(204c) Characterization and CO2 Sorption Properties of Carbon-Based Materials for Carbon Capture Applications

Carbon capture and sequestration (CCS) has become an important option for mitigating CO₂ emission and global climate change by capturing CO₂ from large point sources and sequestering it underground. However, the feasibility of carbon capture is mainly limited by the high cost of carbon capture, and to be more specific, the significant energy requirements during the regeneration of aqueous amine solutions. Sorbent technologies for CO₂ capture have several advantages over the traditional amine-based solvent absorption approaches. For instance, within a sorbent-based approach, water is absent, which may decrease the energy requirement associated with regeneration, since heating water is the greatest energetic expense associated with CO₂ capture using solvent-based approaches. Another benefit of sorbents is the flexibility associated with the choice in pore size, surface functionality, and connectivity, in addition to the advantageous heat properties of materials such as carbon.

 To overcome solvent-based regeneration expenses, micro and mesoporous sorbents have become promising candidates. A considerable variety of sorbent materials have been investigated for the application of CO₂ capture, including metal organic frameworks, zeolites, carbon nanotubes and mesoporous silicas, including SBA-15 and MCM-41. However, the CO₂ sorption capacity and kinetics under realistic flue gas conditions remain unclear. This research focuses on two sets of CO₂ sorbents: amine-functionalized multiwalled carbon nanotubes (aminated MWNTS) and biomimetic micro- and mesoporous carbon-based materials. Multi-walled carbon nanotubes were functionalized with the aminosilane compounds aminopropyltriethoxysilane (APTES) and N-dimethylaminopropyltrimethoxy-silane (DMAPS) and the resulting materials were characterized and tested for CO₂ capture under relevant conditions.  As the first step in developing biomimetic sorbents, silica-based sorbents were functionalized with zinc in order to mimic CO₂ hydration that takes place with carbonic anhydrase, as a means to easily capture and release CO₂.  

Breakthrough experiments have been performed in a temperature-controlled packed-bed reactor with small amounts of sorbent (i.e., < 250 mg). Experiments were performed with a resolution of 0.1 mmol CO₂ per gram of sorbent using an Extrel MAX300-LG quadrupole mass spectrometer downstream of the packed bed.  The inlet gas was either a mixed gas (CO­₂, N₂ and H₂O) for testing under ideal conditions or a simulated flue gas created by burning methane in air, with potential contaminants such as SO₂, HCl and NO_x doped in at part per million levels post-combustion. The breakthrough experiments provide an understanding of CO₂ uptake, sorbent repeatability and impact of flue gas contaminants on capture. In addition, a Quantachrome Autosorb iQ₂ automated gas sorption analyzer is used to determine surface area, pore volume and pore size distribution of the tested CO₂sorbents.