The Preparation Of Polyacrylic Acid Flocculant And Its Application In Low-temperature Heat Treatment Of Printing And Dyeing Sludge

The composition of textile dyeing sludge is very complex.The sludge has high moisture content,strong viscosity and poor dewatering performance.The sludge produced by the pre-treatment of textile dyeing wastewater usually contains strong hydrophilic organic substances,such as starch,polyvinyl alcohol and so on,which increases the difficulty of dewatering.Sludge dewatering is the key link to realize sludge reduction and resource utilization,therefore,it is very important to develop a process to improve sludge dewatering performance.In this study,the preparation of water-borne polyacrylic resin for low temperature thermal treatment of textile dyeing sludge was proposed to improve the dewatering performance of sludge.The dewatering mechanism of sludge was clarified by optimizing the synthesis process of waterborne polyacrylic resin and its low temperature thermal treatment process.It provided theoretical basis for the development of new sludge dewatering technology and forms a new sludge dewatering process.Waterborne polyacrylic resin was synthesized by solution polymerization.The effects of reaction temperature and time on monomer conversion rate were studied by using monomer conversion rate,specific resistance to filtration of sludge and dewatering cake moisture content as evaluation indexes.The effects of the types of monomers,the volume ratio of monomers and the glass transition temperature on the dewatering performance of sludge were discussed.The synthesis process of waterborne acrylic resin was optimized,and then the waterborne acrylic was characterized.The results showed that the optimum technological conditions for the synthesis of waterborne polyacrylic resin were as follows:the volume ratio of methyl methacrylate（MMA）,methacrylic acid（MAA）and butyl acrylate（BA）was 5:3:2,the reaction temperature was 83℃and the reaction time was 6 h,the conversion of monomer reached 92.6%.The glass transition temperature range of waterborne polyacrylic resin was 70.85⁸7.3℃.Apparent morphology of waterborne polyacrylic resin was pale yellow liquid with good fluidity and water solubility.And it had the most significant effect on improving sludge dewatering performance.The product was MAA/BA/MMA copolymer with molecular weight as follows:Mn=7033,Mw=10466,Mw/Mn=1.488.Waterborne polyacrylic resin was used for thermal treatment at low temperature of textile dyeing sludge.The effects of water-borne polyacrylic resin dosage,sulfuric acid dosage,thermal treatment temperature and time on sludge dewatering were investigated with sludge specific resistance to filtration and dewatering cake moisture content as evaluation indexes.The results showed that the optimum technological conditions for low temperature thermal treatment of sludge with waterborne polyacrylic resin were as follows:the dosage of waterborne polyacrylic resin was 15 m g/g sludge（solid content was about 4%）,the dosage of sulphuric acid（volume fraction was 98%）was 0.002 mL/g sludge,and the thermal treatment temperature was 75℃for 30 minutes.The specific resistance to filtration of sludge could be reduced from 3.0×10¹44 m/kg to2.80×10¹² m/kg,the treated sludge belongs to easily filtered sludge.The moisture content of sludge cake could be reduced from 93.0%to 84.59%,the bound water content of sludge could be reduced from 33.82%to 28.27%,and the sludge reduction rate could reach 54.25%.The dewatering mechanism of low temperature thermal treatment of sludge was explored by analyzing the micro-structure,water distribution and surface properties of dewatered sludge cake.The results showed that-COO^-in the molecular chain of waterborne polyacrylic acid resin could react with H⁺in sulfuric acid to form–COOH,and it precipitated after its solubility decreased.The macromolecular chains of waterborne polyacrylic resin were curled up by thermal treatment.The sludge flocculated and contracted through the adsorption of waterborne polyacrylic resin bridging,sedimentation net trapping and the interaction with the intermolecular forces of sludge granules,which enlarged the pore space between sludge particles and weakened the interaction between sludge particles and water molecules.Finally,the combined water in the sludge was converted into free water and released by means of porous channel structure,and the purpose of improving sludge dewatering performance and sludge volume reduction was achieved.