A Better Understanding of the SBA-15 Pores Filling through Textural Changes in CMK-3 Carbon Synthesis and Its CO2:CH4 Adsorption Selectivity

Abstract

This text reports the morphological and textural behavior of the synthesis stages of a CMK-3 carbon type using a silicon matrix of the SBA-15 type calcined at 823 K as a template. During the synthesis, three intermediate materials were obtained because of (i) the addition of sucrose to the SBA-15 template (CCMK3-1st), (ii) the addition of sucrose to the CCMK3-1st material (CCMK3-2nd), and (iii) the carbonization by pyrolysis of the by-product CCMK3-2nd (CCMK3-F). The texture of the above materials was found by analyzing the N2 adsorption isotherms, applying the classical adsorption theories to obtain the BET-specific surface and the meso- and micropore distributions by the BJH and Dubinin–Astakhov (DA) methods, respectively, in addition to the non-localized density functional theory (NLDFT). Similarly, with high resolution, the samples were analyzed morphologically by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Finally, the adsorption isotherms of CO2 and CH4 of the CMK-3 sample were obtained at six different temperatures in the interval of 243 to 303 K to evaluate the behavior of the isosteric enthalpy of adsorption (qst) and its CO2:CH4 ideal selectivity. The final CMK-3 carbon presented two families of micro- and mesopores of 1.5 and 3.2 nm, nanopipe diameters of 3.5 nm, and a specific surface area of 1350 m2/g. It also presented values of 6.0 and 2.4 mmol/g adsorbed CO2 and CH4 at 243 K, respectively, and strong intermolecular interactions, with qst values higher than 22 kJ/mol reflected in high selectivity values for an ideal mixture of CO2:CH4 (30:70%).