Fatty acid methyl ester

In the beginning, FAME was almost exclusively RME, rapeseed oil methyl ester on the market. Later expanded to PME, vegetable oil methyl ester, but in addition to vegetable oils and animal fats are now permitted as a raw material. The abbreviation FAME - fatty acid methyl ester - now only indicates the chemical description of the fuel, not the raw material used. It only needs to be regenerative and the product must then meet the requirements of EN 14 214.

Chemically, these oils are triglycerides. That 3-fatty acids are esterified with a glycerol molecule.
These molecules are extremely large. 3 x 16 - 18 C atoms from the fatty acids plus 3 C atoms from the glycerol give a total C number of 50 - 60.
For comparison: The vast majority of diesel fuel components have a molecular size of 10 to a maximum of 30 carbon atoms.

Chemically, this transesterification proceeds as follows:
Vegetable oil (triglceride) is split with the use of caustic soda in the components fatty acid + glycerol, esterifying the resulting fatty acid with methanol. Thereafter, the product FAME must be cleaned. With water, methanol, glycerol and sodium hydroxide are washed out and residual methanol removed by heating and stripping.
Vegetable oil, caustic soda and glycerine are used. As products you get FAME plus raw glycerine (especially glycerine with caustic soda).
If this produced biodiesel is now used in motor vehicles, regardless of its quality, the suitability of the vehicle for this fuel must be taken into account.
FAME, biodiesel is chemically an ester and esters have solvent properties. As it is e.g. Compared to ethyl acetate (paint solvents, nail polish remover) are very large molecules, these processes are slow. But they run off.
Thus, e.g. Plastic sample containers delivered to the lab are adhesive over time, labels stick to one another and labels become illegible. From varnished sheets that are coated with biodiesel, you can remove the color layer after a few days.

The production of biodiesel, unlike diesel fuel, which is continuously produced in a refinery, a batch production. Similar to baking, you take the ingredients and produce what you want. And as with baking, the result from batch to batch is not always constant.
This is the moment when analytics comes to work.
Quality outliers are extremely rare among a number of (reputable) biodiesel producers, but there are a significant number of companies in this market that are more concerned about compliance.

The following points need to be checked:

- Glycerol and glyceride content
If the transesterification is incomplete, there are still too many mono-, di- and triglycerides present.
Is the downstream purification process incomplete, are still glycerol and / or
Sodium and potassium are detectable by the lye. Too high residual amounts of the glycerides and the glycerol itself then lead to deposits in the engine.

- Methanol content and flash point
If the methanol is not completely removed from the product, the methanol content is too high and the flash point too low. This represents a security risk.

- Ash content, content of alkali and alkaline earth metals, acid number
Limit exceedances in this area are i.a. due to an unclean production process. The cleaning steps required for the product have not been carried out thoroughly enough.

- water content
Due to its polarity, FAME can release significantly more water compared to diesel. If the product has not been sufficiently dried or stored dry after production, it may contain water, which may cause corrosion in the engine.

- Iodine, oxidation stability, content of linolenic acid methyl ester and fatty acid methyl ester with more than 4 fatty acids.
If the oil used contains too many polyunsaturated fatty acids, the FAME produced may be u.U. not sufficiently chemically stable. He tends to harden and oxidize.

He gives information about the purity of the FAME. Is for manufacturing e.g. used oil (frit animal fat) has been used, the ester content will be lowered because some of the fatty acids have already been cracked by thermal stress. But also non-esterifiable components ("unsaponifiable") in oil, which were not separated during production, reduce the proportion of esters.
prEN 14 103: FAME, Determination of ester content and content of linolenic acid methyl ester.

The determination is not carried out according to the 100% (minus impurities) method, but with internal standard. So do not be surprised, results over 100% are possible.
Limit value: ester content at least 96.5% by weight
Rejection limit: ester content at least 94.7% by weight

The acid number determines the content of free organic and mineral acids.
EN 14 104: FAME, determination of acid number
Maximum limit of 0.50 mg KOH per g sample
Rejection limit maximum 0,54 mg KOH per g sample

The iodine value describes how much iodine can be chemically bound by FAME and is a measure of the content of unsaturated and polyunsaturated fatty acids in FAME.
EN 14 111: FAME, determination of the iodine value
Limit value maximum 120 g iodine per 100 g sample
Rejection limit maximum 123 g iodine per 100 g sample

This methyl ester has 3 unsaturated compounds in the fatty acid, so it is unstable against oxidation and resinification. The parameter is determined symtomatically by the oxidation stability and additionally by the iodine value. The content of linolenic acid methyl ester can be additionally determined in the determination of the total ester content from the same analysis without additional effort.

prEN 14 103: FAME, Determination of ester content and content of linolenic acid methyl ester.
Limit value 12.0% by weight of linolenic acid methyl ester
Rejection limit maximum 14.8% by weight linolenic acid methyl ester

One safety aspect, methanol is volatile, highly flammable and toxic. If there is too much of it in FAME, the flashpoint will be significantly lowered. (The converse conclusion is less clear)
EN 14 110: FAME, determination of methanol content
In this case, by heating the methanol contained in the FAME expelled and detected in the gas phase.

Maximum limit of 0.20% by weight of methanol
Rejection limit not more than 0.23% by weight of methanol

At these levels you will already find a significant decrease in the flashpoint.

Too high values are the result of an unclean transesterification. If you find too many glycerides, the transesterification was not complete. If glycerol is detected, the product has not been sufficiently purified. Both lead to motor problems. The coke residue can rise.
EN 14 105: FAME, Determination of free glycerin levels, total glycerol, mono-, di- and triglycerides (reference method)

If it is not possible to determine free glycerine by disturbances (for example diesel components), determine it with
EN 14 106: FAME, Determination of free glycerin content

Arbitration is EN 14 105, as the determination is carried out directly in the sample.

These metals, i.a. potential process liquor residues are determined as follows:
EN 14 108: FAME, Determination of sodium and sodium
EN 14 109: FAME, Determination of potassium content
prEN 14 538: FAME, Determination of calcium and magnesium content with ICP-OES
Limit values: maximum 5.0 mg / kg alkali, sum of sodium + potassium maximum 5.0 mg / kg alkaline earth, sum calcium + magnesium
Rejection limits: maximum 7.1 mg / kg alkali, sum of sodium + potassium maximum 8.1 mg / kg alkaline earth, sum calcium + magnesium

Phosphorus-containing compounds can enter into production as organic constituents of the oil used. If FAME contains too much phosphorus, deposits in the combustion chambers can be the result. The phosphorus content will decrease
EN 14 107: FAME, Determination of phosphorus content by ICP limit value maximum 5.0 mg phosphorus per kg sample
Rejection limit maximum 6.1 mg phosphorus per kg sample

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