Characterization of asphaltenes from hydrotreated products by SEC, LDMS, LAMDI, NMR, and XRD

Maya crude was hydrotreated at different reaction conditions in a pilot plant. Asphaltenes were precipitated from hydrotreated products with n-heptane as a solvent in a pressurized system with heating and stirring. Structural characterization studies have been carried out on asphaltenes from Maya crude. Molecular-weight distributions were obtained by size-exclusion chromatography (SEC) using tetrahydrofuran (THF) and 1-methyl-2-pyrrolidinone (NMP) as solvents. Nonfragmenting techniques, such as laser desorption mass spectrometry (LDMS) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), were also used for determining molecular-weight distributions. Crystallite parameters of asphaltenes were studied by X-ray diffraction (XRD) after they were precipitated. Average structural parameters were calculated from nuclear magnetic resonance (NMR) spectra. The influence of reaction conditions are studied in terms of structural changes in asphaltenes.