Economic, energy, and environmental impacts of alcohol dehydration technology on biofuel production from brown algae

This study evaluates the impact of alcohol recovery technology on the economics, energy consumption, and environment of bioethanol production from brown algae. The process under consideration is the anaerobic digestion of brown algae to produce VFAs (volatile fatty acids), which are then hydrogenated to produce mixed alcohols. Three alternative processes, i.e., hybrid pervaporation/distillation (PV), hybrid vapor-permeation/distillation (VP), and classical molecular-sieves/distillation (classical), are considered for the dehydration and recovery of ethanol. The alternatives are analyzed in terms of product value (i.e., minimum ethanol selling price MESP), capital costs, energy consumption, and carbon footprint. For a plant scale of 400,000 ton/year of dry brown algae, the MESPs for the PV (Pervaporation), VP (vapor permeation), and classical processes were calculated to be $1.06/gal, $1.08/gal, and $1.24/gal, respectively. Results show that the PV, VP, and classical processes have $2.0, $2.6, and $4.6 million/year utility costs, respectively, for the recovery of alcohols and produce 23.1, 30.2, and 62.2 kton CO2-eq/year greenhouse gases. Therefore, PV is more economical and environmentally friendly process, with lower MESP, CO2 emissions, and utility requirements. A sensitivity analysis indicates that the selling price of the heavier alcohols and biomass price have the highest impact on the economics of bioethanol production from brown algae. (C) 2015 Elsevier Ltd. All rights reserved.