Oxidation stability of biodiesel
(fatty acid methyl esters, FAME)
What is biodiesel?
In addition to other alternative fuels such as ethanol, methanol
or biogas (methane), fatty acid methyl esters are increasingly
being found on the market; these are also known as biodiesel
or FAME (fatty acid methyl esters). Fatty
acid methyl esters are usually obtained from oil seeds and
are mainly used in their pure form or mixed with conventional
diesel fuel in the transport sector.
Oxidation stability as a quality criterion for biodiesel
During manufacture the vegetable oil is transesterified with
methanol. This produces the methyl esters of the fatty acids
present in the oil together with glycerol as a byproduct.
Fatty acid methyl esters are relatively unstable on storage,
as like all natural oils and fats they are slowly oxidized
by atmospheric oxygen. The substances produced in this way
could cause motor damage. This is why the oxidation stability
is an important quality criterion for biodiesel; it is regularly
determined during the production process. With the 873 Biodiesel Rancimat this determination can be
carried out quickly and simply. The oxidation process can
be delayed by the addition of antioxidants. The 873
Biodiesel Rancimat can also be used to determine
the effectiveness of the antioxidants.
The use of alternative fuels from renewable vegetable
sources has become increasingly widespread in recent
years, as the life cycle of biogenic fuels is neutral with
respect to CO2 release. The carbon dioxide released
has already been assimilated from the atmosphere during plant
growth. In contrast to fossil fuels, biogenic fuels neither
contributes to the accumulation of CO2 in the atmosphere
nor to global warming. In addition, alternative fuels are
biodegradable and thus less environmentally harmful.
International Standards on Biodiesel Quality
The oxidation stability of fatty acid methyl esters has already
been included in various test methods as a standard parameter
used to define the minimum quality requirements of biodiesel:
- EN 14214 «Automotive fuels – Fatty
acid methyl esters (FAME) for diesel engines – Requirements
and test methods»
- EN 14112 «Fat and oil derivatives –
Fatty acid methyl esters (FAME) – Determination of
oxidation stability (accelerated oxidation test)»
- ASTM D6751-06b «Standard specification for
biodiesel fuel blend stock (B100) for middle distillate
fuels»
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