May 21—Researchers at Washington State University say they have found a novel, cost-effective way to convert recyclable plastics into jet fuel and other valuable products — and in a fraction of the time current plastics recycling methods take.
Led by WSU associate professor Hongfei Lin and graduate student Chuhua Jia, the project seeks to lessen the cost and environmental footprint of plastics recycling.
Lin said this is achieved through a process that combines a catalyst and solvent with recyclable polyethylenes in a pressurized environment at about 220 degrees celsius — or about 430 degrees fahrenheit.
"For our process, we actually combine two effects, so the catalytic effect and the solvent effect," Lin said. "It makes some synergy so that we can better control the activity related to the product that we want to produce."
Polyethylene is one of the most common plastics in the world, with tens of millions of tons of the stuff produced annually. The product is used in everything from shampoo bottles to plastic shopping bags. Polyethylenes and other similar polymers are essentially huge chains of linked hydrocarbon molecules, Lin said, which are held together with hundreds of thousands of carbon-to-carbon bonds. He said with the right process, these can be broken down to become shorter chains like jet fuel.
Lin said the solvent helps by penetrating the matrix contained within polyethylene, which makes it more susceptible to decomposition and degradation. The catalyst is then used to cleave these carbon-carbon bonds apart into smaller chains, he said.
By adjusting certain parameters like the amount of pressure the solution is under, the amount of catalyst used or the type of solvent, Lin said they can attenuate this process to create other, high-value hydrocarbon products like diesel fuel and lubricants.
"All of this plays a role. We can find the optimal combination to design our process to produce one particular hydrocarbon," Lin said.
Jia said this process eliminates the risk of cast-away plastic products from persisting in the environment and shedding microplastics into the environment, where they can eventually end up in the food chain and potentially affect human health. Some reports have found humans ingest about a credit card's worth of microplastic each year. The effects these particles have on human health is still largely unclear.
Jia said their process not only eliminates the opportunity for this waste to enter the environment, it also reduces the time and energy involved in processing recycled plastic. He said plastic typically must be processed at temperatures around 400 degrees celsius — about 750 degrees fahrenheit — and the process usually takes around 24 hours.
Jia said their process, by comparison, offers significant energy savings.
"With our process, with the addition of solvent, we can decrease the temperature almost in half, so here, our optimal temperature is 220 (degrees celsius)," Jia said. "Meanwhile, compared with other technologies, we can also realize a much higher reaction rate ... the reaction time can be shortened to only one hour."
Now that they've proved their process works, Jia said he and Lin's next challenge will be to demonstrate it can be efficiently deployed at an industrial scale, which he thinks is eminently possible.
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