Modified supercritical CO2 extraction of amine template from hexagonal mesoporous silica (HMS) materials: Effects of template identity and matrix Al/Si molar ratio

摘要

In this work, the primary amine template has been extracted from freshly synthesized hexagonal mesoporous silica (HMS) materials by means of modified supercritical carbon dioxide at 60-85 °C under 10.0-20.0 MPa. The influences of amine identity and matrix Al/Si ratio on the extraction efficiencies and structural properties of HMS thus obtained are investigated in detail. The results show that the extraction efficiency is strongly dependent on the pore size of the HMS materials produced by five different templates. For aluminium-incorporated samples, the extraction efficiency is observed to decrease with the Al/Si molar ratio since as the Al/Si molar ratio increases, more amine will get protonated and the matrix/template interactions become stronger, subsequently rendering the extraction more difficult and the efficiency decrease. The formic acid modifier has resulted in better extraction performance than methanol, yielding higher extraction efficiencies. The SFE-treated materials exhibit better structural properties like higher pore volume and specific surface area as compared to those prepared by conventional calcinations. Besides, results of pyridine adsorption and conversion of 2-propanol to propylene suggest that the SFE-treated HMS materials may have higher acidity than the directly calcined samples.