Novel technique converts plastic waste into jet fuel

The researchers at Washington State University (WSU) said they converted 90 per cent of plastic to jet fuel and other valuable hydrocarbon products within an hour at moderate temperatures, and fine-tune the process to create the products that they want.

“In the recycling industry, the cost of recycling is key,” said Hongfei Lin, associate professor in the university’s School of Chemical Engineering and Bioengineering. “This work is a milestone for us to advance this new technology to commercialisation.”

In recent decades, the accumulation of waste plastics has caused an environmental crisis, polluting oceans and pristine environments around the world. As these plastics degrade, experts have found that tiny pieces called microplastics have entered the food chain and have become a potential, if unknown, threat to human health.

Plastics recycling, however, has been problematic. The most common mechanical recycling methods melt the plastic and re-mould it, but that lowers its economic value and quality for use in other products. Chemical recycling can produce higher quality products, but it has required high reaction temperatures and a long processing time, making it too expensive and cumbersome for industries to adopt. Because of its limitations, around 9 per cent of plastic in the US is recycled every year.

The WSU researchers developed a catalytic process to convert polyethylene to jet fuel and high-value lubricants. Polyethylene, also known as #1 plastic, is the most commonly used plastic, used in a vast variety of products from plastics bags, milk jugs and shampoo bottles to corrosion-resistant piping, wood-plastic composite lumber, and plastic furniture.

For the process, the researchers used a ruthenium-on-carbon catalyst and a commonly used solvent. With this, they were able to convert about 90 per cent of the plastic to jet fuel components or other hydrocarbon products within an hour at a temperature of 220°C, which is more efficient and lower than temperatures typically used in such processes.

Graduate student Chuhua Jia was surprised to see just how well the solvent and catalyst worked. “Before the experiment, we only speculated but didn’t know if it would work,” he explained. “The result was so good.”

Adjusting processing conditions, such as the temperature, time or amount of catalyst used, provided the critically important step of being able to fine-tune the process to create desirable products, Lin added. “Depending on the market, they [experts concerned] can tune to what product they want to generate. They have flexibility. The application of this efficient process may provide a promising approach for selectively producing high-value products from waste polyethylene.”

With support from the Washington Research Foundation, the researchers are working to scale up the process for future commercialisation. They also believe their process could work effectively with other types of plastics.