仿多酶型功能酸的构建及其催化木质纤维素类废弃物转化为糠醛的研究

Conventional process for transforming lignocelluloses to furfural is associated with low yield，energy-intensive and negative environment impact, thus the improvement of the chemical technology for producing furfural is needed urgently. In this project the multienzyme-mimetic acid catalysts with both the advantages of multienzyme catalysis and acid catalysis will be studied. Efficient biomimetic catalytic systems with different multienzyme-mimetic acid catalysts and reaction solvents will be established for converting lignocelluloses and their sugar-derivatives to furfural, and the feasibility of cellulose conversion into furfural with high yields will also be investigated. In the hope of catalyzing multi-step sequential reactions of “hydrolysis-isomerization-dehydration”, the catalysts will be designed by mimicing the functions of cellulases, xylanase and glucose/xylose isomerase, and sulfonic group, chlorine group, amino group, imidazole group, phenolic hydroxyl group or carboxy group, and so on, will be used to act as active sites of the catalysts. Besides, the acid sites will also be designed. To reveal the relationship of catalyst molecular structure characteristics and catalytic activity, the effect of molecular structure and functional group on furfural yields, as well as the activation energy of the reactions will be analyzed. By analyzing the solvent properties, the major intermediates and by-products, the synergistic mechanism of catalyst and solvent on reaction process and product distribution, and the reaction mechanism for furfural formation from different feedstocks in different catalytic systems will be explained. The research results of this project will provide new line of thinking for transforming lignocellulose to high-value added chemicals.

由木质纤维素类废物制取糠醛的传统方法效率低、污染严重，亟待改进。本项目拟研制兼有多酶催化和酸催化优点的仿多酶型功能酸催化剂，并通过溶剂筛选，建立木质纤维素及其水解糖向糠醛高效转化的仿生催化体系。除了半纤维素组分，本课题也考察纤维素组分能否大量转化为糠醛。通过模仿纤维素酶、木聚糖酶及葡萄糖/木糖异构酶的功能进行催化剂的分子设计，并设计酸性催化位点，用磺酸基、氯基、氨基、咪唑基、酚羟基、羧基等构成催化剂的活性部位，以期在水解-异构化-脱水反应链中发挥级联催化作用。在分析催化剂分子结构、所含基团对糠醛产率影响规律的基础上，结合反应活化能研究，获得催化剂结构特性与其催化活性关系的认知。并系统分析主要中间产物和主要副产物，结合反应溶剂的特性解析，揭示溶剂和催化剂对反应走向和产物分布的协同作用规律，阐释不同反应体系中生成糠醛的主要反应步骤及反应机理，为木质纤维素类农林废物向高值化学品的转化提供新思路。

由木质纤维素类废物制取糠醛是实现此类废弃物增值利用的有效途径之一，但需要高效清洁的催化体系来实现高产率地制取糠醛，并减少环境污染。本课题从催化剂活性基团的设计入手，开发了三大类固体酸：①不具有仿多酶特性的固体酸，②仿水解酶催化结构域和结合结构域的系列固体酸，③同时仿水解酶和异构酶的功能性固体酸。制得固体酸后，通过溶剂筛选，建立木质纤维素及其水解糖向糠醛高效转化的催化体系。本课题重点对半纤维素衍生糖类和纤维素衍生糖类同步转化为糠醛进行了研究，发现在“内酯+水”溶剂体系中，无论采用我们开发的哪种催化剂，六碳糖类转化的主产物是糠醛，而不是常规认知中的5-HMF。通过分析不同反应体系中的主要中间产物和主要副产物，发现六碳糖类向糠醛转化的关键反应步骤是“C-C”键的断裂和戊糖中间体的形成。溶剂特性、催化剂添加量、反应温度对六碳糖转化的主产物种类有重要影响。此外，内酯类溶剂和催化剂的协同作用是六碳糖类高产率转化为糠醛的关键因素。以原生玉米芯为原料，在我们开发的反应体系中，制取糠醛的摩尔产率已达到90%左右，且确定制得的糠醛中有一部分是源于玉米芯中的六碳糖组分，因为如果仅依据五碳糖计算，糠醛的摩尔产率已经超过了100%。研究成果为木质纤维素废物制取糠醛提供了新思路和理论基础。除了完成原定的研究计划和研究内容，我们又将研究内容延展至利用功能性固体酸，催化糖类、淀粉类、淀粉和油脂共存类的食品废物转化制取生物燃料及燃料添加剂，目标产物为5-乙氧基甲基糠醛、乙酰丙酸乙酯、乙酰丙酸甲酯。初步的研究发现酸位种类及酸量协同影响产物分布和产率，而溶剂组成对反应路径的影响较大。