Plastic feedstock synthesized from a byproduct of Biodiesel

The increased demand for biodiesel due to its environmental benefits creates an excess supply of waste products, such a glycerol, formed during its production.

Glycerol corresponds to around 10% of the product from biodiesel synthesis, and in 2014 alone 2.5 tonnes were produced as a by-product of the formation of the fuel. However, now researchers from the Swiss Federal Institute of Technology (ETH) in Zurich have found a way to convert the waste glycerol into lactic acid; a more useful substance which can be used as a plastic feedstock.

The research, headed by Javier Perez-Ramirez and Konrad Hungerbuehler, has led to a new method of creating lactic acid from glycerol, known as the cascade process. Through this method, glycerol is first oxidised to dihydroxyacetone using an established enzymatic technique. The lactic acid is then produced by isomerising the dihydroxyacetone over a tin-containing zeolite catalyst, which was specifically designed by the ETH Zurich team.

The lactic acid produced can then be used to make commodity commercials chemicals such as acrylic acid or pyruvic acid. Alternatively, the lactic acid can be polymerised to give a biodegradable plastic known as polylactic acid (PLA). PLA has a wide variety of applications, such as a packaging material, and is anticipated as a greener replacement for PET; a common synthetic plastic.

This newly designed process is advantageous over the traditional lactic acid production method of sugar fermentation, confronting the challenges of both sustainability and cost. As the glycerol feedstock is a waste material, the energy requirements and carbon dioxide emissions of the process are significantly decreased.

Through using a zeolite catalyst, which itself is recyclable, the new cascade process is also faster than the old fermentation method. As Perez-Ramierz explains ‘The advantage of an inorganic catalyst is that, if designed properly, it can work effectively and can process solutions which are more concentrated and/or of lower purity.’

The research, published in the journal Energy and Environmental Science, was the work of both the advanced catalysis engineering and environmental technology groups at ETH. Perez-Ramirez considers the interdisciplinary nature of this research to be vital to its progress: ‘When you put together expertise from different fields, like in our case catalyst design and process modelling, you can achieve synergies leading to faster advances and deeper understanding of complex problems.’

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Daniel Di Francesco

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