Cellulosic ethanol production via aqueous ammonia soaking pretreatment and simultaneous saccharification and fermentation

The most important energy challenges of the century are energy growth, energy security and climate protection. Cellulosic based fuels such as ethanol are poised to offer energy security, and economic and environmental benefits if the associated commercialization challenges are overcome. The main objective of this thesis is to evaluate a promising approach for cellulosic ethanol production and to present information to guide. This dissertation, completed in partial fulfillment of the requirements of the Ph.D. degree, is prepared in the journal paper format, and includes four papers that have been published in or are prepared for submission to a journal. The objective of the first research chapter was to evaluate the effectiveness of an aqueous-ammonia soaking pretreatment method on ethanol production from switchgrass at bench scale. We have determined that ammonia soaking pretreatment method can be an effective method for the pretreatment of switchgrass. It was observed that after ammonia soaking, lignin and hemicellulose were partially removed, while the cellulose content of the lignocellulosic feedstock was preserved. The results also show that there is a tradeoff between pretreatment intensity and enzyme loading. The objective of the second paper was to scale up the bench scale simultaneous saccharification and fermentation (SSF) procedure and to identify the key issues of cellulosic ethanol production at larger scales. Pilot scale experiments (50 and 350-L fermentations) showed promising results that were similar to bench scale experiments. Material handling of the feedstock and bacterial contamination were the biggest challenges of the pilot scale fermentations. The third paper presents the techno-economic feasibility analysis of a full scale aqueous-ammonia soaked switchgrass fermentation process. It was determined that even though the aqueous-ammonia soaking pretreatment method provides advantages such as operating at ambient conditions, it is a capital-intensive process when implemented at commercial scale. Soaking time was the most important parameter that affected the total equipment cost. Feedstock and enzyme costs were identified to be the primary drivers of ethanol selling price. The objective of the last paper was to develop a rapid and easily adaptable SSF technique that offers the advantage of running a large number of samples at the same time using ammonia soaking as a pretreatment method. This research showed that ammonia soaking combined with SSF can be used as an easy and effective assay to determine ethanol yields of different feedstock. It was also observed that lignin concentration or near infrared reflectance spectroscopy can be used in directly to predict ethanol yields and can be used to guide biofuel feedstock selection in plant breeding research or in choosing feedstock for biofuel production