Geoscience Reference
In-Depth Information
Fig. 16.21 Reversed-phase HPLC-ED chromatogram of alkylphenols from SPE extract of Miller
oil. See Table
16.7
for identification of peaks. Reprinted from Bennett and Larter (
1997
).
Copyright 1997 with permission of Elsevier
Table
16.7
shows the depletion of alkylphenols from crude oil, by dissolution in
water, after equilibration of the crude oil with deionized water at a pressure of
25 bar and at 25 and 125 C. Based on steric considerations, Bennett and Larter
(
1997
) showed that the aqueous affinity of o-cresol (hindered hydroxyl group) is
expected to be lower than m- and p-cresol (unhindered), because the close prox-
imity of the methyl group to the active hydroxyl functionality may decrease H-
bonding interactions with water. The calculated ratio of hindered to unhindered
cresols (o-cresol/(m-cresol ? p-cresol), abbreviated to o-/(m- ? p-)) in the
equilibrated oil and water, with respect to the ratio determined in the original crude
oil (Table
16.7
), reveals a slightly higher value for the oil. This indicates that o-
cresol is preferentially retained in the oil; it has a lower relative value in the water
sample, suggesting more favored m- and p-cresol partitioning into water.
Overall, dissolution in the electrolyte solutions of all studied compounds led to
substantial decreases in their concentrations in the original crude oil. However, the
rate of decrease was different for each compound, in accordance with the
molecular properties. Bennett and Larter (
1997
) note that, in comparison with the
original crude oil, the concentration of phenol decreased relative to cresol. The
change in phenol content relative to cresol is highlighted by measuring the ratio
(phenol/o- ? m- ? p-cresol), which shows that the reduction of more hydrophilic
phenol relative to cresol is in accord with their relative dissolution in water.
Bennett and Larter (
1997
) also studied the solvation of alkylphenols in crude
oil-water systems at equilibrium to obtain partitioning coefficients under variable
temperature, pressure, and water salinity concentration. Alkylphenol depletion
from crude oil, expressed by phenol, cresols, and 3,5 dimethyl phenol, versus
temperature in a range of 25-125 C, is given in terms of partition coefficient
(P) values (Fig.
16.22
). Partition coefficient values increase with addition of alkyl
groups to the phenol nucleus. Note that the alkylphenol partition coefficient curves
for
different
isomers
tend
to
converge
at
higher
temperatures
and,
as
a
