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BioDiesel Basics

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  • BioDiesel Basics

    Biodiesel Basics
    Purpose of this document:
    This document aims to give a brief understanding of the basics of how BD (biodiesel) is made.
    New and unfamiliar words have been bolded so that you may identify them.

    Generally when a new batch of biodiesel is made using WCO (waste cooking oil) you’ll need to do a Titration test. Titration is the process of determining the amount of reactant (in this case Sodium Hydroxide – NaOH or Potassium Hydroxide – KOH) needed to convert the oil into biodiesel. Too much reactant will soap in the BD, not enough will result in an incomplete conversion.

    Technical stuff
    Ignore this if you don’t want to get to technical but basically there are Triglycerides in vegetable oil. By heating and stirring Sodium Methoxide or Potassium Methoxide into the oil you release the glycerine molecules from a triglyceride to form > diglyceride + methyl ester + glycerine. The methyl ester has a lower SG (specific gravity) and will rise and the glycerine has a higher SG and falls. A complete conversion will convert all of the triglycerides into methyl esters.

    OK stop and focus again…

    Health and Safety considerations – do not ignore this stuff

    The chemicals and compounds you will be making are VERY dangerous. Wear safety glass and gloves and work in a ventilated area. Have running water available.

    What you’ll need to get started
    A few small glass containers and a dish. (1500mls, 500mls) You can NEVER use these again for human consumption
    Blender with a glass bowl or alternate means of mixing
    Sodium Hydroxide – NaOH or Potassium Hydroxide – KOH (You can use either and I have included both in the procedure but you’ll need to use 7 grams of KOH (plus allowance for purity) or 5 grams NaOH (plus allowance for purity)
    250mls Methanol
    1000mls clean (unused) cooking oil
    Temperature gauge – up to 60C will do for this test
    Heated water.

    Making Sodium Methoxide or Potassium Methoxide
    Measure 5 grams of NaOH or 7 grams of KOH onto a dish. (These figures are based on purity of 100% so more may need to be added.) My suggestion is to stick with the basics first then move on to experimentation.
    Pour 250 ml of methanol into a 500 ml glass container, we will be combining the NaOH or KOH with the methanol to create sodium methoxide or potassium methoxide. The NaOH or KOH will need to be added slowly and stirred continuously. Bear in mind you will need adequate ventilation. Leave covered when finished to minimise methanol loss and fumes filling your working area also methoxide will absorb water from the atmosphere.

    Mixing the Methoxide with the Oil
    Heat the oil by placing it in a container in a tray or bowl of warm water. Heat to about 55 C. Take care not to heat the oil above 65 degrees C so the methanol won’t boil away. Add the methoxide to the oil. Mix together for about 15 minutes. The heating of the oil will assist the reaction to occur.

    Biodiesel/Glycerine separation
    Complete reaction should take about 40 minutes after the mixing, but will take up to 8 hours for the lighter glycerides to fall to the bottom. Allow at least this long before attempting to remove the biodiesel.

    Removing the biodiesel
    It has been recommended by many good folk all around the world to remove the BD from the glycerine. You can do this by either tipping the container or pumping or syphoning the BD. The reasoning behind removing the BD and not removing glycerine is for contamination reasons. If you were to remove the glycerine from under the BD, the BD would move down the beaker and occupy the space that the glycerine was in. The glycerine sticks to the walls and would contaminate the separated BD. I’ve read that tipping the beaker or what ever you are using allows you to have great control and will allow you to extract as much of the BD as you wish to.

    Washing the BD
    Washing the biodiesel allows any remaining glycerides, methanol or reactant (NaOH or KOH) in the BD to bond with the water and separate out. After washing the biodiesel it will look like orange juice. The water wash on the bottom will look like milk.
    Add approximately 200mls of water to the newly formed 1 litre of BD. For the first two washes wash very gently to avoid causing emulsion. Recover the biodiesel from the top or syphon the water from the bottom. Repeat for the second mix. For the thrid and remaining mixes, mix vigorously for a few minutes and allow separation. Repeat until the water wash is clear.

    Put the biodiesel in a well ventilated sunny spot for a few days. It will dry and become clear. Its should look like the colour of urine.

    Cleaning up

    Clean everything you used with a vinegar and water mix ready for the next use. Store the glycerine for methanol recovery (we’ll discuss this in another article). Do not use anything for human consumption again.

    Testing the BD
    • Cloud/Gel point test - These include tests to see how BD will perform at cold temperatures, before clouding and turning to gel. They are both OK to use but you may want to consider using BD that gels as summer blend. (Unless you live in QLD.) Sorry I had to throw that in.
    • Add smaller amounts to your diesel and increase as you feel comfortable. Don't forget adding a sacrificial fuel filter.
    This document is by no way meant to be comprehensive and has taken in to account "the sum of the average". By this I mean opinions on BD will vary but this document was written to reflect the general opinions of most users.

    ***This thread is for information only - please post questions in a new thread!***
    Last edited by joe; 9 May 2007, 10:32 PM. Reason: Update a few things
    Joe Morgan
    Brisbane Biodiesel Site Admin

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