The permeation resistance of interface and the directional dependence of permeation in plasma-grafted composite membranes

Composite membranes were prepared by grafting plasma-polymerized films onto the surface of nonporous poly (dimethylsiloxane) films. Gas permeabilities of the composite membranes were measured at 35°C, 1 atm for N₂, 0₂, CO₂ and CH₄. The permeation properties of the composite membrane was analyzed using the series resistance model. There was a great interfacial resistance to CH₄ permeation through the composite membrane. The interfacial resistance was negligible for the other gases. The interfacial resistance seems to be a result of an interfacial layer caused by the interaction between the bulk two layers. For CH₄ gas, the permeation rate through the composite membrane was affected by the direction of flow. The directional dependence was negligible for the other gases.     

Gas permeability of polyacetylenes carrying substituents

The gas permeabilities of three polyacetylene films, prepared from poly[1-(trimethylsilyl)-1-propyne], poly(tert-butylacetylene), and poly(1-chloro-2-phenylacetylene), were studied. Although depending on conditions of polymerization and membrane preparation, typical permeability coefficients P of the polymers to oxygen and nitrogen at 25°C were as follows: poly[1-(trimethylsilyl)-1-propyne], P_O2 = 40 × 10^?8, P_Nr2 = 20 × 10^?8; poly(tert-butylacetylene), P_O2 = 3.0 × 10^?8, P_N2 = 1.0 × 10^?8; poly(1-chloro-2-phenylacetylene), P_O2 = 9.4 × 10^?10, P_N2 = 2.0 × 10^?10 cm³(STP) · cm/(cm² · s · cm Hg). Thus P_O2 of a poly[1-(trimethylsilyl)-1-propyne] film is the largest among those ever known, and the values of poly(tert-butylacetylene) and poly(1-chloro-2-phenylacetylene) films are also fairly large. Influences of polymer structure, measuring temperature, and so forth on the P_O2 and P_N2 of these polyacetylene films were studied. The possibility of applying these films to oxygen enrichment of air are being discussed.     

Exploring the effect of organic–inorganic additives loaded on modified polyethersulfone membranes

In this work, a novel modified polyethersulfone (PES) membrane was made by blending PES with organic biomolecules which were N¹,N⁴-bis(4-sulfamoylphenyl)terephthalamide (SF), and N¹, N⁴-bis[4-(N-(5-methylisoxazol-3-yl)sulfamoyl)phenyl]terephthalamide (SZ) to afford PES-SF and PES-SZ membranes. Antifouling properties of these modified membranes were examined against different types of bacteria and a fungus as well as by measuring the contact angle. The results showed the addition of these organic additives to PES membranes did not improve the hydrophilicity and exhibit any microbial activity. Thus, Cu₂O nanoparticles were used with different concentrations to afford PES-SF-Cu₂O and PES-SZ-Cu₂O nanocomposites membranes. The results showed when Cu₂O nanoparticles (3 wt %) was added to PES-SF₃ and PES-SZ₃ membranes, both membranes showed the best hydrophilicity with 67° for PES-SF₃-Cu₂O membrane and 77° for PES-SZ₃-Cu₂O membranes. PES-SF₃-Cu₂O and PES-SZ₃-Cu₂O membranes showed antibacterial against Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus. To evaluate the anticoagulant activity of the PES-SF and PES-SZ membranes, the clotting times using the activated partial thromboplastin time (APTT) and prothrombin time (PT) were measured. The results showed PT level was prolonged for the pure PES membrane with 13 s and for PES-SF₁ membrane with 12.4 s while the PES-SZ₁ membrane showed no difference from the control (pure plasma). Contrary to the PT factor, APTT level of the PES-SF membrane showed the longest time with 43 s. The results of APPT and PT seemed somewhat satisfactory for the PES-SF while the PES-SZ membrane did not show any difference from the control sample. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47686.     

Plasma deposition modified nylon 4 membranes for hemodialysis

The purpose of this research is to prepare high solute permeability membranes for hemodialysis by plasma depositing hydrophilic monomers onto chemically treated or O₂ plasma etched Nylon 4 substrate. The factors that affect the performances of membranes, such as deposition conditions and chemical or plasma etching conditions, were studied. The monomers used in this study were 1-vinyl-2-pyrrolidone (VP), 2-Hydroxyethyl methacrylate (HEMA), and Methyl methacrylate (MMA). The permeabilities of NaCl, urea, vitamin B₁₂, and albumin were measured, as were the water content, hydration, diffusivity, partition coefficient, and protein adsorption ratio of fibrinogen to albumin by membrane surface of plasma deposited membranes. The permeabilities of NaCl, urea, vitamin B₁₂, and albumin of HEMA 5 w-1 h plasma deposited onto chemical treated Nylon 4 membranes were 2.896 ± 0.192, 3.301 ± 0.325, 0.010 ± 0.007, and 0.000 x 10^?5 cm²/min, respectively. The mole ratio of adsorbed fibrinogen to adsorbed albumin (F/A) is 0.26 ± 0.05, which is much lower than that of the pure Nylon 4 membrane (0.94 ± 0.06) and the Gambro® membrane (0.90 ± 0.15). The HEMA deposited membrane possesses the highest feasibility as hemodialysis material among those plasma deposited membranes considered.     

Pure gas and vapor permeation properties of poly[1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene] (PTMSDPA) and its desilylated analog, poly[diphenylacetylene] (PDPA)

The permeabilities of He, H₂, N₂, O₂, CO₂, CH₄, C₂H₆, C₃H₈, and n-C₄H₁₀ in poly[1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene] (PTMSDPA) and poly[diphenylacetylene] (PDPA) are presented and compared to those of poly(1-trimethylsilyl-1-propyne) (PTMSP), poly(1-phenyl-1-propyne) (PPP), and polysulfone. Like PTMSP, PTMSDPA, a disubstituted glassy acetylene-based polymer, exhibits higher permeabilities to organic vapors than to permanent gases due to its rigid polyacetylene backbone and bulky side groups, which provide a relatively high fractional free volume (FFV) value of 0.26. Desilylation was performed on PTMSDPA. The resulting material, PDPA, is totally insoluble in common organic solvents, so it has much higher chemical resistance than PTMSDPA. Additionally, due to its insolubility in polymerization solvents, desilylation provides the only known route to high molar mass PDPA. The FFV of the resulting membrane (PDPA) is reduced by approximately 12% relative to that of PTMSDPA. This leads to a decrease in gas permeability values and selectivity of organic vapors relative to nitrogen. For example, the oxygen permeability is reduced from 1200 to 500 Barrers upon desilylation. The pure gas selectivities decrease from 9 to 3 for n-C₄H₁₀/N₂ and from 26 to 9 for C₃H₈/N₂.     

Synthesis and stable high oxygen permeability of poly(diphenylacetylene)s with two or three trimethylsilyl groups

We synthesized two new poly(diphenylacetylene)s having two or three trimethylsilyl groups and found these membranes having extremely high oxygen permeabilities of more than 1000 barrers which are of the same order as that for poly[1-(trimethylsilyl)-1-propyne]. Whereas oxygen permeability of poly[1-(trimethylsilyl)-1-propyne] was reported to decrease largely with time, these high oxygen permeabilities were stable for several months. These membranes also showed ethanol permselectivities because of their hydrophobicity. It was found that the introduction of two or three trimethylsilyl groups to poly(diphenylacetylene) was very effective for obtaining stable high oxygen permeable and ethanol permselective membranes.     

Gas permselection properties in silicone-coated asymmetric polyethersulfone membranes

The gas permeation properties of H₂, He, CO₂, O₂, and N₂ through silicone-coated polyethersulfone (PESf) asymmetric hollow-fiber membranes with different structures were investigated as a function of pressure and temperature and compared with those of PESf dense membrane and silicone rubber (PDMS) membrane. The PESf asymmetric hollow-fiber membranes were prepared from spinning solutions containing N-methyl-2-pyrrolidone as a solvent, with ethanol, 1-propanol, or water as a nonsolvent-additive. Water was also used as both an internal and an external coagulant. A thin silicone rubber film was coated on the external surface of dried PESf hollow-fiber membranes. The apparent structure characteristics of the separation layer (thickness, porosity, and mean pore size) of the asymmetric membranes were determined by gas permeation method and their cross-section morphologies were examined with a scanning electron microscope. The results reveal that the gas pressure normalized fluxes of the five gases in the three silicone-coated PESf asymmetric membranes are nearly independent of pressure and did not exhibit the dual-mode behavior. The activation energies of permeation in the silicone-coated asymmetric membranes may be larger or smaller than those of PESf dense membrane, which is controlled by the membrane physical structure (skin layer and sublayer structure). Permselectivities for the gas pairs H₂/N₂, He/N₂, CO₂/N₂, and O₂/N₂ are also presented and their temperature dependency addressed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 837–846, 1997     

Selective permeation of sour gases through polymeric membranes modified by sulfolanes. I. Study of selective permeation of CO2 through modified polymeric membranes determined on different systems

Several sulfolanes such as 3-methylsulfolane, sulfolane, and 3-sulfolene were tested as modifiers in poly(trimethylsilyl methyl methacrylate) (PTMSMMA) and poly(trimethylsilyl propyne) (PMSP) to improve the selectivity of CO₂. The gas permeabilities for the PTMSMMA-blend membranes containing high 3-methylsulfolane content were determined on a nonvacuum system in which the membranes started to be measured at their steady states at 30°C; those for all the other membranes were determined in a vacuum system in which those membranes were measured after they reached their unsteady states at 30°C. The PTMSMMA-blend membrane containing 40% 3-methylsulfolane was found to give the best separation of CO₂ under the conditions in this study compared to all the PTMSMMA-blend membranes and the others prepared in our work; its ideal separation factors for CO₂ over N₂ were above 40 and its permeability coefficients of CO₂ increased to above 250 Barrer. The modifications of PMSP membranes by impregnating with sulfolane and blending with sulfolene were found to be effective in improving the selectivity for CO₂ over N₂ for the PMSP membrane. The ideal separation factors for CO₂ over N₂ for the modified PMSP membranes impregnated with 30% sulfolane and blended with 25% 3-sulfolene were improved to above 10 and 13, respectively. © 1996 John Wiley & Sons, Inc.     

Preparation of microporous silica membranes for gas separation

Microporous silica membranes for hydrogen separation were prepared on a γ-alumina coated α-alumina tube by sol-gel method. The reactants of sol-gel chemistry were tetraethoxysilane (TEOS) and methacryloxypropyl-trimethoxysilane (MOTMS). The silane coupling agent, MOTMS, was added as a template in order to control the pore structure to the silicon alkoxide, TEOS. In particular, the microporous membranes were prepared by changing the molar ratio of MOTMS with respect to other substances, and their pore characteristics were analyzed. Then, the effects of thermal treatment on the micropore structure of the resulting silica membranes were investigated. The pore size of the silica membrane prepared after calcination at 400–700 ‡C was in the range of 0.6–0.7 nm. In addition, permeation rates through the membranes were measured in the range of 100–300 dgC using H₂, CO₂, N₂, CH₄, C₂H₆, C₃H₆ and SF₆. The membrane calcined at 600 ‡C showed a H₂ permeance of 2×10^-7-7×10^-7 molm^-2s^-1Pa^-1 at permeation temperature 300 ‡C, and the separation factors for equimolar gas mixtures were 11 and 36 for a H₂/CO₂ mixture and 54 and 132 for a H₂/CH₄ mixture at permeation temperatures of 100 ‡C and 300 ‡C, respectively.     

Crosslinking and stabilization of nanoparticle filled poly(1‐trimethylsilyl‐1‐propyne) nanocomposite membranes for gas separations

Poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) has been crosslinked using 4,4′‐diazidobenzophenone bisazide to improve its chemical and physical stability over time. Crosslinking PTMSP renders it insoluble in good solvents for the uncrosslinked polymer. Gas permeability and fractional free volume decreased as crosslinker content increased, while gas sorption was unaffected by crosslinking. Therefore, the reduction in permeability upon crosslinking PTMSP was due to decrease in diffusion coefficient. Compared with the pure PTMSP membrane, the permeability of the crosslinked membrane is initially reduced for all gases tested due to the crosslinking. By adding nanoparticles (fumed silica, titanium dioxide), the permeability is again increased; permeability reductions due to crosslinking could be offset by adding nanoparticles to the membranes. Increased selectivity is documented for the gas pairs O₂/N₂, H₂/N₂, CO₂/N₂, CO₂/CH and H₂/CH₄ using crosslinking and addition of nanoparticles. Crosslinking is successful in maintaining the permeability and selectivity of PTMSP membranes and PTMSP/filler nanocomposites over time. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Non-steady-state kinetic analysis of coupled transport of thiocyanate ions through binary liquid membranes

The coupled transport of thiocyanate (SCN⁻) ions through binary liquid membranes of various compositions was investigated using trichloromethane and dichloromethane as membrane components in non-steady-state kinetics. The influence of the membrane composition on the kinetic parameters (k_1d, k_2m, k_2a, R^max_m, t_max) were calculated. The present work shows the importance of the nature of binary liquid membranes in establishing transport efficiency, which is increased by varying membrane composition. Striking variations of the kinetic parameters with the membrane composition were observed. It is shown that transport kinetics obeys the competitive preferential solvation theory in the whole concentration range.     

Gas permeability and permselectivity of plasma‐treated polypropylene membranes

The effects of NH₃‐plasma and N₂‐plasma treatment on rubbery polypropylene (PP) membrane upon permeation behavior for CO₂, O₂, and N₂ were investigated from their permeability measurements. The NH₃‐plasma and N₂‐plasma treatment on PP membranes could increase both the permeability coefficient for CO₂ and the ideal separation factor for CO₂ relative to N₂. For O₂ transport, both the permeability coefficient for O₂ and the ideal separation factor for O₂ relative to N₂ also increased. NH₃‐plasma and N₂‐plasma treatment on PP membranes possibly brings about an augmentation of permeability for CO₂ and permselectivity of CO₂ relative to N₂ simultaneously, but unfortunately the plasma‐treated PP membrane does not reach the level of CO₂ separation membrane. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Carbon molecular sieve membranes derived from trimethylsilyl substituted poly(phenylene oxide) for gas separation

Carbon molecular sieve membranes for gas separation prepared using poly(phenylene oxide) (PPO) as precursor have been examined. The PPO precursor was modified by introducing a trimethylsilyl (TMS) substituent and its effect on the gas transport property of the resulting carbon membrane was examined. TMS-substituted PPO (TMSPPO) was prepared in a high yield by a simple one-step reaction, and its carbon membrane was successfully fabricated. The modification improved the gas permeability of the resulting membrane which also exhibited excellent O₂/N₂ and CO₂/CH₄ separation performance comparable to those of polyimide-derived carbon membranes. From the analysis of the microstructure of the TMSPPO carbon membranes, it is believed that the TMS groups improve gas diffusivity by increasing the micropore volume.     

Hydrogen separation by dense cermet membranes

Novel cermet (i.e. ceramic-metal composite) membranes have been developed to separate hydrogen from mixed gases, particularly product streams generated during coal gasification and/or methane reforming. Hydrogen separation with these membranes is non-galvanic, i.e. it does not use electrodes or an external power supply to drive the separation, and hydrogen selectivity is nearly 100% because the membranes contain no interconnected porosity. The hydrogen permeation rate has been measured as a function of temperature (500-900 °C), membrane thickness (≈22-210 μm), and partial pressure of hydrogen (0.04-1.0 atm) in the feed gas. The hydrogen flux varied linearly with the inverse of membrane thickness, and reached ≈20 cm³(STP)/min cm² for a membrane with a thickness of ≈22 μm at 900 °C with 100% H₂ (at ambient pressure) as the feed gas. The results indicate that the hydrogen flux is limited by bulk diffusion and might be higher for a thinner (<22 μm) membrane. Some of the membranes were tested in a simulated syngas mixture containing H₂, CO, CO₂, and CH₄, and showed no degradation in performance. Hydrogen flux measurements made in H₂S-containing atmospheres for times approaching ≈270 h showed that a 200-μm-thick cermet membrane was stable in gases containing up to ≈400 ppm H₂S. While longer-term studies are needed, these results suggest that the cermet membranes may be suitable for practical hydrogen separation applications.     

The Effect of Process Parameters on the Pervaporation of Alcohols through Organophilic Membranes

Abstract

Several organophilic membranes were utilized to selectively permeate ethanol, n-butanol, and t-butanol from dilute aqueous mixtures using pervaporation (PV). Poly[1-(trimethylsilyl)-1-propyne] (PTMSP) membranes were utilized to investigate the effect of temperature, pressure, and start-up/transient time on the separation of aqueous ethanol mixtures. Results indicate optimal ethanol selectivity and flux at the lowest permeate-side pressure. Increased temperature significantly enhanced the productivity of PTMSP, but extended operation of the PTMSP membranes at high temperatures resulted in flux degradation. Two other hydrophobic membranes, poly(dimethyl siloxane) (PDMS) and a poly(methoxy siloxane) (PMS) composite, were used to separate n-butanol and t-butanol from dilute aqueous mixtures. The effect of feed concentration on the flux and selectivity was investigated. Both membranes were found to be more permeable to n-butanol than t-butanol. The PDMS membrane was found to be more effective than the PMS membrane in terms of flux and selectivity. The effect of membrane thickness on water permeation and on organic selectivity was also studied using the PDMS membrane.     

Nanoporous silica colloidal membranes suspended in glass

We prepared silica colloidal membranes suspended in glass openings and containing no major mechanical defects. The surface of these colloidal membranes was modified with amine groups. The diffusion rate of Fe(bpy)₃²⁺ through the suspended amine-modified colloidal membranes was attenuated by adding acid to the solution. The amine-modified colloidal membranes displayed an average selectivity (the ratio of diffusion rates in the absense and presence of the acid) of 2.6 for Fe(bpy)₃²⁺. This selectivity is believed to result from the electrostatic repulsion between the protonated amine-modified membrane surface and positively charged Fe(bpy)₃²⁺ and was confirmed by observing no change in (1) the diffusion rate of Fe(bpy)₃²⁺ through an unmodified suspended colloidal membrane, and (2) the diffusion rate of a neutral molecule through the amine-modified colloidal membrane with and without the acid present in solution.     

Preparation of plasma-polymerized membranes from fluoroalkyl acrylates and methacrylates and gas permeability through the membranes

Summary Plasma-polymerized membranes were prepared from fluoroalkyl acrylates and methacrylates by two different directions of monomer injection and the permeation rates of O₂ and n₂ through the membranes were investigated. The chemical structure and composition of the plasmapolymerized membranes varied significantly by the direction of monomer injection. The optimum plasma conditions to yield maximum gas separation characteristics was obtained by the remote plasma excitation at the W/FM value of 20 J/mg, where W is the discharge power, F is the monomer flow rate and M is the molecular weight of the monomer.     

Study on the geometric structure of poly[1-(trimethylsilyl)-1-propyne] by 13C and 29Si NMR spectroscopies

Summary The geometric structure of poly[1-(trimethylsilyl)-1-propyne] was investigated by ¹³C and ²⁹Si NMR spectroscopies. According to ¹³C NMR, the geometric structure varied with polymerization catalysts. NbCl₅ was inferred to produce more cis-rich polymer than TaCl₅. On the other hand, polymerization conditions such as solvent, temperature and cocatalyst hardly affected the geometric structure. The cis contents of polymers bearing bulkier substituents (-SiMe₂-nC₆H₁₃,-SiMe₂-CH₂SiMe₃) prepared with TaCl₅ were similar to that of poly (TMSP) with TaCl₅.     

Synthesis and gas permeation properties of various Si-containing poly(diarylacetylene)s and their desilylated membranes

Diarylacetylene monomers having trimethylsilyl groups and other substituents (substituted biphenyl, 1a and 1b; trimethylsilylmethylphenyl, 1c-e) were synthesized and polymerized with TaCl₅-n-Bu₄Sn catalyst to produce the corresponding poly(diarylacetylene)s (2a-d). Polymers 2a-c had high molecular weights and were soluble in common organic solvents. Free-standing membranes of 2a-c as well as previously reported 2f-h were prepared by the solution-casting method. Desilylation of these Si-containing polymer membranes was carried out with trifluoroacetic acid to afford 3a, 3b, and 3f-h. Upon desilylation, biphenyl-containing membranes became less permeable (3a, b), whereas fluorene-containing membranes became more permeable (3f-h). In particular, 3h exhibited extremely high gas permeability (PO₂ = 9800 barrers), which is about the same as that of poly(1-trimethylsilyl-1-propyne). Desilylated membranes 3a and 3f-h showed different gas permeability from that of polymers 2i-k which have the identical chemical structures and obtained directly by the polymerization of the corresponding monomers.     

Enhanced gas transport properties and molecular mobilities in nano-constrained poly[1-(trimethylsilyl)-1-propyne] membranes

Interfacial constraints in ultrathin poly(l-trimethylsilyl-1-propyne) (PTMSP) membranes yielded gas permeabilities and CO₂/helium selectivities that exceed bulk PTMSP membrane transport properties by up to three-fold for membranes of submicrometer thickness. Maximum permeability coefficients of 110 × 10³ Barrer and 27 × 10³ Barrer for carbon dioxide and helium, respectively, were found to occur in membranes of ～750 nm thickness. Indicative of a free volume increase, a molecular energetic mobility analysis (involving intrinsic friction analysis) revealed enhanced methyl side group mobility. This was evidenced by a minimum in the activation energies of ～4 kcal/mol in thin PTMSP membranes with maximum permeation, compared to ～5.5 kcal/mol in bulk films. Aging studies conducted over the timescales relevant to the conducted experiments signify that the free volume states in the thin film membranes are highly unstable in the presence of sorbing gases such as CO₂. These results are discussed and contrasted to PTMSP bulk membrane systems, which were found to be unaffected by aging over the equivalent experimental time scale.