The water consumption of sugarcane bagasse post-washing after protic ionic liquid pretreatment and its impact on 2G ethanol production

Abstract

Despite the water consumption of the first-generation ethanol (1G) production from sugarcane being widely studied, there are only a few experimental studies on water consumption — especially in the pulp washing — in second generation (2G) ethanol production. A quantitative evaluation of water wash consumption in the pretreatment with the protic ionic liquid (PIL) monoethanolammonium acetate [MEA][OAc] has shown that a water consumption between 600−1,000 wt% for two temperatures, 25 and 80 °C, decreased overall enzyme performance in saccharification compared to the full wash sample. The best condition in terms of high yield and low water consumption was found to be 800 wt%/80 °C, with up to 83 and 61.8 % of glucose and xylose yields against 97.9 and 85 % for the full wash sample. However, despite the full wash still presenting a superior ethanol yield, 87.4 %, the best condition with limited amount of water, 800 wt%/80 °C, also had a high ethanol yield of 86.1 %. Mass balance calculations confirmed that optimized [MEA][OAc] pretreatment with 800 wt%/80 °C and full wash conditions provided the highest ethanol yield per ton of biomass amongst several types of PIL and non-PIL pretreatments, 299 and 379 L 2G ethanol per ton of biomass, with an estimated water consumption of 56 and 647 ton, paving the way for an effective and more water-sustainable pretreatment technology for 2G ethanol production.