Electrodialysis Of Solutions Research Articles

Current-Voltage and Transport Characteristics of Heterogeneous Ion-Exchange Membranes in Electrodialysis of Solutions Containing a Heterocyclic Amino Acid and a Strong Electrolyte.

The alterations in current-voltage and transport characteristics of highly basic and strongly acidic ion-exchange membranes, during the electrodialysis of solutions containing a heterocyclic amino acid and a strong electrolyte, were studied. An increase in the catalytic activity of the water splitting process at the surface of heterogeneous MK-40 and MA-41 membranes upon prolonged contact with proline and tryptophan solutions was found. A significant effect of electroconvection on the components mass transfer through the cation-exchange membrane in the intensive current mode of electrodialysis was revealed for the solution containing a heterocyclic amino acid along with mineral salt (NaCl). This led to a reduction in the length of the "plateau" of the membrane's current-voltage characteristics, in comparison with the characteristics for an individual sodium chloride solution with the same concentration. The changes in the characteristics of the studied ion-exchange membranes caused by contact with solutions containing heterocyclic amino acids during electrodialysis were reversible when applying electrochemical regeneration (cleaning in place) using the overlimiting current mode, corresponding to the region of facilitated transport for these ampholytes.

Recovery of the N,N-Dibutylimidazolium Chloride Ionic Liquid from Aqueous Solutions by Electrodialysis Method.

Ionic liquids (ILs), named also as liquid salts, are compounds that have unique properties and molecular architecture. ILs are used in various industries; however, due to their toxicity, the ILs’ recovery from the postreaction solutions is also a very important issue. In this paper, the possibility of 1,3-dialkylimidazolium IL, especially the N,N-dibutylimidazolium chloride ([C4C4IM]Cl) recovery by using the electrodialysis (ED) method was investigated. The influence of [C4C4IM]Cl concentration in diluate solution on the ED efficiency was determined. Moreover, the influence of IL on the ion-exchange membranes’ morphology was examined. The recovery of [C4C4IM]Cl, the [C4C4IM]Cl flux across membranes, the [C4C4IM]Cl concentration degree, the energy consumption, and the current efficiency were determined. The results showed that the ED allows for the [C4C4IM]Cl recovery and concentration from dilute solutions. It was found that the [C4C4IM]Cl content in the concentrates after ED was above three times higher than in the initial diluate solutions. It was noted that the ED of solutions containing 5–20 g/L [C4C4IM]Cl allows for ILs recovery in the range of 73.77–92.45% with current efficiency from 68.66% to 92.99%. The [C4C4IM]Cl recovery depended upon the initial [C4C4IM]Cl concentration in the working solution. The highest [C4C4IM]Cl recovery (92.45%) and ED efficiency (92.99%) were obtained when the [C4C4IM]Cl content in the diluate solution was equal 20 g/L. Presented results proved that ED can be an interesting and effective method for the [C4C4IM]Cl recovery from the dilute aqueous solutions.

Voltammetric and transport characteristics of anion-exchange membranes during electrodialysis of solutions containing alkylaromatic amino acid and a mineral salt

The peculiarities of electrodialysis of an alkylaromatic amino acid-mineral salt solution (model solution of demineralization in a microbiological synthetic procedure) were considered. An analysis of the voltammetric characteristics (VACs) of the anion-exchange membranes showed that the alkylaromatic acid had no significant effect on the limiting state for inorganic ions in the concentration range under study. An addition of an amino acid, however, significantly changed the length of the plateau on the VAC in view of the partial transition of the membrane into the amino acid form accompanied by a decrease in the electric conductivity of the membrane and the adsorption of the aromatic compound on the surface, leading to its hydrophobization. The dependences of the alkylaromatic amino acid flows were correlated with the dependences of pH in the concentration section on the side with the anion-exchange membrane on the current density during electrodialysis, the start of the abrupt change in pH corresponds to the maximum phenylalanine (tyrosine) flow and the first inflection on the VAC.

Polikon composite cation-exchange membranes based on novolac phenol-formaldehyde fibers

The synthesis of sulfonated cation-exchange matrices on novolac phenol-formaldehyde fibers followed by curing at preset pressures has yielded Polikon cation-exchange membranes with a uniform charge distribution and improved transport and electrochemical characteristics. It has been shown that the effect of pressure on the transport and electrochemical characteristics of Polikon membranes is nonlinear in character. These membranes can be recommended for use in dialysis and electrodialysis of solutions containing large organic cations.

Current–voltage curves of ion-exchange membranes in electrodialysis of solutions containing alkyl aromatic amino acids and various mineral salts

The work is aimed at studying electrochemical behavior of ion-exchange membranes in order to optimize the electrodialysis desalination of amino acid solution. The current–voltage and transport characteristics of ion-exchange membranes MA-40, MA-41, and MC-40 in electrodialysis demineralization of tyrosine or phenylalanine solutions containing also one of the mineral salts such as NaCl, NaBr, and KCl have been researched. The influence of the mineral salt ion nature (ion radius and mobility, hydration shell kind) and membrane functional groups on the amino acid and mineral ion fluxes through the membrane at the overlimiting currents has been revealed.

Electrodialysis of solutions containing Mn (II) ions

Electrodialysis of manganese (II) containing solutions has been studied. It was shown that Mn (II) cations themselves do not render any negative impact on the ion-exchange membranes. These ions are highly movable within the cationite membrane phase and may be easily removed during the electrodialysis desalination up to the maximum permissible concentration allowed for the potable water. The reason of possible impairment of the electrochemical characteristics of membranes during the electrodialysis of the Mn (II) containing solutions is scaling on the surface of the anion-exchange membranes in brine side. This is observed under severe concentration polarization conditions. The techniques to avoid deposition of the poorly soluble manganese compounds on the surface of the anionic membranes in brine side are proposed.

Diffusion boundary layers in transport of aliphatic acids in electromembrane systems

The regularities of the formation of diffusion boundary layers during the transport of aliphatic acids in electromembrane systems are studied and their characteristics obtained experimentally are analyzed. It is shown that their concentration profiles in solutions of the electrodialyzer sections are asymmetric near membranes of different polarity. Experimental values of diffusion layer thicknesses are compared with those following from the known theoretical relations. The equation, which is proposed for the surface concentration, permits the prediction of the operation mode of apparatus during electrodialysis of solutions of aliphatic acids and other weak electrolytes. Specific features characterizing the emergence of a limiting state and the character of the distribution of limiting current densities over the height of the membrane channel are revealed.