Application Fields of Ion Exchange Membranes

Applications of Ion Exchange Membranes

Anion Exchange Membranes for Processing of Mineral Acids

Application	Electrodialysis	Concentration of diluted acids from rinsing solutions or waste streams
	Electrolysis, EDBM	Splitting of salts: caustic without chlorine
General Problems	current efficiency	Anion exchange membrane is the weak point in these applications
	ohms resistance	Membranes with improved current efficiency show high ohms resistances. This may result in high bypass currents (due to the high conductivity of product acid) in industrial stacks, which may damage the stack nearby the electrodes
	sealing problems	Membranes with improved current efficiency often have a very hydrophobic surface, causing leakage in industrial stacks
Advantages of PC Acid Series	adjusted for special acids	By adjusting the properties of the membrane matrix to each application, the balance of current efficiency and ohms resistance is optimized. This results in better performances than with an acidblocker type of general use.
	Sealing properties	The membrane surfaces of the PC Acid Series are very hydrophilic. Generally this results in good sealing behavior in industrial stacks.

Application of optimized membranes:

The membranes are optimized for mineral acid treatment in respect to the size of the corresponding anion:

PC Acid 60	monovalent acids like hydrochloric acid, nitric acid as well as nitric acid/hydrofluoric acid mixtures
PC Acid 100	mulitvalent acids like sulfuric acid

Application	Electrolysis, EDBM	Splitting of salts: liberation of acid without additional chemicals. Continuous removal out of fermentation solutions special: as part of a chemical reaction
General Problems		Organic anions possess a wide range of size and absorbtion behavior (mainly determined whether it is aromatic or aliphatic)
	ohms resistance	As the molecular dimension of the channels in anion exchange membranes for the migration of ions is given, the resistance of membranes made for chloride ions is often high, if the migrating anion is organic .
	water transport	The water transported with the anion differs in dependence of the size of the ion exchange matrix. A minimal water transport for each anion can be determined which is given by inner and outer hydrate shells. The water transport may be very high, if a too open membrane matrix is selected for a prarticular anion.
	general permeability	Large anions with molecular weight of more than about 350 D cannot permeate conventional anion exchange membranes due to a too closed matrix.
Advantages of PC Acid series	adjusted for special anion sizes	By adjusting the properties of the membrane matrix to each application it is possible to optimize the balance of current efficiency and ohms resistance. This results in better performances than with an acidblocker type of general use.

Application of optimized membranes:

The membranes are optimized for organic acid treatment in respect to the size of the corresponding anion:

PC 100 D	Acids with molecular mass around 100 D such as acetic-, lactic- and citric acid (due to the threfold negative charge best treated with this type)
PC 200 D	Acids with molecular mass around 200 D such as gluconic acid