Hydrothermal treatment was conducted on alginate in the interest of obtaining organic acids. Formic acid, acetic acid, lactic acid, glycolic acid, 2-hydroxybutyric acid, succinic acid, malic acid, mannuronic acid and guluronic acid were obtained by the hydrothermal treatment of alginate. The total yield of the organic acids were 46% at maximum yield 350 degrees C, 40 MPa and 0.7 s reaction time. The formation of organic acids, suggest that the carboxyl group structure of the alginate was preserved during the hydrothermal decomposition of the alginate. The formation of dicarboxylic acids is evidence that oxidation reactions occur during the hydrothermal treatment, introducing carboxyl groups into the decomposition products. The product distribution indicates that both acid and base catalyzed reactions occurred during the hydrothermal treatment of alginate. Hydrothermal treatment of an uronic acid, glucuronic acid, gave the same organic acids as those obtained from hydrothermal treatment of alginate. The reaction from alginate to organic acids probably proceeds via the formation of hexuronic acid (mannuronic acid and guluronic acid) under hydrothermal conditions. (c) 2012 Elsevier B.V. All rights reserved.