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Thread: The chemistry of the glycerol (and soap) phase

  1. #1
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    The chemistry of the glycerol (and soap) phase

    When making biodiesel, we're mostly concerned with the biodiesel phase, and the thick black syrup is just this annoying stuff that we have to dispose of somehow.

    My method overturns this, however, as it produces a glycerol phase that is so thin that it can be tipped down the sink like water. See the videos in my method.

    So I thought I'd post up an explanation of this phase, and the location of the various components in the system.

    Let's start at the beginning. The state of a substance (gas, liquid, solid) is determined by the intermolecular forces - that is, the degree and type of interaction between molecules of the same type. For our purposes, the two relevant ones are hydrogen bonding and Van der Waals forces. These are the two weakest types of forces between molecules, with VDW being the weakest. Hydrogen bonding occurs when an organic molecule contains and oxhgen-rich atom such as oxygen, nitrogen or sulfor (but mostly O), with whose electron clouds tha naked hydrogen proton can interact.

    Consequently, the first four carbon hydrocarbons are gases - methane, ethane, propane and butane. It's not until you get to C5 - pentane, that we get a liquid at RTP. This is simply because the weak VDW forces are not strong enough to overcome the thermal energy at RTP.

    Let's now look at propane. C3H8. Let's now add a single oxygen, so we have C3H8O. This is propanol. This is now a liquid at RTP, simply because the oxygen provides a site at which hydrogen-bonding can occur. Add a further two oxygens and we have glycerol. Now with three oxygens, we get three sites per molecule at which hydrogen bonding can occur, and we now have a thick, viscous liquid.

    This stuff is not easy to dispose of. It's so thick that it can clog plumbing if you tip it down the sink or toilet, and in any case the foam can cause problems.

    So how is my method different? How is it that it is so thin that it can be tipped down the sink, and doesn't foam?

    Let's look at the chemistry of the transesterification process:

    1. Methoxide solution:

    Eq 1: MeOH + KOH <-> KMeO + H2O

    2. Transesterification reaction

    Eq 2: C6O6H5R3 + 3KMeO + 3H2O -> C3O3H5K3 (potassium salt of glycerol) + 3(MeOCOR) + 3H2O

    3. Regeneration of catalyst

    Eq 3: C3O3H5K3 + 3H2O -> C3H8O3 (glycerol) + 3KOH

    So the final step in the process results in the regeneration of the catalyst and protonation of the potassium salt of the glycerol to form glycerol.

    My method differs in that it removes water from the process, which means that the final state of the glycerol is the potassium salt of the glycerol. Since the hydrogen bonding in glycerol is almost entirely due to the electron-poor hydroxy proton, its absence means that there is less interaction between the molecules. What bonding there is, is almost entirely due to the protons on the carbon backbone, somewhat ameliorated by the fact that the highly electronegative potassium cation will have a substantial electron withdrawing effect on the nonbonding electron pair on the oxygen.

    Here is my process:

    Methoxide solution:

    Eq 1: MeOH + KOH <-> KMeO + H2O

    Drying of methoxide solution:

    Eq 2: H2O + CaO -> Ca(OH)2

    Adding Eq 1 and Eq 2:

    Eq 4: MeOH + KOH + CaO -> KMeO + Ca(OH)2

    Transesterification reaction:

    Eq 5: C6O6H5R3 + 3KMeO + 3H2O -> C3O3H5K3 (potassium salt of glycerol) + 3(MeOCOR) + 3H2O

    And this is the final reaction. As the water has been removed, the KOH is not regenerated, and the final state of the glycerol is the potassium salt, which is much thinner than the glycerol and therefore more easily disposed of.

    One more issue - what happens to the soap?

    When the highly alkaline methoxide is added to the WVO it will obviously first react with the Free Fatty Acids:

    KMeO + RCOOH -> RCOOK (soap) + MeOH

    In other words, the methoxide reacts with the FFA to form soap + methanol.

    So what happens to the soap?

    Soap, of course, is a surfactant. It will then, obviously, look for interfaces. In this case, it will be the interface between the hydrophilic glycerol phase and the hydrophobic phase.

    So the upper phase will be the biodiesel. Below this will be the soap, and underneath that will be the glycerol phase.

    And this certainly aligns with my observations. When I leave the raw material to clarify (by bubbling air), when it has done so (by removing all the excess MeOH) I see a light brown layer settling on top of the dark brown glycerol. And, as I would expect, this light brown material is somewhat gelatinous and clumpy in nature, settling out on top of the liquid glycerol.

    So that's it. Happy to answer any genuine questions from any genuine people. As with all my posts, I will ignore all contributions from a certain individual, a bloke who sees himself as an expert on biodiesel but who has no qualifications in chemistry, whose understanding of chemistry could be written on the back of a postage stamp, and whose posts are nothing more than noise.

  2. #2
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    Re: The chemistry of the glycerol (and soap) phase

    "it will obviously react first with the Free Fatty Acids" . There is reaction rate to consider. I made soap from fairly pure hot/soft octadecanoic acid (present in vegetable oils and animal fats). The soap cures for days or weeks. It's not a fast inorganic reaction like muriatic acid and sodium hydroxide. I expect the transesterification reaction rate might exceed the neutralisation reaction rate especially in very dry conditions. So biodiesel might form as fast as soap forms. Tell me where that's wrong.

  3. #3
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    Re: The chemistry of the glycerol (and soap) phase

    Quote Originally Posted by WesleyB View Post
    "it will obviously react first with the Free Fatty Acids" . There is reaction rate to consider. I made soap from fairly pure hot/soft octadecanoic acid (present in vegetable oils and animal fats). The soap cures for days or weeks. It's not a fast inorganic reaction like muriatic acid and sodium hydroxide. I expect the transesterification reaction rate might exceed the neutralisation reaction rate especially in very dry conditions. So biodiesel might form as fast as soap forms. Tell me where that's wrong.
    The reaction with the FFA is a simple acid-base reaction and is all but instantaneous. In years of teaching and doing analytical chemistry I've not encountered one occasion where an acid-base process wasn't instantaneous. Kinetic data for acid-base reactions simply doesn't exist. And of course we know that because if it wasn't instantaneous, you wouldn't be able to titrate the FFAs with an instant result, as many people on this forum do.

    The transesterification process, OTOH, is a Nucleophilic Substitution reaction with an SN2 mechanism (I think) and is therefore subject to kinetic considerations. We know, for example, that the Free Energy chart has an Activation Energy, which is why it needs a catalyst.

    But even if it wasn't instantaneous it's a moot point, as both reactions go to completion anyway

  4. #4
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    Re: The chemistry of the glycerol (and soap) phase

    Hi Mark,

    Quote Originally Posted by Dr Mark View Post
    When making biodiesel, we're mostly concerned with the biodiesel phase, and the thick black syrup is just this annoying stuff that we have to dispose of somehow.

    My method overturns this, however, as it produces a glycerol phase that is so thin that it can be tipped down the sink like water. See the videos in my method.

    So I thought I'd post up an explanation of this phase, and the location of the various components in the system.
    Interesting.
    However, the more likely reason that your by-product (which you call glycerol) is so thin is that because the largest component of your by-product is probably Biodiesel instead of glycerol.

    You have posted that you have a large by-product layer.
    By using such a huge excess of KOH (20g! KOH per litre of WVO) in the reaction instead of performing a simple 5 minute titration to accurately determine the amount of KOH required, you are likely to be producing an excess of soap.
    The soap, along with about twice it's volume of biodiesel, becomes part of the by-product phase
    My calculations suggest that your by-product composition is probably about 36% biodiesel and only about 30% glycerol.

    I do urge that in the future you perform a simple titration to determine the amount of KOH actually required for the reaction to prevent pouring so much biodiesel down the drain.


    Last edited by tillyfromparadise; 8th March 2019 at 12:18 PM.

  5. #5
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    Re: The chemistry of the glycerol (and soap) phase

    Dr Mark; I believe in the formulas you have not accounted for wetness in waste vegetable oil. You described the neutralization reaction (acid+base--> salt + water) but you did not describe saponification reaction where trifatty acid glyceryl + caustic in the presence of water --> soap + glycerol +regenerated water (saponification). Some of the error in making biodioesel stems from wetness of vegetable oil. Your no titration fool proof method doesn't consider wet oil or very high titration oil. For Example a titration of 20 oil. add the suggested amount of caustic, the instantaneous neutralization reaction consumes the caustic and there's no caustic to form methoxide plus the water formed by the neutralization reaction. Beautiful weather here today sir.

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    Re: The chemistry of the glycerol (and soap) phase

    Quote Originally Posted by WesleyB View Post
    Dr Mark; I believe in the formulas you have not accounted for wetness in waste vegetable oil. You described the neutralization reaction (acid+base--> salt + water) but you did not describe saponification reaction where trifatty acid glyceryl + caustic in the presence of water --> soap + glycerol +regenerated water (saponification). Some of the error in making biodioesel stems from wetness of vegetable oil. Your no titration fool proof method doesn't consider wet oil or very high titration oil. For Example a titration of 20 oil. add the suggested amount of caustic, the instantaneous neutralization reaction consumes the caustic and there's no caustic to form methoxide plus the water formed by the neutralization reaction. Beautiful weather here today sir.
    Correct. I didn't bother with the saponification process. I'm going to do that in a subsequent post devoted to the generation and fate of soap.

    The amount of water in clear, free-phase oil is negligible. For about the millionth time, those of you that use the dr Pepper method (or any method without the drying step) add water to your mixture from the methoxide solution, and given the 1:1 stoichiometric ratio with the methoxide, the amount of water will easily swamp whatever small amount may be present in the oil:

    KOH + MeOH <-> KMeO + H2O

    And as for "high titration" oil, yes, in principle a high concentration of FFAs will neutralise the methoxide solution. But I have been using this method now for about ten years with not a single problem. And if I wasn't going to have any problems at a SVO/MeOH ratio of 100:15 then I'm not going to have any problems with a ratio of 100:20

    Also, unless I'm very much mistaken, the amount of caustic I use in my method is much higher than is used by other methods, so if the conc of FFAs do not inhibit the catalysis in these methods, it certainly isn't going to in mine.

    By way of example, the equivalent concentration of KOH in my mix is about 0.3M.

    But even if this is wrong - even if the amount of caustic in my mixture is less than the Dr Pepper method, my method doesn't have the interfering saponification reaction to consume catalyst.

    The simplicity of my method means that I can toss in as much KOH as I want, and there are never any interfering reactions to get in the way.

    And the water sure makes a difference. I know this as I once had a batch where I was lazy when transferring the WVO and some free-phase water transferred across. She'll be right, I thought and went ahead anyway. When I started the reaction, it wasn't going - not a nice situation to be in when you make 1000L at a time. It was the middle of winter and it was about 14 degrees I think. So I pit my heater in and kept it recirculating overnight. When it got to about 23 the reaction kicked off.

    So the great key to my method is that it is anhydrous and the interfering saponification reaction is eliminated. I'm composing a post about soap at the moment, and this just occurred to me, so I thought I'd better update it
    Last edited by Dr Mark; 9th March 2019 at 10:50 PM.

  7. #7
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    Re: The chemistry of the glycerol (and soap) phase

    Hi Mark,

    Quote Originally Posted by Dr Mark View Post
    For about the millionth time, those of you that use the dr Pepper method (or any method without the drying step) add water to your mixture from the methoxide solution, and given the 1:1 stoichiometric ratio with the methoxide, the amount of water will easily swamp whatever small amount may be present in the oil:

    KOH + MeOH <-> KMeO + H2O
    You seem to keep forgetting, so for about the millionth time I will remind you that water is only produced when you actually Produce methoxide.
    You claim that without your drying procedure, there is very little methoxide produced. That means VERY LITTLE WATER is produced.

    The Chemist Neutral used to point out that when you add KOH to Methanol you are mostly just dissolving KOH in methanol.
    Dissolving KOH in methanol does not produce water.
    It is only when you actually produce a tiny bit of methoxide that an equivalent tiny bit of water is produced.
    That means that those of us who use the Dr Pepper Method
    (or any method without the drying step) are putting Very Little Water in the reaction.

    Last edited by tillyfromparadise; 9th March 2019 at 05:41 PM.

  8. #8
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    Re: The chemistry of the glycerol (and soap) phase

    Quote Originally Posted by tillyfromparadise View Post

    Dissolving KOH in methanol does not produce water.


    Wrong, as usual. Here is the equation:

    KOH + MeOH <-> MeOK + H2O

    In case you don't know, H2O is water. You may look at it and think it is "dihydrogen monoxide" or something, but it's actually water.

    MeOK is the potassium salt of the methoxide. Unlike the methanol (MeOH), in which the hydrogen is covalently bonded to the oxygen, the potassium ion is bound as an ion pair, so it's more accurate to write it as K+MeO-

    This was all explained in my post on Le Chateleir's principle, and it is now clear that you didn't understand a word of it, despite my attempts to put it in layman's terms.

    It is now plain that if you don't understand such a simple equilibrium as this, you are in no position to advise others on anything pertaining to the chemistry of any part of the biodiesel process. Please leave such advice to the professionals. In other words, people with tertiary qualifications in chemistry

    Note: replying in shouty bold text does not increase your credibility. It just makes you look desperate, and very, very much out of your depth.

    Both of which, of course, you are.
    Last edited by Dr Mark; 21st April 2019 at 08:53 PM.

  9. #9
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    Re: The chemistry of the glycerol (and soap) phase

    [quote]Here is the equation: KOH + MeOH <-> MeOK + H2O[/]quote
    As you have stated previously,
    Le Chateleir's principle applies, but you do not give the proportions at STP for this reaction.

    Tilly's statement could be true if the reaction is weighted in favour of the solution over the reaction products.
    So here are my questions:
    1. What is the formula for calculating the ratios?
    2,
    So, if I have 1Kg of KOH and 20 litres of 'MeOH', How much 'MeOK' and H2o would be produced and how much KOH dissolved in H20 would be present at any one point in time?

    As a Chemist you should be able to specify the ratios of each side of the reaction at STP.
    I await your reply with the answers to my questions.

    Last edited by Tony From West Oz; 21st April 2019 at 09:45 PM.
    Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

    Current Vehicles in stable:
    2000 Ford Courier Crew Cab 2.5L Turbodiesel on Blended veggie oil.
    '2014 Toyota Prius (on ULP)


    Previous Vehicles:
    '90 Mazda Capella. (2000 - 2003) My first Fatmobile. Converted to fun on veggie oil with a 2 tank setup. Died when supercharger stuck at max boost for weeks. Stretched head bolts.
    '80 Mercedes 300D. 2 tank conversion [Sold]
    '84 Mercedes 300D. 1 tank, no conversion. Replaced engine with rebuilt OM617A turbodiesel engine. Finally had good power. Donor for current Fatmobile coupe. (body parted out and carcass sold for scrap.)
    '99 Mercedes W202 C250 Turbodiesel (my darling Wife's car)[sold]
    '98 Mercedes W202 C250 Turbodiesel (my car)[sold]
    Parts Car C220 1993 SOLD.
    '85 Mercedes Benz W123 300CD Turbodiesel single tank using 95% used cooking oil and 5% to 10% misfuel (where someone had filled diesel vehicle with petrol).
    '06 Musso Sports Crew Cab. Running on used cooking oil with 5% to 10% misfuel. [Head gasket blew!]


    Searching the Biofuels Forum using Google
    Adding images and/or documents to your posts


  10. #10
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    Re: The chemistry of the glycerol (and soap) phase

    Hi Mark,
    Wrong again, as usual.
    You do seem to have a problem understanding what is written.


    H2O is only produced when you actually produce MeOK.
    As you continually point out, when enough water is produced, the Production of MeOK stops. You may have forgotten, but this is an equilibrium reaction. At the point where the production of MeOK stops because of the presence of too much H2O, the production of H2O also stops. No more MeOK or H2O/ water is produced.
    The remaining unreacted KOH is just dissolved in the methanol without producing H2O or MeOK.
    A real chemist going by the name Neutral who had over 30 years R&D in the alternate fuel field including actually making "biodiesel" in the 70's {before it was called biodiesel) pointed that out to me years ago
    .
    At the same time he told me that he thought that not much MeOK was actually produced when you mixed KOH with methanol so not much H2O was produced. He thought it was mostly just KOH dissolved in methanol

    PS. THIS IS SHOUTING. This is emphasizing an important point.
    If you have any further confusion about any of this please do not hesitate to ask.
    Last edited by tillyfromparadise; 22nd April 2019 at 12:33 AM.

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