Question

If a mixture of water-ethanol containing a significant amount of methanol is being distilled (separation by VLE), can we state that the methanol is not a problem because it boils off first?

Answer 1

No it should not be any problem at all because the mixture of water and ethanol form an azeotropic mixture which boils at constant temperature of 78.2 degree celsius which is lower than their individual boiling ppoint.Now,when you will mix methanol to the water and ethanol mixture both the alcohol will readily mix with each other because of polar interaction and having same nature.Since the methanol is having lower boiling point so with increase in the methanol content to the mixture, the effective boiling point of the methanol and ethanol will shift in lower direction i.e. it will decrease much as compared to boiling point of ethanol which is 78.4 degree celsius.So if we compare the boiling point of water which is 100 degree celsius and the effective boiling point of methanol and ethanol mixture, we will have larger temperature difference and hence a larger amount of driving force for the mass transfer to occur.So mixing methanol with ethanol water mixture will aid in the distillation process while we can get the azeotrope for this mixture also but we will get a larger separation because of larger driving force.So there is no issue at all with methanol mixing.