(374y) Development and Validation of a Hemicellulose Depolymerization Kinetic Model for Aspen During Dilute Acid Hydrolysis
AIChE Annual Meeting
2010
2010 Annual Meeting
Sustainable Engineering Forum
Poster Session: Sustainability and Sustainable Biorefineries
Tuesday, November 9, 2010 - 6:00pm to 8:00pm
Abstract: Research into ethanol production from lignocellulosic biomass has grown significantly over the last few decades, for it offers a potential solution to replace conventional fossil fuels while not competing with food production. The lignocellulosic biomass can be converted to ethanol through pretreatment, enzymatic hydrolysis, fermentation and product purification. Hemicellulose is a major component of lignocellulosic biomass, accounting for 25-35% of total mass. Thus, the efficient conversion of hemicellulose to fermentable sugar is vital to ethanol yield and optimizes the economic performance of the production process. A kinetic mechanism for hemicellulose hydrolysis is highly desired as a tool to understand and improve lignocellulosic biorefining. Therefore, it continues to be modeled by researchers around the world. The most common mechanism is a two-step pseudo first order irreversible reaction where xylan in hemicellulose is hydrolyzed directly to xylose, which is dehydrated subsequently to furfural and eventually tars. However, oligomers are found to be a significant fraction of the product for dilute acid pretreatment, especially at short times, and oligomers are not taken up by fermenting microorganisms unless the oligomers are hydrolyzed further. A four-step first order irreversible reaction mechanism with constant rate constants at each step was proposed in one former study (Morinelly et. al, 2009), where xylan is hydrolyzed to oligomer intermediates, and then to xylose, which is later dehydrated to furfural and other degradation products. This kinetic model successfully described quantitatively and qualitatively the observed xylose monomer profile, oligomer data was also described successfully at early stage, but the model underpredicted at long reactor times. In this current study, a depolymerization model is applied to describe the dilute acid hydrolysis of hemicellulose. The bonds of a polymer composed of n-monomer units are broken during dilute acid hydrolysis, with a hydrolysis rate constant kh which is derived from previous experimental research (Morinelly et al. 2009). This poster will describe the results of this preliminary research into modeling complex depolymerization reactions and comparing model predictions with oligomer data from the laboratory using aspen as a model woody biomass species.