[ayashioki]

This n-butanol is from my methanolic crude extracts (being suspended with water) which is fractionated with petrol ether, chloroform, ethyl acetate and n-butanol. But I found that the butanol extract is very hard to dry.

Can anyone suggest any other ways to dry my n-butanol fractions?

[discodermolide]

Butanol forms an azeotrope with water. If you don't have much water present add anhydrous sodium sulphate, stir a while and filter. It will then be dry.

[curiouscat]

How much water approximately  is there in it, any idea? 1%? 10%? 80%?

@discodermolide:

A question, perhaps related to the OP's post; but more to satisfy my understanding:

My data indicates that 1-Butanol and H2O form an azeotrope (as you had said) at 93°C and 55% (w/w) of 1-Butanol in the liq. at the azeotropic point. 

My question is, say you had a Butanol + H2O mixture with just 5% H2O in it. Now the azeotrope shouldn't affect your ability to distill away the H2O, correct? And this ought to hold for all H2O conc. so long as they are less than 45% H2O?

Just wondering if my analysis is correct.

[Babcock_Hall]

Assuming I am reading this table correctly, 8% by weight for butanol and 4% by weight for pentanol.  Scroll down:
http://faculty.swosu.edu/william.kelly/pdf/ch17.pdf

[curiouscat]

Assuming I am reading this table correctly, 8% by weight for butanol and 4% by weight for pentanol.  Scroll down:
http://faculty.swosu.edu/william.kelly/pdf/ch17.pdf

Thanks @Babcock_Hall. Though I think that table means 8% Butanol in H2O? Not 8% H2O in Butanol. Correct?

I was expecting the OP has something like 80% Butanol and 20% H2O.

http://www.chemeng.ed.ac.uk/people/jack/azeotrope/hetero.html#b

I interpret the solubility gap to mean that in any Butanol-Water mixture you can have H2O either less than 20% or more than 92% but never at any conc. in between those limits.

[Babcock_Hall]

Assuming I am reading this table correctly, 8% by weight for butanol and 4% by weight for pentanol.  Scroll down:
http://faculty.swosu.edu/william.kelly/pdf/ch17.pdf

Thanks @Babcock_Hall. Though I think that table means 8% Butanol in H2O? Not 8% H2O in Butanol. Correct?

Now that I have reread the presentation, I think that you are correct.  The trend for water in the alcohols is probably similar, but I don't have these data at the moment.

[orgopete]

My data indicates that 1-Butanol and H2O form an azeotrope… at 93°C and 55% (w/w) of 1-Butanol in the liq. at the azeotropic point. 

My question is, say you had a Butanol + H2O mixture with just 5% H2O in it. Now the azeotrope shouldn't affect your ability to distill away the H2O, correct? And this ought to hold for all H2O conc. so long as they are less than 45% H2O?

Just wondering if my analysis is correct.

Correct. If more water was present, then all butanol would distill as an azeotrope before water is removed to distill any remaining and higher boiling butanol. If you start with 5% water, the water will be removed as the lower boiling azeotrope with butanol. After the water is exhausted, the pot will now only contain the higher boiling 1-butanol. Continued distillation should see a jump in the boiling point to the pure butanol. Okay, that is the theory, but it will also depend upon the efficiency of the distillation. Water and butanol can co-distill. If excess heat is applied, the temperature of the distillate will increase before all of the water has exited the distillation. Decreasing amounts of water will be present depending on the liquid-vapor equilibrium being established during the distillation. Too much heat will co-distill fractions with less than the azeotropic ratio, depending on the amount of heat, column length, and rate of distillation.

[curiouscat]

Correct. If more water was present, then all butanol would distill as an azeotrope before water is removed to distill any remaining and higher boiling butanol. If you start with 5% water, the water will be removed as the lower boiling azeotrope with butanol. After the water is exhausted, the pot will now only contain the higher boiling 1-butanol. Continued distillation should see a jump in the boiling point to the pure butanol.

Exactly. Thanks.

Even better, since the H2O-Butanol azeotropic composition falls within the miscibility gap it ought to seperate into a Butanol-rich and a butanol-poor layer. The butanol-rich layer being ~80% Butanol will be above the azeotropic-point and thus amenable to the same distillation procedure as before. Right?

The Butanol-poor layer can be distilled into pure-H2O and azeotrope and there you go again.

Is my analysis correct? In theory you'd get a pure seperation, in spite of the azeotrope. My point being, the azeotrope won't really impair your seperation ability here. Not a 100% sure if I am right.

Okay, that is the theory, but it will also depend upon the efficiency of the distillation. Water and butanol can co-distill. If excess heat is applied, the temperature of the distillate will increase before all of the water has exited the distillation. Decreasing amounts of water will be present depending on the liquid-vapor equilibrium being established during the distillation. Too much heat will co-distill fractions with less than the azeotropic ratio, depending on the amount of heat, column length, and rate of distillation.

Agreed. But distillation efficiency is a general matter and not specific to azeotropes. So you could even screw up a simple non-azeotropic distillation if you didn't do it right (say pumped in too much heat as you mention.)

[Babcock_Hall]

An older copy of "Purification of Laboratory Chemicals" lists potassium carbonate and magnesium sulfate as two of the drying agents.  What is in the butanol, and is it likely to react with anhydrous salts?