Of the 400 million tons of plastic we produce each year, at least 14 million tons of it ends up in our oceans, posing an enormous threat to the environment and ocean biodiversity. Thousands of seabirds, sea turtles, seals and other marine mammals die each year from getting entangled in plastic or consuming it.
And it’s getting worse. Experts estimate that if these wasteful habits continue, plastic is expected to outweigh all the fish in the sea by 2050. But a group of engineers here in Massachusetts is working to change that by turning trash into treasure—or fuel.
Through their work, these scientists are spearheading a process to equip diesel ships with the ability to turn plastic garbage into fuel right on board the ship. Michael Timko, Professor of Chemical Engineering at Worcester Polytechnic Institute and one of the researchers on the team, joined GBH’s All Things Considered host Arun Rath to discuss their work. What follows is a lightly edited transcript.
Arun Rath: So, this just sounds unbelievable. Tell us about this idea, because I guess I understand that plastic comes from petroleum products. Is this somehow working in reverse?
Michael Timko: Yes, you could say that. Basically, the chemistry of it is that plastic molecules have the same bonds in them as fuel. They’re just much bigger molecules. You’re not going to put shredded up plastics into your gasoline and diesel engine, but the chemistry we can do breaks down some of those bonds to cut them down to the size that’s similar to what you would use in fuel.
Rath: I have to imagine it sounds like it would be complicated, sort of like taking flour and eggs out of a cake after you’ve baked it.
Timko: Actually, I think getting the eggs and flour back out of your cake is probably harder than what we’re doing, fortunately. The process consists of ... well, first, you would need to scoop up the plastics out of the ocean or somehow get them all together in one place, shred them up a little bit, and then the technology we’ve looked at in particular is called hydrothermal liquefaction—sometimes we call it HTL for short because hydrothermal liquefaction is a mouthful.
Basically, you pump them into a reactor that can hold the contents at elevated pressure, about 100 times what we experience here in the atmosphere, so 100 degrees Celsius. Under those conditions, it’s quite straightforward at that point for the molecules to start breaking to pieces, and the trick is to try to control it so they break about the right amount and not too much. That’s what we’re working on in this study.
Rath: How did this idea come about? Was this out of existing work in the field?
Timko: Absolutely. There are several inspirations. First of all, we knew the numbers that you mentioned at the top of the story, and to be clear, the amount of plastic—it’s not that it’s an eyesore in the ocean. It gets into the food chain and it impacts people’s lives, and so that really inspired us.
There are several firms that are looking at doing similar things. In other words, trying to clean up these plastics. One of them is called The Ocean Cleanup. Maybe you’ve heard of it. What we wanted to know was if we could make the process much more efficient by using the plastic itself to fuel the cleanup process.
In our field, there are a lot of folks that say, “Oh, definitely there is,” and some people that say, “No, no way, there isn’t.” So, we wanted to do a careful analysis to determine if, based on the technology that’s available in the lab today, it would be possible or not.
It turns out that once you start digging into it, things that you would hope would be known really well, like how much plastic there actually is or how densely it’s floating on the surface, these things just aren’t that well known. So we had to do a really careful analysis to understand to the best of our ability with all of these uncertainties if it was feasible or not.
Rath: What sort of fuel is the type of fuel that comes out of this process? Is it similar to gasoline or diesel? What’s it like?
Timko: It depends a lot on the plastic that you’re scooping up and then what any contaminants in there might be, like seaweed and things of that nature. The best estimates we have for the plastic that’s in these—what they call garbage patches, which accumulate in circulation zones in the oceans called “gyres”—the best-known data out there says it’s mostly polyethylene and polypropylene. When you break through this data, you can get a pretty good diesel fuel out of it if you do just the right amount. Not too hard, not too gently.
Rath: And that type of fuel would burn just like regular diesel?
Timko: There are questions remaining, especially if there are impurities and what those do to an engine. But the good news is that marine diesel engines are kind of built to take low-quality fuels, and so that’s one of the places where the chemistries that aren’t allowed in our road diesels have historically gone to the marine diesels. So, they are historically robust, tough engines that can take a beating and accept a lot of different types of fuel qualities.
Rath: This is a fairly brand new project that you’re developing as you go. Give us a sense of where you are right now and what the next steps are.
Timko: So, at this point in time, there’s been quite a bit of small-scale lab work at universities like WPI and others. And then, we’ve done our feasibility study, which was inspired actually by the pandemic, when we couldn’t get to our reactors during that lockdown. We decided to use our time instead to do what you could call a paper analysis of what was possible. That’s where we are.
Probably, the next step would be to look to scale up about a ton per day, do things on land and then push it out into the ocean step-wise.
Rath: Would this fuel require a particular kind of engine to run on?
Timko: That would depend a lot on what plastics we really encounter out in the field. That’s the other side of things that needs to get better; we just need to get better data on what plastics are actually available at the surface of the ocean to scoop up.
You might imagine, for example, that there’s a bunch of plastic water bottles out in the middle of the ocean. Those are made of a plastic called polyethylene terephthalate, or PET for short. It turns out there’s not too many plastic bottles out there. They just don’t make it—they’re probably too dense, they sink, these kinds of things.
Actually, you would think you’d know exactly what’s out there, but we don’t, and we need better data. Once we have that data, then we can test those mixtures on land, put them into engines and really verify not only that they run, but that they run for hundreds or thousands of hours. Because the last thing we want to do is have a ship stranded out there in the middle of the ocean, not able to return to port.