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Thread: Glycerol / glycerine / byproduct pre wash

  1. #1
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    Glycerol / glycerine / byproduct pre wash

    I read somewhere recently on this forum about someone doing a glycerine pre wash on their oil before doing the full reaction. I tried to find the thread again but couldn't easily locate it.

    In typical fashion, I just thought I'd give it a go at the spur of the moment and see what happened.

    I heated up the oil to about 40C, turned on my mixer and added about 15% of the oil volume (180L) of room temp glyc and mixed for about 30 min.

    I drained it off about 24 hrs later as I ran out of time to do the proper reaction that I had intended to do on the same day while the oil was still hot. It was noticeably thicker and darker than when it went in.

    That was several days ago now and I just titrated the oil tonight and it came in at 0.5. Normally this oil titrates at about 2 - 3, which seems amazing on face-value. But then I thought about it and it will only seemingly save about 300g of KOH in this instance.

    So is that the reason most people don't bother with it? Extra time and messing around and that it will only save (in this case) 300g of KOH? And in my case, wasted more electricity as now I need to heat the oil up for a second time which can use up to 4 kWh of electricity to go from 15C - 50C.
    3DB
    1995 Isuzu Rodeo 2.8TD 4X4 - 45,000km & 3.5 years on B100
    1976 Mercedes 300D Turbo 'The Coal Grenade' - 3,000 km on B100, 280,000 Km on the clock, but probably more like 1,280,000
    (@thirddegreeburns on Instagram)

  2. #2
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    Re: Glycerol / glycerine / byproduct pre wash

    Hi 3DB,

    Quote Originally Posted by 3DB View Post
    So is that the reason most people don't bother with it? Extra time and messing around and that it will only save (in this case) 300g of KOH? And in my case, wasted more electricity as now I need to heat the oil up for a second time which can use up to 4 kWh of electricity to go from 15C - 50C.
    There is also some methanol in the glycerine used in the pre-wash that will be used along with the KOH.
    Because the pre-wash is effectively the first stage of a multi stage reaction, besides using some of the methanol and KOH remaining in the glycerine you can get by adding less total methanol.
    However, as you have noted, many people may find the the small savings in methanol and KOH cost is offset by the increased time and heating required to perform the multistage procedure
    That is certainly the reason I do not bother doing a glycerine pre-wash.
    Last edited by tillyfromparadise; 22nd May 2017 at 11:33 PM.

  3. #3
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    Re: Glycerol / glycerine / byproduct pre wash

    Most people here in the UK do bother doing it. During warmer months I actually now do the glyc wash outside at ambient temperature in the IBC where the oil is stored. I just connect up a pump to circulate and away we go. The glycerol is slower to drop doing it at a lower temperature, but it still does drop. If I need to remix the contents without drawing off any glycerol then using an airline connected to the bottom tap to mix is just as good as using the pump.

    This way the oil is ready to use when you want it, also the oil may have been washed more than once. I did a 10/90 warnqvist test on my oil the other day which showed 7.5mls of dropout.

  4. #4
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    Re: Glycerol / glycerine / byproduct pre wash

    Hi smithey,

    Quote Originally Posted by smithy View Post
    Most people here in the UK do bother doing it.
    I am curious how you have determined that most of the people in the UK who make biodiesel use the glycerine pre-wash procedure

  5. #5
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    Re: Glycerol / glycerine / byproduct pre wash

    Simply because of the proportional numbers that mention it on the UK Forums.

  6. #6
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    Re: Glycerol / glycerine / byproduct pre wash

    Thanks, Tilly & Smithy.

    I can definitely see the benefits, but there is just that tradeoff on time and electricity.

    I'm also more inclined to do it at ambient temperature too, although that would put a lot of strain on my 1.5 kW paddle mixer motor here in winter.

    Just to confirm: now that I have reduced my titration number from, say, 3 to 0.5, my total addition of KOH will now be (7 + 0.5) = 7.5 g/L rather than (7 + 3) = 10 g/L?
    3DB
    1995 Isuzu Rodeo 2.8TD 4X4 - 45,000km & 3.5 years on B100
    1976 Mercedes 300D Turbo 'The Coal Grenade' - 3,000 km on B100, 280,000 Km on the clock, but probably more like 1,280,000
    (@thirddegreeburns on Instagram)

  7. #7
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    Re: Glycerol / glycerine / byproduct pre wash

    Hi 3DB

    Quote Originally Posted by 3DB View Post
    Just to confirm: now that I have reduced my titration number from, say, 3 to 0.5, my total addition of KOH will now be (7 + 0.5) = 7.5 g/L rather than (7 + 3) = 10 g/L?
    That is correct

  8. #8
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    Re: Glycerol / glycerine / byproduct pre wash

    Hi Smithy,

    Quote Originally Posted by smithy View Post
    Simply because of the proportional numbers that mention it on the UK Forums.
    The problem with using that as a yardstick of what most people in the UK do is that it does not take into account the thousands of people in the UK who make biodiesel who do not participate on biodiesel discussion forums and have never heard of the glycerine pre-wash procedure.

    I recall one fellow on the UK forum who is a major proponent of the pre-wash procedure saying that he collected glycerine for his pre-wash from other biodiesel producers who do not use the pre-wash procedure.

    A more accurate statement might be that on the UK discussion forum were you participate there are several dozen active members and most of them use the glycerine pre-wash procedure.
    Last edited by tillyfromparadise; 23rd May 2017 at 11:46 AM.

  9. #9
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    Re: Glycerol / glycerine / byproduct pre wash

    I also forgot to ask how much I can reduce my methanol input by, if at all. Normally I would use 20% methanol x 180 L of oil = 36L
    3DB
    1995 Isuzu Rodeo 2.8TD 4X4 - 45,000km & 3.5 years on B100
    1976 Mercedes 300D Turbo 'The Coal Grenade' - 3,000 km on B100, 280,000 Km on the clock, but probably more like 1,280,000
    (@thirddegreeburns on Instagram)

  10. #10
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    Re: Glycerol / glycerine / byproduct pre wash

    Hi 3DB,

    Quote Originally Posted by 3DB View Post
    I also forgot to ask how much I can reduce my methanol input by, if at all. Normally I would use 20% methanol x 180 L of oil = 36L
    Multi stage procedures use less total methanol to achieve the same results as a single stage procedure.
    Some of the unknown amount of methanol in the Glycerol pre-wash will count towards the total amount of methanol used in the reaction.
    There is a procedure that uses the 3/27 test to help determine the amount of methanol to use in the second stage reaction however I can not put my finger on the procedure at the moment

    I am sure Smithy will be able to help you

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