A Review on Ion-Exchange Membranes Fouling during Electrodialysis Process in Food Industry, Part 2: Influence on Transport Properties and Electrochemical Characteristics, Cleaning and Its Consequences

Abstract

Ion-exchange membranes (IEMs) are increasingly used in dialysis and electrodialysis processes for the extraction, fractionation and concentration of valuable components, as well as reagent-free control of liquid media pH in the food industry. Fouling of IEMs is specific compared to that observed in the case of reverse or direct osmosis, ultrafiltration, microfiltration, and other membrane processes. This specificity is determined by the high concentration of fixed groups in IEMs, as well as by the phenomena inherent only in electromembrane processes, i.e., induced by an electric field. This review analyzes modern scientific publications on the effect of foulants (mainly typical for the dairy, wine and fruit juice industries) on the structural, transport, mass transfer, and electrochemical characteristics of cation-exchange and anion-exchange membranes. The relationship between the nature of the foulant and the structure, physicochemical, transport properties and behavior of ion-exchange membranes in an electric field is analyzed using experimental data (ion exchange capacity, water content, conductivity, diffusion permeability, limiting current density, water splitting, electroconvection, etc.) and modern mathematical models. The implications of traditional chemical cleaning are taken into account in this analysis and modern non-destructive membrane cleaning methods are discussed. Finally, challenges for the near future were identified.

Keywords: cleaning; food industry; fouling; ion-exchange membrane; mechanical and electrochemical properties; modelling and experiment; transport.

Figure 1

Influence of traditional chemical cleaning on the structure, mechanical strength and transport characteristics of ion-exchange membranes.

Figure 2

The proposed structure of AEMs that contain PVC as an inert filler, before and after their use in the ED process of wine tartrate stabilization: (1) macro-defects, filled with an external solution; (2) nanoporous medium; (3) nanopore with fixed groups on the walls, filled with an external solution; (4) nanopore with non-electrically charged walls filled with an external solution; (5) reticulated hydraulically permeable colloidal structures; (6) hydraulically impermeable colloidal aggregates. Adapted from [58,59].

Figure 3

Schematic IEM structure represented in terms of microheterogeneous model [68] (a), and the same model, which takes into account colloidal particles (b) formed by polyphenols. EDL is the electric double layer. Adapted from [60].

Figure 4

The conductivity of the AEMs soaked in the synthetic polyphenol-containing solution vs. NaCl concentration. Markers show the experimental data measured for sample soaking duration 0 (1), 24 (2), 100 (3), 500 (4), 750 (5) and 1000 (6) hours; dashed lines are the results of calculations according to the modified microheterogeneous model. Adapted from [60].

Figure 5

The main types of interaction of polyphenols with ion-exchange membranes and the effect of this fouling on the transport characteristics of IEMs.

Figure 6

CVC of pristine and fouled by BSA anion exchange AMX (a) and cation exchange CMX (b) membranes. Insert in (a) shows the scheme of the mechanism of water splitting enhancement due to the formation of a bipolar junction between positively charged fixed AMX groups and negatively charged BSA. Explanations can be found in the text. Constructed using data from [146].

Figure 7

Corrected current–voltage characteristics after ohmic component subtraction, obtained in 0.02 NaCl solution for pristine and fouled in red wine AMX-Sb membrane samples. The insets show optical images of cross-sections of these samples. The value of i_lim^theor was calculated using the Lévêque equation [163]. Adapted from [64].

Figure 8

Chronopotentiometric curve of Nafion-117 membrane in 0.01 M Fe₂ (SO₄)₃ solution in overlimiting current regime. Dashed line shows a typical shape of the curve in NaCl solution. The inset shows the precipitate found on the studied membrane surface after obtaining the chronopotentiometric curve (optical image). Adapted from [176].

Figure 9

Electrochemical impedance spectra of pristine anion exchange membrane AMX-Sb and the same membrane after contact with wine for 10 (AMX-Sb_w10) and 72 (AMX-Sb_w72) hours. The data were obtained in 0.02 M NaCl solution; on the right are optical images of the studied samples. Adapted from [62].

Figure 10

Results of visualization of the front of protons formed due to water splitting (a) and electroconvective vortices (b) at the surface of the anion-exchange membrane. On the left is the pristine membrane; on the right is a membrane on the surface of which single-stranded DNA (ssDNA, which contains dissociated phosphonate groups) is adsorbed. Adapted from [191,192].

Figure 11

The scheme of the effect of fouling of the volume and surface of ion-exchange membranes on their behavior in an electric field.