Browsing by Subject "lime"
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Item Lime pretreatment and enzymatic hydrolysis of corn stover(Texas A&M University, 2005-08-29) Kim, Se HoonRenewable energy sources, such as lignocellulosic biomass, are environmentally friendly because they emit less pollution without contributing net carbon dioxide to the atmosphere. Among lignocellulosic biomass, corn stover is a very useful feedstock to economically produce environmentally friendly biofuels. Corn stover was pretreated with an excess of calcium hydroxide (0.5 g Ca(OH)2/g raw biomass) in non-oxidative and oxidative conditions at 25, 35, 45, and 55oC. The optimal condition is 55oC for 4 weeks with aeration, determined by yields of glucan and xylan. The overall yields of glucose (g glucan hydrolyzed/100 g original glucan) and xylose (g xylan hydrolyzed/100 g original xylan) were 91.3 and 51.8 at 15 FPU/g cellulose, respectively. Furthermore, when considering the dissolved fragments of glucan and xylan in the pretreatment liquors, the overall yields of glucose and xylose were 93.2 and 79.5 at 15 FPU/g cellulose, respectively. The pretreatment liquor has no inhibitory effect on ethanol fermentation using Saccharomyces cerevisiae D5A. At the recommended condition, only 0.073 g Ca(OH)2 was consumed per g of raw corn stover. Under extensive delignification conditions, 87.5% of the initial lignin was removed. Extensive delignfication required oxidative treatment and additional lime consumption. Deacetylation quickly reached a plateau within 1 week. Delignification highly depended on temperature and the presence of oxygen. Lignin and hemicellulose were selectively removed, but cellulose was not affected by lime pretreatment in mild temperatures (25 ?? 55oC). The delignification kinetic models of corn stover were empirically determined by three simultaneous first-order reactions. The activation energies for the oxidative delignification were estimated as 50.15 and 54.21 kJ/mol in the bulk and residual phases, respectively. Crystallinity slightly increased with delignification because amorphous components (lignin, hemicellulose) were removed. However, the increased crystallinity did not negatively affect the 3-d sugar yield of enzyme hydrolysis. Oxidative lime pretreatment lowered the acetyl and lignin contents to obtain high digestibility, regardless of crystallinity. The enzymatic digestibility of lime-treated biomass was affected by the change of structural features (acetylation, lignification, and crystallization) resulting from the treatment. The non-linear models for 3-d hydrolysis yields of glucan and xylan were empirically established as a function of the residual lignin fraction for the corn stover pretreated with lime and air.Item Long-term lime pretreatment of poplar wood(Texas A&M University, 2006-04-12) Sierra Ramirez, RocioLignocellulosic biomass (e.g., poplar wood) provides a unique and sustainable resource for environmentally safe organic fuels and chemicals. The core of this study is the pretreatment step involved in bioconversion processes. Pretreatment is required to realize high yields vital to commercial success. The focus of the pretreatment step is to methodically change key features of the biomass to favor enzymatic hydrolysis. This work assesses the compositional changes due to oxidative and non-oxidative longterm lime pretreatment of poplar wood (up to 4 weeks of pretreatment) at mild temperatures (25?C to 65?C), and their effect on the enzymatic yield of glucan and xylan. The most important pretreatment yield of lignin was 54 g lignin remaining/100 g lignin in raw biomass, and was accomplished for 4-week lime pretreatment at 65?C in oxidative conditions. The corresponding pretreatment yields of glucan and xylan were 85.9 g glucan recovered/100 g glucan in raw biomass and 80.2 g xylan recovered/100 g xylan in raw biomass respectively. For poplar wood oxidatively pretreated with lime for 4 weeks at 65?C and enzymatically hydrolyzed with an enzyme loading of 15 FPU/g glucan in raw biomass during a 3-day period, the best overall yields of glucan and xylan, were 80.7 g glucan hydrolyzed/100 g glucan in raw biomass and 66.9 g xylan hydrolyzed/100 g xylan in raw biomass respectively. The corresponding hydrolysis yields were 94.0 g glucan hydrolyzed/100 g glucan in treated biomass and 83.5 g xylan hydrolyzed/100 g xylan in treated biomass respectively. Because there is a previous study of long-term lime pretreatment of corn stover (Kim, 2004), the data obtained in this work show the effect of using woody lignocellulose as substrate. From the comparison, resulted that in the case of poplar wood oxidatively pretreated at 65?C for 4 weeks, less lignin was removed and more carbohydrates were solubilized, however the hydrolysis yield of glucan was almost equal and the hydrolysis yield of xylan was higher than the reported by Kim for corn stover oxidatively pretreated at 55?C for 4 weeks. The overall yield of glucan resulted lower in the case of poplar wood because of the lower pretreatment yield of glucan. Thus, it is important to complete the mass balances including an analysis on the pretreatment liquor to determine if the solubilized glucan was degraded.