Deactivation of a Y-zeolite based catalyst with coke evolution during the catalytic pyrolysis of polyethylene for fuel oil

Abstract Coke evolution on a Y-zeolite based catalyst and its influence on the active site and catalytic activity during catalytic pyrolysis of polyethylene for fuel oil were investigated. Results show that the coke evolution includes both quantity accumulation and structural condensation. The coke amounts increase from 0.8% at TOS = 1 h to 2.4% and 6.3% at TOS = 2 h and 4 h respectively, and the external coke deposits faster than the internal coke. Structural condensation is evidenced by DTG, H/C, 13C NMR, FTIR and UV-Vis results. The average coke model changes from a tricyclic aromatic to a hexacyclic alkyl aromatic as TOS increases from 1 h to 4 h. Coke evolution causes catalyst deactivation, resulting in the decrease of oil yields but increase of wax yields and heavy oil concentration. The strong acid sites and micropores favor the coke deposition, and fast external deposition leads to slow decrease of acidities with coke yields.