Fractionation and Characterization of Mexican Crude Oils

Crude oils are intricate mixtures of hydrocarbon compounds; different physicochemical characterizations must be performed to get to know their complexity. A series of four typical Mexican Crude Oils (MCOs) with densities ranging from 30 to 9 degrees API was characterized through different physical, spectroscopic, and thermal methods. The four types of MCOs were also fractionated into saturates, aromatics, resins, and asphaltenes (SARA) through high-performance liquid chromatography (HPLC). The fractions obtained were subsequently characterized through different physicochemical techniques such as Fourier transform infrared (FTIR) spectroscopy, vapor pressure osmometry (VPO), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). VPO led to determining the average molar mass of each MCO fraction to be compared to those of the different Mexican petroleums. It was clearly observed that the molar mass of the resin and asphaltene fractions increases when crude oil gets heavier than saturate and aromatic components. The thermal stability of the series of MCOs was evaluated by TGA observing that the decomposition temperature increases with the average molecular mass of the crude oil. The original heavy crude oil and its fractions were studied through differential scanning calorimetry (DSC); the study of heat effects associated to phase transitions was monitored for each fraction, resulting into the Wax dissolution temperature (WDT) and the Wax precipitation temperature (WPT) of the four MCOs investigated. It was established that the different molecular features of crude oils may be clearly correlated to their average molar mass.