The phosphorous acid producing process

The phosphorous acid CAS:13598-36-2, H3PO3, is an important chemical raw material, widely used in pesticides, flame retardant, water treatment agent and other fields. Its production process mainly includes hydrolysis method, oxidation method,etc.

Density: 1.651 g/cm3

Melting point: 73℃

Boiling point: 200℃

Appearance: colorless to pale yellow, ice-like crystals

Solubility: easily soluble in water and ethanol

Chemical properties: slowly oxidized to phosphoric acid in air, heated to 180℃ decomposition into phosphoric acid and 180℃ phosphine (highly toxic). Phosphorous cid is binary acid, which is slightly more acidic than phosphoric acid, it has a strong reduction, easy to reduce Ag ions to metal silver, can reduce sulfuric acid to sulfur dioxide. Have strong hygroscopic and tidal lysis, corrosive. Can cause burns. It is irritating to the skin

Here is a detailed description of these processes:

1. Hydrolysis method (phosphorus trichloride method)

This is the most commonly used phosphorous acid production process in industry, easy access to raw materials, mild reaction conditions, suitable for mass production.

- Raw material : Phosphorus trichloride (PCl3), water (H2O)

-Reaction equation: PCI3+3H2O->H3PO3+3HCI

Process steps :

1.1.Hydrolysis reaction: Add phosphorus trichloride into the water slowly to control the temperature and stirring speed and avoid violent reaction. Reaction heat release, cooling and maintenance temperature at 20-40℃.

1.2.Gas absorption:The generated hydrogen chloride (HCl) gas is absorbed through water or lye to make hydrochloric acid or chloride by-products.

1.3.Solution concentration: After the reaction is completed, filter to remove the insoluble impurities, and get the phosphoric acid solution.

1.4.Crystallize and dry:The solution is concentrated and the crystallization is cooled to get the phosphoric crystal, and then dried to get the finished product.

Advantages: Mature technology, easy to obtain raw materials, suitable for mass production.

2. Oxidation method

Phosphate was prepared by oxidized elemental phosphorus or phosphine.

-Raw material: white phosphorus (P4) or phosphine (PH3), oxygen (O2), or air

-Reaction equation: P4 + 6H2O- -> 4H3PO3 or PH3 + 2O2- -> H3PO3

Process steps :

2.1.Oxidation reaction: white phosphorus or phosphates are reacted with oxygen or air under control conditions to form phosphorate.

2.2. Solution treatment: The reaction product is dissolved in water and filtered to remove unreacted solid impurities.

2.3.Concentrate the crystallization: Concentrate the solution and cool the crystallization to obtain the phosphoric acid crystal.

Advantages: Simple raw materials, suitable for small-scale production.

Disadvantages: The reaction conditions are difficult to control, and the elemental phosphorus and phosphide hydrogen are flammable and explosive, and the safety requirements are high.

3. Acid-base neutralization method

Phosphate was prepared by reaction phosphite with acid.

 -Raw material : phosphite (e. g. Na₂HPO₃), acid (e. g. HCl)

 -Reaction equation:Na2HPO3+HCI-->H3PO3+NaCI

Process steps:

3.1.Neutralization reaction: Mix phosphite with acid to control the pH value to generate phosphite.

3.2. Filter separation: filter the generated salts (e. g., NaCl).

3.3.Concentrate the crystallization: Concentrate the solution and cool the crystallization to obtain the phosphic acid crystal.

Advantages:Simple process, suitable for laboratory or small-scale production.

Disadvantages: The raw material cost is high, and the byproduct salt needs to be treated.

.4. Safety and environmental protection

-Phosphorous trichloride, elemental phosphorus, phosphine and other raw materials are corrosive or flammable and explosive,requiring strict operation.

-Hydrogen chloride gas produced during the reaction shall be properly treated to avoid leakage.

-By-product hydrogen chloride can be recycled to make hydrochloric acid to reduce pollution.

-The waste water shall be treated and discharged after reaching the standard.

Sum up

The production process of phosphoric acid is mainly hydrolysis method, and other methods such as oxidation method are also applied. Different processes have their own advantages and disadvantages, which should be considered based on the source of raw materials, production scale and equipment conditions. Pay attention to safe operation and environmental protection requirements to ensure product quality and environmental friendliness.