Formulation of KMoFe/CNTs catalyst for production of light olefins and liquid hydrocarbons via Fischer-Tropsch synthesis: Fixed-bed reactor simulation

Abstract

Light olefins and C5+ are strategically important products of Fischer-Tropsch synthesis (FTS) over Fe catalysts. In the present work, FTS performance of 0.5K5Mo10Fe/CNTs (DOE 2) and 2 K0.5Mo30Fe/CNTs (DOE 5) catalysts was assessed in terms of CO conversion, C5+ selectivity, and C2-C4 selectivity under industrially relevant FTS conditions (H2/CO = 1.0; GHSV = 2000 h−1; T = 280 ℃; P = 4.13 MPa). The C2-C4 selectivity increased in DOE 2 catalyst to 51.2% with respect to DOE 5 catalyst (2.9%). Meanwhile, the selectivity toward C5+ hydrocarbons decreased from 93.1% in DOE 5 to 8.3% for DOE 2 catalyst. DOE 5 catalyst was more hydrophobic than DOE 2 as confirmed by the water contact angle measurement, lowering CO2 selectivity and water gas shift rate. H2-TPR and CO2-TPD indicated an increase in reducibility and basicity of DOE 5 compared with DOE 2 catalyst, which enhanced iron carbide formation and chain growth probability. The highest amount of metallic Fe in DOE 5 calcined and spent catalysts obtained by XPS and XAS spectra also suggested higher degree of carburization in DOE 5. Additionally, COMSOL Multiphysics software package was employed to provide a 2-dimensional simulation of the FTS fixed-bed reactor. Simulation results were validated using the experimental data for FTS over DOE 2 and DOE 5 catalysts. Effects of temperature on CO conversion as well as distribution of H2, CO, and ethylene were discussed. The simulation illustrated the effects of the fixed-bed reactor wall on both velocity and temperature profiles.