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Thread: Confusing problem with my biodiesel

  1. #1
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    Angry Confusing problem with my biodiesel

    Hey guys, I'm a university student interested in running my car off biodiesel. Because I'm a uni student, I really can't afford to stuff my car up so my biodiesel must be top quality before testing it out. Over the past few months, I've made dozens of 1-litre test batches of biodiesel, which seems to be very high quality:
    • No fallout at all in the 3/27 test
    • Biodiesel and water separate in under 10 minutes after my first wash.
    • Very clear water after the second or third wash - indicating very low amount of soap.
    • The soap titration doesn't even register any soap in the biodiesel! I mix 10g of biodiesel into approximately 100mL of isopropyl alcohol and add the bromophenol blue. The solution stays yellow before adding a single drop of my HCl solution. At first I thought my indicator might be stuffed, so I tested an unwashed sample of bio and got approximately 2,000 ppm, and that sounds about right for unwashed biodiesel.


    Ok so all of this means that it should be good to use, but when I shake the bio up with water, it forms a very soapy looking layer between the water and biodiesel. This layer goes away pretty quickly, but just the sight of it makes me think there's still soap in it. But then my tests are indicating that the soap levels are quite low.

    What do you guys think? Am I over-reacting, and is it normal for the biodiesel to look very soapy even when the soap levels are low?

  2. #2
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    Re: Confusing problem with my biodiesel

    Biodiesel is a methyl fatty acid ester. It is usually made by transesterification, which is described in an organic chemistry book I have. Biodiesel is made from a glyceride tri-fatty acid ester. The long chain (3) fatty acids are bound through a carboxylic acid head on the fatty acid to the glyceride which is a three carbon chain. I don't know how to draw it on a computer. In transesterification the fatty acids switch their bond from glyceride (a polyalcohol) to methanol a mono-alcohol. The ester switches from one alcohol to another (trans-change). I'm not sure but your observed third layer might be mono and di glycerides where the reaction has not gone to completion. A di-glyceride as opposed to a tri-glyceride is one of the fatty acids of the three has become biodiesel, but two more fatty acids remain bonded to the glycerine/glyceride. A monoglyceride has one fatty acid left bonded to the glyceride. The mono and di-glycerides bonded to fatty acids hydrogen bond with water, they are not soap. This might indicate an under reaction. Increase temperature, time and or amount of caustic catalyst to get a more complete reaction. And make sure the oil being used is dry. Also during the normal reaction vigorous mixing must be done. Methanol floats on vegetable oil. The alcohol must be mixed throughout the vegetable oil for the reaction to proceed properly.
    Last edited by WesleyB; 28th March 2019 at 07:20 PM. Reason: added a detail I left out

  3. #3
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    Re: Confusing problem with my biodiesel

    I think Wesley is correct, what you are describing are monoglycerides left in your bio. They emulsify very easily with water and are soluble in methanol (so invisible to the 3/27 test) just use a little extra chemical in your reaction and they will convert (I use an extra 100gms of KOH in a 200 litre batch)

  4. #4
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    Re: Confusing problem with my biodiesel

    Oh wow, didn't know that mono-glycerides don't show up in the 3/27 test. Thanks for the input!

    For reference, this is what I'm currently using:
    - 1L of used cooking oil. Very dry and very low titration (0.3mL - virtually brand new oil). It's quite dry too. Its just used to cook sweets, and has a lot of sugar in it.
    - 220mL of methanol.
    - 3.8g of NaOH (3.5gram base + 0.3g from titration)

    I've heard on some sites that the base amount of NaOH should be as high as 5.5g, and other sites it says 3.5g. Which should I use?

  5. #5
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    Re: Confusing problem with my biodiesel

    Quote Originally Posted by Arvin View Post

    I've heard on some sites that the base amount of NaOH should be as high as 5.5g, and other sites it says 3.5g. Which should I use?
    If I where using NaOH I would be using around 5g as base amount. If you are doing 1L test batches then as a test you could do one at 4.5, 5 and 5.5 and see what works best for you. I have found that when people titrate they will get varying results.

  6. #6
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    Re: Confusing problem with my biodiesel

    Purity of sodium hydroxide can be an issue. When exposed to air carbon dioxide gas reacts with sodium hydroxide solid to form a carbonate. So sodium hydroxide can degrade also. I distilled water out of potassium hydroxide solid by heating it. I expect part of solid sodium hydroxide is water.

  7. #7
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    Re: Confusing problem with my biodiesel

    I made bio for years with Sodium, and I used a base rate of 3.5. A base of 5.0 certainly gave a more complete reaction, but the glycerine went hard in a matter of minutes of settling. When I used 3.5, it would stay runny reliably for about 3 hours after, which gave me a chance to tap it off. I knew i was sacrificing reaction completness, but I reasoned that these cars run straight oil ok so I couldn't see that a small amount of unreacted oil was going to cause a problem. Even when I used a base rate of 3.5 I would still poke a sharpened broom handle down the hole in the drain as there would be continual drop out of glycerine over the following week, which would of course go hard like a cake. Pulling the broom handle out left a neat hole to drain the bio off. A bucket of hot water swished around in the bottom would dissolve any remaining gunk and clean the brewer out neat as a pin for the next batch.

    Now I use potassium and havent look back. the glycerine stays runny all week, so I just let it settle for a week in the brewer and tap it off before I drain the bio and make the next batch.
    Regards,

    Cade.

    2006 Landcruiser HDJ100 (1HD-FTE) 20,000 on bio
    2006 Ford Courier(WLT Motor), 10,000 on bio
    2002 Landcruiser HZJ105r (1HZ motor) 250,000 on bio (sold)
    2006 Mazda B2500 (WLT motor) 80,000 on bio (sold)



  8. #8
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    Re: Confusing problem with my biodiesel

    Hi Arvin,

    Make sure you used methanol and not isopropanol or Metho/ methylated spirits in the 3/27 test


    If you are passing the 3/27 test using a base of 3.5g NaOH, increasing it to 5g should give you very good results and more soap. As long as you have an adequately designed reactor, adequate mixing vigor, and mix for a long enough time you should be making very high conversion biodiesel.
    In my experience, no matter how high conversion biodiesel you have, if you add biodiesel with water and shake hard, there will always be some bubbles at the interface between the biodiesel and water for a small amount of time.
    Of course that will not guarantee that your car will be happy using biodiesel. What vehicle are you using it in?

    As a point of interest,
    Testing I did years ago showed that to a certain point, there is a trade off between chemical amounts used and the results achieved.
    For instance, if you reduced the methanol amount slightly you could "make up" for the reduction of methanol by increasing the amount of NaOH used slightly and still achieve the same test results.
    I notice you used 220ml methanol and a base of 3.5g NaOH and passed the 3/27 test.
    Many formulas call for 200ml methanol and a base of 5g NaOH. You traded additional methanol for a reduced amount of NaOH to pass the 3/27 test

    I would reduce the methanol amount to 200ml and increase the base amount of NaOH to 5g and see what happens.

    PS make sure you were using methanol to perform the 3/27 test


    Last edited by tillyfromparadise; 1st April 2019 at 03:28 PM.

  9. #9
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    Re: Confusing problem with my biodiesel

    Hi wesley,

    Quote Originally Posted by WesleyB View Post
    I expect part of solid sodium hydroxide is water.
    Potassium hydroxide typically claims to be around 90% Purity. The other 10% is mostly water.

    I have never seen a bag of sodium hydroxide claim less than 99% purity
    Last edited by tillyfromparadise; 1st April 2019 at 08:34 PM.

  10. #10
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    Re: Confusing problem with my biodiesel

    Hey guys, thank you so much for your input!!! Changed the base amount to 5.5g and now the completion is awesome! Bio separated from wash water within 5 minutes, even after violent mixing. The biodiesel does get very milky now after a wash, but I'm assuming it just has to dry now.

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