Adsorbent Eases Carbon Capture

Releasing gases from highly selective material takes less energy.

By Chemical Processing Staff

A metal-hydroxyl-functionalized porous solid dubbed NOTT-300 (Figure 1) efficiently adsorbs CO2 and SO2, and doesn't require heating to release the adsorbed gases, report researchers at the University of Nottingham, U.K. "It offers the opportunity for development of an 'easy on/easy off' capture system that carries fewer economic and environmental penalties than existing technologies. It could also find application in gas separation processes where the removal of CO2 or acidic gases such as SO2 is required," notes Martin Schröder, dean of Nottingham's Faculty of Science, who led a team of researchers from Nottingham, Peking University, Oxford University, ISIS and Diamond Light Source.

"The material shows high uptake of CO2 and SO2. In the case of SO2, this is the highest reported for this class of materials to date. It is also selective for these gases, with other gases — such as hydrogen, methane, nitrogen, oxygen — showing no or very little adsorption into the pores," says Schröder. "In addition to high uptake capacity and selectivity, it is also very easy to release the adsorbed gas molecules through simple reduction of pressure. The material has high chemical stability to all common organic solvents and is stable in water and up to temperatures of 400°C," he adds. The non-amine-containing solid reportedly is economically viable to produce because it's synthesized from relatively simple and cheap organic materials with water as the only solvent. (More details in a recent article in Nature Chemistry.)

"…Our calculations show that the energy required to release adsorbed gas molecules from NOTT-300 is significantly less than the energy required to remove CO2 from existing CCS [carbon capture and sequestration] technology such as amine scrubbing," notes Nick Bennett, project manager at Nottingham.

"…We are keen to understand the performance of the material in 'real' flue bed mixture…," comments Bennett. "NOTT-300 is stable when exposed to water vapor. However, given the mechanism by which CO2 and SO2 are adsorbed, it is likely that water will also be adsorbed into the pores. We do not yet know what impact this will have on the CO2 capture properties of NOTT-300 in a mixed gas system of, say, 85% nitrogen, 12% CO2 and 3% water. This experiment is therefore planned in the next stage of development of NOTT-300…" Further experiments should provide insights on how many regeneration cycles are possible, he adds. The researchers also intend to investigate the performance of the material in the presence of other acidic gases, to better understand possible poisoning problems.

"The key challenges are to synthesize the material on a multi-gram scale and then on hundreds of grams. We are currently investigating a number of ways in which this can be achieved," says Bennett. "To date, we have only made 2–3 g of the material and therefore initial scale up is looking at making 10–20 g."

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