Rice University researchers have developed a chemical technique that converts waste plastics into an effective carbon dioxide (CO2) sorbent for industry.
Rice chemist James Tour and co-lead authors Rice alumnus Wala Algozeeb, graduate student Paul Savas and postdoctoral researcher Zhe Yuan reported in ACS Nano that heating plastic waste in the presence of potassium acetate produced particles with nanometer-scale pores that trap carbon dioxide molecules.
These particles can be used to remove CO2 from flue gas streams, they reported.
“Point sources of CO2 emissions, such as power plant tailpipes, could be outfitted with this plastic-derived material to remove massive amounts of CO2 that would normally fill the atmosphere,” Tour said in a statement. “It’s a great way to tackle one problem, plastic waste, another, carbon emissions.”
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A current process to pyrolyze plastic produces oils, gases and waxes, but the carbon byproduct is nearly useless, Tour said, while pyrolyzing plastic in the presence of potassium acetate produces porous particles that are up to 18 percent of their own weight in CO2 at room temperature. .
While typical chemical recycling will not work for low solid carbon polymer wastes to generate CO2 sorbent, including polypropylene and high and low density polyethylene (the main components of municipal waste), these plastics work especially well for capturing CO2 when treated with potassium acetate .
The lab estimated that the cost of capturing carbon dioxide from a point source such as flue gas after combustion would be $21 per ton, which is much less expensive than the amine-based process used to extract carbon dioxide from natural gas feeds, which costs $80. . $160 a ton.
Like amine-based materials, the sorbent can be reused. Heat it to about 75OC releases retained carbon dioxide from the pores and regenerates about 90 percent of the material’s binding sites.
Because it runs at 75OC, polyvinyl chloride drums are enough to replace the expensive metal drums normally needed. The researchers noted that the sorbent is expected to have a longer life than liquid amines, reducing downtime due to corrosion and sludge build-up.
To make the material, waste plastic is turned into powder, mixed with potassium acetate and heated to 600OC for 45 minutes to optimize the pores, most of which are about 0.7 nm wide. Higher temperatures led to wider pores. The process also produces a wax byproduct that can be recycled into detergents or lubricants, the researchers said.