LBussy
Well-Known Member
Just in case anyone was interested, I contacted a few labs. This was a pretty representative response: "A GC analysis with standards is required to determine your objective. The approximate cost will be about $1000.00."
Of Stearic Acids and Idiosyncracies
- Thread starter LBussy
- Start date
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Putting my chem professor hat firmly on my head...
Stearin, CAS 555-43-1, isn't a fatty acid. It is a triglyceride (fat). Please see Post #17.
Look at the chemical structure of stearin ... see http://www.chemicalbook.com/CASEN_555-43-1.htm ... and you'll see the structure of this fat, assuming a pure product. The "O" and "O=H" parts in the center are the glycerin backbone of the fat.
Stearin, CAS 555-43-1, isn't a fatty acid. It is a triglyceride (fat). Please see Post #17.
Look at the chemical structure of stearin ... see http://www.chemicalbook.com/CASEN_555-43-1.htm ... and you'll see the structure of this fat, assuming a pure product. The "O" and "O=H" parts in the center are the glycerin backbone of the fat.
LBussy
Well-Known Member
I get it ... and this is what makes me careful to figure it out. Being a fat and not a fatty acid it will not liberate glycerin (meaning we would want to adjust the glycerin in the recipe) when saponified. If I globally said "fatty acid" I humbly take my lashings and will sit in the corner.
Oh, Lee, I was actually responding to Cpacamper. I don't mean to be picking on anyone -- I just know how very easy it is on the internet to get confused about stuff like this so I hope we can keep the terminology straight. I do not want people reading this thread to get confused or mislead.
The diagram of that idealized stearin molecule reminds me to explain why it is not straightforward to get pure stearic acid from any fat, such as palm, even though the fat happens to be very high in stearic acid. If you look at the diagram, you see three stearic acid arms branching out from the glycerin center. That's an ideal molecule that has the name glyceryl tristearate. If our palm contained such nice organized fats, then the process of getting pure stearic acid would be fairly easy. Separate the stearin (glyceryl tristearate) from the olein (glyceryl trioleate), break down the glyceryl tristearate into glycerin and stearic acid, separate the insoluble stearic acid from the water-soluble glycerin, and package.
It doesn't work that way.
Palm contains oleic, palmitic, and stearic acids (and odds and ends of other stuff, but let's simplify a bit). It turns out any given molecule of palm fat can have any combination of these three fatty acids for its three arms. A palm oil molecule could have 3 palmitic arms (glyceryl tripalmitate), 3 stearic arms (glyceryl tristearate), or 3 oleic arms (glyceryl trioleate). Or it could have one arm of each acid -- glyceryl monostearate monopalmitate monooleate for example. Or two arms of one fatty acid and one arm of a second -- glyceryl distearate monopalmitate. And so on.
So when you cool the palm to solidify the stearin (the higher melt point fats) and filter those fats out of the olein (the lower melt point fats), the solid fat (stearin) recovered from that process is still quite a mixture of fatty acids.
The diagram of that idealized stearin molecule reminds me to explain why it is not straightforward to get pure stearic acid from any fat, such as palm, even though the fat happens to be very high in stearic acid. If you look at the diagram, you see three stearic acid arms branching out from the glycerin center. That's an ideal molecule that has the name glyceryl tristearate. If our palm contained such nice organized fats, then the process of getting pure stearic acid would be fairly easy. Separate the stearin (glyceryl tristearate) from the olein (glyceryl trioleate), break down the glyceryl tristearate into glycerin and stearic acid, separate the insoluble stearic acid from the water-soluble glycerin, and package.
It doesn't work that way.
Palm contains oleic, palmitic, and stearic acids (and odds and ends of other stuff, but let's simplify a bit). It turns out any given molecule of palm fat can have any combination of these three fatty acids for its three arms. A palm oil molecule could have 3 palmitic arms (glyceryl tripalmitate), 3 stearic arms (glyceryl tristearate), or 3 oleic arms (glyceryl trioleate). Or it could have one arm of each acid -- glyceryl monostearate monopalmitate monooleate for example. Or two arms of one fatty acid and one arm of a second -- glyceryl distearate monopalmitate. And so on.
So when you cool the palm to solidify the stearin (the higher melt point fats) and filter those fats out of the olein (the lower melt point fats), the solid fat (stearin) recovered from that process is still quite a mixture of fatty acids.
LBussy
Well-Known Member
Understood.
That all makes me wonder if technical grade (I generally get chems at surplus prices) would be a better choice for .. let's call me a compulsive person.
That all makes me wonder if technical grade (I generally get chems at surplus prices) would be a better choice for .. let's call me a compulsive person.
Quoting myself here, but should the response from ED be taken with a grain of sodium stearate, uh, I mean salt?
LBussy
Well-Known Member
Until/unless they provide a certificate of analysis, we just don't know. It says "triple pressed" and we can see from DeeAnna's post that pressing is not part of what makes pure stearic acid pure. I also looked at other definative sources (at least for their own supplies) and anything that was "triple pressed" and "food grade" is listed as a mixture of Octadecanoic Acid (stearic acid) CAS#57-11-4, and Hexadecanoic Acid (palmitic acid) CAS# 57-10-3.
That's not to say it doesn't make fine soap, just that it's likely not really stearic acid.
That's not to say it doesn't make fine soap, just that it's likely not really stearic acid.
boyago
Well-Known Member
Also if your like me and have been working off Soapcalcs "Stearic Acid" we've been working with an unintended KOH deficit of .085g per 100g of stearic. How's that tickle your OCD?
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LBussy
Well-Known Member
Now I'm confused. Which admittedly is a normal state of affairs.
I thought a "triglyceride" (the major constituent of animal/vegetable fat) is a molecule composed of 3 fatty acids bonded to a glycerol molecule (i.e. 'backbone'). When saponified the triglyceride is first "cleaved" thereby separating the fatty acids and the glycerol, followed by an acid-base reaction where the free fatty acids are converted to soap salts.
Using these definitions and DeeAnna's definition of stearin as a triglyceride, when saponified it *would* liberate glycerine.
"Pure" stearic acid is a free fatty acid with no glycerol and when saponified would only result in a soap salt *without* glycerine.
Correct?
-Dave
I thought their response was pretty weaksauce. I'd assume the "customer relations associate" you spoke with is also the shipping clerk, warehouse clerk, janitor, and secretary. Which is a respectable job ... but with that said I'd also assume that person is merely reading the label back to you with little insight into what we're talking about.
I certainly could be wrong (it wouldn't be the first time, lol) but the pat response IMO is pretty telling.
-Dave
TRBeck
Well-Known Member
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Dave, I think you're right. I do wonder if there was a sudden influx of nearly identical questions that might have contributed to a pat, unhelpful answer. I know I sent two email inquiries (after the first went unanswered). If others were also asking, say a half dozen questions out of the blue in a couple of days, well, this may have been a polite "get-off-my-lawn" thing. Or I'm misreading it. Anyway, it's not shedding any light, especially for those of us who just took delivery of 25 lbs. of their stearic.
"... a "triglyceride" (the major constituent of animal/vegetable fat) is a molecule composed of 3 fatty acids bonded to a glycerol molecule (i.e. 'backbone'). When saponified the triglyceride is first "cleaved" thereby separating the fatty acids and the glycerol, followed by an acid-base reaction where the free fatty acids are converted to soap salts. Using these definitions and DeeAnna's definition of stearin as a triglyceride, when saponified it *would* liberate glycerine. "Pure" stearic acid is a free fatty acid with no glycerol and when saponified would only result in a soap salt *without* glycerine...."
Yes, that's correct. It's easy to get these things backwards sometimes, despite the best of intentions. Been there, done that!
Yes, that's correct. It's easy to get these things backwards sometimes, despite the best of intentions. Been there, done that!
LBussy
Well-Known Member
You can count on my short answers being wrong if there's anything technical in them ... when I type on my phone or my tablet they don't get the read-over after I am done to make sure what I thought I said and what I said are the same.
You were right to be confused. So yeah ... as DeeAnna said Stearic Acid is a fatty acid which will not liberate glycerin, stearin is a triglyceride that is roughly three units of stearic acid. I believe the manufacturing process starts with palm oil, separates that into the constituent triglicerides, then what we hope is solely stearin is hydrolyzed to give us stearic acid.
In theory, it should not make any difference if you start with stearin or stearic acid if the end product is intended to have some glycerin in it. You would of course need to add back in glycerin at a rate of 50g per lb of stearic acid ... more or less. That's 11% which is pretty close to what folks use.
So that's a good backdrop for my issue. If I am using Stearic Acid only for the sake of conversation and I used 11% glycerin then I am at 11% glycerin. If I am using stearin and use 11% glycerin I am at 22% glycerin. If I develop a recipe I like very much and want to be able to make it for ever and ever, I need to know which it was. Second, I need to be able to know what I am buying. In theory I can use either but I need to know what it is.
The SAP value of Palm vs Tallow is nearly identical so we really don't run the risk of making excessively superfatted or lye deficient soap if we consider 100% stearin vs that mixed product. Palm oil has been a part of some very good shaving soaps (European Palmolive Stick) for a very long time. Any difference there is likely only going to affect my OCD and not be a significant difference. I have not experimented with palm oil vs tallow in a real good straight up comparison though. Some day.
kchaystack
Supporting Member
I so do not understand why people do this.
Of course I still want the US to convert to metric measures.
Of course I still want the US to convert to metric measures.
"...50g per lb of stearic acid..."
Oh, my achin' head! Mixed weight measures .... ewww!
LBussy
Well-Known Member
Hey I don't make the rules .. y'all use PPO so I persisted it."...50g per lb of stearic acid..."
Oh, my achin' head! Mixed weight measures .... ewww!
I did convert it to a proper percentage though. DO I get credit for that? :wave:
Extra credit to Lee for a mathematically correct answer: +1 points
Extra credit to Lee for triggering a headache and a belly laugh at the same instant: +5 points
<...heading to the medicine cabinet to pop a couple of headache pills....>
Extra credit to Lee for triggering a headache and a belly laugh at the same instant: +5 points
<...heading to the medicine cabinet to pop a couple of headache pills....>
