Xuan Peng

Capture of Trace Sulfur Gases from Binary Mixtures by Single-Walled Carbon Nanotube Arrays: A Molecular Simulation Study

Adsorption of H(2)S and SO(2) pure gases and their selective capture from the H(2)S-CH(4), H(2)S-CO(2), SO(2)-N(2), and SO(2)-CO(2) binary mixtures by the single-walled carbon nanotubes (SWNT) are investigated via using the grand canonical Monte Carlo (GCMC) method. It is found that the (20, 20) SWNT with larger diameter shows larger capacity for H(2)S and SO(2) pure gases at T = 303 K, in which the uptakes reach 16.31 and 16.03 mmol/g, respectively. However, the (6,6) SWNT with small diameter exhibits the largest selectivity for binary mixtures containing trace sulfur gases at T = 303 K and P = 100 kPa. By investigating the effect of pore size on the separation of gas mixtures, we found that the optimized pore size is 0.81 nm for separation of H(2)S-CH(4), H(2)S-CO(2), and SO(2)-N(2) binary mixtures, while it is 1.09 nm for the SO(2)-CO(2) mixture. The effects of concentration and temperature on the selectivity of sulfide are also studied at the optimal pore size. It is found that the concentration (ppm) of sulfur components has little effect on selectivity of SWNTs for these binary mixtures. However, the selectivity decreases obviously with the increase of temperature. To improve the adsorption capacities, we further modify the surface of SWNTs with the functional groups. The selectivities of H(2)S-CO(2) and SO(2)-CO(2) mixtures are basically uninfluenced by the site density, while the increase of site density can improve the selectivity of H(2)S-CH(4) mixture doubly. It is expected that this work could provide useful information for sulfur gas capture.

Computational Characterization of Hexagonally Ordered Carbon Nanopipes CMK-5 and Structural Optimization for H2 Storage

We performed grand canonical Monte Carlo (GCMC) simulations to characterize the hexagonally ordered carbon nanopipes CMK-5 and further investigated the adsorptive properties of this material for H2. The geometrical model from Solovyov et al. was used to characterize the hexagonal structure of the CMK-5 adsorbent. The interactions between a fluid molecule inside and outside the nanopipe and a single layer were calculated by the potential models proposed by Tjatjopoulos et al. and Gordon et al. When the calculated results were fitted to the experimental isotherm of N2 adsorption at 77 K, the structural parameters of the CMK-5-S material were obtained. To improve H2 adsorption, we also optimized the structural parameters of CMK-5 material. The maximum excess gravimetric and volumetric uptakes of H2 in the CMK-5 material with the optimized structural parameters at T=77 K are 5.8 wt % and 41.27 kg/m3, which suggest that the CMK-5 material with an optimized structure is a promising adsorbent for gas adsorption.