(631f) Dilute Sulfuric Acid Pretreatment of Corn Stover Assisted by Renewable Carbonaceous Catalysts

A range of industrially important fuels and chemicals such as ethanol can be produced from sugars. Xylose and glucose can be effectively extracted from renewable ligno-cellulosic biomass via depolymerization of hemicellulose and cellulose. A cost competitive bioconversion typically involves thermo-chemical pretreatment the ligno-cellulosic substrate followed by enzymatic deconstruction of the remaining cellulose into glucose. Dilute sulfuric acid pretreatment solubilizes much of the xylan into xylose and xylo-oligomers. However, fermentations typically require monomeric sugars to effectively convert sugars to higher value products. Xylo-oligomer conversion into monomers has been demonstrated by a secondary, mild thermochemical hydrolysis step and/or the addition of xylanases and side chain debranching enzymes. Thermochemical hydrolysis suffers from degradation due to lack of product specificity while enzymes are feedback inhibited, which makes it difficult to drive the reaction to completion. We seek a heterogeneous catalyst to selectively assist the hydrolysis of xylo-oligomers to xylose on a process relevant time scale.

We developed a reproducible method of generating a heterogeneous acid catalyst from a renewable source. Literature suggests that the conversion of ligno-cellulosic biomass through heterogeneous catalysis via carbonaceous materials is possible. In order to obtain a range of catalyst activities and support geometries, different polysaccharide candidates were chosen for catalyst generation, including Avicel, starch, cotton, and corn stover. Conditions such as carbonization temperature and method of sulfonation were varied during catalyst generation. The amount of thermal degradation and degree of sulfonation of the catalyst was determined through gravimetric analysis. Catalyst structural information was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy.

Fundamental engineering principles state that significant mass transfer limitations exist when a solid substrate interacts with a solid catalyst. Therefore this study focuses on the conversion of solubilized xylo-oligomers to monomers in the dilute sulfuric acid pretreatment hydrolyzate in bench scale batch and continuous packed bed reactors. Solid catalysts could serve as a solid-liquid separation media, thereby increasing their utility to the process. These results are compared with whole slurry batch catalysis and dilute sulfuric acid catalysis. Catalyst selectivity for xylo-oligomers is investigated, and the yield of xylo-oligomer conversion into monomers determined.