Water content determination of bioethanol by Karl Fischer
Titration
Bioethanol is mixed with gasoline in various ratios in order
to reduce both the demand for gasoline and environmental pollution.
The gasoline-alcohol mixture is known in the USA as gasohol
and in Brazil as Gasolina Tipo C. In the USA the mixtures
E10 and E85, which contain 10% and 85% bioethanol respectively,
are widespread. In Brazil the bioethanol content of most mixtures
lies between 21% and 23%.
The ASTM standard E 1064 «Standard
Test Method for Water in Organic Liquids by Coulometric Karl
Fischer Titration» describes the coulometric Karl
Fischer titration for determining the water content.
For a water content >2% the recommended
test method is volumetric Karl Fischer titration
as per ASTM E 203. The volumetric
KF titrators from Metrohm meet all the specifications
required by the standard and are therefore extremely suitable
for this application.
Coulometric Karl Fischer Titration by Metrohm
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 biofuels 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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Biofuel
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