Molar Gibbs Free Energy Research Articles

Effect of the particle size on the reactivity of MgO-Al2O3 hydrating mixtures: A long-term kinetic investigation of hydrotalcite synthesis

Hydrotalcite-like compounds (HTlc) are commonly known anionic clay that may potentially be used as hydraulic binder component for refractory materials, ion exchangers, catalyst or carrier of bioactive molecules. According to current state of knowledge LDH (Layered Double Hydroxides) can be synthesized using various methods including mechanochemical synthesis, hydrothermal precipitation, sol–gel syntheses and coprecipitation method. Research on the synthesis of hydrotalcite in the mixture of oxide powders of Al2O3 and MgO cured under specific conditions is particularly important in case of the determination of the relationship between the type (susceptibility to hydration, grain size and specific surface area) of initial powders and reaction kinetics. As a result, the hydration of an equimolar mixture of magnesium and alumina oxides nano- or micro-powders has been proven to be an effective low temperature method of synthesis well crystallized MgAl LDH with highly ordered structures. This investigations clearly show that the kinetics of hydration is influenced only by properties of aluminium oxide as initial powder. The synthesis of Mg6Al2CO3(OH)16∙4H2O as a result of hydration is associated with composite matrix formation which firstly consist of partly reacted initial powders bonded by hydration products. The synthesis of Mg6Al2CO3(OH)16∙4H2O was discussed in terms of molar Gibbs free energy change of reactions within the MgO-Al2O3-CO2-H2O system. The calculated formation Gibbs energy was negative, when Mg(OH)2 was formed as an intermediate product. The standard Gibbs free energies of hydrotalcite formation was estimated based on the simple mechanical mixture model that treats Mg6Al2CO3(OH)16∙4H2O as mixtures of simple oxides. Thermodynamic calculations were performed assuming an equilibrium state between aqueous solutions and corresponding precipitates after synthesis.

The density, viscosity, speed of sound, excess properties of binary mixtures of linear polydimethylsiloxane and various alkanes at temperatures in the range (288.15–328.15) K

This article describes the binary system composed of linear polydimethylsiloxane (PDMS) and diesel fuel main components n-decane, n-dodecane, n-tridecane and n-tetradecane at atmospheric pressure, and the density, viscosity and speed of sound were measured at 288.15 K, 298.15 K, 308.15 K, 318.15 K and 328.15 K, respectively. Their excess molar volume (VmE), excess viscosity (ηE), excess molar Gibbs free energy (ΔGEm), molar isobaric thermal expansion (EP,m) and excess molar isentropic compressibility (κEs,m) were calculated. The influence of the intermolecular force, steric hindrance, molecular stacking and other factors on the excessive properties of the binary system solution was discussed. The results indicate that with an increase in carbon chain length, the excess molar volume, excess viscosity, molar isobaric thermal expansion and excess molar isentropic compressibility increased and excess molar Gibbs free energy decreased, which probably ascribe to the increase in steric effect and the stronger interactions between homo-molecular than those of hetero-molecular interactions between PDMS and long-chain alkane molecules.

Estimation of the polarity and applications of the molar surface Gibbs free energy of alanine ionic liquids [Cnmim][Ala] (n = 2, 4)

Estimation of the polarity and applications of the molar surface Gibbs free energy of alanine ionic liquids [Cnmim][Ala] (n = 2, 4)

Viscosity, density, and derived thermodynamic properties of aqueous 2-(ethylamino)ethanol (EAE), aqueous aminoethylethanolamine (AEEA), and its mixture for post-combustion CO2 capture

In the present study, viscosity and density of aqueous 2-(ethylamino)ethanol (EAE), aqueous aminoethylethanolamine (AEEA), and aqueous EAE + AEEA blend were measured in the temperature range of 293.15 K to 333.15 K at atmospheric pressure. Concentration of aqueous amines was used upto 30 wt% that is usually applicable for CO2 absorption from flue gases in post combustion CO2 capture process. EAE/AEEA weight ratio was 9/1, 8/2, and 7/3 in the aqueous EAE + AEEA blend. Viscosity of all mixtures increased by increasing amine concentration and decreased by increasing temperature of samples. Experimental viscosity data were correlated to newly proposed models and average absolute deviation (AAD) % was 1.515, 2.027, and 2.889 for viscosity of EAE + H2O, AEEA + H2O, and EAE + AEEA + H2O, respectively. Density of aqueous EAE and aqueous EAE + AEEA blend (at fixed EAE/AEEA weight ratio) decreased by increasing amount of amine in the mixture but aqueous AEEA showed increased density by increasing concentration of AEEA. Excess molar volume (VE) calculated for all aqueous mixtures and VE of aqueous EAE and aqueous AEEA was fitted in Redlich-Kister equation. Density of aqueous EAE + AEEA blend was correlated to a new empirical model and AAD % for this model was 0.018. Isobaric thermal expansion coefficient (αp) of binary and ternary solutions was calculated from density versus temperature data. Activation molar enthalpy (∆H∗), activation molar entropy (∆S∗), and activation molar Gibbs free energy (∆G∗) at 298.15 K for aqueous EAE, aqueous AEEA, and aqueous EAE + AEEA blend were calculated using viscosity and density data on the basis of Eyring theory of liquid viscosity.

A new activity model for Fe\u2013Mg\u2013Al biotites: I\u2014Derivation and calibration of mixing parameters

A new activity model for Fe–Mg–Al biotites is formulated, which extends that of Mg–Al biotites (Dachs and Benisek, Contrib Mineral Petrol 174:76, 2019) to the K2O–FeO–MgO–Al2O3–SiO2–H2O (KFMASH) system. It has the two composition variables XMg = Mg/(Mg + Fe2+) and octahedral Al, and Fe–Mg and Mg–Al ordering variables resulting in five linearly independent endmembers: annite (Ann, K[Fe]M1[Fe]2M2[Al0.5Si0.5]2T1[Si]2T2O10(OH)2, phlogopite (Phl, K[Mg]M1[Mg]2M2[Al0.5Si0.5]2T1[Si]2T2O10(OH)2, ordered Fe–Mg biotite (Obi, K[Fe]M1[Mg]2M2[Al0.5Si0.5]2T1[Si]2T2O10(OH)2, ordered eastonite (Eas, K[Al]M1[Mg]2M2[Al]2T1[Si]2T2O10(OH)2, and disordered eastonite (Easd, K[Al1/3Mg2/3]M1[Al1/3Mg2/3]2M2[Al]2T1[Si]2T2O10(OH)2. The methods applied to parameterize the mixing properties of the model were: calorimetry, analysis of existing phase-equilibrium data, line-broadening in powder absorption infrared (IR) spectra, and density functional theory (DFT) calculations. For the calorimetric study, various biotite compositions along the annite–phlogopite, annite–siderophyllite (Sid, K[Al]M1[Fe]2M2[Al]2T1[Si]2T2O10(OH)2), and annite–eastonite joins were synthesized hydrothermally at 700 °C, 4 kbar and logfO2 of around − 20.2, close to the redox conditions of the wüstite–magnetite oxygen buffer at that P–T conditions. The samples were characterised by X-ray powder diffraction (XRPD), energy-dispersive scanning electron microprobe analysis, powder absorption IR spectroscopy, and optical microscopy. The samples were studied further using relaxation calorimetry to measure their heat capacities (Cp) at temperatures from 2 to 300 K. The measured Cp/T was then integrated to get the calorimetric (vibrational) entropies of the samples at 298.15 K. These show linear behaviour when plotted as a function of composition for all three binaries. Excess entropies of mixing are thus zero for the important biotite joins. Excess volumes of mixing are also zero within error for the three binaries Phl-Ann, Ann-Sid, and Ann-Eas. KFMASH biotite, therefore, has excess enthalpies which are independent of pressure and temperature (WGij = WHij). A least-squares procedure was applied in the thermodynamic analysis of published experimental data on the Fe–Mg exchange between biotite and olivine, combined with phase-equilibrium data for phlogopite + quartz stability and experimental data for the Al-saturation level of biotite in the assemblage biotite–sillimanite–sanidine–quartz–H2O to constrain enthalpic mixing parameters and to derive enthalpy of formation values for biotite endmembers. For Fe–Mg mixing in biotite, the most important binary, this gave best-fit asymmetric Margules enthalpy parameters of WHAnnPhl = 14.3 ± 3.4 kJ/mol and WHPhlAnn = −8.8 ± 8.0 kJ/mol (3-cation basis). The resulting asymmetric molar excess Gibbs free energy (Gex) departs only slightly from ideality and is negative at Fe-rich and positive at Mg-rich compositions. Near-ideal activity–composition relationships are thus indicated for the Ann–Phl binary. The presently used low value of − 2 kJ/mol for the enthalpy change of the reaction 2/3 Phl + 1/3 Ann = Obi is generally confirmed by DFT calculations that gave − 2 ± 3 kJ/mol for this ∆HFe–Mg order, indicating that Fe–Mg ordering in biotite is weak. The large enthalpy change of ∆HMg-Al disorder = 34.5 kJ/mol for the disordering of Mg and Al on the M sites in Eas (Dachs and Benisek 2019) is reconfirmed by additional DFT calculations. In combination with WHPhlEas = 10 kJ/mol, which is the preferred value of this study describing mixing along the Phl–Eas join, Mg–Al disordering over the M sites of biotite is predicted to be only significant at high temperatures > 1000 °C. In contrast, it plays no role in metamorphic P–T settings.

Experimental measurement – correlation of solubility and dissolution thermodynamics study of itraconazole in pure monosolvents at various temperatures

The information about the solubility and thermodynamic properties of solution is important for pharmaceutically important processes, formulation development, and further theoretical studies. In the present study, the solid–liquid equilibrium (solubility) for itraconazole (ITC) was determined experimentally in 14 monosolvents at temperatures between 293.15 K and 318.15 K under pressure of 0.1 MPa. The mole fraction solubilities were found to increase with increasing temperatures and followed inverse trend with the polarity of selected solvents. Besides, KAT-LSER analysis was performed to study the effect of solvent. The results revealed that the solute–solvent interaction (43.94%) was much higher than that of solvent–solvent interaction (16.59%). Thermodynamic based models like van’t Hoff equation, modified Apelblat equation, Buchowski–Ksiazaczak equation, and polynomial empirical equation were applied to fit and correlate the experimental solubilities. Overall relative average deviation and overall root-mean square deviation () were observed to be minimum with the empirical polynomial equation and attained the values of 0.0033 and 0.0047, respectively. Furthermore, theoretical ideal solubilities, activity coefficients, and thermodynamic properties of dissolution including molar enthalpy, molar entropy, molar Gibbs free energy, and excess enthalpy were estimated. Ideal solubilities were projected considerably higher than experimental solubilities at each studied temperature. Thermodynamic properties of dissolution indicated that the dissolution was not a spontaneous process; observed to be endothermic ( and enthalpy driven Such solid–liquid equilibrium data of ITC will be of immense help in process and formulation development in pharmaceutical sciences.

New insights into the role of calcium in the bioreduction of uranium(VI) under varying pH conditions

The effect of calcium in the uranium-contaminated groundwater on U(VI)aq bioreduction remains uncertain. Some studies indicated that the presence of calcium may inhibit the bioreduction. However, our calculations show the negative standard molar Gibbs free energy of reduction. The bioreduction of the ternary uranyl-carbonate-calcium complexes seems thermodynamically favorable at specific pH. Sorption and reduction experiments were conducted to gain new insights of calcium into the bioreduction. The results show that the complexes were greatly reduced by Shewanella putrefaciens in the slightly acidic pH ~6.0 and alkaline pH ~7.9 solutions with the relatively high CaCl2 (1.0–6.0 mmol/L) although the reduction was difficult at the nearly neutral pH ~6.9. At pH ~6.9, the removal percentage of U(VI)aq decreased from 97.0% to 24.4% with increasing CaCl2 from 0 to 6.0 mmol/L, in contrast to the increasing percentage from 50.9% to 89.7% at pH ~7.9. The obvious removal of U(VI)aq was ascribed to the bioreduction instead of the biosorption, as evidenced by XPS, HRTEM and UV–vis spectra. The calculations such as Eho(CaUO2(CO3)32−/UO2)=−0.5801V and Eho(Ca2UO2(CO3)3(aq)/UO2)=−0.6797V partially accounted for the reduction mechanisms. Accordingly, the U(VI)aq bioreduction is a promising method to remediate the groundwater even rich in calcium and carbonate.

The Effects of Diffusional Couplings on Compositional Trajectories and Interfacial Free Energies During Phase Separation in a Quaternary Ni-Al-Cr-Re Model Superalloy

The temporal evolution of ordered γ´(L12)-precipitates and the compositional trajectories during phase-separation of the γ(face-centered-cubic (f.c.c.))- and γ′(L12)-phases are studied in a Ni-0.10Al-0.085Cr-0.02Re (mole-fraction) superalloy, utilizing atom-probe tomography, transmission electron microscopy, and the Philippe-Voorhees (PV) coarsening model. As the γ′(L12)-precipitates grow, the excesses of Ni, Cr and Re, and depletion of Al in the γ(f.c.c.)-matrix develop as a result of diffusional fluxes crossing γ(f.c.c.)/γ′(L12) heterophase interfaces. The coupling effects on diffusional fluxes was introduced (PV coarsening model) in terms of the diffusion tensor, D, and the second-derivative tensor of the molar Gibbs free energies, G, obtained employing Thermo-Calc and DICTRA calculations. The Gibbs interfacial free energies, σγ/γ', are (16.9±3.4) mJ/m2 with all terms in D and G, which changes to (46.3±5.1) mJ/m2, (92.3±7.9) mJ/m2, and (-18.5±2.6) mJ/m2 without including the off-diagonal terms in D, G, and both D and G, respectively. The experimental APT compositional trajectories are displayed and compared with the PV model in a partial quaternary phase-diagram, employing a tetrahedron. The compositional trajectories measured by APT exhibit curvilinear behavior in the nucleation and growth regimes, t < 16 h, which become vectors, moving simultaneously toward the γ(f.c.c.) and γ′(L12) conjugate solvus-surfaces, for the quasi-stationary coarsening regime, t ≥ 16 h. The compositional trajectories for t ≥ 16 h are compared to the PV model with and without the off-diagonal terms in D and G. The directions including the off-diagonal terms in D and G tensors are consistent with the APT experimental data.

Real-Time Monitoring of the Thermal Effect for the Redox Flow Battery by an Infrared Thermal Imaging Technology

In this study, a new monitoring method was developed, titled infrared thermal imaging technology, which can effectively evaluate the thermal effect of the charge-discharge test in the vanadium/iodine redox flow battery (V/I RFB). The results show that the all-vanadium redox flow battery (all-V RFB) has a greater molar reaction Gibbs free energy change than that of the V/I RFB, representing a large thermal effect of the all-V RFB than the V/I RFB. The charge-discharge parameters, flow rate and current density, are important factors for inducing the thermal effect, because of the concentration polarization and the ohmic resistor. The new membrane (HS-SO3H) shows a high ion exchange capacity and a good ions crossover inhibitory for the V/I RFB system, and has a high coulomb efficiency that reaches 96%. The voltage efficiency was enhanced from 61% to 86% using the C-TiO2-Pd composite electrode as a cathode with the serpentine-type flow field for the V/I RFB. By adopting the high-resolution images of an infrared thermal imaging technology with the function of the temperature profile data, it is useful to evaluate the key components’ performance of the V/I RFB, and is a favorable candidate in the developing of the redox flow battery system.

Comparative thermodynamic analysis of CO2 based dimethyl carbonate synthesis routes

AbstractThe chemical equilibrium analysis of various possible reactions involved in the five CO2‐based routes for the synthesis of dimethyl carbonate (DMC), a green chemical reagent, was performed in the present study. The variation of the molar Gibbs free energy change with temperature for the major reactions of DMC synthesis in all five routes was studied in the specified temperature range of 298.15 K‐453.15 K and at both 1 bar and 28 bar pressures (1 bar = 105 Pa) to observe the thermodynamic favourability of all routes. To observe the temperature effect, the molar heat capacities for various compounds were estimated in terms of temperature. A second‐order group additivity method called the Ruzicka‐Domalski method was used to estimate these heat capacity values. The major reactions of DMC synthesis in urea methanolysis, EC transesterification, PC transesterification, and direct CO2 synthesis routes were compared by investigating the effect of temperature (in the range of 298.15 K‐453.15 K) on the chemical equilibrium constants and the equilibrium conversions of methanol at a constant pressure of 28 bar. The one‐pot propylene oxide (PO) synthesis route was observed to be better among all the five CO2 based routes when it was compared with respect to values of the chemical equilibrium constant and equilibrium conversion of methanol at standard conditions. The reliability of the EC transesterification route was found better among all the routes at initial conditions (T = 298.15 K; P = 28 bar). While the urea methanolysis route was found as least favourable at initial conditions.

Influence of Proton Activity Gaps between Electrodes on Open-Circuit Potential of H2/H2 and H2/Air Cells

Polymer -electrolyte-fuel-cell open-circuit voltages (OCVs) are exactly defined by equation (1), where cathode and anode proton activities [(aH+)cathode and (aH+)anode, respectively] usually are identical, so the third term in the right-hand side of equation (2) is ignored.OCV=E0+RT/2F*ln(a1/2 O2*(a2 H+)cathode/aH2O)-RT/2F*ln((a2 H+)anode/aH2) (1)=E0+RT/2F*ln(a1/2 O2*aH2/aH2O)+RT/2F*ln((a2 H+)cathode/(a2 H+)anode) (2)Water vapor pressure is a colligative property that fundamentally correlates to electrolyte concentrations in aqueous solutions. Proton activity is a function of acid concentration, such as pH, when electrolytes are acids. In polymer-electrolyte membranes, water vapor pressure and acid concentration are understood as relative humidity (RH) and water uptake (λ), respectively, where λ represents number of water molecules per sulfonic acid molecule. Several investigations have reported the relationship between RH and λ, meaning that proton activities and associated water uptakes are intimately related to RH.In actual fuel cell operation, cathode RH is determined by ambient-atmosphere and/or humidifier RH(s), and anode RH depends on hydrogen-circulator RH. Therefore, RH is not always identical at both electrodes, and the difference between electrode RHs is considerable during dry operation of polymer electrolyte fuel cells. Therefore, the third term in the right-hand side of equation (2) may be significant for dry operation.We measured OCVs when hydrogen was supplied to both electrodes at 80°C. One electrode (A) was fixed at 30% RH, while RH at the other electrode (B) was varied (0, 5, 10, 20, and 30%). Measured OCVs varied from 0 to 75 mV. For fuel cell tests, electrode A was supplied with hydrogen at 30% RH; electrode B, oxygen at 0, 5, 10, 20, and 30% RH. OCVs deviated from that measured when RH at electrode B was 30%, increasing from 0 to 60 mV with decreasing RH at electrode B. Results are also shown in Figure 1.Proton activities of both electrodes were thermodynamically calculated. The Gibbs–Duhem relation was applied to obtain molar Gibbs free energies of water and sulfonic acid, and proton activity coefficient was calculated using the Gibbs free energy of sulfonic acid and the relationship between RH and λ1–4, assuming that protons and sulfonic anions show identical ionic-activity coefficients. OCVs were estimated using the third term in the right-hand side of equation (2). Results are shown in Figure 1.Fuel-cell current–voltage performance was poor when RHs at the anode and cathode were 30 and 20%, respectively. To determine kinetic current, we measured the oxygen-reduction reaction (ORR) using a rotating-disk electrode (RDE) in concentrated-acid aqueous solutions, which modeled catalyst-layer ionomers. Kinetic currents decreased with acid concentrations.References T. A. Zawodzinski, Jr., C. Derouin, S. Radzinski, R. J. Sherman, V. T. Smith, T. E. Springer and S. Gottesfeld , J. Electrochem. Soc., 140,1041 (1993)P. K. Das and A. Z. Weber, Proceedings of the ASME 2013 11th Fuel Cell Science, Engineering and Technology Conference, Fuel Cell 18010 (2013)V. A. Sethuraman, J. W. Weidner, A. T. Haug, S. Motupally,b and L. V. Protsailo, J. Electrochem. Soc., 155, B50 (2008)A. Kusoglu and A. Z. Weber, Chem. Rev., 117, 987 (2017) Figure 1

Thermodynamic and transport properties of ternary mixture (ethyl oleate + n-hexadecane +1-butanol) and its binary constituents (ethyl oleate +1-butanol and ethyl oleate + n-hexadecane) at different temperatures and atmospheric pressure

Densities, viscosities, speeds of sound and refractive indices have been measured for the ternary system ethyl oleate + n-hexadecane +1-butanol, and for the corresponding binaries ethyl oleate +1-butanol and ethyl oleate + n-hexadecane, in the temperature range from T = (293.15 to 343.15) K and at atmospheric pressure. Experimental data were employed to calculate some derived thermodynamic parameters, i.e. excess molar volumes (VE), viscosity deviations (Δη) and deviations in refractive index (ΔnD). Additionally, molar excess Gibbs free energies of activation of viscous flow (ΔG⁎E) and deviations in isentropic compressibility (Δκs) were calculated. A graphical representation of excess molar volumes and refractive indices show positive deviation from ideal behavior for both binary systems whereas deviation in viscosity shows negative nature for the ethyl oleate + n-hexadecane system and an inversion sign for ethyl oleate +1-butanol binary system. A negative deviation in isentropic compressibility was confirmed for the systems ethyl oleate +1-butanol while positive deviation was observed in ethyl oleate + n-hexadecane system. It can be concluded that dispersive forces predominate between the components in binary systems and the observed behavior seems to suggest that the properties obtained for the ternary mixture are dominated by the binary effects. The viscosities of the binary systems were modeled by UNIFAC-VISCO, ASOG-VISCO, Teja-Rice and McAllister models. The results showed that McAllister's multibody model is suitable to describe viscosities for binary systems with maximum percentage deviations less than 0.5%.

A calorimetric and thermodynamic investigation of Cs6[(UO2)2(MoO4)3(MoO5)] and calculated phase behaviour in the system (Cs2MoO4 + UO3 + H2O)

A calorimetric investigation of the thermodynamic properties of cesium uranyl molybdate, Cs6[(UO22MoO43MoO5), was undertaken. The investigated phase was synthesized by high-temperature solid-state reaction from a mixture of cesium nitrate, molybdenum (VI) oxide and gamma uranium (VI) oxide. The synthetic product was characterized by X-ray powder diffraction and X-ray fluorescence and they show a successful synthesis giving better than 98% of the intended phase. Low-temperature molar heat capacity, Cp,mo, was measured using adiabatic calorimetry between T = 12.3 and 324.3 K. The data were well behaved and do not show any indication of a phase transition or a Cp,mo anomaly. Using the Cp,mo(T) data, the standard molar third-law entropy at T = 298.15 K, Smo, is calculated as 987 ± 4 J∙K−1∙mol−1. The molar enthalpy of formation of Cs6[UO22MoO43MoO5) was determined using HF-acid solution calorimetry giving: ΔfHmo(T=298.15K,Cs6[UO22MoO43MoO5),cr)=-7873±12kJ∙mol-1. These new calorimetric results, together with thermodynamic data from the literature, are used to calculate the molar Gibbs free energy of formation, ΔfGmo, giving: ΔfGmo(T=298.15K,Cs6[UO22MoO43MoO5),cr)=-7309±13kJ∙mol-1. Best-fit and smoothed Cp,moT values for Cs6[UO22MoO43MoO5) between 0 K and T = 324 K are presented in table form, along with values for Smo and the functions [HmoT-Hmo0] and [ΦmoT-Φmo0]. The amounts and behaviour of a number of different crystalline phases in the system “Cs6[UO22MoO43MoO5)" in aqueous solution as a function of pH are calculated using a Gibbs-free-energy-minimization approach. The pH-crystalline phase stability fields in the Cs2MoO4+UO3+H2O system, with and without CO2, are also calculated.

The experimental physicochemical properties, 1H NMR, and COSMO-RS model calculations for the binary system containing water and 1-ethylimidazole

In order to explore the properties and molecular interactions in the binary systems of 1-alkylimidazole with molecular solvents, the system of x 1-ethylimidazole (herein referred to as 1-Eim) + (1-x) water, in the temperature range (288.15–328.15) K, the density ρ, sound velocity u, viscosity η, refractive index nD, pH and conductivity κ, and the 1H NMR δH, were measured at atmospheric pressure; the excess molar enthalpy HmE, the excess molar Gibbs free energy GmE, and the excess molar entropy SmE were predicted from the COSMO-RS model.The experimental and predicted properties indicate that the H-bonded interactions are the predominant interactions over the whole composition range. 1-Eim protons share more electron densities than water protons via the H-bonds, which are stronger between dissimilar molecules than between similar ones. The stable H-bonded structure of water molecules breaks when x is about 0.1, while the stable H-bonded structure of 1-Eim molecules forms when x is about 0.9. Temperature affects the H-bonded interactions more in the case of dissimilar molecules than similar molecules, especially in the water-rich region. The real mixing process is an enthalpy-driving spontaneous process with the liquid structure more ordered. A lower temperature more greatly benefits spontaneous mixing.

Development of Abraham model correlations for short-chain glycol-grafted imidazolium and pyridinium ionic liquids from inverse gas-chromatographic measurements

Infinite dilution activity coefficients and gas-to-liquid partition coefficients are herein reported for more than 45 organic solutes of varying polarity and hydrogen-bonding character dissolved within the ether-grafted ionic liquids 1-ethyl-3-(2-methoxyethyl)imidazolium bis(trifluoromethylsulfonyl)imide and N-(2-methoxyethyl)pyridinium bis(trifluoromethylsulfonyl)imide. Experimental values were determined in 10 K intervals from 323.15 to 373.15 K using the method of inverse gas chromatography. Measured infinite dilution activity coefficients were then used to determine the partial molar excess Gibbs free energies, enthalpies, and entropies associated with the dissolution of these model solutes into these two short-chain glycol-grafted ionic liquids. Finally, based on the measured infinite dilution activity coefficient data, Abraham model correlations have been established for solute transfer into these ionic liquids, including the calculation of cation-specific equation coefficients. The derived Abraham model correlations were found to back-calculate the observed partition coefficients to within 0.09 to 0.13 log units.

Predictions of thermodynamic properties for hydrogen sulfide

Equilibrium conditions of many chemical and physical processes can be determined from minimization of the Gibbs free energy of the system. Suitable closed-form representations of the Gibbs free energy and entropy of hydrogen sulfide remain unsolved in the communality of science and engineering. Here we report two suitable closed-form representations for the Gibbs free energy and entropy of hydrogen sulfide, which involve merely six molecular constants of the hydrogen sulfide molecule, whereas the conventional computation models require a great many experimental spectroscopy data. In the temperature range from 300 to 6000 K, the average relative deviations of the predicted molar Gibbs free energy and entropy values from the National Institute of Standards and Technology database are 0.185% and 0.191%, respectively. Our study presents a novel pathway of predictions of thermodynamic properties for highly toxic hydrogen sulfide.

Intermolecular Interactions in 1,6-Diaminohexane + Water Mixtures at 293.15 to 333.15 K

The density (ρ) and viscosity (η) of the mixtures of 1,6-diaminohexane (DAH) + water binary system were determined over the whole composition range at p = 101 kPa from 293.15 to 333.15 K. The measured density and viscosity values decrease with the increase of temperature. In addition, the viscosity of the binary system shows a maximum value along with the molar fraction of DAH. According to the experimental data, excess molar volume (VE), apparent molar volume Vϕ, viscosity deviation (Δη), and excess Gibbs free energy (ΔG*E) of the activation of viscous flow were obtained and correlated by the well-known Redlich–Kister type polynomial equation by using the least square method and regression parameters were calculated. It was found that all of the VE values are negative while $$\Delta \eta $$ and ΔG*E values are positive. The intermolecular interactions between DAH and water were characterized by the averaged non-covalent interaction index (aNCI) and thermal fluctuation index (TFI) method. The obtained results proved that N···H–O and O···H–N hydrogen bonds which lightly affected by thermal motion, and some of the flexible van der Waals interactions are the reason for the specific variation of the viscosity and excess properties of the studied binary system.

Utilization of Biomass Fly Ash for Improving Quality of Organic Dye-Contaminated Water.

Development of innovative methodologies to convert biomass ash into useful materials is essential to sustain the growing use of biomass for energy production. Herein, a simple chemical modification approach is employed to functionalize biomass fly ash (BFA) with 3-aminopropyltriethoxy silane (APTES) to develop an inexpensive and efficient adsorbent for water remediation. The amine-functionalized BFA (BFA–APTES) was fully characterized by employing a range of characterization techniques. Adsorption behavior of BFA–APTES was evaluated against two anionic dyes, namely, alizarin red S (ARS) and bromothymol blue (BTB). In the course of experimental data analysis, the computation tools of data fitting for linear and nonlinear form of Langmuir, Freundlich, and the modified Langmuir–Freundlich adsorption isotherms were used with the aid of Matlab R2019b. In order to highlight the misuse of linearization of adsorption models, the sum of the squares of residues (SSE) values obtained from nonlinear models are compared with R2 values obtained from the linear regression. The accuracy of the data fitting was checked by the use of SSE as an error function instead of the coefficient of determination, R2. The dye adsorption capacity of BFA–APTES was also compared with the nonfunctionalized BFA. The maximum adsorption capacities of BFA–APTES for ARS and BTB dye molecules were calculated to be around 13.42 and 15.44 mg/g, respectively. This value is approximately 2–3 times higher than the pristine BFA. A reasonable agreement between the calculated and experimental values of qe obtained from the nonlinear form of kinetic models verified the importance of using equations in their original form. The experimentally calculated thermodynamic parameters including molar standard Gibbs free energy (ΔadGm0) and molar standard enthalpy change (ΔadHm0) reflected that the process of adsorption of dye molecules on the BFA–APTES adsorbent was spontaneous and exothermic in nature. Moreover, the used BFA–APTES adsorbent could be regenerated and reused for several cycles with significant dye adsorption capacity. The remediation capability of the BFA–APTES adsorbent against ARS dye was also demonstrated by packing a small column filled with the BFA–APTES adsorbent and passing a solution of ARS through it. Overall, we provide a simple and scalable route to convert BFA into an efficient adsorbent for water remediation applications.

Theoretical Study of Radical-Molecule Reactions with Negative Activation Energies in Combustion: Hydroxyl Radical Addition to Alkenes.

Many of the radical–molecule reactions are nonelementary reactions with negative activation energies, which usually proceed through two steps. They exist extensively in the atmospheric chemistry and hydrocarbon fuel combustion, so they are extensively studied both theoretically and experimentally. At the same time, various models, such as a two transition state model, a steady-state model, an equilibrium-state model, and a direct elementary dynamics model are proposed to get the kinetic parameters for the overall reaction. In this paper, a conversion temperature TC1 is defined as the temperature at which the standard molar Gibbs free energy change of the formation of the reaction complex is equal to zero, and it is found that when T ≫ TC1, the direct elementary dynamics model with an inclusion of the tunneling correction of the second step reaction is applicable to calculate the overall reaction rate constants for this kind of reaction system. The reaction class of hydroxyl radical addition to alkenes is chosen as the objects of this study, five reactions are chosen as the representative for the reaction class, and their single-point energies are calculated using the method of CCSD(T)/CBS, and it is shown that the highest conversion temperature for the five reactions is 139.89 K, far below the usual initial low-temperature (550 K) oxidation chemistry of hydrocarbon fuels; therefore, the steady-state approximation method is applicable. All geometry optimizations are performed at the BH&HLYP/6-311+G(d,p) level, and the result shows that the geometric parameters in the reaction centers are conserved; hence, the isodesmic reaction method is applicable to this reaction class. To validate the accuracy of this scheme, a comparison of electronic energy difference at the BH&HLYP/6-311+G(d,p) level and the corrected electronic energy difference with the electronic energy difference at the CCSD(T)/CBS level is performed for the five representative reactions, and it is shown that the maximum absolute deviation of electronic energy difference can be reduced from 2.54 kcal·mol–1 before correction to 0.58 kcal·mol–1 after correction, indicating that the isodesmic reaction method is applicable for the accurate calculation of the kinetic parameters for large-size molecular systems with a negative activation energy reaction. The overall rate constants for 44 reactions of the reaction class of hydroxyl radical addition to alkenes are calculated using the transition-state theory in combination with the isodesmic correction scheme, and high-pressure limit rate rules for the reaction class are developed. In addition, the thermodynamic parameter is calculated and the results indicate that our dynamics model is applicable for our studied reaction class. A chemical kinetic modeling and sensitivity analysis using the calculated kinetic data is performed for the combustion of ethene, and the results indicate the studied reaction is important for the low-to-medium temperature combustion modeling of ethene.

Experimental Measurement and Correlation of two α-Amino Acids Solubility in Aqueous Salts Solutions from 298.15 to 323.15 K

By the gravimetric method at atmospheric pressure, the solubility of two α-amino acids was resolved over temperatures from (293.15 to 323.15) K. The α-amino acids studied were L-arginine and L-histidine. Results showed a salting-out effect on the solubility of the tested amino compounds. It is obvious that there was an increase in the solubility, in aqueous chloride solutions, with the increasing temperature. Results were translated regarding the salt hydration shells and the ability of the solute to form hydrogen-bond with water. The solubility data was precisely associated with a semiempirical equation. The standard molar Gibbs free energies of transfer of selected α-amino compounds (ΔtrGo) from pure water to aqueous solutions of the chloride salts have been calculated from the solubility data. The decrease in solubility is correlated to the positive (ΔtrGo) value which is most part of the enthalpic origin.