For mass production of benzaldehyde from toluene, the air oxidation of toluene isn't so bad.
Probably alot easier for some than for others.
But if one wanted to go the electrochemical route, here is one way:
I should emphasise that this assumes recycling of the oxidizer. It is kinder to the environment to recycle the oxidizer, but not at all essential. It
could be skipped if one were in a hurry, simply by following the steps outlined in the last post to make a suitable quantity of MAA for a single
reaction - to make the desired quantity of benzaldehyde. That would shorten the following process greatly.
For 24/7 mass production, there are 9 main steps involved in this process, and some can be carried out at the same time (multi-tasking = good time
management!), and others can be combined - more on that later. Here they are:
1) MAA regeneration. May contain many individual cells, working in shift, with say 1 complete every 2 hours.
2) MAA settling. Pour cell mix into acid-proof container container, it must be left undisturbed for at least several hours to allow the MAA to settle
out at the bottom. This stage may be made up of a few containers, each holding one batch. When one is added for settling, one is transfered to the
next stage.
3) Pour off the saturated acid/MAA. This liquid will now go back to the cell for the next regeneration. You will now be left with a batch equivalent
of dark red paste, it will probably still have an inch of liquid on top, it will not interfere.
4) Put into storage container. It would be a good idea to make this container have a several "batch" capacity. So, lets just say that each "step"
involves 1Kg batches. Then build up a "buffer" inventory in this storage container of perhaps a few to several Kg of MAA. That way, if an accident
occurs or the power goes out, you can still process toluene 'round the clock; this inventory will act as a buffer for your system - though not
essential. Steps 1,2 and 3 simply add to this container, remove oxidizer in portions you are able to react at a time, maybe 3kg reactions at a time
will be possible? Probably easier than 3 separate, time consuming 1kg reactions at 50 C.
5) Remove predetermined portion of MAA from storage container, and place in acid proof reaction vessel. This vessel must be fitted with some form of
overhead mechanical stirring. It should at lest have a partiall sealed top, to help contain odours (and minimise evaporation of your toluene). A large
excess of DRY TOLUENE is added. A large excess will be necessary if you are going to use mechanical stirring. This stirring mechanism would not be
hard to make, easy from a power drill and an acid resistant rod. A fast spinning axle with a small impeller should be good for really whipping up the
reaction mixture into a toluene/MAA milkshake. (The lower the temperature this reaction can be made to happen, then the better it probably will be).
6) Solvent (with large amount of dissolved benzaldehyde) is poured off. You may wish to add additional toluene to extract out as much of the
benzaldehyde as possible. Use the mechanical mixer for each extraction.
7) Washing the solvent. Wash with water to remove excess acid. You may wish to back extract this water to reclaim some residual benzaldehyde/solvent.
You could use a different solvent for the back extraction to conserve toluene. The water extracts could be fractionally distilled to recover some cell
acid.
***This benzaldehyde laden solvent is the output from this process, it is put into a storage container and is removed when practical to do so, for the
distillation process.***
8) MAS is transferred to solvent removal stage. This could be a vacuum vessel, or some kind of evaporator, or a solvent extraction using a low boiling
solvent. Preferably low boiling as in < 50 C low boiling, maybe a higher pb could be used, uncertain at this time. A combination of (low boiling
point) solvent extraction with subsequent vacuum evaporation could be used, or just plain old evaporation in a lowe humidity area, on a large acid
resistant sheet could be used? Lots of possibilities.
9) MAS goes straight back into saturated MAA cell solution (from step 3) for regeneration, in 1 or more separate cells.
***Distillation process is run under vacuum. The first distillation could be run at normal pressure to drive off the toluene, then what remains is
transferred to the vacuum distillation stage. Even a rather small vessel could do this, it would not have to be very big. I'm sure even a 250ml vessel
could handle the output from this process, unless your regen cells were pumping out one heck of a current...No need for large vac. vessels***
Okay, I bet you're thinking this all sounds kinda complicated, well - it doens't have to be. Some of the steps can not only run at the same time, they
can be combined.
For instance, 1 very large single cell could be run with a large hold up, say a few Kg solid material. Then, 1 Kg at a time can simply be removed when
needed for the reaction, and the expended oxidizer from the last reaction (MAS) put back into the cell when convenient to do so.
Using that approach solves alot of practical issues, it just means that the cell will never be 100% regenerated at any given time - but who cares?
Just keep an eye on the colour of the mix, keep it a dark-ish red, and make sure you keep organic solvent out of the regenerating mixture.
That large cell could also be the settling tank as well. Just switch it off for a while, it will settle pretty good in just a couple hours - if you
are in a hurry. A scoop can retrieve the red paste or sludge from teh bottom, it's not difficult, believe me.
For a large single cell, some kind of overhead stirring would be a good idea -though I'm unclear how essential it would be (at this time).
Chunks of oxidizer that collect on the anode could either be A) broken off and mixed EVENLY with the solid material or B) maybe collected and used as
the oxidizer. This would avoid the need to switch it off.
It is perhaps worth noting that this roto-batch style process - like most processes - has it's continual process equivalent, I think people oten refer
to that as "going technical"
The continual process equivalent would use a MAA saturated solution of cell acid, that is pumped via the process equivalent of all the above
steps/stages.
Only that instead of working with a solid mixture, you would be working with an acid solution (at some stages red, at others yellow), which is not
without it's own set of challenges...ie. acid-resistant pipes, pumps, level regulators, flow controllers, etc. would need to be obtained.
Or the batch system could be miniaturised to produce benzaldehyde more regularly, only on a more manageable scale.
Doing EVERYTHING in single individual stages is alot of work.
Although the above proposal may have a solid material (MAA and MAS) holdup of perhaps 8 or 10Kg, running 10kg batches in single steps would be a
nightmare, and very slow. It would be frustrating doing nothing, but waiting for your 10kg to regenerate.
If you were actually able to work with 10Kg batches, you would be thinking, hey I could be reacting another 10kg right now, and then extracting 10Kg,
and then washing...
Maybe someone will actually do that, there's an idea?
10 sounds a lot better than 1.
[Edited on 10-2-2005 by CycloKnight] |
attachment.
because toluene is not an alkene 
Nah... not right, so again,
do be careful if you repeat the process. I am dripping it in, slowly, with cling film (saran wrap) over the top to keep any spitting inside the
beaker.
