Methane Adsorption in Model Mesoporous Material, SBA-15, Studied by Small-Angle Neutron Scattering

Published

March 3, 2016

Author(s)

Wei-Shan NMN Chiang, Emiliano Fratini, Piero Baglioni, Daniel Georgi, Jin-hong Chen, Yun Liu

Abstract

The understanding of methane adsorption is important for may industrial applications, especially for the shale gas production, where it is critical to understand the adsorption/desorption of methane in pores even as small as a few nanometers. Even though gas adsorption in model porous materials has been investigated for Ar and other gases through isotherm measurement and X-ray diffraction, the adsorption mechanism of methane in model porous materials with small pore size is seldom studied. Especially, a detailed structure determination of methane adsorption is missing. Using small-angle neutron scattering (SANS), we have studied the adsorption of deuterated methane (CD₄)into one model mesoporous material, SBA-15, with pore diameter approximately of 6.8 nm at the temperature range from 20 K to 295 K at low pressure ({approximately equal to}kPa). The adsorption behaviors of methane as a function of temperature are resolved. A new scattering model is developed to analyzed the SANS patterns. Through the model fitting, the surface roughness of SBA-15 matrix is estimated. It is found that the rough surface of the solid matrix can retain a large amount of CD₄ at temperatures much higher than the capillary condensation temperature, T_c. The density of the adsorbed CD₄ on the rough surface is significantly higher than the corresponding bulk density at the same temperature and pressure conditions. These findings are important for the shale field in order to better estimate the total gas in place and gas transport properties in the shale rocks. At temperature below T_c, they cylindrical pores are fully by CD₄ and the mass density of confined CD₄ liquid and solid is accurately determined. Detailed theoretical analysis and experimental verification show that SANS patterns at temperature beyond T_c are by far more sensitive to the change of the excess adsorption, Eads,rather than the average density of adsorbed layers commonly used in many studies. The model we establish can be used to analyze future SANS/SAXS data for gas confined in similar model porous materials.

Citation

Journal of Physical Chemistry C

Volume

120

Issue

8

Pub Type

Journals

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Keywords

methane, small-angle neutron scattering, mesoporous material, SBA-15, gas adsorption, shale

Citation

, W. , Fratini, E. , Baglioni, P. , Georgi, D. , Chen, J. and Liu, Y. (2016), Methane Adsorption in Model Mesoporous Material, SBA-15, Studied by Small-Angle Neutron Scattering, Journal of Physical Chemistry C, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=919834 (Accessed April 25, 2024)