Samusan
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Sulphur dioxide separation from air
I need to generate SO2 from elemental sulphur, no big deal there, but I need to separate the air from it as oxygen will interfere with the reaction.
Basically, my plan is to have a dish of sulphur on fire with a funnel above it connected to a tube, with the tube going down into NaOH solution, a
vacuum pump will pull the SO2 through the apparatus. The goal is to get NaHSO3, but if there is oxygen going through the solution it will be oxidised
to NaHSO4. The only thing I can think of is cooling the gas in something below -10 to condense the SO2 but I’d rather not if possible. Any ideas?
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DraconicAcid
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I don't think the oxidation of NaHSO3 by atmospheric oxygen is a particularly fast reaction- unless you really need it free from sulphate, you can
probably ignore the side reaction.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Samusan
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Thank you
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AJKOER
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Quote: Originally posted by DraconicAcid  | | I don't think the oxidation of NaHSO3 by atmospheric oxygen is a particularly fast reaction- unless you really need it free from sulphate, you can
probably ignore the side reaction. |
Not precisely correct in my opinion.
NaHSO3 is one of the known common oxygen scavengers, see, for example, https://www.awt.org/pub/0149322F-0C20-5CEC-AE62-1E826AF61A4C .
Also, per this source, Deuvyst, E. A.; Ettel. V. A.; Mosolu, M. A., "chemical kinetics of intermediates in the autooxidation of so2", CHEMTECH, 1979,
426, to quote:
"A product with the properties of peroxymonosulfate has been observed with a yield up to 30% upon bubbling oxygen through a solution of sodium
sulfite (13). This compound can undergo many possible subsequent reactions. "
In my assessment, it is not only the presence of dissolved oxygen, but any impurities from say transition metals like Fe or especially Mn, or two
metals introducing a galvanic current leading to solvated electrons which with O2 form the superoxide radical anion, which further, as an aerosol at
the solution contact with air, becomes the more active •HO2 radical (which, itself, also breaks down into H2O2). Also, the action of sunlight or lab
light potentially inducing solvated electrons as well along with electron holes, varying with the photo catalytic ability of metal oxide presence.
As an illustrative reaction chain involving superoxide (see Inouye B., et al, 'Participation of superoxide free radical and Mn2+ in sulfite
oxidation', in Toxicol. Appl. Pharmacol. 46: 29-38, 1978, at https://www.sciencedirect.com/science/article/pii/0041008X78...) with my take on a possible reaction chain as follows:
Mn(ll) + O2 (dissolved) = Mn(lll) + •O2-
•O2- + H+ = •HO2 (pKa 4.88)
HSO3- + •HO2 = •HSO3 + HO2- (see Page 1 at https://pubs.acs.org/doi/pdf/10.1021/j100010a023 )
HO2- + H+ (from any source including water) --> H2O2
•HO2 + •HO2 --> H2O2 + O2 (slow)
HSO3- + H2O2 --> HSO4- + H2O (see https://books.google.com/books?id=9GsoDwAAQBAJ&pg=PA104&... )
It is also possible that sulfate creation could also arise from the interaction of dissolved oxygen and a radicalized sulfur species (see this work
citing both oxygen and manganese, 'Kinetics and Mechanism of the Oxidation of HSO3- by O2. 2. The Manganese(II)-Catalyzed Reaction', at https://pubs.acs.org/doi/abs/10.1021/ic951141i ). For example, assuming the creation of the hydroxyl radical (perhaps from the action of light)
interacting with bisulfite ion:
HSO3- + •OH = •SO3- + H2O
Or, with the sulfite ion:
SO3(2-) + •OH = •SO3- + OH- (see Eq(6), page 211, at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1568601/?page=3 )
Then, a possible direct reaction of oxygen with the sulfite radical anion:
•SO3- + O2 = •SO5- (see Eq(22), page 213, at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1568601/?page=3 )
Which could further interact with the bisulfite ion forming bisulfate:
•SO5- + HSO3- = •SO4- + HSO4- (see Eq(30), page 214, at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1568601/?page=3 )
albeit, this reaction is slow as compared to the action of any possibly formed HSO5- (which I have discussed previously on SM at https://www.sciencemadness.org/whisper/viewthread.php?tid=67... where now the HSO5- acts in place of H2O2) on the HSO3- ion.
So, sulfate creation could progress, hypothetically, slow or much more rapidly, in the presence of dissolved oxygen and a transition metal (like Mn)
and likely augmented by solar or lab light.
[Edited on 10-8-2019 by AJKOER]
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