General operating guidelines for DOWEX™ cation and anion resins are given in the following tables. These values are for orientation and should not be regarded as exclusive. Some applications may function outside of the guidelines. For detailed design on ion exchange systems, the CADIX design software is available.
Specific recommended operating conditions for individual DOWEX resins can be found in the product datasheets in the Product Information Section.
| Recommended Operating Conditions for DOWEX Strong Acid Cation Resins | |||||||||||||
| Maximum operating temperature: | 120-150°C (250°F) gel Type I 50°C (300°F) macroporous type |
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| pH range | 0-14 | ||||||||||||
| Swelling Na -> H | 5-8% | ||||||||||||
| Bed depth, min. | 800 mm (2.6 ft) | ||||||||||||
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| Total rinse requirement | 2-6 Bed Volumes | ||||||||||||
| Regenerant: | 1-8% H2SO4 4-8% HCl 8-12% NaCl |
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| Recommended Operating Conditions for DOWEX Weak Acid Cation Resins | |||||||||||||
| Maximum operating temperature: | 120°C (250°F) | ||||||||||||
| pH range | 5 - 14 | ||||||||||||
| Swelling H -> Ca | 15-20% | ||||||||||||
|
800 mm (2.6 ft) 400 mm (1.3 ft) |
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| Rinse | 5-20 m/h (2-8 gpm/ft2) | ||||||||||||
| Total rinse requirement | 3-6 Bed Volumes | ||||||||||||
| Regenerant: | 1-5% HCl 0.5-0.8% H2SO4 |
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| Recommended Operating Conditions for DOWEX Strong Base Anion Resins | |||||||||||||
| Maximum operating temperature: | 60°C (140°F) OH– form 100°C (212°F) Cl– form |
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| pH range | 0 - 14 | ||||||||||||
| Swelling Cl -> OH | 15-25% | ||||||||||||
| Bed depth, min. | 760 mm (2.5 ft) | ||||||||||||
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| Total rinse requirement | 3-6 Bed Volumes | ||||||||||||
| Regenerant: | 2-5% NaOH | ||||||||||||
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Ambient or up to 50°C (122°F) Ambient or up to 35°C (95°F) for silica removal |
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| Recommended Operating Conditions for DOWEX Weak Base Anion Resins | |||||||||||||
| Maximum operating temperature: | 60°C (140°F) | ||||||||||||
| pH range | 0 - 7 | ||||||||||||
| Swelling FB -> HCl | 15-25% | ||||||||||||
|
800 mm (2.6 ft) 600 mm (2 ft) |
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| Total rinse requirement | 2-4 Bed Volumes | ||||||||||||
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2-5% NaOH Ambient or up to 50°C (122°F) |
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Regeneration Parameters and Operating Capacity
Maximizing the chemical efficiency of the system is an important factor in choosing the configuration and regenerant. The following table gives an overview of typical regeneration efficiencies for different resin types and combinations in co-current and counter-current regeneration systems. The regeneration stoichiometry is defined as the ratio of chemical added to capacity obtained.
| Resin Type | Regeneration System | Typical Regeneration Stoichiometry (%) |
| Strong Acid Cation | Co-current HCl Counter-current HCl Co-current H2SO4 Counter-current H2SO4 |
200-250 120-150 250-300 180-200 |
| Weak Acid Cation | 105-115 | |
| Strong Base Anion Type I | Co-current Counter-current |
250-300 140-180 |
| Strong Base Anion Type II | Co-current Counter-current |
200-250 125-140 |
| Weak Base Anion | 120-130 | |
| Layered Bed Anion | 120-130 |
Regeneration Levels and Operating Capacity
An overview of typical regeneration level ranges used in co-current and counter-current regeneration systems with the corresponding operating capacity ranges is given in the following table. The acid and caustic levels used will depend on the quality requirements and the resin operating capacity depends on the regenerant level and feed water composition.
| Regeneration System | Regenerant Level | Typical Operating Capacity | ||
| (g/l) | (lbs/ft3) | (eq/l) | (kgr/ft3) | |
| Co-Current Regeneration: | ||||
| HCl | 80 - 120 | 5 - 7.5 | 0.8 - 1.2 | 17.5 - 26 |
| H2SO4 | 150 - 200 | 9.5 - 12.5 | 0.5 - 0.8 | 11 - 17.5 |
| NaOH | 80 - 120 | 5 - 7.5 | 0.4 - 0.6 | 8.5 - 13 |
| Counter-Current Regeneration: | ||||
| HCl | 40 - 55 | 2.5 - 3.5 | 0.8 - 1.2 | 17.5 - 26 |
| H2SO4 | 60 - 80 | 3.75 - 5 | 0.5 - 0.8 | 11 - 17.5 |
| NaOH | 30 - 45 | 2 - 2.8 | 0.4 - 0.6 | 8.5 - 13 |
Additional Technical Information
Product engineering brochures provide more precise determinations of resin operating capacities. The brochures contain complete engineering information for DOWEX™ resins, including operating capacity and leakage curves as well as backwash and pressure drop data. Select from the list below to download the comprehensive technical information.
Engineering Information for Strong Acid Cation Resins for Water Softening
DOWEX Resins for Softening (68KB PDF)
Engineering Information for Strong Acid Cation Resins for Water Demineralization
DOWEX MARATHON™ C (119KB PDF)
DOWEX MARATHON MSC
Engineering Information for Weak Acid Cation Resins
DOWEX MAC-3 (119KB PDF)
Engineering Information for Strong Base Anion Resins
DOWEX MARATHON A (212KB PDF)
DOWEX MARATHON 11 (202KB PDF)
DOWEX MARATHON MSA
DOWEX MARATHON A2 (252KB PDF)
Engineering Information for Weak Base Anion Resins
DOWEX MARATHON WBA (8KB PDF)
To allow for non-ideal operating conditions and resin aging on a working plant, it is recommended to apply a safety factor to these capacity figures. Typical safety margins are 5% for cations and 10% for anions. Once the operating capacity has been determined, the required resin volume can be calculated from:
| Resin volume = | Resin operating capacity |
| (Feed salinity) x (volume treated) |
Cation Design Considerations
In high hardness waters, H2SO4 requires stepwise regeneration to avoid calcium precipitation. Guidelines for the amounts and concentrations of H2SO4 for different hardness levels in the feed water are given in the following table:
| Calcium in Feed Water (%) | Amount and Concentration of H2SO4 |
| Ca < 10 | 4 % |
| 10 < Ca < 50 | 1/3 at 1.5 % and 2/3 at 4 % |
| 50 < Ca < 70 | 1/2 at 1.5 % and 1/2 at 4 % |
| Ca > 70 | 1 % or use HCl |
Vessel Sizing
Vessel sizing should be adjusted to allow for resin swelling during service, the minimum bed height requirements and the guidelines given for service and regenerant flow rates in the Operating Conditions tables above. A typical resin bed depth for co-current regeneration is 1.2 m (4 ft) and 2 m (6.5 ft) for counter-current packed bed systems. The vessel diameter should be designed for a maximum pressure drop of ~1 bar (15 PSI) across the resin bed to allow for resin settling and accumulation of suspended solids during the service run. A maximum diameter of 3.5 m (11.5 ft) is recommended to assure good flow distribution within the vessel.
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