Recycling used cooking oil

As seen in the text "Cooking Oil and the Environment”, the disposal of used cooking oil should not be done in the sink drain, in the toilet or with the garbage organic, as these incorrect destinations lead to contamination of water sources, soil and atmosphere.

So, the question arises: what to do with used cooking oil? Well, currently the best option is carry out the selective collection of this oil, placing it in PET bottles and disposing of them for recycling.

This recycling of used cooking oil can be done at home or we can take it to collection points that will send it to associations and companies that will recycle it.

At home, we can do this recycling through the soap making. See a recipe for homemade soap with used oil:

1. Put five liters of used cooking oil in a bucket, passing it through a sieve to retain the food scraps left over from frying;

2. Add 1 American cup of cornmeal, 500 ml of liquid coconut detergent and 1 liter of liquid caustic soda (sodium hydroxide – NaOH) and mix well. Take maximum care when handling caustic soda and use personal protective equipment (PPE), such as glasses, mask, apron, closed shoes and gloves, as it is corrosive and can cause burns in the skin;

3. Add a liter of boiling water and, if desired, add some essence of your choice. Also be very careful not to burn yourself in this step;

4. Stir for 40 minutes non-stop;

5. Pour into a mold and let it harden for about ten days. Before complete hardening time, make cuts in the desired shape. You can also put it in smaller shapes.

See how easy it is? In addition to having a product that you can use, representing savings for the family budget, you also help to conserve the environment!

Soaps can be made from used cooking oil

Chemically, the reaction that occurs in this recipe is called saponification reaction. The base (caustic soda) reacts with triglycerides (triesters) that form oils and, as products, glycerol (glycerin) and fatty acid salts that are the molecules responsible for cleaning. You will be able to understand this better in the text. Soap and Detergent Chemistry.

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Example of saponification reaction:

CH₂OCOC₁₇H₃₅ CH₂oh
│ │
CH₂OCOC₁₇H₃₅ + 3 NaOH → CH₂OH + 3C₁₇H₃₅COONa
│ │
CH₂OCOC₁₇H₃₅ CH₂oh
glyceride soda glycerol soap
caustic

But if you prefer to send this used cooking oil for recycling by associations and companies, remember to do so using plastic bottles, as already mentioned, as glass bottles can break, spill all the contents and cause accidents. Also, wait for the oil to cool.

Among the ways of recycling used cooking oil, the most important is biodiesel production. Biodiesel is a biofuel produced from esterification reactions or transesterification of vegetable or animal oils (new or used) that serves as an oil substitute diesel, being renewable, biodegradable and less polluting.

Used oil is formed by triglycerides, which are lipids formed by the union of a glycerin molecule with three fatty acids (triesters). Thus, these compounds have very large carbon chains. Therefore, the cooking oil, after cleaning and dehumidifying, is reacted with alcohols in the presence of a suitable catalyst. At the end of the process, each fatty acid chain is disconnected from the glycerin and each one gives rise to a biodiesel molecule, which has physicochemical characteristics similar to those of diesel.

Recycling used cooking oil produces biodiesel

In addition, recycling used cooking oil can also produce putty, animal feed, paint resins, adhesives and other products.

By Jennifer Fogaça
Graduated in Chemistry

Would you like to reference this text in a school or academic work? Look:

FOGAÇA, Jennifer Rocha Vargas. "Recycling used cooking oil"; Brazil School. Available in: https://brasilescola.uol.com.br/quimica/reciclagem-oleo-cozinha-usado.htm. Accessed on June 28, 2021.

Detergents and Pollution

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