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Why is there saponifiable material in the waste glycerine?
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It's come to my att'n in a soapmaking forum that some people are successfully making soap from the glycerol byproduct fraction of biodiesel prod'n. This is perplexing to me from what I know of the biodiesel process.

AIUI, waste fat/oil which is chiefly fatty glycerides is transesterified with anhydrous methanol to make fatty methyl ester product, and glycerol as byproduct. The process I knew of first used an excess of caustic to make methanolate (methoxide), and then an excess of that was reacted with the fat, the glycerol and alkali being mostly separated dry, and then the product being water washed of further glycerol & methanol. I understand there are other procedures using other catalysts, but my assumption was that in any event at least a slight excess of methanol would be used and the object being to convert as much as possible of the saponifiable material in the original fat to methyl ester, otherwise you might as well just use the fat itself as fuel. Am I right? And that another disadvantage of leaving significant amounts of saponifiable material in the product after glycerol separation is that soaps may be formed on water washing -- that small amounts are to be expected, which is why you're doing the wash, but that large amounts would make the separation difficult.

AFAIK, very high yields should be easily possible with these methods, and as long as the methanol is in excess, nearly all the saponifiable material (glycerides) should be consumed. I could understand the glycerol fraction could be useful to soapmakers for its glycerol, and if alkaline catalysis is used, the caustic could potentially be recovered for their use as well. But what I don't understand is how much fatty material could be left in the glycerol. Seems even if the rxn went badly and left much in the way of glycerides, they would partition mostly into the product fraction rather than the glycerol byproduct, where they would be less soluble, it being a much more polar medium.

And yet I'm seeing these reports of people recovering saponifiable material from the glycerol and making worthwhile amounts of soap from it, and here you have a whole section of this discussion board devoted to doing so. What am I missing?
 
Location: Bronx, NY | Registered: September 26, 2013Reply With QuoteReport This Post
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I had some crud glycerin tested and it contained a surprising amount of fat. I am not sure if soap was showing up as fat, but there was fat.
 
Location: Virginia | Registered: March 17, 2007Reply With QuoteReport This Post
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It's come to my att'n in a soapmaking forum that some people are successfully making soap from the glycerol byproduct fraction of biodiesel prod'n. This is perplexing to me from what I know of the biodiesel process.


Really? You been out of country or away from here for a very long time? My ebook The Guide is in it's 5th edition and it comes with 11 editions of Lather! another emag dedicated to nothing but making soap from the glycerin layer.. I've been at it for almost 10 years now as have many others; and many have also started up small soap making businesses to help supplement their family income.

Ok, now that that is covered; the glycerine layer is, for the most part, an almost completed saponification due to the caustic used to neutralize the fatty acids in the use cooking oil. The reaction does not, however, use up all of the fatty acid or you would end up with a boatload of soap instead of a separation. The unsaponified percentage in the glycerine layer is +/-23% in used oil and closer to 15% in new oil that has been reacted.

In the soap making process we merely add enough caustic & water to complete the saponification process, and toss in some essential oils for scent along the way once the residual methanol has been completely removed from the glycerine.

The glycerine by-product is anything but a "waste"; you can use it to finance your methanol purchases or simply add a few bux to the family coffers or just make it for yourself and friends/family if a small business isn't your thing.

The fact still remains; it makes the absolute best soaps you have ever encountered.

"I had some crud glycerin tested and it contained a surprising amount of fat. I am not sure if soap was showing up as fat, but there was fat."

All of the fat that was in the original oil is now in the glyc layer; the higher the titration the more fat there is (FFA's) and the amount of caustic used in the biodiesel process is designed to break the fat out of solution not consume it all, which is why there is still so much of it available to react into a completed soap. Were the fat completely consumed you would end up with a large amount of soap, as that is the point of soap making. You first get the SAP value of a given oil(acid) and with that value you then proceed to add water into the mix and when an acid, water and caustic meet you get soap. In the biodiesel process we intentionally do not use sufficient caustic to turn the lot into soap as we are interested in the FAME part of the oil as fuel, and so there is plenty of fat left in the separation layer.

And because the glyc layer is mostly saponified it is an excellent degreaser as is once the residual methanol is removed. You can also use it as a shop soap as is, but for that more refined soap you need to complete the process.

HTH



** Biodiesel Glycerine Soap - The Guide
- on 5 continents helping people make & sell soap from the Biodiesel Glycerine.


 
Location: :-) Great White North eh ? | Registered: December 10, 2004Reply With QuoteReport This Post
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Ok, now that that is covered; the glycerine layer is, for the most part, an almost completed saponification due to the caustic used to neutralize the fatty acids in the use cooking oil. The reaction does not, however, use up all of the fatty acid or you would end up with a boatload of soap instead of a separation. The unsaponified percentage in the glycerine layer is +/-23% in used oil and closer to 15% in new oil that has been reacted.


Are those percentages of the glycerine layer, or of the original oil? And if they're of the original oil, why not add another aliquot of methanol and react again?

But to the extent there's anything saponifiable in there, why is it in the glycerine layer rather than in the product layer? Even if the saponifiable matter were all monoglyceride, I would expect it to be of a polarity much closer to that of the product than to that of glycerine + methanol.

quote:
All of the fat that was in the original oil is now in the glyc layer;


Any idea why?
 
Location: Bronx, NY | Registered: September 26, 2013Reply With QuoteReport This Post
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Legal Eagle, I have lost my copy of your soap manual. I had saved it on my hard drive but lost a lot of files recently. How can I go about getting anohter copy and the editions of Lather?


"This biodiesel tis a cruel and heartless mistress we home brewers have chosen"
 
Location: MA | Registered: February 01, 2010Reply With QuoteReport This Post
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send me the email you used when you ordered it to soapinfo@blackcrownsoap.com and I'll resend the lot. If your email has changed then include that in the email.



** Biodiesel Glycerine Soap - The Guide
- on 5 continents helping people make & sell soap from the Biodiesel Glycerine.


 
Location: :-) Great White North eh ? | Registered: December 10, 2004Reply With QuoteReport This Post



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