Hydrotalcite materials for carbon dioxide adsorption at high temperatures:: Characterization and diffusivity measurements

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 N-2 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 m(2)/g for MG30, MG50, and MG70, respectively. The micropore areas calculated by the DR method were 206, 161, and 146 m(2)/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 8.5x10(-3)-15.3x10(-3) s(-1) for MG30, 8.0x10(-3)-10.4x10(-3) s(-1) for MG50, and 6.8x10(-3)-1.3x10(-3) s(-1) for MG70, in the temperature range 423-623 K.