Can metal-organic frameworks attain new DOE targets for on-board methane storage by increasing methane heat of adsorption?

Using grand canonical Monte Carlo (GCMC) simulations, we studied whether the new DOE targets for on-board methane storage can be attained if heat of adsorption at low loading (Q_st°) is increased in eight representative metal-organic frameworks (MOFs) with varied pore volumes and surface areas. Because the deliverable capacity is more relevant to practical applications, we focus our discussions on the volumetric and gravimetric deliverable capacities. We found that the optimal Q_st° for maximum CH₄ delivery is approximately 20 kJ/mol. However, the new DOE targets are difficult to achieve in terms of the deliverable capacities, even after increasing Q_st°. When the storage and discharge pressures are 65 and 1 bar, respectively, the volumetric and gravimetric targets can be attained under special combinations of pore volume and Q_st°. Our results suggest that storing and delivering CH₄ at lower temperatures could be considered to attain the new targets using current technologies, although it would result in some additional cost.