(643d) Effects of Nitrogen Co-Feeding in Fischer Tropsch Synthesis At Low CO Conversion

Fischer–Tropsch (FT) synthesis is a process that converts synthesis gas (syngas) into hydrocarbons and water over a metal catalyst. Despite being studied for over decades the reaction is still not that well understood. The reaction results are often complex and contradictory. Perhaps the complexity is not just due to the reaction mechanism?

The complexity might be caused by a combination of simple phenomena such as reaction kinetics, vapour-liquid equilibrium, and product accumulation inside the reactor or preferential stripping of lighter products and reactants. The individual phenomena are quite simple; however, the interaction of these phenomena could cause quite complex behaviour. Vapour–liquid equilibrium (VLE) modelling shows that the FT reaction may be either kinetically limited or limited by the product stripping rate. The preferential hold-up of heavier products in the reactor affects VLE modelling [1] and the preferential stripping of lighter hydrocarbons is an important part of FT modelling.

To investigate the effect of stripping in the FT reactor we co-fed and inert gas (N₂) with the syngas to the reactor, In order to keep the “reaction kinetics” the same in all runs, we kept the molar flowrate of syngas as well partial pressure of the CO and H₂ constant while varying the molar flowrate of N₂ and the reactor pressure. Two sets of experiments labelled reaction with syngas (RWS) for catalyst testing and reaction with diluted syngas (RWDS) for stripping effect were conducted. Preliminary results showed that diluting syngas with N₂ has a positive effect on the activity and selectivity of products even at low CO conversion.  The effect of N₂ on the FT reaction rate is modelled. This helps identify the region in which stripping is rate limiting as opposed to the region in which the reaction is kinetic limited.