Extraction of ethylene glycol from aqueous salt solutions

A method is proposed for extracting ethylene glycol from aqueous salt solutions by dialysis through ion-exchange membranes, based on the Donnan exclusion of the electrolyte. Dialysis is performed in the continuous and batch modes. It is found that the batch mode of dialysis is more effective for extracting ethylene glycol from its aqueous salt solutions. The effect of the ionic form of the membrane on ethylene glycol fluxes is explained through computer simulation.     

Swelling of polyacrylamide gels in aqueous solutions of ethylene glycol oligomers

Addition of a small amount of ethylene glycol oligomers (OEG), with the number of repeat units y = 2–4, in an aqueous solution leads to the contraction of both linear and cross-linked poly(acrylamide-co-acrylic acid) chains. The results present clear evidence for the screening effect of OEG on the ionic groups of the polymer chains. Measurements indicate that the pre-swollen poly (acrylamide-co-acrylic acid) gels immersed in aqueous OEG solutions are at equilibrium. However, as the molecular weight of OEG increases, these gels cannot attain their equilibrium swelling ratio due to the appearance of non-equilibrium structures. The stability of these structures increases as the initial swelling degree of the gels increases.     

Conductometric studies of hexadecyltrimethylammonium bromide in aqueous solutions of ethanol and ethylene glycol

The effect of cosolvent on micellization of hexadecyltrimethyl ammonium bromide (CTAB) in aqueous solutions was studied. The conductivity of a mixture (cosolvent + water) as function of CTAB concentration was measured at different temperatures. Ethylene glycol and ethanol were used as a cosolvent. The conductivity data were used to determine the critical micelle concentration (CMC) and the effective degree of counterion dissociation of micelle in the temperature range 303.2 to 313.2 K. In all the cases studied, a linear relationship between log([CMC]_mix/mol dm⁻³) and the mass fraction of cosolvent in solvent mixture has been observed. The free energy (ΔG _mic ⁰ ), enthalpy (ΔH _mic ⁰ ), and entropy (ΔS _mic ⁰ ) of micellization were determined using the temperature dependence of CMC. The dependence of these thermodynamic parameters on solvent composition was determined. The standard free energy of micellization was found to be negative in all cases and becomes less negative as the cosolvent content increases. The enthalpy and entropy of micellization are independent of temperature in pure water, while ΔH _mic ⁰ and ΔS _mic ⁰ decrease dramatically with temperature in mixed cosolvents. Furthermore, the entropic contribution is larger than the enthalpic one in pure water, while in the mixed solvents, the enthalpic contribution predominates. The text was submitted by the authors in English.     

Solvation of amides of carboxylic acids in aqueous solutions of ethylene glycol

Enthalpies of solution of amides of formic, acetic, and propionic acids with different degrees of N-substitution in aqueous solutions of ethylene glycol were measured at 298.15 K. The concentration of ethylene glycol did not exceed 4 mol kg^–1. The reasons for increasing endothermic values of the enthalpies characterizing the amide transfer from water to a mixed aqueous-organic solvent on going from primary to tertiary amides and from formamides to the corresponding acetamides are discussed. The enthalpic coefficients of pair interactions between amides and ethylene glycol in water were calculated. The endothermicity of the interaction of the alkyl groups of the amide molecules with ethylene glycol results in positive values of the coefficients. The coefficient values increase with the enhancement of the hydrophobic properties of hydrophilic non-electrolytes (urea, formamide, ethylene glycol) due to an increase in the contribution of the hydrophobic component and a decrease in the contribution from the interaction of the polar groups of amides to the total interaction.     

Solubility of amino acids in aqueous poly (ethylene glycol) solutions

The solubilities of amino acids have been measured in water and aqueous poly(ethylene glycol) (PEG) solutions as a function of temperature and PEG concentration. The free energies of transfer from water to aqueous PEG solutions forl-alanine,l-valine,l-isoleucine andl-leucine were positive, while those forl-phenylalanine andl-tryptophan were negative. The corresponding enthalpies of transfer were almost zero for all amino acids. The equilibrium constants of the binding of amino acids to PEG chain were estimated from the solubility data. Amino acids with larger hydrophobicity are bound more strongly to the PEG chain due to the hydrophobic interaction between the methylene groups of PEG and the side chain of amino acid. The equilibrium constants showed a correlation with the dynamic hydration number (n _DHN) which expresses the hydration properties of amino acids in aqueous solution.     

Enthalpy characteristics of L-asparagine interaction with glycerol, ethylene glycol, and 1,2-propylene glycol in aqueous solutions

Integral dissolution enthalpies ??_sol H ^m of L-asparagine in the mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol at the concentration of organic solvents up to 0.24 mole fraction were measured by the calorimetry method. The standard enthalpies of dissolution (??_sol H ⁰) and transport (??_tr H ⁰) of amino acids from water to the mixed solvents were derived. The calculated enthalpy coefficients of the molecule pair interactions of L-asparagine-cosolvent are positive, except for the amino acid-glycerol-water system. The data obtained are interpreted in terms of prevalence of different types of interactions in solution and effect of the cosolvent nature on the thermochemical characteristics of the L-asparagine dissolution.     

Thermochemical characteristics of interactions of DL-alanine in aqueous solutions of glycerol, ethylene glycol, and 1,2-propylene glycol

The method of dissolution calorimetry was used to measure the integral enthalpy of dissolution ??_sol H ^m of DL-alanine in mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol at a concentration of organic solvent up to 0.32 mole fraction. The standard dissolution enthalpy (??_sol H ⁰) and transport enthalpy of amino acids from water to mixed solvent (??_tr H ⁰) were calculated. The calculated enthalpy coefficients of pair interactions of the DL-alanine molecules with the polyol molecules are positive and less than these values for L-alanine. The effect of interactions of different types in solution and the structural features of biomolecules and co-solvents on the enthalpy of dissolution characteristics of amino acids were considered.     

Thermochemical investigation of interaction of L-serin with glycerol,ethylene glycol,and 1,2-propylene glycol in aqueous solutions

By the method of dissolution calorimetry integral enthalpies of dissolution Δ_sol H ^m of L-serine are measured in the mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol at the concentration of the organic solvent up to 0.42 mole fraction. The standard values of enthalpies of dissolution (Δ_sol H ⁰) and transfer (Δ_tr H ⁰) of amino acids from water to mixed solvents are calculated. The calculated values of the enthalpy coefficients of pair interactions of L-serine with the molecules of co-solvents are positive. The data obtained are interpreted in terms of prevalence of different types of interactions in solutions and the influence of nature of co-solvents on the thermochemical characteristics of the dissolved amino acids.     

Molar volumes,viscosity, and isentropic compressibility of some primary monoalkanols in aqueous N,N-dimethylformamide solutions

The densities (ρ) and viscosities (η) for the ternary liquid mixtures of water + N,N-dimethylformamide + monoalkanols, have been measured as a function of the composition at 298.15, 308.15, and 318.15 K. From the experimental measurements excess molar volumes (V ^E), Viscosity deviation (Δη), and synergy index (I _s) have been evaluated. The speeds of sound have been also measured and excess isentropic compressibilities (K _s^E) are calculated al 298.15 K. The results are discussed and interpreted in terms of molecular package and specific interaction predominated by hydrogen bonding, been investigated.     

Viscosity of aqueous solutions of poly(ethylene glycol)s at 298.15 K

The viscosities of aqueous solutions of some poly(ethylene glycol)s (PEG) with nominal molecular weights ranging from 300 to 35 000 g mol⁻¹ were determined up to a concentration of 0.3 g cm⁻³ at 298.15 K. From these data the intrinsic viscosity and the viscosity average molecular weight of the solute were calculated. The viscosity coefficients B were evaluated and hence the partial molar Gibbs free energy of activation of viscous flow of solute at infinite dilution was calculated and interpreted in terms of the relative effects of solute on the ground and transition state solvent. The hydration numbers were determined and compared with available values in the literature.     

Isotherms of poly(ethylene glycol) adsorption from aqueous solutions by carbon adsorbents

Isotherms of adsorption of poly(ethylene glycols) PEG300, PEG6000, and PEG15 000 from aqueous solutions on graphitized carbon black and active carbon were measured at 25°C. Isotherms of excess adsorption of PEG6000 and PEG15 000 from aqueous solutions on both adsorbents were characterized by a distinct maximum. Comparison of adsorption isotherms for PEG6000 and PEG15 000 on a mesoporous AU-87 carbon testified to the existence of a sieve effect upon the adsorption of large PEG15 000 macromolecules in the accessible pores of this adsorbent. The analysis of the dependence of maximal adsorption values on the PEG molecular mass indicated a possible unfolding of macromolecular coils in the field of adsorption forces. As a result, all oxygen and carbon atoms of PEG macromolecules in a monolayer tend to approach active sites on the surface of a carbon adsorbent. The calculated values of thickness of dense adsorption monolayers of PEG300, PEG6000, and PEG15 000 lie within 0.36–0.63 nm for both adsorbents. PEG300 adsorption monolayers also contain, in addition to macromolecules, molecules of a solvent (water).Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 856–859.Original Russian Text Copyright © 2004 by Eltekov, Eltekova, Roldughin.     

Thermochemical characteristics of the interaction of L-cysteine with glycerol,ethylene glycol,and 1,2-propylene glycol in aqueous solutions

Integral enthalpies of dissolution Δ_sol H ^m of L-cysteine in mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol at concentrations of organic solvents of up to 0.37 mole fraction were measured by calorimetry of dissolution. The standard values of the dissolution enthalpies (Δ_sol H°) and the transfer enthalpies (Δ_tr H°) of amino acid from water to the mixed solvent were calculated. It was shown that the calculated enthalpic coefficients of the pair interactions of L-cysteine with cosolvent molecules have positive values. The obtained data are interpreted from the viewpoint of the prevalence of different types of interactions in the solutions and influence of the cosolvents nature on the thermochemical characteristics of amino acid dissolution.     

Molar absorption coefficient of ozone in aqueous solutions

The value of the molar absorption coefficient of ozone in aqueous solutions (2992 ± 71 M^–1 cm^–1 at 260 nm) is found based on the determination of ozone concentration by iodometry. This value is confirmed by the results of determination of O₃ concentration by reaction with the bromide ion and virtually coincides with the maximum absorption coefficient of ozone in the gas phase in the region the Hartley band. In the determinations of ozone concentration in aqueous solutions by direct spectrophotometry, we recommend the value of the molar absorption coefficient ε(О₃)₂₆₀ = 3000 M^–1 cm^–1.     

Formation of poly(ethylene glycol) inclusion complexes in aqueous solutions of mixed cyclodextrins

Even though the addition of modified cyclodextrins (modified CDs) accelerates the precipitation in aqueous solutions of poly(ethylene glycol) (PEG) and α-cyclodextrin (α-CD) the final amount of formed solid complex remains unchanged, with no significant presence of modified CDs detected by MALDI-TOF mass spectrometry. Thus unsuitability of kinetic turbidity measurements for determination of binding parameters was confirmed. On the other hand, theoretical calculations based on a model of a chain of freely accessible binding sites demonstrated that the results do not necessarily contradict the finding that individual modified CD molecules can thread onto PEG chains with the efficiency comparable to that of natural (unmodified) α-CD.     

On pseudo-clathrate hydrate structure in aqueous solutions of tetrahydrofuran

Dielectric relaxation in aqueous solutions of tetrahydrofuran is reported and the results interpreted in terms of the pseudo-clathrate hydrate model of the structure of the liquid state. The lifetime of any given pseudo-clathrate configuration is 10^–11 sec.Issued as NRCC Publication No. 17436     

Dipolarity, hydrogen-bond basicity and hydrogen-bond acidity of aqueous poly(ethylene glycol) solutions.

Poly(ethylene glycol) (PEG) in water is known to alter the structure and/or state of water to give a different polarity from that of pure water. We determined using the solvatochromic comparison method the dipolarity/polarizability (pi*), hydrogen bond (HB) accepting basicity (beta) and HB donating acidity (alpha) of aqueous solutions of PEGs of variegated molecular weights at different concentrations in order to understand the influence of the polymer on these properties of water. It was observed that PEG decreases alpha for water while it does not change pi* and beta appreciably in the range of the molecular weight and compositions studied.     

The interaction between triton X series surfactants and poly (ethylene glycol) in aqueous solutions

 A series of Triton X surfactants with different ethylene oxide chain length and poly(ethylene glycols) with different molecular weight were used, to find the effects of polymer chain length and size of the micelles on the cloud point of the surfactants. Two possible models are considered on the basis of cloud point changes of the solutions, to describe the polymer–surfactant interactions. One model considers that intra-chain micelles of polysoap are formed among the surfactant monomers and long polymer chains. The bridging attraction between two intra-chain micelles in such structures can enhance the collisions among the micelles, due to the exchange of amphiphilic monomers among the neighboring micelles. The other model suggests that flocculation depletion for the polymer chains exists between two regular micelles. This provides the driving force for the neighboring micelles to approach each other and destabilize the colloidal system. The flocculation effect is more significant for polymer with a long chain. Polymers with a shorter chain block the approach of the micelles, since there is no typical polymer–surfactant association formed but just simple small molecule associations in which the steric and solvation effects of the polymer chains make the inter-micelle interactions repulsive. Received: 19 August 1997 Accepted: 11 December 1997     

Role of the counterion in the effects of added ethylene glycol to aqueous alkyltrimethylammonium micellar solutions

The influence of the addition of various amounts of ethylene glycol, EG, up to a weight percent of 50%, on the micellization process in N-hexadecyl, N-tetradecyl, and N-dodecyltrimethylammonium chloride micellar solutions was investigated. Conductivity, fluorescence, and spectroscopic measurements give information about changes in the cmc, in the micellar ionization degree, in the aggregation number and in the polarity of the interfacial region upon changing the percentage by weight of the organic solvent. These changes were compared to those found when ethylene glycol was added to the analogous alkyltrimethylammonium bromide aqueous micellar solutions, results showing that the effects caused by the presence of the organic solvent were practically independent of the counterion nature. This conclusion was in agreement with the micellar kinetic effects observed on the spontaneous hydrolysis of phenyl chloroformate in both water-ethylene glycol alkyltrimethylammonium bromide and chloride micellar solutions.     

Volume and compressibility changes on mixing aqueous solutions of the amino acid and poly(ethylene glycol)

The volume and compressibility changes on mixing aqueous solutions of the amino acid and poly(ethylene glycol) were measured with a vibration densimeter and a sing-around velocimeter at 298.15 K. For the system of alanine-PEG-H₂O, the additivity rule for the mean apparent molal volume and compressibility at infinite dilution held, and the excess volume and compressibility changes on mixing were obtained. For the system of glycine-PEG-H₂O, the additivity rule for the mean apparent molal compressibility at infinite dilution did not hold. While the mean apparent molal volume and compressibility changes were negative and positive for the systems of another amino acid-PEG-H₂O, respectively, where amino acids were valine, isoleucine, leucine, phenylalanine, and tryptophan. These results suggest that glycine and alanine are excluded from the hydration layer around PEG chain and the amino acids with a larger side chain than alanine are bound to the PEG chain due to the hydrophobic interaction. The hydration number per monomer around PEG chain was estimated to be 3.9.