Centrifuging Diethyl ether. Safety concerns

[soma_seeker]

Hi everyone, this is my first post here on your forums. Thanks in advance for your time.

Ok, so I'm performing a hydrothermal liquefaction of lignocellulosic material in an aqueous (basic) solvent system. After performing the reaction I am left with an aqueous mixture of;
- Solid starting material/char
- Base-soluble breakdown products and starting material
- Organic solvent soluble breakdown products and starting material

I then wish to perform an extraction with diethyl ether (from previous work performed by others both within my lab and elsewhere, diethyl ether and dichloromethane are the only solvents capable of extracting a sufficient range of breakdown products). I've found that this forms a fairly stubborn emulsion and is further complicated by the presence of solid material (filtering the solids prior to extraction is not a convenient option).

Ultimately I've devised a workup process that is extremely convenient but involves the centrifuging of diethyl ether, which I'm concerned will not pass the OH&S requirements of the lab. Dichloromethane is obviously safer, however being denser than water the workup procedure then becomes SIGNIFICANTLY less convenient that with diethyl ether.

My question is, is centrifuging 50 mL screw-cap glass centrifuge tubes containing approximately 20 mL of aqueous solution and the same volume of diethyl ether a significant explosion risk/safety concern? Does the fact that the diethyl ether is water-saturated significantly reduce the risks involved?

If the safety risk is in fact too high, can you suggest any ways in which I could reduce the risks involved without changing solvent? The workup process is so ideal as is that I have even considered looking into a hand-operated bench-top centrifuge (although so far I've only found such instruments that can handle 15mL sample vials).

Thanks very much for any assistance you can offer.

[hypervalent_iodine]

If your centrifuge is chilled it might be okay. Regular centrifuges tend to warm up when you use them and this might be an issue if your glassware isn't built to withstand high than normal internal pressures. For the purposes of risk minimisation, I think it would be better to try and work out a way to get your liquid-liquid extraction operational.

 

The density of DCM should not pose a problem for normal liquid-liquid extraction and if this overcomes your emulsion issue, why not just go with that? Another suggestion is to add brine to your aqueous phase to help with the emulsion. I also have to ask why filtering it is inconvenient (vacuum filtration is fairly easy if you have the right adapter)?

[soma_seeker]

Hi, thank you very much for your response.

 

I was fairly brief in the description of my process for the sake of brevity and because it is not something I wish to alter if possible. I'd like to leave the solid material in the system at this stage so that any diethyl ether soluble material will be extracted. By centrifuging, I produce a tri-layer system, the aqueous layer on the bottom, a solid 'disc' of material at the phase boundary and then the organic layer on top.

 

I don't want to use DCM as it is more dense than water. Having the organic layer on top is very convenient for removing it, adding more, stirring up the solid material and repeating the process.

 

I do have the ability to chill the centrifuge. What temperature range would you suggest? Do you think this will significantly reduce any explosion risks?

 

Thanks again for your help.

[Enthalpy]

Could someone explain me why chemists are so uneasy with diethyl ether?

 

I understand it can form peroxides, is flammable, a bit toxic... But households use it commonly, and I haven't heard about so many related accidents in houses. 50mL suggested here are a small bottle as available from the drugstore. Ullage would limit the overpressure.

[hypervalent_iodine]

Could someone explain me why chemists are so uneasy with diethyl ether?

 

I understand it can form peroxides, is flammable, a bit toxic... But households use it commonly, and I haven't heard about so many related accidents in houses. 50mL suggested here are a small bottle as available from the drugstore. Ullage would limit the overpressure.

 

You kind of answered your own question there, don't you think? Diethyl ether is extremely flammable in addition to being quite volatile. And I doubt there are many household products that use pure ether. Anyway, it's not that chemists are uneasy with it (any chemist who is afraid or uneasy with the chemicals they are working with is not a chemist I want to be around) it's that you have to be a little more cautious when you're using it. In general, i's a very easy solvent to use and won't cause any trouble if you aren't stupid with it.

Hi, thank you very much for your response.

 

I was fairly brief in the description of my process for the sake of brevity and because it is not something I wish to alter if possible. I'd like to leave the solid material in the system at this stage so that any diethyl ether soluble material will be extracted. By centrifuging, I produce a tri-layer system, the aqueous layer on the bottom, a solid 'disc' of material at the phase boundary and then the organic layer on top.

 

I don't want to use DCM as it is more dense than water. Having the organic layer on top is very convenient for removing it, adding more, stirring up the solid material and repeating the process.

 

I do have the ability to chill the centrifuge. What temperature range would you suggest? Do you think this will significantly reduce any explosion risks?

 

Thanks again for your help.

 

I realise you want to stick with using a centrifuge, but just a quick note regarding the solid mass and liquid-liquid extraction (just in case you end up going back to it). You could easily wash this with vacuum filtration and collect the filtrate in a receiving flask. You should loose no more of your organic soluble compounds doing this than you would using your method.

 

As for temperature range, I would suggest cold-ish (sorry for the vagueness). The potential source of explosion would be from the pressure build up caused by the ether evaporating in the vessel. Chilling it would mean it stays in the liquid phase. The explosion itself, if it were to happen, wouldn't really be all that disastrous. It might mess up your centrifuge, but I suspect you'd otherwise be fine.

[John Cuthber]

. Ullage would limit the overpressure.

 

I understand it can form peroxides, is flammable, a bit toxic

Not really, no.

The pressure rise isn't caused so much by the expansion of the liquid (where ullage would help) but by the rise in vapour pressure.

A closed bottle of ether in hot water can generate nearly 7 bar pressure.

 

It's rather noticeably flammable.

It's got a pretty low autoignition temperature

http://en.wikipedia.org/wiki/Autoignition_temperature

and broad flammable limits

http://en.wikipedia.org/wiki/Flammability_limit

[the.alchemist]

What u have done seems to be somehow a pulping process.

 

Of course, u have end with a very messy thing.

 

I do not clearly understand the meaning of extraction with diethylether.

 

I think it will be better to centrifuge the aqueous mixture and then to perform Soxhlet extraction upon solid mater and percolation upon supernatant.

 

and then simply rotoevap organic solvent and do what u want with end products.

 

Once again...what do u have in mind to obtain? I kindly ask this question because I was involved some time again in pulp and paper science...

 

regards

[Enthalpy]

[...] Diethyl ether is extremely flammable in addition to being quite volatile. And I doubt there are many household products that use pure ether.

 

The pressure rise isn't caused so much by the expansion of the liquid (where ullage would help) but by the rise in vapour pressure. A closed bottle of ether in hot water can generate nearly 7 bar pressure.

 

It's rather noticeably flammable.It's got a pretty low autoignition temperature and broad flammable limits

 

Thank you both!

 

My mom had a bottle of pure ether when I was a kid (looong ago, probably removed from sale meanwhile). Sold in pharmacy to remove surgical tape. Hence I noticed how nicely flammable it was, even better than ethanol.

 

On an other forum, someone asked "how to dispose of 5L diethyl ether" and among refined answers, I proposed "burn it" as the result is clean, but apparently this is a swearword for chemists. Hence I wondered if a few peroxide crystals would knock over sand bags, or some other nefarious behaviour by ether.