Fisher-Tropsch Synthesis in the Presence of Bifunctional Catalysts Based on Hierarchical Zeolite MFI

Abstract

The effect of the hierarchical pore structure of ZSM-5 zeolites obtained by alkali modification on the composition of the synthesized products and the catalytic properties of bifunctional cobalt catalysts for the Fischer-Tropsch synthesis was studied. The bifunctional catalysts were prepared by mechanically mixing the Co-Al2O3/SiO2 catalyst, HZSM-5 zeolite and boehmite binder. The HZSM-5 zeolite was preliminarily subjected to alkali modification with different alkali concentrations (0.1, 0.25, 0.5, and 1.0 M) to create a hierarchical porous structure and change the acidic properties of the zeolite. The samples of ZSM-5 zeolites and the bifunctional catalysts prepared on their basis were characterized by SEM, low-temperature nitrogen adsorption-desorption, X-ray diffraction and H2 TPR. Catalytic tests were carried out in a tubular reactor with a fixed catalyst bed at a pressure of 2.0 MPa, a temperature of 250 °C and a gas space velocity of 1000 h–1. The tests were performed for 70–80 h of continuous operation. The fractional composition of the Fischer-Tropsch synthesis products was studied at a temperature of 250 °C. It was shown that preliminary treatment of zeolite ZSM-5 with a 0.5 M alkali solution contributed to an increase in the yield and productivity of branched hydrocarbons to 62% and 70.3 kg/(m3 cat∙h) compared to a similar bifunctional catalyst based on the industrial microporous zeolite HZSM-5.