How to Repurpose Used Cooking Oil into Environmentally Friendly Biofuel

How to Repurpose Used Cooking Oil into Environmentally Friendly Biofuel


Recycling used cooking oil into biofuel is a great way to reduce waste while creating a renewable fuel source. With some simple equipment and techniques, anyone can transform used cooking oil into biodiesel fuel to power diesel engines. This article will provide a step-by-step guide on how to safely and efficiently repurpose used cooking oil into biofuel at home.

Gathering Used Cooking Oil

The first step is collecting a sufficient quantity of used cooking oil. Here are some tips:

  • Save oil from frying foods at home. Strain out food particles and store oil in an airtight container.
  • Ask restaurants, fast food joints, cafeterias, etc. to set aside their used fryer oil. Ensure they haven’t mixed it with other waste grease.
  • Check local regulations on maximum quantities allowed for home processing. Getting more than you can legally process wastes time and money.
  • Aim for oils high in mono- and poly-unsaturated fats like canola, peanut, and vegetable oil. These work best for biodiesel. Avoid animal-based fats.
  • Only use oil that’s liquid at room temperature. Solid fats like lard won’t work.
  • Make sure the oil is free of water and food particles to avoid processing problems. Strain if needed.

With a consistent source, you can gather 5-10 gallons of used oil (about 18-37 liters) to make a decent batch of biodiesel.

Making Biodiesel Through Transesterification

The most common DIY way to convert used cooking oil into biodiesel is through a chemical process called transesterification. This involves:

  • Mixing the waste oil with methanol and sodium hydroxide (lye).
  • Heating the mixture so the oil and methanol chemically react and split the oil’s molecules into biodiesel and glycerin.
  • Separating the biodiesel and glycerin. The glycerin sinks to the bottom and can be drawn off.
  • Washing and drying the biodiesel with water to remove impurities like leftover catalyst, methanol, soaps, and glycerin traces.

Equipment Needed

You’ll need the following equipment:

  • Reactor vessel – A food-grade plastic or steel drum to mix and react the oil/methanol/catalyst. It should be 2-3 times the volume of your oil.
  • Electric heating element – To heat oil to the 140-150°F (60-66°C) needed for transesterification.
  • Thermometer – To monitor the reaction temperature.
  • Gloves and eye protection – When handling corrosive methanol and lye.
  • Funnel – For transferring liquids between containers.
  • Kitchen scale – For weighing out catalyst.
  • Cooker/hot plate – For heating methanol.
  • pH strips – To test if biodiesel is fully washed.

Optional but helpful tools include mixer/drill attachments to mix chemicals and a titration kit to check catalytic conversion.


You’ll need:

  • Used cooking oil – The feedstock.
  • Methanol – The reactant that splits the oil molecules into biodiesel. Use at a 20% ratio to oil volume.
  • Catalyst – Sodium hydroxide (lye) at a 0.5% ratio to oil weight speeds up the chemical reaction. Potassium hydroxide can also work.
  • Water – For washing the biodiesel at the end to remove contaminants.

Step-by-Step Process

Follow these steps closely for safe, effective DIY production:

1. Safety First

  • Work outdoors or in a very well ventilated area due to methanol fumes.
  • Wear gloves and goggles when handling methanol and lye – they can burn skin and eyes.
  • Avoid open flames or sparks near methanol.
  • Work slowly and carefully to avoid spills or splashes.

2. Measure Oil and Methanol

  • Use a measuring cup or sight glass to measure out the used oil, then pour into the reactor vessel.
  • Measure out the needed methanol at a 20% ratio to the oil volume using a graduated cylinder. For example, for 10 liters oil, use 2 liters methanol.

3. Mix Catalyst with Methanol

  • Weigh out the sodium hydroxide catalyst at 0.5% of the oil’s weight. For 10 liters oil (~8.5 kg), use 42.5 grams lye.
  • Carefully pour the lye into the methanol and mix until fully dissolved.

4. Combine Mixture and Heat

  • Pour the methanol/catalyst mixture into the oil in the reactor.
  • Attach the heating element and thermometer.
  • Heat to 140-150°F while mixing vigorously for 1-2 hours. Mixing helps the transesterification reaction occur.

5. Let Mixtures Separate

  • Turn off the heat and allow the mixtures to settle overnight.
  • The biodiesel will form a clear golden layer at the top, while the denser glycerin settles to the bottom.

6. Draw Off Glycerin

  • Carefully drain off the glycerin from the bottom valve into a separate container.
  • You can refine the glycerin into other products like soap or compost it.

7. Wash Biodiesel

  • Mix in soft water at a 20% volume ratio and gently stir for 5 minutes.
  • Allow to settle and draw off the water which contains contaminants.
  • Repeat 2-3 times until the wash water reaches a neutral pH.

8. Dry and Store Biodiesel

  • Allow biodiesel to sit overnight to dry fully. Methanol evaporates off.
  • Perform a final filter through a coffee filter or linen cloth.
  • Store in sealed containers away from heat, sparks, and sunlight.

And that’s it – you’ve produced high-quality biodiesel from used cooking oil! Now it’s ready to pour into a diesel vehicle’s fuel tank and displace traditional diesel.

Using Homemade Biodiesel

Here are some tips on using your homemade biodiesel:

  • Test in small quantities first in diesel engines to check for any issues.
  • Mix with regular diesel at 5-20% ratios to ease engine transition.
  • Use within 6 months before it starts to degrade. Storing properly extends shelf life.
  • Add fuel line antifreeze if operating in cold temperatures.
  • Adjust to biodiesel’s higher solvent properties with appropriate engine modifications like fuel line upgrades.
  • Ensure any diesel engine warranties allow for biodiesel use. Check with your engine manufacturer.

Benefits of Biodiesel From Used Cooking Oil

Converting used cooking oil into biodiesel has many advantages:

  • Far less toxic emissions compared to regular diesel – less unburned hydrocarbons, carbon monoxide, sulfates, and aromatics.
  • Reduces waste oil disposal issues for households and restaurants.
  • Provides a locally produced, renewable fuel source to displace petroleum diesel.
  • Can provide extra income for restaurants by selling their waste oil for biodiesel conversion.
  • Economical to produce on a small scale with basic equipment and ingredients.
  • Works in any unmodified diesel engine for transportation, generators, machinery, etc.

So if you want to lower your environmental impact, reduce waste, and create free fuel, then transforming used cooking oil into biodiesel is a great eco-friendly solution!