Catalytic conversion of plastics to jet fuel

ENGINEERS at Washington State University (WSU) have developed a novel microwave-assisted catalytic process to turn waste polyethylene into jet fuel-range alkanes.

Plastic use continues to grow around the world but recycling and reuse options are limited at best. The idea of converting them into useful fuels and chemicals is attracting increasing interest. Researchers at WSU, led by Shulin Chen, note that the demand for jet fuel is predicted to rise by 27% more than vehicle fuel over the next decade, and say that their novel process to turn plastics into different grades of jet fuel is a “clear breakthrough”.

The process has two stages. The first stage is catalytic microwave degradation. The researchers place low density polyethylene (LDPE) pellets, which are placed in a quartz flask in a microwave oven and heated to 350?C for 20 minutes until completely vaporised. The gases are then passed over a packed bed reactor filled with an activated ZSM-5 zeolite-based catalyst, with the temperature kept at 375?C.

The raw hydrocarbons are largely unsaturated, so the second phase is a hydrogenation stage, using a Raney nickel catalyst. The researchers mix the hydrocarbons in n-heptane and load the mixture into a sealed reactor with the catalyst. The hydrogenation reaction takes two hours at 200?C.

Using different ratios of catalyst gives slightly different results. Using a catalyst-to-feed mass ratio of 0.1 in the first degradation stage gives a higher liquid hydrocarbon yield of 66.18%. After the second hydrogenation phase, these hydrocarbons turn into fuels equivalent to the JP-5 Navy grade of jet fuel, used for aircraft on aircraft carriers. Using a catalyst to feed mass ratio of 0.2 in the degradation stage gives a lower liquid hydrocarbon yield of 56.32%, but when hydrogenated, these hydrocarbons are converted into fuels equivalent to the higher energy density jet fuel grades of RJ-5 and JP-10, which are used for military purposes.

The researchers say that their new process is a “novel and feasible pathway” for refineries to produce different grades of jet fuels.

Fuel DOI: 10/btnz