The race to turn plastic waste into useful fuel is increasingly important, as the world simultaneously tries to reduce pollution and find new sources of energy. New work from China shows a laboratory method that can convert plastic waste and hard-to-degrade plastics into hydrocarbons suitable for jet fuel, with high liquid-phase yields.
The research was conducted by scientists from Fudan University in collaboration with the Shanghai Advanced Research Institute. The process is based on the hydrogenolysis of polyolefin, a type of plastic that makes up a large part of global plastic waste. Polyolefins are found in everyday products such as bags, shampoo bottles and similar packaging.
The basic idea seems simple, because plastics and fossil fuels share a similar chemical basis: carbon and hydrogen. Plastic is created by connecting these atoms into very long and resistant polymer chains. Converting plastic back into fuel is therefore a kind of reverse process, in which those long chains are chemically cut into shorter molecules useful for fuel.
Plastic waste could become jet fuel thanks to a cheaper cobalt-nickel catalyst
The problem is that jet fuel requires hydrocarbons with 8 to 16 carbon atoms, or C8–C16 alkanes. Previous attempts to break down plastic often gave uneven results, because the bonds at the ends of the molecular chains were the easiest to break. Instead of liquid fuel, mostly gases such as methane were obtained, which is not what commercial aviation needs.
According to a report by the South China Morning Post, the Chinese team tried to solve this problem with a special catalyst that combines cobalt and nickel. The cobalt adjusts the electronic state of the nickel, thereby increasing the catalyst’s ability to activate hydrogen and selectively cut the internal carbon bonds in the plastic. The goal is to break down the long polymer chains into just the midrange of molecules needed for jet fuel, without the excessive fragmentation that gas creates.
Laboratory results show a liquid yield of 82.3 percent under relatively mild reaction conditions. In addition, the process achieved 79 percent selectivity toward C8–C16 alkanes, meaning that a large portion of the obtained liquid was in the range relevant for jet fuel.
The advantage of this approach is also in the choice of metal. Cobalt and nickel are much more available and cheaper than precious metals such as platinum or ruthenium, which were previously often used in similar chemical processes. This potentially lowers the cost of the technology if it is someday scaled up on an industrial scale.
The ecological gain can also be significant. According to a life cycle assessment, if the process is powered by renewable energy, greenhouse gas emissions could be up to 80 percent lower compared to conventional fossil fuel production.
However, the technology is not yet ready for practical use. What works in a laboratory vessel may not be easily transferred to large industrial reactors. An additional problem is the real plastic waste, which is often dirty and mixed with impurities. Such additives can quickly deactivate the metal catalyst, so reliable waste pretreatment systems will be key.
Plastics in aviation fuel for now remains in the phase of pilot projects and serious testing. The closest to a practical application are facilities such as Clean Planet Technologies’ facility in Kent, UK, designed to convert waste plastic into sustainable jet fuel. Until the moment when a passenger plane will actually take off on fuel made from bags and packaging, there is still a lot of engineering work to be done, reports Interesting Engineering.