近临界水/醇介质中原本木质素催化氢解制备酚类化合物的机理研究

The present lignocellulosic biorefinery strategies usually concerned with carbohydrates while neglected the valorization of lignin. In addition, the chemical structure of the obtained lignin precipitates from all aforementioned fractionation biorefinery strategies is inevitably degraded to some extent, when compared to that of the original ‘protolignin’, which resulting in harsh conversion conditions, low product yield, and poor selectivity. Lignin recovery and its subsequent valorization to chemicals have never been of primary concern. In view of these, this work promotes a lignin-first biorefinery approach in a near-critical water/alcohol medium, converting lignin into useful phenolic chemicals during fractionation, while keeping the pulp fraction available for further processing. This mild conversion method of the original protolignin can reduce the structural loss of lignin activity and improve the efficiency of atomic conversion, thus improving the yield and selectivity of monophenols. This study begins with the interpretation of the macromolecular structure of original lignin. The experiment was carried out by various novel methods, containing one-pot catalytic hydrogenolysis experiment, advanced qualitative and quantitative analysis of the depolymerized products, synthesis and conversion of typical lignin model compounds, and computer simulation and quantum chemical calculation etc. Thus, the preferential dissolution, depolymerization mechanism of protolignin and the dissociation characteristics of carbohydrate under different reaction conditions were explored. The effects of lignin structure and reaction parameters on the products yield and distribution were investigated. The mechanism of breakage and recombination of critical chemical bond during the process of lignin catalyzed hydrogenolysis, as well as the formation and regulation of phenolic compounds in liquid products were all revealed and thoroughly analyzed. The research results will provide a basis and theoretical guidance for the development of new lignin catalyzed conversion routes, and for efficient conversion of lignin to produce high value-added chemicals.

针对生物质炼制过程中残余木质素后续转化反应条件苛刻、产物得率低、选择性差等技术难题，提出在近临界水/醇介质中优先催化氢解木质纤维中的原本木质素制备高值酚类化学品的协同生物炼制新思路。本研究从原本木质素大分子结构入手，采用温和的一步法催化氢解方法，通过木质素典型模型物构建与转化实验验证、计算机模拟与量子化学计算及定性定量分析产物，探索不同反应条件下木质素的优先解聚溶出规律及碳水化合物解离特性，明晰外加工条件与原本木质素结构对解聚产物得率与分布的影响，揭示木质素催化氢解过程中关键化学键的断裂与重组机制，阐明液相产物中酚类化合物的成因与调控途径，从而达到减少木质素活性结构损失、提高原子转化效率、提高单酚类化合物得率和选择性的目标。研究结果可为木质素的高效转化和高值化利用提供理论指导，进一步完善生物质炼制过程中木质素催化转化相关理论体系。

加快生物质资源开发利用，对于替代化石资源、发展循环经济、建设资源节约型和环境友好型社会具有重大意义。本项目针对生物质炼制过程中残余木质素后续转化反应条件苛刻、产物得率低、选择性差等技术难题，采用在近临界水/醇介质中优先催化氢解木质纤维中的原本木质素制备酚类化学品的新方法。本研究从纤维原料木质素的化学结构特征着手，探索了近临界水/醇（甲醇、乙醇、异丙醇）介质中杨木、竹柳木质素的优先解聚溶出规律及碳水化合物解离特性，优化了酸、碱辅助水/醇体系解离木质纤维组分的工艺条件，实现了在较温和的条件下获得可后续精炼加工的纤维浆料（酶解糖化效率可达94.4%）和高活性、低分子量解聚木质素产品（Mw 1550~4240 g/mol，PDI 1.67~2.51）；开展了近临界水/醇体系下原本木质素催化解聚制备酚类化合物的研究，揭示了溶剂种类与配比、反应温度、时间等对木质素解聚产物生成规律的影响；进一步结合木质素自身结构特点，通过对反应介质、催化剂等因素的选择，调控了木质素解聚酚类化合物得率，结果发现在近临界水/醇体系下，NaBH4与Ru/C可以协同催化木质素生产单体化合物，单体收率可达56.1%，其中酚单体收率约占其二分之一，而NaBH4的存在会促进苯酚的生产，此外，木质素化学结构会影响其向单体产物转化。通过对原本木质素、模型木质素、及木质素解聚生物油的分离分析及二维核磁结构解析，揭示了关键木质素化学连接键的断裂方式，探讨了液相产物中酚类化合物的成因。初步建立了在近临界水/醇热液催化体系下木质纤维生物质分离解聚制备高值酚类化学品和碳水化合物浆料的理论和技术基础。研究结果可为木质素的高效转化和高值化利用提供理论指导，并进一步完善生物质炼制过程中木质素催化转化相关理论体系。