Study On Preparation And Properties Of Piperidine And Pyrrolidone Anion Exchange Membranes

Anion exchange membranes（AEMs）have been widely used in the fields of electrodialysis,fuel cells and diffusion dialysis.As a key component of electrodialysis,AEM can achieve the transport of anions and inhibit the passage of cations under electric field forces.However,most AEMs are prepared through chloromethylation of aromatic rings on the polymer chain using reagents such as chloromethyl ether and dichloromethyl ether,and then by quaternization.However,these reagents are highly carcinogenic and dangerous.Therefore,the preparation of AEM through a safer route without the use of hazardous reagents has become the focus of research.In addition,the lack of stability of most AEMs limits their use under severe conditions（eg,under strong alkaline conditions）,and long-term alkaline stability has a significant impact on the life of AEM.Therefore,in practical applications,it is particularly important to prepare AEM with good mechanical stability,alkaline stability and dimensional stability.This paper is mainly devoted to the preparation of AEM with high alkaline stability,good dimensional stability,green preparation route and simple preparation process.The specific experiments are as follows:（1）The piperidine-type AEM based on brominated polyphenylene ether（BPPO）.BPPO with bromomethyl group in side chain was used as the membrane substrate.Three different alicyclic quaternary ammonium groups,N-methylpyrrolidine（MPY）,N-methylpiperidine（MPRD）and N-methylmorpholine（MMPH）were used as quaternization reagents to prepare membranes by quaternization with BPPO respectively.A new preparation route without toxic chloromethylation reagents was designed.The experimental results show that after 15 days immersion in 60 ℃ 1.0 M KOH solution,the retention rate of ion exchange capacity（IEC）of BPPO-MPRD membrane is about 86%,while that of the control BPPO-TMA membrane is about 65%,which indicates that BPPO-MPRD membrane has good alkaline resistance;In electrodialysis experiments,the NaCl desalination rate of BPPO-MPRD membrane reaches 98.8%in 2.5 hours,and the energy consumption is only 12.58 kWh·kg^-1 NaCl,which is better than commercial membrane Neosepta AMX(desalination rate 97.4%,energy consumption 15.76 kWh·kg^-1 NaCl),Which shows that the BPPO-MPRD membrane has excellent desalination performance.（2）An internally crosslinked pyrrolidine-type anion exchange membrane is constructed based on polysulfone（PSF）.Chloromethylated polysulfone（CMPSF）was prepared by chloromethylation using PSF as a substrate and reagents such as trimethylchlorosilane and paraformaldehyde,and then crosslinked modification of CMPSF was carried out by 4,4’-trimethylenedipiperidine（TMDP）.Finally,the above-mentioned network structure is quaternized with 1-methylpyrrolidine（MPY）to prepare series of AEM with different degrees of crosslinking.The water uptake（WU）and swelling ratio（SR）test results show that under the same conditions,the crosslinked membrane CAPSF-5 exhibits better dimensional stability than the uncrosslinked APSF membrane.For example,at room temperature,the WU and SR of the cross-linked membrane CAPSF-5 are 13.04%and 9.42%,while the WU and SR of the uncrosslinked APSF membrane are 19.45%and 13.26%,respectively.In alkaline stability experiments,after the crosslinked membrane CAPSF-5 is immersion for 15 days in 60℃ 1.0 M KOH solution,the IEC retention rate remained above 60%,while the uncrosslinked APSF membrane shows obvious embrittlement and rupture within 24hours,and subsequent tests cannot be subsequently measured.It indicates that the crosslinked membranes have good alkali resistance.