and is not affiliated with, nor has it been authorized, sponsored, or otherwise approved by any of the aforesaid companies. ART and Advanced Refining Technologies are trademarks, registered in the United States and/or other countries, of Advanced Refining Technologies LLC. ApART, AT, DX, LS, HSLS and StART are trademarks of Advanced Refining Technologies LLC. This trademark list has been compiled using available published information as of the publication date of this brochure and may not accurately reflect current trademark ownership.