Different residue for different distillation methods?

[David Hendriks]

Hi. I work in a petrochemical lab, and there is some debate over how much of a difference different weathering techniques have on the final composition of the leftover residue.

For instance, say we have a natural crude oil, complete with waxes, asphalts, and all the light-end organic compounds. We reduce the volume by 20% of several portions of this oil using the following methods:

1. Distilling with a rotating distillation device,
2. Distilling with a simple ASTM style method using a round flask sitting in a heating device,
3. Doing both of the previous distillations but under a vacuum,
4. Leaving a pool of the oil in a tray and letting the wind from a fan blow over it, and finally
5. Sparging the oil in a plastic bucket with a pump feeding air into a dispersion-stone in the bottom

Anyways, with all these methods performed on the same starting oil and all removing the same % of volume, can we expect the final product from all these tests to be similar in composition? Do you think some will have more light-ends left over, while others will have more heavy?

Any thoughts and literature recommendations welcome.

[Sensei]

Quote

Different residue for different distillation methods?

If traditional fractional distillation will result in creation of azeotrope, there is needed appropriate for compound azeotropic distillation.

e.g. vacuum distillation will give you more ethanol than 96% (4% of water).

High enough temperature during traditional distillation can split compounds, or cause unpredictable reactions with other compounds present in solution.

 

[John Cuthber]

Apart from any water present (and I think that's typically  removed) the components of crude oil are unlikely to form an azeotrope. But it's still likely that the relative volatility of the components at different temperatures will change, so it's likely that you will end up with a different composition depending on temperature.
I'd not like to have to predict what the changes are except that I'd guess that it would affect polar materials more than non polar ones (for a given normal boiling point).

It's going to be complicated- especially if the blowing air through it  oxidises things.
 The only way to find out is to do the experiment.

 

[David Hendriks]

Yeah, i suppose so. If we end up doing some tests I might come back and say to some degree what the results were, but i'm generally told not to share much. Thanks for the help though!