On the Chemistry of Liquid Soap Making Processes...

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Hello Soap Making Forum!

This is my first post on the site (although I have been lurking in the shadows for some time now lol). I should start by saying what an excellent resource this site is for soap makers, with such detailed content and expert opinions. Great work everyone! :)

I am a bit of a Newb when it comes to soapmaking (I have been making soap for my family and friends for about a year now). However I am not a Newb when it comes to chemistry. I have a Masters degree in Pharmaceutical Science and a PhD in Organometallic Chemistry and have worked in the chemical industry for years now. I therefore feel somewhat qualified to make the following critique of soapmaking methods (despite being a Newbie soapmaker):

This post concerns the "New" method of making soap from KOH and glycerol (as featured on the Soaping 101 Youtube video and mentioned quite a bit on this site - heralded as a much more convenient method for making liquid soap - and of course it is more convenient).

I find this method interesting on an academic level. Although I am sure that the product which is made by this method creates a very nice 'soap', I have reason to believe that this product is not truly 'soap' (or at least not the "natural soap" that has been made for hundreds of years). Rather than producing a mixture of potassium salts of fatty acids and glycerol, I think this method actually produces a complex mixture of mono- and di-glycerides.

Now bear with me. I am not saying there is anything wrong with the method. I know alot of very well respected soapmakers use this method and the last thing I want to do here is annoy anyone on my very first post on SMF, rather I am just asking a question about the actual chemical composition of the soap made by this new 'glycerin method'.

I have been doing some pondering... Which lead to some scribbling... I know most of you guys aren't chemists and I apologise to everyone for the technical nature of this post, but it is, I'm afraid, unavoidable. I have attached my scribbles for anyone on here who might be chemically inclined.

So, the point I am making is this: when you combine KOH and glycerol and heat up the mixture, you see bubbles. These bubbles are actually water boiling off - water that has been produced by the reaction between KOH and glycerol (the bubbles must be water because glycerol itself has a much higher boiling point - 290 oC). This initial reaction involves KOH acting as a base and 'deprotonating' the glycerol to form a potassium alkoxide species and water.

Now for the fun part: when the KOH/glycerol mixture is combined with the plant oils, it is the potassium alkoxide species that actually reacts with the triglycerides in the oil! "Who cares?" I hear you cry...

Well, I *think* that this will lead to a substantially different mixture of products compared to the 'old', 'cooking for four hours', method. The old method produces potassium salts of fatty acids and glycerol. This new method would, I reckon, produce a complicated mixture of mono- and di-glycerides by a process known as "transesterfication".

So I could sum up this post by saying that the old method is a process of saponification, while the new 'glycerin' method is largely transesterfication reactions.

Now mono- and di-glycerides do make good emulsifying agents and could therefore be used as soap, but *technically* they are not the good, ole fashioned, natural soaps that the hardcore soap enthusiasts love so much...

The files I have attached are very much a simplified representation of what may be going on in the KOH/glycerol reaction. I would love to discuss this further with anyone who is interested because there are several topics which I have not touched upon including; the fate of the alkoxide species formed in this process (which are very reactive and, I assume, are quenched by some of the more acidic unsaponifiable components) and the possibility of the formation of potentially dangerous degradation products of glycerol in that initial step (depending very much on how hot that KOH/glycerol mixture gets). I suppose the 'soap' produced in this new method should be considered safe, because we would know about it by now if it wasn't! But this would certainly be a relevant concern for anyone planning on taking this product to market as it is not technically 'natural' soap (i.e. not composed of potassium salts of fatty acids) and should not be labelled as such.

Phew! Apologies for the long post, but to a chemistry geek like me, these issues matter! lol

I personally will be sticking to the old method of making liquid soap. I do hope I haven't offended absolutely everyone. Of course everything I have said here is just the opinion of a humble chemist and we could confirm or deny all this pretty easily by conducting a full chemical analysis on the 'soap' made using the 'glycerin method'... Correction, the analysis would by horribly complicated, but HPLC, for instance, would certainly be able to highlight the different product distributions (or confirm if they are identical and I am spectacularly wrong in all of my assumptions lol).

Happy soaping folks! :)

traditional KOH method.jpg


New KOH method.jpg
 

ngian

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Hi curiouschemist and thank you for your chemistry point of view and explanation of the glycerine method of liquid soap.

If all these you are saying are true ( I am not a chemist so I can not evaluate anything), you think that these alkoxide species do not produce Potassium soap molecules? And which molecules are producing these bubbles in the final product?

There is also a method that you dissolve koh into equal weight of water and glycerin is inserted into the oils. Then you add the lye (KOH / water solution) into the oils / glycerin mixture and you reach the paste stage in 15 minutes max.
Is this method also creating the alkoxide species?

And lastly if anyone else has ever created liquid soap with all three methods (only water, only glycerin, and one part water with two parts glycerin) was there any difference in the feeling while washing with each of the 3 types of liquid soap?
 
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Hi ngian,

To be clear: what I am saying is that this method would not produce potassium salts of fatty acids. Of course, the potassium is still present! The alkoxide species I am referring to is actually a potassium alkoxide, which is also a salt. It is simply a different salt to the potassium salts of fatty acids.

I don't think the potassium alkoxide species would be present in the final product as they tend to be quite reactive. But to answer your question: the bubbles that are formed when using this soap are most likely the result of the mono- and di-glycerides - which are soapy things in their own right. They would behave as surfactants and act as emulsifying agents. If, for some reason, the alkoxides survived (unlikely) - I imagine they too would have soapy (surfactant) qualities too!

If the KOH were to be dissolved in water first, that would certainly cut down on the formation of alkoxide species, but I think as soon as you mixed the KOH solution with glycerol/oil mixture, you would get some deprotonation (forming alkoxides). Now that you mention it, we probably see some alkoxides (a small amount) forming in the traditional process too since glycerol is naturally produced during the reaction... Interesting.

Finally, your idea of comparing soap made by all three different methods (but of course keeping all other factors such as oil composition, glycerol content and water content as constant as possible) is an excellent idea - I think I will try this! Watch this space... :)
 
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IrishLass

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Welcome Curiouschemist! :wave:

It's always good to have another chemist come on board. As the good Gent said, we have a few other chemistry whizzes as part of our forum family, and it will be a wonderful learning experience to read the back and forth exchanges that will take place. I am not a chemist myself, but I love reading and learning more and more about it as it relates to soap.

Welcome aboard!


IrishLass :)
 
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Hi IrishLass,

Thanks for your reply, I feel a little giddy as you are somewhat of a celebrity on here! :)

I know you are a big fan of the glycerol/KOH method. Have you ever done a comparison between the soap made by this method and (an identical) one made by the traditional method? I'm going to try this myself based on a suggestion from ngian (above).

If I'm right about the different chemical compositions, then there are bound to be differences in the way the soaps perform... Problem is, I wouldn't be great at evaluating the 'feel' of soaps. Might have to enlist the help of a seasoned veteran such as yourself... ;)

Looking forward to some interesting discussions.

Cheers!
 

Susie

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DeeAnna did a study on the water/glycerin issue a while back. It is in our infamous liquid soap thread found here, starting on page 8, and going from there:

http://www.soapmakingforum.com/showthread.php?t=46114&page=8

I am wondering, however, how my basic CP liquid soap compares to the old fashioned "cook for hours" soap as far as how the oils break down. My thought is that zapless paste is zapless paste, whether it takes 20 minutes or 4 hours. I know the KOH is all used up by the lack of zap. And it had to saponify the oils to get used up, after all. So, now you have me curious.

If you need samples of my soap, send me a PM, and I will be happy to send them. Or if you would like more help sampling yours, I would be happy to help.
 
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Susie

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I am not a chemist, but I could actually follow lots of your typed out explanation. That is why I am curious.
 
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DeeAnna did a study on the water/glycerin issue a while back. It is in our infamous liquid soap thread found here, starting on page 8, and going from there:

http://www.soapmakingforum.com/showthread.php?t=46114&page=8

I am wondering, however, how my basic CP liquid soap compares to the old fashioned "cook for hours" soap as far as how the oils break down. My thought is that zapless paste is zapless paste, whether it takes 20 minutes or 4 hours. I know the KOH is all used up by the lack of zap. And it had to saponify the oils to get used up, after all. So, now you have me curious.

If you need samples of my soap, send me a PM, and I will be happy to send them. Or if you would like more help sampling yours, I would be happy to help.
Thanks for that, Susie. I will have a look...

So, your CP liquid soap... Is that made by dissolving KOH in glycerin before adding it to the oils? If so, I am suggesting that it may have transesterfied rather than saponified... It could be zapless because the KOH has indeed been consumed in that process, the difference is whether we have mostly salts of fatty acids in the final product (like the old method) or, as I am postulating, mostly mono- and di-glycerides? I think the product will be zapless either way. If you are using a mixture of water and glycerin to dissolve the KOH, then your soap is probably more like the that of 'old' method. This idea of mine relates more to processes involving only glycerin and KOH (no water).

Thanks very much for the offer of samples! I will definitely let you know. I am going to do an experiment myself (mentioned above) to compare these processes. i will take lots of pictures and post my findings on here. :)

Like I said, It's more of an academic curiosity than anything else - I am sure your soap is wonderful. Perhaps I will try it someday...

Thanks again for your reply! :)
 
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I don't think that putting forward thought through ideas based on a good background should ever be offensive to anyone. If so, they are easily hurt!

We have a few chemistry whizzes on here who will I am sure provide some peer review soon and I look forward to it as this is an interesting view
Thanks for your reply Efficacious Gentleman! I have just been checking out your website and facebook page - I love the concept of the Efficacious Gentleman. :)
 

Sapo

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So in essence you're saying that:

1. Goold ole' fashioned soap produces surfactants.
2. Glycerin "soap" produces emulsifiers.

Which are basically the same thing in terms of functionality, but differ chemically.

This raises an interesting question... Could one of them, despite using the same oil proportions and recipe etc., be a more effective cleaner than the other, "pound for pound"? Basically a case of one of them being able to bind a larger amount of fats to water than the other.

Edit: the insight that we aren't even talking about the same chemical process (saponification) when making glycerin soap also explains why saponification presumably happened so much quicker and easier. Because it didn't!
 
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Susie

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So in essence you're saying that:

1. Goold ole' fashioned soap produces surfactants.
2. Glycerin "soap" produces emulsifiers.

Which are basically the same thing in terms of functionality, but differ chemically.

This raises an interesting question... Could one of them, despite using the same oil proportions and recipe etc., be a more effective cleaner than the other, "pound for pound"? Basically a case of one of them being able to bind a larger amount of fats to water than the other.

Edit: the insight that we aren't even talking about the same chemical process (saponification) when making glycerin soap also explains why saponification presumably happened so much quicker and easier. Because it didn't!
Except that I made liquid soap paste in the same time frame without using glycerin many, many times without any cooking whatsoever. The glycerin only changes whether the soap feels stripping, and the thickness (you will have a much thicker liquid soap with the glycerin), IMHO.
 
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So in essence you're saying that:

1. Goold ole' fashioned soap produces surfactants.
2. Glycerin "soap" produces emulsifiers.

Which are basically the same thing in terms of functionality, but differ chemically.

This raises an interesting question... Could one of them, despite using the same oil proportions and recipe etc., be a more effective cleaner than the other, "pound for pound"? Basically a case of one of them being able to bind a larger amount of fats to water than the other.

Edit: the insight that we aren't even talking about the same chemical process (saponification) when making glycerin soap also explains why saponification presumably happened so much quicker and easier. Because it didn't!
Hi Sapo! I suppose you could say it that way, but I really don't find the terms surfactant and emulsifier too helpful (like you said, they basically mean the same thing unless we are prepared to get super technical). But yes, the essence of what I said is that these two processes would *I think* produce chemically different products.

It is indeed an interesting question and I think the answer has to be Yes: the two different products would have different properties when used as soap (if only slightly different).

I am wondering now, following Susie's recent post, whether Susie's soap feels "less stripping" because of the presence of a larger portion of glycerides Vs. fatty acid salts. I would expect them to be less aggressive detergents. However the fact that she added quite a bit of extra glycerin into her soap might explain it too.

I'm just going to have to do the experiment under scientifically rigorous conditions: make two batches of soap using the same oils, same water content and the same amount of added glycerin. One batch will use the standard method (saponification using KOH) while the other will combine the KOH with glycerin in the absence of water. I'll take pictures and make enough so that I can issue a few strategic samples to some of the more experienced soapers on this site: that way, it won't just be my opinion on how the two different products 'feel'. Hopefully this will confirm or deny my hypothesis.

I plan to do this experiment in the next couple of weeks so watch this space.

Cheers! :)
 

Dahila

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I am with Susie on it. My glycerine soap is slowly dissolving in Slow cooker:)) This time I had added the paste approximately 60 g to my oils and 1 part of water to dissolve KOH and 2 parts of glycerin, The trace was in like 5 minutes, and the paste is beautiful. Glycerin will make thick soap and gentle on skin. I made both water and is thin and I really do not like it. Of course I use Irishlass and Susie way not cooking!!!, What is even better I mix it in my plastic bowl, not pot and put the old comforter over, It took probably 8 hours to fully saponify ( I think) the zap test ; sweet taste no zap:)
 

Sapo

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...that way, it won't just be my opinion on how the two different products 'feel'. Hopefully this will confirm or deny my hypothesis.
If you also figure out a way of comparing the cleaning efficacy between them, do document it :D. I can't think of a method beyond staining a piece of fabric and soaking/stirring equally...or perhaps intentionally getting your hands greasy with some oil and then testing how well each of them wash it off. Not exactly empirically trustworthy data but it would do I guess :p.

Keeping my eye on this for sure, thanks!
 

topofmurrayhill

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Hello Soap Making Forum!
Welcome and thanks for your post! It's very interesting. I suppose these matters might be more familiar to the biofuel people than to the soapers.

I will try to learn more about this, but my first thought in response is to wonder what sort of conditions, temperature and otherwise, are required to produce alkoxides from glycerol and alkaline metal hydroxides and whether they are stable enough to play a role when triacylglycerols are introduced. KOH typically contains roughly 10% moisture, which I always thought could easily account for the bubbling when KOH is added to hot glycerol. Also, wouldn't it make a difference whether KOH is dissolved directly in glycerol at a high temp versus dissolved in water and combined with glycerol at quite moderate (below 100 C) temp? I haven't compared personally, but I've not yet heard anyone describe a significant difference. So do you think we are "in the envelope" at all for the reactions you describe to be a significant consideration?

Thanks again for your contribution.
 
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Welcome and thanks for your post! It's very interesting. I suppose these matters might be more familiar to the biofuel people than to the soapers.

I will try to learn more about this, but my first thought in response is to wonder what sort of conditions, temperature and otherwise, are required to produce alkoxides from glycerol and alkaline metal hydroxides and whether they are stable enough to play a role when triacylglycerols are introduced. KOH typically contains roughly 10% moisture, which I always thought could easily account for the bubbling when KOH is added to hot glycerol. Also, wouldn't it make a difference whether KOH is dissolved directly in glycerol at a high temp versus dissolved in water and combined with glycerol at quite moderate (below 100 C) temp? I haven't compared personally, but I've not yet heard anyone describe a significant difference. So do you think we are "in the envelope" at all for the reactions you describe to be a significant consideration?

Thanks again for your contribution.
Hi topofmurrayhill,

Finally! A rational argument to challenge my controvertial post! :)

I really do appreciate your comment because sometimes I can get carried away when I start scribbling. I absolutely agree that there would be a significant difference in the product distribution depending on whether the KOH was added directly to hot glycerin (and heated at >100 oC) or whether it was first dissolved in water and the combined with glycerin (and temperatures were kept <100 oC). The original video I watched on Youtube involved adding the KOH to hot glycerin and then continuing to heat "on high" until the KOH completely dissolved. This method seemed to produce loads of bubbles (water vapour), which to me, suggested that we were "in the envelope" for the kind of chemistry that I discussed.

Again, sorry soapers, it's about to get technical in here...

So this reaction, the deprotonation of glycerin, would certainly be expected to happen to some extent based on the pKa of glycerin (quoted at 14.4 - that first proton is easily labile enough to be removed by a strong base such as KOH) [source: https://pubchem.ncbi.nlm.nih.gov/compound/glycerol]. Importantly to this discussion, this would be a reversible process. The alkoxide salt produced is free to react with water to reform the reactants glycerin and KOH as follows;

ROH + KOH ---------> ROK + H2O
(Glycerin + KOH --> Potassium Alkoxide + Water)

We shall call this the 'forward reaction'. The 'backward reaction' also happens;

ROK + H2O ---------> ROH + KOH
(Potassium Alkoxide + Water) --> Glycerin + KOH

In reality these reactions are both occuring simultaneously, although they may be happening at different rates of reaction due to the reaction conditions (temperature, concentration of reactants, and other, more complicated factors). A system like this that reaches a steady state is said to be in equilibrium, meaning there is no Net change in the amount of reactants or products present in the mixture. If the rate of the forward reaction was equal to the rate of the backwards reaction, we would have a 50:50 mixture of products (in our case alkoxides and water) and reactants (KOH and glycerin).

I am getting to the point, honest. As you rightly pointed out, KOH contains a certain amount of water as an impurity. My KOH is quoted at "90% MINIMUM", so at most, there is 10% (by weight) water present. Realistically we should allow for the presence of a small amount of potassium carbonate (resulting from reaction with atmospheric CO2) and other impurities. I would estimate the 'actual' amount of water present to be in the region of 8.5 - 9% by weight.

So the real question becomes: Is the amount of water present in this mixture (say 9%), under the reaction conditions employed, enough to completely inhibit the forward reaction to prevent the formation of significant amounts of alkoxides?

In lieu of any actual scientific analysis of soaps made by this new method, the question becomes a very academic one. But I do have some thoughts on the matter...

To be continued (later this evening)...
 

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