Background and overview[1][2]
Hexamethylphosphoric acid triamide is a new chemical product with wide range of uses and good performance that has emerged in recent years. It is widely used in national economic production activities such as rubber, textile printing and dyeing, and aviation reagents. However, its synthesis process There are certain risks in operating conditions. For example, the raw materials used in the synthesis reaction of hexamethylphosphoryltriamide, such as phosphorus oxychloride and xylene, are highly toxic and flammable and have acute toxicity. Moreover, higher heating temperatures are required in the synthesis reaction process, which can easily cause secondary reactions and cause accidents.
Properties and Applications[1]
Pure hexamethylphosphoric acid triamide is a colorless and transparent liquid at room temperature, miscible with water in any proportion, and also miscible with other polar or non-polar organic substances. It is very harmful to polymers. The substance also has good solubility. It is an ideal bridge solvent that can dissolve two or more mutually immiscible substances into a uniform liquid phase. This opens the door for many chemical reactions that are difficult to carry out in aqueous solutions or other organic solvents. The door of convenience.
Hexamethylphosphoric acid triamide has good light stability, and the thermal stability of hexamethylphosphoric acid triamide is better than other phthalamines, but it will decompose significantly when stored at high temperature of 200°C. , Hexamethylphosphoric acid triamide is heated continuously for five days and nights at 157°C. When alkaline oxides or hydroxides or certain salts are added as stabilizers, hexamethylphosphoric acid triamide decomposes on average per day. The thermal decomposition rate of the non-heated stabilizer is only 0.014-0.018%, and the average daily thermal decomposition rate of the stabilizer is above 0.2%.
Hexamethylphosphoric acid triamide is relatively stable in water, especially when heated in alkaline aqueous solution. It hydrolyzes very little in cold water solutions of weak acids and low-concentration acids, but in the presence of strong acids, especially after heating, it can quickly hydrolyze to release dimethylamine, and form a salt with the acid to become the final product.
Hexamethylphosphoramide (HMPA for short) is a solvent miscible with polar and non-polar solvents, alkali metals, alkaline earth metals and polymer compounds. It can be extracted from aqueous solutions by alkyl chloride to form a colorless polar aprotic liquid complex. It has the characteristics of higher boiling point, higher dielectric constant, strong alkalinity, etc. It is widely used as a medium for chemical reactions, isolating metal complexes, dissolved gases, dissolved organic and inorganic salts and polymers.
The specific uses are as follows: it can be used as an anti-aging additive for agricultural films and a cocatalyst for propylene bulk polymerization; it can be used as a gas chromatography fixative, a purple light inhibitor and an additive for rocket fuel to lower the freezing point. Its toxicological studies have confirmed that it is a potential carcinogen. Contact with skin for 24 hours can cause inflammation. Inhalation of formaldehyde produced by the metabolism of hexamethylphosphoric acid triamide can cause a series of toxic reactions in the human body. Animal experiments show that the lethal dose in mice is oral LD50: 6000mg/kg.
Preparation [2]
(1) Under nitrogen protection, put 1150kg of xylene into the high-level tank and put it into the synthesis reaction kettle. Take a sample to detect the moisture. If it is qualified, use vacuum to pump 250kg of phosphorus oxychloride into the reaction kettle. If it is not qualified, Remove the lower layer (to dry) and test again.
(2) Turn on dimethylamine (gas) for stirring, and control the temperature in the kettle to be less than 60°C and the rotation speed to be within a certain range. Pass 250kg of dimethylamine gas to the liquid surface, turn off the chilled water, continue to pass 30kg, control the final temperature to be less than 75°C and keep it warm for 30 minutes.
(3) Pass ammonia gas to control the temperature of the kettle to be less than 75°C and the rotation speed within a certain range. Pour in 75kg of ammonia gas, stop aeration and continue stirring for one hour, and turn on chilled water to cool the materials.
(4) Press filtration: Use vacuum to pump the material into the filter and drain it dry. The filtrate enters the temporary storage tank or distillation kettle. The filter cake is soaked and washed with xylene. The filtrate enters the temporary storage tank and the filter residue is to be recycled.
(5) When the filtrate of crude product preparation is distilled under reduced pressure and about 1000kg of xylene is obtained, stop the distillation, cool the material and put it into an iron drum for weighing.
(6) Ammonium salt treatment: Add 1000kg of drinking water to the filter residue produced in the second batch, raise the temperature to 80°C and let it stand for stratification. Add water and a small amount of hydrochloric acid to the upper layer for extraction twice, add water and a small amount of liquid alkali to the upper layer for extraction once, add 20kg of potassium carbonate to the upper layer and stir still, transfer the upper layer to barrels for later use; transfer the lower layer to the recovery distillation kettle to steam water under reduced pressure until the solid precipitates. After cooling to room temperature, filter using a centrifuge.
(7) Finished product distillation: Pump 8 batches of crude products into the finished product distillation kettle, raise the temperature, start the vacuum unit to distill isoparaffin under reduced pressure, control the kettle temperature to be less than 120°C and receive it into the boiling storage tank, and receive the finished product to the finished product. Can. Frozen brine is used. According to the process requirements, -15°C brine is required and sent to the jacket of the process equipment to cool the materials. The operating conditions are that the brine supply temperature is -15°C and the brine return water temperature is -10°C. The cooling water supply temperature is ≤32°C. Under this condition, the operating conditions of the refrigeration unit are evaporation temperature -20°C and condensation temperature 40°C.
Main reference materials
[1] Yu Peiqian, Xie Meiju, & Yu Zili. (2002). Solvent extraction method for treating wastewater containing hexamethylphosphoric acid triamide. Chemical Research and Application, 14(3), 342-343.
[2] Ding Xiangsheng, & Fang Xiaodong. (1993). Application of hexamethylphosphoric acid triamide. Zhejiang Chemical Industry (1), 51-53.
[3] Liang Chen. (2014). Research on thermal risk assessment method of hexamethylphosphoric acid triamide synthesis process. (Doctoral dissertation, Jiangxi University of Science and Technology).
