Prediction of Critical Temperature and Pressure of Hydrocarbons Using Simple Molecular Properties

Fitting their critical temperature (Tc) and critical pressure (Pc) as functions of molecular weight and carbon atomic fraction was done using 470 hydrocarbons (CnHm). Tc=a*(Cfrac)b*(MW)c and Pc=a*(Cfrac)1/3+b*(MW)1/3+c are the non-linear regressed parameters for the given model; Cfrac is the carbon atomic fraction in a molecule, which is equal to n/(n+m) for a hydrocarbon compound; and MW is the molecular weight, which is measured as (12n + m). The model was found to accurately predict both Tc and Pc, as shown by the curve-fitted Tc and Pc’s related percent relative error (PRE). Low MW compounds were found to have PRE values greater than 10% for expected Tc values out of the 470 hydrocarbons studied. Higher PRE values were observed for higher molecular weight compounds, with C26 and above, when it came to Pc prediction. Despite the fact that the proposed model does not strictly distinguish between isomers of the same molecular weight and chemical formula, the difference in Tc and Pc between isomers is not large enough for an easy, straightforward model to detect. Despite the fact that a more rigorous model would work harder to offset such small differences in Tc and Pc among isomers at the cost of model simplicity, a more rigorous model will work harder to offset such small differences in Tc and Pc among isomers.

Author (s) Details

Kamal I. Al-Malah
Department of Chemical Engineering, Higher colleges of Technology, Abu-Dhabi, UAE

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