SELECTIVE SEPARATION OF WATER-ETHANOL MIXTURE THROUGH COPOLYMERIC MEMBRANES. I . ACRYLONITRILE AND MALEIC ANHYDRIDE COPOLYMERIC MEMBRANES

Acrylonitrile (AN) and maleic anhydride (MA) copolymer has been synthesized by radical polymerization using ammonium persulfate and sodium bisulfite as initiator. The pervaporation properties of the copolymeric membranes prepared have been investigated for the first time. The dependences of pervaporation characteristics on copolymer composition , feed concentration and operating temperature have been studied. In order to improve the separation properties of the copolymeric membranes, the membranes were hydrolyzed with 10 wt% sodium hydroxide or potassium hydroxide aqueous solution. The hydrolyzed membranes containing more than 0. 069 MA mol fraction showed higher tensile strength and separation properties than the original membranes.     

ORGANIC PERMSELECTIVE PERVAPORATION CHARACTERISTICS OF POLY(SILYLPROPYNE) AND COPOLYMER DENSE MEMBRANES

An investigation into the organic permselective separation through poly [1-trimethylsilyl-1-propyne] (PTMSP) and (1-trimethylsily1)-1-(1-penta-methyl-disilyl)-1-propyne copoly-mer (TMSP-PMDSP) dense membranes was made to gain an insight into the effect ofthe chemical structure of membrane materials on pervaporation (PV) characteristics. Theresults show that the copolymer has a higher separation factor α_(org/water) but with a rela-tively lower value of flux J_t (g/m~2·h) than pure PTMSP. This phenomenon may be at-tributed to the introduction of side chain with large bulk volume in copolymer, whichbrought about a decrease of excess free volume and the improvement of diffesion selectivityto some extent. With the same molar concentration of organic liquids in feed, THF/watersolutions have the highest value of α_(org/water) as well as J_t in comparison with ethanol/water,iso-propanol/water and THF/water mixtures.     

PERVAPORATION SEPARATION OF WATER-ACETIC ACID MIXTURES THROUGH AN-co-AA MEMBRANES TREATED WITH RARE EARTH METAL IONS

Pervaporation separation of water-acetic acid mixtures through Poly (AN-co-AA)membranes and rare earth metal ions treated Poly(AN-co-AA)membranes was investigatedfor the first time. The results showed that the treatment with rare earth metal ions couldgreatly improve the characteristics of the separation of water-acetic acid mixtures.     

Pervaporation separation of ethanol/water mixtures with chlorosilane modified silicalite-1/PDMS hybrid membranes

<正>Ultra-fine silicalite-1 particles were modified with four kinds of chlorosilanes(dodecyltrichlorosilane, octyltrichlorosilane,hexadecyltrichlorosilane and octadecyltrichlorosilane) and characterized by FI-IR,TGA,contact angle measurements and BET analysis.It was found that the surface hydrophobicity of silicalite-1 particles was improved significantly as the alkyl group was strongly bonded to the particle surface.Modified silicalite-1 particles were incorporated into PDMS(poly(dimethylsiloxanediol)) membranes,which were applied for the pervaporation separation of ethanol/water mixtures.The effect of surface properties,zeolite loading and operation conditions on pervaporation performance of the membranes was investigated.The separation factor of PDMS membranes filled with modified silicalite-1 increased considerably compared with that filled with unmodified ones,and the total flux decreased with increasing zeolite loading. The solution and diffusion selectivity of hybrid membranes were also measured to explain the pervaporation properties of silicalite-1 filled PDMS membranes.It was found that modification of silicalite-1 with dodecyltrichlorosilane effectively improved the solution and diffusion selectivity of silicalite-1 filled PDMS membranes with high zeolite loading.This may be attributed to the high surface hydrophobicity of modified silicalite-1 and its good integration with PDMS membranes.Both the high separation factor and solution selectivity indicated that modification of silicalite-1 with chlorosilanes was an effective method to improve the selectivity of silicalite-1/PDMS hybrid membranes for ethanol.     

PREPARATION OF POLYVINYLIDENE FLUORIDE／POLYVINYL DIMETHYLSILOXANE COMPOSITE HOLLOW FIBER MEMBRANES AND THEIR SEPARATION PROPERTIES

Microporous polyvinylidene fluoride (PVDF) hollow fibre membranes were spun using the dry-wet phase inversion method. By means of dip-coating technique, a uniform coating with thickness of around 5-12μm of polyvinyl dimethylsiloxane (PVDMS) was formed on the surface of porous PVDF hollow fibers. The structural parameters of PVDF substrate membrane were estimated by gas permeation test. Using N2/O2 as the medium, the separation properties of PVDMS-PVDF composite hollow fiber membranes were also evaluated experimentally. The experimental data of both permeability and selectivity are in good agreement with the theoretical results predicted by the presented pore-distribution model, in order to obtain the compact composite membrane free of defects by the dip-coating technique, the thickness of PVDMS skin must be higher than 5μm.     

Catalytic Membranes and Membrane Reactors： An Integrated Approach to Catalytic Process with a High Efficiency and a Low Environmental Impact

The design of new heterogeneous photooxygenation systems able to employ visible light,oxygen,mild temperatures,and solvent with a low environmental impact has been investigated. In particular,the heterogenization of decatungstate (W10O4-32),a polyoxometalate with photocatalytic activity in oxidation reactions,has been carried out in polymeric membranes of polyvinylidenefluoride. The polymeric catalytic membranes prepared by phase inversion technique have been successfully applied in the aerobic mineralization of phenol in water,which was used as an example of organic pollutant. In order to evaluate the effect of the polymeric environment on the overall catalyst behavior,we have also heterogenized the decatungstate (opportunely functionalized) in perfluorinated membrane made of Hyflon. The photocatalytic composite membranes are characterized by different and tuneable properties depending on the nature of the polymeric micro-environment,in which the catalyst is confined. Moreover,the selective separation function of the membrane results in enhanced performance in comparison with homogeneous reactions.     

Polymerizable ionic liquid copolymer P(MMA-co-BVIm-Br) and its effect on the surface wettability of PVDF blend membranes

Polymerizable ionic liquid copolymer P(MMA-co-BVIm-Br) was synthesized by radical polymerization technique, and characterized by Fourier transform infrared spectrometry(FTIR), 1H Nuclear magnetic resonance(1H-NMR) and gel permeation chromatography(GPC). The resulting copolymer was used to prepare poly(vinylidene fluoride)(PVDF) blend membranes via a phase inversion method. The effects of the copolymer on the polymorphism, surface wettability and zeta potential(ζ) of the blend membranes were investigated by ATR-FTIR, contact angle instrument and zeta potential analyzer. Scanning electron microscopy(SEM and SEM-EDS) was also applied to investigate the morphology and the surface element changes of the fabricated membranes. The results indicated that P(MMA-co-BVIm-Br) copolymer existed on the surface of the membrane which made the blend membrane have a positive surface during the experimental p H range. The copolymer was also in favor of the formation of β crystal phase in PVDF membranes. The contact angle experiment indicated that P(MMA-co-BVIm-Br) copolymer could switch the wettability of the blend membranes from hydrophilic to hydrophobic by exchanging Br-anion with PF-6. Compared with pure PVDF membranes, the water flux and water recovery flux of the blend membranes were enhanced obviously. The results from the flux recovery ratio(FR) and total fouling ratio(Rt) all suggested that the blend membranes had good anti-fouling properties.     

Studies on Pervaporation Separation of Ethanol/Water Mixtures with Membranes of Polypropylene Sulfonate Salts

Sulfonated polypropylene membranes loaded with different kinds of counter-ions were prepared by heterogeneous chiorosulfonation reaction of polypropylene membrane followed by hydrolysis and ion-exchange reaction. The membranes obtained were used for selective separation of ethanol/water mixtures by pervaporation. The effects of counter-ion species, ion-exchange capacity, solution composition, thickness of membrane and temperature on the separation behavior of the membranes were investigated. Microstructure and morphology of the membranes were examined by X-ray and SEM as well.     

INFLUENCE OF ALCOHOL-BASED NONSOLVENTS ON THE FORMATION AND MORPHOLOGY OF PVDF MEMBRANES IN PHASE INVERSION PROCESS

Through the preparation of PVDF membranes using various nonsolvent coagulation baths following the phase inversion process, the influence of alcohol-based nonsolvents on the formation and structure of PVDF membranes were investigated. The light scattering and light transmission measurements were used to characterize the equilibrium phase diagram and the gelation speed, respectively. The locations of the crystallization-induced gelation boundaries for various systems and precipitation processes were explained from the corresponding thermodynamic and kinetic parameters. It was found that the better affinity between alcohol-based nonsolvents and DMAc solvent caused the gelation boundaries further away from the PVDF-DMAc axis with the coagulation bath varying from water, methanol, ethanol to iso-propanol. Due to the lower exchange rate of DMAc and alcohols, the delayed demixing took place for the membrane-forming using alcohols as baths, and the delayed time became longer when the coagulation bath was changed from methanol, ethanol to iso-propanol. The characterization results of membranes indicate that the influence of nonsolvents on the phase diagram and the precipitation process are in agreement with those on the membrane morphology. The better thermodynamic stability and a low exchange diffusion rate of PVDF/DMAc/alcohols favor the liquid-solid phase separation in gelation process, and therefore yield the membranes with a porous upper surface, a particular bottom surface and symmetrical structure.     

Pervaporation for separating benzene/cyclohexane mixture by P(AA-MA) copolymer membranes

P(AA-MA)copolymers composed of acrylic acid and methyl acrylate with different molecular weights and sequence structures were synthesized by combination of ATRP and selective hydrolysis.These copolymers were used as membrane materials to separate benzene/cyclohexane mixture by pervaporation.The effects of molecular weight and sequence structure of the copolymers on the pervaporation performance were investigated in detail.For the random copolymers,the permeate flux decreased rapidly with the increasing of molecular weight.The separation factor was also influenced by the molecular weight,which was changed from no selectivity to cyclohexane selectivity with increasing the molecular weight.Contrarily,the block copolymer membrane showed good benzene selectivity with separation factor of 4.3 and permeate flux of 157 g/(m~2h)to 50 wt%benzene/cyclohexane mixture.     

Preparation of PFSA/PSf hollow fiber composite membranes with recovered PFSA for the pervaporation separation of EtOH/H_2O

Perfluorosulfonic acid/Polysulfone(PFSA/PSf) hollow fiber composite membranes have been prepared by dip-coating method using PSf ultrafiltration(UF) membrane as substrate with recovered PFSA.The composite membranes were applied to the pervaporation separation of 95% ethanol(EtOH)/H2O mixture.SEM images show that the thickness of the PFSA skin layer of the composite membranes is about 2 μm,much thinner than those of other PFSA composite membranes revealed in the literatures.Effects of annealing temperature,c...     

TEMPERATURE DEPENDENCE OF AIR SEPARATION OF LIQUID CRYSTALLINE TRIHEPTYL CELLULOSE/ETHYL CELLULOSE MEMBRANES

Triheptyl cellulose/ethyl cellulose(3/97)binary blend membranes were preparedfrom tetrahydrofuran,chloroform and dichloromethane solutions and their air separation capabit-ities were studied at different temperatures.With increasing temperature from 25 to 85℃,theflux QOEA of O_2-enriched air(OEA),O_2 permselectivity and the O_2 concentration Yo_2 in the OEA allincrease.The membranes show a unique trend in their Yo_2～QOEA relationship,that is,the airseparation capability increases simultaneously with the OEA permeation capability.The magnitudesof QOEA and Yo_2 for 17μm-thick membrane after the testg time of 36hours at 70℃ are 5×10~(-4)cm~3(STP)/s·cm~2 and 37.6%,respectively.The air separation capability depends slightly on membraneforming solvents.     

DETERMINATION OF PERMEATION PROPERTIES OF GAS THROUGH POLYMER MEMBRANE BY GAS CHROMATOGRAPHY

An apparatus constructed for measuring permeation properties of polymer membranes using a mixture of gases is described. A gas chromatographic system was applied to determine the individual transport characteristics of component gases without a vacuum line. This paper also discusses some experimental factors effecting the precision of measurement. The results show that there is a linear relationship between the permeation time and the volume of the gas permeated through the membrane within certain permeation period, which depends on the permeation rate (from 10~(-4) to 10~(-7) cm~3 (STP)/cm~2. sec. cmHg) of the membrane. The reproducibility has been found to be good with a relative standard deviation of 3.5%. This method is more sensitive, considerably faster and more convenient for determining both the permeability coefficient and the separation factor of a polymer membrane from a chromat ogram using mixed penetrant gases.     

催化膜和催化膜反应器: 整合的高效和环保催化过程

 The design of new heterogeneous photooxygenation systems able to employ visible light, oxygen, mild temperatures, and solvent with a low environmental impact has been investigated. In particular, the heterogenization of decatungstate (W10O4-32), a polyoxometalate with photocatalytic activity in oxidation reactions, has been carried out in polymeric membranes of polyvinylidenefluoride. The polymeric catalytic membranes prepared by phase inversion technique have been successfully applied in the aerobic mineralization of phenol in water, which was used as an example of organic pollutant. In order to evaluate the effect of the polymeric environment on the overall catalyst behavior, we have also heterogenized the decatungstate (opportunely functionalized) in perfluorinated membrane made of Hyflon. The photocatalytic composite membranes are characterized by different and tuneable properties depending on the nature of the polymeric micro-environment, in which the catalyst is confined. Moreover, the selective separation function of the membrane results in enhanced performance in comparison with homogeneous reactions.     

STUDIES ON RESPONSE CHARACTERISTICS OF DRUG ION-SELECTIVE ELECTRODES (Ⅱ)——SULPHA-DRUG SENSITIVE ELECTRODES USING QUATERNARY PHOSPHONIUM AND ARSONIUM COMPOUNDS

Ion-pair complexes of sulphonamide derivatives with quaternary phosphonium and quaternary arsonium have been synthesized and their electrode performances studied. It has been found that the electrode functions depend mainly on the site cation rather than on the anionic species and deteriorate in the order of cetyhrioctylammonium>cetyltriphenylphosphonium> cetyhriphenylarsonium. The electrode selectivity for different sulpha-drugs decreases in the order of sulphathiazole>sulphamethoxazole>sulphadimethoxine, sulphadoxine>sulphacetamide>sulphadiazine>sulphanilamide. Selectivity coefficients depend not only on the molecular connectivity index χ, but also on the electronic charge at the ionizing amide nitrogen atom σ and pK, according to the following formula: logK_(ij)=aχ+bσ—CpK_a—d. The quaternary phosphonium type electrodes have been suggested for use in the potentiometric determinations of sulpha-drugs.     

MORPHOLOGIES AND GAS SEPARATION PROPERTIES OF MELT-SPUN ASYMMETRIC POLY(4-METHYL-1-PENTENE)HOLLOW FIBER MEMBRANES*

Poly(4-methyl-1-pentene) (PMP) hollow fiber membranes were prepared by the melt-spun and cold-stretch(MSCS) method. Scanning electronic microscopy (SEM) was used to characterize the section and surface structures of themembranes with special asymmetric structure. The preliminary results of gas permeation measurements indicated that the resultant hollow fiber membranes have the potential ability for oxygen/nitrogen separation.     

PREPARATION OF EVOH MICROPOROUS MEMBRANES via THERMALLY INDUCED PHASE SEPARATION USING BINARY SOLVENTS

Microporous ethylene-vinyl alcohol copolymer （EVOH） flat membranes and hollow-fiber membranes with 38 mol% ethylene content were prepared via thermally induced phase separation （TIPS） using the mixture of 1,4-butanediol and poly（ethylene glycol）（PEG400） as diluents. Effects of the ratio of 1,4-butanediol to PEG400 on the phase diagrams, phase separation mechanism and membrane morphology were studied by small angle light scattering （SALS） measurements, differential scanning calorimetry （DSC）, and scanning ele~：tron microscopy （SEM）. It was found that by varying the composition of the binary solvent, the phase diagrams and membrane morphology can be controlled successfully. Moreover, the phase diagrams showed that broader regions of Liquid-Liquid （L-L） phase separation were obtained, as well as closer distances between L-L phase separation lines and Solid-Liquid （S-L） phase separation lines, Interconnected structures observed both in the flat membrane and hollow fiber membrane consist with the above results.     

Facile preparation of compact LTA molecular sieve membranes on polyethyleneimine modified substrates

A facile preparation strategy was proposed for preparation of compact zeolite LTA membranes on polyethyleneimine(PEI) modified substrates without seeding.Through the functionalization of substrates by using PEI,compact LTA membranes can be formed on various kinds of substrates.A well-intergrown and phase-pure LTA membrane with a thickness of about 3.0 μm is successfully prepared on the a-Al_2 O_3 disk after crystallization for 24 h at 60℃.Besides LTA membrane,wellintergrown zeolite FAU membranes can also be formed on PEI-modified a-Al_2 O_3 substrates,suggesting the universality of this strategy.The zeolite LTA membranes synthesized on PEI-modified a-Al_2 O_3 tubes we re evaluated fo r the separation of alcohols/water mixture through pervaporation.The as-synthesized zeolite LTA membranes display high pervaporation performances.For the separation of 10 wt% isopropanol/water solution at 90℃,a high separation factor of44991 and a water flux of 1.73 kg m ~2 h ~1 are achieved.     

Polyvinyl acetate/poly(amide-12-b-ethylene oxide) blend membranes for carbon dioxide separation

In this paper,blend membranes from polyvinyl acetate(PVAc)and block copolymer poly(amide-12-b-ethylene oxide)(Pebax1074)are prepared by solution casting and solvent evaporation method.Although they are homogeneous on a macro-scale,the observations from DSC and SEM indicate micro-phase separation for PVAc/Pebax1074 blend membranes.With the increase of Pebax1074 content,gas permeabilities of CO2,H2,N2and CH4all increase greatly.PVAc/Pebax1074 blend membranes with high PVAc content are appropriate for CO2/CH4separation.The temperature dependence of gas permeability is divided into rubbery region and glassy region.The activation energies of permeation in rubbery region are smaller than those in glassy region,and they all decrease with increasing Pebax1074 content.For N2,H2and CH4,their gas permeation properties are mainly influenced by the dual-mode sorption and hydrostatic pressure effect.But for CO2,its permeability increases with the increase of pressure due to CO2-induced plasticization effect,which is more obvious for PVAc/Pebax1074 blend membranes with high PVAc content.     

Preparation of high density polyethylene/polyethylene-block-poly(ethylene glycol) copolymer blend porous membranes via thermally induced phase separation process and their properties

<正>High density polyethylene(HDPE)/polyethylene-block-poly(ethylene glycol)(PE-b-PEG) blend porous membranes were prepared via thermally induced phase separation(TIPS) process using diphenyl ether(DPE) as diluent.The phase diagrams of HDPE/PE-b-PEG/DPE systems were determined by optical microscopy and differential scanning calorimetry(DSC).By varying the content of PE-b-PEG,the effects of PE-b-PEG copolymer on morphology and crystalline structure of membranes were studied by scanning electron microscopy(SEM) and wide angle X-ray diffraction(WAXD). The chemical compositions of whole membranes and surface layers were characterized by elementary analysis,Fourier transform infrared spectroscopy-attenuated total reflection(FTIR-ATR) and X-ray photoelectron spectroscopy(XPS).Water contact angle,static protein adsorption and water flux experiments were used to evaluate the hydrophilicity,antifouling and water permeation properties of the membranes.It was found that the addition of PE-b-PEG increased the pore size of the obtained blend membranes.In the investigated range of PE-b-PEG content,the PEG blocks could not aggregate into obviously separated domains in membrane matrix.More importantly,PE-b-PEG could not only be retained stably in the membrane matrix during membrane formation,but also enrich at the membrane surface layer.Such stability and surface enrichment of PE-b-PEG endowed the blend membranes with improved hydrophilicity,protein absorption resistance and water permeation properties,which would be substantially beneficial to HDPE membranes for water treatment application.