Fabrication and fundamental understanding of cellulase-mimetic bifunctional solid acids for hydrolyzing cellulose

使用碳水化合物/糖平台将木质纤维素生物质资源转化为燃料的第一步是将生物质中的纤维素形成糖。然而，有效地从生物质中生产糖仍然是一个重大挑战。生物质中纤维素的化学转化使用酶（纤维素酶）和均质酸（如硫酸）产生葡萄糖，通常需要两步过程。所需的酶目前很昂贵；它们需要严格的操作条件（温度和pH值），并且需要更长的时间（天）才能实现令人满意的纤维素转化。均质酸存在设备腐蚀、回收和废水处理等问题。本项目旨在设计一种新型的仿生聚合物固体酸催化剂，将目前使用的酶和无机酸的功能按顺序结合起来。通过模拟纤维素酶/酶，该研究项目将涉及基础研究，设计和制造双功能仿生固体酸催化剂，用于水解纤维素以生产所需的单糖。该项目的综合教育计划将针对不同层次的学生，包括高中，本科和研究生。将特别关注来自STEM（少数民族和女性）中代表性不足群体的高中生和本科生。新概念、研究成果、获得的知识和创新技术将通过出版物、演讲和课堂教学向学术界、工业界、学生和公众传播。所有这些都将直接和/或间接地有利于生物能源和生物产品领域的研究、生产、教育和决策。该研究项目将涉及高效、稳健、低成本的纤维素酶模拟固体酸催化剂的基础研究，用于从生物质的主要成分之一纤维素中生产糖。该项目的成功将促进从生物质糖中生产生物燃料。采用分子和结构设计，固体酸催化剂将包含两种类型的官能团。第一组，酸性功能，如磺酸，负责水解纤维素。第二组，结合功能，将使用官能团，如羟基，羧基，卤素和硼酸基团。这种结合功能在固体酸催化剂上的作用是将催化剂的酸性功能带到纤维素上，增强固体酸-纤维素的相互作用。新催化剂的两个功能分别模拟了纤维素水解酶（纤维素酶）的纤维素水解结构域和纤维素结合结构域。预计固体酸的仿生功能化将显著提高其在纤维素水解中的性能。具体来说，双功能和纤维素酶模拟固体酸将通过两步法制造。在第一步中，通过Friedel-Crafts聚合，从精心挑选的含有所需纤维素结合基团的芳香单体合成聚合物，这将导致具有多孔结构（更大的表面积）和纤维素结合基团的骨架聚合物。在第二步，合成的聚合物磺化，引入磺酸作为纤维素水解基团。所得的纤维素酶模拟固体酸水解纤维素的性能将被评价。研究重点是从根本上了解纤维素酶模拟固体酸的结构性质（如表面积、多孔结构和官能团）与纤维素水解性能之间的关系。将特别关注纤维素酶模拟固体酸与纤维素之间的相互作用（亲和，吸附或吸引）以及固体酸在纤维素水解中的机制和动力学。

The first step in converting lignocellulosic biomass resources to fuels using the carbohydrate/sugar platform is to form sugars from the cellulose in the biomass. However, efficiently producing sugars from biomass remains a significant challenge. Chemical conversion of the cellulose in the biomass uses enzymes (cellulases) and homogenous acids (e.g. sulfuric acid) to produce glucose, usually in a 2-step process. The required enzymes are currently expensive; and they need restrictive operating conditions (temperature and pH) and take longer time (days) to achieve satisfactory conversion of the cellulose. Homogenous acids have issues such as equipment corrosion, recycling, and wastewater treatment. This project aims to design a novel biomimetic polymeric solid acid catalyst that combines the functions served by the enzymes and inorganic acids currently used in sequence. By mimicking the cellulase/enzyme, the research project will involve fundamental research to design and fabricate bifunctional biomimetic solid acid catalysts for hydrolyzing cellulose to produce the required simple sugars. The integrated education plan of the project will target different levels of students, including high school, undergraduate, and graduate students. Special attention will be paid to high school students and undergraduate students from underrepresented groups in STEM (minorities and women). New concepts, research findings, acquired knowledge, and innovative technologies will be disseminated to academia, industry, students, and the Public through publications, presentations, and classroom teaching/learning. All these will directly and/or indirectly benefit research, production, education, and policy-making in the area of bioenergy and bioproducts.The research project will involve fundamental research of efficient, robust, and low-cost cellulase-mimetic solid acid catalysts for producing sugars from cellulose, one of the major components of biomass. The success of the project would promote the production of biofuels from biomass sugars. Using molecular and structural design, the solid acid catalysts will contain two types of functional groups. The first group, the acidic function, such as sulfonic acid, is responsible for hydrolyzing cellulose. The second group, the binding function, will use functional groups such as hydroxyl, carboxylic, halogen, and boronic acid groups. The role of this binding function on the solid acid catalyst is to bring the acidic function of the catalyst to cellulose to enhance the solid acid-cellulose interaction. The two functions of the new catalyst mimic the cellulose-hydrolytic domain and the cellulose-binding domain of cellulose-hydrolytic enzymes (cellulases), respectively. It is expected that the biomimetic functionalization of the solid acids would significantly improve their performance in cellulose hydrolysis. Specifically, the bifunctional and cellulase-mimetic solid acids will be fabricated via a two-step approach. In the first step, a polymer is synthesized from carefully selected aromatic monomer containing the desired cellulose-binding group(s) by Friedel-Crafts polymerization, which will lead to a backbone polymer with porous structure (larger surface area) and cellulose-binding groups. In the second step, the resultant polymer is sulfonated to introduce sulfonic acid as the cellulose-hydrolytic group. The performance of the resultant cellulase-mimetic solid acids in hydrolyzing cellulose will be evaluated. The research focus is to fundamentally understand the relationships between the structural properties (e.g., surface area, porous structure, and functional groups) of the cellulase-mimetic solid acids and their performance in cellulose hydrolysis. Special attention will be paid to the interactions (affinity, adsorption or attraction) between the cellulase-mimetic solid acids and cellulose and the mechanisms and kinetics of the solid acids in cellulose hydrolysis.