Porous Material Densification While Maintaining Its Pore Structure

Abstract

We report a compression shaping technique for metal organic frameworks (MOFs), which are a class of material that is attracting attention as a methane adsorbent, to maintain its pore structure. Some MOFs have high methane adsorption capacity per weight due to a much larger specific surface area and pore volume compared to other porous materials. However, the packing density of MOFs can be increased by compression shaping, but since the pores are flexible, compression shaping destroys the pore structure, resulting in a decrease in the methane capacity per weight. This is because the pores become blocked when MOF is compressed and shaped. Therefore, gas was adsorbed into the MOF near critical pressure, and compression shaping was performed while maintaining the equilibrium adsorption state to equalize the pressure inside and outside the pores of the MOF, thereby maintaining the pore structure. By performing compression shaping while adsorbing gas, the packing density was greatly improved while maintaining the pore volume and the surface area, and the amount of methane capacity/uptake per volume of the shaped MOF was also greatly improved. Using this technique, the packing density of HKUST1 pellets was improved to 1.28 g/cm³, and the methane adsorption amount was 8.88 mmol/g, which was almost the same as that of its powder, which was 8.93 mmol/g. This forming technique can improve the packing density of MOF without using binders, while maintaining the pore structure of MOF, and is a significant advance toward the practical use of MOF as a methane adsorbent.