Prophecy of Common Boiling Points of Hydrocarbons Using Simple Molecular Properties

S. M. Subhani; B. Srinivas

Abstract: Four hundred and seventy-six hydrocarbons (CnHm) were utilized to fit their normal boiling point temperatures (NBPT) as a function of molecular weight and carbon atomic fraction. The proposed model is of the following form: NBPT=a*(Cfrac) ^b* (MW) ^ c where a; b; and 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 calculated as 12* n+1*m. The model was found to predict NBPT with an adequate accuracy; manifested via the associated percent relative error (PRE) of the curve-fitted NBPT. Out of the examined 476 hydrocarbons; methane; ethylene; and acetylene were found to have PRE values higher than 10%. If the confidence interval is further reduced to PRE value less than 5%; then 43 compounds will be excluded; and then NBPT for the other 433 compounds could be well predicted by the proposed model. Although the proposed model does not differentiate among isomers having the same molecular weight and chemical formula; nevertheless; the difference in NBPT among isomers is not really significant to be picked up by a simple; straight forward model. A more rigorous model will work hard to offset such small differences in NBPT among isomers; nevertheless; at the expense of model simplicity.

Keywords: common boiling point; hydrocarbons; carbon atoms; model; molecular formula