自催化乙醇法制浆低沸点有机酸产生机理及其作用机制研究

Auto-catalyted ethanol pulping is actually one of many acid catalytic processes, just in which the acid of formic and acetic acid playing a role of catalysis is self-generated from the system during the period of cooking process. The advantage of this process is including the investment saving, high pulp yield, lower water consumption, less pollutants, practicability of realizing biomass refining and good adaptability of using grasses material, from which this technique has got wide attention recently; however, some shortcomings are still existing in this process, for example, some viewpoints or findings are being controversial and some phenomenon can not be reasonably explained with the present achievements, special one is the generation mechanism of organic acid with low molecular weight and it's impaction on the system which will lead some problems in the pulp quality control and make the recovery of cooking waste liquor difficult resulting from the complicated compositions of azeotropic substances forming from the cooking process, and all these problems have not been resolved up to now. This project proposed here is based on the concept of cleaner production and energy saving and emission reduction, the research will begin with the generation mechanism of organic acid with lower boiling point, and the emphasis is to clarify some key problem, for example the source of formic and acetic acid, the interaction between the forming of them and the degradation of fiber components and it's impaction mechanism on the recovery of waste liquor. The potential achievements of this project will be able to build a theory base-frame for the mechanism research of auto-catalyzed ethanol pulping process, resolve the problems of lower recovery rate of alkali puling waste liquor of grasses in the alkali recovery process resulting from the silicon-trouble, poor economical efficiency and poor runnability to seek a path to the cleaner production. In view of the statements above, this project has important scientific significance and application value.

自催化乙醇法制浆是酸催化中的一种，起催化作用的酸是蒸煮时体系自己生成的，主要是低沸点有机酸- - - - 甲酸和乙酸。自催化乙醇法制浆具有投资省、成浆得率高、用水量少、污染小、可实现生物质资源"精炼"和对禾草类原料适应性好等优点，因而广受瞩目；但也存在一定不足，特别是蒸煮过程中低沸点有机酸的生成机理及其作用机制问题，以及由此带来的纸浆质量控制问题，蒸煮废液因"恒沸物"组成复杂带来的回收困难等问题，一直没有解决。本项目基于清洁制浆和节能减排理念，围绕低沸点有机酸的生成机理及其作用机制开展研究，重点阐明：甲酸、乙酸的来源；甲酸、乙酸的生成与纤维组分降解间的交互关系；甲酸、乙酸对废液回收的影响机制等关键问题。预期研究成果能够为自催化乙醇法制浆机理研究构建理论支撑，实现禾草类原料清洁生产，解决传统碱法制浆黑液因"硅干扰"问题而导致的回收效率偏低、经济性差和运行困难等问题，具有重要的科学意义和应用价值。

本项目研究了自催化乙醇法制浆低沸点有机酸的生成规律，产物分析。自催化乙醇法制浆具有投资省、成浆得率高、用水量少、污染小、可实现生物质资源“精炼”和对禾草类原料适应性好等优点，广受瞩目；但也存在一定不足，特别是蒸煮过程中低沸点有机酸的生成机理及其作用机制问题，以及由此带来的纸浆质量控制问题，蒸煮废液因“恒沸物”组成复杂带来的回收困难等问题。本项目基于清洁制浆和节能减排理念，围绕低沸点有机酸的生成机理及其作用机制开展研究，重点阐明了甲酸、乙酸的来源：甲酸、乙酸的生成与纤维组分纤维素、木素、半纤维素的降解都有关系，芦苇等禾本科原料与杨木等阔叶材生成有机酸量不同，芦苇以甲酸为主，杨木以乙酸为主。甲酸、乙酸与体系中的水、乙醇、糠醛、乙酰丙酸等形成的恒沸物可以通过添加碱性物质来破环，实现组分回收，由于发现逆流抽提可以使用全组分回收废液，无需组分进行分离，可低成本回收废液，回用废液，保温温度降低20℃左右。木聚糖和木糖降解的反应活化能分别为289.71KJ·mol-1和206.24KJ·mol-1。对自催化乙醇/水体系中葡萄糖的降解动力学进行了研究，纤维素首先降解为葡聚糖，进一步降解为葡萄糖，而葡萄糖可接着降解为5-HMF，进而降解为乙酰丙酸和甲酸。研究中将纤维素与葡萄糖的联合反应视为一步反应，以纤维素的转化率为基准建立动力学模型，根据线性系数推断葡萄糖降解为一级反应，并依据Arrhenius方程可得纤维素转化为5-羟甲基糠醛反应活化能为101.488 KJ·mol-1。废液回收糖中，D2-D6木糖总含量为27.83%，D7≥木糖含量为34.02%，100g绝干芦苇原料，乙醇制浆蒸煮废液蒸馏可得到粗糖7.15g。乙醇木素经弱酸-酶解两步法处理，相对纯度可达95%以上。预期研究成果能够为自催化乙醇法制浆机理研究构建理论支撑，实现植物纤维类原料清洁生产，制备高附加值副产品，具有重要的科学意义和应用价值。