Supercritical CO 2 intercalation of layered silicates

Abstract

In this study, we use supercritical CO 2 as the processing medium for intercalating the structure of natural clay, Cloisite Na +, and depositing CO 2-philic sugar acetate, β- d-galactose pentaacetate, between the layers of the clay. Based on our measurements of the phase behavior of the β- d-galactose pentaacetate–CO 2 system, we select two processing conditions: a dense gas solution (DGS) at 40 °C and 11.7 MPa with 2.4 wt.% sugar acetate in CO 2 and a gas-expanded liquid (GEL) at 40 °C and 7.9 MPa with 6.1 wt.% sugar acetate in CO 2. The morphology of the as-received natural clay and clay samples processed under the DGS and the GEL conditions is determined by wide-angle X-ray diffraction (XRD), transmission electron microscopy (TEM) and low-energy electron diffraction (LEED) methods. The XRD results indicate intercalation of the clay layers. While the ordered structure remains, the gallery spacing between Cloisite Na + layers is doubled, from 0.3 1 to 0.52 and 0.59 nm for DGS- and GEL-processing conditions, respectively. The LEED patterns of the processed clays show bright spots characteristic of the highly crystalline sugar acetate superimposed on the halo pattern of the clay, confirming the deposition of the sugar acetate in the intercalated structure of the clay after scCO 2 processing.