1. Introduction
HEDP (Hydroxyethylidene Diphosphonic Acid), Chinese name is Hydroxyethylidene Diphosphonic Acid, is an organic phosphonic acid compound. It has excellent chelating ability and good thermal stability, widely used in water treatment, industrial cleaning, metal surface treatment and other fields.
2. Chemical structure formula
The chemical structure formula of HEDP is CH2(PO3H2)2.
3. Physical and chemical properties
- Appearance: white crystalline powder or colourless transparent liquid (according to different product forms)
- Solubility: soluble in water, slightly soluble in alcohols
- Stability: stable in a wide pH range, good thermal stability
- Toxicity: low toxicity, environmentally friendly
4 Main uses
4.1 Water treatment
- Scale inhibitor: HEDP can effectively chelate calcium, magnesium, iron and other metal ions in water to prevent the deposition of insoluble salts such as calcium carbonate, calcium sulphate, barium sulphate, etc. It is widely used in cooling water system, boiler water treatment, reverse osmosis system and so on.
- Corrosion inhibitor: HEDP can form a protective film on the metal surface to prevent metal corrosion and prolong the life of equipment, applicable to steel, copper, aluminium and other metal materials.
- Dispersant: HEDP can disperse fine particles and colloids in the water, prevent them from being deposited on the surface of the equipment and keep the water clear.
4.2 Industrial cleaning
- Cleaning agent: HEDP is used in the cleaning of industrial equipment, especially for carbonate and rust cleaning effect is remarkable, applicable to boilers, heat exchangers, cooling towers and other equipment cleaning.
- Pre-film agent: Before the new equipment is put into operation, HEDP is used for pre-film treatment, which can form a protective film on the metal surface to prevent initial corrosion.
4.3 Metal surface treatment
- Passivator: HEDP is used for passivation treatment of metal surface to improve the corrosion resistance of metal, applicable to steel, copper, aluminium and other metal materials.
- Rust preventive agent: HEDP can be used as a rust preventive agent to prevent rust and corrosion of metals during storage and transport.
4.4 Other applications
- Textile printing and dyeing: HEDP is used in textile printing and dyeing process to prevent the effect of calcium, magnesium and other metal ions on dyes and improve the dyeing effect.
- Agriculture: HEDP is used as chelating agent for fertiliser to improve the absorption rate of trace elements in fertiliser.
- Oilfield water treatment: HEDP is used in oilfield water injection and extraction water treatment to prevent scaling and corrosion of downhole equipment and improve oilfield development efficiency.
5 Usage
5.1 Dissolve and dilute
- Dissolution: Add HEDP slowly into stirred water to ensure full dissolution. The general recommended concentration is 0.1%~0.5%.
- Dilution: According to the actual demand, further dilute the dissolved agent to the required concentration.
5.2 Dosing method
- Metering pump dosing: the agent is continuously or intermittently dosed into the water to be treated by a metering pump to ensure that the agent is fully mixed with the water.
- Manual dosage: For small systems, manual dosage can be used to add chemicals regularly.
5.3 Dosage
- Scale inhibition: according to the water quality and treatment objectives to determine the dosage. Generally, when the hardness of raw water is high, the dosage is 1~5mg/L.
- Corrosion inhibition: according to the metal material and corrosion risk to determine the dosage. In general, the dosage is 1~3mg/L.
5.4 Precautions
- Avoid over dosage: over dosage may lead to water pollution and increase treatment cost.
- Avoid mixing: do not mix with other chemicals to avoid adverse reactions.
- Storage conditions: store in a cool, dry and ventilated place, avoid moisture and high temperature.