Ethylenediamine Enhances Ionic Liquid Pretreatment Performance at High Solid Loading

Abstract

Higher biomass loading (≥20% w/w) in pretreatment unit operations for lignocellulosic biorefineries will lead to a better economic feasibility and higher green efficiency. However, the industrial development behind high biomass loading in ionic liquid pretreatment has been hindered by unsatisfactory lignin fractionation and fermentable sugar release. Here, this study demonstrates that the addition of ethylenediamine (EDA) effectively improved glucose and xylose release in pretreatment using a 1-ethyl-3-methylimidazolium acetate ([Emim][OAc])-based system at corn stover loadings as high as 36% w/w under facile conditions. It was discovered that synergistic pretreatment with a 10% v/v EDA ratio in [Emim][OAc] was optimal for maximizing fermentable sugar yields, showing glucose yields of 94% and xylose yields of 48% based on untreated biomass; meanwhile, xylan loss was avoided due to low EDA loading. Additionally, the synergistic effect between [Emim][OAc] and EDA further reduced cellulose crystallinity when compared to the single pretreatment with [Emim][OAc] or EDA. In synergistic pretreatment, it was revealed that EDA played a crucial role in the cleavage of lignin–carbohydrate complex linkages, lignin relocalization, and removal at high solid loading, which provided “easy and simple” pathways for [Emim][OAc] to attack crystalline domains of native cellulose. Also, there were more native β-O-4 structures preserved in treated lignin after this synergistic pretreatment, offering a potential to make downstream lignin valorization even easier and more efficient. In addition, to achieve excellent performance, synergistic pretreatment could diminish requirements for pretreatment severity relative to single [Emim][OAc] pretreatment, which reduced glucan loss as well as energy consumption in the pretreatment process. This new approach sheds further light on understanding solid-state pretreatment and forward bioconversion in biomass.