Uncertainty analysis applied to thermodynamic models and process design – 1. Pure components

A simple model is proposed to estimate the critical temperature and critical pressure of hydrocarbons in the range of C5–C36 with parameters determined using weighted linear least squares and weighted non-linear least squares taking into consideration the experimental uncertainty in the data as well as in the correlating parameters. The correlation model was parameterized using the normal boiling point and specific gravity at 60 °F. The uncertainties of parameters and associated covariance matrix necessary for error propagation calculations are reported and a comprehensive evaluation of acentric factors uncertainties based on the experimental vapor pressures was conducted. In addition, a simple sensitivity analysis designed to determine how the uncertainty of properties used for calculations based on the equations of state propagate thorough the model and affect the final results. The normal boiling points of two pure components, n-hexane and n-dodecane were calculated using an equation of state and the estimated error in the calculations is presented together with estimated uncertainties for the prototype pressure–temperature envelopes for two binary mixtures of methane–n-hexane and methane–n-dodecane.

► Estimation methods for hydrocarbon critical temperature, pressure and acentric factor using evaluated physical property data with uncertainties.
► Re-derivation of a simple cubic equation of state (Peng–Robinson) using uncertainties on vapor pressure, acentric factor, critical temperature and critical pressure.
► Development of database of physical properties of interest for the natural gas industry taking into account recommended uncertainties.
► Calculation of pressure–temperature envelopes for prototype gas mixtures taking into account physical property uncertainty.