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Document Type

Thesis - University Access Only

Award Date

2011

Degree Name

Master of Science (MS)

Department / School

Agricultural and Biosystems Engineering

Abstract

Fossil fuel represents the main form of transportation energy today. However, with the increasing demand for fossil fuels, the supply is decreasing. Hence, there is a need for alternative energy sources to replace fossil fuels. Ethanol is used to supplement fossil fuels to some extent in many countries. Brazil and the USA are the major producers of ethanol in the world utilizing the fermentable sugars in sugarcane and corn, respectively. With the use of corn and sugarcane producing the ethanol, food versus fuel debate arises. Therefore, research has been done for the last three decades to produce ethanol from renewable non-food sources like biomass. The research findings show that ethanol produced from biomasses has benefits such as low greenhouse gas emissions and high fuel efficiency. Soybeans, a protein-rich leguminous crop, are cultivated throughout the world. The USA is one of the major producers of soybeans, and soybean crushing plants extract the oil by solvent extraction process, soybean hull, white flakes (WF), and defatted soybean meal (DSM) are obtained as by-products. Among these by-products, soybean hull has a high amount of cellulose and hemicellulose. On the other hand, white flakes or defatted soybean meal have considerable portion of raffinose-family oligosaccharides and small amounts of cellulose. These by-products, therefore, have the potential to serve as feedstocks for ethanol production. Three processing methods used in the food industry – extrusion, microwave, and ultrasound were investigated as pretreatment processes to improve sugar recovery from defatted soybean meal, white flakes, and soybean hull. In the first study, we determined the enzyme combination and enzyme dosage for the hydrolysis of defatted soybean meal and white flakes. Two enzyme combinations, Novozym 960 + Cellic CTec + Cellic HTec and Novozym 960 + Celluclast 1.5L + Novozym 188, were evaluated for the hydrolysis of DSM and WF. The Novozym 960 + Cellic CTec + Cellic HTec enzyme cocktail gave favorable results for hydrolysis. Since the enzymes used in the study had different optimum temperatures, another study was conducted to fix the hydrolysis temperature. Temperatures of 50 and 55 C were investigated. A temperature of 55 C was found to be optimum for a hydrolysis time of 72 hours. The findings from this study were used in the further pretreatment studies. In the second study, a high-shear extrusion process was evaluated as a pretreatment for DSM, WF, and SBH. The effects of extruder barrel temperature, screw speed, and feedstocks moisture content were investigated for maximum sugar recovery. Extruded samples were subjected to subsequent enzymatic hydrolysis and the hydrolysates were analyzed for sugar content. All the studied parameters significantly affected sugar yields from defatted soybean meal and white flakes. The effects was either linear or non-linear. A maximum sugar recovery of 84% was noted for DSM with extrusion conditions of 20% moisture content, 175 oC, and 50 rpm. Similarly, the conditions of 15% moisture content, 50oC, and 75 rpm were found to be favorable for a maximum sugar recovery of 80% from WF. Soybean hull moisture content and screw speed significantly affected sugar recoveries. Soybean hull extruded at 130 oC and 60 rpm with 12.5% w.b. moisture content resulted in 98%, 38%, and 80% recoveries for glucose, xylose, and combined sugar, respectively. The third study explored microwave irradiation for pretreating DSM, WF, and SBH. Microwave power level, processing time, and solid loading were evaluated to determine the optimum conditions. Solid loading and power level statistically influenced sugar yields from DSM, while all the studied parameters affected sugar recoveries from WF. Microwave pretreatment recovered 73% of the sugars from defatted soybean meal after hydrolysis with Novozym 960, Cellic CTec, and Cellis HTec with the pretreatment conditions of 20% solid loading rate, 180 W power, and 5 min processing time. Likewise, the conditions of 20% solid loading rate, 900 W power, and 3 min processing time achieved a 6% total sugar recovery from white flakes. The effect of microwave power level was significant on sugar recovery from soybean hull, while that of processing time was significant. The soy hull pretreated at 360 W for 2.5 min had 80.22%, 26.91%. 52.26% and 64.5% recoveries for glucose, xylose, arabinose and combined sugar respectively. Ultrasonication, a widely-used technique in wastewater treatment plants, was analyzed for extracting sugars from DSM, WF, and SBH in the fourth study. We investigated the effects of solid loading, amplitude, and sonication time on sugar recovery from feedstocks. Similar to microwave pretreatment, all the studied variables had significant effects on sugar yields from DSM and WF. The pretreatment recorded a 69% total sugar recovery from both DSM and WF. The optimum conditions for DSM were 15% solid loading, 80% amplitude, and 3 min sonication time, while the same for WF were 20% solid loading, 90% amplitude, and 4 min sonication time. The effect of amplitude was very significant, whereas the effect of sonication time was statistically insignificant. The favorable conditions of 10% solid loading, 70% amplitude, and 25 mi recovery 62% off total sugars from soybean hulls. All the above discussed pretreatments did not produce any fermentation inhibitors such as HMF and furfural. Sugar recoveries were in the range of 60% to 85%. Based on these findings, it could be concluded extrusion might be an effective pretreatment for soybean processing by-products due to its increased combined sugar recovery over microwave and ultrasonication pretreatments.

Library of Congress Subject Headings

Soybean

Extrusion process -- By-products

Biomass energy

Ethanol fuel industry

Format

application/pdf

Number of Pages

219

Publisher

South Dakota State University

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