Supercritical Fluid Technology: Silica Preparation And Impregnation Of 2-Phenyl Ethanol

This study has highlighted two different applications of supercritical fluid:sol-gel method following supercritical fluid drying for preparing fine silica particles(silica aerogel) and flavor impregnation(2-phenyl ethanol) into silica particles by using supercritical fluid carbon dioxide (ScCO₂).Sol-gel preparation of silica particles followed by ScCO₂ drying(extraction) has been addressed. The prepared silica particles were characterized by scanning electron microscope(SEM),BET analysis,laser particle size analyzer and Fourier transform infrared spectrometer(FT-IR).In particular,the effect of the drying pressure and temperature on the specific surface area of the produced silica particles was evaluated.Silica with specific surface area of 81-499m²/g were produced under the investigated pressures and temperatures.Keen focus was done on impregnation 2-phenyl ethanol(flavor) into prepared silica particles in comparison with MCM 41.The impregnation process involved:(1) vapor flavor impregnation (VFI) method by saturating the flavor through heating and suspending the dried silica,which allows the flavor to be adsorbed onto silica.(2) Supercritical fluid impregnation(SFI) method by immersing silica in a high pressure CO₂ tank containing flavor,which allows ScCO₂ to carry the flavor into the silica.For the later method,the effect of the impregnation pressure and temperature on the impregnation capacity was investigated.Results show that the modification of surface by drying silica in oven at 600℃for 2hrs was found to yield better flavor holding capability compared to the undried silica.Results also show the advantages by using SFI over VFI in fast impregnation and high impregnation capacity.These results were further tested using thermo gravimetric analysis and FT-IR,indicating the effect of SFI to the structure of the silica materials.Langmuir adsorption model was applied to the correlation of the adsorption isotherms from SFI,and the second Fickian diffusion equation was applied to the calculation of the SFI process,providing a fairly good description of the process.