The 756 and 831 KF Coulometers from Metrohm easily meet all the specifications demanded by the standard and are outstandingly suitable for this application
Water in biodiesel has been reported to have a number of effects.
The amount of water in biodiesel determines the calorific value and above all the shelf-life of the fuel.
Biodiesel with a higher water content has a clearly lower oxidation stability.
The lower the stability, the greater the probability that oxidation products will be formed during long storage periods.
These can cause engine problems due to deposits, particularly in the injection system.
Biodiesel is also hygroscopic (absorb water during storage) and water can collect at the bottom of storage tanks.
This free water promotes biological growth and the sludges and slimes produced may cause blockage of fuel filters and fuel lines and also corrosion of zinc and chrome parts within the engine/injection system can occur from prolonged exposure to water.
In order to avoid these effects from water, EN 14214 limits the maximum allowable water content to 500ppm.
The EN ISO standard 12937, Petroleum products - determination of water - Coulometric Karl Fischer method, describes the Karl Fischer coulometric titration for determining water content.
The 756 and 831 KF Coulometers from Metrohm easily meet all the specifications demanded by the standard and are outstandingly suitable for this application.
In most cases the sample can be directly injected into the reaction solution with a syringe.
Biodiesel normally mixes well in KF reagent but to increase solubility, xylene can be added.
Annex B of the standard also describes the volumetric determination of water content.
Metrohm also has suitable titrators for this application.
Many biofuels contain additives that can form side reactions during the KF titration.
In such cases Metrohm recommend using a KF oven instead of direct injection into the KF cell.
Using either the 832 Thermoprep or the 774 oven sample processor the sample is heated to 120C and the water is driven off and carried to the titration cell of the coulometer via a dry carrier gas.
Metrohm UK can offer Karl Fischer analysis as part of a comprehensive biodiesel analysis package.
