Lime pretreatment and enzymatic hydrolysis of corn stover

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Title: Lime pretreatment and enzymatic hydrolysis of corn stover
Author: Kim, Se Hoon
Abstract: Renewable 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 .
URI: http : / /hdl .handle .net /1969 .1 /2208
Date: 2005-08-29

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Lime pretreatment and enzymatic hydrolysis of corn stover. Available electronically from http : / /hdl .handle .net /1969 .1 /2208 .

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