Thermodynamic analysis of oligomeric blends by applying the Kirkwood-Buff theory of solutions

The accurate prediction of the thermodynamic properties of oligomeric blends and, in general, binary liquid mixtures from atomistic simulations is a challenging task. In this work we develop a methodology for the full thermodynamic analysis of oligomeric blends and the extraction of the Flory-Huggins interaction parameter from the Gibbs energy of mixing, combining Flory-Huggins thermodynamics with Kirkwood-Buff theory of solutions. We perform a series of Molecular Dynamics (MD) simulations of 2-methylpentane/n-heptane mixtures, at various mole fractions. Firstly we validate the forcefield we apply in our MD simulations, comparing the density and excess volume we obtain against the corresponding experimental estimates found in the literature. Then we calculate the Kirkwood-Buff integrals in the isothermal-isobaric (NpT) ensemble, applying the particle fluctuations method, and we extract the component activity coefficients, the excess Gibbs energy, the excess enthalpy, and the excess entropy of mixing as functions of the mole fraction. Finally we calculate the Flory-Huggins interaction parameter χ by interpreting the Gibbs energy of mixing in the framework of Flory-Huggins theory, and explore its dependence on composition. All results are compared against experimental measurements in order to evaluate our methodology. Agreement is found to be very good.

Prediction of Excess Enthalpy Using Volume-Translated Peng–Robinson Equation of State

In this work volume-translated Peng–Robinson group contribution equation of state was used to calculate excess enthalpies. Four model systems were selected with the purpose to compare experimental and predicted enthalpy values at different temperatures. After the calculations were performed in Matlab software, results were verified with free software tool of Dortmunder Datenbank (DDB). In a next step, the mixing process and interaction forces were described on the basis of the sign and course of enthalpy values. The endothermic behavior of three systems could be well predicted, while for the most polar system, predictions were less precise. Furthermore, the discrepancy between experimental data from the literature and predicted values was discussed to evaluate the accuracy of the selected model. Lowest mean deviations (<75 J/mol and <15% at all temperatures) could be stated for alkane/benzene mixtures, while highest deviations could be again observed for the most polar mixture. Although the magnitude of deviations was in agreement with the literature, it could be shown that the selected temperature is of major importance for the quality of predictions. Furthermore, a review of different literature values for the n-hexane/benzene system could reveal that the reliability of experimental data has to be carefully checked.

Theoretical analysis of superadiabatic combustion for non-stationary filtration combustion by excess enthalpy function

The superadiabatic combustion for non-stationary filtration combustion is analytically studied. The non-dimensional excess enthalpy function ( H ) equation is theoretically derived based on a one-dimensional, two-temperature model. In contrast to the H equation for the stationary filtration combustion, a new term, which takes into account the effect of non-dimensional combustion wave speed, is included in the H equation for transient filtration combustion. The governing equations with boundary conditions are solved by commercial software Fluent. The predictions show that the maximum non-dimensional gas and solid temperatures in the flame zone are greater than 3 for equivalence ratio of 0.15. An examination of the four source terms in the H equation indicates that the thermal conductivity ratio ( Γ s ) between the solid and gas phases is the dominant one among the four terms and basically determines H distribution. For lean premixed combustion in porous media, the superadiabatic combustion effect is more pronounced for the lower Γ s .

Theoretical and Economic Evaluation of Low-Cost Deep Eutectic Solvents for Effective Biogas Upgrading to Bio-Methane

This paper presents the theoretical screening of 23 low-cost deep eutectic solvents (DESs) as absorbents for effective removal of the main impurities from biogas streams using a conductor-like screening model for real solvents (COSMO-RS). Based on thermodynamic parameters, i.e., the activity coefficient, excess enthalpy, and Henry’s constant, two DESs composed of choline chloride: urea in a 1:2 molar ratio (ChCl:U 1:2), and choline chloride: oxalic acid in a 1:2 molar ratio (ChCl:OA 1:2) were selected as the most effective absorbents. The σ-profile and σ-potential were used in order to explain the mechanism of the absorptive removal of CO2, H2S, and siloxanes from a biogas stream. In addition, an economic analysis was prepared to demonstrate the competitiveness of new DESs in the sorbents market. The unit cost of 1 m3 of pure bio-methane was estimated to be in the range of 0.35–0.37 EUR, which is comparable to currently used technologies.

Complete power cycle exhaust heat regeneration and second law logic

It is demonstrated, given a sufficiently large positive excess enthalpy of solution reaction between a molecular solid solute and a low boiling point solvent, that the differential in excess enthalpies of solution between the reaction in the solvent's dense liquid and expanded supercritical states will enable the solution, when used as the working fluid in a closed condensing power cycle, to attain complete exhaust heat regeneration. Xenon is used as the solvent to demonstrate the potential. Errors in 18th century logic that helped establish the second law are explained.