Hydrolysis of near neutral hemicellulose extracts catalyzed by SO2
Hydrolysis of near neutral hemicellulose extracts catalyzed by SO2.
Jim Grundy’s project supervised by Adriaan van Heiningen and Rory Jara
Abstract
Hemicellulose extracts have been identified as a feed stock for the production of higher value added products such as ethanol in addition to pulp in an Integrated Forest Biorefinery (IFBR) based on a kraft pulp mill. In this process hemicelluloses are partially extracted as oligomers (mainly xylan-oligomers) and monomers from wood chips prior to pulping. These oligomers cannot be directly metabolized by microorganism during the fermentation process for the production of ethanol. This means oligomers must be broken down into monomers. Acid hydrolysis using sulfuric acid as a catalyst is the most widely employed process for this purpose. However, after this step, neutralization of the acidity is needed before the fermentation process. There are two major problems with this technology: the spent acid is not recyclable and the neutralization process produces a solid (gypsum) which often doesn’t have a market and must be disposed off at a cost. Sulfur dioxide (SO2) is a gas that can be used as a catalyst for the hydrolysis of hemicellulose oligomers. Because it is a gas it could be recovered downstream of the hydrolysis process and then reused to significantly reduce operational costs.
This project will investigate conditions under which hydrolysis catalyzed by SO2 are most favorable for degradation of xylan oligomers to their monomer constituents. Parameters that will be examined are SO2 concentration (goal of 4-8-12% concentration by mass), reaction time (30-60-90-120 minutes), temperature (120, 140, 150, 160 oC) and solvent (pure water and green liquor). For thorough experimentation, hydrolysis will be carried out using all ninety-six parameter combinations and sugar analysis using HPAEC will be carried out on each product to determine efficiency of monomer production. The products will also be tested for furfural content using HPLC to determine the amount of xylose monomers that were further degraded in the reaction process. Using the data from these experiments, the optimum conditions for hydrolysis of xylan using SO2 can be determined.
