TAILORING MICROPORE DIMENSIONS IN PILLARED CLAYS FOR ENHANCED GAS-ADSORPTION

A systematic investigation has been undertaken for tailoring the micro pore structure of the pillared clay. Besides the type of metal oxide ( e.g. Al2O3 vs. ZrO2) being used as the pillars, the important factors for determining the micropore structure are OH/Al ratio (for Al2O3-pil lared clay), calcination temperature and the starting clay. The effect of the cation exchange capacity (CEC) of the clay on the microporous structure (and consequently the adsorption properties) is reported for the first time. Two clays with widely different CECs are used: Arizon a montmorillonite (CEC=1.40 mequiv./g) and Wyoming montmorillonite (CE C=0.76 mequiv./g). The interlayer spacings of the pillared clays from these different clays are essentially the same, since the interlayer s pacing is controlled by the sizes of the oligomers that intercalate be tween the clay layers. However, the pillar density in the pillared cla y is substantially higher with a high CEC in the starting clay, and is shown to be approximately proportional to the CEC. Consequently, the interpillar spacing is substantially lower resulting from the higher C EC. The CH4 adsorption on the pillared clay is nearly doubled by the s maller interpillar spacing, due to the back-to-back overlapping potent ial in the micropores. The N-2 adsorption was not significantly influe nced because of its low polarizability (hence low inductive potential) . Increasing the calcination temperature of the Al2O3-pillared clay fr om 400 degrees C to 600 degrees C can decrease the interlayer spacing, but only by 1 Angstrom (from 8.7 Angstrom to 7.7 Angstrom). The CH4/N -2 adsorption ratio of 2.35 is reached on the Al2O3-pillared Arizona c lay that is calcined at 600 degrees C. Finally, the surface and pore v olume are influenced by the OH/Al ratio (or pH) during pillaring, sinc e this ratio determines the size and charge of the oligomers. A peak s urface area is reached at OH/Al=2.2.