Renewable Energy, Vol.138, 585-597, 2019
Influence of the operating conditions on the behavior and deactivation of a CuO-ZnO-ZrO2@SAPO-11 core-shell-like catalyst in the direct synthesis of DME
The behavior of the CuO-ZnO-ZrO2@SAPO-11 core-shell catalyst in the direct synthesis of DME from H-2 + CO + CO2 mixtures has been assessed. The effect of the reaction conditions (temperature, pressure, space-time) and feed composition (CO2 and H-2 concentration) on the DME yield and selectivity, CO2 and COx (CO2+CO) conversions and stability of the catalyst have been studied. The experiments have been carried out in a fixed-bed reactor in the following condition ranges: 250-325 degrees C; 10-50 bar; space-time, 1.25-15 g h mol(c)(-1); CO2/COx molar ratio in the feed, 0-1; and H-2/COx molar ratio in the feed, 2.5-4; time on stream, up to 48 h. Under mild conditions (275-300 degrees C range, 20-30 bar, space-time over 5 g h mol(c)(-1), CO2/COx molar ratio in the 0.5-0.75 range, and H-2/COx molar ratio around 3) a good compromise is reached between the yield of DME and the conversion of CO2, with high catalyst stability. Coke deposition is the main cause of catalyst deactivation, formed by condensation of the hydrocarbon byproducts, blocking the metallic sites in the core. The formation rate of this fraction of coke is greater than that of the coke deposited in the SAPO-11 of the shell. Increasing reaction temperature favors the formation of coke, while co-feeding CO2 attenuates this formation, due to the increase of H2O concentration. (C) 2019 Elsevier Ltd. All rights reserved.