Design, Sustainability Analysis and Multiobjective Optimisation of Ethanol Production via Syngas Fermentation

Ethanol production from non-edible feedstock has received significant attention over the past two decades. The utilisation of agricultural residues within the biorefinery concept can positively contribute to the renewable production of fuels. To this end, this study proposes the utilisation of bagasse in a hybrid conversion route for ethanol production. The main steps of the process are the gasification of the raw material followed by syngas fermentation to ethanol. Aspen plus was utilised to rigorously design the biorefinery coupled with Matlab to perform process optimisation. Based on the simulations, ethanol can be produced at a rate of 283 L per dry tonne of bagasse, achieving energy efficiency of 43% and according to the environmental analysis, is associated with low CO₂ emissions. The conduction of a typical discounted cash flow analysis resulted in a minimum ethanol selling price of 0.69 $ L⁻¹. The study concludes with multiobjective optimisation setting as objective functions the conflictive concepts of total investment costs and exergy efficiency. The total cost rate of the system is minimised whereas the exergy efficiency is maximised by using a genetic algorithm. This way, various process configurations and trade-offs between the investigated criteria were analysed for the proposed biorefinery system.