Acid number in Lubricating oil | Autotitrator COM-A19 - JM Science
HIRANUMA APPLICATION DATA Automatic Titrator Data No. L1 Jun.6. 2017
Lubricant petroleum products Acid number in Lubricating oil

1. Abstract

 The acid number of lubricant oil is one of the important index for judging its quality.
Measurement of acid number is defined in several standard test methods. It is indicated by “milligrams of potassium hydroxide required to neutralize acidic components contained in 1 g of the sample”.
The international standard methods for acid number are shown as bellow.
 ・ JIS K2501 2003:Petroleum products and lubricants – Determination of neutralization number
 ・ ASTM D664-1995 : Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration
The potentiometric titration process is as follows:
 1) Weigh sample exactly corresponding to acid number and dissolve it in a titration solvent.
 2) Immerse glass electrode and reference electrode.
 3) Start titration with alcoholic potassium hydroxide solution.
Inflection point is defined as the end point if it obtained sharply. If it’s not clear, the pH obtained from measurement of buffer solution is defined as the end point. The measurement with the latter end point detection will be introduced here.

2. Configuration of instruments and Reagents

(1) Configuration of instruments
  Main unit : Hiranuma Automatic Titrator COM Series
  Electrode : Glass electrode GE-101B
    : Reference electrode RE-201Z
    : Thermistor electrode TE-403
(2) Reagents    
  Titrant : 0.1 mol/L potassium hydroxide in 2-propanol
  Titration solvent : Mixture of 500 mL of Toluene, 495 mL of 2-Propanol and 5 mL of water
  Buffer : Mixture of 10 mL of “Buffer B” and 100 mL of titration solvent, “Buffer B” is regulated in “JIS K 2501”

3. Measurement procedure

(1) Determination of the end point pH
i) Put the stir bar in buffer solution and immerse electrodes.
ii) Read the pH after the pH reading stabilizes within 5 mV or 0.1 pH per minute.
  The time required for stabilization is about 5 minutes as a guide.
(2) Measurement of Acid number
i) Take 5 g of sample into 200 mL tall beaker and weigh accurately to 0.1 mg digits.
  Note that the weight of sample will be changed depending on the acid number.
ii) Add 125 mL of titration solvent and dissolve sample by stirrer.
  The stirrer speed must be adjusted to avoid the scattering of contents or taking the air into the solution.
iii) Immerse the electrodes and titrate by alcoholic KOH titrant until the end point pH.
  Also, perform the blank test with the same procedure of sample measurement.

4. Measurement conditions and results

Examples of titration conditions

Measurement of blank

Cndt No. 1
Method Set
Buret No. 1
Amp No. 1
D. Unit pH
S-Timer 120 sec
C.P. mL 0 mL
Direction
D.P. mL 0 mL
End Point pH 11.6 pH
Over mL 0.2 mL
Max.Vol. 1 mL
ConstantNo. 2
Size 0 g
Blank 0 mL
Molarity 0.1 mol/L
Factor 1.006
K 56.1
L 0
Unit mL
Formula D
Digits 4
Auto In Pram. Non
Mode No. 15
Pre Int 0 sec
Del K 0
Del Sens 0 mV
Int Time 60 sec
Int Sens 0 mV
Brt Speed 2
Pulse 40

 

Measurement of sample

Cndt No. 2
Method Oill
Buret No. 1
Amp No. 1
D. Unit pH
S-Timer 120 sec
C.P. pH 10.5 pH
Direction
D.P. pH 10.5 pH
End Point pH 11.6 pH
Over mL 0.1 mL
Max.Vol. 20 mL
ConstantNo. 1
Size 5.0012 g
Blank 0.075 mL
Molarity 0.1 mol/L
Factor 1.006
K 56.1
L 0
Unit mg/g
Formula (D-B)*K*F*M/S
Digits 3
Auto In Pram. Non
Mode No. 1
Del mL 0.2 mL
Int Timel 60 sec
Tran Timer 120 sec
Del mL2 0.05 mL
Int Time2 60 sec
Int Time 0 sec
Int Sens 0 mV

Measurement results

Measurement of blank Measurement of sample
Number of
Measurement
Size
(g)
Titer
(mL)
Size
(g)
Titer
(mL)
Acid number
(mg KOH/g)
1 0.074 4.9901 1.923 2.0900
2 0.076 4.9989 1.890 2.0490
3 5.0012 1.892 2.0500
Avg. 0.075 mL Avg. 2.06 mgKOH/g
SD 0.02 mgKOH/g
RSD 1.13 %

Examples of titration curves

Measurement of blank  Measurement of sample

5. Note

(1) Management of electrode
  It is recommended to activate the electrodes for about 5 minutes to pure water for each measurement. This is because when glass electrode is used for a long time in a nonaqueous solvent, the response speed and electromotive force decrease. Also potassium chloride crystallizes around the liquid junction of the reference electrode, which causes pH fluctuation.
(2) Maintenance of buret
  It is recommended to wash the flow channel of buret with water. This is because alcoholic KOH titrant have a tendency toward crystallization. When not using for a long time, please discharge titrant and then wash flow channel with water.
Keywords: JIS K2501, ASTM D664, Lubricant oil, neutralization number, Acid number, Potentiometric titration, Non-aqueous neutralization titration

 

*Some measurement would not be possible depending on optional configuration of system.

Hiranuma aquacounter autotitrator com-a19Lubricant petroleum products

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