Data No.

HIRANUMA APPLICATION DATA

Automatic Titrator

Lubricantpetroleum products

Acid numberin Lubricating oil

L1Jun.6.
2017

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 ofpotassium 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 byPotentiometric 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 frommeasurement of buffer solution is defined as the end point. The measurement with the latter end pointdetection will be introduced here.

2. Configuration of instruments and reagents(1) Configuration of instruments
Main unit：

Hiranuma Automatic Titrator

COM Series

Electrode：

Glass electrodeGE-101B：

Reference electrodeRE-201Z：

Thermistor electrodeTE-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” isregulated in “JIS K 2501”

3. Measurement procedure(1) Determination of the end point pHi) 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 numberi) 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 thesolution.
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 blankCndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mL
Direction
D.P. mL
End Point pH
Over mL
Max.Vol.

1Set
11pH
1200↑
0
11.6
0.2
1

ConstantNo.
SizeBlank
Molaritysec Factor
mL KL
mLpH UnitmL FormulamL Digits
Auto In Pram.

20 g
0 mL
0.1 mol/L
1.006
56.10Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

1500060
0240sec
mV
sec
mV

mL
D
4
Non

Measurement of sample

Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. pH
Direction
D.P. pH
End Point pH
Over mL
Max.Vol.

2
Oil1
11pH
120
10.5
↑
10.5
11.6
0.1
20

ConstantNo.
SizeBlank
Molarity
FactorKL

15.0012 g
0.075 mL
0.1 mol/L1.006
56.10pH
pH UnitmL FormulamL Digits
Auto In Pram.

mg/g(D-B)*K*F*M/S
3Nonsec
pH

Mode No.
Del mLInt Time1Tran Timer
Del mL2Int Time2Int Time
Int Sens

10.2
60
120
0.05
60
00mL
sec
sec
mL
sec
sec
mV

Measurement results
Measurement of blank
Number ofSize
Titer
measurement(g)(mL)
10.074－20.076－
3―－
Avg.

0.075 mL

Measurement of blank

Size
(g)
4.9901
4.99895.0012

Measurement of sample
Titer
Acid number(mL)(mg KOH/g)
1.923
2.09001.890
2.04901.892
2.0500Avg.
2.06 mgKOH/g
SD0.02 mgKOH/g
RSD
1.13 %

Measurement of sample

Examples of titration curves

5. Note(1) Management of electrode
It is recommended to activate the electrodes for about 5 minutes to pure water for each measurement. Thisis because when glass electrode is used for a long time in a nonaqueous solvent, the response speed andelectromotive force decrease. Also potassium chloride crystallizes around the liquid junction of thereference 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 thenwash flow channel with water.

Keyword：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.