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.
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.
Introduction
Generally when a new batch of biodiesel is made using WVO (waste vegetable 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 vegetable oil into biodiesel. Too much reactant will leave excess “stuff” such as NaOH, KOH or methanol in the BD, not enough will result in an incomplete conversion.
But for the sakes of Biodiesel basics we will be using clean vegetable oil that won't need titration.
Technical stuff
Ignore this if you don’t want to get too technical but basically there are Triglycerides in vegetable oil. By heating the oil and stirring Sodium Methoxide or Potassium Methoxide into the oil you release one of the glyceride molecules from a triglyceride to form > diglyceride + methyl ester + glycerine. The methyl ester has a lower specific gravity and will rise and the glycerine has a higher specific gravity and falls and the diglyceride hangs around waiting for another reaction to release some more methyl ester and glycerine. A complete conversion will convert all of the tri/di/glycerides into methyl esters. So if you hear people talking about tri or diglycerides left in the BD after the reaction you will know that it was incomplete. And yes you can add more Methoxide to the biodiesel to start the reaction over again. This is the basis of the "80/20" process which uses 80% of the Methoxide to convert the WVO into BD then uses the remaining 20% to complete the process.
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
2 or 3 litre glass bottle
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 1.4 times more KOH than NaOH)
200mls Methanol
1000mls clean (unused) vegetable oil
Temperature gauge – up to 60C will do for this test. We will only be heating the oil to 50C
Heated water.
Method
Making Sodium Methoxide or Potassium Methoxide
Measure 5 grams of NaOH or 7 grams of KOH. 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. Some instructions on the web say pour the methanol and NaOH or KOH into a glass bowl and stir with an old disused blender for a minute or so. I advise against this as a spark from the old blender could ignite the methanol fumes. If you are howver going to do this bear in mind you will need adequate ventilation. You can do this or mix by manually for a few minutes. You would be advise to mix the two in a closed container to prevent water vapour from entering the mix. Leave covered or sealed when finished to minimise methanol loss, water comtamination and fumes filling your working area.
Mixing the Methoxide with the Oil
Heat the oil to about 50C by placing the oil into a container and placing that container into a pot of the heated water. The same as you would do to heat a baby's bottle. Take care not to heat the oil above 65 degrees C as the methanol will boil away when added. Add the methoxide to the oil. Mix together for about 15-20 minutes. The heating of the oil will assist the reaction to occur. For small test batches a shake every few minutes will suffice. In the interest of power consumption heating the oil with the use of solar enery will work sufficiently provide the oil is heated to the mid fortys.
Biodiesel/Glycerine separation
Separation will begin as soon as 30 minutes or less and will generally continue for a few hours if kept warm and continually stirred. It will take up to 8 hours for the process to complete. Allow at least this long before seperating the glycerine and biodiesel.
Removing the biodiesel
It has been recommended by many good folk all around the world to remove the BD from the glycerine. Although this is often not practicle. The logic behind this so as not to recontaminate the BD with the glycerine after seperation. You can do this by either tipping the container or pumping the BD. For smaller test batches this will suffice however for larger batches removing the glycerine is often more practical and easier to do before decanting the BD. In the case of small to medium sized processors (20 - 200Lts) seperation is done by opening the valve at the bottom of the processor and allowing the glycerine to flow out and then stopping when biodiesel starts to flow out of the valve. You can then redirect the flow of the biodiesel into another container for washing or settling.
Washing the BD
Washing the biodiesel will allow any remaining soap, glycerides or methanol in the BD to bond with the water and separate out. To your 1 litre of Biodiesel add 200 mls of water. Roll slowly. Do not shake at this stage or you will form soap. The water will become milky. Seperate and repeat as many times as needed until you have clear water. After washing, the biodiesel may look murky and will need to be dried to remove suspended water. You can do this by allowing to become heated in the sun. Another method is called bubble drying. This uses a bubble stone from a fish tank to pass air through the misture for a few hours. The water will slowly evaporate.
Settling the BD
Some users prefer to settle their biodiesel. This process allows and particles to settle on the bottom of the tank. Its recommended you settle for a minimum of two weeks and for up to 4 weeks.
Cleaning up
Clean everything with warm water ready for the next use. Ensure every thing has sufficient time to dry before 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
• Warnqvest conversion test 3/27 Test - tests for unreacted oil read here.
• PH - should be neutral to slightly alkaline 7-8pH. The water from the water wash can be tested. Not the biodiesel its self
• Cloud/Gel point test - These include tests to see how cold the BD will go before clouding and turning to gel. They are both OK to use but you may want to consider using BD that gels as a summer blend.
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.
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