Biodiesel Basics
Purpose of this document:
This document aims to give a brief understanding of the basics of how to make BD (biodiesel) is made from WVO (Waste Vegetable Oil).
In a nutshell
All WVO should be titrated. This is the process of determining how much reactant will bee needed for complete conversion of WVO into Biodiesel.
Make methoxide.
Heat oil.
Filter oil.
Add/Mix Methoxide.
Allow Glycerine to settle.
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 VO 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 leaving Tri-Glycerides and Di-Glycerides.
But for the sakes of Biodiesel basics we will be using clean VO that won't need titration.
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 VO you release one of the glyceride 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 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 methol 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 BD 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.
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
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
Heated water.
Method
Making Sodium Methoxide or Potassium Methoxide
Measure 3.5 grams of NaOH or 4.9grams (5 grams will be fine) of KOH onto a dish. I've been reading lately some discussion about using a base level of 5 grams of NaOH and 7 grams of KOH. My suggestion is to stick with the basics first then move on to experimentation.
Heat some water in a pot to about 60 C and take it off the stove (and/or away from the source of heat.)
Pour 200 ml of methanol into a 500 ml glass container, place the whole 500ml glass container into the pot of heated water, stir the methanol and heat it to about 50-55C. Do not raise the methanol to above 65 as the methanol will boil and the fumes are dangerous.
We will be combining the NaOH or KOH with the heated 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. If you are going to do this bear in mind you will need adequate ventilation. You can do this or mix by hand for a few minutes. The heating of the methanol will assist the process. Leave covered when finished to minimise methanol loss and fumes filling your working area.
Mixing the Methoxide with the Oil
Heat the oil as you did with the methanol to about 50-55 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 or vice versa. Mix together for about 15 minutes. The heating of the oil will assist the reaction to occur.
Biodiesel/Glycerine separation
Separation will take place as soon as 1 hour after the mixing (or less), 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 will allow any remaining glycerides or methanol in the BD to bond with the water and separate out. To your 1 litre od Biodiesel add 300 mls of water. Roll slowly. Do not shake at this stage or you will form soap. The water will look 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.
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
• Hydrometer - The Specific Gravity Biodiesel will be around .86 - .90. Typically .88
• PH - should be neutral
• 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 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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