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Ion Exchange Membranes

Ion Exchange Membrane Types

 

 

PCA produces different types of homogenous ion exchange membranes in its facility in the Saarland. The membrane types are developed and designed for different applications.
As all of these membranes are homogeneous, their thickness is pretty low and the PCCell spacers are developed to build very seal stacks. Thermal pretreatment of freshly assembled stacks is not regularly necessary.

Standard ion exchange membranes

Ion Exchange Membranes

PCA produces a series of standard anion and cation exchange membranes (PC-SK and PC-SA) useful in general desalination applications by electrodialysis. In addition, there are two series of special anion exchange membranes by modification of the selectivity profile of those membranes or by modification of shape (reinforced, non reinforced, extra thin etc):


 

 


 

Membranes for the treatment of mineral acids

PC Acid 60 for the production of hydrochloric acid from sodium chloride or for the concentration of diluted nitric acid

PC Acid 100 for the concentration of diluted sulfuric acid

Many industrial processes produce dilute acid streams which have to be deposited because of their low concentration. Acid-ED leads to a reconcentrated acid product of a concentration level useful for recycling it in the same process. An example is the reconcentration of a pickling acid out of a rinsing water.

If mineral acids are to be produced from their salts by electrolysis or electrodialysis with bipolar membranes , high current efficiencies are necessary. Acidblocker anion exchange membranes developed at PCA provide this characteristic due to a minimized proton leakage. The loss of product over the acidblocker anion exchange membrane is minimized.

Membranes for the production of organic acids

In the liberation of a wide variety of organic acids out of their salts, the voltage drop across the anion exchange membrane gives a considerable part to the energy consumption of the process. This electrochemical processing technology enables the processing of acids like acetic acid, citric acid, gluconic acid, lactobionic acid etc., which are produced by fermentation or by chemical processes.

PCA has developed membranes for the treatment of organic acids with a low electric resistance:

PC 100 D for small anions with a mass of about 100 dalton

E.g. for lactic acid recovery from a fermentation broth with high glucose rejection (Y. H. Kim, S.-H. Moon J. Chem. Technol. Biotechnol. 2001, 76(2),169-178) by means of a water splitting electrodialysis process.

PC 200 D for medium anions with a mass of about 200 dalton

The type of membranes used and the process conditions choosen are determined by the requirements of application. For more information about typical applications of the different types of membranes please confer our overview (DE) .
When choosing the membrane type, the chemical and physical properties of the membranes listed below have to be taken into account.
PCA offers support at all stages of process realization from the first application screening through to the engineering and planning of the plant to you.

 

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 features 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 properties 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

 

Anion Exchange Membranes for Processing of Organic Acids

 

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 Features   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

 

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