Micro-Mesoporous Monolithic Carbons with Ultra-High Methane Adsorption Capacity for Cyclic Capture and Delivery of Liquefied Natural Gas Vapors at Cryogenic Conditions

Abstract

The liquefied natural gas (LNG) terminal performance can be enhanced by incorporating a unit for storing LNG vapor in an adsorbed state (ALNG) at subcritical temperatures. The ALNG storage efficiency can be improved using a micromesoporous monolithic adsorbent that exhibited a high gravimetric methane uptake through the impacts of volume filling of micropores, monolayer formation on the mesopore surface, and capillary condensation in transient micro- and mesopores. A high volumetric storage capacity is achieved when using an adsorbent in monolithic form. Micromesoporous carbons are produced from wood chips and sawdust using two-stage KOH and combined H₃PO₄/KOH activation methods, respectively, and shaped into monoliths. Experimental methane adsorption data for the powdered and monolithic carbons over a temperature range of 143–293 K and up to 0.12 MPa are used for gas uptake predictions under sub- and supercritical conditions by considering the adsorption mechanisms in micro- and mesopores. The volumetric storage capacity of an ALNG storage prototype loaded with the ES-1M-CMC-SHC monolithic carbon is measured up to methane saturation pressure under subcritical conditions. The deliverable volumetric capacity of the ALNG tank reaches 380 m³(NTP)/m³ under the charging/discharging conditions of 143/293 K and 0.8/0.1 MPa, respectively, exceeding the performance reported for most promising adsorbents.