Possible to unreact biodiesel?

[yaric008]

We finally got our methanol recovery working really well the other day then we were wondering if we could actually reverse the reaction in the biodiesel. Basically we reacted our mixture then let settle for a day, pulled out the glycerin then we heated it up to around 150 and pulled a vacuum on it and recovered a couple liters of methanol out of the bio. We just kept getting more and more methanol so like i said we were wondering if we could actually reverse the reaction. If there were still glycerin in the mixture it seems like it could, but if we got all the glycerin out and then you pulled methanol out i don't even know what would be left...

Anyways, just wondering.

[Spencnaz]

If you go below the stoichiometric level (I think it's about 13% methanol), you can have the methyl esters recombine with the glycerin molecules.

However since you've probably used a base line of about 20%, I doubt you'd be able to boil off enough methanol for the reaction to reverse itself.

I take it this is with unwashed biodiesel?

[yaric008]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Spencnaz</div><div class="ubbcode-body">I take it this is with unwashed biodiesel? </div></div>

Indeed. Also this was after we drained off 95% of the glycerol after settling for 12 hours. So it'd have a tough time reversing with the glycerin without the glycerin being there. I don't guess the methanol and glycerin could break off and leave some weird crap eh?

[girlmark]

If your biodiesel wasn't fully reacted in the first place, ther ecould be extra methanol in it that you didn't think should be there. Basically, this would happen if you had low catalyst amounts of poor mixing or low heat for the length of time you mixed.

What's your reaction procedure?

[girlmark]

Anyway, I think you've got more excess in there (correctly) than you expect, and what you're experienceing is normal. ALso, if you're not taking the temperature at the condensor, you do'nt know if you're boiling off methanol or water (Remember, the temp of the heater element is quite higher than what you're sensing at the temp gauge)

[girlmark]

Just to get some idea,

in the last Advanced Topics class I did, the host, who demonstrated his methanol recovery still, was getting about 16 gallons of methanol out of 50 gallons of glycerine (ie he saved three batches or so of glycerine and then did recovery on it all at once) and something like 1.5 gallons of methanol out of a 50-gallon batch of biodiesel. However, whether the methanol goes into the biodiesel or into the glycerine layer seems to depend a bit on how long you let it settle for. If you're doing recovery after a short settling period you might find more methanol in the biodiesel than if you'd let it settle for a week. I'm not sure how much this number varies.

[yaric008]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: girl_mark</div><div class="ubbcode-body">What's your reaction procedure? </div></div>

Well first off we filled our reactor with oil, then we heated it up to 120 degrees, circulated it for a bit, then we put in our methanol and lye in the amounts we determined appropriate, next we circulated with a pump for 2 hours, with the water heater completely sealed.

Next we let it settle for about 12-16 hours, drained off the glycerin, turned the heat up to 150F then circulated and ran our recovery unit and got out around 6 liters of methanol. At which time the methanol recovery slowed way down and then we started thinking about it possibly reversing so we stopped and moved on the the washing phase.

We need to get a specific gravity tester to see how pure the methanol we recovered it. It was a very humid day so there could have been a bit of water, but we were doing the recovery via a closed vacuum loop so only the air that got in there at first would have gotten in. After that it should have all been methanol.

Here are some pictures.

http://www.samantha.cc/images/pic009.jpg
that is part of our recovery, that is where the methanol collects.

http://www.samantha.cc/images/pic010.jpg
that is the unit from above. We don't have it prettied up yet as we just started making biodiesel finally the other day and built that thing yesterday. It seems to work very well though and all the fumes are contained the way we have it set up.