Base number in lubricating oil (Hydrochloric acid method) | Autotitrat

HIRANUMA APPLICATION DATA

Automatic Titrator

Data No.

Oct. 7,2022

Lubricant petroleum products

Base number in lubricating oil
(Hydrochloric 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, hydrochloric acid method will be introduced. The international standard methods for base number with hydrochloric acid method are shown as bellow.
　・ JIS K2501 2003：Petroleum products and lubricants – Determination of neutralization number
　・ ASTM D4739-2011：Standard Test Method for Base Number Determination by Potentiometric Hydrochloric 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 alcoholic hydrochloric acid 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 hydrochloric acid 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 A” and 100 mL of titration solvent, “Buffer A” 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 Base 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 base 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 HCl 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.	47
Method	Set
Buret No.	1
Amp No.	1
D. Unit	pH
S-Timer	120	sec
C.P. mL	0	mL
Direction	↓
T Timer	0	sec
D.P. mL	0	mL
End Point pH	3.71	pH
Over mL	0.1	mL
Max.Vol.	20	mL

ConstantNo.	47
Size	0	g
Blank	0	mL
Molarity	0.1	mol/L
Factor	0.9985
K	0
L	0

Unit	mL
Formula	D
Digits	3
Auto In Pram.	Non

Mode No.	15
Int Time Max	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.	48
Method	Oil1
Buret No.	1
Amp No.	1
D. Unit	pH
S-Timer	120	sec
C.P. pH	6	pH
Direction	↓
T Timer	0	sec
D.P. pH	6	pH
End Point pH	3.71	pH
Over mL	0.3	mL
Max.Vol.	20	mL

ConstantNo.	48
Size	5.0066	g
Blank	0.018	mL
Molarity	0.1	mol/L
Factor	0.9985
K	56.1
L	0

Unit	mg/g
Formula	(D-B)KF*M/S
Digits	3
Auto In Pram.	Non

Mode No.	11
Del mL	0.2	mL
Int Time1	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

Number of Measurement	Size (g)	Titer (mL)
1	–	0.020
2	–	0.015
Avg. （Blank）		0.018 mL

Measurement of sample

Number of Measurement	Size (g)	Titer (mL)	Base number (mgKOH/g)
1	5.0066	1.786	1.978
2	5.0291	1.770	1.951
3	5.0086	1.747	1.934
Statistic calculation		Avg. SD RSD	1.95 mgKOH/g 0.022 mgKOH/g 1.14 %

Examples of measurement 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
	When you do not use the equipment for a long time, it is recommended to wash the flow channel of buret with water.