Fabrication Of PANI/PVDF Membdrane And Its Application In Simultaneous Desulfurization And Denitrification By Electrodialysis

In recent years,simultaneous desulfurization and denitrification technology has received considerable attention owning to its simple operation,less space demand and lower cost.However,the desulfurization and denitrification products of existing technologies was mixed and with low concentrations,which cannot meet industrial production requirements.In this paper,a method of simultaneous desulfurization and denitrification by electrodialysis was proposed.Which integrated the desulfurization,denitrification,product separation and concentration into a reaction system.Meanwhile,aimed at recycle sulfuric acid with high concentration,a ptoton block and acid-resistant anion exchange membrane was prepared to solve the serious problem of proton leakage.The main conclusions of this study are as follows:?1?A polyaniline?PANI?/polyvinylidene fluoride?PVDF?membrane was prepared by the method of heat treatment-liquid phase conversion.The membrane structure was half-dense and half-porous,corresponding to a glossy and lusterless surface,respectively.Anions in sulfuric acid solution migrate mainly through the molecular chains of PANI in the form of HSO₄^-under the driving force of the electric field.The migration of HSO₄^-through membrane could be directed owing to the different structure.Leakage of HSO₄^-was inhibited by glossy surface of membrane facing concentrate chamber.Proton leakage was also inhibited due to the dense structure and hydrophobic nature of the PANI/PVDF membrane.?2?According to the experimental phenomena that PANI dissolves partially in concentrated sulfuric acid,the PANI/PVDF membrane was etched with concentrated sulfuric acid solutions.The solubility,structure and electrical performance variation of PANI/PVDF membrane in different concentrated sulfuric acid solutions was investigated.As the result,the membrane was insoluble and stable when the concentration below 60 wt.%.While,at the concentration range from 90 wt.%to 98wt.%,PANI/PVDF membrane was etched due to part dissolution of PANI.The electrical performance of membrane,especially for the conductivity,was significantly improved.Meanwhile,the proton leakage of etched PANI/PVDF membrane was also inhibited comparing with commercial aion exchange membrane?AEM?.The etched PANI/PVDF membrane was part hydrophilic and part hydrophobic.The anions were mainly migrated through molecular chains of PANI.The protons,migrated as protonated water clusters,were excluded by the hydrophobic part of membrane.?3?Based on the study of PANI/PVDF membrane,simultaneous desulfurization and denitrification by electrodialysis was researched.In electrodialysis system,the simulate flue gas was entered from the cathode chamber,FeSO₄ was used as an absorption liquid to promote the oxidation absorption of SO₂ and increase the solubility of NO.On the condition that current was 0.3 A,oxygen content was 20%,Fe?II?concentration was 0.1 mol/L,intake gas flow was 200 mL,the removal rates of SO₂and NO_x are 98%and 78%,respectively.During the simultaneous desulfurization and denitrification process,the effect of electric current on the purification rate was increased firstly and then decreased.H₂S was produced at the current range that SO₂removal rate decrease,and promoted the increasing of NO_x removal.A better removal rate of SO₂ and NO_x were occurred with a lower O₂ content.While the low O₂ content decreased the proportion of SO₄^2-.Fe?II?concentration mainly affects the purification efficiency of desulfurization products and NO_x.When 0.1 mol/L Fe?II?was added to the system,the NO_x removal rate was significantly improved,while dereased as the Fe?II?furter increase.?4?During the process of simultaneous desulfurization and denitrification,the desulfurization products were SO₄^2-and SO₃^2-.SO₄^2-was formed by the reaction among SO₂,O₂ and Fe²⁺/Fe³⁺,and continuous migrated to anode chamber through PANI/PVDF membrane to produce H₂SO₄.The the concentration of obtained sulfuric acid was as high as 63 wt.%.SO₃^2-was reducted at cathode and produceing S^2-and H₂S.The denitrification products were N₂,NH₃ and a few NO₃^-.N₂ was formed by the reaction beteewn NO₂ and S^2-/SO₃^2-.NH₃ was the electrochemical reduction product of NO₂^-.S^2-/H₂S promoted the absorption and conversion of SO₂ and NO_x.While the overflow will cause the secondary contamination.The content S^2-/H₂S of can be controlled by increasing O₂ content and reducing the voltage or increasing the intake gas flow rate.