PRE-HYDROLYSIS OF THE PHENYL GLYCOSIDIC BOND IN A MODEL COMPOUND

A model compound, phenyl-β-Dglucopyranoside, was used to investigate if hydrolysis of the glycosidic bond occurred during different pretreatment methods of wood such as auto hydrolysis, green liquor pretreatment and acid hydrolysis. It was found that hydrolysis of the phenyl glycoside model compound at near neutral aqueous conditions (pH 6) was minimal (4 %) at 170 °C. On the other hand hydrolysis was nearly complete (95 %) at this temperature with the addition of acetic acid at a concentration expected to be generated from deacetylation of xylan in hardwoods (about 10 g/L). At acid conditions of pH 1.65 the temperature may be lowered to 105 or 121 °C while still obtaining a significant (80-90 %) hydrolysis yield. Green liquor pre-treatment (at pH 12.5) produced phenol and levoglucosan while no glucose is formed, and at 155 °C, the hydrolysis was essentially complete with quantitative formation of levoglucosan and phenol. Total Organic Carbon (TOC) measurements confirmed that no other degradation products than glucose, phenol and levoglucosan were formed at any of the experimental conditions studied.