應用界面活性劑於超臨界二氧化碳萃取親水性物質

Abstract

反微胞的形成為改善超臨界二氧化碳萃取極性物質的一個策略，但是幾乎所有商業上可購買到的界面活性劑在超臨界二氧化碳中溶解度皆不理想。然而，在超臨界二氧化碳中加入有機修飾劑可以有效改善這些界面活性劑的溶解度。在本研究我們測量了七種商業上可購買到離子性界面活性劑在超臨界二氧化碳中的溶解度，我們發現其中DDAB（didodecyldimethylammonium bromide）和AOT（sodium bis-2-ethylhexyl sulfosuccinate）在壓力高於225 bar、修飾劑乙醇濃度20%v/v的狀況下可以有高於18000 mg/l的溶解度。如此高的溶解度可確保界面活性劑於超臨界二氧化碳中形成反微胞，進而溶解親水性物質。我們成功地使用AOT和DDAB萃取出離子性染料（亞甲藍和甲基橙），但蛋白質-細胞色素C的萃取未能成功。另外，非離子性界面活性劑－Tetraethylene glycol n-lauryl ether證明能成功萃取出離子性染料。由於非離子性界面活性劑比離子性界面活性劑具有更低的極性，所以其在超臨界二氧化碳中具有較佳溶解度。因此我們可以在更低的操作壓力及修飾劑濃度下進行親水性物質的萃取。

Reverse micelle formation is presented in this study as a strategy for improving the extraction of polar species with supercritical carbon dioxide (SC CO2). Only mediocre solubilities of almost all commercial surfactants in neat SC CO2 have been reported in the literature. However, adding organic modifiers to SC CO2 can increase the surfactant solubilities. We measured the solubilities of seven commercially available ionic surfactants in the modifier-containing SC CO2. The solubilities of DDAB (didodecyldimethylammonium bromide) and AOT (sodium bis-2-ethylhexyl sulfosuccinate) exceeded 18000 mg/L at 225bar while the concentration of ethanol was 20% v/v. The high surfactant solubilities ensured formation of reverse micelle in SC CO2 for dissolving hydrophilic compounds. We successfully used AOT and DDAB to extract two ionic dyes (methylene blue & methyl orange), but failed to extract protein molecules - cytochrome c. In addition, a nonionic surfactant, i.e. tetraethylene glycol n-lauryl ether, was demonstrated to be able to extract the ionic dyes. Due to the relatively lower polarity of this nonionic surfactant and thus higher solubility in SC CO2, the extraction could be accomplished under relatively lower applied pressure and modifier concentration.