MeOH-Water Separation

[Camarena]

I´m running a simulation and I´m trying to separate a stream with MeOH (98 %w) and H2O (2 %w). The natural way to separate this stream would be by distillation, obtaining MeOH on the distillate (bp 64.6 ºC) and water on the bottoms (bp 100 ºC),the problem is the distillation column would need great amounts of duty in the reboiler to separate the bigger quantities of MeOH on the distillate.
The question is if there would be any other way to separate MeOH from water when the stream is concentrate on MeOH.
Is there any entrainer that would be soluble in water and no in MeOH, so it would be possible to separate both compounds by extraction or decantation?
Thank you for your help.

 

[klem]

You should look at Activated Alumina, Silica Gel and Molecular Sieves. All are used to dehydrate gases and liquids. Energy is still required to reactivate the bds, but should be less than a distillation column. Look for suppliers in CE Buyer Guide.

Good hunting,

Klem

 

[bchoate]

bchoate

Of the three methods commonly used to dry alcohols (distillation, pervaporation, and mole sieves), mole sieves are the most economical means to dry methanol. A 3A sieve which absorbs water not methanol should be used. The unit OP would contain two mole sieve beds; one online and one drying under vacuum.

 

[phex]

molecular sieves are actually better suited to longer alcohols (ethanol and above). normally a purity of 99.9 % should be reachable with distillation without a problem.

as for your simulation, try to specify the content of water in the bottoms as 99.9% pure. use an activity model like nrtl, best would be one modified for alcohols as PRO/II is offering for example. do not specify the purity of the alcohol at the top of the column, this will not help solving the column in my experience.

distillation is a very energy consuming process. it is not really exceptional to need a very high duty from the reboiler. alternatives like pervaporation or molsieves might be a viable solution with "smaller" streams.

molsieve is always dependent on the total amout of water to be adsorbed. with a large throughput and high water content, this can lead quickly towards non-economic sizes for this separation stage. also you need to keep in mind the above said fact, that molsieve is not normally used for methanol drying due to substantial losses of methanol through the adsorbent. pervaporation is less dependent on total amount of water, here the limiting factor is the water content expected after the separation process. below .5 wt% water content, pervaporation becomes to costly to be an effective solution, at least as far as investment cost is concerned.

both processes are useful in debottlenecking an existing alcohol/water-separation by distillation. e.g. use a dist. column to reach 1% water content and dry the final bit by molsieve or pervap. contact sulzer chemtech concerning pervaporation and vogelbusch concewrning molsieve for further info.

 

[25362]

Have you considered freezing the water into ice followed by filtration ?

 

[25362]

I'm afraid I've committed a blunder. Methanol at high concentrations, may reduce the freezing point of water down to that of methanol, about -97[sup]o[/sup]C. Methanol is, in fact, used as an anti-freeze.
Sorry.

 

[25362]

Would you care to try CaO + redistillation as Raymond Lully did in the 13th century to get absolute alcohol (ethanol) from aqua vitae ?