Plastic is anathema to many among the eco-conscious — but what if manufacturers could stop making so much of it from oil and start making more of it from plants?
In a study in the journal Science, researchers in the Netherlands say they have developed a class of iron catalysts that help turn plant material — such as fast-growing trees and certain grasses — into the chemical building blocks used to make plastic products, drugs and even cosmetics.
Plastic typically is made from a crude oil derivative and therefore depends on Earth's finite oil supplies. But plant material can also yield plastics if it is burned, producing a mixture of hydrogen and carbon monoxide known as synthesis gas. In the presence of a catalyst, typically iron-based, the so-called syngas yields lower olefins, which form plastic when they're chemically strung together.
But today's catalysts aren't very effective and produce a lot of methane as a byproduct, which has to be separated from the mix. The reaction also creates carbon "dust" that can clog the equipment.
A team led by study senior author Krijn P. de Jong, who specializes in inorganic chemistry at Utrecht University in the Netherlands, began chemically fiddling with different catalysts to see whether they could create ones that worked better.
They found that an iron-based catalyst worked best when it consisted of much smaller grains — 20 nanometers, as opposed to a more typical size of 500 nanometers — and when the grains were kept evenly spaced from one another instead of clustering together.
They also found — by pure luck — that adding a smidgen of sodium and sulfur improved the catalyst's effectiveness too. They made this discovery because a chemical they had used to accelerate the catalyst's reactions was inadvertently contaminated with sodium and sulfur.
"You might call it serendipity," De Jong said.
This new, improved catalyst yielded about 50% more lower olefins than conventional catalysts do — consisting of approximately 60% of final products by carbon weight compared with 40%, give or take — and less natural gas.
The system isn't perfect, said Abhaya Datye, a professor of chemical engineering at the University of New Mexico in Albuquerque who was not involved in the study, which was released Thursday. Even though it produces relatively more lower olefins and less natural gas, "it's not night and day."
"They may get up to 60% ... but then you have to deal with the other 40% too," Datye said.
The ultimate goal, he said, would be to create a catalyst that turns all of the syngas into lower olefins.
Also, the researchers have not yet used the catalyst all the way through from wood- or grass-burning to plastic formation, said Burtron Davis, a chemist at the University of Kentucky who was not involved in the study. The catalyst addresses just one stage of a complicated and potentially expensive process, he said.
"It's a useful scientific presentation," he said. "Whether it is economical would depend on a number of issues."