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

Abstract

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 CO 2 , H 2 O, CH 4 , C 2 H 4 , C 2 H 6 , C 3 H 8 , n-C 4 H 10 , i-C 4 H 10 and C 6.05 H 12.36 (C 5+ ) 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 (11 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%.The model predicts the influence of reaction rates on the performance of the fixed bed FT reactor using an unpromoted Co/SiO 2 catalyst at 503 K, 15 bar and 6 L g cat -1 h -1 . As a result, the conversions of 91.57 and 97.26% were achieved for CO and H 2 , respectively with the FT C 5+ synthesis reaction rate of 7.81×10 -5 mol g cat -1 s -1 . The higher rate of C 5+ formation was found by increasing FT reaction rates compared to the rate of lighter the hydrocarbons' formation. At the same condition, only 5.04 and 8.91% methane and C 2 -C 4 selectivity respectively, were predicted; while the highest value of 86.05% liquid (C 5+ ) selectivity was obtained in this case. It was concluded that the higher rate of conversion of H 2 inside the pores filled with liquid products, compared to that of CO, caused an increase in the H 2 /CO ratio in the catalyst pores; and thus, a shift towards the formation of lighter hydrocarbons.

A comprehensive study of kinetics mechanism of Fischer-Tropsch synthesis over cobalt-based catalyst

“…From the predicted results, it was found that at high temperature conditions, especially when T ≥ 528 K, the predicted results were not in good agreement with the measured data in which the predicted values presented a higher relative residual than those obtained at a lower temperature. However, the results presented in the past studies [33][34][35][36]52] revealed that with the narrower temperature range, for instance when T changes between 500-528 K,…”

Parametric Study and Multiobjective Optimization of Fixed-Bed Fischer–Tropsch (FT) Reactor: The Improvement of FT Synthesis Product Formation and Synthetic Conversion

“…To achieve an optimum in performance for the whole process, the mathematical development of the kinetics and the reactor model are essential. Also, the details of the products' distribution, selectivity and reactants conversion should be achieved by the developed mathematical model 15 . By modelling and optimizing the reactor's operation, it is possible in many cases to achieve significantly enhanced throughput;…”

“…To achieve an optimum in performance for the whole process, the mathematical development of the kinetics and the reactor model are essential. Also, the details of the products’ distribution, selectivity, and reactants conversion should be achieved by the developed mathematical model . By modeling and optimizing the reactor’s operation, it is possible in many cases to achieve significantly enhanced throughput, better and more consistent product quality, rising conversion and selectivity, as well as a significant effect on the scaling up of the processes from the laboratory to production scale.…”

“…Also, the details of the products' distribution, selectivity, and reactants conversion should be achieved by the developed mathematical model. 15 By modeling and optimizing the reactor's operation, it is possible in many cases to achieve significantly enhanced throughput, better and more consistent product quality, rising conversion and selectivity, as well as a significant effect on the scaling up of the processes from the laboratory to production scale. Only a few studies 16−25 are available regarding the development of a mathematical model of a fixed-bed reactor for FTS.…”

Metal-Supported Biochar Catalysts for Sustainable Biorefinery, Electrocatalysis, and Energy Storage Applications: A Review

“…The large specific surface area (ca. 757 m 2 g −1 ) of activated biochar favored a higher dispersion of Ru nanoparticles (>70%) compared to other usual support such as Al 2 O 3 (43%) and SiO 2 (17%), which may account for the effective catalytic performance [86]. Later on, the same authors observed a high CH 4 selectivity (98%) and a CO conversion of 100% and also an excellent stability for a period of at least 100 h on stream over the Ru activated biochar catalysts [87].…”