Pretreatment Methods for the Efficient Conversion of Soybean Products to Bioethanol

The accessibility of cellulose by hydrolytic enzymes during enzymatic saccharification, in the conversion of biomass to bioethanol, is restricted by the morphological structure of plant cell wall. The recalcitrance of hemicellulose and lignin needs to be removed or compromised prior to the treatment of biomass with enzymes for the hydrolysis of cellulose and hemicellulose into fermentable sugars. With enzymeinhibitory by-products, toxicity, expensive production cost, and low product yield being setbacks facing the traditional pretreatment methods, new, environmentally benign, less expensive, and efficient pretreatment methods comparable to the traditional methods are therefore needed to maximize the production of fermentable sugars. This dissertation studied the use of ionic liquids (ILs), an organosolv fractionation, CO2-saturated water, 0.5% glycerol, and 1% glycerol as green pretreatment methods for the conversion of soybean meal, flakes, and hulls into fermentable sugars needed for bioethanol production. The ILs 1-butyl-3-methylimidazolium chloride (BmimCl), 1-allyl-3- methylimidazolium chloride (AmimCl), and 1-ethyl-3-methylimidazolium acetate (EmimAc) successfully dissolved and fractionated soybean meal, flakes, and hulls at approximately 19, 15, and 12 hours respectively, at an optimum temperature range of 65- 70 oC. Each of the four major components of the samples, that is, cellulose, hemicellulose, protein, and lignin, were successfully, isolated, regenerated, and characterized. The maximum glucose yield after enzymatic saccharification of the regenerated cellulose was 46.920 mg/g with an uncertainty of ±0.050 mg/g. The ILs used were recycled at 96% mass recovered and characterized using nuclear magnetic resonance spectrometry (1H NMR). Soybean meal, flakes and hulls successfully pretreated using organosolv fractionation, CO2-saturated water, 0.5% glycerol, and 1% glycerol at 50-70 oC and 1500 psi. Pretreatment efficiencies were determined relative to the amount of glucose and xylose present in the pretreatment hydrolyzate. Xylose yields for the organosolv method was 9.10±0.27, 8.83±0.67, and 10.20±0.42 mg/g for soybean meal (SM), soybean flakes (SF), and soybean hulls (SH) respectively. CO2-saturated water pretreatment obtained 6.64±0.030, 6.560±0.020, and 6.720±0.010 mg/g xylose for SM, SF, and SH, respectively. For 0.5% glycerol pretreatment, 8.37±0.13, 8.080±0.050, and 10.010±0.014 mg/g glucose for SM, SF, and SH was found. 1% glycerol pretreatment yielded 19.30±0.63, 18.50±0.43, and 22.040±0.014 mg/g glucose for SM, SF, and SH respectively. The relative amount of lignin recovered from the organosolv hydrolyzate for the SM, SF, and SH samples were 6.30±0.52, 6.10±0.43, and 11.90±0.14% of total sample mass respectively. In the final part of this work, the cellulose digestibility of the pretreated soybean meal, flakes, and hulls was determined to be 56.70±0.25 mg/g for the organosolv process, 47.9±2.3 mg/g for CO2-saturated water, 40.53±0.60 mg/g for 0.5% glycerol, and 50.00±0.60 mg/g for 1% glycerol pretreatment. The results of this dissertation show that BmimCl, AmimCl, EmimAc, CO2- saturated water, organosolv fractionation, 0.5% glycerol, and 1% glycerol pretreatment methods can efficiently pretreat biomass to produce cellulose digestibilities comparable to the traditional methods. These pretreatment methods are green, cost effective, and capable of replacing some of the traditional pretreatment methods currently being used for bioethanol production