Reactive distillation in conventional Fischer–Tropsch reactors

• Considers the interaction between reaction and vapour–liquid equilibrium
• Describes the Fischer–Tropsch reactor as a reactive distillation system
• Shows that the production rate is dependent on either the stripping or reaction rate
• Explains results of switching from CSTR to batch reactor
• Is consistent with the two-alpha product distribution observed experimentally

The Flory distribution that is often observed in Fischer–Tropsch (FT) reactors could be described by reaction equilibrium between species. Furthermore, it has been suggested that vapour–liquid equilibrium (VLE) exists in the reactor and this could cause the two-alpha product distribution that is often observed experimentally. Simultaneous reaction and VLE lead us to ask the question: can we not describe the FT reaction as a reactive distillation system? In this paper we develop a mathematical model to describe the behaviour and performance of an FT reactor by considering the dynamic interaction between reaction and VLE. The model results show that the rate of formation of component hydrocarbons is dependent on either the reaction rate or stripping rate, depending on which one is rate-limiting. Furthermore we show that at steady state, the rate of formation of hydrocarbons is proportional to the stripping rate. We conducted an experiment which showed a reaction rate increment when the reactor was switched from CSTR to batch mode. The CO rate increases because reactant stripping was limiting the reaction rate. Modelling an FT reactor as a reactive distillation column is also consistent with the two-alpha positive deviation product distribution observed experimentally and industrially.

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