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• 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]

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]

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]

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]

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]

Graphical abstract Highlights • Carbon molecular sieves were produced from chestnut shell by CVD treatment. • CMSs were characterized by gas adsorption, elemental, FTIR and SEM analysis. • The produced carbon molecular sieves are more selective for carbon dioxide. • Maximum CO 2 adsorption capacity was obtained as 525.7 mg/g. Abstract In this study, carbon molecular sieves (CMS) were produced from chestnut shell by chemical activation process followed by chemical vapor deposition (CVD) of methane. The influences of deposition temperature (800–900 °C), time (15–60 min) and flow rate of CH 4 (100–300 mL/min) on pore development of carbon molecular sieve were investigated. The produced CMSs were characterized by several techniques such as N 2 adsorption, CO 2 adsorption, CH 4 adsorption, elemental analysis, FTIR analysis and SEM analysis. The textural analysis of the CMS samples showed the successful deposition of methane on pores of the produced activated carbon derived from chestnut shell to yield a microporous CMS with a narrow pore size distribution. The deposition temperature, time and flow rate of CH 4 were shown to strongly affect the pore structure of the CMS. The maximum CO 2 adsorption capacity (525.7 mg/g) was obtained at a deposition temperature of 850 °C, time of 30 min, and CH 4 flow rate of 100 mL/min. [ABSTRACT FROM AUTHOR]

Abstract Carbon molecular sieve is introduced as flexible supercapacitor electrode for the first time. The carbon molecular sieve electrode generates a specific capacitance of 108.0 F·g−1 and demonstrates an excellent stability with 98.5% preservation of its initial capacitance after 10,000 charging-discharging cycles. To further enhance the electrochemical performance, a flexible 3-D structured composite electrode is synthesized via an electrochemical polymerization method by depositing poly 3,4‑ethylenedioxythiophene film on the carbon molecular sieve surface, denoted as carbon molecular sieve@poly 3,4‑ethylenedioxythiophene. The specific capacitance of the composite electrode is up to 126.0 F·g−1, higher than both poly 3,4‑ethylenedioxythiophene (115.7 F·g−1) and carbon molecular sieve (108.0 F·g−1). Moreover, the flexible composite electrode preserves 96.0% of its initial capacitance after 10,000 charging-discharging cycles at 1.00 A·g−1. The superior performance of the composite electrode is attributed to the combined merits of the superior conductivity and excellent cycle stability of the carbon molecular sieve and 3-D porous network configuration of the poly 3,4‑ethylenedioxythiophene. [ABSTRACT FROM AUTHOR]

The adsorption, formation, and interaction energies between carbon dioxide (CO 2 ) and carbon oxide functional groups on porous carbon surface were analyzed through XPS, textural analysis, CO 2 gas adsorption, and theoretical study. Carbon molecular sieves (CMSs) as porous carbon were modified by several concentrations of hydrogen peroxide (H 2 O 2 ) solution under atmospheric conditions in an attempt to introduce carbon oxide groups and increase their CO 2 adsorption capacity. Created oxide groups on carbon surface of CMSs were determined by XPS analysis and the CO 2 adsorption capacities were investigated through the CO 2 adsorption isotherms at 273 and 298 K at low pressure (max. 800 mmHg). The CO 2 uptake capacity on CMSs modified by H 2 O 2 was increased compared to an unmodified CMS and increased with increasing carboxylic (-COOH) group concentration on the carbon surface of CMSs. For a theoretical approach, binding energies between CO 2 and various functional groups on the surface of CMSs have been investigated using several electronic structure calculations. As the result of the computational study by the MP2 method, a carboxylic group has the highest binding energy for CO 2 (-COOH····CO 2 ) of 4.45 kcal/mol, compared to quinone (dbndO) of 3.9, phenol (-OH) of 3.2 and lactone (-O-C=O) of 3.57 kcal/mol. This work demonstrates that introducing -COOH groups on CMS by H 2 O 2 are a suitable modification for CO 2 adsorption. [ABSTRACT FROM AUTHOR]

In this work, carbon molecular sieve (CMS) dense film membranes derived from 6FDA-DAM:DABA (3:2) polyimide precursor were studied for separation of mixed olefins (C 2 H 4 and C 3 H 6 ) from paraffins (C 2 H 6 and C 3 H 8 ). Olefin-selective CMS membranes with high performance can be made by pyrolysis of metal-containing polymeric precursors. Pyrolyzed at 550 °C with a fast ramp rate, CMS membranes with integrated Fe 2+ (2.2 wt% in the precursor) showed 19% higher C 2 H 4 /C 2 H 6 and 11% higher C 3 H 6 /C 3 H 8 sorption selectivity than that of the neat CMS membrane. Additional investigations with a quaternary mixture feed (C2 and C3 hydrocarbons) show that C 2 H 4 permeability above 10 Barrers with C 2 H 4 /C 2 H 6 permselectivity near 11 were achieved for the 3.2 wt% Fe loading case. Although Fe incorporation did not appear to promote C 3 H 6 /C 2 H 6 permselectivity, Fe is useful to improve C2 pair olefin/paraffin separation. Deconvolution of the C 2 H 4 /C 2 H 6 permselectivity for our more extensively studied 2.2 wt% loading case was also revealing. While both sorption and diffusion selectivity increased due to the Fe incorporation, a larger influence is seen on the diffusion selectivity versus the sorption selectivity. Hypotheses to explain this surprising outcome are offered to guide future work. [ABSTRACT FROM AUTHOR]

This work presents an experimental approach aiming the production of a gas mixture composed of H 2 and CH 4 , which should serve as natural gas substitute in industrial applications. Therefore, a lab-scale process chain employing a water gas shift unit, scrubbing units, and a pressure swing adsorption unit was operated with tar-rich product gas extracted from a commercial dual fluidized bed biomass steam gasification plant. A gas mixture with a volumetric fraction of about 80% H 2 and 19% CH 4 and with minor fractions of CO and CO 2 was produced by employing carbon molecular sieve as adsorbent. Moreover, the produced gas mixture had a lower heating value of about 15.5 MJ·m −3 and a lower Wobbe index of about 43.4 MJ·m −3 , which is similar to the typical Wobbe index of natural gas. [ABSTRACT FROM AUTHOR]

For the first time, boron embedded carbon membranes have shown superior C 2 H 4 permeability and C 2 H 4 /C 2 H 6 selectivity to the upper bound line under both pure and mixed gas tests. The precursors of the carbon membranes were prepared by incorporating various boron compounds with different molecular sizes into a hydrolyzed polymer of intrinsic microporosity (PIM-1) and then carbonized at 700 °C. The increments in C 2 H 4 permeability and C 2 H 4 /C 2 H 6 selectivity followed the order of molecular size of the boron compounds. Both PALS results and CO 2 adsorption isotherms confirmed the enlarged pore size and increased pore amount. The enhancements in C 2 H 4 permeability and C 2 H 4 /C 2 H 6 selectivity were mainly due to the higher C 2 H 4 diffusivity and greater diffusion selectivity resulting from proper choices of boron additives and carbonization conditions. When 9,9-dihexylfluorene-2,7-diboronic acid (DHFDA) was embedded into the hydrolyzed PIM-1 and then carbonized at 700 °C, the C 2 H 4 permeability and C 2 H 4 /C 2 H 6 selectivity of the carbonized membrane under mixed gas tests increased from 7.5 to 13.7 Barrer and from 9.3 to 9.7, respectively. [ABSTRACT FROM AUTHOR]

This study was carried out to characterize CO 2 adsorption equilibrium and kinetics of commercial adsorbents that have potential for use in the pressure swing adsorption (PSA) process and also to provide a better understanding of CO 2 adsorption behaviour under wide ranges of operating conditions. A comprehensive set of data and the analysis for CO 2 adsorption equilibrium and kinetics are presented for six commercial adsorbents, i.e. zeolite 13x, zeolite 5A, zeolite 4A, carbon molecular sieve (MSC-3R), and activated carbons (GCA-830 and GCA-1240). The adsorption equilibrium and the kinetic data were taken at a temperature range of 293-333 K and pressure up to 35 atm. The CO 2 adsorption isotherm was found to follow typical a type-I isotherm classification according to IUPAC, representing a monolayer adsorption mechanism. Among the six commercial adsorbents tested, activated carbon GCA-1240 offered the highest adsorption capacity, and zeolite 4A provided the lowest capacity. The obtained isotherm data were correlated as a function of temperature and pressure to fit with different model equations ( i.e. Langmuir, Toth, Sips, and Prausnitz). The Sips model showed the best fit with the equilibrium data for zeolite 13X, zeolte 5A, zeolite 4A, and carbon molecular sieve (MSC-3R) while the Prausnitz model provided an excellent fit with the data for activated carbons (GCA-830 and GCA-1240). The isosteric heat of CO 2 adsorption was also estimated for individual adsorbents according to the Clausius-Clapeyron equation. The CO 2 adsorption kinetic, presented in terms of mass transfer coefficients ( k ), were analyzed from the plots of CO 2 uptake rate using the well-recognized linear driving force (LDF) model. The k values were correlated by non-linear regression to reveal effects of adsorption temperature and pressure. Activation energies of CO 2 adsorption on the individual adsorbents were also calculated and correlated according to the Arrhenius equation. [ABSTRACT FROM AUTHOR]

Carbon molecular sieve (CMS) membranes are ideal candidates for natural gas separation due to their rigid pore structures and stability. The chemical composite and spatial configuration of the used precursors for deriving CMS membranes can greatly influence the final microporous structure and separation performance of the membranes. Most CMS membranes are transformed from amorphous precursors such as polymers nowadays. Here, for the first time, we report a new type of CMS membrane derived from a crystalline porous hydrogen-bonded organic framework membrane (named HCMS). The conversion process has been studied with the characterization of TGA, FTIR, XRD, SEM, and pore size distribution. The effect of pyrolysis temperature on the membrane structure has been investigated to achieve optimized CO 2 /CH 4 separation performance. On the one hand, as the pyrolysis temperature increases from 550 to 650 °C, the pore size distribution of HCMS membrane is narrowed, which is conducive to improving the molecular sieving effect of the membrane. On the other hand, higher ratios of graphitic N and pyrrolic N, which show better affinity for CO 2 molecules than pyridinic N, are obtained on the HCMS membranes, leading to more favorable adsorption of CO 2. The optimized HCMS membrane pyrolyzed at 600 °C shows a remarkable CO 2 /CH 4 selectivity of 128 and excellent separation stability at varying temperatures and pressures. The HCMS membranes derived from the crystalline HOF precursor can also maintain a stable separation performance against physical aging. The results reported in this work may open the door to constructing CMS membranes with the precursor of crystalline porous membranes. Crystalline porous hydrogen-bonded organic framework membrane is employed as a new kind of precursor for the first time to derive carbon molecular sieve membrane with a narrow pore size distribution, which reveals good separation selectivity and stability for CO 2 /CH 4. [Display omitted] • For the first time, a HOF membrane is used as a precursor to derive HCMS membrane. • Ordered porosity of HOF leads to a narrow pore size distribution of HCMS membrane. • Effect of pyrolysis temperature on membrane structure and CO 2 affinity is studied. • The HCMS-600 membrane reveals the optimized CO 2 /CH 4 separation selectivity of 128. • The HCMS-600 membrane is long-term stable at variable temperatures and pressures. [ABSTRACT FROM AUTHOR]

We utilize gas sorption experiments, neutron pair distribution function, and small-angle X-ray scattering studies on carbon molecular sieves (CMSs) to gain new insight into their ultramicroporous structure. CMS materials derived from the pyrolysis of PIM-1 (PIM = polymer of intrinsic microporosity) under an inert atmosphere (PIM-1-CMS) and H 2 atmosphere (4% H 2 -PIM-1-CMS) were studied. Neutron total scattering studies of these materials reveal these CMS materials to be mainly graphene-like ribbons with short-range atomic ordering. Small-angle X-ray scattering and low angle diffraction peaks corroborate the presence of well-defined ultramicroporosity observed in carbon dioxide and cryogenic neon adsorption studies suggesting, expectedly, that these materials are non-graphitizing carbon structures. Our findings provide microscopic evidence of the non-graphitizing and ribbon-like structure of these CMS materials and suggest a possible hypothetical microporous structure. [Display omitted] • Neutron total scattering shows short-range atomic ordering graphenic CMS structures. • Developed a proposed microstructure of CMS via scattering and gas sorption studies. • CO 2 and cryogenic Ne adsorption detect ultramicropores inaccessible to cryogenic N 2. [ABSTRACT FROM AUTHOR]

• The equilibria and kinetics of N 2 , O 2 , and Ar in CMS were evaluated at sub-ambient temperatures. • Pressure swing frequency response technique revealed the combined resistances of a surface barrier and micropore diffusion for the system studied. • Activation energy follows the order A r > N 2 > O 2 , with values of 36.9, 28.7, and 21.2 kJ/mol for Ar, N 2 , and O 2 respectively. • Kinetic selectivity increases with decreasing temperature and correlates well with the differences in activation energy. Carbon molecular sieves (CMS) are among the most promising materials for industrial gas separations, including their utilization for the kinetical removal of O 2 from N 2 and Ar in commercial pressure swing adsorption processes. However, little is known about the characteristics of these kinetics processes at lower temperatures. In this article, a kinetic study was carried out at three temperatures (-25, 0, and 25 °C) for pure O 2 , N 2 , and Ar using a commercially available Shirasagi MSC-3K-172. A pressure-swing frequency response technique was applied to determine the dominating mass transfer resistances, as well as corresponding temperature dependences, revealing that a combined resistance model of surface barrier and micropore diffusion best describes the behavior of all three gases. In addition, this MSC-3K-172 exhibited higher kinetic rates but lower kinetic selectivities as compared to Shirasagi MSC-3R-162 and −170, which showed only surface barrier resistances for N 2 and Ar. When the temperature was reduced from 25 °C to −25 °C, the equilibrium capacities for three gases increase similarly, but the kinetic rates decrease to varying extents, resulting in an unexpected increase in kinetic selectivity – the value near doubled (from 17 to 33) for O 2 /N 2 and more than tripled (from 24 to 88) for O 2 /Ar. The observed kinetic selectivities were found to correlate well with the difference of the activation energies between the gas pairs. These activation energies are 36, 29, and 21 kJ/mol for Ar, N 2 , and O 2 , respectively, greater than the isosteric heats of adsorption, which follow the reverse order. Together, these results indicate a delicate balance among kinetic selectivities, controlling mass transfer resistances and rate parameters, and equilibrium capacities, and can be utilized for the design of kinetic separations with CMSs, especially when extended to sub-ambient temperatures. [ABSTRACT FROM AUTHOR]

Carbon molecular sieves (CMS) are widely used in the separation of dioxide carbon and methane. In this research, three commercial CMS were utilized to analyze the pore structure and chemical properties. The adsorption isotherms of CO 2 and CH 4 were studied at 298 K, 308 K and 318 K over the pressure range of 0–1 MPa by an Intelligent Gravimetric analysis (IGA-100B, UK). Langmuir model was adopted to fit the experimental data. The working capacity and selectivity were employed to evaluate the adsorbents. The adsorption thermodynamics were discussed. The adsorbed amounts of both CO 2 and CH 4 are found to be highly related with the BET specific surface area and the volume of micropores, and also are interrelated with the total pore volume and micropore surface area. The standard enthalpy change ( ΔH Θ ), standard Gibbs free energy ( ΔG Θ ) and standard entropy change ( ΔS Θ ) at zero surface loading are negative, manifesting the adsorption process is exothermic and spontaneous, and the system tends to be ordered. With the increasing surface coverage, the absolute values of Gibbs free energy ( ΔG ) decrease whereas the absolute values of enthalpy change ( ΔH ) and entropy change( ΔS ) increase. This indicates that as the adsorbed amount increases, the degree of the spontaneity reduces, the intermolecular forces among the adsorbate molecules increase, the orderliness of the system improves and the adsorbed amount approaches the maximum adsorbed capacity. [ABSTRACT FROM AUTHOR]

High performance thermally-rearranged (TR) and carbon molecular sieve (CMS) membranes made from an intrinsically microporous polymer precursor PIM-6FDA-OH are reported for the separation of propylene from propane. Thermal rearrangement of PIM-6FDA-OH to the corresponding polybenzoxazole (PBO) membrane resulted in a pure-gas C 3 H 6 /C 3 H 8 selectivity of 15 and C 3 H 6 permeability of 14 Barrer, positioning it above the polymeric C 3 H 6 /C 3 H 8 upper bound. For the first time, the C 3 H 6 /C 3 H 8 mixed-gas properties of a TR polymer were investigated and showed a C 3 H 6 permeability of 11 Barrer and C 3 H 6 /C 3 H 8 selectivity of ~11, essentially independent of feed pressure up to 5 bar. The CMS membrane made by treatment at 600 °C showed further improvement in performance as demonstrated with a pure-gas C 3 H 6 /C 3 H 8 selectivity of 33 and a C 3 H 6 permeability of 45 Barrer. The mixed-gas C 3 H 6 /C 3 H 8 selectivity dropped from 24 to 17 from 2 to 5 bar feed pressure due to a decrease in C 3 H 6 permeability most likely caused by competitive sorption without any evidence of plasticization. [ABSTRACT FROM AUTHOR]

Distinct percentages of carbon molecular sieve (CMS) were added to Polyethersulfone (PES) matrix to generate mixed matrix membranes (MMMs) using solution casting method. The characterization was conducted by thermogravimetric analysis (TGA) to find out the residue solvent in the membranes and field emission scanning electron microscopy (FESEM) analysis to check the morphology of membrane. TGA results demonstrated no remaining solvent and also FESEM images demonstrated acceptable bonds between the filler particles and the polymer chains. The gas permeation results divulged that both CO 2 permeance and CO 2 /CH 4 selectivity went up with CMS loadings increment as compared to pure PES membrane. Obtained results revealed that the greatest value of CO 2 permeance (68 GPU) and CO 2 /CH 4 selectivity (11.15) at a pressure of 8 bars can be accomplished with 15 wt. % loading of CMS particles. This can be related to the kinetic diameter of CMS particles that places between CO 2 and CH 4 kinetic diameters. [ABSTRACT FROM AUTHOR]

Carbon molecular sieve (CMS) has been proposed as counter electrode (CE) catalyst in dye-sensitized solar cells (DSCs) for the first time. We evaluate the catalytic activities of CMS for the regeneration of different redox couples of I 3 − /I − , T 2 /T − , and Co 3+/2+ , and compare them with those of the traditional Pt CE, which is very expensive. For the I 3 − /I − redox couple, the CMS shows a relatively lower catalytic behavior than Pt due to large charge transfer resistance and low mass transport rate. Toward the organic T 2 /T − redox couple, the CMS is a much better catalyst than Pt, and the DSCs exhibits a power conversion efficiency (PCE) of 5.30%, which is a great enhancement of 42.09% over the Pt CE based DSCs. Cyclic voltammograms depict that CMS displays a high peak current density and a low peak-to-peak separation, indicating a high catalytic activity of CMS toward T 2 /T − redox couple. For the Co 3+/2+ redox couple, CMS presents a competitive catalytic activity relative to Pt and the DSCs shows a PCE of 8.73%. [ABSTRACT FROM AUTHOR]

Fine-tuning the microporosity of PIM-1 by heat treatment was applied to develop a suitable carbon molecular sieve membrane for ethylene/ethane separation. Pristine PIM-1 films were heated from 400 to 800 °C under inert N 2 atmosphere (<2 ppm O 2 ). At 400 °C, PIM-1 self-cross-linked and developed polar carbonyl and hydroxyl groups due to partial dioxane splitting in the polymer backbone. Significant degradation occurred at 600 °C due to carbonization of PIM-1 and resulted in 30% increase in cumulative surface area compared to its cross-linked predecessor. In addition, PIM-1-based CMS developed smaller ultramicropores with increasing pyrolysis temperature, which enhanced their molecular sieving capability by restricted diffusion of ethylene and ethane through the matrix due to microstructural carbon densification. Consequently, the pure-gas ethylene permeability (measured at 35 °C and 2 bar) decreased from 1600 Barrer for the pristine PIM-1 to 1.3 Barrer for the amorphous carbon generated at 800 °C, whereas the ethylene/ethane pure-gas selectivity increased significantly from 1.8 to 13. [ABSTRACT FROM AUTHOR]

An intrinsically microporous polymer with hydroxyl functionalities, PIM-6FDA-OH, was used as a precursor for various types of carbon molecular sieve (CMS) membranes for ethylene/ethane separation. The pristine polyimide films were heated under controlled N 2 atmosphere at different stages from 500 to 800 °C. All CMS samples carbonized above 600 °C surpassed the polymeric ethylene/ethane upper bound. Pure-gas selectivity reached 17.5 for the CMS carbonized at 800 °C with an ethylene permeability of about 10 Barrer at 2 bar and 35 °C, becoming the most selective CMS for ethylene/ethane separation reported to date. As expected, gravimetric sorption experiments showed that all CMS membranes had ethylene/ethane solubility selectivities close to one. The permselectivity increased with increasing pyrolysis temperature due to densification of the micropores in the CMS membranes, leading to enhanced diffusivity selectivity. Mixed-gas tests with a binary 50:50 v/v ethylene/ethane feed showed a decrease in selectivity from 14 to 8.3 as the total feed pressure was increased from 4 to 20 bar. The selectivity drop under mixed-gas conditions was attributed to non-ideal effects: (i) competitive sorption that reduced the permeability of ethylene and (ii) dilation of the CMS that resulted in an increase in the ethane permeability. [ABSTRACT FROM AUTHOR]

Mixed matrix membranes (MMMs) containing diethanolamine (DEA) and carbon molecular sieve (CMS) in polyethersulfone (PES) were synthesized and characterized to study the efficiency of CO 2 separation from CH 4 . The membranes were fabricated by adding fixed amount of CMS and polymer into a solvent with DEA at different concentrations. These membranes were characterized for physicochemical properties by employing field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). The permeability and selectivity studies were carried out by using pure carbon dioxide and methane in a small laboratory test cell. The characterization results revealed that the structure of the membranes was dense and non-porous. It was also found that carbon molecular sieve was uniformly distributed in the polymer matrix. The addition of DEA significantly enhanced the performance of the investigated MMMs such that the CO 2 permeance and CO 2 /CH 4 selectivity were enhanced up to 172.41% and 283.21% respectively at a pressure of 6 bar. A comparison with the performance of a few other membranes decisively establishes the superiority of the membranes prepared and tested in this study. [ABSTRACT FROM AUTHOR]

The adsorption equilibrium and rate of H 2 and D 2 on a Carbon Molecular Sieve (CMS) with wide pore size distribution were measured at 77 K using a volumetric method. The adsorption equilibrium or kinetic ratios for D 2 to H 2 decreased with increasing pressure. The adsorption uptake curve showed a slow adsorption rate with time after displaying a fast adsorption rate in the initial period. Adsorption rate constants of D 2 were larger than those of H 2 at low pressure, and the ratio of D 2 to H 2 decreased with an increase in pressure. However, in breakthrough experiments for dynamic separation efficiency of hydrogen isotope separation, the CMS showed higher breakthrough separation factors than the corresponding adsorption equilibrium or kinetic ratios. The breakthrough separation factor reached 1.53 at a total gas pressure of 400.0 kPa and a flow rate of 129.8 cm 3 /min in the adsorption bed length of 1.0 m. In addition, the shape of D 2 breakthrough curve was slightly affected by the change of flow rate, but that of H 2 breakthrough curve showed almost constant pattern. And meso and macropores of the CMS gave a negative effect on the separation of H 2 and D 2 . Therefore, the key factor in separating H 2 and D 2 from the mixture depended not only on their equilibrium selectivity but also on their dynamic diffusional difference in the CMS bed due to the quantum molecular sieving effect in space-limited pore at low temperature. [ABSTRACT FROM AUTHOR]

A set of CMS adsorbents was synthesized by pyrolyzing gel-type cation exchange resins (IERs) based on sulfonated poly(styrene-co-divinylbenzene). Fifteen different materials were synthesized following a design of experiments (DOE) that included variations on four factors. These factors were divinylbenzene (DVB) content, plus three factors associated with pyrolysis (peak temperature, hold time, and temperature ramp rate). Results revealed that the peak temperature has a significant impact on the micropore volume and the effective pore size of the resultant CMS adsorbents, but the other three input variables have very little impact. High throughput single gas adsorption was conducted on the fifteen CMS adsorbents using nine probe gas molecules: CO 2 (kinetic diameter 3.3 Å), N 2 (3.64 Å), CH 4 (3.8 Å), C 2 H 4 (3.9 Å), C 3 H 6 (4.0 Å), C 2 H 6 (4.1 Å), C 3 H 8 (4.3 Å), i-C 4 H 10 (5.0 Å), SF 6 (5.5 Å). Based on gas pair selectivities calculated from the single gas adsorption data, pyrolysis process boundaries were defined to make suitable CMS adsorbents with effective micropore size in the range of 3.5–4.6 Å. Based on the high throughput findings, four additional CMS adsorbents were produced for the industrially significant separations: C 3 H 6 /C 3 H 8 , C 2 H 4 /C 2 H 6 , N 2 /CH 4 , and CO 2 /N 2 . Breakthrough performance of the four target gas pairs was characterized in a packed bed configuration using binary gas mixtures of the four target gas pairs. The four CMS adsorbents exhibited high separation factors, 43 for C 3 H 6 /C 3 H 8 , 10 for C 2 H 4 /C 2 H 6 , 9 for N 2 /CH 4 , and 12 for CO 2 /N 2 , illustrating the validity of the high throughput results. [ABSTRACT FROM AUTHOR]

Abstract: A carbon molecular sieve adsorbent (CMS-IMP12) obtained from the pyrolysis of a poly(vinylidene chloride-co-vinyl chloride) (PVDC-PVC, Saran™) material was tested and compared with other molecular sieve materials for the separation of a multi-component hydrocarbon mixture. Liquid phase experimental adsorption curves at 303K were obtained in a stirred tank using a model mixture composed by n-heptane, 2-methylheptane, 2,5-dimethylhexane and 2,2,4-trimethylpentane, considering the last one as a non-adsorbing solvent. Materials compared against the CMS-IMP12 were zeolites ZSM-5 (Si/Al=15), ZSM-5 (Si/Al=140), ZSM-22, ZSM-23, Silicalite-1 and Silicalite-2. The CMS-IMP12 adsorbed at least three times the amount adsorbed by the other material tested (i.e. 206 versus 79mg/gads for Silicalite-1) mainly because three components of the mixture (linear, methyl and non-geminal dimethyl alkanes) were adsorbed in higher proportions. None of the other tested materials adsorbed non-geminal dimethyl branched compounds. Regarding the kinetics of adsorption as represented by their second order rate constants, all the materials except the CMS-IMP12 adsorbed the methyl alkane molecule at the same rate as the n-alkane. The slower adsorption rate observed for 2-methylheptane as compared to n-heptane in the CMS-IMP12 may be due to the competition for adsorption sites between the two slow diffusing species: 2-methylheptane and 2,5-dimethylhexane. [Copyright &y& Elsevier]

Hydrogen is an emerging energy source with a wide range of applications in transportation, electricity generation, and manufacturing of important chemicals such as ammonia and methanol. Hydrogen is commonly coproduced with CO 2 using steam reforming of methane and its purification is typically achieved using energy-intensive processes such as pressure swing adsorption (PSA) and cryogenic distillation. Membrane technology with potentially lower energy consumption and lower carbon footprint could play an important role in developing a more sustainable hydrogen economy. In this study, we prepared carbon molecular sieve (CMS) membranes by the pyrolysis of a highly aromatic catalytic arene-norbornene annulation (CANAL)-Tröger's base ladder polymer of intrinsic microporosity precursor — CANAL-TB-1. CMS membranes obtained by pyrolysis between 600 and 900 °C displayed excellent gas separation performance for hydrogen/carbon dioxide separation and related applications. The CANAL-CMS-800 °C membrane showed a pure-gas hydrogen permeability of 41 Barrer with H 2 /CO 2 , H 2 /N 2 , and H 2 /CH 4 selectivity values of 39, 1952, and >8200 at 35 °C. Increasing the pyrolysis temperature to 850 and 900 °C further boosted the selectivity. For example, the CANAL-CMS-900 °C exhibited a stable long-term mixed-gas performance over a period of 38 days with an unprecedented H 2 /CO 2 selectivity of 174 and H 2 permeability of 8.2 Barrer at 10 bar total feed pressure and 100 °C, which significantly exceeded the performance of previously reported polymers and related CMS membrane materials. [Display omitted] • A microporous ladder polymer CANAL-TB-1 was employed as a precursor for CMS membranes fabrication. • CMS membranes pyrolized at high temperatures showed excellent H 2 /CO 2 gas separation performance. • CMS membranes pyrolyzed at 900 °C exhibited pure-gas H 2 /CO 2 selectivity of 248. • CMS membranes showed stable long-term mixed-gas H 2 /CO 2 selectivity of 174 at 10 bar and 100 °C. [ABSTRACT FROM AUTHOR]

Natural gas sweetening, one of the most promising venues for the growth of the membrane gas separation industry, is dominated by polymeric materials with relatively low permeabilities and moderate selectivities. One strategy towards improving the gas transport properties of a polymer is enhancement of microporosity either by design of polymers of intrinsic microporosity (PIMs) or by thermal treatment of polymeric precursors. For the first time, the mixed-gas CO2/CH4 transport properties are investigated for a complete series of thermally-rearranged (TR) (440°C) and carbon molecular sieve (CMS) membranes (600, 630 and 800°C) derived from a polyimide of intrinsic microporosity (PIM-6FDA-OH). The pressure dependence of permeability and selectivity is reported up to 30bar for 1:1, CO2:CH4 mixed-gas feeds at 35°C. The TR membrane exhibited ~15% higher CO2/CH4 selectivity relative to pure-gas feeds due to reductions in mixed-gas CH4 permeability reaching 27% at 30bar. This is attributed to increased hindrance of CH4 transport by co-permeation of CO2. Interestingly, unusual increases in mixed-gas CH4 permeabilities relative to pure-gas values were observed for the CMS membranes, resulting in up to 50% losses in mixed-gas selectivity over the applied pressure range. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid-typed Pt electrocatalyst using Pt-carbon molecular sieve (Pt-CMS) synthesized by zeolite template method and commercial Pt-carbon black (Pt-CB) is prepared with different ratios of Pt-CB to Pt-CMS. Their physical and electrochemical properties are characterized using X-ray diffraction (XRD), transmission electron micrograph (TEM) and Brunauer–Emmet–Teller method (BET). Pt nanoparticles of 2–4nm are synthesized and successfully dispersed onto CMS by polyol method and comparable with that of commercial Pt-CB. Cyclic voltammetric analysis is conducted to estimate electrochemical active surface area (ECSA). The cell test is conducted for the various membrane electrolyte assemblies (MEAs) fabricated with different catalysts such as Pt-CB, Pt-CMS, various hybrid-typed Pt-CBx/Pt-CMS100−x named as Pt-CBx/CMS100−x. The cell performance is fairly consistent with ECSA and the MEA fabricated with equal mass fraction of Pt-CB and Pt-CMS (Pt-CB50/CMS50) shows the best cell performance, indicating a significant dependence on pore structure of carbon support. [Copyright &y& Elsevier]

Abstract: The adsorption rates of pure O2, N2, and Ar have been measured at pressures from 0.125bar to 1bar on two carbon molecular sieve materials, Shirasagi MSC-3R type 162 and type 172, using pressure-swing frequency response. For each material, O2 adsorbs much faster than the other two gases, with Ar being the slowest of the three. Adsorption rates of N2 and Ar on both materials obey the linear driving force rate equation, indicating that a barrier resistance is rate limiting. Adsorption of O2 on both materials is best described using a combined resistance model, which treats a barrier resistance in series with a micropore diffusion resistance. However, the contribution of micropore diffusion to O2 adsorption rates is small. The experimental barrier resistance coefficients for all gases on both materials increase with pressure. The pressure dependence of the barrier coefficient can be explained by the existence of either Langmuir kinetics with a distribution of pore sizes or shell diffusion where the adsorbent with constricted pores in the shell has different equilibrium characteristics than the adsorbent in the core of a particle. The two materials investigated in this work demonstrate high kinetic selectivity for O2 over N2 and Ar, suggesting that they could be useful in pressure-swing adsorption processes designed to generate a high-purity O2 product. [Copyright &y& Elsevier]

Abstract: In this paper, the development of asymmetric carbon molecular sieve (CMS) hollow fiber membranes and advanced processes for olefin/paraffin separations based on the CMS membranes are reported. Membrane-based olefin/paraffin separations have been pursued extensively over the past decades. CMS membranes are promising to exceed the performance upper bound of polymer materials and have demonstrated excellent stability for gas separations. Previously, a substructure collapse phenomenon was found in Matrimid® precursor derived CMS fiber. To overcome the permeance loss due to the increased separation layer thickness, 6FDA-DAM and 6FDA/BPDA-DAM precursors were selected as potential new precursors for carbon membrane formation. Defect-free asymmetric 6FDA-DAM and 6FDA/BPDA-DAM hollow fibers were successfully fabricated from a dry-jet/wet-quench spinning process. Polymer rigidity, glass–rubber transition and asymmetric morphology were correlated. CMS hollow fiber membranes produced from 6FDA-polymer precursors showed significant improvement in permeance for ethylene/ethane and propylene/propane separations. Further studies revealed that the CMS membranes are olefins-selective, which means the membranes are able to effectively separate olefins (ethylene and propylene) from paraffins (ethane and propane). This unique feature of CMS materials enables advanced hybrid membrane-distillation process designs. By using the olefins-selective membranes, these new processes may provide advantages over previously proposed retrofitting concepts. Further applications of the membranes are explored for hydrocarbons processes. Significant energy savings and even reduced footprint may be achieved in olefins production units. [Copyright &y& Elsevier]

Abstract: A carbon molecular sieve (CMS) was modified through oxyfluorination to investigate its carbon dioxide (CO2) adsorption characteristics. The oxyfluorination was performed at various F2/O2 ratios at room temperature. The surface chemical properties and pore size distributions on the CMSs were altered by oxyfluorination and analyzed through XPS and isothermal gas adsorption. The CO2 adsorption capacity on the oxyfluorinated CMSs was different from that of unmodified CMSs due to changes in the functional groups on the carbon surface. The CO2 uptake at 273K was unchanged compared with untreated CMS and measured approximately 2.5mmol/g. However, at 298K, the CO2 adsorption capacity increased from 1.61mmol/g for an unmodified CMS to 2.07mmol/g for the oxyfluorinated CMS. We suggest that introduced oxygen and fluorine functional groups on carbon surface by oxyfluorination increased basicity on carbon surface. Consequently, interaction energy between functional groups and CO2 molecular are increased at room temperature and it contributed to enhance CO2 adsorption amount. [Copyright &y& Elsevier]

Abstract: The surface of carbon molecular sieves (CMSs) was fluorinated to investigate the separation behavior of CH4/CO2. The fluorination of CMSs was carried out at various F2 partial pressures to determine the effect of the F2 content. Fluorine functional groups were effectively introduced on the surface of the CMSs, and the volume of pores in the CMSs was increased due to fluorination, especially those with a diameter less than 8Å. As the fluorine partial pressure was increase, an increase in the CO2 adsorption capacity of CMSs was observed due to Lewis acid–base interactions between the functional groups of CMSs and CO2. Based on the selective CO2 adsorption results, the CO2 breakthrough with fluorinated CMS occurred at later stages of CH4/CO2 gas separation process compared to Raw-CMS. Therefore the presence of fluorine on the surfaces of CMSs affects the pore volumes of CMSs. According to the adsorption isotherms, the CO2 adsorption efficiency of CMSs was improved from 1.61 to 2.04mmol/g at 298K. [Copyright &y& Elsevier]

Abstract: Polyetherimide (PEI) was used as polymeric precursor to prepare selective carbon molecular sieve (CMS) layer supported by a porous Al2O3 ceramic disk. The effects of the porous structure and surface roughness of the ceramic support on the interfacial adhesion and texture of the PEI/Al2O3-derived composite CMS membrane were investigated by modulating the sintering temperature and holding time. When the surface roughness of the ceramic support increased, the pore size and its distribution of the selective CMS layer were found to have shifted to the larger one and its roughness increased from the top to the bottom surface. This structure resulted in high permeability and low selectivity. Our results indicate that the porous structure of the ceramic support also played an important role in dominating the pore size and its distribution of the selective CMS layer, which influences the gas separation performance. [Copyright &y& Elsevier]

A very simple preparation process was designed to successfully prepare monolithic Carbon Molecular Sieves (CMS) from very cheap precursors (an activated carbon (AC), obtained from a low rank coal, and coal tar pitch). This process consists of using a slurry of AC, coal tar pitch and toluene, which permits the monoliths to be moulded at room temperature. The AC/coal tar pitch ratio and the final pyrolysis temperature have been the main parameters analysed. The porosity blockage occurring during preparation of monoliths has been studied based on the results obtained by gas adsorption (i.e. N2 at −196°C and CO2 at 0°C) and thermal analysis. An important aspect of this method is that a previous oxidation step of the binder is not necessary before the carbonisation of the monolith. The obtained results show that the proposed method is effective for the CMS preparation from the selected precursors. In this method, the use of coal tar pitch as binder is adequate since it plays a multiple role: (i) it confers an important mechanical stability to the monoliths and; (ii) it modifies the final porosity of the AC leading to the molecular sieving properties. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of methanol steam reforming was studied in a carbon membrane reactor over a commercial CuO/ZnO/Al2O3 catalyst (Süd-Chemie, G66 MR). Carbon molecular sieve membranes supplied by Carbon Membranes Ltd. were tested at 150°C and 200°C. The carbon membrane reactor was operated at atmospheric pressure and with vacuum at the permeate side, at 200°C. High methanol conversion and hydrogen recovery were obtained with low carbon monoxide permeate concentrations. A sweep gas configuration was simulated with a one-dimensional model. The experimental mixed-gas permeance values at 200°C were used in a mathematical model that showed a good agreement with the experimental data. The advantages of using water as sweep gas were investigated in what concerns methanol conversion and hydrogen recovery. The concentration of carbon monoxide at the permeate side was under 20ppm in all simulation runs. These results indicate that the permeate stream can be used to feed a polymer electrolyte membrane fuel cell. [Copyright &y& Elsevier]

Abstract: Carbon molecular sieve (CMS) membranes have shown promising separation performance compared to conventional polymeric membranes. Translating the very attractive separation properties from dense films to hollow fibers is important for applying CMS materials in realistic gas separations. The very challenging ethylene/ethane separation is the primary target of this work. Matrimid® derived CMS hollow fiber membranes have been investigated in this work. Resultant CMS fiber showed interesting separation performance for several gas pairs, especially high selectivity for C2H4/C2H6. Our comparative study between dense film and hollow fiber revealed very similar selectivity for both configurations; however, a significant difference exists in the effective separation layer thickness between precursor fibers and their resultant CMS fibers. SEM results showed that the deviation was essentially due to the collapse of the porous substructure of the precursor fiber. Polymer chain flexibility (relatively low glass transition temperature (T g) for Matrimid® relative to actual CMS formation) appears to be the fundamental cause of substructure collapse. This collapse phenomenon must be addressed in all cases involving intense heat-treatment near or above T g. We also found that the defect-free property of the precursor fiber was not a simple predictor of CMS fiber performance. Even some precursor fibers with Knudsen diffusion selectivity could be transformed into highly selective CMS fibers for the Matrimid® precursor. To overcome the permeance loss problem caused by substructure collapse, several engineering approaches were considered. Mixed gas permeation results under realistic conditions demonstrate the excellent performance of CMS hollow fiber membrane for the challenging ethylene/ethane separation. [Copyright &y& Elsevier]

Abstract: The objective of the present work is to develop a simple procedure, which avoids the need of a binder, to obtain activated carbon monoliths from a waste precursor (coal tar pitch) suitable for CO2 capture and/or separation. The main task of this process consists of a nitration process of the coal tar pitch. This nitration step over the coal tar pitch is characterised by different techniques, such as infrared spectroscopy and thermogravimetric analysis. The nitration treatment produces the oxidation of the pitch molecules, leading to hydrogen consumption and generating oxygenated and nitrogenated surface complexes. As a consequence of this oxidation, nitrated coal tar pitch is an infusible material, which allows the carbonization of monolithic pieces avoiding their fusion. Decomposition of these surface complexes during the carbonization of monoliths generates narrow microporosity, which is suitable for CO2 capture from gas streams at room temperature. The molecular sieving properties of these materials are studied by CH4 and CO2 adsorption kinetics. [Copyright &y& Elsevier]

Abstract: A literature review on preparation of carbon molecular sieve (CMS) from lignocellulosic biomass is presented. The effect of various operation parameters such as pyrolytic temperature, flow rate of the carbonizing agent and time of pyrolysis on the carbonization of the lignocellulosic biomass as a carbon precursor was reviewed. Various physical and chemical processes for the activation of the biomass-based char and their effects on textural properties of the activated char were discussed. Conversion of activated chars to CMS as the final stage of the preparation process through different techniques of chemical vapor deposition (CVD) and controlled pyrolysis was assessed. Survey of literature revealed that production of CMS with BET surface area of 1247m2/g and micropore volume of 0.51cm3/g, under appropriate conditions has been reported. Also, maximum selectivity of 7.6 and 400 for separation of O2/N2 and CO2/CH4 was devoted to palm shell and coconut shell-based CMS, respectively. [Copyright &y& Elsevier]

We report a novel approach to economically fabricate dual-layer composite nanoparticle-containing carbon molecular sieve (CMS) hollow fiber membranes having excellent gas separation performance. The economically favored process comprises dip coating engineered support layer fibers to form a dense skin layer in a CMSCMS precursor. The coated fibers are then pyrolyzed to form a high-performance CMS hollow fiber membrane. The nano-particle containing composite carbon molecular sieve hollow fiber membranes showed very attractive selectivities and productivities. This work shows how to produce high performance CMS hollow fiber membrane by coating, which exceeds that achieved with the standard sol-gel support stabilization technique. [Display omitted] • Dual-layer nanoparticle containing precursor fiber membranes were developed. • Precursor membranes dip-coated with two polyimide polymers were employed to fabricate carbon molecule sieve (CMS) membranes. • CMS membranes generated from coating at low relative humidity (RH) have very attractive CO 2 /CH 4 separation performance. • No sol-gel support stabilization was required for the pyrolysis. [ABSTRACT FROM AUTHOR]

Abstract: In this work, a new catalyst was prepared by employing carbon molecular sieve (CMS) with natural kaolinite clay and is named UDCaT-8. The catalyst was fully characterized by XRD, DTA–TGA, FTIR, SEM and BET surface area and pore size analysis. o-Xylene nitration was conducted under solventless and room temperature condition using UDCaT-8 to get high regioselectivity. The process is eco-friendly, less expensive and leads to high selectivity to 4-nitro-o-xylene which is an important intermediate for synthetic vitamin B2 as well as a raw material for dyes and other chemicals. [Copyright &y& Elsevier]

Abstract: The objective of the present research work was to develop a membrane with a high H2O/alcohol selectivity for pervaporation and for use in direct alcohol fuel cells. Sulfonated poly (ether ether ketone) (SPEEK) was coated with a thin continuous carbon molecular sieve (CMS) layer. The membranes obtained had 180- and 400-nm thick CMS layers that led to a clear reduction of alcohol crossover. The water/alcohol selectivity increased with the size of the alcohol molecules as follows: methanol

Abstract: The stabilisation of pitch fibres (PFs) is the most important step for their subsequent use in the preparation of carbon fibres (CFs) and their resulting characteristics. The present work studies the influence that the stabilisation time has on the porosity of the CFs, and on the subsequent properties as carbon molecular sieve (CMS). The increase of the stabilisation time carried out at 573K, from 2 to 8h favours their CMS properties producing a decrease in the microposity accessible to N2, which gets completely blocked after 6 and 8h, while the narrow microporosity (V-DR CO2) remains accessible. Adsorption kinetic studies with CH4 and CO2 were performed to assess the possibility of using these CFs as CMS by comparing them with Takeda 3A CMS. The results suggest that there is an optimal stabilisation time which allows the preparation of CFs from an abundant raw precursor with properties similar to Takeda 3A CMS. [Copyright &y& Elsevier]