J. of Supercritical Fluids 67 (2012) 22–28 Contents lists available at SciVerse ScienceDirect The Journal of Supercritical Fluids jou rn al h om epa ge: www.elsevier.com/locate/supflu Hydrogen production from some agricultural residues by catalytic subcritical and supercritical water gasification Tülay Güngören Madeno˘ glu ∗ , Sinem Kurt, Mehmet Sa˘ glam, Mithat Yüksel, Dilek Gökkaya, Levent Ballice Ege University, Engineering Faculty, Department of Chemical Engineering, 35100 Bornova, ˙ Izmir, Turkey a r t i c l e i n f o Article history: Received 30 November 2011 Received in revised form 30 January 2012 Accepted 7 February 2012 Keywords: Agricultural biomass Hydrogen Supercritical water gasification a b s t r a c t The subcritical and supercritical water gasification of residue of some agricultural biomass samples (cotton and tobacco stalks) was investigated in a batch reactor at temperature range of 300–600 ◦ C and experiments were performed by addition of 10 wt.% of different natural mineral catalysts (Trona, Dolomite and Borax). The yield and composition of gaseous, aqueous products and residue were identi- fied by different analytical techniques. Gaseous products consisted mainly of permanent gases such as hydrogen, carbon dioxide, methane, carbon monoxide and C 2 –C 4 compounds. Aqueous products con- sisted mainly of carboxylic acids (hydroxyacetic acid, formic acid and acetic acid), furfurals, phenols (phenol and cresols), aldehydes (formaldehyde and acetaldehyde). The effectiveness of three differ- ent natural mineral catalysts in SCWG can be classified as being Trona [Na 3 (CO 3 )(HCO 3 )·2H 2 O] > Borax [Na 2 B 4 O 7 ·10H 2 O] > Dolomite [CaMg(CO 3 ) 2 ]. The results showed that the addition of Trona as catalysts at reaction temperature of 600 ◦ C, hydrogen yields of tobacco and cotton stalks were increased by 42.9% and 39.9%, respectively. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. 1. Introduction Continued growth in energy demands will require a contin- ued supply of inexpensive and sustainable resources. In addition, concerns about greenhouse gas emissions from fossil fuels are gen- erating new sets of technological requirements. Instead of using fossil fuels, if biomass is used, the concentration of carbon diox- ide in the atmosphere would remain constant. Supercritical water gasification (SCWG) is one of the most promising technologies for conversion of biomass into energy sources and chemical feedstock. SCWG method offers a good opportunity to gasify high moisture content biomass, also water serves as hydrogen donor and a reac- tion medium. Ionic and free-radical reactions are affected by the critical condition of water. Ionic reactions mechanism is dominant below the critical point because of high ionic product of water. At temperature above the critical point, density of water is lower and free-radical reactions mechanism dominates to produce gaseous products. In the last two decades, Forschungszentrum Karlsruhe in Ger- many, U.S. Pacific Northwest Laboratory, National Institute for ∗ Corresponding author. Tel.: +90 232 3111490; fax: +90 232 3887776. E-mail addresses: tulay.gungoren@ege.edu.tr, tulay.gungoren@yahoo.com.tr (T.G. Madeno˘ glu). Resources and Environment in Japan, Hawaii Natural Energy Insti- tute and other research centers have had many detailed studies on SCWG of some organic compounds to produce hydrogen. To under- stand chemistry of biomass conversion to degradation products and intermediates, SCWG studies in literature mainly focused on gasi- fication of model compounds (cellulose, glucose, xylan and lignin) and real biomass [1–5]. Yoshida and Matsumura were tried to explain interaction between cellulose, xylan (hemicellulose) and lignin. They pre- pared cellulose/organosolv-lignin, cellulose/xylan and organosolv- lignin/xylan mixtures to gasify at 673 K, 25 MPa and a reaction time of 20 min. They reported that presence of lignin suppress pro- duction of hydrogen [6]. The subcritical and supercritical water gasification of cellulose, starch, and glucose as representative biomass model compounds and biomass has been investigated in a heated batch reactor. The results have shown that differences in chemical structures produce significantly different product yields [7]. Investigation of parametric effects of pressure, temperature, residence time, reactor size, reactor types, heating rate, reac- tor wall properties, biomass types, particle size, catalysts and solution concentration, on biomass gasification in supercritical water (SCW) was important to optimize process conditions and overcome technical problems such as chars and tars forma- tion. However, catalysis should be the solution to obtain higher 0896-8446/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.supflu.2012.02.031