On Validity of Supercritical Petroleum Ether Drying as AlternativeMethod for Preparation of Carbon Aerogels from Sol-gelPolymerization of Phenolic Resole and Methylolated Melamine

摘要

Drying of organic gels under supercritical fluid is an effective way to alleviate structure change sufferedrnfrom drying of gels by other methods, such as evaporating-desiccation, cryo-desiccation, etc. because no surfacerntension is imposed on the walls of nanopores. However, the process is quiet long if carbon dioxide is used asrnsupercritical solvent mainly because temperature is low and as a result diffusive coefficient of acetone intornsupercritical carbon dioxide is quiet low, which is resulted from strain of acetone within backbone of organic gels.rnIn this paper, organic and carbon aerogels were synthesized from sol-gel polymerization of phenolic resole andrnmethylolated melamine. Supercritical petroleum ether (30~60rn) drying (SPD) and supercritical carbon dioxiderndrying (SCD) of organic gels was compared. It was found that, the SPD , which was carried out at 240℃rnandrn6.0 Mpa for one hour, caused volume reduction of 38.9% based on volume of original solution, while the SCDrncaused volume reduction of 27.5%. However, after organic aerogel obtained by SCD was heat-treated at the samerntemperature profile as used in the SPD, the total volume shrinkage of gels by the two methods was almost the same.rnAlthough BET surface area and mesopore volume of organic aerogel from SCD are higher than that of organicrnaerogel from SPD, BET surface area, mesopore volume and external surface area of carbon aerogel from SPD arernhigher than that of carbon aerogel from SCD, indicating that SPD can be used as an alternative method for SCDrnfor the preparation of carbon aerogel.