The definition of the term "Asphaltenes" should not be a problem since it is clearly defined both in standard IP 143 and ASTM 6560. The definition is simply "n-wax free organic material insoluble in heptane, but soluble in hot toluene".

The reason for the confusion is that there have been a tendency to extend the use of the term asphaltenes beyond the definition above to all kind of materials, which have shown to precipitate from crude oils and bitumen. The confusion has even been worse by the use of the term "asphaltenes" also for assumed dispersed material in the bitumen and crude oil although it can not be possible that the different fractions isolated as "asphaltenes" all can be identical to the dispersed phase in bitumen. Recent findings during work with solubility parameters have shown that there in fact is unlimited ways of causing instability by dilution of bitumen and crude oil with unsuitable solvents or combination of solvents.

A suggestion how to solve the question about definition is to simply restrict the use of the term "asphaltene" to the definition in ASTM 6560 and use another expression for all other fractions which may precipitate from bitumen. A suggestion may be to use "(solvent name) insolubles" for example "n-pentane insolubles" or "2-butanone insolubles" etc to describe a precipitate caused by diluting the bitumen with a particular solvent.

I also suggest that we do not use the term "micelles" to describe a dispersed phase in bitumen, because this will lead to the ideas of micelle formation well known from the emulsion science. All scientific evidence point in the direction that this kind of micelles with a high degree of order does not exist in bitumen. SAXS experiments have clearly shown that the particles, which scatter X-rays are highly amorphous. If we would like to address a dispersed phase in bitumen we could call it "bitumen insolubles" or even better use the name for the particular bitumen followed by insolubles.

In practical applications the term "asphaltene" is sometimes also used for a lot of different types of unspecific precipitates or depositions seen in tanks or pipelines. In this case it is really misleading and a serious mistake to use this term since this may (and probably has) led to a lot of research in unfruitful directions. The most common misconception is that the material which is causing the precipitate is a kind of dispersion in the oil which is identical with the "asphaltenes" which in the laboratory is precipitated by any of the n-alkanes commonly used.

Per Redelius
Product Technology
NYNÄS ABP