One of the big issues related to petroleum chemistry is the definition of asphaltenes.  We all have in mind that asphaltenes are similar to asphalt.  They are black, viscous and sticky.  The scientific definition of asphaltenes should not be vague.  The isolation of asphaltenes from crude oils and bitumen has been accomplished under different conditions.  Usually, users and analysts refer to standard methods, and because they are standard, the assumption is that these methods are good, in terms of precision and accuracy.  Most of the time this is true from the analytical perspective but for asphaltenes, separated and extracted as a group of unknown compounds, these assumptions have a big chance for failure. 

Because asphaltenes are not well understood, they are very loosely defined.  Several factors influence the quantity and most probably the quality of asphaltenes. 

• The main factor is solvent.  Many solvents are tested. There is a correlation between the amount of precipitated asphaltenes and the carbon number of the solvent.  The higher the carbon number of the solvent is the smaller the asphaltenes quantity will precipitate out. 

• The contact time between the solvent and the crude oil or bitumen also has an influence on the amount of asphaltenes.  Studies on the effect of time showed a plateau reached after 2 to 4 hours; but do all crude oils behave in a same way?

• The volume of solvent compared to the volume of crude oil or bitumen, 20, 30 or 40 times higher.  What is the best ratio that is not sensitive to the crude oil and to the solvent?

• The precipitation temperature could also have an impact on the asphaltenes precipitation.  Cold isolation versus hot isolation.  Do they lead to the same asphaltenes?

There is always a dilemma on the relationship between quantity and quality.  During a precipitation experiment, are the first asphlatenes coming out of the solution similar to the last ones?

There is a big confusion among the users who do not have time to collect all the information of asphaltenes methodologies and decide on an “appropriate one”.  Analysts should make an effort to standardize asphaltenes isolation protocol.  This is very challenging because analysts have many questions on asphaltenes.  But one thing for sure: if we do not start to put our effort at the same direction the chance of sorting this issue will be very slim.

The main parameters to start with are solvent, time, temperature and ratio solvent/feedstock.  Let’s agree on these parameters in order to be able to move forward with quality identification tools. 

To illustrate the idea behind what I wrote I compiled the following data:

RT: room temperature; C5 and C7 are pentane and heptane respectively

Isn’t it confusing?!

The danger is that Scientists around the world build models and study the behavior of asphaltenes, establish correlations etc. with high chance of having different types of asphaltenes.  Heavy oils and bitumen are more and more of interest for exploration and upgrading nowadays; asphaltenes impact will be of greater potential in the future.  We should act now.