Submitted to: Bioresource Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/18/2010
Publication Date: 2/20/2011
Citation: Xu, J., Chen, Y., Cheng, J.J., Sharma-Shivappa, R.R., Burns, J.C. 2011. Delignification of Switchgrass Cultivars for Bioethanol Production. Bioresource Technology. 6:707-720. Interpretive Summary: Bioethanol production from biomass holds promise as an alternative to fossil fuels. Switchgrass (Panicum virgatum L.) has been noted to be one of the more promising warm-season perennial grasses with most potential. This study examined the potential of three recently released switchgrass cultivars adapted to the Southeastern USA for their sugar production efficiency when treated with NaOH. Of the three cultivars evaluated (ie. ‘Performer’, ‘BoMaster’, and ‘Colony’) Performer was selected based on a greater weighting for dry matter digestibility with some reduction in yield, whereas BoMaster and Colony were selected based on a greater weighting for dry matter yield with some reduction in digestibility. Pretreatment with NaOH was effective in reducing lignin concentration which should enhance enzymatic hydrolysis of carbohydrates to ethanol. Increased pretreatment, however, may lead to greater biomass solubilization and not benefit overall conversion efficiency. Total reducing sugars were examined and although pretreatment did reduce lignification, enzymatic conversion efficiency of total reducing sugars was not affected. Performer produced the greatest amount of sugar (425 mg/g raw biomass) followed by BoMaster (386 mg/g) and Colony (381 mg/g). A model was developed that combined the effects of alkaline pretreatment involving concentration, time of exposure, and temperature during exposure that effectively predicted lignin reduction and sugar production of the most promising cultivar, Performer. However the hecterage potential of these cultivars, which differs, was not addressed relative to sugar production and their potential as an economic sugar source on a land area basis.
Technical Abstract: Three switchgrass cultivars (‘Performer’, ‘BoMaster’, and ‘Colony’ switchgrass) were delignified using NaOH at varying concentrations and residence times at 121 oC for improved sugar production in enzymatic hydrolysis. Because of its greater carbohydrate/lignin ratio and the more substantial lignin reduction upon alkaline attack, ‘Performer’ switchgrass gave greater sugar productions under all the pretreatment conditions investigated. Maximum sugar production from ‘Performer’ was 425.43 mg/g raw biomass, which was achieved at 1% NaOH and 0.5 h. Sugar production increased with the improvement of delignification until the lignin reduction reached 30%. The more severe pretreatment conditions, which led to greater lignin reductions, did not favor the increase of sugar production because of greater solid losses. Linear models were proven effective in correlating a modified severity parameter log(Mo) to lignin reduction and sugar production of ‘Performer’ switchgrass.