Gas Permeation Properties Of Membranes Research Articles

Mixed matrix membrane based on PEBAX® filled with layered double hydroxides

The effect of incorporating layered double hydroxide (LDH) nanoparticles containing different molar ratios of metals on the thermal, mechanical, and gas permeation properties of membranes based on PEBAX® was evaluated. The three nanoparticles were synthesized using molar x-ratios (x = Al/(Mg + Al)) equal to 0.20, 0.25 and 0.33. The dispersed nanoparticles changed thermal resistance, improved mechanical properties and CO2/CH4 separation performance of MMM when compared to the membranes of neat PEBAX®. The addition of 2 % of LDH in PEBAX® 1657 promoted an increase of about 17 % in the elastic modulus and 10 % in the stress at break. The best result of permeation tests (1657–0.33–5 % MMM at 0.5 bar), shows increase CO2 permeability by 44 % and CO2/CH4 selectivity by 115 % as compared to the neat material. Gas permeation results showed that LDH with more anions favors the facilitated transport of CO2.

Fabrication and characterization of dual layer PEBAX‐SiO2/polyethersulfone nanocomposite membranes for separation of CO2/CH4 gases

AbstractA new method of fabricating thin film composite (TFC) membranes is presented through a one‐step co‐casting technique. In this method a dense layer of poly(ether‐block‐amide) (PEBAX‐1657) was formed on a porous support of polyethersulfone (PES) in one step by immersing the cast films in a coagulation bath of n‐hexane. To assess the impact of silica (SiO2) nanoparticles on characteristics of the fabricated membranes, dual‐layer nanocomposite membranes containing 2.5, 5, and 7.5 wt% of SiO2 nanoparticles in the dense layer were also prepared. Physical and mechanical properties of membranes were evaluated using scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy, X‐ray diffraction, water contact angle and tensile strength measurements. SEM images revealed that a defect‐free top‐layer was formed on a porous substrate and both layers were adhered together properly. These images also showed that sub‐layer's microstructure was affected by addition of SiO2 nanoparticles to the PEBAX matrix. Gas permeation properties of membranes were recorded for pure CO2 and CH4 at room temperature and pressures in the range of 4–6 bars. Addition of SiO2 nanoparticles up to 5 wt% enhanced CO2/CH4 selectivity of the membranes, while at higher SiO2 nanoparticles loading (7.5 wt%), the selectivity was reduced.

CH4‐Selective Mixed‐Matrix Membranes Containing Functionalized Silica for Natural Gas Purification

AbstractMixed‐matrix membranes were prepared by incorporating functionalized silica nanoparticles (SNPs) into the poly(ether‐block‐amide). The gas permeation properties of membranes were investigated for the separation of N2 and CO2 from CH4. Results revealed that chemical modification of SNPs and incorporation of the carboxylic groups on its surface had a strong interaction with the polymer matrix and improved the distribution of the nanofiller in the membrane matrix. According to the gas permeation experiments at various SNPs loadings and feed pressures, different trends were observed for the permeability and selectivity. Incorporation of the modified‐SNPs nanofiller into the membrane enhanced the CH4 permeability, as well as the CH4/N2 and CO2/N2 selectivities.

Intensification of CO2 separation performance via cryogenic and membrane hybrid process — Comparison of polyimide and polysulfone hollow fiber membrane

Cryogenic-membrane hybrid CO2 capture process has been considered as a promising alternative for the standalone processes to mitigate the critical challenge of energy penalty. In this work, two different commercial hollow fiber membranes were tested at low temperature condition to find the possibility of consisting a novel cold-membrane-cryogenic hybrid process. The gas permeation properties of membranes were evaluated at different operating temperature, CO2 concentration and stage cut. The experimental results indicated that cryogenic condition could facilitate to improve the CO2/N2 selectivity with a minimum permeance reduction. Specifically, with the operating temperature dropped to −20 °C and feed pressure set at 0.7 MPa, the CO2 selectivity of polyimide membrane increased by 166% with the permeance declined by 31%. Meanwhile, the CO2 recovery and purity of polyimide membrane achieved 92% and 49% at the temperature of −20 °C and pressure 0.7 MPa, respectively. It can be observed that operating membrane at cold condition could be a promising approach to intensify the CO2 separation, and thus decrease the energy consumption of subsequent CO2 liquefaction or desublimation in the hybrid process.

Effect of heating rates on the microstructure and gas permeation properties of carbon membranes

High performance tubular carbon membrane (TCM’s) for CO2 separation were prepared by controlling the carbonization heating rates in range of 1-7 oC/min carbonized at 800 oC under Argon environment. A single permeation apparatus was used to determine the gas permeation properties of the membrane at room temperature. Fine turning of the carbonization condition was necessary to obtain the desired permeation properties. The preparation of PI/NCC-based TCM at low heating rate caused the gas permeance for the examined gas N2 and CO2 decreased whereas the selectivity of CO2/N2 increased. It was also identified that the gas permeation properties of the resultant TCM and its structure was highly affected by the heating rate. The best carbonization heating rate was found at 3oC/min for the fabrication of TCM derived via polymer blending of PI/NCC for CO2/N2 separation.

Short fiber/polyurethane composite membrane for gas separation

In this research, short fiber/polymer composite membranes is introduced for gas separation. Our attempt is to increase the membranes performance by using wide interface between fiber and polymer. Short glass wool fiber (SGWF) was used as a polar micro size reinforcement and was mechanically dispersed in polyurethane matrix. Scanning electron microscope (SEM) images showed that fibers have a good dispersion and adhesion to polymer matrix. In order to survey the phase separation and crystallization behavior of polyurethane segments, differential scanning calorimetery (DSC) and dynamic mechanical thermal analysis (DMTA) were used. The results indicated that polar surface of glass wool is a suitable site for attraction of hard segments. Thermal transition of soft segments were assisted using DMTA. Obtained results were showed that the presence of glass wool fiber remarkably reduced the soft segments glass transition temperature (Tg). Gas permeation properties of membranes were assisted using pure CO2, CH4 and N2 gases. Presence of SGWF caused a simultaneous increase in permeability and ideal selectivity (permselectivity) in a way that composite membranes showed high performance. Thus, using of fiber instead of nanoparticles in polymeric membranes can be more beneficial in view of economic and performance for industrial applications.

Preparation, characterization, and gas permeation properties of blend membranes of polysulfone and polyethylene glycol inclusive alumina nanoparticles

The effect of incorporation of alumina nanoparticles on the gas separation properties of the polysulfone–polyethylene glycol blend membranes containing 20% polyethylene glycol was examined. At first, a number of nanocomposite polysulfone–polyethylene glycol/alumina membranes were synthesized with alumina nanoparticles loaded into the polymer matrixes. The hybrid membranes were synthesized with six different alumina contents of 2.5, 5, 10, 15, 20, and 30 wt%. The polysulfone–polyethylene glycol and their hybrids inclusive alumina membranes were prepared via thermal phase-inversion method. The membranes were initially characterized using Fourier transform infrared spectroscopy, scanning electron microscope, and X-ray diffraction. Gas permeation properties of these membranes with different alumina contents were investigated for pure CO2, CH4, N2, and O2 gases. The results showed that not only these gases permeability but the CO2/N2, CO2/CH4, and O2/N2 ideal selectivity were improved with increasing alumina nanoparticle content of the membrane as well. Also the effect of feed pressure on the permeation properties of these membranes was investigated for pure CO2 gas. Finally, the results from the synthesized membranes were compared with Robeson’s upper bound line.

Structural and transport properties of polydimethylsiloxane based polyurethane/silica particles mixed matrix membranes for gas separation

Mixed matrix membranes of synthesized polyurethane (PU) based on toluene diisocyanate (TDI), polydimethylsiloxane (PDMS) and polytetramethylene glycol (PTMG) with polyvinyl alcohol based polar silica particles were prepared by solution casting technique. The homogeneity and thermal properties of the prepared PDMS-PU/silica membranes were characterized using scanning electron microscope (SEM), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The SEM micrographs confirmed the distribution of silica particles in the polymer matrix without agglomerations. Gas permeation properties of membranes with different silica contents were studied for pure CO2, CH4, O2, He and N2 gases. The obtained results indicated the permeability of the condensable and polar CO2 gas was enhanced whereas permeability of other gases decreased upon increasing the silica content of the mixed matrix membranes. The permeability of CO2 and its selectivity over N2 was increased from 68.4 Barrer and 22 in pure PDMS-PU to 96.7 Barrer and 64.4 in the mixed matrix membranes containing 10 wt% of the silica particles.

Assessment of role of morphology in gas permselectivity of membranes based on polypropylene/ethylene vinyl acetate/clay nanocomposite

This paper reports on the influence of morphology on gas permeability and selectivity of membranes made from polypropylene (PP)/ethylene vinyl acetate copolymer (EVA)/clay (OMMT) nanocomposites. The morphology was adjusted by variation in the EVA (25, 50wt%), OMMT (0 and 5wt%) and compatibilizer (PP-g-MAH) (0 and 5wt%) contents. Gas permeation properties of membranes with different morphologies, were studied for pure CO2, O2 and N2 gases. X-ray diffraction (XRD) patterns showed no changes in crystalline structure of samples. TEM analysis confirmed high tendency of OMMT flacks for locating in the EVA phase. SEM results revealed that an increase in OMMT loading decreases the EVA droplet size (Dn) in samples with droplet type morphology and increases continuity index of EVA (CCI) in the samples with co-continuous morphology. Changes in compatibilizer/OMMT ratio imposed a dual effect on the morphology of the system with respect to Dn and CCI. A good correlation could be established between these morphological parameters with gas solubility parameters, gas permeability and CO2/N2 as well as CO2/O2 gas selectivity. Annealing was shown to change the morphology which in turn had a very strong influence on the membranes gas permeability behavior.

Preparation, characterization and gas permeation properties of polyurethane–silica/polyvinyl alcohol mixed matrix membranes

Silicon based particles were synthesized by using tetraethoxysilane (TEOS) as silica precursor, and low concentration of cetyltrimethyl ammonium bromide (CTAB) with polyvinyl alcohol (PVA) as templating agents. The synthesized particles had a higher hydrophilicity and polarity than conventional silica particles. PU and PU/silica composite membranes were prepared by solution casting technique. Hybrid membranes were characterized using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), thermal gravimetric analysis (TGA) and differential scanning calorimetery (DSC). FT-IR result indicated the existence of PVA in the final structure of silica network. The SEM micrographs confirmed the nano-scale distribution of silica particles in the polymer matrix. Gas permeation properties of membranes with different silica contents, was studied for pure CO2, CH4, O2 and N2 gases. The results showed an increase in the solubility and a corresponding reduction in the diffusivity of the gases through the membranes by increasing the silica content in the polymer matrix; consequently, the permeability of the condensable and polar CO2 gas was enhanced whereas that of other gases decreased. In the membrane with 10wt% silica content an enhancement of CO2/CH4 (α≈10.1) and CO2/N2 (α≈70.7) selectivities was observed. Finally, the experimental permeability values were compared with theoretical predictions based on gas solubility and diffusivity.

Preparation, characterization and gas permeation properties of a polycaprolactone based polyurethane-silica nanocomposite membrane

The effect of silica nanoparticles on the gas permeation properties of polycaprolactone-based polyurethane membranes was investigated. Polyurethane and polyurethane-silica nanocomposite membranes were prepared by solution blending and casting-evaporation methods. Silica nanoparticles were prepared by sol–gel method using hydrolysis of tetraethoxysilane (TEOS). Polyurethane was synthesized by bulk two-step polymerization, including polycaprolactone 2000(PCL)/hexamethylene diisocyanate (HMDI)/1,4-butanediol (BDO). The homogeneity and nano scale distribution of the prepared polyurethane-silica membranes were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and thermal gravimetric analysis (TGA). Gas permeation properties of these membranes with different silica contents, was studied for pure CO2, CH4, N2 and O2 gases. The results showed reduction in gas permeability, but enhancement in CO2/N2, CO2/CH4 and O2/N2 ideal selectivity. Also the effect of temperature and pressure on permeation properties of these membranes was investigated. The modified Higuchi model was applied to predict the permeability of polyurethane-silica nanocomposite membranes. Good agreement between the experimental data and the predicted gas permeability was obtained.

Tailoring of phase-segregation structures in two-soft-segment urethane/urea polymer membranes

The synthesis of two-soft-segment urethane/urea polymeric membranes with various proportions of the two soft segments, poly(propylene oxide) and polybutadiene, yielded very distinct morphologies depending on the degree of phase segregation. The morphologies were identified with transmission electron microscopy. With a low concentration of polybutadiene, this soft segment segregated into ellipsoidal microdomains dispersed in a poly(propylene oxide) matrix. With an intermediate concentration of polybutadiene, the morphology was characterized by nanoscale phase separation and could be described as a disordered, wormlike domain structure. With a high concentration of polybutadiene, a single phase was observed. This was attributed to molecular mixing of the two soft segments and was associated with membranes that under the application of a shear stress developed bands that efficiently scattered light. These bands were identified by field emission scanning electron microscopy with a periodicity of approximately 4–5 μm. The change in the membrane morphology from microscale phase segregation to nanoscale phase segregation led to very different membrane gas-permeation properties, that is, a reduction of the CO2 permeability from 191 to 90 Barrer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 315–320, 2007