Liquid chromatographic studies for essential fatty acids on a commercial alkyl phenyl bonded silica column

Summary Retention studies on arachidonic acid 5, 8, 11, 14 all cis eicosatetraenoic acid, C20:46), eicosapentaenoic acid (5, 8, 11, 14, 17 all cis eicosapentaenoic acid, C2053) and docosahexaenoic acid (4, 7, 10, 13, 16, 19 all cis docosahexaenoic acid C2263) were performed on a commercial Bondapak free fatty acid analysis column. The ternary mobile phase consisting of acetonitrile, water and tetrahydrofuran was used in an isocratic mode with differential refractometry detection. Retention data were mesured at various flow rates with two different, mobile-phase compositions. Capacity factors and enthalpy of adsorption were calculated from the retention data. Finally the retention mechanism is explained.     

新型分子筛的生成焓计算

The enthalpies of formation of some compounds are not easy to be measured experimentally. This paper reports the calculated values of the heat of formation for some novel moleclar sieves by a method of consistant molecular mechanics force field. The enthalpies of formation of novel type molecular sieves: ZSM-48, ZSM-22, ZSM-23 and ZSM-18, have been calculated.     

Enthalpies of proton transfer of hydroxy amines and maltol in methanol-water mixtures by direct calorimetry

Enthalpies of proton transfer in methanol-water mixtures (0–90 wt. % methanol) have been measured by direct calorimetry for the bases 2-amino-2-methyl-1-propanol, 2-amino-2-methyl-1,3-propanediol and 2,2-bis(hydroxymethyl)-2,2,2-nitrilotriethanol at 25°C. Also reported are the data for 3-hydroxy-2-methyl-4-pyrone. The results are discussed in terms of an adaptation of classical electrostatic formula.     

Solvation enthalpies and heat capacities of n-alkanes in four polymer phases by capillary gas chromatography

Molar solvation enthalpy (deltasol H(o)298) and molar heat capacity changes (deltasol C(o)p) were determined by gas chromatography for the C6-C12 n-alkanes on four preferred stationary phases (100% polydimethyl siloxane, 50% diphenyl-50% dimethyl polysiloxane, 50% trifluoropropyl methylsiloxane, and polyethylene glycol) in commercial FSOT. Statistical evaluation indicated the temperature independence of deltasol C(o)p in the range 303-393 K. Deltasol H(o)298 depends linearly on the number of carbon atoms in the n-alkanes, but no linearity could be established for deltasol C(o)p of higher homologues on polar columns, which may be due to a more ordered state on the liquid phase. The homologues for which a linear temperature dependence exists demonstrated that deltasol C(o)p is related linearly to the van der Waals volume and the temperature derivative of the density of the stationary phase. The results are consistent with a simple physical explanation at the molecular level.     

An experimental investigation and modelling of the solubility, density and surface tension of 1,1,1,3,3-pentafluoropropane (R-245fa)/synthetic polyolester compressor oil solutions

This paper reports experimental data for the solubility, density and capillary constant for solutions of refrigerant 1,1,1,3,3-pentafluoropropane (R-245fa) with polyolester compressor oil Planetelf ACD 100FY over a wide range of temperatures and concentrations. The experimental data were obtained in the temperature range from 333 to 425 K and at pressures up to 33 bar using static methods. Based on information for the capillary constant, the surface tension of the solutions R-245fa/Planetelf ACD 100FY is determined. The enthalpy of liquid phase of the R-245fa/Planetelf ACD 100FY solutions is calculated. The analysis of the behaviour of the excess thermodynamic functions is carried out. Information about the changing concentration of refrigerant in the liquid phase of the refrigerant/oil solutions (ROS) and in the surface layer of the liquid phase of the ROS at increasing temperature is presented.     

Solubility and solution thermodynamics of 2,3,4,5-tetrabromothiophene in (ethanol + tetrahydrofuran) binary solvent mixtures

The solubility of 2,3,4,5-tetrabromothiophene in (ethanol + tetrahydrofuran) binary solvent mixtures was measured within the temperature range from (278.15 to 322.15) K. The solubility increases with the rise of temperature, while it decreases with increasing ethanol content at constant temperature. The experimental data were fitted using the two variants of the combined nearly ideal binary solvent/Redlich–Kister (CNIBS/R–K) equation and the Jouyban–Acree equation, respectively. All the three equations were proven to give good representations of the experimental values. Computational results showed that the variant two of CNIBS/R–K equation was superior to the other two equations. The thermodynamic properties of the solution process, including the Gibbs free energy, enthalpy, and entropy, were calculated by the van’t Hoff analysis. The values of both the enthalpy change and the standard molar Gibbs free energy change of solution were positive, which indicated that the process was endothermic.     

Heat flux calorimetry in intermetallic compound–H2(g) systems: heat measurements and modeling in the low pressures range

A heat conduction calorimeter has been used to determine enthalpies of solid–gas reactions in systems, such as intermetallic compounds–H₂(g). It is shown that the significance of the heat measurements must be carefully analyzed by controlling several parameters, which may influence the heat transfer conditions during the absorption and desorption reactions.

For this type of reaction, the measured heat flow is strongly dependent on the heat transfers through the gas phase in the low pressure range (Knudsen regime). It is demonstrated, experimentally and confirmed with simple models, that heat measurements can provide erroneous enthalpies due to our inability to account for the unavoidable modifications of the heat losses in the transition region. Experiments were carried out on the ZrNi–H₂ system.     

Thermodynamic modeling of CO2 and H2S solubilities in aqueous DIPA solution, aqueous sulfolane-DIPA solution, and aqueous sulfolane-MDEA solution with electrolyte NRTL model

A thermodynamic model developed for CO₂ and H₂S solubilities in aqueous MDEA solution is extended to cover CO₂ and H₂S solubilities in aqueous DIPA solution, aqueous sulfolane-DIPA solution, and aqueous sulfolane-MDEA solution. The model makes use of the 2009 version of the electrolyte NRTL model for liquid phase activity coefficient calculations and the PC-SAFT equation of state for vapor phase fugacity coefficient calculations. The NRTL binary parameters for the molecule-electrolyte pairs required for the H₂O-DIPA-CO₂ ternary and the H₂O-sulfolane-DIPA-CO₂ quaternary are regressed against the solubility data of CO₂ in aqueous DIPA solution and aqueous sulfolane-DIPA solution, respectively. The NRTL binary parameters for the molecule-electrolyte pairs required for the H₂O-DIPA-H₂S ternary and the H₂O-sulfolane-DIPA-H₂S quaternary are regressed against the solubility data of H₂S in aqueous DIPA solution and aqueous sulfolane-DIPA solution simultaneously. The NRTL binary parameters for the electrolyte-electrolyte pairs involved in the H₂O-DIPA-CO₂-H₂S quaternary are regressed against the solubility data of the acid gas mixtures in aqueous DIPA solution. Likewise, the NRTL binary parameters for the sulfolane-electrolyte pairs required for the H₂O-sulfolane-MDEA-CO₂ quaternary and the H₂O-sulfolane-MDEA-H₂S quaternary are regressed against the solubility data of the acid gases in aqueous sulfolane-MDEA solution. The predicted enthalpies of acid gas absorption are compared favorably with the literature data available for the H₂O-DIPA-CO₂ system, the H₂O-DIPA-H₂S system, and the H₂O-sulfolane-MDEA-CO₂ system.     

Solution thermodynamics of valnemulin hydrogen fumarate in different pure solvents

Solubility of valnemulin hydrogen fumarate in five pure solvents was determined within temperature range of (278.15 to 323.15) K by a gravimetric method. The results show that the solubility of valnemulin hydrogen fumarate in tested pure solvents increases with the increasing temperature. The solubility values were correlated by the Wilson model, NRTL model and UNIQUAC model. The UNIQUAC volume parameter, area parameter, and Wilson liquid molar volume parameter of valnemulin hydrogen fumarate were estimated by the group contribution method. It was found that the correlated results are in good agreement with the experimental results. Furthermore, the mixing thermodynamic properties of valnemulin hydrogen fumarate in solutions, including the mixing Gibbs energy, the mixing enthalpy and entropy, were determined by using the Wilson model and the experimental solubility results.     

On thermodynamic potentials in linear thermoelasticity

The four thermodynamic potentials, the internal energy u=u(ε_ij,s), the Helmholtz free energy f=f(ε_ij,T), the Gibbs energy g=g(σ_ij,T) and the enthalpy h=h(σ_ij,s) are derived, independently of each other, by using the Duhamel–Neumann extension of Hooke's law and an assumed linear dependence of the specific heat on temperature. A systematic procedure is then presented to express all thermodynamic potentials in terms of four possible pairs of independent state variables. This procedure circumvents a tedious transition from one potential to another, based on the formal change of variables, and inversions of the stress–strain and entropy–temperature relations. The general results are applied to uniaxial loading paths under isothermal, adiabatic, constant stress, and constant strain conditions. An interplay of adiabatic and isothermal elastic constants in the expressions for exchanged heat along certain thermodynamic paths is indicated.