Diffusion coefficients of methane in liquid hydrocarbons at high pressure and temperature

The accurate prediction of diffusion coefficients of methane in liquid hydrocarbons is one of the key parameters for improving the prediction of compositional oil reservoir simulators, for designing surface facilities, and for high pressure gas/liquid mass transfer operations. In this investigation, a precision high pressure and temperature diffusion cell apparatus has been used to measure diffusion coefficients of methane in dodecane and in a typical Iranian crude oil at high pressures and temperatures. The diffusion cell is modelled using a finite-domain moving boundary method. Extensive experimental results are presented at high pressures and temperatures, especially for regions where published data were insufficient. The mechanism of mass transfer during the incubation period is analysed by solving the equation of continuity for the diffusion cell numerically and considering that the diffusion coefficient is changing with time and concentration. The effects of pressure, liquid phase viscosity and operating temperature on the diffusion coefficient of the solute gas in the solution are discussed. The results indicate that uncertainties which generally exist in the physical and thermodynamic properties of the crude oils may have a significant effect on the diffusion coefficient of a solute gas in a complex mixture like crude oil.