Impact of volatile fatty acid recovery on economics of ethanol production from brown algae via mixed alcohol synthesis

• Mixed alcohols production from brown algae via VFA platform is assessed.
• MESP values of 1.24 and 3.61 $/gal are calculated for two VFA recovery cases.
• VFA recovery from dilute fermentation products is the main bottleneck of the process.
• Pervaporation would be costly for recovery of dilute VFAs from fermentation broth.
• Higher solids loading can strongly reduce the VFA recovery costs.

This study evaluates the economics of production of mixed alcohols from brown algae. Mixed alcohols (MA) were generated by hydrogenation of volatile fatty acids (VFA) that were produced by anaerobic digestion (AD) of brown algae. The process units including AD, VFA recovery, hydrogenation, and MA recovery were simulated in Aspen plus v.8.4. Two alternative processes, i.e., extraction/distillation (case 1) and hybrid pervaporation (PV) combined with extraction/distillation (case 2), were considered for recovery of VFAs from the dilute fermentation broth. Techno-economic models were developed to evaluate the plant economics and calculate a minimum ethanol-selling price (MESP). Sensitivity analysis of the economic and process parameters was performed to rigorously explore the uncertainties and main parameters affecting the MESP. The respective MESPs for cases 1 and 2 were calculated to be 1.24 and 3.61 $/gal. The results of the study showed that application of PV for dilute streams results in higher capital and energy costs primarily because of increased refrigeration, heating, and membrane costs.