Dowex MWA-1

Summary

Product identification

DOWEX MWA-1 Ion Exchange Resin

General Information

DOWEX MWA-1 is a macroporous, weak base anion exchange resin with a polydispersed bead size distribution. It is based on a styrene-divinylbenzene copolymer matrix with dimethylamine functional groups. This resin is designed for high throughput and economical operation in both water and non-water applications. It offers high chemical efficiency and reversible removal of the organic fraction soluble at operating pH. Its high reversibility to organics provides good resistance to fouling and protects downstream strong base anion resins.

DOWEX MWA-1 can be used in a two-stage plant for good quality water, but without silica or carbon dioxide removal. It can also be used in combination with a strong base anion resin, such as DOWEX SBR, in a separate vessel. For layered bed configurations with a strong base anion resin, DOWEX MARATHON WBA, a uniform particle sized resin, is recommended for excellent kinetic performance and separation.

The swelling of DOWEX MWA-1 is important for engineering design. Maximum operational swelling from the free amine form to the fully exhausted state is approximately 20%. Operational swelling is around 15%. The resin's properties allow for use in organic solvents or highly concentrated solutions.

Typical Physical and Chemical Properties

• Ionic form as delivered: FB (free base)
• Total exchange capacity, min.: 1.2 eq/l (26.2 kgr/ft³ as CaCO₃)
• Water content: 50 - 60 %
• Bead size distribution: Range 0.3 - 1.2 mm

  • 1.2 mm, max.: 2 %

  • <0.3 mm, max.: 3 %
• Total swelling (FB ↔ HCl), approx.: 20 %
• Whole beads, min.: 95 %
• Particle density, approx.: 1.04 g/ml
• Shipping weight, approx.: 640 g/l (40 lbs/ft³)

Recommended Operating Conditions

• Maximum operating temperature:
  • FB form: 60°C (140°F)
  • HCl form: 100°C (212°F)
• pH range: 0-7
• Bed depth, min.: 800 mm (2.6 ft)
• Flow rates:
  • Service/fast rinse: 5-50 m/h (2-20 gpm/ft²)
  • Backwash: See Figure 1 in the original document.
  • Co-current regeneration/displacement rinse: 1-10 m/h (0.4-4 gpm/ft²)
  • Counter-current regeneration/displacement rinse: 5-20 m/h (2-8 gpm/ft²)
• Regenerant: 2-4% NaOH
• Total rinse requirement: 3-5 Bed volumes

Hydraulic Characteristics

Backwash Expansion

Backwashing should expand the bed between 50% and 100% of its original height in the free base form. Refer to Figure 1 in the original document for detailed percent bed expansion at various flowrates for both regenerated and exhausted resin forms. Temperature corrections for flowrates are provided.

Pressure Drop Data

Figure 2 in the original document shows pressure drop per unit bed depth as a function of flow velocity and water temperature for a new resin bed in the free amine form. This data is indicative; total head loss depends on design, fines, suspended solids, and vessel geometry. Formulas for temperature correction of pressure drop are provided.

Operating Characteristics

General

DOWEX MWA-1 used alone removes free mineral acidity (FMA) from cation effluent. It does not remove carbon dioxide or silica, except for a short period at the beginning of the operational cycle. The presence of carbon dioxide slightly increases resin capacity.

Chemical Efficiency

Figure 3 in the original document illustrates operating capacity for different feeds and typical caustic soda requirements (135% of stoichiometric equivalent). Chemical usage may vary based on organic content and water temperature. Heating to 40°C (104°F) may be economical if caustic soda is expensive.

Operational capacity and regeneration requirements can be calculated using the graphs in Figure 3, considering carbon dioxide, water temperature, and chloride percentage of FMA.

Regeneration Chemicals

Caustic soda is the typical regenerant, but sodium carbonate or ammonium hydroxide can also be used. Using these alternatives with the equivalent amount of sodium hydroxide will result in a 10% drop in operational capacity. Organic matter elution remains excellent with any regenerant, provided the correct regeneration level is used.

Combination of Weak Base and Strong Base Anion Resins

Combining DOWEX MWA-1 or DOWEX MARATHON WBA with a strong base anion resin allows for complete demineralization, especially for waters high in FMA. "Thoroughfare" regeneration, using excess caustic from strong base regeneration for the weak base, can extend chemical efficiency. This combination also increases overall operating capacity and protects the strong base resin from organic fouling.

Overrun

With the weak base resin upstream of a strong base resin, the weak base can be run to an FMA endpoint, allowing the strong base to adsorb silica and carbon dioxide. Alternatively, running the weak base through the FMA breakpoint allows the strong base to absorb leakage, increasing operating capacity.

Layout

Three configurations are possible for using weak and strong base anion resins:

1. Separate vessels.
2. One vessel with two compartments separated by a nozzle plate.
3. A single vessel as a layered bed (DOWEX MARATHON WBA is recommended for this).

Silica Precipitation

During thoroughfare regeneration, care must be taken to prevent silica precipitation. Silica solubility is lowest at neutral pH. Dilute the silica peak from the strong base resin by controlling caustic temperature and concentration, and ensuring adequate chemical injection velocity.

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Disclaimer: This extraction may miss figures, footnotes, or revisions. Contractual data must match the OEM PDF revision used on the project.

Official datasheet (PDF)

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