Synthesis and characterization of poly(ether-block-amide) copolymers/multi-walled carbon nanotube nanocomposite membranes for CO2/CH4 separation

Graphene-Oxide-Modified Metal-Organic Frameworks Embedded in Mixed-Matrix Membranes for Highly Efficient CO2/N2 Separation

MOF-74 (metal-organic framework) is utilized as a filler in mixed-matrix membranes (MMMs) to improve gas selectivity due to its unique one-dimensional hexagonal channels and high-density open metal sites (OMSs), which exhibit a strong affinity for CO2 molecules. Reducing the agglomeration of nanoparticles and improving the compatibility with the matrix can effectively avoid the existence of non-selective voids to improve the gas separation efficiency. We propose a novel, layer-by-layer modification strategy for MOF-74 with graphene oxide. Two-dimensional graphene oxide nanosheets as a supporting skeleton creatively improve the dispersion uniformity of MOFs in MMMs, enhance their interfacial compatibility, and thus optimize the selective gas permeability. Additionally, they extended the gas diffusion paths, thereby augmenting the dissolution selectivity. Compared with doping with a single component, the use of a GO skeleton to disperse MOF-74 into Pebax®1657 (Polyether Block Amide) achieved a significant improvement in terms of the gas separation effect. The CO2/N2 selectivity of Pebax®1657-MOF-74 (Ni)@GO membrane with a filler concentration of 10 wt% was 76.96, 197.2% higher than the pristine commercial membrane Pebax®1657. Our results highlight an effective way to improve the selective gas separation performance of MMMs by functionalizing the MOF supported by layered GO. As an efficient strategy for developing porous MOF-based gas separation membranes, this method holds particular promise for manufacturing advanced carbon dioxide separation membranes and also concentrates on improving CO2 capture with new membrane technologies, a key step in reducing greenhouse gas emissions through carbon capture and storage.

The State-of-the-Art Functionalized Nanomaterials for Carbon Dioxide Separation Membrane

Nanocomposite membrane (NCM) is deemed as a practical and green separation solution which has found application in various fields, due to its potential to delivery excellent separation performance economically. NCM is enabled by nanofiller, which comes in a wide range of geometries and chemical features. Despite numerous advantages offered by nanofiller incorporation, fabrication of NCM often met processing issues arising from incompatibility between inorganic nanofiller and polymeric membrane. Contemporary, functionalization of nanofiller which modify the surface properties of inorganic material using chemical agents is a viable approach and vigorously pursued to refine NCM processing and improve the odds of obtaining a defect-free high-performance membrane. This review highlights the recent progress on nanofiller functionalization employed in the fabrication of gas-separative NCMs. Apart from the different approaches used to obtain functionalized nanofiller (FN) with good dispersion in solvent and polymer matrix, this review discusses the implication of functionalization in altering the structure and chemical properties of nanofiller which favor interaction with specific gas species. These changes eventually led to the enhancement in the gas separation efficiency of NCMs. The most frequently used chemical agents are identified for each type of gas. Finally, the future perspective of gas-separative NCMs are highlighted.

CO2 capture using membrane contactors: a systematic literature review

With fossil fuel being the major source of energy, CO2 emission levels need to be reduced to a minimal amount namely from anthropogenic sources. Energy consumption is expected to rise by 48% in the next 30 years, and global warming is becoming an alarming issue which needs to be addressed on a thorough technical basis. Nonetheless, exploring CO2 capture using membrane contactor technology has shown great potential to be applied and utilised by industry to deal with post- and pre-combustion of CO2. A systematic review of the literature has been conducted to analyse and assess CO2 removal using membrane contactors for capturing techniques in industrial processes. The review began with a total of 2650 papers, which were obtained from three major databases, and then were excluded down to a final number of 525 papers following a defined set of criteria. The results showed that the use of hollow fibre membranes have demonstrated popularity, as well as the use of amine solvents for CO2 removal. This current systematic review in CO2 removal and capture is an important milestone in the synthesis of up to date research with the potential to serve as a benchmark databank for further research in similar areas of work. This study provides the first systematic enquiry in the evidence to research further sustainable methods to capture and separate CO2.

The assessment of honeycomb structure UiO-66 and amino functionalized UiO-66 metal-organic frameworks to modify the morphology and performance of Pebax®1657-based gas separation membranes for CO2 capture applications

A new type of honeycomb structured UiO-66 metal-organic frameworks (MOF) was synthesized and amino functionalized followed by employing them to prepare mixed matrix membranes (MMM). The influences of dimethylformamide (DMF) and H₂O/ethanol (70/30 wt.%) blend were firstly investigated on morphology, structure, and CO₂/CH₄ separation efficiency of Pebax®1657 membranes. Based on the transmission electron microscopy (TEM) analysis, the synthesized MOF has 15 nm in diameter. DMF led to the formation of a more crystalline (based on X-ray diffraction (XRD) analysis) and more porous structure. Higher CO₂ permeability and CO₂/CH₄ selectivity were observed as DMF was employed to fabricate neat membranes. Scanning electron microscopy (SEM) exhibited MOF agglomeration as the UiO-66 was used while the nanoparticle dispersion was enhanced when UiO-66-NH₂ was exploited. Fourier transform infrared spectroscopy (FTIR) confirmed the successful MOF incorporation into the MMMs. Ultimately, the gas separation experiments showed that CO₂ permeability was enhanced compared to the neat membrane by 44.7% and 49.4% as 10 wt.% UiO-66 and UiO-66-NH₂ were used, respectively. Moreover, the Pebax®1657-UiO-66-NH₂ MMMs exhibited 71.7% and 34.5% improvement in selectivity of CO₂/N₂ and CO₂/CH₄, respectively, owing to enhancing CO₂-OH interactions while the CO₂/O₂ was declined by 8.8%.

Effect of montmorillonite on PEBAX® 1074-based mixed matrix membranes to be used in humidifiers in proton exchange membrane fuel cells

To meet the increasing requirements of membrane humidification in proton exchange membrane fuel cells (PEMFCs), a series of montmorillonite (MMT)/PEBAX® 1074 mixed matrix membranes (MMMs) were fabricated using the solvent casting method. Pristine MMT and poly(oxyalkylene)amine (APOP)-modified MMT were added as the filler. Using the XRD, FT-IR, SEM, and TEM, the morphology and chemical structure of MMT during modification were investigated. Using the tests of water vapor permeability, air permeability, water contact angle, and crystallinity, the effects of montmorillonite on membrane properties were investigated. The results showed that surface hydrophilicity and crystallinity of MMMs increased as the MMT content increases, which leads to higher vapor permeability and selectivity than the pure PEBAX® 1074 membrane. After modification, APOP-MMT/PEBAX® 1074 MMMs showed better performance in vapor permeability and vapor/air selectivity. The best selectivity was 1.7 × 105, which is three times higher than that of pure PEBAX® 1074 membrane.

Pebax® 1041 supported membranes with carbon nanotubes prepared via phase inversion for CO2/N2 separation

This work shows the preparation of Pebax® 1041 films from solutions in DMAc and water-DMAc emulsions as alternatives to those prepared by extrusion that can be found in the literature. These membranes were tested in post-combustion CO2 capture, in the separation of a 15/85 (v/v) CO2/N2 mixture. Self-supported membranes of Pebax® 1041 were prepared by solvent evaporation and phase inversion. The characterization of these films defined the intrinsic properties of this polymer in terms of chemical structure, crystallinity, thermal stability and gas separation performance (a CO2 permeability of 30 Barrer with a CO2/N2 selectivity of 21 at 35 °C and 3 bar feed pressure). Supported Pebax® 1041 membranes were also developed to decrease the Pebax® thickness (in the 1.5-10 μm range), resulting in a higher permeance. These membranes were prepared by a phase inversion process consisting of the precipitation of a Pebax® 1041/DMAc solution in water and dispersing it to form a stable emulsion that was drop-cast on PSF asymmetric supports. Once dried, the polymer formed a dense continuous layer. The phase inversion methodology is "greener" than solvent evaporation since dimethylacetamide is not released as toxic vapour during membrane preparation. The amount drop-cast led to a different selective layer thickness, which was enhanced by the dispersion of MWCNTs in the polymer emulsion. The properties of the Pebax® selective layer were studied by thermogravimetry and by measuring the contact angle of the membrane surface, and the optimal CO2/N2 selectivity (22.6) was obtained with a CO2 permeance of 3.0 GPU.

Facilitating CO2 Transport Across Mixed Matrix Membranes Containing Multifunctional Nanocapsules

Mixed matrix membranes (MMMs) have exhibited advantages in overcoming the trade-off effect, although it is still intensively demanded in the design of multifunctional fillers to improve CO₂ separation performance. At present, MMMs with transport channels present an effective strategy to obtain ultrahigh CO₂ permselectivity. In this work, Pebax-based MMMs was fabricated by incorporating nanocapsules (NCs), whose exterior, interior and transverse shell surfaces contained abundant carboxylic acid groups. NCs, similar to vesicles in cells, provide favorable physical and chemical microenvironments to the constructed CO₂ transport channels, enhancing the CO₂ permselectivity via both a facilitated transport mechanism and a solution-diffusion mechanism. CO₂ permselectivity of MMMs doped with 20 wt % NCs surpassed the 2008 Robeson limit; an increase in CO₂ permeability was up to 1431 ± 35 Barrer for pure gas, which was a 362% enhancement from the pure membrane, and an increase of the CO₂/CH₄ and CO₂/N₂ ideal selectivities to 46 ± 1.4 and 69 ± 2.7, corresponding to 44% and 23% enhancements from the pure membrane, respectively. This study provides an ingenious strategy to enhance the gas permselectivity of MMMs.