Experimental investigations on olefin to paraffin ratio in Fischer-Tropsch products using syngas of low Ribblet ratio

Abstract

Biosyngas generated from gasification of agricultural and forest wastes can be utilized as feed in a Fischer-Tropsch reaction after raising its Ribblet ratio (H2/(2CO+3CO2)) to unity through energy-intense steps of Water-Gas-Shift reaction and carbon dioxide removal. The direct utilization of raw biosyngas with low Ribblet ratio is a sustainable approach for the production of carbon-neutral synthetic fuel from waste biomass. This work investigates the olefin to paraffin ratios in C2 -C3 range of hydrocarbons among the Fischer-Tropsch products under different process conditions. A deviation from the classical Anderson-Schulz-Flory (ASF) distribution for enhancing product selectivity towards fuel range hydrocarbons, is possible due to the higher activity of C2 olefins in various secondary reactions. The investigations in this study also indicate the presence of equilibrium in the ratio of bulk C3 (olefin + paraffin) / C2 (olefin + paraffin) irrespective of reaction feed composition. A laboratory prepared 0.5Fe/ComesoHZSM-5 catalyst was used with model biosyngas of 0.6, 0.4, and 0.2 Ribblet ratios as feed and the reaction were performed in a continuous fixed-bed reactor in the temperature range of 220–260 °C and space velocities of 1800-3400 mLh−1gcat−1. The experimental results show a similar trend in carbon monoxide conversion per gram of catalyst for Ribblet ratios of 0.6 and 0.4. The olefin to paraffin ratio in lower hydrocarbon range (n ≤ 5) for various carbon monoxide conversions is used as an indicator of chain growth efficiency in Fischer-Tropsch synthesis.