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Thread: Reprocessing a batch

  1. #1
    Join Date
    Dec 2006
    Canberra-Goulburn area

    Reprocessing a batch

    I have a batch that failed the 3/27 test.

    It's a pain in the proverbial and a waste of materials, but it should simply be a matter of reprocessing. I had washed about half of it and used some, so I pumped it back into the processor and added around 14 % waste veg oil to make up for the fuel that I had already used.

    So how much NaOH and methanol to use? I did some lab tests on a sample to find out.

    1. Titrate as normal, use the resulting amount of NaOH with the standard amount of methanol results in glycerine falling out but fuel turns to jelly!

    2. Neutral recommends testing a finished batch for completion by processing 1 litre of oil with 50 ml methanol plus 1g NaOH. Result: no reaction.

    3. Add another 1g NaOH and 50 ml of meth to the previous batch (total 2g NaOH plus 100ml meth): turns to jelly

    4. Measure the amount of unreacted oil that fell out during 3/27 test and mix standard NaOH and methanol to suit. I found around 76% unreacted oil (yes, it seems high) so I mixed up the NaOH and meth to suit that volume. Result: no reaction

    5. Perhaps KOH won't have the same jelling effect. Try mixing a standard batch of KOH and meth and processing as normal. Result: Batch changes colour as normal during processing, but there is no settling!

    6. Perhaps there is already so much methanol in the batch that it is simply not settling because it is basically too dilute. Halve the amount of methanol for a standard mix. Result: reaction occurs but still no settling.

    So .... any ideas anybody? Or does anybody have any good uses for a few hundred litres of not quite biodiesel?

    Tomorrow's just another batch.

  2. #2
    Join Date
    Sep 2005

    Re: Reprocessing a batch

    When reprocessing, do not add unprocessed oil, it adds another variable to the equation.
    For all processing, where you are not sure of the outcome, it is wise to process a small sample (eg 1 or 2 litres). This is economical on inputs and avoids the possible situation you now have.

    You could add a little of this batch (10%?) to your next few batches, to use up the failed batch. Again, do a trial sample to ensure you are getting a good reaction, before processing the mix.

    Why do you need high conversion biodiesel?
    Could you just add 10% of the failed batch to the product you make for the next 10 batches?

    I hope you are able to use the failed batch in one of the ways suggested.
    Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

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    Previous Vehicles:
    '90 Mazda Capella. (2000 - 2003) My first Fatmobile. Converted to fun on veggie oil with a 2 tank setup.
    '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. Engine donor for W123 coupe. (body parted out and carcass sold for scrap.)
    '85 Mercedes Benz W123 300CD Turbodiesel
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  3. #3
    Join Date
    Nov 2010
    Fort Worth, Texas, USA

    Re: Reprocessing a batch

    Nuciferos: You washed about half of your batch? I guess you mean wet wash with water, as opposed to dry washing. There's no mention of drying, or how drying might have been done. Vegetable oil plus caustic plus water makes soap. So if your reaction liquid is wet it won't make the methyl ester, it will make soap. On the biodiesel Ireland forum is a description of how to test for water content in a batch. Removing water by bubble drying will also evaporate the methanol that's present. I've only dried biodiesel product by using drying agent, for very small batches, after water washing. Using chemical drying agent for a large batch wouldn't be economically feasible. In addition to water being present causing the production of soap (saponification), too much water being present decomposes the methoxide ion which is necessary for the production of the methyl ester (biodiesel).
    Last edited by WesleyB; 20th June 2015 at 09:08 PM.

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