Anomalous Isosteric Enthalpy of Adsorption of Methane on Zeolite-Templated Carbon

Abstract

A thermodynamic study of the enthalpy of adsorption of methane on high surface area carbonaceous materials was carried out from 238 to 526 K. The absolute quantity of adsorbed methane as a function of equilibrium pressure was determined by fitting isotherms to a generalized Langmuir-type equation. Adsorption of methane on zeolite-templated carbon, an extremely high surface area material with a periodic arrangement of narrow micropores, shows an increase in isosteric enthalpy with methane occupancy; i.e., binding energies are greater as adsorption quantity increases. The heat of adsorption rises from 14 to 15 kJ/mol at near-ambient temperature and then falls to lower values at very high loading (above a relative site occupancy of 0.7), indicating that methane/ methane interactions within the adsorption layer become significant. The effect seems to be enhanced by a narrow pore-size distribution centered at 1.2 nm, approximately the width of two monolayers of methane, and reversible methane delivery increases by up to 20% over MSC-30 at temperatures and pressures near ambient.

Enthalpy–entropy compensation for isosteric state adsorption at near ambient temperatures

“…In the case of the tested system of solid phase and gas, the isosteric heat of adsorption in view of a is either: a. constant (Czepirski and Jagiełło 1989;Sircar et al 1999;Stadie et al 2012), b. monotonically decreasing (Burevski et al 1991;PeraTitus 2016;Zukal et al 2009;Terzyk et al 2016;Gauden et al 2016;Kowalczyk et al 2017;Czepirski and Jagiełło 1989;Sircar et al 1999;Stadie et al 2012;Barrer and Gibbons 1963a;Guo et al 2006), c. anomalous (increase and decrease) Gauden et al 2016;Kowalczyk et al 2017;Stadie et al 2012),…”

A Generalized Law of Corresponding States for the Physisorption of Classical Gases with Cooperative Adsorbate–Adsorbate Interactions

“…6,7,8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 As seen in Figure 1, there is good agreement between the measured methane and krypton isotherms using Quinn's hypothesis of corresponding states, with only moderate discrepancies (less than 25%). The ethane isotherms, however, deviate significantly from those of the other gases, with discrepancies of ~50%.…”

“…11,6,7 Methane and krypton isotherms were fitted with a superposition of Langmuir isotherms to extract thermodynamic quantities 11,6,7 . This yields analytically differentiable fits that are useful in determining the absolute adsorption, and the isosteric enthalpy of adsorption.…”

Large-scale synthesis of high-quality zeolite-templated carbons without depositing external carbon layers

“…This can lead to significantly enhanced electrochemical properties under high current density conditions [15]. ZTCs are also known as a very promising adsorbent for methane storage due to their large micropore volume and narrow micropore size distribution [16,17]. Another remarkable feature of ZTCs is that template zeolites such as NaX and NaY are very cheap and currently produced at an industrial scale.…”