Development of the system for membrane separation of fatty aicd from supereritical carbon dioxide

采用溶胶-凝胶法制备了平均孔径为3.3 nm的多孔硅薄膜，并将其用于超临界二氧化碳中溶质的分离。从溶质的吸附性质、溶质从膜上的脱附速率以及溶质在二氧化硅表面附近的势能等方面研究了溶质的渗透特性。结果表明，咖啡因先强烈吸附在表面，然后缓慢脱附，形成吸附层，使微孔变窄，产生分子筛效应。因此，拒收值为正值。另一方面，正辛酸，这是很好的吸附和快速解吸，截留值为负值。据推测，分子由于其势能而填充孔，然后通过跨膜压力被迫流过孔。用沸石膜从超临界二氧化碳中分离咖啡因，并进行了渗透蒸发试验。Dubininin-Astakhov分析结果表明，NaY分子筛膜的孔径为亚纳米级。沸石膜对月桂酸的截留率为0.88。沸石膜在超临界CO_2膜分离中有良好的应用前景。

A thin porous silica membrane (average pore size of 3.3 nm) was prepared by the sol-gel method and used to separate the solute from supercritical carbon dioxide. The characteristics of solute permeation were investigated in respect of the adsorption properties of the solute, the desorption rate of the solute from the membrane being measured and the potential energy of soulte near the silica surface being calculated by the molecular modeling technique. It was found that caffeine was strongly adsorbed to the surface and then slowly desorbed to form an adsorption layr, making the pores narrower and causing a molecular-sieving effect. Therefore, the rejection value was positive. On the other hand, the rejection value of n-octanoic acid, which was well adsorbed and rapidly desorbed, was negative. It is presumed that the molecules filled the pores due to their potential energy and were then forced to flow through the pores by the transmembrane pressure. Separation of caffeine from supercritical carbon dioxide was carried out with a zeolite membrane that has been tested in pervaporation. The pore size of a NaY zeolite membrane was evaluated to be subnanometer scale from the result of Dubinin-Astakhov analysis. The rejection of lauric acid was 0.88 for the zeolite membrane. A zeolite membrane was shown to be useful in SCCO_2 membrane separation.