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Hydrogen is a green clean fuel and chemical feedstock. Its separation and purification from hydrogen-containing mixtures is the key step in the production of hydrogen with high purity (>99.99%). In this work, carbon molecular sieve (CMS) membranes with ultrahigh permselectivity for hydrogen purification were fabricated by high-temperature (700–900...
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... increased and then decreased, which was consistent with the changes of the ultramicropore surface area of CMS membranes, while the diffusion coefficients were gradually reduced. Additionally, for all three gas pairs, the diffusion selectivity was the dominant contributor to the overall selectivity, as illustrated in Table 5. The sorption selectivity changed little, while the diffusion selectivity was significantly enhanced with increasing the carbonization temperature. ...Citations
... Phenolphthalein-based cardo poly (arylene ether ketone) (PEK-C) is a special engineering plastic, with good film-forming properties, thermal resistance, chemical resistance, mechanical stability, and strong chlorine resistance. PEK-C has been widely used in the field of water treatment [17]. However, PEK-C polymer backbone is often too hydrophobic to function effectively as selective layer against small molecules and salt. ...
... Finally, the films were dried in a vacuum oven at 80 • C for 12 h to remove residual solvent. In this work, two thickness of films (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25) μm and 100-200 μm) were prepared. The 15-25 μm and 100-200 μm films were prepared from the casting thicknesses of 200 μm and 1500 μm, respectively. ...
A series of novel poly (arylene ether ketone) with pendant zwitterion groups were designed. Three molecules, 1,4-butane sultone, sodium 2-bromoethanesulphonate and sodium bromoacetate were selected to quaternize with tertiary amine-containing poly (arylene ether ketone) to prepare sulfobetaine poly (arylene ether ketone) (PAEK-SB4 and PAEK-SB2) and carboxylbetaine poly (arylene ether ketone) (PAEK-CB) with controllable content of zwitterion group. The fundamental water and salt transport properties in zwitterionic PAEKs were characterized. Except PAEK-SB2, the water and salt diffusivity and permeability of PAEK-SB4 and PAEK-CB increase with the increase of water sorption, which follows the trend of Yasuda's free volume theory. Salt diffusivity and permeability in PAEK-SB2 were suppressed relative to PAEK-SB4 and PAEK-CB with comparable water sorption, which is due to shorter distance between positively charged group (-N + (CH 3) 2-) and negatively one (SO 3 −) in SB2 group leading to stronger self-association interaction between zwitterions. The water/salt permeability selec-tivity of PAEK-SB2 and PAEK-CB change little with the increase of diffusive water permeability, which break through the trade-off between them. The permeability selectivity of zwitterionic PAEKs is more than one order of magnitude higher than sulfonated polysulfone (BPS), and its orders is PAEK-SB2>PAEK-CB > PAEK-SB4>BPS at the comparable diffusive water permeability. This study suggests that shorter distance between positively charged group and negatively one in zwitterion group benefits water/salt selectivity of zwitterionic PAEKs.
... The investigation of recent works revealed that CMSMs could represent superior H 2 -selective membranes. CMSM fabricated by Xu et al. [130] showed a high H 2 permeability of 5260 Barrer with H 2 /CH 4 , H 2 /N 2 and H 2 /CO selectivities of 311, 142, and 75, respectively. CMSM fabricated by Hou et al. [131] showed an H 2 permeability of around 3500 Barrer and a superior H 2 /N 2 selectivity of>400. ...
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
... This behavior is typical of the dual-sorption mechanism [43], wherein sorption sites gradually saturate with increasing feed pressure. Previous studies have reported [40,60,61] that, of the gases considered here, the sorption level of H 2 in CMS membranes is the lowest, following by N 2 , CH 4 and CO 2 , which is largely consistent (excluding CO 2 ) with the inverse order of measured permeability changes observed in Fig. 10a for the CTB-700 membrane. Because H 2 permeation is the least affected by feed pressure, the corresponding H 2 -based selectivities improve overall, with the H 2 /CH 4 gas pair exhibiting the most promising results in Fig. 10b. ...
... Carbon molecular sieve membranes (CMSMs) are regarded as one of the most suitable candidates for high-performance membranes, and various feasible methods for the fabrication of CMSMs have been reported. The first CMSM was fabricated by Koresh and Soffer [22] by the pyrolysis of cellulose hollow fibers, and most CMSMs since reported have been fabricated via similar means; that is, the thermal pyrolysis of polymeric materials under controlled conditions [23][24][25][26][27][28]. This is because the resulting CMSMs have rigid structures and therefore do not undergo plasticization, a process that degrades the gas separation properties of polymeric membranes. ...
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.
... XRD patterns of the TB/PSS-derived CMS membranes are shown in Fig. 3. All spectra exhibited broad peaks, which are indicative of the amorphous nature of the precursor and the CMS samples [43]. TB/PSS thermally treated at 550 • C appeared to have one broad amorphous peak with a much higher average d-spacing of ~3.72 Å compared to the pristine TB/PSS (~4.29 Å). ...
... Similar to other CMS membranes [49], as the feed pressure increase from 2 bar to 6 bar, the permeabilities of H 2 and He are nearly constant, remaining at around 650 and 400 Barrer, respectively. On the other hand, compared to light gases (e.g., H 2 and He), as a more condensable gas, CH 4 is more sensitive to feed pressure, the CH 4 permeability increased as the feed pressure increment [43,52], leading to a much lower H 2 /CH 4 and He/CH 4 selectivity. P N2 is less sensitive to feed pressure thus the selectivity was also only slightly reduced as the feed pressure increased from 2 bar to 6 bar. ...
... During the thermal treatment process, the disordered polymeric structures tend to form ordered slit-like carbon structures as the pathway for H 2 gas transport. 28,29 Different kinds of polymeric materials, including polyimide and its derivatives, [30][31][32][33][34] cellulose and its derivatives, 35 poly(arylene ether ketone), [36][37][38] poly(phenylene oxide) 39,40 and polybenzimidazole, 41 have been employed as the precursors to fabricate CMS membranes for H 2 purication. Compared to pristine polymeric membranes, CMS membranes have excellent gas separation performance for hydrogen purication, which can exceed the Robeson upper bounds of polymeric membranes that plot a trade-off relationship between the gas permeability and selectivity. ...
Hydrogen is an important energy carrier for the transition to a carbon-neutral society, the efficient separation and purification of hydrogen from gaseous mixtures is a critical step for the implementation of a hydrogen economy. In this work, graphene oxide (GO) tuned polyimide carbon molecular sieve (CMS) membranes were prepared by carbonization, which show an attractive combination of high permeability, selectivity and stability. The gas sorption isotherms indicate that the gas sorption capability increases with the carbonization temperature and follows the order of PI-GO-1.0%-600 °C > PI-GO-1.0%-550 °C > PI-GO-1.0%-500 °C, more micropores would be created under higher temperatures under GO guidance. The synergistic GO guidance and subsequent carbonization of PI-GO-1.0% at 550 °C increased H2 permeability from 958 to 7462 Barrer and H2/N2 selectivity from 14 to 117, superior to state-of-the-art polymeric materials and surpassing Robeson's upper bound line. As the carbonization temperature increased, the CMS membranes gradually changed from the turbostratic polymeric structure to a denser and more ordered graphite structure. Therefore, ultrahigh selectivities for H2/CO2 (17), H2/N2 (157), and H2/CH4 (243) gas pairs were achieved while maintaining moderate H2 gas permeabilities. This research opens up new avenues for GO tuned CMS membranes with desirable molecular sieving ability for hydrogen purification.
... For example, polyimidebased polymers can be made into gas separation membranes with good physicochemical properties [12]. Xu et al. [13] investigated the carbon molecular sieve (CMS) membrane to operate in the room temperature surrounding. Non-noble metals can also be used to manufacture membranes. ...
This study uses a palladium membrane to separate hydrogen from an H2/CO2 (90/10 vol%) gas mixture. Three different operating parameters of temperature (320–380 °C), total pressure difference (2–3.5 atm), and vacuum degree (15–49 kPa) on hydrogen are taken into account, and the experiments are designed utilizing a central composite design (CCD). Analysis of variance (ANOVA) is also used to analyze the importance and suitability of the operating factors. Both the H2 flux and CO2 (impurity) concentration on the permeate side are the targets in this study. The ANOVA results indicate that the influences of the three factors on the H2 flux follow the order of vacuum degree, temperature, and total pressure difference. However, for CO2 transport across the membrane, the parameters rank as total pressure difference > vacuum degree > temperature. The predictions of the maximum H2 flux and minimum CO2 concentration by the response surface methodology are close to those by experiments. The maximum H2 flux is 0.2163 mol s⁻¹ m⁻², occurring at 380 °C, 3.5 atm total pressure difference, and 49 kPa vacuum degree. Meanwhile, the minimum CO2 concentration in the permeate stream is t 643.58 ppm with the operations of 320 °C, 2 atm total pressure difference, and 15 kPa vacuum degree. The operation with a vacuum can significantly intensify H2 permeation, but it also facilitates CO2 diffusion across the Pd membrane. Therefore, a compromise between the H2 flux and the impurity in the treated gas should be taken into account, depending on the requirement of the gas product.
... The dense flat polymeric membranes with thickness of 65-75 μm were cut into 2 ⅹ 2 cm 2 pieces, and then went through oxidative pretreatment in a muffle furnace at 200 mL/min air flow prior to carbonization treatment. The purpose of the pretreatment is to prevent the membranes from melting during heat treatment to obtain intact CMS membranes due to the thermoplasticity of PEK-C polymer [42,43]. The heat treatment protocols for the preparation of CMS membranes were illustrated in Fig. S1. ...
... The TG-DTG curves of PEK-C precursor membranes (Fig. S2) show that the rapid weight loss starts at about 400 • C, and the maximum weight loss is as high as 36.4% in the range of 400-650 • C, corresponding to the intense pyrolysis of polymer chains which involves many chemical reactions, such as thermal crosslinking induced by the decomposition of Cardo moieties [42,48,49], structural rearrangement, scission of polymeric backbone, and aromatization reactions, resulting in the transformation from random coil polymer precursor to rigid and amorphous carbon [25,43]. As the pyrolysis temperature is higher than 650 • C, the weight loss gradually decreases, corresponding to the carbonization stage during which the reactions of aromatization, structural rearrangement, dehydrogenation and condensation occur and lead to the formation of carbon structure with carbon crystallites stacking [39]. ...
... The spacing formed between graphene-like carbon layers and carbon microcrystallines composes the pore structure of the derived CMS membranes, in which the large micropores shrink or disappear, and the two-dimensional slit-like ultramicropores are formed instead, implying that the ultramicropore structure of CMS membranes can be tailored by tuning the sp 3 /sp 2 Fig. 4. WAXD patterns of CMS membranes pyrolyzed at different temperature. [43]. c La and Lc are calculated using the Scherrer's equation (L a/c = Kλ/β cosθ) [43]. ...
... The most frequent methods for assessing the pore size distribution of cellulose-based materials are N 2 and CO 2 physisorption, as well as CO 2 high-pressure adsorption. Many studies have shown that N 2 physisorption at 77 K can produce pore size distributions of micropore ranges [90][91][92][93][94][95][96][97][98][99]. However, the utilization of N 2 physisorption is limited by the difficulty of diffusing N 2 molecules (3.64 Å) into the ultra-micropores. ...
... It has been previously hypothesized that the sp 3 hybridization carbon defect occurs when the ratio is [105]. SEM images of (c) self-supported hollow fiber [100], (d) supported carbon membrane [113], (e) High-resolution TEM image of a CMS membrane [92], (f-h) Raman spectrum, C1s XPS spectrum, and EELS of carbon membranes [110], [91], and [113], respectively. (a-b) Reproduced from [105] with permission from Elsevier. ...
Mitigating carbon dioxide emission on a large scale requires implementing low-cost and abundantly available selective materials. The inherent qualities of natural cellulosic materials, such as availability, eco-friendliness, high processability, and remarkable physical-mechanical characteristics, have led to widespread usage for diverse applications. Nanostructured surface modifications and incorporation of metal-organic frameworks (MOFs) onto the cellulose materials to form composites hold viable opportunities for enhancing the performance of these materials. This study presents recent advancements in cellulose and cellulose-MOFs (CelluMOFs) for CO 2 adsorption and separation. Different CO 2 capturing processes, families, and preparation methods of cellulose and CelluMOF materials, as well as the corresponding characterization techniques for CO 2 separation and adsorption were discussed. These were followed by different cellulose materials comprising inorganic particle-base cellulose and chemically modified nanocellulosic materials for CO 2 adsorption. Various cellulosic and polymer-based cellulose membranes for CO 2 separation were also discussed. Unlike previous literature, the present study also discussed the cellulose-MOF-based materials as the new generation of materials for CO 2 adsorption and separation , suggesting that MOFs integration onto the cellulosic matrices without forfeiting their intrinsic performances remains a viable approach for a gigantic breakthrough in the field. Finally, this study reveals the associated shortcomings and preparation strategies and challenges/gaps in knowledge to enable the development and exploration of new dimensions and also, the direction of specific research for large or industrial-scale applications.
... The degradation of the polymer chain and the elimination of elements were associated with internal structural changes, including changes in the d-spacing between adjacent chains and in the polymer porosity [22]. To investigate the effect of pyrolysis on chain packing, we analyzed the membranes using WXRD (Fig. 2f). ...
Organic solvent nanofiltration is an energy-efficient separation process for solutes and solvents. Robust membranes that show stability in harsh environments are highly desirable. In this study, we developed free-standing integrally skinned asymmetric carbon molecular sieve membranes that synergize the advantages of stable carbon materials and porous polymer membranes. The membranes were prepared using a polyimide of intrinsic microporosity (PIM), known as 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA)-3,3′-dimethylnaphthidine (DMN), via a phase inversion technique. Carbonization preserved the surface porosity and finger-like porous morphology of the membranes after structural rearrangement. The effects of pyrolysis temperature, membrane thickness, dope solution concentration, and polymer porosity on separation performance were investigated. The molecular sieving performance of the membranes was investigated using five solvents with different polarities. The membranes showed no swelling and high stability in strong acids, bases, and organic solvents, as well as an excellent rejection profile and reasonable permeance. The membrane pore size, molecular-weight cutoff, and performance were fine-tuned by controlling the pyrolysis temperature, dope solution concentration, and polymer porosity. The polymer porosity and the asymmetric structure of the membrane strongly affected the molecular sieving performance. Carbonizing porous 6FDA-DMN afforded a 10-fold higher permeance than that obtained by carbonizing nonporous 6FDA-m-phenylenediamine (mPDA). To the best of our knowledge, the developed membrane fabrication platform yielded one of the tightest, most robust, and highly solvent-resistant nanofiltration membranes reported thus far.
