UC Riverside

Biomass is one of the most important renewable energy which can reduce the energy consumption of fossil fuels and carbon dioxide emission. Ethanol converted from celluloses and hemicelluloses in lignocellulosic biomass by biochemical technology has great potential to replace gasoline for transportation fuels. Hemicelluloses content abundant of fermentable five carbon sugars which can be release by thermal/chemical pretreatment process. Dilute acid and hydrothermal pretreatment are two efficient ways to hydrolyze hemicellulose into xylose. However, most of hemicelluloses are hydrolyzed into its oligomers form which cannot be fermented to ethanol during hydrothermal pretreatment. Although, dilute acid pretreatment can easily hydrolyze hemicelluloses to monomeric xylose, the degradation products from xylose are dramatically increased when the pretreatment severity goes higher. This study focus on maximizing xylose yields of pretreatment and minimizing degradation products during the process. Two steps pretreatment was applied to achieve this goal. The first step is hydrothermal pretreatment which convers hemicellulose into both oligomers and monomers form, and following the second step dilute sulfuric acid hydrolysis at low temperature to convert oligomers into monomers with minimum degradation products. Combine severity factor was used to estimate reaction time with certain temperature and acid concentration. The results show that high xylose yields and low degradation products were observed. The kinetics of oligomers hydrolysis was developed and the acid concentration and temperature effects were considered. Rate constants (k) based on first order homogeneous kinetic models and activation energy were also estimated. NREL biochemical ethanol conversion process was applied to estimate both capital and operating costs of the two step hemicellulose hydrolysis process. Consequently, the dilute acid hydrolysis process convers most of the xylooligomers into xylose without forming large degradation products. And both capital and operating costs are reduced by using this two-step hemicellulose hydrolysis.