Abstract: A process for producing polycarboxylic acids or their salts from polysaccharides is provided. Solid particulate polysaccharides having at least one primary alcohol group in the polysaccharides are oxidized with nitrogen dioxide in a fluid bed. The fluidizing gas contains nitrogen dioxide and the process is operated at a pressure of from 0.5 to 12 bars and a temperature between the boiling point of nitrogen dioxide and 160.degree. C. At least two moles of nitrogen dioxide for the equivalent of the primary alcohol groups reacted over the entire reaction are provided.

Abstract: A process for the production of polycarboxylic acids or salts thereof from polysaccharides by oxidation with nitrogen dioxide/dinitrogen tetroxide with at least partial conversion of the primary alcohol groups of the polysaccharides into carboxyl groups and optionally at least partial neutralization of the carboxylic acid groups formed is provided. The oxidation reaction is carried out in a closed reaction system in the presence of oxygen under pressures of 2 bar to 10 bar and at a temperature above room temperature. Nitrogen dioxide/dinitrogen tetroxide is used in such quantities that, in the event of a theoretically complete shift of the equilibrium onto the nitrogen dioxide side, the nitrogen dioxide is present in quantities of at most 2 mole equivalents, based on the content of monomer unit of the polysaccharide containing one primary alcohol group.