Activated Carbon Helps Recycle Plastics into Aviation Fuel

WSU Researchers Melt Waste Plastics with Carbon Catalyst to Produce Jet Fuel

Scientists at Washington State University have described a new way to recycle plastic waste products into jet fuel in a paper published in the journal Applied Energy.

From

WSU associate professor Hanwu Lei, left, and his team, in the Bioproducts, Sciences and Engineering Laboratory.

Scientists at Washington State University (WSU) have described a new way to recycle plastic waste products into jet fuel in a paper published in the journal Applied Energy.

WSU’s Hanwu Lei and colleagues melted plastic waste at high temperature with activated carbon, a processed carbon with increased surface area, to produce jet fuel.

“Waste plastic is a huge problem worldwide,” said Lei, an associate professor in WSU’s Department of Biological System Engineering. “This is a very good, and relatively simple, way to recycle these plastics.”

How it works
In the experiment, Lei and colleagues tested low-density polyethylene and mixed a variety of waste plastic products, like water bottles, milk bottles, and plastic bags, and ground them down to around three millimeters, or about the size of a grain of rice.

The plastic granules were then placed on top of activated carbon in a tube reactor at a high temperature, ranging from 430 degree Celsius to 571 degrees Celsius. That’s 806 to 1060 degrees Fahrenheit (571°C). The carbon is a catalyst, or a substance that speeds up a chemical reaction without being consumed by the reaction.

“Plastic is hard to break down,” explained Lei. “You have to add a catalyst to help break the chemical bonds. There is a lot of hydrogen in plastics, which is a key component in fuel.”

Once the carbon catalyst has done its work, it can be separated out and re-used on the next batch of waste plastic conversion. The catalyst can also be regenerated after losing its activity.

After testing several different catalysts at different temperatures, the best result they had produced a mixture of 85 percent jet fuel and 15 percent diesel fuel.

Environmental impact
According to the Environmental Protection Agency, landfills in the U.S. received 26 million tons of plastic in 2015, the most recent year statistics are available. China has recently stopped accepting plastic recycling from the U.S. and Canada.

The researchers noted conservative estimates by scientists which say that at least 4.8 million tonnes of plastic enters the ocean each year worldwide. They said that not only could this new process reduce that waste, very little of what is produced is wasted.

“We can recover almost 100% of the energy from the plastic we tested,” said Lei. “The fuel is very good quality, and the byproduct gasses produced are high quality and useful as well.”

He added that the method for this process is easily scalable. It could work at a large facility or even on farms, where farmers could turn plastic waste into diesel.

“You have to separate the resulting product to get jet fuel. If you don’t separate it, then it’s all diesel fuel,” concluded Lei.

The work was funded by the Agriculture and Food Research Initiative Competitive Grant no. 2014-38502-22598, 2016-67021-24533, 2018-67009-27904 from the National Institute of Food and Agriculture, United States Department of Agriculture.

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