Sorption of CO₂ and CH₄ on Raw and Calcined Halloysite—Structural and Pore Characterization Study

• Main Authors: Anna Pajdak, Norbert Skoczylas, Arkadiusz Szymanek, Marcin Lutyński, Piotr Sakiewicz
• Format: Article
• Language: English
• Published: MDPI AG 2020-02-01
• Series: Materials
• Subjects: halloysite; pore structure; sorption capacity of ch₄ and co₂; kinetics of diffusion; effective diffusion coefficient
• Online Access: https://www.mdpi.com/1996-1944/13/4/917

The article presents comparative characteristics of the pore structure and sorption properties of raw halloysite (R-HAL) and after calcination (C-HAL) at the temperature of 873 K. Structural parameters were determined by optical scanning and transmission electron microscopy methods as well as by mercury porosimetry (MIP, Hg) and low-pressure nitrogen adsorption (LPNA, N₂, 77 K). The surface area parameter (LPNA) of halloysite mesopores before calcination was 54&#8722;61 m²/g. Calcining caused the pore surface to develop to 70&#8722;73 m²/g. The porosity (MIP) of halloysite after calcination increased from 29% to 46%, while the surface area within macropores increased from 43 m²/g to 54 m²/g. The total pore volume within mesopores and macropores increased almost twice after calcination. The course of CH₄ and CO₂ sorption on the halloysite was examined and sorption isotherms (0&#8722;1.5 MPa, 313 K) were determined by gravimetric method. The values of equilibrium sorption capacities increased at higher pressures. The sorption capacity of CH₄ in R-HAL was 0.18 mmol/g, while in C-HAL 0.21 mmol/g. CO₂ sorption capacities were 0.54 mmol/g and 0.63 mmol/g, respectively. Halloysite had a very high rate of sorption equilibrium. The values of the effective diffusion coefficient for methane on the tested halloysite were higher than <i>De</i> &gt; 4.2 &#215; 10^&#8722;7 cm²/s while for carbon dioxide <i>De</i> &gt; 3.1 &#215; 10^&#8722;7 cm²/s.