Study On The New Pulping And Bleaching Technology And Its Mechanism Of Cotton Stalks

Cotton stalk is an abundant agricultural residue in north China. Application of cotton stalk in paper industry was stagnant. In this thesis, the development and the current status of pulp and paper industry were reviewed, and a proposal was put forward for using cotton stalk reasonably according to the situation of using non-wood fiber in China.Main chemical components of cotton stalk from Xiajin Shandong province were tested and lignin of that was analyzed by means of ultraviolet spectra, infrared spectra and ¹³C-NMR. The results indicated that lignin of cotton stalk was belonged to GSH and there were many conjugated C=O units at side chain of lignin in cotton stalk bark, which caused more chromophore groups and dark color of pulps.A novel experimental and calculating method for the study of cooking kinetics was established. By application of identical liquor ratio as used in actual cooking conditions, determinations of effective alkali concentration and residual lignin contents during a short time interval and calculation of reaction rate constant, activation energies of Soda-AQ cooking and Kraft cooking of cotton stalk were obtained according to Arrhenius formula. Activation energy of Soda-AQ cooking of cotton stalk was 89.42 kJ/mol, and activation energy of KP cooking of cotton stalk was 76.94 kJ/mol which was lower than that of Soda-AQ cooking of cotton stalk, which indicated that delignification of Kraft cooking of cotton stalk was easier than that of Soda-AQ cooking.Kraft and Soda-AQ cooking mechanism of cotton stalk were studied. The results indicated that the delignification of both Kraft and Soda-AQ cooking could be devided into 3 stages: (1) the initial deligninfication stage, which was from temperature rising to 140℃, and its delignification rate was about 45%; (2) the bulk deligninfication stage, which was from 140℃ to 160℃ and at 160℃ for the total delignification rate was about 90%; (3) the supplementary deligninfication stage, which was from 30min at 160℃ to the end of cooking; Both Soda-AQ and Kraft process, the time at maximum temperature was necessary, which was different from other straw stalk(wheat straw, rich straw, etc). Rejects rate and yields of pulp were determined and defiberation points of cooking were set up. Defiberation point during Kraft cooking was at 160℃ for 30min, with a rejects rate of 1.2%, Kappa number of 30.16 and pulp yield of 52.68%. Defiberation point during Soda-AQ cooking was at 160℃ for 60min, with a rejects rate of 1.1%, Kappa number of 25.31 and pulp yield of 43.72%.The cooking conditions of KP and soda-AQ process of whole cotton stalk were optimized by orthogonal experiment. Dosage of NaOH, sulphidity and time at maximum temperature was optimized during Kraft cooking and dosage of NaOH,...