Conversion Of Xylose In The Pre-hydrolysis Liquor (PHL) Of Dissolving Pulp

The conventional pulping process mainly focus on the extraction of cellulose, however the hemicelluloses and lignin dissolved in the black liquor are combusted which leads to horrible waste. Recently, the kraft-based dissolving pulp process hydrolyses raw materials before cooking in the aim of extracting the hemicelluloses and obtaining high quality dissolving pulp. The pre-hydrolysis liquor (PHL) contains some organics, such as lignin, furfural, acetic acid as well as the hemicelluloses. These components can be recycled and converted to other value-added chemicals. This can not only alleviate the pressure from environmental pollution, but also can bring extra revenue for the plants.In this dissertation, we first discussed about the sodium dodecyl benzene sulfonate (SDBS) assisted pretreatment of poplar chips. We investigated the relation between the components in the pre-hydrolysis liquor (PHL) and the P factor. Also, the hemicellulose extraction mechanism was studied. In this process, the sodium dodecyl benzene(SDBS), on the one hand facilitates mass transfer between the poplar chips and hot water, and on the other the degradation of the hemicelluloses are promoted by adding minor hydrogen ion. This can guarantee the raw materials can be pretreated under low P factor (<1500) but obtain high yield of xylooligosaccharides (48.9%). Adding more SDBS means higher pH in the PHL, which is not good for the extraction of hemicelluloses. Thus, the extraction of hemicelluloses improved and the degradation of hernicelluloses decreased by adding appropriate SDBS and minor hydrogen ion. The SDBS promote the mass transfer and alleviate recalcitrance of poplar chips, and minor hydrogen ion can promote the hydrolysis of hemicelluloses.This dissertation also conducted the separation and purification of the xylooligsaccharides in the PHL. We investigated the effects of the separation and purification by various methods including activated carbon for one stage adsorption, activated carbon for two stages adsorption, wet oxidation of activated carbon for the adsorption, and resin treatment. In the wet oxidation of activated carbon adsorption experiment, we found that the acid groups on the surface of the activated carbon increased after the activated carbon was treated by stronger HNO3, while the BET surface area decreased except under low concentration (2%). The adsorption capacity of lignin increased by 7.3% when the activated carbon was treated under 2% HNO3. The adsorption isotherm and adsorption kinetic results showed that both physical adsorption and chemical adsorption affect the activated carbon adsorption toward saccharides and lignin in the PHL. Physical adsorption played the main role in this process. Activated carbon two stages have significant effect for the removal of lignin. The first stage lignin removal can reach 69%, and the second stage can reach 89.7%. The model solution of acetic acid and furfural were treated with chromatography column loaded with D301 ion exchange resin. Almost all the acetic acid were removed and the furfural removal can reach 50%.At last, this dissertation proposed a combined process including activated carbon two stages adsorption, ion exchange resin treatment and membrane concentration for the separation and purification of xylooligosaccharides in the PHL.