Polymer Inclusion Membranes And Electrodialysis Combined System For Phenol Removal Performance And Mechanism Research

With the rapid development of the coal chemical industry,the amount of phenol-containing wastewater from coal chemicals continues to increase and is currently one of the main causes of phenol-containing wastewater.The discharge of highly concentrated phenol-containing wastewater causes serious environmental pollution and waste of resources.The research and development of a green treatment method for highly concentrated phenol-containing wastewater is of great significance for environmental protection and resource recovery.Polymer Inclusion Membrane(PIM)is a membrane separation technology that allows for the selective transport of specific substances using different carriers and providing better stability than supported liquid membranes.In order to achieve the separation and recovery of high concentrations of phenols from phenol-containing wastewater,this study used PIM to treat phenol-containing wastewater,and investigated the effects of different carriers,bases polymer types and their composition ratios in the PIM on the extraction efficiency.The transport mechanism of phenol in the PIM was also analyzed.Based on this,this study proposes a synergistic hybrid carrier PIM to improve the transport properties and system stability of the PIM to phenols.In this study,Electrodialysis(ED)was coupled with a PIM to further improve the transport properties and reduce the transport time of the PIM.The main research elements and related conclusions are as follows:(1)Tertiary amine-based PIM was prepared for the transport separation of phenol.The differences in the transport properties of phenols by different tertiary amines were compared.The effects of the tertiary amine content and changes in experimental conditions such as initial feed solution concentration,p H and stripping concentration during transport were investigated on the transport performance of phenol.The experimental results showed that PIM with PVDF-HFP as base and TOA as carrier had higher crystallinity and lower spatial potential resistance,which was more suitable for phenol transport.The transport efficiency of phenol increased with increasing TOA content.The permeation threshold was identified,suggesting that the transport followed a fixed site jumping mechanism.The efficient transport of phenol was dependent on the p H in the solution.Under acidic conditions,the phenol in the molecular state formed complexes with the carrier in the PIM for transport.In addition,the initial flux of PIM to phenol was up to 340?mol m^-2 s^-1 over a range of feed solution phenol concentrations from 1-20 g L^-1.PIM can remove phenol,p-nitrophenol,m-cresol and o-chlorophenol(all at 1 g L^-1)from mixed solutions with an efficiency of over 90%.Excellent performance was demonstrated in stability tests,with phenol extraction efficiency remaining above 85%and stripping efficiency above 80%after 8 cycles.(2)The different ionic liquids were screened and the component selected was PVC/Aliquat 336 of PIM for the separation and recovery of phenol.It was similarly confirmed that PIM transport of phenol conforms to a fixed site jumping mechanism.Unlike the transport of phenol by the tertiary amine PIM,some of the phenol dissociates to the ionic state at solution p H above p Ka of phenol.Complexation extraction and ion exchange coexist to complete the transport of phenol.It was found that at p H=2,the PIM showed excellent stability and the system was stable for 15 cycles;however,at p H=8,the transport performance of the PIM decreased significantly after the 3rd cycle.To further improve the transport properties and stability of the PIM,TBP was used as a synergistic blend carrier with Aliquat 336.The prepared modified PIM increased the permeability coefficient of phenol from 3.49?m s^-1 to 5.88?m s^-1 and completed 15continuous and stable runs.The mixed carrier system improved the efficiency and stability of the PIM in the transport of phenol.In addition,the separation of phenol and p-nitrophenol was expanded by adjusting the p H of the solution,providing a practical solution for the removal and recovery of phenols from wastewater.(3)Electrodialysis was introduced to combine with PIM for the removal and recovery of phenolics such as phenol.The effects of factors such as current density,feed solution p H,salt ion type and concentration in the feed and receiving solutions on phenol transport in the electric field were investigated.The experimental results showed that the extraction efficiency of phenol increased from 16.6%to 91.2%and the permeability coefficient increased from 1.74?m s^-1 to 17.26?m s^-1 as the current density increased by 10 m A cm^-2 from 0 m A cm^-2.A change in the transport mechanism was found.In the presence of electric field forces,the transport of phenol no longer relies on the complex jumping through the fixed sites of the carrier,but is rapidly transported within the membrane in the form of ion-like channels.In addition,the ionic state of phenol remains to be driven by the electric field forces and transported rapidly through the membrane.Compared to current commercial anion exchange membranes AGU,the extraction efficiencies of PIM and AGU for phenol were 87.9%and 79.1%respectively,and the permeability coefficient of PIM for phenol was 2.0 times higher than that of AGU.The PIMED system was also suitable for the transport and separation of a wide range of phenolics,with the prospect of achieving the separation of phenol and p-nitrophenol.