Hot Water Pre-extraction Of Hemicelluloses From Bamboo And Its Influence On Kraft Pulping And ECF Bleaching Performance

The technology of hot water pre-extraction, as an economical and environmentally friendly pretreatment technology, has the advantages of lower corrosion to equipment, higher content of oligosaccharides, smaller damage to cellulose, lower degradation rate of monosaccharides and less dissolving rate of lignin. It has been extensively studied in biorefinery integrated with pulp and papermaking. Bamboo is a non-wood raw material in south China. The research of bamboo biorefining integrated with pulping and papermaking is important for the resource utilization of biomass and sustainable development of pulp and paper industry in China. Hence, this dissertation studied on the bamboo hot water pre-extraction, kraft pulping and elemental chlorine free bleaching of the pulp. The effect of the hot water pre-extraction conditions on the changing behaviors of main components in extracts and the following kraft pulping and ECF bleaching were analysed. This research will provide the fundamental base and technology support for the biorefinery integrated with pulping and papermaking of bamboo.The yields of main saccharides (glucose, xylose and arabinose) extracted from bamboo and its degradation products (furfural and HMF) were studied at different maximum temperature and holding time of hot water pre-extraction, using HPAEC and HPLC as detection apparatus. The variations of yields of monomers and oligomers of xylose, glucose and arabinose and the concentrations of furfural and HMF as reaction temperature and time were discussed. Furthermore, the changing behaviors of the above components as the logarithm of H-factor (LogH) during hot water pre-extraction were analysed. The reasonable range of LogH and the optimal range of reaction temperature were established for maximizing yield of saccharides and minimizing the concentrations of degradation products from saccharides.The kinetic characteristic of hemicellulose hot water pre-extraction was studied for understanding dissolution and degradation of saccharides, and the kinetic models of the saccharides and its degradation products were built. It was found that there was a relationship (exponent or lineal) between hydrogen ion concentration and the dissolving and degradating reaction rate coefficient of xylan, arabinose polymer, xylose oligomer, xylose, arabinose, furfural and HMF. The kinetic models for predicting the yields of xylose oligomer, xylose, arabinose, and the concentrations of furfural and HMF were set up. The relative coefficients (R2) of the models for the four compounds are above 0.985.The extraction extent of saccharides from bamboo has an important influence on following kraft pulping and the pulp ECF bleaching. Thereby, there was concernment significance to build an empirical model of the formation of pentose, hexose, furfural and HMF. Hydrogen ion concentration was introduced to the calculating formula of H-factor , obtaining H '-factor, according to the dynamic characteristics. The models for predicting the formation of pentose, hexose, furfural and HMF using modified activation energies were built. The results show that the models are precise, the R2 are greater than 0.965.Three hot water pre-extraction H-factors (0, 500 and 1000) and three cooking effective alkali dosages (15%, 18% and 21%) were selected. The effect of hot water pre-extraction on the kraft pulping performance of bamboo was researched by comparing the consumption of effective alkali, formation of volatile organic compounds and the Kappa number, yield, viscosity, hexenuronic acid content, beating performance of the resulted pulps. The results show that hot water pre-extraction of bamboo could improve the delignification efficiency of pulping, save about 2%-3% of the effective alkali, obtain higher pulp viscosity, lower VOC and HexA content based on the same Kappa number (20). However, there are obvious decrease in the yield and beating performance of pulp.The bamboo pulps with similar Kappa number (20) after hot water pre-extraction and kraft pulping was chosen as unbleached pulp for DQP bleaching. The effect of hot water pre-extraction on the ECF bleaching performance of bamboo pulp was studied, through comparing brightness, PC number, decreasing rate of Kappa number, viscosity and beating performance of bleached pulp, and handsheet's strength properties of bleached pulp with same brightness (85%ISO) and beating degree (450SR) under different dosages of chlorine dioxide and hydrogen peroxide. The results indicate that hot water pre-extraction before kraft pulping could obtain higher decreasing rate of Kappa number, higher brightness, lower PC number, similar viscosity of bleached pulp at the same total active chlorine factor. For the same brightness bleached pulp(85%ISO), hot water pre-extraction could save 1.4% bleaching chemical, but the PC number was slightly higher, beating performance and strength properties of bleached pulp were also lower.The saccharides yield in extracts and the positive and negative influence of pre-extraction on subsequent kraft pulping and ECF bleaching were compared under different conditions of hot water pre-extraction. It was found that H-factor 1000 of hot water pre-extraction could obtain higher yield of saccharides (2.5 times as that of H-factor 500), however, the yield loss of kraft pulp increased from 7% to 10%, PFI revolutions to beat the kraft pulp to the same 0SR increased about 0.3 times, the PC number of bleached pulp has no much difference, the loss of the strength properties of bleached pulp was not obvious. Forasmuch, the higher the intensity of hot water pre-extraction, the lower the negative effect of unit saccharides yield in extracts on subsequent kraft pulping and ECF bleaching. Consequently, the optimal H-factor of hot water pre-extraction is one thousand under the experimental conditions.