Sorption Of N2 Research Articles

N2 in ZIF-8: Sorbate induced structural changes and self-diffusion

In the field of nanoporous materials, guest-induced structural changes in metal–organic frameworks (MOFs) attracted great attention over the last years. One example concerns a gate-opening effect in MOF ZIF-8 which was found to occur upon sorption of N2. To mirror these structural changes in molecular simulations, suitable force fields for the proper description of framework flexibility are required.We demonstrate that our previously published force field is able to reproduce these structural changes in classical MD simulations. In particular, with our parameter set the diameter of the windows connecting adjacent cavities is found to match the X-ray values almost perfectly. We focus on investigating the impact of the structural changes on the mobility of N2 molecules in ZIF-8 framework and compare the results with those of another parameter set, which was published recently by Zhang and coworkers.The size of the windows increases notably, when the critical “gate-opening” loading is surpassed. Most surprisingly, this pronounced increase does not result in a speed-up of the N2 self-diffusivity. It appears, that a complex interplay of host-host and host-guest interactions increases the mutual hindrance of the N2 molecules and counter balance the acceleration of the mobility due to the larger window size.

Sorption of 4He, H2, Ne, N2, CH4, and Kr impurities in graphene oxide at low temperatures. Quantum effects

Sorption and the subsequent desorption of 4He, H2, Ne, N2, CH4, and Kr gas impurities by graphene oxide (GO), glucose-reduced GO (RGO-Gl) and hydrazine-reduced GO (RGO–Hz) powders have been investigated in the temperature interval 2–290 K. It has been found that the sorptive capacity of the reduced sample RGO–Hz is three to six times higher than that of GO. The reduction of GO with glucose has only a slight effect on its sorptive properties. The temperature dependences of the diffusion coefficients of the GO, RGO-Gl, and RGO-Hz samples have been obtained using the measured characteristic times of sorption. It is assumed that the temperature dependences of the diffusion coefficients are determined by the competition of the thermally activated and tunneling mechanisms, the tunneling contribution being dominant at low temperatures.

Gas sorption properties of zwitterion-functionalized carbon nanotubes

We have functionalized carbon nanotubes with carboxylic acid and zwitterion groups. We have evaluated the effect of functionalization by measuring the sorption of CO2, CH4, and N2 at 35°C for pressures up to 10bar. Zwitterion functionalized nanotubes were found to be highly hygroscopic. Thermal gravimetric analysis indicates that water can be desorbed at about 200°C. The adsorption of gases in zwitterion functionalized nanotubes is dramatically reduced when compared with nanotubes functionalized with carboxylic acid groups. The presence of water on the zwitterion functionalized nanotube reduces the sorption even further. Molecular simulations show that three or more zwitterion groups per tube entrance are required to significantly reduce the flux of CO2 into the tubes. Simulations also show that gas phase water is rapidly sorbed into the zwitterion functionalized nanotubes, both increasing the free energy barrier to CO2 entering the tube and also lowering the equilibrium adsorption through competitive adsorption.

Experimental study and PC-SAFT simulations of sorption equilibria in polystyrene

The knowledge of sorption equilibria of blowing agents in polystyrene (PS) is necessary for the optimization of PS foam production. The sorption equilibria were studied experimentally using a gravimetric apparatus and simulated by the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state. As chlorinated and fluorinated hydrocarbons are being phased out, alternative blowing agents are important. We place emphasis on n-pentane, as sorption data for the PS+n-pentane system are scarce in the literature. The measured n-pentane and iso-pentane sorption isotherms were used to evaluate the PC-SAFT binary interaction parameters. The sorption of CO2, N2 and He in PS was also studied. Cosorption of pentanes in PS was predicted and comparison of the results with our experimental data proved good performance of the PC-SAFT model. The industrially interesting sorption enhancement and inhibition effects were studied using both experimental and simulated ternary data.

Sorption of CO, CH4, and N2 in Alkali Metal Ion Exchanged Zeolite-X: Grand Canonical Monte Carlo Simulation and Volumetric Measurements

Sorption of CO, CH4, and N2 in zeolite-X exchanged with different alkali metal ions was studied by volumetric measurements and Grand Canonical Monte Carlo simulation. CO and CH4 sorption is observed to show higher sorption capacity than N2 in all cation exchanged zeolite samples. The adsorption capacity of CO in alkali metal exchanged zeolites is observed to decrease on moving from LiX to CsX, whereas for the methane adsorption capacity varies in reverse order. The isosteric heat of sorption data show stronger interactions of CO and N2 molecules with alkali metal ion exchanged zeolites. The isosteric heat of CH4 show nearly same value (21−24 kJ/mol) for all alkali metal ion exchanged zeolites. Simulation of the CO and N2 sorption in alkali metal zeolite -X clearly shows that the adsorbed CO and N2 molecules are located in proximity to the extra-framework cations in the super cage. Simulated data of adsorption isotherms and heats of adsorption of CO, N2, and CH4 in alkali metal ion exchanged zeolite-X agree reasonably well with the experimental results.

Preparation and C3H8/Gas Separation Properties of a Synthesized Single Layer PDMS Membrane

In this paper, a new polydimethylsiloxane (PDMS) membrane was synthesized and its ability for separation of heavier gases from lighter ones was examined. Sorption, diffusion, and permeation of H2, N2, O2, CH4, CO2, and C3H8 in the synthesized membrane were investigated as a function of pressure at 35°C. PDMS was confirmed to be more permeable to more condensable gases such as C3H8. This result was attributed to very high solubility of larger gas molecules in hydrocarbon−based PDMS in spite of their low diffusion coefficients relative to small molecules. The synthesized membrane showed much better gas permeation performance than others reported in the literature. Increasing upstream pressure increased solubility, permeability and diffusion coefficients of C3H8, while these values decreased slightly or stayed constant for other gases. Local effective diffusion coefficient of C3H8 and CO2 increased with increasing penetrant concentration which indicated plasticization effect of these gases over the range of penetrant concentration studied. C3H8/gas solubility, diffusivity and overall selectivities also increased with increasing feed pressure. Ideal selectivity values of 4, 13, 18, 20, and 36 for C3H8 over CO2, CH4, H2, O2, and N2, respectively, at upstream pressure of 7 atm, confirmed the outstanding separation performance of the synthesized mebrane.

Sorption of Methane, Nitrogen, Oxygen, and Argon in ZSM-5 with different SiO2/Al2O3 Ratios: Grand Canonical Monte Carlo Simulation and Volumetric Measurements

Sorption of CH4, N2, O2, and Ar in ZSM-5 with different SiO2/Al2O3 ratios was studied by volumetric measurements and grand canonical Monte Carlo simulation. Sorption capacity for all the gases studied was observed to decrease with an increase in the SiO2/Al2O3 ratio of ZSM-5. The sorption selectivity of CH4 over N2 increases, whereas sorption selectivities of N2 over O2 and Ar decrease with an increase in the SiO2/Al2O3 ratio of ZSM-5. ZSM-5 with SiO2/Al2O3 of 900 showed higher selectivity for CH4 over N2, whereas the SiO2/Al2O3 ratio of 25 showed higher N2 selectivity over O2 and Ar. The heats of adsorption for CH4 and N2 decrease and that for O2 and Ar remain unaffected with an increase in SiO2/Al2O3 ratio of ZSM-5. The values of Henry’s constant were also calculated for CH4, N2, O2, and Ar for adsorption in ZSM-5 having varied SiO2/Al2O3 ratio. The experimental results were compared with theoretically calculated data using grand canonical Monte Carlo (GCMC) simulation. Simulation studies expectedly showed the proximity of N2 molecules to the sites occupied by extraframework sodium cations.

The influence of the guest ion on the synthesis and sorption properties of an open framework lanthanide tetrakisphosphonate

The influence of the guest ion on the synthesis of the flexible anionic open framework NaLa[(PO3H)2CH-C6H4-CH(PO3H)2]·4H2O, NaLa(H4L), was investigated. In a high throughput screening of the synthesis parameters, Na+ was identified as a strong structure-directing agent (SDA) for this framework. In addition, a series of compounds MLa(H4L) with M = Li+, Na+, K+, NH4+ and Rb+ were prepared by synthesis or ion exchange and characterized using X-ray powder diffraction, elemental analysis and scanning electron microscopy. Sorption of N2, Kr and H2O in these compounds revealed a preference of the network for water molecules. Furthermore, a strong influence of the guest ions on the shape of the water sorption isotherms could be observed. The isotherms of LiLa(H4L), NaLa(H4L) and KLa(H4L) show one distinctive step of adsorption that can be correlated with the expansion of the flexible framework upon hydration. The required partial pressure for the pore expansion depends on the incorporated guest ion and increases with the decreasing hydration enthalpy from Li+ to K+.

Enhanced Adsorption of Ammonia on Metal‐Organic Framework/Graphite Oxide Composites: Analysis of Surface Interactions

AbstractComposites of the metal‐organic framework (MOF), MOF‐5, and graphite oxide (GO) with different ratios of the two components are prepared and tested in ammonia removal under dry conditions. The parent and composite materials are characterized before and after exposure to ammonia by sorption of N2, X‐ray diffraction, thermal analyses, and FT‐IR spectroscopy. The results show a synergetic effect resulting in an increase in the ammonia uptake compared to the parent materials. It is linked to enhanced dispersive forces in the pore space of the composites. Additionally, ammonia interacts with zinc oxide tetrahedra via hydrogen bonding and is intercalated between the layers of GO. Retention of a large quantity of ammonia eventually leads to a collapse of the MOF‐5 structure in the composites. The effect resembles that observed when MOF‐5 is exposed to water. Taking into account the similarity of ammonia and water molecules, it is hypothesized that ammonia causes a destruction of the MOF‐5 and composite structure as a result of its hydrogen bonding with the zinc oxide clusters.

Natural Rubber Nanocomposites With Organo-Modified Bentonite

AbstractEnhancement of the physico-chemical properties of elastomers can be achieved by the addition of fillers, such as silica, but the search for less expensive alternative materials continues. The objective of this study was to investigate natural or organically modified clay minerals as such an alternative. Organo-clays modified by quaternary ammonium cations with three methyl groups and longest alkyl chains of different lengths were prepared by ion-exchange reaction of the commercial product JP A030 (Envigeo, Slovakia) based on Jelšový Potok bentonite with organic salts: tetramethylammonium (TMA) chloride, octyltrimethylammonium (OTMA) bromide, and octadecyltrimethylammonium (ODTMA) bromide. Physico-chemical characterizations of the organo-clays used as fillers in rubber nanocomposites and their mechanical properties were measured using Fourier transform infrared (IR) spectroscopy, which provided information on the chemical composition of the mineral and on the amount of organic moieties adsorbed. X-ray diffraction analysis (XRD) was used to monitor the arrangement of organic chains in galleries of montmorillonite and showed that the longest-chain alkylammonium ODTMA+ ions were intercalated between layers, adopting a pseudotrimolecular conformation, while OTMA+ and TMA+ were in monomolecular arrangement. Surface areas were measured by sorption of N2 and ethylene glycol monoethyl ether. Natural rubber-clay nanocomposites were prepared by melt intercalation, in some cases also with addition of silica, a conventional reinforcing filler. The microstructure of montmorillonite in these composites was characterized by XRD analysis. The effect of clay and organo-clays loading from 1 to 10 phr (parts by weight per hundred parts of rubber) on stress at break, strain at break, and Modulus 100 (M100) was investigated by tensile tests. Filler ODTMA-JP A030 appears to be the most effective among the organoclays; surprisingly similar values of composite elongation and strength were obtained with unmodified bentonite JP A030.

Activated Carbons from Coal/Pitch and Polyethylene Terephthalate Blends for the Removal of Phenols from Aqueous Solutions

Blends of two bituminous coals and a coal-tar pitch (CTP) with polyethylene terephthalate (PET) were evaluated as precursors of activated carbons (ACs). The intensity of the interactions between the raw materials, coal/CTP and PET during copyrolysis was closely observed by means of thermogravimetric analysis. In addition, the homogeneity of the carbon matrix of the chars produced at 800 °C in a horizontal oven was studied by polarized light optical microscopy. Activated carbons were prepared from single components and their blends (1:1 w/w) by subjecting them to carbonization up to 800 °C in a horizontal oven and then activation with steam at 800 °C to 50% burnoff. The porous structure of the ACs was determined by sorption of N2 at 77 K and of CO2 at 273 K. The PET-containing blends produced microporous activated carbons with a maximum BET surface area of nearly 1100 m2 g−1 and a maximum micropore size distribution of 0.6−0.8 nm in the case of the AC from the CTP/PET blend. The addition of PET to a bituminous coal was compared with the preoxidation of coal P in air as a way to reduce thermoplasticity and to promote the development of the porous structure. The modification of bituminous coals by PET appeared to be more effective than conventional coal preoxidation treatment. The resultant ACs were tested by measuring their effectiveness in removing phenols from an aqueous solution. The adsorption of p-chlorophenol (PCP) by the ACs prepared from the PET-containing blends was slightly higher than for the commercial activated carbon. The ability to adsorb PCP was found to be related to the volume of the super-micropores.

Modification and characterization of montmorillonite fillers used in composites with vulcanized natural rubber

AbstractParent Ca-montmorillonite (Jelšový Potok, Slovakia, Ca-JP) and Na-montmorillonite Kunipia-F (Japan, Na-KU) were ion-exchanged with octadecyltrimethylammonium (ODTMA) cations. Characteristics of the samples were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (IR) and thermogravimetry (TG). Surface areas were measured by sorption of N2 and ethyleneglycol monoethyl ether. Scanning electron microscopy photographs (SEM) were used to characterize the texture of samples. The XRD patterns show that, upon intercalation, the basal spacing of montmorillonite is expanded and corresponds to the pseudotrimolecular arrangement of organic cations in the interlayers. The IR spectra of organically modified montmorillonite show C-H stretching and bending bands of both CH3 and CH2 groups in the 3000–2800 cm−1 and 1500–1400 cm−1 region, respectively. Modification of montmorillonite by organic cations decreased the hydrophilicity of their mineral surface and adsorbed water evaporated at lower temperatures. The SEM photographs reveal a tendency towards lump formation and agglomeration of the ODTMA-montmorillonite particles. The modification introducing organic moiety lead to a substantial decrease in the surface area of both montmorillonites; however, it remained remarkably high, being at the level typical for silica. Completely characterized fillers were used to prepare rubber compositions with enhanced physical properties, as described in Hrachová et al. (2008).

Single and Multicomponent Sorption of CO2, CH4 and N2 in a Microporous Metal-Organic Framework

Single and multicomponent fixed-bed adsorption of CO2, N2, and CH4 on crystals of MOF-508b has been studied in this work. Adsorption equilibrium was measured at temperatures ranging from 303 to 343 K and partial pressures up to 4.5 bar. MOF-508b is very selective for CO2 and the loadings of CH4 and N2 are practically temperature independent. The Langmuir isotherm model provides a good representation of the equilibrium data. A dynamic model based on the LDF approximation for the mass transfer has been used to describe with good accuracy the adsorption kinetics of single, binary and ternary breakthrough curves. It was found that the intra-crystalline diffusivity for CO2 is one order of magnitude faster than for CH4 and N2.

Simulated annealing effects on Na-FAU crystal reconstruction and sorption efficiency

The accurate reconstruction of zeolite frameworks at the atomic scale is of critical importance for the study of the sorption and separation properties of these materials. In this work, the atomistic description of NaX form of the aluminosilicate faujasite (FAU) crystals is accomplished using lattice reconstruction and simulated annealing techniques. The effect of temperature on the NaX framework structure and on the precise positioning of the extra-framework cations has been thoroughly investigated using annealing cycles at several temperatures. The effects of the framework details including the cation positions on the sorption of CO2 and N2 in these structures are studied using molecular simulations. Comparison of simulated adsorption isotherms in non-annealed structures to experimental data reveals that the agreement is a strong function of the cation positions in the framework. More consistent results are obtained when annealing is performed, in which case the deviation in the energy calculations is reduced by almost two orders of magnitude. Cation tracking during several annealing cycles is also implemented that reveals the existence of strongly preferred positions for cations close to the Al atoms within the super cage. Comparison of the calculated and experimental values for the heat of adsorption obtained in this work reveals satisfactory agreement in both CO2 and N2 sorption cases for structures that have undergone simulated annealing.

Hysteretic sorption of light gases by a porous metal–organic framework containing tris(para-carboxylated) triphenylphosphine oxide

The porous metal-organic framework (MOF) PCM-4, based on tris(para-carboxylated) triphenylphosphine oxide, contains atypical, polar organic substituents; the material exhibits a hysteretic sorption of Ar, N2 and O2, and demonstrates the advantage of ligands of this type.

On the computation of long-range interactions in fluids under confinement: Application to pore systems with various types of spatial periodicity

The problem of computing accurately the long-range Coulomb interactions in physical systems is investigated focusing mainly on the atomistic simulation of fluids sorbed in porous solids. Several articles involving theory and computation of long-range interactions in charged systems are reviewed, in order to explore the possibility of adapting or developing methodology in the field of computer simulation of sorbate molecules inside nanostructures modeled through a three-dimensional (crystal frameworks), two-dimensional (slit-shaped pores), or one-dimensional (cylindrical pores) replication of their unit cell. For this reason we digitally reconstruct selected paradigms of three-dimensional microporous structures which exhibit different spatial periodicities such as the zeolite crystals of MFI and FAU type, graphitic slit-shaped pores, and single-wall carbon nanotubes in order to study the sorption of CO(2), N(2), and H(2) via grand canonical Monte Carlo simulation; the predicted data are compared with experimental measurements found elsewhere. Suitable technical adjustments to the use of conventional Ewald technique, whenever it is possible, prove to be effective in the computation of electrostatic field of all the categories studied in this work.

Sorption of H2, D2, N2 and Ar by CsC24 prepared from carbons heat treated at different temperatures

CsC24 samples were prepared from artificial graphite materials, derived from petroleum cokes and additional pitch binder, with different heat-treatment temperatures (HTTs) between 1300 and 2800°C. The sorption isotherms for the systems, CsC24-H2, -D2, -N2 and-Ar at 77K were determined. All the CsC24 samples were able to take up these molecules, irrespective of the HTT of the host materials. The saturated amount of sorption, (nmolecule/nCs) sat., increased with HTT of the host carbons. For H2-and D2-sorption, (nmolecule/nCs) sat. increased monotonically with HTT from HTT-1300 up to-2000, and then stepwise increase was observed from HTT-2000 up to -2800. This behavior was considered to be a manifestation of the drastic change of the structure of host carbons at around HTT-2000. The sorption isotherms were well fitted by the Langmuir equation. This fact suggested the sorbed molecules are accommodated in the interlayer nanospace even for CsC24 samples prepared from carbons with low HTT such as HTT-1300.

Effect of Clay Binder on Sorption and Catalytic Properties of Zeolite Pellets

Sorption of N2 ,O 2, Ar, and CH4 in zeolites X, Y, and mordenite in powder as well as pellets was studied using gas chromatography. Heats of sorption in pellets formed using clay as a binder increased by 34-78% for N2 and 7-18% for CH4 relative to the respective zeolite powder. Surface acidity of zeolites upon pelletization as measured by ammonia temperature-programmed desorption showed that high-strength acid sites completely disappear for both zeolite Y and mordenite when bound with bentonite and attapulgite. Decreases in weaker acid sites upon pelletization for mordenite and HY are 47-52% and 34%, respectively. Fourier transform infrared spectroscopy also showed a decrease in acidity upon pelletization of zeolite powders as observed from the reduction in the intensity of the peaks corresponding to acidic hydroxyl groups. Influence of the decrease in surface acidity upon pelletization was also observed from conversion values for alkylation of toluene with methanol in zeolite pellets. For example, reduction in total xylene formed was by 50%, 87%, and 100% for HY520, HY510, and HM510, respectively. These observations have been interpreted in terms of solid-state migration of cations present in clay interlayer space to zeolite extraframework sites during pelletization. Reexchange of cations in zeolites HY and HM with an aqueous solution of Na + /Ca 2+ salts shows sorption isotherms closer to the respective pelletized samples. X-ray diffraction studies of zeolites in powders as well as pellets confirm migration of clay cations to zeolite extraframework sites.

Simulation Study of Sorption of CO2 and N2 with Application to the Characterization of Carbon Adsorbents

The Monte Carlo method was used in its grand ensemble variant (GCMC) in combination with CO2 and N2 experimental isotherm data at low (77 and 195.5 K) and ambient temperatures (298 and 308 K), in order to characterize microporous carbons and obtain the corresponding pore size distribution (PSD). In particular, the CO2 and N2 densities and the isosteric heats of adsorption inside single, slit shaped, graphitic pores of given width were found on the basis of GCMC for pre-defined temperatures and different relative pressures. In a further step, we determined the optimal PSD for which the best match is obtained between computed and measured isotherms. Comparisons were made between the PSDs found for the same carbon sample at low and ambient temperatures for different gases, and conclusions concerning the applicability of the method and the reliability of the resulting micropore size distributions were drawn.

Specific Sorption Sites for Nitrogen in Zeolites NaLSX and LiLSX

Specific sorption sites for nitrogen, N2, in NaLSX and LiLSX zeolites were investigated using a DRIFT spectroscopic method. Sorption of molecular hydrogen, H2, by NaLSX or LiLSX zeolite at 77 K with DRIFT control of perturbation of sorbed molecules allowed to discriminate two or three different types of specific sorption sites in the respective zeolites. Their H–H stretching frequencies are 4077 and 4081 cm−1 for NaLSX, and 4061, 4084 and 4129 cm−1 for LiLSX. With reference to an independent investigation by methods of both sorption thermodynamics and molecular modeling for N2 sorption on LiLSX, the first two of the corresponding bands were ascribed to H2 sorption on lithium cations, Li+, localized in supercages of the faujasite, FAU, zeolite framework at sites SIII and SIII′, while the latter band most likely belongs to H2 sorption on Li+ cations at sites SII, and on hydroxyl groups, OH. Sorption of N2 by Li+ cations at sites SIII and SIII′ is the strongest, resulting in a decrease of intensity of the corresponding DRIFT bands that stem from subsequent H2 sorption. Nitrogen sorption by Li+ cations at sites SII is much weaker. Sorption of N2 on Na+ cations at sites SIII in NaLSX zeolite is also stronger than by Na+ cations at sites SII.