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Solvent/Water/Heavy Separation Development

Solvent/Water/Heavy Separation Development

Solvent/Water/Heavy Separation Development

I am working with some of our lab folks on development of a process. Some of the chemistry is still in flux, but we are creating a heavy component that will be mixed in with a solvent (THF or similar) and water (it is soluble in both). I need to eliminate the solvent from the mixture to isolate all of the component in the aqueous phase.

Since the solvent is the low-boiler here, my first thought was distillation. The heavy component has negligible vapor pressure, so yield should not be an issue. The solvent and water mixture may still form an azeotrope, depending on how the third component affects the equilibrium curve.

I’ve never done any determination of equilibrium curves or interaction parameters before in a lab setting, so I was hoping someone could point me to a good reference for that and scaling distillation processes. If you have any other separation ideas as well, I’d like to hear them.

RE: Solvent/Water/Heavy Separation Development

Have a read of the section on enhanced distillation in the distillation chapter in the 7th edn of Perry - table 13-19 on page 13-77 cites a few ways to separate the THF - water mix and break the THF-water min boiling azeotrope :(a) Extractive distillation with propylene glycol as the extraction solvent (b)pressure swing distillation.
(a) might concentrate all of the solute in the PPEG phase in the PPEG-water column if it is soluble in PPEG; dont know if that makes this infeasible for this case.

VLE table for this system at 101.3kpa is in table 13-1 which shows the azeotrope at about 65degC at 0.8 mole fraction THF. Table 13-2 provides BIP data, but I suspect these are only valid at 101.3kpa, since this system's min boiling azeotrope temp appears to be pressure dependent.

RE: Solvent/Water/Heavy Separation Development

Thanks. I'll give that a read. I was initially leaning towards vacuum distillation to avoid complications from additional chemicals. Yes, the solvent/water mixture azeotrope disappears at a certain vacuum, I think. Given that, vacuum distillation was my first thought.

Given that this component is soluble in both phases, but also has basically zero vapor pressure, do you think the equilibrium curves of pure solvent/water would still be valid?

Is there a resource that details a method to determine equilibrium information in the lab? We have a rotary evaporator unit in the lab that can control temperature and pressure (vacuum).

RE: Solvent/Water/Heavy Separation Development

Agreed, the solute may have some effect on VLE for this THF-water mix, more likely so if it is a polar organic.
At the outset, looks like you could use this rot evap for lab generation of VLE for subatmospheric operation-is this procedure in the ops manual. The manufacturer may be able to assist also with details, I would guess.
For pressure swing distillation, research articles on the net show the first column running close to 1atm, while the second runs at 8bar or so ( the azeotrope point shifts down to 0.65 mole fraction THF at 8bar), so does this rot evap allow you to generate VLE at such high pressures?

RE: Solvent/Water/Heavy Separation Development

I’ll see if they have any specifics in the manual or if the manufacturer has any ideas. The rotary evaporator is all glassware - I doubt it was designed to operate under any significant pressure. If the azeotrope drops to 0.65 at 8 bar, I wonder if vacuum distillation would push the azeotrope higher, possibly breaking it completely.

Thank you for the suggestions- I have a couple of ideas to explore from your advice.

RE: Solvent/Water/Heavy Separation Development

The lowest pressure I could find on the net for this binary is at 0.5bar abs, and the azeotrope still exists at this pressure.

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