(A) study on deactivation of catalysts by coke formation on catalytic conversion of methanol to propylene

Abstract

Propylene, mainly produced as a by-product in ethylene production by the naphtha steam-cracking process, is one of the important raw materials for petrochemistry. However, due to the growing demand for propylene and the shortage of petroleum resource in the future, new processes with high yield of propylene are required. Methanol to propylene (MTP) process using zeolite catalysts for propylene production has been studied by many researchers. Catalyst deactivation with time-on-stream is one of the important problem related to life time of catalyst and high yield of propylene. The HZSM-5 catalysts were prepared with various $SiO_2/Al_2O_3$ (40,280 and 500). The MTP reactions over prepared HZSM-5 catalysts were carried out at several reaction temperatures. The HZSM-5 catalyst with the highest acidic sites $(SiO_2/Al_2O_3 = 40)$ was deactivated more rapidly than other catalysts $(SiO_2/Al_2O_3 = 280,500)$ due to the formation of a lot of coke. Also, the presence of polycyclic aromatics including 3 to 4 benzene rings was observed in the organic phase extracted from used catalysts with the highest acidic sites density. It was suggested that the formation of such large polycyclic aromatics interrupted the access of reactant as blockage of the pores and deactivated the HZSM-5 catalyst. The HZSM-5 catalyst $(SiO_2/Al_2O_3 = 280)$ was applied to the MTP reaction at several reaction temperature (400,450 and 500℃) and the effect of reaction temperature on catalyst deactivation was investigated. The faster deactivation was observed at higher reaction temperature. Surface area and pore volume of catalysts decreased due to coke formation. It was considered that coke formation is the main cause of catalyst deactivation. The MTP reaction over the catalyst with lower acidic sites density $(SiO_2/ Al_2O_3 = 280,500)$ at higher reaction temperature (500℃) showed high propylene selectivity was obtained. However, catalyst deactivation proceeded faster at higher react...