Amy K. Falcon

Date of Graduation

2016

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Wood Science and Technology

Committee Chair

Jingxin Wang

Committee Co-Chair

Benjamin Dawson-Andoh

Committee Member

David DeVallance

Committee Member

Ping Wang

Committee Member

Xinfeng Xie

Committee Member

John Zondlo

Abstract

Biomass pretreatment is a key techno-economic factor affecting the yield and economics of bioenergy or bioproduct production. The cost of pretreatment significantly increases if the sugars cannot be efficiently recovered once they are removed from the complex wood structure. Separation of the liquid extract from the solid particulates is important, especially in cellulose and hemicellulose recovery. A urea pretreatment of woody biomass was studied in this paper due to the ability of urea to decompose into ammonia molecules and carbon dioxide. Glucose separation from woody biomass was analyzed as an indication of pretreatment efficiency using three separation techniques: Whatman 113 filter paper, centrifugation, and a stainless steel mesh screen. The solid residues consist mainly of decrystallized cellulose, hemicellulose and lignin. The liquid extract, however, contains partial carbohydrate removal, thus inefficient separation techniques could potentially result in the loss of these soluble sugars. The stainless steel mesh screen provided the most reproducible method of sugar recovery, measurable in grams of glucose per gram of biomass (g/g), measuring 0.624 g/g +/- 0.015 on average for the solid residue. The filter paper was capable of recovering 0.710 g/g +/- 0.017, and the centrifuge recovered 0.820 g/g +/- 0.055. Filter paper and stainless steel mesh screen filtration methods are not significantly different from each other at low urea concentrations. Centrifugation has the largest variation in its ability to efficiently recover sugars.;Among many characteristics, an effective pretreatment of woody biomass should be able to consistently overcome the lignocellulosic recalcitrance, produce high yields of sugars, and be cost effective. To this end, urea is a promising additive to a hot water extraction of woody biomass because when one molecule of urea is hydrolyzed, two molecules of ammonia are produced. This characteristic, when applied in a hot water treatment of woody biomass, can react with lignin and decrystallize cellulose. Pretreated red oak biomass was tested and analyzed for sugar content according to the National Renewable Energy Laboratory (NREL) Analytical Procedures to determine the structural carbohydrates and lignin. Glucose is used as an indicator for total sugar content, and response surface modelling was employed to optimize the urea concentration for maximum sugar yield with consideration of temperature, holding time, and urea concentration. It was found that temperature and holding time were insignificant in the recovery of glucose, and urea concentration was the major significant factor in maximizing the quantity of glucose recovered. Of the factors analyzed, the optimal extraction factors were determined to be: temperature at 170°C, holding time of 60 minutes, and a urea concentration ranging between 12%--15% (w/w). These conditions produced a maximum glucose yield of 1.05 grams glucose per gram biomass.;Hybrid willow is a short rotation wood crop (SWRC) that can be used for the extraction of sugars for biofuels or bioproducts. In the extraction of sugars from the woody biomass feedstock, the pretreatment process is the most critical and costly step. Chemical pretreatments can partially destroy this recalcitrance of biomass and make it accessible for further conversion agents. A 2 x 4 factorial design was applied to analyze the use of urea as a chemical additive to a hot-water extraction process for the recovery of glucose from two cultivars of hybrid shrub willow: Belleville SV1 and Belleville Owasco. A reaction temperature of 170°C with a holding time of 60 minutes and varying urea concentration level were employed. A urea concentration of 13.27% produced the 0.37 grams of glucose per gram of biomass, recovered from hybrid shrub willow cultivar SV1 while 0.41 grams glucose per gram biomass were recovered from cultivar Owasco. There was no significant difference in the quantity of total lignin determined in cultivars SV1 (37.9%) and Owasco (44.7%).;Densified biomass, such as pellets, could be an ideal feedstock for the production of biofuels and bioproducts due to their advantages of long-term storage, resistance to degradation, and transportation. This study compared and tested whether pelletized biomass could produce the same quantity and quality of sugars as non-pelletized biomass using two cultivars of hybrid willow biomass: Belleville SV1 and Belleville Owasco. Biomass was pretreated with hot water and urea, filtered, and a Nelson-Somogyi assay was used to determine the reducing sugar content of the liquid fraction of the biomass as an indication of total sugar content. The National Renewable Energy Laboratory, Laboratory Analytical Procedure (LAP) for the determination of structural carbohydrates and lignin was performed on the solid fraction, and the extracted sugars were quantified. The results of this study showed that no significant difference in the sugar yield existed between pelletized and non-pelletized biomass for cultivar SV1. However, there was a significant difference in the quantity of glucose extracted based on cultivar, regardless of pelletization. Pelleted cultivar SV1 yielded the greatest quantity of glucose, measurable in grams of glucose per gram of biomass (g/g), at 0.49 g/g, while pelleted cultivar Owasco contained 0.16 g/g. Non-pelleted SV1 contained 0.48 g/g, while non-pelleted Owasco contained 0.38 g/g.

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