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Carbon dioxide generation by "electrolysis?" of Oxalic acid (ethanedioic acid)
Dear list members
A friend seen a CO2 generator in a hydroponics shop that was
supposed to work on electrolysis of Oxalic acid. The price was
ridiculous. Could have been another con. So I did a little
exploration in a chemical encyclopaedia and internet search and
discovered that:-
When Oxalic acid absorbs oxygen it is converted to carbon dioxide
and water. Indeed lots of chemicals, light etc., make oxalic acid
break down to carbon dioxide and water. Thus the idea is probably
possible.
The salesman trying to sell my friend the commercial product
claimed that it could be turned on and off by turning on or off
the DC supply to the electrolysis cell.
Obviously the oxygen liberated at the anode as the water is
electrolysed into hydrogen and oxygen combines with oxalic acid
converting it to carbon dioxide and water. No doubt if conditions
are correct the oxygen molecules combine with the oxalic acid and
it appears that carbon dioxide is liberated at the anode. There is
a hydrogen outlet in the commercial unit.
There is a catalyst used. It is a liquid. My friend did not find
out what it was or what colour the solution was. Potassium
permanganate causes oxalic acid to break down into carbon dioxide
and water but that is no good. It can't be switched off.
There was sodium bicarbonate supplied with the pack but I assume
that that was to put in the hydrogen filter and carbon dioxide
filters (supposed to be in the pack) to wash any oxalic acid
vapour from the gas.
The real beauty of this unit is the switch on switch off. For
example using two pressure switches like those used in washing
machines to limit the quantity of water put in, one could make a
low pressure control that would suit application to a CO2 bell and
not waste CO2. It could be turned off at night etc., etc.
Has anyone got any ideas of what the catalyst could be, optimal
cell voltage (I could find that by using a variable power supply)
and whether stainless steel would be suitable for the anode and
cathode. I would rather not have to use noble metals such as Pt,
Au etc.
>From a list of incompatible chemicals I found on the internet I
think that Ag and Hg would cause the oxalic acid to rapidly break
down, probably dangerously so.
Any ideas, comments please. Replies to the list would seem
appropriate as many list members would probably be interested, but
I welcome any comments, even if you want to keep them private.
Regards
Denis Daly
Sydney, Australia
(Before you ask I am in the southern part of the city that has the
good clean water.)
dalymob at bigpond_com