Optimization of a MOF Blended with Modified Polyimide Membrane for High-Performance Gas Separation

The preparation, characterization and gas separation properties of mixed matrix membranes (MMMs) were obtained from polyimide capped with ionic liquid and blended with metal-organic frameworks (MOFs). The synthesized MOF was amine functionalized to produce UiO-66-NH2, and its amino group has a higher affinity for CO2. Mixed matrix membranes exhibited good membrane forming ability, heat resistance and mechanical properties. The polyimide membrane exclusively capped by ionic liquid exhibited good permselectivity of 74.1 for CO2/CH4, which was 6.2 times that of the pure polyimide membrane. It is worth noting that MMM blended with UiO-66-NH2 demonstrated the highest ideal selectivity for CO2/CH4 (95.1) with a CO2 permeability of 7.61 Barrer, which is close to the 2008 Robeson upper bound. The addition of UiO-66-NH2 and ionic liquid enhanced the permselectivity of MMMs, which may be one of the promising technologies for high performance CO2/CH4 gas separation.

Mixed-Gas Selectivity Based on Pure Gas Permeation Measurements: An Approximate Model

An approximate model based on friction-coefficient formalism is developed to predict the mixed-gas permeability and selectivity of polymeric membranes. More specifically, the model is a modification of Kedem’s approach to flux coupling. The crucial assumption of the developed model is the division of the inverse local permeability of the mixture component into two terms: the inverse local permeability of the corresponding pure gas and the term proportional to the friction between penetrants. Analytical expressions for permeability and selectivity of polymeric membranes in mixed-gas conditions were obtained within the model. The input parameters for the model are ideal selectivity and solubility coefficients for pure gases. Calculations have shown that, depending on the input parameters and the value of the membrane Peclét number (the measure of coupling), there can be both a reduction and an enhancement of selectivity compared to the ideal selectivity. The deviation between real and ideal selectivity increases at higher Peclét numbers; in the limit of large Peclét numbers, the mixed-gas selectivity tends to the value of the ideal solubility selectivity. The model has been validated using literature data on mixed-gas separation of n-butane/methane and propylene/propane through polymeric membranes.

Preparation and Characterization of Metal Membranes for Gas Separation

The purpose of this article is the characterization of permeability and the ideal selectivity of new metallic brass membranes with a “sandwich” structure. Characterization is an important factor related to the morphology, structure, and properties of the membrane. The membranes were examined for simple gas phases, including various exogenous factors on their performance (temperature, pressure, durability). To evaluate their performance, permeate measurements were made at temperatures from -18 to 300°C and at various pressures from 1 to 10 bar. Results have shown that permeability is influenced by the molecular weight and exhibits ideal selectivity greater or equal by Knudsen’s ideal separation factor in a sequence of Η2>He>CH4>N2>O2>Ar≥CO2. The permeability is also a function of the thickness of the membrane, as it shows there’s a decrease in permeability and an increase in selectivity when the thickness is increased. The effect of temperature on these metal membranes is considered an important factor in the operation of membranes and membrane systems. The main feature is the reduction of permeability with the increase of temperature.

CO2/N2 Gas Separation Using Pebax/ZIF-7—PSf Composite Membranes

In this study, we mixed the zeolitic imidazolate framework-7 (ZIF-7) with poly(ether-b-amide)® 2533 (Pebax-2533) and used it as a selective layer for a composite membrane. We prepared the composite membrane’s substrate using polysulfone (PSf), adjusted its pore size using polyethylene glycol (PEG), and applied polydimethylsiloxane (PDMS) to the gutter layer and the coating layer. Then, we investigated the membrane’s properties of gases by penetrating a single gas (N2, CO2) into the membrane. We identified the peaks and geometry of ZIF-7 to determine if it had been successfully synthesized. We confirmed that ZIF-7 had a BET surface area of 303 m2/g, a significantly high Langmuir surface area of 511 m2/g, and a high CO2/N2 adsorption selectivity of approximately 50. Considering the gas permeation, with ZIF-7 mixed into Pebax-2533, N2 permeation decreased from 2.68 GPU in a pure membrane to 0.43 GPU in the membrane with ZIF-7 25 wt%. CO2 permeation increased from 18.43 GPU in the pure membrane to 26.22 GPU in the ZIF-7 35 wt%. The CO2/N2 ideal selectivity increased from 6.88 in the pure membrane to 50.43 in the ZIF-7 25 wt%. Among the membranes, Pebax-2533/ZIF-7 25 wt% showed the highest permeation properties and the characteristics of CO2-friendly ZIF-7.

A Facilitated Gas Transport Strategy: 3D Porous Hyper-crosslinked Polymers Incorporating 6FDA-based Polyimide Matrix for the Design and Fabrication of Mixed Matrix Membranes with High Permeability

Economic membrane technologies are a perennial hot topic in the field of natural gas purification and O2 enrichment. In this work, novel hyper cross-linked polymers (HCPs) incorporating 6-FDA based polyimide (PI) MMMs were prepared via a casting method for enhancing different gas transport (CO2, CH4, O2, and N2). The gas permeation experiments showed that compared with pure PI films, adding HCPs effectively promotes gas transport, increases gas permeability, and maintains ideal selectivity. The permeability of HCPs/PI MMMs toward CO2 and O2 was as high as 105.85 barrer and 24.03 barrer, respectively, and the ideal selectivity of CO2/CH4 and O2/N2 was 15.67 and 3.00, respectively. Molecular dynamic simulations further verified that adding HCPs was beneficial to gas transport thanks to large FFV of MMMs. Thus, HCPs have potential utility in the fabrication of MMMs for facilitating gas transport in the field of natural gas purification and O2 enrichment.

The Effects of PEI Hollow Fiber Substrate Characteristics on PDMS/PEI Hollow Fiber Membranes for CO2/N2 Separation

The CO2 separation from flue gas based on membrane technology has drawn great attention in the last few decades. In this work, polyetherimide (PEI) hollow fibers were fabricated by using a dry-jet-wet spinning technique. Subsequently, the composite hollow fiber membranes were prepared by dip coating of polydimethylsiloxane (PDMS) selective layer on the outer surface of PEI hollow fibers. The hollow fibers spun from various spinning conditions were fully characterized. The influence of hollow fiber substrates on the CO2/N2 separation performance of PDMS/PEI composite membranes was estimated by gas permeance and ideal selectivity. The prepared composite membrane where the hollow fiber substrate was spun from 20 wt% of dope solution, 12 mL/min of bore fluid (water) flow rate exhibited the highest ideal selectivity equal to 21.3 with CO2 permeance of 59 GPU. It was found that the dope concentration, bore fluid flow rate and bore fluid composition affect the porous structure, surface morphology and dimension of hollow fibers. The bore fluid composition significantly influenced the gas permeance and ideal selectivity of the PDMS/PEI composite membrane. The prepared PDMS/PEI composite membranes possess comparable CO2/N2 separation performance to literature ones.

Nano-porous Zeolite and MOF Filled Mixed Matrix Membranes for Gas Separation

The commercial SAPO-34 zeolite with 0.38 nm pore size and ZIF-8 particles with 0.34 nm aperture size were separately dispersed into different polymer matrix, to prepare the mixed matrix membranes (MMMs) for gas separation. The dispersed situation of the SAPO-34 and ZIF-8 particles in matrix and the influence of the fillers on the separation performance of the membrane had been investigated in this study. The as-synthesized MMMs showed a better trade-off between permeability and selectivity than the pure polymer membrane and the performance could exceed or close to the upper bound line of polymer membrane for CO2 and CH4 separation. The CO2 permeability and CO2/CH4 ideal selectivity of the 6FDA-mDAT MMM containing 40 wt% SAPO-34 zeolite was 190 barrer and ca. 60, respectively. The 6FDA-TrMPD based MMMs containing 20 wt% ZIF-8 provided a permeability of C3H6 and an ideal selectivity of C3H6/C3H8 at 24 barrer and ca. 17, respectively. These separation performances were in a suitable agreement of the theoretical value from Maxwell model.

Electron beam induced modification of ZIF-8 membrane permeation properties

Modification of the gas permeation properties of ZIF-8 membranes using electron beam irradiation is reported. 3.8 and 3.2 fold enhancements in ideal selectivity for CO2/N2 and CO2/CH4 can be achieved...

Development and Performance Evaluation of Cellulose Acetate-Bentonite Mixed Matrix Membranes for CO2 Separation

Membrane science is a state-of-the-art environmentally green technology that ascertains superior advantages over traditional counterparts for CO2 capture and separation. In this research, mixed matrix membranes (MMMs) comprising cellulose acetate (CA) with various loadings of bentonite (Bt) clay were fabricated by adopting the phase-inversion technique for CO2/CH4 and CO2/N2 separation. The developed pristine and MMMs were characterized for morphological, thermal, structural, and mechanical analyses. Several techniques such as scanning electron microscopy, thermogravimetric analysis, Fourier transformed infrared spectroscopy, and nano-indentation investigations revealed the promising effect of Bt clay in MMMs as compared to pristine CA membrane. Nano-indentation test identified that elastic modulus and hardness of the MMM with 1 wt. loading was increased by 64% and 200%, respectively, compared to the pristine membrane. The permeability decreased with the incorporation of Bt clay due to uniform dispersion of filler attributed to enhanced tortuosity for the gas molecules. Nevertheless, an increase in gas separation performance was observed with Bt addition up to 1 wt. loading. The opposite trend prevailed with increasing Bt concentration on the separation performance owing to filler agglomeration and voids creation. The maximum value of ideal selectivity (CO2/CH4) was achieved at 2 bar pressure with 1 wt. % Bt loading, which is 79% higher than the pristine CA membrane. For CO2/N2, the ideal selectivity was 123% higher compared to the pristine membrane with 1 wt. % Bt loading at 4 bar pressure.

Synthesis and properties of highly processable asymmetric polyimides with bulky phenoxy groups

A series of new aromatic polyimides (PIs) and co-PIs containing bulky tert-butyl phenoxy group was synthesized by one-step high-temperature polycondensation of 1,3-diamino-4-(4′- tert-butylphenoxy)benzene ( tBuPDAB) with different commercially available aromatic dianhydrides. The polymers were obtained in quantitative yields with inherent viscosities of 0.40–0.70 dL g−1. They exhibited high thermal stability with 10% weight loss above 480°C and were cast in films with good mechanical properties capable to be tested as gas separation membranes. These PIs were compared with analogs bearing phenoxy group (PDAB). The incorporation of tBu improved the solubility of the PIs, their free volume fraction, d-spacing, and gas permeability coefficients in comparison with their analogs obtained from PDAB. The permeability enhancement was from 2.5 to 8 times depended on the gas tested. The PI, based on tBuPDAB and 4,4’-(hexafluoroisopropylidene)diphtalic anhydride and, thus, containing two different bulky pendant groups, showed the highest gas permeability coefficient for CO2 (58.3 Barrer) and moderate ideal selectivity to the gas pair CO2/CH4 ( α = 18.0).