Direct conversion of CO2 and H2 to liquid fuels via Fischer–Tropsch synthesis: Novel process concept and design optimization

This work proposes a new conceptual design for the direct conversion of CO 2 and H 2 to syncrude, which consists of three reactors in series with intermediate water removal and H 2 feeding. The first reactor is a low-temperature Fischer–Tropsch (FT) reactor with a cobalt catalyst using syngas as a feed, followed by two high-temperature FT reactors with an iron catalyst simultaneously active for both Reverse Water Gas Shift (RWGS) and FT reactions, fed with CO 2 containing 1 % inert. The process design incorporates tail gas recycling to improve CO 2 conversion and partial oxidation to reform light hydrocarbons and produce syngas. The process flowsheet was developed in Aspen Plus using a custom kinetic model that accounts for the variable chain growth probability distribution ( α ) along the reactor length. The process was optimized using the Particle Swarm Optimization (PSO) algorithm implemented in Python. The objective function of the optimization model is to minimize the total annualized cost per kilogram of product produced. The optimum design, with a minimum selling price of 1.68 $ kg -1 excluding the cost of captured CO 2 , exhibits a high tail-gas recycle ratio and a carbon efficiency of about 95 %. A sensitivity analysis is performed by varying the electricity price and the capital investment factor by ± 40 % to investigate the impact on the design parameters and the objective function. The majority of the total cost consists of the electricity required to produce green hydrogen and capital expenditures related to electrolyzer investment (about 74 % of total capital investment).