[justreaction]

Hi,

We're struggling with forming an edible calcium soap.

Using calcium hydroxide and heating with oil seems to work to form a soap, but when it begins to react it's very much exothermic, and the soap seems to oxidize quickly.

I'm hard pressed to find standard practice on this.
I hope to avoid both excessive oxidation, and any hydrogenation in the process.

[Hunter2]

Easier is to use a sodium soap dissolved in water and then add calcium ions. The calcium soap will precipitate, because less water soluble.

[justreaction]

Thanks for the suggestion!

The calcium soap will precipitate, because less water soluble.

Right, it will, the calcium soap is like a wax; virtually insoluble in water.
But, as far as I know, the reaction would be very slow, and wouldn't strongly favor formation of the calcium soap.

Do you know how to accelerate the process?

Easier is to use a sodium soap dissolved in water and then add calcium ions.

Another concern I have is that this adds another step (the oil must first be turned into a sodium salt).  That's not a big deal, but if it could be done in one step that would be great. (Anybody have any ideas?)

Also, what source of calcium ions would you suggest?

It's worth a try if there's a way to get the calcium fatty acid salts to precipitate faster.  It's essentially the same process that forms soap scum due to hard water, and that is a very slow one (at least with the ion source being hard water, which I think are carbonates).

Thanks again, I'll explore this.

[Arkcon]

Hi,

We're struggling with forming an edible calcium soap.

I wonder why you believe any soap is edible.  You're going to have to explain why you think is is so.  Soluble soaps may not be particularly toxic, but they do hurt the GI tract, at least a little bit.

Using calcium hydroxide and heating with oil seems to work to form a soap, but when it begins to react it's very much exothermic, and the soap seems to oxidize quickly.

Interesting, given that calcium hydroxide isn't particularly soluble in water, and calcium soaps of fatty acids aren't either.   Given that its usually hard enough to get the fats into water solution, and much heat is needed for the manufacture of sodium salts of fatty acids, and they seem to reasonably oxidation free over the production time.  How do you know your calcium soap is oxidizing?  How do you test?  What oil, in particular, do you start with?

I'm hard pressed to find standard practice on this.

Calcium and magnesium salts of fatty acids are insoluble soaps formed when sodium soaps are mixed with solutions of calcium and magnesium ions.  This precipitation reaction occur when "soft" soaps are used in hard water.  People do know about calcium soap, they just try to avoid it.

I hope to avoid both excessive oxidation,

When we understand the extent of the problem, and how you know its extent, we'll work to minimize.

and any hydrogenation in the process.

Generally, not a problem with saponification.  Where do you believe hydrogen is available to hydrogenate the fatty acid, and by what mechanism?

[justreaction]

Thanks Arkcon!

I wonder why you believe any soap is edible.  You're going to have to explain why you think is is so.  Soluble soaps may not be particularly toxic, but they do hurt the GI tract, at least a little bit.

I don't mean in large amounts, as in making a meal out of it.

Calcium soaps are standard practice in agriculture as animal feed, to stabilize oils, and to bypass the rumen in cows to supplement calories from fat without interfering with the bacteria in the rumen as oil does.  I don't think there's any reason to believe they would be harmful in small amounts for humans either.

In the stomach:
2HCl + Ca(Fatty Acid) = CaCl2 + free Fatty Acid + H2

Neutralizing stomach acid may be an issue in large amounts, although that's the same issue as found with antacids or calcium supplements and isn't a significant problem in small amounts.

Generally, not a problem with saponification.  Where do you believe hydrogen is available to hydrogenate the fatty acid, and by what mechanism?

As above, but I don't think the conditions would be right in that case.

I had considered using HCl to liberate the fatty acids from sodium soap in a three step process to get to the calcium soap also (since the reaction from sodium to calcium soap is so slow from just adding calcium ions to a soap solution).

Interesting, given that calcium hydroxide isn't particularly soluble in water, and calcium soaps of fatty acids aren't either.

Water was unnecessary.  The (approximately) stoichiometrically mixed paste of slaked lime and oil reacted (exothermically) when heated (slightly over 100°C) and stirred, and solidified into a hard, brittle, insoluble waxy material when cooled (consistent with the expected properties of a calcium soap).

How do you know your calcium soap is oxidizing?  How do you test?  What oil, in particular, do you start with?

Smell, caustic burnt/plastic sort of odor, and dark color

Sunflower oil.  It may have also been an issue with the unsaponifiables.  Unsure how to confirm that.

[Intanjir]

Right, it will, the calcium soap is like a wax; virtually insoluble in water.
But, as far as I know, the reaction would be very slow, and wouldn't strongly favor formation of the calcium soap.

Do you know how to accelerate the process?

Potassium instead of sodium should allow you to keep a higher concentration dissolved in water. Might result in faster precipitation when adding the calcium.

[Intanjir]

Using calcium hydroxide and heating with oil seems to work to form a soap, but when it begins to react it's very much exothermic, and the soap seems to oxidize quickly.

How exothermic are we talking? Some varieties of sunflower oil are not very tolerant to heat, as evidenced by a low smoke point. Have you tried diluting the oil in something first to keep temperatures low?

[Intanjir]

You can increase the rate of a reaction by increasing the concentration of the reagents. I mentioned above that you could perhaps increase the concentration of the fatty acid by using the potassium salt. It would be more helpful to increase the concentration of the calcium ions given that you have so few because CaOH is so insoluble. How might you do that?

[justreaction]

Thanks!

KOH, that could work.  Potassium soap does tend to be liquid, so that seems like a good idea if it's cost effective.

Exothermic to over the smoke point, I think.  It very nearly burst into flames.

Didn't try diluting; it would have to be something unsaponifiable, but that the oil is soluble in, and I'm not sure what that could be (particularly considering it should be food safe).

It would be more helpful to increase the concentration of the calcium ions given that you have so few because CaOH is so insoluble. How might you do that?

I'm thinking Calcium Chloride, which is extremely soluble.

Is there any reason that might not work?

[Intanjir]

Yep, any soluble calcium salt should do. When there are enough calcium and fatty acid ions floating around they will precipitate simply as a matter of exceeding the solubility of the calcium fatty acid. Should be totally unnecessary to use potassium; you will have no trouble having enough calcium and fatty acid floating around if you used the chloride and sodium forms respectively.

You could probably do it in one step by just using a sodium soap procedure but with adding calcium chloride to the sodium hydroxide solution.

You might instead try limiting the reaction rate by continually mixing in the calcium at a slow enough rate to allow the heat to dissipate. I would guess that nothing is particularly different here compared to when you make sodium soap. If you added NaOH directly to oil I think you would see the same results. The role of the water in soap making may be as much about heat dissipation than anything else. Boiling it removes heat helping to prevent thermal runaway. Of course for sodium it can also potentially slow down the reaction by dilution.

So if for some reason you didn't want to use alkali you might try simply adding water to your original process whether or not it dissolves the calcium. Just be aware of the dangers of hot oil droplets being launched into the air by vigorously produced steam. Hopefully the water keeping everything at boiling temperature should keep the reaction slow enough that the steam leaves gently producing heat. Keeping things mixed may be a problem.

[justreaction]

Thanks!

You could probably do it in one step by just using a sodium soap procedure but with adding calcium chloride to the sodium hydroxide solution.

My chemistry intuition tells me that would give me oil floating on top of salt water (dissolved NaCl), with non-reacting calcium hydroxide precipitated at the bottom.  Three layers, and no desired reaction.

You might instead try limiting the reaction rate by continually mixing in the calcium at a slow enough rate to allow the heat to dissipate.

That might work, but I'm not sure how to do that practically.  Any ideas?
I'm also thinking the lack of water could be the source of the oxidation issue.

So if for some reason you didn't want to use alkali you might try simply adding water to your original process whether or not it dissolves the calcium.

It seems not to react when there's water present.  At all.  Not even with hours of time.

It may be because it just doesn't happen under 100 degrees.  Calcium is less reactive than Sodium, so maybe it needs a little more energy to take the glycerine out.

Maybe salt water could raise the temperature just enough to allow the reaction, but still moderate by boiling off.

Or it could be just because of the three layer problem.  Oil at the top, then water, then the calcium hydroxide at the bottom.
I would think vigorous stirring would resolve that problem, but it doesn't seem to.  And it's not practical to stir for more than thirty minutes or so.

[Intanjir]

My chemistry intuition tells me that would give me oil floating on top of salt water (dissolved NaCl), with non-reacting calcium hydroxide precipitated at the bottom.  Three layers, and no desired reaction.

Yep, I did not think that one through.

It seems not to react when there's water present.  At all.  Not even with hours of time.

Perhaps even with vigorous stirring the solid particles of calcium hydroxide retain a protective film of water. Add surfactant? Takes soap to make (calcium) soap?

It may be because it just doesn't happen under 100 degrees.  Calcium is less reactive than Sodium, so maybe it needs a little more energy to take the glycerine out.

Well why not add just a little sodium as catalyst?
Saturated limewater has a pH of 12.3 so as long as your sodium is contributing less than that you shouldn't be displacing too many calciums from being dissolved. As the reaction proceeded the precipitation of calcium fatty acid would allow more lime to dissolve. Of course it might not dissolve fast enough. If only calcium were more hydrophilic...

Turns out you can increase the solubility of lime by adding sucrose.
http://www.chemicalforums.com/index.php?topic=66785.0

Anyways really bending over backwards here, it seems that just doing it in two steps would be a lot easier.

[justreaction]

Perhaps even with vigorous stirring the solid particles of calcium hydroxide retain a protective film of water. Add surfactant? Takes soap to make (calcium) soap?

That might help.

Well why not add just a little sodium as catalyst?

Not sure if it would work, but that's an interesting idea.

Turns out you can increase the solubility of lime by adding sucrose.
http://www.chemicalforums.com/index.php?topic=66785.0

That's surprising.  Do you think the sugar would be stable, giving all that's going on?

Thanks for the tips, lots to think about.

[Intanjir]

Probably not.

Sugars can react with lipids particularly at high temperature.
https://en.wikipedia.org/wiki/Glycation
Polyunsaturated fatty acids are particularly vulnerable.

Sucrose isn't a reducing sugar which can help so long that it doesn't break down into glucose and fructose with heat + alkalinity.
https://en.wikipedia.org/wiki/Caramelization

And who knows what the Calcium Saccharate might do with its carboxyls.

So I dunno it might work if the temperature is kept in check, but again bending over backwards here.

[Alberto]

Please check this video on YouTube  (https://www.youtube.com/watch?v=5IQQPcj8Rck )

On the video they made calcium soap, using palm oil, NaOH, CaCl2, it seems to be easy but trying to emule like 10 times and still don't get the product, sincerely I don't know how they got it, they even don't control the temperature or the reaction time but they got the product.

Did you get the elaborated product?, maybe you could please help me with the temperature and the time needed, or let me know if is necessary use water with NaOH.

Best regards,
Alberto