Energy

Materials Could Capture CO2 and Make It Useful

Novel molecular structures are a first step toward economical carbon capture at a wide scale.

A viable technology for economical carbon capture would be a huge step in reducing greenhouse gas emissions.

Although progress has been made in limiting carbon emissions in some countries, particularly in Europe and North America, it’s clear that finding ways to capture carbon dioxide from smokestacks—or from the atmosphere—is becoming increasingly imperative. Available systems dramatically increase the cost of electricity from plants equipped with the technology. And what to do with all that carbon dioxide after it’s separated remains problematic.

The intricate, highly porous structure of covalent organic frameworks makes them uniquely suited for capturing carbon dioxide.

Now a team of scientists at Lawrence Berkeley National Laboratory and the University of California, Berkeley, have devised a method that uses super-porous molecular structures known as covalent organic frameworks, with catalysts to convert the carbon dioxide to carbon monoxide, which can be used in making a range of materials including fuels, plastics, and even pharmaceuticals.

The new materials, says Chris Chang, a chemist with Berkeley Lab’s Chemical Sciences Division and one of the co-leaders of the research team, are based on “a highly stable, porous structure that’s decorated with all of these catalysts.” Though it’s early stage research and nowhere near ready to scale up to power plant levels, it’s an important step toward finding practical ways to absorb and use carbon dioxide in both waste streams and the air.

Embedding the frameworks with chemical catalysts enables them to convert carbon dioxide to carbon monoxide, which can be used as the starting material for useful chemicals.

First developed in the mid-2000s by Omar Yaghi, now a professor of chemistry at UC Berkeley and the co-director of the Kavli Energy NanoSciences Institute, covalent organic frameworks are intricate, highly porous crystals that have a range of potential applications in gas storage, photonics, and various chemical processes. They are especially valuable as carbon capture materials because they function in the presence of water, which means you can eliminate the toxic organic solvents that are used in other forms of carbon capture; you’re no longer “fixing one problem and creating another,” as Yaghi puts it. 

Capturing the carbon is half of the solution; turning it into usable materials is the second half. “The challenge has always been, could you convert it into some starting material that can be used as feedstocks for useful chemicals?” says Yaghi. “This work is the first step toward that challenge.” 

Work on carbon capture from the waste streams of power plants has stalled in recent years (see “What Carbon Capture Can’t Do”). Current approaches center on postcombustion capture, generally using amine-based solvents; precombustion methods, such as gasifying coal before burning it; and oxy-combustion, which burns coal in pure oxygen rather than air. All are effective, but they’re expensive and inefficient. And none will work for removing carbon from the atmosphere (see “Can Sucking CO2 Out of the Atmosphere Really Work?”).

Work on novel techniques, like the research of Yaghi and Chang and their team, could open up new avenues to make carbon capture more feasible. One limitation is that the catalysis requires energy: thus, the system to capture and convert carbon dioxide would itself consume electricity. Chang says one goal is to link devices for carbon capture and conversion with solar panels.

“Capturing carbon selectively is a daunting challenge,” says Yaghi. “And converting it into a useful material adds to that. Five years ago we couldn’t have said we could do it. Now I wouldn’t say we’ve solved it, but we’re now in a position to say that this is feasible.”

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