Kinetic Model for the Direct Conversion of CO2/CO into Light Olefins over an In2O3–ZrO2/SAPO-34 Tandem Catalyst

An original kinetic model is proposed for the direct production of light olefins by hydrogenation of CO2/CO (COx) mixtures over an In2O3–ZrO2/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 H2O and H2 (as agents attenuating coke formation). The experimental results were obtained in a fixed-bed reactor under the following conditions: In2O3–ZrO2/SAPO-34 mass ratio, 0/1–1/0; 350–425 °C; 20–50 bar; H2/COx ratio, 1–3; CO2/COx ratio, 0–1; space time, 0–10 gIn2O3–ZrO2 h molC–1, 0–20 gSAPO-34 h molC–1; time, up to 500 h; H2O and CH3OH 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 CO2/COx ratio). The model predicts an olefin yield higher than 7% (selectivity above 60%), a COx conversion of 12% and a CO2 conversion of 16% at 415 °C and 50 bar, for a CO2/COx = 0.5 in the feed. Additionally, an analysis of the effect of In2O3–ZrO2 and SAPO-34 loading in the configuration of the tandem catalyst is conducted, yielding 17% olefins and complete conversion of CO2 under full water removal conditions.