Rice researchers find amines cross-linked with buckyballs an effective, selective CO2 absorbent

4 December 2014

Rice University scientists have found that amine-rich compounds combined with carbon-60 molecules (buckyballs) are highly effective at selectively capturing CO₂. The Rice lab of chemist Andrew Barron, in a proof-of-concept study, combined buckyballs with amines in a compound (PEI-C₆₀) that absorbs a fifth of its weight in carbon dioxide. It shows potential as an environmentally friendly material for capturing carbon from natural gas wells and industrial plants. The research is the subject of an open-access paper in Nature’s online journal Scientific Reports.

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Polyethyleneimine (PEI) with carbon-60 atoms, aka buckminsterfullerenes, form a spongy brown compound that absorbs a fifth of its weight in carbon dioxide but no measurable amount of methane. That may make it suitable for capturing carbon dioxide at wellheads and from industrial flue gases. Courtesy of the Barron Research Group.

We had two goals. 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.

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.

Carbon-60 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.

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.

When Barron and his team began combining carbons and amines several years ago, they noticed an interesting progression: Flat graphene absorbed carbon dioxide well, multi-walled nanotubes absorbed it better, and thinner single-walled nanotubes even better. That suggested the curvature was important, Barron said. “C-60, being a sphere, has the highest possible curvature among carbon materials.”

He said the Rice compound compared favorably with other carbon-capture candidates based on metal organic frameworks (MOFs). The Rice material is far more selective, Barron said; “Methane just doesn’t absorb. He also noted the Rice compound absorbed wet carbon dioxide as well as dry, unlike MOFs.

Barron said it’s just as important that the compound releases carbon dioxide efficiently at lower temperatures for reuse. Industrial amine-based scrubbers must be heated to 140 degrees Celsius to release captured carbon dioxide; lowering the temperature would save energy.

Compared to the cost of current amine used, C-60 is pricy. But the energy costs would be lower because you’d need less to remove the carbon dioxide.

He also noted industrial scrubbers lose amines through heating, so they must constantly be replenished.

The researchers are pursuing ways to improve the compound’s capacity and rate of absorption.

Lead author Enrico Andreoli is a former Rice postdoctoral researcher and now a senior lecturer at Swansea University, Wales. Co-authors are former graduate student Eoghan Dillon, undergraduate alumna Laurie Cullum and senior research scientist Lawrence Alemany, all of Rice. Barron is the Charles W. Duncan Jr.-Welch Professor of Chemistry and a professor of materials science and nanoengineering.

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

Resources

• Enrico Andreoli, Eoghan P. Dillon, Laurie Cullum, Lawrence B. Alemany Andrew R. Barron (2014) “Cross-Linking Amine-Rich Compounds into High Performing Selective CO₂ Absorbents” Scientific Reports 4, Article number: 7304 doi: 10.1038/srep07304