Hydrocarbon Processing - April 2021 - 70

Water Management
such, they have a lower polarity and smaller base strength than
classical amines. This results in better controllability within the
target pH range (red line in FIG. 1), as well as neutralization salts
characterized by lower salt point temperatures and improved
tendencies for salt formation downstream of water condensation to better avoid salt laydown. Using a mix of amines also decreases relevant partial pressures, which lower salt deposition
risk. While these same properties might, at first, lead to the
expectation of higher injection rates needed to elevate the pH
to target, in practice, additional complex behaviors cause the
amines in these blends to significantly partition to oil phases
in a beneficial and targeted way when oil and water mix under
typical operating conditions. As this article will examine, this
phenomenon significantly reduces practical injection rate requirements and makes these programs cost effective, with better controllability and salt property benefits.
The partitioning effect outlined is highly pH dependent
and is unique for each amine species used in an amine neutralizing product. This strongly impacts the amount of amine in
both the hydrocarbon phase of the overhead circuit and in the
desalter through the addition of desalter wash water returned
from topping.
FIG. 2 shows theoretical partitioning curves for three amines
used in the service provider's neutralizer programs outlined
here. It shows that some amines start to partition to the hydrocarbon as pH rises above 8, while others can start partitioning

as pH rises above 5. Traditional primary amines generally have
effectively no hydrocarbon partitioning potential in the range
of desired boot water (BW) pH control. This property was
confirmed by the detailed analytical plan developed in cooperation between TOTAL and the service provider.
Amine partitioning can cause amines to recirculate when
water containing amines is contacted with a hydrocarbon
stream, which will be reinjected to the column through the
desalter. These recycle contributions can result in higher levels of amines in the overhead line than would be expected
based only on the mass flowrate of amines injected in the
overhead vapor line as a neutralizer. Due to a low salt point
temperature, it has no expected impact in the column, as it is
important to avoid any salt-induced corrosion in the lower
side draw of the crude unit.
Amine analysis in the different streams of a crude unit
can be very important and will lead to a better knowledge of
concentrations for various amines inside the tower and the
overhead system. This is important because the information
can be used to better monitor real-time amine salt points and
practical corrosion control tactics. This is especially true for
the amines, where, due to the partitioning and recycle phenomenon previously described, simple mass balance calculations tend to overestimate the amount of neutralizer required
to meet ongoing demand.
Analytical plan. The service provider developed a new

HCI neutralization with amine product
Service provider vs. Prod B

10
9
8
7
pH

Control ranges

5
4
3
2
1
0
0.5

Control ranges
1

1.5

2
Amine, wt HCT

2.5

3.5

FIG. 1. Comparative neutralization strength and needs.

method for amine speciation in overhead water sample by ion
chromatography mass spectrometry (IC-MS), with a detection limit as low as 0.1 ppm for each amine and that avoids
the interferences and coelution issues usually seen between
amines of the same family (FIG. 3). Comprehensive and detailed amine analysis using this method is economical, precise,
accurate and make the analysis of a wide variety of key amines
available in overhead water samples.
Conversely, for hydrocarbon samples, it is necessary to first
extract the amines from the hydrocarbon phase with acidified
water. This works well for light hydrocarbon cuts like naphtha,
but reliable results are more difficult in crude oil due to numerous interferences and the potential for column contamination
by long eluting compounds. Therefore, the amines in desalted
crude oil are calculated by material balance using the wash water and brine, respectively entering and leaving the desalter.
Case 1: Simple crude unit. The first unit where TOTAL

45
A
B
C

40
Amine in hydrocarbon phase, %

and the service provider transitioned to the amine-neutral-

Model for effect of pH on partitioning of amines

30
25

20
15
10
5
0
0

FIG. 2. Effect of pH on amine partitioning in hydrocarbon phase.

APRIL 2021 | HydrocarbonProcessing.com

FIG. 3. Amine speciation device.

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Hydrocarbon Processing - April 2021

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