Study On SPORL And Dilute-acid Pretreatment For Woody Biomass

Although current research and development attention has been focused mainlyon agricultural residues and dedicated energy crops such as corn stover andswitchgrass, woody biomass (hard wood and soft wood) remains a very importantfeedstock for bioenergy production. This work focused on SPORL (SulfitePretreatment to Overcome Recalcitrance of Lignocellulose) and dilute-acidpretreatment for woody Biomass.The different effects of SPORL and dilute-acid pretreatment on earlywood andlatewood cell walls of Douglas-fir were studyed firstly in this study. The resultsindicated that dilute acid pretreatment removed almost all the hemicelluloses, whileSPORL pretreatment at initial pH4.5removed significant amount of lignin between20~25%. But both are not sufficient for effective enzymatic saccharification for softwood. SPORL at low initial pH combines the advantage of both dilute-acid andSPORL pretreatment at high pH to achieve approximately90%hemicelluloseremoval and significant delignification of10~20%. Results also showed that Wooddensity does not appear to contribute to wood recalcitrance and enzymaticsaccharification. Cell wall chemical composition, especially lignin and hemicellulosecontent, contribute to cell wall recalcitrance.Forest residue from commercial plantation havesting and forest thinningoperations is a substantial biomass resource that can be utilized for bioenergyproduction in China. While the quality of forest residue is low since the high barkcontent. This study investigated the bark effect on SPORL pretreatment anddeveloped an effective strategy for collecting forest residues and converting tofermentable sugars. Pretreatment of Douglas-fir forest residues by SPORL andsubsequent enzymatic hydrolysis revealed the presence of14.3%bark can reducesubstrate enzymatic digestibilities (SED)16%compared with that from a bark freesample. The SED of a bark is41%compared with73%for wood when pretreatedunder the same conditions. The variation of chemical compositions of forest residueswith particle size results showed that physical fractionation of Douglas-fir forestresidues through sieving can effectively fractionate bark and ash and therefore ligninfrom carbohydrates.The kinetic approach taken in this study is effective to design viable lowtemperature pretreatment processes for effective bioconversion of lignocelluloses.Comparing analytical results for SPORL pretreatment of Douglas-fir at two different temperatures in this study shows that changing the temperature and duration ofpretreatment can balance the production of inhibitors against substrate enzymaticdigestibility (SED).Three solid substrates from dilute acid pretreatment of two poplar wood sampleswere enzymatically hydrolyzed by cellulase preparations supplemented with xylanasein this study. The results indicated more enzymatic xylose and glucose yields wereobtained for a substrate with lower xylan content after a severer pretreatment at thesame xylanase dosage. The effectiveness of xylanase at increased dosages dependedon the substrates structure or accessibility. High xylanase dosages were moreeffective on well pretreated substrates than on under-pretreated substrates with highxylan contnet. The application sequence of xylanase and cellulase affected cellulosesaccharification.