Yu. K. Vail and L. N. Gorshkova UDC

Transcription

1 Chemistry and Technology of Fuels and Oils, Vol. 40, No. 6, 2004 TECHNOLOGY HYDROTREATING IN A TWO-BED SYSTEM OF MODIFIED SERIES GP CATALYSTS Yu. K. Vail and L. N. Gorshkova UDC Due to the increase in the requirements for the quality of gasolines and diesel fuels at the beginning of the 1990s, series GP catalysts were developed [1] and have been successfully used in oil refineries (OR) in Russia and CIS countries in hydrotreating of both straight-run diesel cuts [2] and vacuum gasoil in the sections of 100 G complexes [3, 4]. In the middle of that period, the requirements for the content of not only sulfur (maximum of 500 ppm) but also aromatic hydrocarbons (maximum of 5 and 20 vol. %) were stiffened. To satisfy these requirements, VAMIK-KATALIZ together with SORBENT Co. developed GP-497S catalyst based on a support obtained by fast thermal decomposition of gibbsite. The strength of the catalyst is greater than 20 N/mm. One-stage technology for hydrotreating of straight-run diesel cuts mixed with secondary distillates in the industrial L-24-5 unit at Ufa OR Co. was created in 1996 using this catalyst [4]. GP-497S catalyst was loaded in reactor R-2, the second in the process, and GP-497G was contained in the first reactor R-1, which had previously run for three years with mixed feedstock and had been regenerated once. In summer, a mixture of the straight-run diesel cut with catalytic cracking gasoils are refined in the unit, and winter diesel fuel is refined in winter (from December to February). The data on the work of GP-497S catalyst for more than eight years are reported in Table 1. During this time, the catalyst, regenerated three times, stably ensured obtaining winter diesel fuel with a sulfur content of less than 300 ppm in the winter and environmentally clean diesel fuel with a sulfur content of less than 350 ppm and polyaromatic hydrocarbons of less than 11 vol. % according to TU or with a sulfur content of wt. % as needed in the summer. The degree of removal of aromatic hydrocarbons as a function of the feedstock composition was 25-40%. After eight years of use in refining mixed straight-run diesel cut and catalytic gas oil, diesel fuel with a sulfur content of less than 350 ppm was obtained. With stiffening of the standards for the sulfur content of gasolines (10-50 ppm) and benzene (under 1%) after 2005, refineries will be required to use new catalysts and technologies [5]. Two versions of the solution of the problem are possible: VAMIK-KATALIZ Ltd. Nizhegorodskie Sorbenty CJSC. Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 6, pp. 8 11, November December, /04/ Springer Science+Business Media, Inc.

2 Table 1 Indexes L-24-5 unit with system of catalysts in R-1: GP-497G, first regeneration in 1993; in R-2: fresh GP-497S after use for three months after use for two years in R-1: GP-497G, second regeneration; in R-2: fresh GP-497S, first regeneration (after use for four months) in R-1: GP-497G, third regeneration; in R-2: GP-497S, third regeneration; (after use for eight years) Mixed straight-run Feedstock Mixed straight-run diesel Winter diesel cut cut and catalytic gasoil diesel fuel and catalytic gasoil Temperature, C 350/ / / /362 Overall pressure, MPa 29.5/30 34/34 31/ /30 Feedstock space velocity, h / / / /2.9 Hydrogen-containing gasoil (HCG) circulating ratio, m 3 /m 3 250/ / / /260 Concentration of nitrogen in circulating HCG, % 70/ /71 72/68 72/73 Content sulfur, wt. % in feedstock 0.8/ / / /0.92 in hydrogenation product 0.045/ / / / aromatic hydrocarbons in feedstock, vol. % 18.2/ /22 16/ /25 polyaromatic hydrocarbons in hydrogenation product, vol. % 2.6/ / /2.4 8/10 Note. In the numerator: in conditions 1; in the denominator: in conditions 2. hydrotreating of vacuum gasoil in the presence of G complexes using catalysts or systems of catalysts (for example, Haldor Topsoe) up to a sulfur content of ppm in the hydrogenation product: at Mazheikyai and Moscow OR for production of export gasolines; at Moscow OR for production of gasolines satisfying the environmental requirements; a less expensive version of hydrotreating of catalytic naphtha with a minimal decrease in the octane number: in units under construction at Nizhnekamsk OR, Tatneft Oil Co., Salavatnefteorgsintez Industrial Association, and LUKOIL Nizhegorodnefteorgsintez OJSC. 359

3 Table 2 Indexes 1: AKO process wide cut Catalytic cracking feedstock 2: C vacuum gasoil 3: (85:15) mixture of feedstock 2 and delayed-coking gasoil Density at 20 C, kg/m Coke, wt. % 2 0,26 0,28 Content, wt. % sulfur nitrogen asphaltenes Content, g/ton vanadium nickel iron Group chemical composition, % hydrocarbons paraffin-naphthenic aromatic light medium heavy resins Distillation, vol. % Table 3 below 350 C 34 6 below 500 C in top part Catalyst in reactor in bottom part Ratio of catalysts in upper and lower parts of reactor Initial temperature of 82% hydrodesulfurization Deactivation of catalyst, deg/month GP-600 GP-526К 1: GP-526К GP-600 1: GP-600 GP-526К 2: GP % GP-526К 100%

4 375 t, C τ, h Fig. 1. Temperature t of hydrotreating of feedstock 1 vs. duration τ of process on GP GP-526K catalyst system in production of hydrogenation product with a sulfur content of les than 0.3 wt. %. Table 4 Indexes Feedstock after 48 h Hydrogenation product on GP GP-526K system at 350 C at 355 C after 840 h after 1140 h after 2160 h at 360 C after 2788 h Density at 20 C, kg/m Yield of cuts below 350 C, % Content, ppm sulfur 1.9* nitrogen 0.12* vanadium 0.5 <9.5 <0.5 <0.5 <0.5 <0.5 nickel 0.2 <0.5 <0.5 <0.5 <0.5 <0.5 Coke (Konradson), wt. % Note. * In wt. % At oil refineries not owned by crude oil production companies, crude is delivered in a limited volume so that the feedstock resources for the G and KT-1 complexes at these OR are clearly insufficient. To expand them, we improved the technology for hydrotreating of catalytic cracking feedstock of different types vacuum gasoil with an end point of t EP = C and mixed vacuum gasoil and delayed-coking heavy gasoil in two-bed systems of GP GP-600 catalysts [3]. In our opinion, use of two to three [6, 7] functional catalysts that combine high activity in transformation of sulfur and nitrogen compounds, hydrogenation of polycyclic aromatic hydrocarbons, and removal of organometallic compounds and also have optimum pore radius distribution for each type of feedstock is most promising. This allows decreasing their deactivation and consequently increasing the lifetime and degree of treatment of the feedstock. 361

5 t, C τ, h Fig. 2. Temperature t of hydrotreating of feedstock 3 vs. duration of process τ: 1) on GP-526K catalyst; 2) on GP GP-526 K catalyst system. Table 5 Components of hydrogenation product Hydrocarbons Content (wt. %) after hydrotreating of mixed vacuum gasoil and delayed-coking gasoil on GP-600 and GP-526K on GP-526K catalyst catalyst system paraffin-naphthenetic aromatics light medium heavy Resins We investigated hydrotreating in modified systems of series GP catalysts:* vacuum gasoil with t EP = 540 C for obtaining hydrogenation products with a maximum sulfur content of ppm and ensuring production of catalytic naphtha cuts with a maximum sulfur content of 500 ppm and after mixing with high-octane components (alkylate, MTBE, TAME, and oligomerization product) commercial gasolines with an octane number above 92 and maximum sulfur content of ppm; missed C vacuum gasoil and delayed-coking gasoils; catalyzate of high-boiling cuts from adsorption treatment of atmospheric resid with the AKO process [8], the analog of the RCD process not used in industry abroad. The physicochemical properties of these types of feedstock are reported in Table 2. The activity (initial temperature ensuring 82% hydrodesulfurization at a pressure of 5 MPa and space velocity of 1 h -1 ) and stability, or deactivation (deg/month) were selected as the basic criteria for assessing the catalysts for hydrotreating of AKO products. In addition, the catalyst was evaluated by the degree of removal of nitrogen and degree of hydrogenation of heavy aromatic hydrocarbons at 82% hydrodesulfurization. *Developed from aluminum oxide obtained by fast thermal decomposition which ensures the optimum pore structure for different kinds of feedstock, using promoters that improve the dispersion of the active components of the catalysts. 362

6 For determining the optimum ratio of GP-600 and GP-526K catalysts, the experiments were conducted with feedstock 1 (see Table 2) at a pressure of 5 MPa, feedstock space velocity of 1 h -1, HCG circulating ratio of 500 m 3 /m 3, and temperature ensuring 82% hydrodesulfurization. As Table 3 shows, the GP-600 and GP-526K catalyst system used in the ratio of 1:2 is the most active and stable: at an initial hydrotreating temperature of 335 C, deactivation of this system was 4 deg/month. At the selected catalyst ratio, hydrotreating of feedstock 1 (see Table 2) at overall pressure of 7.5 MPa (the concentration of hydrogen in HCG was maintained at a minimum of 75 vol. %) and feedstock space velocity of 1 h -1 was conducted in a pilot unit with a cm 3 catalyst load in the reactor. As Fig. 1 shows, in these hydrotreating conditions for 9024 h, deactivation of the system when the temperature increased from 335 to 375 C was 3.2 deg/month, and the degree of hydrodesulfurization was greater than 85%. Prolonged pilot tests of the same catalyst system were performed in hydrotreating of C vacuum gasoil and a mixture of this gasoil (85:15) with delayed-coking gasoil. The results of hydrotreating of this gasoil at a pressure of 5 MPa, feedstock space velocity of 1 h -1, and initial process temperature of 350 C for 2788 h are reported in Table 4. They indicate the high efficiency of this system: deactivation was 2.5 deg/month, and the sulfur content in the hydrogenation product did not exceed 1120 ppm. Hydrotreating of feedstock of the second kind on the same catalytic system to a maximum sulfur content of 1500 ppm in the hydrogenation product is attained at a temperature 10 C lower than on GP-526K catalyst alone (Fig. 2). According to the data in Table 5, more exhaustive hydrogenation of heavy polycyclic aromatics takes place on this system than on the single catalyst. This finding is important to take into consideration in selecting catalysts for hydrotreating of catalytic cracking feedstock, since polycyclic aromatic hydrocarbons are the basic source of coke formation. It follows from these findings that the domestic catalyst GP-497S has better activity and stability in hydrotreating of mixed feedstock than foreign and other domestic catalysts used in Russian OR. Systems of modified series GP catalysts are as good as foreign samples in hydrotreating of vacuum gasoils and mixed vacuum and delayed-coking gasoils, as prolonged pilot tests showed, and they can be recommended for use in domestic OR. REFERENCES 1. M. V. Landau, Yu. K. Vail, A. A. Krichko, et al., Khim. Tekhnol. Topl. Masel, No. 2, 2-4 (1991). 2. 2, 2-4 (1991). 2. L. N. Osipov, B. Yu. Vainora, Yu. K. Vail, et al., Ibid., No. 2, (1993). 3. Yu. K. Vail, A. N. Chagovets, and L. N. Osipov, Ibid., No. 3, Yu. K. Vail, A. M. Sukhorukov, V. N. Nikolaichuk et al., Ibid., No. 1, (1998). 5. E. de la Fuente, P. Christensen, and M. C. Johansen (Haldor Topsoe), in: European Conference on Oil Refining Technologies [in Russian], France (1999). 6. Yu. K. Vail et al., Hydrorefining of Residual Types of Feedstock (Chemistry, Kinetics, Catalysts) [in Russian], TsNIITEneftekhim, Moscow (1984). 7. Proceedings of Haldor Topsoe Seminar on Oil Refining [in Russian], Moscow (1995). 8. P. Yu. Serikov and V. N. Erkin, Khim. Tekhnol. Topl. Masel, No. 11, (1990). 363