Adsorption of a H2-Ne binary mixture on NaA zeolite

Co-adsorption of hydrogen and neon on NaA zeolite was studied volumetrically at 40 K, 50 K, and 90 K over the pressure range 3–65 kPa. As the adsorption of hydrogen increases at constant pressure, the adsorption of neon linearly decreases through the entire temperature range. The coefficients of displacement of components from the sorption volume were determined. The adsorption selectivity coefficient of H₂ () in the H₂-Ne-NaA system was calculated over the temperature range 35–100 K. The increase in a by a factor of 5 while the temperature decreases by 30 K makes it possible to remove the microimpurities of H₂ from Ne by a cryoadsorption method.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 840–842, May, 1993.     

Adsorption of helium on zeolite NaA

Isotherms of helium adsorption on zeolite NaA were measured by the volumetric method under static conditions at 23–50 K and pressures from 1 Pa to 65 kPa. The Henry constants and the initial heat of helium adsorption were calculated; the isosteric heat was calculated, and its dependence on the adsorption was determined.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1291–1292, May, 1996.     

Adsorption phenomena at high pressures and temperatures 4. Isotherms of excess and absolute adsorption of Kr on NaA zeolite

The problem of conversion of an isotherm of excess adsorption measured experimentally into values of the total amount of the adsorbate (absolute adsorption) has been formulated. Five isotherms of excess adsorption of krypton on NaA zeolite were measured (at 334–500 K) at equilibrium pressures of -160 MPa. The corresponding isotherms of the total amount were calculated and the temperature dependences of the parameters of an equation describing the isotherms of excess adsorption were identified. It was shown that at high temperatures and pressures, krypton atoms diffuse into the -cavities of the NaA zeolite.For Part 3, seeRuss. Chem. Bull., 1996, 45, 534 (Engl. Transl.).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1138–1142, May, 1996.     

Effects of the Operating Conditions on Coke Deactivation of 5A Molecular Sieve in N-Decane Adsorption/Desorption

The influence of operating conditions (time-on-stream, temperature, pressure and paraffin feed concentration) on the deactivation of a 5A molecular sieve during the adsorption/desorption of n-decane has been studied using a cyclic operating procedure. After 10 adsorption/desorption cycles, the 5A molecular sieve used in this study showed the same deactivation level as an used industrial molecular sieve provided that the deactivation of the zeolite was due to coke deposition by site coverage and pore blockage. The temperature effect was studied in the range of 373–523 K, obtaining a minimum deactivation at 448 K. The pressure does not influence adsorption parameters in the range of 1–3 MPa, but it does affect the nature of the coke deposited on the zeolite. The influence of paraffin concentration can be considered negligible.     

Adsorption phenomena at high pressures and temperatures.

Equilibrium isotherms of adsorption of methane on crystalline Rho zeolite were measured with the use of a precision volumetric gravimetric setup that was developed for determining the equilibrium and Kinetic parameters of adsorption in the pressure range of 0.1–160 MPa and temperature range of 300–600 K. The method of determining the accessible volume of an adsorption system (free volume + micropore volume) and the micropore volume of a sorbent was used. Two independent methods for calculation of micropore volume on the basis of the isotherms of excess adsorption were used. The discrepancy in the results of the calculation of the micropore volume by three independent methods is within the limits of the calculation accuracy. An evaluation of a change in the isosteric heats of the excess and absolute adsorption of methane on Rho zeolite was carried out in relation to filling and temperature. An evaluaton of the adsorption volume above the outer surface of the zeolite crystals was performed. The results of experimental investigations of methane adsorption on Rho zeolite can be used to solve the problem of encapsulation of gases by solid sorbents. kg]Key words kw]adsorption kw]micropore volume kw]surface kw]isostere kw]heat kw]zeoliteFor Part 1 see Ref. I.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 568–573, March, 1996.     

Discrete site model for methane adsorption on microporous adsorbents

A statistical thermodynamic treatment of adsorption on zeolites assuming quasiindependent sites has been applied to methane adsorption on the zeolite NaX and the carbon adsorbent PAU-10 from polyvinylidenechloride in the pressure range 0.1–10⁷ Pa and 120–410 K. The relation between the isosteric adsorption heats and the magnitude of adsorption at different temperatures was calculated for both adsorption systems. A sharp decrease in these heats was observed at high adsorption values up to and in the supercritical temperature range.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 974–978, May, 1990.The authors would like to thank V. A. Bakaev for discussions about this work.     

Study of intracrystalline diffusion in zeolites 6. Comparison of the results obtained by the method of densitometry of light and the adsorption method

The use of the method of densitometry of light passing through a layer of zeolite crystals permits determining the limiting stage of diffusion during adsorption by zeolites. Diffusion in transport pores and external heat exchange play the basic role in adsorption of benzene by NaX zeolite, while diffusion in crystals is the determining mechanism of transport in adsorption of water by NaA and NaX zeolites. The diffusion coefficients of water in NaX zeolite have an order of magnitude of 10^–17 m²/sec and increase with an increase in the degree of filling. An explanation for the anomalous behavior of the kinetic adsorption curve for brief times of adsorption of water by zeolite is proposed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1224–1228, June, 1990.     

Oxygen Selectivity on Partially K Exchanged Na-A Type Zeolite at Low Temperature

In previous work by the authors on Na-A zeolite (Izumi et al., Japan Patent Toku-Kou-Shou 63-058614, 1988), it was shown that the combination of high-temperature calcination and operation of the adsorption step at low temperatures improved the selectivity for oxygen over nitrogen from air (Izumi et al., CATS J Meeting Abstracts, 31(2A), 10, 1989; Izumi and Suzuki, Adsorption, 6, 2000). Berlin discloses in his U.S. Patent 3282028 (1966) that the partial exchange of potassium ions for sodium ions in the Na-A type zeolite also improved selectivity for oxygen by reducing the uptake rate of nitrogen. It was therefore expected that the oxygen selectivity of Na-K-A with high-temperature calcination and low-temperature adsorption might be enhanced. For the confirmation of optimum conditions for the appearance of oxygen selectivity on Na-K-A, samples were prepared with a K exchange ratio varied from 0–20 mol% (0–2.4 K ions/unit cell), and a calcination temperature varied from 923 to 1073 K, and an experiment concerning oxygen and nitrogen adsorption on Na-K-A was undertaken with a small adsorbent column under pressure swing adsorption (PSA) conditions at adsorption temperatures from room temperature to 213 K. It was found that (a) the K exchange ratio of 7 mol% (0.84 K ions/unit cell), and (b) the calcination temperature of 993 K, resulted in a remarkable increase in oxygen selectivity. Under optimum conditions for Na-K-A, the oxygen separation factor was about 8. Na-K-A has the potential to effectively separate oxygen and nitrogen from air by means of PSA.     

Adsorption phenomena at high pressures and temperatures 5. Heats of excess and total adsorption of krypton on zeolite NaA

Thermodynamic principles for the calculation of differential heats of excess and absolute adsorption were considered. A set of isosteres of excess adsorption of krypton on zeolite NaA are presented, from which the coverage and temperature dependences of the heats of excess adsorption are calculated and analyzed. The reasons for infinitely high values of the excess heats at finite values of adsorption are discussed. The problems of recalculation of the excess adsorption to absolute adsorption are considered.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1946–1950, August, 1996.     

Kinetics of the adsorptional deformation of zeolites

Adsorptional deformation in the Xe-CaA system has been studied at 303 K; the kinetics of adsorption and deformation has been investigated. A kinetic model of deformation is proposed based on the principle of the instantaneous establishment of local deformational equilibrium. Kinetic deformation curves based on this model are plotted that have local extrema above equilibrium values or in the negative region. It is shown that when Xe is adsorbed by CaA zeolite and trans-2-butene is adsorbed by NaA zeolite, the time required for deformational equilibrium to be established is negligibly small, and that deformation at any point of time at any point in the crystal is in equilibrium with respect to adsorption and temperature.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1948–1951, September, 1990.     

Adsorption of gases on adsorbents of various nature and porous structure at high pressures

The isotherms of excess adsorption of argon, nitrogen, and carbon dioxide on adsorbents with various porous structures (active carbon AU-71, polymeric sorbent MN-200, and synthetic zeolite NaA) were measured on the precision volumetric-gravimetric device in the pressure range of 0.1—150 MPa and at temperatures 300—400 K. The results of determination of the adsorption volumes of the studied adsorbents were compared using two methods. The first method is based on the Dubinin-Radushkevich equation, whereas the second one involves a conditional division of the weight of the substance in an ampule into the adsorbed portion and the part existing in the gas phase. The behavior of the adsorbed substance is described by the equation of adsorption of complete content corresponding to the physics of the adsorption process. The relation of the parameters of the empirical Dubinin—Radushkevich equation to the energy characteristics of the system was established.     

Heats of xenon adsorption on Nax zeolite at high pressures and various temperatures

The heats of xenon adsorption on zeolite NaX at 299–467 K and 0–21 MPa were measured on a Tian-Calvet differential calorimeter. A significant temperature dependence of the heats measured at high occupancies of the adsorption surface was demonstrated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 223–226, January, 1991.     

On the variation in the composition of zeolite NaA crystals

The conditions for crystallization of zeolite NaA, whose small cages are partially or completely (one molecule per unit cell) filled with NaAlO₂ molecules, were outlined. These molecules are occluded into cuboctahedra of zeolite NaA only during crystallization rather than during formation, aging, and modification of the initial aluminosilicate gels. Based on the data on the adsorption capacity for water in NaA zeolite samples, a small cage of this zeolite (cuboctahedron) adsorbs about four water molecules.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1565–1569, August, 2004.     

Zeolite-Polymer Composite Materials as Water Scavenger

The influence of the charge compensating cation nature (Na⁺, Mg²⁺) on the water adsorption properties of LTA-type zeolites used as filler in composite materials (zeolite/polymers) was investigated. Large scale cation exchanges were performed on zeolite powder at 80 °C for 2 h using 1 M magnesium chloride (MgCl₂) aqueous solutions. XRF, ICP, and EDX analyses indicate a successful cationic exchange process without the modification of the zeolite structure as shown by XRD and solid-state NMR analyses. Composite materials (granulates and molded parts) were manufactured using to extrusion and injection processes. In the case of MgA zeolite, nitrogen adsorption–desorption experiments allowed us to measure a microporous volume, unlike NaA zeolite, which is non-porous to nitrogen probe molecule. SEM and EDX analyses highlighted the homogeneous distribution of zeolite crystals into the polymer matrix. Water adsorption capacities confirmed that the trends observed in the zeolite powder samples are preserved after dragging zeolites into composite formulations. Granulates and molded parts composite samples containing the magnesium exchanged zeolite showed an increase of their water adsorption capacity up to +27% in comparison to composite samples containing the non-exchanged zeolite. The MgA composite is more promising for water decontamination applications due to its higher water adsorption properties than the NaA composite.     

Oxygen Selectivity of Calcined Na-A Type Zeolite

Na-A type zeolite (Na-A) pellet showed a greater oxygen selectivity than Na-A powder (Izumi, J. and M. Suzuki, Adsorption, submitted; Izumi, J. et al., Japan Patent Toku-Kou-Shou 62-026808 (1987)). It was considered that a water adsorption at calcination stage influenced a window diameter shrinkage to increase the oxygen selectivity. For the confirmation of an optimum preparation condition for the oxygen selectivity enhancement of Na-A pellet, an experiment of oxygen and nitrogen adsorption on calcined Na-A was undertaken with a small adsorbent column under a pressure swing adsorption (PSA) condition at a temperature from 298 K to 213 K. It was found that the secondary calcination (953–1033 K) after the water vapor adsorption provided a remarkable increase of the oxygen selectivity. At the optimum condition for calcined Na-A, the oxygen separation factor is greater than 6. Calcined Na-A has a potential to separate oxygen and nitrogen from air by PSA effectively.     

Propane–Propylene Binary Adsorption on Zeolite 4A

In this work we report new experimental data of pure and binary adsorption equilibrium of propane and propylene on zeolite 4A at 423 and 473 K. The pressure range studied was 0–500 kPa, which is the entire pressure range used in PSA–VSA (Pressure–Vacuum Swing Adsorption) units. The amount adsorbed of propane is much higher than that reported in previous literature. Propane diffusivity was estimated from uptake curves in the linear isotherm region. Adsorption of propane was extremely slow and equilibrium was established only after three days of adsorbate–adsorbent contact. The IAST (Ideal Adsorbed Solution Theory) using the Generalized Dubinin model to describe the pure propylene equilibrium and the Langmuir model for propane predicted with acceptable accuracy the binary adsorption data. Alternatively, the multisite model of Nitta was used to fit pure component isotherms and used in the IAST. Predictions were worse than those with the other strategy.     

Temperature dependence of NaA zeolite nucleation in silicoalumina gels

Conclusions For the same linear growth rate of crystals, the duration of the crystallization of NaA zeolite at 90°C exhibits a minimum dependence on the temperature at which the silicoalumina gels are held (0-90°C) prior to crystallization, which corresponds to the temperature-dependent maximum found in the dependence of the nucleation of NaA zeolite on temperature.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 727–730, April, 1988.The authors wish to express their gratitude to S. P. Zhdanov for discussing the results and for advice rendered during the writing of this paper.     

Pure and binary adsorption isotherms of ethylene and ethane on zeolite 5A

Pure and binary adsorption equilibrium data of ethylene and ethane on zeolite 5A were collected with a volumetric method for the temperature range 283 K to 323 K and pressure up to 950 kPa. The applicability of the binary adsorption prediction by the vacancy solution theory (VST) was investigated. Further individual adsorption and selectivity were obtained by VST prediction. According to the experimental results, zeolite 5A has a high adsorption capacity and selectivity for ethylene in the ethylene/ethane system. VST predicts that ethylene selectivity increases with pressure; it also shows that the amount of ethylene separated by zeolite 5A increases as the temperature decreases at a specified pressure.     

Synthesis, Ion-exchange, Structural Characterization and Adsorption of K, Na-FER Type Zeolite

Synthesis of K, Na -FER type zeolite wasstudied in the reactant system ofK ₂O-–Na ₂O-–Al ₂O ₃-–SiO ₂-–CO ₃-–HCO ₃-ndash;H ₂O.Sodium silicate, silica sol andfumed silica were tested as the silica source, andsolid aluminum sulfate, aluminum hydroxide andmeta-kaolinite as the alumina source. The startingmaterials, the composition of the reactant, and thesynthesis temperature greatly influence the phasescrystallized. A pure phase of K, Na-FER zeolite washydrothermally prepared at 208 °C with sodiumsilicate and solid aluminum sulfate as startingmaterials. The optimum composition of the reactantfor synthesis of the pure FER zeolite was determined. Chemical analysis, XRD, FT-IR, ²⁹Si and ²⁷AlMAS NMR, TG/DTA, and adsorption of nitrogen, methanoland n-hexane were used to characterize the zeolite andcompared with the reference sample of perfect singlecrystals of siliceous FER zeolite. The content ofK⁺and Na⁺in the zeolite decreases graduallywith the times of the treatment ofion-exchange/calcination, leading to an increase in theadsorption capacities of nitrogen and methanol, anda decrease of the loading of n-hexane. The location ofthe K⁺, the stacking faults, and dealumination of thezeolite framework are discussed based on the ion exchange and adsorption behavior.     

Adsorption properties of low-silica zeolite ZK-5

Water vapor, methanol, and argon adsorption isotherms, as well as the heat of adsorption of ammonia, methanol, and carbon dioxide have been determined on zeolite types A, ZK-4, and ZK-5. The results are explained by the distribution and the bond lengths of cations in the zeolite crystal lattice. It was shown that the exchange of 10–15% of the Na⁺ ions with Li⁺ in zeolite ZK-5 leads to a deformation of the 8-membered ring impeding the diffusion of adsorbed molecules. Cations contained in the 8-membered ZK-5 zeolite ring are bound more strongly to the framework, than in zeolite NaA, resulting in their smaller adsorption capacity.I. V. Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences, 199164 St. Petersburg, Russia. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2494–2500, November, 1992.