How to make BIODIESEL (part 5)

1/Acid-stage questions

• A question will probably arise: why not mix the methanol with the sulphuric acid before adding them to the oil/fats? Two major reasons: (a) the reaction between methanol and concentrated H2SO4 is quite violent and it could splash, which doesn't happen if you mix it as described; and (b) dimethyl ether can form. Mixing alcohols with concentrated H2SO4 is a way to dry the alcohols (which is good) and also a way to make di-alcohol ethers, not good: dimethyl ether is a gas, colourless and highly explosive.

2/Base-stage questions

• The second-stage product should be quite murky. This is no problem, as it will wash out.
  After the processed oil/fat has turned straw-yellow (step 16), you've let it settle for an hour and drained the glycerine, you should have a total of about 120 ml of glycerine per litre of oil/fat used. If it's less than about 100 ml/litre oil, something's wrong, even if the colour is right -- the process hasn't gone far enough.

• This will almost certainly be due to carbonated lye. Lye has a really limited shelf life: CO2 from the air neutralizes it and forms sodium carbonate. Carbonated lye is much whiter than pure lye, which is almost translucent. The carbonate in the lye won't harm the reaction, but you'll have to use more lye.

• The solution: Repeat the procedure from step 13. Prepare a fresh batch of methoxide with 0.03 litres of methanol and 0.75 grams of lye for each liter of oil/fat. Reheat the biodiesel to 55 deg C (131 deg F), add the fresh methoxide and mix as before. No need this time to remove glycerine during the processing as in step 15, and don't worry about the colour. Mix for one hour, settle, drain off the extra glycerine, and proceed from step 18.

• If you plan to continue using the carbonated lye, make sure to increase the amount by 25% next time you make biodiesel. Store lye at room temperature, in dry conditions if possible, with the container lid really tightly closed.

3/Methanol recovery (optional)

• To keep costs down, even amateur biodiesel producers try to salvage the unreacted methanol. There are two major methods to do this: heat extraction and vacuum/heat extraction.
  

*Heat extraction

• Heat the second-stage product to 70 deg C (158 deg F) in a sealed boiler/vessel and lead the fumes into a condenser. Intercept the condensed methanol in a liquid trap. Take great care because methanol is highly flammable and the fumes are explosive. The temperature will need to be increased as the amount of unreacted methanol in the mixturedecreases.
  

*Vacuum/heat extraction

• This is basically the same as heat extraction, but it requires less energy. The drawback of this method is that you need a special vessel and equipment to do this. A good example is Dale Scroggins's reactor:http://home.swbell.net/scrof/Biod_Proc.html
  When building your reactor it may be a good idea to take one step at a time. Build the reactor, get confident with the process and eventually upgrade to methanol recovery.

At least a quarter of the methanol used can be recovered -- ie, 50+ ml per litre of oil/fat. Mix it with fresh methanol for preparing the next batch of methoxide.

4/Quality

• Diesel engines require quality fuel. You just can't pour poor-quality biodiesel into the tank and expect the engine to go on and on without problems. You have three very dangerous enemies: free glycerine, poorly converted oils/fats and lye. Free glycerine and mono-, di- and triglycerids (poor ester conversion) will form gum-like deposits around injector tips and valve heads, lye can damage the injector pump. The key to good fuel is to just do it right and finish it! Use pure chemicals (sulphuric acid, sodium lye and methanol) and measure them accurately, and follow the instructions carefully -- this will take care of poor conversion. Proper washing will get rid of the glycerine and neutralize any remaining lye.

• There are also kits available for various quality tests. I was told in a letter from one of the visitors to our site of a test used by the motor industry for determination of glycol in motor oil. This should work for free glycerine determination.

• "For glycerine analysis I suggest that you get a test kit for determining ethylene glycol in motor oil. This test is simple and it generates a purple colour if substantial free glycerol is present. Just analyze the biodiesel as if it were motor oil. Used-car dealers use the test to determine if there are leaks in the cooling system. Glycol and glycerol give the same result in the test." (With thanks to Martin Reaney)

• Paper chromatography and thin layer chromatography will tell you the conversion rate, and titration may tell you about any remaining lye.