Gas Separation Applications Research Articles

CO2-selective poly (ether-block-amide)/polyethylene glycol composite blend membrane for CO2 separation from gas mixtures

This work focuses on the preparation of composite blend membranes based on poly (ether-block-amide) (Pebax-1657) by incorporating polyethylene glycol (PEG) for gas separation applications. The influence of PEG with different molecular weights (PEG600, PEG1500, and PEG4000) at loading content in the range of 10%wt. to 40%wt. was investigated on the microstructure and gas separation performance of the prepared blend membranes. The fabricated membranes were characterized using SEM, XRD, and water contact angle analyses. Based on the experimental results, the blending of low molecular weight PEG (PEG600) into the Pebax-1657 matrix increased the chain mobility of the membrane, led to a smooth microstructure, and improved the hydrophilicity of the blend membranes, as well as enhanced the gas permeability of N2, O2, CH4, and CO2, but only slightly affected the ideal selectivity of O2/N2, CH4/N2, CO2/N2, and CO2/CH4. In contrast, the incorporation of PEG1500 and PEG4000 meaningfully increased the membrane crystallinity, decreased chain mobility, resulted in a rough microstructure, and reduced the blend membranes' hydrophilicity. For CO2/N2 mixture, the Pebax/40%PEG600 membrane had CO2 permeability of 62.9 Barrer and selectivity of 83.8, while the Pebax/20%PEG600 showed the CO2 permeability of 63.12 Barrer and selectivity of 23.6 for CO2/CH4 separation.

Development of Novel Polyamide-Imide/DES Composites and Their Application for Pervaporation and Gas Separation.

Novel polymer composites based on polyamide–imide Torlon and deep eutectic solvent (DES) were fabricated and adapted for separation processes. DES composed of zinc chloride and acetamide in a ratio of 1:3 M was first chosen as a Torlon-modifier due to the possibility of creating composites with a uniform filling of the DES through the formation of hydrogen bonds. The structure of the membranes was investigated by scanning electron microscopy and X-ray diffraction analysis; thermal stability was determined by thermogravimetric analysis and mass spectrometry. The surface of the composites was studied by determining the contact angles and calculating the surface tension. The transport properties were investigated by such membrane methods as pervaporation and gas separation. It was found that the inclusion of DES in the polymer matrix leads to a significant change in the structure and surface character of composites. It was also shown that DES plays the role of a plasticizer and increases the separation performance in the separation of liquids and gases. Torlon/DES composites with a small amount of modifier were effective in alcohol dehydration, and were permeable predominantly to water impurities in isopropanol. Torlon/DES-5 demonstrates high selectivity in the gas separation of O2/N2 mixture.

Mixed Matrix Membranes Based on Fluoropolymers with m- and p-Terphenyl Fragments for Gas Separation Applications.

Novel mixed matrix membranes (MMMs) based on fluoropolymers with m- and p-terphenyl fragments and NaX zeolites were prepared. The fluoropolymers were synthesized by a one-pot, room-temperature, metal-free superacid-catalyzed stoichiometric and nonstoichiometric step polymerization of 2,2,2-trifluoroacetophenone with two multiring aromatic nonactivated hydrocarbons (p-terphenyl and m-terphenyl). MMMs were characterized by scanning electron microscopy (SEM) and infrared (Fourier transform infrared (FTIR)) spectroscopy and used in gas permeability tests. SEM analysis showed interfacial voids in MMMs prepared in N-methyl-2-pyrrolidone (NMP), The interfacial adhesion in the polymer–zeolite system was considerably improved when chloroform was used as a solvent. Permeability coefficients for pristine polymer membranes were 1.3-fold higher in CHCl3 than in NMP for p-terphenyl fragment and 2.0 times higher in NMP than in CHCl3 for the polymer with m-terphenyl fragment. The incorporation of NaX zeolites in the polymeric matrices improved the gas permeability coefficients compared to the pristine membranes. The effects of polymer architecture, casting solvent, and interaction between the organic matrix and the inorganic particles on the gas separation performance of the developed MMMs were investigated.

Polyoctahedral Silsesquioxane Hexachlorocyclotriphosphazene Membranes for Hot Gas Separation.

There is a need for gas separation membranes that can perform at high temperatures, for example, for CO2 capture in industrial processes. Polyphosphazenes classify as interesting materials for use under these conditions because of their high thermal stability, hybrid nature, and postfunctionalization options. In this work, thin-film composite cyclomatrix polyphosphazene membranes are prepared via the interfacial polymerization reaction between polyhedral oligomeric silsesquioxane and hexachlorocyclotriphosphazene on top of a ceramic support. The prepared polyphosphazene networks are highly crosslinked and show excellent thermal stability until 340 °C. Single gas permeation experiments at temperatures ranging from 50 to 250 °C reveal a molecular sieving behavior, with permselectivities as high as 130 for H2/CH4 at the low temperatures. The permselectivities of the membranes persist at the higher temperatures; at 250 °C H2/N2 (40), H2/CH4 (31) H2/CO2 (7), and CO2/CH4 (4), respectively, while maintaining permeances in the order of 10–7 to 10–8 mol m–2 s–1 Pa–1. Compared to other types of polymer-based membranes, especially the H2/N2 and H2/CH4 selectivities are high, with similar permeances. Consequently, the hybrid polyphosphazene membranes have great potential for use in high-temperature gas separation applications.

Recovery of free volume in PIM-1 membranes through alcohol vapor treatment

Physical aging is currently a major obstacle for the commercialization of PIM-1 membranes for gas separation applications. A well-known approach to reversing physical aging effects of PIM-1 membranes at laboratory scale is soaking them in lower alcohols, such as methanol and ethanol. However, this procedure does not seem applicable at industrial level, and other strategies must be investigated. In this work, a regeneration method with alcohol vapors (ethanol or methanol) was developed to recover permeability of aged PIM-1 membranes, in comparison with the conventional soaking-in-liquid approach. The gas permeability and separation performance, before and post the regeneration methods, were assessed using a binary mixture of CO2 and CH4 (1:1, v:v). Our results show that an 8-hour methanol vapor treatment was sufficient to recover the original gas permeability, reaching a CO2 permeability > 7000 barrer.

A review on recent advances in CO2 separation using zeolite and zeolite-like materials as adsorbents and fillers in mixed matrix membranes (MMMs)

Anthropogenic emissions have developed the environmental demands for proficient carbon dioxide (CO2) separation technologies. Adsorption and membrane technologies are widely used to separate CO2 from other light gases due to their multiple technological benefits, including but not limited to factors such as energy efficiency and low environmental footprint. In this context, zeolites are often used due to their intrinsic molecular sieving capacity. This review initially addresses recent technological advances to enhance the gas separation performance of zeolite materials. Current trends directed toward improving CO2 adsorption capacity of zeolites include amine, silica, and ion-exchange modifications. Other promising efforts to improve the adsorption performance of zeolites involve processing zeolite nanoparticles, nanofibers, and zeolite-based foams. The second part of the review deals with pristine and modified zeolites beneficial properties for designing polymer-based mixed matrix membranes (MMMs), which enable to adapt a desirable gas separation performance. The gas transport mechanisms and morphological properties of MMMs are essential. This review addresses the most current strategies used to improve interfacial adhesions between zeolite particulates and polymer matrices to overcome the trade-off between gas selectivity and permeability faced by pure polymeric membranes. Filler shape and size play vital roles in determining the filler and polymer matrix's interfacial adhesions. New structures of inorganic fillers have been designed to fabricate MMMs with excellent gas transport properties. Hollow zeolite spheres (HZSs) are particularly interesting as they effectively minimize agglomeration and improve filler dispersion in the polymer matrix. Furthermore, approaches that employ nanoporous layered fillers, including AMH-3 and Jilin-Davy-Faraday, layered solid No. 1 (JDF-L1), have been reviewed to overcome the limitation of incorporating high contents of zeolites, which are required to improve the gas transport properties of MMMs. Furthermore, this review explores implementing zeolitic imidazolate frameworks (ZIFs) in MMMs because of their tunable pore structure and remarkably high adsorption capacity and surface area as well as excellent chemical and thermal properties. Lastly, we address the prospects and future developments in gas separation applications.

Development of H2 selective silica membranes: Performance evaluation through single gas permeation and gas separation tests

To prove the usefulness and achieve penetration of microporous ceramic membranes in gas separation applications of industrial interest, their behavior needs to be validated and predicted at relatively realistic conditions. In this respect, the present study employed hybrid silica (HybSi) membranes, modified by chemical vapor infiltration (CVI) in order to render them more selective to hydrogen in hydrogen/carbon dioxide binary mixtures, which are representative to effluent streams of methane or biogas steam reforming/water gas shift processes. Experimental studies with a single modified membrane exhibited high hydrogen permeance (1.5.10−7 mol.m−2.s−1.Pa−1, at 250 °C) and H2/CO2 permselectivity (H2/CO2 = 61.3, at 250 °C). Gas separation tests with binary gas mixtures revealed that high hydrogen purity values (>99%) can be reached at different process conditions. The mathematical model, also developed in this study in order to interpret the experimental results, can reliably predict hydrogen separation process performance over a wide range of operating conditions and also serve as a tool for subsequent optimum process engineering purposes.

A Review on Glassy and Rubbery Polymeric Membranes for Natural Gas Purification

AbstractA comprehensive overview of membrane technology used for natural gas purification and other gas separation applications including methods, materials, and results described in previous studies is presented. Different membrane categories are elaborated thoroughly followed by comparisons made between glassy and rubbery polymeric membranes. Various approaches to improve membrane separation performance, such as incorporation of inorganic fillers and blending technique, are discussed. Gas separation in different membranes, e.g., glassy/rubbery polymer blend membranes, mixed matrix membranes, and polymeric blend mixed matrix membranes, are considered. Adopted techniques by researchers to solve existing issues in membrane fabrication and performance are explained in detail.

A Review on Ionic Liquid Gas Separation Membranes.

Ionic liquids have attracted the attention of the industry and research community as versatile solvents with unique properties, such as ionic conductivity, low volatility, high solubility of gases and vapors, thermal stability, and the possibility to combine anions and cations to yield an almost endless list of different structures. These features open perspectives for numerous applications, such as the reaction medium for chemical synthesis, electrolytes for batteries, solvent for gas sorption processes, and also membranes for gas separation. In the search for better-performing membrane materials and membranes for gas and vapor separation, ionic liquids have been investigated extensively in the last decade and a half. This review gives a complete overview of the main developments in the field of ionic liquid membranes since their first introduction. It covers all different materials, membrane types, their preparation, pure and mixed gas transport properties, and examples of potential gas separation applications. Special systems will also be discussed, including facilitated transport membranes and mixed matrix membranes. The main strengths and weaknesses of the different membrane types will be discussed, subdividing them into supported ionic liquid membranes (SILMs), poly(ionic liquids) or polymerized ionic liquids (PILs), polymer/ionic liquid blends (physically or chemically cross-linked ‘ion-gels’), and PIL/IL blends. Since membrane processes are advancing as an energy-efficient alternative to traditional separation processes, having shown promising results for complex new separation challenges like carbon capture as well, they may be the key to developing a more sustainable future society. In this light, this review presents the state-of-the-art of ionic liquid membranes, to analyze their potential in the gas separation processes of the future.

Zirconium-Based Metal–Organic Framework Particle Films for Visible-Light-Driven Efficient Photoreduction of CO2

Metal–organic framework (MOFs) films have a wide range of applications in gas separation and chemical sensing. By contrast, MOF films have rarely been reported in the field of photocatalysis. Compa...

Towards the synthesis of greener membranes: Interest of PVA as porous support for membrane application in gas and liquid separations

Most of the porous supports are prepared by phase inversion method by using classical and toxic solvents: NMP, DMF, THF, DMSO, … These supports present 95–99% of total thickness and the active layer presents only 0.1 1–3 µm. It is necessary to find new green method and material to prepare these supports. This paper describes the possibility to use a biodegradable polymer polyvinyl alcohol (PVA) to prepare porous support by using water as a solvent and aqueous or alcohol solutions as a coagulation bath. The SEM microscope is used to study the influence of the composition of polymer solution and the coagulation bath on the structure of prepared membrane. In addition, the life cycle assessment (LCA) tool is used to evaluate the environmental impacts for different preparations and compared with others from bibliography. Finally, a membrane with PVA dense and porous structure was prepared.

Remarkably enhanced gas separation properties of PIM-1 at sub-ambient temperatures

Sub-ambient temperature membrane-based separation is attracting more and more attention in solving the industrial energy intensive separation challenges. However, the research on low temperature gas separation properties of polymeric membranes is limited. Here, gas separation performance of an intrinsic microporous polymer (PIM-1) at temperatures of −30, −20, −10, 0, 10, and 30 °C were fully characterized for the first time. As the temperature decreases, there was a continuous drop in He, H2, N2, O2, CH4 and CO2 permeability coupled with a sharply increased ideal gas pair selectivity with the overall performance gradually outperformed the latest trade-off curves for H2/N2, O2/N2, CO2/CH4 and CO2/N2. In which, the O2 and CO2 permeability of PIM-1 at −30 °C reached as much as 159 and 1380 Barrer, combined with O2/N2 and CO2/N2 ideal selectivity of 9.35 and 81.2, respectively. The drop in permeability originated from the decresaed diffusion coefficients that overweigh the solubility increase, whereas the increased ideal selectivity was due to the enhanced ideal diffusion selectivity (aD), especially the energetic factor of the ideal diffusivity selectivity upon decreasing temperatures. The higher performance induced by low temperatures derived from the shrinkage of the micropore in PIM-1 to more size sieving ultra-micropore region. Additionally, an O2 permeability of 157 Barrer and O2/N2 selectivity of 8.0 for mixed-gas at −20 °C under upstream pressure of 16 bar was observed. The results indicate that PIM-1 operates at sub-ambient temperature has great perspective in gas separation applications.

Rapid temperature-assisted synthesis of nanoporous γ-cyclodextrin-based metal–organic framework for selective CO2 adsorption

We present a rapid and surfactant-free temperature-assisted synthesis route to prepare γ-cyclodextrin-based metal–organic framework (γ-CD-MOF). The cubic crystals of the CD-MOF with an average edge length of 10–15 µm, specific surface area of 775 m2 g−1 and total pore volume of 0.229 cm3 g−1 were synthesized in much shorter time than conventional CD-MOFs. To show the efficiency of the synthesized CD-MOF as adsorbent of gas, the uptake of CO2 at different temperature and pressure was investigated. It is shown that the CO2 uptake increases with increasing pressure and decreasing temperature. Further microgravimetric investigation on gas adsorption at low pressure demonstrated superior gas uptake (ca. 147 mg g−1) than previous reports. At the maximum equilibrium pressure, the uptake amounts of CO2 were found to be 326 and 268 mg g−1 at 303 and 323 K, respectively. The synthesized CD-MOF has great potential to be used in gas storage and separation applications.

One-step synthesis of hydroxyl-functionalized fully carbon main chain PIMs via a Friedel-Crafts reaction for efficient gas separation

High performance, robust polymeric membranes are playing more and more important roles in recent large scale industrial gas separation applications. One of the biggest challenges is scaling up the high performance polymeric materials. Herein, a one-step super-acid catalyzed condensation reaction was reported to synthesize two novel hydroxyl-functionalized fully carbon main chain intrinsic microporous polymers (HSBI-Is and HBIN-Is) with high efficiency. Both polymers demonstrated high molecular weight, good thermal stability with Td above 360 °C, and modest microporosity. HSBI-Is exhibited a more open structure with higher BET surface area (523 vs 57 m2 g−1), larger fractional free volume (0.212 vs 0.162), and d-spacing (5.16 vs 3.68 Å) than HBIN-Is due to its more rigid and bulky spirobisindane (SBI) site of contortion. Membranes based on HSBI-Is and HBIN-Is showed moderate to high permeabilities and selectivitites with H2/N2, H2/CH4, O2/N2 and CO2/CH4 close to or even beat the 2008 trade-off curves. In which, the HBIN-Is showed a remarkable CO2/CH4 selectivity of 73.8, and the HSBI-Is demonstrated a remarkable O2/N2 selectivity of 10.4 at −20 °C due to the sharply increased diffusion selectivity. Both polymer membranes showed excellent plasticization resistance up to 25 bar upstream pressure, endowing the polymerization method and the hydroxyl functionalized intrinsic microporous polymers of great potential in real gas separation applications.

ZIF-95 as a filler for enhanced gas separation performance of polysulfone membrane.

Metal–organic frameworks (MOFs) are found to be promising porous crystalline materials for application in gas separation. Considering that mixed matrix membranes usually increase the gas separation performance of a polymer by increasing selectivity, permeability, or both (i.e., perm-selectivity), the zeolitic imidazole framework-95 (ZIF-95) MOF was dispersed for the first time in polysulfone (PSF) polymer to form mixed matrix membranes (MMMs), namely, ZIF-95/PSF. The fabricated ZIF-95/PSF membranes were examined for the separation of various gases. The characterization of solvothermally synthesized ZIF-95 was carried out using different analyses such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), porosity measurements, etc. ZIF-95 was mixed with PSF at 8%, 16%, 24%, and 32% weight percent to form different loading MMMs. SEM analysis of membranes revealed good compatibility/adhesion between the MOF and polymer. The permeability of He, H2, O2, CO2, N2, and CH4 were measured for the pure and composite membranes. The ideal selectivity of different gas pairs were calculated and compared with reported mixed matrix membranes. The maximum increases in permeabilities were observed in 32% loaded membrane; nevertheless, these performance/permeability increases were at the expense of a slight decrease of selectivity. In the optimally loaded membrane (i.e., 24 wt% loaded membrane), the permeability of H2, O2, and CO2 increased by 80.2%, 78.0%, and 67.2%, respectively, as compared to the pure membrane. Moreover, the selectivity of H2/CH4, O2/N2, and H2/CO2 gas pairs also increased by 16%, 15%, and 8% in the 24% loaded membrane, respectively.

A self-assembling, biporous, metal-binding covalent organic framework and its application for gas separation

A self-assembling, biporous covalent organic framework has been constructed from a single monomer and applied to gas separations. Coordination of transition metals in the monomer leads to highly ordered arrangements of metals in the 2D-materials.

Computational modelling of adsorption and diffusion properties of CO2 and CH4 in ZIF-8 for gas separation applications: a density functional theory approach

Understanding of zeolitic imidazolate framework-8 (ZIF-8) interaction with different gas molecules is crucial when ZIF-8 is used in gas separation.

The development of a comprehensive toolbox based on multi-level, high-throughput screening of MOFs for CO/N2 separations.

The separation of CO/N2 mixtures is a challenging problem in the petrochemical sector due to the very similar physical properties of these two molecules, such as size, molecular weight and boiling point. To solve this and other challenging gas separations, one requires a holistic approach. The complexity of a screening exercise for adsorption-based separations arises from the multitude of existing porous materials, including metal–organic frameworks. Besides, the multivariate nature of the performance criteria that needs to be considered when designing an optimal adsorbent and a separation process – i.e. an optimal material requires fulfillment of several criteria simultaneously – makes the screening challenging. To address this, we have developed a multi-scale approach combining high-throughput molecular simulation screening, data mining and advanced visualization, as well as process system modelling, backed up by experimental validation. We have applied our recent advances in the engineering of porous materials' morphology to develop advanced monolithic structures. These conformed, shaped monoliths can be used readily in industrial applications, bringing a valuable strategy for the development of advanced materials. This toolbox is flexible enough to be applied to multiple adsorption-based gas separation applications.

Room-Temperature Synthesis of BPH Zeolite Nanosheets Free of Organic Template with Enhanced Stability for Gas Separations

BPH-type synthetic aluminosilicate zeolite (Linde Q) nanosheets are synthesized at room temperature without organic structure-directing agents (OSDAs). The BPH nanosheets (7 nm thick, 90 nm across; Si/Al = 1.3) are formed in a colloidal suspension using a mixture of structure-directing cations (Cs+, K+, and Na+). In situ XRD reveals the high stability of the BPH nanosheets up to 500 °C under vacuum (0.021 mbar) due to the presence of Cs+. The high CO2 adsorption capacity (3.78 mmol/g) and stability of the BPH nanosheets open the door for the preparation of oriented thin films and membranes for gas separation applications.

Gas permeation properties of highly cross-linked castor oil-based polyurethane membranes synthesized through thiol-yne click polymerization

In this paper, a new chemistry approach was developed for synthesis of castor oil (CO)-based polyurethane (PU) membranes to attain improved structural properties for gas separation applications. For this purpose, propyne-terminated CO-based PU prepolymer (PTPU) was synthesized by the reaction of CO and isophorone diisocyanate (IPDI), followed by propargyl alcohol (PrAl) and isocyanate (NCO) terminated prepolymer reaction. The ultimate membranes were prepared through thiol-yne cross-linking reaction of PTPU and pentaerythritol tetrakis (3-mercaptopropionate) (PETMP), in presence of azobisisobutyronitrile (AIBN), as a reaction initiator. It was revealed that mechanical and thermal properties of the prepared membranes were improved owing to the formation of flexible thioether linkages through cross-linking reaction. The gas permeation measurements were carried out in the temperature and pressure ranges of 298–338 K and 200–1200 kPa, respectively. The results exhibited reverse size selective performance, as a typical transport behavior of rubbery membranes. The infinite dilution permeability coefficient of CO2 at 298 K was found identical to 2.78 Barrer, along with the infinite dilution perm-selectivity values for CO2/CH4 and CO2/H2 obtained equal to 25.27 and 7.94, respectively. Furthermore, higher permeation activation energies were found in this work compared to a number of cross-linked rubbery membranes in the literature, such as poly (dimethylsiloxane) (PDMS) and poly(ethylene glycol) diacrylate (PEGDA).