Advantage of nanoporous styrene-based monolithic structure over beads when applied for methane storage

Nanoporous polymers with permanent porous structure and high surface areas of up to 2084m2/g have been prepared via hypercrosslinking of polystyrene copolymers using Friedel-Crafts alkylation reaction. The hypercrosslinked polymers were prepared in two formats, continuous “monolithic” blocks, and beads. Optimization of the preparation process and hypercrosslinking conditions enabled generation of microporous beads and monoliths with a pore volume of 0.70–0.78cm3/g and a pore size of around 0.63nm. The total gravimetric uptake of methane calculated from adsorption isotherms was 0.156g/g at 65bar and 273K and represented a volumetric uptake of 164cm3 CH4 (STP) per 1cm3 of the sorbent. While the total gravimetric uptake of methane using beads is similar to that of monolith, their volumetric storage capacity is only 82.7cm3 (STP) per 1cm3 at 65bar and 273K due to the inevitable presence of void volumes between the particles. Therefore, the novel continuous “monolithic” format of the hypercrosslinked polymer was found more advantageous since the monolith can fill the available volume of the container completely and exhibit a volumetric storage capacity that is twice as large as that found for the hypercrosslinked beads. The isosteric heat of CH4 adsorption by both monolith and beads was 14.5kJ/mol and 15.0kJ/mol, respectively, which is large enough to adsorb methane at room temperature. The hypercrosslinked monolith could be reused and did not lose its storage capacity even after twenty cycles of repeated use.