ABSTRACT
The high demand for energy worldwide and fossil fuel reserves depletion have generated increasing interest in renewable biofuel sources [1]. The use of bioethanol produced from lignocellulosic material can reduce our dependence on fossil fuels [2]. Lignocellulosic material, for example, waste products from many agricultural activities, is a promising renewable resource for bioethanol production [3]. This generally cheap and abundant material does not compete with food production compared with agricultural crops [4]. The conversion of lignocellulosic material to bio-
ethanol has been a research focus in China for the past decades [5]. In China, corn stover is an agricultural residue that is produced annually. Therefore, research on ethanol production from corn stover is of high importance in the new energy resource development [6]. The conversion process of lignocellulosic material to bioethanol generally includes four steps, namely, pretreatment, enzymatic hydrolysis, fermentation, and distillation [7]. Pretreatment technologies are necessarily applied to lignocellulosic material to decrease recalcitrance and to improve the yield of fermentable sugars [8], [9]. Many pretreatment methods have been proposed and investigated, such as alkaline [10], [11], steam explosion [12], [13], ammonia fiber expansion [14], [15], organic solvent [16], dilute acid [17], [18], and so on. Different pretreatment methods have different mechanisms, for example, they can decrease cellulose crystallinity and/or the polymerization degree, increase accessible surface areas, or selectively remove hemicellulose and lignin from the lignocellulosic material [19]. However, economic and environmental requirements limit the applicability of these methods. An effective pretreatment strategy should also minimize carbohydrate degradation and the production of enzyme inhibitors and toxic products for fermenting microorganisms [20]. One of the most promising pretreatment processes for lignocelluloses material is liquid hot water (LHW) pretreatment [21]–[23]. Some studies have been conducted on the mechanisms of LHW pretreatment [24]–[26]. However, different biomass types have different structures and show different reaction mechanisms.
