Comparison of Different Methods on Determining Wax Appearance Temperature of Crude Oils

Wax appearance temperature (WAT) is an important parameter for waxy crude oils. Viscometry, differential scanning calorimetry (DSC), and polarization thermomicroscopy are main methods used to determine the WAT. The dynamic viscosity in the Newtonian temperature range of the crude oils generally obeys a simple Arrhenius type of temperature dependence. Activation energies of viscous flow will increase after wax precipitation from oils, and the WAT can be evaluated from the increment of the activation energies. The results of WAT of crude oils determined by viscometry, DSC, thermomicroscopy, and from the increment of the activation energies are compared and discussed. It is concluded that viscometry should not be used to determine the WAT of crude which has characteristic of slow precipitation of wax or low wax content. DSC has the strengths of simpleness, less sample amount and good repeatability. WAT from ther-momicroscopy depends on factors such as thickness of the sample and light intensity.WAT evaluated from the increment of the activation energies is simple and has good repeatability. Good agreement is obtained among the DSC, thermomicroscopy and from the increment of the activation energies.