摘要
A series of MIL-101 samples with hierarchical pore structures and different surface areas (2000-4800 m(2)/g) was synthesized by hydrothermal method and characterized by X-ray diffraction, thermogravimetric analysis and 77-K N-2 adsorption isotherm. The adsorption equilibrium and kinetics of CO2 were studied at 288, 298 and 308 K within a pressure range of 0-5 MPa by a volumetric method. The adsorption heat, mass-transfer constant, diffusion coefficient and diffusion activation energy were also investigated in this work. The results showed that the chromium-based MIL-101 adsorbent exhibited an impressive selectivity for CO2 over N-2, and had an adsorption capacity of 20 mmol/g of CO2 at 298 K and 5.0 MPa, which was much better than that of other conventional adsorbents (e.g. SBA-15, MCM-41, SG-A). The adsorption heat of CO2 on MIL-101 was in the range of 21-45 kJ/mol, which decreased with the loading of CO2. The mass-transfer constants and diffusion coefficients increased with the temperature and decreased with the pressure, whereas the diffusion activation energy decreased with the increased pressure, indicating that adsorption of CO2 at high pressures was easier. In addition, a linear correlation was found between CO2 uptake and surface areas at low pressure, which showed that the adsorption capacity of CO2 could be controlled by adjusting the surface area of the prepared adsorbents in this condition.
