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Copyright of Biomass Chemical Engineering is the property of Editorial Office of Biomass Chemical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The removal of the main impurity CO2 is a crucial step in biogas upgrading. In this work, the separation of CO2 from CH4 on electrospun polyacrylonitrile-based carbon nanofibers (CNFs) is investigated using breakthrough experiments. The CNFs are prepared at various carbonization temperatures ranging from 600 to 900 °C and feature a tailorable pore size that decreases at higher carbonization temperatures. The adsorption properties of the different CNFs are studied measuring pure component isotherms as well as column breakthrough experiments. Adsorption kinetics are discussed using a linear driving force approach to model the breakthrough experiment and obtain the adsorption rate constant. Moreover, different approaches to determine the selectivity of the competitive CO2/CH4 adsorption are applied and discussed in detail. The results clearly prove that a size exclusion effect governs the adsorption selectivity on the CNFs. While CH4 cannot adsorb in the pores of CNFs prepared at 800 °C or above, the smaller CO2 is only excluded from the pores of CNFs prepared at 900 °C. For CNFs carbonized in the range from 600 to 750 °C, values of the CO2/CH4 selectivity of 11–14 are obtained. On the CNFs prepared at 800 °C the CH4 adsorption is severely hindered, leading to a reduced adsorbed amount of CH4 and consequently to an improved CO2/CH4 selectivity of 40. Furthermore, owing to the shrinking pores, the adsorption rates of CH4 and CO2 decrease with higher carbonization temperature. [ABSTRACT FROM AUTHOR]

The new kinetically limited linear driving force (KLLDF) model was assessed against the traditional LDF model in the prediction of twelve different ternary and quaternary experimental breakthrough curves. These breakthrough curves comprised mixtures of CO2, N2 and CH4 in He adsorbed on carbon molecular sieve MSC 3 K 172 and were conducted at various pressures (30, 50 and 100 psia) and at ambient temperature. The LDF and KLLDF models were implemented in the dynamic adsorption process simulator (DAPS) with the loading dependent LDF mass transfer coefficients and the single gas equilibrium adsorption isotherms measured independently with gravimetric uptake experiments. To make the comparison between the LDF and the KLLDF models as fair as possible, they utilized the same set of thermodynamic and kinetic parameters in DAPS, with no adjustments to any of them. Both the LDF and KLLDF models provided reasonable predictions of the experimental breakthrough curves and in-bed temperature histories, with general trends of no CH4 uptake, gradual N2 uptake and fast CO2 uptake. However, the KLLDF model always provided better predictions, especially when CO2 was present. The results revealed that the traditional LDF model led to depressed adsorbed phase loadings of CO2, thereby underpredicting its breakthrough time in all cases. This depression stemmed from the equilibrium loading in the LDF driving force of the LDF model depending on the gas phase partial pressure of each component outside the pore structure. In contrast, the KLLDF model corrects this issue by making the equilibrium loading in its LDF driving force dependent on the actual loading of each component inside the pore structure. In conjunction with the mixed gas extended Langmuir model, the KLLDF model is perhaps the more appropriate model to use instead of the LDF model for any multicomponent adsorbate-adsorbent systems, whether diffusion limited or not, since it reduces to the LDF model for systems that do not exhibit significant diffusional limitations. [ABSTRACT FROM AUTHOR]

The process-based evaluation of adsorbents is considered the most foolproof method with respect to a particular application, as it provides data about the separation effectiveness in authentic operating conditions. This paper presents empirically obtained performance results of the kinetically-controlled air separation on multiple carbon molecular sieves carried out in a twin-bed pressure swing adsorption unit. The effect of adsorbent pellet size on nitrogen productivity and air demand is studied at different product purity levels (10–10,000 ppm O2 of the residual oxygen concentration), operating temperatures (25–45 °C), and half-cycle times (35–70 s). The selected process conditions correspond to the majority of practical applications. Guidelines for the suitable particle size depending on the desired nitrogen purity are given. [ABSTRACT FROM AUTHOR]

• Maximum specific capacitance of 68F g−1 at 5 mV s−1 was observed. • High porosity was achieved by controlled thermal annealing. • Outstanding electrosorption performance with a capacity of 36.9 mg g−1 was obtained. • High electrosorption capacity and low energy consumption were achieved using 6FDA-DMN-based CMS electrodes. Capacitive deionization (CDI), a promising process for desalinating low-salinity water, is currently characterized by the prevalent use of activated carbon (AC) electrodes that exhibit somewhat suboptimal performance. One potential method for increasing the electrosorption capacity of an electrode involves boosting its porosity and conductivity by using conductive polymers or applying heat treatment to porous polymers. This study examines the performance of the capacitive deionization (CDI) process using a range of highly porous carbon molecular sieve (CMS) electrodes. These electrodes are derived from intrinsically microporous polyimide 4,4′-(hexa -fluoroisopropylidene) diphthalic-anhydride (6FDA)-3,3′ dimethyl-naphthidine (DMN) (6FDA-DMN) and prepared at temperatures of 600, 800, and 1000 °C. The electrodes that were produced exhibited a high Brunauer-Emmett-Teller (BET) surface area ranging from 574 to 729 m2g−1. Additionally, they displayed a symmetric cyclic voltammetry (CV) plot with a specific capacitance ranging from 17.75 to 67.91 Fg−1 at a scan rate of 5 mVs−1. The charge transfer resistance (Rct) values for the 6FDA-DMN-based CMS P1, P2, and P3 electrodes were measured to be 9.7 Ω, 1.2 Ω, and 0.9 Ω, respectively, in a 1 M NaCl solution. The CMS electrode, synthesized at a temperature of 800 °C (P2), exhibits exceptional electrosorption capabilities in a saline solution with a concentration of 600 mgL−1. It displays a remarkable capacity of 36.9 mgg−1 and a rate of 2 mgg−1min−1, surpassing the performance of activated carbons (ACs). This research establishes a pathway for optimizing the characteristics and performance of electrodes by thermal treatment. This research demonstrates for the first time the effect of thermal annealing on the CDI performance of CMS materials, which will aid in developing electrode materials for large-scale water desalination. [ABSTRACT FROM AUTHOR]

Continuous long-term evaluation of propylene and propane permeation through narrow slit carbon molecular sieve (CMS) membranes is essential for an in-depth study of their steady-state separation performance. CMS membranes are characterized by finely tuned ultramicroporous structures, exceptional thermal and chemical stability, and hold great promise for the energy-intensive separation of propylene and propane. However, the gradual changes in their performance over time due to penetrant-induced structural chain rearrangements have often been overlooked. In this study, we prepared CMS membranes using a polymer of intrinsic microporosity (PIM) with a highly aromatic tetraphenylethylene (TPE) based building block. The presence of bulky and sterically hindered TPE repeat units renders this polymer an excellent precursor for the fabrication of high-performance CMS membranes. The TPE-PIM-based precursor underwent pyrolysis at temperatures ranging from 550 to 700 °C for 1 h. Pure- and mixed-gas permeation tests were accompanied by various characterization techniques to assess the carbonization state of the CMS materials. The CMS pyrolyzed at 700 °C exhibited a decline in pure-gas C 3 H 6 /C 3 H 8 selectivity from an initial value of 300 to 161 at steady state over a 20-day period. Even more notable, under equimolar mixed-gas feed conditions, the isotropic CMS film displayed a substantial C 3 H 6 /C 3 H 8 selectivity reduction from 214 to 62 over a 24-day period. This performance decline can be attributed to competitive sorption and very slow dilation kinetics, which led to moderately reduced propylene permeability while significantly enhancing propane permeability. Our study suggests that long-term, continuously performed mixed-gas permeation experiments are essential to assess the 'steady-state' performance of CMS membranes for mixtures containing highly sorbing feed components, as observed for propylene/propane separation. [Display omitted] • TPE-PIM-derived CMS films require very long time to reach steady-state permeability for C 3 H 8. • Propane sorption at 1 bar in TPE-PIM-based CMS pyrolized at 600–700 °C requires ∼ 3–4 days to reach equilibrium. • Continuous long-term mixed-gas permeability experiments are essential to obtain reliable performance data for C 3 H 6 /C 3 H 8. • Steady-state mixed-gas C 3 H 6 permeability of 7.5 Barrer and C 3 H 6 /C 3 H 8 selectivity of 62 for TPE-PIM-700 °C after 24 days. [ABSTRACT FROM AUTHOR]

Xenon/krypton (Xe/Kr) separation is an important task in industry, yet it remains challenging to develop adsorbents with high Xe/Kr selectivity and adsorption capacity of Xe, especially at low partial pressures. Herein, we report a series of microporous carbon molecular sieves (CMSs) for Xe/Kr separation. Those materials have ideal bimodal pore size distributions that not only provide substantial space for the accommodation of gas molecules, but also allow selective diffusion of gas molecules. Additionally, the carbon frameworks decorated with polar oxygen-containing functional groups afford higher affinity for Xe than Kr, which is proven by density functional theory (DFT) calculations and charge density difference analysis. The optimal C-PVDC-700 exhibits a high selectivity of Xe/Kr and, more importantly, a record-high uptake of Xe (2.93 mmol g−1) at 0.2 bar and 298 K, which is the highest among all the reported carbon adsorbents. Breakthrough experiments confirm the excellent performance of such CMSs for Xe/Kr separation, and the dynamic adsorption uptake of Xe and productivity of high-purity Kr are calculated to be 2.91 mmol g−1 and 208 mL g−1 (9.29 mmol g−1), respectively, which also set up a new benchmark for Xe/Kr separation of carbon adsorbents. [ABSTRACT FROM AUTHOR]

Lithium-sulfur batteries offer an attractive energy storage alternative independent of critical minerals such as cobalt or nickel. However, their inadequate stability under long term cycling, and storage capacity on a volumetric basis hampers their uptake. These limitations can be addressed by seeking to control the formation and crossover of polysulfides, oligomers generated through reaction of solvated sulfur moieties with the lithium anode, and by seeking to restrict the consumption of active materials. Here, we report the development of a triple-functional carbon molecular sieve (CMS) interlayer. The microporous, polar, and conductive structure of the CMS provides physisorption, chemisorption, and reactivation capabilities concurrently. Therefore, the soluble polysulfides can be trapped, suppressed from shuttling, and reutilized to not only improve the kinetics of the redox reaction but also hinder the loss of active materials. As a result, our CMS-based Li–S batteries deliver combined exceptional gravimetric (1282 mAh g−1) and areal (7.05 mAh cm−2) capacities at 0.1 C rate as well as cycling stability up to 1000 cycles at 0.2 C rate over 9 months. A triple-functional PIM-1 derived carbon molecular sieve (CMS) interlayer provides polysulfide physisorption, chemisorption, and reactivation capabilities to address a "performance trilemma" facing the development of practical Li–S batteries. At current rate of 0.2 C, our CMS-based Li–S batteries deliver combined high gravimetric capacity (1028 mAh g−1), areal capacity (5.65 mAh cm−2), and capacity retention (75% after 500 cycles). [Display omitted] [ABSTRACT FROM AUTHOR]

Copyright of Inorganic Chemicals Industry is the property of Editorial Office of Inorganic Chemicals Industry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The activation effect of boric acid as an activator is good, and we investigate the best activation conditions for the boric acid impregnation method. To represent the structural characteristics and adsorption performance of the Stellera Chamaejasme based carbon molecular sieves, we use Brunner-Emmet-Teller (BET) measurements, scanning electron microscope (SEM), Raman spectra (Raman), X-ray diffraction (XRD), and adsorption property measurement. When the loading ratio was 0.68:1, the specific surface area was 532.21 m2/g, the total pore volume was 0.24 cm3/g, the average pore size was 1.81 nm, the adsorption value of methylene blue was 145.28 mg/g, and the adsorption value of iodine was 713.33 mg/g, the results showed that boric acid had better activation effect. The carbon molecular sieves made from Stellera Chamaejasme and activated with boric acid produce two peaks on the aperture distribution graph that are densely distributed in the micropore range. This indicates that boric acid's pore-forming tendency is primarily micropore. [ABSTRACT FROM AUTHOR]

The efficient adsorption-based separation of krypton (Kr) and xenon (Xe) is of paramount importance but is challenged by their similar physicochemical properties. While carbon adsorbents are theoretically promising for Kr/Xe sieving, practical success has remained elusive. Here, a series of ultramicroporous carbon molecular sieves synthesized from sucrose-derived hydrochar is reported. The study employs careful characterization and controlled thermal pyrolysis to tailor ultramicropore formation and elucidate the evolution of the carbon framework. The leading material, C-Suc-750, has an ideal pore size of ≈4.0 Å. In particular, C-Suc-750 has achieved a remarkable Kr/Xe uptake ratio of 39.3 at ambient conditions, setting a new benchmark for selective Kr adsorption and molecular sieving of Kr/Xe. Breakthrough experiments further confirm the superior molecular sieving performance of C-Suc-750, highlighting its potential for Kr recovery in nuclear waste treatment. Moreover, molecular dynamics (MD) simulations demonstrate the critical role of narrow slit-pore of the carbon molecular sieve in molecular sieving separation of Kr/Xe, providing insights into the mechanism driving this selectivity., (© 2024 Wiley‐VCH GmbH.)

Carbon molecular sieves (CMSs) are the key adsorbents for gas separation through pressure swing adsorption (PSA), a promising technique that has found many applications in air separation and natural gas purification. However, the current process of preparing CMSs with finely tuned nanopores based on the repeated CVD process is technically challenging and energy-consuming. In this work, we report a facial method of preparing CMSs through the one-step carbonization of a metal–organic framework. The direct carbonization of an rht-type metal–organic framework (MOF) affords a type of CMSs with an ultramicro–nanoporous structure that is comparable with the kinetic diameter of small gases (N2, O2, CO2, and CH4). As a result, this type of CMSs shows significant differences in both equilibrium adsorption properties and diffusion rates for O2/N2 and CO2/CH4. The kinetic separation coefficient for O2/N2 and CO2/CH4 is high up to 47 and 105, respectively. In addition to excellent equilibrium and kinetic selectivity, this MOF-CMS shows compatibility between equilibrium and kinetic adsorption properties, giving rise to a thermodynamic–kinetic synergistic effect for O2/N2 and CO2/CH4 separation. These outstanding separation performances can be attributed to the ultramicro–nanopores of CMSs, which are modulated by the uniform pore structure of the MOF precursor. The high selectivity combined with the facial preparation process for this CMS may open an avenue of preparing nanoporous CMSs with desired functionalities. [ABSTRACT FROM AUTHOR]

The reactive gases perfluoroisobutene and carbonyl fluoride are highly toxic and difficult to analyze in air. For this paper, the available sampling and analysis methods involving gas chromatography/mass spectrometry were investigated for their potential to give unambiguous identification and quantification of perfluoroisobutene and carbonyl fluoride, for which no such methods exist. Although high concentrations of perfluoroisobutene could be analyzed directly by manual split injection, sorbent sampling followed by thermal desorption GC/MS allowed lower concentrations to be analyzed. However, a significant degradation of perfluoroisobutene observed after thermal desorption analysis inspired the use of derivatization of perfluoroisobutene with 3,4‐dimercaptotoluene. The use of Tenax TA sorbent tubes spiked with 3,4‐dimercaptotoluene and trimethylamine in a molar ratio of 1:8 proved successful for the quantification of a unique perfluoroisobutene derivative, and the method was validated for atmospheres in the range of 0.13–152 ppb with a relative standard deviation of less than 20% and an accuracy of 90%. Although carbonyl fluoride was less stable than perfluoroisobutene, direct analysis was possible at high concentrations but the response was not linear. The 3,4‐dimercaptotoluene derivatization method developed was also applicable for quantification of carbonyl fluoride atmospheres. [ABSTRACT FROM AUTHOR]

The adsorption excess isotherms of ethanol–water and propanol–water mixtures are studied on a series of carbon molecular sieves with well-separated micro- and mesoporosity at 298.15 K. The preferential adsorption of one component from a mixture is measured by using vibration densitometry for the concentration analysis. Microcalorimetrically measured enthalpies, which are released upon immersion of the carbon materials in the binary mixtures, complement the adsorption excess data. It is shown that (i) density measurements are well applicable for studying liquid-phase adsorption, (ii) liquid-adsorption isotherms are sensitive to smallest chain length differences of the adsorptives, (iii) the calculated separation diagrams depend strongly on the assumptions about the adsorbed phase, and (iv) the combined determination of gas, vapor and liquid adsorption isotherms and immersion enthalpies offers advantages for the analysis of complex adsorption systems. [ABSTRACT FROM AUTHOR]

The recovery of levulinic acid (LA) and formic acid (FA) from aqueous solutions and actual biomass hydrolysates by using the stepwise adsorption method was investigated for the first time. The carbon molecular sieve was used as the adsorbent for FA and microporous activated carbon was used as the adsorbent for LA according to the steric hindrance effect of the pore channels and the difference in molecular diameter of FA and LA. The adsorption data of LA and FA onto their respective adsorbents were measured and numerically analyzed by adopting batch adsorption experiment and fixed-bed column methods. In the study of static adsorption equilibrium experiment, the Langmuir equation fitted the data of LA adsorption on activated carbon, while the Freundlich equation fitted well the adsorption data of FA adsorption on carbon molecular sieve. In the kinetic study, the LA adsorption on activated carbon and FA adsorption on carbon molecular sieve confirmed the PSO model. Moreover, the effect of various conditions on fixed-bed column adsorption progress was investigated, which indicated that the adsorption property improved with feed flow rate, column length, temperature decreasing and initial concentration increasing. The Yoon-Nelson model was adopted to predict and analyze the whole process of adsorption breakthrough and consistent well with the experimental data. The separation of LA and FA was realized by continuous fractional adsorption. [Display omitted] • Fractional adsorption to separate levulinic and formic acid from aqueous solution. • Use carbon molecular sieve to adsorb small molecular substances in solution. • LA and FA were exothermically on adsorbents following PSO kinetic model. • Factors affecting the dynamic adsorption process were studied. • Dynamic breakthrough curves were predicted and analyzed by Yoon-Nelson model. [ABSTRACT FROM AUTHOR]

Carbon molecular sieve (CMS) membranes have excellent gas separation property over conventional polymeric membranes and superior anti-swelling property. PMDA-ODA polyimide has high thermal stability and good mechanical property. It has been extensively adopted as the precursor of CMS membrane. However, due to the insoluble nature, PMDA-ODA CMS membranes are limited to configurations like dense symmetric films or composite membranes using porous inorganic or metal substrates. In this work, CMS hollow fiber composite membranes based on an asymmetric PMDA-ODA hollow fiber were successfully prepared for the first time. The neat PMDA-ODA hollow fiber membrane was crosslinked by polyethyleneimine to alleviate pore collapsing during carbonization and then dip-coated by a PMDA-ODA PAA solution to seal the surface defects. The PDMA-ODA CMS composite hollow fiber membranes showed gas permeances of 93.4 GPU, 19.6 GPU, 6.5 GPU, and 4.7 GPU for CO2, O2, N2, and CH4, respectively, with an ideal selectivity of 14.4, 3.0, and 19.8 for CO2/N2, O2/N2, and CO2/CH4 gas pairs, respectively. The attractive gas separation property shows a great potential for industrial application. [ABSTRACT FROM AUTHOR]

Spent bleaching earth (SBE) as an industrious solid rubbish seriously causes the environmental pollution problem. The resourceful utilization of SBE has become increasingly important. In this work, silicon and carbon ingredients derived from SBE were coincidently employed to synthesize a 4A zeolite/carbon composite molecular sieve (4A/CMS). Therein, the graphite carbon components in the form of porous lamellar scattering among the interlayer, surface, and periphery of 4A zeolite promote the rate of mass transfer for the lipophilic gas, which can effectively improve the adsorption property for the volatile organic compounds. The obtained 4A/CMS has large specific surface area, hierarchical pore structure, satisfactory adsorption capacity, and regeneration performance, and its equilibrium adsorption capacity of p-xylene can achieve 209.57 mg·g−1. The pseudo-first-order rate equation is appropriate for the adsorption kinetics. In the end, the formation mechanism of 4A/CMS was illuminated in detail. □ Spent bleaching earth (SBE) as an industrious solid rubbish were utilized resourcefully. Silicon and carbon ingredients from SBE were coincidently employed to synthesize 4A/CMS. Graphitic carbon with hierarchical pore promoted the rate of mass transfer of organic gas. 4A/CMS exhibited excellent adsorption capacity and regeneration performance of p-xylene. [ABSTRACT FROM AUTHOR]

Selective separation of ethylene and ethane (C 2 H 4 /C 2 H 6 ) is a formidable challenge due to their close molecular size and boiling point. Compared to industry-used cryogenic distillation, adsorption separation would offer a more energy-efficient solution when an efficient adsorbent is available. Herein, a class of C 2 H 4 /C 2 H 6 separation adsorbents, doped carbon molecular sieves (d-CMSs) is reported which are prepared from the polymerization and subsequent carbonization of resorcinol, m-phenylenediamine, and formaldehyde in ethanol solution. The study demonstrated that the polymer precursor themselves can be a versatile platform for modifying the pore structure and surface functional groups of their derived d-CMSs. The high proportion of pores centered at 3.5 Å in d-CMSs contributes significantly to achieving a superior kinetic selectivity of 205 for C 2 H 4 /C 2 H 6 separation. The generated pyrrolic-N and pyridinic-N functional sites in d-CMSs contribute to a remarkable elevation of Henry selectivity to 135 due to the enhancement of the surface polarity in d-CMSs. By balancing the synergistic effects of kinetics and thermodynamics, d-CMSs achieve efficient separation of C 2 H 4 /C 2 H 6 . Polymer-grade C 2 H 4 of 99.71% purity can be achieved with 75% recovery using the devised d-CMSs as reflected in a two-bed vacuum swing adsorption simulation., (© 2024 Wiley‐VCH GmbH.)

At present, nitrogen production from air by pressure swing adsorption (PSA) is simulated almost exclusively at low product purity levels (< 99% N2). However, with increasing global demand for highly purified gases provided by energy-efficient separation processes the requirement for either extensive experimental research in the high-purity range or predictive computer simulations arises. This paper presents a mathematical model of a twin-bed PSA plant equipped with a carbon molecular sieve (Shirasagi MSC CT-350) for the generation of high-purity nitrogen (99.9–99.999% N2). The model is implemented in the process simulator Aspen Adsorption™. The influence of operating conditions as well as the cycle organisation on the process performance is validated, especially the influence of pressure, temperature, half-cycle time, purge flow rate, and cutting time. The precision of the performance prediction by numerical simulations is critically discussed. Based on the new insights efficiency improvement strategies with a focus on reduced energy consumption are introduced and discussed by means of radar charts. [ABSTRACT FROM AUTHOR]

Polymeric blend mixed matrix membranes (PB3Ms) are synthesized with different blend compositions at a fixed content of carbon molecular sieve (CMS) inorganic filler. The resulting membranes are characterized by FESEM, TGA, DSC and FTIR analyses. Polyethersulfone (PES)/polyvinyl acetate (PVAc)/CMS polymeric blend mixed matrix membranes are prepared by solution casting method. A homogenous mixture of all these components is formed and cast on a clean glass plate. The produced PB3Ms show drastic enhancement in CO2 permeance and CO2/CH4 selectivity in both single and mixed gas permeation tests in comparison with pure PES membrane. Significant CO2 permeance of 132.47 GPU with CO2/CH4 selectivity of 75.27 at 6 bar is obtained for the PB3M having 80 wt%/20 wt% blend ratio of PES/PVAc and 20 wt% CMS loading. The synthesized polymeric blend mixed matrix membranes in this research study demonstrate competitive CO2/CH4 separation performance in comparison with the reported literature on PB3Ms for gas separation. [ABSTRACT FROM AUTHOR]

A laboratory-scale fixed-bed column is employed to study the dynamic behavior of the carbon molecular sieve MSC CT-350 for CO 2 /CH 4 separation. Breakthrough adsorption tests in single-component systems are carried out at different pressures (1, 3, 5, 6.5 and 8 bar) and constant temperature (20 °C). Moreover, an additional test is conducted with a 40% CO 2 /60% CH 4 binary mixture at 3 bar. Desorption tests are performed by varying the purge-to-feed ratio (P/F) at 50%, 30% and 20%, optionally using a vacuum pump. Experimental results show that MSC CT-350 has a good CO 2 adsorption capacity for each pressure, considerably higher than CH 4. In the binary test, very slight differences are experimentally found in the adsorption kinetics and equilibrium adsorption capacity with respect to single-compound tests, which results equal to 2.16 mol kg−1 for CO 2 and 0.302 mol kg−1 for CH 4 at 3 bar, compared with 2.29 mol kg−1 for CO 2 and 0.262 mol kg−1 for CH 4 for the single-compoound counterparts. The time required for a complete regeneration decreases with the increase in purge flowrate and with the simultaneous use of the vacuum pump. Finally, CO 2 adsorption is a reversible process as the CO 2 adsorption capacity of the adsorbent is not significantly reduced when utilized in subsequent adsorption-desorption cycles. [Display omitted] • Detailed characterization of molecular sieve MSC CT-350 for CO 2 /CH 4 separation • Experimental data of adsorption kinetics and equilibrium at varying pressure • Impact of methane purge flow rate and pressure on bed regeneration time • MSC CT-350 adsorbent is very suitable for biogas upgrading by VPSA technology. [ABSTRACT FROM AUTHOR]

With increasing nitrogen purity, PSA plants require an over-proportional air demand with the consequence that high-purity PSA systems engender a distinct interest in energy-saving measures. This paper presents process intensification strategies with the focus on a reduced energy consumption. Therefore, the influence of PSA configuration and cycle organisation on process performance was investigated. Results are presented at two product purity levels (10 ppm/1000 ppm O2) and two operating temperatures (25 °C/45 °C) in a lab-scale twin bed PSA (2 × 2 L). It is shown that dedicated strategies are available to intensify the PSA process; however, their effects are dependent on ambient conditions and product purity levels. [ABSTRACT FROM AUTHOR]

The performance of carbon molecular sieves and zeolite 5A was compared in a four-bed vacuum pressure swing adsorption process. The purpose of the process is to sequester CO2 from a CH4/CO2 mixture gas, such as coal bed methane or landfill gas. This study investigated the effects of the design variables and operating variables on methane purity, recovery, and specific power through simulations of the process using the two adsorbents. The adopted design variables for the investigation are the packing bed length and the diameter of the adsorption bed, and the selected operating variables are the adsorption pressure and vacuum pressure. The simulation results show that zeolite 5A is better than carbon molecular sieve in terms of power, especially under low-pressure operating conditions with a vacuum pressure of 1,000 Pa. However, carbon molecular sieves are better in terms of purity enhancement when the vacuum pressure is higher than approximately 2,000 Pa. [ABSTRACT FROM AUTHOR]

Methane (CH4) and carbon dioxide (CO2) are the main components of a renewable energy source of biogas. Separation of CO2 from biogas is significantly important to improve biogas performance, due to heating value in biogas depends on the concentration of methane. One of the gas separation technologies that has been widely used in chemical industries is carbon molecular sieve (CMS). This research explores the potential of CMS for biogas purification. CMS was prepared by modification of palm kernel shell-derived porous carbon using amine groups such as monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), and diethanolamine (DEA). The effect of amine types on the separation parameters was studied by using a breakthrough experiment to obtain the most potential CMS materials. The methods of this research include the process of carbon oxidation using hydrogen peroxide, impregnation with an amine group, characterization of the CMS material obtained, CO2 and CH4 gas separation testing with a breakthrough system. The CMS was characterized by using N2 sorption analysis, fourier transform infrared spectroscopy, and scanning electron microscopy. The breakthrough experiment showed that CMS-MEA had the highest performance for separating CO2 and CH4 gases. In addition, the results also showed that loading of amine groups on carbon caused an increase in the uptake capacity of CO2, and the highest capacity was achieved by CMSMEA of 13.2 mg/g. [ABSTRACT FROM AUTHOR]

Gas separation by adsorption processes such as pressure swing adsorption (PSA) presents an attractive alternative for upgrading biogas to biomethane. A new vacuum pressure swing adsorption (VPSA) cycle is proposed for a unit designed to purify pre-cleaned biogas (40% CO2 and 60% CH4) in industrial conditions (feed flow rate more than 500 Nm3/h and large-volume equipment). The process simulations performed to optimize the VPSA unit consider the kinetic separation of the feed components by using an appropriate carbon molecular sieve (CMS) adsorbent having a high kinetic separation selectivity for CO2 with respect to CH4. The designed VPSA unit is composed of five columns that perform three equalization steps. Minimizing methane losses during the regeneration steps necessitates injecting part of the off-gas rich in CO2 at the bottom of the column during the production step to push the CH4 forward. The produced biomethane meets the specification (97% CH4) of grid injection purity. The developed cycle allows a CH4 recovery of 92% to be obtained with a specific energy consumption of 0.35 kWh/Nm3, thus meeting the initial requirements for industrial exploitation of VPSA technology for biomethane purification from biogas sources. [ABSTRACT FROM AUTHOR]

The global demand on highly purified gases provided by energy-efficient separation processes grows steadily since decades. An example of particular industrial relevance is nitrogen generated by pressure swing adsorption from compressed air. A kinetically based separation of oxygen from nitrogen is possible by means of carbon molecular sieves (CMS) since oxygen adsorbs remarkably faster in CMS than nitrogen. Even high product purities (5–1000 ppm O2) are easily achievable in commercial generators. However, only a few studies present experimental findings in this purity range. That comes as no surprise, since experimental conditions are not standardised and the determination of N2-PSA performance indicators still creates an experimental challenge. Moreover, the design of the set-up remarkably influences the experimental results. Thus it is the motivation of this study to develop a multi-step strategy, comprising the definition of a reference process, the derivation of explicit and implicit performance indicators based on either flow meter readings or macroscopic material balances, a verification strategy for experimentally obtained data, and an error consideration, which advices accuracy requirements for analysers and flow meters. The effect of cycle time and operating temperature on the performance indicators is exemplarily studied at high purities by means of the proposed strategy. [ABSTRACT FROM AUTHOR]

The asymmetric polyethersulfone (PES‐15 wt.%) mixed‐matrix membranes were prepared by incorporation of carbon molecular sieve (CMS) with varying concentrations (1, 3, and 5 wt.%). Physicochemical characterization of synthesized membranes was carried out using field emission scanning electron microscope, atomic force microscopy, contact angle, thermogravimetric analysis, zeta potential analyzer, porosity, and mean pore sizes. Performance analysis of synthesized mixed‐matrix membranes was carried out by varying the operating parameters such as pressure (2–10 bar), feed concentration (100–1,000 mg/L), and cations type (Na+, Ca2+, Mg2+, and Sn2+). Effect of operating parameters and CMS concentration was investigated on pure water flux (PWF), permeate flux, and rejection of membranes. It was found that mixed‐matrix membrane containing 15 wt.% PES with 1 wt.% CMS displayed the superior physicochemical characteristics in terms of hydrophilicity (37.9°), surface charge (−13.8 mV), mean pore diameter (6.04 nm), and thermal properties (Tg = 218.5°C), and overall performance. E5C1 membrane showed 1.5 times higher PWF (75.5 L m−2 hr−1) and incremented in rejection for all salts than the nascent membrane. Practitioner points: Carbon molecular sieve‐embedded mixed‐matrix membranes were synthesized by phase inversion method.The resultant membranes experienced improved hydrophilicity, roughness, surface charge, porosity, and mean pore diameter with 1 wt.% CMS loading.The pure water flux was improved from 55.77 to 75.05 L m−2 hr−1 when 1 wt.% CMS was added in pure PES.The observed rejection of a mixed‐matrix membrane with 1 wt.% CMS was the maximum for all salts. [ABSTRACT FROM AUTHOR]

Pressure swing adsorption (PSA) appears to be an effective technology for biogas upgrading under different operating conditions with low greenhouse gas emissions. This study presents the simulation of biomethane adsorption with the adsorption bed filled with a carbon molecular sieve (CMS). A six dual-bed six-step PSA process was studied which produced a high purity of biomethane. The design of the adsorption bed was followed by the real process of which the biomethane capacity was more than 5000 Nm3/h. For the adsorbent, a CMS-3K was used, and a biomethane gas with a minimum 92% purity was produced at 6.5 bar adsorption pressure. To understand the adsorption characteristics of the CH4 and CO2 gases, the Langmuir isotherm model was used to determine the isotherm of a mixed gas containing 55% CH4 and 45% CO2. Furthermore, the experimental data from the work of Cavenati et al. were used to investigate the kinetic parameter and mass transfer coefficient. The mass transfer coefficients of two species were determined to be 0.0008 s−1 and 0.018 s−1 at 306 K for CH4 and CO2, respectively. The PSA process was then simulated with a cyclic steady state until the relative tolerance was 0.0005, which was then used to predict the CH4 and CO2 mole fraction along the adsorption bed length at a steady state. Moreover, the optimal conditions were analyzed using Aspen Adsorption to simulate various key operating parameters, such as flowrate, adsorption pressure and adsorption time. The results show a good agreement between the simulated results and the real operating data obtained from the company REBiofuel. Finally, the sensitivity analysis for the major parameters was presented. The optimal conditions were found to be an adsorption pressure of 6 bar, an adsorption time of 250 s and a purity of up to 97.92% with a flowrate reducing to 2000 Nm3/h. This study can serve as a commercial approach to reduce operating costs. [ABSTRACT FROM AUTHOR]

Carbon molecular sieve membranes (CMSM) were prepared from the pyrolysis of polyimide films within a temperature range of 600°C‐800°C under nitrogen stream. The membrane samples were characterized and tested for the permeation of He, CH4, CO2, and N2 at different pressures and temperatures, respectively. The CMSM700 membrane (pyrolyzed at 700°C) showed an ideal selectivity of ~ 11 for N2/CH4 with a permeability of 2.18 × 10−15 mol · m/m2 · s · Pa for N2. The separation mechanism for the N2/CH4 pair was shown to be largely molecular sieving rather than surface flow. The membrane showed an ideal selectivity of ~ 500 for the CO2/CH4 pair with a CO2 permeability of 9.72 × 10−14 mol · m/m2 · s · Pa. The permeability of He was lower than that of CO2, suggesting that the surface flow played a significant role in the CO2 permeation. The updated permeability‐selectivity tradeoff curves show that this CMSM membrane compared favourably with other membrane materials reported in the literature for the removal of N2 and CO2 from CH4 for natural gas upgrading. [ABSTRACT FROM AUTHOR]

This study experimentally evaluates the performance of different sorbent tubes for sampling acetone vapor in workplace air. A dynamic atmosphere system produced an acetone alone and a mixture with other analytes containing ~73, 483, and 1898 µg acetone mass loading at 25, 50, and 75% relative humidity (RH) at 25°C. Sorbent samples were analyzed in accordance with OSHA Method 69 (Carbosieve S-III) and NMAM 1501, modified to use Anasorb 747 sorbent. Both methods were modified to include the additional analytes. Additional extraction procedures with and without 1% dimethylformamide and anhydrous magnesium sulfate were included in the modified NMAM 1501 using Anasorb 747. Silica gel sorbent tubes analyzed according to NMAM 2027 were included. There were significant reductions in the recovery of acetone from both Anasorb 747 and Carbosieve S-III collected from air at 75% RH, relative to collection at 25 or 50% RH at very low loading compared with that of samples collected at mid to high loading. Silica gel provided a consistent recovery of acetone at all RHs and in the presence of other chemical interferences at 75% RH. The likely cause of mass dependence may arise from the humidity effect on acetone adsorption onto both beaded active carbon and carbon molecular sieve either in sampling or in analysis. The present study confirms not only previous observations but also adds to the literature showing carbonaceous sorbents are not well suited for sampling ketones at high humidity and low concentration. [ABSTRACT FROM AUTHOR]

In this study, the chemical vapor deposition of methane on the activated carbon has been identified as an effective approach to prepare the CMS for the adsorption of CO 2. The effects of deposition parameters on the properties of the CMSs were both experimentally and statistically investigated. The deposition temperature as the most influential factor on the CO 2 adsorption capacity was determined based on the response table. CMS6 exhibited large volume of narrow-micropore centered at 0.56 nm in size, showed a maximum CO 2 adsorption of 1.7275 mmol g−1 at 273 K and 1 bar. The isosteric heat of adsorption and CO 2 /N 2 selectivity were 40.37 kJ mol−1 and 22.84 at 273 K and 1 bar, respectively. As a result, this particular study can be used for the main challenges associated with the design of CMS adsorbents to provide a perspective and opportunities to accelerate novel molecular sieve carbon production in the future. Unlabelled Image • Carbon molecular sieve was prepared through the chemical vapor deposition of methane. • The influence of the parameters on the CO 2 adsorption was determined by Taguchi method. • The prepared carbon molecular sieve exhibited large volume of narrow-micropore centered at 0.56 nm. • The CO 2 adsorption capacity of CMS6 was 1.7275 mmol g−1 at 273 K and 1 bar. • CMS6 exhibited CO 2 /N 2 selectivity of 22.84 at 273 K. [ABSTRACT FROM AUTHOR]

• Adsorption of N 2 O on activated carbon and carbon molecular sieve was studied. • The adsorbed amount of N 2 O on AC and CMS was much greater than those for O 2 and N 2. • The adsorption rate of N 2 O was slower than N 2 on AC, but much faster than N 2 on CMS. • The adsorption rate of N 2 O was affected by the kinetic diameter and Lewis structure. To evaluate candidate adsorbents for the recovery of nitrous oxide (N 2 O) from adipic acid off-gases, the equilibrium and kinetics of N 2 O and O 2 adsorption on activated carbon (AC) and of N 2 O, O 2 , and N 2 adsorption on a carbon molecular sieve (CMS) were evaluated at 293, 308, and 323 K under pressures up to 1000 kPa using a high-pressure volumetric system. Adsorption amount of N 2 O on AC and CMS exceeded those of N 2 and O 2 , and the adsorption isotherms for O 2 and N 2 were similar. The experimental N 2 O and O 2 uptakes on AC and CMS were fitted to a non-isothermal adsorption model, whereas the model was ineffective for predicting N 2 uptake on CMS. The isothermal dual-resistance model, considering surface barrier resistance and pore diffusion, adequately predicted N 2 uptake on CMS. The rate of adsorption of N 2 O on AC was much lower than that of O 2 and N 2 whereas the rate of adsorption on CMS flowed the order: O 2 > N 2 O ≫ N 2 , even though N 2 O has higher adsorption affinity and smaller kinetic diameter than O 2. The Lewis structure of N 2 O was also found to influence the adsorption kinetics. [ABSTRACT FROM AUTHOR]

• Nitrogen rejection from methane was achieved with a kinetic DR PSA process. • A non-isothermal numerical model was shown capable of simulating kinetic DR PSA cycles. • A feed with 75% CH 4 + 25% N 2 was separated to achieve 90% CH 4 purity and 90% recovery. • Simulations provide insight into the separation mechanism of a kinetically N 2 selective adsorbent. Dual-reflux pressure swing adsorption (DR PSA) processes using a kinetically nitrogen selective molecular sieve carbon, MSC-3K 172, were investigated for the removal of nitrogen from a gas mixture consisting of 75 mol% CH 4 + 25 mol% N 2. The four DR PSA configurations (PL-A, PH-A, PL-B and PH-B) were experimentally demonstrated and compared in terms of their nitrogen rejection and methane recovery performance. The experimental results indicated the PH-B configuration in general performed the best in terms of the methane product purity and recovery using the kinetic MSC-3K 172 adsorbent. A non-isothermal numerical model was constructed for the kinetic DR PSA process to simulate and optimise the performance of the PH-B configuration. Model predicted gas loadings on the adsorbent indicated that selectively removing nitrogen from methane was feasible when a feed step time close to the characteristic adsorption time of nitrogen was selected. The effective usage of the adsorption bed in the PH-B configuration was also numerically studied via the capacity ratio C , with the feed step time and light reflux flow as key operational parameters, at fixed heavy product-to-feed ratio, bed pressure ratio and feed location. The numerical model for the PH-B configuration was also employed to study the effect of pressure in the purge step beyond those conditions accessible in the experiment. The simulation results revealed that the PH-B configuration could achieve a separation performance of 90 mol% CH 4 in the light product with 90% CH 4 recovery when the pressure in the light purge column was lower than 40 kPa while the adsorption pressure was maintained at 500 kPa. This result opens new opportunities for efficiently upgrading sub-quality natural gas reserves. [ABSTRACT FROM AUTHOR]

Graphical abstract Simple description: The CMS samples were modified by two types of modification methods. One is impregnation modification with three different organic reagents and the other is low temperature plasma modification with different gas atmosphere as depicted in the graphical abstract. Highlights • The carbon molecular sieves (CMS) were modified by two types of modification methods. One is impregnation modification with organic reagents and the other is low temperature plasma modification with different gas atmosphere. • The separation coefficient (3.3) of CH 4 /N 2 was obtained for the CMS modified by low temperature plasma modification under nitrogen atmosphere. This value is higher than that of previous other reports. • The low temperature plasma modification for the CMS may supply a promising approach towards adsorption separation of CH 4 /N 2. Abstract Coal-based carbon molecular sieves (CMS) were modified by organic reagents with affinities for hydrocarbons including tetracosane (C24), lauryl sodium sulfate (SDS), and polyethylene imine (PEI), and low temperature plasma treatment in a CH 4 and N 2 atmosphere, respectively. The modified CMS samples were characterized by FT-IR analysis, low-temperature N 2 adsorption tests and SEM. In addition, the adsorption capacities of pure CH 4 and N 2 were measured by the static volume method and the CH 4 /N 2 separation coefficients of the modified samples were also compared. The saturated adsorption capacities q m after modification and separation coefficients were investigated. CH 4 was more strongly adsorbed on all the modified samples. The sample of CMS-P-N has the best modification effect and its saturated adsorption capacities q m were 6.76 mmol/g for CH 4 and 5.56 mmol/g for N 2 , respectively. The separation coefficient of CH 4 /N 2 of CMS-P-N was 3.32. Besides, CH 4 breakthrough tests were performed using a fixed bed apparatus. The breakthrough curves confirmed that low temperature plasma treatment of CMS in an N 2 atmosphere was beneficial for the adsorption separation of CH 4 /N 2. [ABSTRACT FROM AUTHOR]

Highlights • Adsorption behaviors of CO 2 , CO, and N 2 on carbon molecular sieve were measured. • Adsorbed amounts and heats of adsorption on carbon-based adsorbents were compared. • The adsorption rates on CMSs were affected by electrical properties of adsorbates. • The validity of results was confirmed by predicting experimental breakthrough curve. Abstract Adsorption equilibria and kinetics of CO 2 , CO, and N 2 on carbon molecular sieves (CMSs) were measured by a gravimetric method at temperatures of 298, 308, and 318 K and pressures up to 10 bar. The validity of the experimental isotherms and kinetics was confirmed by comparing with experimental results from an additional volumetric method. Experimental adsorption isotherms were well correlated with a temperature-dependent Sips model and the results were compared with the Langmuir and Sips models. The order of the adsorbed amounts and isosteric heats of adsorption were CO 2 > CO ≥ N 2 and their heats of adsorption changed from vertical interactions to lateral interactions with an increase in loading amount. The adsorbed amounts and heats of adsorption were lower for the CMSs than those of activated carbon, which has higher surface area and pore size. The microporous diffusional time constants (D μ /r2) of CO and N 2 could be obtained from an isothermal kinetic model, while a non-isothermal kinetic model was required for CO 2 due to its higher heat of adsorption and adsorption rate. In addition, the variation in D μ /r2 with surface coverage were well correlated by the Darken relation combined with Sips isotherm model, and a steep variation was observed from a surface coverage of 0.2 in all the components. The adsorption rate was highly affected by the electrical properties of the adsorbate rather than kinetic diameters. The order of adsorption rate was CO 2 ≫ CO > N 2 , while the order of the activation energies in the Arrhenius equation was opposite. The validity of obtained equilibria and kinetics results was confirmed by comparing the experimental breakthrough curves and dynamic simulation results in a CMS bed. [ABSTRACT FROM AUTHOR]

In this study, we augment our analysis of pyrolysis temperature dependence of carbon molecular sieve (CMS) membranes derived from a polyimide, Matrimid® useful for advanced CMS membranes. Our direct sorption results prove that the strong pyrolysis temperature dependence of permselectivity for the CO 2 /CH 4 gas pair is promoted by an unusual trend in sorption selectivity reported here. This trend complements conventional diffusion selectivity trends for this pair with increasing pyrolysis temperatures. Our results show that the elimination of pyridinic and pyrrolic groups over the same pyrolysis temperature range occurs. Elimination of such CO 2 -philic pyridinic and pyrrolic groups typically would be expected to cause a trend opposite to that actually measured directly for CO 2 /CH 4 selectivity. The resulting trend for pyrolysis temperatures between 550 °C and 900 °C, however, can be explained in terms of microporous and ultramicroporous properties of the CMS for increasing pyrolysis temperatures. Specifically, apparent thermodynamic exclusion selectivity of the 0.5 Å larger CH 4 vs. the slim 3.3 Å CO 2 provides a consistent explanation of the trends. This discovery provides additional options to tune permselectivity of CMS membranes to complement molecular sieving based on diffusion contributions. • CO 2 and CH 4 sorption isotherms for Matrimid®-derived CMS membranes were measured. • The sorption isotherms were analyzed with dual mode sorption model. • Such analysis explains trends in S CO2 and S CH 4 vs. pyrolysis temperatures. • High pyrolysis temperature enables thermodynamic exclusion selectivity of CH 4 vs. CO 2. • The exclusion selectivity could also enable ultrahigh selectivities for H 2 /CH 4. [ABSTRACT FROM AUTHOR]

Pressure swing adsorption (PSA) appears to be an effective technology for biogas upgrading under different operating conditions with low greenhouse gas emissions. This study presents the simulation of biomethane adsorption with the adsorption bed filled with a carbon molecular sieve (CMS). A six dual-bed six-step PSA process was studied which produced a high purity of biomethane. The design of the adsorption bed was followed by the real process of which the biomethane capacity was more than 5000 Nm3/h. For the adsorbent, a CMS-3K was used, and a biomethane gas with a minimum 92% purity was produced at 6.5 bar adsorption pressure. To understand the adsorption characteristics of the CH4 and CO2 gases, the Langmuir isotherm model was used to determine the isotherm of a mixed gas containing 55% CH4 and 45% CO2. Furthermore, the experimental data from the work of Cavenati et al. were used to investigate the kinetic parameter and mass transfer coefficient. The mass transfer coefficients of two species were determined to be 0.0008 s−1 and 0.018 s−1 at 306 K for CH4 and CO2, respectively. The PSA process was then simulated with a cyclic steady state until the relative tolerance was 0.0005, which was then used to predict the CH4 and CO2 mole fraction along the adsorption bed length at a steady state. Moreover, the optimal conditions were analyzed using Aspen Adsorption to simulate various key operating parameters, such as flowrate, adsorption pressure and adsorption time. The results show a good agreement between the simulated results and the real operating data obtained from the company REBiofuel. Finally, the sensitivity analysis for the major parameters was presented. The optimal conditions were found to be an adsorption pressure of 6 bar, an adsorption time of 250 s and a purity of up to 97.92% with a flowrate reducing to 2000 Nm3/h. This study can serve as a commercial approach to reduce operating costs.