Determination of the Asphaltene Precipitation Envelope and Bubble Point Pressure for a Mexican Crude Oil by Scanning Transitiometry

In this work, the phase transitions (liquid-solid, liquid-vapor, and solid-liquid) for a Mexican crude oil were measured with the transitiometric technique over wide temperature and pressure ranges to determine its asphaltene envelope. A titration of this crude oil with n-heptane based on ASTM D3279 and ASTM D4124 standard methods was carried out to make sure that the phase transition corresponds to the asphaltene precipitation. As a result of the experimental work performed here, it is shown that scanning transitiometry is a suitable experimental technique that can be used to determine the asphaltene precipitation onset and the bubble point pressures for a variety of crude oils, where the density of the crude oil is not a limiting factor. The thermodynamic modeling of the asphaltene precipitation envelope was successfully performed using the statistical associating fluid theory for potentials of variable range (SAFT-VR) equation of state (EoS) in the framework of the McMillan-Mayer theory, as reported by Buenrostro-Gonzalez et al. (AIChE J. 2004, 50, 2552-2570). A satisfactory representation of the bubble pressures line was obtained using the Peng-Robinson (PR) EoS.