木质纤维自水解过程中低分子生物活性抑制性物质产生途径及其动力学研究

On the Kraft-based dissolving pulp prduction process,the thermal water self-hydrolyzed process has been known an environment friendly process of hemi-cellulose extraction with low pllution and high efficiency. Under the self-hydrolyzed conditions of high temperature and acid, it is often accompanied by the generation of low molecular organic acid, furfural and dissolved phenols substances with biological activity inhibtion. The more complex the chemical component and tissue structure of wood fiber is and the more severity the self-hydroyzed conditions is applied, the more complex happens to this part substances generation mechanism and qualitativty and quantitativity. This project will adapt combination research method of theoretical analysis, experimental research, model simulation and numerical analysis, with the tissue structure and chemical properties as breakthrough point, with extracted hemi-cellulose, milled lignin and oligomeric model as reference, the formation mechanism and path of degradation products from hemi-cellulose and lignin will be researched with different temperature, time and liquor ratio of self-hydrolyzed conditions; With the least square algorithm and based on the principle of lumped kinetics, the transformation conditions for the main component of wood fiber to hydrolysis, degradation and into low molecular and the criterion of boundary conditions for consecutive homogeneous and biphasic pattern hydrolysis will be investigated under different self-hydrolyzed phase of high temperature thermal water enviroment. Through which, dynamic model including the generation of low molecular biological activity inhibition of wood fiber self-hydrolysis and degradation under therrmal water conditions will be established to provide principle basis and technical support for the construction of integrative pulping and biorefinery industry mode of wood fiber.

利用硫酸盐法生产溶解浆技术中，水热自水解被公认为是一种低污染、高效率的环境友好型半纤维素提取技术。在高温酸性自水解条件下木质纤维极易转化成低分子有机酸、糠醛和溶解性酚等生物活性抑制性物质。木质纤维化学成分和组织结构越复杂，自水解条件越高，这部分物质产生机制及定性和定量越复杂。项目采用理论分析、试验研究、模型物模拟和数值分析相结合的研究方法，以木质纤维组织结构和化学特性为切入点，以提取半纤维素、磨木木素及其低聚模型物为参照物，研究不同自水解温度、时间和液比条件下半纤维素和木素降解产物形成机制与途径；采用最小二乘算法，基于集总动力学原理，研究高温水热条件下不同自水解阶段，木质纤维主成分水解、降解及低分子化转化条件、连续均相水解和两相水解边界条件判据；建立纳入低分子生物活性抑制性物质的木质纤维水热自水解、降解动力学模型。为木质纤维制浆-生物质精炼一体化工业模式构建提供理论依据和技术支撑。

自水解预抽提半纤维素是木质纤维生物质精炼产业领域的共性关键技术，课题首先采用IC技术系统地研究并揭示了木质纤维中半纤维素组分首先以聚糖形式溶出，再逐步发生解聚至单糖、单糖降解生成糠醛、有机酸等低分子物质的转化规律，温度是水解过程中半纤维素去除率和速度，水解液中糖浓度和聚糖解聚转化的关键影响因素。采用硼氢化钠还原处理和紫外光谱（UV280nm）建立水解过程中溶解性木素酚和糠醛类物质的定量分析方法，解决了低分子有机酸在205nm和糠醛在280nm处对木素测定影响，确定了糠醛物质形成随水解强度提高而增加的关系规律。采用UV、FTIR、IC、NMR和GPC技术研究了自水解过程中分离半纤维素的化学组成和分子量分布，确定了溶解半纤维素中含有少量LCC结构、且主要以聚木糖为主75.5%，葡萄糖占比10.71、半乳糖含量为7.80%，分子链上残留有乙酰基存在，水解强度提高，半纤维素聚合度降低趋势，乙醇分离半纤维素聚合度低于40，显著低于碱性抽提分离的半纤维素。乙醇沉淀可有效分离水解液中的溶解性半纤维素，水解强度显著影响乙醇沉淀半纤维素的得率，且存在最佳自水解条件，浓缩水解液和增大乙醇/水解液的体积比可提高沉淀半纤维素得率。醋酸强化自水解可加速木质纤维半纤维素的提取，但水解液中最大半纤维素浓度低于自水解抽提液中的最大半纤维素浓度，且相同水解强度下，醋酸强化自水解分离半纤维素分子量低于自水解分离的半纤维素分子量。醋酸强化自水解分离半纤维素与自水解分离半纤维素NMR分析比较显示，存在明显的LCC结构。自水解/乙醇沉淀分离半纤维素后（乙醇/水解液）抽提水解木质纤维木质素研究显示，水解液中低分子有机酸可有效补充水解后木质纤维半纤维素去除的乙酰基含量降低对乙醇提取木素的影响，自水解有利于木质素的提取，且分离木质素中羟基含量增加，有利于木质素的化学改性反应。