Determination of Salt Content in Crude Oil

Overview

Crude oil is a liquid petroleum mixture extracted from underground, in which a certain amount of inorganic salts (mainly sodium chloride) are dissolved and entrained. Salts in crude oil will cause various hazards during the refining process: they easily lead to equipment corrosion and scaling, shortening the service life of heat exchangers and heating furnaces; meanwhile, substances generated by salt decomposition can also cause catalyst poisoning and deactivation, directly affecting the quality of finished petroleum products. Therefore, the salt content of crude oil is a key testing indicator for crude oil incoming acceptance and refining process control.

The detection of crude oil salt content is based on the principle of coulometric titration, and quantitative analysis is completed in accordance with Faraday's laws of electrolysis. The SH0536 Salt Content Tester adopts this principle to detect the salt content in crude oil samples.

Test Purpose

To determine the salt content in crude oil, evaluate crude oil quality, provide data reference for the refining production process, and avoid damage risks caused by high-salt crude oil to processing equipment and catalysts. The SH0536 Salt Content Tester completes crude oil salt content detection based on the coulometric method.

Test Procedure

Test Sample

Crude oil sample

Test Instruments

1. SH0536 Salt Content Tester main unit
2. Stirrer, constant temperature water bath, mixer, centrifuge
3. Auxiliary appliances such as centrifuge tubes, syringes, pipettes, etc.
4. Reagents such as xylene, alcohol-water mixed extraction solution, hydrogen peroxide (for interference elimination), etc.

Operation Steps

1. Heat the crude oil sample in a water bath to 50–70℃ and shake thoroughly to ensure sample homogeneity. Weigh a certain amount of crude oil, transfer it to a centrifuge tube, and add xylene and alcohol-water mixed extraction reagent.
2. Place the centrifuge tube in a 70–80℃ water bath for heating, and perform repeated oscillatory extraction with a mixer to extract the salts inside the crude oil into the aqueous phase. After extraction, place the tube in a centrifuge for high-speed centrifugation to separate the oil phase from the aqueous phase. If sulfide interference in the sample is obvious, a small amount of hydrogen peroxide can be added dropwise to eliminate the interference.
3. Debug the instrument: complete the electrode inspection of the titration cell, prepare the electrolyte, adjust the endpoint voltage, and turn on stirring to ensure normal mixing inside the titration cell.
4. Use a long needle to draw the lower aqueous phase extract, select an appropriate injection volume according to the estimated salt content, and inject the extract into the titration cell.
5. The instrument performs coulometric electrolytic titration in accordance with Faraday's laws, automatically calculates the salt content value of the sample, and completes data storage and output.

Data Analysis and Result Evaluation

The salt content measuring range of this instrument is 0.2–10000 mg NaCl/L.

• When the salt content is below 3 mg NaCl/L, the repeatability error ≤ 0.3 mg NaCl/L;
• When the salt content is 3–10 mg NaCl/L, the repeatability error ≤ 1.2 mg NaCl/L;
• When the salt content is above 10 mg NaCl/L, the repeatability error ≤ 10%.

The test results can be used to judge whether the salt content of crude oil meets the incoming control indicators, and guide refineries to adjust the crude oil desalting pretreatment process.