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.     

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.     

Concentrated electrolyte solutions at high temperatures and pressures

A survey is given of recent experimental results obtained from high-temperature, high-pressure investigations with water, aqueous solutions, and ionic fluids. Data on the static dielectric constant of water to 550°C and 5 kbar are given and discussed with respect to their relation to water structure. Infrared and Raman spectra of HDO in pure water have been obtained to 400°C and 4 kbar, which give information on hydrogen bonding. Xe–H₂O and CO₂–H₂O mixtures were investigated in the infrared. Ni(II) and Cu(II) complexes were investigated by absorption spectroscopy in aqueous solutions of high chloride content to 350°C and 2–6 kbar. The gas-liquid critical point of ammonium chloride was found at 880°C and 1635 bars. This fluid appears to be predominantly ionic even in the critical region. The possibility of converting pure polar fluids such as ammonia and water into concentrated ionic solutions by self-ionization at very high pressures is mentioned.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank.     

Adsorption of gases on layered silicates at high pressures

Equilibrium adsorption of nitrogen, carbon dioxide, and argon was examined on the sodium and pyridinium forms of montmorillonite and on the hydrogen form of bentonite. The measurements were carried out at 303, 343, 373, and 400 K over pressure ranges of 0.1–90 MPa (Ar and N₂) and 0.1–6 MPa (CO₂). The amount of nitrogen vapor adsorbed was determined at 77 K and pressures from 0 to 0.1 MPa. The porous structure parameters of the studied samples were determined using adsorption isotherms of nitrogen, argon, and carbon dioxide vapors. At elevated temperatures and pressures >10 MPa, Ar and N₂ adsorption processes on the Na-form of montmorillonite and Ar adsorption on bentonite are activated, since the amounts of the gases adsorbed and adsorption volumes increase with temperature. No activated adsorption is observed for carbon dioxide adsorption on these adsorbents. A comparison of the excess adsorption isotherms of gases on the Py-form of montmorillonite and H-form of bentonite shows that adsorption in micropores predominates for the Py-form of montmorillonite, whereas for the Na-form of bentonite and H-form of bentonite adsorption occurs mainly in meso- and macropores.     

Probing hydrogen-rich molecular systems at high pressures and temperatures

Information on the behavior of hydrogen-containing simple molecular systems at high pressures and temperatures is central to many problems in chemistry and allied sciences. The combination of increasing pressure and temperature causes a redistribution of the electronic density, and the resulting alterations in interatomic interactions give rise to changes in macroscopic properties. Experimental studies of hydrogen-rich systems under extreme conditions have advanced considerably in recent years as a result of improvements in diamond anvil cell technology in combination with resistive- and laser-heating techniques. These experimental methods are combined with spectroscopic and diffraction techniques, and the results interpreted with the aid of molecular simulations. In this tutorial review we discuss recent findings in hydrogen, water, and other selected hydrogen-rich systems including compounds formed from these materials. The results are examined in terms of the evolution of effective potentials and interatomic vibrational coupling, molecular dissociation and recombination, ionization and polymerization, quantum effects, and order-disorder phenomena.     

Spectroscopic study of water-NaCl-benzene mixtures at high temperatures and pressures

Near-infrared and ultraviolet spectra of water-NaCl-benzene mixtures have been measured in the 473-573 K and 100-400 bar range and 373-498 K and 50-300 bar range, respectively. Concentrations of water in the benzene-rich phase and benzene in the water-rich phase were estimated from integrated intensities of the absorption bands. It is found that addition of NaCl in the aqueous phase suppresses transfer of water into the benzene-rich phase, and the relative decrease in water solubility in benzene exhibits good correlation with an increase in density of the aqueous NaCl solution relative to that of neat water. The salting-out constant for the water-NaCl-benzene system, which is estimated from a relative decrease in benzene solubility in the aqueous phase by addition of sodium chloride, increases significantly with increasing temperature. It is suggested that the effect of sodium chloride on the water-benzene mutual solubilities can be explained by ion-induced electrostriction of the aqueous phase.     

Viscosity of aqueous calcium chloride solutions at high temperatures and high pressures

Viscosity of six (0.10, 0.33, 0.65, 0.97, 1.40, and 2.00) mol kg⁻¹ binary aqueous CaCl₂ solutions has been measured with a capillary-flow technique. Measurements were made at pressures up to 60 MPa. The range of temperature was from 293 to 575 K. The total uncertainty of viscosity, pressure, temperature, and composition measurements was estimated to be less than 1.6%, 0.05%, 15 mK, and 0.014%, respectively. The effect of temperature, pressure, and concentration on viscosity of binary aqueous CaCl₂ solutions was studied. The measured values of viscosity of CaCl₂(aq) were compared with data, predictions, and correlations reported in the literature. The temperature and pressure coefficients of viscosity of CaCl₂(aq) were studied as a function of concentration and temperature. The viscosity data have been interpreted in terms of the extended Jones–Dole equation for the relative viscosity (η/η₀) to accurate calculate the values of viscosity A- and B-coefficients as a function of temperature. The derived values of the viscosity B-coefficients were compared with the values calculated from the ionic B-coefficient data. The physical meaning parameters V and E in the absolute rate theory of viscosity and hydrodynamic molar volume (effective rigid molar volume of salt) V_k were calculated using present experimental viscosity data. TTG model has been used to compare predicted values of the viscosity of CaCl₂(aq) solutions with experimental values at high pressures.     

Density measurements of methyl fluoride at high pressures and temperatures

The densities of methyl fluoride were reported at T = (298.15 to 573.15) K and at p = (10 to 300) MPa. Experiments were performed with a thin-walled sample holder which was under equal pressure, both inside and outside. The volume change of the sample was determined with a separation system at T = 298.15 K by making use of a float on mercury and a linear variable differential transformer. The density of methyl fluoride varies in this region ρ = (2.218 to 29.602) mol · dm⁻³. The uncertainty of data for densities was estimated to be better than ±0.37%. The experimental data are described by the Tait equation.     

Adsorption phenomena at high pressures and temperatures 1. Method of investigation; adsorption of nitrogen on NaA zeolite

A simple precision volumetric-gravimetric setup was elaborated and created for determining the equilibrium and kinetic parameters of adsorption in the 1–160 MPa pressure range and the 300–600 K temperature range. The isotherms of adsorption of nitrogen on crystalline NaA zeolite in the indicated temperature and pressure range were measured. A method was proposed for determining the pore volume of zeolites based on conducting adsorption measurements at high pressures of the gas phase. The isosteric heats of adsorption of nitrogen on NaA zeolite at 305, 334, and 373 K were estimated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1233–1238, June, 1990.     

Infrared spectra of ammonium nitrate at high pressures and low temperatures

Infrared spectra showing the symmetric stretching vibration band, γ₁, of the nitrate ion (rendered weakly infrared active by the crystal field) were recorded for sample pressures up to 6 k bar at temperatures ranging between room temperature and liquid nitrogen temperature. A pressure-temperature phase diagram for the λ-transition of ammonium nitrate has been obtained. The spectra at low temperatures and low pressures are shown to be due to mixtures of phase IV and phase VII and the importance of long-range as well as short-range order is considered.     

The rate of methyl radical decomposition at high temperatures and pressures

Rate constants are calculated for CH₃ (+ Ar) ? CH₂ + H (+ Ar) at the limiting low-pressure, the limiting high-pressure, as well as the intermediate fall-off ranges. The results show that published experimental rate constants for methyl dissociation correspond to the fall-off region close to the low-pressure limit. At the low-pressure limit the activation energy is less than the bond dissociation energy, in agreement with experimental results. Forward and backward rate coefficients at the high-pressure limit are compared with other theoretical calculations. More theoretical and experimental work is necessary to understand the reverse reaction and its competing reactions, as well as the decomposition channel leading to CH + H₂. © 1994 John Wiley & Sons, Inc.     

Near infrared study of water-benzene mixtures at high temperatures and pressures

Near-infrared absorption of water-benzene mixtures has been measured at temperatures and pressures in the ranges of 473-673 K and 100-400 bar, respectively. Concentrations of water and benzene in the water-rich phase of the mixtures were obtained from the integrated absorption intensities of the OH stretching overtone transition of water and the CH stretching overtone transition of benzene, respectively. Using these concentrations, the densities of the water-rich phase were estimated and compared with the average densities before mixing, which were calculated from literature densities of neat water and neat benzene. It is found that anomalously large volume expansion on the mixing occurs in the region enclosed by an extended line of the three-phase equilibrium curve and the one-phase critical curve of the mixtures, and the gas-liquid equilibrium curve of water. Furthermore, magnitude of the relative volume change increases with decreasing molar fraction of benzene in the present experimental range. It is suggested that dissolving a small amount of benzene in water induces a change in the fluid density from a liquidlike condition to a gaslike condition in the vicinity of the critical region.     

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.     

Methane adsorption on the Zr-BDC metal-organic framework structure at supercritical temperatures and pressures

Russian Chemical Bulletin - Methane adsorption by the sample of the metal-organic framework structure (MOF) Zr-BDC (BDC is benzene-1,4-dicarboxylate) containing zirconium ions was studied in a...     

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.     

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.     

Adsorption deformation of zeolite NaX at high pressures of xenon

The deformation of pellets of crystalline zeofite NaX upon adsorption of Xe at pressures from 0.001 to 7 MPa and temperatures from 252.5 to 333 K was studied. In the temperature range studied, the relative linear deformation of zeolite crystals is negative in the initial adsorption region. When the adsorption of Xe increases, its value passes through a minimum and then increases sharply taking positive values at high adsorption volume filling of micropores.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 336–338. February, 1996     

Thermodynamics of aqueous association and ionization reactions at high temperatures and pressures

Electrochemical and electrical conductance cells have been widely used at ORNL over the years to quantitatively determine equilibrium constants and their salt effects to 300°C (EMF) and 800°C (conductance) at the saturation pressure of water (EMF) and to 4000 bars (conductance). The most precise results to 300°C for a large number of weak acids and bases show very similar thermodynamic behavior, which will be discussed. Results for the ionization constants of water, NH₃(aq), HCl(aq), and NaCl(aq), which extend well into the supercritical region, have been fitted in terms of a model with dependence on density and temperature. The entropy change is found to be the driving force for ion-association reactions and this tendency increases (as it must) with increasing temperature at a given pressure. Also, the variation of all thermodynamic properties is greatly reduced at high fixed densities. Considerable variation occurs at low densities. From this analysis, the dependence of the reaction thermodynamics on the P-V-T properties of the solvent is shown, and the implication of large changes in hydration for solutes in the vicinity of the critical temperature will be discussed. Finally, the change in the molar compressibility coefficient for all reactions in water is shown to be the same and dependent only on the compressibility of the solvent.