Preparation And Peryaporation Performance Of Poly (4-vinylpyridinium)-based Polyelectrolyte Complex Membranes

Pervaporation (PV) is considered to be a promising technology for its high efficiency and cleanness. The hydrophilicity and stability of membrane materials are very important for PV dehydration. Polyelectrolyte complex (PEC) has attracted much attention for its excellent hydrophilicity and mechanic property. In this thesis, soluble PECs were synthesized and homogeneous membranes (PECM) were prepared. The membranes were then subjected to the dehydration of alcohol. The relationship between the membrane structure and PV performance was concluded, and the separation mechanism was also investigated.At first, soluble PECs were synthesized based on poly (N-alkyl-4-vinylpyridinium) salts (PAVP) and sodium carboxymethyl cellulose (CMCNa). A series of PECs with different length of alkyl groups were obtained by controlling the alkyl groups on PAVP. The ionic complexation degrees (ICD) of PECs can be effectively controlled by tuning either quaternization degree (QD) of PAVP polycation or carboxylate group (-COO~-) content on CMCNa polyanion, which were characterized by Elemental analysis (EA) and Fourier Transform infrared (FTIR). The thermal stability of PECs was also studied by Thermal gravity analysis (TGA).PECs homogeneous membranes (PECMs) were obtained by casting solution method and they were used for the PV dehydration of alcohol. The experiment results showed that the permeation flux decreased while the separation factor increased with increasing of the molecule weight of poly (4-vinylpyridine) (P4VP). With the increase of the length of alkyl groups on PECs, flux increased while the separation factor decreased.At last, poly (N-ethyl-4-vinylpyridiniumbromide) (PEVP) with low molecule weight was selected as the polycation. The dilute solution viscosity behavior of the corresponding PECs was investigated by Ubbelohde viscometer. The hydrophilicity and surface morphologies of polyelectrolyte complex membranes (PECMs) were examined by contact angle meter and field emission scanning electron microscopy (FESEM), respectively. The PECMs were subjected to dehydration of ethanol and showed very high separation performance. Interestingly, the flux of PECMs increased while water content in permeate decreased with increasing ionic complexation degree (ICD). The performance was discussed in terms of the unique structural characteristics of PEVP, PECs and PECMs.