With concerns about the long-term supply of petroleum and the desire to decrease U.S. dependence on foreign oil, renewable fuels are increasingly being considered as replacements for petroleum-based fuels. Cellulosic ethanol from perennial energy crops, crop residue, and forestry biomass could replace a significant percentage of the current United States petroleum consumption. The challenge in producing ethanol from cellulose is the difficulty in breaking down cellulosic matter to sugars. Two primary methods are used for cellulose hydrolysis: mineral acids and enzymes. Mineral acids give fast hydrolysis rates, but their use requires expensive materials due to their corrosivity and they must be separated and reused or neutralized and discharged. Enzymes are more selective than acids towards glucose, but are expensive and cannot be reused.
Principal Investigators Hohn and Wang of the Department of Chemical Engineering at Kansas State University propose a new type of catalyst for pretreatment and hydrolysis of lignocellulosic materials: acid-functionalized magnetic nanoparticles. Their hypothesis is that active, separable lignocellulose hydrolysis catalysts can be synthesized by combining a magnetic core with ligands that provide strong acidity and enhanced interaction with lignocellulosic biomass. The approach is to synthesize magnetite nanoparticles and utilize the strong interaction between magnetite and acid functionalities to bind ligands to the nanoparticle. These ligands will contain multiple acid groups: some that bind to the nanoparticle, but others that are available to act as Brønsted acid sites. In addition, the ligand will contain functional groups (like aromatic rings) that will enhance the interaction between crystalline cellulose and the acid-functionalized nanoparticles. The experimental plan covers many aspects, including characterization of the catalysts and the reaction products after hydrolysis treatments, and the separability and reusability of the catalyst particles.
Hohn and Wang will be able to probe what catalyst properties such as acid site strength or the presence of hydroxyl groups are important for production of glucose from biomass. The intellectual merit of the proposed research is that it will be the first to investigate acid-functionalized nanoparticles for hydrolysis. It will generate new knowledge in lignocellulose hydrolysis, and will pave the way for future research in using nanotechnology in biomass conversion. In addition, glucose is a representative of sugars that can be derived from biomass. These sugar molecules then may be used as platform molecules for chemicals or fuels, thus serving to advance the replacement of petroleum. The broader impact of the proposed research is the benefit to society associated with developing technology to convert biomass to fuel that can decrease U.S. dependence on foreign oil. In addition, this research will be incorporated into a hands-on workshop that will be used in an established program designed to enhance recruitment of women in science and engineering.
The goal of this project was to develop novel catalysts for breaking down cellulose (one of the main components of biomass) to the simple sugar glucose. This reaction is a key step in producing renewable fuel from biomass since glucose can be fermented to produce ethanol, an important fuel additive. Our approach was to attach acid groups to magnetic nanoparticles. The acid groups are active for breaking apart cellulose to sugars, while the magnetic nanoparticle allowed us to easily separate the catalyst from the products so that it can be reused. We attached the acid groups through two different methods. In the first, a silica shell was placed around the magnetic nanoparticle and then the silica was functionalized with sulfonic acid groups. In the second method, acid group were directly attached by the interaction of the nanoparticle with sulfonic acid ligands that we synthesized in our laboratory(see accompanying image). Both types of acid-functionalized nanoparticles were found to be active for breaking down model polymeric sugars (starch, cellobiose, and sucrose) to glucose, and could be used multiple times, though some loss of activity was noted upon reuse. The silica-coated particles were demonstrated to be active for breaking down polymeric sugars in wheat straw to fructose withsmall amounts of glucose. Our approach of directly attaching acid groups to the magnetic particles was the first report of this approach, adding a new route to heterogeneous acid catalysts to the scientific literature. The project also contributed to the training of the future generation of scientists and engineers. The two PIs both participated in the Multicultural Academic Program Success (MAPS) program run by the Multicultural Engineering Program. This program recruits incoming multicultural students to come to Kansas State University in the summer prior to their normal admission into the university to better prepare them for college success. Drs. Hohn and Wang engaged the students in a hands-on activity to synthesize biodiesel from vegetable oil. In addition, two graduate students and nine undergraduate students contributed to this research, in the process gaining valuable experience in conducting cutting-edge research and a new understanding for how to produce renewable fuels.
