HIRANUMA APPLICATION DATA

Lubricantpetroleum products

Automatic Titrator

Data No.

L5Oct. 7.
2022

Acid numberin Refrigerating machine oil

1. Abstract
Refrigerating machine oil is used in a state mixed with refrigerant such as hydrofluorocarbon. The
official standard of refrigerant (e.g. JIS K 2211) specifies the acid number test according to JIS K 2501.
It is indicated by "milligrams of potassium hydroxide required to neutralize acidic components containedin 1 g of the sample".
In this article, we apply the color-indicator titration method described in JIS K2501 to automatic titrator,
and introduce measurement of acid number in refrigerating machine oil by photometric titration. Acidand base number with color-indicator titration is also regulated in ASTM D974. p-Naphtholbenzein isused as color indicator.

2. Configuration of instruments and reagents(1) Configuration of instruments
Main unit: Hiranuma automatic titrator COM Series with photometric unit M type

Electrode: Interference filter 650 nm(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 waterIndicator: 1 g of p-naphtholbenzein dissolved in 100 mL of titlation solvent

3. Measurement procedure(1) Take 20 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.
(2) Add 100 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.
(3) Immerse the electrodes and titrate by alcoholic KOH titrant. Also, perform the blank test with the sameprocedure 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. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

37
B-Cross
12T%
60 sec
0 mL
0 sec
0 mL
1000
0.3 mL
1 mL

ConstantNo.
SizeBlank
Molarity
Factor
KL

370 g
0 mL
0.1 mol/L
0.977556.10Unit
FormulaDigits
Auto In Pram.

Mode No.
Int Time MaxDel K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

4160
00102028Mode No.
Int Time Max
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

4260001020220sec
mVsec
mVmL
D4Non

Measurement of sample

Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

38
B-Cross
12T%
60 sec
0 mL
0 sec
0 mL
1000
0.5 mL
20 mL

ConstantNo.
SizeBlank
Molarity
FactorKL

38
20.059 g
0.123 mL
0.1 mol/L
0.977556.10Unit
FormulaDigitsAuto In Pram.

mg/g(D-B)*K*F*M/S
4NonsecmVsecmV

Measurement results
Measurement of blank

Measurement of sample

Measurement

Size

Titer

Measurement

Size

Titer

Base number

number(g)(mL)

number(g)(mL)(mgKOH/g)

1－

0.123

1

20.05900.151

0.0077

2－

0.122

2

20.0084

0.157

0.0093

Average

0.123

Average0.0085 mgKOH/g

Measurement of blank

Measurement of sample

Examples of titration curves

5. Note(1) Management of the photometric probe
As the probe is used, it becomes dirty on light path and the transmittance decreases. Therefore it isnecessary to wipeout adherents with soft cloth on regular bases.
(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 andthen wash flow channel with water.
(3) End point detection
When the endpoint is not detected sharply, it may be due to the absorption of carbon dioxide. In thiscase, purging nitrogen gas in the head space of the beaker improves end point detection.
Keyword：JIS K2211, JIS K2501, ASTM D974, Refrigerating machine oil, Refrigerant, Acid number, Color indicatortitration, Photometric titration.