FCC operation with split feed injections

A laboratory Riser Simulator unit was used to study the conversion of n-hexadecane on an equilibrium FCC catalyst, which was injected split into two fractions with different volume ratios (R-v, from 1:1 to 3:1) and times for the second injection (t(1), 2-6 s), and the same total contact time of 12 s at 500 and 550 degrees C. Results were compared with reference experiments with single injections. It was observed that the conversions and gasoline yields under the split injections were equal or Tower than the standard ones at both temperatures, that the yields of different hydrocarbon groups were unaltered, and that coke yields were always lower. Significant changes were observed in product Light olefins C-4-C-6: at the same conversion, the split injections increased their selectivities, improvements being more important at lower temperature and higher R-v, while the influence of t(1) was less important. Heavier olefins showed the highest sensitivity to these changes. The shifts were justified with basis on the partial catalyst deactivation imposed by the coke formed during the first step that would interfere more importantly with hydrogen transfer reactions in the second step, thus helping to preserve olefins.