Novel ethanol production using biomass preprocessing to increase ethanol yield and reduce overall costs

Abstract

1 Background: Ethanol biorefineries need to lower their overall production costs to become economically 2 feasible. Two strategies to achieve this are to reduce costs by using cheaper feedstocks or to increase the 3 ethanol production yield. Low-cost feedstocks usually have high non-structural components (NSC) content, 4 therefore a new process is necessary to accommodate these feedstocks and overcome the negative effects 5 of NSC. This study developed a novel ethanol biorefinery process including a biomass preprocessing step 6 that enabled the use of lower-cost feedstocks while improving ethanol production without detoxification 7 (overliming). Two types of poplar feedstocks were used, low-quality whole-tree chips (WTC) and high-8quality clean pulp chips (CPC), to determine if the proposed process is effective while using feedstocks 9 with different NSC contents. 10Results: Technical assessment showed that acidic preprocessing increased the monomeric sugar recovery 11 of WTC from 73.2% (untreated) to 87.5% due to reduced buffering capacity of poplar, improved sugar 12 solubilization during pretreatment, and better enzymatic hydrolysis conversion. Preprocessing alone 13 significantly improved the fermentability of the liquid fraction from 1-2% to 49-56% for both feedstocks, 14 while overliming improved it to 45%. Consequently, it was proposed that preprocessing can substitute for 15 the detoxification step. The economic assessment revealed that using poplar WTC via the new process 16 increased annual ethanol production of 10.5 million liters when compared to using CPC via overliming 17 (base case scenario). Also, savings in total operating costs were about $10 million per year when using 18 cheaper poplar WTC instead of CPC, and by using recycled water for preprocessing lowered its total 19 operating costs by 45-fold. 20 Conclusions:The novel process developed in this study was successful in increasing ethanol production 21 while decreasing overall costs, thus facilitating the feasibility of lignocellulosic ethanol biorefineries. Key 22 factors to achieving this outcome included substituting overliming by preprocessing, enabling the use of 23 lower-quality feedstock, increasing monomeric sugar recovery and ethanol fermentation yield, and using 24 recycled water for preprocessing. In addition, preprocessing enabled the implementation of an evaporator-1 combustor downstream design, resulting in a low-loading waste stream that can be treated in a wastewater 2 treatment plant with a simple configuration. 3