Product distributions and olefin-to-paraffin ratio over an iron-based catalyst for Fischer-Tropsch synthesis

An iron-based catalyst was prepared by the co-precipitation method. The product distributions and olefin-to-paraffin ratio (O/P ratio) with chain length of Fischer-Tropsch synthesis over the iron-based catalyst were investigated under different reaction conditions in an integral fixed bed reactor. It is found that the product distributions are non-ASF situation, and the deviation from ASF law was analyzed by taking the physisorption, solubility, volatility of products and the subsequent secondary reactions into consideration. It is noted that the contents of hydrocarbons decline with increasing carbon number and higher temperature, space velocity, H-2/CO in feed gas and lower pressure is preferential for the formation of light hydrocarbons but against the chain propagation. The O/P ratio shows an exponential decrease with chain length except for ethylene and ethane because of the special adsorption character of ethylene. The O/P ratio is also affected by operating conditions. The results indicate that higher reaction temperature, space velocity of feed gas, lower pressure and higher H-2/CO in the feed gas are preferential for the formation of olefins and the enhancement of O/P ratio.