Azeotrope

Azeotrope- is mixture of two or more liquids whose proportions cannot be separated by simple distillation. It is about phsycal chemistry I

1. AZEOTROPE by Narmin Hakhverdiyeva Nijat Quliyev Rehime Salmanova 27.12.2017

2. WHAT IS AZEOTROPE? “ An azeotrope ( a constant boiling mixture) - is a mixture of two or more liquids whose proportions cannot be separated by simple distillation . An azeotrope is formed when the liquid and vapour compositions are the same. W hen an azeotrope is boiled , the vapour has the same proportions of combining as the unboiled mixture. The name comes from the Greek words for ‘ boiling without changing’ . When the azeotropic composition has been reached , distillation cannot separate the two liquids.

3. WHAT IS AZEOTROPE? Azeotropes can form only when a mixture deviates from Raoult's law. Separation by conventional distillation is not possible Dewpoint and bubble point are the same at the azeotrope.

4. Minimum Boiling Azeotropes Each azeotrope has a chara c t eris t ic bo i ling p o int. The boiling point of an azeotrope is less than the boiling point temperatures of any of its is a Minimum boiling azeotrope.

5. The d i agram o n t h e ri g ht sho w s a p o si t ive a z eotr o pe of hypothetical constituents, X and Y. The bottom trace illustrates t h e boiling temperature of various compositions. Below liquid phase is in equilibrium. t h e bottom trace, only t he The top t r a c e ill u str a tes t h e vap o ur c o m p o sition t h e li q uid a t a temperatur e . above given Abo v e the top trac e , i s i n o n ly t h e vap o ur equilibrium.

6. Between the two traces, liquid and vapor phases exist simultaneously in equilibrium: for example, heating a 25% X : 75% Y mixture to temperature AB would generate vapor of composition B over liquid of composition A. The azeotrope is the point on the diagram where the two curves touch. The horizontal and vertical steps show the path of repeated distillations. Point A is the boiling point of a nonazeotropic mixture. The vapor that separates at that temperature has composition B. The shape of the curves requires that the vapor at B be richer in constituent X than the liquid at point A.

7. The vapor is physically separated from the VLE (vapor- liquid equilibrium) system and is cooled to point C, where it condenses. The resulting liquid (point C) is now richer in X than it was at point A. If the collected liquid is boiled again, it progresses to point D, and so on. The stepwise progression shows how repeated distillation can never produce a distillate that is richer in constituent X than the azeotrope .

8. Minimum boiling azeotropes examples separation of isobutanol and water separation of benzene and cyclohexane main application is to separate ethanol and water( dehydration of ethanol)

9. Entrainers - How do they work? An entrainer is an agent, which affects volality of one of the azeotrope combinings more than another If one of the combinings is more volatile, so it can be separated by distillation

10. The use of entrainers in the azeotropic distillation of alcohol The water+ethanol azeotrope can be separated by adding the entrainer nenzene or cyclohexane. When cyclohexane is added, it engages all of the water from the azeotrope , and then boiled, azeotrope vapouring and leaving the desired ethanol free of water Benzene has toxic effects,that is why cyclohexane has replaced it

11. Maximum Boiling Azeotropes Each azeotrope has a chara c t eris t ic bo i ling p o int. The boiling point of an azeotrope is more than the boiling point temperatures of any of its constituents is a Maximum boiling azeotrope .

12. The diagram on the right shows a negative azeotrope of hypothetical constituents, X and Y. Again the bottom trace illustrates the boiling temperature at various compositions, and again, below the bottom trace the mixture must be entirely liquid phase. The top trace again illus t r a tes t h e con d e n s at i on temperature co m p o sition s , o f vari o us and again , tr a ce t h e above the top m i x t u re m u s t be enti r e l y vapor phase

13. p o i nt with a The point, A, shown here is a boiling composition chosen very near to the azeotrope. The vapor is collected at the same temperature at point B. That vapor is cooled, condensed, and collected at point C. Because this example is a negative azeotrope rather than a positive one, the distillate is farther from the azeotrope than the original liquid mixture at point A was. So the distillate is poorer in constituent X and richer in constituent Y than the original mixture

14. Because this process has removed a greater fraction of Y from the liquid than it had originally, the residue must be poorer in Y and richer in X after distillation than before. If the point, A had been chosen to the right of the azeotrope rather than to the left, the distillate at point C would be farther to the right than A, which is to say that the distillate would be richer in X and poorer in Y than the original mixture. So in this case too, the distillate moves away from the azeotrope and the residue moves toward it. This is characteristic of negative azeotropes.

15. Maximum boiling azeotropes examples nitric acid  (68%) /  water , boils at 120.2 °C at 1 atm (negative azeotrope) perchloric acid  (71.6%) / water, boils at 203 °C (negative azeotrope) hydrofluoric acid  (35.6%) / water, boils at 111.35 °C (negative azeotrope) An  example  of a negative  azeotrope  is hydrochloric acid at a concentration of 20.2% and 79.8% water (by mass).

16. EXAMPLES ethanol  (96%) / water, boils at 78.1 °C sulfuric acid  (98.3%) / water, boils at 338 °C acetone  /  methanol  /  chloroform  form an intermediate boiling (saddle) azeotrope diethyl ether  (33%) /  halothane  (66%) a mixture once commonly used in  anaesthesia . benzene  /  hexafluorobenzene  forms a double binary azeotrope

17. Applications of azeotropes The use of specially chosen azeotropes is proposed as standards when testing gas chromatographs, detectors, columns and sample introduction systems. These azeotropic mixtures permit us to minimize the errors due to composition changes during sampling and sample introduction systems (intended for gases or liquids). The potentialities and advantages of such applications are illustrated using the azeotropic mixture of benzene and cyclohexane as an example. .

18. Applications of azeotropes These  azeotropic  mixtures permit us to minimize the errors due to composition changes during sampling and sample introduction systems (intended for gases or liquids). The potentialities and advantages of such  applications  are illustrated using the  azeotropic  mixture of benzene and cyclohexane as an example.

19. References: www.google.com www.cool.conservation-us.org www.wikipedia.org Atkin’s Elements of physical chemistry

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