Cellulose pretreatment with 1-n-butyl-3-methylimidazolium chloride for solid acid-catalyzed hydrolysis Soo-Jin Kim a,b , Adid Adep Dwiatmoko a,c , Jae Wook Choi a , Young-Woong Suh a, * , Dong Jin Suh a , Moonhyun Oh b a Clean Energy Center, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea b Department of Chemistry, Yonsei University, Seoul 120-749, Republic of Korea c Clean Energy and Chemical Engineering Department, University of Science and Technology, Daejeon 305-355, Republic of Korea article info Article history: Received 5 March 2010 Received in revised form 27 May 2010 Accepted 7 June 2010 Available online 1 July 2010 Keywords: 1-n-Butyl-3-methylimidazolium chloride Pretreatment Hydrolysis Solid acid abstract This study has been focused on developing a cellulose pretreatment process using 1-n-butyl-3-methyl- imidazolium chloride ([bmim]Cl) for subsequent hydrolysis over Nafion Ò NR50. Thus, several pretreat- ment variables such as the pretreatment period and temperature, and the [bmim]Cl amount were varied. Additionally, the [bmim]Cl-treated cellulose samples were characterized by X-ray diffraction analysis, and their crystallinity index values including CI(XD), CI(XD-CI) and CI(XD-CII) were then calcu- lated. When correlated with these values, the concentrations of total reducing sugars (TRS) obtained by the pretreatment of native cellulose (NC) and glucose produced by the hydrolysis reaction were found to show a distinct relationship with the [CI(NC)–CI(XD)] and CI(XD-CII) values, respectively. Consequently, the cellulose pretreatment step with [bmim]Cl is to loosen a crystalline cellulose through partial trans- formation of cellulose I to cellulose II and, furthermore, the TRS release, while the subsequent hydrolysis of [bmim]Cl-treated cellulose over Nafion Ò NR50 is effective to convert cellulose II to glucose. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction A great deal of attention has been recently paid to development of biofuels and biochemicals technologies, which is associated with high dependency on fossil fuels and release of greenhouse gases that cause global climate change. Cellulose ((C 6 H 10 O 5 ) n ), the major component in lignocellulosic materials (35–50%), is a biodegrad- able polymer of simple carbohydrates (1000 < DP < 15,000) composed of b(1 ? 4)-linked D-glucose units, which has been rec- ognized as a potential renewable source for biofuels and bio-based chemicals production (O’Sullivan, 1997). However, due to the extensive network of inter- and intra-molecular hydrogen bonding between its fibrils, cellulose is insoluble in either water or most or- ganic solvents. It is, thus, recalcitrant to process and hydrolyze in solution (Murakami et al., 2007). Therefore, a pretreatment process is highly required to make cellulose more susceptible for subse- quent process, implying that the effective and economical pretreat- ment is the main key for the success of cellulose processing (Mosier et al., 2005; Hamelinck et al., 2005). To date, numerous methods have been applied for cellulose pretreatment prior to hydrolysis (Mosier et al., 2005; Hamelinck et al., 2005; Kumar et al., 2009; Sousa et al., 2009; Zheng et al., 2009). Although several processes including alkali and acid, oxidation and other chemical treatments have been reported to be a capable method in reducing the crystallinity of cellulose, they are high energy-demanding and often require severe conditions (Taherzadeh and Karimi, 2008). In recent years, a new type of non-volatile solvent, ionic liquids (ILs) have been thoroughly investigated to act as a powerful sol- vent for cellulose dissolution and hydrolysis owing to their solvent properties and process benefits (Kamiya et al., 2008; Zhao et al., 2009; Li et al., 2009). Swatloski et al. (2002) first reported that the ILs could act as the non-derivatizing solvent for cellulose and chloride-based ILs appear to be the most effective solvent solubi- lizing cellulose, where the greatest solubility of up to 25 wt.% was achieved under microwave irradiation with 1-n-butyl-3- methylimidazolium chloride ([bmim]Cl). This resulted from forma- tion of hydrogen bonding between hydroxyl functions of cellulose and chloride anions of ILs (Remsing et al., 2006). According to re- cent reports (Zhao et al., 2009), anions of chloride, formate, acetate or alkylphosphonate in ILs would be usually beneficial to dissolv- ing cellulose due to such a strong bonding at elevated temperatures. Aside from their use for cellulose dissolution, ILs have been ap- plied for cellulose pretreatment prior to enzymatic hydrolysis (Dadi et al., 2006, 2007; Liu and Chen, 2006; Li et al., 2009; Zhao et al., 2009; Lee et al., 2009; Samayam and Schall, 2010) or utilized as a medium for the hydrolysis reaction (Li and Zhao, 2007; Rinaldi et al., 2008, 2010; Kamiya et al., 2008; Li et al., 2008; Rinaldi et al., 2010). Particularly, Rinaldi et al. (2008, 2010) reported that the 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.06.047 * Corresponding author. Tel.: +82 2 958 5193; fax: +82 2 958 5209. E-mail address: ywsuh@kist.re.kr (Y.-W. Suh). Bioresource Technology 101 (2010) 8273–8279 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech