Rice University scientists have discovered an environmentally friendly carbon-capture method that could draw carbon dioxide emissions from industrial flue gases and natural gas wells, using a combination of amine-rich compounds and carbon-60 molecules.

The research is the subject of an open-access paper published Wednesday (Nov. 4) in Nature’s online journal Scientific Reports.

“We had two goals,” Rice chemist Andrew Barro said. “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 Rice lab used buckyballs* as crosslinkers between amines — nitrogen-based molecules drawn from polyethyleneimine. The lab produced a brown, spongy material in which hydrophobic (water-avoiding) buckyballs forced the hydrophilic (water-seeking) amines to the outside, where passing carbon dioxide could bind to the exposed nitrogen.

Among the key benefits:

Tests from one to 50 atmospheric pressures showed the Rice compound captured a fifth of its weight in carbon dioxide but no measurable amount of methane, Barron said, and the material did not degrade over many absorption/desorption cycles.

Industrial amine-based scrubbers must be heated to 140 degrees Celsius to release captured carbon dioxide; lowering the temperature would save energy.

Costs: “Compared to the cost of current amine used, C-60 is pricy,” Barron admitted. “But the energy costs would be lower because you’d need less to remove the carbon dioxide.” He noted industrial scrubbers lose amines through heating, so they must constantly be replenished.

The Apache Corp., the Robert A. Welch Foundation, and the Welsh Government Ser Cymru Program supported the research.

* Carbon-60, the soccer ball-shaped molecule also known as buckminsterfullerene (or the “buckyball”) was discovered at Rice by Nobel Prize laureates Richard Smalley, Robert Curl and Harold Kroto in 1985. The ultimate curvature of buckyballs may make them the best possible way to bind amine molecules that capture carbon dioxide but allow desirable methane to pass through.

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Abstract of Cross-Linking Amine-Rich Compounds into High Performing Selective CO2 Absorbents

Amine-based absorbents play a central role in CO2 sequestration and utilization. Amines react selectively with CO2, but a drawback is the unproductive weight  f solvent or support in the absorbent. Efforts have focused on metal organic frameworks (MOFs) reaching extremely high CO2 capacity, but limited selectivity to N2 and CH4, and decreased uptake at higher temperatures. A desirable system would have selectivity (cf. amine) and high capacity (cf. MOF), but also increased adsorption at higher temperatures. Here, we demonstrate a proof-of-concept where polyethyleneimine (PEI) is converted to a high capacity and highly selective CO2 absorbent using buckminsterfullerene (C60) as a cross-linker. PEI-C60 (CO2 absorption of 0.14 g/g at 0.1 bar/906C) is compared to one of the best MOFs, Mg-MOF-74 (0.06 g/g at 0.1 bar/906C), and does not absorb any measurable amount of CH4 at 50 bar. Thus, PEI-C60 can perform better than MOFs in the sweetening of natural gas.