Hi Farmer,

I just did my first distillation from glycerol. I have a basic GL processor and so was able to use the venturi during distillation. I started with 50 gallons of glycerol and started getting methanol out at 165F. The pot stayed at 165 to 180 for about 4 hours at which time I had gotten about 10 gallons of methanol out. I ran the pot temp up to 200 over the next 2 hours and got an additional 2 gallons out. I had to stop at that point as my Mazzei venturi is rated at 200F and I really didn't want to test it above that. The glycerol was from several batches and about half had had the 5% prewash done. My purity measured with the hydrometer started at 98% @70F and the last 2 gallons were at 92% @70F. This was with a straight Plumbers Delight condensor and o reflux column. I think that with no prewash water and a metal venturi I could do much better as i could drive to a higher temp without the loss of purity. The venturi continued to pull vapors thru till the end although it did slow down somewhat at the end. I too wonder about the chart, it would seem there is something else at work here as both of our experiences seem similar.

This is a thread worth reviving,
Tony

Hi Farmer and tgomes

If you are using the venturi to recirculate vapours thru the condenser, you will be able to recover at much lower temperatures than for traditional distillation, because the venturi introduces evaporation to the cycle.

I can start to recover methanol at 25C, for example.

Hi Graham,

Thanks for jumping in here. I noticed on the UK forum that a rule of thumb for the PD condensor seems to be 1'/KW. Is that for the original 22mm jacket with 15mm center tube? I need to go larger due to my 5.5kw heater especially when demething glycerol. My condensor is 4' now, would a larger diameter serve as well as a longer condensor?

BTW.....This processor ROCKS!

Thanks,
Tony

Thanks GL, we are adding a venturi based on your suggestions. Will be glad to report back after we retool.

I have a 4 foot PD with 4500 W of heating power, works fine if I keep the cooling water flowing fast enough on GLY distillation.

Anyway I posted the same question about methanol in soap over at the glycerol thread.

Farmer

Hi Gang,

We just got the results back from our glycerol testing at the PA Department of Environmental Protection:

AFTER going through methanol recovery to 190F or higher, our glycerol had a flash point of 39.5C (about 89 F) and contained about 8% methanol. According to the DEP, this is still classified as a hazardous material due to the low flash point.

This is troubling news for soap production unless we can get some chemist to tell us why glycerol with 8% methanol should be considered safe for use as soap.

Any thoughts?

We are going to re-run the methanol tests after paying a little closer attention to the variables in our methanol recovery process. The batch I gave the DEP came out of a bulk barrel where we store our GLY after recovery, but I am not sure if it was recovered to 190 F or to 212 F, which is our normal shop practice.

Stay tuned!
Farmer

PS GL we built the venturi design from your website that uses the brass tee filled with solder. It came out OK but does not produce much suction... back to the drawing board!

I think one of the issues with the temperatures required to remove methanol from biodiesel is the imperfect nature of the solution. Partial pressure calculations assume full solution, which is not the case with methanol and biodiesel. The case for glycerin and methanol will likely be closer to theory.