May 10, 2010

Pressure Swing Distillation - Use it Ecnomically - 1

All the process engineers must have come across the term azeotropic distillation in some or the other way. Most of the time the conventional approach of handling an azeotropic mixture is to carry out extractive distillation using some solvent.

Very easy know. So many lists of such solvents are available in the literature or on internet and then we go ahead with that age old philosophy.

You know, I NEVER follow conventinal things. So Pressure Swing Distillation (which is now becoming more popular) is an effective answer to such problems.

To define it & understand it properly, I would like to first cover up few basics of azeotropes which you may be knowing if you were good in theory during your college days.

Azeotrope - means a mixture of liquid which generates vapor of same composition as that of liquid.



There are two types of azeotropes - Negative azeotropes & Positive Azeotropes.

Negative Azeotropes are those in which the azeotropic boiling point is higher than any of its constituent's boiling point e.g. the mixture of Formic acid & water as given on wikipedia.



Positive Azeotropes are those in which the azeotropic boiling point is lesser than any of its constituent's boiling point e.g. the mixture of Chloroform & Methanol.



Now curves represented in above diagrams are simple T-x-y OR P-x-y curves which are commonly found in distillation textbooks, but what we forget or do not know is that these curves are pressure dependant curves. This means the phase envelope changes with change in system pressure. So if you alter the pressure of the system the azeotrope point or composition will change. You can find it out how? YES...Whenever something goes out of track always remember RAOULT's LAW.

Rest in next post.........


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