基于纤维素溶剂的木质纤维素预处理及其酶解性能的研究

发布时间：2018-04-03 22:49

本文选题：纤维素溶剂　切入点：玉米秸秆　出处：《江苏大学》2017年硕士论文

【摘要】：木质纤维素是地球上储量最大的可再生资源,利用木质纤维素制备生物乙醇是缓解环境和能源问题的重要途径之一。在长期的自然进化过程中,植物细胞壁形成了抵御酶降解及外部微生物的复杂结构。由于底物结构及酶解过程体系的复杂性,传统预处理方式存在着效率低和能耗高等缺点。与传统预处理相比,基于纤维素溶剂的木质纤维素预处理方法在预处理条件和预处理效果等方面具有一定的优势。本论文使用纤维素溶剂对玉米秸秆进行预处理,通过对比不同纤维素溶剂的预处理效果,筛选出适用于玉米秸秆的预处理方法,从经过高效预处理的玉米秸秆中提取木质素,初步探索预处理对木质素物理化学结构的影响;进一步扩大筛选出的纤维素溶剂的适用范围,研究其对麦秆的预处理效果,同时分析预处理液固比对预处理效果的影响;对传统的预处理与酶解糖化工艺进行改良,提出利用预处理与酶解糖化“一锅法”制备可发酵糖的方法,探究该方法可行性,并与传统“分步法”进行对比,分析其优越性。本论文的主要研究成果归纳如下:(1)酸性和碱性纤维素溶剂预处理后,玉米秸秆的酶解转化率都得到了大幅提升。它们都是通过破坏纤维素分子内和分子间的氢键,从而破坏纤维素的刚性结构,同时去除玉米秸秆中一定量的半纤维素和木质素,降低生物质的顽抗性,提高酶解糖化效果。与85%浓磷酸相比,低温NaOH/尿素溶液对玉米秸秆预处理效果较好。其中,在酶加载量为15 FPU/g底物的条件下,酶解24 h后,葡聚糖可以完全转化为葡萄糖。(2)85%浓磷酸预处理后,底物中存在大量的木质素,虽然纤维素结晶度降低较多,但没有获得较高的酶解转化率。研究表明,与纤维素结晶度相比,木质素对玉米秸秆酶解糖化的效果影响较大。通过对木质素的初步探索发现,低温NaOH/尿素预处理后的木质素“核心”结构没有被破坏,含有较多的化学活性基团,可能具有较好的化学活性。(3)低温NaOH/尿素溶液对麦秆同样具有良好的预处理效果。在酶加载量为15 FPU/g底物条件下,酶解糖化48 h,葡聚糖转化率可达95%,木聚糖转化率为84%。不同预处理液固比对麦秆中纤维素结晶度具有一定影响,但对麦秆的化学成分和酶解性能没有显著影响,这为高固载量预处理生物质的进一步研究提供了参考。(4)低温NaOH/尿素预处理与酶解糖化“一锅法”是可行的。最优预处理与酶解糖化条件下,葡聚糖与木聚糖的酶解转化率均可达到90%以上。“一锅法”可以产生比传统“分步法”更多的可发酵糖,其产生的可发酵糖占原料中总糖的90.24%,明显高于传统“分步法”的73.17%。低温NaOH/尿素预处理液中不含有如糠醛和5-羟甲基糠醛发酵抑制物,该方法具有广阔的应用前景。
[Abstract]:Lignocellulose is the largest renewable resource on the earth. Bioethanol using lignocellulose is one of the important ways to alleviate the environmental and energy problems.During long term natural evolution, plant cell walls formed complex structures resistant to enzyme degradation and external microorganisms.Because of the complexity of substrate structure and enzymatic hydrolysis process, the traditional pretreatment method has the disadvantages of low efficiency and high energy consumption.Compared with the traditional pretreatment, the lignocellulose pretreatment method based on cellulose solvent has some advantages in pretreatment conditions and pretreatment effect.In this paper, cellulose solvent was used to pretreat corn straw. By comparing the pretreatment effect of different cellulose solvents, the suitable pretreatment method for corn straw was selected, and the lignin was extracted from the corn straw which was pretreated with high efficiency.The effect of pretreatment on the physicochemical structure of lignin was explored preliminarily, the suitable range of cellulose solvent was expanded, the effect of pretreatment on wheat stalk was studied, and the effect of pretreatment liquid / solid ratio on pretreatment effect was analyzed.The traditional pretreatment and enzymatic saccharification process were improved, and the method of preparing fermentable sugar by pretreatment and enzymatic saccharification "one pot method" was put forward. The feasibility of this method was explored, and compared with the traditional "step by step method", the superiority of the method was analyzed.The main research results of this paper are summarized as follows: 1) after pretreatment with acidic and alkaline cellulose solvents, the conversion rate of enzymatic hydrolysis of corn straw was greatly improved.All of them destroy the rigid structure of cellulose by destroying the hydrogen bond in and between molecules of cellulose. At the same time, they remove a certain amount of hemicellulose and lignin from corn straw, reduce the resistance of biomass, and improve the effect of enzymatic hydrolysis and saccharification.Compared with 85% concentrated phosphoric acid, the pretreatment effect of low temperature NaOH/ urea solution was better than that of 85% concentrated phosphoric acid.Under the condition of enzyme loading of 15 FPU/g substrate and enzymatic hydrolysis for 24 h, dextran could be completely converted into glucose, 2n 85% concentrated phosphoric acid pretreatment, and there was a large amount of lignin in the substrate, although the crystallinity of cellulose decreased more.But no higher enzymatic conversion was obtained.The results showed that lignin had a greater effect on the enzymatic hydrolysis and saccharification of corn straw than cellulose crystallinity.Through the preliminary study of lignin, it was found that the "core" structure of lignin treated with NaOH/ urea at low temperature was not destroyed and contained more chemical active groups.NaOH/ urea solution at low temperature also has good pretreatment effect on wheat straw.The conversion rate of dextran and xylan was 95 and 84 respectively under the condition of enzyme loading of 15 FPU/g substrate and enzymatic hydrolysis and saccharification for 48 h.The crystallinity of cellulose in wheat straw was influenced by different ratio of pretreatment liquid to solid, but had no significant effect on the chemical composition and enzymatic hydrolysis performance of wheat stalk.This provides a reference for the further study of biomass pretreatment with high solid load.) the pretreatment of low temperature NaOH/ urea and enzymatic hydrolysis and saccharification are feasible.The conversion rate of dextran and xylan could reach above 90% under the optimal pretreatment and enzymatic saccharification conditions.The "one-pot method" can produce more fermentable sugar than the traditional "step method". The fermentable sugar accounted for 90.24% of the total sugar in the raw material, which is obviously higher than that of the traditional "step method" 73.17%.Low temperature NaOH/ urea pretreatment solution does not contain such as furfural and 5-hydroxymethylfurfural fermentation inhibitors. This method has a broad application prospect.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ352.1;X712

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