Two Birds, One Stone: Researchers Turn Plastic into Carbon Capture Material

Humanity is doing almost incalculable damage to the planet, seen most prominently in the rapid build-up of carbon dioxide in the atmosphere. A team of researchers from Rice University say it may be possible to address this crisis with an unlikely resource: plastic. And not just any plastic. The researchers took hard-to-recycle plastic and turned it into a material that can soak up excess carbon dioxide from the atmosphere. It’s not a magic bullet, but it could be a step in the right direction.

The energy industry has been talking about carbon capture technology for years, but there has been little progress in making such technologies viable. Current methods rely on amine-based processes, which can cost upward of $80-120 per ton of carbon extracted. The work at Rice University is still in the laboratory stage, but the team believes this technology could be useful in industry, for example to remove carbon dioxide from flue gas streams.

At the heart of the research is a new approach to pyrolyzing plastic. That simply means decomposing a material with heat. Current methods of pyrolyzing plastic result in oil, gas, and wax waste products, and the carbon product is essentially useless. The team developed a method of pyrolyzing plastic in the presence of potassium acetate. It starts with pulverized plastic, which is mixed with the potassium acetate at a specific ratio. The mixture is then heated to more than 1,000 degrees Fahrenheit for 45 minutes.

This produced a carbon-based material with 0.7-nanometer pores (see top image), giving it impressive absorbance capacity. You can even reset the “sorbent” material by heating it to a much lower temperature of 167 degrees Fahrenheit (about 75 C). This frees up 90 percent of the material’s carbon dioxide binding sites.

Without any additional modification, the porous carbon particles can soak up 18 percent of their weight in carbon dioxide at room temperature. Most of the plastics people throw out have low fixed carbon content, like polypropylene and polyethylene. It’s not possible to pyrolyze these materials to produce sorbent materials. However, it’s the opposite when these plastics are treated with potassium acetate — they are among the best sources to produce these microscopic carbon sinks. The researchers estimate that it would only cost about $21 to remove a ton of carbon from the air using this material. The team also believes the oil byproducts from this process could be recycled into lubricants or detergents.

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