Hydrogen separation and purification in membranes of miscible polymer blends with interpenetration networks

Hydrogen Separation Membranes: A Material Perspective

The global energy market is shifting toward renewable, sustainable, and low-carbon hydrogen energy due to global environmental issues, such as rising carbon dioxide emissions, climate change, and global warming. Currently, a majority of hydrogen demands are achieved by steam methane reforming and other conventional processes, which, again, are very carbon-intensive methods, and the hydrogen produced by them needs to be purified prior to their application. Hence, researchers are continuously endeavoring to develop sustainable and efficient methods for hydrogen generation and purification. Membrane-based gas-separation technologies were proven to be more efficient than conventional technologies. This review explores the transition from conventional separation techniques, such as pressure swing adsorption and cryogenic distillation, to advanced membrane-based technologies with high selectivity and efficiency for hydrogen purification. Major emphasis is placed on various membrane materials and their corresponding membrane performance. First, we discuss various metal membranes, including dense, alloyed, and amorphous metal membranes, which exhibit high hydrogen solubility and selectivity. Further, various inorganic membranes, such as zeolites, silica, and CMSMs, are also discussed. Major emphasis is placed on the development of polymeric materials and membranes for the selective separation of hydrogen from CH4, CO2, and N2. In addition, cutting-edge mixed-matrix membranes are also delineated, which involve the incorporation of inorganic fillers to improve performance. This review provides a comprehensive overview of advancements in gas-separation membranes and membrane materials in terms of hydrogen selectivity, permeability, and durability in practical applications. By analyzing various conventional and advanced technologies, this review provides a comprehensive material perspective on hydrogen separation membranes, thereby endorsing hydrogen energy for a sustainable future.

Efficient Helium Separation with Two-Dimensional Metal-Organic Framework Fe/Ni-PTC: A Theoretical Study

Helium (He) is one of the indispensable and rare strategic materials for national defense and high-tech industries. However, daunting challenges have to be overcome for the supply shortage of He resources. Benefitted from the wide pore size distribution, sufficient intrinsic porosity, and high specific surface area, metal–organic framework (MOF) materials are prospective candidates for He purification in the membrane-based separation technology. In this work, through first-principles calculations and molecular dynamics (MD) simulations, we studied the permeability and filtration performance of He by the newly synthesized two-dimensional Fe-PTC MOF and its analogue Ni-PTC MOF. We found that both Fe-PTC and Ni-PTC have superior high performance for He separation. The selectivity of He over N₂ was calculated to be ~10¹⁷ for Fe-PTC and ~10¹⁵ for Ni-PTC, respectively, both higher than most of the previously proposed 2D porous membranes. Meanwhile, high He permeance (10⁻⁴~10⁻³ mol s⁻¹ m⁻² Pa⁻¹) can be obtained for the Fe/Ni-PTC MOF for temperatures ranging from 200 to 500 K. Therefore, the present study offers a highly prospective membrane for He separation, which has great potential in industrial application.

Penetration and Displacement Behavior of N2 in Porous Interlayer Structures Containing Water/Salt Component by Molecular Dynamics Simulation

The penetration and displacement behavior of N₂ molecules in porous interlayer structures containing a water/salt component with porosities of 4.29%, 4.73%, 5.17%, 7.22%, and 11.38% were explored using molecular dynamics simulations. The results demonstrated that the large porosity of the interlayer structures effectively enhanced the permeation and diffusion characteristics of N₂. The water and salt in the interlayer structures were displaced during the injection of N₂ in the porosity sequence of 4.29% < 4.73% < 5.17% < 7.22% < 11.38%. The high permeance of 7.12 × 10⁻⁶ indicated that the interlayer structures with a porosity of 11.38% have better movability. The strong interaction of approximately 15 kcal/mol between N₂ and H₂O had a positive effect on the diffusion of N₂ and the displacement of H₂O before it reached a stable equilibrium state. The distribution of N₂ in porous interlayer structures and the relationship between the logarithm of permeability and breakthrough pressure were presented. This work highlighted the effects of porosity on the permeability and diffusion of N₂/H₂O in the interlayer, thus providing theoretical guidance for the development of petroleum resources.

Mechanochemical Synthesis of Rosin-Modified Montmorillonite: A Breakthrough Approach to the Next Generation of OMMT/Rubber Nanocomposites

The current investigation presents a green mechanochemical procedure for the synthesis of a special kind of rubber-compatible organo-montmorillonite (OMMT) for use in the inner liner compound of tires. The compatibility character of the OMMT arises from the mechanochemical reaction of the raw bentonite mineral and gum rosin as some of the organic constituents of the inner liner composition. The monitoring of OMMT synthesis by various characterization techniques reveals that gum rosin gradually intercalates into the montmorillonite (MMT) galleries during milling and increases the interlayer spacing to 41.1 ± 0.5 Å. The findings confirm the simultaneous formation of single- or few-layered OMMT platelets with average sizes from the sub-micron range up to several micrometers during the milling process. The mechanical properties of the OMMT/rubber nanocomposite, such as tensile strength, tear resistance and elongation, present a good enhancement in comparison to the un-modified material. Moreover, the organo-modification of the inner liner composition also leads to a property improvement of about 50%.

Miscible blend polyethersulfone/polyimide asymmetric membrane crosslinked with 1,3-diaminopropane for hydrogen separation

Efficient purification technology is crucial to fully utilize hydrogen (H2) as the next generation fuel source. Polyimide (PI) membranes have been intensively applied for H2 purification but its current separation performance of neat PI membranes is insufficient to fulfill industrial demand. This study employs blending and crosslinking modification simultaneously to enhance the separation efficiency of a membrane. Polyethersulfone (PES) and Co-PI (P84) blend asymmetric membranes have been prepared via dry–wet phase inversion with three different ratios. Pure H2 and carbon dioxide (CO2) gas permeation are conducted on the polymer blends to find the best formulation for membrane composition for effective H2 purification. Next, the membrane with the best blending ratio is chemically modified using 1,3-diaminopropane (PDA) with variable reaction time. Physical and chemical characterization of all membranes was evaluated using field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR). Upon 15 min modification, the polymer membrane achieved an improvement on H2/CO2 selectivity by 88.9%. Moreover, similar membrane has demonstrated the best performance as it has surpassed Robeson’s upper bound curve for H2/CO2 gas pair performance. Therefore, this finding is significant towards the development of H2-selective membranes with improved performance.

Exploring the Potential Application of Matrimid® and ZIFs-Based Membranes for Hydrogen Recovery: A Review

Hydrogen recovery is at the center of the energy transition guidelines promoted by governments, owing to its applicability as an energy resource, but calls for energetically nonintensive recovery methods. The employment of polymeric membranes in selective gas separations has arisen as a potential alternative, as its established commercial availability demonstrates. However, enhanced features need to be developed to achieve adequate mechanical properties and the membrane performance that allows the obtention of hydrogen with the required industrial purity. Matrimid^®, as a polyimide, is an attractive material providing relatively good performance to selectively recover hydrogen. As a consequence, this review aims to study and summarize the main results, mechanisms involved and advances in the use of Matrimid^® as a selective material for hydrogen separation to date, delving into membrane fabrication procedures that increase the effectiveness of hydrogen recovery, i.e., the addition of fillers (within which ZIFs have acquired extraordinary importance), chemical crosslinking or polymeric blending, among others.

Nanoparticles influence miscibility in LCST polymer blends: from fundamental perspective to current applications

Polymer blending is an effective method that can be used to fabricate new versatile materials with enhanced properties. The blending of two polymers can result in either a miscible or an immiscible polymer blend system. This present review provides an in-depth summary of the miscibility of LCST polymer blend systems, an area that has garnered much attention in the past few years. The initial discourse of the present review mainly focuses on process-induced changes in the miscibility of polymer blend systems, and how the preparation of polymer blends affects their final properties. This review further highlights how nanoparticles induce miscibility and describes the various methods that can be implemented to avoid nanoparticle aggregation. The concepts and different state-of-the-art experimental methods which can be used to determine miscibility in polymer blends are also highlighted. Lastly, the importance of studying miscible polymer blends is extensively explored by looking at their importance in barrier materials, EMI shielding, corrosion protection, light-emitting diodes, gas separation, and lithium battery applications. The primary goal of this review is to cover the journey from the fundamental aspects of miscible polymer blends to their applications.

Theoretically designed two-dimensional γ-C4O as an effective gas separation membrane for hydrogen purification

A high-performance gas separation membrane for hydrogen (H₂) purification is still highly desirable for the sustainable development of our society. Based on the structure of γ-graphyne, we theoretically designed the two-dimensional nanomaterials γ-C₄X (X = O, S or Se) with intrinsic pores that may be suitable for gas separation. By first-principles calculations, we obtained the geometric structures of γ-C₄X, and confirmed that γ-C₄O and γ-C₄S are stable at room temperature. Due to the moderate size of the intrinsic pores, γ-C₄O exhibits a lower diffusion barrier and higher permeance for H₂ than those of γ-C₄S. It is worth noting that at room temperature, the high selectivity (10¹⁹) for separating H₂ from a H₂/CH₄ mixture by γ-C₄O shows great potential for H₂ purification. Moreover, the classic molecular dynamics simulations at 300 K demonstrate that H₂ can easily permeate through the intrinsic pores of γ-C₄O membranes with high permeability and selectivity, which supports our first-principles calculations.

High-efficiency helium separation through an inorganic graphenylene membrane: a theoretical study

Appropriate interactions between an IGP membrane and He molecules result in efficient helium separation.

Synthesis of Imidazolium based PILs and Investigation of Their Blend Membranes for Gas Separation

Polymeric (ionic liquid) (PIL) copolymers bearing cationic imidazolium pendants and polar acrylic acid groups (P(VBCImY-co-AA_x)), which both favor the interaction with CO₂ molecules, have been synthesized and blended with film forming, high glass transition temperature aromatic polyether-based pyridinium PILs (PILPyr). The blend membranes based on the above combination have been prepared and characterized in respect to their thermal and morphological behavior as well as to their gas separation properties. The used copolymers and blends showed a wide range of glass transition temperatures from 32 to 286 °C, while blends exhibited two phase morphology despite the presence of polar groups in the blend components that could participate in specific interactions. Finally, the membranes were studied in terms of their gas separation behavior. It revealed that blend composition, counter anion type and acrylic acid molar percentage affect the gas separation properties. In particular, PILPyr-TFSI/P(VBCImTFSI-co-AA₂₀) blend with 80/20 composition shows CO₂ permeability of 7.00 Barrer and quite high selectivity of 103 for the CO₂/CH₄ gas pair. Even higher CO₂/CH_4. selectivity of 154 was achieved for PILPyr-BF₄/P(VBCImBF₄-co-AA₁₀) blend with composition 70/30.

Transport Properties of Thermoplastic R-BAPB Polyimide: Molecular Dynamics Simulations and Experiment

The present work evaluates the transport properties of thermoplastic R-BAPB polyimide based on 1,3-bis(3,3',4,4'-dicarboxyphenoxy)benzene (dianhydride R) and 4,4'-bis(4-aminophenoxy)biphenyl (diamine BAPB). Both experimental studies and molecular dynamics simulations were applied to estimate the diffusion coefficients and solubilities of various gases, such as helium (He), oxygen (O2), nitrogen (N2), and methane (CH4). The validity of the results obtained was confirmed by studying the correlation of the experimental solubilities and diffusion coefficients of He, O2, and N2 in R-BAPB, with their critical temperatures and the effective sizes of the gas molecules, respectively. The solubilities obtained in the molecular dynamics simulations are in good quantitative agreement with the experimental data. A good qualitative relationship between the simulation results and the experimental data is also observed when comparing the diffusion coefficients of the gases. Analysis of the Robeson plots shows that R-BAPB has high selectivity for He, N2, and CO2 separation from CH4, which makes it a promising polymer for developing gas-separation membranes. From this point of view, the simulation models developed and validated in the present work may be put to effective use for further investigations into the transport properties of R-BAPB polyimide and nanocomposites based on it.

A brief review on carbon selective membranes from polymer blends for gas separation performance

The development of carbon membranes for the separation of various gases has gained interest among researchers due to their superior performance in gas separation. The preparation of carbon membranes by blending materials has many advantages including time and cost effectiveness for tuning the properties of the membranes. Here we review the recent research progress that has been made in the context of breakthroughs and challenges in the development of carbon membrane materials. In addition, we provide information regarding carbon membrane fabrication in terms of the selection of precursors and additives, carbon membrane process conditions, and coating conditions that influence the performance of gas separation of the resulting carbon membranes. The perspectives and future research directions for carbon membranes are also presented.

Improved Hydrogen Separation Using Hybrid Membrane Composed of Nanodiamonds and P84 Copolyimide

Membrane gas separation is a prospective technology for hydrogen separation from various refinery and petrochemical process streams. To improve efficiency of gas separation, a novel hybrid membrane consisting of nanodiamonds and P84 copolyimide is developed. The particularities of the hybrid membrane structure, physicochemical, and gas transport properties were studied by comparison with that of pure P84 membrane. The gas permeability of H₂, CO₂, and CH₄ through the hybrid membrane is lower than through the unmodified membrane, whereas ideal selectivity in separation of H₂/CO₂, H₂/CH₄, and CO₂/CH₄ gas pairs is higher for the hybrid membrane. Correlation analysis of diffusion and solubility coefficients confirms the reliability of the gas permeability results. The position of P84/ND membrane is among the most selective membranes on the Robeson diagram for H₂/CH₄ gas pair.