Preparation Of Alkali Lignin Graft Copolymer And Its Application In Wastewater Treatment

As one of the three components of plants, tignin is rich in content. The production of alkali lignin is huge in paper making industry. The black liquor not only destroys the balance of water environment itself, but also a serious waste of resources if discharged directly. Therefore the efficient way should be developed for utilization of lignin in a maximum degree. Whether from an environmental point of view or from the utilization of solid waste, the application of lignin has greater economic and social significance.In this paper pulp byproduct-alkali lignin was modified and the products were used to treat kaolin-containing wastewater. The lignin purification and performance analysis was conducted in the research and CHPTAC (3-chloro-2-hydroxypropyltrimet hylammonium chloride) was reacted with alkali lignin to form cationic lignin derivatives using sodium hydroxide as catalyst performed in aqueous solution and in a solid state. The effects of all the factors on the properties of cationic lignin derivatives were analyzed in detail. Analysis of the structure of lignin derivatives was as follows: elemental analysis, FTIR,1H-NMR, ESEM and TGA. Furthermore the flocculating effect of cationic lignin derivatives on kaolin suspension was studied and the effects of lignin derivatives amount, flocculating time, setting time, pH, temperature and the corresponding mechanisms were discussed.The lignin purification results indicated that water contents in wheat straw alkali lignin and poplar alkali lignin were 5.17%,4.23%, ash contents were 6.32%,2.61% and the N contents were 0.68%,0.89%, respectively.The preparation of cationic lignin derivatives indicated the optimal reaction conditions:CHPTAC 1.3g, the molar ratio of NaOH and CHPTAC 1.00,40℃ and 3 h. Under this condition the N contents in wheat straw lignin derivative and poplar lignin derivative prepared in aqueous solution were 2.64%,2.25%, the charge density 1.5mmol/g,1.35mmol/g, respectively. The same effect can be achieved with less CHPTAC when the reaction occurred in a solid state.The analysis results of FTIR,’H-NMR, ESEM and TGA indicated CHPTAC was reacted with wheat straw lignin and poplar lignin. CHPTAC containing quaternary ammonium functional group was successfully grafted on wheat straw lignin and poplar lignin.The flocculating results of cationic lignin derivatives indicated the optimal lignin derivatives amount of 0.3g/L, the optimal flocculating time and setting time were 30min and the flocculating performance increased with lower pH and temperature. The structure and distribution state of kaolin particles before and after flocculation were analyzed by FTIR and optical microscope. The results indicated that strong electrostatic attraction and bridging between kaolin particles and cationic lignin derivatives occurred and this accelerated settlement of kaolin particles.