Chinese chemists have devised a system to turn polyethylene into liquid fuel, paving the path for a new way to get rid of plastic waste instead of dumping it into the ocean or burning it. This seems to be as promising as the recent breakthrough involving the discovery of an Ideonella sakaiensis strain of bacteria which can eat such waste, the only byproducts of the process being two eco-friendly monomers.
Organic chemist Zheng Huang, and his colleagues have been working for years on the new method of converting plastic into diesel fuel. Their finding involves breaking down polyethylene (PE) at 150° Celsius under argon in a sealed vessel, in a mixture containing an organometallic catalyst. The process currently takes about 3 days transform the PE into oil and wax products.
The conversion mainly works as a two-part system called CAM – one catalyst is utilized for alkane dehydrogenation and a second catalyst comes into play for olefin metathesis. Alkane metathesis helps tear the bonds holding together the PE structure. The molecular pincer-type iridium complex is necessary to dehydrogenate the PE and the light alkane.
The unsaturated PE and light alkene that is obtained from this process undergo rhenium-catalyzed cross metathesis. The resulting olefins are then hydrogenated by the iridium catalyst to produce saturated alkanes. Polyethylene bags, bottles, films and more can be recycled by using the CAM method. But there are two main hurdles to cross first.
The iridium needed for converting plastic into fuel is expensive to obtain and thus asks to be replaced by a cheaper alternative if possible. Secondly, Huang and his team still have to find a way to scale up the process from grams to tons so that it’s usable beyond the laboratory environment.