Start with size reduction

Each day, Tigard, Oregon-based Agilyx Inc. converts about 10 tons of polystyrene (PS) scrap into styrene oil via pyrolysis. But before this complex chemical process can begin, basic size reduction is a key step to ensure that a reliable flow of feedstock makes it to the reactor.

Agilyx Chief Executive Officer Joe Vaillancourt says his company receives PS scrap from about 500 suppliers. “We’ve got customers all over the country wanting to give us feedstocks,” he says. “The physical cost of feedstock is obviously important to the overall economic profile of the system. It’s sort of less to do with size than it is to do with weight. So, we’re always trying to find more effective and efficient ways to aggregate and transport [material] … so that we’re shipping lower volume, heavier weight.”

The suppliers and types of scrap vary widely. The material is collected at drop-off sites or shipped by businesses, municipalities, schools and waste management companies. It includes foam food trays, egg cartons, clamshell packaging, agricultural seedling trays, CD cases, utensils and lids for coffee cups.

To reduce transportation costs, some of Agilyx’s suppliers densify material, such as expanded PS (EPS), before shipping it to the pyrolysis treatment facility.

“Once we have the material, we do tend to try to size-reduce it for the purposes of creating a more dense material to feed into the system because this is, after all, a thermal conversion process, and your last energy balance is really a bit sensitive to how much you’re putting in [and] how fast,” Vaillancourt says. “And so, the more you can control the average density, the better. And one of the ways to do that, obviously, is to size-reduce,” he explains.

Agilyx uses a shredder from SSI Shredding Systems, Wilsonville, Oregon, to process the PS scrap, usually chopping it to a size ranging from 0.5 inch to 1 inch. When appropriate, it also densifies material at its facility.

“If you came to our facility, you’d see hundreds and hundreds of Super Sacks that look like chopped-up rocks. And that’s typically sort of the size that we manage. It approximates the density that we’re looking for,” Vaillancourt says.

The company currently uses some commercial densifiers that are fed by top-loaded shredders. The process involves applying heat to polymers such as EPS so they melt and can be formed into a block through compaction. “Whether we have foam or rigids, all feedstock is ultimately shredded before pyrolysis,” he says.

But, he says, existing densification systems aren’t really the best match for the company’s needs.

“Most densifiers we have used have been designed for discrete materials,” he says. “Agilyx accepts and processes a wide variety of materials, and we have not found a unit versatile enough to process all of these slipstreams with the same unit.”

The company is developing its own line of densifiers in-house, but he says he’s unable to provide details about the system it is creating.

While size reducing material isn’t central to pyrolysis, Vaillancourt says, “Our system does require certain densities of material … to optimize some of the chemical reactions.”

Vaillancourt stresses the importance of knowing what’s in the feedstock before it’s cut down to size. Understanding what fillers are in the material is particularly important. Each heavy-duty bulk bag of material is marked according to customer, date and chemical profile. “If you were to densify material without knowing what’s in it, you’d almost have no way to predict what it’ll be converted to. So, all of that work happens before we densify,” he says.

Using a thermal chemical process, Agilyx turns the PS scrap into eight chemical precursors used in plastics and fuels, including styrene monomers and an oil. Vaillancourt says the process is distinct from other pyrolysis plants. “Agilyx has developed a very sophisticated set of aggregation, testing, densification and preprocessing procedures to prep the PS material so that we can convert it consistently to a high-quality product specification,” he says, adding that the procedures are proprietary.

The author is a correspondent for Plastics Machinery Magazine and can be emailed at agerlat@plasticsmachinerymagazine.com.