In the present study, hydrothermal treatments on sawdust (real biomass) and cellulose taken as a model biornass were performed at 225 degrees C, 300 degrees C and 375 degrees C. The effect of the various catalysts (K2CO3, HZSM-5, Ni on SiO2) on the gas composition was investigated. The aqueous phases were also characterized by ion chromatography, high performance liquid chromatography (HPLC), UV-vis spectroscopy and total organic carbon analyzer (TOC). The main intermediates in the water soluble fraction were acetic acid, formic acid and glycolic acid, aldehydes (acetaldehyde, formaldehyde), phenol and phenol derivatives, furfural, methyl furfural, hydroxymethyl furfural. The experimental results for the actual biomass (sawdust) were compared with those for the cellulose. Thus, the effect of the inorganic constituents found in sawdust such as minerals, metals, etc. on the formation and degradation pathways of the intermediates was elucidated by comparing the results obtained from actual and model biomass conversion. The yields of the solid particles obtained at the end of the experiments on dry basis were also calculated. The particles were characterized by thermogravimetric and elemental analysis. (C) 2009 Elsevier B.V. All rights reserved.