Case Study Improvement of biomass properties by pretreatment with ionic liquids for bioconversion process Piyarat Weerachanchai, Susanna Su Jan Leong, Matthew Wook Chang, Chi Bun Ching, Jong-Min Lee ⇑ School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459, Singapore article info Article history: Received 10 November 2011 Received in revised form 1 February 2012 Accepted 2 February 2012 Available online 14 February 2012 Keywords: Biomass Pretreatment Ionic liquid Lignin extraction Sugar abstract Cassava pulp residue and rice straw were used as a precursor for pretreatment with ionic liquids to study the effects of pretreatment conditions on product yield and properties. Cassava pulp residue is a potential biomass in the bioconversion process due to it requiring mild pretreatment conditions while providing a high sugar conversion. The maximum sugar conversion and lignin extraction are attained from pretreat- ment of biomasses with particle size of <38 lm and ionic liquid of 1-Ethyl-3-methylimidazolium acetate at 120 °C for 24 h. The effectiveness of ionic liquid for biomass pretreatment process follows the sequence: 1-Ethyl-3-methylimidazolium acetate > 1-Ethyl-3-methylimidazolium diethyl phosphate > 1,3-Dimethy- limidazolium methyl sulfate. The increase of pretreatment temperature from 25 to 120 °C and decrease of biomass particle size renders higher sugar conversion, lignin extraction and lower crystallinity index. However, pretreatment at temperatures higher than 120 °C shows a sharp decline of regenerated biomass yield, sugar conversion and lignin extraction and giving higher crystallinity index at pretreatment temper- ature of 180 °C. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Lignocellulosic materials are a natural, abundant and renewable feedstock for production of fuels and chemicals. The materials have complex structures and compositions consisting of three main components: cellulose, hemicellulose and lignin (Brandt et al., 2010). To convert the materials into energy and valuable chemical feedstocks, biological conversion process has been known as a promising technology. This process provides a variety of products: for example, ethanol, butanol, biogas and hydrogen (Polman, 1994; Tadesse and Luque, 2011). In addition, sugars, the primary product from biological conversion process, can be reduced by hydrogen gas to form alkanes or can be catalyzed by ionic liquid and metal or acid catalyst to produce hydroxymethylfurfural (HMF), which can be applied as chemical feedstocks or alternative fuels (Bell and Berkeley, 2010; Tadesse and Luque, 2011). However, the recal- citrance of lignocellulosic biomass limits significantly its sustain- able and cost-effective utilization for bioconversion process. Lignin composing of phenylpropanoid units acts as a glue binding cellulose and hemicellulose, giving a remarkable resistance against chemical and microbial attacks. In addition, the high crystallinity of cellulose impedes chemical and biological degradation. To over- come these restrictions, biomass pretreatment is required to im- prove the bioconversion process. Various pretreatments have been developed, such as; mechanical, thermal, chemical and bio- logical methods (Lee et al., 2009; McMillan James, 1994). However, all these methods have several drawbacks, like requiring extreme conditions, high toxicity and destroying the fermentable sugar content (Yang et al., 2010). Ionic liquids (ILs) are environmentally friendly molten salts, representing a new class of solvents which have high polarities, a low melting point, nonvolatility and design- ability (Lee et al., 2008; Lee, 2011; Lee and Prausnitz, 2010). They have been known as a promising pretreatment solvent for lignin extraction and carbohydrate dissolution to decrease its crystallin- ity (Fu et al., 2010; Lee et al., 2009). This provides several attractive features compared to the conventional methods (Nguyen et al., 2010). There are various parameters affecting the process of biomass pretreatment using ionic liquids: for instance, physicochemical properties of ionic liquid, reaction time and temperature, ratio of biomass to ionic liquid, biomass type and water content of sample (Zakrzewska et al., 2010). However, the most important factor for this process is the physicochemical properties of ionic liquid (Zakrzewska et al., 2010). It was reported that several properties of ionic liquid (viscosity, melting point, dipolarity and hydrogen bond basicity) have significant effects on pretreatment of lignocel- lulosic material (Mäki-Arvela et al., 2010). Suitable ionic liquid for biomass pretreatment process should have most of the features as follows: being able to dissolve biomass at low temperatures, pos- sessing low viscosity, chemical stability and no decomposition of biomass, ease of regeneration and recycle, being cost effective and 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2012.02.023 ⇑ Corresponding author. Tel./fax: +65 6513 8129. E-mail address: jmlee@ntu.edu.sg (J.-M. Lee). Bioresource Technology 111 (2012) 453–459 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech