Page 106 - Petrophysics 2E

PETROLEUM CHEMISTRY 79

CLAV-GEL EXTRACTION COLUMN

GLASS WOOL PLUG

Figure 2.24. Clay-gel column used for separation of resins, aromatics, andparaflns
from crude oils 1351.

The various homologous series discussed above may be readily
separated by first diluting a sample of crude oil with pentane and then
filtering. The asphaltenes are insoluble in pentane and can thus be
removed and weighed. The diluted sample may then be percolated
through a double column of active clay mineral on top of a column of
silica gel, as shown in Figure 2.24, and eluted with pentane. The resins are
adsorbed by the clay, whereas the paraffins and aromatics pass through
the clay column. The aromatics are adsorbed by the silica gel column and
the non-adsorbing paraffins are collected in the bottom flask. The resins
and aromatics are removed from the clay and silica gel with a mixture
of equal parts benzene and acetone, and can be obtained quantitatively
by evaporation of the solvent [35] (Figure 2.25). A high-pressure liquid
chromatograph (HPLC) also may be used to obtain the same fractions
using less than one milliliter of sample. The response from the HPLC is
shown in Figure 2.26.
Organometallic compounds are usually associated with the resins
because of their polar characteristics. Alkyl derivatives of nickel and
vanadium porphyrins have been isolated from crude oils, especially the
Boscan heavy oil from Venezuela. The porphyrins are characterized by