Dear Asma

Azeotropic mixtures may often be effectively separated by distillation by adding a third component, called entraine.In chemistry azeotropic distillation[s any of a range of techniques used to break anazeotropein distillation In chemical engineering, azeotropic distillation usually refers to the specific technique of adding another component to generate a new, lower-boiling azeotrope that is heterogeneous (e.g. producing two, immiscible liquid phases), such as the example below with the addition of benzene to water and ethanol. This practice of adding an entrainer which forms a separate phase is a specific sub-set of (industrial) azeotropic distillation methods, or combination thereof. In some senses, adding an entrainer is similar to extractive distillation. Separation of azeotropic mixtures is a topic of great practical and industrial interest. Most liquid mixtures of organic components form nonideal systems. The presence of some specific groups, particularly polar groups (oxygen, nitrogen, chlorine and fluorine), often results in the formation of azeotropes. Azeotropic mixtures may often be effectively separated by distillation by adding a liquid material (entrainer) to the system.

In most cases, azeotropic mixtures require special methods to facilitate their separation. There is a need to search for a separating agent other than energy, and this agent might be a membrane material for pervaporation or an entrainer for extractive distillationy adding a liquid material (entrainer) to the system. Entrainer completely miscible with the original components . Entrainer may (or not) form additional azeotropes with the original components . The distillation is carried out in a sequence of columns .The addition of the entrainer results in a residue curve map promising for separation. Both original components must belong to the same distillation region .e.g.

When the positive deviations from ideality are sufficiently large, the mixture is said to form a minimum-boiling azeotrope. The Figures below show the constant temperature phase diagram (Above) and constant pressure phase diagram plus equilibrium curve (Below) for a minimum-boiling azeotropic mixture of carbon disulfide (CS2) and acetone. The characteristic of such mixture is that the total pressure goes through a maximum (constant temperature phase diagram), and therefore the temperature goes through a minimum (constant pressure phase diagram), shown as point L.At point L, the concentration in the vapour phase is the same as the concentration in the liquid phase ( y = x ), and a = 1.0. This concentration is known as the azeotropic composition (0.61 mole fraction CS2). At this point, the mixture boils at a constant temperature (39.25 oC under 1 atm) and without change in composition. On the equilibrium diagram, it can be seen that at this point, the equilibrium curve crossed the 45o diagonal.

regards,

Prem Baboo

Add a new component maybe help. You could do some simulations using Aspen plus

Michael Päch sir. third component should only facilitate the separation by breaking azeotrope and not by changing pressure (that becomes pressure swing distillation problem nor any adsorption).

Edward Mausolf sir. components can be any ..we can have any azeotropic mixture with two components and entrainer will be third one.

Chenlin Lu ·sir. i have added a third component as entrainer with low boiling point using Aspen Plus but the entrainer is not facilitating in the separation of azeotropic mixture.

in a physical equipment if you add some amount of your mixture with the composition of other side of azeotrop to your second column your system would yourk as you want.

the other solution is to change pressure or temperature temporally and return to your desire point after some time

Azeotropes can be separated by distillation (azeotropic distillation, extractive distillation, pressure swing distillation). In the case of azeotropic distillation a solvent is added which forms a lower boiling azeotrope (e.g. separation of aliphatics-aromatics using acetone. example: benzene-cyclohexane-acetone (cyclohexane-acetone forms the low boiling azeotrope). But also in the case of extractive distillation a low boiling entrainer can be applied. But in most cases high boiler are preferred, since the entrainer should change the activity coefficients to be separated in the liquid phase. But a great part of a low boiling entrainer is in the vapor phase.

Juergen Gmehling sir, is there any way to perfectly separate azeotropic mixtures with a low boiling point entrainer ??

 Saeed Taji  sir, i am not doing this work experimentally. i am using a simulation software Aspen Plus.

Hi

Reactive Distillation is the solution to your problem.

Regards

Binoy Shah

Binoy Hasmukh Shah sir..how reactive distillation is its solution.

Hello Khan, better try with other entrainer, it seems your entrainer is not forming a mixture with any of the solvent in the mixture.

The first question is, whether your entrainer candidate changes the VLE of the original components favourably or not. If yes, your process is theoretically feasible. Of course, you have to find the right value of the entrainer flow rate, reflux ratio, feeding locations, etc. to function correctly. (Note that a light entrainer should be fed lower than the feed). So, if the process works, you'll get the entrainer and one of your original components in the top of the column.

@Laszlo Hegely. Thanks for your comment. I would like to add that entrainer is making azeotrope with one of the components of the binary mixture, hence changing its VLE. Parameters like RR, stage locations etc are correctly chosen. Issue is that entrainer is having low boiling point than the two components which are to be separated, so entrainer comes from the top of column ist and rest of the binary mixture is passing to  column 2. So, how can we break the azeotrope of that binary mixture with this low boiling entrainer.

Adding a third component which might absorb one of the components of the binary mixture and also shifting the dew point temperature of that particular component might be useful

@ Kofi Owusu Ansah Amano sir. I am adding third component but on distillation, being low boiling, it comes from the top of column 1 and the base mixture of azeotrope from the bottom of the column. so, this way entrainer doesn't facilitate the separation process.

Can you tell us more?

• Have you used Residue Curve Maps for your simulations?

@Asma, how are you doing on this?

I would like to advice you starting with your mass balances for this azeotropic distillation in combination with the residue curve maps. If you are able to understand this and calculate all the streams, then u will manage the simulation.

@ Panagiotis Kagioulis Sir. Thanks for the valuable suggestion.