Enhancement strategies of poly(ether-block-amide) copolymer membranes for CO2 separation: A review

Poly(ether-block-amide) (Pebax) membranes have become the preferred CO2 separation membrane because of their excellent CO2 affinity and robust mechanical resistance. Nevertheless, their development must be considered to overcome the typical obstacles in polymeric membranes, including the perm-selectivity trade-off, plasticization, and physical aging. This article discusses the recent enhancement strategies as a guideline for designing and developing Pebax membranes. Five strategies were developed in the past few years to improve Pebax gas transport properties, including crosslinking, mobile carrier attachment, polymer blending, filler incorporation, and the hybrid technique. Among them, filler incorporation and the hybrid technique were most favorable for boosting CO2/N2 and CO2/CH4 separation performance with a trade-off-free profile. On the other hand, modified Pebax membranes must deal with two latent issues, mechanical strength loss, and perm-selectivity off-balance. Therefore, exploring novel materials with unique structures and surface properties will be promising for further research. In addition, seeking eco-friendly additives has become worthwhile for establishing Pebax membrane sustainable development for gas separation.

One pot synthesis of UiO-66@IL composite for fabrication of CO2 selective mixed matrix membranes

In this study, a facile and extensible one pot approach was utilized to synthesize ionic liquid inside a porous metal organic framework (UiO-66). Different characterization techniques were used to confirm the successful synthesis of UiO-66@IL composite. The MMMs were characterized and tested for CO₂ separation from CH₄ or N₂ at ambient and elevated temperatures. SEM images exhibited well dispersion of the filler particles with no notable defect even at high loadings. Single and mixed gas permeation results indicated significant performance (CO₂ permeability: 143 Barrer and CO₂/CH₄, CO₂/N₂ selectivity: 28.32, 61.11 respectively) by enhancing the permeability of CO₂ by 74% and selectivity to 31% and 26% for CO₂/CH₄ and CO₂/N₂ compared with neat Pebax®1657 membrane.

Effect of process parameters over carbon-based ZIF-62 nano-rooted membrane for environmental pollutants separation

The paper evaluates the routes towards the evaluation of membranes using ZIF-62 metal organic framework (MOF) nano-hybrid dots for environmental remediation. Optimization of interaction of operating parameters over the rooted membrane is challenging issue. Subsequently, the interaction of operating parameters including temperature, pressure and CO₂ gas concentration over the resultant rooted membranes are evaluated and optimized using response surface methodology for environmental remediation. In addition, the stability and effect of hydrocarbons on the performance of the resulting membrane during the gas mixture separation are evaluated at optimum conditions to meet the industrial requirements. The characterization results verified the fabrication of the ZIF-62 MOF rooted composite membrane. The permeation results demonstrated that the CO₂ permeability and CO₂/CH₄ selectivity of the composite membrane was increased from 15.8 to 84.8 Barrer and 12.2 to 35.3 upon integration of ZIF-62 nano-glass into cellulose acetate (CA) polymer. Subsequently, the optimum conditions have been found at a temperature of 30 °C, the pressure of 12.6 bar and CO₂ feed concentration of 53.3 vol%. These optimum conditions revealed the highest CO₂ permeability, CH₄ permeability and CO₂/CH₄ separation factor of 47.9 Barrer, 0.2 Barrer and 26.8. The presence of hydrocarbons in gas mixture dropped the CO₂ permeability of 56.5% and separation factor of 46.4% during 206 h of testing. The separation performance of the composite membrane remained stable without the presence of hydrocarbons for 206 h.

Cellulose acetate-based membranes by interfacial engineering and integration of ZIF-62 glass nanoparticles for CO2 separation

Composite membranes typically used for gas separation are susceptible to interfacial voids and CO₂ plasticization which adversely affects the gas permeation performance. This paper evaluates routes towards the enhancement of CO₂ permeation performance and CO₂ plasticization resistance of composite membranes using non-stoichiometric ZIF-62 MOF glass and cellulose acetate (CA). Single and mixed gas permeation results, obtained with CO₂ and CH₄, demonstrate that the presence of ZIF-62 glass in CA polymer enhanced the CO₂ permeability and CO₂/CH₄ ideal selectivity from 15.8 to 84.8 Barrer and 12.2-35.3, respectively. The composite membrane loaded with 8 wt% of ZIF-62 glass showed the highest CO₂ permeability and CO₂/CH₄ ideal selectivity of 84.8 Barrer and 35.3, which were 436.7% and 189.3% higher compared to the pristine CA membrane, respectively. A CO₂ plasticization pressure of 26 bar was achieved for the composite membranes, which is 160% higher compared to the pristine CA membranes, at about 10 bar. The mechanisms for the materials stabilization and greater separation performance were attributed to higher pore size (7.3 Å) and significant CO₂ adsorption on the unsaturated metal nodes followed by metal cites electrostatic interaction with CO₂. These findings confirm the potential of ZIF-62 glass materials as promising materials solutions towards the design of composite membranes for CO₂ separation at industrial scale.

Tailoring the CO2-selectivity of interfacial polymerized thin film nanocomposite membrane via the barrier effect of functionalized boron nitride

Membrane-based separation is an appealing solution to mitigate CO₂ emission sustainably due to its energy efficiency and environmental friendliness. Attributed to its excellent separation endowed by nanomaterial incorporation, nanocomposite membrane is rigorously developed. This study explored the feasibility of boron nitride (BN) embedment and changes to formation mechanism of ultrathin selective layer of thin film nanocomposite (TFN) are investigated. The effects of amine-functionalization on nanosheet-polymer interaction and CO₂ separation performance are also identified. Participation of nanosheets during interfacial polymerization reduced the crosslinking of selective layer, hence, improved TFN permeance while the formation of contorted diffusion paths by the nanosheets favors transport of small gases. Amine-functionalization enhanced the nanosheet-polymer interaction and elevated the membrane affinity towards CO₂ which led to enhanced CO₂ selectivity. The best TFN prepared in this study exhibited 37% and 20% increment in permeability and selectivity, respectively with respect to neat thin film composite (TFC). It is found that the CO₂ separation performance of BN incorporated TFN is on par with many non-porous nanosheet-incorporated TFNs reported in literatures. The transport and barrier effects of BN and functionalized BN are discussed in detail to provide further insights into the development of commercially attractive CO₂ selective TFN membranes.

Modeling the transport of CO2, N2, and their binary mixtures through highly permeable silicalite-1 membranes using Maxwell-Stefan equations

Carbon dioxide (CO₂) is the main contributor to global warming; therefore, research efforts aim at its capture. Membranes, in particular, zeolite membranes offer a promising approach for CO₂ separation and capture. Membranes are typically characterized by their selectivity and permeance that are highly dependent on the operating conditions namely, total feed pressure and composition. Therefore, more reliable characterization parameters are required such as Maxwell- Stefan exchange diffusivities. In this work, a model based on Maxwell-Stefan equations and Extended Langmuir isotherm was developed to investigate the transport of binary mixtures of CO₂ and N₂ through thin silicalite-1 membranes. The exchange diffusivities, D₁₂ and D₂₁, of CO₂ and N₂ were determined at different total feed pressures and feed compositions. All gas separation tests were conducted at stage cut not exceeding 5%. The single component diffusivities of CO₂ and N₂ required by the model were found experimentally using the results of the respective single gas permeation tests. The results displayed that as CO₂ concentration in the feed increased from 15% to 85%, the values of D₁₂ and D₂₁ decreased from 2.8 × 10^-10 to 1.1 × 10^-10 m²/s and 2.8 × 10^-10 to 1.3 × 10^-10 m²/s, respectively, while the N₂ permeance decreased by about one order of magnitude from 2.7 × 10^-7 to 2.4 × 10^-8 mol/m².s.Pa. Consequently, the exchange diffusivities showed considerably smaller dependence on the operating conditions compared to the permselectivity and permeance. Hence, they are more appropriate in describing the intrinsic transport characteristics of silicalite-1 membranes.

Influence of ionic liquid-like cationic pendants composition in cellulose based polyelectrolytes on membrane-based CO2 separation

Cellulose acetate (CA) is an attractive membrane polymer for CO₂ capture market. However, its low CO₂ permeability hampers its application as part of a membrane for most relevant types of CO₂ containing feeds. This work investigates the enhancement of CA separation performance by incorporating ionic liquid-like pendants (1-methylimidazol, 1-methylpyrrolidine, and 2-hydroxyethyldimethylamine (HEDMA) on the CA backbone. These CA-based polyelectrolytes (PEs), synthesised by covalent grafting of cationic pendants with anion metathesis, were characterised by NMR, FTIR, DSC/TGA, and processed into thin-film composite membranes. The membrane performance in CO₂/N₂ mixed-gas permeation experiments shows a decrease in CO₂ and N₂ permeability and an initial decrease and then gradual increase in CO₂/N₂ selectivity with increasing HEDMA content. The amount of HEDMA attached to the CA backbone determines overall separation process in bifunctional PEs. This indicates that the hydroxy-substituted cationic pendants alter interactions between PEs network and permeating CO₂ molecules, suggesting possibilities for further improvements.

Designing silica xerogels containing RTIL for CO2 capture and CO2/CH4 separation: Influence of ILs anion, cation and cation side alkyl chain length and ramification

CO₂ separation from natural gas is considered to be a crucial strategy to mitigate global warming problems, meet product specification, pipeline specs and other application specific requirements. Silica xerogels (SX) are considered to be potential materials for CO₂ capture due to their high specific surface area. Thus, a series of silica xerogels functionalized with imidazolium, phosphonium, ammonium and pyridinium-based room-temperature ionic liquids (RTILs) were synthesized. The synthesized silica xerogels were characterized by NMR, helium pycnometry, DTA-TG, BET, SEM and TEM. CO₂ sorption, reusability and CO₂/CH₄ selectivity were assessed by the pressure-decay technique. Silica xerogels containing IL demonstrated advantages compared to RTILs used as separation solvents in CO₂ capture processes including higher CO₂ sorption capacity and faster sorption/desorption. Using fluorinated anion for functionalization of silica xerogels leads to a higher affinity for CO₂ over CH_4. The best performance was obtained by SX- [bmim] [TF₂N] (223.4 mg CO₂/g mg/g at 298.15 K and 20 bar). Moreover, SX- [bmim] [TF₂N] showed higher CO₂ sorption capacity as compared to other reported sorbents. CO₂ sorption and CO₂/CH₄ selectivity results were submitted to an analysis of variance and the means compared using Tukey's test (5%).

Ionic liquid tethered PEG-based polyurethane-siloxane membranes for efficient CO2/CH4 separation

This study introduces a new polyethylene glycol (PEG) based polyurethane-siloxane membrane containing a quaternary ammonium ionic liquid for CO₂/CH₄ separation. The designed ionic liquid was prepared in two steps: (i) (3-chloropropyl)triethoxysilane (CPS) and N,N-dimethylpropyl amine (NDPA) were reacted with each other to form the methoxysilane-functionalized quaternary ammonium component, then (ii) chloride ion (Cl^-) of the product was exchanged with tetrafluoroborate ion (BF₄^-). The resulting compound, a reactive methoxysilane-functionalized ionic liquid (Si-IL) was chemically anchored to the polymer backbone through the sol-gel hydrolysis and condensation reaction. Based on the permeation tests, the IL containing PEG-based polyurethane-siloxane membranes at different concentration of Si-IL (XSi-PPUIL) were found to be potential candidates for CO₂ removal from CH₄. For instance, the CO₂/CH₄ selectivity of XSi-PPUIL membranes with the Si-IL content of 10 wt% was 3.3-fold greater than the Si-IL free membranes; while, the CO₂ permeability for IL tethered membranes was 9.7% higher than the corresponding IL-free membrane.