Weak acid + Strong base produces a base. I do not remember presently why that's true, I would have to look it up. Also Soap making to react all the caustic 100% takes a long time. I made sodium and potassium soap at hot temperatures, therefore a faster reaction time, and the reaction continued maybe at least several hours. I expect glycerine from the last batch of biodiesel is basic still with some unreacted caustic in it. and Acid plus base yields a salt. so using a glycerine prewash to dry used vegetable oil reacts some base present in the methanol, caustic, soap, glycerine, water solution with present free fatty acids in the used vegetable oil, which is kind of confusing to me as to determining an accurate titration number. It transfers a base to a liquid I'm trying to test with phenolphthalein which changes colour near pH 7. It seems that might be a problem. I've never done a glycerine pre wash.

Thanks for this Wesley.
I don't titrate any more. all my oil is T3 Naoh more or less, Then add glycerol and heat. Drain Glycerol and process.
Any discrepancy I deal with after processing and with 270/30 test. I have seen some yellow stuff on top of the Glycerol after the first water wash and wasn't sure what it was. So could be soap. However my yields have gone up from 75% to 85/90% so I'm happy. Also the more batches I do the more snots get returned to the beginning of the process this also adds to the yield.

Hi WestleyB,

quote:

Originally posted by WesleyB:
Weak acid + Strong base produces a base... It seems that might be a problem. I've never done a glycerine pre wash.

Thank you for your response.
As I read your reply, you are saying that you have never heard of soap affecting the FFA titration and do not know why it should.

The glycerine from a former batch will not be 100% converted soap as the glyc layer is lacking approx 25% in order to fully saponify (otherwise we would never get BD we would get a batch of finished soap).

The hypothesis is that the residual unsaponified soaps from the glyc will affect the titration as these would also reflect a certain amount of unreacted FFA's.

This would not "confuse" the titration although it could conceivably increase it if the original oil was of low titration to start with or diminish it if the originating oil was of a high FFA content to start and some was transfered to the input glycerine. Why someone would want to add a glycerine "wash" prior to reaction if the FFA count is low does not make sense, but if the count is high then perhaps it can be of benefit being that the mixture would stabilize the overall FFA count and thereby reducing it in high titrating oil.

Anyway, that's my nickel's worth.

Hi Legal Eagle,

I do a glycerine pre-treatment with low titrating oil. A 10/90 test after this process shows sometimes only 7.5mls dropout.

The glycerine I use very often comes from another brewer that uses plenty of chemicals. If he wants to give me his residual chemicals then so be it.

Thanks for the info with the soap/titration.

quote:

Originally posted by Legal Eagle: "unsaponified soaps"

Bit of a contradiction in terms - how can a soap be unsaponified?

Hi Legal Eagle,

quote:

Originally posted by Legal Eagle:
The hypothesis is that the residual unsaponified soaps from the glyc will affect the titration as these would also reflect a certain amount of unreacted FFA's.

This would not "confuse" the titration although...

Ah yes, I forgot the claim was that soap would "confuse" the titration.
Yes, the soap will be caustic as well as the methoxide that is in the glycerine/ byproduct.
Both woulld tend to neutralize FFA's which is what we want to have happen.
If the FFA's are neutralized then the titration number would be less but that is because they have been neutralized.
I do not see the confusion.

quote:

Why someone would want to add a glycerine "wash" prior to reaction if the FFA count is low does not make sense,

I actually asked Dgs this very question and his reply was that it was often easier to do a multi stage reaction over several days rather than doing a single stage reaction in one morning.
I still have not quite figured that one out but I am working on it.

I will answer that Tilly. You are asking questions that the Russian intelligence service were asking in the USA. But aren't you Tilly from Paradise (Australia)? I do not mind if I help to improve people world wide to increase our ability to capture energy from sunlight via chemical means. That's increasing entropy that can be done by plant life using photosynthesis to gain energy from the sun. Anyway there's no such thing as "unsaponified soaps", there is no such thing. As far as unreacted free fatty acids present in solution, I expect that's a relatively fast reaction compared to saponification. Saponifaction is making a soap from a triglyceride which has a slow reaction rate (weeks?). The hardest thing I recall from freshman college chemistry was calculating the pH of buffer solutions where, a strong acid or base is reacted with a weak base or acid, then calculating mathmatically the pH of the product in a particular concentration in pure water. Since used vegetable oil has only a small per centage of water, possibly you can explain how to mathmatically calculate and predict what the titration number might be after a glycerine pre-wash? Would you call that "confusing?". Possibly you understand it better than I know.

Hi WesleyB,

quote:

Originally posted by WesleyB:
I will answer that Tilly. You are asking questions that the Russian intelligence service were asking in the USA.

Really?!!!
Do you mean the Russian intelligence service also wonders how soap in the oil can confuse the FFA titration.
I find that remarkable!!

quote:

But aren't you Tilly from Paradise (Australia)?

I am Tilly from ลึก ประเทศอินเดีย

quote:

Anyway there's no such thing as "unsaponified soaps", there is no such thing.

Are you sure?
I thought that making soap from FFA's was Neutralization and not Saponification.
https://books.google.com.au/bo...ponification&f=false

quote:

As far as unreacted free fatty acids present in solution, I expect that's a relatively fast reaction compared to saponification.

If you mean neutralizing FFA's then yes, I am sure it is a fast reaction or you would have to wait for weeks for the titrration results.

quote:

Possibly you understand it better than I know.

Possibly.

You are a lot of fun Tilly. I do not even recognize the alphabet you use to list what part of the world you are in. Paradise is a small town in central Australia. That's fine. Saponifaction is a reaction involving triglycerides caustic and water. The water inserts itself between the free fatty acid and the glycerine so that the molecule separates resulting in two molecules, a diglyceride and one free fatty acid. Saponifacation has nothing to do with the neutralization reaction where an organic carboxylic acid reacts with the strong caustic base. An acid plus a base react to form a salt, a soap. That's not saponification, that's neutralization.

Hi All,

Sorry for posting under yet another name but I forgot my login details and my email address has changed since I last posted so I couldn't recover it.

I have now a page page dedicated to this method on my website website. It's free to visit and comment on.

One problem with the initial posting was that there was a limit on the number of characters and so I had to trim it somewhat, so I couldn't go into as much detail as I wanted to. But of course on my own website that wasn't a problem.

It's divided into two sections - the first explains the chemistry and the second is the method. You don't have to have understood the chemistry to follow the method. There's a place at the bottom where you can make comments or ask questions.

Note that I will be making no further contributions to this thread on this forum as I simply don't have the time to plough through all the comments (many are unfortunately based on a limited understanding of chemistry) or conduct online chemistry tutorials. And the beauty of this method is that it is so simple that you don't actually need to understand a thing about the method.

Mark Imisides (aka Dr Chemical)