Chi-Lan Li

Dehydration of acetic acid by pervaporation through an asymmetric polycarbonate membrane

Abstract Dehydration of acetic acid by pervaporation through an asymmetric polycarbonate membrane was investigated. Investigations focused on the effects of feed composition, degree of swelling, and the molar volume of non-solvent additive on the pervaporation performances. The membrane formation systems are discussed in terms of the presence of a nonsolvent in the casting solution, the kinds of coagulation media, and the polymer concentration. The rate of liquid–liquid demixing decreases with increasing alcohol molar volume of the coagulation medium. The durability of the asymmetric polycarbonate membranes with n -hexanol additive was tested for 3 wt.% aqueous acetic acid solution at 25°C for two months and it was found to be stable.

Dehydration of water–alcohol mixtures by pervaporation and vapor permeation through surface resintering expanded poly(tetrafluoroethylene) membranes

For the purpose of separating aqueous alcohol mixtures by the use of the pervaporation and vapor permeation techniques, a surface resintering expanded poly(tetrafluoroethylene) (e-PTFE), membrane was investigated. The surface properties of the modified e-PTFE membranes were characterized by atomic force microscopy, scanning electron microscopy, and contact angle meter. The X-ray diffraction measurements show that the crystallinity of the e-PTFE membrane decreases with increasing the surface resintering temperature. The surface roughness decreases with the surface resintering temperature increases. The membrane exhibited water selectivity during all process runs. The effects of feed composition, surface resintering temperature, and molar volume of the alcohols on pervaporation and vapor permeation were investigated. Compared with the e-PTFE membrane without surface modified, the e-PTFE membrane with surface resintering treatment effectively improve the separation factor for pervaporation of aqueous alcohol mixtures. The separation performances of e-PTFE membranes in vapor permeation are higher than that in pervaporation.

Application of aromatic polyamide membranes for pervaporation and vapor permeation

Abstract In this article, three types of aromatic polyamides were prepared by the direct polycondensation of bis[4-(4-aminophenoxy) phenyl] diphenyl methane (BAPDM) with various of aromatic diacids such as terephthalic acid (TPAc), 5-tert-butylisophthalic acid (TBPAc), and 4,4′-hexafluoroisopropylidenedibenzoic acid (6FDAc). The pervaporation and vapor permeation performance of the above novel aromatic polyamide membranes for dehydrating an aqueous alcohol solution was investigated. Compared with pervaporation, vapor permeation effectively increases the perm-selectivity of water. Moreover, the effect of aromatic diacids on the polymer chain packing density, pervaporation, and vapor permeation performance was investigated. It was found that the permeation rate can be increased by introduction of a bulky group into the polymer backbone.

Relationship between polymer structure and gas transport properties in a series of fluorine-containing aromatic polyamide membranes for oxygen enrichment

Abstract In this work, a series of fluorine-containing aromatic polyamide membranes were prepared by direct polycondensation of 4,4′-hexafluoroisopropylidene-dibenzoic acid with various aromatic diamines, and the associated gas transport and sorption properties were investigated. The properties of the prepared aromatic polyamides were examined by elemental analysis, FTIR, and X-ray diffraction. It was found that both gas diffusivity and permeability can be increased by the introduction of bulky substituted groups and arylene ether groups into the polymer backbone. Membranes with oxygen permeability of 3.8 barrers and O2/N2 selectivity of 4.6 were obtained by using the polyamide with 2,5 di-tert-butylbenzene group in the polymer backbone. It was also found that the relationship between the membrane structure and the sorption properties can be well explained by the dual sorption model.

EFFECT OF SURFACE RESINTERING ON THE SURFACE MORPHOLOGY AND VAPOR PERMEATION PROPERTIES OF SKIVED POLY(TETRAFLUOROETHYLENE) MEMBRANES

Surface sintering of skived poly(tetrafluoroethylene) membrane was carried out to improve the water permselectivity of the membrane. The surface morphologies of the modified and unmodified membranes were studied by scanning electron and atomic force microscopy. The results indicate that the surface sintering process can make the surface denser and smoother, resulting in higher water permselectivity but lower permeation rate. In addition, the vapor permeation performances were strongly related to the surface resintering temperature.

Pervaporation of aqueous alcohol mixtures through functionalized syndiotactic poly(styrene-co-4-methylstyrene) membrane

Abstract The pervaporation performances of a series of functionalized syndiotactic poly(styrene-co-4-methylstyrene) (SPSM) membranes for various alcohol mixtures were investigated. The effect of functionalization on the thermal properties and polymer structure of the SPSM membranes were also investigated. The crystallinity of the functionalized SPSM membrane is lower than that of the unfunctionalized SPSM membranes. The water molecules preferentially permeate through the SPSM membranes. Compared with unfunctionalized SPSM membranes, the functionalized SPSM membrane effectively increases the membrane formation performances and the pervaporation performances. The optimun pervaporation performance (a separation factor of 510 and permeation rate of 220 g/m2h) was obtained by the bromination of SPSM (SPSMBr) membrane with a 90wt% aqueous ethanol solution.