A safety caution about heating KOH and glycerin

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DeeAnna

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One method for making the lye solution for liquid soap is to heat KOH in glycerin until the KOH dissolves. This method was developed by pharmacists some time ago as an alternative to dissolving the KOH in water to make soap for medical purposes.

The advantage of using glycerin rather than water is the KOH-glycerin mixture saponifies fats very quickly. The obvious downside to the "pharmacist's method" of dissolving the KOH in glycerin is the mixture must be heated carefully to get the KOH to dissolve. The mixture foams furiously while it is heated, so the liquid must be stirred constantly and the heat controlled to keep the mixture from boiling over.

A cautionary comment on a YouTube video about the pharmacist's method was brought to my attention this past weekend. The author advised against using the pharmacist's method and suggested soapers instead use the alternative method of dissolving KOH in water at room temperature. Glycerin can later be added to the KOH-water mixture to gain most of the benefits of the pharmacist's method with fewer of the risks.

The obvious risk of the pharmacist's method is the danger of heating a strong alkali (KOH). If the hot caustic mixture spills onto the skin, severe chemical and thermal burns will result in seconds. Prompted by information given in the YouTube comment, I looked deeper into the chemistry involved with hot KOH-and-glycerin mixtures and found other serious risks to this method that I want to share with you.

The heated mixture bubbles and foams so furiously because the KOH and glycerin are reacting with each other to form bubbles of water vapor and hydrogen gas. The amount of combustible hydrogen gas is large enough that this reaction has been studied as a way to recover useful energy from waste glycerin formed by commercial biodiesel and soap production. Needless to say, it is not safe to mix combustible hydrogen gas with an open flame or hot burner! Hydrogen is a light, buoyant gas, so it will most likely rise safely away from the stove burner, but I'm not sure I want to trust the idea that hydrogen gas will always rise out of harm's way rather than burn or explode.

When glycerin decomposes, it can also form toxic and irritating byproducts such as acrolein, acetic acid, formaldehyde, and formic acid as well as carbon dioxide, water, and combustible gases. Although pure glycerin decomposes only when heated to temperatures that would be unusually hot for a kitchen stove, when mixed with other chemicals, glycerin decomposes at much lower temperatures.

Acrolein is one of the most hazardous chemicals formed by this decomposition. It is a colorless to yellow liquid with an acrid, disagreeable odor and is a severe respiratory irritant. It is flammable and unstable and can form explosive compounds. The US Occupational Safety and Health Administration (OSHA) limits acrolein exposure to a maximum of 0.3 ppm in one short term exposure and an average of 0.1 ppm per 8 hour exposure. http://www.cdc.gov/niosh/docs/81-123/pdfs/0011-rev.pdf

In summary, the pharmacist's method carries the risk of severe chemical and thermal burns from a spill, the risk of combustible hydrogen gas near open flame or hot burner, and the risk of toxic, irritating compounds being released into the air.

I do not think most of us soapers, even the ones who use the pharmacist's method with good results, are fully aware of these potentially serious risks. It was certainly an eye opener for me. I am sharing this information not to stir controversy, but so people have the knowledge to make an informed choice whether to use the pharmacist's method or to dissolve KOH in water at room temperature.

Thanks -- I appreciate your taking the time to read this!
 

IrishLass

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Wow! Thanks DeeAnna! I've been using the pharmacist method since I first started making GLS (it was the only method offered to me at that time). I personally haven't had any problems with it- I'm always extremely careful and take all the necessary precautions, part of which is to mix the KOH/Glycerin both together cold before heating- but after reading your post, methinks I shall cease from using the pharmacist method from here on out. I also think I shall go back and post a disclaimer on my tutorials, with a link to this thread.


IrishLass :)
 

The Efficacious Gentleman

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Would be interesting to see something like a 50% KOH in water solution being mixed with enough glycerine to bring it up to the usual weight, how that would work. I don't need to make any LS for a while (my Nag Champa "Hippy" soap is lasting much longer than I would hope) but I wonder if someone who is making a batch soon and who usually uses the Apothe"scary" method could try the mixed option.
 

DeeAnna

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"...Would be interesting to see something like a 50% KOH in water solution being mixed with enough glycerine to bring it up to the usual weight..."

If I am following you correctly, Gent, that's how I make my KOH solution. Dissolve a given weight of KOH in an equal weight of water. After the KOH is dissolved, add additional liquid (water or glycerin or both) equal to 2 times the KOH weight. I have done Irish Lass' olive, castor, and coconut soap with three different mixtures -- (1 part water + 2 parts glycerin) and (2 parts water and 1 part glycerin) and all water. It all works good. The more glycerin there is, the stiffer the paste tends to be, at least for me, but it saponifies well and dilutes nicely. http://www.soapmakingforum.com/showthread.php?t=51237

***

I want to thank the SMF member who let me know about this issue!
 

lenarenee

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Would be interesting to see something like a 50% KOH in water solution being mixed with enough glycerine to bring it up to the usual weight, how that would work. I don't need to make any LS for a while (my Nag Champa "Hippy" soap is lasting much longer than I would hope) but I wonder if someone who is making a batch soon and who usually uses the Apothe"scary" method could try the mixed option.
Apothe"scary"! I would pay money to have a sense of humor like yours!
 

KristaY

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Wow, DeeAnna. As usual, you've provided us with very important, detailed info. I've never been one to blindly accept "just do it this way" or "it's always been done that way". I like to know why. Drove my parents crazy when I was a kid, lol. So I really appreciate you not only saying there's a safety caution, but giving us the specifics as to why. If you've helped just one person avoid a serious injury, it's definitely time well spent in the research and typing it all out. So today I'm really grateful for DeeAnna's generosity!
 

topofmurrayhill

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This is rather alarmist. I don't see people making informed decisions based on it. I see them getting scared and "blinded by science."

I've been concerned about this technique also, but entirely due to the risk of chemical and thermal burns. It has always struck to as contrary to the usual high degree of safety consciousness among crafters.

The other concerns are not realistic. To get any significant degree of degradation products, you would need much more caustic and much more time (hours) and preferably much more heat. The minutes it takes to dissolve a smallish amount of KOH in a largish amount of glycerin should do no harm. You get more acrolein and other degradation products from cooking. So definitely don't fry anything, try not to sautee, and avoid eating food if possible.

Your KOH is 10% water. The glycerin can be heated above the boiling point of water, which creates a lot of bubbling when the water is driven off. That's all. It's not hydrogen.
I SAID IT WAS LAVA!!
This is why I did it in a deep pot and poured the oils in on it. Maybe next time Ill dissolve the KOH in water first...
Yep, THAT is the point. It's really hot and caustic and it boils.
 
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lenarenee

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Alarmist?

We just received information that would increase our safety during the process of making gls. Using water to dissolve koh instead of heating the glycerin and dissolving the koh doesn't change the product outcome. It does reduce the potential risks.

I soap in the kitchen of a house I don't own. We have pets and kids running around....not to mention me....standing over a pot of lye. I'm intelligent and cautious, but far from being a 100% expert soap chemist. DeAnna just gave me the knowledge to make even safer choices that will protect me, the ones I love and our home.

I can't soap in a lab with equipment that can measure gasses my method does or doesn't release. Nor is there anything that can guarantee my environment is utterly conducive to preventing complications from the hot glycerin method.

I've been on the forums for 2 years and never found DeeAnna's info to be half baked or superfluous.
She's given us researched info, and left us to choose for ourselves. I'm taking it.
 

topofmurrayhill

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Alarmist?

We just received information that would increase our safety during the process of making gls. Using water to dissolve koh instead of heating the glycerin and dissolving the koh doesn't change the product outcome. It does reduce the potential risks.

I soap in the kitchen of a house I don't own. We have pets and kids running around....not to mention me....standing over a pot of lye. I'm intelligent and cautious, but far from being a 100% expert soap chemist. DeAnna just gave me the knowledge to make even safer choices that will protect me, the ones I love and our home.

I can't soap in a lab with equipment that can measure gasses my method does or doesn't release. Nor is there anything that can guarantee my environment is utterly conducive to preventing complications from the hot glycerin method.

I've been on the forums for 2 years and never found DeeAnna's info to be half baked or superfluous.
She's given us researched info, and left us to choose for ourselves. I'm taking it.
Alarmist is an apt description.

I'm not interested in forum politics. I don't care who posted the information. I don't comment for people who are interested in personalities rather than facts. I have no problem with your believing what you want, but you can do so without criticizing me when you don't know better.

The method is risky because it involves a very hot caustic mixture plus water boiling off. For that reason I agree with dissolving the KOH in water before adding glycerol. Simple as that.

People like IL are smart and well aware of the true risks of dissolving KOH in glycerin, and they choose to do it. If they stop on the basis of this post, it is because the information is misleading and, for practical purposes, inaccurate.
 

Arimara

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I, for one, am thankful DeeAnna made this post. I had forgotten about this method as I only use H2O in my liquid soaps. I prefer to know the risks of a said method than not to. I like perspectives.
 

lenarenee

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Alarmist is an apt description.

I'm not interested in forum politics. I don't care who posted the information. I don't comment for people who are interested in personalities rather than facts. I have no problem with your believing what you want, but you can do so without criticizing me when you don't know better.

The method is risky because it involves a very hot caustic mixture plus water boiling off. For that reason I agree with dissolving the KOH in water before adding glycerol. Simple as that.

People like IL are smart and well aware of the true risks of dissolving KOH in glycerin, and they choose to do it. If they stop on the basis of this post, it is because the information is misleading and, for practical purposes, inaccurate.
There is absolutely no criticism in my post. Nor politics. Please notice that I didn't quote your post, or use your name. I gave my opinion, (explained why I didn't find the info alarmist) as did you and others, and shared my observation regarding DeeAnna's posting habits.
 

The Efficacious Gentleman

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The most important part of the post that stuck out for me was about the super-heated lye/gly mix, which seems to be the part we all agree is a danger to soapers even if they are careful. The results of a spill would be terrible.

That is enough for me to classify the post as 'not alarmist'. Parts of it, however, might be on the outside edges of practicable in common methods (there might be people who cook for longer than is needed, leading to some degradation and breakdown), but that means that the post is not alarmist, rather that parts of it maybe.
 

topofmurrayhill

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Please notice that I didn't quote your post.
Don't BS me. The very first word of your post was quoting me and it was obviously a response.

Hydrogen is obtained from glycerin oxidation when you drip small amounts slowly into molten caustic. Sodium and potassium hydroxide melt at over 600 degrees. The best you can do is a eutectic mixture of the two with a lower melting point, but the lowest temperature referenced for this reaction is 500 F and it takes many hours to complete at that temperature.

There is nothing of consequence happening between KOH and glycerin on anyone's stove top aside from making a hot a caustic liquid that threatens to boil over from the water content. Everyone should be scared about that, but they already know about it if they've been doing this -- and the risk is evident from every description or demonstration of the technique.

Nobody should get scared by the other stuff mentioned. Making french fries is way more dangerous in terms of being hotter, more flammable, and producing quite measurable quantities of toxic decomposition products that you breathe and eat with the food. If you barbecue hamburgers, you can enjoy some tasty acrolein.

I don't know what kind of forum it is that downright swoons over incorrect or misleading information and goes passive-aggressive when it's pointed out.
 
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