2 replies to this topic

[adeliry]

For energy saving in our plant( Styrene monomer plant), we use azeotrope mixture of Ethylbenzene and water as reactor feeds. azeotrope of EB/Water is 67/33 and boil at 92 0c. we try to vaporize this mixture in azeotropic condition but we can  only  change the flowrate of the EB or Water and every time we use this proportion to flow of them. some times Ethylbenzene vaporize more that this proportion and boiling temperature is also change and some times water boils more. we dont have any means to control condition.

I want know how is it possible to force vaporization in azeoptropic condition. pressure of EB/Water containing vesel depend on system pressure and is constant and we dont use pressure change to effect on vaporization because it effect on reaction section.



It is good to know that EB/Water main vaporizer is a heat exchanger that cooled down the EB/SM distillation tower's overhead by vaporization of EB/Water, also we have a little exchanger to tuning the vaporization.

[adeliry]

Can any one help me?

[cjohn]

Adeliry,
I do not have an answer for you, but I do have some questions that may lead there. In my limited experience with azeotropes, I have found that when you are at the azeotropic conditions, you will not be able to change the composition. However, you have stated that sometimes you have more EB boiling off and sometimes you have more water boiling off. Some of my questions may be based off my own confusion with the process, so I apologize ahead of time if they are not on track.

1. Could you have an EB/water mixture that is significantly different than your stated 67/33 at different times? If you do not have a stable feed composition, then you are going to see the boiling point and composition move, although it should be moving towards your azeotrope.

2. Are you sure that this is an azeotropic mixture at the pressure of the operation? You can break an azeotrope by changing the pressure. I am not familiar with the EB/water.

3. It appears that your control scheme is to add a pure stream of EB to a stream of water at the 67/33 composition. This may be a silly question, but is this on a mass, mole, or volume basis? Is the 67/33 on the same basis? Are your instruments and controls accurate enough to maintain the 67/33?

4. Could you provide a sketch of the process for others to see? That may help someone to get a clearer understanding of the problem.

I hope that, when you think of answers to these questions, you are able to see another layer into your problem and can find your issue.

Take care,

CJohn