Heat Capacity Of Hydrocarbons Research Articles

Predicting entropy and heat capacity of hydrocarbons using machine learning

Chemical substances are essential in all aspects of human life, and understanding their properties is essential for developing chemical systems. The properties of chemical species can be accurately obtained by experiments or ab initio computational calculations; however, these are time-consuming and costly. In this work, machine learning models (ML) for estimating entropy, S, and constant pressure heat capacity, Cp, at 298.15 K, are developed for alkanes, alkenes, and alkynes. The training data for entropy and heat capacity are collected from the literature. Molecular descriptors generated using alvaDesc software are used as input features for the ML models. Support vector regression (SVR), v-support vector regression (v-SVR), and random forest regression (RFR) algorithms were trained with K-fold cross-validation on two levels. The first level assessed the models' performance, and the second level generated the final models. Between the three ML models chosen, SVR shows better performance on the test dataset. The SVR model was then compared against traditional Benson's group additivity to illustrate the advantages of using the ML model. Finally, a sensitivity analysis is performed to find the most critical descriptors in the property estimations.

Application of the One-Third rule in hydrocarbon and crude oil systems

Thermodynamic and transport properties of hydrocarbon systems are determined, in part, by the van der Waals attractions between molecules. These van der Waals attractions (or London dispersion interactions) are related to the electronic polarizability and molar refractivity of the molecules. Molar refractivity is related to refractive index and molar volume through the Lorentz–Lorenz equation. In this work we present a method that relates the refractive index of a hydrocarbon substance with its mass density. This is based on the observation that the molar refractivity is approximately proportional to the molecular weight of a hydrocarbon molecule. The proportionality constant is approximately equal to one-third for hydrocarbons and crude oil systems. Although both the refractive index and the mass density are functions of temperature, it has been found that the proportionality constant of this model is nearly invariable over a wide range of pressures and temperatures. Therefore, given the temperature dependence of one of the variables, it is possible, by applying the “One-Third” rule, to estimate the temperature dependence of the other variable. This correlation has been validated with over 200 crude oil samples, in a wide range of densities (10–55°API) and temperatures (10–70 °C), and the results obtained are remarkable. The applications of the One-Third rule in the calculation of properties such as solubility parameter, viscosity, thermal conductivity, diffusivity and heat capacity of hydrocarbons and crude oil systems, as a function of the mass density, are presented and discussed. This approach also provides an alternative to calculate the refractive index based on densities obtained from an equation of state. The method presented in this work is promising in offering a new, simple and reliable method for estimating hydrocarbon and crude oil properties as a function of their mass density.

First Principles Based Group Additive Values for the Gas Phase Standard Entropy and Heat Capacity of Hydrocarbons and Hydrocarbon Radicals

In this work a complete and consistent set of 95 Benson group additive values (GAVs) for standard entropies S(o) and heat capacities C(p)(o) of hydrocarbons and hydrocarbon radicals is presented. These GAVs include 46 groups, among which 25 radical groups, which, to the best of our knowledge, have not been reported before. The GAVs have been determined from a set of B3LYP/6-311G(d,p) ideal gas statistical thermodynamics values for 265 species, consistently with previously reported GAVs for standard enthalpies of formation. One-dimensional hindered rotor corrections for all internal rotations are included. The computational methodology has been compared to experimental entropies (298 K) for 39 species, with a mean absolute deviation (MAD) between experiment and calculation of 1.2 J mol(-1) K(-1), and to 46 experimental heat capacities (298 K) with a resulting MAD = 1.8 J mol(-1) K(-1). The constructed database allowed evaluation of corrections on S(o) and C(p)(o) for non-nearest-neighbor effects, which have not been determined previously. The group additive model predicts the S(o) and C(p)(o) within approximately 5 J mol(-1) K(-1) of the ab initio values for 11 of the 14 molecules of the test set, corresponding to an acceptable maximal deviation of a factor of 1.6 on the equilibrium coefficient. The obtained GAVs can be applied for the prediction of S(o) and C(p)(o) for a wide range of hydrocarbons and hydrocarbon radicals. The constructed database also allowed determination of a large set of hydrogen bond increments, which can be useful for the prediction of radical thermochemistry.

New Generalized Equations for the Calculation of Isobaric Heat Capacity of Hydrocarbons at the Saturation Curve

The experimental data obtained by the authors on the isobaric heat capacity of n-alkanes on the saturation curve in the liquid phase and the literature data on C"pof hydrocarbons representing different homologous series are used to analyze the known formulas recommended for predictions of C"p. It is demonstrated that, in order to increase the accuracy of calculations, one needs, first of all, to refine the description of heat capacity in the vicinity of the temperature of the triple point. The universal behavior of the temperature dependence of C"pin the vicinity of the triple point temperature is revealed. Based on these findings, new generalized equations are developed, which are recommended for the calculation of C"pof hydrocarbons in the temperature range from the triple point to critical.

Heat capacity of petroleum fractions

Heat capacity is an important thermodynamic parameter that is needed in calculating phase equilibria, particularly for petroleum disperse systems in predicting the low-temperature behavior of petroleum products. For hydrocarbons and other organic compounds in the ideal-gas state, heat capacities can be determined by means of many different formulas and tables. A formula is given in for calculating the heat capacity of petroleum fractions in the gas phase on the basis of data from structural-group analysis. The calculation of heat capacities of petroleum fractions in the liquid phase is much more complicated. A number of correlations with density and average boiling point have been proposed. However, none of these differ greatly in accuracy of calculation from the well-known formula of Cragoe. The error may be as much as 20%, which is not acceptable in thermodynamic calculations of equilibria in petroleum systems in the liquid phase. The authors have correlated the rather scanty literature data on the liquid-phase heat capacity of hydrocarbons, nonhydrocarbon components, and fractions of crude oil, as well as some data on the partial heat capacities of groups of organic compounds.

Heat capacity of hydrocarbons in the normal liquid range

Heat capacity of hydrocarbons in the normal liquid range