Yes, EDTMPA (Ethylenediaminetetra(methylene phosphonic acid)) and its salts (e.g., sodium or ammonium salts) can be and are used in the pulp and paper industry, primarily for their excellent chelating, dispersing, and scale inhibition properties. However, its application is more specialized and targeted compared to common scale inhibitors like ATMP or HEDP used in cooling water systems.
Here’s a breakdown of its roles, advantages, and considerations in papermaking:
1. Primary Functions and Applications in Papermaking
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Metal Ion Chelation (Key Role):
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Peroxide Stabilization: During hydrogen peroxide (H₂O₂) bleaching, trace metal ions like iron (Fe³⁺), manganese (Mn²⁺), and copper (Cu²⁺) catalyze the rapid decomposition of peroxide, wasting chemicals and reducing bleaching efficiency. EDTMPA strongly chelates (sequesters) these metal ions, stabilizing the peroxide bleach liquor and improving brightness gain.
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Control of Transition Metals: It prevents metal-catalyzed degradation of cellulose (viscosity loss) and enhances the brightness stability of the final pulp.
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Scale Inhibition and Dispersancy:
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Prevents the deposition of calcium-based scales (e.g., calcium oxalate, calcium carbonate) and other insoluble salts on paper machine wires, felts, and dryer cylinders. This is crucial in closed white water systems where dissolved and colloidal substances accumulate.
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Dispersing Agent:
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Helps disperse fine particles, fillers (e.g., calcium carbonate, clay), and pitch (wood resins) in the pulp slurry, preventing their agglomeration and deposition, which improves paper quality and runnability.
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De-inking Aid (Recycled Fiber Processing):
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In recycled paper production, it helps chelate metals that can interfere with the de-inking process and stabilize hydrogen peroxide used for brightness reversion control.
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2. Advantages of EDTMPA for This Application
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Strong Chelation Power: It forms exceptionally stable, water-soluble complexes with a wide range of di- and trivalent metal ions, especially with iron (Fe³⁺), which is highly problematic in peroxide bleaching.
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Stability under Alkaline Conditions: It performs well in the high-pH environment typical of peroxide bleaching stages (pH 9-11).
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Thermal Stability: It is stable at the temperatures used in papermaking processes.
3. Considerations and Potential Limitations
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Cost vs. Alternatives: EDTMPA is generally more expensive than other common chelants like DTPA (Diethylenetriaminepentaacetic acid) or even citric acid. Therefore, its use is often justified in situations where its superior chelation strength, particularly for iron, is critical for process efficiency or product quality.
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Phosphorus Content: Like all phosphonates, EDTMPA contains phosphorus. Its discharge in effluent can contribute to eutrophication if not properly managed. Mills with stringent phosphorus discharge limits may need to optimize dosage or consider phosphorus-free alternatives (e.g., gluconates, certain polymers) for less demanding chelation tasks.
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Not a Primary Scale Inhibitor for Common Scales: For general calcium carbonate scale control in paper machine white water, more cost-effective polymers or phosphonates (like ATMP) are often preferred. EDTMPA is used when its metal chelation benefit is the primary driver.
Typical Use Cases in a Paper Mill
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Peroxide Bleach Plant: Added to the peroxide bleach tower as a stabilizer. Dosage is carefully optimized based on the metal ion content (especially iron) of the pulp.
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Pulp Stock Chests: Added to protect pulp from metal-catalyzed degradation.
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White Water Loop: Added as a dispersant and scale inhibitor, often in combination with other polymers.
Comparison with Common Chelant DTPA
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DTPA is also widely used for peroxide stabilization. EDTMPA often provides comparable or better stabilization performance at a lower dosage due to its high stability constants with metals. However, the final choice depends on cost, system specifics, and effluent requirements.
Conclusion
Yes, EDTMPA is a viable and effective specialty chemical in papermaking, primarily valued as a high-performance chelant for peroxide stabilization and metal ion control. Its use is most economically justified in:
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High-quality bleached pulp production (e.g., for tissue, fine paper) where brightness and chemical efficiency are critical.
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Systems with high transition metal ion content (especially iron) in the furnish or process water.
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Situations where a single additive can provide both metal chelation and scale/dispersion benefits.
The decision to use EDTMPA involves a technical-economic assessment balancing its superior performance against its higher cost and potential environmental considerations related to phosphorus discharge.