(32d) Fischer-Tropsch Synthesis: Effect of Start-up Solvents In a Slurry Reactor

Fischer-Tropsch (FT) synthesis is a promising route for the gas-to-liquids (GTL) process which has recently received a renewed interest as a versatile catalytic route for producing high quality ultra-clean fuels from synthesis gas.  Fixed and fluid beds as well as slurry bubble columns are reactor configurations employed for commercial FT synthesis.  The main advantages of the slurry reactor over other reactors are that (a) heat removal is easier, and consequently, control of the overall exothermic reaction is better; (b) it is cheaper and simpler to build, operate, and maintain; and (c) specific volume is smaller (for similar production) [1, 2].  In fact it is common practice to initially load a slurry reactor with a start-up solvent, to suspend the fresh catalyst, before starting the reactor.

The present work aims to study the effect of start-up solvents on the performance of cobalt based catalysts and potassium promoted precipitated iron catalysts were investigated during FT synthesis using a continuously stirred tank reactor (CSTR).  In this study, four different molecular weight start-up solvents were tested such as Polywax-3000, Polywax-2000, Polywax-500 and C₃₀ oil.  The activity and selectivities (methane, C₅₊ and CO₂) were essentially the same for all the start-up solvents tested for the potassium promoted precipitated iron catalysts.  Results indicated that there is no significant effect on activity and selectivity by using different startup solvents in a slurry reactor for iron catalysts.  However, for the cobalt catalysts activity was found to vary with solvent media, which may be due to the particle size of the iron catalysts being very small relative to the cobalt alumina particles used.  The activity was found to be increase with decreasing molecular weight of the solvent media.  This may be as a result of pore filling rate in the interior of the catalyst, which increases with increasing start-up solvent molecular weight.

References:

1.                  C.H. Barholomew, R.J. Farrauto, Fundamentals of Industrial Catalytic Processes, 2nd ed.; John Wiley & Sons, Inc.: Hoboken, NJ, 2006.

2.                  M.E. Dry, Appl. Catal., A 138 (1996) 319.