Manufacture of Levulinic Acid from Pine Wood Hemicelluloses: A Kinetic Assessment

Pinus pinaster wood samples were subjected to two consecutive treatments with hot, compressed water, in order to remove water-solubles in the first step and to cause hemicellulose solubilization in the second. The liquid phase from the second stage, containing hemicellulose-derived saccharides (mainly of oligomeric nature), was mixed with sulfuric acid and heated to convert the saccharides into levulinic acid. Experiments were carried out at different acid concentrations, temperatures, and reaction times. The concentration profiles were interpreted using a model involving the following major steps: conversion of oligomers into monosaccharides, conversion of hexoses into hydroxymethyl furfural, decomposition of this latter into levulinic and formic acids, dehydration of pentoses into furfural, and conversion of this latter into formic acid. Parasitic reactions limited the theoretical yields in the target products. The kinetic coefficients governing the various reactions were determined by analysis of data. Under the best conditions assayed, the yield in levulinic acid accounted for 66% of the stoichiometric value.