Using an inexpensive polymer called melamine, researchers from UC Berkeley, Texas A&M and Stanford have created a cheap, easy and energy-efficient way to capture carbon dioxide from smokestacks. The process for synthesizing the melamine material, published in an open-access paper in the journal Science Advances, could potentially be scaled down to capture emissions from vehicle exhaust or other movable sources of carbon dioxide.

A new method for removing CO₂ from flue gases involves piping the emissions through a porous material based on the chemical melamine (center). DETA, a chemical bound inside the porous melamine, grabs CO₂ and removes it from the gas, with nitrogen vented to the atmosphere. (Image courtesy of Haiyan Mao and Jeffrey Reimer, UC Berkeley)

Here, we demonstrate new sustainable, solid-state, polyamine-appended, cyanuric acid–stabilized melamine nanoporous networks (MNNs) via dynamic combinatorial chemistry (DCC) at the kilogram scale toward effective and high-capacity carbon dioxide capture. Polyamine-appended MNNs reaction mechanisms with carbon dioxide were elucidated with double-level DCC where two-dimensional heteronuclear chemical shift correlation nuclear magnetic resonance spectroscopy was performed to demonstrate the interatomic interactions.

We distinguished ammonium carbamate pairs and a mix of ammonium carbamate and carbamic acid during carbon dioxide chemisorption. The coordination of polyamine and cyanuric acid modification endows MNNs with high adsorption capacity (1.82 millimoles per gram at 1 bar), fast adsorption time (less than 1 minute), low price, and extraordinary stability to cycling by flue gas. This work creates a general industrialization method toward carbon dioxide capture via DCC atomic-level design strategies.

—Mao et al.

The new material is simple to make, requiring primarily off-the-shelf melamine powder—which today costs about $40 per ton—along with formaldehyde and cyanuric acid, a chemical that, among other uses, is added with chlorine to swimming pools.

The melamine porous network captures carbon dioxide with an efficiency comparable to early results for another relatively recent material for carbon capture, metal organic frameworks, or MOFs. UC Berkeley chemists created the first such carbon-capture MOF in 2015, and subsequent versions have proved even 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 who is 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. The low cost of porous melamine means that the material could be deployed widely.

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 polymerization 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 3 minutes.

The addition of cyanuric acid also allowed the material to be used over and over again.

The work is a collaboration among a group at UC Berkeley led by Reimer; a group at Stanford University led by Yi Cui, who is director of the Precourt Institute for Energy, the Somorjai Visiting Miller Professor at UC Berkeley, and a former UC Berkeley postdoctoral fellow; 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. Reimer is also a faculty scientist at Lawrence Berkeley National Laboratory.

The best carbon capture technique today 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 150 degrees Celsius (250-300 degrees Fahrenheit) to regenerate the CO₂.

In contrast, the melamine porous network with DETA and cyanuric acid modification captures CO₂ at about 40 degrees Celsius, slightly above room temperature, and releases it at 80 degrees Celsius, below the boiling point of water. The energy savings come from not having to heat the substance to high temperatures.

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 tweak the pore size and amine groups to improve the carbon capture efficiency of melamine porous networks, while maintaining the energy efficiency. This involves using a technique called dynamic combinatorial chemistry to vary the proportions of ingredients to achieve effective, scalable, recyclable and high-capacity CO₂ capture.

This work was partly supported by the US Department of Energy.

Resources

• Haiyan Mao et al. (2022) “A scalable solid-state nanoporous network with atomic-level interaction design for carbon dioxide capture” Science Advances doi: 10.1126/sciadv.abo6849