Acid number in Lubricating oil | Autotitrator COM-A19

HIRANUMA APPLICATION DATA

Automatic Titrator

Data No.

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)KF*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.