Strategies for the Cellulosic Ethanol Production by Using High-Concentration Poly(ethylene glycol) in the Pretreatment, Enzymatic Hydrolysis, and Fermentation Steps

The addition of poly(ethylene glycol) (PEG) in the pretreatment and enzymatic hydrolysis steps has become attractive to increase second-generation ethanol titers. Recent studies have shown the benefits of using high-concentration PEG on the yeast vitality and enzymatic digestibility of untreated biomass. Thus, this study investigated the ideal concentration of PEG in the second-generation ethanol production and the best step to add it. In the acid pretreatment, PEG 4000 favored the delignification (59.2%) and reduced the non-productive adsorption of cellulases onto corn cob, but its use was not significant on the sodium carbonate-based pretreatment. Changes in PEG dosage and PEG molecular weight strongly affected the performance of enzymatic hydrolysis and simultaneous saccharification and fermentation (SSF). PEG 4000 (150 g/L) increased the production of reducing sugars by up to 30.1% and the ethanol production via SSF by up to 44.7% from untreated corn cob. In turn, PEG slightly affected the enzymatic digestibility and fermentability of the pretreated corn cob. One-pot ethanol production from corn cob was performed using PEG as an additive. The addition of 150 g/L PEG 1500 and PEG 4000 increased the ethanol yield values (> 52%) in the one-pot processes; however, the ethanol concentration was lower than in the experiments with the pretreated corn cob. SSF experiments with high solid loadings were tested using PEG 1500. Under these conditions, PEG 1500 slightly increased ethanol production, from 53.4 to 55.7 g/L ethanol (equivalent to 92.8% ethanol yield) using 20% (w/v) acid-pretreated corn cob.