A general equation for predicting the chemical exergy of gaseous hydrocarbons

The lack of chemical exergy data restricts the application of exergy analysis in chemical processes. Existing methods for predicting the chemical exergy of gaseous hydrocarbons either suffer from insufficient accuracy, or require complex microscopic parameters and involve tedious calculation processes. To address this issue, this study combines microscopic theoretical derivation for qualitative analysis with macroscopic data fitting to propose a general predictive equation for the chemical exergy of gaseous hydrocarbons. Taking gaseous hydrocarbon CxHy as the research object, based on the thermodynamic laws of its reaction with oxygen, the prediction of chemical exergy was decomposed into the separate predictions of ΔrSm⊖ and ΔrHm⊖. The correlation between Sm⊖ and molecular structure was derived via the Schrödinger equation of the three-dimensional potential box, the ΔrHm⊖ was calculated by combining chemical bond energies, and multiple linear regression analysis was introduced to avoid error accumulation. Eventually, a chemical exergy predictive equation that can be calculated only from the molecular structural formula was established. The equation was validated using 170 sets of gaseous hydrocarbon data, and the results showed that R2 = 0.9991, ABE = −0.017%, ARE = 0.66%. In addition, this semi-empirical equation can partially distinguish isomers with different macroscopic bond types and only requires easily obtainable parameters such as relative molecular mass and the number of chemical bonds. The predictive equation proposed in this study provides a new method for the rapid and accurate calculation of the chemical exergy of gaseous hydrocarbons, and can offer data support for exergy analysis and thermodynamic performance evaluation of chemical processes.