Promoting transfer of endogenous electrons well increases the carbon and energy efficiency of lignocellulosic biomass conversion to fuels and chemicals

A new coupled process was developed by combining several technologies including biomass pretreatment, direct biomass-to-electricity conversion and electrochemical reduction of the CO₂ produced during microbial fermentation of the enzymatic hydrolysate of pretreated substrates. This process was achieved by the assistance of several electron carriers for mediating the transfer of biomass endogenous electrons. Pretreatment of corn stover to increase cellulose accessibility for bioethanol production with the electron carriers being reduced works as a “charging” or “electron extraction” step. Re-oxidization of the reduced electron carriers in a liquid flow fuel cell works as an “electricity generation” step. Electrochemical reduction of CO₂ to form formic acid with co-production of hydrogen gas works as an “electricity consumption” step. Under the respective optimal condition of each step, this coupled process would obtain 155.6 g bioethanol, 145.3 g formic acid and 23.3 g hydrogen gas from 1000 g corn stover, achieving 47.0% increase in carbon efficiency and 88% increase in system energy efficiency. This coupled process could well increase the carbon efficiency of lignocellulose polysaccharide conversion, which thus may provide new technical routes for lignocellulose conversion with more carbon negativity.