Catalytic conversion of methyl chloride to lower olefins over modified H-ZSM-34

Abstract

Among several typical zeolites, H-ZSM-34 was found to be an efficient catalyst for the conversion of methyl chloride to lower olefins, i.e., ethylene, propylene, and butenes. Treatment of H-ZSM-34 with a Na2H2EDTA (EDTA = ethylenediaminetetraacetate) aqueous solution followed by ion exchange and calcination enhanced the catalytic performance significantly. The selectivity to lower olefins increased significantly for certain Na2H2EDTA aqueous solution concentrations; when the H-ZSM-34 catalyst was treated with a 0.1 mol/L Na2H2EDTA solution, the selectivity and yield of C2–C4 olefins reached 82% and 61%, respectively, at 673 K and a CH3Cl partial pressure of 9.2 kPa. The modification of H-ZSM-34 with Ce ions improved C2–C4 olefin selectivity and yield. Catalyst characterization suggests that treatment with Na2H2EDTA or modification by Ce decreases the acidity of H-ZSM-34. The weakened acidity of the treated or modified H-ZSM-34 may suppress the hydrogen transfer reaction and prevent lower olefins from further transformation to paraffins.