Electro Membrane (separation) processes
Electromembrane Processes consist of those technologies that apply the electric potential gradient as the driving force of ion transport. They are increasingly important group of separation methods for removal of charged components from solutions such as for producing potable water from brackish water.
The main electromembrane processes are:
- Electrodeionization (EDI)
- Electrodialysis (ED)
- Electrodialysis reversal (EDR)
- Electrodialysis with bipolar membrane (EDBM)
- Capacitive deionization (CDI)
Fig.1, Schematic description of the electrodialysis reversal process
Lately these processes they have started to be applied into such areas as energy production, food processing, personal care products, healthcare, production of high quality water, biomolecules separation, sensors, organic separation, industrial effluent treatment, etc.
The basic elements of the Electromembrane technologies can be ion-exchange or bipolar. Ion migration is taking place across these charged membranes (a polymeric matrix with fixed charged groups, counterbalanced with mobile counter-ions) which are placed in the electric field. According to the type of fixed ion-exchange (IX) groups, the membranes can be categorized to,
- a. Cation-exchange membranes (CM)
These membranes contain in their polymeric matrix acid ion-exchange groups that have negative electric charge (-SO3-, COO-), allowing for free passage only of those particles with positive charge. Negatively charged particle passage is drastically reduced.
- b. Anion-exchange membranes (AM)
These membranes contain in their polymeric matrix basic cation-exchange fixed groups (-NR3+, where R is hydrogen or alkyl group), allowing for free passage only of particles with negative charge. Positively charged particle passage is drastically reduced.
- Advantages of electromembrane processes:
- high efficiency of separation of substances without phase transitions,
- easy continualization and automation, low demands for space,
- lower energy consumption, compared to traditional procedures,
- possibility to create closed waste-free technological junctions or entire technologies.
- Disadvantages of membrane processes:
- removal of so-called membrane poisons by pre-treatment of solutions,
- fouling (creation of coating of poorly soluble substances on the membrane surface).
The overview of the most important and widely used electromembrane processes is given in this section.