  A classical density functional theory (cDFT) based on the PC-SAFT equation of
state is proposed for the calculation of adsorption equilibria of pure
substances and their mixtures in covalent organic frameworks (COFs). Adsorption
isotherms of methane, ethane, n-butane and nitrogen in the COFs TpPa-1 and
2,3-DhaTph are calculated and compared to results from grand canonical Monte
Carlo (GCMC) simulations. Mixture adsorption is investigated for the
methane/ethane and methane/n-butane binary systems. Excellent agreement between
PC-SAFT DFT and GCMC is obtained for all adsorption isotherms up to pressures
of 50 bar. The cDFT formalism accurately predicts the selective accumulation of
longer hydrocarbons for binary mixtures in the considered COFs. This
application shows substantial predictive power of PC-SAFT DFT solved in
three-dimensional geometries and the results suggest the method can in the
future also be applied for efficient optimization of force field parameters or
of structural properties of the porous material based on an analytical theory
as opposed to a stochastic simulation.
