Study On The Mechanism Of Delignification By Co-salen Biomimetic System And It's Application

For the requirement of developing low impact bleaching technology and new technology of pulp and paper effluent treatment, many researchers try to use microorganisms, their enzymes and biomimetic system in pulp bleaching process to reduce the pollution and develop new environmental friendly bleaching technology. Biomimetic catalyst has characteristics of both enzymatic catalyst and chemical catalyst. Therefore, it is an efficient approach of green chemistry. The Co-salen biomimetic delignification system which is composed of Co(â…¡)-salen, pyridine, sodium hydroxide, hydrogen peroxide, oxygen is one of the most promising biomimetic system of lignin peroxidase. In order to understand the reaction mechanism of lignin with Co-salen biomimetic delignification system, a lignin model compound of phenolicβ-O-4 type, i.e. guaiacylglycerol-β-guaiacyl ether and milled wood lignin (MWL) from triploid clones of Populus tomentosa wood were treated with Co-salen biomimetic delignification system. In the present research, we have carried out many researches about the mechanism of the degradation ofβ-O-4 type lignin model compound and milled wood lignin (MWL). The application of bleaching softwood kraft pulp and paper effluent treatment by Co-salen biomimetic system. These results could help us to apply Co-salen biomimetic system in industrial non-pollution bleaching.In this paper, a model compound of phenolicβ-O-4 type, i.e. guaiacylglycerol-β-guaiacyl ether was synthesized. The synthesis method of an impant intermediate, i.e. 4-[α-(2-methoxylphenoxy)-acetyl]-guaiacol was improved. The time of reduced pressure distillation shorten. The combination of infrared spectra, 1H-NMR analysis was used to identify the chemical structure of the product and related precursors.The lignin model compound of guaiacylglycerol-β-guaiacyl ether was treated with Co-salen biomimetic system. The reaction products were analyzed by GC-MS. The mechanism of the biomimetic degradation of thisβ-O-4 structure was also explored. Results showed that Co-salen type biomimetic system had strong ability in degradation of phenolicβ-O-4 type model compound. It was found there were a lot of carbonyl and hydroxyl groups in the degraded products. It is suggested that the following reactions were caused by the Co-salen system: ether-bond cleavage, Cα-Cβcleavage, alkyl-aryl cleavage and aromatic ring opening. Co-salen type biomimetic system had strong ability in degradation of MWL. After MWL was treated, the content of hydroxyl and carboxyl groups increased. Some low molecule compounds as syringic acid and vanillic acid were produced. The results could prove that the oxidation of side chain lead to the cleavage of the linkage between the units of lignin substructure.In this paper, unbleached softwood kraft pulp was treated with a biomimetic bleaching system, i.e. Co-salen system comprised of Co(â…¡) -salen, pyridine,hydrogen peroxide, oxygen. The effect of temperature, time, NaOH dosage, hydrogen peroxide dosage, pyridine dosage, Co-salen dosage and oxygen pressure on brightness and viscosity of the pulp after biomimetic treatment followed by EP bleaching were analyzed. The experimental condition was improved. The study found that optimum conditions are as follows: Co-salen 0.03%, molar ratio of Co-salen to pyridine 1:1, NaOH 3%, H₂O₂ 1.5%, oxygen pressure 0.2 MPa, pulp consistency 5%, temperature 90℃, time 5h. Kappa number of softwood kraft pulp declined by 4.1 atter treated by Co-salen biomimetic system. Brightness was improved 10.3%ISO. After alkali treatment, Kappa number can further reduce 5.2, pulp brightness increased 18.1%ISO. According to the conclusion of lignin model compound experiment, lignin was oxidized and some low molecule compounds as syringic acid and vanillic acid were produced. These products were dissolved during biomimetic bleaching and alkali extraction. It was manifested mainly in improving brightness during biomimetic bleaching and alkali extraction.In this paper, Co-salen biomimetic flocculation was used to treat the mixed wastewater treatment of a paper mill. The effect of temperature, hydrogen peroxide dosage, the kind and dosage of flocculant, sedimentation time were analyzed. The experimental conditions was optimized. The study found that optimum conditions are as follows: temperature 90℃, H₂O₂ dosage 0.15g/L, aluminium sulfate dosage 0.4g/L, sedimentation time 4h. The study found that CODCr can be improved 19.6% by using Co-salen biomimetic flocculation. Through lignin massive removing, the effect of subsequent biochemical was also enhanced. It made it easier for the following treatment.