tupence_hapeny - 29-5-2007 at 04:07
I am looking for input as to whether a certain scheme has any prospect of success... The entire system is essentially a modified Castner-Kellner
process (http://en.wikipedia.org/wiki/Castner-Kellner_process).
NB The system pictured in Wiki is actually what caused the idea to forment.
The overview (which is effectively all that I have at the present time, is basically in a short tube - with one end having an input hole for
super-concentrated saline solution and a hole to allow Chlorine gas to escape - probably through a solution of alkali carbonate - thereby preventing
its escape.
In the guts of the tube there is an alkali solution and a lead anode, which extends almost down to the top of the mercury solution.
The mercury is in the bottom of the cell, however the bottom of the cell itself is pierced, and the mercury sits at its level and is in contact with
the fluid outside the cell as well as the saline solution inside the cell (the mercury is the cathode, connected to the voltage via a graphite
electrode).
The idea is that the mercury cathode will absorb the sodium forming amalgam. The amalgam will be distributed throughout the mercury, including that
part of the mercury exposed to the reagents outside the electrolysis cell - being utilized by the reagents, releasing the mercury from the amalgam -
allowing more sodium/mercury amalgam to be generated by the cell (because the temperature will be lower than that at which the mercury vaporises)
(I may need to design a stir-bar specifically to stir the mercury pool - I am unsure about how well the amalgam distribution will be without some
help).
The reason I thought of this is basically because although it is possible (even known) to generate sodium amalgam in-situ, to do so requires the use
of strong acids and electrolysis within the vessel containing the reagents (both of which may interfere with the reaction)
http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1...
http://www.orgsyn.org/orgsyn/prep.asp?prep=CV1P0485
This idea has the capacity to fix both problems (although a shitload of alkali will probably form in such reactions - allowance will have to be made
for removing or neutralizing the same).
So, will it work?
Could it be used to generate alkoxides? Especially for reactions in which they serve as nothing more than strong bases?
Could it be used for Birch-type reactions, in either alcohol or ammonia?
If it did work, what would be the best way to destroy any remaining Na/K/Li/Ca from the amalgam before removing the unit and storing it?
My best idea to date would be to carefully run the unit without the electrolysis in a vessel containing pure (or almost pure) alcohol and destroying
the alkali metal in a 'normal' manner - then collecting the mercury and storing it again. I think this would work provided that I can think of a way
to stir the mercury pool.
I also need assistance on how one would determine via the amount of electricity put into the unit (also probably by the amount of gas given off - both
Cl2 and CO2) just how much sodium (or other alkali metal - perhaps even magnesium) has been given off and how to measure this quickly and simply in
order to judge the molar quantity of reagent provided to the reaction in order not to stuff things up...
Finally, what materials do those here think would be best? I have limited access to glass (or at least proper glass) at the present time, so how about
PVC/PP for the demonstration model - what range of solvents etc. would that limit me to?
Please do contribute, I need assistance with this... On the plus side, I do intend to set up a web page with details of how it works and the
construction details etc. once I can get it to work