greentiger87
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isolating free fatty acids from triacylglycerols
Sorry if this is a really basic question - I'm still very much an amateur at practical chemistry.
So, I want to isolate free fatty acids from plant oil sources - for example, linoleic acid from grapeseed oil, alpha-linolenic acid from flaxseed oil,
or gamma-linolenic acid from borage seed oil.
I'm *definitely* not planning on eating any of these, don't worry. I'm also not trying making biofuel.
My basic game plan was to dissolve oil in ethanol, and then saponify with NaOH. Add H2SO4 to neutralize sodium salts, and release the free fatty
acids. Chill to separate layers, pour off glycerol, ethanol, and other waste.
I know I'm a little mixed up here, I'm just not sure where. I realize the free fatty acids will be really impure and a mixture of all the different
types present in the plant oils - but that's totally fine.
Any advice would be appreciated. Thanks!
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aonomus
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Welcome to the forums. What you are doing is essentially making biodiesel and then hydrolyzing the result. You have the steps somewhat mixed up though
because if you attempt to go from a glycerol/fatty acid ester mixture to a glycerol/fatty acid mixture, you end up with an unbreakable emulsion. A
better method would be along the lines of:
- Dissolve NaOH in anhydrous ethanol (water content critical for workup).
- Transesterify triacylglycerol
- Separate ethyl esters (biphasic system with fast separation)
- Wash with water a few times to extract carboxylate salts, residual glycerol
- Hydrolyze with water, catalytic sulfuric acid, and distill off ethanol to drive the reaction to completion
- Wash the fatty acids with water to remove the acid, (bi)carbonate washes not recommended due to possibility of forming salts which are in essence
soaps
- Dry with MgSO4, NaSO4
I recommend you use the search engine to fill in the details and learn more about organic chemistry though.
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ldanielrosa
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This sounds promising. How do you plan to separate the fatty acids from each other? I might try this if I don't need to distill at 360c.
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not_important
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For myself, I' go with the soapmakers' hydrolyse by boiling with aqueous NaOH, and NaCl brine to separate the soap (sodiumm salts of fatty acids),
was the soap with dilute brine. After that add hydrochloric acid to the soap to free the fatty acids, evaporate to dryness, extract with EtOH or
acetone or DCM to separate the FFA from NaCl.
You can somewhat separate the saturated frm the unsaturated FFA by cooling, the saturated acids have higher melting points and crystallise out.
Sometimes doing this from a solution in organic solvent gives better separations, depends on the original oils and YMMV. Repeated recrystallisation
from solvent solution further purifies the saturated acids, but it's tougher to isolated a specific acid as opposed to a group of them. For higher
purity conversion to the methyl esters and fractional distillation at reduced pressure is the way to go.
[Edited on 23-1-2011 by not_important]
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greentiger87
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Thanks for the advice! I think i was getting mixed up between the biodiesel processes and the soapmaking processes - but i believe its the soapmaking
I want. I'd rather avoid making methyl or ethyl esters if at all possible...removing glycerol and purifiying specific fatty acids isn't important to
me. I just need the free fatty acids, as oppose to the bound triglycerides, and commercial sources of these are far too expensive.
Thanks again!
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silkox
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Exposing the TG to xs NaOH or KOH will give you the Na or K salt of the fatty acids, not the "free" fatty acids. If that's what you want, you can
probably get some separation of the different FA by fractional crystallization, as suggested by not_important. An analytical method, not preparative,
would be thin layer chromatography with the right solvent system.
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not_important
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But turning the alkali soaps into FFA is easy, hydrochloric acid to pH < 3, evaporate to dryness, extract with acetone or DCM to pull out the FFA.
Pretty easy, reagents are usually easy to get (H2SO4 or H3PO4 are usable, although you can do better than Na2HPO4), while there's some contamination
from traces of sterols and other natural hydrocarbons they are minor parts of normal fats.
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greentiger87
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Yup, apparently the process I was looking for is called "soapstock acidulation". I've got plenty of resources now 
Do you think adding some BHT to prevent the FFA's from oxidizing would be wise?
Thanks for everyone's advice!
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