Abstract
Human population is drastically increasing; in turn, it increases human activities that contribute to CO2 emissions, resulting in global warming. Effective CO2 mechanisms that can mitigate CO2 emissions to the environment are in high demand. One among the other approaches would be to develop processes that can utilize CO2 as feedstock to produce useful products. In this study CO2 is used as feedstock for hydrocarbons production via modified FTS over a cobalt-based (Co/γ-Al2O3) catalyst in a fixed bed reactor. The catalyst was prepared by precipitation-deposition method and characterized by using atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and temperature programmed reduction (TPR) analysis. The feed to the reactor consisted of CO2/H2/N2 with a H2 to CO2 ratio of 3:1. The project aimed at evaluating the effect of operating temperature, pressure and mixing cobalt-based catalyst with methanol synthesis catalyst (Cu/ZnO/ZrO2) on CO2 conversion and product selectivity during CO2 hydrogenation. The effect of operating temperature was studied in a range of 200-250 ⁰C in two ways: i) step-up experiment where the temperature was increased from 200-250 ⁰C in steps of 10 ⁰C and ii) step-down where the reverse temperature variation was used. The effect of operating pressure was studied over a pressure range from atmospheric to 20 bar at an operating temperature of 220 ⁰C while the other operating parameters were kept unchanged. The effect of methanol synthesis catalyst (Cu/ZnO/ZrO2) on CO2 hydrogenation over the Co/γ-Al2O3 catalyst was studied by physically mixing the two catalysts in equal proportions. CO2 conversions were found to increase with the increase in operating temperature and went through a maximum at 230 ⁰C and started decreasing due to catalyst deactivation. The methane selectivity decreased while the CO selectivity increased as the operating temperature was increased suggesting that high temperatures favoured the RWGS reaction. CO2 conversions were higher at high operating pressures with no clear trend on methane selectivity. CO was only detected at atmospheric pressure suggesting that at high pressures CO is readily hydrogenated to hydrocarbons. When the methanol synthesis catalyst was mixed with the Co/γ-Al2O3 catalyst the CO2 conversion was observed to increase with the increase in operating temperature up to 300 ⁰C above which rapid decline in catalyst activity was observed. The presence of Cu/ZnO/ZrO2 shifted the deactivation temperature of the Co/γ-Al2O3 catalyst to higher temperature, i.e. above 300 ⁰C compared to 230 ⁰C...
M.Tech. (Chemical Engineering)