How to Turn Used Cooking Oil into Biodiesel Fuel

How to Turn Used Cooking Oil into Biodiesel Fuel

How to Turn Used Cooking Oil into Biodiesel Fuel


Converting used cooking oil into biodiesel fuel is an excellent way to recycle waste oil and produce your own renewable fuel for diesel vehicles and equipment. Biodiesel is an eco-friendly and low-emission alternative to regular petroleum diesel that can be made through a chemical process called transesterification. With some simple equipment and ingredients, I was able to make high-quality biodiesel fuel at home. In this guide, I will share the step-by-step process I followed to turn used cooking oil into usable biodiesel.

Gathering Used Cooking Oil

The first step is collecting a sufficient quantity of waste vegetable oil (WVO). Good potential sources include:

  • Restaurants and commercial kitchens
  • Fast food establishments
  • Food processing plants
  • Donut shops
  • Catering services

I called around to restaurants in my area and found several willing to save their used fryer oil for me to pick up. Establishing relationships with restaurant owners is key, as biodiesel production requires a steady supply of waste oil. Most restaurants are happy to give away used oil instead of paying to dispose of it.

I collected the waste oil in 5-gallon plastic jugs and transported it home to start processing. Any food particles in the oil will need to be filtered out before moving onto the next steps.

Required Materials and Equipment

Producing biodiesel requires some specific materials and equipment:

  • Methanol: Also called methyl alcohol, this serves as the processing alcohol to chemically react with the triglycerides in the waste vegetable oil.

  • Lye: Also known as sodium hydroxide (NaOH). This catalyst starts the transesterification reaction.

  • Titration kit: Used to determine the precise acid level of waste oil samples. This helps calculate the exact amount of lye needed.

  • Conical flask: For mixing the methanol/lye reactant.

  • Electric mixer: To blend the oil and methanol/lye reactant together.

  • Separation funnel: Lets the biodiesel separate from the glycerin byproduct after processing.

  • Storage containers: For holding the finished biodiesel fuel. 55-gallon metal drums work well.

Safety gear like goggles, gloves, and a mask are also essential when handling methanol and lye, which can cause burns.

Step 1: Titrate the Waste Oil

The first step is to take a sample of the collected waste oil and titrate it using the titration kit. This determines the precise acid number of the oil, measured in mg KOH/g. Oils with higher acidity require more lye to properly react.

To titrate:

  • Add oil sample to solvent in titration kit
  • Add phenolphthalein indicator and titrant
  • Titrate while swirling until color changes
  • Use formula to calculate acid number

Knowing the acid value then lets you calculate exactly how much catalyst is required.

Step 2: Make the Methanol/Lye Mixture

Next, I prepared the methanol/lye reactant mixture that gets combined with the waste oil. This requires:**

  • 1 liter methanol per 1 liter oil
  • 22 grams lye per 1 liter oil
  • Adjust lye amount based on titration results

I carefully measured out the methanol and lye in a fume hood while wearing protective equipment. The lye was added slowly while mixing to fully dissolve. The mixture was then allowed to cool to avoid evaporating the methanol.

Step 3: Combine and Mix the Oil and Reactant

With safety gear on, I gradually combined the waste oil and methanol/lye reactant in a large mixing container. It’s crucial to mix thoroughly for at least 15-20 minutes to complete the transesterification reaction. The mixture begins warm and opaque, then cools and clears as the reaction finishes.

I used an electric mixer with high shear ability to fully incorporate the two liquids together. Mixing well is vital so be patient and mix for a full 20 minutes minimum. Poor mixing can result in reduced yields.

Step 4: Settle and Separate the Biodiesel

After mixing and reacting, the mixture is allowed to settle overnight. The biodiesel portion separates from the denser glycerin byproduct.

I let mine sit for 24 hours to fully separate, then drained off the glycerin from the bottom of the container. Be sure to avoid cross-contamination when drawing off the glycerin.

The glycerin byproduct contains leftover alcohol, catalyst, and soaps. It requires further processing before disposal or reuse.

Step 5: Wash and Dry the Biodiesel

With the glycerin removed, the last step is to purify the biodiesel through a series of wash and dry cycles. This involves:

  • Washing with soft water to remove residual soaps
  • Allowing to settle and drying any water
  • Repeating wash cycle 2-3 times

I washed the biodiesel in 5-gallon batches using a soft water hose, settling container, and pump. Three full wash cycles produced a high purity finished fuel ready for storage and use.

Storing and Using Homemade Biodiesel

After drying, I transferred my homemade biodiesel to 55-gallon metal drums for storage. The fuel can keep for 6 months or more when properly stored. Over time, it may require periodic reprocessing to maintain purity.

The finished biodiesel has properties similar to conventional petroleum diesel. It can be used to fuel any diesel engine vehicle, generator, or heating system. Always start with blended fuel until confirming the engine can handle pure biodiesel.

By recycling waste oil from restaurants, I was able to produce clean-burning biodiesel fuel to power my diesel truck. Converting cooking oil into biodiesel takes time and effort, but nets fuel savings and environmental benefits.