Strategies for the intensification of CO2 valorization in the one-step dimethyl ether synthesis process

Abstract

The intensification of CO2 valorization has been theoretically studied in the direct synthesis of dimethyl ether (DME) carried out in a packed-bed reactor by means of two strategies pursuing the attenuation of the thermodynamic limitations of the process. Thus, the recycling of the nonconverted reactants, and the use of H2O perm-selective membranes, with different sweeping strategies has been studied. Special attention has been paid to improving the yield of DME and the conversion of CO2, seeking for a good balance between both objectives. The study has been conducted using the kinetic model previously established for a CuO−ZnO−MnO/SAPO-18 catalyst. Quantifying the deactivation kinetics in the kinetic model has allowed us to ascertain that both strategies contribute to attenuating deactivation. With a recirculation factor of 0.97, for a CO2/COx ratio in the feed of 0.25, at 275 °C and 30 bar, a CO2 conversion of 70% and a DME yield of 60% are achieved. Using in the simulation a membrane with a H2O permeability of 1 × 10−7 mol s−1 m2 Pa−1 and a H2O/H2 selectivity of 4, feasible with H-SOD type zeolite membranes, increases CO2 conversion up to 3.5−5% with regard to that obtained in a packed-bed reactor, and the upgrade in DME yield stands out, reaching an improvement of 25% for the hydrogenation of pure CO2, regardless of the sweeping strategy used (parallel or countercurrent mode, or the use of pure H2 or H2 + CO + CO2).