Processing of microporous VPI-5 molecular sieve by using supercritical CO2:: stability and adsorption properties

The stability and adsorption behavior of the microporous molecular sieve VPI-5, an AlPO4 hydrate phase, processed using supercritical carbon dioxide (SCCO2) as a solvent, were explored. Different thermal treatments up to 373 K were carried out on samples of VPI-5 previously treated with methanol, ethanol or 2-propanol. The thermally treated samples were characterized by X-ray diffraction and low-temperature N-2 adsorption. VPI-5 was completely transformed to AlPO4-8 when it was heated up to 373 K in ambient air. By previously shaking VPI-5 samples with methanol the transformation was partially avoided. Additionally, when the thermal treatment was carried out in an SCCO2 atmosphere, the VPI-5 structure was preserved. VPI-5 was charged with low molecular weight organic compounds using a high-pressure apparatus and employing SCCO2 as a solvent. The adsorption behavior of either a pure solute or a mixture of two solutes into the channels of VPI-5 was studied as a function of time, pressure and temperature of adsorption. A significant time, pressure- and temperature-dependence for the absorbed amount was found. (C) 2002 Elsevier Science Inc. All rights reserved.