Isolation of wood hemicelluloses from birch wood: distribution of wood components and preliminary trials in dehydration of hemicelluloses

General aspects of autohydrolysis at varied temperatures, treatment intensities and liquid-to-wood ratios were investigated. Overall solid balance of the selected samples was determined using gravimetrical methods. Analytical methods for carbohydrates and lignin were used to represent componential mass balance. Water hydrolysis activates lignin by homolytic cleavage which results in partial transfer to the hydrolysates in the form of dissolved and dispersed lignin while parts of the residue reveal an increased solubility in acetone. The amount of acetone soluble matter increases with P-factor and decreasing liquor-to-wood ratio. Moderate autohydrolysis, representing a P-factor of about 200, which might be suitable for subsequent paper pulp production releases sugar components in an amount of about 6-7% on wood, while this value increases up to 12% and more when autohydrolysis conditions are applied, P-factor ~ 800, which are typical for dissolving pulp production. Preliminary dehydration studies with glucose as model substance at 160oC over ZrO2 and TiO2 catalysts have been conducted. The objective is to develop a low-cost process for the manufacture of hydroxymethylfurfural (HMF) from C6-sugars, preferably glucose and mannose. It has been shown that ZrO2 is slightly more effective in catalyzing isomerisation to fructose, while TiO2 was more active in dehydration. However, both catalysts exhibit not enough acidic sites to catalyze the overall reaction effectively.