Adsorptive separation of Xe/Kr using nanoporous carbons in the presence of I2 and CH3I

Abstract

• Better Xe/Kr separation performance achieved in CNTs than amorphous carbons. • The presence of I 2 and CH 3 I excludes the adsorption of Xe/Kr completely. • Adequate adsorption of CH 3 I and high CH 3 I/I 2 selectivity in (6, 6) CNT. • High adsorption of I 2 and high I 2 /CH 3 I selectivity in (15, 15) CNT. • Enhanced amorphization reduces the adsorption kinetics significantly. Grand canonical Monte Carlo (GCMC) and molecular dynamic (MD) simulations were systematically conducted to reveal the influence of volatile radionuclides, I 2 and CH 3 I, on the adsorption of Xe/Kr/N 2 mixtures in well-shaped carbon nanotubes (CNTs), stratified activated carbon fiber (ACF-15) and completely disordered silicon carbide derived carbon (SiC-DC). In the absence of radioactive impurities, the (6, 6) CNT with a pore size of 0.81 nm achieves adequately high adsorption of Xe (0.37 mol/kg) and Xe/Kr selectivity (45.3), presenting significantly superior performance than other CNTs and amorphous carbons. Albeit enhancing the amorphization of nanoporous carbons hardly impacts the sorption capacity, it hinders the adsorption kinetics dramatically by introducing the energy barriers to diffusion. However, when either I 2 or CH 3 I presents in the gas phase, the adsorptions of Xe and Kr are severely excluded in nanoporous carbons due to the dominant adsorption of I 2 and CH 3 I. For the Xe/Kr/N 2 /I 2 /CH 3 I mixture, the intense competitive adsorption occurs between I 2 and CH 3 I in nanoporous carbons. It is found while the (6, 6) CNT demonstrates the greatest potential on separating CH 3 I from the quinary mixture, the (15, 15) CNT achieves the best performance on separating I 2 among the carbon structures considered.