The ever-useful buckminsterfullerene, or buckyball, has a new potential application: carbon capture. Researchers at Rice University in Texas used buckyballs (carbon-60 molecules, technically) as a “cross-linker” with polyethyleneimine (PEI), and produced a compound that binds carbon dioxide very well, avoids binding methane, and can be used at lower temperatures than other materials.
“We had two goals,” said Andrew R. Barron, of Rice, senior author of the paper describing the advance, in a press release. “One was to make the compound 100 percent selective between carbon dioxide and methane at any pressure and temperature. The other was to reduce the high temperature needed by other amine solutions to get the carbon dioxide back out again. We've been successful on both counts.”
The researchers published their findings in Nature’s Scientific Reports. They discovered that the PEI-C60 compound bound about one-fifth of its weight in carbon dioxide, and essentially zero methane—a big deal for carbon capture materials. The buckyballs are hydrophobic, and push the hydrophilic amines of the PEI to the outer surface of the compound; carbon dioxide floats past, and binds to exposed nitrogen atoms.
The PEI-C60 captured carbon better than materials known as metal organic frameworks (MOFs), which are nanoporous materials considered among the most promising for trapping CO2. The idea of using buckyballs was a natural progression for Barron’s lab; in previous work, the team found that single sheets of graphene did well at absorbing carbon dioxide. Multiwalled carbon nanotubes did better, and nanotubes with thinner single walls did even better still. The spherical buckyball takes the level of curvature to its extreme, which Barron said clearly plays a role in how well the molecules bind.
Another advantage comes up when the CO2 needs to let go of its new home—the final step on its road to toward the “sequestration” part of CCS. Other materials require temperatures to reach 120 and 130 degrees Celsius for the “amine scrubbing process” where the carbon dioxide is released. PEI-C60, meanwhile, has a lower “temperature of regeneration,” below 90 degrees Celsius.
The downside? Cost. “Compared to the cost of current amine used, C60 is pricy,” says Barron. “But the energy costs would be lower because you’d need less to remove the carbon dioxide.”
Progress toward deployment of a practical CCS regime remains slow, so any advances are obviously welcome. One of the first utility-scale CCS plants did recently open in Canada—a billion-dollar add-on to a half-century old coal plant. But without some major advances, or political shifts involving huge infusions of cash to the idea, projects like that are going to remain exceptions rather than the rule.