Determination of Acid Value of Petroleum Products

Determination of Acid Value of Petroleum Products

Petroleum products are a general term for various commodities directly produced from petroleum or its components, mainly including six categories: fuels, chemical raw materials, lubricating oils, paraffin wax, asphalt, etc. Among them, fuels such as gasoline, diesel oil and aviation kerosene account for the vast majority of refined oil products, with about 85% of crude oil eventually converted into various fuels for transportation and industrial use. In addition, petroleum also provides basic raw materials for chemical products such as plastics, chemical fibers and rubbers, and about 15% of a barrel of crude oil is used to produce high value-added products such as light chemical oil and ethylene.

Petroleum products are essentially mixtures of various hydrocarbons, mainly composed of organic compounds, so they fall into the category of organic compounds in chemical classification. Although it is a mixture, since all components contain carbon elements, which meets the definition of organic matter, it is usually classified as an organic compound in examination and industrial contexts.

Experimental Purpose

1.Assess the risk of corrosion to metals: The higher the acid value, the more acidic substances (such as organic acids, naphthenic acids, etc.) contained in the oil. In the presence of moisture, these acidic components will significantly corrode metal equipment and affect the service life of refining units, engines or lubrication systems. By measuring the acid value, it can be judged in advance whether the oil will cause corrosion damage to storage, transportation and operating equipment.

2.Judge the refining degree and quality of oil products: The acid value of new oil can reflect its refining degree. The more thorough the refining, the fewer acidic impurities and the lower the acid value. Therefore, acid value is one of the important indicators to measure the purity of oil products in factory inspection.

3.Monitor the oxidative deterioration of oil products during use: Lubricating oil, transformer oil and other products will produce acidic products due to oxidation during long-term operation, leading to an increase in acid value. When the acid value exceeds a certain limit (e.g., a change of > +0.01 mgKOH/g), it indicates that the oil has begun to deteriorate, which may produce sludge or affect insulation performance, requiring timely replacement.

4.Guide the processing and utilization of high-acid crude oil: Crude oil with an acid value greater than 0.5 mgKOH/g is called "acidic crude oil", which is prone to cause corrosion of refining equipment and difficult to process. Accurate determination of acid value helps to optimize deacidification processes, adjust blending ratios, and select appropriate corrosion inhibition measures.

5.Guarantee the service performance of fuels and lubricating oils: High-acid diesel oil may cause nozzle coking and piston wear; an increase in the acid value of lubricating oil means a decline in lubrication function. Regular testing can ensure that oil products operate within a safe range and avoid mechanical failures.

Experimental Sample and Instruments

Experimental Sample: Petroleum products

Experimental Instrument:SH108C Potentiometer titration TAN/TBN Tester ，in compliance with ASTM D664

Experimental Procedure

1.Electrode CalibrationTurn on the power of the potentiometric titrator and preheat for 30 minutes. Calibrate the electrode with pH = 7.00, 4.00 and 10.00 buffer solutions in sequence to ensure the potential measurement error ≤ ±2 mV.

2.Sample Determination

Weighing: Weigh the sample according to the estimated acid value, accurate to 0.001 g, and place it in a 250 mL beaker.

Dissolution: Add 100 mL of titration solvent and start the magnetic stirrer to fully dissolve the sample (if stratification occurs, the proportion of toluene may be increased appropriately).

Titration Operation: Immerse the electrode tip into the solution, avoiding contact with the bottom of the beaker.

Parameter Setting: Set the titration speed to 0.5 mL/min, and the endpoint identification mode to "potential jump" (jump range ≥ 50 mV).

Titration: Titrate with standard potassium hydroxide isopropanol solution, record the titration volume (V₁) and endpoint potential.

Blank Test: Perform a blank titration with only 100 mL of titration solvent under the same conditions, and record the blank volume (V₀).

3.Duplicate TestConduct at least two parallel determinations on the same sample. The difference between the two results shall meet the precision requirements (repeatability of new oil ≤ 0.044(X+1), where X is the average of the two results).

Experimental Results

The measured acid value of the lubricating oil is 0.084 mgKOH/g, which meets the factory standard. This indicates that the oil has sufficient refining depth, low content of acidic impurities, and low corrosion risk to equipment. The relative deviation of duplicate determinations is ≤ 2.1%, which meets the repeatability requirement in ASTM D664-24 (RSD ≤ 2%), proving that the experimental data is accurate and reliable.