Overview【1】
Dimethyl phosphite (hereinafter referred to as dimethyl phosphate) is one of the important organophosphorus chemical raw materials and is widely used in pesticides, textiles, rubber, food and other industries. Industrial production has been carried out abroad as early as the 1960s, with a dimethyl ester content of 95% and stable performance. Domestic research began in the 1970s. In the 1980s, there were dimethyl ester synthesis sections in larger pesticide factories, and the dimethyl ester content was only about 35%. Although a small amount of industrial products have been produced in recent years, the performance of the products is unstable and the dimethyl ester content is only about 80%.
Production purposes【2】
Dimethyl phosphite is an important chemical raw material and intermediate. It is widely used in the preparation industry of organophosphoric acid corrosion inhibitors, synthetic plastic additives, dye additives, combustion accelerants and pesticides. The organic phosphoric acid type and organic phosphonic acid-containing acid type water corrosion and scale inhibitors prepared with it are widely used in industrial and chemical circulating water treatment; a variety of phosphite compounds prepared with it are widely used in plastics It is used as a phosphorus additive with different functions in industry, an additive in the dye industry and oil products; at the same time, it is also used in the preparation of organophosphorus pesticides such as trichlorfon, dichlorvos, rice blast, omethoate, glyphosate, etc. Important intermediates. The domestic manufacturers that produce dimethyl phosphite mainly include Zhejiang Xin’an Chemical Group Company, Fujian Sannong Chemical Co., Ltd., Zhejiang Linghu Chemical Group Company, Shandong Pesticide Factory, etc. The main foreign manufacturers include OLDBURYELECTROCHENICALCOMPA, UNIVERRSALOxLPRODCO, etc.
Development of process technology
The synthesis methods of dimethyl phosphite can be divided into more than ten types according to different raw materials, among which there are two main ones with industrial value. (1.) A method using phosphorus trichloride, methanol and water as raw materials. This method is to react in an organic solvent under the action of a catalyst to obtain the product. The reaction is essentially an esterification reaction between phosphorous acid and methanol. Its chemical reaction formula is:
This method uses less methanol and has high product purity, but the reaction time is long and the yield is generally around 85%. Only by finding a suitable and efficient catalyst can this method have a future.
(2.) Method using phosphorus trichloride and methanol as raw materials.
This method is to prepare dimethyl phosphite by reacting phosphorus trichloride directly with methanol. It is the most studied topic at home and abroad. The industry has been industrialized, and its industrial production technology can be divided into the following two situations:
(l) Industrial production technology in which reactions are carried out in organic media. This technology is usually produced by directly reacting phosphorus trichloride with methanol in an inert or halogenated organic solvent at a lower temperature (usually 10°C) without or in the presence of an acid binding agent. Dimethylphosphite. Industrial production includes batch methods and continuous methods. The reaction conditions of this method are mild, the operation is safe and easy to control, but the yield is affected by many factors and is unstable. The yield calculated based on phosphorus trichloride is usually between 65 and 90%, and the best yield in small experiments can reach 93%. However, in industry, the unit consumption is often high due to unstable production, and the recycling of solvents increases operating costs. (2) Solvent-free continuous industrial production technology. In this kind of industrial production technology, some use gas phase reaction, and the yield of dimethyl phosphite silicone coating additive is about 90%; some use liquid phase reaction, and the yield is about 86 to 93%. The common advantages of solvent-free production are that as long as it is properly controlled, the production speed is fast, the product yield is high, and the purity of the product can reach 98.9%. And because no solvent is used in the production process, production costs and operating expenses are low. Compared with the gas phase method and the liquid phase method, the former has huge equipment and large production investment, while the latter has much less production investment. However, the solvent-free method has higher requirements on raw materials, especially methanol. This method is now accepted by domestic and foreign manufacturers and will become the mainstream of production in the future.
Brief description of production process
The production of dimethyl phosphite by Zhejiang Xin’an Chemical Group Co., Ltd. began in the 1980s, mainly to provide chemical intermediates for glyphosate. It is a solvent-free continuous production process using methanol and phosphorus trichloride as raw materials. Over the years, through unremitting technological development and improvement, not only the consumption of raw materials ranks first in the country, but also major breakthroughs have been made in the treatment of three wastes and the development of comprehensive utilization.
1, Schematic diagram of the process flow.
The above is a schematic block diagram of the entire process of dimethyl phosphite.
In actual production, the production of dimethyl phosphite is divided into four major sections: reaction section, refining section, pump and hydrochloric acid recovery section, and methyl chloride recovery section. Among them, the reaction section is the core of the system.
2. Reaction section.
Under negative pressure conditions, phosphorus trichloride and methanol are fed and reacted at a feeding ratio (molar ratio) of 1:305 to 31. The large amount of reaction heat generated by the reaction is removed in time by the coolant in the jacket. , a large amount of methyl chloride gas and hydrogen chloride gas produced by the reaction are pumped away by the vacuum system. By adjusting the ratio, the reaction temperature is kept below 50°C and the vacuum degree of the system is kept at around 0.85MPa. The mixed liquid flowing out of the reactor enters the two-stage deacidification kettle. In the deacidification kettle, the feed liquid is heated to about 60-80°C, so that the hydrogen chloride gas dissolved in it can fully escape. The deacidified material liquid enters the crude product intermediate storage tank.
3. Refining section.
In this section, the crude product undergoes continuous distillation to obtain refined dimethyl phosphite product with a purity greater than 97%. First, the crude product is distilled under reduced pressure to separate out the low-boiling substances, which are mainly…Alcohol is sent to the reaction section for recycling. Then, through continuous distillation, the refined dimethyl phosphite product that meets the requirements can be obtained. The operating pressure is controlled at around 0.0113MPa, the tower top temperature is controlled at around 110°C, and the tower bottom temperature is controlled at around 160°C.
4. Hydrochloric acid recovery section.
This section is an auxiliary section, which mainly recovers the hydrogen chloride gas produced during the reaction. After water absorption, the finished product hydrochloric acid with a concentration greater than 30% is obtained.
5. Methyl chloride recovery 3m section in the United States.
The reaction gas product after passing through the hydrochloric acid recovery section is mainly methyl chloride gas. In this section, liquid methyl chloride product is obtained through purification and compression.
1.4 Dimethylphosphite process flow chart
In this device, the domestic general production capacity is SOOt/a, and the yield based on phosphorus trichloride is 83% to 85%, which is significantly lower than the batch method yield of 90%.
The significance of production technology research and amplification
After more than ten years of transformation and improvement, the dimethylol phosphite production equipment of Zhejiang Xin’an Chemical Group Co., Ltd. has taken a leading position in the domestic industry, but there are still some problems as follows:
(l) Although the best yield of the current device calculated based on phosphorus trichloride has reached 85%, there is still a large gap compared with the yield of about 90% in the batch process.
(2) Due to the lack of a set of rigorous and systematic theoretical research data, the process technology transformation carried out still has a certain degree of blindness, and the empirical component accounts for a large proportion.
(3) With the continuous expansion of the glycerin market, the amount of dimethyl phosphite, the main raw material of glycerin, continues to expand, and the intensification of competition in the international market of glycerin has also increased the cost of glycerin. The reduction of dimethyl phosphite has become a topic of urgent concern for enterprises. As its main raw material, the cost reduction of dimethyl phosphite has also become a major issue for enterprises. In particular, glyphosate, as the main product of Xin’an Chemical, faces fierce market competition. It not only needs to further reduce costs, but also needs to expand scale.
References
[1]Zhang Zhiping. Research on the synthesis method of dimethyl phosphite[J]. Hebei Chemical Industry, 1997(01):29-30.
[2]Ji Chengjian. Research on reaction kinetics and synthesis process of dimethyl phosphite[D]. Zhejiang University of Technology, 2005.
