Please cite this article in press as: F.M. Yedro, et al., Hydrothermal fractionation of grape seeds in subcritical water to produce oil extract, sugars and lignin, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.07.053 ARTICLE IN PRESS G Model CATTOD-9219; No. of Pages 9 Catalysis Today xxx (2014) xxx–xxx Contents lists available at ScienceDirect Catalysis Today j our na l ho me page: www.elsevier.com/locate/cattod Hydrothermal fractionation of grape seeds in subcritical water to produce oil extract, sugars and lignin Florencia M. Yedro, Juan García-Serna ∗ , Danilo A. Cantero, Francisco Sobrón, M. José Cocero High Pressure Processes Group, Department of Chemical Engineering and Environmental Tech., University of Valladolid, Escuela de Ingenierías Industriales, 47011 Valladolid, Spain a r t i c l e i n f o Article history: Received 10 January 2014 Received in revised form 28 June 2014 Accepted 30 July 2014 Available online xxx Keywords: Biomass Biorefinery Hydrothermal Pretreatment Carbonization Grape seeds a b s t r a c t In this work, the fractionation of grape seeds as a model biomass was studied using a combination of two processes: solvothermal extraction and hydrothermal fractionation-hydrolysis process in a semicontinu- ous reactor. First, grape seeds were subjected to an extraction process with ethanol/water (70/30 wt.%) at 90 ◦ C during 60 min obtaining ca. 13.0 wt.% of oil and extractable components with 4.46 wt.% of polyphe- nols (66% of the maximum). Afterwards, the solvent was water and the biomass was treated in steps at different temperatures (150 ◦ C to 340 ◦ C). During the hydrolysis the pH decreased from 5.5 down to 3.0 due to acetyl group liberation. The total quantity of recovered sugars varied around 20.0 to 23.1 wt.%. The best experimental condition for obtaining the maximum amount of pentoses + hexoses + oligosaccharides was 180 ◦ C (45 min) + 250 to 265 ◦ C (45 min) + 330 to 340 ◦ C (45 min). © 2014 Elsevier B.V. All rights reserved. 1. Introduction The most abundant source of carbon in the world is biomass. Nowadays, the global primary production of biomass rounds 100 PgC/y (P = Peta = 10 15 ) [1], being the global carbon emissions nearly 10 PgC/y [2]. The production of fuels and value added prod- ucts from biomass has been widely investigated in the last years. Like any other lignocellulosic residue, grape seeds primarily com- prise three major fractions: hemicellulose, cellulose and lignin. In addition, low amounts of minerals (ash) and other compounds, such as extractives, can be found in grape seeds (i.e. grape seed oil and polyphenols). There are several solvents available for performing the biomass fractionation, such as organic solvents [3], ionic liquids [4] or sim- ply water [5–7]. Fractionation is often considered a pre-treatment process, prior to produce sugars and lignin by conversion. After this process, there are many alternatives for conversion to produce value added components by catalytic or non-catalytic transforma- tions [8]. In 2004 the U.S. Department of Energy and Renewable Energy prepared a comprehensive report including series of ∗ Corresponding author. Tel.: +34 983184934. E-mail addresses: jgserna@iq.uva.es, jgserna@gmail.com (J. García-Serna). compounds and building blocks chosen as candidates to be pro- duced from cellulose, hemicellulose [9,10] and lignin [11]. Hydrothermal treatment is the processing of biomass in water at high pressures and temperatures in liquid phase. This tech- nology is a promising alternative to perform the fractionation of biomass because the reaction medium allows the transformation of the different fractions of biomass by choosing the appropriate conditions [12,13]. Furthermore, water is a clean, safe and environ- mentally benign solvent [14]. Hydrothermal fractionation can be carried out at soft conditions (<100 ◦ C) to remove the water-soluble extractives and hydrolyze hemicelluloses (<180 ◦ C), yielding a solid phase enriched in lignin and cellulose. The autohydrolysis process (reactions catalyzed by H + and OH − produced by H 2 O dissociation [13–15] due to the acetyl group liberation and organic acids pro- duced) can produce oligosaccharides that maintain the polymeric structure. A subsequent hydrolysis at more severe conditions or with enzymes will yield monomeric sugars [16]. On the other hand, hydrothermal carbonization can be an option when the production of a carbon-based nanomaterial is pursued. The hydrothermal treatment can be used for a double fold, to produce bio-oils or to produce bio-based streams (C5’s, C6’s and lignin) [17]. Analyzing the production of bio-based streams, Requejo et al. demonstrated that the use of olive tree biomass to produce soluble hemicellulose-derived saccharides can be car- ried out in a hydrothermal medium obtaining near 26% of the http://dx.doi.org/10.1016/j.cattod.2014.07.053 0920-5861/© 2014 Elsevier B.V. All rights reserved.