Release of monomeric sugars from Miscanthus sinensis by microwave-assisted ammonia and phosphoric acid treatments P. Boonmanumsin, S. Treeboobpha, K. Jeamjumnunja, A. Luengnaruemitchai, T. Chaisuwan, S. Wongkasemjit ⇑ The Petroleum and Petrochemical College and the National Center of Excellence for Petroleum, Petrochemicals, and Advanced Materials, Chulalongkorn University, Bangkok 10330, Thailand article info Article history: Received 14 February 2011 Received in revised form 26 September 2011 Accepted 30 September 2011 Available online 8 October 2011 Keywords: Miscanthus sinensis Microwave irradiation Two-stage pretreatment abstract Microwave-assisted ammonium hydroxide (NH 4 OH) followed by phosphoric acid (H 3 PO 4 ) treatments were used to release monomeric sugars from Miscanthus sinensis grown in Cha-Chueng-Sao province, Thailand. Treatment with 1.0% (w/v) NH 4 OH, 15:1 liquid-to-solid ratio (LSR) at 120 °C temperature for 15 min liberated 2.9 g of monomeric sugars per 100 g of dried biomass, whereas the corresponding yield for a treatment with 1.78% v/v H 3 PO 4 , 15:1 LSR at 140 °C for 30 min was 62.3 g/100 g. The two-stage pre- treatment, treatment with NH 4 OH at 120 °C temperature for 15 min followed by treatment with H 3 PO 4 at 140 °C for 30 min, impressively provided the highest total monomeric sugar yield of 71.6 g/100 g dried biomass. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The unavoidable depletion of fossil fuels and the increased con- cerns on greenhouse gas emissions have resulted in a worldwide interest in exploring alternative energy sources to replace fossil fuels. Various agricultural residues or lignocellulosic biomass, such as corn stover, wheat straw, rice straw, and sugarcane bagasse, can be used to produce ethanol as alternative transportation fuel and other chemicals. Unlike fossil fuels, biofuels are produced from plants grown today and the short cycle of growing plants and burning fuel made from those plants add CO 2 to the atmosphere less than fossil fuels. Miscanthus sinensis, widely found in South East Asia, is believed to have a great potential as an energy crop for ethanol production. It naturally grows using a C 4 photosynthesis system (Acaroglu and Aksoy, 2005; Sørensen et al., 2008) and is highly tolerant toward salt and drought. Cultivation of this grass can be done with a low energy input and little use of fertilizers or pesticides (Guo et al., 2008; Chou, 2009). The main problem of ethanol production from lignocellulosic biomass is the low conversion of lignocellulosic biomass to fer- mentable sugars, which is the result of lignin and hemicellulose affecting to the digestibility of cellulose (Mosier et al., 2005). Sev- eral pretreatment strategies are available to make cellulose more accessible to enzymes or acid for conversion into fermentable sug- ars (Kumar et al., 2009; Hendriks and Zeeman, 2009). Alkali pre- treatment is used to remove lignin (Chang and Holtzapple, 2000; Han et al., 2009), and microwave heating improves the efficiency of this process (Ooshima et al., 1984; Hoz et al., 2005; Zhu et al., 2005, 2006). In this study, microwave heating was used during the pretreat- ment processes of M. sinensis biomass, and the effects of tempera- ture, time, liquid-to-solid ratio, alkali and acid concentration, and different acid types, viz. HCl, HNO 3 ,H 2 SO 4 ,H 3 PO 4 , were deter- mined. A two-stage pretreatment process, consisting of an alkali/ microwave followed by an acid/microwave treatment, was also conducted. 2. Experimental 2.1. Materials and chemicals M. sinensis was obtained from Cha-Chueng-Sao province, Thai- land. Before any pretreatment, M. sinensis (only leaves and stems) was washed with tap water and dried under sunlight. It was then milled to obtain small particles using herb grinder. The ground bio- mass (moisture content of 3.68%) was then stored in sealed plastic bags, keep it in a desiccator prior to use. The main composition of the Miscanthus was analyzed, following the method described by Lin et al. (2010), and found to be: 8.6% extractives, 42.7% cellulose, 31.3% hemicellulose, and 17.4% lignin. 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.09.136 ⇑ Corresponding author. Tel.: +66 2 2184133; fax: +66 2 2154459. E-mail address: dsujitra@chula.ac.th (S. Wongkasemjit). Bioresource Technology 103 (2012) 425–431 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech