Study on the Catalytic Cracking of Heavy Oil by Proper Cut for Higher Conversion and Desirable Products

Abstract

To improve the product distribution in the residue fluid catalytic cracking (RFCC) process, two representative heavy oils were, respectively, cut into five fractions by true boiling point (TBP) distillation and their catalytic cracking performance was tested in a fixed fluidized bed reactor. The results indicated that they appeared to have diverse reaction characteristics and that about 6.3–19.3 wt % fractions with better crackability were still contained in the vacuum residual (VR). On the basis of the above, a feasible cut temperature of heavy oil was determined and the fractions were classified into two groups: the high-quality fraction (HF) group and the poor-quality fraction (PF) group. Compared with heavy oil before being cut, the product distribution of heavy oil after being cut was improved. With the increase in the blend levels of VR in the vacuum gas oil (VGO), the desired products yield of heavy oil after being cut was enhanced gradually, especially under the optimal reaction conditions. To describe the reaction behavior of the PF catalytic cracking, a six-lump kinetic model was proposed. Kinetic constants and apparent activation energies were determined with the improved Marquardt method. The effect test showed that the kinetic model could predict product yields well.