Development of Chloride Traps Containing Zinc Oxide for. CCR Type Catalytic Reforming Process

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1 Development of Chloride Traps Containing Zinc Oxide for CCR Type Catalytic Reforming Process Kaoru Fujiwara, Takayuki Ninomiya Japan Energy Corporation, Mizushima Oil Refinery, -1 Ushiodori, Kurashiki-shi, Okayama, , Japan Abstract Net hydrogen off-gas from the continuous catalyst regeneration type catalytic reforming process (CCR process) contains inorganic and organic chlorides. In order to prevent potential problems such as corrosion in the downstream processes, such chlorides are commonly removed by using fixed-bed chloride traps. However, the widely used activated alumina based chloride traps have the disadvantage of formation of organic chloride from inorganic chlorides on the surface and leakage of the organic chlorides to the downstream processes. And zinc oxide based chloride traps have problems with pellet breakage and pressure drop buildup due to the deliquescence of zinc chloride derived from zinc oxide and some chloride compounds. To solve these problems, the chemical and physical properties of zinc oxide based chloride traps have been improved. Consequently, we developed a new zinc oxide based chloride trap. Demonstration tests of this new chloride trap showed the effective removal of both inorganic and organic chlorides without pressure drop buildup or pellet breakage. This development was performed by the joint business of Japan Energy Corporation and Süd Chemie Catalysts Japan, Inc. 1. Introduction The continuous catalyst regeneration type catalytic reforming process (CCR process) is a very popular process to produce Benzene, Toluene, Xylene and so on from heavy naphtha as raw material. In the process of catalyst regeneration, some organic chloride compounds are generally injected to that system in order to regulate the performance of the reforming catalyst [1]. So, the net hydrogen off-gas from CCR process is including inorganic chloride (HCl) and some organic chloride compounds, and they may lead to some problems in the downstream processes, for example, (1) chloride stress corrosion cracking, () plugging of the fuel burner, and so on. In order to prevent these potential problems, chloride compounds are commonly removed by using fixed bed chloride traps. Several materials have been used for chloride removal. These 1/1

2 include activated aluminas and zinc oxide/calcium oxide materials. [-3]. Although activated aluminas have certain disadvantage of the potential to promote formation of organic chlorides, gums and green oils. Zinc oxide based chloride traps generally eliminate these problems, but may have problems with pellet breakage and pressure drop build-up. Through a close cooperative effort between Japan Energy Corporation and Süd Chemie Catalysts Japan, Inc, a series of improved chloride traps have been developed [-5]. These new products and their commercial performance will be discussed in detail.. Background Since 1991, Japan Energy Corporation (JE) Mizushima oil refinery employed activated alumina based chloride traps for removing chlorides from the net hydrogen off-gas of CCR process. Operation condition of chloride trap vessel is following, chloride trap volume: m 3, GHSV:,73hr -1, temperature: 35 degree C, and pressure: 3.MPa. JE were experiencing persistent chloride corrosion and plugging of burner nozzles in the downstream processes between [], on investigation, notwithstanding no detection of HCl in the outlet of chloride trap vessel by Draeger Tube, detected some organic chloride compounds in drained oil and chloride in the material of corrosion. The only source from which the chlorides could be coming was the CCR net hydrogen off-gas. Aluminas were adequately removing HCl, but organic chlorides were found in the outlet of the chloride trap vessel. It was determined that alumina was promoting the formation of organic chlorides. It is thought that the following reaction may occur [7]. Al O 3 + HCl AlCl 3 + 3H O (Formula 1) Formation of Lewis Acid This aluminum chloride may, in turn, promote polymerization of olefins, leading to gums and green oils and it is also thought that Lewis acid can promote the formation of organic chloride by the following reaction. R-CH =CH -R + HCl R-CH 3 CH Cl-R (Formula ) Formation of organic chloride First, we investigated the behavior of organic chloride concentration in the case of alumina chloride trap. Fig.1 is the concentration behavior of HCl both the inlet gas and the outlet gas treated by chloride trap and Fig. is that of organic chloride. Alumina chloride trap could remove HCl, but the organic chloride concentration of outlet is much higher than that of inlet, and it shows the formation of organic chloride promoted by alumina. /1

3 1 Inorganic chloride conc. (mg-cl/nm 3 ) Outlet Organic chloride conc. (mg-cl/nm 3 ) Outlet Net gas treated (1 m 3 Standard ) Net gas treated (1 m 3 Standard ) Fig.1 and Fig. Time dependence of HCl removal (left) and organic chloride removal (right) in the alumina based chloride trap To solve this problem, we had a screening test of 13 chloride traps with side-stream of the net hydrogen off-gas from the CCR. At that time, there were three kinds of chloride trap on the market and they had the characteristics mentioned below [7], (1) Aluminas: material itself promotes formation of organic chloride from inorganic chloride on the surface, () Molecular sieves: capacity of adsorption is small and material itself is weak and its strength is easy to decrease with absorbing water, (3) Zinc oxides: it doesn t promote polymerization. This side-stream test was done with the following condition, volume of chloride trap: 15ml, GHSV:,5hr -1 (this value is about twice as large as SV of the plant operation), temperature: ambient, and pressure: 3.MPa. Zinc oxide based chloride trap (C15-1-1P, supplied by Süd Chemie Catalysts) showed the best performance in removing not only HCl but also organic chloride from the net hydrogen off-gas and the results were following (Fig.3 and Fig.). In comparison with alumina based chloride trap, it had more than five times longer life in removing HCl and could remove organic chloride efficiently []. Regarding HCl removing by zinc oxide based chloride traps, it is thought that the following reaction may occur. ZnO + HCl ZnCl + H O (Formula 3) Formation of zinc chloride ZnCl may promote the decomposition of organic chloride to some organic compounds and HCl, then zinc oxide can remove this HCl. This estimation is supported by Table 1 data. These values were chloride content in spent chloride trap extracted by water (the 3/1

4 content of HCl) and organic solvent (the content of organic chlorides), and no organic chlorides were trapped by zinc oxide based chloride traps. Inorganic chloride conc. (mg-cl/nm Inorganic chloride conc. (mg-cl/nm 3 3 ) ) Alumina Type Alumina Type ZnO ZnO Type Type Organic chloride conc. (mg-cl/nm 3 ) 5 Alumina Type ZnO Type Net Net gas treated (1 vol-net gas/vol-trap) Net gas treated (1 vol-net gas/vol-traps) Fig.3 and Fig. Relationship of HCl (left) and organic chloride (right) concentration as a function of net gas treated in alumina and zinc oxide (C13-1-1P) chloride trap Table 1 Results of water and Toluene extraction of spent samples after side-stream test By H O extraction Cl pick-up (mass%) By Org. solvent extraction 3.1 <.1 After getting these results, JE employed C15-1-1P in the plant and got the enough performance of removing organic chlorides, unfortunately, pressure drop build-up was encountered at the vessel of chloride trap, and JE stopped the operation of chloride treater. This pressure drop buildup was caused by pellet breakage, Fig. 5 shows the appearance of fresh pellets of C15-1-1P (left side) and spent pellets (right side). It is thought that the reason of this pellet breakage is deliquescence of zinc chloride derived from the reaction of chloride compounds and zinc oxide (Formula 3). Generating zinc chloride is the substantial reaction of chloride removing of zinc oxide based chloride traps but it is also the main reason of pressure drop problems. /1

5 Fresh Spent Fig.5 Photographs of Fresh and Spent C15-1-1P To solve this problem and to develop new chloride traps, a co-development project between Süd Chemie Catalysts Japan, Inc. and JE began in In this program, Süd produced and supplied various chloride trap candidates which JE would test with CCR side-stream first, and, subsequently, would operate a commercial charge at JE Mizushima oil refinery. 3. Development of zinc oxide based chloride traps We investigated the detail of C15-1-1P spent chloride trap pellets by EPMA (electron probe micro analysis). Zn Pellet cross section Ca Cl Fig. EPMA results of spent pellet of C15-1-1P This result showed (1) distribution of zinc and chlorine seem to be similar, () zinc and chlorine are located near the outside of pellet, (3) distribution of calcium and chlorine are different. From above information, the strategy of development is the following, (1) Calcium didn t have any performance of chloride removing in C15-1-1P, so 5/1

6 calcium should be removed from components. () Zinc oxide content of C15-1-1P was 8%, and zinc oxide located at the center of pellet didn t function efficiently. So, if we make zinc oxide located at the center of pellet function more efficiently, the decrease of zinc oxide content may be possible and it may decrease the possibility of pellet breakage. From the analysis data of spent C15-1-1P, we knew pellet breakage started after adsorbing chloride about -5wt%. This chloride ratio is corresponding to zinc oxide content 3%. So we can decrease zinc oxide content from 8% to 3%. (3) Zinc oxide based chloride trap must produce zinc chloride after removing chloride and zinc chloride is deliquescent, so, it is necessary to make pellet skeletal structure stronger. We selected some diatomite Kieselghur as an additive. It has some special characters, (1) possibility of making pellet skeletal structure stronger, () no reaction with chlorides, (3) porous material structure which can introduce HCl and organic chloride to the center of pellets and can hold zinc oxide in the pellet. The new zinc oxide based chloride trap was designated JCL-1. Table is a comparison of JCL-1 to C15-1-1P. JCL-1 has surely large pore volume. Table Physical properties of JCL-1 and C15-1-1P Existing ZnO type New ZnO type C15-1-1P JCL-1 Chemical composition (mass%) ZnO 8 3 CaO 5 - Kieselghur - 5 Bentonite balance balance Shape pellet pellet Diameter (mm).8.8 Bulk density (kg/m 3 ) 87 8 Pore volume (ml/g).3.5 JE Mizushima refinery employed JCL-1 by way of trial in Its performance can be seen in Fig. 7 - Fig. 11. /1

7 1 Inorganic chloride conc. (mg-cl/nm 3 ) Outlet 1 3 Organic chloride conc. (mg-cl/nm 3 ) Outlet 1 3 Net gas treated (1 m 3 Standard ) Net gas treated (1 m 3 Standard ) Fig. 7 and Fig.8 Time dependence of HCl removal (left) and organic chloride removal (right) in the new ZnO type trap (JCL-1) JCL-1 C15-1-1P Fresh Spent Net gas treated (1 m 3 ) Fig. 9 Differential pressure profiles during plant operation for C15-1-1P and JCL-1 traps. Fig.1 Photographs of Fresh and Spent JCL-1 Pellet cross section Fig. 11 EPMA results of spent pellet of JCL-1 7/1

8 Fig. 8 shows that JCL-1 performance of removing organic chlorides was maintained sufficient level till *1 m 3 of the treated gas volume that means about days, after then it was decreasing and finally at the point of 7*1 m 3, chloride removing performance was gone. On the other hand, JCL-1 performance of removing HCl was still enough at *1 m 3 point (Fig. 7). Regarding pressure drop build-up, there was no increase during 5 days operation (Fig. 9). The appearance of spent pellet was same as that of fresh pellet and there is no pellet breakage (Fig.1). The result of EPMA measurement of JCL-1 spent pellet (Fig.11) shows that the color distributions of zinc and chlorine are same and zinc oxide located at the core of pellet removed chloride effectively. From chemical analysis data, we knew that the average chloride pick-up of JCL-1 in whole vessel was 13.7g Cl/1ml-chloride trap and that of C15-1-1P was 13.9g Cl/1ml-chloride trap. JCL-1 has almost same chloride pick-up performance as C15-1-1P, though zinc oxide content of JCL-1 is 3% and it was reduced from 8% that is the content of C15-1-1P. JE Mizushima refinery has employed JCL-1 and its improvements commercially since We haven t met any equipment troubles in the downstream processes since then. After employing JCL series, the maintenance cost of burners in the downstream processes decreased by 7%. After commercializing JCL-1, a co-development project has continued working on improving the performance of zinc oxide based chloride trap. (1) To make trap life longer, the zinc oxide content was increased to % by weight, this product is designated JCL-3. () To make organic chloride removing more efficiently, a new additive was added to component, these products are designated JCL-5 and T-83. Physical properties of improved taps are shown in Table 3 and the performance of removing HCl and organic chloride in side-stream test is in Fig.1 and Fig.13. Table 3 Physical properties of the improved zinc oxide based chloride traps JCL-1 JCL-3 JCL-5 T-83 Chemical composition (mass%) ZnO Kieselghur 5 5 NA SpecialAdditive NA NA 5 Bentonite NA NA Shape pellet pellet pellet pellet Bulk density (kg/m 3 ) Pore volume (ml/g) /1

9 Inorg. Chlorid conc. mg-cl/nm Outlet T-83 Outlet JCL-5 Outlet JCL-3 Org. Chlorid conc. mg-cl/nm 3 Outlet T-83 Outlet JCL-5 Outlet JCL Gas treated 1 vol-gas/vol-traps Gas treated 1 vol-gas/vol-traps Fig. 1 and Fig.13 Time dependence of HCl removal (left) and organic chloride removal (right) in the improved zinc oxide based chloride traps (side-stream test) JE Mizushima refinery has employed these improved zinc oxide traps in turn and they have shown the sufficient performance of removing HCl and organic chloride estimated from the side-stream tests.. Conclusion On investigation of organic chloride behavior in inlet and outlet of chloride trap vessel, (1) activated alimina based chloride trap doesn t remove organic chloride and promotes the formation of organic chloride, () obsolete zinc oxide based chloride trap could remove organic chloride but was easy to break itself and made pressure drop increase easily, above two were cleared. To solve these problems, zinc oxide traps were modified, (1)adding porous additive for example Kieselghur, ()decreasing zinc oxide content properly. Improved zinc oxide trap designated JCL-1 showed the excellent chloride removing performance for not only HCl but also organic chloride and no pressure drop build-up in the chloride trap vessel. After commercializing JCL-1, JCL series of products have gained rapid acceptance, in Japan: 1 units of 15 CCRs in the World: 18 units of nations. 9/1

10 The authors wish to sincerely acknowledge all effort from the support staffs of Süd Chemie Catalysts Japan, Inc. 5. Reference [1] The Japan Petroleum Institute, Petroleum Refining Processes, Kodansha, Tokyo (1998), p.18. [] Craig, H. L., Pap. Corros., No8-19, P1 (198). [3] Groysman, A., Kaufman, A., Feldman, B., Man, Y., Mater. Performance, 39 (), - (). [] Fujiwara, K., Ninomiya, T., Takase, T., Shioya, Y., J. Jpn. Petrol. Inst., 5 (3), 1 (7). [5] Süd-Chemie Catalysts Japan, Inc., Japan Energy Corporation, Kokai Tokkyo Koho, JP A (1999). [] Matsuoka, J., Aizawa, S., Fujiwara, K., Takase, T., Shioya, Y., Brown, R. S., NPRA Annual Meeting, AM--5, New Orleans (1). [7] Kawabata, T., Aromatics, 9, 3 (1997). 1/1