Water content determination of biodiesel by Karl Fischer
Titration according to EN ISO 12 937
Water content as a quality parameter
The water content of biodiesel determines the calorific value
and, above all, the storage life of the fuel. Biodiesel with
a high water content has a clearly lower oxidation stability.
The lower the oxidation stability, the greater the probability
that oxidation products will be formed during a longer storage
period. These could damage the motor, in particular the fuel
injection system, by forming deposits. In order to avoid this,
DIN EN 14 214 limits the water
content of biodiesel to 500 ppm. Read
more ...
Coulometric Karl Fischer Titration by Metrohm
The EN ISO standard 12 937
«Petroleum products – Determination of water
– Coulometric Karl Fischer titration method»
describes the coulometric Karl Fischer titration for determining
the water content. The 756 and 831 KF Coulometers
from Metrohm easily meet all the specifications
stipulated in the standard and are outstandingly suitable
for this application. In most cases the sample can be injected
directly into the reaction solution. In order to improve the
solubility of the samples, xylene (dimethylbenzene) is added
to the KF reagent.
Get rid of side-reactions and contaminations
Many biodiesel fuels contain additives that could participate
in side-reactions during the direct coulometric
Karl Fischer titration. In such cases Metrohm recommends that
the biodiesel sample is not injected directly into the reaction
solution. Instead the water contained in the biodiesel should
be driven off in a Karl Fischer oven. The
832 KF Thermoprep oven is suitable for this.
The water is driven off at 120 °C and transported to the
titration cell of the KF Coulometer in a stream of carrier
gas (dry air or inert gas). This process can be completely
automated with the 774 Oven Sample Processor.
An additional option is reagent exchange using an automated
dosing device. The KF vessel does not have to be
opened during this procedure. This means that no hazardous
reagents have to be handled, which results in increased operator
safety.
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