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The power of waste

Date: 2020-07-31 11:43:03.0
Author: Jon Evans

 

Button cell lithium-ion batteries

Button cell lithium-ion batteries.

Photo: kiri11/Shutterstock.

One way to reduce the cost of producing biofuels is to utilize waste material as much as possible. For biodiesel, this doesn’t just mean using waste cooking oil as a feedstock, but also producing the catalysts required for the transesterification reaction from waste material.

Traditionally, these catalysts are liquid bases such as sodium or potassium hydroxide or acids such as sulfuric or hydrochloric acid, but recently researchers have shown that a variety of waste organic material can be transformed into effective transesterification catalysts. Not just plant-based waste material such as rice husks, banana peels and coconut shells, but also animal material such as bones and eggshells.

To transform both plant and animal waste material into catalysts, they simply need to be ground into a powder and then heated at high temperatures, usually above 500°C, for several hours. The resultant ash contains high concentrations of alkaline metal oxides such as potassium, sodium, calcium and magnesium, which can efficiently catalyze the transesterification reaction between oils and alcohols such as methanol to produce biodiesel.

As well as being cheaper and greener than conventional liquid bases and acids, catalysts made from waste material also boast several other advantages. As solid materials, they are easier to separate from the liquid biodiesel, thus generating less wastewater, and can also be reused. Furthermore, they are often better at coping with oils that contain high concentrations of free fatty acids, as is the case with waste cooking oil, because liquid bases are prone to converting free fatty acids into unwanted soap rather than biodiesel. They can also easily be modified to enhance their catalytic abilities by reacting them with other substances or combining them with support materials.

Now, however, Gilberto Brito and his colleagues from the Federal University of Espírito Santo in Brazil have shown that an entirely different kind of waste material can also act as an effective transesterification catalyst – waste batteries. This is because the lithium-ion batteries that power everything from cell phones to electric cars can act as a source of lithium hydroxide, which is similar to sodium and potassium hydroxide.

When Brito and his colleagues added lithium hydroxide taken from waste lithium-ion batteries to potassium and sodium hydroxide, such that lithium hydroxide accounted for 5%, they found that this mixture could convert waste cooking oil into a good quality biodiesel with a yield of 90%. As they report in a paper in the Journal of Renewable and Sustainable Energy, this approach not only offers a cheaper, greener way to produce biodiesel, but also provides a use for waste lithium-ion batteries, which are difficult to recycle by other means.

Obviously, a mixture containing just 5% lithium hydroxide is still mainly potassium or sodium hydroxide, but Brito and his colleagues found that mixtures containing higher concentrations of lithium hydroxide didn’t work as well. So they are now working on developing new transesterification catalysts based on lithium hydroxide and lithium oxide from waste battery material.

What is certain is that there will be no shortage of waste lithium-ion batteries in the future, driven particularly by the rise of electric cars. This might be seen as rather ironic, seeing as electric cars are a direct competitor of biofuels. But the rise of the electric car shouldn’t lead to a fall in the demand for biodiesel, which will still be required for forms of transport that don’t lend themselves to electric power, such as aircraft and ships.
 

The views represented here are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd. or of the SCI.


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