Study the transport properties of anion and cation exchange membranes toward various ions using chronopotentiometry
The transport properties of various anion and cation exchange membranes were studied in different electrolyte solutions using chronopotentiometry technique to get insight about the influence of the counter ion on the transport properties of the membranes. The investigated samples include heterogeneous ion exchange membranes varying in the functionality of fixed charged groups, physical properties of the polymer and the preparation procedure. Chloride and nitrate were investigated as counter-ion in their sodium salts for anion exchange membranes while sodium, calcium, potassium, and magnesium were selected as counter-ion in their chloride salts to study cation exchange membranes transport properties. First, the current – voltage curve of an ion exchange membrane in a given solution was recorded to obtain the limiting current, then a constant current above the limiting current was used for chronopotentiometry measurement. In all the studied membranes the potential across the membrane remained constant for a time interval called the transition time , when a constant current was applied. Then the potential increased rapidly to reach the steady state potential. The permselectivty and the transport number of a membrane were calculated using the corresponding transition time.
Characterization of electrodialysis membranes by chronopotentiometry
Abstract In the present work, chronopotentiometry is used to measure transport numbers of ion-exchange membranes in contact with solutions having a concentration up to 1 M , similar to that found in applications of electromembrane separation processes. Usually, only dilute solutions, with a concentration lower than 0.01 M , can be used for the determination of transport numbers of membranes. For the case of concentrated solutions up to 1 M , we finally used a flat bilayer membrane where one layer consists of the ion-exchange membrane under study, the other being a neutral membrane of agar-agar. But, for the calculation of transport numbers, it was necessary to measure the diffusion coefficient in the neutral agar-agar layer for the electrolyte used; this was done by means of varying the concentration. Then, the determination of the passage of chloride ions through a heterogeneous Rhone-Poulenc ion-exchange membrane, shows a decrease in transport numbers when the concentration of counter-ions rises, in agreement with the reduction of the Donnan exclusion.
Synthesis of 2,4-dideoxy-.beta.-D-erythro-hexopyranosyl nucleosides
The synthesis of 1-(2,4-dideoxy-β-D-erythro-hexopyranosyl)thymine (12) 1 was accomplished using two different synthetic routes. It was obtained starting either from 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose or from tri-O-acetyl-D-glucal. The other modified nucleosides, with either a cytosine, guanine, or adenine moiety, were synthesized using the second reaction scheme. Deoxygenation reactions were accomplished with the (2,4-dichlorophenoxy)thiocarbonyl derivatives generated in situ