Sodium Hypophosphite Monohydrate CAS 10039-56-2

One-step method refers to the method of directly preparing sodium hypophosphite by reacting yellow phosphorus with one of the following reactants: (1) NaOH, (2) a mixture of alkaline earth metal hydroxide and NaOH (mainly NaOH), (3 ) A mixture of alkaline earth metal hydroxides and Na2CO3. For example, yellow phosphorus reacts with the mixture of milk of lime and Na2CO3 solution by heating under an inert atmosphere to release phosphine and hydrogen. Calcium phosphite, calcium phosphate and other components. The filtrate is passed through CO2 to remove calcium hydroxide dissolved therein, filtered, and the filtrate is concentrated under reduced pressure to obtain NaH2PO2·H2O.

The one-step process is relatively simple, can produce a thicker solution, has lower energy consumption, and has a higher product yield. The one-step method has become the main method for the industrial production of sodium hypophosphite at present.

The two-step method is to first use yellow phosphorus to react with alkaline earth metal hydroxides or a mixture of alkaline earth metal hydroxides and NaOH (based on alkaline earth metal hydrides) under an inert atmosphere to obtain alkaline earth metal hypophosphite. Then the alkaline earth metal hypophosphite and sodium carbonate are subjected to double decomposition to obtain sodium hypophosphite. Nitrogen is commonly used as an inert gas. The most commonly used alkaline earth metal hydroxide is Ca(OH)2. Barium hydroxide, magnesium hydroxide, etc. can also be used, but the cost of raw materials is higher.

The process flow of the two-step method is longer, and there is one more process of filtration and washing, and the solubility of calcium hypophosphite is lower than that of sodium hypophosphite. In order to reduce the amount of residual hypophosphite in the filter cake, the amount of washing water must be increased and the washing liquid Combined with the filtrate, the solution obtained in this way is very dilute, and the energy consumption of evaporation and concentration is a lot.

Use the anode part of the diaphragm electrolyzer to electrochemically oxidize phosphorus in alkali metal hydroxide to obtain alkali metal hypophosphite. Under the current intensity of 2~3A, perform electrochemical oxidation to generate toxic PH3 The amount is reduced, so that working conditions can be improved.

One-step continuous production of elemental phosphorus, sodium hydroxide or calcium hydroxide, the pure sodium hypophosphite solution is sent to the continuous crystallizer, and the steam in each process is recycled to save energy. The waste water is fully recycled, and the by-product gases phosphine and hydrogen are converted into phosphoric acid by a continuous combustion chamber, and calcium phosphite is filtered out. The whole process is controlled by an electronic computer. In case of danger, the computer can close the relevant process to eliminate the operator’s wrong instructions. Due to the use of computer control, the sodium hypophosphite produced is of good quality and the purity exceeds 99%.

Phosphorus trihalide is hydrolyzed to generate hypophosphorous acid, which reacts with sodium hydroxide to generate sodium hypophosphite. This method produces more expensive raw materials, and if the waste (such as hydrogen halide gas) is not used properly, it will be troublesome to deal with. However, the production process of this method is simple, and the trace element impurities in the product are less, which can meet the requirements of some special industries for high-quality sodium hypophosphite. Therefore, it also has certain industrial application value.

Phosphorous sodium hypophosphite reacts directly with oxygen at high temperature to generate phosphorous or hypophosphorous anhydride, which is hydrolyzed to obtain the corresponding acid, and reacts with sodium hydroxide after separation to generate sodium hypophosphite and sodium phosphite. The method has high production efficiency and high yield of total phosphorus. However, what is obtained is a mixture, and the separation process is more complicated, so it is generally less used.

Both the two-step method and the one-step method produce PH3 exhaust gas. The gas is poisonous and burns when exposed to air, which is very dangerous. The usual treatment method is to absorb it with water after burning to make dilute phosphoric acid. A better method is to react PH3 with peroxide (such as H2O2), NaClO, or halogen (such as I2, Br2, etc.), strictly control the reaction process to oxidize it into hypophosphorous acid, and then react with alkali to generate sodium hypophosphite . This method has two advantages: one is waste utilization, and the other is that the product is of high quality and basically does not contain trace element impurities, which can meet the special needs of some high-tech industries. As a comprehensive utilization of one-step method, it is valued by manufacturers.