Distinguished discriminatory separation of CO2 from its methane-containing gas mixture via PEBAX mixed matrix membrane

Highly selective separation of CO2 from its methane-containing binary gas mixture can be achieved by using Poly(ether-block-amide) (PEBAX) mixed matrix membranes (MMMs).According to FESEM and AFM analyses,silica-based nanoparticles were homogenously integrated within the polymer matrix,facilitating penetration of CO2 through the membrane while acting as barrier for methane gas.The membrane containing 4.6 wt％ fumed silica (FS) (PEBAX/4.6 wt％ FS) exhibits astonishing selectivity results where binary gas mixture of CO2/CH4 was used as feed gas.As detected by gas chromatography,in the permeate side,data showed a significant increase of CO2 permeance,while CH4 transport through the mixed matrix membrane was not detectable.Moreover,PEBAX/4.6 wt％ FS greatly exceeds the Robeson limit.According to data reported on CO2/CH4 gas pair separation in the literature,the results achieved in this work are beyond those data reported in the literature,particularly when PEBAX/4.6 wt％ FS membrane was utilized.     

Effect of copolymer composition on the solubility and diffusivity of water and methanol in a series of polyether amides

Sorption and diffusion of water and methanol in polydimethylsiloxane and a series of PEBAX™ copolymers (polyether block amide copolymers) were measured over a wide range of activities near room temperature. The goal was to identify a membrane material for separation of the hazardous air pollutant methanol from wet air streams in the pulp and paper industry. The PEBAX™ copolymer series used here allows a unique insight into transport of small molecules, because solubilities are virtually constant, while diffusion coefficients vary. This is due to the similar chemical structure, but different chain mobility of the homopolymers. The grade PEBAX™ 2533 is most promising for the separation process due to high solubility and diffusivity. The unwanted simultaneous highly selective separation of methanol and water from the targeted air/vapor streams will be addressed in future work. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1983–1993, 1997     

Investigation of Methane and Carbon Dioxide Gases Permeability Through PEBAX/PEG/ZnO Nanoparticle Mixed Matrix Membrane

This paper presents a new kind of mixed matrix membrane using polyethylene glycol (PEG) as organic filler. In this mix, PEG and ZnO nanoparticles (as inorganic modifier) were added to a PEBAX polymer matrix at different concentration to study their effects on the morphology, permeability and selectivity of the membrane. To characterize the chemical structure of samples FTIR and for morphological characterization, XRD and SEM were employed. The permeability of pure gases CO₂ and CH₄ in PEBAX, and PEBAX/PEG/ZnO with different ZnO and PEG contents were determined by the constant pressure-variable volume method. Also influences of temperature and pressure on permeation properties of these membranes were studied. The results were indicative of an increase in gas permeability and enhancement which for neat PEBAX membrane, CO₂/CH₄ permeability of 44.6 and 2.193 Barrer and selectivity of 20.39 were obtained. The permeability of PEBAX/PEG (40 wt.%)/ZnO (4 wt.%) membrane was enhanced to 94.49 Barrer for CO₂ and 3.933 for CH₄. The selectivity of PEBAX/ZnO(4 wt.%) improved to 31.58 for the CO₂/CH₄ gas pair.     

Syndiotactic polypropylene as potential material for the preparation of porous membranes via thermally induced phase separation (TIPS) process

This work reports the flat sheet membrane preparation from syndiotactic polypropylene (sPP) by thermally induced phase separation (TIPS) process. sPP obtained by polymerization using metallocene catalysts and isotactic polypropylene (iPP) also obtained via metallocene catalysis with similar molecular weight were used. The phase diagrams of sPP and iPP with diphenylether as diluent were obtained. The properties of three representative membranes from sPP and three from iPP, prepared using different PP concentrations were evaluated with respect to membrane pore structure, gas flow, liquid displacement (bubble point), and water permeability. Two selected membranes, one from sPP and one from iPP were analysed with regard to polypropylene bulk morphology (X-ray diffraction) and mechanical properties (tensile strength). Under the same formation conditions, membranes with less inter-connected pores and less porous surface were obtained from sPP compared with iPP. Overall, lower permeabilities had been found for the sPP membranes, which were attributed to the difference in pore morphology. The differences between sPP and iPP were also discussed in terms of different driving forces for liquid-liquid demixing as deduced from the phase diagrams. The X-ray analysis had shown that the sPP membranes had a higher amorphous phase content than that in iPP, and the mechanical test had revealed a pronounced ductile behaviour for sPP samples. These results helped to explain the lower permeabilities of the sPP membranes, and their pressure-dependency.     

有机溶剂纳滤膜的润湿性对渗透和分离性能的影响

有机溶剂纳滤是一种绿色、高效、节能的新型膜分离技术,在回收和处理有机溶剂中具有广泛的应用前景。本文采用浸渍法分别将聚合物聚二甲基硅氧烷（PDMS）、嵌段聚醚酰胺（PEBAX2533）和聚乙烯醇（PVA）与聚砜（PS）超滤基膜复合,制备了3种不同润湿性的聚合物耐溶剂纳滤膜,研究了PDMS/PS、PEBAX/PS和PVA/PS复合膜对甲醇、乙醇、异丙醇、正己烷、正庚烷的渗透性能,考察了3种聚合物膜对伊文思蓝/甲醇溶液的有机溶剂纳滤性能。结果表明,有机溶剂在不同润湿性复合膜的渗透和传递性能与溶剂本身的溶度参数、分子量、黏度和极性等有很密切的相关性,溶剂的分子量、黏度、分子动力学直径越小,在同一极性复合膜中渗透通量越大;对伊文思蓝/甲醇溶液的有机溶剂纳滤分离表明,PDMS/PS和PEBAX/PS复合膜的截留率均可达90%以上,通量分别为 58.0L/(m²·h·MPa)和72.2L/(m²·h·MPa);PVA/PS复合膜的截留率为85.1%左右,通量为57.5L/(m²·h·MPa)。     

复层固液分离膜的制备及性能研究

采用聚丙烯（PP）粉末在非织造布表面烧结的方式来制备多孔质复层固液分离膜,并通过粘合剂及烧结时间2个变量来控制分离膜的孔径、渗透率等性能。结果表明：随着粘合剂的增加,分离膜的渗透性能下降明显,孔径变小;同时热压时间的延长也会影响分离膜各项性能,但比粘合剂影响小。     

Pore size control technique in the spinning of polysulfone hollow fiber ultrafiltration membranes

Conditions for finger-like void formation in polysulfone (PS) ultrafiltration membranes were studied empirically. It was found that both the “mixability parameter” which was obtained in separate titration experiments and the viscosity of coagulants could be used to predict membrane morphology. It was also found that finger-like void layers appeared under the conditions which dope had concentrations quite apart from the phase separation area and which coagulant had both a low mixability parameter and low viscosity.

These factors proved to play a very important role in controlling the pore size of membranes. The results of this study were applied to obtaining pore size variations of PS hollow fiber membranes.     

Development of kevlar‐supported novel polypropylene membranes: Effect of the concentration of the nucleating agent on the properties and performance

Novel membranes were fabricated with woven Kevlar fabric sandwiched between two isotactic polypropylene layers and with various concentrations of adipic acid as the nucleating agent (NA). A thermally induced phase‐separation dip‐coating method was adopted to generate and control the microporosity in the developed membranes. Scanning electron microscopy and atomic force microscopy were used to directly observe and confirm the morphologies and micropores in the fabricated membranes. We observed that with an increase in the concentration of the NA in the fabricated membranes, both the pore density and pore size decreased. The average pore sizes were observed to be 1.686, 0.925, 0.372 μm, respectively, for 0.3, 0.5, and 0.7 pphr concentrations of the NA, respectively. The flux characteristics of the prepared membranes were also tested at various pressures with water, methanol, ethanol, and isopropyl alcohol as solvents in a custom‐made filtration cell. The results obtained indicate the dependence of the flux on the type of solvent, pressure, and membrane. The flux for the solvents was observed to decrease with increasing concentrations of NA in the prepared membranes and was attributed to the decrease in the pore density and pore size. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2821–2831, 2013     

疏水性聚丙烯中空纤维膜中n-甲酰吗啉膜吸收含苯废气过程模拟

以疏水性聚丙烯中空纤维膜为气液膜接触器,n-甲酰吗啉水溶液为吸收剂,研究了膜气体吸收工艺分离C6H6/N2的传质过程. 在非润湿条件下,建立了膜气体吸收C6H6传质微分模型,模拟了C6H6在疏水性聚丙烯中空纤维膜管程及膜孔内的传质过程,并对C6H6的吸收速率进行预测. 结果表明,在实验条件下,膜气体吸收C6H6的速率为(0.89~6.13)′10-2 mg/(m2×s),微分模型对吸收速率预测的平均误差为1.9%,能准确描述中空纤维膜吸收C6H6的过程.     

Enhanced performances of polypropylene membranes by molecular layer deposition of polyimide

Molecular layer deposition(MLD) for the deposition of polyimide(PI) at low temperature of 110 °C has been firstly introduced into the field of membrane separation. With the optimized MLD deposition parameters, such low deposition temperature has successfully expanded the application of MLD for the surface modification of polymeric materials. Globular PI particulates grow on both the free surfaces as well as the pore walls of the polypropylene(PP) membranes as isolated islands during progressive precursor exposures. The PI-deposited PP membranes exhibit synergistically improved performances in various aspects. Evidently improved surface hydrophilicity and permeation performance(30%) have been achieved via the MLD deposition of polyimide films. The overall separation efficiency maintained higher than 85% even after 250 cycles of MLD deposition. More importantly, the thermal stability has been improved and the integrity of the porous structure for PI-deposited PP membranes has been well preserved even after harsh treatment, which ensures its potential application in industries.     

聚丙烯微孔膜的研究进展

介绍了由熔融纺丝-冷却拉伸法和热致相分离法制备聚丙烯微孔膜的原理和过程。对当前膜研究领域的热点即膜的亲水化改性研究进行了重点评述,包括暂时性改性和永久性改性。阐述了各种改性方法的特点,着重讨论了亲水化改性对膜性能如膜的微孔孔径、孔隙率、透水量等的影响,强调膜表面亲水性的提高可改善膜的耐生物污染性。指出聚丙烯微孔膜的应用领域和发展前景。     

Catalytic Dehydrogenation of Cyclohexane Using Coated Silica Oxide Ceramic Membranes

Experiments were conducted to characterize US Filter ceramic membranes used in the catalytic dehydrogenation of cyclohexane to benzene. The reaction yield was studied as a function of membrane pore size for 50, 100, 200, and 2000 Å membranes. The effect on reaction yield, membrane permeability, and membrane selectivity of altering pore size by addition of successive thin film layers (silica oxide particles in an iron(III) supported solution) to the membrane surfaces was the primary focus of the study. The membranes were also characterized with a nonreactive He/N₂ separation to determine the effect of successive thin film layers on the extent of Knudsen diffusion as the transport mechanism. This characterization demonstrated that Knudsen behavior could be obtained in a large pore diameter membrane by adding thin film layers to the surface. Reaction experiments showed a 300% increase in yield from that which was obtained in an impermeable reactor under similar conditions. Most significantly, the coated membranes operating in the Knudsen regime rendered a higher reaction yield than the uncoated 50 Å membrane, whose transport mechanism was also Knudsen dominated. This phenomena can be explained by favorable surface effects between the thin film material and the reaction species. Thus, it was concluded, that a thin film (added to the surface membrane), which operates in the Knudsen regime and creates favorable surface effects to enhance membrane selectivity, can shift reaction equilibrium to a higher product yield than a membrane which only exhibits Knudsen diffusion.     

稀释剂对TIPS法等规聚丙烯中空纤维微孔膜孔径及其连通性的影响

热致相分离（TIPS）法制备等规聚丙烯（iPP）中空纤维微孔膜,邻苯二甲酸二丁酯（DBP）与邻苯二甲酸二辛酯（DOP）的混合溶剂作为制膜稀释剂。干/湿氮气流量法测定了α（稀释剂中DBP的质量分数）和β（铸膜液中聚合物的质量分数）对膜样品的平均孔径及其分布的影响,并采用膜孔曲折因子定量表达膜孔连通性。发现全部膜样品均体现窄孔径分布特征。对于相同的β, α增加导致平均孔径及膜孔连通性下降。α=0.20时,β增加,膜的平均孔径先增加后降低,膜孔曲折因子稍下降; α=0.35或0.50时,β增加,膜的平均孔径降低,膜孔曲折因子下降。膜孔连通性体现了膜内部的拓扑结构,共溶剂组成和铸膜液固含量能够调节iPP中空纤维微孔膜的孔径及其连通性。     

Nanolayer enhancement of biaxially oriented polypropylene film for increased gas barrier

An order of magnitude improvement in the oxygen barrier of biaxially oriented polypropylene (BOPP) films was achieved using a layer-multiplying, forced assembly process. The improvement was achieved without sacrificing clarity and toughness of the films. Sheets with 33 alternating layers of polypropylene (PP) (17 layers) and poly(?-caprolactone) (PCL) (16 layers) were coextruded using layer-multiplication and two thick PP skins were added to the multilayered core as the last step in the continuous coextrusion process. The sheets were subsequently biaxially oriented to draw ratios from 4 × 4 to 6 × 6. Biaxial orientation at elevated temperature reduced the thickness of the melted PCL layers from the microscale to the nanoscale, which created 2-dimensional confinement for subsequent crystallization of the PCL layers. It was anticipated that the PCL layers would recrystallize as highly oriented, in-plane lamellae that would resemble single crystals. However, the PCL lamellae were oriented perpendicular to the film surface, which actually facilitated oxygen permeation through the PCL layers and increased the oxygen permeability of the oriented films. Crystallization as on-edge lamellae was attributed to nucleation by the polypropylene surface. However, the surface nucleation was prevented by inserting buffer polystyrene (PS) layers in between the PCL and PP layers. In this case, the PCL lamellae were oriented in-plane. With the very high aspect ratio lamellar crystals oriented perpendicular to the flux direction, the permeation pathway of oxygen became very tortuous and the oxygen barrier was significantly improved.     

Water recovery from flue gas using polyether block amide 2533/sulfonated poly(ether ether ketone) composite membrane

Recycling water from flue gas of coal-fired power plants is of great significance to save energy and water resources and reduce environmental pollution. In the present work, two potential polymers (polyether block amide 2533(PEBAX 2533) and sulfonated poly(ether ether ketone) (SPEEK)) were investigated and showed high water vapor permeability and selectivity, respectively. Combined with the advantages of the two materials, a novel PEBAX 2533/SPEEK composite membrane with an ultra-thin SPEEK selection layer on the outer surface of the high permeable PEBAX 2533 layer was prepared by dip coating. The composite membranes were assembled into a membrane capsule module and tested directly in artificial and real flue gas. The condensed water vapor fluxes were 1006.9 g/m².h in artificial flue gas and 600–900 g/m².h on average in real flue gas during a period of 30 days, exhibiting good water vapor permeability and durability in real flue gas.     

Effect of stretching on continuous oil/water separation performance of polypropylene hollow fiber membrane

In this work, polypropylene (PP) hollow fiber membranes were fabricated by thermal-induced phase separation method. The influence of cold-stretched and hot-stretched treatment on the morphology and permeability of the PP hollow fiber membranes was investigated. The results showed that there were cracks and crystalline particulate structures on the outer and inner surfaces of the stretched PP hollow fiber membranes, which were not isolated but linked together through fiber-like connections. Compared to the original PP hollow fiber membrane, the mean pore sizes, the porosities, the hydrophobicity and water entry pressure of the stretched PP hollow fiber membranes improved significantly. When applied in conjunction with a vacuum system, the PP hollow fiber membranes could continuously remove oils from water surface, and separate surfactant-free and surfactant-stabilized water-in-oil emulsions, as well. The initial kerosene fluxes of the hot-stretched PP hollow fiber membrane were higher than that of the membranes prepared from original PP hollow fibers or cold-stretched PP hollow fibers. The permeate fluxes of the hot-stretched PP hollow fiber membrane for all different emulsion separations were higher than those of the original PP hollow fiber membrane. There could be seen no emulsion droplet in the optical micrographs after separation, indicating that the water-in-oil emulsions were effectively separated in one-step method.     

pH-driven phase separation: Simple routes for fabricating porous TiO2 film with superhydrophilic and anti-fog properties

A series of TiO₂ surfaces with different pore sizes were easily fabricated via pH-driven phase separation in the sol–gel under template-free conditions. The approach is to obtain TiO₂ films with well-defined macropores by utilizing neutralization reaction from acid–base combination. The tuning of solution pH from neutralization could reduce the miscibility of solvent and solute and enable the formation of phase separation. The influence of preparation conditions (ratios of acid-to-base, aging time and solvents) on the pore formation was investigated. The porous TiO₂ films prepared through pH-driven phase separation exhibit promising super hydrophilic characteristic anti-fog property.     

Membrane Gas-Solvent Contactor Pilot Plant Trials of CO2 Absorption from Flue Gas

Membrane gas-solvent contactors have received much attention for CO₂ absorption, as the approach incorporates advantages from both solvent absorption and membrane gas separation. This study reports on pilot plant trials of three membrane contactors for the separation of CO₂ from flue gas. The contactors were porous polypropylene (PP), porous polytetrafluoroethylene (PTFE), and non-porous polydimethylsiloxane (PDMS), with the solvent PuraTreatTM F^TM. To enable performance comparison, laboratory measurements based on a gas mixture of 10% CO₂ in N₂ were also undertaken on the same contactor–solvent systems. It was found that the PP contactor experienced significant pore wetting in both laboratory and pilot plant studies. In contrast, the PTFE contactor experienced only minor pore wetting in the laboratory. However, in the pilot plant trial of the PTFE contactor extensive pore wetting was observed, and the overall mass transfer coefficient measured was comparable with the PP contactor. The non-porous PDMS contactor had an overall mass transfer coefficient two orders of magnitude less than the PP contactor, due to the greater mass transfer resistance of the polymeric film. However, the non-porous membrane does not experience pore wetting, which resulted in the overall mass transfer coefficient being similar for both laboratory and pilot plant measurements.     

膜孔形态结构图象分析研究——Ⅱ.膜孔结构定量表征

本文通过对多种微孔滤膜和超滤膜进行电镜照像及计算机图象分析,定义和得出了下列定量表征膜孔形态结构的参数:几何孔径分布、有效孔径分布、孔形不圆度、孔隙率以及孔形的分形(Fractal)维数。这些参数有利于成膜条件—膜孔结构—膜分离性能三者之间关系的研究,有利于膜成孔机理的研究,从而促进研制性能更好的膜。     

Effect of processing on the crystalline orientation, morphology, and mechanical properties of polypropylene cast films and microporous membrane formation

Cast films of a high molecular weight linear polypropylene (L-PP) were prepared by extrusion followed by stretching using a chill roll. An air knife was employed to supply air to the film surface right at the exit of the die. The effects of air cooling conditions, chill roll temperature, and draw ratio on the crystalline orientation, morphology, mechanical and tear properties of the PP cast films were investigated. The crystallinity and crystal size distribution of the films were studied using differential scanning calorimetry (DSC). It was found that air blowing on the films contributed significantly to the uniformity of the lamellar structure. The orientation of crystalline and amorphous phases was measured using wide angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR). The amount of lamellae formation and long period spacing were obtained via small angle X-ray scattering (SAXS). The results showed that air cooling and the cast roll temperature have a crucial role on the orientation and amount of lamellae formation of the cast films, which was also confirmed from scanning electron microscopy (SEM) images of the films. Tensile properties and tear resistance of the cast films in machine and transverse directions (MD and TD, respectively) were evaluated. Significant increases of the Young modulus, yield stress, tensile strength, and tensile toughness along MD and drastic decreases of elongation at break along TD were observed for films subjected to air blowing. Morphological pictograms are proposed to represent the molecular structure of the films obtained without and upon applying air cooling for different chill roll temperatures. Finally, microporous membranes were prepared from annealed and stretched films to illustrate the effect of the PP cast film microstructure on the morphology and permeability of membranes. The observations of SEM surface images and water vapor transmission rate of the membranes showed higher pore density, uniform pore size, and superior permeability for the ones obtained from the precursor films prepared under controlled air cooling.