Mesoporous alumina and alumina-titania supported KCuFe catalyst for Fischer-Tropsch synthesis: Effects of CO2 and CH4 present in syngas

Abstract

In this work, mesoporous alumina (mAl2O3) and alumina-titania (mAl2O3-TiO2) were synthesized and used as support materials for promoted (K, Cu) iron catalyst. The catalysts were tested for Fischer-Tropsch synthesis in a fixed bed flow reactor operating at 2000h−1 GHSV, 270°C, 330psi and H2/CO ratio of 1.25. The catalytic activity was measured in terms of CO conversion, CO2 selectivity and hydrocarbon selectivity. The catalyst KCuFe/mAl2O3 performed better and showed ~17% higher CO conversion to hydrocarbons as compared to that shown by KCuFe/γ-Al2O3.The effect of CO2 and CH4 present in produced syngas (through gasification/reforming) and recycled syngas was also studied for KCuFe/mAl2O3 and KCuFe/mAl2O3-TiO2 catalyst. 0–15% of CO2 and 0–12.5% of CH4 was added in syngas, while maintaining GHSV constant. Methane in syngas acted as diluent and resulted in increase in CO residence time, which helps in increase in CO conversion. However, increase in CO conversion and decrease in partial pressure of CO leads to increase in CH4 and CO2 selectivity, thus, lowering the amount of percentage of CO converted to C5+ hydrocarbons. Addition of CO2 in syngas leads to decrease in CO2 selectivity, indicating hydrogenation of CO2 to hydrocarbons. Hence, slight increase in amount of percent CO converted to hydrocarbons was observed. Both catalysts showed increase in chain growth probability and alcohol production with increasing CH4 and CO2 content in syngas. However, the catalyst KCuFe/mAl2O3 performed better with CO2 and CH4 present in syngas, and has the potential to bring economic benefits to FTS process by relaxing the expensive syngas purification process for complete removal of CO2 and CH4.