| At present, the rapid growth of paper making industry is gradually restricted by problems of wood shortage, environment pollution and energy preservation, which is commonly concerned by most of the related experts and scholars. This study is aimed at making full use of non-wood meterials for pulping with advanced soda-oxygen pulping method, additional to the application of the black liquor back-cycling, to open a new path to clean and energy-saving production of pulp, instead of wood material. As a part of the project supported by a grant-in aid (20567001) for National Nature Science Foundation of China, soda-oxygen pulping of bagasse with or without soda pretreatment and black liquor back-cycling based on it were studied in this thesis, in order to establish a clean, energy-saving pulping systerm of bagasse.1) Through the research of soda-oxygen pulping of bagasse at low-temperature, the optimal pulping conditons are alkali charge 22%, Tmax 105℃, time to Tmax 60min, time at Tmax 120 min, initial pressure of oxygen 0.6 MPa, MgSO4 charge 0.5%, AOA-10.5%, and depithed bagasse consistency 12%. And the resultant pulp exhibited the screened yield up to 63.7%, kappa number was 15.3, viscosity was 843mL/g, and brightness was 62.3% (SBD).2) The effect of many additives on the pulping was compared under the optimal pulping conditions. It was found that Mg2+ is the most effective for protecting carbohydrates, and increasing Mg2+ usage could improve the viscosity of the pulp. But, according to the study on Mg(OH)2 as part of alkali sources, increasing Mg2+ usage could bring down the brightness of unbleached pulp. As additives, the appropriate usage of MgSO4 is between 0.5% and 1.0%. Secondly, in the premise of good pulp properties, EDTA also is active in enhancing viscosity of the pulp.3) The brightness of the pulp can be enhanced to 68%(SBD) or above by increasing alkili charge, also extending time at Tmax because of bleaching ability of soda-oxygen pulping. However, the pulp viscosity and yield dropped as carbohydrates degradation. It is helpful for enhancing the viscosity of the pulp with brightness and yield kept steady, by keeping temperature below 100℃for some time. 4) The optimal conditions in two stage of alkaline soaking and soda-oxygen pulping of bagasse were at 90℃for 10min with NaOH charge 10% and bagasse consistency 10% for alkaline soaking stage, and 105℃for 120 min with 15% NaOH charge, MgSO4 0.5%, AOA-1 0.5%, pulp consistency 12%, and 0.6MPa initial oxygen pressure for pulping stage. The resultant pulps had yield above 58%, kappa number ranging from 12.57 to 18.22, viscosity above 700mL/g, brightness above 55.6%.5) TCF bleaching of pulps from soda-oxygen pulping of bagasse was studied. It was showed that X-Eop bleaching sequence was effectively. The optimal conditions were:50℃for 60 min,0.5% xylanse usage, pH was controlled at 5.5 in xylanse treatment stage, and H2O2 charge 2.0%, NaOH charge 1.2%, 85℃for 80 min, Na2SiO3 2.5%, MgSO4 0.5%, EDTA 0.5%, consistency 10% in Eop stage. The bleached pulps had brightnenss above 78% ISO, enhanced above 20 percentages, and its viscosity was 872mL/g and kappa number was 12.56.6) The structure of lignin in pulps and black liquor gained from soda-oxygen pulping at different Tmax were studied by the means of 1H-NMR,13C-NMR and GPC. And some structural characters of the corresponding celluloses were tested as well. The results showed that bagasse lignin contains all of G,S,H units, and the content of G unit comes first. It could be concluded that different pulping temperatures had little effect on the keys broken locations of the lignin. With the decrease of pulping temperature, the bonds ofβ-0-4,β-1,β-5 andβ-βbecame inactive to pulping agents. Low temperature cooking can keep good viscosity and crystallinity of the celloluse. The lignin structural information revealed by these instrumental methods can help us to understand the reaction mechanism of bagasse lignin during soda-oxygen pulping, and is of importance to optimize the pulping system furthermore. |
PDF Full Text Request