Whether wood residues, wheat straw, dairy residues or microalgae: In the production of important chemicals, fossil raw materials are increasingly being replaced by bio-based raw and residual materials. The utilisation of industrial residues and waste materials in particular offers enormous potential for recycling resources and thus protecting the environment. One promising source of raw materials is used cooking oil, which is produced in large quantities in commercial kitchens and restaurants. Until now, used cooking oil has mainly been processed into biofuels. Researchers from the Leibniz Institute for Catalysis (LIKAT) in Rostock have now found a way to produce new bio-based chemicals from used frying oil.

Amines synthesised from used cooking oil

‘Our aim is to utilise used cooking oil as a useful chemical starting material for the manufacture of valuable products. Amines were an obvious choice,’ says Fairoosa Poovan, PhD student at LIKAT.

Amines are organic compounds derived from ammonia. These so-called derivatives are used in organic chemistry as starting materials for the manufacture of various products such as pharmaceuticals, detergents, cleaning agents and disinfectants.

Kobalt-basierter Katalysator entwickelt

In Matthias Beller's research group at LIKAT, Fairoosa Poovan developed a cobalt-based catalyser that can efficiently convert used cooking oil into primary fatty acid amines. The aim was to develop a catalyser that can produce these primary amines from biowaste cost-effectively and efficiently. Until now, fatty acid amines have been produced in three steps via the so-called nitrile pathway. This not only requires ‘harsh reaction conditions’ such as high temperatures. The end result is a product mixture of different amines that are structurally very similar and therefore difficult to separate.

Bio-based amines produced in one step

The catalyst developed at LIKAT, on the other hand, can synthesise the amines from used cooking oil at moderate temperatures and in just one step. The primary amine is produced with ‘excellent selectivity’ due to the high efficiency of the catalyst and also cost-effectively by using cobalt as a base metal, reports the researcher. Commercially available sunflower oil was used for this in laboratory tests.

‘Our aim was to keep the process as simple as possible and to develop a one-pot system in which we combine all substances including the catalyst as a solution in one vessel. This significantly improves resource, atomic and reaction efficiency,’ says Fairoosa.

Sunflower oil, like other edible oils, consists of various fatty acid components with chains of different lengths ranging from 16 to 18 carbon atoms. According to Poovan, it is important to know the ratio of the different fatty acids in the edible oil used in order to be able to assess the reaction as well as the function and efficiency of the catalyst.

Utilising carbon in the cycle

The new catalyst can therefore not only be used to recycle raw materials. The further utilisation of the waste material also prevents the atomic carbon contained in the old cooking oil from being burnt during the production of biospirit and being released into the environment. According to the researchers, the same process can also be used to upcycle plastics.

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