Catalytic conversion of methanol/dimethylether to light olefins over microporous Silicoaluminophosphates catalysts

Abstract

Light olefins (C2-C4), important raw feeds in the petrochemical industry, are produced from crude oil. For various reasons including geographical, economic, political, and diminished supply considerations, the art has long sought for sources other than petroleum for the massive quantities of raw materials that are needed to supply the demand for light olefins. Methanol and dimethyl ether that can be produced from natural gas and renewable biomass via the syngas route are alternative sources for light olefins. Previous studies have shown that microporous silicoaluminophosphates (SAPOs) are promising catalysts to convert methanol to olefins (MTO) and dimethylether to olefins (DTO). However, one of the critical issues of the SAPO catalysts is rapid deactivation due to carbon coking.

In this work, four SAPOs, namely, SAPO-34, SAPO-18, SAPO-17 and SAPO-44 with different Si contents were synthesized and characterized using XRD, SEM, MAS NMR, NH3-TPD, and physical adsorption of nitrogen techniques. The catalytic properties of the SAPO catalysts in the MTO and DTO processes were evaluated. The influence of catalyst acidity on catalytic activity and selectivity to light olefins were examined and analyzed. Results showed that the catalytic performance of the SAPO catalysts significantly depends upon the pore size, strength and density of acidic sites, and catalyst preparation method. How to control catalyst stability and enhance product selectivity were suggested.