Multi-objective optimization of syngas production for Fischer-Tropsch synthesis based on biogas catalytic reforming and upgrading

The conversion of biogas into synthesis gas, for its subsequent application in Fischer-Tropsch synthesis, is one of the most studied processes for the production of liquid biofuels. However, this conversion still has economic and environmental disadvantages. This study evaluated the technical feasibility of a syngas production plant from biogas upgrading and reforming, through water scrubbing and bi-reforming processes. Aspen Plus modeling and a multi-objective optimization (MOO) were used to minimize CO2 emissions and maximize profitability. The multi-objective differential evolution with tabu list method was used to resolve the MOO design problem. The results reveal inherent trade-offs between both objectives. In particular, certain process parameters exerted a notable influence on the outcomes. Keeping a low water flow in the absorption column is essential to reduce environmental impact, but this also results in a lesser removal of impurities from biogas. Conversely, a higher water flow in the reactor promotes methane conversion, but concurrently raises the environmental impact. Nevertheless, the profitability of the Pareto front ranged from 5,200 to 6,500 k$ with a 1,000 Nm³/h biogas feed and the calculated CO2 equivalent net flow values varied between -11,900 and -11,550 kg/h. Therefore, it was successfully validated that calculated solutions of the Pareto allowed to demonstrate the feasibility of the proposed process.