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 composition, Six catalysts have been investigated by two separate research teams. Most studies have employed a strategy using periodic exposure of the catalyst to pure H-2. Experimental evidence is that H-2 pulsing provides a significant increase in the time-average rate of formation of the lower carbon number paraffins for all the catalysts considered. Cobalt is the only catalyst for which olefin production also increases. For the lower paraffins, formation rates exceed the maximum rates attainable under steady-state operation at a specified temperature and pressure. Product distribution is also modified by H-2 pulsing, but the modification depends on the catalyst. For Ru and Co catalysts, there is 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 depress rates of hydrocarbon formation, With Fe, CH4 formation is strongly stimulated, but the product distribution of the other hydrocarbon products is unchanged. FTS mechanisms proposed in the recent literature seem adequate to explain qualitatively the composition forcing experiments. There is opportunity for further investigation and suggestions for such are given.