Accumulation of liquid hydrocarbons during cobalt-catalyzed Fischer–Tropsch synthesis - influence of activity and chain growth probability
During Fischer–Tropsch (FT) synthesis higher liquid hydrocarbons accumulate in the catalyst pores. The resulting mass transport limitations may lead to a decrease in reaction rate and also an unwanted higher methane formation, particularly for catalysts of mm-size as used in fixed bed reactors. The time required for complete pore filling and to reach steady state conditions, respectively, depends on the activity, chain growth probability α and pore structure (pore radii distribution) of the catalyst. The pore filling process was investigated in a magnetic suspension balance for two catalysts with a high and low α-value, Co/Al2O3 (α = 0.89) and Co/SiO2 (0.64). The resulting filling times are significantly different, two days for α = 0.89 and more than 400 days for α = 0.64. The modelling of the pore filling process is in good agreement with the experimental data. Therefore, the model was also utilized to predict the general influence of activity and α-value on the pore filling time of a FT catalyst.