Yanqiao Shi

Influence of acetylation degree of cellulose acetate on pervaporation properties for MeOH/MTBE mixture

Abstract The pervaporation separation of the MeOH/MTBE mixture was performed with three cellulose acetate membranes under various feed compositions and operation temperatures. The results show that the acetylation degree has great influence on the pervaporation properties because the quantity of hydroxyl groups in the polymer matrix leads to different crystallinty degrees. The different extent of the plasticization effect resulted in membranes performing their special flux trend and selectivity over the range of feed compositions and caused the permeants to transport through the membrane in different diffusion modes under various operation temperatures. The IR sorption spectra evidenced that for membranes with different acetylation degrees there existed different sorption sites for penetrants and provided a proof for different pervaporation properties of the tested membranes.

Pervaporation separation of meOH/MTBE through CTA membrane

In the present work, the pervaporation (PV) separation of a MeOH/MTBE mixture system was studied using a CTA dense membrane. The PV performances were characterized by changing the operating conditions, such as the feed composition and permeation temperature. The results show that the CTA membrane favors MeOH permeation and exhibits specificity during the PV separation process for the MeOH/ MTBE system due to the existence of the plasticization effect from the MeOH component. Furthermore, the swelling sorption measurements reaffirm that the plasticization effect has a dominant effect on the transport of the penetrants through the membrane and substantially determines the PV permeation properties.

Properties and pervaporation characteristics of chitosan–poly(N-vinyl-2-pyrrolidone) blend membranes for MeOH–MTBE

Clear blends of chitosan with poly(N-vinyl-2-pyrrolidone) (PVP) made from aqueous solutions appear to be miscible from visual appearance. Infrared (IR) spectra used to investigate the carbonyl—hydroxyl hydrogen bonding in the blends indicated compatibility of two polymers on a molecular level. The IR spectra were also used to determine the interaction change accessing with increasing temperature and indicated that a significant conformational change occurred. On the other hand, the blend membranes were evaluated for separation of methanol from methyl tert-butyl ether. The influences of the membrane and the feed compositions were investigated. Methanol preferentially permeates through all the tested membranes, and the partial flux of methanol significantly increase with the poly(N-vinyl-2-pyrrolidone) content increasing. The temperature dependence of pervaporation performance indicated that a significant conformational change occurred with increasing temperature. Combined with the IR results, the pervaporation properties are in agreement with characteristics of interaction between chain–chain within the blend membranes.

Preparation and characterization of high-performance dehydrating pervaporation alginate membranes

In a previous work, sodium alginate dense membranes demonstrated a good combination of selectivity and permeation flux for dehydrating organic solvents by pervaporation. In this article, the pervaporation performances of alginate composite membranes has been investigated to find out the best condition of membrane formation and the optimum operating conditions. Some ultrafiltration membranes made of poly-(vinylidene fluoride), polyacrylonitrile, and hydrolyzed polyacrylonitrile—either commercially available or prepared in our laboratories—were used as supports for the composite membranes. Sodium alginate dense membranes, modified through ion exchange of sodium with multivalent metal ions (such as Al3+, Cr3+, Fe3+, and Mg2+) have also been prepared, and their permselectivities have been tested for the water–ethanol mixture. An interesting stability of the modified membranes in long-term operation is expected.

Permeation behaviour in cellulose triacetate dense membrane during pervaporation separation of methanol/methyl tert-butyl ether mixture

The pervaporation separation of methanol/methyl tert-butyl ether through cellulose triacetate dense membranes has been carried out under different feed compositions, permeation temperatures and temperature cycles to investigate the permeation behaviour of the membrane during pervaporation process. The experimental data indicate that the plasticization effect has a decisive influence on pervaporation flux, permselectivity and permeation activation energy. The results show that the penetrants of different feeds are transported through the membrane by different pathways with the influence of plasticization effect at different temperatures. It has also been observed that plasticization had great effect on the membrane swelling and sorption selectivity. Furthermore, DSC results show that the membranes retain the influence of the plasticization effect after pervaporation separations are tested. © 2000 Society of Chemical Industry

Effect of Diluent Mixture on Porous Structure of Polyphenylene Sulfide via Thermally Induced Phase Separation

Polyphenylene sulfide (PPS) microporous membranes were prepared via the thermally induced phase separation process using diluent mixtures of diphenyl ether (DPE) and diphenyl ketone (DPK). The effects of DPE ratio to DPK in the diluent mixture on the microstructure were investigated. The results showed that the pore morphology of the membranes prepared from the diluent mixture was different from those of fabricated from pure diluents. Moreover, the pore structures of the membranes were changed along with the variation of the diluent composition.

Thermodynamic description of geometrical confinement. Application to the glassy state and the glass transition of amorphous polymers

Based on the analysis of the geometrical confinements and the interactions between neighbor segments in polymeric systems, besides the quasi-lattice model used in Gibbs–DiMarzio entropy theory, an alternative theoretical method was developed here to investigate the thermodynamic aspect of the glassy state and the glass transition of amorphous polymers. A glass forming process through solvent evaporation from amorphous polymer-good solvent system was investigated, and the functional relationship between the glass transition temperature (Tg) and Kauzmann temperature (TK) at which configurational entropy equals zero was derived. The ratio Tg/TK=e1/4 was also deduced as a good approximation for a large amount of glassy polymers. The ratio is consistent with the empirical result Tg/TK=1.30±8.4%, which was proposed by Adam and Gibbs. The theoretical method presented here was also applied to investigate the compositional variation of glass transition temperatures; equations, which are consistent with experiments, were also derived.