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As Richard Sexton pointed out, oxalic acid is toxic. It's also a fairly
strong acid, which causes safety problems for storage and handling. On
the up side, it's available as a powder, which eases some of the storage
and handling problems when compared to some other acids.
Aside from that, it looks to me like electrolysis of oxalic acid could
make a practical CO2 generator. For a while. Then I suspect that
maintenance and upkeep costs will set in.
Oxalic acid is HOOC-COOH, and above a pH of 5 or so it's present in
solution as -OOC-COO-. The negative charges are easily removed by either
chemical means (it reacts with tarnished metals) or by electrolysis.
Electrolysis rearranges -OOC-COO- into 2 CO2. Pretty simple. No oxygen
On the downside, I speculate that the process will work only in dilute
solution (so the pH will stay high enough) which will limit the production
rate and require some device to maintain the solution concentration - a
pH contoller perhaps or maybe manual monitoring and adjustment. It will
also produce hydrogen gas as a by-product and this is quite dangerous
(remember the Hindenburg?). Whatever mechanism is used to control the
hydrogen gas will also require attention and maintenance. The electrodes
probably will be subject to corrosion and/or deposition so will require
periodic maintenance and replacement. And of course there's the
electrical cost, whatever that is.
Maybe at the scale of a commercial greenhouse this sort of CO2 generator
makes some sense. Compared to bottled gas there might be a cost savings
when generating large volumes of CO2 that offsets the upfront costs and
maintenance of the electrolysis unit. I doubt that's true at a hobby
If I were looking into this system I'd want detailed answers to questions
about maintenance requirements, material costs, replacement costs, power
costs, dependability and operations - in particular I'd want to know if
the machine produces CO2 at a constant rate. The sales person should be
ready with quick answers to those questions.
All in all, bottled gas is likely to give an aquarium hobbiest more
dependable results and lower long term cost. And of course, yeast
generated CO2 is just simpler - especially if you have more than one
in Albuquerque, where I'm wondering if George Booth hasn't already added
one of these marvels to his equipment collection.