Its my understanding that the reaction to form acrolein from glycerol requires a catalyst. As yet, no acrolein, even in nano-quantities has been detected in the vapor of a VG-juice. True there are thinners in it, like flavorings and perhaps water, so the BP is significantly less than VGs BP. If you are concerned about acrolein forming from a flash boiling, you could add maybe 5% water to the VG, which will lower the BP a fair amount.
1. That said, acrolein is something I think would be really evident if it had formed. Its a very strong lacrymator (mucus membrane irritant, like tear-gas), and it takes VERY little to produce a strong nasal and eye reaction. Yes, it is toxic, but we would reject it, and in a rather unpleasant way. I certainly have not experienced anything like that with my PTE, let along my other VG juices.
2. My pipe tobacco that I used was moist, thus adding some water to the mix.
3. Water will do a couple of things. One, it will lower the BP. Two, the reaction to form acrolein is a glycerol dehydration. Water is the other product that is formed if acrolein forms. Thus adding a little water pushes the equilibrium to the glycerol side, inhibiting the dehydration. You must remove the water entirely before dehydration will be thermodynamically favored. Plus, the kinetics are such that it seems to need a catalyst. All the papers I have seen about acrolein from glycerol include a catalyst. Tungsten oxide is one that is used. I use a non-stick pan for PTE.
I have not seen that pure VG is actually 10% water. It evidently does not form an azeotrope with water that I can find. OTOH, ethanol-water forms a 5% water azeotrope, and thus ethanol cannot be distilled to higher than 95% from water. Seems reasonable glycerol would too, but maybe not. I have seen that crude glycerol is 10% water, but not pure. That said, adding a little water to the VG will lower its BP and shift equilibrium away from acrolein, but I do not think the stove-top conditions would at all promote acrolein production, regardless. Just heating will not do it, in general. But again, a little added water will remove any uncertainty you may have, and still work great. Not something I am concerned about, but it's not a bad idea.
1. That said, acrolein is something I think would be really evident if it had formed. Its a very strong lacrymator (mucus membrane irritant, like tear-gas), and it takes VERY little to produce a strong nasal and eye reaction. Yes, it is toxic, but we would reject it, and in a rather unpleasant way. I certainly have not experienced anything like that with my PTE, let along my other VG juices.
2. My pipe tobacco that I used was moist, thus adding some water to the mix.
3. Water will do a couple of things. One, it will lower the BP. Two, the reaction to form acrolein is a glycerol dehydration. Water is the other product that is formed if acrolein forms. Thus adding a little water pushes the equilibrium to the glycerol side, inhibiting the dehydration. You must remove the water entirely before dehydration will be thermodynamically favored. Plus, the kinetics are such that it seems to need a catalyst. All the papers I have seen about acrolein from glycerol include a catalyst. Tungsten oxide is one that is used. I use a non-stick pan for PTE.
I have not seen that pure VG is actually 10% water. It evidently does not form an azeotrope with water that I can find. OTOH, ethanol-water forms a 5% water azeotrope, and thus ethanol cannot be distilled to higher than 95% from water. Seems reasonable glycerol would too, but maybe not. I have seen that crude glycerol is 10% water, but not pure. That said, adding a little water to the VG will lower its BP and shift equilibrium away from acrolein, but I do not think the stove-top conditions would at all promote acrolein production, regardless. Just heating will not do it, in general. But again, a little added water will remove any uncertainty you may have, and still work great. Not something I am concerned about, but it's not a bad idea.
