Hydrotalcite Materials for Carbon Dioxide Adsorption at High Temperatures: Characterization and Diffusivity Measurements

Abstract

Hydrotalcites are receiving considerable attention as adsorbents, catalysts, and catalyst precursors. However, the use of hydrotalcites as an adsorbent material for carbon dioxide has only been considered recently. In this work, three commercial hydrotalcites, Puralox MG30, MG50, and MG70, were used for the removal of CO₂ at temperatures in the range 423–623 K. The adsorbent materials were characterized by use of scanning electron microscopy/energy dispersive x‐ray, mercury porosimetry, and N₂ adsorption at 77 K, which indicated the presence of micropores. The HK plot suggested pore‐width values around 0.55 nm. The BET surface areas were 199, 154, and 144 m²/g for MG30, MG50, and MG70, respectively. The micropore areas calculated by the DR method were 206, 161, and 146 m²/g. The diffusivity of CO₂ onto hydrotalcite adsorbents was measured by the zero length column method. Kinetic studies indicated that the controlling mechanism for mass transfer inside the extrudate was micropore diffusion. The reciprocal of the time constants for micropore diffusion (D _c/l ²) were 8.5 × 10⁻³–15.3 × 10⁻³ s⁻¹ for MG30, 8.0 × 10⁻³–10.4 × 10⁻³ s⁻¹ for MG50, and 6.8 × 10⁻³–11.3 × 10⁻³ s⁻¹ for MG70, in the temperature range 423–623 K.

Keywords:

• Adsorption
• Carbon dioxide
• Hydrotalcite
• ZLC

Acknowledgments

José L. Soares was a Ph.D. student supported by CNPq (Brazil) and Carlos A. Grande is a Ph.D. student at the LSRE, supported by the Foundation for Science and Technology (FCT‐Portugal). This work is part of an on‐going LSRE project “Adsorption‐enhanced methane steam‐reforming process for hydrogen production.”