Investigation of the effect of pristine and functionalized carbon nanotubes in cellulose acetate butyrate for mixed-gas separation: A molecular simulation study

•Grand Canonical Monte Carlo simulations are applied to study CO2/CH4 and CO2/N2 separation.•Addition of CNT and CNT-functionalized to the CAB structure positively affects the thermodynamics of adsorption.•The selectivity of CO2 increased by adding CNT and CNT-functionalized with –NH2 and –COOH to the CAB structure.•The surface potential, Gibbs free energy and entropy change of CO2 for all composites is higher than CH4 and N2. Pristine carbon nanotubes (CNTs) and functionalized carbon nanotubes (F-CNTs) with –NH2 and –COOH functional groups were placed in the cellulose acetate butyrate (CAB) structure as a filler to study gas separation. Grand Canonical Monte Carlo (GCMC) simulations were performed to evaluate the separation performance of two gas mixtures CO2/CH4 and CO2/N2, on CAB and composites made from pristine CNT and F-CNTs at 300 K as a function of pressure. Adsorption isotherms, selectivity and isosteric heats were calculated which showed that the CNT and F-CNTs provide the selective adsorption of CO2 among CH4 and N2 gases. Furthermore, thermodynamic parameters and Henry’s constant (KH) were calculated, indicating that CH4 and N2 have smaller KH than CO2, and their affinity for composite surfaces is weaker. Compared to CH4 and N2, CO2 has higher Gibbs free energy change and surface potential, indicating that CO2 adsorption on composites is more favorable and spontaneous. In addition, the higher entropy change of CO2 adsorption illustrates that CO2 molecules constitute a much more stable rearrangement in comparison to CH4 and N2 molecules. Number density and radial distribution function profiles are drawn and used to describe the selectivity of CO2 in mixed-gas separation. We may conclude that the excellent properties of F-CNTs make them ideal fillers of CAB for CO2 separation.