Azeotrope iii

The previous entry dealt with the first type of azeotrope. This time we will go through the second one.

2) This type of azeotrope is caused by a strong negative deviation from Raoult's law.

P-x diagram in this case will look like this:

Since we know the overall pressure is lower than that of an ideal mixture, we can expect to see a minimum point. This again marks the azeotropic composition of the liquid mixture.

T-x diagram:

Since the vapour pressure at the minimum point is the lowest, a maximum boiling temperature at exactly the same composition is expected. The azeotrope has the highest boiling point. That is why this type of azeotrope is also called 'maximum-boiling azeotrope'.

If we perform the separation process via distillation with feed composition lower than azeotropic composition, we will get azeotrope at the bottom and pure A at the top of the column. In this case Azeotrope will always come out at the bottom.

Similarly it is also impossible to obtain both pure A and B regardless of the feed composition.

Next we will have a look at several ways or solutions that have been applied to overcome this problem.