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Introduction
petroleum asphaltenes by FCS experiments [26, 27], yielding molecular weight ap-
proximations. Non-aggregated Asphaltene molecular weights were found to be in
the range of ∼ 750 g/mol.
1.1.5 Separation of SARA fractions
Figure 1.4 shows a typical SARA fractionation from dead crude oil samples [28]. As-
phaltenes are isolated as a separate fraction by precipitating with n-heptane (40:1).
This is because their highly polar nature would cause irreversible adsorption and
thus damage the LC column. Precipitated asphaltenes are separated by vacuum fil-
tration, dried in an oven and weighed. The soluble compounds left after asphaltenes
have precipitated is called the ‘maltenes’ fraction.
Figure 1.4: SARA fractionation protocol for dead crude oils. Adapted from [28].
Normal-phase LC elution can be performed on the maltenes in an open-column
by a gravitational flow of solvent or by a force-flow using medium pressure (MPLC)
to increase separation speed [17] (this technique was used to produce the fraction-
ation data for the crude oil samples described in Chapter 2). Usually, saturates
are eluted with an n-alkane such as n-hexane and the aromatics and resins/polars
are eluted with solvents or solvent mixtures of higher eluotropic strengths such as
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