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From the Frying Pan into the Engine? Cooking up biodiesel from waste oil

Biodiesel, an alternative to fossil fuels, is costly. And complex to synthesise. Though many are turning to used cooking oil to produce biodiesel, the method produces crude glycerol as byproduct. The crude glycerol produced, when separated from biodiesel, has unspent methanol and glycerides, moisture and some amount of the catalyst used. The Environmental Protection Act dictates that raw glycerol has to be disposed of quickly, and so it is often sold off at a minimum price. This makes biodiesel extraction from waste cooking oil commercially not very attractive.

Mehulkumar Savaliya from the Shree M. & N. Virani Science College, Rajkot  and Bharatkumar Dholakiya, from the  Surat decided to tweak the process of converting waste frying oil into biodiesel and to find a way to transform the byproduct, crude glycerol, into something useful.

The scientists chose a melamine trisulfonic acid catalyst. Porous solid catalysts have better activity and are easier to separate out, later. But the material tends to clump together, reducing accessible catalytic sites. So the researchers added silica gel to the catalyst. When linked with silica gel, the catalyst was distributed in irregular pentamerous shapes.

The scientists sourced waste frying oil from a restaurant. They synthesised biodiesel at various oil to methanol molar ratios, reaction temperatures, catalyst loading and reaction times.The researchers found that the most favourable reaction conditions for biodiesel synthesis include 1:10 oil to methanol molar ratio, 5 % melamine trisulfonic acid-Si (w/w), and 130 °C reaction temperature. In 10 hours, there was 98.22 % yield of biodiesel.

To deal with raw glycerol, the researchers added lauric acid. Melamine trisulfonic acid-silica as a catalyst is tolerant to high amounts of free fatty acids. So esterification of glycerol with lauric acid to glycerides was achieved by the same catalyst. The triglycerides can easily be separated and could, in turn, be used to make biodiesel.

“The protocol offers many advantages. The catalyst can be recycled and reused without loss in efficiency,”says Bharatkumar Dholakiya, Sardar Vallabhbhai National Institute of Technology, Surat.

“And the problem of glycerol is overcome” adds Mehulkumar Savaliya, Shree M. & N. Virani Science College, Rajkot. The main side products from the process is water.

This research makes waste frying oil a cheap raw material for biodiesel extraction. Costs can be recovered and wastage avoided. Good news for restaurant owners.

Ind. Eng. Chem., 64: 352-366 (2018); DOI: 10.1016/j.jiec.2018.03.036

Sushmitha Baskar, IGNOU

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Categorised in: Energy, Gujarat, Science

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