Mesa
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Is it possible(safe) to microwave H2SO4/H2O?
From what I understand of microwave heating, it should be possible to boil off the water from an aqueous solution of sulfuric acid simply by
microwaving it. The dipole moment of H2SO4 is higher than that of water, so superheating would be more of an issue than with pure H2O, however if a
high surface area/volume ratio is used(i.e. a long flat container) and heating is done in short bursts, most of the bumping could be avoided.
Alternatively, using an overhead stirrer should provide sufficient agitation to prevent superheating.
At lower concentrations it would probably not be worthwhile to do this, however given how difficult it can be to boil down sulfuric acid past ~70%
using normal methods, it seems like it'd be a much easier way to get to the desired concentrations for practical use.
Obviously, the microwave would need to be altered to allow for removal of the water vapor. I'd planned to modify one for use in microwave assisted
organic reactions regardless so this isn't a problem.
The main reason why I'm asking for advice was the experience from attempting to microwave dry a small fuse containing KNO3 and succhrose. I've since
learnt never to put anything containing KNO3 in a microwave.
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Bot0nist
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I imagine it would splatter and overheat quickly and gas your microwave with corrosive oxides of sulfur. I would not reccomend it, but hey, if you
have a "throw away" microwave, use an extension cord and give it a shot outside on a breezy day and see how it works.
U.T.F.S.E. and learn the joys of autodidacticism!
Don't judge each day only by the harvest you reap, but also by the seeds you sow.
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papaya
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Take one more free idea from me: electrolyze sulfuric acid to get rid of water.
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Mesa
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Quote: Originally posted by Bot0nist  | | I imagine it would splatter and overheat quickly and gas your microwave with corrosive oxides of sulfur. I would not reccomend it, but hey, if you
have a "throw away" microwave, use an extension cord and give it a shot outside on a breezy day and see how it works. |
With a sufficient amount of water in a separate container, wouldn't this issue be avoided? I'm not being argumentative for arguments sake here,
however it seems like an idea that hasn't been explored in any capacity from what I've found. Electrolysis is an idea I'd thought of, however I'd
assumed the electrodes required to prevent contamination would probably be pretty expensive/unavailable.
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papaya
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You are right - electrodes, but at least lead could be tried.
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DerAlte
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See http://www.sciencemadness.org/talk/viewthread.php?tid=11129#... for a comprehensive discussion of many of the points raised here.
My experience has been that using a microwave to concentrate H2SO4 solution requires care. (See the thread above). Adding a ballast of water in a
separate container, per Mesa above, is a very good idea to avoid virtual short circuiting (large reflection coeff. at the magnetron). A large surface
area and small depth of liquid also help. If these precautions are taken, the process is quite successful, but cut off the process before significant
vapor pressure of H2SO4 occurs (70 - 75%). Significant Vapor of acid will ruin the microwave. Final concentration should be done via heat until dense
white fumes are seen, when a ~95% solution is obtained.
Re lead, read the above thread. Of course lead works, as you would have found by using the search engine.
Der Alte
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bismuthate
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i wouldn't recomend it but if you do never microwave it in the microwave used for food find a cheep one at a yard sale. also i wouls recomend puting
the vessel in a dish that has baking soda in it.
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