Analytical Methods in Environmental Chemistry Journal Vol 1(2018) 23-28
Research Article, Issue 1
Analytical Methods in Environmental Chemistry Journal
Journal home page:
The Investigation of precision of analytical methods for
determination of salt content in Iranian crude oils
Ali Asghar Pasbana* and Behrouz Nonahala
a Research Institute of Petroleum Industry, Tehran, Iran
A R T I C L E I N F O:
Received 2 Sep 2018
In crude oil analysis, the determination of salt content is one of the most
important parameters especially for refining and exporting industries. In
Revised form 30 Oct 2018
this study, extraction followed by volumetric titration and electrometric
Accepted 15 Nov 2018
procedure are performed for determining salt content for several Iranian
Available online 29 Dec 2018
crude oils. Also, the effects of disturbing agents such as increasing
associated water for determining salt in crude oil were investigated for
both methods. The results show when water content in crude oil is less than
0.05 weight percent, both methods are equally accurate for determining
salt content, but when there is an increase in associated water content
in crude oil, the electrometric method followed by volumetric titration
Salt content
method shows more accurate results in comparison with the extraction
crude oil
electrometric method
volumetric titration
1. Introduction
the pollution of the crude oil transportation route
Existing salt content in crude oils can lead to serious
may also be somewhat effective. The presence of
problems during petroleum production, refining
salts in crude oil in addition to corrosion causes the
process, transportation, and also some related
following problems.
chemical and petroleum engineering processes.
During the production of crude oil, due to the minor
[1]. Sodium, magnesium, and calcium chlorides
evaporation of the associated water happens in the
are almost always present in crude oils. Moreover,
effect of pressure drop between the bottom and the
calcium cement and calcium carbonate should also
top of the well, causing the chloride to settle sodium
be mentioned. The amount of mineral salts in crude
is at the entrance to the well wall and the diameter of
oil depends on the formation pattern of crude oil
the well decreases.
and can reach up to 200000 ppm [2-3]. In addition,
To cater for such issues, fresh water well is injected
to the well. In refineries, the existence of salt along
with other factors such as wax and asphaltene causes
* Corresponding author email:
the formation of deposits inside the exchanger tubes.
Analytical Methods in Environmental Chemistry Journal; Vol. 1 (2018)
Consequently, the formation of deposits inside the
methods to control the quality of crude oil exports.
exchanger tubes reduces the heat transfer; moreover,
For the time being, many of the production areas and
the formation of deposits
(or sedimentation) in
exporting terminals use extraction and volumetric
furnace tubes will produce coke [4].
titration methods. Also, recently, it was stipulated
Also, the presence of water and salt in some crudes
or stated that volumetric titration method should be
and heavy crudes will cause an increase in the
gradually replaced by the electrometric method.
acidity number. In order to control and reduce the
The purpose of this research is to study the current
effect of water and salt on the acidity number, water
methods of salt determination in petroleum
washing process (dehydration) is employed prior to
laboratories and investigate comparative advantages
the desalter unit [5-7].
and disadvantages of each method in conjunction
In order to control the corrosion caused by salt,
with the project performed on
“Salt content
its content should be less than 4 ppm or 2 pounds
determination of Iran’s crude oils at the Research
in 1000 bpd of the crude oil [8]. In crude oil sales
Institute of Petroleum Industry in 2018”.
contracts, salt content is one of the important
parameters whose permissible amount is mentioned
2. Experimental Procedure
in the contract, and the seller is obliged to control
2.1. Material and Methods
it when producing and exporting. Therefore, in the
In the laboratory investigation, crude oils with
laboratory of exporting terminals, the salt content is
different characteristics for salt determination
determined, and if it exceeds the permissible limit,
were selected to obtain a better comparison of
the cargo will not be shipped to the oil tanker. Also,
the performance of standard methods at different
if the buyer finds a discrepancy in the amount of
salt received, inform the seller should be informed.
For this purpose, 6 samples of crude oils produced
Moreover, if the buyer’s claim is confirmed, the seller
by National Iranian South Oil Company (NISOC)
will be obligated to pay compensation on the basis
were selected. NISOC is regarded as one of the
of the contract. It should be noted that a salt content
largest crude oil producers in the world and produces
increase in crude oil exports could be detrimental to
85 percent of crude oil in Iran. The specifications of
the reputation of the exporting company in the oil
selected crudes are shown in Table 1.
In this study, for measurement of API grade of crude
With reference to the above, standard salt content
oils, a SVM equipment (model 2000) manufactured
determination during production, transportation,
by Austrian company (Anton Paar) has been used
storage, and exportation to a petroleum company
to determine dynamic density and viscosity of the
are important. Crude oil producing company has to
crude oils [12]. Also, for water and sediment tests,
control this parameter in equipped laboratories. Oil
Hermle centrifuge
(model ZK510) equipment
companies can monitor the amount of salt along with
manufactured by German company (Carlowitz) has
other key parameters such as API grade, water and
been used along with ASTM D95 method [13].
sediment, hydrogen sulfide, and sulfur on a daily
For the determination of water content in crude oil,
basis [10-11]. In addition to controlling the quality
Carl Fisher (805 model titrando) test procedure has
of production of its subsidiaries, they can well defend
been adopted with the aid of ASTM D4377 [14].
the interests of participating in necessary situations
For this purpose, a titration apparatus manufactured
and avoid unnecessary losses as much as possible.
by Metrohm has been used. This apparatus uses a
The National Iranian Oil Company (NIOC) has also
dual combination of platinum electrode to measure
created a hardware infrastructure and the necessary
the amount of water in crude oil. The asphaltene is
software in this field, and its experts try to carry
determined in weight percent using normal heptane
out the necessary research and update the present
and APD-500A automatic machinery manufactured
standards. They use the best internationally accepted
by a Japanese Company called Cosmo which works
Analytical methods in salt of crude oils; Ali Asghar Pasban, et al
based on the ASTM D6560 which is equivalent to
and discharged through the valve embedded under
the standard IP 143 [15].
the flask, and then the water phase is separated, and
Also, a titration apparatus manufactured by
chlorine ion content in the water phase is neutralized
Metrohm (805 Titrando model ) is used to determine
by a mohair volumetric titration method. In this way,
the estimate the effect of salt on the acidity number
by using normal 0.01 silver nitrate, chloride ions are
of the selected crudes. Moreover, the titration
titrated in the presence of a few drops of potassium
apparatus manufactured by Metrohm is equipped
dichromate solution with a concentration of
with a combination of a silver glass electrode and
gram. At the end of the neutralization of chlorine
silver chloride
(Ag/AgCl) as reference electrode
ions, the ambient color changes from yellow to
surrounded by the same electrode [16].
light red. In this way, the concentration of chlorine
The acidity number is the amount of consumed
ion is obtained in milligrams per cubic meter from
hydroxides for neutralization of one gram of sample
Equation 1.
mgKOH/gram oil. The results obtained in this study
X = [VA/(V1-VB/V2)].N.58500.VE/VS
showed that the crude oils used in this study had low
where, VA is the volume of silver nitrate solution
acidity numbers and did not cause much disorder in
used for the titration extraction in ml, VB is the
the performance of desalting units [17].
volume of silver nitrate used as the titration witness,
V1 is the volume of consumed extraction used
2.2. Salt content determination by standard method
in titration, V2 is the volume used as witness in
IP 77
the titration process, VE is the total volume of the
In this method, salt content in the crude oil is
extract, VS is the sample volume of crude oil used,
separated by a glass system manufactured by
and N is the normality of the silver nitrate solution.
Petrotest which is designed based on the standard
IP 77 [14]. In this extraction method, the sample is
2.3. Salt content determination by ASTM method
heated by an electric heater in a glass flask with the
volume of 55 cm3. About 155 ml of crude oil with
To determine salt content by the above method, a
155 ml of distilled water are poured inside the flask.
digital analyzer (694-SICT Model) is used which
After mixing, 100 milligrams of toluene and then 20
is manufactured by Kohler Corporation. This
ml of acetone were added to the mixture. The flask
apparatus measures the electrical current passing
is heated by the electric heater to the boiling point
through the crude oil solved in a beaker of solution
of the mixture, and the resulting vapors are cooled
mixture of alcohols with the aid of an electrode
and returned to the flask by a vertical condenser
based on the electrometric measurement method
mounted on top of the flask. This operation lasts
[17]. With respect to standard calibration curve of
for at least 45 minutes. To make sure that full salt
the apparatus, the passing flow is reported in terms
extraction can be performed at a greater time. After
of Micro Siemens to milligrams which is directly
completion of the extraction stage, the contents of
converted to cubic meter and displayed on the
the cooled water phases and organics are separated
monitor. The electrode used consists of two platinum
Table 1. The specification of crude oils.
Crude oil No.
Water V
Water and Sediments V
Acidity No. mgKOH/gr Asphaltene wt.%
Analytical Methods in Environmental Chemistry Journal; Vol. 1 (2018)
The results of salt determinations are reported in
plates with the dimensions of 25 mm × 50 mm which
are placed in parallel facing each other.
Table 2. As it can be seen from Table 2, at low salt
The spacing between the plates is 2 mm, and the
concentrations in crude oils, the values obtained
maintaining material which holds the plates next
are close to each other by both methods, b u t at
to each other is insulated. For calibration of the
higher concentrations, the measured values in the
system, according to ASTM D3230, standardization
electrical conductivity method are very di f f e rent
of apparatus solution has been carried out through
from extraction method and in the case of c r u de
a mixture of alcohols that were diluted in a mixture
oil, the difference is approximately 1.5 times more
of sodium, magnesium, and calcium solution
than the amount of extraction method due t o t he
chlorides of 70%, 20% and 10% respectively. The
restriction in neutralizing process IP 77 m e t hod
purpose of dilution is to prepare salts mixtures with
because in volumetric titration, the 0.01 solution of
a concentration of 0.1 g/m3. The mixture of alcohols
normal silver nitrate is used. Silver nitrate reacts
contains 37 % vol. of pure ethanol in isobutanol,
only with the chlorine ions of the water-s o l u ble
for any liter of which, 3ml of distilled water is
salts derived from the extraction, and sin c e the
added. At this stage, a quantity of about 10 ml of
amount of silver nitrate which has been consumed
an oil cut like paraffin was thoroughly dissolved in
is the calculation criteria for the determination of
40 ml of an organic solvent such as Xylene. Then
50 ml of alcohol mixture was added to this mixture
salt, the presence of the other forms of salts in the
and severely stirred. Then the final solution was
aqueous phase cannot be reported in this method.
poured inside a clean beaker and its conductivity
As stated in this standard, only the amount of chloride
was measured. This result is in fact, the amount
ion should be reported in the final report. Therefore,
of conductivity of the control solution. Then to
it is suggested that in laboratories, which crude oil
completely cover measuring range of the apparatus
quality control is performed, should not report the
(0-430 mg/cm3), standard solutions were used to
final result as salt content when working with this
match the table presented in ASTM standard D-3230
standard. In this study, for further analy s i s of the
containing 50 ml of solution of mixture of alcohols
reasons for the difference in the results, associated
with a suitable amount of salt mixtures. During each
water of 6 samples of crude oils related to desalting
step, the conductivity was recorded on the apparatus.
units were analyzed for the above-mentione d
In this way, there are about 10 points to plot the
methods. Table 3 shows the analysis of the results
calibration curve.
of 6 samples of associated water with crud e oils.
After calibration of the apparatus, salt content of
For determination of ions in water of crud e oils,
crude samples were determined. To do this, 10 ml
despite high chlorine ions, the other ions are not
of each crude oil sample was dissolved in an organic
negligible. By increasing associated water , the
solution containing xylene and
50cc of alcohol
error of measurement of ions using the conductivity
mixtures. At this stage, the mixture was stirred for 90
method was increased (Table 3). In additio n , this
seconds by hand. Then the sample remains constant
difference is shown in figure 1. As shown i n this
for 5 minutes. Finally, the content was poured in the
figure, the results of the salt obtained t h rough the
special beaker, and the salt content was measured.
electrometric method are higher than the extraction
and volumetric method, which indicates tha t this
3. results and discussion
method is more precise. As shown in Table 3 with
increasing associated water in crude oil, the amount
Salt content of samples of crude oils were measured
of salt will also increase proportionally. On the other
using extraction and volumetric method (IP 77). In
hand, as shown in Table 3, sulphate, and bicarbonate
addition, the electrical conductivity measurement
foundations can also be problematic for refineries,
(ASTM D3230) reported in Table
and therefore, the salt determination for c rude oil
Analytical methods in salt of crude oils; Ali Asghar Pasban, et al
Table 2. The results of salt determination in crude oils.
of crude oil cannot be determined by this method.
Crude Sample Chlorine Ion (mg dm-3) Salt (mg dm-3)
c) In the electrometric method, a smaller sample
IP 77
ASTM D3230
volume is needed compared to the time-consuming
extraction method.
d) Repeatability and reproducibility of the results
in the electrometric method are better than the
extraction method and volumetric analysis.
e) It is recommended that the electrometric method
for determining salt content be used when the amount
should be calculated and total salt amounts should
of water in the crude oil is high. Therefore, in this
be reported for desalting units, so, the technical
method, the passing flow through the medium is
section will be able to control the output salt content
used. Moreover, in this method, the concentration of
by optimizing of parameters in desalting unit.
total ions can be calculated, and thus a more accurate
calculation of the inorganic salts can be achieved.
This method also helps the utilization of optimized
4. Conclusions
operation of existing oil installations against
In this study, the determination of salt content in
damages inflicted from corrosion and sediments.
crude oils was evaluated by two methods which
was exported and transported to domestic Iranian
refiners. This procedure, was carried out on six
5. Acknowledgments
petroleum products, produced by NISOC (National
The authors would like to thank National
Iranian Southern Oil Company) using extraction and
Iranian South Oilfield Company’s staffs for their
volumetric methods by (IP 77) and ASTM method D
contributions and guidance during the course of this
3230. The results show that the electrometric method
has some advantages in comparison to the extraction
method, outlined as follows:
6. Refrences
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Table 3. Ion compounds in water with crude oil number of chlorine ion.
Chlorine Ion
Sulphate Ion
Bicarbonate Ion
Specific Gravity
g L-1
g L-1
g L-1
Analytical Methods in Environmental Chemistry Journal; Vol. 1 (2018)
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