Synthesis And Coagulation-flocculation Performances Of Organic Polymer Flocculants With Cationic Block Structure

Organic polymer flocculants are common water treatment agents.The improvement of their flocculation performances contributes to the efficiency enhancement of water treatment.The cationic monomers randomly distribute in molecular chain of cationic polyacrylamide（CPAM）synthesized by traditional preparation methods.The interaction among CPAM and pollutants through bridging is weak in coagulation-flocculation.In order to overcome this disadvantage,the CPAM with cationic block structure was prepared via template polymerization in this study,which improved the utilization of cationic monomer and the performance of the CPAM.The organic polymer flocculant with different cationic block length,P（AM-DAC）,was synthesized through adjusting the molecular weight of template.Molecular dynamics was used to calculate the binding force between P（AM-DAC）with different cationic block length and kaolinite colloid and predict the flocculation performance of P（AM-DAC）.The prediction was confirmed by coagulation experiments of P（AM-DAC）in the treatment of colloidal particles,Congo red,chrome black-T and toluidine blue.In addition,the organic polymer flocculant with block structure and branched structure,PADS,was synthesized by introducing branching agents using thermal initiation and template polymerization.Their composition,structures,flocculation efficiencies and coagulation mechanisms were investigated via various characterization methods.The research contents and conclusions of this paper are as follows:（1）A serious of P（AM-DAC）flocculants with different cationic block lengths were synthesized by template polymerization under UV irradiation.In the synthesis,it was found that acrylamide（AM）and acryloxyethyl trimethylammonium chloride（DAC）as raw materials,sodium polyacrylate with different molecular weight as anionic template and VA-044 as initiator.The molecular structure of P（AM-DAC）was characterized by FTIR and ~1H-NMR.The thermal stability of P（AM-DAC）was analyzed by differential thermal gravimetric（TG-DSC）.The results indicated that although P（AM-DAC）with different cationic block lengths had the same functional groups,their cationic block lengths,molecular weights and thermal stability were significantly different.Increasing the molecular weight of the anion template was able to increase the cationic block length of P（AM-DAC）,but the excessive molecular weight of the template leaded to an obvious decrease of cationic block length of P（AM-DAC）.The P（AM-DAC）_（104:1）synthesized by sodium polyacrylate with a template molecular weight of 10 k Da has the longest cationic block length and the best thermal stability.Its molecular weight reaches 3780.6 k Da.（2）The binding energy between P（AM-DAC）_（104:1）and colloidal particle was the highest in MD simulation due to its long and centralized cationic block structure.It indicated that the strong interaction was found between them and the excellent flocculation performance of P（AM-DAC）_（104:1）.P（AM-DAC）_（104:1）had the best treatment efficiency of colloidal particles in the treatment of simulated kaolinite wastewater.Its pollutant removal rate,floc particle size and electric neutralization capacity were respectively 1.05-2.46 times,1.34-1.89 times and 2.24-9.79 times higher than other P（AM-DAC）.In the coagulation test of dye wastewater,P（AM-DAC）_（104:1）also had the highest removal rate and the largest floc size.The long block structure was beneficial to the improvement of neutralization capacity and adsorption bridging capacity of P（AM-DAC）.（3）PADS flocculant with block structure was synthesized with AM and DAC as monomers,trimethylolpropane（TMP）as branching agent and sodium polyacrylate as template under thermal initiation.The optimum synthesis conditions of PADS were obtained through optimizing the initiator dosage,branching agent dosage,monomer ratio,reaction temperature and reaction time.Under the optimum synthesis conditions,the maximum molecular weight of PADS₁₀ was 4925.2 k Da and that of PADS₃ was4040.69 k Da.In the analysis of FTIR and ~1H-NMR,it was found that PADS was prepared by the copolymerization of AM,DAC and TMP.PADS owned carbonyl（-C=O-）,methyl（-CH₃）,methylene（-CH₂-）and amide（-CO-NH₂）.PADS had branched structure and good thermal stability.（4）PADS performed well in the coagulation-flocculation treatment of Congo red,chrome black-T and toluidine blue wastewater.PADS₁₀ had the better flocculation efficiency than PADS₃ for its longer cationic block structure.The removal rate of Congo red,chrome black-T and toluidine blue by PADS₁₀ were 90.16%,88.41%and 80.10%in wastewater treatment.The floc size was small in the treatment by only PAC.The composite flocculants,PAC and PADS₁₀,the large floc was found for the branched structure of PADS₁₀.PADS played an essential role of bridging in the treatment while PAC played a role of charge neutralization.