Treating a water stream with 13 wt% Isopropanol

[StoneCold]

Greetings all
I have a small stream intermittent stream of water that contains 13 wt% isopropanol. I would like to remove the isopropanol down to about 2% so the flash point is high enough to go to a POTW.

The water stream is generated in 100 gallon batches about 4 times a day.
The water is at room temperature.


I don't have a lot of room to dedicate to the isopropanol removal.
What unit operation do you think is the best way to handle this stream?

I was thinking that air stripping is a good choice.
Distilling it is possible in a single stage flash but I end up with about a 50% IPA solution that I have no use for.

Other ideas?

Thanks
Brad

 

[bimr]

Have you considered shipping it off site for disposal by a 3rd party?

 

[EdStainless]

Where is the IPA coming from?
I would think that if you flashed it out the resulting 50% solution would have value to someone.

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P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

Off the cuff, how about extracting the IPA with a high boiling point entrainer like toluene in a mixing tank? You could then easily decant the water phase off to the POTW via a intermediate holding tank. If the trace amount of TOL in water going to the POTW presents some HSE concerns, use vegetable oil as the entrainer instead of TOL.

 

[MortenA]

or a membrane process

 

[georgeverghese]

The British uni text "Chemical Engineering " by Coulson and Richardson Vol 2 states that this IPA water separation can be effected by a hydrophilic polymer resin, and this does indeed appear to be the case; got this off the internet:
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The present invention involves a process for removing water from mixtures of alcohols and water by contacting such a mixture with an ion exchange resin of either the cation or anion type. Prior to use for alcohol dehydration, the ion exchange resin itself is dehydrated if necessary or desired by contacting it with methanol, propanol, isopropanol, acetone or other like low molecular weight hydrophilic solvents. After use for alcohol dehydration, the ion exchange resin is regenerated by contacting it with these dehydrating/regenerating agents.

An ion exchange resin useful in accordance with this invention is an insoluble support containing polar functional groups holding a cation or anion which can be exchanged with a free ion in solution. These insoluble supports are usually synthetic polymers, in bead form, crosslinked sufficiently to give insolubility and rigidity to the structure. A common use for ion exchange resins is to remove ions of specific types from solutions contacting the resins.

Ion exchange resins differ from molecular sieves in the mode used for separation of a desired species. Molecular sieves have uniform channels of specific size that trap small molecules based on the physical dimensions of the molecule. Indeed, a prominent use of molecular sieves is to dry gases or organic solvents by causing the small water molecules to contact and become trapped within the molecular sieve, while larger molecules are excluded by their bulk. Ion exchange resins, by contrast, depend on electrical charge of a species to effect entrapment. Thus, trivalent aluminum ion has a strong affinity for a cation resin and can easily replace a monovalent ion, such as sodium, not because of the size of the aluminum ion compared to sodium ion, but principally because of the differences between the charges on the ions.

Representative ion exchange resins suitable for use in the present invention are Dowex® 50W×2, sodium form, Dowex® 50W×8, hydrogen form, Dowex® 1×2, chloride form, Dowex® 1×4, chloride form, Dowex® 1×8, chloride form, all available from Dow Chemical USA, Midland, Mich., Duolite® C-26, sodium form, available from Diamond Shamrock, Cleveland, Ohio, Rexyn® 101 hydrogen form, Rexyn® 201 chloride form, available from Fisher Scientific Co., Fair Lawn, N.J., and Amberlite® 1R-120 hydrogen form, available from Rohm & Haas Co., Philadelphia, Pa.
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But it sounds like you dont have room for all this kit.

 

[bimr]

This is a waste stream and may contain other components. Have you tried a salt separation?

Salt Separation

 

[chicopee]

Not getting involved in the properties of isopropanol, check out on the feasibility of vacuum extraction then either burn the vapor or condense it.

 

[georgeverghese]

Better than an ion exchange resin route for this separation would be to use RO membranes (as suggested by @mortenA). This would not require regeneration of the resin bed, and is more compact. This particular application for IPA - water separation is quoted in Perry Chem Engg Handbook 6th edition table 17-17,page 17-26 indicating much better stage separation efficiency with Du Pont Permasep B-9 polyamide membranes than with generic cellulose acetate membranes. Good prefiltration of the feedstream is usually key to long life of these RO mebranes.

 

[moltenmetal]

Relative to the cost of disposal of this stream, you'll need something which is quite low in capital to make treating it worthwhile, meaning using equipment you already have to the extent practical.

I'll take George's word for it that RO will work, but frankly I'm having a hard time to understand how it would. Pervaporation on the other hand might work, but isn't a low capex option.

The boiling points are different enough and the azeotrope is up around 80% isopropanol which should satisfy your need to get below 2%. A simulation will tell you how an air stripper would work- it might be an option, depending on what you have to do with the vapour.