5 replies to this topic

[ton]

Dear All member
I would like to correlate Reid vapor pressure and distillation curve. Please correct me if I am wrong. RVP is a vapor pressure at a measurement temperature of 37.8°C (100°F). Assume RVP of oil A> oil B> oil C. If I have a distillation curve. Is it always that at temperature of 37.8 C (in the distillation curve), the volume evaporated of oil A > oil B > oil C.
Thank you very much.

[Zauberberg]

In theory - no, in practice - most likely. For example, imagine heavy vacuum residue with high amounts of dissolved light ends: this petroleum cut will give you higher vapor pressure at 38C than, for example, debutanized gasoline.

However, for practical purposes, straightforward relationship between RVP and distillation curve is almost always the case - but keep in mind that distillation profile which is affected by RVP is only the front-end. If you observe D86 or TBP curves of debutanized gasoline, and of the same gasoline from which C5-cut is removed, you'll notice the biggest difference only in the front end of distillation curves. The difference exists through the whole temperature range, though, but the front end is one which is affected the most.

[ton]

The attached figure shows the distillation curve for three oil. Note that RVP of oil A> oil B> oil C.
As Zauberberg said, distillation profile which is affected by RVP is only the front-end.
However, is it strange when we look at the temperature at starting to evaporate which should be affected by RVP. Oil A is the highest RVP, however, oil B start to evaporate at lower temperature(at 36 C) than that of oil A (at 42C). Thank you very much.

Attached Files

•  Distill_curve.jpg   24.91KB   61 downloads

[Root]

You can't correlate RVP and Distillation curve because Distillation is based on different boiling point and RVP is based on composition. As in your question oil A> lighter than oil C, the RVP of oil C is less obeviously. but distillation curve boiling point of oil C will be high.

Therefore, as Zaubeberg quoted, on a practical basis you can't justified the correlation or RVP and Disttilation curve.

Thanks

[Zauberberg]

Distillation curves for oils A and C look very strange, and probably they are not accurate. You'll hardly see such shape (look at 50% point) anywhere with existing petroleum cuts/blends.

In my opinion it is not strange to have such differences in RVP, especially if blends are in question. Imagine, for example, one heavy diesel sample with equilibrium methane dissolved in it, and another sample of abovementioned debutanized gasoline. It is very much likely that heavy diesel with methane will have higher RVP than gasoline, but distillation profile would be quite different. I believe 5% D86 or TBP point for diesel sample would be much above than the one of gasoline.

Best regards,

[ton]

Thank you very much for Zauberberg and Toor. Could you please give me some reference?
Or some results that shows the oppose between front end of Distiilltion curve and RVP.
Thank you again.

Best regards,