Gas sorption and kinetics of CO2 sorption and transport in a polymorphic microporous MOF with open Zn (II) coordination sites

Abstract

Sorption equilibrium and kinetics of CO2, N2 and CH4 on a newly reported Zn-based metal organic framework (Zn4(pydc)4(DMF)2·3DMF (1)) were studied to evaluate its efficacy for CO2 capture under realistic post-combustion conditions. Adsorption and desorption equilibria were measured gravimetrically for temperatures between 308K and 338K and pressures up to 5bar.The Langmuir adsorption model was used to fit sorption data and the Ideal Adsorbed Solution Theory (IAST) was used to calculate selectivity from single-component isotherms suggesting that separation can be enhanced by a decrease in temperature. The MOF exhibited preferential CO2 adsorption based on the high enthalpy of adsorption and adsorption selectivities of CO2 over N2 and CH4. Kinetics of adsorption and desorption of CO2 (308K–338K, pressures up to 1bar) were fitted to the linear-driving force (LDF) kinetic model, showing a relatively fast adsorption and a low activation energy for adsorption and desorption. Diffusion inside the pores was found to be the rate-limiting step based on fits to the LDF model and the micropore diffusion model. Desorption kinetics studies at 1bar indicated that CO2 has greater average residence times at all temperatures and lower values of activation energy for desorption than N2 and CH4. This suggests the selective adsorption and capture of CO2 on (1) will be favored.