Some quick numbers tell us that global polyethylene production is around 80 million metric tons per year. Where does most of it end up? Take a guess. Separating and recycling plastics isn't always possible or economically viable, but there is another option, which is to transform them into fuel. That's the proposal from a group of Chinese scientists, who anticipate a selective and efficient degradation of polyethylene into liquid fuels and waxes under reasonably practical parameters.
Every now and then some article declares landfills as "the energy sources of the future", and if we think about it for a moment, it's not crazy. Certain countries (Sweden is the first one that comes to mind) have reached such high levels of recycling and "waste-to-energy" conversion that they must import garbage from other places, but the rest have a real challenge ahead.
One of the most frequently cited obstacles is separation. Not all garbage is the same, and this applies in a very special way to plastic, yet most of it falls under the shadow of polyethylene. I say "under the shadow" because polyethylene is a fairly generic term these days, thanks to the number of variants that exist. So, how do we degrade polyethylene? After all, it can remain for decades (at minimum) in a landfill...
How the process works
A group of Chinese scientists from the Chinese Academy of Sciences together with a chemist from the University of California (Irvine) published an extensive study on a degradation technique capable of converting polyethylene into liquid fuels and waxes under conditions reproducible in any processing plant. A combination of light alkanes and two catalytic processes (the first with an iridium complex, and the second using rhenium) puts polyethylene through a cycle of 96 hours at an average of 175 degrees Celsius until achieving complete degradation, and according to different adjustments (mainly reaction time and temperature), obtaining liquid fuels at diesel level or waxes with industrial applications.
It is a more efficient process compared to other previous attempts, however, the graphs accompanying the study indicate that samples on the order of milligrams were used, and in solutions of this type, scale is everything. To that we must add the involvement of rhenium and iridium, two of the rarest, and by extension most expensive, metals on the planet, with constant demand in dozens of fields. The chemistry revealed by the study is excellent, but there is surely room for optimization.
