不同NaOH/球磨复合预处理对玉米秸秆酶解效果的影响

农作物秸秆的生物转化是木质纤维类生物质能源化利用的重要手段之一。为了探究室温条件下不同机械化学复合预处理对玉米秸秆酶解效果的影响，该研究以玉米秸秆为研究对象，以单独NaOH处理为对照，在不同NaOH质量分数（0、1%、2%和3%）条件下，分别进行了干法和湿法2种NaOH/球磨复合预处理。使用CellicCtec2（Novozymes，丹麦）进行了不同预处理玉米秸秆72 h酶解试验，系统表征了不同预处理玉米秸秆的粒径、结晶度、表面微观形貌、木质纤维组成和官能团变化，分析了不同预处理玉米秸秆理化性质对酶解影响及其相关性。结果表明：干法和湿法NaOH/球磨复合预处理均显著提高了玉米秸秆葡萄糖产率，且随NaOH质量分数增加（从1%提升至3%），不同NaOH/球磨复合预处理玉米秸秆葡萄糖产率显著提升（P＜0.01），当NaOH质量分数为3%时，其葡萄糖产率分别达到71.0%和73.1%。无论干法和湿法NaOH/球磨复合预处理，其酶解葡萄糖产率均与纤维素质量分数和平均粒径D50显著正相关（P＜0.01），与木质素质量分数显著负相关（P＜0.01）；干法NaOH/球磨复合预处理显著降低了玉米秸秆的结晶度，从而一定程度增强改善了玉米秸秆酶解葡萄糖产率。该研究为深入揭示和解析玉米秸秆机械化学复合预处理作用机理提供了数据支撑。

Effects of different NaOH/ball milling combined pretreatments on the enzymatic hydrolysis of corn stalks

The bioconversion technique is one of the important methods for producing environmentally friendly bioenergy from lignocellulosic biomass. The objective of this study is to explore the effect of different mechanochemical combined pretreatments on the enzymatic hydrolysis of corn stalks at room temperature. In this study, corn stalk was used as biomass material, lower load of NaOH with mass fractions 0, 1%, 2%, and 3% was used in the groups of NaOH pretreatment alone, the dry NaOH/ball milling combined pretreatment and the wet NaOH/ball milling combined pretreatment, respectively. The following 72 h enzymatic hydrolysis experiments for different pretreated corn stalks were carried out by using the enzyme CellicCtec2 (Novozymes, Denmark). The particle size, crystallinity, surface micromorphology, lignocellulosic composition, and the functional group changes of the pretreated corn stalk samples were systematically characterized. The effects of the different NaOH/ball milling combined pretreatments on samples' physicochemical properties on enzymatic hydrolysis yield and their correlations were further investigated and discussed in detail. The results showed that both dry and wet NaOH/ball milling combined pretreatment significantly improved the corn stalk glucose yield compared with NaOH pretreatment (P<0.01). And with the increase of NaOH mass fraction (from 1% to 3%), the glucose yield of corn stalk with dry and wet NaOH/ball milling combined pretreatment increased clear (P<0.01). When the mass fraction of NaOH was 3%, the glucose yield of the dry and wet NaOH/ball milling combined pretreatment reached 71.0% and 73.1%, respectively. The dry NaOH/ball milling combined pretreatment effectively reduced the particle size and crystallinity of the corn stalk, compared with the NaOH pretreatment. Once the NaOH mass fraction was 0, the particle size and crystallinity of the corn stalk treated by the dry NaOH/ball milling were the lowest, 15.8μm and 25.9%, respectively. But, the particle size and crystallinity of the corn stalk pretreated by the wet NaOH/ball milling were higher than those of the dry NaOH/ball milling combined pretreated samples. The cellulose mass fraction of different combined pretreatment samples gradually increased, with the increase of NaOH mass fraction. There was no significant difference in the cellulose mass fraction between the two pretreatment samples under the same NaOH loading conditions. The cellulose mass fraction was up to 48.5% in the wet NaOH/ball milling combined with pretreated samples, when the NaOH mass fraction was 3%. The lignin mass fraction decreased significantly with the increase of NaOH mass fraction (P<0.01). The lignin mass fraction of corn stalk with the wet NaOH/ball milling combined pretreatment was lower than that of dry ones. Once the NaOH mass fraction was 3%, the lignin mass fraction of the wet NaOH/ball milling combined pretreatment was the lowest at 14.9%. Regardless of the dry and wet NaOH/ball milling combined pretreatment, the enzymatic glucose yields were significantly positively correlated with cellulose mass fraction and average particle size D50 (P<0.01), and significantly negatively correlated with lignin mass fraction (P<0.01). The dry NaOH/ball milling combined pretreatment significantly reduced the crystallinity of the corn stalk, thereby enhancing the yield of enzymatic hydrolysis of the corn stalk to a certain extent (P<0.05). This study provides data support to help further reveal the mechanism of biomass mechanochemical combined pretreatment behind.