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  • Glycerol - water separation

    Posted by luiscuevasii on May 22, 2022 at 3:06 am

    Greetings, im tryign to make atleast technical grade glycerin from spent lye.

    Im neutralizing, filtering, and atmosferic distilling the mixture to separate the soaps, salts, and Freefatty acids, so far i have a dark brown water:glycerin liquid arroung 90:10 (i have not caracterized it), but acording to literature that must be pretty close to the real composition.

    Decorolizing: I have tryed activated charcoal to decolorize the product but i think that the procedure isnt the correct, would appreciate any input here.

    Vacuum distilling: I have make 3 attemps distilling all the product but with out any separation, almost all the water and glycerin comes together on the condesation i think that i have a strong azeotrope here, i dont know if several condensers in series would help me to get different water-glycerin concentration or i need a fracionation tower

    Reverse osmosis: Some new researchs talks about ussing RO, but i made the experiment with no results, i got the same liquid coming from both sides of the RO, in fact the color was the same for both products.

    ketchito replied 2 days, 9 hours ago 4 Members · 13 Replies
  • 13 Replies
  • Pharma

    Member
    May 22, 2022 at 10:50 am
    Glycerol and water don’t form azeotropes. Besides, it is extremely difficult to evaporate glycerol under vacuum unless you happen to have a molecular distillary. Water on the other hand is easily removed.
    However, you’ll only end up with 80-98% glycerol depending on the simplicity of the apparatus and the number of distillation steps.
    My guess is that you’re doing something wrong. BTW Using less water in the reaction mixture would already result in a more concentrated form of glycerol.
    There’s tons of papers describing the How To of saponification and glycerol purification ;) .
  • luiscuevasii

    Member
    May 22, 2022 at 4:01 pm

    @Pharma thanks for your answer,  it’s kind of difficult to have less water in the initial product, my initial goal is to separate de glycerol, excess naoh and salt from soap, and having excess water is very helpful.

    By the other hand, I have made experiment evaporating the water at atmospheric pressure 110celcius, and I’m not having glycerol in the residue only brown salt, so I was guessing that must be and azeotrope.

    Almost all the literature I have read so far uses vacuum distillation  , I’m capable of using -600 to -720 vacuum in laboratory and in big equipments, but I did trials with the same results as the atmospheric distillation. For example I made one trial at -700mmhg 120celcius, and I was left with only salt at the end, and other trial -700mmhg 200 Celsius with the same result.

    I thinkt that using several condensers in series could work like a fractional distillation, but any input would be helpful, working with out the proper guidance is troublesoem

  • Pharma

    Member
    May 22, 2022 at 6:32 pm
    I would first evaporate water. This can be done at a water bath temperature of just 60°C and a standard vacuum pump (vacuum in the one digit mbar range; if I calculate it right, -700 mmHg equals 70 mbar… that’s just good enough for volatile solvents).
    You could as well just boil water off at atmospheric pressure.
    Because glycerol is hygroscopic, you might not obtain totally dry glycerol (but you can dry it for example with anhydrous magnesium sulfate).
    Afterwards, evaporate glycerol off. There you’d likely have to heat up to 200°C or even more depending on your vacuum. Given that you don’t care for the solids, a charred residue isn’t too much of a problem (good luck with cleaning the flask, though :smiley: ) and you might want to re-distill your glycerol.
    A cleaner way would be to separate glycerol/water from residues by extracting with alcohol (which you can easily recycle with your rotary evaporator) first and then ‘dry’ your glycerol by evaporating first the water off and then glycerol. If you werer to add alcohol (ethanol or methanol) directly to the reaction mixture (before or after saponification doesn’t matter as long as you don’t heat above the alsohol’s boiling point), you could use a lot less water.
    As a last thought: Maybe your saponification didn’t work and you don’t have glycerol at all? There’s no way you’ve boiled off glycerol at 110°C at atmospheric pressure but the 110°C boiling temperature indicates that you don’t have pure water but a solution (question is, is the boiling point increase caused by glycerol or salts). Not to speak that you would have noticed if you didn’t saponify your oil LoL.
  • luiscuevasii

    Member
    May 22, 2022 at 10:24 pm

    @Pharma my first guess was that i didnt had glycerol and something went wrong with the saponification, but saponification is a  very standard reaction, after is complete i use salt to precipitate the glycerine, water, impurities, naoh and salt.  If the saponification went wrong i must have two results:

    #1 a soap with a lot of unreacted oils, ór
    #2 a soap with excess naoh plus salt

    The batch where i draw the Glycerol-salt-naoh-impurities, was a 5ton batch, the soap obtained was excellent, so i can assume that i must have Glycerol on the spent lye

    —-

    I did evaporation two times, but the result was the same, only brown salt was left

  • Pharma

    Member
    May 23, 2022 at 4:31 am

    You add salt to separate soap from water? Well, that likely explains it. The effect you get is called ‘salting out’; it means that saturating water with salt reduces solubilities of other solutes and pushes these out especially if there’s a second phase wherein those solutes are soluble. In your case, the second phase is soap and soap dissolves glycerol.

  • luiscuevasii

    Member
    May 23, 2022 at 4:45 pm

    @Pharma  yes, indeed im salting out the soap, but i belive that the glycerol separates from the tri-gliceride molecule when neutralization ocours and salting out is used for taking the glycerol and all the non-soap sustances with water.  Im making right now a 50liters evaporation, so far i have made only laboratory batchs,  i must have arround 5kg of glycerol acoording to the texts books. 

  • Pharma

    Member
    May 23, 2022 at 7:14 pm
    You don’t have triglycerides (at least, you should have <10% if you’re ‘super-fatting’) but mostly fatty acid sodium salts. By instinct, I would expect glycerol to remain in the water phase upon salting out, given that glycerol isn’t an electrolyte (it’s not dissolved in water but mixed with water, so you could say that water is mixed with glycerol as well). According to a quick Google search, this should be true.
    However, you seem to have no glycerol and so I wonder: Do you add too much salt? After all, fatty acid sodium salts are amphiphilic and especially sodium salts of unsaturated and/or medium chain fatty acids dissolve nicely in glycerol. And from gylcerol soap we know already that glycerol dissolves well in soap…
    An alternative approach to salting out can be boiling as has been traditionally done. Sodium soap is insoluble in hot water and will floculate and float to the top. I’ve tried that myself and ended up with fairly clean sodium soap and a glycerol-water-sodium hydroxide blend.
  • luiscuevasii

    Member
    July 5, 2022 at 4:13 am

    @Pharma thanks for your reply, im a Chemical engineer, so my knowledge of small scale procedure and lab is almost None, i made the experiment in a bigger batch, and eureka, there was a lot of glycerin after salting, separation and evaporation.  

    Right now im looking to clarify the remaining glycerin, it has a dark brown color, i have tryed with reverse-osmosis and mixing with activated charcoal at 90°celcius and the brown color remains

  • Pharma

    Member
    July 11, 2022 at 8:44 am
    Then you have three options:
    A: Distillation (which isn’t easy)
    B: Use a manufacturing process which doesn’t result in colour
    C: Discard the gue and buy pure glycerin
  • rav

    Member
    May 14, 2024 at 10:42 pm

    Greeting from Rav, I just joined in this group. I am trying to remove glycerol from my sample (protein solution in glycerol, 23%). I want remove the glycerol leaving the protein in water so that I can spray dry the protein sample. I know it can be done by filtration method which is not cost effective in terms of industrial scales. Is there anyway to precipitate the protein and separate it by centrifuge or convert the free glycerol in to fatty acid and recover protein. Many thanks

  • ketchito

    Member
    May 16, 2024 at 7:07 am

    Is it a commercial product or raw material that you want to remove the protein from? If it’s an extract where glycerol is the solvent, then you might not have any valuable protein or to be more precise, peptide fraction to recover (proteins are mostly insoluble, that’s why suppliers hydrolyze them first).

    • rav

      Member
      May 16, 2024 at 5:33 pm

      Thanks Ketchito. It was not a solvent extract product, this is an waste product from the industry and it does contain the protein and glycerol (22%). I tried filtration (MWCO) with excess amount of water and able to remove most of the glycerol. I am currently looking for alternative methods to minimize the usage of large quantities of water. Cheers

  • ketchito

    Member
    May 17, 2024 at 6:39 am

    @Rav Proteins are mostly insoluble, so you shouldn’t have any problem to separete them from glycerol. I believe you might have peptides (hydrolyzed protein). There are ways to coagulate them. The one I remember is making them react with cationic surfactants, but I don’t remember how to remove cationics after, I need to check.

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