Solubility of carbon dioxide in the solvent system (2-amino-2-methyl-1-propanol + sulfolane + water)

New sets of data for the solubility of CO₂ in the amine solvent system of 2-amino-2-methyl-1-propanol (1) + sulfolane (2) + water (3) were presented in this work. The measurements were done at temperatures of 313.2, 333.2, 353.2, and 373.2 K and CO₂ partial pressures up to 193 kPa. The investigated compositions were as follows: (i) w₁=16.5%$w_1=16.5\%$, w₂=32.2%$w_2=32.2\%$; (ii) w₁=8.2%$w_1=8.2\%$, w₂=41.2%$w_2=41.2\%$; (iii) w₁=22.3%$w_1=22.3\%$, w₂=27.7%$w_2=27.7\%$; and (iv) w₁=30.6%$w_1=30.6\%$, w₂=19.4%$w_2=19.4\%$, where w$w$ is the mass percent of the component. The present solubility data was correlated by a modified Kent–Eisenberg model. The model reasonably represents the present solubility data, not only over the considered conditions, but also for a wider range of temperatures, partial pressures, and compositions.     

Dehydration performance of a hydrophobic DD3R zeolite membrane

The all silica DDR membrane turns out to be well suited to separate water from organic solvents under pervaporation conditions, despite its hydrophobic character. All-silica zeolites are chemically and hydrothermally more stable than aluminum containing ones and are therefore preferred for membrane applications, including for dehydration, even though these type of membranes are hydrophobic. Permeation of water, ethanol and methanol through an all-silica DDR membrane has been measured at temperatures ranging from 344 to 398 K. The hydrophobic membrane shows high water fluxes (up to 20 kg m⁻² h⁻¹). The pure water permeance is insensitive to temperature and is well described assuming weak adsorption. Excellent performance in dewatering ethanol (N=2$N=2$ kg m⁻² h⁻¹and _αw=1500${\alpha }_{\text{w}}=1500$ at 373 K and _xw=0.18$x_{\text{w}}=0.18$) is observed and the membrane is also able to selectively remove water from methanol (N=5$N=5$ kg m⁻² h⁻¹ and _αw=9${\alpha }_{\text{w}}=9$). Water could also be removed from methanol/ethanol/water (_αwater_/EtOH=1500${\alpha }_{\text{water}/\text{EtOH}}=1500$, _αMeOH_/EtOH=70${\alpha }_{\text{MeOH}/\text{EtOH}}=70$ at 373 K) mixtures, even at water feed concentrations below 1.5 mol%.     

On the computation of the fundamental derivative of gas dynamics using equations of state

The value of the fundamental derivative of gas dynamics, Γ$\mathrm{\Gamma }$, is a quantitative measure of the variation of the speed of sound with respect to density in isentropic transformations, such as those occurring, for example, in gas-dynamic nozzles. The accurate computation of its value, which is a constant for a perfect gas, is key to the understanding of real-gas flows occurring in a thermodynamic region where the polytropic ideal gas law does not hold. The fundamental derivative of gas dynamics is a secondary thermodynamic property and so far, no experiments have been conducted with the aim of measuring its value. Several studies document the estimation of Γ$\mathrm{\Gamma }$ for fluids composed of complex molecules using mainly simple thermodynamic equations of state, e.g., that of Van der Waals. A review of these studies has revealed that the calculated values of Γ$\mathrm{\Gamma }$ are affected by large uncertainties; these uncertainties are due to the functional form of the adopted equations and because of uncertainties in the available fluid property data on which these equations were fitted. In this work, the fundamental derivative of gas dynamics of molecularly simple fluids is computed with the aid of, among other models, modern reference equations of state. The accuracy of these computations has been assessed. Reference thermodynamic models however, are not available for molecularly complex fluids; some of these molecularly complex fluids are the substances of interest in studies on the so-called nonclassical gas dynamics. Therefore, results of the computation of Γ$\mathrm{\Gamma }$ for few, molecularly simple hydrocarbons, like methane, ethane, etc., are used as a benchmark against which the performance of simpler equations of state, can be assessed. For the selected substances, the Peng–Robinson, Stryjek–Vera modified, cubic equation of state yields good results for Γ$\mathrm{\Gamma }$-predictions, while the modern multiparameter technical equations of state, e.g., the one in the Span–Wagner functional form, are preferable, provided that enough accurate thermodynamic data are available. Another notable result of this study, is that Γ$\mathrm{\Gamma }$ for a fluid composed of complex molecules is less affected by the inaccuracy of _Cv$C_v$-information (_Cv$C_v$ is the isochoric heat capacity), if compared to the estimation of Γ$\mathrm{\Gamma }$ for simple molecules. Inspection of the results of the calculation of Γ$\mathrm{\Gamma }$ in the proximity of the critical point confirms that analytical equations of state fail to predict the correct physical behavior, even if they include terms which allow for the correct estimation of thermodynamic properties.     

Study of copper complexes in saturated and unsaturated aqueous ammonium oxalate solutions containing Cu(II) impurity

The influence of Cu(II) impurity on chemical equilibria in unsaturated and saturated ammonium oxalate (AO) aqueous solutions was investigated as a function of concentration _ci$c_{\text{i}}$ of impurity. Using the computer programme “Hyss” the species present in the solutions were analysed. It was found that in the aqueous solutions of ammonium oxalate containing Cu(II) ions the following species are formed: Cu²⁺, Cu(OH)⁺, Cu(OH)₂, CuC₂O₄⁰ and Cu(C₂O₄)₂²⁻ in addition to C₂O₄²⁻, HC₂O₄⁻, H₂C₂O₄ and (NH₄)₂C₂O₄⁰ species, and their concentration depends on concentrations _ci$c_{\text{i}}$ of Cu(II) impurity and c of ammonium oxalate. The dependences of solution pH and of absorbance A   and the corresponding wavelength λ$\lambda$ for unsaturated aqueous solutions on ammonium oxalate concentration c   containing different concentrations _ci$c_{\text{i}}$ of Cu(II) ions showed three well-defined regions characterised by transition values of solution pH or solute concentration c. Speciation analysis revealed that Cu²⁺ and CuC₂O₄⁰, CuC₂O₄⁰ and Cu(C₂O₄₎₂²⁻, and Cu(C₂O₄)₂²⁻ complexes are predominantly present in the solute concentration intervals c≤0.01$c\le 0.01$ mol/dm³, 0.01 mol/dm³ <c<0.03$<c<0.03$ mol/dm³ and c≥0.03$c\ge 0.03$ mol/dm³, respectively. The concentration interval range 0.01 mol/dm³ <c<0.03$<c<0.03$ mol/dm³ corresponds to the pH interval where Cu(OH)₂ is precipitated. It was found that the solubility of ammonium oxalate at 30 °$°$C increases practically linearly with an increase in the concentration of Cu(II) impurity. Speciation analysis of saturated aqueous solutions of ammonium oxalate revealed that Cu(II) ions contained in AO saturated solutions exist mainly as Cu(C₂O₄)₂²⁻-type complexes, and the increase in the solubility of AO in the presence of Cu(II) impurity is essentially due to an increase in the ratio of the concentrations of CuC₂O₄⁰ and Cu(C₂O₄)₂²⁻ species.     

Vapor–liquid equilibria of copper using hybrid Monte Carlo Wang—Landau simulations

Because of the large temperatures and pressures involved, the experimental determination of the vapor–liquid equilibria and of the critical properties of metals is fraught with difficulties. We show in this work how we determine these properties for a metal using hybrid Monte Carlo Wang–Landau simulations in the isothermal–isobaric ensemble on the example of copper. We use a many-body potential, known as the quantum corrected Sutton–Chen embedded atom model, to model the interactions between Cu atoms. We obtain the following estimates for the critical temperature _Tc=5696±50$T_c=5696\pm 50$ K, the critical density _ρc=1.80±0.03${\rho }_c=1.80\pm 0.03$ g/cm³, and the critical pressure _Pc=1141±100$P_c=1141\pm 100$ bar. Our results lie within the range of values found in experiments for the critical temperature (between 5140 K and 7696 K), for the critical pressure (between 420 bar and 5829 bar) and for the critical density (1.9 g cm⁻³).     

Investigation of the adsorption mechanism of a peptide in reversed phase liquid chromatography,from pH controlled and uncontrolled solutions

The single-component equilibrium adsorption of the tripeptide Leucyl-Leucyl-Leucine (LLL) on a high-efficiency Jupiter Proteo column (C₁₂$C_{12}$) was investigated experimentally and modeled theoretically. The experimental equilibrium isotherms of LLL for adsorption on a C₁₂$C_{12}$ packing material from an aqueous solution of methanol (48%) and trifluoroacetic acid (0.1%) were measured by frontal analysis (FA). The FA measurements were done with two solutions, one in which the pH was controlled, the other in which it was not. Two solutions of LLL in the mobile phase were prepared (4.3 and 5.4 g/L) and their pH measured (2.94 and 2.88), respectively. The first solution was titrated with TFA to match the pH of the mobile phase (2.03), so its pH was controlled. The pH of the other solution was left uncontrolled. In both cases the isotherms could be modeled by a bi-Langmuir equation, a choice consistent with the bimodal affinity energy distribution (AED) obtained for LLL. The isotherm parameters derived from the inverse method (IM) of isotherm determination under controlled pH conditions (by fitting calculated profiles to experimental breakthrough profiles) are in a good agreement with those derived from the FA data. Under uncontrolled pH conditions, the application of IM suggests the coexistence of two different adsorption mechanisms. According to the isotherm parameters found by these three methods (FA, AED and IM), the C₁₂$C_{12}$-bonded silica can adsorb around 500 and 70 g/L of LLL under controlled and uncontrolled pH conditions, respectively. The adsorption of LLL on the C₁₂$C_{12}$ material strongly depends on the pH of the mobile phase and on the quantity of TFA added, which plays the role of an ion-pairing agent.     

Synthesis,photophysical and photochemical studies of water soluble cationic zinc phthalocyanine derivatives

Peripherally and non-peripherally 2-diethylaminoethanethiol tetra-substituted zinc phthalocyanine (5a and 6a) and their quaternized derivatives (5b and 6b) have been synthesized and characterized. The quaternized derivatives (5b and 6b) show excellent solubility in aqueous medium. The photophysical and photochemical properties of the 2-diethylaminoethanethiol appended zinc phthalocyanine in dimethylsulfoxide (DMSO) for the non-ionic (5a and 6a) and in both DMSO and aqueous medium (phosphate buffered saline solution PBS, pH 7.4) (in the presence and absence of cremophore EL (CEL)) for the quaternized (5b and 6b) derivatives were studied and compared with that of the peripherally octa-substituted derivatives (7a and 7b). The complexes have intense absorption in the visible/near-IR region though the quaternized forms (5b, 6b and 7b) were slightly blue shifted and highly aggregate in aqueous solution. The triplet state quantum yields (_ΦT${\Phi }_{\text{T}}$) and the triplet lifetimes (_τT${\tau }_{\text{T}}$) were found to be higher in DMSO (_ΦT${\Phi }_{\text{T}}$ values ranged from 0.57 to 0.75 while _τT${\tau }_{\text{T}}$ values ranged from 190 to 220 μs in DMSO for all complexes) compared to aqueous medium (_ΦT${\Phi }_{\text{T}}$ values ranged from 0.15 to 0.17 while _τT${\tau }_{\text{T}}$ values ranged from 20 to 70 μs in pH 7.4 buffer). Addition of cremophore EL in aqueous solution resulted in induced disaggregation leading to increased _ΦT${\Phi }_{\text{T}}$ and _τT${\tau }_{\text{T}}$.     

A ratiometric chemodosimeter for highly selective naked-eye and fluorogenic detection of cyanide

A simple indole-based chemosensor (1) with a very low molecular weight of 207 g mol⁻¹ has been synthesized for the highly reactive and selective detection of CN⁻ in aqueous media, even in the presence of other anions, such as F⁻, Cl⁻, Br⁻, AcO⁻, S₂⁻${{\mathrm{S}}_2}^{-}$, SCN⁻, NO₂⁻${{\text{NO}}_2}^{-}$, NO₃⁻${{\text{NO}}_3}^{-}$, CO₃⁻${{\text{CO}}_3}^{-}$, BzO⁻, H₂PO₄⁻${{\mathrm{H}}_2{\text{PO}}_4}^{-}$, and HSO₄⁻${{\text{HSO}}_4}^{-}$. The sensor achieves rapid detection of cyanide anion in 2 min, and the pseudo-first-order rate constant is estimated as 1.576 min⁻¹. The colorimetric and ratiometric fluorescent response of the sensor to CN⁻ is attributable to the addition of CN⁻ to the electron-deficient dicyanovinyl group of 1, which prevents intramolecular charge transfer. The sensing mechanism is supported by density functional theory and time-dependent density functional theory calculations. Moreover, sensor 1 exhibits both high accuracy in determining the concentration of CN⁻ in real samples and 1-based test strips can conveniently detect CN⁻ without any additional equipment. The detection limit of the sensor 1 (1.1 μM) for cyanide is lower than the maximum permissible level of CN⁻ (1.9 μM) in drinking water.     

Buoyancy density measurements for 1-alkyl-3-methylimidazolium based ionic liquids with tetrafluoroborate anion

Density measurements are reported performed on three 1-alkyl-3-methylimidazolium-based ([C_n-mim], n=2,4,6$n=2\text{,}4\text{,}6$) ionic liquids with tetrafluoroborate anion at atmospheric pressure at 15 temperatures from 281 to 353 K. The buoyancy method was employed, using the microbalance of the Krüss K100MK2 tensiometer. At each temperature from 33 to 55 individual buoyancy readings were taken in most cases. The density average values at particular temperatures are presented with estimated total standard uncertainty less than ±0.4$\pm 0.4$ kg m⁻³ (3.3 ×10⁻⁴?$\times 10^{-4}?$). An empirical density–temperature equations have been developed describing the temperature dependence of each ionic liquid density. The 58 new experimental data points on the density–temperature relation of the three ionic liquids of interest are means calculated from about 3000 individual density readings, which have been altogether taken in the present study.     

Investigation of interactions between some anionic dyes and cationic surfactants by conductometric method

The interactions of cationic surfactants with anionic dyes were studied by conductometric method. Benzyltrimethylammonium chloride (BTMACl), benzyltriethylammonium chloride (BTEACl) and benzyltributylammonium chloride (BTBACl) were used as cationic surfactants and indigo carmine (IC) and amaranth (Amr) were chosen as anionic dyes. The specific conductance of dye–surfactant mixtures was measured at 25, 35 and 45 °C. A decrease in measured specific conductance values of dye–surfactant mixture was caused by the formation of non-conducting or less-conducting dye–surfactant complex. The equilibrium constants, K₁, the standard free energy changes, ΔG₁°$\mathrm{\Delta }{G}_1°$, the standard enthalpy changes, ΔH₁°$\mathrm{\Delta }{H}_1°$ and the standard entropy changes, ΔS₁°$\mathrm{\Delta }{S}_1°$ for the first association step of dye–surfactant complex formation were calculated by a theoretical model. The results showed that the equilibrium constants and the negative standard free energy change values for all systems decreased as temperature increased. Also these values decreased for all systems studied with increasing alkyl chains of surfactants due to the steric effect. When the equilibrium constant values, K₁, for the first association step of IC–surfactant and Amr–surfactant systems with the same surfactant were compared, the values of K₁ for IC–surfactant system were higher than that of Amr–surfactant system.     

Spin-frustrated V3 and Cu3 nanomagnets with Dzialoshinsky–Moriya exchange. 2. Spin structure,spin chirality and tunneling gaps

The spin chirality and spin structure of the Cu₃ and V₃ nanomagnets with the Dzialoshinsky–Moriya (DM) exchange interaction are analyzed. The correlations between the vector κ$\kappa$ and the scalar χ$\chi$ chirality are obtained. The DM interaction forms the spin chirality which is equal to zero in the Heisenberg clusters. The dependences of the spin chirality on magnetic field and deformations are calculated. The cluster distortions reduce the spin chirality. The vector chirality is reduced partially and the scalar chirality vanishes in the transverse magnetic field. In the isosceles clusters, the DM exchange and distortions determine the sign and degree of the spin chirality κ$\kappa$. The correlations between the chirality parameters _κn${\kappa }_n$ and the intensities of the EPR and INS transitions are obtained. The vector chirality _κn${\kappa }_n$ describes the spin chirality of the Cu₃ and V₃ nanomagnets, the scalar chirality describes the pseudoorbital moment of the DM cluster. It is shown that in the consideration of the DM exchange, the spin states DM mixing and tunneling gaps at level crossing fields depend on the coordinate system of the DM model. The calculations in the DM exchange models in the right-handed and left-handed frame show opposite magnetic behavior at the level crossing field and allow to explain the opposite schemes of the tunneling gaps and levels crossing, which have been obtained in different treatments. The results of the DM model in the right-handed frame are consistent with the results of the group-theoretical analysis, whereas the results in the left-handed frame are inconsistent with that. The correlations between the spin chirality of the ground state and tunneling gaps at the level crossing field are obtained for the equilateral and isosceles nanoclusters.     

A new oxovanadium(IV)–cucurbit[6]uril complex: Properties and potential for confined heterogeneous catalytic oxidation reactions

This work presents a new oxovanadium(IV)–cucurbit[6]uril complex, which combines the catalytic properties of the metal ion with the size-excluding properties of the macrocycle cavity. In this coordination compound, the VO²⁺${\text{VO}}^{2+}$ ions are coordinated to the oxygen atoms located at the rim of the macrocycle in slightly distorted square-pyramidal configurations, which are in fact _C2v$C_{2v}$ symmetries. This combination results in a size-selective heterogeneous catalyst, which is able to oxidize linear alkanes like n-pentane at room temperature, but not styrene, cyclohexane or z-cyclooctene, which are too big to enter the cucurbit[6]uril cavity. The results presented here contribute to understanding the mechanism of alkane catalytic oxidation by oxovanadium(IV) complexes.