Crystallization and Glass Transition in Crude Oils and Their Fractions at High Pressure

Two sequential phase transitions, a wide-range crystallization and glass transition, were detected for crude oils and their fractions at high pressures by the transient hot-wire method and at atmospheric pressure by differential scanning calorimetry. The range of pressures investigated was up to 1.2 GPa in the temperature interval of 150–370 K. The presence of the glass transition in the oil and heavy fractions after the crystallization leads to a conclusion that crystallization does not lead to the formation of a continuous crystalline network, but rather to many separate crystalline regions. These regions are present in a liquid matrix, which after the sequential change of pressure/temperature undergoes the glass transition.