The Influence Of Acid Mass Transfer Through Anion-exchange Membrane On Membrane Fouling During Bipolar Membrane Electrodialysis Of Butyl-acrylate Wastewater

Butyl acrylate is an important material in organic chemical engineering,and large amount of high-concentration wastewater is discharged in its' production.The wastewater is difficult to treatment,because.of high salinity,organic concentration and toxicity.At present,it is usually treated with biological processes after mixing with low-concentration wastewater or with incineration processes.The incineration processes cost a lot and face scaling and corrosion problems because of high salinity.The organics in the wastewater are mainly sodium acrylate and showed high potential for recovery as resource.Application of bipolar membrane electrodialysis(EDBM)for recovery of acrylic acid and alkaline from the wastewater showed good potential,which could reduce salinity,toxicity and treatment difficulties with low chemical consumption.EDBM for butyl acrylate treatment is still stay in pilot scale,and its industrial application required to solve problems of membrane fouling.In EDBM,there are also leakage of proton and diffusion of week acid molecular from acid chamber to material chamber,besides directed migration by the electrical field.Theses processes will reduce the efficiency of the electrodialysis.Both proton leakage and week acid migration closely related to ion-exchange membrane properties,which could be changed by membrane fouling.Membrane fouling could affect proton leakage and week acid migration,which could also affected membrane fouling process.Therefore,relations between acid transfer(proton leakage and week acid migration)and membrane fouling were required to investigate.It was indicated by previous studies that polyacylic acid(PAA)was an important pollutant resulting in fouling of anion-exchange membrane(AEM)in EDBM of butyl-acrylate wastewater.PAA could increase electrical resistance and reduce transference number.As a result,efficiency decrease and energy consumption increase of AEM membrane.PAA was a polyvalent ion compounds,and its species were affected by pH of the wastewater.In this thesis,influence factors of PAA adsorption on AEM were investigated.Furtherly,influences of PAA adsorption on membrane properties and EDBM process were investigated.The main conclusions were as follows.(1)Adsorption of PAA on AEM increased with the increase of PAA concentration in wastewater.At the same time,membrane surface resistance would increase while membrane transfer number would decrease.When the adsorption increased from zero to 0.0068g/cm2,membrane surface resistance increased from 3.2?·cm2to 16.8?·cm2,transfer number increased from78% to 56%.(2)As pH of the wastewater increased from 3 to 9,adsorption of PAA on AEM would increase.When pH was above 9,increase of pH had little effect on PAA adsorption.So,decrease of pH in salt chamber solution resulted from proton leakage and weak acid diffusion from acid chamber to salt chamber has little promoting effect on membrane fouling.(3)In EDBM process,as adsorption of PAA on AEM increased from zero to 68 mg/cm2,membrane selectivity decreased.Proton leakage would be tensified by 110%.Current efficiency between 0~40min decreased from67.33% to 43.33%.Solution yolume of acid chamber decreased by 13% during the later phase of EDBM.pH of salt chamber solution would decrease from 4 to 2.5.