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Thread: Dewatering WVO with petrol.

  1. #1
    Join Date
    Dec 2016
    York UK

    Dewatering WVO with petrol.

    Hi Everyone, someone on one of the UK forums asked me to do a little test some weeks ago and I thought the info would be interesting for you guys 'down under'

    I think we all realise that adding petrol to WVO encourages water and residue to fall. The test was to see the difference in water content before and after.

    I tested the water in some (not good quality) but well settled oil with my Sandy Brae water tester.
    It came out at 1425ppm.

    I added 10% petrol and shook well. After a few hours I noticed a residue layer forming at the bottom of the separating funnel. I left the sample 30 hours and tested again for water. The result was 345ppm.

  2. #2
    Join Date
    Sep 2005

    Re: Dewatering WVO with petrol.

    Does your Sandy Brae water tester measure water in the presence of vegetable oil as accurately as it measures water in the presence of petrol and/or other fluids?

    Your test results show a significant reduction in water content after the petrol / oil mix was settled for 30 hours. Did you decant the oil from above the residue layer before testing? Would it have made any difference ?

    Now you need to determine the optimal amount of petrol to add to wet oil, for the most cost effective dewatering.
    What impact does the reduction of water from 1425ppm to 345ppm on a typical batch of biodiesel? Would it be cost effective to reduce the water content further, if using the oil for biodiesel production?

    What other "contaminants" were present in the residue layer?

    Keep up the good work
    Last edited by Tony From West Oz; 24th July 2018 at 12:15 AM. Reason: added last question
    Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

    Current Vehicles in stable:
    '06 Musso Sports 4X4 Manual Crew Cab tray back.
    '04 Rexton 4X4 Automatic SUV
    '2014 Toyota Prius (on ULP) - Wife's car

    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
    '99 Mercedes W202 C250 Turbodiesel (my darling Wife's car)[sold]
    '98 Mercedes W202 C250 Turbodiesel (my car)[sold]
    '06 Musso Sports Crew Cab well body. [Head gasket blew!]
    '04 Rexton SUV 2.9L Turbodiesel same as Musso - Our Family car.
    '06 Musso sports Crew Cab Trayback - My hack (no air cond, no heater).

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  3. #3
    Join Date
    Dec 2016
    York UK

    Re: Dewatering WVO with petrol.

    I can't answer all of your questions Tony as I've never ran on WVO. I assume the SB is as accurate with oil as it is for bio. The sample size of 30mls (variable) is added to 10mls of anhydrous petroleum distillate which I assume releases most of the dissolved water so the calcium hydride reacts faster.

    I used a pipette to draw the 30ml sample from the top of the treated oil.

    The amount of dissolved water that biodiesel will hold is around 1000ppm depending on temperature, so at 1400ppm bio would be cloudy with suspended water.

    Although I've been concious over the years re water in my finished bio and dry it to <300ppm most others don't.A lot of the samples (hundreds over the years) that I've tested for other brewers are over the limit of 500ppm. Unless the bio is cloudy with suspended water I have never known anyone to have trouble with water a content of around 800ppm.

    It seems as though the old yardstick of 'clear and bright' is accurate enough.

    I don't think this proceedure would be of use to dry oil for bio production. It wouldn't be cost effective and I don't know what effect the petrol would have on the process.

    The residue formed after the petrol addition was quite light in colour. After a few days a small brown layer appeared at the bottom of the residue.

    I'll do some more tests when I have time.
    Last edited by smithy; 24th July 2018 at 02:06 AM.

  4. #4
    Join Date
    Oct 2011

    Re: Dewatering WVO with petrol.

    Sorry you're right - didn't notice. It's deleted


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