Kinetic Model for the Direct Conversion of CO 2 /CO into Light Olefins over an In 2 O 3 -ZrO 2 /SAPO-34 Tandem Catalyst.

An original kinetic model is proposed for the direct production of light olefins by hydrogenation of CO 2 /CO (CO x ) mixtures over an In 2 O 3 -ZrO 2 /SAPO-34 tandem catalyst, quantifying deactivation by coke. The reaction network comprises 12 individual reactions, and deactivation is quantified with expressions dependent on the concentration of methanol (as coke precursor) and H 2 O and H 2 (as agents attenuating coke formation). The experimental results were obtained in a fixed-bed reactor under the following conditions: In 2 O 3 -ZrO 2 /SAPO-34 mass ratio, 0/1-1/0; 350-425 °C; 20-50 bar; H 2 /CO x ratio, 1-3; CO 2 /CO x ratio, 0-1; space time, 0-10 g In2O3-ZrO2 h mol C -1 , 0-20 g SAPO-34 h mol C -1 ; time, up to 500 h; H 2 O and CH 3 OH in the feed, up to 5% vol. The utility of the model for further scale-up studies is demonstrated by its application in optimizing the process variables (temperature, pressure, and CO 2 /CO x ratio). The model predicts an olefin yield higher than 7% (selectivity above 60%), a CO x conversion of 12% and a CO 2 conversion of 16% at 415 °C and 50 bar, for a CO 2 /CO x = 0.5 in the feed. Additionally, an analysis of the effect of In 2 O 3 -ZrO 2 and SAPO-34 loading in the configuration of the tandem catalyst is conducted, yielding 17% olefins and complete conversion of CO 2 under full water removal conditions.