A sustainable method to synthesise platform chemical lactic acid from waste glycerol, a byproduct of biodiesel production, has emerged from research in Switzerland.
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| A significant amount of glycerol (bottom layer) is leftover when making biodiesel (top layer) © Bo Cheng/ETH Zurich |
Collaboration
between the advanced catalysis engineering and the safety and
environmental technology groups at the Swiss Federal Institute of
Technology (ETH) in Zurich, headed by Javier Pérez-Ramírez and Konrad Hungerbuehler,
respectively, gave way to the new cascade process. Glycerol is first
oxidised to give dihydroxyacetone through an established enzymatic
process. Dihydroxyacetone is then isomerised over a tin-containing
zeolite catalyst, which was designed by ETH Zurich team, to give lactic
acid.
The increasing demand for biodiesel means an oversupply of glycerol
and, currently, any excess glycerol must be disposed of. Glycerol
corresponds to around 10wt% of the fuel made. Predictions expect
glycerol production from biodiesel to reach about 3.7 million tons in
2020, having seen around 2.5 million tons produced in 2014.
Lactic acid
is commonly used to produce commodity chemicals like acrylic acid and
pyruvic acid. However, polymerising lactic acid can give a biodegradable
plastic called polylactic acid (PLA). PLA has a variety of applications
as a packaging material and is anticipated to be a greener replacement
for the common synthetic polymer PET.
The
new process for synthesising lactic acid confronts the challenges of
sustainability and costs faced by its traditional production method,
sugar fermentation. Using waste material as a feedstock decreases the
process’ energy requirements and carbon dioxide emissions, which in
conjunction with the recyclability of the zeolite catalyst, contribute
to the economic advantages offered by the new cascade route.
Another
benefit is that the cascade process is faster than the fermentation
method. ‘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,’ explains Pérez-Ramírez.
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| Plastic cup made of polylactic acid in one of the ETH Zurich canteens © Bo Cheng/ETH Zurich |
Plastic cup made of polylactic acid in one of the ETH Zurich canteens © Bo Cheng/ETH Zurich
Catalysis scientist, Esben Taarning
from Haldor Topsoe in Denmark, comments on the advantageous results
this research offers: ‘Selective conversion of bio-based feedstocks to
chemicals is often complicated by the high cost associated with
fermentation techniques. This work elegantly illustrates the potential
there is in combining biological conversion with chemocatalytic
conversion in order to lower the overall processing costs.’
Pérez-Ramírez
considers the interdisciplinary nature of this research to be central
to their 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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