One-step synthesis of dimethyl ether from the gas mixture containing CO2 with high space velocity

Abstract

Dimethyl ether (DME) has been considered as a potential hydrogen carrier used in fuel cells; it can also be consumed as a diesel substitute or chemicals. To develop the technique of DME synthesis, a bifunctional Cu–ZnO–Al2O3/ZSM5 catalyst is prepared using a coprecipitation method. The reaction characteristics of DME synthesis from syngas at a high space velocity of 15,000mL (gcath)−1 are investigated and the effects of reaction temperature, pressure, CO2 concentration and ZSM5 amount on the synthesis are taken into account. The results suggest that an increase in CO2 concentration in the feed gas substantially decreases the DME formation. The optimum reaction temperature always occurs at 225°C, regardless of what the pressure is. It is thus recognized that the DME synthesis is governed by two different mechanisms when the reaction temperature varies. At lower reaction temperatures (<225°C) the reaction is dominated by chemical kinetics, whereas thermodynamic equilibrium is the dominant mechanism as the reaction temperature is higher (>225°C). For the CO2 content of 5vol.% and the pressure of 40atm, the maximum DME yield is 1.89g (gcath)−1. It is also found that 0.2g of ZSM5 is sufficient to be blended with 1g of the catalyst for DME synthesis.