BIOTECHNOLOGICAL PRODUCTS AND PROCESS ENGINEERING Investigation of acetic acid-catalyzed hydrothermal pretreatment on corn stover Jian Xu & Mette Hedegaard Thomsen & Anne Belinda Thomsen Received: 6 August 2009 / Revised: 13 October 2009 / Accepted: 2 November 2009 / Published online: 20 November 2009 # Springer-Verlag 2009 Abstract Acetic acid (AA)-catalyzed liquid hot water (LHW) pretreatments on raw corn stover (RCS) were carried out at 195 °C at 15 min with the acetic acid concentrations between 0 and 400 g/kg RCS. After pretreatment, the liquor fractions and water-insoluble solids (WIS) were collected separately and tested in terms of the recoveries of glucan and xylan from both the liquor fractions and the WIS, toxicity level of the liquors, and the convertibility of WIS to ethanol. The highest glucan recoveries was found to be 97.42% and 97.94% when 15 and 30 g AA/kg RCS were employed, respectively. The highest xylan recovery of 81.82% was observed by the pretreatment with 10 g AA/kg RCS. The toxic test on liquors showed that the inhibition effect happened to Baker's yeast when the acetic acid used in the pretreatment was higher than 100 g/kg RCS. The WIS obtained from the pretreatment with 15 g and 30 g/kg RCS were subjected to enzymatic hydrolysis and more easily converted to ethanol by Baker's yeast, which gave the ethanol concentration of 33.72 g/L and 32.06 g/L, respectively, higher than 22.04 g/L which was from the non-catalyzed LHW pretreatment (195 °C, 15 min). The ethanol concentration from the RCS was only 8.02 g/L. Keywords Pretreatment . Baker's yeast . Glucan/xylan recovery . Convertibility . Fermentability Introduction Bioethanol, which is considered as an ideal alternative in environmental sustainability and development to fossil fuels, can be produced from lignocellulosic materials (Bennett and Anex 2009; Cáceres-Farfán et al. 2008; Demirbas 2008; Matsushita et al. 2009). Among the different conversion technologies from lignocellulosic materials to ethanol, the most promising one for large- scale application is pretreatment followed by enzymatic hydrolysis and fermentation (Saddler and Brownell 1983; Sonderegger et al. 2004). Due to the complex chemical structure (Adler 1977; Fan et al. 1982; Fengel and Wenger 1989; Saka 1991), raw lignocellulosic need to be pretreated in order to make cellulose more accessible to enzymatic breakdown (Cara et al. 2008; García-Cubero et al. 2009; Kim and Mazza 2008). According to a base case carried out by the National Renewable Energy Laboratory (NREL), pretreatment process is one of the most expensive steps, accounting for up to 33% of the total cost (Lynd 1996). Different pretreatment processes have been developed during the last few years. Acid and alkaline pretreatments have been extensively studied (Mosier et al. 2005a, b). Pretreatment with diluted or concentrated sulfuric acid has shown to be effective in the hydrolysis of hemicellulose while producing very highly digestible remaining cellulose (Nguyen et al. 2000; Varga et al. 2002). Ammonia recycled percolation has been intensively investigated to pretreat different feedstocks including herbaceous biomass (Iyer et al. 1996; Kim and Lee 1996; Kim and Lee 2005; Kim et al. 2003), hardwood (Yoon et al. 1995), and paper mill sludge (Kim et al. 2000). Chang et al. (1998) found that pretreatment with 0.1 g Ca(OH) 2 /g wheat straw at 120 °C for 1 h resulted in glucan and xylan yields of 60% and 80%, respectively. However, high costs come simultaneously with the use of acid/alkaline resistant materials, rinsing of pretreated materials, and the treatment of effluents in the neutralization process. J. Xu (*) : M. H. Thomsen : A. B. Thomsen Biosystems Department, National Lab for Sustainable Energy, Risø-DTU, P.O. Box 49, DK-4000 Roskilde, Denmark e-mail: super_xujian@yahoo.com Appl Microbiol Biotechnol (2010) 86:509–516 DOI 10.1007/s00253-009-2340-x