Biodiesel from Waste Vegetable Oil (WVO)

Several billions of gallons of waste vegetable oil are produced every year around the world, mainly from industrial deep fat fryers found in potato processing plants, factories manufacturing foods, and restaurants. Some of this wastage is already being re-used by other industries, such as in animal feed and cosmetics, but the amount that is still being wasted and ending up in land-fill sites is alarming. Therefore it makes commercial and environmental sense to re-use this oil for making biodiesel.

Making biodiesel from waste vegetable oil (WVO) is much the same as when using straight vegetable oil, except that the oil will need filtering first to remove debris, and because it has been used and most likely re-heated several times, more fatty acids will be present so we need to determine how much more sodium hydroxide (or potassium hydroxide) to add to neutralise these acids. This is called a titration test.

To make 1 litre of biodiesel from WVO you will need:

1. 1 litre of waste vegetable oil;
2. 200ml of methanol (95% pure);
3. 5 grams of sodium hydroxide (or 7g of potassium hydroxide);
4. A glass mixing container with tight fitting lid;
5. 2 litre plastic drinks bottle;
6. 2 or 3 funnels;
7. Thermometer;
8. Scales accurate to 0.1g or less.

And for the titration test:

9. Phenolphthalein or ph paper (to test for acidity - don't use phenol red indicator);
10. Bottle of distilled water (see note);
11. 1 litre bottle (for tester solution);
12. Isopropyl alcohol;
13. 3 oral syringes graduated in ml or eyedroppers;
14. Several small glass jars or beakers;
15. Stainless steel stirrers/spoons.

Water can contain microscopic contaminants along with dissolved minerals like calcium and iron. Boiling water until it changes to steam is one way to remove these, a process known as distillation. When the steam cools and condenses into liquid again, a more purified water is formed called distilled water. Ideally distilled water should simply be hydrogen and oxygen molecules with a PH level of 7 with no additional contaminants.

Sourcing the Ingredients

Methanol, sodium hydroxide and potassium hydroxide can be sourced as per the section on making biodiesel from SVO. Isopropyl alcohol, also known as rubbing alcohol, can be purchased at chemists and even some electrical stores (as it's good for cleaning electrical contact areas). As for Phenolphthalein or ph paper, this may take more work, perhaps online or using toy chemistry set suppliers.

Step 1: Settling

This is an important step. Allow the oil to settle for at least 24 hours (2 weeks being preferable). The top layer will be shiny and translucent with a yellow/brown tint. This is the good oil (really clean oil will not have a cloudy bottom layer).

Step 2: Filtering

Used oil needs filtering down to between 5-10 microns, and it is advisable to have at least one pre-filter stage before this stage. Filters can be bought or made, using materials such as denim. For example: an old pair of jeans, sewn up the bottoms of the legs, will hold about 5 gallons per leg. This will filter out the larger food items. After that, bag filters are available relatively cheaply for the finer filtering. Don't heat the oil before filtering or what you're trying to filter out may liquefy and pass through the filter.

Step 3: Pre-heat the oil

As this is WVO, heat the oil to 120°C to remove water. If water is present the oil will spit (if a lot is present this may get violent so take care). Once the water has gone and the oil is calm, let it cool down to 60°C for mixing with the sodium methoxide.

Step 4: Titration test

Dissolve 1 gram of sodium hydroxide into 1 litre of distilled water to make a 'tester solution' (this can be stored for future tests). For more accuracy, dissolve 3 gram into 3 litres.

Step 4a: Blank titration test on the isopropyl alcohol

Alcohol can become a little acidic with age, which would affect the titration results. A blank titration test neutralises these acids so the real titration test only detects the free fatty acids in the oil, instead of those in the isopropyl alcohol.

Add 10ml of isopropyl alcohol to a beaker. Add a few drops of phenolpthaleine and swirl (it will be a yellowish color). Add the tester solution drop by drop and keep swirling. The instant it turns purple, the acids have been neutralised so stop. If only 5 to 10 drops of tester solution were needed then it's not very acidic and this test can be omitted for the next few titrations. Otherwise a blank titration is required every time this particular alcohol is used.

Step 4b: The Titration test

Measure 1ml of oil into a jar or beaker with about 10ml of isopropyl alcohol using different syringes - note the amount of oil is crucial but not the isopropyl (the isopropyl/phenothalein mixture from the blank titration can be used here). If a blank titration hasn't been performed add roughly 5 drops of phenolpthaleine. Swirl the jar to dissolve the contents, which will be a murky yellow color.

Slowly add the tester solution drop by drop while swirling the beaker until the contents turn a pink color that lasts for 30 seconds of swirling (it will start to change to pink but will keep reverting back to yellow initially). Once it's uniformly pink and stays that way for at least 30 seconds, stop adding the tester solution and count how many mililitres have been added.

Alternatively, with an eyedropper, drop the tester solution into the oil mixture 1ml at a time. After each drop check the ph level of the oil mixture with the ph paper. An eventual rise in the ph level will occur. Continue to add the tester solution, one drop at a time, until it reaches a ph of 8-9.

It's worth repeating the titration test to try to obtain the same result more than once, as it is easy to make mistakes when measuring such small quantities of liquids (the liquids can be thrown down the drain too as they are fairly benign).

Step 5: Calculation

Each 1ml of tester solution added means 1 extra gram of sodium hydroxide will need to be added when making the 1 litre batch of biodiesel (to eliminate the free fatty acids in the oil). If the oil required more than 4ml of tester solution (or 5ml with potassium hydroxide) then don't use it until more experience is gained. Decent restaurant oil will require about 3ml of tester solution, and really bad fast food grease can take 10ml or more (which is completely unusable with sodium hydroxide as the catalyst). Note that the titration should be done using the same catalyst intended for use in making the biodiesel.

Working With Batches Larger Than 1 Litre

To calculate the materials for larger batches of biodiesel is rather straightforward:

For a 90 litre batch, for example, if the titration test results were 2ml, then 2 extra grams of catalyst is required for each litre of oil. Therefore:

Step 6: Proceed to Step 3 in SVO

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