Synthesis Of DMDAAC Graft Modified Chitosan And Its Flocculation Properties

In order to make effective use of water resources in our country and alleviate the pollution of rivers and lakes,the treatment and reutilization of wastewater have become effective ways to solve the problems of water shortage and environmental pollution in our country.For the treatment of wastewater containing small suspended solids and sol-like contaminants,flocculation and sedimentation methods are widely used due to their advantages of simple operation,high efficiency of removing impurities and low cost.In water treatment applications,chitosan has its own adsorption and flocculation performance,but its application is limited due to its adsorption capacity and poor water solubility.In order to improve the water solubility of chitosan and increase the adsorption site of chitosan,the chitosan needs to be chemically modified to expand its application range.Therefore,in this paper,succinylation,hydroxyethylation and quaternary ammonium modificationofchitosanwerecarriedouttosynthesizethe corresponding derivatives and the flocculation performance of the synthesized derivatives was studied.This thesis mainly includes the following contents:1.Chitosan,benzaldehyde,succinic anhydride,2-chloroethanol and dimethyldiallylammonium chloride were used as starting materials to synthesize benzaldehyde chitosan Schiff base?B-CTS?,Succinyl chitosan?SACTS?,succinyl chitosan quaternary ammonium salt?SAQCS?and hydroxyethyl chitosan quaternary ammonium salt?HEQCS?.The structure and morphology of the product were characterized by FTIR,¹H NMR,XRD and ESEM.The effects of various factors on the synthesis of each derivative were explored,and the synthesis of each derivative was optimized.The solubility of SACTS was measured and the flocculation performance of SAQCS and HEQCS on kaolin simulated wastewater was studied.The result indicated that,The optimum technological conditions of B-CTS were as follows:the reaction temperature was 70?,p H=6,the amount of benzaldehyde 1.30g,the condensation rate of product under this condition was 92.93%;The optimum conditions of SACTS were as follows:m?B-CTS?:m?TEA?:m?SAA?=1:4:5,reaction time 6.5 h and reaction temperature 65?.The carboxyl content and the esterification rate of SACTS synthesized in this process was 93.01%and 71.13%;The optimum conditions of SAQCS were as follows:the dosage of initiator was 2%,the molar ratio of m?DMDAAC?:m?SACTS?was 5.4,the reaction temperature was 70?and the reaction time was 7h.The cationic degree of SAQCS synthesized in this process was 42.26%;The optimum conditions of HEQCS were as follows:the reaction temperature was 71?,m?DMDAAC?:m?HECS?=4.1 and the amount of initiator was 2%.Under this process,the cationic degree and intrinsic viscosity of HEQCS was 81.14%141.23 m L/g.Solubility determination results show that SACTS has good solubility at p H values of 1-2 and 5-13.The results of flocculation experiment showed that when the flocculation conditions were p H=2⁵,dosage of 3⁹ mg/L and temperature of 25⁵0?,turbidity removal rate of the supernatant after using SAQCS was over 96%;At p H=4⁶,dosage was 3⁶mg/L,HEQCS cationic degree was 58%⁷1%,turbidity removal rate of supernatant was over 98%.2.With pyronine dye wastewater as flocculation object,the flocculation performance of SACTS was studied.Using turbidity removal rate and dye residual rate as indexes,the effects of p H,initial turbidity and temperature on the flocculation were investigated.The experimental results show that the turbidity removal rates of the supernatant were over 95%at flocculation conditions of p H=1⁴,dosage of 1¹0 mg/L,initial turbidity of 200⁸00NTU and temperature of 20³0?.The dye residue rate of supernatant were less than 10%.By measuring the Zeta potential of the supernatant,it was found that the Zeta potential of the supernatant was close to zero at p H=1 to 4,and the Zeta potential rapidly decreased to a negative value at p H>4.When the dosage of SACTS was 1-4 mg/L,the turbidity removal rate of the simulated wastewater remained high although the supernatant Zeta potential was negative.An-N⁺peak with a binding energy of 400.94 e V and an N-Si peak with a binding energy of 398.06 e V appeared in the N element decomposition spectra of the floc.Through the analysis of Zeta potential and XPS spectra of flocs,it is concluded that flocculation of SACTS and pyronine wastewater is mediated by both electric neutralization and adsorption bridging.The chemisorption may occur between the Si on kaolin surfaces and the N-containing groups of pyronine and SACTS.3.The flocculation effect of SAQCS,HEQCS,CTS and commercial CPAM on the water of the Weiyang Lake was studied.Using turbidity removal rate and COD_Crr as indexes,the effects of p H and dosage on the flocculation efficiency were investigated.The experimental results show that the optimum flocculation conditions of SAQCS are as follows:the p H range is 4⁶,the dosage range is 1¹0 mg/L.The optimal flocculation conditions for HEQCS are as follows:p H range 4¹0,dosage range 3⁸ mg/L.The optimal turbidity removal rates of SAQCS and HEQCS were 99.92%and 99.37%,respectively.The lowest value of COD_Crr in the supernatant was 47.08 mg/L and 76.79 mg/L,respectively.Through the analysis of the Zeta potential of the supernatant under different conditions,it is considered that both the electric neutralization and the adsorption bridging effect are present in the flocculation process of SAQCS and HEQCS.