Biodiesel from Straight Vegetable Oil (SVO)
When first making biodiesel it is a good idea to start with straight vegetable oil (SVO) rather than trying to use waste oil initially, as the process for using SVO is slightly simpler. Vegetable oil is usually a blend of several oils rather than a single oil, and the oils commonly used are palm, soybean, rapeseed, sunflower seed, peanut, cottonseed, palm kernel, coconut, olive and maize. You can buy SVO in bulk from your local supermarket, but shop around for the best price as these can fluctuate greatly. Even if you find oil prices becoming too high for making your own biodiesel worthwhile, it is important to start with SVO and become comfortable with the process before venturing onto using waste oil, which will be worthwhile.
Making small amounts of biodiesel will never be as cost effective as making larger batches; however, it is important to start using smaller amounts while learning the process. This will be less costly should you make a mistake or find you need to fine tune your methods. Making a 1 litre test batch is a good place to start. To make 1 litre of biodiesel from SVO you will need:
- 1 litre of unused vegetable oil;
- 200ml of methanol (95% pure);
- 5 grams of sodium hydroxide (or 7g of potassium hydroxide);
- Glass mixing container with tight fitting lid;
- 2 litre plastic bottle;
- 2 or 3 funnels;
- Thermometer;
- Scales accurate to 0.1g or less.
Sourcing the Ingredients
Vegetable oil is readily available in the supermarkets, but what about methanol and sodium hydroxide? Methanol is difficult to source neat and in large quantities. It is available in other products such as fuel antifreeze (such as Heet in the US), however, many antifreeze products are becoming methanol free. Methanol can also be purchased from camping stores, where it is used in stove burners, and at some model stores / race tracks, where it is used for fuel. Sourcing methanol will be the hardest part of making biodiesel, and whatever form it comes in, it must be at least 95% pure (95% methanol). Sodium hydroxide, also known as caustic soda or lye, is rather more available and can also be found in the supermarkets and chemists, where it is sold as a heavy duty cleaner (such as for drains). Potassium hydroxide, also known as potash, is also sold as a drain cleaner but tends to be more expensive.
Step 1: Pre-heat the oil
Pre-heat the vegetable oil to 60°C in a saucepan. SVO shouldn't contain any water so this temperature is enough and will make for easier mixing. Although vegetable oil has a relatively high flash point, never leave heating oil unnatended and always keep a thermometer in the pan.
Step 2: Making the sodium methoxide (caution required)
Using a funnel, pour 200ml of methanol into the glass container. Methanol absorbs water from the atmosphere so do it quickly and replace the methanol container lid tightly. Also be quick in measuring out the sodium hydroxide because it too absorbs water, which would interfere with the biodiesel reaction. With a second dry funnel, drop the 5g of sodium hydroxide into the methanol, replace the lid immediately and shake or swirl the mixture for about 10 minutes until all of the sodium hydroxide has dissolved. These chemcials don't mix easily and heat will be generated during this process. Do not use a plastic bottle as the sodium hydroxide will attract plastic particles and create holes. After the sodium hydroxide has disolved, top up to 200ml with fresh methanol, as there may be some evaporation during mixing.
Step 3: Making the biodiesel
Using a clean funnel pour the warm oil into the plastic bottle and then add the sodium methoxide. Replace the bottle top, screwing it down tightly, and shake vigorously for 30 seconds. For best results shake the mixture for 5 seconds four times over the space of an hour (no appreciable pressure is generated). The mixture can then be left to settle.
Step 4: Settling and Separation
Settling takes about 8 hours but within 1 hour most of the glycerine will have settled at the bottom with biodiesel appearing at the top - this is referred to as seperation. The glycerine layer is usually about the same or slightly more than the amount of methanol used (KOH mixes quicker). It is best to leave the mixture overnight to settle more fully. Slowly pour off the biodiesel to use as fuel and put the glycerine on your compost heap or use it to make soap (expose the glycerine to air and sunlight for 1 week first).
Step 5: Washing
The quality of the biodiesel will be greatly improved by washing to remove more soap. Pour the 1 litre of biodiesel into another 2 litre bottle. Gently add half a litre of 40°C water. Replace the top tightly and then turn the bottle end over end very gently for 30 seconds. As long as care is taken, the cloudy (soapy) water and biodiesel will separate quickly. Turn the bottle upside down and slowly release the water (which will form a layer at the bottom) using your thumb as a valve. Repeat this process 2 or 3 times, slowly increasing the level of agitation and the length of time the bottle is rotated (1 min for wash 2, and gently shake the bottle in wash 3). By washes 4 and 5 you can shake the bottle fairly vigorously although it will take considerably longer to separate. If the bottle is shaken too early an emulsion will form that will take days if not weeks to settle out. When finished the water should come out of the bottle fairly clear.
Step 6: Drying
Finally the water must be removed before using the biodiesel to prevent risk of damaging the engine. The easiest method of drying is settling. Leave the washed biodiesel, which will be very cloudy and much lighter in colour than unwashed biodiesel, for at least 2 days to settle. Water will settle to the bottom, and will also evaporate over time. This can be drained off, and once dry it will be clear and ready for use.
Working With Batches Larger Than 1 Litre
We already know that to make 1 litre of biodiesel requires 1 litre of vegetable oil, about 210ml of methanol (including topping up) and 5g of sodium hydroxide (or 7g of potassium hydroxide). To make larger batches of biodiesel you simply need to scale these figures up.