Organic template removal from hexagonal mesoporous silica by means of methanol-enhanced CO2 extraction: Effect of temperature, pressure and flow rate

Supercritical fluid extraction was evaluated for removing the amine surfactant from hexagonal mesoporous silica materials. In this study, methanol-enhanced supercritical CO2 extraction was carried out on freshly synthesized materials by means of a dynamic method. Experiments were performed at pressure ranging from 10.0 to 25.0 MPa, temperature from 45 to 105 °C, CO2 flow rate from 0.45 to 4.5 ml/min, and methanol flow rate from 0.05 to 0.5 ml/min. The influence of these parameters on the extraction has been evaluated in terms of the surfactant recovery. The results show that by using this method up to 96% of the total amine surfactant used is extracted out of as-synthesized mesoporous materials within 1 h extraction whereas only 78% of the surfactant can be removed by liquid ethanol extraction. The materials processed by supercritical CO2 extraction are found to possess better structural properties as reflected by the X-ray diffraction analysis and N2 adsorption results, and thus have higher thermal and hydrothermal stability than those obtained by liquid ethanol extraction or high temperature calcination.

Temperature and pressure dependence of amine recovery from as-synthesized HMS powders: liquefied CO2 with flow rate = 1.8 ml/min, methanol modifier with flow rate = 0.2 ml/min, time = 1 h.Figure optionsDownload as PowerPoint slideResearch highlights▶ Amine recovery varies up to 96% dependent on extraction conditions. ▶ Isobaric recovery shows two maximum values at about 50 and 85 °C. ▶ Recovery isotherm has two minimum values at about 15.0 and 22.5 MPa. ▶ Amine recovery initially increases fast with the fluid rate of CO2 or methanol. ▶ SFE technology performs better than liquid ethanol extraction or calcination.