Degradation and Redeposition of the Chemical Components of Aspen Wood during Hot Water Extraction

Hot water extraction (HWE) prior to pulping of wood is a promising method in constructing a platform for traditional pulping or for biorefinery processing. In this study, HWE of aspen wood at a maximum reaction temperature (Treaction) between 140 and 180 oC was investigated to obtain an optimal extraction condition for wood-derived products. The effect of extraction temperature and reaction time on the extraction performance of the chemical constituents was evaluated, and the degradation and redeposition of lignin and carbohydrates during the HWE process were assessed. Results showed that a minimum Treaction of 160 oC was necessary for satisfactory carbohydrate removal. The dissolution and readsorption of sugars reached a balance, such that no more sugars in pre-extraction liquor (PEL) were adsorbed on the wood surface under more severe extraction conditions. The reduction of sugars dissolved in PEL should result from the formation of furfural or its derivatives. At the final extraction stage, the dissolved lignin in PEL could redeposit on the exothecium rather than the endothecium of the wood chips.