UV-Initiated Template Polymerization Of Cationic Polyacrylamide And Its Application In Flocculation

Polyacrylamide flocculant is the most commonly used agents for water treatment and sludge dewatering,It can be divided into four types,namely Cationic,anionic,neutral and amphoteric polyacrylamide.Among them,cationic polyacrylamide(CPAM)is the most extensively applied to sewage treatment because most sewage is negative-charged.More and more cationic polyacrylamide will be demanded to treat the sharply increased sewage,the by-product of population growth and economic development,so improving the flocculation performance of cationic polyacrylamide has important significance to the development of water supply and drainage.Ultraviolet(UV)-initiated polymerization for CPAM preparation has been widely advocated because of its low toxicity and energy consumption.However,like CPAM prepared with other traditional methods,that prepared with UV-initiated polymerization has a significant drawback that the randomly-scattering cationic units can’t work completely;with the result that the flocculation efficiency will be reduced.To make up for the above defect,this paper tried to synthesize a novel cationic polyacrylamid by using UV-initiated template polymerization.The template will assemble the cationic monomer in the process of polymerization,and which can be used to control polymerization,optimize the molecular sequence distribution of polymer and improve the flocculation performance of CPAM.So far there have been some researches about both template polymerization and UV-initiated polymerization.However,the study on UV-initiated template polymerization for preparing CPAM has been rarely reported in literatures.In this study,the impact of factors on the flocculation performance of CPAM was investigated;the template polymer(TPDA)of dimethyl diallyl ammonium chloride(DMD)and acrylamide(AM)were synthesized with ultraviolet-initiated template polymerization,and polyacrylic acid sodium(PAAS)with low molecular weight was selected as template,the reactivity ratios of AM and DMD were calculated,and the sequence distribution of TPDA molecule was statistically analyzed;the properties of TPDA were characterized by Fourier transform infrared spectroscopy(FT-IR),hydrogen proton nuclear magnetic resonance(1HNMR)spectroscopy,scanning electron microscopy(SEM)and thermog-ravimetric analysis(TGA).Finally,the flocculation tests for treating coal mine wastewater and sludge dewatering were carried out to investigate the flocculation performance and mechanism of TPDA.Meanwhile,the common polymer(CPDA)of DMD and AM was prepared with UV-initiated polymerization,the necessary controlled trials were also done,and the results were compared with those of TPDA to research the impact of template addition on polymer.The main contents and conclusions of this study are as follows:(1)The investigation result of the impact of factors on the flocculation performance of CPAM showed that the intrinsic viscosities and cationic degree of polymers,the wastewater pH,stirring time and settling time all had effect on CPAM flocculation performance.The best flocculation efficiency can be obtained only when every factor is in appropriate conditions.The intrinsic viscosities and cationic degree of CPAM both had significant impact on its flocculation performance.The CPAM with higher intrinsic viscosity and cationic degree in the range of experiment had better flocculation performance.(2)Synthetic conditions of polymers were studied and optimized by single-factor and Response surface methodology(RSM).The results showed that an intrinsic viscosity of the TPDA up to 11.06dL/g was attained with the condition of total monomer mass fraction of 27.2%,the monomer mole ratio(n(DMD)/(AM))of 3:7,initiator V-50 of 0.047%,the polymer solution pH of 7.3,UV irradiation of 80 min and the mole ratios of PAAS and DMD(n(T)/n(DMD))of 1.0;total monomer mass percentage,the polymer solution pH,initiator concentration all had significant impact on the intrinsic viscosity of TPDA.The significant sequence was total monomer mass percentage> the polymer solution pH> initiator concentration.(3)The template addition improved DMD reactivity ratio,increased the number and length of DMD segments in polymer molecules,weakened those of AM segments,and prompted formation of DMD block structure in polymer molecules.When n(T)/ n(DMD)equaled to 1.0,the above function of template was most obvious,and the reactivity ratio of DMD(r)and AM(r)were 0.93 and 3.84,respectively,and the composition curves of TPDA were closest to the ideal copolymerization curve,and the average lengths of DMD and AM segments(`NDMD and `NAM)in TPDA were 1.93 and 4.84,respectively.It could be inferred according to the research results of the monomer reactivity ratio and composition equations of TPDA that the template polymerization of DMD and AM belonged to Zip type.The electrostatic interaction of template with DMD monomer was the main reason for formation of DMD block structure.(4)The template polymer was further characterized by FT-IR,TGA,1H NMR and SEM.1H NMR spectra proved that TPDA was compolymerized by AM and DAC,and the blocked cationic structure were generated in TPDA molecule.The SEM photographs demonstrates TPDA possesses had larger specific surface area and fraction than CPDA,and which contribute to the TPDA adsorption.The TGA result showed that TPDA had satisfactory thermal stability.(5)The flocculation test result of TPDA,CPDA and CCAM demonstrated that the DMD block structure improved the flocculation performance of TPDA,especially charge neutralization.The result of single-factor and RSM experiment showed that a lowest value of approximately 16.3 mg·L-1 could be gained with the condition of TPDA dose of 6.1 mg·L-1,wastewater pH of 6.4,stirring time of 6.40 mins.TPDA dose,wastewater pH,stirring time all had significant impact on the SS removal,and the significant sequence was TPDA dose>wastewater pH>stirring time.The result of sludge dewatering with TPDA,CPDA and CCAM showed that a sludge water content down to 72.5% was attained with the condition of TPDA dose of 45.0 mg·L-1and sludge pH of 7.0.TPDA had a wilder pH range for application than CPDA and CCAM,and the flocs produced by TPDA were not only large,compact,rapid to settle,but also uneasy to restabilize.(6)The comparison of economic and environmental benefits of TPDA and CCPAM showed TPDA has a broader market application prospect because of its better flocculation performance and lower cost than CCPAM...