Researchers have developed a new class of materials that can readily and efficiently absorb carbon dioxide from a smokestack or even directly from the atmosphere. The substances can help alleviate problems associated with carbon dioxide emissions, like climate change and ocean acidification.

At the University of Southern California, scientists used a polymer called polyethylenimine (PEI) as the basis for their new materials, which offered several advantages over existing strategies to filter carbon. "It's very easy to prepare," explained Alain Goeppert, a senior research scientist at the Loker Hydrocarbon Research Institute at USC.

The polymer is coated with a substance called fumed silica in differing amounts to determine the optimal coating. "It's much easier than the synthesis of other adsorbers, for example metallic organic frameworks," said Goeppert. Adsorption refers to atoms sticking to a given material's surface, as opposed to absorption, where the atoms permeate the material.

"It's also cheap," he said, noting that PEI is available for sale commercially at low cost.

To collect carbon dioxide, Goeppert said the material can be packed into columns, which are then inserted into flues and chimneys in factories and power plants. The adsorber collects carbon dioxide as waste gases flow through it. When it becomes saturated, the PEI device is replaced.

The PEI materials also have a strong enough affinity for carbon dioxide that they can remove carbon dioxide directly from the air, where it is present in very low concentrations and factors like humidity impede other adsorbers.

Pushing to make material 'dirt cheap'
The nitrogen atom in the polymer forms a reversible link to carbon in the gas's presence. When the adsorber is heated above 100 degrees Celsius, it releases the carbon. This allows the material to be reused, but it also creates an easy way to collect and concentrate carbon dioxide.

The collected gas can then be put to work by converting it into fuel, according to G.K. Surya Prakash, a professor of chemistry at USC who conducted the study with Goeppert. He envisions an economy structured around recycling carbon instead of mining more fossil fuels and views PEI materials as a step in that direction.

"We are interested in CO2 capture because we think CO2 is the best source of carbon for mankind. As a chemist, I tell people, 'Hey, guys! CO2 is the solution,'" said Prakash. "Earth doesn't have an energy problem; the Earth has an energy carrier problem."

Nonetheless, it may still be some time before PEI materials see widespread use. "For CO2 applications, there still needs to be work done," said Prakash, who wants to improve the materials' durability and wants to drive their already low costs down further. "You need to make it dirt cheap" before PEI gains acceptance, he said.

Goeppert, Prakash and their collaborators, including Nobel laureate George Olah, published their findings in November last year in the Journal of the American Chemical Society. The trio also laid out their vision for synthetic fuels in "Beyond Oil and Gas: The Methanol Economy."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500