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.     

Modelling LLE and VLE of methanol + n-alkane series using GC-PC-SAFT with a group contribution kij

The fluid phase diagrams (LLE and VLE) of methanol + n-alkane mixtures series (from C₄ up to C₁₆) were modelled using GC-PC-SAFT EOS (Tamouza et al., Fluid Phase Equilibria 222–223 (2004) 67–76) combined with a recent method for computing k_ij based on the London theory (NguyenHuynh et al., Industrial & Engineering Chemistry Research 47 (2008) 8847–8858). This latter method requires pure compound adjustable parameters: pseudo-ionization energies J that may be calculated by group contribution in the case of n-alkane series. J_alkane is calculated from group parameters JCH₃$J_{\text{C}{\text{H}}_3}$ and JCH₂$J_{\text{C}{\text{H}}_2}$.     

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%.     

Surface tension of dimethyl ether + propane from 243 to 333 K

The surface tension of the binary refrigerant mixture dimethyl ether (RE170)(1) + propane (R290)(2) at three mass fraction of w₁=0.3007,0.4975 ??and ??0.6949$w_1=\mathrm{0.3007,0.4975}\text{\hspace{0.17em}??}\text{and}\text{\hspace{0.17em}??}0.6949$ was measured in the temperature range from 243 to 333 K with a differential capillary rise method. The uncertainties of the measurement of the temperature and the surface tension were estimated to be within ±10 mK and ±0.2 mN m⁻¹, respectively. A correlation for the surface tension of the binary refrigerant mixture RE170 + R290 was developed as a function of the composition.     

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.     

Solid–liquid metastable equilibria in the quaternary system Li2SO4 + MgSO4 + Na2SO4 + H2O at T = 263.15 K

Solubility in the liquid–solid metastable system Li₂SO₄ + MgSO₄ + Na₂SO₄ + H₂O at T = 263.15 K was studied using the isothermal evaporation method. Based on experimental data, dry-salt phase and water-phase diagrams of the system were plotted. The dry-salt phase diagram of the system includes one three-salt co-saturation point, three metastable solubility isotherm curves, and three crystallization regions corresponding to lithium sulphate monohydrate (Li₂SO₄·H₂O), epsomite (MgSO₄·7H₂O), and mirabilite (Na₂SO₄·10H₂O). Neither a solid solution nor double salts were found. Based on the extended Harvie–Weare (HW) model and its temperature-dependent equation, the values of the Pitzer parameters β⁽⁰⁾, β⁽¹⁾, β⁽²⁾, and C^Φ for Li₂SO₄, MgSO₄, and Na₂SO₄, the mixed ion-interaction parameters θ_Li,Na, θ_Li,Mg, θ_Na,Mg, ΨLi,Na,SO₄${\Psi }_{\text{Li,Na,S}{\text{O}}_4}$, ΨLi,Mg,SO₄${\Psi }_{\text{Li,Mg,S}{\text{O}}_4}$, and ΨNa,Mg,SO₄${\Psi }_{\text{Na,Mg,S}{\text{O}}_4}$, and the Debye–Hückel parameter A^Φ in the quaternary system at 263.15 K were obtained. The solubility of the quaternary system Li₂SO₄ + MgSO₄ + Na₂SO₄ + H₂O at T = 263.15 K was also calculated. A comparison between the calculated and experimental results shows that the predicted solubility agrees well with experimental data.     

A pyrazole-based orthogonal ferromagnetically coupled [2 × 2] homoleptic square Cu4 grid: Magnetostructural correlations

The synthesis and structure of a pyrazole-based orthogonal ferromagnetically coupled tetracopper(II) 2 × 2 homoleptic grid complex [Cu₄(PzOAPyz)₄(ClO₄)₂](ClO₄)₂ · 6H₂O (1), formed by the reaction between the ditopic ligand PzOAPyz and Cu(ClO₄)₂ · 6H₂O, are described. The ligand contains terminal pyrazole and pyrazine residues bound to a central flexible diazine subunit (N–N) as well as one potentially bridging alkoxo group. The two adjacent metal centers are linked by an alkoxo oxygen forming essentially a square Cu₄(μ-O₄) cluster. In the Cu₄(μ-O₄) core, out of the four copper centers, two copper centers are penta-coordinated and the remaining two are hexa-coordinated. In each case of hexa-coordination, the sixth position is occupied by one of the oxygen atoms of a coordinated perchlorate ion. Complex 1 has been characterized structurally and magnetically. Although the large Cu–O–Cu bridge angles (137–138°) and short Cu–Cu distances (3.964–3.970 Å) are suitable for the transmission of the expected antiferromagnetic coupling, the square-based Cu₄(μ-O₄) cluster exhibits an intramolecular ferromagnetic exchange (J = 7.47 cm⁻¹) between the metal centers with an S = 2 magnetic ground state associated with the quasi orthogonal arrangement of the magnetic orbitals (d_x2-y2${\text{d}}_{x^2-y^2}$). The exchange pathway parameters have been evaluated from density functional calculations.     

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.     

Thermal treatment of poly(ethylene oxide)-segmented copolyimide based membranes: An effective way to improve the gas separation properties

Copolyimide membranes with different poly(ethylene oxide) (PEO) content (from 28 to 68 wt percent, wt.%) have been thermally treated at different temperatures (from 200 to 300 °C) to evaluate the effect of the thermal protocol on the gas transport properties to O₂, N₂, CO₂ and CH₄. The permeability coefficients (P) for all gases increased after the thermal treatment of the membranes and were related to the PEO content, being this enhancement higher for membranes with lower PEO content. Thermal treatment at 300 °C of the membranes with 28 and 43 wt.% of PEO, yielded more productive materials for CO₂/N₂ separation since the permeability coefficients for CO₂ (PCO₂$P_{\text{C}{\text{O}}_2}$) increased 9.8 and 3.2 times, respectively, while the selectivity just suffered a small drop (less than 1.3 times in both cases). Overall, the membrane with 43 wt.% of PEO exhibited the best performance, with a PCO₂$P_{\text{C}{\text{O}}_2}$ of 78 Barrer and a CO₂/N₂ selectivity of 52. For CO₂/CH₄ separation, an increase on selectivity of 1.8 times was obtained in the copolyimide with 43 wt.% of PEO, reaching the selectivity a value of 18. This enhancement of productivity has been associated to an improvement of phase segregation.     

Application of the generalised SAFT-VR approach for long-ranged square-well potentials to model the phase behaviour of real fluids

In a recent generalisation of the SAFT-VR equation of state the method was extended so as to deal with short as well as long square-well ranges, namely, 1.2≤λ≤3.0$1.2\le \lambda \le 3.0$ [B.H. Patel, H. Docherty, S. Varga, A. Galindo, G.C. Maitland., Mol. Phys. 103 (1) (2005) 129–139]. Here, we confirm the accuracy of the approach by comparison with numerical calculations of the first perturbation term and with vapour pressure and coexistence density computer simulation data. The approach is then used to model a number of real substances, from non-polar to strongly polar. We discuss in particular the values of the square-well potential model found. For this purpose we construct a relative least squares objective function and the percentage absolute average deviation (%AAD) to determine the intermolecular model parameters (m  , λ$\lambda$, σ$\sigma$, ?/_kB$?/k_B$, _?hb/_kB${?}_{hb}/k_B$ and _rc$r_c$) by comparison to experimental vapour-pressure and saturated liquid density data. In order to ensure in each case that the global minimum is identified, the dimensionality of the problem is reduced by discretising the parameter-space [G.N.I. Clark, A.J. Haslam, A. Galindo, G. Jackson., Mol. Phys. 104 (22–24) (2006) 3561–3581]. Applying this method to the study of argon, n  -alkanes, nitrogen, benzene, carbon dioxide, carbon monoxide, the refrigerant R1270, hydrogen chloride hydrogen bromide and water we find that the optimal models always present square-well ranges λ<1.8$\lambda <1.8$, meaning that an upper bound value of λ=1.8$\lambda =1.8$ set in the original approach is sufficient to model real fluids; even polar ones. This finding is explained in terms of the averaged dipole–dipole interaction and of the long-range mean-field limit of the square-well potential.     

Molecular motility and affinity of expanded carbon dioxide + ketone systems analyzed by molecular dynamics simulations

We perform a molecular dynamics simulation for CO₂ + ketone mixtures to study the molecular motility and elucidate how CO₂ molecules are dissolved in a mixture. The self-diffusion coefficients increase with increasing CO₂ mole fraction (xCO₂)$(x_{\text{C}{\text{O}}_2})$ and decreased with increasing molecular weight. These results mean that the mobility of molecules depends on the molecular size. To study molecular aggregation around CO₂ molecules, radial distribution functions (RDFs) and the distance from neighboring molecules to CO₂ molecules were calculated. The RDFs indicate that the CO₂ molecule exists near the carbonyl oxygen atom. Because of the distance of the neighboring molecule from the CO₂ molecule, the CO₂ molecule is less likely to exist around a branched alkyl ketone than a normal alkyl ketone.     

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).