Abstract: Crystallization of wax from diesel fuels and the interaction of pour point depressant with wax were studied by solid-liquid equilibrium method. The solid phase and liquid phase of partially frozen diesel fuels were separated at the cold filter plugging point by isothermal filtration using a cold filter plugging point tester and were analyzed by gas chromatography. The amount and compositions of both phases were deduced from mass balance after correction by a distribution factor Z (the mass fraction of liquid in solid deposit). Four kinds of fuels were used to test including model fuel, model fuel with depressant, base diesel fuel and diesel fuel with depressant, and their crystallization rate and the content of n-paraffin in wax at cold filter plugging point were compared. Results showed that using said separation technique and calculation method to study the crystallization behavior of diesel fuels at cold filter plugging point was feasible.

Key words: phase equilibrium, crystallization, diesel fuel