In 2014 the lab of Rice chemist Andrew Barron found that carbon-60 molecules (aka buckyballs) gain the ability to sequester carbon dioxide when combined with polyethyleneimine (PEI).
In the American Chemical Society journal Energy and Fuels the scientists address how and how well carbon-60 molecules and PEI (PEI-C60) works.
The amine-rich combination of C60 and PEI showed its potential in the previous study to capture emissions of carbon dioxide from sources including industrial flue gases and natural-gas wells.
In the new study, the researchers found pyrolyzing the material – heating it in an oxygen-free environment – changes its chemical composition in ways that may someday be used to tune PEI-C60 for specific carbon-capture applications.
“One of the things we wanted to see is at what point, chemically, it converts from being something that absorbed best at high temperature to something that absorbed best at low temperature,” Barron said in a statement. “In other words, at what point does the chemistry change from one to the other?”
Lead author Enrico Andreoli pyrolyzed PEI-C60 in argon at various temperatures from 100 to 1,000 degrees Celsius and then evaluated each batch for carbon uptake.
He discovered the existence of a transition point at 200oC, a boundary between the material’s ability to soak in carbon dioxide through chemical means as opposed to physical absorption.
The material that was pyrolyzed at low temperatures became gooey and failed at attracting carbon from high-temperature sources by chemical means. The opposite was true for PEI-C60 pyrolyzed at high heat. The now-porous, brittle material became better in low-temperature environments, physically soaking up carbon dioxide molecules.
At 200oC, they found the heat treatment breaks the polymer’s carbon-nitrogen bonds, leading to a decrease in carbon capture by any means.
“One of the goals was to see if can we make this a little less gooey and still have chemical uptake, and the answer is, not really,” Barron said. “It flips from one process to the other. But this does give us a nice continuum of how to get from one to the other.”
Andreoli found that at its peak, untreated PEI-C60 absorbed more than a 10th of its weight in carbon dioxide at high temperatures (0.13 grams per gram of material at 90oC). Pyrolyzed PEI-C60 did nearly as well at low temperatures (0.12 grams at 25oC).
The researchers are continuing with efforts to refine the process. “This has definitely pointed us in the right direction,” Barron said.
Andreoli is a former postdoctoral researcher in Barron’s group at Rice and a senior lecturer at Swansea University in the United Kingdom. Barron is the Charles W. Duncan Jr.–Welch Professor of Chemistry and a professor of materials science and nanoengineering at Rice and the Ser Cymru Chair of Low Carbon Energy and Environment at Swansea.
The Apache Corp., the Robert A. Welch Foundation and the Welsh Government Ser Cymru Program supported the research.