Synthesis and Oxidation of Lignin-Carbohydrate Model Compounds

To decrease our dependence on foreign oil supply and in an effort to decrease the amount of green house gases into the atmosphere, researchers are focusing on ways of producing fuels and chemicals from renewable resources. A renewable source such as wood has great potential for the production of biofuels and biochemicals. An integrated biorefinery process that maximizes the usage of wood and complements existing pulp and paper technology was proposed to extract underutilize hemicelluloses and covert them into bioethanol. In this process, not only hemicelluloses are extracted; lignin, since it is covalently bonded to hemicelluloses is extracted as well. It is reported that lignin is an inhibitor for enzymes and yeast during the conversion of hemicelluloses into ethanol, which decreases the yield of ethanol and increases the cost of production. Therefore, lignin needs to be removed prior to the production of bioethanol from hemicelluloses. Based on previous work in our lab, my project focuses on investigating oxidative methods to cleave lignin from hemicelluloses. Two glycosidic lignin-carbohydrate compounds were synthesized for this study. Knowledge of the mechanisms will allow us to determine the potential for such processes in the production of biochemicals and biofuels. We want to apply the oxygen delignification process to study this mechanism. Due to the presence of many oxygen species during this process, the mechanism is complicated. These oxygen species can be generated using H2O2 and UV radiation at 254 nm. Oxidative mechanisms of lignin-carbohydrate compounds were studied with superoxide anion (pH 12) and hydroxyl radical (pH 9.5). We are able to cleave the glycosidic bond between carbohydrate and lignin. Further oxidation of aromatic and carbohydrate was occurred. Less than 50% of glucose is obtained after the majority of lignin-carbohydrate model compound is reacted and none of the lignin portion is obtained any point of the reaction. Hence, this technique is useful for the cleavage of the glycodic linkages between lignin and carbohydrate. In order for this process to be a useful technique to obtain sugar from hemicelluloses, a process that is able to stop the further oxidation of carbohydrate must be developed