Polylactic acid is a degradable plastic used mostly for packaging. To meet the rising demand, ETH researchers have developed an eco-friendly process to make large amounts of lactic acid from glycerol, a waste by-product in the production of biodiesel.
Waste product of biofuel manufacturing
Making use of this waste feedstock by converting it into lactic acid already constitutes an advantage that makes the new method more eco-friendly. 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.
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.Industrial processes are often turned “sustainable” simply by switching to a renewable resource. “However, taking the whole process into account – from the source of the feedstock to the final product and including waste management – you will often find that a supposedly sustainable production method is not necessarily more sustainable than the conventional one”, adds Cecilia Mondelli, a senior scientist in the Advanced Catalysis Engineering group who is also involved in the study.