Catalytic performance of cobalt-silica catalyst for Fischer-Tropsch synthesis: Effects of reaction rates on efficiency of liquid synthesis

摘要

A one-dimensional pseudo-homogeneous mathematical model of a fixed bed reactor for Fischer-Tropsch (FT) synthesis was developed for the flow of simulated N-2-rich syngas over an in-house cobalt-silica catalyst. This study aims at improving the efficiency of FT synthesis by maximizing the liquid productivities and selectivity, as well as maximizing the syngas conversion and minimizing the methane formation. The developed model predicts the fraction of the reactants and products along the reactor bed length. The rate of syngas conversion and the rate of CO2, H2O, CH4, C2H4, C2H6, C3H8, n-C4H10, i-C4H10 and C6.05H12.36 (C5+) formation were calculated by developing advanced codes in MATLAB. The reaction equations were proposed as a number of lumped chemical reactions (8 reactions, including water gas shift reaction) by means of the molar coefficients of reaction molecules (II reactive species). The kinetic parameters were estimated by global optimization in MATLAB using the global search method. Optimum values were achieved during the search process. The results predicted by the model were in very good agreement with those measured experimentally at different operating conditions, with respect to conversion and the FT products' selectivity. The rates of production and consumption were derived from a modified power-law rate expression. This study shows that the adapted rate model can deliver a better prediction of final conversion and selectivity. The accuracy of the fitted model relative to the experimental data was determined by a quantitative analysis method using the mean absolute relative residual percentage (MARR %) for the total of 35 data points. It was found that the model based on the modified equation provided a better fit to the experimental data with a MARR of 6.57%, compared to the classic equation with a MARR of 12.24%.