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Alkaline Pretreatment of Corn Stover, Switchgrass and Prairie Cord Grass for Bioethanol Production
Thesis - University Access Only
Master of Science (MS)
Department / School
Agricultural and Biosystems Engineering
In lieu of diminishing crude oil and coal for future fuel, lignocellosic materials have the potential of providing fuels and other chemicals. Thus, in this regard, use of lignocelluloses in production of fuels and valuable chemicals are studied worldwide. The major polysaccharides in plants are the cellulose and hemicelluloses which are the major feed material for plant ethanol; however, these compounds cannot be easily utilized due to their inherent chracteristics like crystallinity, degree of polymerization and also the presence of other plant materials like lignin and hemicelluloses are intertwined and associated with cellulose fibers in such a way making it difficult for the hydrolytic enzymes, responsible for production of monomers from cellulose, to act on cellulose. Among different pretreatment strategies, alkaline treatment of biomass was adopted due to its low cost, less corrosiveness, lignin solubility, relatively easy handling and recyclability. This study was undertaken with an objective to study the effect of alkaline pretreating agent on the sugar recoveries of various biomasses like corn stover, switchgrass and prairie cord grass. In all cases, a steel pressure reactor (Model: 4563, Parr Instrument, Moline, Illinois) was used to contain the biomass in a closed environment and let it react with the alkaline chemicals (aqueous ammonia and lime). The study and divided into three major pretreatment parts which involved the treatment with aqueous ammonia, lime and a combination of ultrasound and ammonia. In the first study, corn stover and switchgrass samples were subjected to aqueous ammonia at high temperatures to make it bring about changes for maximum hydrolysis. In the case of corn stover, the biomass was treated at 100oC, 120oC and 140oC for 30, 60 and 120 min each, while for switchgrass the temperatures were maintained at 80oC, 100oC and 140oC for 20, 40, 60 and 120 min each with 14.5% and 29% aqueous ammonia for both biomasses. The best pretreatment condition was determined based on the highest sugar recovery from the biomass. For corn stover, a processing temperature of 100oC for 120 min with 14.5% aqueous ammoni was produced on hydrolysis, the highest recovery of glucose and xylose of 59.9% and 39.0% respectively. A processing temperature of 120oC for 120 min with 29% aqueous ammonia was the best condition for switchgrass which yielded glucose and xylose recovery of 67.3% and 15.3% respectively. The SEM images of the samples revealed that there was considerable physical damage in the structure of the lignocelluloses as a result of aqueous ammonia treatment in comparison to untreated samples. The ammonia-treated samples, especially the corn stover, developed porous structure in the walls, while the switchgrass was physically disrupted, making the fibrillary structure visible. The second study involved the use of line, which is a weak base. It is cheap, easy to handle and widely available. Similar to aqueous ammonia treatment, lime treatment was performed by subjecting the corn stover and switchgrass to 100oC, 120oC and 140oC for 30, 60 and 120 min using 0.1g lime/g biomass, while prairie cord grass was subjected o an extra level of 80oC temperature in addition to the above temperatures, time and concentration combination. On hydrolysis, the best strategy, based strategy, based on sugar recovery was 100oC for 60 min, which led to recovery of 63.9% glucose and combined sugar yield of 47.8%, a glucose recovery three times greater than from control sample. For switchgrass, the best treatment condition identified was 140oC for 30 min which gave a hydrolysis recovery of 56.7% glucose and 44.0% combined sugar. In case of prairie cord grass, the highest recovery was obtained for the sample treated at 120oC for 120 min which was able to yield hydrolysis recovery of 70.8% glucose and 57.4% combined sugar. This glucose recovery increase was about 75% in comparison to an untreated sample. In the third and last study, the effect of ultrasound/ozone in combination with ammonia treatment in hydrolysis sugar recovery from the corn stover, switchgrass and prairie cord grass was studied. The preliminary study indicated ultrasound was a more effective pretreatment. Thus, all the biomass were subjected to 40%, 60% and 80% amplitude levels of ultrasound for 5, 10 and 15 min period in presence of aqueous ammonia; they were then heated in a Parr reactor (Model: 4563, Parr Instrument, Moline Illinois) at 100oC for 120 min with 14.5% aqueous ammonia for corn stover, and at 120oC for 120 min with 29% for switchgrass and prairie cord grass. The cord stover (60% amplitude level for 5 min) gave the glucose recovery of 64.6%, which was significantly higher than the control sample. For switchgrass, ultrasound treatment of 40% amplitude level for 5 min was able to bring 59.5% glucose recovery, and for prairie cord grass, an ultrasound treatment of 40% amplitude level for 15 min brought glucose recovery of 73.5%, which was high than the control sample and more than twice the recovery from untreated prairie cord grass. The results of this pretreatment study concluded that the alkaline pretreatment has the potential of being use as an effective pretreatment strategy. In overall comparison, a single aqueous ammonia treated sample (100oC/ 120 min with 14.5% aqueous ammonia concentration) was found to have sugar yield, in the case of corn stover, not significantly different than ultrasound-ammonia treated yield, in the case of corn stover, not significantly different than ultrasound-ammonia treated samples. For switchgrass and prairie cord grass, ultrasound treatment combined with ammonia was found to have significantly high sugar yield than only ammonia treated sample.
Library of Congress Subject Headings
Lignocellulose -- Biotechnology
Ethanol as fuel
Number of Pages
South Dakota State University
Rijal, Prawesh K., "Alkaline Pretreatment of Corn Stover, Switchgrass and Prairie Cord Grass for Bioethanol Production" (2012). Electronic Theses and Dissertations. 5998.