A comparison of dilute aqueous p-toluenesulfonic and sulfuric acid pretreatments and saccharification of corn stover at moderate temperatures and pressures Ananda S. Amarasekara ⇑ , Bernard Wiredu Department of Chemistry, Prairie View A&M University, Prairie View, TX 77446, USA highlights " Aqueous p-toluenesulfonic acid is better than H 2 SO 4 for corn stover saccharification. " Highest sugar yield is produced in aq. p-toluenesulfonic acid at 150 °C after 1 h. " Pentoses and hexoses decompose differently in aq. p-toluenesulfonic acid and H 2 SO 4 . article info Article history: Received 18 March 2012 Received in revised form 21 July 2012 Accepted 24 August 2012 Available online 1 September 2012 Keywords: Corn stover p-Toluenesulfonic acid Sulfuric acid Pretreatment Saccharification abstract Single step pretreatment–saccharification of corn stover was investigated in aqueous p-toluenesulfonic and sulfuric acid media. Dilute aqueous solution of p-toluenesulfonic acid was a better catalyst than aqueous sulfuric acid of the same H + ion concentration for single step pretreatment–saccharification of corn stover at moderate temperatures and pressures. For example, 100 mg corn stover heated at 150 °C for 1 h in 0.100 M H + aqueous sulfuric acid produced 64 lmol of total reducing sugars (TRS), whereas the sample heated in 0.100 M H + p-toluenesulfonic acid produced 165 lmol of TRS under iden- tical conditions. Glucose yield showed a similar trend, as aq. sulfuric acid and p-toluene sulfonic acid media produced 29 and 35 lmol of glucose respectively after 2.5 h. Higher catalytic activity of p-toluene- sulfonic acid may be due to an interaction with biomass, supported by repulsion of hydrophobic tolyl group by the aqueous phase. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Efficient and economical saccharification of lignocellulosic bio- mass to fermentable sugars is the major hurdle for the production of cellulosic ethanol from abundant cellulosic biomass (Geddes et al., 2011; Huang et al., 2011; Hallac and Ragauskas, 2011; Zhu and Pan, 2010; Brethauer and Wyman, 2010). The most widely tested technology for this step is high-pressure, high-temperature dilute aqueous sulfuric acid pretreatment followed by the use of a cellulase enzyme cocktail for saccharification. Since these opera- tions are expensive, the cellulosic-ethanol process is facing major challenges in making cellulosic fuel-ethanol cost-competitive with gasoline (Martin et al., 2009). A number of factors contribute to the high cost of these steps, including the cost of energy involved in the high pressure–temperature pretreatment (Pedersen and Meyer, 2010; Alvira et al., 2010; Zhu et al., 2010), need for the neu- tralization of sulfuric acid with lime, inability to recycle the acid, high cost of currently available enzyme preparations, and inability to recycle the enzymes (Sukumaran et al., 2009). Gasification of biomass and use of microorganisms to convert the syngas to etha- nol generally suffers from poor efficiency due to the insolubility of these gases in water (Munasinghe and Khanal, 2010). Single-step pretreatment–saccharification using dilute aqueous sulfuric acid at high temperature and pressure is a viable alterna- tive to the acid pretreatment-cellulase two-step method. The main drawback of the dilute aqueous sulfuric acid direct saccharification technique is its poor sugar yield due to incomplete depolymeriza- tion and degradation of glucose and xylose under acidic conditions (Torget et al., 2000). The other disadvantage is the high energy cost associated with operating at temperatures above 250 °C at high pressures (Lenihan et al., 2010; Torget et al., 2000). A number of studies on dilute aq. sulfuric acid-catalyzed single-step saccharifi- cation of various biomass types has been reported (Yat et al., 2008; Hua et al., 2010; Gurgel et al., 2012; Lee and Jeffries, 2011; Sanchez et al., 2004), generally with 0.07–1% dilute aq. sulfuric acid at 160–220 °C. Hydrolysis of aspen, balsam fir, basswood, red maple wood and switchgrass (Yat et al., 2008) at 160–190 °C, achieved 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.08.112 ⇑ Corresponding author. Tel.: +1 936 261 3107; fax: +1 936 261 3117. E-mail address: asamarasekara@pvamu.edu (A.S. Amarasekara). Bioresource Technology 125 (2012) 114–118 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech