Special extracting agent for purifying phosphoric acid and synthesis method of tributyl phosphate

Abstract

The invention belongs to the field of tributyl phosphate synthesis and extraction separation, and provides a special extraction agent for purifying phosphoric acid and a tributyl phosphate synthesis method. The synthesis method of the tributyl phosphate comprises the following steps: mixing a diluent at 1-5 DEG C with phosphorus oxychloride, dropwise adding the mixture into n-butyl alcohol containing a catalyst, then carrying out two-stage heating reaction, filtering, washing and phase-splitting the obtained reaction liquid, adding organic amine into a water phase obtained by phase-splitting, carrying out reaction, heating, concentrating, cooling, crystallizing, and separating out organic amine hydrochloride, thereby obtaining the tributyl phosphate. N-butyl alcohol in the organic phase obtained through phase splitting is separated through distillation, a tributyl phosphate / diluent mixture is obtained, distillation continues to be conducted on the tributyl phosphate / diluent mixture, the diluent is separated out, and tributyl phosphate is obtained. The special extracting agent for purifying phosphoric acid is prepared by mixing a tributyl phosphate / diluent mixture generated in a tributyl phosphate synthesis process with a phase modifier. According to the method, side reactions caused by local high temperature can be reduced, the yield of tributyl phosphate can be increased, and the value of byproducts can be increased.

Description

Technical Field

[0001] The present invention belongs to the field of synthesis and extraction separation of tributyl phosphate, and relates to a special extractant for purifying phosphoric acid and a method for synthesizing tributyl phosphate. Background Art

[0002] Tributyl phosphate is a colorless and almost odorless organic compound, which can dissolve in a variety of organic solvents and has a wide range of uses in the chemical industry. Tributyl phosphate can be used as an extractant for metals, a plasticizer for nitrocellulose, polyvinyl chloride, etc., a gas chromatography stationary liquid, and an industrial defoamer. At present, in industry, tributyl phosphate is mainly synthesized by reacting phosphorus oxychloride with n-butanol at room temperature. Specifically, high-concentration phosphorus oxychloride is dropped into n-butanol for reaction. A large amount of hydrogen chloride is generated during the reaction between the two, and hydrogen chloride will undergo side reactions with both n-butanol and tributyl phosphate. The reaction between hydrogen chloride and n-butanol will generate water, and phosphorus oxychloride will undergo a violent hydrolysis reaction when encountering water. At the same time, the reaction between high-concentration phosphorus oxychloride and n-butanol is a highly exothermic reaction, and the reaction process will cause the temperature to rise. However, the higher the temperature, the more serious the aforementioned side reactions will be. In addition, when high-concentration phosphorus oxychloride is dropped into n-butanol, there is also the problem of local over-concentration of phosphorus oxychloride. The local over-concentration of phosphorus oxychloride will further intensify the severity of the reaction, resulting in local high temperature and aggravated side reactions. In order to solve the problem of serious side reactions during the reaction between phosphorus oxychloride and n-butanol, researchers in this field have conducted a large number of studies.

[0003] For example, CN 117447511 A discloses a method for preparing tributyl phosphate by reacting n-butanol, phosphorus oxychloride and an acid-binding agent under a vacuum condition. The acid-binding agent used is an organic amine compound, such as triethylamine, N,N-diisopropylethylamine, etc. Fine and light ammonium salts are generated during the reaction process, which are difficult to separate from the reaction system. The organic amine compounds used are volatile and have a large loss under vacuum conditions, resulting in high production costs and large pollution. CN 101993454 A discloses a method for synthesizing tributyl phosphate by mixing a large amount of sodium formate as an acid-binding agent with butanol and then dropping phosphorus oxychloride into it. Sodium formate reacts with the generated hydrogen chloride to form formic acid and sodium chloride. After separating the obtained formic acid, it reacts with sodium hydroxide to be converted into sodium formate to realize the recycling of sodium formate. However, the formic acid generated during the reaction will react with phosphorus oxychloride to form unnecessary substances. At the same time, converting formic acid into sodium formate requires a large amount of sodium hydroxide, which will not only increase the production cost, but also the generated by-product sodium chloride has a low value. CN 102040622 A uses sodium acetate as an acid-binding agent and has similar problems to CN 101993454 A.

[0004] For example, CN 104211727 A uses butanol to react with an alkali metal or alkali hydroxide to produce sodium butoxide, which is then esterified with phosphorus oxychloride to synthesize tributyl phosphate. This method requires the consumption of large amounts of alkali metals or alkali hydroxides, resulting in high production costs and difficulties in industrialization. CN 107522736 A also first reacts n-butanol with metallic sodium in a solvent to produce a mixture containing sodium butoxide, which is then reacted with phosphorus oxychloride, but suffers from similar problems as CN 104211727 A.

[0005] For another example, CN 104230983 A first esterifies phosphorus oxychloride and n-butanol under vacuum conditions, then introduces ammonia to neutralize hydrogen chloride, then heats to remove unreacted n-butanol, and finally washes and distills to obtain tributyl phosphate. Although this method can remove some of the generated hydrogen chloride by conducting the esterification reaction under vacuum conditions, it also removes butanol, resulting in an increase in butanol unit consumption, and the process of neutralization by ammonia does not reduce the occurrence of side reactions. CN104892666 A uses a multi-stage water scrubber to wash the mixture formed by the reaction of n-butanol and phosphorus oxychloride to remove most of the generated hydrogen chloride, neutralizes the resulting organic phase with ammonia, stands for phase separation, crystallizes the aqueous phase obtained by phase separation to form ammonium chloride, washes the organic phase obtained by phase separation with water, separates the phases again, and dealcoholizes the resulting crude ester layer to recover most of the n-butanol. Finally, water is added as an entrainer to perform reduced pressure distillation to recover the n-butanol, ultimately obtaining tributyl phosphate. This method focuses on separating the mixed reaction products formed by the reaction of n-butanol and phosphorus oxychloride, but cannot reduce the occurrence of side reactions during the reaction of n-butanol and phosphorus oxychloride, and has similar problems as CN 104230983 A.

[0006] While the above methods can improve the purity and yield of tributyl phosphate to a certain extent, they still fail to address the problem of localized over-concentrations caused by the dropwise addition of high concentrations of phosphorus oxychloride to n-butanol during the tributyl phosphate preparation process, which in turn leads to localized high temperatures and exacerbates side reactions. Furthermore, the sodium chloride and ammonium chloride byproducts produced by the above methods during the preparation of tributyl phosphate are relatively low in value. Summary of the Invention

[0007] In view of the fact that existing tributyl phosphate synthesis methods are unable to solve the problem that the local high temperature of the reaction system caused by the dropwise addition of high-concentration phosphorus oxychloride exacerbates side reactions, and the problem that the value of the by-products produced during the preparation of tributyl phosphate is relatively low, one object of the present invention is to provide a tributyl phosphate synthesis method to alleviate the local high temperature caused by the dropwise addition of high-concentration phosphorus oxychloride, thereby reducing the side reactions caused by the local high temperature, improving the yield of tributyl phosphate and enhancing the value of the by-products. A second object of the present invention is to provide a special extractant for purifying phosphoric acid based on the tributyl phosphate synthesis method.

[0008] To achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0009] A method for synthesizing tributyl phosphate, comprising the following steps:

[0010] (1) Diluent at a temperature of 1 to 5 °C and phosphorus oxychloride are fully mixed at a mass ratio of (0.5 to 2):1 to obtain a diluent / phosphorus oxychloride mixture, and the diluent is one or more mixtures of C6~C 15 alkanes;

[0011] (2) Add n-butanol and a catalyst to a reaction kettle, and dropwise add the diluent / phosphorus oxychloride mixture to the reaction kettle. During the dropping process, control the temperature of the reaction kettle at 5 to 15 °C. After the dropping is completed, raise the temperature to the first reaction temperature, keep the temperature for 30 to 60 min, then raise the temperature to the second reaction temperature, and keep the temperature for 60 to 120 min to obtain a reaction solution;

[0012] Control the second reaction temperature to be higher than the first reaction temperature. The first reaction temperature is 30 to 65 °C, and the second reaction temperature is 40 to 80 °C; control the mass ratio of the catalyst to phosphorus oxychloride to be (0.5 to 5):100;

[0013] (3) Filter the reaction solution obtained in step (2), wash the filtered filtrate with water, let it stand for phase separation to obtain an aqueous phase and an organic phase;

[0014] (4) Add organic amine to the aqueous phase obtained in step (3) and react fully to convert hydrogen chloride in the aqueous phase into organic amine hydrochloride, then raise the temperature for concentration, cool and crystallize, and perform solid-liquid separation to obtain high-purity organic amine hydrochloride;

[0015] Distill and separate n-butanol from the organic phase obtained in step (3) to obtain a tributyl phosphate / diluent mixture. Subject the tributyl phosphate / diluent mixture to vacuum distillation to separate the diluent and obtain high-purity tributyl phosphate. The separated n-butanol and diluent are recycled.

[0016] In step (1) of the technical solution of the above-mentioned method for synthesizing tributyl phosphate, the role of the catalyst is to promote the reaction between phosphorus oxychloride and n-butanol. For the specific catalyst, reference can be made to the prior art for selection. Generally, the catalyst can be zinc chloride or aluminum chloride.

[0017] In step (1) of the technical solution of the above-mentioned method for synthesizing tributyl phosphate, the diluent can be C6~C 15 alkanes or cycloalkanes, that is, alkanes or cycloalkanes with 6 to 15 carbon atoms.

[0018] In step (2) of the technical solution of the above-mentioned method for synthesizing tributyl phosphate, it is preferably controlled that the total dropping amount of the diluent / phosphorus oxychloride mixture makes the molar ratio of n-butanol to phosphorus oxychloride be (4-9):1.

[0019] In step (3) of the technical solution of the above-mentioned method for synthesizing tributyl phosphate, it is preferably controlled that the number of washing times is 2-3 times. When washing for the first time, water is added to the filtrate for washing according to the mass ratio of water to the filtrate of 1:(2.5-4). When washing for the 2nd-3rd times, water is added to the organic phase obtained from the previous washing for washing according to the mass ratio of water to the organic phase obtained from the previous washing of 1:(2.5-4).

[0020] In step (2) of the technical solution of the above-mentioned method for synthesizing tributyl phosphate, when dropping the diluent / phosphorus oxychloride mixture into n-butanol, it is preferably controlled that the dropping rate of the diluent / phosphorus oxychloride mixture is 6-18 g / min.

[0021] In step (4) of the technical solution of the above-mentioned method for synthesizing tributyl phosphate, the function of adding an organic amine to the aqueous phase obtained in step (3) is to fix hydrogen chloride by reacting the organic amine with hydrogen chloride to form an organic amine hydrochloride, and avoid side reactions of hydrogen chloride with n-butanol, tributyl phosphate, etc. The organic amine is preferably triethylamine, diethylamine, tributylamine or dibutylamine.

[0022] In step (4) of the technical solution of the above-mentioned method for synthesizing tributyl phosphate, the reaction time after adding the organic amine to the aqueous phase obtained in step (3) is based on the principle of fully converting hydrogen chloride in the aqueous phase into an organic amine hydrochloride. Usually, after adding the organic amine to the aqueous phase, the reaction is carried out for 10-30 min, and then heating and concentration are carried out.

[0023] In step (4) of the technical solution of the above-mentioned method for synthesizing tributyl phosphate, the amount of the organic amine in step (4) is based on the principle of converting as much hydrogen chloride in the aqueous phase into an organic amine hydrochloride as possible. Preferably, the amount of the organic amine is 80%-105% of the molar amount of hydrogen chloride in the aqueous phase obtained in step (3).

[0024] In step (4) of the technical solution of the above-mentioned method for synthesizing tributyl phosphate, the purpose of heating and concentration is to make the organic amine hydrochloride in the solution obtained after the reaction of the organic amine with hydrogen chloride reach a supersaturated state, so as to facilitate the subsequent cooling crystallization of the organic amine hydrochloride. The temperature and time of heating and concentration can be determined according to the concentration of the organic amine hydrochloride in the solution obtained after the reaction of the organic amine with hydrogen chloride. Usually, the concentration temperature can be controlled at 80-100 °C and the concentration time at 10-40 min.

[0025] In step (4) of the technical solution of the above-mentioned method for synthesizing tributyl phosphate, n-butanol can be distilled and separated from the organic phase obtained in step (3) by means of vacuum distillation, or the diluent can be distilled and separated from the tributyl phosphate / diluent mixture by means of vacuum distillation. For example, step (4) can be carried out under the conditions of a pressure of -0.99 to -0.96 MPa and a temperature of 95 to 105 °C to distill and separate n-butanol, and step (4) can be carried out under the conditions of a pressure of -0.99 to -0.96 MPa and a temperature of 200 to 250 °C to distill and separate the diluent from the tributyl phosphate / diluent mixture. However, the feasible distillation method is not limited to vacuum distillation, and the conventional distillation methods of the prior art can be selected according to actual application requirements.

[0026] In the technical solution of the above-mentioned method for synthesizing tributyl phosphate, the high-purity organic amine hydrochloride refers to an organic amine hydrochloride with a purity of at least 99%, and the high-purity tributyl phosphate refers to a tributyl phosphate with a purity of at least 99%.

[0027] The yield of tributyl phosphate in the technical solution of the above-mentioned method for synthesizing tributyl phosphate is at least 93%.

[0028] The present invention also provides a special extractant for purifying phosphoric acid, which is formed by mixing the tributyl phosphate / diluent mixture obtained in step (4) of the technical solution of the above-mentioned method for synthesizing tributyl phosphate with a phase modifier.

[0029] In the technical solution of the above-mentioned special extractant for purifying phosphoric acid, the phase modifier is an alcohol with 4 to 13 carbon atoms. For example, common phase modifiers include butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, etc.

[0030] In the technical solution of the above-mentioned special extractant for purifying phosphoric acid, in the special extractant, the mass ratio of the tributyl phosphate / diluent mixture to the phase modifier is preferably (6 to 9):1.

[0031] The technical concept and principle of the technical solution of the present invention are mainly as follows:

[0032] The core technical concept of the present invention lies in using C6 to C 15A mixture of one or more alkanes is mixed with phosphorus oxychloride as a diluent and then reacted with n-butanol. First, a diluent at a temperature of 1-5°C and phosphorus oxychloride are mixed in proportion. The resulting diluent / phosphorus oxychloride mixture is added dropwise to n-butanol to which a catalyst has been added. After the addition is complete, the reaction between the phosphorus oxychloride and n-butanol is promoted by heating and catalysis. The mixture is then filtered, washed, and phase-separated. An organic amine and hydrogen chloride are added to the aqueous phase obtained by phase separation and allowed to react fully. The mixture is then concentrated and crystallized to obtain a high-purity organic amine hydrochloride. The n-butanol in the organic phase obtained by phase separation is then separated by distillation to obtain a tributyl phosphate / diluent mixture. This tributyl phosphate / diluent mixture can be directly used as a special extractant for purifying phosphoric acid after being mixed with a phase conditioning agent. Alternatively, the tributyl phosphate / diluent mixture can be distilled to separate the diluent to obtain high-purity tributyl phosphate.

[0033] On the one hand, the addition of a diluent can appropriately reduce the concentration of phosphorus oxychloride, alleviating the problem of localized overheating caused by excessive phosphorus oxychloride concentration during the dropwise addition of phosphorus oxychloride alone, which can exacerbate side reactions. Simultaneously, the addition of a diluent can also reduce the concentration of hydrogen chloride generated in the reaction system, thereby reducing side reactions between hydrogen chloride and butanol and between hydrogen chloride and tributyl phosphate, thereby reducing butanol consumption. Furthermore, controlling the diluent temperature between 1 and 5°C helps to appropriately lower the system temperature during the dropwise addition of the diluent / phosphorus oxychloride mixture, avoiding the problem of excessively high system temperature caused by the vigorous exothermic reaction between phosphorus oxychloride and n-butanol, which can exacerbate side reactions and reduce butanol consumption. On the other hand, the diluent acts as an extractant. When the filtrate is washed with water, the diluent can completely extract the organic phase. The resulting aqueous phase after washing is a high-purity hydrogen chloride solution. By adding an organic amine to the solution and allowing it to fully react to form an organic amine hydrochloride, the hydrogen chloride is immobilized. This reduces side reactions of hydrogen chloride with n-butanol, tributyl phosphate, and the like, while increasing the value of the byproduct hydrogen chloride, resulting in a more valuable organic amine hydrochloride. It also reduces the generation of pollutants and avoids the treatment of high-salt wastewater. All three of these aspects contribute to improving the purity and yield of the tributyl phosphate product.

[0034] Currently, when tributyl phosphate is used as an extractant (e.g., a specialized extractant for purifying phosphoric acid), it is necessary to add a certain proportion of a diluent. Therefore, in practical applications, the diluent added during the preparation of tributyl phosphate in the present invention can be used without separation. After the n-butanol is separated by distillation, the resulting tributyl phosphate / diluent mixture is mixed with a phase modifier and then used as an extractant. This eliminates the need for separate tributyl phosphate, reduces the number of separation steps, and eliminates the need for mixing tributyl phosphate with a diluent when using tributyl phosphate as an extractant. Of course, depending on application requirements, the diluent in the tributyl phosphate / diluent mixture can also be separated by distillation to obtain high-purity tributyl phosphate.

[0035] In order to solve the problem that the addition of diluent will cause a decrease in the concentration of phosphorus oxychloride, affecting the reaction rate between phosphorus oxychloride and n-butanol, the method of the present invention adopts a two-stage temperature-rising reaction and the use of a catalyst to increase the reaction rate between phosphorus oxychloride and n-butanol, shorten the reaction time, and improve the utilization rate of the equipment. In addition, the reaction process between phosphorus oxychloride and n-butanol in the method of the present invention is carried out under normal pressure without vacuum pumping, which can also reduce the consumption of butanol and production costs.

[0036] Compared with the prior art, the technical solution provided by the present invention has the following beneficial technical effects:

[0037] 1. The present invention provides a method for synthesizing tributyl phosphate, mainly by mixing a diluent with phosphorus oxychloride in an appropriate ratio and then reacting with n-butanol. By introducing a diluent to reduce the concentration of phosphorus oxychloride, the problem of local over-concentration of phosphorus oxychloride causing local overheating and aggravating side reactions is solved. The introduced diluent can also reduce the concentration of hydrogen chloride generated in the reaction system, reducing the occurrence of side reactions between hydrogen chloride and butanol, as well as between hydrogen chloride and tributyl phosphate. Further, by controlling the temperature of the diluent at 1-5 °C, the increase in the temperature of the reaction system during the dropping process of the diluent / phosphorus oxychloride mixture can be effectively limited, avoiding the aggravation of side reactions due to too high a temperature of the reaction system. In addition, the introduced diluent also acts as an extractant, which can completely extract the organic phase after the reaction, and then use organic amine to fix hydrogen chloride in the aqueous phase, avoiding side reactions between hydrogen chloride and n-butanol, tributyl phosphate, etc., and converting the by-product hydrogen chloride into a more valuable organic amine hydrochloride. The present invention provides a different idea from the prior art for reducing side reactions between phosphorus oxychloride and n-butanol. Based on the above aspects, the present invention can not only improve the purity and yield of tributyl phosphate products, but also obtain high-purity and high-value organic amine hydrochloride. The purity of the prepared tributyl phosphate is above 99%, the yield is above 97%, and organic amine hydrochloride with a purity above 99% is obtained.

[0038] 2. In the method for synthesizing tributyl phosphate of the present invention, the reaction process between phosphorus oxychloride and n-butanol is carried out under normal pressure without vacuum pumping, which is beneficial to reducing the consumption of butanol and production costs. At the same time, the method of the present invention adopts a segmented temperature-rising reaction and the use of a catalyst to increase the reaction rate between phosphorus oxychloride and n-butanol, and will not cause an obvious adverse effect on the reaction rate between phosphorus oxychloride and n-butanol due to the introduction of the diluent reducing the concentration of phosphorus oxychloride.

[0039] 3. At present, when tributyl phosphate is used as an extractant (such as a special extractant for purifying phosphoric acid), a certain proportion of diluent needs to be added for use. Therefore, in practical applications, the diluent added in the method for preparing tributyl phosphate according to the present invention can be used without separation. After n-butanol is separated by distillation, the obtained tributyl phosphate / diluent mixture can be directly used as an extractant after being mixed with a phase modifier without specifically separating tributyl phosphate, reducing the separation process and the operation of mixing tributyl phosphate with the diluent when using tributyl phosphate as an extractant. Based on this, the present invention also provides a special extractant for purifying phosphoric acid formed by mixing the obtained tributyl phosphate / diluent mixture with a phase modifier in the above-mentioned tributyl phosphate synthesis method. Detailed Embodiments

[0040] The following further illustrates the special extractant for purifying phosphoric acid and the tributyl phosphate synthesis method provided by the present invention through examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Those skilled in the art can still fall within the protection scope of the present invention when making some non-essential improvements and adjustments to the present invention based on the above-mentioned invention content for specific implementation.

[0041] Example 1

[0042] In this example, the steps of the tributyl phosphate synthesis method are as follows:

[0043] (1) Cyclohexane, octane, tridecane, and tetradecane were mixed in a mass ratio of 1:1:5:3 to obtain a diluent. The diluent was frozen to 5 °C, and the frozen diluent was fully mixed with phosphorus oxychloride in a mass ratio of 0.7:1 to obtain a diluent / phosphorus oxychloride mixture.

[0044] (2) n-Butanol and zinc chloride were added to a reaction kettle. The diluent / phosphorus oxychloride mixture was added dropwise to the reaction kettle at a rate of 6.5 g / min. During the dropping process, the cooling system of the reaction kettle was turned on to control the temperature of the reaction kettle at 10 ± 2 °C, and the total dropping amount of the diluent / phosphorus oxychloride mixture was controlled so that the molar ratio of n-butanol to phosphorus oxychloride was 5.7:1. After the dropping was completed, the temperature was raised to 40 °C, and the reaction was kept warm for 60 min. Then the temperature was raised to 55 °C, and the reaction was kept warm for 90 min to obtain a reaction solution. In this step, the mass ratio of zinc chloride to phosphorus oxychloride was controlled at 2:100.

[0045] (3) The reaction solution was filtered by suction to separate zinc chloride, and the obtained filtrate was washed. Specifically:

[0046] First washing: Deionized water was added to the filtrate according to the mass ratio of deionized water to the filtrate being 1:2.7, and they were fully mixed. After standing for phase separation, an aqueous phase and an organic phase were obtained. Second washing: Deionized water was added to the organic phase obtained from the first washing according to the mass ratio of deionized water to the organic phase being 1:2.7, and they were fully mixed. After standing for phase separation, an aqueous phase and an organic phase were obtained.

[0047] The aqueous phases obtained from the first and second washings were combined. The resulting aqueous phase was hydrochloric acid; the organic phase obtained from the second washing was a mixture of n-butanol, tributyl phosphate, and a diluent.

[0048] (4) Triethylamine was added to the combined aqueous phase from step (3) according to the molar ratio of triethylamine to hydrogen chloride in the aqueous phase being 0.8:1, and they reacted for 30 min to convert the hydrogen chloride in the aqueous phase into triethylamine hydrochloride. Then, it was concentrated at 100 °C for 20 min, cooled for crystallization, and filtered to obtain triethylamine hydrochloride.

[0049] The organic phase obtained from step (3) was distilled under the conditions of a temperature of 100 °C and a pressure of -0.99 to -0.96 MPa to separate out n-butanol, obtaining a tributyl phosphate / diluent mixture. The tributyl phosphate / diluent mixture was distilled under the conditions of a temperature of 230 °C and a pressure of -0.99 to -0.96 MPa to separate out the diluent, obtaining tributyl phosphate. The separated n-butanol and diluent were recycled.

[0050] The purity of the triethylamine hydrochloride prepared in this example was 99.6%, the purity of the tributyl phosphate was 99.3%, and the yield of the tributyl phosphate was 97.2%.

[0051] Example 2

[0052] In this example, the steps of the method for synthesizing tributyl phosphate were as follows:

[0053] (1) Nonane, undecane, dodecane, and tridecane were mixed according to the mass ratio of 1:3:3:1 to obtain a diluent. The diluent was frozen to 5 °C, and the frozen diluent was fully mixed with phosphorus oxychloride according to the mass ratio of 1:1 to obtain a diluent / phosphorus oxychloride mixture.

[0054] (2) Add n-butanol and aluminum chloride into the reaction kettle, and drop the diluent / phosgene mixture into the reaction kettle at a rate of 10.2 g / min. During the dropping process, turn on the cooling system of the reaction kettle to control the temperature of the reaction kettle at 10 ± 2 °C, and control the total dropping amount of the diluent / phosgene mixture so that the molar ratio of n-butanol to phosgene is 7.4:1. After the dropping is completed, raise the temperature to 50 °C, hold the temperature for 50 min, then raise the temperature to 60 °C, and hold the temperature for 75 min to obtain the reaction solution. In this step, control the mass ratio of aluminum chloride to phosgene at 2.25:100.

[0055] (3) Filter the reaction solution to separate aluminum chloride, and wash the obtained filtrate. Specifically:

[0056] First washing: Add deionized water to the filtrate according to the mass ratio of deionized water to the filtrate of 1:3, mix well, let it stand for phase separation to obtain an aqueous phase and an organic phase. Second washing: Add deionized water to the organic phase obtained from the first washing according to the mass ratio of deionized water to the organic phase of 1:3, mix well, let it stand for phase separation to obtain an aqueous phase and an organic phase.

[0057] Combine the aqueous phases obtained from the first and second washings. The obtained aqueous phase is hydrochloric acid solution; the organic phase obtained from the second washing is a mixture of n-butanol, tributyl phosphate, and diluent.

[0058] (4) According to the molar ratio of triethylamine to hydrogen chloride in the aqueous phase of 0.85:1, add triethylamine to the combined aqueous phase in step (3) and react for 30 min to convert the hydrogen chloride in the aqueous phase into triethylamine hydrochloride, then concentrate at 100 °C for 20 min, cool and crystallize, and filter to obtain triethylamine hydrochloride.

[0059] Distill the organic phase obtained in step (3) under the conditions of a temperature of 100 °C and a pressure of -0.99 to -0.96 MPa to separate n-butanol to obtain a tributyl phosphate / diluent mixture. Distill the tributyl phosphate / diluent mixture under the conditions of a temperature of 230 °C and a pressure of -0.99 to -0.96 MPa to separate the diluent to obtain tributyl phosphate. The separated n-butanol and diluent are recycled.

[0060] The purity of the triethylamine hydrochloride prepared in this example is 99.8%, the purity of tributyl phosphate is 99.2%, and the yield of tributyl phosphate is 97.3%.

[0061] Example 3

[0062] In this example, the steps of the synthesis method of tributyl phosphate are as follows:

[0063] (1) Mix heptane, decane, dodecane, and pentadecane according to a mass ratio of 1:4:3:1 to obtain a diluent. Freeze the diluent to 5 °C, and then fully mix the frozen diluent with phosphorus oxychloride according to a mass ratio of 1.96:1 to obtain a diluent / phosphorus oxychloride mixture.

[0064] (2) Add n-butanol and zinc chloride to a reaction kettle. Dropwise add the diluent / phosphorus oxychloride mixture into the reaction kettle at a rate of 18 g / min. During the dropping process, turn on the cooling system of the reaction kettle to control the temperature of the reaction kettle at 10 ± 2 °C. Control the total dropping amount of the diluent / phosphorus oxychloride mixture so that the molar ratio of n-butanol to phosphorus oxychloride is 9:1. After the dropping is completed, raise the temperature to 60 °C and keep the temperature for 45 min, then raise the temperature to 70 °C and keep the temperature for 60 min to obtain a reaction solution. In this step, control the mass ratio of zinc chloride to phosphorus oxychloride at 1.5:100.

[0065] (3) Filter the reaction solution to separate out aluminum chloride, and perform a washing operation on the obtained filtrate. Specifically:

[0066] First washing: Add deionized water to the filtrate according to a mass ratio of deionized water to the filtrate of 1:4 and mix well. Let it stand for phase separation to obtain an aqueous phase and an organic phase. Second washing: Add deionized water to the organic phase obtained from the first washing according to a mass ratio of deionized water to the organic phase of 1:4 and mix well. Let it stand for phase separation to obtain an aqueous phase and an organic phase.

[0067] Combine the aqueous phases obtained from the first and second washings. The obtained aqueous phase is a hydrochloric acid solution; the organic phase obtained from the second washing is a mixture of n-butanol, tributyl phosphate, and the diluent.

[0068] (4) According to a molar ratio of triethylamine to hydrogen chloride in the aqueous phase of 0.9:1, add triethylamine to the combined aqueous phase in step (3) and react for 30 min to convert the hydrogen chloride in the aqueous phase into triethylamine hydrochloride. Then concentrate at 100 °C for 20 min, cool and crystallize, and filter to obtain triethylamine hydrochloride.

[0069] Distill the organic phase obtained in step (3) under the conditions of a temperature of 100 °C and a pressure of -0.99 to -0.96 MPa to separate out n-butanol to obtain a tributyl phosphate / diluent mixture. Distill the tributyl phosphate / diluent mixture under the conditions of a temperature of 230 °C and a pressure of -0.99 to -0.96 MPa to separate out the diluent to obtain tributyl phosphate. The separated n-butanol and diluent are recycled.

[0070] The purity of the triethylamine hydrochloride prepared in this example is 99.5%, the purity of tributyl phosphate is 99.2%, and the yield of tributyl phosphate is 97.2%.

[0071] Comparative Example 1

[0072] In this comparative example, the steps of the synthetic method of tributyl phosphate are as follows:

[0073] (1) Add n-butanol to the reaction kettle, and drop phosphorus oxychloride into the reaction kettle at a rate of 6.5 g / min. During the dropping process, turn on the cooling system of the reaction kettle to control the temperature of the reaction kettle at 1 +- 2 °C, and control the total dropping amount of phosphorus oxychloride so that the molar ratio of n-butanol to phosphorus oxychloride is 5.7:1. After the dropping is completed, raise the temperature to 40 °C, keep the temperature for 60 min, then raise the temperature to 55 °C, and keep the temperature for 90 min to obtain a reaction solution.

[0074] (2) First washing: Add deionized water to the reaction solution according to the mass ratio of deionized water to the reaction solution of 1:2.7, and mix well. Let it stand for phase separation to obtain an aqueous phase and an organic phase. Second washing: Add deionized water to the organic phase obtained from the first washing according to the mass ratio of deionized water to the organic phase of 1:2.7, and mix well. Let it stand for phase separation to obtain an aqueous phase and an organic phase.

[0075] Combine the aqueous phases obtained from the first and second washings. The obtained aqueous phase is a hydrochloric acid solution; the organic phase obtained from the second washing is a mixture of n-butanol and tributyl phosphate.

[0076] (3) According to the molar ratio of triethylamine to hydrogen chloride in the aqueous phase of 0.8:1, add triethylamine to the combined aqueous phase in step (2) and react for 30 min to convert the hydrogen chloride in the aqueous phase into triethylamine hydrochloride. Then concentrate at 100 °C for 20 min, then cool and crystallize, and filter to obtain triethylamine hydrochloride.

[0077] Distill the organic phase obtained in step (2) under the conditions of a temperature of 100 °C and a pressure of -0.99 to -0.96 MPa to separate out n-butanol and obtain tributyl phosphate. The separated n-butanol is recycled.

[0078] The purity of the triethylamine hydrochloride prepared in this comparative example is 99.5%, the purity of the tributyl phosphate is 98.7%, and the yield of the tributyl phosphate is 77.8%.

[0079] The method of Comparative Example 1 is the most commonly used synthetic method of tributyl phosphate in the prior art. Combining Example 1 and Comparative Example 1, it can be seen that the method of the present invention can effectively improve the yield of tributyl phosphate and at the same time improve the purity of the obtained tributyl phosphate by mixing the diluent with phosphorus oxychloride and then reacting with n-butanol.

[0080] Comparative Example 2

[0081] In this comparative example, the steps of the synthetic method of tributyl phosphate are as follows:

[0082] (1) Add n-butanol and zinc chloride into the reaction kettle, and drop phosphorus oxychloride into the reaction kettle at a rate of 6.5 g / min. During the dropping process, turn on the cooling system of the reaction kettle to control the temperature of the reaction kettle at 10 ± 2 °C, and control the total dropping amount of phosphorus oxychloride so that the molar ratio of n-butanol to phosphorus oxychloride is 5.7:1. After the dropping is completed, raise the temperature to 40 °C, keep the temperature for reaction for 60 min, then raise the temperature to 55 °C, and keep the temperature for reaction for 90 min to obtain the reaction solution. In this step, control the mass ratio of zinc chloride to phosphorus oxychloride to be 2:100.

[0083] (2) Filter the reaction solution by suction to separate zinc chloride, and perform a washing operation on the obtained filtrate. Specifically:

[0084] The first washing: Add deionized water to the filtrate according to the mass ratio of deionized water to the filtrate of 1:2.7, mix well, let it stand for phase separation to obtain an aqueous phase and an organic phase. The second washing: Add deionized water to the organic phase obtained from the first washing according to the mass ratio of deionized water to the organic phase of 1:2.7, mix well, let it stand for phase separation to obtain an aqueous phase and an organic phase.

[0085] Combine the aqueous phases obtained from the first and second washings. The obtained aqueous phase is a hydrochloric acid solution; the organic phase obtained from the second washing is a mixture of n-butanol and tributyl phosphate.

[0086] (4) According to the molar ratio of triethylamine to hydrogen chloride in the aqueous phase of 0.8:1, add triethylamine to the combined aqueous phase in step (3) and react for 30 min to convert the hydrogen chloride in the aqueous phase into triethylamine hydrochloride, then concentrate at 100 °C for 20 min, then cool and crystallize, and filter to obtain triethylamine hydrochloride.

[0087] Distill the organic phase obtained in step (3) under the conditions of a temperature of 100 °C and a pressure of -0.99 to -0.96 MPa to separate n-butanol and obtain tributyl phosphate. The separated n-butanol is recycled.

[0088] The purity of the triethylamine hydrochloride prepared in this comparative example is 99.5%, the purity of tributyl phosphate is 98.9%, and the yield of tributyl phosphate is 88.2%.

[0089] It can be seen from Example 1 and Comparative Examples 1 - 2 that although Comparative Example 2 promoted the reaction of phosphorus oxychloride with n-butanol by introducing a catalyst and improved the yield of tributyl phosphate to a certain extent compared with Comparative Example 1, however, the yield of tributyl phosphate in Comparative Example 2 is still less than 90%, and there is an obvious difference from the yield of tributyl phosphate in Example 1 (97.2%).

[0090] Comparative Example 3

[0091] In this comparative example, the steps of the synthesis method of tributyl phosphate are as follows:

[0092] (1) Mix cyclohexane, octane, tridecane, and tetradecane according to a mass ratio of 1:1:5:3 to obtain a diluent. Mix the diluent at room temperature (about 20 °C) and phosphorus oxychloride according to a mass ratio of 0.7:1 to obtain a diluent / phosphorus oxychloride mixture.

[0093] (2) Add n-butanol and zinc chloride to the reaction kettle. Dropwise add the diluent / phosphorus oxychloride mixture to the reaction kettle at a rate of 6.5 g / min. During the dropping process, turn on the cooling system of the reaction kettle to control the temperature of the reaction kettle at 10 ± 2 °C. Control the total dropping amount of the diluent / phosphorus oxychloride mixture so that the molar ratio of n-butanol to phosphorus oxychloride is 5.7:1. After the dropping is completed, raise the temperature to 40 °C, hold the temperature for reaction for 60 min, then raise the temperature to 55 °C, hold the temperature for reaction for 90 min to obtain a reaction solution. In this step, control the mass ratio of zinc chloride to phosphorus oxychloride to be 2:100.

[0094] (3) Filter the reaction solution to separate zinc chloride, and perform a washing operation on the obtained filtrate. Specifically:

[0095] First washing: Add deionized water to the filtrate according to a mass ratio of deionized water to filtrate of 1:2.7 and mix well. Let it stand for phase separation to obtain an aqueous phase and an organic phase. Second washing: Add deionized water to the organic phase obtained from the first washing according to a mass ratio of deionized water to organic phase of 1:2.7 and mix well. Let it stand for phase separation to obtain an aqueous phase and an organic phase.

[0096] Combine the aqueous phases obtained from the first and second washings. The obtained aqueous phase is a hydrochloric acid solution; the organic phase obtained from the second washing is a mixture of n-butanol, tributyl phosphate, and diluent.

[0097] (4) According to a molar ratio of triethylamine to hydrogen chloride in the aqueous phase of 0.8:1, add triethylamine to the combined aqueous phase in step (3) and react for 30 min to convert the hydrogen chloride in the aqueous phase into triethylamine hydrochloride. Then concentrate at 100 °C for 20 min, cool and crystallize, and filter to obtain triethylamine hydrochloride.

[0098] Distill the organic phase obtained in step (3) under the conditions of a temperature of 100 °C and a pressure of -0.99 to -0.96 MPa to separate n-butanol, obtaining a tributyl phosphate / diluent mixture. Distill the tributyl phosphate / diluent mixture under the conditions of a temperature of 230 °C and a pressure of -0.99 to -0.96 MPa to separate the diluent, obtaining tributyl phosphate. The separated n-butanol and diluent are recycled.

[0099] The purity of the triethylamine hydrochloride prepared in this comparative example was 99.6%, the purity of tributyl phosphate was 98.9%, and the yield of tributyl phosphate was 84.4%.

[0100] It can be seen from Example 1 and Comparative Examples 1-3 that although by introducing a room temperature diluent and mixing it with phosphorus oxychloride and then reacting with n-butanol, the yield of tributyl phosphate can be increased to a certain extent compared with Comparative Example 1 without introducing a diluent. However, the yield of tributyl phosphate in Comparative Example 2 was still less than 85%, showing an obvious difference from the yield of tributyl phosphate in Example 1 (97.2%).

[0101] Combining Example 1 and Comparative Examples 1-3, it can be seen that the reason why the method of the present invention can effectively increase the yield of tributyl phosphate is closely related to the following factors: mixing a diluent with phosphorus oxychloride, controlling the temperature of the diluent at a lower temperature, and using a catalyst to promote the reaction between phosphorus oxychloride and n-butanol. None of these three factors can be omitted.

[0102] Example 4

[0103] In this example, a special extractant for purifying phosphoric acid was provided.

[0104] The tributyl phosphate / diluent mixture in step (4) of Example 1 was fully mixed with the phase modifier cyclohexanol, and the mass ratio of the tributyl phosphate / diluent mixture to the phase modifier was controlled to be 9:1 to obtain a special extractant for purifying phosphoric acid.

[0105] The extractant was dropped into wet dilute phosphoric acid with a phosphoric acid concentration of 40 wt%, the volume ratio of the extractant to the phosphoric acid was controlled to be 5:1, the temperature of the phosphoric acid was controlled to be maintained at 50 °C. After the dropwise addition of the extractant was completed, the reaction continued for 20 min, then it was left to stand for phase separation, and the obtained organic phase was washed with purified phosphoric acid, and industrial purified phosphoric acid was obtained by water back-extraction.

[0106] In this example, the extraction rate of the extractant for phosphoric acid was 80%, and the extracted phosphoric acid met the quality requirements of first-class industrial purified phosphoric acid.

[0107] Example 5

[0108] In this example, a special extractant for purifying phosphoric acid was provided.

[0109] The tributyl phosphate / diluent mixture obtained in step (4) of Example 1 was fully mixed with the phase modifier octanol, and the mass ratio of the tributyl phosphate / diluent mixture to the phase modifier was controlled to be 7.5:1 to obtain a special extractant for purifying phosphoric acid.

[0110] The extractant was dropped into wet-process dilute phosphoric acid with a phosphoric acid concentration of 40 wt%, the volume ratio of the extractant to the phosphoric acid was controlled to be 5:1, the temperature of the phosphoric acid was controlled to be maintained at 50 °C. After the addition of the extractant was completed, the reaction continued for 20 min, then it was allowed to stand for phase separation. The obtained organic phase was washed with purified phosphoric acid, and industrial purified phosphoric acid was obtained by back-extraction with water.

[0111] In this example, the extraction rate of the extractant for phosphoric acid was 80.1%, and the extracted phosphoric acid met the quality requirements of first-class industrial purified phosphoric acid.

[0112] Example 6

[0113] In this example, a special extractant for purified phosphoric acid was provided.

[0114] Octanol, decanol, and undecanol were mixed in a mass ratio of 3:3:2 as a phase modifier. The tributyl phosphate / diluent mixture obtained in step (4) of Example 1 was fully mixed with the phase modifier, and the mass ratio of the tributyl phosphate / diluent mixture to the phase modifier was controlled to be 6:1 to obtain a special extractant for purified phosphoric acid.

[0115] The extractant was dropped into wet-process dilute phosphoric acid with a phosphoric acid concentration of 40 wt%, the volume ratio of the extractant to the phosphoric acid was controlled to be 5:1, the temperature of the phosphoric acid was controlled to be maintained at 50 °C. After the addition of the extractant was completed, the reaction continued for 20 min, then it was allowed to stand for phase separation. The obtained organic phase was washed with purified phosphoric acid, and industrial purified phosphoric acid was obtained by back-extraction with water.

[0116] In this example, the extraction rate of the extractant for phosphoric acid was 80.3%, and the extracted phosphoric acid met the quality requirements of first-class industrial purified phosphoric acid.

[0117] Example 7

[0118] In this example, the steps of the tributyl phosphate synthesis method were as follows:

[0119] (1) Using dodecane as a diluent, the diluent was frozen to 1 °C, and the frozen diluent was fully mixed with phosphorus oxychloride in a mass ratio of 0.5:1 to obtain a diluent / phosphorus oxychloride mixture.

[0120] (2) Add n-butanol and zinc chloride into the reaction kettle, and drop the diluent / phosphorus oxychloride mixture into the reaction kettle at a rate of 6 g / min. During the dropping process, turn on the cooling system of the reaction kettle to control the temperature of the reaction kettle at 7 ± 2 °C, and control the total dropping amount of the diluent / phosphorus oxychloride mixture so that the molar ratio of n-butanol to phosphorus oxychloride is 4:1. After the dropping is completed, heat up to 35 °C, keep the temperature for reaction for 45 min, then heat up to 40 °C, keep the temperature for reaction for 120 min to obtain the reaction solution. In this step, control the mass ratio of zinc chloride to phosphorus oxychloride at 0.5:100.

[0121] (3) Filter the reaction solution by suction to separate zinc chloride, and perform a washing operation on the obtained filtrate. Specifically:

[0122] First washing: Add deionized water to the filtrate according to the mass ratio of deionized water to the filtrate of 1:2.5 and mix well, then let it stand for phase separation to obtain an aqueous phase and an organic phase. Second washing: Add deionized water to the organic phase obtained from the first washing according to the mass ratio of deionized water to the organic phase of 1:2.5 and mix well, then let it stand for phase separation to obtain an aqueous phase and an organic phase.

[0123] Combine the aqueous phases obtained from the first and second washings. The obtained aqueous phase is hydrochloric acid; the organic phase obtained from the second washing is a mixture of n-butanol, tributyl phosphate, and diluent.

[0124] (4) According to the molar ratio of triethylamine to hydrogen chloride in the aqueous phase of 1.05:1, add triethylamine to the combined aqueous phase in step (3) and react for 20 min to convert the hydrogen chloride in the aqueous phase into triethylamine hydrochloride, then concentrate at 80 °C for 40 min, cool and crystallize, and filter to obtain triethylamine hydrochloride.

[0125] Distill the organic phase obtained in step (3) under the conditions of a temperature of 95 °C and a pressure of -0.99 to -0.96 MPa to separate n-butanol, obtaining a tributyl phosphate / diluent mixture. Distill the tributyl phosphate / diluent mixture under the conditions of a temperature of 210 °C and a pressure of -0.99 to -0.96 MPa to separate the diluent, obtaining tributyl phosphate. The separated n-butanol and diluent are recycled.

[0126] The purity of the triethylamine hydrochloride prepared in this example is 99.4%, the purity of the tributyl phosphate prepared in this example is 99.2%, and the yield of tributyl phosphate is 97.1%.

[0127] Example 8

[0128] In this example, the steps of the synthesis method of tributyl phosphate are as follows:

[0129] (1) Using tridecane as a diluent, the diluent was frozen to 2 °C, and the frozen diluent was thoroughly mixed with phosphorus oxychloride at a mass ratio of 2:1 to obtain a diluent / phosphorus oxychloride mixture.

[0130] (2) n-Butanol and zinc chloride were added to a reaction kettle, and the diluent / phosphorus oxychloride mixture was added dropwise to the reaction kettle at a rate of 8 g / min. During the dropping process, the cooling system of the reaction kettle was turned on to control the temperature of the reaction kettle at 13 ± 2 °C. The total amount of the diluent / phosphorus oxychloride mixture added dropwise was controlled so that the molar ratio of n-butanol to phosphorus oxychloride was 6.5:1. After the dropping was completed, the temperature was raised to 65 °C and the reaction was kept at this temperature for 30 min. Then the temperature was raised to 80 °C and the reaction was kept at this temperature for 60 min to obtain a reaction solution. In this step, the mass ratio of zinc chloride to phosphorus oxychloride was controlled at 5:100.

[0131] (3) The reaction solution was filtered by suction to separate zinc chloride, and the obtained filtrate was washed. Specifically:

[0132] First washing: Deionized water was added to the filtrate at a mass ratio of deionized water to the filtrate of 1:3 and thoroughly mixed, and then allowed to stand for phase separation to obtain an aqueous phase and an organic phase. Second washing: Deionized water was added to the organic phase obtained from the first washing at a mass ratio of deionized water to the organic phase of 1:3 and thoroughly mixed, and then allowed to stand for phase separation to obtain an aqueous phase and an organic phase. Third washing: Deionized water was added to the organic phase obtained from the second washing at a mass ratio of deionized water to the organic phase of 1:3 and thoroughly mixed, and then allowed to stand for phase separation to obtain an aqueous phase and an organic phase.

[0133] The aqueous phases obtained from the first to the third washings were combined, and the obtained aqueous phase was hydrochloric acid; the organic phase obtained from the third washing was a mixture of n-butanol, tributyl phosphate, and diluent.

[0134] (4) Triethylamine was added to the combined aqueous phase obtained in step (3) at a molar ratio of triethylamine to hydrogen chloride in the aqueous phase of 0.9:1 and reacted for 30 min to convert the hydrogen chloride in the aqueous phase into triethylamine hydrochloride. Then it was concentrated at 100 °C for 10 min, cooled and crystallized, and filtered to obtain triethylamine hydrochloride.

[0135] The organic phase obtained in step (4) was distilled at a temperature of 105 °C and a pressure of -0.99 to -0.96 MPa to separate n-butanol, obtaining a tributyl phosphate / diluent mixture. The tributyl phosphate / diluent mixture was distilled at a temperature of 230 °C and a pressure of -0.99 to -0.96 MPa to separate the diluent, obtaining tributyl phosphate. The separated n-butanol and diluent were recycled.

[0136] The purity of the triethylamine hydrochloride prepared in this example is 99.5%, the purity of the tributyl phosphate prepared in this example is 99.3%, and the yield of tributyl phosphate is 97.4%.

[0137] Example 9.

[0138] In this example, the synthesis method of tributyl phosphate is basically the same as that in Example 8, except that the triethylamine in step (4) is replaced with diethylamine, and after adding diethylamine, the reaction is carried out for 10 min to prepare diethylamine hydrochloride.

[0139] The purity of the diethylamine hydrochloride prepared in this example is 99.4%, the purity of the tributyl phosphate prepared in this example is 99.4%, and the yield of tributyl phosphate is 97.3%.

[0140] Example 10.

[0141] In this example, the synthesis method of tributyl phosphate is basically the same as that in Example 8, except that the triethylamine in step (4) is replaced with tributylamine, and after adding tributylamine, the reaction is carried out for 30 min to prepare tributylamine hydrochloride.

[0142] The purity of the tributylamine hydrochloride prepared in this example is 99.5%, the purity of the tributyl phosphate prepared in this example is 99.5%, and the yield of tributyl phosphate is 97.5%.

[0143] Example 11.

[0144] In this example, the synthesis method of tributyl phosphate is basically the same as that in Example 8, except that the triethylamine in step (4) is replaced with dibutylamine, and after adding dibutylamine, the reaction is carried out for 30 min to prepare dibutylamine hydrochloride.

[0145] The purity of the dibutylamine hydrochloride prepared in this example is 99.2%, the purity of the tributyl phosphate prepared in this example is 99.4%, and the yield of tributyl phosphate is 97.4%.

[0146] The above examples are only partial examples of the present invention and are not used to limit the present invention. Those skilled in the art can make equivalent replacements or non-essential adjustments such as changes according to the technical concept and technical solution of the present invention, and all equivalent replacements and non-essential adjustments should be included within the protection scope of the present invention.

Claims

1. A method for synthesizing tributyl phosphate, characterized in that, It includes the following steps: (1) Dilute the diluent at a temperature of 1 - 5 °C with phosphorus oxychloride in a mass ratio of (0.5 - 2):1 and mix well to obtain a diluent / phosphorus oxychloride mixture. The diluent is a mixture of one or more of C6 - C 15 alkanes; (2) Add n-butanol and a catalyst into a reaction kettle, and dropwise add a diluent / phosgene mixture into the reaction kettle. During the dropping process, control the temperature of the reaction kettle at 5-15 °C. After the dropping is completed, raise the temperature to the first reaction temperature, keep the temperature for reaction for 30-60 min, then raise the temperature to the second reaction temperature, and keep the temperature for reaction for 60-120 min to obtain a reaction solution; Control the second reaction temperature to be higher than the first reaction temperature, the first reaction temperature is 30-65 °C, and the second reaction temperature is 40-80 °C; control the mass ratio of the catalyst to phosgene to be (0.5-5):100; (3) Filter the reaction solution obtained in step (2), wash the filtered filtrate with water, stand for phase separation to obtain an aqueous phase and an organic phase; (4) Add an organic amine to the aqueous phase obtained in step (3) and react fully to convert hydrogen chloride in the aqueous phase into an organic amine hydrochloride, then raise the temperature for concentration, cool for crystallization, and perform solid-liquid separation to obtain a high-purity organic amine hydrochloride; Distill and separate n-butanol from the organic phase obtained in step (3) to obtain a tributyl phosphate / diluent mixture, distill the tributyl phosphate / diluent mixture, separate the diluent to obtain high-purity tributyl phosphate, and recycle the separated n-butanol and diluent.

2. The synthetic method of tributyl phosphate according to claim 1, characterized in that, The catalyst described in step (1) is zinc chloride or aluminum chloride.

3. The method for synthesizing tributyl phosphate according to claim 1, characterized in that, In step (2), control the total dropping amount of the diluent / phosgene mixture so that the molar ratio of n-butanol to phosgene is (4-9):

1.

4. The method for synthesizing tributyl phosphate according to any one of claims 1 to 3, characterized in that, In step (3), control the number of washing times to be 2-3 times. For the first washing, add water to the filtrate according to the mass ratio of water to the filtrate of 1:(2.5-4) for washing. For the 2nd-3rd washings, add water to the organic phase obtained from the previous washing according to the mass ratio of water to the organic phase obtained from the previous washing of 1:(2.5-4) for washing.

5. The method for synthesizing tributyl phosphate according to any one of claims 1 to 3, characterized in that, When dropping the diluent / phosgene mixture into the reaction kettle in step (2), control the dropping rate of the diluent / phosgene mixture to be 6-18 g / min.

6. The method for synthesizing tributyl phosphate according to any one of claims 1 to 3, characterized in that, The organic amine described in step (4) is triethylamine, diethylamine, tributylamine or dibutylamine.

7. The method for synthesizing tributyl phosphate according to any one of claims 1 to 3, characterized in that, In step (4), the amount of the organic amine used is 80%-105% of the molar amount of hydrogen chloride in the aqueous phase obtained in step (3).

8. A special extractant for purifying phosphoric acid, characterized in that, It is composed of a tributyl phosphate / diluent mixture prepared by the method for synthesizing tributyl phosphate according to any one of claims 1 to 7 and a phase modifier.

9. The special extractant for purifying phosphoric acid according to claim 8, characterized in that, The phase modifier is an alcohol substance with 4-13 carbon atoms.

10. The special extractant for purifying phosphoric acid according to claim 8 or 9, characterized in that, In this special extraction agent, the mass ratio of the tributyl phosphate / diluent mixture to the phase modifier is (6-9):1.