Kinetics of enzyme-catalyzed hydrolysis of steam-exploded sugarcane bagasse Rodrigo Souza Aguiar a,b , Marcos Henrique Luciano Silveira a , Ana Paula Pitarelo a , Marcos Lucio Corazza b , Luiz Pereira Ramos a,⇑ a Research Center in Applied Chemistry (CEPESQ), Department of Chemistry, Federal University of Paraná (UFPR), Curitiba PR 81531-990, Brazil b Department of Chemical Engineering, Federal University of Paraná (UFPR), Curitiba, PR 82530-990, Brazil highlights  The fractal kinetic model provided a good fit of the enzymatic hydrolysis data.  Phosphoric acid is a better catalyst for steam explosion than sulphuric acid.  Water washing is essential to remove inhibitors from steam-treated substrates.  The fractal exponent revealed that alkali washing was not critical for hydrolysis.  The fractal kinetics was useful to predict pretreatment performance. article info Article history: Received 31 May 2013 Received in revised form 8 August 2013 Accepted 9 August 2013 Available online 20 August 2013 Keywords: Sugarcane bagasse Steam explosion Enzymatic hydrolysis Fractal kinetics abstract This work presents the experimental kinetic data and the fractal modeling of sugarcane bagasse steam treatment and enzymatic hydrolysis. Sugarcane bagasse (50 wt% moisture) was pretreated by autohydro- lysis at 210 °C for 4 min. Acid catalysis involved the use of 9.5 mg g 1 of H 2 SO 4 or H 3 PO 4 in relation to the substrate dry mass at these same pretreatment conditions. Unwashed, water-washed and alkali-washed substrates were hydrolyzed at 2.0 wt% using 8 and 15 FPU g 1 (108.22 and 199.54 mg/g) total solids of a Celluclast 1.5 L and Novozym 188 mixture (Novozymes). The fractal kinetic modeling was used to describe the effect of pretreatment and both washing processes on substrate accessibility. Water and/ or alkali washing was not strictly necessary to achieve high hydrolysis efficiencies. Also, the fractal model coefficients revealed that H 3 PO 4 was a better pretreatment catalyst under the experimental conditions used in this study, resulting in the most susceptible substrates for enzymatic hydrolysis. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction In the past decade, important issues about the world climate change, along with the rising demand for renewable energy and the increased dependence on imported oil, have led several compa- nies and research groups to develop alternative technologies for the production and use of liquid biofuels such as ethanol and bio- diesel. In this scenario, short rotation herbaceous crops have been identified as one of the best sources for cellulosic ethanol mainly due to their high growth yield, suitable chemical composition and renewable characteristics (Soccol et al., 2010). One of such materials is sugar cane bagasse, an agro-industrial residue that is produced in large scale as a result of sugar and ethanol production in tropical countries like Brazil. Lignocellulosic materials are mostly composed of cell wall poly- saccharides (cellulose and hemicelluloses) from which fermentable sugars can be produced by acid or enzymatic hydrolysis and these can be converted to ethanol using suitable microbial strains. How- ever, the plant cell wall was designed by nature to withstand bio- degradation and, for this reason, the viability of cellulosic ethanol still relies on pretreatment and its full integration with other pro- cess operations such as enzymatic hydrolysis, fermentation and ethanol recovery (Cardona and Sanchez, 2007). A good pretreat- ment method must provide a considerable increase in cellulose accessibility to enzymatic hydrolysis while ensuring high recovery yields of the main components of the plant cell wall and a low gen- eration of inhibitory compounds that are detrimental to ferment- ing microorganisms (Mosier et al., 2005; Ramos, 2003). Steam explosion involves the pretreatment of lignocellulosic materials with saturated steam at 160–240 °C for reaction times ranging from 2 to 30 min in the absence (autohydrolysis) or 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.08.067 ⇑ Corresponding author. Tel.: +55 41 3361 3175; fax: +55 41 3361 3186. E-mail address: luiz.ramos@ufpr.br (L.P. Ramos). Bioresource Technology 147 (2013) 416–423 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech