Analytical Methods in Environmental Chemistry Journal Vol 1(2018) 23-28

Research Article, Issue 1

Analytical Methods in Environmental Chemistry Journal

Journal home page: www.amecj.com/ir

AMECJ

The Investigation of precision of analytical methods for

determination of salt content in Iranian crude oils

Ali Asghar Pasban^a*and Behrouz Nonahal^a

^aResearch Institute of Petroleum Industry, Tehran, Iran

A R T I C L E I N F O:

A B S T R A C T

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

Keywords:

in crude oil, the electrometric method followed by volumetric titration

Salt content

method shows more accurate results in comparison with the extraction

crude oil

procedure.

electrometric method

extraction

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: pasbanaa@ripi.ir

https://doi.org/10.24200/amecj.v1.i01.33

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

conditions.

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.

market.

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

(1)

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

D3230

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.

API

Water V

ol.%

Water and Sediments V

ol.%

Acidity No. mgKOH/gr Asphaltene wt.%

33.3

0.025

0.05

1.0

33.2

0.025

0.10

0.08

1.1

30.4

0.20

0.30

0.15

1.9

31.3

0.75

1.0

0.17

2.0

24.3

1.0

0.31

4.7

18.5

2.0

0.40

8.4

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

50^cc 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,

method

(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

No.

IP 77

ASTM D3230

volume is needed compared to the time-consuming

33±2

34±1

extraction method.

65±1

72±3

d) Repeatability and reproducibility of the results

146±5

160±2

in the electrometric method are better than the

194±7

295±5

extraction method and volumetric analysis.

203±6

344±4

207±12

395±9

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

research.

has some advantages in comparison to the extraction

method, outlined as follows:

6. Refrences

a) With respect to the need for refiners the salt

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content of the crude oil as feed should be reduced to

On the Determination of Crude Oils Salt Content:

less than 3 ppm. For such scenarios, only the ASTM

Application of Robust Modeling Approaches, J.

method D 3230 should be used because the lowest

Taiwan Institute Chem. Eng., 44(2015)27-35.

limit of measurement for the IP 77 method is about

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20 ppm.

A.A.Miran Beigi, Acidity removal of Iranian heavy

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crude oils by nanofluid demulsifier: An experimental

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Table 3. Ion compounds in water with crude oil number of chlorine ion.

Sample

Chlorine Ion

Sulphate Ion

Bicarbonate Ion

Specific Gravity

No.

g L-1

0.41

0.27

0.9882

0.35

0.27

1.0006

0.34

0.27

1.0961

0.32

0.33

1.0983

0.47

0.28

1.1024

105

1.42

0.30

1.1196

Analytical Methods in Environmental Chemistry Journal; Vol. 1 (2018)

Fig. 1. Effect of increasing associated water in salt content determination.

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