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.
