SH/T 0163-1992 Determination of Total Acid Number of Petroleum Products (Semimicro Color Indicator Method)

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Card type: Test method

1. Method number / full title / English title / replacement relationship

• Standard number: SH/T 0163-92 (confirmed in 2000)
• Chinese title: Determination of Total Acid Number of Petroleum Products (Semimicro Color Indicator Method)
• English title: not provided in the available source
• Replacement relationship: replaces ZB E30 004-87
• Reference adoption: ASTM D3339—80 "Determination of Total Acid Number of Petroleum Products (Semimicro Color Indicator Method)"

2. Scope of application and non-applicability

• Applicable to the determination of acidic constituents dissolved or nearly dissolved in a mixture of toluene and isopropanol in new and used petroleum products and lubricants.
• Particularly suitable for cases where the sample amount is small.
• Applicable to the determination of acids whose dissociation constant in water is greater than 10⁻⁹ (original text is "10", requires confirmation against the source standard (source-text extraction)); extremely weak acids whose dissociation constant is less than 10⁻⁹ (original text is "10°", requires confirmation against the source standard (source-text extraction)) will not interfere; salts whose hydrolysis constant is greater than 10⁻⁹ (original text is "10°", requires confirmation against the source standard (source-text extraction)) will react.
• Can determine the relative change in acid number of oils under oxidizing conditions; because the titration is carried out under specified equilibrium conditions, it cannot give the absolute acid content to predict the performance of the oil under service conditions; it is known that there is no definite correlation between bearing corrosion and acid number.
• For cutting oils, rust-preventive oils and oils with similar components, or oil samples that are too dark or too black, the endpoint color is difficult to distinguish, so the use of this standard is relatively difficult; in such cases, potentiometric titration may be selected for the determination.
• For new or oxidized turbine oils or hydraulic oils, measurement with this standard and with GB/T 4945 can give similar results that meet the precision requirements of both methods.

3. Method principle

Dissolve the sample in a solvent composed of toluene, isopropanol and a small amount of water, and at room temperature under nitrogen protection, titrate with potassium hydroxide isopropanol standard titration solution until the added α- naphtholbenzein indicator solution changes from red to a stable green as the endpoint.

4. Reagents and materials (purity / preparation)

Unless otherwise specified, all reagents shall be analytical grade reagents, and the water used shall be carbon dioxide-free deionized water.

• 6.1 Titration solvent: add 500mL toluene and 5mL water to 495mL isopropanol, and mix well.
• 6.2 α- naphtholbenzein indicator: dissolve 1g α- naphtholbenzein in 100mL titration solvent.
• 6.3 Soda lime (or soda asbestos).
• 6.4 Barium hydroxide.
• 6.5 Isopropanol: anhydrous (water content less than 0.9%).
• 6.6 Potassium hydroxide.
• 6.7 Potassium hydrogen phthalate: primary standard reagent.
• 6.8 Phenolphthalein indicator: prepare as 10g/L phenolphthalein indicator solution.
• 5.2 Material: Nitrogen: high-purity nitrogen free of carbon dioxide.

5. Apparatus and equipment

• 5.1.1 Microburette: 2mL, graduation 0.01mL (original text "0.0ImL", requires confirmation against the source standard (source-text extraction)).
• 5.1.2 Titration beaker: 100mL tall-form beaker without spout, inner diameter about 51mm, height about 71mm.
• 5.1.3 Titration beaker stopper (or cover): made of an elastic material that does not react with the titration solvent, such as neoprene, upper diameter about 53mm, lower diameter about 45mm, height about 25mm; a glass tube with outer diameter 8mm and length about 80mm is inserted into the stopper, extending 15mm±2mm beyond the bottom of the stopper as the nitrogen inlet tube; there are two additional holes with diameter 7mm±1mm, one serving as the titration hole and the other as the nitrogen outlet; the centers of the three holes are at a distance of 30mm±2mm and are evenly distributed on the stopper. A glass cover may also be made, height about 25mm, diameter matching the titration beaker, with the nitrogen inlet tube, outlet and titration hole having the same size and position as the above stopper (see Figure 1).
• 5.1.4 Gas flow meter: glass rotameter, range 0～250mL/min.
• 5.1.5 Electromagnetic stirrer.
• 5.1.6 Stirring bar: cylindrical iron bar about 25mm long and about 8mm in diameter, sealed externally with glass or polytetrafluoroethylene.
• 5.1.7 Dropping bottle: 30mL.
• 5.1.8 Graduated cylinder: 50mL.
• 5.1.9 Glass absorption tube: for holding soda asbestos, size compatible with the burette.

6. Recommended operating conditions

• Titration temperature: below 30°C room temperature.
• Nitrogen purging: pass nitrogen at a flow rate of 3.0～4.0L/h for about 20s.
• Nitrogen titration flow rate: adjust to 1.0L/h±0.1L/h.
• Stirring: start and adjust the electromagnetic stirring speed so that the solution is mixed uniformly but does not splash out.
• Endpoint determination: the solution changes from orange through bright yellow to a stable green and does not fade within 15～20s (original text "15~20S", requires confirmation against the source standard (source-text extraction)).
• Burette tip protection: throughout the titration process, the burette tip must be protected with a glass tube containing soda lime (or soda asbestos).

7. Sampling and sample preparation

• 7.2 Sample preparation: heat the used sample in the original container to 60°C±5°C, and stir continuously until all sediment is uniformly dispersed in the sample.
• If the sample container is opaque or the sample volume exceeds three-quarters of the container volume, transfer all the sample to a glass bottle whose volume is one-third larger than the sample volume; before and during transfer, the original container should be shaken vigorously to ensure that sediment in the sample is also transferred to the glass bottle.
• Filter an appropriate amount of sample through a 150 mesh sieve to remove large particulate contaminants.
• Because used samples may undergo significant changes during storage, the sampling date should be noted after sampling and analysis should be carried out as soon as possible.
• For new oils and, although used, oils that obviously have no sediment, heating and filtration may be omitted.

8. Analysis procedure

• 8.1 Titration of test sample: according to the range in the table below, take an appropriate amount of test sample (accurate to 0.0001g) and place it in a beaker.

Note: For dark-colored samples, the sample amount may be appropriately reduced.

• Place the magnetic stirring bar into the beaker, and successively inject 40mL titration solvent and 0.1mL±0.02mL α- naphtholbenzein indicator solution.
• Quickly place the stopper (or cover) connected to nitrogen onto the titration beaker, and insert the burette tip into the titration hole.
• Immediately pass nitrogen into the beaker at a flow rate of 3.0～4.0L/h for about 20s to expel the air in the beaker.
• Then adjust the nitrogen flow rate to 1.0L/h±0.1L/h, start and adjust the electromagnetic stirring speed so that the solution is mixed uniformly but does not splash out.
• Using potassium hydroxide isopropanol standard titration solution at below 30°C room temperature, titrate until the solution changes from orange through bright yellow to a stable green and does not fade within 15～20s as the endpoint, read and record the milliliters of potassium hydroxide isopropanol standard titration solution consumed (V₂).
• 8.2 Blank test: omit the test sample, perform a blank test daily according to the corresponding steps of clause 7.1, and record the milliliters of potassium hydroxide isopropanol standard titration solution consumed (V₃).

9. Qualitative and quantitative determination and calculation formulas

• 7.1.1 Preparation of potassium hydroxide isopropanol standard titration solution: weigh 3g potassium hydroxide and add it to a round-bottom flask containing about 1L isopropanol (water content less than 0.9%), place in a water bath with continuous stirring and boil slowly for about 15min to completely dissolve the potassium hydroxide and prevent caking. Then add about 1g barium hydroxide, continue boiling for 10min, cover the flask stopper to prevent contact with carbon dioxide in the air, cool to room temperature and let stand overnight. Filter the supernatant through a corrosion-resistant funnel with pore size 10μm; the filtrate should be protected from contact with carbon dioxide in the air. Dilute the filtrate with isopropanol to 5L; the concentration c(KOH) of this solution is about 0.01mol/L. This solution should be stored in a corrosion-resistant brown bottle, avoid contact with cork stoppers, rubber stoppers or easily saponifiable stopcock grease, and preferably protected with a glass tube containing soda lime or soda asbestos. Note: Because isopropanol has a large coefficient of volume expansion, the room temperature during standardization and use of this solution should be similar.

• 7.1.2 Standardization: weigh about 0.01g (accurate to 0.0001g) of the primary standard reagent potassium hydrogen phthalate dried at 110°C for 1h into a titration beaker, use 40mL±1mL water as solvent, add 6 drops of phenolphthalein indicator solution (6.8), standardize the potassium hydroxide isopropanol solution according to the corresponding test steps in clause 7.1, titrate until the solution changes from colorless to pink as the endpoint, and record the volume of potassium hydroxide isopropanol solution consumed (V₁). Perform a blank test in the same steps, and record the volume of potassium hydroxide isopropanol solution consumed in the blank test (V₀).

• The actual concentration c(KOH), mol/L, of the potassium hydroxide isopropanol standard titration solution is calculated according to formula (1):

  c(KOH) = m / [0.2042 × (V₁ − V₀)] …(1)

  Where:

  • m—— mass of potassium hydrogen phthalate, g;
  • V₁——amount of potassium hydroxide isopropanol solution used, mL;
  • V₀——amount of potassium hydroxide isopropanol solution used in the blank test, mL;
  • 0.2042—— mass of potassium hydrogen phthalate, expressed in grams, equivalent to 1.00mL potassium hydroxide isopropanol standard titration solution [c(KOH)=1.000mol/L].

• Take the average of at least two titration results as the actual concentration of the potassium hydroxide isopropanol standard titration solution; the difference between repeated determination results shall not exceed 0.0003mol/L.

• 9 Calculation: the total acid number X of the test sample (expressed as mgKOH/g) is calculated according to formula (2):

  X = c × 0.0561 × (V₂ − V₃) × 1000 / m₂ …(2)

  Where:

  • c—— the actual concentration of the potassium hydroxide isopropanol standard titration solution, mol/L;
  • V₂——the volume of the potassium hydroxide isopropanol standard titration solution consumed in titrating the test sample, mL;
  • V₃——the volume of the potassium hydroxide isopropanol standard titration solution consumed in the blank test, mL;
  • m₂——the mass of the test sample, g;
  • the mass of acid (expressed as potassium hydroxide) in grams equivalent to 0.0561—— and 1.00mL potassium hydroxide isopropanol standard titration solution [c(KOH)=1.000mol/L].

• 3 Definition: Total acid value: the number of milligrams of potassium hydroxide required to neutralize the acid (or salt) contained in 1g of the test sample whose dissociation constant (or hydrolysis constant) is greater than 10⁻⁹ (the original text is "10", requires confirmation against the source standard (source-text extraction)).

10. Precision

Judge the reliability of the test results according to the following provisions (95% confidence level).

• 10.1 Repeatability: the difference between two results obtained by the same operator shall not exceed the following provision (or according to the repeatability provision in Figure 2).

X is the average total acid value of the test sample.

• 10.2 Reproducibility: the difference between two results obtained by different operators in different laboratories shall not exceed the following provision (or according to the reproducibility provision in Figure 2).

X is the average total acid value of the test sample.

• Note: The precision specified here applies only to new and used antioxidant-containing turbine oils and hydraulic oils; no provision is made for other oils due to insufficient data.

11. Report

Take the arithmetic mean of two repeat determination results as the determination result of this test.

12. Normative references

• GB/T 4945 Petroleum products and lubricants—Determination of neutralization number (Color indicator method)
• Editor's note: The standard numbers and standard names of the normative references in this standard have changed as follows:
  • Original standard number: GB/T 4945
  • Current standard number: GB/T 4945
  • Current standard name: Petroleum products and lubricants—Determination of acid number and base number (Color indicator method)

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Q&A