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In this work, we report the experimental values of the excess quantities H m E and V m E and the isobaric equilibrium data (VLE) at 101.32 kPa for the four mixtures of alkyl methanoates (methyl to butyl) and hexane. The results indicate that for these four mixtures (∂H m E /∂T) p > 0 and(∂V m E /∂T) p > 0. VLE data were found to be thermodynamically consistent with the Fredenslund method. All the binary mixtures presented here, except for the system (butyl methanoate + hexane), present a minimum-boiling temperature azeotrope with coordinates (x az , T az /K), (0.832, 302.62) for (methyl methanoate + hexane), (0.703, 323.32) for (ethyl methanoate + hexane), and (0.283, 339.10) for (propyl methanoate + hexane). Simultaneous correlations performed with the VLE data and excess enthalpies using a simple polynomial model, with temperature-dependent coefficients, produced acceptable estimations. Application of the UNIFAC model in the versions of Hansen et al. (Ind.

Electrochemical double-layer capacitors (EDLC), also known as supercapacitors or ultracapacitors, are devices in which diffusion phenomena play an important role. For this reason, their modeling using integer-order differential equations does not yield satisfactory results. The higher the temporal intervals are, the more problems and errors there will be when using integer-order differential equations. In this paper, a simple model of a real capacitor formed by an ideal capacitor and two parasitic resistors, one in series and the second in parallel, is used. The proposed model is based on the ideal capacitor, adding a fractional behavior to its capacity. The transfer function obtained is simple but contains elements in fractional derivatives, which makes its resolution in the time domain difficult. The temporal response has been obtained through the Mittag-Leffler equations being adapted to any EDLC input signal. Different charge and discharge signals have been tested on the EDLC allowing modeling of this device in the charge, rest, and discharge stages. The obtained parameters are few but identify with high precision the charge, rest, and discharge processes in these devices.

The application of the fractional calculus for modeling electrochemical double layer capacitors is a novel way to get simpler and precise models. On using the impedance spectroscopy method, experimental results for different values have been obtained. In this paper, several classical mathematical models are studied and a different method is introduced in order to get a model from electrochemical double layer capacitors. This method is based on distinct models with fractional elements, and some parameters of the models are fitted to the experimental data, with minimal error. Finally, a Havriliak–Negami function based model is proposed. It achieves excellent fitting to the whole frequency interval analyzed.