Difference between Steam and Vacuum Distillation

[Gandhar NImkar]

Hello Guys...

I know this is simple but this two concepts confuse me a lot. Like in vacuum distillation Pressure is reduced to increase the difference in boiling point between two components and steam distillation is where steam is introduced in the mixture to reduce the vapor pressure. So what is the actual difference between these two concepts? or is it similar concepts?

Thankyou in advance.

 

[jambaugh]

The two are similar in that one is reducing the boiling point for the distillate so that it can be distilled at a lower temperature, typically to keep it below temperatures where undesired reactions may occur such as breakdown of organic compounds. Vacuum distillation does this directly since boiling occurs when the vapor pressure at a given temperature exceeds the environmental pressure. Lower the environmental pressure and the substance boils at a lower temperature.

Steam distillation is an earlier method (according to Wikipedia) which accomplishes the same effect due to the fact that it is the total vapor pressure of both water and the desired distillate which must exceed ambient pressure. Thus the partial pressures of each (and thus the temperature) can be less than would be required for the pure substance to boil. The reason air doesn't have the same effect as the steam in this process has to do (I think) with the other end of things, the condensation process. To recover the distillate in a steam distillation process you need to condense both steam and distillate (and hopefully they are miscible in liquid form or otherwise easily separated). This still doesn't quite ring clear in my mind and there may be some other aspect of the phenomenon I'm missing.

 

[Gandhar NImkar]

The two are similar in that one is reducing the boiling point for the distillate so that it can be distilled at a lower temperature, typically to keep it below temperatures where undesired reactions may occur such as breakdown of organic compounds. Vacuum distillation does this directly since boiling occurs when the vapor pressure at a given temperature exceeds the environmental pressure. Lower the environmental pressure and the substance boils at a lower temperature.

Steam distillation is an earlier method (according to Wikipedia) which accomplishes the same effect due to the fact that it is the total vapor pressure of both water and the desired distillate which must exceed ambient pressure. Thus the partial pressures of each (and thus the temperature) can be less than would be required for the pure substance to boil. The reason air doesn't have the same effect as the steam in this process has to do (I think) with the other end of things, the condensation process. To recover the distillate in a steam distillation process you need to condense both steam and distillate (and hopefully they are miscible in liquid form or otherwise easily separated). This still doesn't quite ring clear in my mind and there may be some other aspect of the phenomenon I'm missing.

Yeah I guess in steam distillation steam has to be immiscible with the two components otherwise it would be a type of azeotropic distillation wherein steam is added as third component to effect separation.