No-harm list of oxidation stabilizers for biodiesel

Whenever additives for biodiesel (FAME) are used as blending component in diesel fuel it is very important that the additives are not interacting with the mineral fuel, the additives of the mineral fuel or the engine oil in any forbidden way. In addition to the substance BHT (3,5-di-tert-butyl-4-hydroxy-toluene), known as stabilizer of biodiesel for a long time, other substances and products are available in the market. To ensure the safe use, negative impacts of these additives on the performance of the engine must be excluded, from the mixing with the biodiesel (solution behaviour) and the use as blending component in diesel fuel (B7).

According to the state of the art, the blending components in biodiesel are no flow improvers but increasingly oxidation stabilizers to ensure that the ready biodiesel has sufficient oxidation stability. The diesel fuel norm - DIN 51628 - as norm for a B7 blended fuel - "recommends urgently" raising the limit of the oxidation stability for added fatty acid methyl esters from 6 hours to 8 hours and prescribing a minimum addition of 200 mg BHT/kg (or a quantity of another suitable stabilizer which ensures an equivalent effect). The recommended maximum addition of oxidation stabilizers which the DIN norm permits is 500 mg/kg irrespective of the composition of the stabilizer. On the request of the involved additive suppliers, oxidation stabilizers were tested for compliance with the so called no-harm criteria. The tests were made using methods agreed between the mineral oil industry and the AGQM. The criteria comprised the following tests:

Test for compliance with minimum requirements, among them no change of the safety characteristics of the biodiesel (e.g., flash point, water hazard class), no illegal change of the norm parameters according to EN 14214 for biodiesel, availability of clear application descriptions for the additive
- XUD9 test according to CEC F-23-1-01 (engine test – nozzle fouling)
- DGMK filtration test 663
- Test for engine compatibility (based on DGM 531-1)

Products complying with these requirements are published in a list. Reference to this list is made in the diesel fuel norm DIN 51628. In addition to this, a defined testing algorithm (Relative Efficiency Test - RET) is applied to define, by way of four different scenarios, the quantities of other additives which produce the same effect as 200 mg BHT/kg.

The no-harm list is maintained by AGQM as open list, i.e., interested suppliers of additives can file an application for testing their product(s) at any time.

Products of the following suppliers have passed the no-harm test successfully
(as of December 29, 2008):

The relative efficiencies in comparison with BHT were defined for four different scenarios for all products listed above. If there is justified interest, the results can be disclosed with the approval of the respective company.

The final project report and the test procedure are available via download (only with costs) from the AGQM website: www.agqm-biodiesel.de (Downloadarea)