Adsorbents for Gas Storage: Gas Energy, Sorbent Energy and Their Relationship to Capacity

Generalized variables make it possible to reveal the nuances of the structure of porous materials and divide samples into their series with similar properties (Titelman, L. AMPC 2021, vol. 11, No. 11). Adsorbents for gas storage have a unique set of variables that can be combined: textural and mechanical properties of the adsorbent, preparation conditions, pressure and temperature of gas during storage and delivery. Taking gas pressure and mechanical strength as forces, textural properties as displacements, we obtained the energies of gas and sorbent as generalized variables. The interrelationships between them and the storage capacity for metal-organic frameworks, porous organic polymers and activated carbons were studied. Due to the variety of sorbents and the attracting effect of micropore walls on gas adsorption, the previously proposed average thickness of the probing gas layer is useful as estimation of the pore size. Its effect on adsorbent capacity was tested. The ratio of the gas layer to the kinetic diameter of the molecule gives the packing of molecules inside the pores and makes it possible to represent the pore model. Excessive surface area results in too small pores, repulsive forces and reduced capacitance. Sometimes the gas energy correlates better with the residual adsorption uptake than with the total or delivery capacity. Compared to texture parameters, the proposed generalized variables correlate better with sorbent capacity.