Fatty acid methyl ester
Fatty acid methyl esters (abbreviated FAME from English f atty a cid m ethyl e ster ) are compounds of a fatty acid and the alcohol methanol . A mixture of FAMEs obtained from vegetable or animal fats (e.g. rapeseed oil) and used as fuel for diesel engines is called biodiesel .
properties
FAME made from vegetable fats are liquid at room temperature and some of their properties come very close to those of diesel fuel (hence the name "biodiesel"), but are also solvents with different effects than diesel fuel, which can lead to technical problems with sealing materials in engine systems . Fatty acid methyl esters can be used as an alternative fuel if the sealing materials are resistant to FAME.
FAME should be stored with as little oxygen as possible, as FAME reacts with oxygen from the air due to the double bonds in the long-chain unsaturated fatty acid methyl esters and can become resinous through the formation of bridges between the individual molecules. When using FAME as fuel it is necessary to maintain a high quality standard. The iodine number is a measure of the tendency to resin formation, as it is proportional to the carbon-carbon double bonds present. Fatty acid methyl esters with a high iodine number therefore resinify more easily than those with a low iodine number.
Manufacturing
Fatty acid methyl ester (FAME) may be by transesterification of fats or oils ( triglycerides ) with methanol produced. This reaction is catalyzed by acid or base. The trivalent alcohol glycerine is exchanged for methanol. There arise glycerol wherein, is obtained with the use of natural fats, always a mixture of various fatty acid methyl ester (having an even number of carbon atoms), as natural triglycerides generally include several different fatty acid residues and FAME as reaction products.
In technology, the equilibrium of the transesterification reaction is shifted to the side of the products, i.e. to the side of the fatty acid methyl esters, by removing the glycerine or by using an excess of alcohol (methanol).
FAME can also be made by esterifying man-made fatty acids. However, this route does not play a significant role in industry. Since one of the largest producers of FAME is biodiesel production, the proportion of FAME from purely synthetic fatty acids is decreasing. Another variant, which is also of little technical importance, is specific enzymatic transesterification using special 1,3-lipases. This specificity is not possible chemically and is used for the production of cocoa butters, margarine, butter and baking fats.
use
|
Fatty acid methyl esters are mainly used today for the production of biodiesel and can be used as a pure fuel as well as in any mixture with conventional diesel fuel . As an admixture component for diesel, the fatty acid methyl ester must meet specific, precisely defined quality parameters that are defined in the DIN EN 14214 standard.
FAME have a significantly lower viscosity than untreated vegetable oil; therefore it can be used as a substitute for the mineral diesel fuel without having to adapt the diesel engine . However, the fuel system components that come into contact with fuel, such as hoses and seals, must be resistant to the methyl ester and made of polytetrafluoroethylene (Teflon) or fluororubber (e.g. Viton). The solvent properties of FAME can lead to the dissolution of diesel residues in the fuel system and thereby clog the fuel filter, and biodiesel can also attack painted surfaces. Further problems can arise from the accumulation of biodiesel in the engine oil , which means that shorter oil change intervals are necessary.
Fatty alcohols and fatty amines , which are used, for example, to produce surfactants and emulsifiers , can also be produced from FAME . In the manufacture of engine and transmission housings in the automotive industry , casting molds are used that are made from molding sand and resins. For this so-called cold box system, SME, but also RME ( rapeseed methyl ester ), is used on a larger scale as a binder for the resin component. This enables emissions of problematic solvents in the BTX fraction ( benzene , toluene and xylene ) to be reduced; Furthermore, the use of methyl esters should also lead to technical advantages over the classic cold box systems.
The most common fatty acid methyl esters for biodiesel production are soybean oil methyl esters (SME; mainly in North and South America, also imported in Europe), rapeseed methyl ester (RME; mainly in Central Europe), palm oil methyl ester (PME) and fatty methyl ester (FME) obtained from animal fats . FAME from the oil of the physic nut ( Jatropha curcas ) and other oils are currently under development, but have not yet been used on a large scale.
Sulfonated fatty acid methyl esters are used as anionic surfactants , such. B. the α-methyl ester sulfonate (MES).
Individual evidence
- ^ Karl Laux, Günther Täuber, Joachim Gohlke, Dieter Schirmer: Tenside , Volume 7 (Organic Technology III, editors: Heinz Harnisch, Rudolf Steiner, Karl Winnacker), ISBN 3-446-13186-8 , pp. 85-148, there P. 105.
- ↑ Martin Kaltschmitt, Hans Hartmann and Hermann Hofbauer (eds.): Energy from biomass. Basics, techniques and procedures. Springer Verlag, 2nd edition 2009, p. 757; ISBN 978-3-540-85094-6 .
- ↑ German Institute for Standardization: DIN EN 14214: Fuels for motor vehicles - Fatty acid methyl esters (FAME) for diesel engines - Requirements and test methods. German version Beuth, Berlin 2003.
- ↑ Bernd Fabry: Surfactants, properties, raw materials, production, applications . In: Chemistry in Our Time . tape 25 , no. 4 , 1991, pp. 214–222 , doi : 10.1002 / ciuz.19910250407 .
literature
- Norbert Schmitz, Jan Henke, Gernot Klepper: Biofuels: A Comparative Analysis . Ed .: Agency for Renewable Raw Materials . 2nd Edition. Gülzow 2009 ( fnr-server.de [PDF; 2.0 MB ; accessed on January 13, 2017]).
- Martin Kaltschmitt, Hans Hartmann and Hermann Hofbauer (eds.): Energy from biomass. Basics, techniques and procedures. Springer Verlag, 2nd edition 2009, pp. 757-758; ISBN 978-3-540-85094-6 .