Concentration-dependent molecular diffusion coefficient of dimethyl ether in bitumen

A new experimental apparatus was developed to conduct concentration-dependent diffusivity measurements for systems of gaseous dimethyl ether (DME) in heavy oil. The designed, fabricated and validated experimental apparatus is capable of significantly reducing the duration of the concentration-dependent diffusivity study through: a) fulfilling the sensitivity requirement necessary for the diffusivity measurement under constant pressure conditions, b) conducting two simultaneous concentration-dependent experiments, and c) utilizing a rocking/mixing arrangement to accelerate the establishment of the initial concentration within the two distinct measurement units. The setup is then used to study the concentration dependency of the molecular diffusion of DME in Athabasca bitumen through building on the data sets reported previously. The concentration-dependent diffusivity measurements are conducted at temperatures ranging from 70 to 110 degrees C and pressures up to 2.76 MPa. The reported values are in the range of - 0.17-3.72 x 10(-9) m(2)/s. The measured diffusivity values are also analyzed against their liquid mixture properties (e.g., solubility and viscosity) showing that in certain cases, the diffusivity can be doubled when concentration dependency is concerned. The results indicate that the diffusional mass transfer is, to a large extent, influenced by the concentration of the liquid mixture, and therefore, cannot be treated as a constant value when systems of hydrocarbon solvents and heavy oils are studied. The developed methodology and the reported data have applications in design and evaluation of solvent injection processes for heavy oil recovery.