BASF
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Oleum prep
What about boiling/heating H2SO4 with a big portion of dissolved + undissolved KHSO4(or NaHSO4).
Sulfuric acid boils at approx. 340deg C, NaHSO4 decomposes at approx. 400-450deg C to give the pyrosulfate.
But i think with the help of a water-drawing agent as it is sulfuric acid, the decomp might take place at lower temps.
Another advantage is the good heat conduction to all of the KHSO4(heat dry KHSO4, and only the lower regions of the KHSO4-heap will decompose, THIS IS
SHI..)
At higher temps(450deg+), the pyrosulfate decomposes to K2SO4 and SO3, which can be dissolved in COLD H2SO4, or for the purpose of dehydrating acetic
acid, led through a pipe(temp must be significantly above 30deg C to prevent condensation) into the reaction container.
The remaining K2SO4 can be reconverted to KHSO4 with an excess of H2SO4....
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rikkitikkitavi
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there is no problem heating dry KHSO4 , but you have to do it gently so there is no temperature gradient over the "KHSO4-heap". And this
will lead to a slow decomposition rate
Patience , my dear BASF. Patience is the virtue of any good chemist 
I did some experimenting with NaHSO4 and discovered that there is a fine line between decompostion into pyrosulfate and decomposition of the
pyrosulfate, but I only had a very crude way of heating, no thermostatic control. Very easy to create sulfuric acid mist.. cough cough..
The idea you propose could perhaps work, because the so called decompostion temperature of KHSO4 is where the vapour pressure of H2O over the molten
salt is so high that it leads to a shift of the following equlibrium:
2KHSO4 = H2O + K2S2O7
'
How will you separate the K2S2O7 from the sulfuric acid?
Problem is that these salts reacts with sulfuric acid forming all kinds of disulfates, trisulfates e t c, but I think these salts all to decompose
upon heating , releasing SO3 (or SO2 and O2 if to high temperature)
for dehydrating acetic acid, can you just use vaccum distillation together with sulfuric? H2O and Acetic doesnt form an azeotrop si with a good
distillation column you could separate them fully , even without a dehydrating agent. But it will take time.
But of course, there are many more uses for SO3
/rickard
[Edited on 14-9-2003 by rikkitikkitavi]
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BASF
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| Quote: |
Patience , my dear BASF. Patience is the virtue of any good chemist
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 I know that too well...have a look into the library, there´s "my"
calcium nitrate-synth...it takes from hours to days...
 After that i am already quite old, my only fear is to get old enough for this
all.
| Quote: |
there is no problem heating dry KHSO4 , but you have to do it gently so there is no temperature gradient over the "KHSO4-heap". And this
will lead to a slow decomposition rate
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I had another idea...why not mixing NaHSO4 with KHSO4 or another inorganic salt that helps in lowering the melting point without decomposing by
forming an eutectic mixture. The heat conduction would probably be much better...
[Edited on 16-9-2003 by BASF]
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