Experimental and kinetic studies of the advantages of coke accumulation over Beta and Mordenite catalysts according to the pore mouth catalysis hypothesis

Abstract

Coke formation inside heterogeneous reactors is an important industrial problem that leads to reduced catalyst efficiency. However, this study aims to prove the benefits of coke build-up in improving catalyst performance. The formation and decomposition of coke on six different zeolite structures was studied. The dissociation kinetic model of the spent catalysts during the toluene alkylation with 1-heptene inside a stainless-steel autoclave reactor at different temperatures was carried out. Various techniques (XRD, XRF, TPO, CHNS and TGA-DTG) were used. It was found that the conversion and selectivity of the desired product were higher on the parent H-mordenite and the dealuminated H-beta catalysts with conversions of 85.3% and 84.67%, respectively, at a 360 min reaction time. This was attributed to the reduction of the ratio of hard:soft coke. It is confirmed that the decomposition activation energies of hard coke, 140.1–202.6 kJ/mol, are much higher energies than those of soft coke, 89.9–118.7 kJ/mol. It is also noted that the hypothesis of pore mouth catalysis is dominated by non-polyaromatic coke on the surface of the H-beta catalysts, while the hypothesis is dominated by polyaromatic coke on the surface of the H-mordenite catalysts.

Keywords

• Toluene alkylation
• H-beta zeolite
• H-mordenite zeolite
• Dealuminated and desilication zeolites
• Pore mouth catalysis
• Coke kinetic decomposition