AsianScientist (Jul. 6, 2016) – We have a serious plastic problem. Plastic waste is fast clogging up landfills, poisoning marine life and polluting the oceans. Worse still, plastic does not degrade easily, and will remain on Earth for hundreds of years.
So what is being done about this international environmental crisis? Scientists are on it: Asian Scientist Magazine previously reported on plastic-munching bacteria that uses a common type of plastic polymer as its primary source of carbon for growth. Now, researchers in China and the US have developed a method to convert plastic waste into useful liquid fuels or chemical feedstocks. The research was published in Science Advances.
Most plastics are polymers made up of various structural combinations of carbon and hydrogen. Led by corresponding author Professor Huang Zheng from the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, and Professor Guan Zhibin from the Department of Chemistry at the University of California, the researchers developed a cross-alkane method that can degrade polyethylene (PE), the most widely-used synthetic polymer in the world, with very cheap and widely-available light alkanes. These alkanes, which are hydrocarbons, were initially developed by scientists from Rutgers University and the University of North Carolina in the US.
Thanks to the large amount of light alkanes used, the multi-step catalytic process degrades the long chain length of PE multiple times into short hydrocarbons suitable for transportation oils.
There are several advantages to this process: the resulting fuel solution has low viscosity, avoiding the mass and heat transfer issues encountered in conventional catalytic processes involving PE. The catalysts used are compatible with various plastics, and therefore, common plastic waste such as post-consumer bottles, bags, and films could be converted into valuable chemical feedstocks without any pre-treatment. Furthermore, it requires much milder temperatures than most pyrolysis, or high-temperature decomposition, methods.
“Our process can be carried out at 150-200°C, which is much lower than the temperature needed for the pyrolysis process—typically over 400°C,” Huang told Asian Scientist Magazine.
“Furthermore, the process can be used to degrade various types of PE, including high-density PE, low-density PE, linear low-density PE and polypropylene.”
Co-authors Jia Xiangqing, Huang Zheng and Qin Chuan from the China-based team. Credit: Huang Zheng
Importantly, the degradation can be controlled by the catalyst structure and reaction time to produce different liquid products. The researchers believe that after some purification processes and the addition of some additives, these products may one day be used as diesel fuel.
As this point, the team is focusing on improving the catalyst’s efficiency and reducing its cost, according to Huang.
The article can be found at: Jia et al. (2016) Efficient and Selective Degradation of Polyethylenes into Liquid Fuels and Waxes under Mild Conditions.
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Copyright: Asian Scientist Magazine; Photo: Lisa Risager/Flickr/CC.
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