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Received for review February 8, 1988 Revised manuscript received April 14, 1988 Accepted May 2, 1988
Catalytic Cracking of High-Nitrogen Petroleum Feedstocks: Effect of Catalyst Composition and Properties Julius S c h e m e r * and D e n n i s P. M c A r t h u r Unocal Corporation, Science and Technology Division, P.O. Box 76, Brea, California 92621
Eight experimental FCC catalysts have been evaluated for cracking high-nitrogen feedstocks. The data obtained from microactivity tests show a decrease in conversion with increasing nitrogen content in feedstock. At constant conversion, an increase in feedstock nitrogen content results in a decrease in gasoline yield, while coke, light hydrocarbons, and hydrogen yields increase. High-zeolite content, as well as the presence of acid sites, high surface area, and a broad pore size distribution in the catalyst matrix, is beneficial in cracking high-nitrogen feedstocks. At constant feed nitrogen content, an increase in catalytic conversion results in a decrease in percent nitrogen recovered in the liquid products. Most of the nitrogen-containing compounds in the liquid product are in the decant oil (355+ " C ) and light cycle oil (232-355 O C ) fractions.
I. Introduction The change in the quality of feedstocks processed by refiners over the last decade has led to significant changes in refinery operations. Feedstocks today are heavier, more aromatic, and contain higher levels of sulfur, nitrogen, and metals. The impact of feedstock quality upon the operation of FCC units has been reviewed in several papers (Magee et al., 1979; Ritter et al., 1981). Although the deleterious effect of nitrogen compounds on the performance of cracking catalysts has been known for several decades (Mills et al., 1950; Voge et al., 1951; Villand, 19571, only a limited number of papers has been published more recently on this subject. The correlation between nitrogen content of a FCC feedstock and its effect on cracking catalysts is discussed by Jacob et al. (1976) and Schwab and Baron (1981). Fu and Schaffer (1985) reported the effect of individual nitrogen compounds on the activity and selectivity of two commercial FCC catalysts. They found a correlation between the gas-phase proton affinity of the nitrogen-containing molecule and its poisoning effect on cracking catalysts. Young (1986) has found correlations between catalyst composition and its ability to crack feedstocks blended with different amounts of quinoline. Silverman et al. (1986) have shown that, if the surface area of the catalytic matrix is increased, the nitrogen tolerance of an FCC catalyst can be increased. Corma et al. (1987) have investigated the effect of basic nitrogen on n-heptane cracking over high-silica zeolites. In a recent publication (Scherzer and McArthur, 1986), we discussed the nitrogen resistance of several commercial FCC catalysts, used for cracking high-nitrogen feedstocks. The evaluation of commercial FCC catalysts indicated that high-zeolite-containing catalysts are suitable for cracking high-nitrogen feedstocks. Furthermore, the data obtained suggested that differences in activity and selectivity werre also due to differences in the non-zeolitic components of these catalysts. In order to establish more specific correlations between catalyst composition, their cracking properties, and the nitrogen distribution in liquid products, we have prepared
Table I. Feedstock Prooerties feed no. F-1 gravity, OAPI 22.0 1.19 s, wt % 0.30 N,wt % basic N, wt % 0.094 0.12 Conradson, C, w t 70 19 aniline pt, "C 12.3 Br no. refraction index (at 67 "C) 1.4950 metals, ppm 4 Fe 0.6 Ni
