Sciencemadness Discussion Board - Aluminum soaps

Aluminum soaps

night429 - 5-3-2024 at 01:36

I've been testing some aluminum soaps from a few fats and oils I have on hand. I decided to detail the synthesis using vegetable shortening because the fatty acid composition is more or less saturated, and that I haven't had much luck with coconut or olive oils.

I added an arbitrary amount of vegetable shortening to a flask. I microwaved this until it melted. I then added it to a flask with a ground-glass joint. To this, I added about 8mL of 80% sulfuric acid and 100mL of water. I refluxed this for about 3 hours, then let everything cool overnight.

The next day, I was left with a disk of (presumably) fatty acids. I drained the aqueous layer from this, and gently washed it twice with about 200mL of water each time. I let this sit for a few days in the flask for no reason in particular.

I then let everything stir and melt on a hotplate and added it to a beaker, which came out to roughly 42g. To this, I added 190mL of water. After stirring and heating until it was all melted, I added a solution containing 12.0g of potassium hydroxide and 200mL of water. There was an immediate color-change from cream-colored to very slight-pink, and I let this react for a couple hours until the solution was nearly-homogenous (the solution became very viscous once the solution hit near-boiling). I poured it into a separate flask with 200mL of water and let it stir until homogenous.

In a separate flask, I measured out 15.6g of potassium aluminum sulfate dodecahydrate (common alum), and stirred it until dissolved. I added 400mL of water in total to this solution. I then poured the fatty acid solution in with the potassium aluminum sulfate solution in a funnel, draining to a separate container, which gave some amount of precipitate.

I dissolved a total of 17.6g of potassium aluminum sulfate in about 150mL of hot water in a separate flask. Once added, all of the precipitate fully coagulated, giving a solid precipitate floating on top of a near-transparent liquid. I did this in two separate portions, and after the first portion, the pH was about 7, and the solution was milky-white with some coagulated precipitate. After adding all of the solution, the pH was about 5 and there was a definite separation of solids and liquid.

I filtered this all through a coffee filter, then washed with about 2 x 100mL of cold water, with very gentle sirring each time. I let it filter. After a few hours, I squeezed it dry through some paper towels, then let it dry on a fan for a few days, manipulating the solids on occasion.

After these few days, I was left with a cream-colored, slightly-oily solid. The mass was about 38.2g, or roughly 89%, assuming everything I added to the base solution was both fatty acids (and not triglycerides) and anydrous (which it wasn't). A small amount was able to dissolve in VM&P naphtha with some mild hand stirring, and a more homogenous mixture was made using an hour of magnetic stirring. After dissolving, the viscosity had increased significantly. I tested 5%, 10%, and 15% of the aluminum salt by mass.

The 5% was more viscous than the raw naphtha, but still quite fluid. The 10% wasn't as viscous, but still quite pour-able. The 15% was quite viscous, and was similar to the thickness of polystyrene-based thickening agents.

So, I believe I was able to make some aluminum soaps from vegetable shortening, as they were were able to cause VM&P naphtha to become very viscous.

I've tried to make these soaps from coconut oil and olive oil in the past. I got good results from coconut oil once, and my failures made me realize that the neutralization of fatty acids during the base-neutralization step is imperative, and, if the heating isn't left for long enough during that step, there are fatty acids that remain past the aluminum salt addition, which cause significant issues with the quality of soap produced.

Sulaiman - 5-3-2024 at 03:49

Please excuse my ignorance but what is aluminium soap for?
A quick google gave mostly results for actual washing soap,
why would I want to wash with aluminium soap?
I try to avoid aluminium in or on my body.

EF2000 - 5-3-2024 at 05:41

Only use that comes to mind is old fashioned napalm. The OP also mentioned polystyrene thickeners (used in homemade napalm B: petrol+PS in acetone) and used aluminium soap to thicken naphta.
So it's for napalm without doubt, not washing soap.

bnull - 5-3-2024 at 06:19

Aluminum soaps are also used as lubricants, food additives, and impermeabilization of paper and some other materials. Leather, maybe.

Quote: Originally posted by night429

I've tried to make these soaps from coconut oil and olive oil in the past. I got good results from coconut oil once, and my failures made me realize that the neutralization of fatty acids during the base-neutralization step is imperative, and, if the heating isn't left for long enough during that step, there are fatty acids that remain past the aluminum salt addition, which cause significant issues with the quality of soap produced.

You don't need to hydrolise the oils. Just make the soap (the glycerol formed won't affect the reaction) and dissolve it in water. Add hydroxyde to a solution of aluminum sulfate until the precipitate dissolves and mix the two solutions. That's how I did some 20 years ago. It avoids the entrapment of oil in the fatty acids, which happened more than once when I tried to isolate fatty acids from oils.

For copper soaps you need ammonium hydroxide. The thing has a beautiful blue color that gradually turns green as the soap ages/oxidises.

night429 - 5-3-2024 at 11:35

Quote: Originally posted by EF2000

Only use that comes to mind is old fashioned napalm. The OP also mentioned polystyrene thickeners (used in homemade napalm B: petrol+PS in acetone) and used aluminium soap to thicken naphta.
So it's for napalm without doubt, not washing soap.

I now realize that I completely forgot to flesh out an introduction. Yes, I wanted to see if aluminum salts from available sources acted the same as the soaps of naphthenic and palmitic acids in thickening alkane mixtures—the classic napalm "A". I was following a patent (example I), doing a rough average molar mass conversion between the oleic acid and vegetable shortening fatty acids.

The properties of the soap are horrible for any kind of use with water. It coats materials with a waxy film that only gets stickier at higher temperatures. I had to remove it using dilute HCl.

Quote: Originally posted by bnull

I should see how that compares to the procedure I used, since it'd streamline the process a lot. I opted to first hydrolyze the oil with acid because I had poor success in making soap solutions. Copper soaps aren't something I thought of before, but should look into.

night429 - 5-3-2024 at 11:36

Also, here's a picture of the product I made that I forgot to post in the original text.

bnull - 5-3-2024 at 11:58

Quote: Originally posted by night429

The properties of the soap are horrible for any kind of use with water. It coats materials with a waxy film that only gets stickier at higher temperatures. I had to remove it using dilute HCl.

While still fresh you can remove it that way. Let it age for some time and you'll see the mess I was in eons ago.

I guess I still have a calcium soap from around the same time (2002-2003). It was when I first bought Ca(OH)₂ and NaOH.

Not entirely related to the matter but, did you try to react aluminum sulfate with glyphosate? It forms a soft mass that becomes a brittle solid after some days. Completely useless, of course.

[Edited on 5-3-2024 by bnull]