Optimization and evaluation of the distribution of Fischer-Tropsch products over a cobalt-based catalyst utilising design expert software

Roick Chikati; Tawanda A Mpandanyama; Diankanua Nkazi; Phathutshedzo Khangale; Joshua Gorimbo

doi:10.1016/j.heliyon.2023.e23145

Optimization and evaluation of the distribution of Fischer-Tropsch products over a cobalt-based catalyst utilising design expert software

Heliyon. 2023 Dec 14;10(1):e23145. doi: 10.1016/j.heliyon.2023.e23145. eCollection 2024 Jan 15.

Authors

Roick Chikati¹, Tawanda A Mpandanyama¹, Diankanua Nkazi¹, Phathutshedzo Khangale², Joshua Gorimbo³

Affiliations

¹ Department of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, South Africa.
² Department of Chemical Engineering, University of Johannesburg, Doornfontein, 2028, Johannesburg, South Africa.
³ Institute for Catalysis and Energy Solution (ICES), College of Science, Engineering and Technology, University of South Africa (UNISA), Private Bag X6, Florida, 1710, Johannesburg, South Africa.

Abstract

Modelling biomass to liquid via the Fischer-Tropsch synthesis (FTS) system allows researchers to investigate the most efficient parameters while running the system under optimal conditions. As part of the design of experiments (DOE) procedure, a special data simulation method based on response surface methodology (RSM) is utilized to thoroughly analyse the impact of operating circumstances. The objective of this study was to examine the factors that affect the production of C₁, C₂-C₄, and C₅₊ in FTS process, and then optimize the critical factors utilising factorial design and response surface techniques. The parameters evaluated were reaction temperature, reaction pressure and the crystallite size of cobalt. The effects of these factors and their potential for synergy were explored simultaneously using multivariate DOE, with the yield of different hydrocarbon composition selectivity's as the measured responses. In the concept generation phase, optimization was based on the literature consulted, which proved to be an effective method for determining the optimization parameters. The detailed conceptual design included the generation of models using statistical methods and response surface models. Finally, the optimized design was validated using catalysts and parameters obtained during the optimization process, and this were compared to the output recorded in the theoretical modelling. The optimized parameters resulted in performance consistency, with the theoretical model for each group of hydrocarbons being validated by actual experiments. The established models were seen to characterize hydrocarbon distributions accurately and repeatedly over a wide range of reaction conditions (200-270 °C, 5-20 Bar, and 3-26 nm) using a cobalt-based catalyst. According to the detailed quantitative models developed, for higher C₅₊ production, 220 °C, 10 bar_g and 11 nm (cobalt crystallite) benchmark parameters were set to produce 19.3 % C₁, 11.4 % C₂-C₄ and 69 % C₅₊ selectivity's. Comparative analysis showed a 1.9 %, 3.9 % and 0.3 % percentage difference between the theoretical output and the actual output of C₁, C₂-C₄ and C₅₊, respectively.

Keywords: Clinoptilolite; Design of experiments (DOE); Fischer-Tropsch synthesis (FTS); Response surface methodology (RSM).