Comparing separation alternatives for recovering 2,3 butanediol in a biorefinery: Multi-objective optimization of economic and environmental performance

In this study, two separation pathways for recovering 2,3-butanediol (BDO) from a dilute aqueous fermentation stream were compared: distillation and simulated moving bed (SMB) adsorption followed by distillation. A multi-objective optimization framework employing Pareto fronts was used to evaluate the economic and environmental impact of integrating each pathway into a biorefinery producing renewable fuel from corn stover-derived BDO. Minimum fuel selling price (MFSP) and lifecycle greenhouse gas (GHG) emissions of the renewable fuel were chosen as the objective functions. Using a single distillation column to recover BDO resulted in GHG emissions of 43 g_CO2e (CO₂ equivalent)/MJ, ∼50 % lower than petroleum-based fuel (93 g_CO2e/MJ), but an MFSP of $2.55/GGE (gallon of gasoline equivalent, 1GGE = 121.3 MJ), exceeding the $2.50/GGE threshold set by the U.S. Department of Energy. In comparison, the SMB system lowered energy demand in the distillation columns and reduced GHG emissions to 18 g_CO2e/MJ and MFSP to $2.40/GGE. Further exploration of this pathway led to the use of heat pumps to replace fossil-based steam utilities in the distillation columns. The final separation process design recommendation was an SMB system followed by two distillation columns, with only one column electrified by a mechanical vapor recompression (MVR) heat pump loop. This configuration attained GHG emissions of 13 g_CO2e/MJ and an MFSP of $2.50/GGE. These findings highlight the economic and environmental advantages of employing a material-based separation such as SMB adsorption and integrating heat pump-assisted distillation to efficiently reduce reliance on fossil-based utilities.