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Membranes for water treatment processes

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The membranes for water treatment applications cover the fields of electrodialysis with or without bipolar membrane (EDBM or ED), diffusion dialysis (DD), electro-coat as surface treatment, electro-deionisation (EDI) and other related applications, such as capacitive de-ionization (CDI), electro-dialysis with reversal polarity (EDR), e.g. Special type among water treatment processes membranes is FAP membrane that enables high-purity HOCl production via NaCl electrolysis for disinfection-purposes in beverage industry or for other antivirus/antibacterial treatment.

EDBM applications

The membranes for EDBM are typically used for concentrating up of water-soluble substance during salt splitting process involved in recycling business of Li-ion industry or paper industry. The FBM membrane as bipolar membrane secures the splitting of water to H+ and OH- ions to cathode and anode, respectively. The monopolar membranes FAB and FKL transfer the anions and cations for combining them with released H+/OH- species. For example, the salts such as Lithium Sulfate or waste Natrium Sulfate are converted to sulfuric acid and LiOH/NaOH. In case of other organic/inorganic salts the conversion is carried out to corresponding acids and hydroxides.

Typical properties of FC membranes for EDBM applications

MembraneFAB-PK-130  FAB-PK-75FKL-PK-130  FKL-PK-75FBM
ReinforcementPEEK woven webPEEK woven webPEEK woven web
Resin typeAnionCationBipolar Anion/Cation
Thickness / µm130/75130/75150
Resistance of 130/75 µm / mOhm.cm2 (1)08.Apr6,5 / 3,5110
Selectivity / % (1)> 95> 98> 95
Swelling at 80 °C per dimension / %< 4< 4< 5
E-Modulus / MPa> 1.500> 1.500> 1.500

Remark:
(1) Measured in 1 M NaCl solution

ED applications

The membranes for ED application are used for water desalination to the low concentration of salts. The examples include desalination processes in various applications including beverages or food industry. Unlike the EDBM, the salts are not split to hydroxide and acids, but split to cations and anions in the feed chamber and after transfer through particulate membranes they are recombined and concentrated in the permeate chambers.

Typical properties of membranes for ED applications

MembraneFAS-PK-130FAS-PET-130FKB-PK-130 FKS-PET-130
ReinforcementPEEKPETPEEKPET
Resin typeAnionAnionCationCation
Thickness / µm
 		130130130130
Resistance / Ohm.cm2 (1)886,56,5
Selectivity / %> 95> 95> 97> 97

Remark:
(1) Measured in 1 M NaCl solution

DD applications

The membranes for DD applications are typically used for recycling of acid or alkali and for increase of concentration of said chemicals. The choice of membrane for acid recycling can be met depending on the oxidative nature of feed. The membranes can be built into spiral or flat sheet modules.

 

Typical properties of FC membranes for DD applications

MembraneFAD-PET-75FAPQ-PET-275FKD-PK-75
ReinforcementExtruded PETExtruded PETPEEK woven web
Transferred speciesAcidAcidBasic
Typical diluted feed (1)HCl/H2SO4H2SO4/HFNaOH, KOH
Thickness / µm757575
H+ or OH- transfer rate / nmol/(cm2.min)4.0002.800800
Selectivity / %> 92> 94> 98
Swelling at 80 °C per dimension / %< 5< 5< 2
E-Modulus / MPa> 500> 500> 1.500

Remark:
(1)FAD membrane features only limited oxidative durability toward Cl2, H2O2, HNO3 etc.; FAPQ membrane features high oxidative durability and FAPQ is not attacked by HF either.

Electro-coat and EDI applications

The membranes for electro-coat and EDI applications are typically thick micro-heterogeneous membranes enabling high mechanical durability and easy handling. The membranes are used for heavy-duty application in painting as well as for continuous production of high-end purity desalinated water on level 18MOhm or higher. The membranes fit to flat sheet as well as spiral-wound modules.

Typical properties of membranes for electro-coat/EDI applications

MembraneFAMFKM
ReinforcementPPPP
Transferred speciesAnionsCations
Thickness / µm
 		500500
Resistance / Ohm.cm2 (1)1512
Selectivity / %> 87> 90
Swelling at 80 °C per dimension / %< 8< 8
Bubble point / bar> 5> 6

Remark:
(1) Measured in 1 M NaCl solution

CDI and EDR applications

The membranes for CDI and EDR applications are typically thin membranes enabling high energy efficiency for ion removal from water solutions up to low-ppm level of left-over species. Due to the high selectivity, the membranes suit well to the technology that meets the demand of zero-liquid-discharge policy.

Typical properties of FC membranes for CDI/EDR applications

MembraneFAB-30FKL-30
Reinforcementnonenone
Transferred speciesAnionsCations
Thickness / µm
 		3030
Resistance / Ohm.cm2 (1)1,51,2
Selectivity / %> 92> 95
H+ or OH- transfer rate / nmol/(cm2.min)30050
Bubble point / bar> 5> 6

Remark:
(1) Measured in 1 M NaCl solution

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