Polylactic acid is a biodegradable plastic used primarily for packaging materials. In order to meet the rising demand for it, researchers have developed an environmentally friendly process for preparing large amounts of lactic acid from glycerol, which is itself a byproduct in the production of biodiesel.
[Translation by Dr. Nachmani Moshe]
Polylactic acid is a biodegradable plastic used primarily for packaging materials. In order to meet the rising demand for it, researchers have developed an environmentally friendly process for preparing large amounts of lactic acid from glycerol, which is itself a byproduct in the production of biodiesel.
Plastic waste is one of the main environmental problems today. Most types of plastic do not biodegrade, rather they crumble into smaller and smaller pieces while remaining a polymeric material. In addition, most types of plastic are made from petroleum, which is a rapidly dwindling resource. At the same time, there are promising alternatives to plastic, and one of them is the polylactic acid polymer (Wikipedia, PLA): it is a biodegradable material produced from renewable sources. Manufacturers use this polymer to make disposable cups and bags, and other packaging materials. The demand for this polymer is constantly increasing and it is estimated that it will reach a rate of one megaton per year by the year 2020.
The research group from the Zurich Institute of Technology (ETH), led by Professor Konrad Hungerbühler from the Institute for Biological and Chemical Engineering, is now presenting a new method for the production of lactic acid. The process is more productive, cheap and environmentally friendly than processes of sugar fermentation, the process used today to produce lactic acid. The biggest advantage of the new method lies in the fact that it utilizes a starting material that is usually thrown away - the substance glycerol.
Glycerol is a by-product in the production of first generation biofuels and as such its quality is not high since it contains residues of ash and methanol. "No one knows what to do with these large amounts of unclean glycerol," says one of the researchers. This waste material is becoming more and more common, with 3 megatons in 2014, a rate expected to increase to over 4 megatons in 2020. Due to its impurities, glycerol is not suitable for use in the chemical or pharmaceutical industry. Moreover, it does not burn well and is therefore not a good source of energy.
![Raw biodiesel contains significant amounts of glycerol (the dark layer at the bottom). [Image courtesy: Bo Cheng / ETH Zurich]](https://www.hayadan.org.il/images/content3/2014/12/ga-biodisel-500x441.jpg)
The utilization of this waste material by converting it into lactic acid is in itself an advantage that makes the new method more environmentally friendly. In this method, glycerol is first converted with the help of enzymes into an intermediate substance known as dihydroxyacetone, which itself is then converted into lactic acid using a chemical catalyst. The catalyst used has high reactivity and a long lifetime. It consists of a microporous mineral, zeolite, whose internal structure enables effective chemical reactions within the pores.
If you take into account the energy saved thanks to the use of glycerol that is not thrown into waste and the improved production, the new method reduces the total carbon dioxide emissions by 30% compared to fermentation: in the new method, for every kilogram of lactic acid produced, an amount of 6 kg of carbon is emitted dioxide, this compared to 7.5 kg under normal methods. "Although most of the bio-plastic companies are currently located in the USA, the process is quite simple and can be applied in other countries that produce biofuel and receive the glycerol by-product," concludes the lead researcher.
