ABSTRACT
Ion exchanges by aromatic anions (AAs) of varying volumes on anion exchange resins of different cross linking (CL)-degrees were studied. The exchanges on the resins with low CL-degrees having the larger and the less independent exchange sites proceeded fast and completely at a high AA concentration; the selectivity coefficient increased with the progress of the exchange, due to the cooperative interaction between exchanged AAs. In contrast, in the exchanges on the resins with a CL-degree of 8% having the smaller (more specifically, having the average volume of 300 Å3 with a variance) and the more independent exchange sites, the large AA may not enter the exchange sites having sizes smaller than the volume of AA to cause mid-saturation of ion exchange and to increase the reaction time because of the need for detouring; the selectivity coefficients were substantially independent of the progress of the exchange, due to the isolation of each AA.
ABSTRACT
Penetration of salt solutions into cation exchange resins was used to measure the volume of a space within the resin phase (the inner space), which was usable for ion exchange in principle but not fully in practice. The average volume of the inner space per functional group was significantly dependent on the type and the concentration of the salt (250 - 450 Å3) for a resin having the cross-linking degree of 8%, while being less dependent on the type and the concentration of the salt (160 - 240 Å3) for a resin having the cross-linking degree of 12%. The salt concentration ratio of the solution filling the inner space to the outer solution decreased with a decrease in concentration of the outer salt solution due to the osmotic pressure, and decreased with an increase in cross-linking degree due to the smaller volume and the higher independency of the inner space.
