Andreaus J, Draxler J, Marr R, Lohner H
Department of Chemical Engineering and Environmental Technology, Technische Universitat Graz, Inffeldgasse 25, Graz, A-8010, Austria
J Colloid Interface Sci. 1997 Jan 15;185(2):306-12. doi: 10.1006/jcis.1996.4556.
The solubility and the partitioning of p- and o-xylene in aqueous solutions containing M-alpha-CD, a partially methylated alpha-cyclodextrin, and the anionic surfactant sodium dodecyl sulfate (SDS) were studied by extraction experiments to evaluate the applicability of liquid membrane permeation for the separation of xylene isomeres. Experiments were carried out with the pure xylenes and 1:1 mixtures of o- and p-xylene. The interactions of M-alpha-CD and SDS and their effects on the solubility and partitioning of xylenes were investigated. M-alpha-CD was found to form 1:1 complexes with p- and o-xylene. Formation constants were determined as 141 M-1 for p-xylene and 48 M-1 for o-xylene, respectively, which are higher than those reported with nonmethylated alpha-CD. This can be explained by additional hydrophobic interactions with the methyl groups of the cyclodextrin. In contrast to the solubility in CD solutions, o-xylene was found to be more soluble than p-xylene in aqueous solutions of SDS. At constant concentrations of M-alpha-CD the addition of SDS led to the displacement of p-xylene from the cyclodextrin cavity, which resulted in a decrease in its solubility. This decrease lasted until micelles were formed. Due to the solubilization of p-xylene in the micelles, further addition of SDS resulted in a linear increase in the solubility of p-xylene. However, at constant CD concentrations the solubility of o-xylene increased with the addition of SDS until about 5 mmol/liter SDS. This might be attributed to the formation of a ternary complex consisting of cyclodextrin, o-xylene, and SDS. At SDS concentrations greater than 5 mmol/liter, the solubility of o-xylene decreased, which was probably due to the formation of a more stable complex between SDS and M-alpha-CD. An addition of SDS beyond a critical concentration (CMC), where micelles are formed, resulted again in a linear increase of o-xylene solubility. The CMC was found to depend linearly on the concentration of M-alpha-CD in aqueous solution. Extraction experiments with a 1:1 mixture of o- and p-xylene showed that the two xylenes and SDS are in competition for M-alpha-CD. Since surfactants are always present when using emulsion liquid membranes and due to the complex interactions between SDS, the xylenes, and M-alpha-CD, no sufficient selectivity for the separation of the xylenes by liquid membrane permeation could be achieved.
通过萃取实验研究了对二甲苯和邻二甲苯在含有部分甲基化α-环糊精（M-α-CD）及阴离子表面活性剂十二烷基硫酸钠（SDS）的水溶液中的溶解度和分配情况，以评估液膜渗透法用于分离二甲苯异构体的适用性。实验使用了纯二甲苯以及邻二甲苯和对二甲苯的1:1混合物。研究了M-α-CD与SDS的相互作用及其对二甲苯溶解度和分配的影响。发现M-α-CD与对二甲苯和邻二甲苯形成1:1络合物。对二甲苯和邻二甲苯的形成常数分别测定为141 M⁻¹和48 M⁻¹，高于未甲基化α-环糊精的报道值。这可以通过与环糊精甲基的额外疏水相互作用来解释。与在环糊精溶液中的溶解度相反，发现邻二甲苯在SDS水溶液中的溶解度比对二甲苯更高。在M-α-CD浓度恒定的情况下，添加SDS导致对二甲苯从环糊精腔中被置换出来，这导致其溶解度降低。这种降低一直持续到形成胶束。由于对二甲苯在胶束中的增溶作用，进一步添加SDS导致对二甲苯溶解度呈线性增加。然而，在环糊精浓度恒定的情况下，邻二甲苯的溶解度随着SDS的添加而增加，直至约5 mmol/L的SDS。这可能归因于由环糊精、邻二甲苯和SDS组成的三元络合物的形成。在SDS浓度大于5 mmol/L时，邻二甲苯的溶解度降低，这可能是由于SDS与M-α-CD之间形成了更稳定的络合物。在形成胶束的临界浓度（CMC）以上添加SDS，再次导致邻二甲苯溶解度呈线性增加。发现CMC与水溶液中M-α-CD的浓度呈线性相关。用邻二甲苯和对二甲苯的1:1混合物进行的萃取实验表明，两种二甲苯和SDS竞争M-α-CD。由于在使用乳液液膜时总是存在表面活性剂，并且由于SDS、二甲苯和M-α-CD之间复杂的相互作用，通过液膜渗透法分离二甲苯无法实现足够的选择性。
