A present challenge in the mitigation of anthropogenic CO2 emissions involves the design of less energy- and water-intensive capture technologies. Traditional capture methods, e.g., MEA solvent scrubbing, have prohibitive regeneration costs, and recent concerns in drought-ridden states like California have brought these water-intensive processes under increased scrutiny. Sorbent-based capture represents a promising solution to the aforementioned hurdles, as they do not incur the heavy energy penalties associated with solvent regeneration. However, to be considered competitive with their more mature, solvent-based counter-parts, these sorbents must exhibit both high CO2 loading capacity and high CO2:N2 selectivity. Having adequate microporosity and surface nitrogen functionality have been reported to be of great importance to the enhancement of CO2 capacity and CO2:N2 selectivity; however, the role of pore size in combination with surface functionalities in the enhancement of these properties remains unclear. To investigate these effects, grand canonical Monte Carlo (GCMC) simulations were carried out on pure and functionalized 3-layer graphite slit pore models. Theoretical isotherms were constructed as the PSD-weighted sum of individual slit-pore models of width ranging from 3.5Å to 200Å. In addition to pure and monovacancy-graphite, the following functional groups were isolated for testing at ~3.0 N wt%: pyridinic nitrogen, pyrollic nitrogen, quaternary nitrogen, pyridine-N-oxide, and two tautomers of pyridonic nitrogen (2-hydroxypyridine and 2-pyridone). Our results indicate that enhancements to CO2 loading and CO2:N2 selectivity increased on the order of pure graphene &lt; monovacancy &lt; pyrrolic &lt; 2-pyridone &lt; 2-hydroxypyridine &lt; pyridinic &lt; quarternary &lt; pyridine-N-oxide, with upwards of ca. 244% increase to the 0.1 bar loading capacity over the unmodified surface. These results correlate directly with the isosteric heats of adsorption, with stronger heats corresponding to greater CO2 loading (up to 1.72 mmol/g for pyridine-N-oxide) and higher IAST selectivity (up to 47:1 for pyrindine-N-oxide). Further enhanced loading is achieved by increasing the N wt%.

GCMC simulations of nitrogen-doped micro and mesoporous carbon sorbents for CO2 capture

252nd National Meeting (2016)

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