THE EFFECT OF THE DISPERSITY OF SULFOCATION-EXCHANGER OF HETEROGENEOUS MEMBRANES ON THE DEVELOPMENT OF DIFFUSION BOUNDARY LAYERS UNDER INTENSIVE CURRENT MODES

Abstract

Recently, an idea regarding the surface optimization of ion-exchange membranes, aimed at increasing the overlimiting mass transfer by the development of heteroelectroconvection, has been extensively developed. Therefore, the purpose of the work is to conduct a laser-interferometric study of the effect which sulfocation-exchangers of experimental samples of heterogeneous Ralex CM Pes of varying dispersity have on the thickness of diffusion layers in a solution of the interphase boundary. Experimental samples of heterogeneous sulfocation-exchange membranes Ralex CM Pes (“MEGA” a.s., Czech Republic) were selected for the study. They were obtained by rolling a homogenized mixture of the milled ion-exchanger of various degrees of dispersity with polyethylene. The volume ratio of cation-exchanger to polyethylene was kept the same. The degree of dispersity of the sulfocationexchanger varied due to different milling times of 5 to 80 minutes. The experiments were performed in a seven-compartment electrodialysis cell with stable concentration-temperature stratifi cation of the electrodialyzerin in a gravitational fi eld. An interferometric setup was used to visualize the transport processes at the membrane-solution boundary. A comparative analysis of the effect the electrical and geometric heterogeneity of the surface of the heterogeneous sulfocation-exchanger Ralex CM Pes membranes has on the conditions for the formation and development of diffusion layers under intense current modes was carried out. It was established that an increase in the milling time for the ion-exchanger particles leads to a decrease in the magnitude of the electrical inhomogeneity spacing of the surface and the fraction of macropores. Also, microrelief smoothing takes place. An increase in the time of the ion-exchanger milling from 5 to 80 min results in a 1.5 times decrease of the potential drop of the membrane. At this point the effective thickness of the diffusion layer begins to decrease. The study revealed the tendency of a decrease in the total and effective thickness of the diffusion layer with a decrease in the electrical inhomogeneity spacing of the membrane surface.

Keywords

• heterogeneous sulfocation-exchange membrane
• surface inhomogeneity
• diffusion boundary layer
• electroconvective instability
• overlimiting current regimes.