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

Forage quality and composition measurements as predictors of ethanol yield from maize (Zea mays L.) stover

<p>Abstract</p> <p>Background</p> <p>Improvement of biofeedstock quality for cellulosic ethanol production will be facilitated by inexpensive and rapid methods of evaluation, such as those already employed in the field of ruminant nutrition. Our objective was to evaluate whether forage quality and compositional measurements could be used to estimate ethanol yield of maize stover as measured by a simplified pretreatment and simultaneous saccharification and fermentation assay. Twelve maize varieties selected to be diverse for stover digestibility and composition were evaluated.</p> <p>Results</p> <p>Variation in ethanol yield was driven by glucan convertibility rather than by glucan content. Convertibility was highly correlated with ruminal digestibility and lignin content. There was no relationship between structural carbohydrate content (glucan and neutral detergent fiber) and ethanol yield. However, when these variables were included in multiple regression equations including convertibility or neutral detergent fiber digestibility, their partial regression coefficients were significant and positive. A regression model including both neutral detergent fiber and its ruminal digestibility explained 95% of the variation in ethanol yield.</p> <p>Conclusion</p> <p>Forage quality and composition measurements may be used to predict cellulosic ethanol yield to guide biofeedstock improvement through agronomic research and plant breeding.</p

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.</p

Drying characteristics of zucchini and empirical modeling of its drying process

The aim of the study was to dry zucchini (Cucurbita pepo) by two different methods (convective hot-air (CHD) and microwave-assisted drying (MWD)). The effect of air temperature (60, 70 and 80°C), microwave (MW) power (180, 360, 540 W) and sample thickness (5 and 10 mm) on some drying characteristics of zucchini were investigated. Thirteen mathematical models available in the literature were fitted to the experimental moisture ratio data. The coefficients of the models were determined by non-linear regression analysis. It was determined that the model that fits the moisture ratio data the best varies at different drying conditions. Increasing drying temperature and MW power and reducing sample thickness improved the drying rate and drying time. Drying in microwave has reduced the drying time by 52-64% for zucchini. It was found that the effective moisture diffusivities increased with increasing temperature and MW power. MWD samples had better rehydration ratios compared to ones dried only in tray drier for 5 mm thickness.  </p

Optimization of Ethanol Production From Microfluidized Wheat Straw by Response Surface Methodology

In this study, wheat straw was pretreated with a microfluidizer to improve its enzymatic hydrolysis and ethanol yields. The pretreatment was performed at various pressures (500, 1000, and 1500bar) and solid loadings (1, 2, and 3%). The microfluidized biomass was then subjected to hydrolysis and simultaneous saccharification and co-fermentation (SSCF) experiments at different enzyme loadings (5, 10, and 15 FPU/g dry wheat straw) using a mutant yeast. The results indicated that the microfluidization method alters the structure of biomass and leads to a reduction in lignin content. The samples pretreated at 1% solid loading contained the minimum lignin concentration and provided the maximum sugar and ethanol yields. These results signified that the microfluidization method is more effective on biomass at low solid loadings. The process conditions were optimized for higher ethanol and sugar yields using response surface methodology (RSM). The optimum pressure and solid and enzyme loadings were found as 1500bar, 1%, and 15 FPU/g dry wheat straw, respectively. The yields obtained at this condition were 82%, 94%, and 65% for glucose, xylose, and ethanol, respectively. High sugar yields implied that microfluidization is an effective pretreatment method for cellulosic ethanol production. On the other hand, low ethanol yield may indicate that the microorganism was sensitive to inhibitory compounds present in the fermentation medium

Design and Testing of a Pilot-Scale Aqueous Ammonia Soaking Biomass Pretreatment System

Scale-up of the aqueous ammonia soaking (AAS) biomass pretreatment method to 75-L soaking vessel size was accomplished in this work. A novel, pilot-scale AAS system capable of pretreating 4 kg of switchgrass per cycle was designed, fabricated, and tested. The pretreatment process involved soaking biomass in 29.5% aqueous ammonium hydroxide at a liquid: solid ratio of 5 L/kg. Major vessel design criteria included (1) allowing thorough washing of the soaked biomass in the pretreatment reactor; (2) simple, low-cost fabrication; and (3) limiting safety hazards by minimizing ammonia fumes from the system. Based on these constraints, commercially available 75-L HDPE tanks were selected as the primary vessels for pretreatment. The pretreatments were conducted outside, without agitation during the summer months in Iowa, with ambient temperatures ranging from 15°C to 33°C. During the first experimental cycle, clogging of the outlet resulted in leakage from the vessel during rinsing, and led to redesign of the washout prevention system. The redesigned system used a "teabag" approach in which dry biomass was preloaded into a cylindrical mesh bag, and the filled bag was placed into the soaking vessel. This modification eliminated outlet clogging, simplified biomass loading and unloading, but slightly reduced washing efficiency. Through five soaking cycles, an average of 22% to 25% delignification was achieved (Klason lignin basis) compared to the 35% removal seen at the bench-scale as reported by our group. Approximately 50% to 60% of the pretreated switchgrass was recovered, dry basis, compared to 75% previously achieved at the bench-scale. Overall, the system successfully generated moderate quantities (10 kg/wk) of pretreated biomass for pilot-scale fermentation experiments while illustrating some of the materials handling challenges that must be addressed as pretreatment methods are scaled-up.This article is from Applied Engineering in Agriculture, 25, no. 6 (2009): 953–959.</p

Effect of Drying on Porous Characteristics of Orange Peel

The purpose of the study was to determine the effects of different temperatures (40, 50 and 60 degrees C) and air velocities (1 and 2 m/s) on shrinkage, porosity, pore size distribution, color and microstructure of orange peel. Empirical models were also proposed to predict shrinkage and porosity as a function of moisture. A strong negative correlation was determined between moisture and shrinkage. Air temperature had no significant impact on the final shrinkage and porosity values. During drying, porosity of the samples first increased until a critical value, at which point further decrease in moisture resulted in collapse of pores. The porosity of the orange peel was correlated with moisture by a third- order polynomial. Pore size distribution curve of raw sample showed two major peaks, a wider and a sharper peak at around 19.8 and 7.18 mu m, respectively. After drying, the peaks became shorter and the curve shifted to the left, indicating that the amount of pores and their diameter decreased. The SEM analysis revealed that at extreme process conditions, the orange peel surface was cracked and the characteristic distribution of the waxy components was obstructed