(396g) Experimental and Theoretical Comparative Study of Methane Adsorption On Activated Carbons and MOF-Basolite

Experimental and Theoretical Comparative
Study of Methane Adsorption on Activated Carbons and MOF-Basolite

Yuguo
Wang^*, Cemal Ercan, Mohammed Hashim, Anwar Khawajah, Rashid Othman

Research & Development Center, Saudi Aramco, Dhahran, 31311, Saudi Arabia

(yuguo.wang@aramco.com)

Adsorbed natural gas (ANG)
is type of natural gas storage at low to intermediate pressure ranges (35-50
bars) by adsorption on porous solid materials that are packed into a vessel. Compared
with the compressed natural gas (CNG), ANG offers higher energy density and higher volume to
volume (V/V) storage capacity at typical natural gas pipeline conditions,
pressure less than 50 bars and temperature less than 55°C. For
ANG applications, microporous
activated carbons and metal-organic frameworks (MOF) are
potential candidate materials¹. In this paper, five granular activated
carbons labeled as AC1, AC2, AC3, AC4 and AC5 and one commercial MOF ? Basolite pellets (3×3 mm) were
used in the comparative experimental and theoretical study of methane
adsorption.

Adsorbed amount based on the moles of methane
adsorbed per gram of activated carbon increases in the order with the BET
surface area as Basolite(867 m²/g)<AC4(999 m²/g) <
AC1(1235 m²/g) < AC3(1426 m²/g) <<AC5(1510 m²/g)
<AC2(1589 m²/g). Due to the synergistic effect of BET surface
area, micropore volume, packing density and pore size
distribution, the adsorbed amount based on V/V increases in a different order
of Basolite<AC4<AC2<AC1<AC3<AC5.

Numerical optimization is done by fitting the
temperature dependent empirical adsorption isotherm equation - Toth equation for methane adsorption on AC5 and Basolite ? Figure 1. The isothermal adsorption data is
fitted with high accuracy of average relative error, 1.4532% and 5.1070% respectively
for methane-AC5 and methane-Basolite adsorption
systems.

To obtain one of the key design factors of an adsorber, the above numerically optimized parameters were
used in calculating the isosteric heat of adsorption at
different fractional loading at 21°C. The isosteric heat of adsorption versus fractional loading,
Figure 2, shows that at less than 0.3 fractional loading, the initial isosteric heat of adsorption for methane-Basolite system is higher than that for methane-AC5 system,
but it decreases faster as fractional loading increases. This indicates the
higher degree of heterogeneity and could explain the close to rectangular
isotherm shape of the methane-Basolite system in
Figure 1. This isosteric heat of adsorption is
further numerically integrated to calculate the integral heat of adsorption
during the whole adsorption process using the novel procedure reported earlier².

References

[1] A. Celzard, V. Fierro. 
Energy & Fuels, (2005), 19, 573-583.

[2]Y. Wang, C. Ercan,
A. Khawajah, R. Othman. AIChE Journal, (2012), 58,
782-788.