Molecular coupling behavior of relay catalytic upgrading of heavy oil fast pyrolysis vapor to produce light olefins

Abstract

The relay catalytic upgrading of vacuum residue (VR) fast pyrolysis vapor process, which combines the VR fast pyrolysis and pyrolysis vapor catalytic cracking on the molecular level, is proposed to produce the chemicals. In this research, the composition and molecular distribution of Changqing vacuum residue (CQ-VR) pyrolysis vapor at 550–650 °C are investigated firstly. In the pyrolysis vapor, the alkanes and alkenes which have high catalytic cracking reactivity are both distributed from C5–C18, whereas the aromatics with high adsorption capacity is consist of monocyclic and polycyclic aromatics. For further catalytic cracking, the optimal reaction temperature for CQ-VR pyrolysis process is 600 °C due to the fact that the pyrolysis vapor at this temperature contains more alkenes and less aromatics. Then, the pyrolysis vapor is catalyzed over FCC catalyst, ZSM-5 catalyst, ZSM-5/calcium aluminate composite catalyst (Z-C catalyst), and ZSM-5/FCC composite catalyst (Z-F catalyst), which has different pore structure and acidity, respectively. The yield of light olefins after catalytic cracking of pyrolysis vapor over Z-C catalyst is 43.26%, which is higher than that over FCC, ZSM-5, and Z-F catalysts. Coupling the molecular distribution of pyrolysis vapor with the composition structure of catalyst can achieve the maximum conversion of CQ-VR to light olefins, and realize the efficient conversion of inferior heavy oil.