FISCHER-TROPSCH SYNTHESIS UNDER PERIODIC OPERATION

The published literature is reviewed on the performance of the Fischer -Tropsch Synthesis (FTS) under forced cyclical changes in feed composi tion, Six catalysts have been investigated by two separate research te ams. Most studies have employed a strategy using periodic exposure of the catalyst to pure H-2. Experimental evidence is that H-2 pulsing pr ovides a significant increase in the time-average rate of formation of the lower carbon number paraffins for all the catalysts considered. C obalt is the only catalyst for which olefin production also increases. For the lower paraffins, formation rates exceed the maximum rates att ainable under steady-state operation at a specified temperature and pr essure. Product distribution is also modified by H-2 pulsing, but the modification depends on the catalyst. For Ru and Co catalysts, there i s a decrease in the mean carbon number and a shift towards paraffinic products, The Mo catalysts investigated showed an increase in the mean carbon number under composition forcing, but at cycle periods that de press rates of hydrocarbon formation, With Fe, CH4 formation is strong ly stimulated, but the product distribution of the other hydrocarbon p roducts is unchanged. FTS mechanisms proposed in the recent literature seem adequate to explain qualitatively the composition forcing experi ments. There is opportunity for further investigation and suggestions for such are given.