Analysis of the microporous structure of the low-cost activated carbon fibres obtained from flax and jute cloth

The paper presents the results of research devoted to obtaining the low-cost activated carbon fibres from waste flax and jute cloth by carbonisation in inert atmosphere and activation with air as well as to the analysis of the microporous structure of materials obtained on the basis of the nitrogen, argon and benzene adsorption isotherms, using among others, the unique LBET method with implemented of the new models of the multilayer adsorption on the heterogeneous surfaces of the carbonaceous adsorbents. As part of the research conducted, imaging of the surface of the low-cost activated carbon fibres obtained has also been done using scanning electron microscopy.     

Potentiometric Studies on Complexation of Cu(II) Ion with Methyl/Nitro-Substituted 1,10-Phenanthrolines and Selected Amino Acids

Protonation constants of methyl/nitro substituted 1,10-phenanthrolines {(m/n-sphen): 4-methyl-phenanthroline (4-mphen), 5-methyl-1,10-phenanthroline (5-mphen), 4,7-dimethyl-1,10-phenanthroline (dmphen), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen) and 5-nitro-1,10-phenanthroline (5-nphen)] and the amino acids (aa) l-tyrosine (tyr) and glycine (gly), and their corresponding binary and ternary stability constants with Cu(II), were determined in aqueous 0.1 mol·L^?1 KCl ionic media at 298.15 K. The protonation constants of the ligands and the stability constants of the binary and ternary complexes of Cu(II) with the ligands were calculated from the potentiometric data using the “BEST” software package. The species distribution diagrams were obtained using the “SPE” software package under the experimental conditions described. The order of stability of the ternary complexes in terms of the primary ligands is [Cu(tmphen)(aa)]⁺ > [Cu(dmphen)(aa)]⁺ > [Cu(4-mphen)(aa)]⁺ > [Cu(5-mphen)(aa)]⁺ > [Cu(5-nphen)(aa)]⁺. The stability constants of the ternary complexes decrease in the following order: [Cu(m/n-sphen)(gly)]⁺ > [Cu(m/n-sphen)(tyr)]⁺, which is identical to the sequence found for the binary complexes of Cu(II) with gly and tyr.     

Effect of Base–Acid Properties of Mixtures of Ethanol with Water on the Enthalpy of Solution of Cyclic Ethers in these Mixtures at <Emphasis Type="Italic">T</Emphasis> = 298.15 K

The enthalpies of solution of the cyclic ethers 1,4-dioxane, 12-crown-4 and 18-crown-6 in mixtures of ethanol and water have been measured within the whole mole fraction range at T = 298.15 K. The enthalpy of solvation has been calculated. In pure ethanol and pure water, the solvation enthalpy of the investigated cyclic ethers depends linearity on the number of –CH₂CH₂– groups in the cyclic ether molecules. Based on the analysis of the preferential solvation model proposed by Waghorne, it can be concluded that the 1,4-dioxane, 15C5 and 18C6 molecules are preferentially solvated by water molecules in the range of low water content in these mixtures. The effect of base–acid properties of ethanol–water mixtures on the enthalpy of solution of cyclic ethers in these mixtures has been analyzed. The enthalpy of solution of cyclic ethers correlates with the acidic properties of ethanol–water mixtures in the range of high and medium water content. The results presented are compared with analogous data obtained for the methanol–water and propan-1-ol–water mixtures.     

Phase Diagram of the Quaternary System KCl–MgCl<Subscript>2</Subscript>–NH<Subscript>4</Subscript>Cl–H<Subscript>2</Subscript>O at <Emphasis Type="Italic">t</Emphasis> = 60.00 °C and Their Application

Based on the requirement for the comprehensive exploitation and utilization of the salt lake resources magnesium chloride and potassium chloride, a new technology to produce KCl and ammonium carnallite (NH₄Cl·MgCl₂·6H₂O) by using NH₄Cl as salting-out agent to separate carnallite is proposed. The solubilities of quaternary system KCl–MgCl₂–NH₄Cl–H₂O were measured by the isothermal method at t = 60.00 °C and the corresponding phase diagram was plotted and analyzed. The analysis of this phase diagram shows that there are seven saturation points and eight regions of crystallization. These eight regions of crystallization represent salts corresponding to KCl, NH₄Cl, MgCl₂·6H₂O, (K_1?n (NH₄) _n )Cl, ((NH₄) _n K_1?n )Cl, (K_1?n (NH₄) _n )Cl·MgCl₂·6H₂O, KCl·MgCl₂·6H₂O and NH₄Cl·MgCl₂·6H₂O. According to the phase diagram analysis and calculations, ammonium carnallite (NH₄Cl·MgCl₂·6H₂O) and KCl can be obtained using carnallite as raw materials and ammonium chloride as salting-out agent at t = 60.00 °C. The new technology shows the advantages of being easy to operate and having low energy consumption. The research on this quaternary phase diagram is the foundation for reasonable development of carnallite resources and comprehensive utilization of the salt lake brines.     

Comments on “Thermodynamic Models for Correlation of Solubility of Hexaquocobalt(II) Bis(<Emphasis Type="Italic">p</Emphasis>-toluenesulfonate) in Liquid Mixtures of Water and Ethanol from 288.15 to 333.15 K”

Mathematical representations reported by Yu et al. for the CNIBS/R–K model and a hybrid model are carefully examined in regards to the model’s ability to predict the solubility of hexaquocobalt(II) bis(p-toluenesulfonate). The equation coefficients reported by Yu et al. were found to give calculated mole fraction solubilities in ethanol that exceed unity for both models.     

Density and Viscosity of a Ternary $$ x_{1} $$ 1-He xene(1) + $$ x_{2} $$ x2 1-Octene(2) + (1 − − x2) 1-Decene(3) Mi xture at High Temperatures and High Pressures

The density and viscosity of a ternary 1-hexene(1) + 1-octene(2) +1-decene(3) mixture (\( w_{1} = w_{2} = w_{3} = 0.333 \) weight fractions or \( x_{1} = 0.4257 \),\( x_{2} = 0.3190 \), \( x_{3} = 0.2553 \) mole fractions of 1-hexene, 1-octene, and 1-decene, respectively) have been simultaneously measured over the temperature range from (298 to 471) K and at pressures up to 196 MPa using a combined method of hydrostatic weighing and falling-body techniques, respectively. The combined expanded uncertainties of the density, pressure, temperature, concentration, and viscosity measurements at the 95% confidence level with a coverage factor of k = 2 are estimated to be (0.15 to 0.30)%, 0.05%, 0.02 K, 0.005 mol%, and (1.5 to 2.0)%, respectively. The measured densities and viscosities were used to calculate the excess molar volumes and viscosity differences. The excess molar properties (\( G_{\text{m}}^{\text{E}} , \, H_{\text{m}}^{\text{E}} , \, S_{\text{m}}^{\text{E}} \) and \( C_{\text{pm}}^{\text{E}} \)) and their pressure derivatives as a function of temperature and pressure have been calculated using the derived excess molar volumes. The measured viscosities were used to develop a theoretically based viscosity correlation model (Arrhenius–Andrade type equation) for the mixture.     

Measurement and Modeling of Phase Equilibrium,Volumetric Properties and Molar Refractivity of 2-Methylpropan-2-ol + Ethane-1,2-diol

2-Methylpropan-2-ol, an important fine chemical, may be dehydrated during extractive distillation with glycols as entrainer. Experimental isobaric phase equilibrium studies were carried out on binary mixtures of 2-methylpropan-2-ol with ethane-1,2-diol, as an entrainer, at the local atmospheric pressure of 94.99 kPa and at sub-atmospheric pressures of 19.99, 39.99, 59.99, 78.79 kPa using a Sweitoslawski-type ebulliometer. The Wilson and NRTL activity coefficient models were used to correlate the experimental results and the binary interaction parameters were obtained using the Generalized Reduced Gradient optimization technique. UNIFAC was also used to predict the deviations in bubble temperatures. Moreover, the variation in density, refractive index values and other derived properties (excess molar volumes, partial molar volumes and deviations in molar refractivity) were explored at 303.15, 313.15, 323.15 and 333.15 K to understand the shift of equilibrium with the variation in the mixture composition for the conformational state of the molecules. The Redlich–Kister polynomial equation was used to correlate the excess molar volumes and deviations from molar refractivity. Different theoretical mixing rules (Lorentz–Lorenz, Wiener, Heller, Gladstone–Dale and Arago–Biot) are investigated and reported in terms of average percentage deviation. Furthermore, the Prigogine–Flory–Patterson theory was used to predict the trend of the dependence of excess molar volumes on composition for the present system.     

Compensation Between the Entropic and Enthalpic Changes Arising from Changes in Solvent–Solvent Interactions in Mixed Solvents

A theorem presented by Professor Ben-Naim (J Phys Chem 82:874–885, 1978) states that the standard state enthalpy and entropy changes arising from changes in the solvent structure that are induced by solvation of a solute cancel exactly in the standard state Gibbs energy. In this paper this is explored by consideration of the thermodynamics of transfer of electrolytes in mixed solvents, using previously developed models of the solvation process. Two cases are considered. One is random solvation, where curvatures in plots of the transfer enthalpies and entropies, which arise from changes in solvent–solvent interactions, exactly compensate in the transfer Gibbs (free) energies, which are sensibly linear with solvent composition. The second type of system are those with strong preferential solvation where it is found that the transfer Gibbs energies can be accounted for quantitatively in terms of changes in the solute–solvent interactions, with no contribution from changes in solvent–solvent interactions. The results are entirely consistent with the Ben-Naim theorem.     

Speciation and Multinuclear NMR Spectroscopic Studies of Di- and Trimethyltin(IV) Moieties with MESNA in Aqueous Medium

The interaction of Me₂Sn(IV)²⁺ and Me₃Sn(IV)⁺ with a prodrug, sodium 2-mercaptoethane sulfonate (HSCH₂CH₂SO₃Na, MESNA) abbreviated as (HL), has been studied potentiometrically in aqueous solution (I = 0.1 mol·L^?1 KNO₃, 298 K). The concentration distribution of various species formed in the solution was studied with changes in pH (~3–11). A strong coordination of MESNA with metal through the S atom of thiol group has been found. In the Me₂Sn(IV)–HL system, the species [Me₂Sn(L)]⁺ (53.1–75.6%) is predominant at acidic pH (3.73 ± 0.02) and the species [Me₂Sn(L)₂OH]^? (29.4–38.5%) is predominant at basic pH (10.32 ± 0.08). In contrast, for the Me₃Sn(IV)⁺ system, [Me₃SnL] (37.0–57.4%) is the major species at pH 7.65 ± 0.03 and [Me₃Sn(OH)] (49.9–67.2%) and [Me₃Sn(L)(OH)]^? (30.2–46.5%) are the major species at pH 11.05 ± 0.01. However, at physiological pH (7.01 ± 0.32), in both (1:1) and (1:2) Me₂Sn(IV)–HL systems, the species [Me₂Sn(L)(OH)] (67.2–89.9%) is predominant, whereas for Me₃Sn(IV)–HL (1:1) and (1:2) systems, [Me₃Sn(OH)] (53.5%) and [Me₃SnL] (56.8%) are the respective predominant species. In order to characterize the possible geometry of the proposed complex species, multinuclear (¹H, ¹³C and ¹¹⁹Sn) NMR studies were carried out at different pHs. No polymeric species were detected in the experimental pH range.