Model validation of a packed bed LTA membrane reactor for the direct synthesis of DME from CO/CO2

Abstract

A model for simulating the direct synthesis of dimethyl ether (DME) in a packed bed membrane reactor (PBMR) has been validated, using a LTA zeolite hydrophilic membrane in a lab-scale reaction equipment. In the model, membrane permeability data and the kinetic model corresponding to a CuO-ZnO-ZrO2/SAPO-11 catalyst have been used. Experimental runs have been carried out under the following conditions: 275-325 ºC; 20-40 bar; space time, 10 g h (molC)-1; CO2/COx ratio, 0, 0.5 and 1; H2/COx ratio, 3. The model is suitable for predicting the molar fractions of the compounds of the reaction medium (H2, CO, CO2, H2O, DME, methanol and hydrocarbons) in the reaction and permeate sections of the PBMR, and their evolution with time on stream. DME yield, CO and CO2 conversions are greater in the PBMR than without using the membrane, due to the displacement of the thermodynamic equilibrium by the partial separation of H2O from the reaction medium. For H2+CO feeds, the maximum DME yield is 68% at 325 ºC and 40 bar with a space time value of 10 g h (molC)-1. Otherwise, feeding H2+CO2, CO2 conversion reaches 17%, with a DME yield over 5 %.