Indexed on: 11 Apr '19Published on: 10 Apr '19Published in: Journal of Chemical & Engineering Data
Process intensification, with the aim of reducing the energy consumption of the existing processes, opens the path to exploring diverse operating conditions. As far as adsorption-based processes are concerned, cryogenic temperatures and high pressures are less-explored conditions. In this work, the adsorption equilibria of carbon dioxide, methane, carbon monoxide, nitrogen, and hydrogen are assessed at temperatures of between 223 and 373 K and at pressures of up to 60 bar for acid-functionalized UiO-66(Zr) MOF, the UiO-66(Zr)_(COOH)2, shaped as small granules. UiO-66(Zr)_(COOH)2 is selective for carbon dioxide, presenting the highest adsorption capacities among all of the tested gases. The adsorption capacity then follows the order methane, nitrogen, carbon monoxide, and hydrogen. Indeed, the very low capacity toward carbon monoxide is a remarkable feature of this material. The carbon dioxide/methane ideal selectivity at 220 K, 40 bar, and a feed composition of 99% methane and 1% carbon dioxide is 44. The isosteric heats of adsorption mirror the adsorption capacity, carbon dioxide has an adsorption heat of between 40 and 20 kJ·mol–1, and methane has a adsorption heat of between 25 and 10 kJ·mol–1. Nitrogen and carbon monoxide have the lowest adsorption heats of about 20–10 and 15–10 kJ·mol–1, respectively. Thus, UiO-66(Zr)_(COOH)2 presents a high potential for relevant industrial processes such as the natural gas/biogas upgrade, hydrogen production, and syngas composition tuning.