Phase behavior and reverse micelle formation in supercritical CO with DTAB and F-pentanol for decontamination of radioactive wastes

放射性廃棄物の除染を目標としたDTABとF-pentanolによる超臨界二酸化炭素での逆ミセルの生成と相挙動の研究

倉橋 健介; 富岡 修 ; 目黒 義弘  

Kurahashi, Kensuke; Tomioka, Osamu; Meguro, Yoshihiro

放射性廃棄物の除染を目標とした超臨界二酸化炭素への金属分離法を開発するため、超臨界二酸化炭素での逆ミセルの研究を行った。DTABとF-pentanolを用いることで逆ミセルの生成が確認され、38MPaで0.42mol/Lの水を超臨界二酸化炭素に溶解することができた。これは純粋な超臨界二酸化炭素に対する水の溶解度の3倍にあたる。水の代わりに0.1mol/Lの硝酸の溶解を試みたところ、水と変わらぬ条件で硝酸を溶解することができた。また、F-pentanolの存在によって逆ミセルに含まれない水分子の溶解が向上し、F-pentanolと水の比率が超臨界二酸化炭素での水の相挙動に影響を与えることがわかった。

To develop a metal separation method using supercritical CO (scCO) solvent for the decontamination process of radioactive wastes, the reverse micelle formation in scCO was investigated. Dodecyltrimethylammonium bromide (DTAB) as a surfactant to form the reverse micelles and 2,2,3,3,4,4,5,5-octafluoro-1-pentanol (F-pentanol) as a modifier to increase the solubility of DTAB into scCO were used. The reverse micelles could be formed by using 0.02 mol/dm DTAB and 0.45 mol/dm F-pentanol. A water concentration dissolved in scCO was increased with an increase of pressure, and 0.42 mol/dm water, which was 3 times larger than that in the neat CO, could be dissolved in scCO at 38 MPa. Moreover, 0.1 mol/dm HNO could dissolve at the same pressure as water. On the other hand, it was found that the solubility of water at outside of reverse micelles increased with F-pentanol. The ratio of water and F-pentanol affected the phase behavior of water in scCO.