Product Process and Application Introduction of 98.5% Phosphorous Acid
1. Basic Product Information
CAS No.: 13598-36-2
98.5% phosphorous acid appears as white highly hygroscopic crystals. It is a dibasic inorganic weak acid with excellent strong reducibility and moderate corrosiveness. Featuring stable chemical properties, it can be slowly oxidized to phosphoric acid by air under normal conditions and decomposes to produce toxic phosphine gas at high temperatures. It shall be kept away from strong alkalis and strong oxidants during storage and use. In addition to traditional synthetic methods, industrial production mainly adopts various by-product recovery and purification processes, which are refined from industrial phosphorus-containing waste residues and waste liquids, featuring environmental friendliness and controllable costs.
2. Core Processing Technologies of By-Product Recovery Method
The raw materials for phosphorous acid by-product recovery mainly include phosphite calcium waste residues from sodium hypophosphite production, distillation residual liquid of phosphite esters, and phosphorus-containing waste liquid from electroless plating. There are five mature purification and processing technologies in the industry, which can be applied according to raw material impurity conditions and product purity requirements. Combined processes can stably produce 98.5% high-purity phosphorous acid:
2.1 Bipolar Membrane Electrodialysis Method (Mainstream Industrial Process)
Industrial phosphorus-containing by-products are mixed with water and pulped, then filtered to remove residues to obtain clean crude phosphite solution. The crude solution is sent to a bipolar membrane electrodialysis device, where phosphite is directly converted into phosphorous acid under the electric field, and impurities such as sodium salts are separated simultaneously. This process eliminates the traditional acidification step, and the separated lye can be recycled and reused in the front-end production process. Subsequent procedures including precision filtration, vacuum concentration, cooling crystallization, and centrifugal drying are carried out to finally produce 98.5% high-purity phosphorous acid. This technology features low slag output, low impurity content in finished products and high environmental performance. Its disadvantage lies in the high investment of membrane components, which requires regular cleaning and maintenance to prevent membrane pollution by colloids and heavy metals.
2.2 Solvent Extraction and Purification Method
Taking by-product waste residues as raw materials, crude aqueous phosphorous acid solution is obtained after water pulping, double decomposition reaction and solid-liquid filtration. A special selective organic extractant is used to precisely extract phosphorous acid from the aqueous solution, retaining metal ions, sulfate radicals, phosphate radicals and other impurities in the water phase. High-purity phosphorous acid solution is obtained through water back-extraction. Follow-up procedures including activated carbon decolorization, deep impurity removal, vacuum concentration, crystallization and drying are adopted to complete finished product preparation. This method is suitable for crude materials with complex impurities and has high purification accuracy. However, it has the disadvantages of extractant loss and strict solvent volatilization control with relatively high cost, and is mostly used for the refining of small-batch 98.5% high-purity products.
2.3 Cation Exchange Resin Purification Method (Traditional Mainstream Purification Process)
Phosphite calcium waste residues are pulped, subjected to double decomposition, and filtered to remove precipitates to obtain crude phosphite solution. The crude liquid continuously passes through a strong acid cation exchange resin column, which thoroughly removes cation impurities such as sodium ions, calcium ions, iron ions and various heavy metals through resin replacement, directly generating dilute phosphorous acid solution. After arsenic removal and decolorization purification, finished products are prepared via MVR vacuum concentration, cooling crystallization and centrifugal drying. This process has simple operation, stable product quality and is suitable for large-scale production. The disadvantages are that the resin requires regular regeneration, producing a small amount of saline wastewater, and high-impurity raw materials are prone to pollute the resin and reduce purification efficiency, so it is often used in combination with other processes.
2.4 Membrane Pretreatment + Evaporation Crystallization Combined Method (Suitable for Liquid By-Product Raw Materials)
This process is mainly applicable to liquid phosphorus-containing by-products such as high-boiling residual liquid from dimethyl phosphite distillation. Firstly, ultrafiltration and nanofiltration membrane equipment are used for raw liquid pretreatment to effectively intercept colloids, organic macromolecules and suspended impurities in the solution, avoiding scaling and blockage of subsequent evaporation equipment from the source. The pretreated clean liquid is concentrated by multi-stage vacuum evaporation, and stepwise crystallization is performed by accurately controlling the cooling rate. The mother liquid can be recycled for production. Mother liquid with enriched impurities after long-term circulation is separately treated for deep impurity removal and then reused. Finally, 98.5% phosphorous acid is obtained after crystallization and drying. This technology has high automation and strong continuous production capacity, and is only applicable to liquid by-product recovery rather than solid waste residue raw materials.
2.5 Precipitation Impurity Removal + Recrystallization Method (Low-Cost Simple Process)
It is an entry-level purification process with low equipment investment and simple operation. After pulping, double decomposition and filtration of by-product waste residues, special heavy metal removal agents are added into the crude phosphite solution to precipitate and filter out impurities such as lead, arsenic and various heavy metals. Crude phosphorous acid solution is obtained after acidification. After preliminary concentration of the crude liquid, one or multiple recrystallization processes are adopted to separate and remove phosphate, salts and other impurities, and finished products are finally obtained after concentration and drying. This process has the advantages of low production cost and low technical threshold. However, multiple crystallization will reduce product yield with poor purity stability. A single process cannot stably produce 98.5% high-purity products for a long time, and is only suitable for ordinary industrial-grade production.
Process Summary: At present, the combined process of electrodialysis and ion exchange is widely adopted in the industry for the stable production of 98.5% export-grade and industrial high-purity phosphorous acid, which balances purity, yield and environmental performance and serves as the preferred mainstream scheme for by-product recovery.
3. Main Product Applications
3.1 Agriculture Industry
It is a core organophosphorus chemical intermediate for the synthesis of common pesticides such as glyphosate and ethephon. Meanwhile, it can be used to prepare functional phosphite products including potassium phosphite and ammonium phosphite. As a new type of disease-resistant foliar fertilizer, it is widely applied in agricultural planting, which can effectively inhibit crop fungal diseases, improve crop stress resistance and achieve significant yield-increasing effects.
3.2 Polymer Material Industry
It is commonly used to prepare special plastic heat stabilizers such as dibasic lead phosphite, which is widely applied in polymer systems including polycarbonate, nylon and PET. It can effectively improve the oxidation resistance, high temperature resistance and aging resistance of materials, and also has the functions of nylon whitening and improving material forming stability, serving as an important auxiliary raw material for plastic and chemical fiber processing.
3.3 Water Treatment Industry
As the core raw material for the synthesis of organic phosphine scale and corrosion inhibitors such as ATMP, it is widely used in industrial circulating water, boiler water and central air conditioning water treatment systems. It can effectively chelate metal ions in water, inhibit scaling and corrosion of pipelines and equipment, and deliver excellent scale inhibition, corrosion inhibition and water quality stabilization effects.
3.4 Fine Chemical Industry
It can be used to prepare various high-purity phosphite and phosphite ester fine chemical products; it acts as a high-quality reducing agent in organic synthesis reactions and electroless nickel plating processes with stable reduction performance and low impurity interference.
3.5 Other Fields
It can be used as a synthetic intermediate for bisphosphonate drugs in the pharmaceutical industry, and also serves as a chemical analytical reagent and special chemical fiber auxiliary, covering pharmaceutical, detection, textile and other industries
Product technical consultation: E-mail:Sales@hxochem.com Whatsapp: +8613330004268, WeChat: +8613285168509