J. of Supercritical Fluids 107 (2016) 243–249 Contents lists available at ScienceDirect The Journal of Supercritical Fluids j our na l ho me page: www.elsevier.com/locate/supflu Influence of temperature and pressure on hydrogen and methane production in the hydrothermal gasification of wood residues Nihal Üremek Cengiz ∗ , Seda Eren, Mehmet Sa˘ glam, Mithat Yüksel, 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 15 June 2015 Received in revised form 19 September 2015 Accepted 21 September 2015 Available online 25 September 2015 Keywords: Hydrothermal gasification Biomass Energy Hydrogen Supercritical water a b s t r a c t Hydrothermal gasification of woody wastes, pine tree and fir tree sawdust, was performed in a batch autoclave at 500 and 600 ◦ C and a pressure range of 20.0–42.5 MPa with or without a 10 wt.% of K 2 CO 3 . The products in the gaseous state (H 2 , CO 2 , and CH 4 , CO, and C 2 –C 4 compounds) and in the aqueous state (carboxylic acids, furfurals, phenols, aldehydes, and ketones) were analyzed by gas chromatography and high performance liquid chromatography. The produced gas amount and the hydrogen and methane yields were found maximized at 600 ◦ C with the addition of K 2 CO 3 . The decreasing pressure promoted hydrogen yields while decreasing the methane yields. The aqueous product was mainly composed of acetic acid, formic acid, and little amount of hydroxyacetic acid in the group of carboxylic acids and 5- methyl furfural and 5 hydroxymethyl furfural as furfurals. Supercritical water gasification of wood wastes is promising as a source in the production of hydrogen and methane. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Fossil fuels such as oil, gas, and coal are finite resources consid- ering the proved reserves. Researches on fossil fuels and renewable sources indicate that a shift from fossil sources to renewable alternatives should be supported to prevent both climate change and the possible shortage of energy resources [1]. In addition to the existing renewable resources in use, biomass is an abundant resource for chemical and biofuel production by thermochemical conversion technologies. One of the promising technologies is the gasification of biomass to the H 2 - and CH 4 -rich gas in a supercrit- ical water (SCW) medium. Organic compounds such as biomass becomes miscible with SCW due to the relatively lower dielectric constant of it. Also a homogenous reaction environment for gasi- fication is being formed eliminating mass transfer resistances and provides high reaction rates [2]. The hydrothermal gasification of biomass model compounds and real biomasses have been intensively focused on in recent years [3–9]. Since biomass has various constituents and a complex nature to enlighten the degradation of real biomass, many researches have been done on the model compounds such as glucose [5–7,9–12], xylose and xylan [8,13], phenol [11,14], and glycerol [15]. Hao et al. [9] gasified glucose with varying concentrations and sawdust ∗ Corresponding author. E-mail address: nihal.cengiz@ege.edu.tr (N. Üremek Cengiz). with some CMC (sodium carboxymethylcellulose) at 600–650 ◦ C and 22.5–30.0 MPa. The complete gasification of 0.1 M glucose was achieved with a reaction time of 3.6 min at 650 ◦ C and 25.0 MPa and the sawdust with some CMC has a gasification efficiency of about 95%. Weiss-Hortala et al. [11] investigated the interactions in super- critical water gasification (SCWG) of a lignocellulosic biomass using phenol (substitute for lignin) and glucose (substitute for cellulose). They reported that the amount of gas produced was less than the quantity of the obtained gas with the solutions of each compound. It can be concluded that phenol affects the glucose degradation and interactions between cellulose and lignin reduces gasification yields. Some pioneering studies have been done by research groups around the world with real biomass to contribute to the devel- opment of SCWG technology. Yanik et al. [3] worked with eight different types of biomass including lignocellulosic and tannery wastes. It was concluded that the highest gas yields were reached in the gasification of corn stalk and sunflower stalk and the high- est amount hydrogen (39.47%) was obtained with tobacco stalk. Yoshida et al. [5] investigated the gasification of cellulose, five lignin reagents and their mixtures, in the presence of a nickel catalyst at 673 K and 25 MPa. The gasification of rice straw and sawdust as real biomass were also carried out with the same con- ditions. The interactions between the constituents in the biomass led to lower gasification ratios than expected. Various kinds of lignin show different gasification characteristics due to their typical structures. http://dx.doi.org/10.1016/j.supflu.2015.09.018 0896-8446/© 2015 Elsevier B.V. All rights reserved.