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  1. #1
    Join Date
    Mar 2013
    Location
    Sydney, NSW
    Posts
    199

    Incomplete reaction advice

    In making recent batches of bio I have tried to do the reaction and let the product sit as long as possible before washing. I've found this to be beneficial in that more byproduct drops out with time and I have to wash less and seem to get less 'tarry substance' in the bottom of my cubies and filter sedimenter.

    So I had what I thought was a reacted batch (that has been sitting for more than 2 months) but went to transfer it to the wash tank the other day it had the consistency and colour of unreacted WVO.

    I just assumed that I'd forgotten that I hadn't already processed it and set about making some methoxide. I then realised I only had about 18L of methanol handy, but plenty of KOH. I am getting quite low on fuel, so I thought - I'll take a gamble here and try to use 18L of methanol instead of the normal 36L with the (fairly standard) 2 kg of KOH. I have about 2L of correctly mixed methoxide that I saved previously and thought I could just do a secondary reaction with it in the event that I didn't get 100% conversion.

    So I went ahead and processed the batch with 50% less methanol than normal and it is clear that it hasn't worked. The oil still looks largely unprocessed. Fairly murky looking, similar viscosity to WVO, rather than biodiesel and no obvious heavier glycerol layer in the bottom of the tank. I thought I'd probably get a partial conversion, but hadn't gambled on what seems like a fairly homogeneous product.

    What is my smartest move from here?
    3DB
    1995 Holden (Isuzu) Rodeo 2.8TD 4X4 - B100 since April 2013
    1976 Mercedes 300D Turbo 'The Coal Grenade' - B100 since May 2016
    (@thirddegreeburns on Instagram)

  2. #2
    Join Date
    Nov 2010
    Location
    Fort Worth, Texas, USA
    Posts
    273

    Re: Incomplete reaction advice

    I would assume you refer to using 20% methanol as a normal amount to get a fairly complete reaction. I did the numbers on a stiochiometric amount of methanol to get 100% reaction in the past, it was about 12.5%. I'm not clear on the exact quantities present or if there's a possibility of wet oil or wet methanol. Test the oil with a hot pan test if a few drops are left in the container. I found my notes on the stoichiometric amount of methanol to react 1 litre of lard, it is 119.9 milliliters of methanol.
    Last edited by WesleyB; 8th January 2018 at 07:01 AM. Reason: found a more accurate amount

  3. #3
    Join Date
    Dec 2016
    Location
    York UK
    Posts
    99

    Re: Incomplete reaction advice

    Hello 3DB. I think you will find that there has been some reaction. Sometimes if the reaction is small this can happen where the (small) amount of glycerol formed is reluctant to drop.

    What you can try is to re-heat and add some glycerol from a previous batch, I think you will find when it all settles the amount of glycerol will be greater than the amount you added. (it is a little like seeding an over saturated solution with crystals, as the sugar boilers do when they seed a pan of sugar)

    You would then need to conduct a 3/27 or 10/90 test to indicate the chemicals to add to get complete conversion.

  4. #4
    Join Date
    Jan 2006
    Location
    ลึก ประเทศอินเด&
    Posts
    1,950

    Re: Incomplete reaction advice

    Hi 3DB,
    Can you give us some numbers-
    1. Amount of WVO reacted
    2. Oil Titration
    3. Amount of methanol used per litre of WVO reacted
    4. Amount of NaOH/ KOH used per litre WVO

    I have found that once you start using less than the stoichiometric amount of methanol in a standard single stage base reaction, separation becomes questionable.

    As smithy has pointed out, there will have been some reaction happen, that is what happens when you mix methoxide with Veg oil
    Last edited by tillyfromparadise; 8th January 2018 at 01:06 PM.

  5. #5
    Join Date
    Mar 2013
    Location
    Sydney, NSW
    Posts
    199

    Re: Incomplete reaction advice

    Hi all,

    Thanks for the responses so far.

    Tilly, to answer your questions:


    1. 180L WVO
    2. Titration was 3.4. Adding the baseline 7.7 = 11.4 g/L
    3. I normally use 20% methanol: WVO, so in this case I would use 36L. But I only had 18L available this time.
    4. KOH used = 2,000 g
    3DB
    1995 Holden (Isuzu) Rodeo 2.8TD 4X4 - B100 since April 2013
    1976 Mercedes 300D Turbo 'The Coal Grenade' - B100 since May 2016
    (@thirddegreeburns on Instagram)

  6. #6
    Join Date
    Mar 2013
    Location
    Sydney, NSW
    Posts
    199

    Re: Incomplete reaction advice

    So I heated the batch up to 55C again and added 7L of methanol + a similar amount of left over glycerol, mixed for 3.5 hrs and now have a good visible separation.

    Still didn't pass the 3/27 test, so I'll now mix up the appropriate methoxide and re-process.
    3DB
    1995 Holden (Isuzu) Rodeo 2.8TD 4X4 - B100 since April 2013
    1976 Mercedes 300D Turbo 'The Coal Grenade' - B100 since May 2016
    (@thirddegreeburns on Instagram)

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