Relating Feedstock Composition to Product Slate and Composition in Catalytic Cracking. 2. Feedstocks Derived from Brass River, a High-Quality Nigerian Crude

Abstract

The fluid catalytic cracking (FCC) behavior of compound types present in the >650 °F resid from Brass River (Nigerian) crude was investigated. Liquid chromatography and distillation were employed for separation of selected compound type fractions from the resid; the resulting fractions were then cracked using a bench scale FCC unit. The FCC behavior for each compound type was defined in terms of the resulting product distribution (yields of gas, gasoline, etc.) sulfur and nitrogen partitioning, and in selected cases, gasoline composition. Results obtained from Brass River fractions were compared to those obtained from an earlier FCC study of compound types from Wilmington, CA, >650 °F resid. Correlations were derived for gasoline and coke yields from feedstocks derived from either crude. Brass River is a sweet, paraffinic crude which gives rise to a >650 °F resid with very favorable FCC characteristics. Although the bulk of the FCC gasoline was produced from cracking hydrocarbon types present, significant gasoline production also occurred from heteroatomic compounds (acids/bases) in Brass River. Conversely, negligible gasoline production was observed previously from cracking Wilmington acid/base types. However, feedstocks from both crudes exhibited greater conversion of sulfide sulfur to H2S compared to thiophenic forms of sulfur, and greater carryover of acidic forms of nitrogen (e.g., carbazole) compared to basic forms (e.g., quinoline). Overall gasoline composition depended on hydrocarbon type composition of feedstocks but was also influenced by presence of acids and/or bases in the feed. On the other hand, the detailed distribution of isomers within a given gasoline homolog, e.g., C3-benzenes or C9 isoparaffins, was nearly independent of feed composition. Results obtained for Brass River will serve as benchmarks for future FCC data obtained from low-quality feedstocks.

Relating Feedstock Composition to Product Slate and Composition in Catalytic Cracking. 5. Feedstocks Derived from Lagomedio, a Venezuelan Crude†

“…The feeds exhibiting the lowest conversion and gasoline yield were those containing the distillate base fractions. Sulfur partitioning to H 2 S was relatively high for most feeds, as observed previously. − Similarly, nitrogen partitioning to liquid products was appreciably higher for feeds enriched in distillate acids or bases. As with the other crudes, relative carryover of nitrogen into liquids was highest for feeds enriched in distillate acids.…”

“…Table compares isomeric distributions of C 7 isoparaffins and C 3 -alkylbenzenes in gasoline for selected Lagomedio feeds with average distributions from other crudes as well as theoretical benchmark distributions. , Good correspondence between all distributions for C 3 -alkylbenzenes was observed. The higher proportions of 2-methyl C 7 isoparaffin isomers in FCC products compared to the benchmark distribution relates to the β-cleavage mechanism for alkane cracking as explained earlier . The somewhat erratic ratio of 2,3-dimethylpentane versus 2-methylhexane isomers for Lagomedio results from replacement of the gas chromatographic column midway through the work; the new column gave improved resolution of these isomers and thus higher relative concentrations of 2,3-dimethylpentane.…”

“…A variety of possibilities exist for expressing negative attributes, including elemental analysis, functional group content, etc. ; eq 2 was used as a starting point owing to its success in predicting gasoline yield of neutrals . Parameters selected for negative effects were effective metals (M eff ) and basic nitrogen (N B ), based on their success in predicting coke yield (eq 5).…”

“…The feedstocks were charged to the unit over a 30 s time period. The sweep gas (N 2 ) velocity was set such that the catalyst volume was displaced approximately every 20 s. The FCC unit, catalyst, and procedures for carrying out cracking experiments were unchanged from the prior work, except for refinements added later . Good correlation of results obtained using this methodology with those from commercial-scale FCC units has been reported …”

“…This information is being sought in an effort to improve FCC processing of conventional feedstocks and to extend FCC to lower quality feedstocks, such as atmospheric resids from heavy oils. The first three papers presented results from feedstocks derived from Wilmington (CA), Brass River (Nigeria), and Maya (Mexico) crudes; the fourth dealt with a model for calculating nine product subclasses from mass spectral analysis of hydrocarbon and sulfur types in the feed. − …”