Base number in lubricating oil (Perchloric acid method) | Autotitrator COM-A19 - JM Science
HIRANUMA APPLICATION DATA Automatic Titrator Data No. L3 Jun.6. 2017
Lubricant petroleum products Base number in lubricating oil
(Perchloric acid method)

1. Abstract

The base number of lubricant oil is one of the important index for judging its quality. Measurement of base number is defined in several standard test methods. It is indicated by “milligrams of potassium hydroxide equivalent weight to acid required to neutralize basic components contained in 1 g of the sample”. There are two methods of base number, hydrochloric acid method and perchloric acid method. In this article, perchloric acid method will be introduced. The international standard methods for base number with perchloric acid method are shown as bellow.
 ・ JIS K2501 2003:Petroleum products and lubricants – Determination of neutralization number
 ・ ASTM D2896-06 : Standard Test Method for Base Number of Petroleum Products by Potentiometric Perchloric Acid Titration
The potentiometric titration process is as follows:
 1) Weigh sample exactly corresponding to base number and dissolve it in a titration solvent.
 2) Immerse glass electrode and reference electrode.
 3) Start titration with perchloric acid in acetic acid solution.
There are two procedures for perchloric acid titration, A and B on ASTM D2896. Procedure A and B use different titration solvent volume and sample weight. In this article, measurement with procedure B will be applied. Inflection point is defined as the end point if it obtained sharply. If it’s not clear, back-titration method could be applied. Back-titration method is mentioned in “HIRANUMA APPLICATION DATA No. L11”.

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
Inner solution should be changed; it is described below. to below described
(2) Reagents    
  Titrant : 0.1 mol/L perchloric acid in glacial acetic acid standard solution
  Titration solvent : Mixture of 500 mL of glacial acetic acid and 1 L of chlorobenzene.
Refer; Toluene can be used instead of chlorobenzene
  Inner solution : Saturated sodium perchlorate in glacial acetic acid

3. Measurement procedure

(1) Take 1 g of sample into 100 mL beaker and weigh accurately to 0.1 mg digits.
Note that the weight of sample will be changed depending on the base number.
(2) Add 60 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.
(3) Immerse the electrode and titrate by 0.1 mol/L Perchloric acid-Acetic acid standard solution.
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. 42
Method Auto
Buret No. 1
Amp No. 1
D. Unit mV
S-Timer 10 sec
C.P. mL 0 mL
T Timer 0 sec
D.P. mL 0 mL
End Sens 500
Over mL 0.1 mL
Max.Vol. 2 mL
ConstantNo. 42
Size 0 g
Blank 0 mL
Molarity 0.1 mol/L
Factor 1.003
K 0
L 0
Unit mL
Formula D
Digits 4
Auto In Pram. Non
Mode No. 19
Pre Int 0 sec
Del K 0
Del Sens 0 mV
Int Time 5 sec
Int Sens 3 mV
Brt Speed 2
Pulse 40

 

Measurement of sample

Cndt No. 41
Method Auto
Buret No. 1
Amp No. 1
D. Unit mV
S-Timer 30 sec
C.P. mL 0 mL
T Timer 0 sec
D.P. mL 0 mL
End Sens 200
Over mL 0.3 mL
Max.Vol. 20 mL
ConstantNo. 41
Size 1.0126 g
Blank 0.025 mL
Molarity 0.1 mol/L
Factor 1.003
K 56.1
L 0
Unit mg/g
Formula (D-B)*K*F*M/S
Digits 4
Auto In Pram. Non
Mode No. 8
Pre Int 0 sec
Del K 5
Del Sens 0 mV
Int Time 5 sec
Int Sens 3 mV
Brt Speed 2
Pulse 40

 

Measurement results

Measurement of blank

Number of

Measurement

Size

(g)

Titer

(mL)

1

0.025

2

0.025

Avg.

(Blank)

0.025 mL

 

Measurement of sample

Number of

Measurement

Size

(g)

Titer

(mL)

Base number

(mgKOH/g)

1

1.0126

2.227

12.236

2

0.9114

1.998

12.181

3

1.0073

2.218

12.250

Statistic

calculation

Avg.

SD

RSD

12.2 mgKOH/g

0.0366 mgKOH/g

0.30 %

Examples of measurement curves

Measurement of blank

 Measurement of sample

 

5. Note

(1)

Management of the 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. Since the electrolyte of the inner solution and the oil sample may adhere around the liquid junction of reference electrode and cause the fluctuation of the potential. Therefore it is recommended to clean the liquid junction periodically.

(2)

Experiment temperature

Acetic acid used as a solvent for the titrant has a relatively large thermal expansion coefficient, and when the temperature changes by 1 ° C, the titrant causes a volume change of 0.1 %. For accurate measurement, factor titration and sample measurement should be performed at the same room temperature as much as possible.

(3)

The inner solution of the reference electrode RE-201Z is filled with saturated KCl aqueous solution when purchased. For this measurement, it is necessary to replace inner solution to saturated sodium perchlorate in acetic acid solution. Replacement procedure is described below.

i)

Prepare the saturated solution of sodium perchlorate in acetic acid with reagent grade of these.

ii)

Discharge inner solution from reference electrode RE-201Z and wash inside it with water and then acetic acid.

iii)

Fill the prepared inner solution into reference electrode from the supply port.

iv)

Leave the electrode for one day before use.

 

Keywords:

JIS K2501, ASTM D2896, Lubricant oil, Neutralization number, Base number, Potentiometric titration, Perchloric acid titration

 

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

 

Hiranuma aquacounter autotitrator com-a19Lubricant petroleum products

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