Evaluating metal–organic frameworks for natural gas storage

TLDR

Metal–organic frameworks are promising adsorbents for natural gas storage, but inconsistent high‑pressure data and few comparative studies hinder evaluation of new and existing materials. This paper reviews high‑pressure adsorption measurements and evaluates six representative MOFs and an activated carbon to illustrate key properties for natural gas storage. The authors compare high‑pressure methane isotherms of the materials, assessing gravimetric and volumetric capacities, isosteric heats, usable storage, and system‑level factors such as thermal management and impurities. They find that volumetric capacity is more important than gravimetric capacity for extending natural gas vehicle range, and they discuss how thermal management, mechanical properties, and impurities affect overall performance.

Abstract

Metal–organic frameworks have received significant attention as a new class of adsorbents for natural gas storage; however, inconsistencies in reporting high-pressure adsorption data and a lack of comparative studies have made it challenging to evaluate both new and existing materials. Here, we briefly discuss high-pressure adsorption measurements and review efforts to develop metal–organic frameworks with high methane storage capacities. To illustrate the most important properties for evaluating adsorbents for natural gas storage and for designing a next generation of improved materials, six metal–organic frameworks and an activated carbon, with a range of surface areas, pore structures, and surface chemistries representative of the most promising adsorbents for methane storage, are evaluated in detail. High-pressure methane adsorption isotherms are used to compare gravimetric and volumetric capacities, isosteric heats of adsorption, and usable storage capacities. Additionally, the relative importance of increasing volumetric capacity, rather than gravimetric capacity, for extending the driving range of natural gas vehicles is highlighted. Other important systems-level factors, such as thermal management, mechanical properties, and the effects of impurities, are also considered, and potential materials synthesis contributions to improving performance in a complete adsorbed natural gas system are discussed.