Acid catalytic hydrothermal conversion of carbohydrate biomass into useful substances

Acidic hydrothermal degradation of glucose was examined in the presence of HCl, H₂SO₄, and H₃PO₄ with pH varying from 1.5 to 2.5 and reaction time varying from 1 to 10 min at 523 K, to investigate the effect of different acid catalysts and acid concentration on the production of 5-hydroxymethyl-2-furaldehyde (HMF) and levulinic acid from glucose. At lower acidities of pH 2.5, a considerably higher amount of HMF was produced. The increase in acid concentration accelerated the conversion of HMF to levulinic acid. The order for the production of HMF using the three acids is in the sequence of H₃PO₄ > H₂SO₄ > HCl. On the contrary, the order for production of levulinic acid follows HCl > H₂SO₄ > H₃PO₄. In the experimental conditions used in this study, the highest yield of levulinic acid is about 55%, which was obtained at pH 1.5 for 5 min in the case of HCl as an acid catalyst, and the total highest yields of HMF and levulinic acid are about 50%, which occurred at pH 2.0 for 5 min in the case of H₃PO₄ as an acid catalyst.