The role of vapour–liquid equilibrium in Fischer–Tropsch product distribution

This work uses vapour–liquid equilibrium (VLE) to explain the observed two-alpha product distribution in Fischer–Tropsch (FT) reactors. We discuss three possible scenarios or cases of Anderson–Schulz–Flory (ASF) product distribution and VLE. The three cases assume the following: (1) the reaction sets up a single alpha ASF distribution in the total (vapour+liquid) products, (2) the vapour phase follows a single alpha distribution and (3) a single alpha distribution is set up in the liquid phase. We then look at the consequences of these assumptions in conjunction with a simple Raoult's law VLE model on the exit product distributions. We find that only Case 3 gives rise to a two-alpha model in accordance with experimental results that is frequently observed in FT reactors. This model further predicts a relationship between the two values of alpha that are consistent with the measured experimental results.

► Uses vapour–liquid equilibrium (VLE) to explain the observed two-alpha product distribution in Fischer–Tropsch (FT) reactors.
► Confirms that pure vapour phase FT can only be carried out at an alpha less than 0.7.
► Shows that negative deviations from classical ASF are due to product hold-up inside the reactor.