Performance of a multi-tubular Fischer–Tropsch reactor with two catalytic zones of different intrinsic chemical activity

Abstract

The effect of axial distribution of the intrinsic catalytic activity on the performance of a multi-tubular fixed bed Fischer–Tropsch reactor was investigated. The reactor was modelled based on kinetic data for a cobalt catalyst. The influence of pore diffusion on the effective rate of CO conversion was considered. The maximum temperature was limited to 240 °C to avoid excessive methane formation. In each case, the cooling temperature was set to a value 5 K below the ignition temperature to ensure a sufficient safety distance to thermal runaway. At first, the optimal activity for the standard case of a uniform axial activity was determined. The activity should then be limited for the given conditions to a value corresponding to a Co content in the catalyst of 13 wt% to reach the highest CO conversion, here X_CO = 41%. For a reactor with two zones of equal length, but different catalytic activity, a mean value of the Co content of 31 wt% is optimal, 23 wt% in the front zone and 40 wt% in the rear part of the tubes. X_CO is then 51% compared to only 38% for uniform distribution and a Co content of 31 wt%.