Dynamics of joint adsorption of mutually soluble substances by activated carbons

A model for the dynamics of isothermal absorption of a binary mixture of an organic substance, soluble in water, and water vapor in a fixed bed of activated carbon was proposed. It includes the equations of material balance and the Myers—Prausnitz model for equilibrium adsorption. The possibility of formation of the condensed phase during the adsorption of an organic substance on moist activated carbon was shown. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1491–1495, August, 1998.     

Selectivity of Low- and High-Silica Clinoptilolites with Respect to Alkali and Alkaline–Earth Metal Cations

The ion-exchange equilibria involving K⁺ and Ca²⁺ cations were studied using the Na-forms of nine different clinoptilolite samples. The high-silica (in the native state, sodium–potassium form) clinoptilolites were shown to have the increased selectivity with respect to K⁺ ions, whereas the low-silica (in the native state, calcium form) clinoptilolites to Ca²⁺ ions. The phenomenon found is interpreted as a structural memory of clinoptilolites with respect to alkali and alkaline-earth metal ions which had been present during zeolite crystallization under natural conditions.     

Analysis of the state of stress of cylindrically orthotropic rings subjected to concentrated loads

The state of stress of rings of different thickness with high degrees of anisotropy ²=E/E_r, ²=E_gq/G_r is analyzed on the basis of the solution of the plane problem for a cylindrically orthotropic body. The accuracy of the stress determination in accordance with approximate theories of bending of curved bars is estimated. The radial tensile stresses that develop when rings are bent by concentrated loads are calculated.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 445–452, May–June, 1976.     

Thermodynamic characteristics of ion-exchange sorption of Co2+ cations on Na-vermiculite

The exchange of Na⁺ ions of vermiculite for Co²⁺ cations is measured by sorption-analytical and microcalorimetric methods. The previously revealed growth of the equilibrium constant with a rise in the degree of filling θ of vermiculite exchange sites with Co²⁺ cations is confirmed. This result is explained by the segregation of Co²⁺ and Na⁺ cations being exchanged in separate interlayer regions of vermiculite. The negative heats of exchange of Na⁺ cations for Co²⁺ cations are associated with the energy consumption for the rearrangement of the segregated interlayer regions in vermiculite. The positive entropy changes resulting from the exchange indicate the formation of a more disordered Co-Na-layered “cake” in comparison with the initial Na-form vermiculite. A decrease in the integral molal free-energy change ΔG _m of the mixed form of the mineral is determined by the entropy factor. It is shown that, as θ increases, the ΔG _m(θ) dependence passes from a positive to a negative range of values. This pattern of the curve may be interpreted as a gradual phase transition from the Na-form to the mixed Co-Na-segregated form. The first derivatives of the enthalpy and entropy changes with respect to the degree of filling θ exhibit distinct maxima at θ ～ 0.20 as a result of the transition from the ideal mixing of Co²⁺ and Na⁺ cations being exchanged to their segregation.     

Host-guest complexes of carotenoids with beta-glycyrrhizic acid

The structure, stability, and reactivity of the host-guest complexes between a set of carotenoids and the triterpene glycoside, beta-glycyrrhizic acid (GA), were investigated by different physicochemical techniques: high-performance liquid chromatography, optical absorption, and fluorescence spectroscopy. It has been demonstrated recently that the molecular complexes of GA with a number of drugs are characterized by reduced toxicity and increased therapeutic activity of these drugs. In the present work it was found that carotenoids form 1:2 complexes with GA in aqueous solutions as well as in polar organic solvents, methanol, acetonitrile, and dimethylsulfoxide. We assume that the structure of the complex is a cycliclike dimer of GA encapsulating a carotenoid molecule. The stability constants in all solvents are near 10(4) M(-1). In addition, GA forms inclusion complexes with carotenoid radical cations, which results in their stabilization. Complex formation (a) decreases the rate of electron transfer from carotenoids to electron acceptors (Fe3+ or quinone) and (b) considerably increases the lifetime of the carotenoid-quinone charge-transfer complex and the yield of the major product (a carotenoid-quinone adduct). A thermodynamic study shows that hydrophobic interactions are the main driving force of the carotenoid-GA complex formation. These results are important for understanding both the nature of GA complexes and the influence of GA on the therapeutic activity of some drugs. Furthermore, carotenoid-GA complexes could be used for the design of artificial light-harvesting, photoredox, and catalytic systems.     

A calorimetric adsorption study on the interaction of water with hydroxylated surface of γ-Al2O3

The curve for the differential heat of adsorption of water on γ aluminum oxide has parts related to the interaction of the adsorbed water molecules with surface molecules of coordinated water and with acid and basic hydroxyl groups. Estimates have been made of the effective charges and hydration numbers for three of these adsorption centers. Textural changes have been observed in the γ-Al₂O₃ particles related to interplate swelling in the secondary sorbent packets into which the primary particles are linked. A. V. Dumanskii Institute for Colloid and Water Chemistry, National Academy of Sciences of Ukraine, 42 Prospekt Akademika Vernadskogo, Kiev-142 03680, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 2, pp. 121–125, March–April, 2000.     

Ion-exchange equilibria and exchange heats on clinoptilolite involving singly-charged cations

Isotherms and integral heats of exchange of alkali metal, ammonium, and silver cations on sodium clinoptilolite were measured. Exchange involving K₊, NH₄ ⁺, Cs⁺, and Ag⁺ displacing cations was found to be exothermic for all occupancies of the clinoptilolite exchange sites. Exchange was exothermic for Li₊ cations up to = 0.15. The dependence of the differential ion-exchange heats on was determined. Clinoptilolite was found to have two types of exchange sites with different heats of ion exchange. The experimental data were used to calculate the selectivity coefficients, thermodynamic constants, and ion-exchange entropy. These findings are discussed relative to the differences in the cation properties and structural features of clinoptilolite.A. V. Dumanskii Institute of Colloid Chemistry and the Chemistry of Water, National Academy of Sciences of Ukraine, 42 Prospekt Akademika Vernadskogo, 252680 Kiev-142, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 5, pp. 315–319, September–October, 1996. Original article submitted February 12, 1996.     

Equilibrium adsorption of a cyclopentane—benzene vapor mixture on active carbon

The data on adsorption of cyclopentane, benzene, and their mixture on active carbon were analyzed by the statistical thermodynamic model. A method to describe the state of a binary mixture in single micropores was offered. A substantial negative deviation from Raoult's law predicted by the concept of an ideal adsorption solution is a consequence of a decrease in the excessive Helmholtz energy brought about by progressive filling when values of the excessive energy are positive over a wide range of adsorption. The excessive values found for the entropy and internal energy of a mixture of molecules in a single micropore are negative due to the heterogeneity of the adsorption field. The approach suggested adequately describes the experimental data and can be used for the determination of differential heats of adsorption. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1070–1076, June, 1999.     

Weakly coordinating anions HA2-generated from oxoanions A- and their conjugate acids. Coordination equilibria,ionic conductivities,and the structures of [Cu2(H(CH3SO3)2)4]n and [Cu(CO)(H(CF3CO2)2)]2

The coordination or ion pairing of the hydrogen-bonded anions H(CF3CO2)2- and H(CH3SO3)2- to NEt4+, Li+, Cu+, and/or Cu2+ was investigated. The structure of [Cu2(H(CH3SO3)2)4]n consists of centrosymmetric dimeric moieties that contain two homoconjugated (CH3SO2O-H...OSO2CH3)- anions per Cu2+ ion, forming typical Jahn-Teller tetragonally elongated CuO6 coordination spheres. The oxygen atoms involved in the nearly linear O-H...O hydrogen bonds (O...O approximately 2.62 A) are not coordinated to the Cu2+ ions. The structure of Cu2(CO)2(H(CF3-CO2)2)2 consists of pseudo-C2-symmetric dimers that contain one homoconjugated (CF3COO-H...OCOCF3)- anion per Cu+ ion, forming highly distorted tetrahedral Cu(CO)O3 coordination spheres. Three of the four oxygen atoms in each hydrogen-bonded H(CF3CO2)2- anion are coordinated to the Cu+ ions, including one of the oxygen atoms in each O-H...O hydrogen bond (O...O approximately 2.62 A). Infrared spectra (v(CO) values) of Cu(CO)(CF3CO2) or Cu(CO)(CH3SO3) dissolved in acetonitrile or benzene, with and without added CF3COOH or CH3SO3H, respectively, demonstrate that HA2- anions involving carboxylates or sulfonates are more weakly coordinating than the parent anions RCO2- and RSO3-. Direct current conductivities of THF solutions of Li(CF3CO2) containing varying concentrations of added CF3COOH further demonstrate that Li+ and NEt4+ ion pair much more weakly with H(CF3CO2)2- than with CF3CO2-.     

Equilibria and heats of exchange of alkaline-earth metal ions on the Na form of mordenite

Sorption-analytic studies of ion exchange equilibria combined with direct calorimetric measurements of the heats of ion exchange sorption of the Ca²⁺, Sr²⁺, and Ba²⁺ cations were performed over the whole range of solid phase fillings with sorbed cations on the Na forms of two mordenites prepared from natural specimens rich in Na⁺ and Ca²⁺ cations. Ion exchange constants were determined and the Gibbs energies and entropies of ion exchange were calculated. The thermodynamic characteristics obtained were analyzed taking into account the preferable localization of alkaline-earth metal ions on certain exchange centers in the structure of mordenite. The presence of natural mordenite memory effects with respect to extra-framework Ca²⁺ cations in the presence of which these zeolites were crystallized in nature was established.