Particle size, solvent, oxygen, temperature and pressure effects on the contents of insoluble fractions from solid vacuum residua

n-Heptane insoluble contents were determined for an extraheavy-oil vacuum r esidue, one petroleum and one coal pitch as a function of particle size. Th is variable was found to affect the yields of insoluble material, aspect wh ich was also observed during extractions carried out with aromatic and halo genated solvents. The precision of results was observed to be independent o n the operators. A study was carried out to determine the effect of sample drying time on fraction yields. It was found that maltene fractions were st rongly dependent on this variable, whereas asphaltene fractions were totall y independent. Predissolution in aromatic solvents proved worthless from the repeatability point of view. However, predissolution of the oil residue in CH2Cl2 follow ed by filtration and asphaltene precipitation with simultaneous solvent rem oval, was deemed to be a suitable technique to remove mineral matter and is olate asphaltenes in a single step. Sample oxidation during asphaltene precipitation and isolation was detected by gravimetric and spectroscopic techniques. This fact is very important s ince common precipitation techniques do not address this issue. Preliminary accelerated extraction experiments carried out with pitch sampl es at high temperature and pressure, revealed that this approach can be a v ery interesting research tool to investigate solubility properties.