Effect of the content of CO2 and H2 in the feed on the conversion of CO2 in the direct synthesis of dimethyl ether over a CuO[sbnd]ZnO[sbnd]Al2O3/SAPO-18 catalyst

Abstract

The behavior of a CuOZnOAl2O3/SAPO-18 (CZA/S-18) catalyst on the synthesis of dimethyl ether (DME) in a single-step has been studied, and the effect of the CO2/COX and H2/COX ratios on the conversion of CO2 and on other reaction indices as COx conversion (CO + CO2), yield and selectivity of DME, methanol and paraffins has been determined. The experiments have been carried out in a fixed bed, high pressure isothermal reactor, under the following reaction conditions: 275 °C; 30 bar; space time, 10.18 gcath/molC; CO2/COx ratio, 0–0.5; H2/COx ratio, 3 and 4. The deposition of coke on the spent catalysts has been studied by means of temperature programmed oxidation (TPO), quantifying three types of coke, considered to be located in each function of the catalyst and in the interface between both.The results show the capacity of the CZA/S-18 catalyst for the valorization of CO2, attributable to the activity of the CuOZnOAl2O3 metallic function for the r-WGS reaction. The conversion of CO2 is enhanced by increasing CO2/COX and H2/COX ratios in the feed. Moreover, the augment in the water content in the reaction medium when increasing the concentration of CO2 attenuates coke formation, particularly, of the coke fraction deposited on the acid function.