Adsorptive removal of fermentation inhibitors from concentrated acid hydrolyzates of lignocellulosic biomass Tuomo Sainio ⇑ , Irina Turku, Jari Heinonen Lappeenranta University of Technology, Laboratory of Industrial Chemistry, Skinnarilankatu 34, FIN–53850 Lappeenranta, Finland article info Article history: Received 19 October 2010 Received in revised form 26 February 2011 Accepted 26 February 2011 Available online 4 March 2011 Keywords: Hydrolyzate Inhibitors Adsorption Detoxification Process design abstract Adsorptive purification of concentrated acid hydrolyzate of lignocellulose was investigated. Cation exchange resin (CS16GC), neutral polymer adsorbent (XAD-16), and granulated activated carbon (GAC) were studied to remove furfural, HMF, and acetic acid from a synthetic hydrolyzate containing 20 wt.% H 2 SO 4 . Adsorption isotherms were determined experimentally. Loading and regeneration were investi- gated in a laboratory scale column. GAC has the highest adsorption capacity, but regeneration with water was not feasible. XAD-16 and CS16GC had lower adsorption capacities but also shorter cycle times due to easier regeneration. Produc- tivity increased when regenerating with 50 wt.% EtOH(aq) solution. To compare adsorbents, process performance was quantified by productivity and fraction of inhibitors removed. GAC yields highest performance when high purity is required and ethanol can be used in regen- eration. For lower purities, XAD-16 and GAC yield approximately equal performance. When using ethanol must be avoided, CS16GC offers highest productivity. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Lignocellulosic biomass is an abundant source of monosaccha- rides that can be used as substrates for the production of ethanol by fermentation. Utilization of such biomass requires a pre-treat- ment step, in which polymeric carbohydrates decompose to sugar monomers. This hydrolysis reaction can be carried out enzymati- cally (Duff and Murray, 1996; Taherzadeh and Karimi, 2008; Sun and Cheng, 2002), with a concentrated mineral acid or by the impact of high temperature and a mildly acidic or basic environment (Taherzadeh and Karimi, 2008; Sun and Cheng, 2002). In addition to fermentable monosaccharides, also byproducts are formed. These include furfural, 5-hydrohymethylfurfural, as well as carboxylic acids such as formic, levulinic, and acetic acid (Larsson et al., 1999a). The presence of these by-products during fermentation of sug- ars may seriously impact the ethanol productivity, and has been studied extensively (Delgenes et al., 1996; Nigam, 2001). The liter- ature has been reviewed by, e.g., Mussatto and Roberto (2004) and Palmqvist and Hahn-Hagerdal (2000). Furfural concentration above 2 g/L stopped the cell growth of Pichia stipitis almost com- pletely, whereas a concentration lower than 0.5 g/L was reported to have a positive effect (Roberto et al., 1991). Nigam (2001) ob- served that 0.25 g/L of furfural exhibited no significant effect on the ethanol yield, whereas a concentration of 1.5 g/L reduced the yield by 90%. At the same time, productivity decreased by 85%. Delgenes et al. (1996) showed that furfural concentrations of 0.5, 1.0 and 2.0 g/L reduced P. stipitis growth by 25%, 47% and 99%, respectively. Delgenes et al. (1996) observed that HMF concentra- tion in the range of 1–5 g/L reduces ethanol production by 71–96%. Also Mussatto and Roberto (2004) have reported that HMF is an inhibitor for Saccharomyces cerevisiae metabolism at concentration level of 1 g/L. Several techniques have been proposed for the hydrolyzate detoxification, including overliming (Larsson et al., 1999b), adsorp- tion (Weil et al., 2002; Ranjan et al., 2009; Nilvebrant et al., 2001; Xie et al., 2005), evaporation (Larsson et al., 1999b), and enzyme or microorganism treatment (Larsson et al., 1999b). Effectiveness of the detoxification methods depends on the type of hydrolyzate and the concentration of inhibitors. A comprehensive review of detoxification methods was recently given by Wang and Feng (2010). The literature on purification of biomass hydrolyzates for bio- ethanol production mostly considers dilute acid hydrolyzates (Ranjan et al., 2009; Horváth et al., 2004). In this work, we focus on purification of concentrated acid hydrolyzates of lignocellulose. The main difference is the solution environment: concentrated acid hydrolyzates contain typically 20–30 wt.% sulfuric acid. As will be shown below, this has a strong influence on the adsorption behavior of the hydrolyzate components. Concentrated acid hydrolysis is a straightforward process and provides the highest conversion of lignocelluloses to monosaccha- 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.02.107 ⇑ Corresponding author. Tel.: +358 403578683. E-mail address: tuomo.sainio@lut.fi (T. Sainio). Bioresource Technology 102 (2011) 6048–6057 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech