Special EBI Seminar
Wednesday, May 8, 2013
Dr. Hirokazu Kobayashi, Hokkaido University
Catalysis of Activated Carbons for Hydrolysis of Cellulose
Hirokazu Kobayashi is an assistant professor in the Catalysis Research Center at Hokkaido University, Sapporo, Japan. Within his specialization of catalysis, he is focusing his research on the conversion of biomass by solid catalysts, such as ruthenium and platinum. A member of the Chemical Society and Catalysis Society of Japan, Dr. Kobayashi is a Research Fellow of the Japan Society for the Promotion of Science.
He received his bachelor’s, masters and doctorate of engineering from the Tokyo Institute of Technology.
Cellulose has attracted great interest as a renewable fundamental feedstock for practical use in chemical industry, since this material is very abundant and does not compete with food sources for biomass. Cellulose is a polymer of glucose, and glucose is a versatile precursor to plastics and fuels such as ethanol. However, the hydrolysis of cellulose to glucose has remained a grand challenge because of the well-known recalcitrance of cellulose and the relative chemical instability of glucose. In this regard, we have unexpectedly found that a mesoporous carbon (CMK-3) can depolymerize cellulose to glucose, although the yield is only 16%. Hence, the objectives of this work are the high-yielding one-pot synthesis of glucose from cellulose, using carbon catalysts and clarification of the reaction mechanism.
In screening tests of carbons, an alkali-activated carbon K26 gave the highest yields of glucose (36%) and oligomers (3%) at 503 K in water. Considering that the hydrolysis of cellulose by K26 occurs at the solid-solid interface, their limited collision is a major obstacle in this type of reaction. Therefore, cellulose and K26 were ball-milled together, in a mix-mill process, as a pretreatment to improve their contact. The mix-milled cellulose was hydrolyzed to glucose (20%) and oligomers (70%) in total 90% yield even at a lower temperature of 453 K. HCl aq. at a practically available concentration (0.012%) was used as a solvent instead of water to convert the remaining oligomers to glucose in one-pot, resulting in 88% yield of glucose. Physicochemical measurements have shown that the active sites of carbons are carboxylic, lactonic, and phenolic groups. It is suggested that neighboring carboxylic and phenolic groups synergistically work for this reaction in model experiments using molecular catalysts. Phenols adsorb glucans and carboxylic acids cleave glycosidic bonds of the adsorbed molecules.