Methanol Recovery from Glycerin

Are you saying that you are not removing all of the methanol from the glycerine you are making? If so, what is the percentage of methanol is in the glycerine? How are you removing unreacted methanol now? Is there a chance that the separation process that you already have could be improved?

Actually Mikey, the glycerin is the by product of the process. during the settling stage the product is cooled, the glycerin layer drops out and is then sent to storage. The separated product is then heated to 95c, sparged with n2 under vacuum, condensed and recovered. The meoh loss is during the glycerin removal. During a 250 gal. reprocess batch I regained 46 gal. I have tried to flash off before the settling stage but end up re-chaining.

I believe I may have to set up a secondary recovery loop off from the glycerin storage.

methanol can be adsorbed into some dry compounds like water into anhydrous copper sulphate, which is then filtered and heated to remove the water, and in your case the methanol. if you can find the right compound?

The secondary recovery loop would seem the only practical way to go. Unless (if I understand your setup properly), is it possible to pressurize the storage vessel with N2 enough to counteract the vapor pressure of methanol at 130° F, to keep it from evaporating?

Thanks for the post Greg,

Hopefully to answer your question, the vessel is blanketed by N2 for obvious reasons. The vessel is traced at a temp to keep the gylcerin at a solluble state. During the process, the glycerin is drawn off at fairly low temp, (30c) and then heated for the flash (100c). During this settling phase I suspect that a large amount of the methanol is dropping out with the Glycerin and then sent to storage.

You should be using about 100% excess methanol to drive the reaction to completion. This equates to about 24% by weight of the total feed weight. About 85% of the excess methanol will end up in the glycerin phase after settling and the other 15% or so ends up in the ester phase. These numbers vary somewhat. At the industrial level this mehtanol is recovered from the glycerin and reused. The process involves drivng the methanol out with a great deal of heat and low pressure (vacuum) depending on how much methanol you wish to leave in the glycerin. I don't see a practiccal (or safe) way to do this on a small scale. The methanol that is left in the BD is washed out with the wash water. Again, at the industrial level this is recovered. If you try and use much less methanol you will end up with an incomplete reaction and the creation of more soaps and by products

If you do not want to use additional heating, and skipping the idea of any absorbant which would very likly be expensive, the only idea I have is to vacuum strip. Of course, the equipment to do this can be very expensive. I am not sure that the recovered methanol would pay for the equipment but you would also have no emissions of methanol which you would have if you just boil it off.

If I'm not mistaken methanol is a reactant in your transesterification reaction. I think you should be able to minimize the amount of unreacted methanol by taking a sample of your raw material and titrate to determine the amount of caustic soda needed to neutralize your raw material. Then just add the amount of caustic soda and methanol solution needed to reach a stoichiometric reaction leaving you with very little methanol (in theory) Problem with this is that you would need to circulate more and allow more time as the gradients driving the reaction would become very small near the end of the process.

Since I probably don't know what I'm talking about there are most likely many more problems with my suggestion.

Best of luck with your still. :)

Thanks JJ,

I've not researched this theory as yet, but will look into it. Obviously time is an important factor in the process and "I wanna go fast!" When you comment about the caustic soda are you refering to another chemical addition besides the NaOCH_3/CH₃OH reaction?

Caustic Soda is the reactant NaOH (SodiumHydroxide) aka lye etc. I assume you are mixing that with your methanol before adding it to the SVO?

Here are links to sites I found:

back yard practice

Titrating

My bad, the NaOH is a catalyst, not reactant. Methanol and the triglycerides are the reactants.

Are you keeping your lye super dry? If not you will make soap instead of the desired alkyl esters, and the soap will "lock up" your methanol. So maybe that's where it's going is into the soap?

Hey J Diesel, did you get anywhere with your methonal loss problem?