Specialty Chemistry Forums > Chemical Engineering Forum

Distilling large quantities of acetone for reuse

<< < (2/3) > >>

Enthalpy:
I like the freezing method, but at what temperature?

For instance, ethanol and methanol are commonly used to produce real cold (like -70°C), by mixing them with water ice that they force to melt and absorb heat. I expect acetone to act the same way: prevent diluted water from freezing at 0°C - much like any antifreeze.

What kind of acetone dryness is sought? If it must be dried from 5% to 0.5% water, the temperature that lets the residual water freeze out must be really chilly.

curiouscat:

--- Quote from: Enthalpy on May 27, 2013, 08:10:42 PM ---I like the freezing method, but at what temperature?

For instance, ethanol and methanol are commonly used to produce real cold (like -70°C), by mixing them with water ice that they force to melt and absorb heat. I expect acetone to act the same way: prevent diluted water from freezing at 0°C - much like any antifreeze.

What kind of acetone dryness is sought? If it must be dried from 5% to 0.5% water, the temperature that lets the residual water freeze out must be really chilly.

--- End quote ---

True. I was trying to find a freezing curve for the system. That'd let us answer these questions more accurately.

Archer:
(posted this on the wrong thread by mistake  :-[

You definitely need a safer set up.

If you need it just for your process you can get a falling film, short path distiller which is a closed system (and therefore much safer). The solvent runs over a heat exchanger set to just above acetone bp. Then it gets condensed on a cooling plate which is in close proximity. You control the flow rate so that you have a continuous process.

This will at least work as a fist step, you may find that with the right conditions that this is all you need.

Enthalpy:
This shall illustrate the successive acetone baths suggested in reply #1, which saves acetone: it gets a dry product but uses acetone until very moist. The upper part of the illustration is done often, with product batches; the lower part is done from time to time, when the baths are used. I believe the process is very well-known.

Enthalpy:
This shall illustrate the combined fractional disitllation of the dessicating fluid (here acetone) with the progressive dessication of the product (silica gel in the original post), as suggested in reply #1.

It's a fractional distillation column where the product to be dessicated serves as random packing material - somewhat similar to the dry cleaning of clothes. The product enters the column where the dessicant is less dry and leaves the column where the dessicant is driest. The dessicant condenses and vapourizes at the product, getting driest at the top (in the case of acetone, which boils more easily than water).

Since the column can further eliminate water from the dessicant, the input dessicant needs not be very dry; then its inlet is lower than the top of the column. It should be pre-heated, or even vaporized partly, to disturb minimally the column's temperature profile.

To save dessicant, its outlet can contain much water - up to essentially water - in which case some permanent packing material can replace the product at the bottom.

Some, err, details are not shown on the sketch: how to introduce and extract the product (a screw pump may contribute to the solution), how to move the product in the column (superimposed trays? A dessicant boiling less easily than water, to reverse the product's path?)...

I didn't check if this is commonly done. Comments welcome as usual!
Marc Schaefer, aka Enthalpy

Navigation

[0] Message Index

[#] Next page

[*] Previous page