Implementing Metal-Organic Frameworks for Natural Gas Storage

Abstract

Methane can be stored by metal-organic frameworks (MOFs). However, there remain challenges in the implementation of MOFs for adsorbed natural gas (ANG) systems. These challenges include thermal management, storage capacity losses due to MOF packing and densification, and natural gas impurities. In this review, we discuss discoveries about how MOFs can be designed to address these three challenges. For example, Fe(bdp) (bdp 2− = 1,4-benzenedipyrazolate) was discovered to have intrinsic thermal management and released 41% less heat than HKUST-1 (HKUST = Hong Kong University of Science and Technology) during adsorption. Monolithic HKUST-1 was discovered to have a working capacity 259 cm 3 (STP) cm −3 (STP = standard temperature and pressure equivalent volume of methane per volume of the adsorbent material: T = 273.15 K, P = 101.325 kPa), which is a 50% improvement over any other previously reported experimental value and virtually matches the 2012 Department of Energy (Department of Energy = DOE) target of 263 cm 3 (STP) cm −3 after successful packing and densification. In the case of natural gas impurities, higher hydrocarbons and other molecules may poison or block active sites in MOFs, resulting in up to a 50% reduction of the deliverable energy. This reduction can be mitigated by pore engineering. of 9.2 MJ L −1 , which is 70% less than that of gasoline [2,15]. However, carrying an extremely pressurized tank raises safety concerns in vehicles in the case of accidents and has an energy cost associated with compression. Furthermore, CNG, which is the established and predominant technology for NGVs, has a driving range of 350-450 km as compared to 400-600 km for gasoline-powered vehicles [16]. Based on this, there is a need to develop gas storage technology beyond that which is already established in real life applications. Further improvements in natural gas storage for NGV technology should seek to improve driving range to decrease time at the pump and the corresponding number of required tank recharges. Increasing driving range would be helpful to implement the technology in areas where natural gas filling stations are not as abundant. In addition, the CNG tank that holds the fuel takes up cargo space and technological advancements that decrease the volume of the natural gas fuel tank are beneficial. Another approach to store natural gas is LNG, which has an energy density of 22.2 MJ L −1 . Some drawbacks of LNG are the energy and cost associated with liquefaction (−162 • C), which present major technological obstacles [17,18] Lastly natural gas can be stored as ANG. Fairly large volumetric capacities of 4-6 MJ L −1 at pressures of around 35 bar at room temperature for different adsorbents were achieved [19]. The presence of sorbent materials in high pressure tanks reduces the pressure requirement of the tanks, making storage and delivery safer and allows for the use of single-stage compressors. ANG may increase the driving range and decrease the volume required of the fuel tank to achieve a specific driving dis...

Evolution of the Design of CH4 Adsorbents

“…Furthermore, solvent exchange steps should be minimized to simplify the process. Adsorbent designs should consider such problems, in addition to packing losses and material cyclability [174]. For the practical implementation of such systems, thermal management, and the effect of impurities on the performance should be considered.…”

Adsorbed Natural Gas Storage for Onboard Applications

“…[ 22,65,83,161 ] Regeneration is another option to mitigate the adverse impact of impurity accumulation and regain the uptake performance of the ANG system. [ 162 ] In the case of Maxsorb MSC‐30 (a commercial AC adsorbent), a 50% deterioration in volumetric storage capacity was observed after 100 sorption cycles. [ 162 ] This deterioration could be mitigated by desorbing at 673 K under vacuum for 2 h. [ 162 ] Considering their thermal stability, a lower regeneration temperature may be required for MOF adsorbents.…”

“…[ 162 ] In the case of Maxsorb MSC‐30 (a commercial AC adsorbent), a 50% deterioration in volumetric storage capacity was observed after 100 sorption cycles. [ 162 ] This deterioration could be mitigated by desorbing at 673 K under vacuum for 2 h. [ 162 ] Considering their thermal stability, a lower regeneration temperature may be required for MOF adsorbents. In terms of onboard applications, a strategic design could be proposed, in which the exchangeable NG storage tanks undergo a centralized regeneration at refueling stations.…”

Preparation of Porous Carbons from Petroleum Pitch and Polyaniline by Thermal Treatment for Methane Storage

“…The textural characteristics of the activated carbons have been evaluated by N 2 adsorption at -196 ºC and CO 2 at 0 ºC [11,23] in a volumetric Autosorb-6B apparatus from Quantachrome. Before the analysis, the samples were outgassed at 250 ºC for 4 h.…”

“…To solve this problem, new materials have been tested with the aim to obtain high adsorption capacities in materials with high mechanical resistance [5,6,8]. Recent studies reported the preparation of HKUST-1 MOF in form of monolith that reported absolute volumetric methane and excess volumetric adsorption values of 259 and 230 V/V at 68 bar, respectively [11,12]. This monolith shows a delivery capacity, using the real bulk density, of 172 cm 3 (STP)cm −3 at 68 bar which are among the highest reported for monolithic materials, although the preparation of these monoliths are only tested in small monoliths [13].…”