Effect of addition of zeolite to iron-based activated-carbon-supported catalyst for Fischer-Tropsch synthesis in separate beds and mixed beds

In-reactor upgrading of the products of Fischer-Tropsch (FT) reactions using synthesis gas was studied by adding zeolite ZSM-5 to a supported iron-based FT catalyst. The effects of ZSM-5 amounts and bed arrangements on the product distribution were investigated. Product profiles were analyzed for changing the ZSM-5 weight from 50 to 200% of the FTS amount. Oligomerization, aromatization, isomerization, and cracking reactions are enhanced with increasing ZSM-5 weight. The base catalyst showed no selectivity toward aromatic compounds, but addition of ZSM-5 formed C7-10 aromatic compounds. Long-chain hydrocarbon molecules (C13+) formed by the base catalyst are effectively cracked, and the products are isomerized on the ZSM-5 catalyst surface. Two catalyst-bed configurations were used: separate-bed and mixed-bed. Both arrangements show conversion of alcohols to hydrocarbons and water. The separate-bed arrangement gave higher conversions of CO and H-2, and higher yields of liquid hydrocarbons. The relative decline in FT activity for the mixed bed is probably due to metal migration from FT catalyst to ZSM-5, as confirmed by energy-dispersive X-ray spectroscopy of the spent ZSM-5. The maximum amount of i-C5-12 plus aromatics (a measure of high-octane gasoline-range hydrocarbons) is formed in the separate bed using equal amounts of zeolite and base catalyst. (C) 2012 Elsevier B.V. All rights reserved.