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Author: Subject: Synthesis of fatty acids from expired soap
palico
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[*] posted on 13-3-2024 at 03:58
Synthesis of fatty acids from expired soap


Hello people !

today another episode of the waste to resource series. I am thinking to rename it into " Scrap chemicals from whatever ". The experiment is based on a acid-base reaction, that is the synthesis of fatty acids by neutralization of soap.

Years ago I bought this pure olive oil soap, but since it is natural it has an expiration date, and as it looked like, I thought it was definitevely already expired. So, why do not get all possible fatty acids from it ? I am doing this with the future intentions to esterified those fatty acids with ethanol, so the full procedure would be a two-step solution to biodiesel from waste. I already made biodiesel from waste cooking oil, this one would be biodiesel from waste soap.

So let's find out fatty acids are really fatty.

The reaction is a simple acid-base between the sodium soap and hydrochloric acid

reaction fatty acids.jpg - 84kB

However, since soap producer does not remove glycerol from product, and also by expiration there were some brown insoluble material, I preferred to pre-treat the waste soap before the neutralization reaction.

Procedure

316 grams of waste soap are weighed out, cutted in pieces, placed in a steel pot and dissolved in 3 liters of tap water.

fig 1.jpg - 357kB

This is filtered while still hot through a tablecloth. The hot solution is let cool overnight. The day after a precipitate is found. The suspension, which is very viscous, is filtered again through tablecloth, but once stucked, the residue and remaining suspension is added of 2 liters of tap water and brought to 80 Celsius to dissolve. The combined soap suspension, are almost 5 liters, are divided in two portions; to each 100 grams of sodium chloride is added, and quickly the common ion effect, let the sodium carboxylates to precipitate out. All is left standing overnight.

The day after, a net separated suspension is obtained, with white solid floating on top. This is filtered through nylon woman socks, to avoid clogging, then residue treated with tap water, and brine solution, let dry in open air for some hours.

The white residue obtained it suspended in 2 liters of tap water, brought to 80 Celsius. This suspension shows a pH of 10, then while still hot to this 25 ml of concentrated HCl is added; pH goes down to 9. Other 50 ml of acid is added and a solid immediately forms, pH is now 5. Since the suspension is still hot, the formed fatty acids melt on top. The pot is covered, and left overnight. The day after a perfect yellowish solid is found floating on top. This is recovered carefully with a spoon, pressed on paper, let dry in open air for a morning

This waxy, oily solid is the mixture of solid and liquid fatty acids, which the latter are partially absorbed and lost on paper. The yield is 216 grams, 68.4% of initial mass, considering those losses, it is a good yield.

The acid function is tested positively with bicarbonate solution.

fig 2.jpg - 280kB

Discussion

Looking back, I would have avoided all those tedious dissolution, filtration and neutralized directly once the soap was dissolved in the first three liters of tap water.

But for me it is good in this way, it is another example of chemical recycling, to get some resource from a waste. I am happy like that.
EDIT: I did not try to recover the glycerol, because evaporate 5 liters of water to get 30 grams of glycerol, it looked too much economically not convenient to me.

The products smell of something closed in the wardrobe for long, remind something expired and old but the smell it is not unpleasant.

As usual I link you to the YT video for a more detailed procedure.

thanks for attention,

see you,

palico

[Edited on 13-3-2024 by palico]




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chornedsnorkack
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[*] posted on 13-3-2024 at 04:13


Quote: Originally posted by palico  
Hello people !

today another episode of the waste to resource series. I am thinking to rename it into " Scrap chemicals from whatever ". The experiment is based on a acid-base reaction, that is the synthesis of fatty acids by neutralization of soap.

Years ago I bought this pure olive oil soap, but since it is natural it has an expiration date, and as it looked like, I thought it was definitevely already expired. So, why do not get all possible fatty acids from it ? I am doing this with the future intentions to esterified those fatty acids with ethanol, so the full procedure would be a two-step solution to biodiesel from waste. I already made biodiesel from waste cooking oil, this one would be biodiesel from waste soap.

So let's find out fatty acids are really fatty.

The reaction is a simple acid-base between the sodium soap and hydrochloric acid



However, since soap producer does not remove glycerol from product, and also by expiration there were some brown insoluble material, I preferred to pre-treat the waste soap before the neutralization reaction.


What did you have besides fatty acids? Like, what do the fatty acids of the soap expire TO?
Oleate seems to have several possible reactions:


  1. C8H17-CH=CH-C7H14COONa -> C8H17-CHOH-CHOH-C7H14COONa
  2. C8H17-CH=CH-C7H14COONa ->OHC-C7H14COONa
  3. 2C8H17-CH=CH-C7H14COONa ->(C8H17)2C4H4(C7H14COONa)2

So which of these had happened?


[Edited on 13-3-2024 by chornedsnorkack]
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clearly_not_atara
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[*] posted on 13-3-2024 at 05:08


Soap doesn't really expire. They just want you to buy more. Granted there will be some rancidity, but a lot of that probably happened during the manufacturing process. The insoluble material is probably fragrance and wax that was used to make the soap.

Anyway nice work.




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Ubya
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[*] posted on 13-3-2024 at 06:57


i don't think you even need 3L of water.
i converted back 250g of soap back to the costituent fatty acids by heating it in 1L of water, adding some HCl, and check the ph until neutral.
the melted fatty acids don't stay in solution, so you don't actually need to actually dissolve the whole soap.

Anyway great job





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palico
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[*] posted on 13-3-2024 at 08:12


@chornedsnorkack: I have no idea which one those degradation reaction has occurred to my soap.

@clearly_not_atara: ehm no, there were no preservatives, fragrances and so on added, I purchased pure natural olive oil soap, I know the man who made it, the starting olive oil was even mine. The degradation of the soap was evident. It changed color, darkened, changed smell and made a fluffy powder similar to fungi. The soap is basic, the glycerol suffer from degradation and also the double bond of side chain can be oxidized.






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Lionel Spanner
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[*] posted on 13-3-2024 at 13:19


Quote: Originally posted by palico  
@clearly_not_atara: ehm no, there were no preservatives, fragrances and so on added, I purchased pure natural olive oil soap, I know the man who made it, the starting olive oil was even mine. The degradation of the soap was evident. It changed color, darkened, changed smell and made a fluffy powder similar to fungi. The soap is basic, the glycerol suffer from degradation and also the double bond of side chain can be oxidized.

It's most likely yeast or mould. Saponified soaps are alkaline and contain very little water at the point of manufacture, but while they're in use, they are in constant contact with unsterilised neutral water, don't absorb that water and are rarely dried after use; yeasts and moulds need relatively little water to grow, compared to bacteria, so they can potentially form colonies over very long periods.

This can even occur in long-term storage if the product is not sufficiently protected from atmospheric moisture.




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bnull
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[*] posted on 13-3-2024 at 14:32


Or sodium carbonate. It happens with homemade soaps. There's almost always an excess sodium hydroxide that gets carbonated. Like this:

20240313_184214.jpg - 134kB

This one is about eight months old, it is wrapped in a plastic bag inside a cabinet and doesn't smell (yet). The color comes from the used soybean oil. It is slightly dehydrated.

@chornedsnorkack: It is way more complicated. The most probable is attack by free-radicals. Oxygen may: either break the double bonds, the products being mainly octanoic acids (with and without hydroxy groups, mono- and dicarboxylic versions) and aldehydes; or form peroxides and ketones. Or even break the double bonds and form peroxides and ketones, in the case of oleic acid, as well as forming (the smelly) butyric and propanoic acids in the case of linoleic acid.




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palico
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[*] posted on 14-3-2024 at 06:48


Your considerations are all correct.



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[*] posted on 14-3-2024 at 14:23


Thank you. I was into homemade soaps and fatty acids some 20 years ago.



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