The Metrohm 873 is specifically designed to analyse the oxidative stability of biodiesel, diesel and blends
For the last year Metrohm says it has been developing a new instrument for analysis of diesel and biodiesel.
It has improved on the existing technology of the 743 Rancimat to specifically design an instrument for the biofuels market.
The principle behind the 873 Rancimat is as follows: during the measurement a stream of air is passed through the sample which is contained within a sealed and heated reaction vessel.
These conditions accelerate the rate of oxidation of the fatty acid methyl esters in the sample, with peroxides being initially formed as the primary oxidation products.
After some time the fatty acid methyl esters disintegrate completely; the second oxidation products formed include low-molecular organic acids in addition to other volatile organic compounds.
These are transported in a stream of air to a second vessel containing distilled water.
The conductivity in this vessel is recorded continuously.
The organic acids can be detected by the increase in conductivity.
The time elapsed until these secondary reaction products appear is known as the induction time or induction period.
The 873 has been modified to manage the very aggressive nature of biodiesel.
Modifications include chemically resistant iso-versinic tubing and chemically resistant glass measuring vessels.
Metrohm says it has also proved that this principle method can be used to measure the oxidative stability of diesel and biodiesel/diesel blends.
When developing the method, it was found that with volatile oils, mineral diesel and diesel blends there was a degree of evaporation on heating, resulting in wrong determination values.
This was overcome by developing longer (250mm) reaction vessels for measurements with these particular samples.
These longer vessels reduce evaporation loss through the refluxer condensation principle which occurs within the longer vessels giving accurate reproducible results.
The updated software includes flexible and comfortable user administration with login functions; this can be used to define detailed access rights for groups of users and individuals.
The software parameters are now also specific for biodiesel and diesel analysis.
