High pressure adsorption of CO2 and CH4 on Zr-MOFs

Adsorption equilibrium of CO2 and CH4 at three different temperatures was measured on three isoreticular Zr-MOFs: Zr(1,4-BDC) (UiO-66), Zr(4,4′-BPDC) UiO-67, and Zr(2,6-NDC) (DUT-52). Adsorption equilibrium data was measured at 298, 313, and 343 K up to 30 bar for CO2 and 80 bar for CH4. The three adsorbents have increasing surface areas, pore volumes, and pore sizes in the order UiO-66 < DUT-52 < UiO-67. The maximum CO2 and CH4 loading and selectivity follow the same trend. The relatively low isosteric heats of adsorption of CO2 for the three adsorbents indicate potential application at high partial pressures of CO2 in so-called precombustion schemes. Since equilibrium selectivity was higher for UiO-67, adsorption kinetics of pure gases was also measured in this adsorbent. Diffusion of both molecules is very fast, allowing the use of equilibrium theory for estimation of process performance of this adsorbent.