Demand for PLA degradable plastic to reach one megaton per year by 2020

The research team, of ETH professors Konrad Hungerbühler and Javier Pérez-Ramírez at the Institute for Chemical and Bioengineering, claim the process is more productive, cost-effective and environmentally-friendly than sugar fermentation, the current method.

Can surpass sugar fermentation

The lactic acid is made from glycerol, a waste by-product in the production of biodiesel.

“Without the assessment and comparison with the conventional method, we might have been happy with an initial catalyst design used for our study, which turned out to be less eco-friendly than fermentation​”, said Pierre Dapsens, a PhD student in the Pérez-Ramírez group.

“Although today’s major bioplastic companies are based in the US, the process is relatively simple and could be implemented in other countries that produce biofuel and the by-product glycerol​.

“By improving several aspects of the catalyst design, the researchers were finally able to surpass sugar fermentation both from an environmental and an economic point of view​.”

In the study, researchers of the Advanced Catalysis Engineering group of professor Pérez-Ramírez designed a catalyst with high reactivity and a long life span.

Reduces CO₂​ emission by 20%

It consists of a microporous mineral, a zeolite, whose structure facilitates chemical reactions within the pores. The close collaboration between the two research groups allowed the catalyst to be improved step by step while at the same time performing the life cycle assessment of the procedure as a whole.

Taking into account the energy saved by using the waste feedstock glycerol and the improved productivity, the procedure reduces the overall CO₂​ emission by 20% compared to fermentation: per kilogram of lactic acid produced, 6 kilograms of CO₂​ are emitted with the new method compared to 7.5 kilograms with the conventional technology.

By lowering the overall cost of the process, the researchers calculated a 17-fold increase of the profit possible by using the alternative process.

Plastic waste is becoming an environmental concern because most of it does not biodegrade but breaks up into smaller pieces and some are made from oil, a dwindling resource.

One of the alternatives is PLA which is used in disposable cups, bags and other sorts of packaging. The demand for PLA is constantly rising and has been estimated to reach about one megaton per year by 2020.

Glycerol waste

Glycerol is a by-product in the manufacturing of first-generation biofuels and as such is not high-grade but contains residues of ash and methanol.

“Nobody knows what to do with this amount of waste glycerol​,” said Merten Morales, a PhD student in the Safety and Environmental Technology group of professor Hungerbühler.

“This waste substance is becoming more and more abundant, with 3 megatons in 2014 expected to increase to over 4 megatons by 2020. Because of its impurity, glycerol is not suitable for the chemical or pharmaceutical industry.​

“It does not burn well and is not a good energy source. Normally, it should go through waste water treatment, but to save money and because it is not very toxic, some companies dispose of it in rivers or feed it to livestock. But there are concerns about how this affects the animals​.”

Making use of this waste feedstock by converting it into lactic acid already constitutes an advantage that makes the method more eco-friendly.

Glycerol is first converted enzymatically to an intermediate called dihydroxyacetone, which is further processed to produce lactic acid by means of a heterogeneous catalyst.

SOURCE:​ ETH Zurich

PUBLISHED:​November 5, 2014. DOI: 10.1039/C4EE03352C​

TITLE:​ Environmental and economic assessment of lactic acid production from glycerol using cascade bio- and chemocatalysis. Energy & Environmental Science,

AUTHOR(S):​ Morales M, Dapsens PY, Giovinazzo I, Witte J, Mondelli C, Papadokonstantakis S, Hungerbühler K, Pérez-Ramírez J.