Novel pyrolysis process is a win-win for the environment

In what seems like a win-win for a pair of pressing environmental problems, researchers at Rice University have discovered a new chemical technique for turning waste plastic into an effective carbon dioxide (CO₂) sorbent for industry.

In a paper in ACS Nano, Rice chemist James Tour and his team reported that heating plastic waste in the presence of potassium acetate produced particles with nanometer-scale pores that can trap CO₂ molecules. Such particles could be used to remove CO₂ from flue gas streams.

“Point sources of CO₂ emissions like power plant exhaust stacks can be fitted with this waste-plastic-derived material to remove enormous amounts of CO₂ that would normally fill the atmosphere,” said Tour. “It is a great way to have one problem, plastic waste, address another problem, CO₂ emissions.”

According to Tour, an existing process for pyrolyzing plastic known as chemical recycling produces oils, gases and waxes, but the solid carbon by-product is nearly useless. In contrast, by pyrolyzing plastic in the presence of potassium acetate, he and his team were able to produce porous particles that can hold up to 18% of their own weight in CO₂ at room temperature.

In addition, while typical chemical recycling doesn’t work for plastic wastes with a low fixed-carbon content, including polypropylene and high- and low-density polyethylene, the main constituents in municipal waste, those plastics work especially well for capturing CO₂ when treated with potassium acetate.

The researchers estimate that the cost of CO₂ capture from a point source like post-combustion flue gas would be $21 a ton, far less expensive than the energy-intensive, amine-based process commonly used to pull CO₂ from natural gas feeds, which costs $80–160 a ton.

Like amine-based materials, the sorbent can be reused. Heating it to about 75°C (167°F) releases trapped CO₂ from the pores, regenerating about 90% of the material’s binding sites.

Because the sorbent cycles at just 75°C, polyvinyl chloride vessels can be used instead of the expensive metal vessels that are required for amine-based materials. The researchers noted that the sorbent is also expected to have a longer lifetime than liquid amines, cutting downtime due to corrosion and sludge formation.

To make the sorbent material, the waste plastic is first turned into powder, and then mixed with potassium acetate and heated at 600°C (1112°F) for 45 minutes to optimize the pores, most of which are about 0.7nm wide. Higher temperatures lead to wider pores. Theis process also produces a wax by-product that can be recycled into detergents or lubricants, the researchers said.

This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.