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![Figure 14. Chemical structures of PAEK and Azide. Adapted from [113]...](publication/352829146/figure/fig5/AS:1040087429173249@1624987575928/Chemical-structures-of-PAEK-and-Azide-Adapted-from-113-with-permission-Copyright_Q320.jpg)
Carbon molecular sieve (CMS) membranes have been developed to replace or support energy-intensive cryogenic distillation for olefin/paraffin separation. Olefin and paraffin have similar molecular properties, but can be separated effectively by a CMS membrane with a rigid, slit-like pore structure. A variety of polymer precursors can give rise to di...
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... addition, it is believed that the bulky 6F group gives rise to a CMS membrane with higher gas permeability if derived from 6FDA-based polymers than if derived from Matrimid [116]. Furthermore, the 6FDA-based polyimides facilitate tuning of the chemical structure, which allows the polymer precursor to provide a variety of physical properties, as shown in Figure 8. ...
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Surplus lignin, which is inefficiently used, is generated in the forestry industry. Currently, most studies use lignin instead of phenol to synthesize thermosetting resins which cannot be reprocessed, thus affecting its application field. Thermoplastic phenolic resin has an orderly structure and excellent molding performance, which can greatly impr...
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... Membrane-based gas separations have become an active research topic over the past few decades [1][2][3][4][5][6]. Among the different types of membrane systems studied, carbon molecular sieve membranes (CMSMs) are attractive due to their stability under harsh industrial conditions (e.g., high temperature), their chemical resistance, and their unprecedented gas separation performance [7][8][9][10]. ...
The use of immiscible polymer blends in gas separations is limited due to uncontrollable phase separation. In contrast, compatibilized immiscible polymer blends can be used as precursors with controlled morphologies that allow for a unique pore architecture. Herein, an immiscible polymer blend (1:1) comprising polybenzimidazole (PBI) and the copolyimide 6FDA-DAM:DABA [3:2], derived from reacting 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 2,4,6-trimethyl-1,3-phenylenediamine (DAM) and 3,5-diaminobenzoic acid (DABA), were combined with durene diamine as a compatibilizer. The compatibilizer helped reduce the 6FDD domain sizes from 5.6 µm down to 0.77 µm and induced a more even 6FDA distribution and the formation of continuous thin-selective PBI layers. The carbon–carbon composite membranes derived from the compatibilized immiscible polymer blends showed a 3-fold increase in both H2 permeability and H2/CO2 selectivity compared to the membranes derived from non-compatibilized polymer blends. The H2 permeability of the compatibilized immiscible polymer blends increased from 3.6 to 27 Barrer, and their H2/CO2 selectivity increased from 7.2 to 20. The graphitic domain size of the carbon–carbon composite membranes derived from the polymer blends also increased from 6.3 nm for the non-compatibilized blend to 10.0 nm for the compatibilized blend.
... Regardless of the metal present in the composition, CPO-27 exhibits a honeycomb-like structure with a pore opening of around 11 Å. Each M 2+ is also coordinated to an oxygen atom from an adsorbed water molecule, which can be desorbed upon heating, generating an unsaturated metal site [8,9], with a high potential for σ and π bond interactions [10,11]. Thus, this material can play a role in hydrogen storage [4,12], CO 2 adsorption [13][14][15], CH 4 capture [16], ammonia adsorption [17], xylene isomers separation [18], CH 4 /CO 2 separation [19,20], CO 2 /N 2 separation [21], ethane/ethylene separation [22], propane/propene separation [22,23], ...
The employment of metal-organic frameworks in powder form is undesirable from an industrial perspective due to process and safety issues. This work is devoted to evaluating the impact of compression on the textural and structural properties of CPO-27(Ni). For this purpose, CPO-27(Ni) was synthesized under hydrosolvothermal conditions and characterized. Then, the resulting powder was compressed into binderless pellets using variable compression forces ranging from 5–90 kN (37–678 MPa) and characterized by means of nitrogen adsorption/desorption, thermogravimetric analysis and powder X-ray diffraction to evaluate textural, thermal and structural changes. Both textural and structural properties decreased with increasing compression force. Thermal stability was impacted in pellets compressed at forces over 70 kN. CPO-27(Ni) pelletized at 5, 8 and 10 kN, and retained more than 94% of its initial textural properties, while a loss of about one-third of the textural property was observed for the two most compressed samples (70 and 90 kN) compared to the starting powder.
... The precursors with different molecular weights will result in different degrees of structural rearrangement and pore size distribution. Some polymer precursors with lower molecular weight would have higher chain mobility and fractional free volume [104]. A variety of polymer precursors such as phenolic resin, polyetherimide, polyimide (and aromatic polyimide), polyfurfuryl alcohol, poly(2,6-dimethyl-1,4-phenylene oxide), poly(phthalazinone ether sulfone ketone), cellulose have been investigated for H 2separation carbon membranes [105]. ...
Hydrogen is a clean energy carrier that will allow the world to accomplish its strategic targets of zero-emission and the decarbonization of industry. The development of environmentally friendly, energy-efficient hydrogen production processes gains increased attention from both academia and industry. Blue hydrogen produced from the steam methane reforming process integrated with CO2 capture is considered the bridge for an energy transition from fossil fuels to a hydrogen economy. While green hydrogen production from water electrolysis using renewable energies of wind and solar power is becoming a hot topic, and several large-scale green hydrogen projects are under deployment. Membrane technology can be instrumental for hydrogen production and enrichment either in the blue or green form. The challenge of bringing down the costs for membrane materials such as hydrogen-selective membranes, polymer electrolyte membranes (PEM), and anion exchange membranes (AEM), etc. must be addressed to enhance their competitiveness compared to the grey hydrogen produced from fossil fuels. Other challenges including the aging phenomenon, long-time stability, performance enhancement, and upscaling should be also overcome for hydrogen rainbow towards industrial decarbonization. Furthermore, suitable process intensification techniques based on membranes can effectively enhance the energy efficiency of the whole process to enable the practical deployment of this technology. Herein, this work conducts a critical review of the status of membrane material performances and the challenges of membrane processes for hydrogen production, purification, and recovery. Some emerging materials like two-dimensional (2D) nanomaterials and carbon membranes show a particular interest in this field. However, to meet the requirements of different scenarios, further developments of materials and modules, combining membranes with other processes or technologies, and incorporating process simulation are necessary and urgent. 50 days' free access: https://authors.elsevier.com/a/1hK-Z4x7R2gOu%7E
... While previous review articles have examined the use of conventional membrane precursors such as Kapton®, P84, polyphenylene oxide (PPO), poly(furfuryl alcohol) (PFA), phenolic resins, and polyetherimide (PEI) [29][30][31][32], there are still gaps in the literature that need to be addressed to provide a more comprehensive review of CMSMs. For instance, previous reviews have primarily focused on specific gas pairs, such as CO 2 separation [33] or olefin/paraffin separation [34], with less emphasis on other factors such as mass transfer, characterization tools, and economic analysis. Liu et al. [35], provided a review from a materials standpoint, but did not provide an in-depth discussion on membrane performance. ...
... The selection of appropriate polymeric precursors is the first and one of the most important steps in the fabrication of CMSMs. Although thermoplastic polymers have been used as the raw material for CMSMs, thermosetting polymers are most commonly used as precursors, as they do not liquefy at high temperatures or soften during pyrolysis [34,36]. The polymeric precursor used, irrespective of its type, should have a high glass transition temperature (T g ), high aromatic carbon content, and high chemical stability, such that the resulting CMSM has sufficiently good gas separation performance. ...
Carbon molecular sieve membranes (CMSMs) have drawn substantial research attention in recent years due to their ability to overcome the trade-off limitation between permeability and selectivity that is commonly observed in polymeric membranes used for gas separation. The performance of CMSMs is governed by various factors, such as the choice of polymeric precursors and their pre-treatment, pyrolysis, and post-treatment conditions. This review examines the critical aspects in the process of developing CMSMs based on polyimide precursors for gas separation. In addition, the mass transfer mechanism and characterization methods of CMSMs are discussed. Then, the performances of various CMSMs developed so far are examined against the Robeson upper bound limit, and pilot-scale applications and an economic analysis of CMSM-based gas separation are provided. Finally, the challenges and perspective are presented as the concluding remarks.
... In addition, by carefully choosing the precursors and precisely tuning the pore size of the CMS membranes, high gas permeability and selectivity can be obtained simultaneously due to their rigid and microporous bimodal pore structures [8]. CMS membranes have shown promising separation performances in many different applications, such as hydrogen (H 2 ) purification [9,10], helium (He) recovery [11], olefin/ paraffin separation [12] and CO 2 capture [13]. Furthermore, CMS membranes can be also fabricated into flexible, asymmetric hollow fibers, making it into a rather attractive separation material for various separation applications [6]. ...
... Various polymer precursors, including polyimides, polybenzimidazoles, phenolic resin, polyacrylonitrile (PAN), polyfurfuryl alcohol (PFA), PIMs, cellulose, polysulfones, etc., have been fabricated into CMSMs via pyrolysis. 74 During this process, H 2 evolution forms a graphite-like structure and heteroatom elimination results in polymer chain rearrangement. 75 Therefore, the microporosity of CMSMs is primarily manipulated by the polymer precursors and the pyrolysis conditions such as the pyrolysis atmosphere, temperature, pyrolysis time, and ramp rate. ...
The implementation of synthetic polymer membranes in gas separations, ranging from natural gas sweetening, hydrogen separation, helium recovery, carbon capture, oxygen/nitrogen enrichment, etc., has stimulated the vigorous development of high-performance membrane materials. However, size-sieving types of synthetic polymer membranes are frequently subject to a trade-off between permeability and selectivity, primarily due to the lack of ability to boost fractional free volume while simultaneously controlling the micropore size distribution. Herein, we review recent research progress on microporosity manipulation in high-free-volume polymeric gas separation membranes and their gas separation performance, with an emphasis on membranes with hourglass-shaped or bimodally distributed microcavities. State-of-the-art strategies to construct tailorable and hierarchically microporous structures, microporosity characterization, and microcavity architecture that govern gas separation performance are systematically summarized.
Keywords: Gas separation membranes; Hierarchical microporosity; Micropore size distribution; Configurational free volume; Solution–diffusion mechanism.
... Facilitated transport membranes have shown impressive separation performance for C 2 H 4 /C 2 H 6 based on the strong π-bonding interaction between ethylene and metallic carriers (e.g., Ag + , Cu + ) [14]. The membranes, however, typically show rapid and large performance loss because the metallic carriers are easily lost or poisoned by impurities, making them questionable for industrial application [15]. Molecular sieve membranes, including crystalline molecular sieve (e.g., zeolites, metal organic frameworks MOFs) and carbon molecular sieve membranes, consist of rigid pore structures that can provide the possibility of size and shape selective separations for C 2 H 4 /C 2 H 6 , thus exhibiting excellent gas separation performance [12]. ...
... Aromatic polyimides have been the most studied precursors due to their good thermochemical stability and elevated carbon yield. 11,12,17,18 Additionally, they are easy to produce with high molecular weights, and a large variety of polyimide structures have been synthesized to date. 19 Several studies on the relationship between the precursor polyimide structure, pyrolysis conditions, and properties of the final CMSMs have been published. ...
... Up to now, numerous polymeric precursors have been subjected to a variety of carbonization processes in order to develop CMSMs with excellent separation performances. These precursors include polyimides, cellulose, poly(furfuryl alcohol), polyetherimide, polyacrylonitrile, poly(vinylidene chloride), phenolic resins, and resorcinol-formaldehyde resins, etc. [30,31]. Amorphous microporous carbon membranes are promising materials for gas separation applications because of their superior thermal resistance, chemical stability in corrosive environments, higher gas permeabilities, and exceptional separation selectivity compared to available polymeric membranes. ...
In the present study, the concept of Ionic Liquid (IL)-mediated formation of carbon was applied to derive composite membranes bearing a nanoporous carbon phase within their separation layer. Thermolytic carbonization of the supported ionic liquid membranes, prepared by infiltration of the IL 1-methyl-3-butylimidazolium tricyanomethanide into the porous network of Vycor® porous glass tubes, was applied to derive the precursor Carbon/Vycor® composites. All precursors underwent a second cycle of IL infiltration/pyrolysis with the target to finetune the pore structural characteristics of the carbonaceous matter nesting inside the separation layer. The pore structural assets and evolution of the gas permeation properties and separation efficiency of the as-derived composite membranes were investigated with reference to the duration of the second infiltration step. The transport mechanisms of the permeating gases were elucidated and correlated to the structural characteristics of the supported carbon phase and the analysis of LN2 adsorption isotherms. Regarding the gas separation efficiency of the fabricated Carbon/Vycor® composite membranes, He/CO2 ideal selectivity values as high as 4.31 at 1 bar and 25 °C and 4.64 at 0.3 bar and 90 °C were achieved. In addition, the CO2/N2 ideal selectivity becomes slightly improved for longer second-impregnation times.
... In order to broaden the application of the technology, it is important to develop novel membrane materials with excellent gas separation performance [3]. Carbon molecular sieve (CMS) membrane is a carbon-based membrane fabricated from the pyrolysis of polymeric precursor film [4,5]. As a novel membrane for gas separation with a broad development prospect, CMS membrane has the advantages of excellent gas permeability and selectivity, high thermal and chemical stability, and anti-plasticization. ...
... The radar map (Figure 7) was applied to represent the absolute values of the normalized weights for each influencing factor (calculated by |w i |/Σ|w i |, where w i is the original weight of the independent variable i). The factors with underline, which had a negative weight value, were negatively related to the permeability according to Equations (3) and (4), and were shown in absolute value in the radar map in order to realize an intuitive comparison among the weight of each independent variable. Moreover, the weights of the independent variables corresponding to the SVR models with the RBF kernel and the quartic polynomial kernel were different. ...
Gas separation performance of the carbon molecular sieve (CMS) membrane is influenced by multiple factors including the microstructural characteristics of carbon and gas properties. In this work, the support vector regression (SVR) method as a machine learning technique was applied to the correlation between the gas separation performance, the multiple membrane structure, and gas characteristic factors of the self-manufactured CMS membrane. A simple quantitative index based on the Robeson’s upper bound line, which indicated the gas permeability and selectivity simultaneously, was proposed to measure the gas separation performance of CMS membrane. Based on the calculation results, the inferred key factors affecting the gas permeability of CMS membrane were the fractional free volume (FFV) of the precursor, the average interlayer spacing of graphite-like carbon sheet, and the final carbonization temperature. Moreover, the most influential factors for the gas separation performance were supposed to be the two structural factors of precursor influencing the porosity of CMS membrane, the carbon residue and the FFV, and the ratio of the gas kinetic diameters. The results would be helpful to the structural optimization and the separation performance improvement of CMS membrane.
