Multiple coal fossil fuel power plant smokestacks - AdobeStock/jzehnder
The new material is said to be simple to make, requiring primarily off-the-shelf melamine powder — which currently costs about $40 per ton — along with formaldehyde and cyanuric acid. The process for synthesising the melamine material is described in Science Advances.
“We wanted to think about a carbon capture material that was derived from sources that were really cheap and easy to get. And so, we decided to start with melamine,” said Jeffrey Reimer, Professor of the Graduate School in the Department of Chemical and Biomolecular Engineering at the University of California, Berkeley, and one of the corresponding authors of the paper.
The so-called melamine porous network captures carbon dioxide with an efficiency comparable to early results for another relatively recent material for carbon capture, metal organic frameworks (MOFs).
UC Berkeley chemists created the first such carbon-capture MOF in 2015, and subsequent versions have proved more efficient at removing carbon dioxide from flue gases, such as those from a coal-fired power plant.
Haiyan Mao, a UC Berkeley postdoctoral fellow and first author of the paper, said that melamine-based materials use much cheaper ingredients, are easier to make and are more energy efficient than most MOFs.
“In this study, we focused on cheaper material design for capture and storage and elucidating the interaction mechanism between CO2 and the material,” Mao said in a statement. “This work creates a general industrialisation method towards sustainable CO2 capture using porous networks. We hope we can design a future attachment for capturing car exhaust gas, or maybe an attachment to a building or even a coating on the surface of furniture.”
The work is a collaboration among a group at UC Berkeley led by Reimer; a group at Stanford University led by Yi Cui, UC Berkeley Professor of the Graduate School Alexander Pines, and a group at Texas A&M University led by Hong-Cai Zhou. Jing Tang, a postdoctoral fellow at Stanford and the Stanford Linear Accelerator Center and a visiting scholar at UC Berkeley, is co-first author with Mao.
According to UC Berkeley, the current best technique for carbon capture involves piping flue gases through liquid amines, which bind CO2. But this requires large amounts of energy to release the carbon dioxide once it’s bound to the amines, so that it can be concentrated and stored underground. The amine mixture must be heated to between 120 and 150oC to regenerate the CO2. In contrast, the melamine porous network with DETA and cyanuric acid modification captures CO2 at about 40oC and releases it at 80oC.
Treating melamine powder with formaldehyde — which the researchers did in kilogram quantities — creates nanoscale pores in the melamine that the researchers thought would absorb CO2.
Mao said that tests confirmed that formaldehyde-treated melamine adsorbed CO2 somewhat, but adsorption could be much improved by adding another amine-containing chemical, DETA (diethylenetriamine), to bind CO2. She and her colleagues subsequently found that adding cyanuric acid during the polymerisation reaction increased the pore size dramatically and radically improved CO2 capture efficiency: nearly all the carbon dioxide in a simulated flue gas mixture was absorbed within about three minutes.
The addition of cyanuric acid also allowed the material to be used repeatedly.
Mao and her colleagues conducted solid-state nuclear magnetic resonance (NMR) studies to understand how cyanuric acid and DETA interacted to make carbon capture so efficient. The studies showed that cyanuric acid forms strong hydrogen bonds with the melamine network that helps stabilize DETA, preventing it from leaching out of the melamine pores during repeated cycles of carbon capture and regeneration.
The Reimer and Cui groups are continuing to adjust the pore size and amine groups to improve the carbon capture efficiency of melamine porous networks, while maintaining the energy efficiency.