5. Function Tools
MKC-710 59
Bromine number and index
5-2.
The degree of unsaturated hydrogen carbide in oil and petroleum products is indicated by
bromine number or index. The volumetric test method is specified in ASTM D2710, JIS
K2605 and K2435. The coulometric method with this unit is easier than volumetric,
however, it is recommended to refer to the volumetric testing procedure and specifications.
< Bromine number and index >
Bromine number
：
The amount of bromine (unit: g/100) consumed in 100g sample.
Bromine index
：
The amount of bromine (unit: mg/100) consumed in 100g sample.
< Principle of measurement >
The unsaturated hydrogen carbon reacts with bromine as follows:
R-CH=CH-R+Br
2
→
R-CHBr-CHBr-R
-
（
1
）
In coulometric titration, bromine is generated by electrolysis of anolyte containing
bromine ion:
2Br
-
Br
2
+2e
-
（
2
）
When generated bromine is consumed according to Eq. (1), the electrode detects
bromine consumption, and continues generating bromine according to Eq. (2).
Such bromine is generated in proportion to the electricity determined by Faraday’s Law.
From Eq. (1), Bromine reacts with coupled C=C evenly (1:1). Thus, one mol of bromine
(159.8g) is equivalent to 2
u
96500 coulomb, which means 1.2 coulomb/1mgBr
2
.
Based on the above principle, the electricity consumed in electrolysis is converted to the
exiting bromine.
Note
Follow the below instructions in order to obtain correct measurement results:
Replace anode and cathode reagent with new one respectively each day.
When the anolyte turns to white turbidity, change it with new one.
When the same anolyte and catholyte are continuously used, the measurement
results may produce larger amount in value than expected. Change the
anolyte in this case.
Do not share the titration cell with moisture titration.
