Showing papers on "Permeation published in 2015"

Physical Aging, Plasticization and Their Effects on Gas Permeation in "Rigid" Polymers of Intrinsic Microporosity

Abstract: Long-term physical aging and plasticization, two mobility-based phenomena that are counterintuitive in the context of “rigid” polymers of intrinsic microporosity (PIMs), were evaluated using pure- and mixed-gas permeation data for representative ladder and semiladder PIMs PIMs between 1 and 4 years old retained from 10- to 1000-fold higher H2 and O2 permeabilities than commercial membrane materials with similar or higher selectivities A triptycene-based ladder polymer (TPIM-1) exhibited very large selectivity gains outweighing permeability losses after 780 days, resulting in unprecedented performance for O2/N2 (P(O2) = 61 Barrer, α(O2/N2) = 86) and H2/N2 (P(H2) = 1105 Barrer, α(H2/N2) = 156) separations Interestingly, TPIM-1 aged more and faster than its more flexible counterpart, PIM-1, which exhibited P(O2) = 317 Barrer and α(O2/N2) = 50 at 1380 days Additionally, the more “rigid” TPIM-1 plasticized more significantly than PIM-1 (ie, TPIM-1 endured ∼93% increases in mixed-gas CH4 permeability ov

Permeation of platinum and rhodium nanoparticles through intact and damaged human skin

Abstract: The aim of the study was to evaluate percutaneous penetration of platinum and rhodium nanoparticles (PtNPs: 5.8 ± 0.9 nm, RhNPs: 5.3 ± 1.9 nm) through human skin. Salts compounds of these metals are sensitizers and some also carcinogenic agents. In vitro permeation experiments were performed using Franz diffusion cells with intact and damaged skin. PtNPs and RhNPs, stabilized with polyvinylpyrrolidone, were synthesized by reduction of Na2PtCl6 and RhCl3·3H2O respectively. Suspensions with a concentration of 2.0 g/L of PtNPs and RhNPs were dispersed separately in synthetic sweat at pH 4.5 and applied as donor phases to the outer surface of the skin for 24 h. Measurements of the content of the metals in the receiving solution and in the skin were performed subsequently. Rhodium skin permeation was demonstrated through damaged skin, with a permeation flux of 0.04 ± 0.04 μg cm−2 h−1 and a lag time of 7.9 ± 1.1 h, while no traces of platinum were found in receiving solutions. Platinum and rhodium skin-analysis showed significantly higher concentrations of the metals in damaged skin. Rh and Pt applied as NPs can penetrate the skin barrier and Rh can be found in receiving solutions. These experiments pointed out the need for skin contamination prevention, since even a minor injury to the skin barrier can significantly increase penetration.

Thin film composite polyamide membranes: parametric study on the influence of synthesis conditions

Abstract: Preparation of thin film composite (TFC) polyamide (PA) membranes by interfacial polymerization (IP) reaction is remarkably sensitive to the interactions between synthesis parameters. Here we report the effect of the simultaneous change in four synthesis parameters, namely monomers concentrations (m-phenylenediamine, MPD, and trimesoyl chloride, TMC), reaction time and curing temperature, on the surface morphology and on the permeation properties of TFC membranes. By varying several synthesis parameters at the same time using a Taguchi robust design (L9 orthogonal arrays), it was found that monomers concentration and curing temperature significantly affected water permeation by creating a substantial change in morphology of the PA films. More importantly, a strong interaction between monomers concentration was observed, which demonstrates the importance of smart adjustment of these parameters in the preparation process. Permeation properties were justified by thickness and by the cross-link density of the synthesized films; the latter was found to be more influential. Based on analysis of variance (ANOVA), the contribution of the synthesis parameters towards change in water permeation was determined as: curing temperature (40.7%) > MPD concentration (28%) ∼ TMC concentration (27.8%) > reaction time (1.9%). The findings will provide valuable guidelines to develop practical low cost, robust and high performance membranes by changing the curing temperature and the monomer concentrations as critical parameters.

Highly Permeable Benzotriptycene-Based Polymer of Intrinsic Microporosity

Abstract: A novel polymer of intrinsic microporosity (PIM) was prepared from a diaminobenzotriptycene monomer using a polymerization reaction based on Troger’s base formation. The polymer (PIM-BTrip-TB) demonstrated an apparent Brunauer, Emmet, and Teller (BET) surface area of 870 m2 g–1, good solubility in chloroform, excellent molecular mass, high inherent viscosity and provided robust thin films for gas permeability measurements. The polymer is highly permeable (e.g., PH2 = 9980; PO2 = 3290 Barrer) with moderate selectivity (e.g., PH2/PN2 = 11.0; PO2/PN2 = 3.6) so that its data lie over the 2008 Robeson upper bounds for the H2/N2, O2/N2, and H2/CH4 gas pairs and on the upper bound for CO2/CH4. On aging, the polymer demonstrates a drop in permeability, which is typical for ultrapermeable polymers, but with a significant increase in gas selectivities (e.g., PO2 = 1170 Barrer; PO2/PN2 = 5.4).

Gas Permeation through Nafion. Part 1: Measurements

Abstract: This study focuses on the characterization of gas permeation through Nafion, the most commonly used polymer electrolyte membrane (PEMs) for low-temperature fuel cells and water electrolyzers. In the first part of this study, novel modifications of the electrochemical monitoring technique to precisely measure the hydrogen and oxygen permeabilities of Nafion are presented. With these techniques, the gas permeabilities of Nafion were observed to be independent of pressures, which was ascribed to a solely diffusive process. Moreover, the temperature dependence of the hydrogen and oxygen permeabilities through Nafion in the fully hydrated state (where the water content is independent of the temperature) were measured in order to determine the activation energies of the permeation mechanisms. On the basis of the measured influence of temperature and relative humidity on the gas permeabilities of Nafion, the pathways for gas permeation through its aqueous and solid phase are qualitatively discussed. The second p...

Quest for anionic MOF membranes: continuous sod-ZMOF membrane with CO2 adsorption-driven selectivity.

Abstract: We report the fabrication of the first continuous zeolite-like metal–organic framework (ZMOF) thin-film membrane. A pure phase sod-ZMOF, sodalite topology, membrane was grown and supported on a porous alumina substrate using a solvothermal crystallization method. The absence of pinhole defects in the film was confirmed and supported by the occurrence of quantifiable time-lags, for all studied gases, during constant volume/variable pressure permeation tests. For both pure and mixed gas feeds, the sod-ZMOF-1 membrane exhibits favorable permeation selectivity toward carbon dioxide over relevant industrial gases such as H2, N2, and CH4, and it is mainly governed by favorable CO2 adsorption.

Oriented two-dimensional zeolitic imidazolate framework-L membranes and their gas permeation properties

Abstract: A two-dimensional zeolitic imidazolate framework (ZIF), ZIF-L, with a unique anisotropic pore system makes it an excellent material for investigating ZIF membranes with crystallographically preferred orientation and their effects on gas separation properties. A b-oriented ZIF-L membrane was successfully prepared from a randomly oriented seed layer. In contrast, a c-oriented ZIF-L crystal layer was attached to a support through vacuum filtration in the presence of polyethyleneimine. After a short-time secondary growth, the oriented layer grew into a continuous membrane with a high degree of c-out-of-plane orientation. Gas separation studies demonstrated the orientation-dependent separation behavior. In single gas permeation experiments, the c-oriented ZIF-L membrane has higher ideal selectivities of 8.1 for H2/N2 and 24.3 for H2/CO2 compared to the corresponding values of 3.9 and 5.5 for the b-oriented ZIF-L membrane. The results of binary gas permeation showed decreased separation factors of the c-oriented membrane, but were still much higher than those of the b-oriented membrane. This work provides new insights into controlling ZIF membrane orientation for achieving desirable gas separation performance.

Desalination by Membrane Distillation using Electrospun Polyamide Fiber Membranes with Surface Fluorination by Chemical Vapor Deposition

Abstract: Fibrous membranes of poly(trimethyl hexamethylene terephthalamide) (PA6(3)T) were fabricated by electrospinning and rendered hydrophobic by applying a conformal coating of poly(1H,1H,2H,2H-perfluorodecyl acrylate) (PPFDA) using initiated chemical vapor deposition (iCVD). A set of iCVD-treated electrospun PA6(3)T fiber membranes with fiber diameters ranging from 0.25 to 1.8 μm were tested for desalination using the air gap membrane distillation configuration. Permeate fluxes of 2–11 kg/m2/h were observed for temperature differentials of 20–45 °C between the feed stream and condenser plate, with rejections in excess of 99.98%. The liquid entry pressure was observed to increase dramatically, from 15 to 373 kPa with reduction in fiber diameter. Contrary to expectation, for a given feed temperature the permeate flux was observed to increase for membranes of decreasing fiber diameter. The results for permeate flux and salt rejection show that it is possible to construct membranes for membrane distillation even ...

Desalination by Membrane Distillation using Electrospun Polyamide Fiber Membranes with Surface Fluorination by Chemical Vapor Deposition

Abstract: Fibrous membranes of poly(trimethyl hexamethylene terephthalamide) (PA6(3)T) were fabricated by electrospinning and rendered hydrophobic by applying a conformal coating of poly(1H,1H,2H,2H-perfluorodecyl acrylate) (PPFDA) using initiated chemical vapor deposition (iCVD). A set of iCVD-treated electrospun PA6(3)T fiber membranes with fiber diameters ranging from 0.25 to 1.8 μm were tested for desalination using the air gap membrane distillation configuration. Permeate fluxes of 2–11 kg/m2/h were observed for temperature differentials of 20–45 °C between the feed stream and condenser plate, with rejections in excess of 99.98%. The liquid entry pressure was observed to increase dramatically, from 15 to 373 kPa with reduction in fiber diameter. Contrary to expectation, for a given feed temperature the permeate flux was observed to increase for membranes of decreasing fiber diameter. The results for permeate flux and salt rejection show that it is possible to construct membranes for membrane distillation even ...

Polymer functionalization to enhance interface quality of mixed matrix membranes for high CO2/CH4 gas separation

Abstract: Hydroxyl-functionalized homo- and co-polyimides 6FDA–(DAM)x–(HAB)y (with x : y molar ratio of 1 : 0; 2 : 1; 1 : 1; 1 : 2) and two metal–organic frameworks (MOFs), MIL-53(Al) and NH2-MIL-53(Al) were synthesized for preparation of mixed matrix membranes (MMMs). The MOF loadings were varied over the range of 10–20 wt% for NH2-MIL-53(Al) and 10–15 wt% for MIL-53(Al). The incorporation of hydroxyl groups into the polyimide backbone is expected to improve the interfacial interaction between the polymer matrix and fillers, consequently, enhancing gas separation performance of MMMs. A big increase in glass transition temperature (Tg) for MMMs confirmed the polymer chain rigidification, which was caused by a strong interaction between the hydroxyl groups in the copolyimides and the amine groups in NH2-MIL-53(Al). Additionally, SEM results showed that the hydroxyl groups facilitated the particle dispersion in the MMMs, either was NH2-MIL-53(Al) or MIL-53 used as filler. Gas separation performances of MMMs were characterized by both CO2/CH4 pure gas and binary permeation measurements at 35 °C and 150 psi. The incorporation of NH2-MIL-53(Al) in the hydroxyl-copolyimides was found to significantly improve the CO2/CH4 separation factor while maintaining CO2 permeability of the MMMs as high as those of the neat corresponding copolyimides, therefore greatly enhancing the MMM separation performance. For example, the MMM prepared from 6FDA–DAM–HAB (1 : 1) copolyimide and 10 wt% NH2-MIL-53(Al) showed a permeability/selectivity behavior approaching the 2008 Robeson's upper bound making it attractive for practical usage. The significant improvement in CO2/CH4 separation factor observed for the MMMs made of the hydroxyl-copolyimides and the amine-functionalized MOFs was due to (i) the enhanced polymer–filler compatibility originating from a mutual interaction between the polymer-functional moieties and the amine-functionalized MOF surface yielding defect-free MMMs and (ii) the high CO2/CH4 selective adsorption in the NH2-MIL-53(Al) framework.

Chiral Polymers of Intrinsic Microporosity: Selective Membrane Permeation of Enantiomers

Abstract: Following its resolution by diastereomeric complexation, 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane (TTSBI) was used to synthesize a chiral ladder polymer, (+)-PIM-CN. (+)-PIM-COOH was also synthesized by the acid hydrolysis of (+)-PIM-CN. Following characterization, both (+)-PIM-CN and (+)-PIM-COOH were solvent cast directly into semipermeable membranes and evaluated for their ability to enable the selective permeation of a range of racemates, including mandelic acid (Man), Fmoc-phenylalanine, 1,1'-bi-2-naphthol (binol), and TTSBI. High ee values were observed for a number of analytes, and both materials exhibited high permeation rates. A selective diffusion-permeation mechanism was consistent with the results obtained with these materials. Their high permeability, processability, and ease of chemical modification offer considerable potential for liquid-phase membrane separations and related separation applications.

Beyond the H2/CO2 upper bound: one-step crystallization and separation of nano-sized ZIF-11 by centrifugation and its application in mixed matrix membranes

Abstract: The synthesis of nano-sized ZIF-11 with an average size of 36 ± 6 nm is reported. This material has been named nano-zeolitic imidazolate framework-11 (nZIF-11). It has the same chemical composition and thermal stability and analogous H2 and CO2 adsorption properties to the conventional microcrystalline ZIF-11 (i.e. 1.9 ± 0.9 μm). nZIF-11 has been obtained following the centrifugation route, typically used for solid separation, as a fast new technique (pioneering for MOFs) for obtaining nanomaterials where the temperature, time and rotation speed can easily be controlled. Compared to the traditional synthesis consisting of stirring + separation, the reaction time was lowered from several hours to a few minutes when using this centrifugation synthesis technique. Employing the same reaction time (2, 5 or 10 min), micro-sized ZIF-11 was obtained using the traditional synthesis while nano-scale ZIF-11 was achieved only by using centrifugation synthesis. The small particle size obtained for nZIF-11 allowed the use of the wet MOF sample as a colloidal suspension stable in chloroform. This helped to prepare mixed matrix membranes (MMMs) by direct addition of the membrane polymer (polyimide Matrimid®) to the colloidal suspension, avoiding particle agglomeration resulting from drying. The MMMs were tested for H2/CO2 separation, improving the pure polymer membrane performance, with permeation values of 95.9 Barrer of H2 and a H2/CO2 separation selectivity of 4.4 at 35 °C. When measured at 200 °C, these values increased to 535 Barrer and 9.1.

A Mixed Ionic and Electronic Conducting Dual‐Phase Membrane with High Oxygen Permeability

Abstract: To combine good chemical stability and high oxygen permeability, a mixed ionic-electronic conducting (MIEC) 75 wt % Ce0.85Gd0.1Cu0.05O2−δ-25 wt % La0.6Ca0.4FeO3−δ (CGCO-LCF) dual-phase membrane based on a MIEC–MIEC composite has been developed. Copper doping into Ce0.9Gd0.1O2−δ (CGO) oxide enhances both ionic and electronic conductivity, which then leads to a change from ionic conduction to mixed conduction at elevated temperatures. For the first time we demonstrate that an intergranular film with 2–10 nm thickness containing Ce, Ca, Gd, La, and Fe has been formed between the CGCO grains in the CGCO-LCF one-pot dual-phase membrane. A high oxygen permeation flux of 0.70 mL min−1 cm−2 is obtained by the CGCO-LCF one-pot dual-phase membrane with 0.5 mm thickness at 950 °C using pure CO2 as the sweep gas, and the membrane shows excellent stability in the presence of CO2 even at lower temperatures (800 °C) during long-term operation.

Permeability of the Blood–Brain Barrier: Molecular Mechanism of Transport of Drugs and Physiologically Important Compounds

Abstract: A new molecular model for the permeability of drugs and other physiologically important compounds to cross the blood–brain barrier has been developed. Permeability (log PS) is dependant on desolvation, lipophilicity, molecular volume and dipole moment. Previous models for BBB permeability have not considered desolvation and dipole moment as critical factors. The model applies to passive diffusion processes, and some facilitated diffusion processes. Passive permeability models may not apply to active transport processes, where complex membrane protein binding processes (e.g. stereoselectivity) are involved. Model phosphatidylcholine lipid bilayer membranes have been used to evaluate how charged or polar neutral compounds can interact through their molecular dipoles with the cell membrane to induce electromechanical changes in the cell membrane which facilitate permeation. The free energy of solvation in n-octanol has been shown to be a good measure of membrane lipophilicity by calculating the solvation free energy of a model PC lipid membrane in a series of closely related alcohols. The passive diffusion model for alcohols correlates with the known modulation of membrane bilayers which showed a size-dependent “cut-off” point in potency. For most drugs and related molecules, the neutral species are the permeating species.