Alkaline pre-treatment of oilseed rape straw for bioethanol production: Evaluation of glucose yield and pre-treatment energy consumption Anil Kuruvilla Mathew ⇑ , Keith Chaney, Mitch Crook, Andrea Claire Humphries Harper Adams University College, Newport, Shropshire, TF10 8NB, UK article info Article history: Received 24 December 2010 Received in revised form 18 March 2011 Accepted 19 March 2011 Available online 27 March 2011 Keywords: Alkaline pre-treatment Enzymatic hydrolysis Rapeseed straw Glucose Energy efficiency abstract The objective of the research was to investigate the effect of biomass loading, alkali (NaOH) concentration and pre-treatment time on the yield of glucose obtained following alkaline pre-treatment and enzymatic hydrolysis of oilseed rape (OSR) straw. A maximum glucose yield of (440.6 ± 14.9) g glucose kg 1 biomass was obtained when OSR straw was pre-treated at a biomass loading of 50 g kg 1 and an alkali concentra- tion of 0.63 mol dm 3 NaOH for 30 min. The energy efficiency of glucose extraction (0.39 kg glucose MJ 1 consumed) was highest when OSR straw was pre-treated at a biomass loading of 50 g kg 1 and an alkali concentration of 0.63 or 0.75 mol dm 3 for 30 min. The study demonstrated alkaline pre-treatment of OSR straw is superior to acid pre-treatment in terms of glucose yield and energy efficiency. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The production and use of biofuels has been stimulated by International, European and national policy and legislation that is concerned with minimising climate change by reducing the emis- sion of greenhouse gases (GHG’s). In the case of the transportation sector, GHG’s are produced by the combustion of fossil fuels (e.g. gasoline and diesel). The use of bioethanol in blended form with conventional gasoline provides one approach to reducing these emissions. First-generation bioethanol can be produced through the fermentation of feedstocks containing simple (e.g. sugar cane) or complex carbohydrates (e.g. wheat). The use of first-generation feedstocks for commercial bioethanol production is associated with increasing pressure on land to meet targets for both food and fuel as land availability is limited. Bioethanol production from second-generation lignocellulosic feedstocks (e.g. municipal wastes and agriculture residues such as straw) has the potential to contribute to renewable fuel and GHG reduction targets and to reduce reliance on first-generation feedstocks. Second-generation feedstocks are generally less expensive than first-generation feed- stocks and provide the opportunity to create valuable products from materials that are currently considered waste materials. Fur- thermore, it is predicted bioethanol produced from second-gener- ation feedstocks could deliver higher land use efficiency and GHG savings compared to first-generation bioethanol (Larson, 2008). However, further technical improvements are required to improve the energy balance and economics of the conversion process in comparison to first generation biofuels, and as such the production of bioethanol from lignocellulosic biomass is yet to be commercia- lised (Larson, 2008). Lignocellulosic bioethanol production entails an additional processing step known as pre-treatment, which is re- quired because cellulose accessibility is hindered by the physio- chemical, structural and cell wall properties of lignocellulosic bio- mass. The aim of pre-treatment is to enhance the extraction of glu- cose from biomass by altering the structure of lignin or hemicellulose and to disrupt the crystalline structure of cellulose prior to hydrolysis (Alvira et al., 2010). Alkaline pre-treatment involves solvation and saphonication that causes the biomass to swell, increasing the accessibility of en- zymes during subsequent hydrolysis (Hendriks and Zeeman, 2009). Alkaline pre-treatment removes mainly lignin, acetyl and other uronic substitutions present on the hemicellulosic portion of the biomass (Mosier et al., 2005). During alkaline pre-treatment some of the alkali is converted into irrecoverable salts that become asso- ciated with biomass, which can cause the cellulose to become den- ser and more stable than native cellulose and is the limitation of alkali treated biomass (Hendriks and Zeeman, 2009). Xu et al. (2010) compared the digestibility of alkali pre-treated (0.1 g Ca (OH) 2 g 1 of dry biomass) switch grass at mild temperatures (21 and 50 °C for 1–96 h) with a temperature of 121 °C at different time intervals (0.25–1.5 h). At 121 °C, only 30 min was required for maximum glucose and xylose yield, representing approxi- mately 66.3% of glucan conversion and 53.4% of xylan conversion. At 50 °C, 24 h was required to reach a maximum sugar recovery representing 67.4% of glucan and 62.5% of xylan conversion into 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.03.067 ⇑ Corresponding author. E-mail address: amathew@harper-adams.ac.uk (A.K. Mathew). Bioresource Technology 102 (2011) 6547–6553 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech