16. Dec 2014
Researchers make PLA monomer derived from glycerol
PLA is is one of bioplastics success stories. Due to its biodegradable properties, the material has gained wide acceptance in packaging and disposable appications, and its popularity continues to grow. The demand for PLA is constantly rising and has been estimated to reach about one megaton per year by 2020.
At ETH Zurich, a leading international university for technology, the research groups of professors Konrad Hungerbühler and Javier Pérez-Ramírez at the Institute for Chemical and Bioengineering have developed a new method to produce one of the monomers of PLA, namely lactic acid. The process is more productive, cost-effective and climate-friendly than sugar fermentation, which is the technology currently used. The new method’s greatest advantage is that it makes use of a waste feedstock: glycerol. In this procedure, glycerol is first converted enzymatically to an intermediate called dihydroxyacetone, which is further processed to produce lactic acid by means of a heterogeneous catalyst.
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”, says Merten Morales, a PhD student in the Safety and Environmental Technology group of professor Hungerbühler.
“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.”
The researchers of the Advanced Catalysis Engineering group of professor Pérez-Ramírez designed a catalyst with high reactivity and a long life span. 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. “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”, explains Pierre Dapsens, a PhD student in the Pérez-Ramírez group. 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.
The use of biodegradable plastic packaging made of polylactic acid (PLA) is spreading. Since this year, PLA cups are available also in the ETH canteens. (Photo: Bo Cheng / ETH Zurich)
All in all, compared to the fermentation route, the new technology reduces overall CO2 emissions by 20 per cent: per kilogram of lactic acid produced, 6 kilograms of CO2 are emitted compared to 7.5 kilograms using the conventional technology. Moreover, the lower overall cost of the new process resulted in a 17-fold profit growth, according to the researchers. “Our calculations are even rather conservative”, says Morales. “We assumed a glycerol feedstock of relatively good quality. But it also works with low-quality glycerol, which is even cheaper.” Thus, manufacturers could increase their profit even further.
“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”, concludes Dapsens.(KL)
Image taken from ETH website