Turning waste plastic into fuel isn’t a new idea. Many researchers have achieved it through a process called pyrolysis, which involves heating plastic to between 300º C and 900º C in an oxygen-free environment. This breaks the substance down into fuel, along with some additional chemicals. Hongfei Lin, associate professor with The Gene and Linda Voiland School of Chemical Engineering and Bioengineering at WSU, thinks that he and his team have discovered a way to make the process more efficient and environmentally friendly. //

Pyrolysis is an old technology, Rollinson told Ars. It was used to make things like creosote and methanol from wood, prior to the widespread use of petrochemicals, he said. Since the 1950s, attempts have been made to use the process on plastics. So far, it has not worked out, according to Rollinson.

Though the paper says the process is high-efficiency, it’s likely not, Rollinson says, as it requires a good deal of hydrogen pressure. Reaching the necessary pressure requires a lot of energy. Making and storing hydrogen also takes a lot of energy, reducing any green benefits. He said that the experiment was only in a laboratory setting. It would require a far greater amount of hydrogen and energy to pressurize it, if introduced at a commercial scale.

Further, Rollinson noted that the catalyst and solvents used would also need to be scaled up for larger amounts of plastics. Hexane, the solvent, is toxic, explosive, and environmentally harmful if released into the wild, he added. There’s also an energy input in the process of making these chemicals. In an email to Ars, Lin acknowledged that solvent recovery and reuse would add costs, but the technology itself would work to keep costs low. All the same, Rollinson has his doubts.

“No way it’s a go-er at all,” he said. “For science’s sake, it’s quite interesting. But as a practical answer to plastic … it’s not workable.” //

RindanArs Tribunus Militumet Subscriptorreply2 days agoignore user
SharpieFiend wrote:
If we want to reduce the amount of oil that gets pumped out of the ground then something needs to be done about jet fuel - it's a major demand driver. Even if the process is less efficient than refining crude it can still be worth while.

Sure, but why "recycle"? We know how to make jet fuel. We can make fossil fuels with no problem. The Germans were doing it during World War II when they couldn't important gas, and we have surely only gotten better at the process. There is a reason why we don't do this though; it isn't worth the cost. The amount of energy you have to dump in isn't worth it. It's like using electrolysis for to get hydrogen. Yeah, you can technically do that, you just have to accept a massive loss of energy and cost. The process that we end up using for carbon neutral jet fuel is going to end up being whatever is cheapest at scale, and we are only going to use that once the cost of jet fuel rises so that it

We don't need to recycle things into jet fuel; we need a process that is scalable and the least energy intensive possible. If starting from a plastic component gets us there, great, but recycling shouldn't be the goal, just a happy side effect if that's the path that ends up being the cheapest. I'm skeptical that this is the cheapest. We are far better off to bury our plastic in the ground and then make carbon neutral jet fuel, then to spend extra energy to recycle plastic into jet fuel. Plastic in a landfill isn't hurting anyone. Using a bunch of energy on the other hand, especially with our current electricity mix, is definitely hurting someone.

Maybe I'm being too skeptical, but this seems like a gimmick to me. We don't need to recycle plastic into jet fuel, we need jet fuel, and maybe if someone can find something energetically worthwhile, a separate method of recycling plastic. It's okay if those are two independent and completely different steps, especially if it takes less energy. //

WickwickArs Legatus Legionisreply2 days agoReader Favignore user
I wish people would get off the idea that high-temperature processes must be low-efficiency. There's nothing that says one cannot have heat exchangers used to preheat products headed to the pyrolysis chamber. This isn't a combustion cycle. There's no requirement to reject heat to the environment to make it work.

The only thermodynamic limit is that the fuel probably has lower entropy than the plastic (though that's not a given). If it does, you have to invest in some amount of energy to execute that conversion.