The fischer‐tropsch synthesis with cobalt catalysts: The effect of process conditions on the composition of the reaction products

Abstract

The effects of the process variables on the alcohol and olefin contents of the liquid products and on the molecular weight of the total product obtained by synthesis with cobalt catalysts have been investigated.Within the range of reaction conditions hitherto employed, the generally accepted variations in product composition are confirmed, but, over the whole range of conditions within which cobalt catalysts are active for the synthesis, the effects of changes in conditions are more complicated and some new effects have been observed.The results suggest that the composition of the product is determined partly by the direct influence of the catalyst, the temperature, pressure, mean ratio of hydrogen to carbon monoxide, and space velocity of fresh gas, and partly by an indirect effect of these variables exerted through the extent of conversion of carbon monoxide and hydrogen. There is evidence that suggests that the olefin content varies inversely with the average molecular weight of the product.I t is considered that the results provide support for the hypothesis that the mechanism of the synthesis reaction involves step-wise growth of carbon chains, giving rise to alcohols, or alcohols and olefins, as the initial, desorbed products, the chemical identity of the molecules as they appear in the final product being determined by the extent to which secondary reactions occur. When cobalt catalysts are used a t atmospheric pressure it seems probable that, under certain conditions, some hydrogenation cracking takes place.