Fischer–Tropsch synthesis in a bench-scale two-stage multitubular fixed-bed reactor: Simulation and enhancement in conversion and diesel selectivity

Abstract

A process based on a two-stage multitubular fixed-bed reactor is presented to enhance in conversion and diesel selectivity for the Fischer–Tropsch synthesis (FTS) process, which is characterized by the condensation and separation of liquid products and water from the outlet of the first-stage reactor. A two-dimensional pseudohomogeneous reactor model is proposed to simulate the temperature profile and CO conversion of the two-stage fixed-bed process. Model calculations indicate that the condensation and separation of liquid products and water between the two stages of the multitubular fixed-bed reactor plays an important role by changing temperature profile and synthesis gas partial pressure of the second-stage reactor. The model validation has been verified on the basis of the bench-scale test data in a single-stage and two-stage fixed-bed reactor, respectively, which demonstrates the understandable products distribution shift toward diesel-range hydrocarbon. The combined action of higher temperature, syngas/H2 partial pressure and readsorption of olefins at the two-stage fixed-bed reactor make CO conversion and C5+ selectivity increase, while CH4 and CO2 selectivity keep decreasing trends. Compared with the single-stage fixed-bed reactor process, the total CO conversion increases from 79% to 89% in the two-stage fixed-bed reactor process. The high valuable diesel range (C12–C22) increases significantly from 67% to 78%, while the gasoline range (C5–C11) decreases from 27% to 18%. The catalysts exhibit more stability and less deactivation rate over the two-stage fixed-bed process. The results are helpful to obtain more valuable diesel products and effective utilization of the syngas by the multi-stage fixed-bed process without tail gas recycling, which provides a practical case for multi-stage short reactor rather than one long reactor for FTS to improve products distribution.