How to make BIODIESEL (part 3)

1/Introduction

• To make biodiesel fuel efficiently from used vegetable oils and animal fats we have to avoid one major problem: soap formation. Soap is formed during base-catalyzed transesterification (using lye) when sodium ions combine with free fatty acids present in used (and some virgin) vegetable oils and animal fats. The soaps diminish the yield because they bond the methyl esters to water. The bonded esters get washed out at the washing stage but make water separation more difficult and increase water consumption. This process takes care of the free fatty acids.

• In one early test I used a mixture of 50% heavily used cooking oil and 50% pork lard. The result was a pure product with absolutely no trace of soap! The biodiesel looked nice, and smelt nice, as if made from virgin oil.

• This is a simple procedure. The first-stage process is not transesterification, but pure and simple ESTERIFICATION. Esterification is followed by transesterification, but under acid conditions it's much slower than under caustic conditions and it won't do a complete oil-to-methyl ester conversion as the reaction is much more equilibrium-sensitive. Without methanol recovery, the alcohol overdose required would make the price of your fuel jump, and even with recovery it would still be much more expensive. Hence the second base-stage.

• For the first stage you'll form a compound out of an acid and an alcohol. The alcohol is still methanol, but instead of using lye (sodium hydroxide), the CATALYST in this reaction is sulphuric acid ("battery acid"). It needs 95% sulphuric acid (battery acid is around 50%). Sulphuric acid is one of the commonest chemicals on Earth, just like lye. More concentrated sulphuric acid -- 98% and above -- costs more, but 95% works just fine if you follow these directions. Other acids won't work: it must be sulphuric acid. The second stage uses lye, as usual -- but it only uses about half as much as other methods.

• The sulfate ion in the sulphuric acid combines with the sodium ion in the lye during the second-stage reaction to form sodium sulphate, which is a water-soluble salt and is removed in the wash. No sulphur remains in the biodiesel fuel product.

2/Equipment

• You don't need a special processor for the Foolproof method. Generally, a bottom-drained reactor vessel is best, closed on top. Tall, narrow containers work better than wide, shallow ones. Use a circulating pump for mixing rather than a mechanical stirrer. The pump should take the mixture from near the bottom of the reactor and return it via the top, to splash down on the surface. For a 35-litre reactor, a 100-W washing-machine pump will do, along with a 1.5kW washing-machine immersion heater to heat the mixture (get a heater that's coated with stainless steel). You could use a thermostat to control the temperature, but they're expensive: just use a thermometer and switch on the heater as required.

• Ordinary iron and steel implements and containers will eventually corrode because of the acid used in this process. However, you can still use the usual 55-gal (200-litre) drum. The proportion of acid used in this process is very low -- you should be able to use an uncoated drum for a year or more before the rust gets out of control. I use a polypropylene plastic reaction vessel. Any plastic that won't deform at 100 deg C (212 deg F) or a bit more is fine. Stainless steel is also fine. Use an immersion heater with plastic containers. With steel containers you can use propane heaters to heat the oil, then switch to an immersion heater before adding the methanol.

3/Test batches

• Whenever you're trying a new method, it's always a good idea to make small test batches of a litre or less first to familiarize yourself with the process before moving on to bigger batches.
• Most people use kitchen blenders for this -- but don't use it for food again afterwards!

4/The process

1. Filter the used cooking oil first as usual.

2. For a successful reaction the oil must be free of water. Here are two methods of removing the water content:

• (a) Settling the water out: This method saves energy. Heat the oil to 60 deg C (140 deg F), maintain the temperature for 15 minutes and then pour the oil into a settling tank. Let it settle for at least 24 hours. Make sure you never empty the settling vessel more than 90%.
• (b) Boiling the water off: Less-preferred method as it uses more energy and helps to form more FFAs in the oil. Heat the oil to 100 deg C (212 deg F). As the heat rises water separates out and falls to the bottom -- drain it off to avoid steam explosions. Maintain the temperature until no more steam bubbles rise.

5/First stage

3. Measure the volume of oil/fats to be processed (preferably in litres).

4. Heat the oil to 35 deg C (95 deg F) -- make sure that all solid fats are melted.

5. Methanol: use only 99%+ pure methanol. Measure out the methanol -- 0.08 litres of methanol for each litre of oil/fats (8% by volume). Add the methanol to the heated oil.

6. Mix for five minutes -- the mixture will become murky because of solvent change (methanol is a polar compound, oil is strongly non-polar; a suspension will form).

7. For each litre of oil/fats add 1 millilitre of 95% sulphuric acid (H2SO4). Use a graduated eyedropper, a graduated syringe or a pipette. TAKE CARE when handling the concentrated sulphuric acid!

8. Mix gently at LOW rpm (don't splash!) while keeping the temperature at 35 deg C. The rotation of your stirrer should not exceed 500 to 600 rpm -- speed is not crucial and splashed oil is a mess to clean.

9. Maintain the temperature at 35 deg C for one hour then stop heating. Continue stirring.

10. Stir the unheated mixture for another hour, a total of two hours, then stop mixing. Let the mixture sit for at least eight hours, overnight is better.

11. In the meantime prepare the sodium methoxide: measure 0.12 litre of methanol for each litre of oil/fat (12% by volume) and weigh 3.1 grams (up to 3.5 grams if purity is in doubt) of sodium lye (sodium hydroxide, NaOH) per litre of oil/fat. Mix the lye into the methanol until the lye is completely dissolved.

-Sodium methoxide is a DANGEROUS CHEMICAL. Take full safety precautions when working with methanol, lye and sodium methoxide, wear safety goggles, protective gloves and clothing, have running water nearby.

**NOTE: This process uses only about half the usual amount of lye as there is less fat left to transesterify. Use 99%+ pure sodium hydroxide lye. After opening the container, close it again as quickly as possible to prevent moisture getting in. Weigh the lye carefully -- using too much will complicate the washing process later.

12. After settling for eight hours, or the next morning, pour half of the prepared methoxide into the unheated mixture and mix for five minutes. This will neutralize the sulphuric acid and boost the base catalysis. If you've used solid fat, it probably solidified during settling -- gently melt the mixture first.

Now you can continue with the normal procedure with the lye as the second stage.