A process for the synthesis of phosphoric acid mono-esters using a stripping method

Abstract

This invention relates to the field of isomeric alcohol phosphate monoester preparation technology, specifically a method for synthesizing phosphate monoesters using a stripping method, comprising the following steps: S1, esterification reaction: adding isomeric alcohol to a reaction vessel, adding phosphorus pentoxide in batches while controlling the temperature at 40-60℃, and then raising the temperature to 80-100℃ and holding the reaction for 3-5 hours to obtain crude phosphate ester; S2, catalytic stripping purification: adding TCC catalyst to the crude phosphate ester, and sequentially performing steam stripping and nitrogen stripping to obtain isomeric alcohol phosphate monoesters with an esterification rate >98% and a monoester content >95%; wherein, the steam stripping conditions are: temperature 100-140℃, pressure 600-1500Pa, steam flux 120-180g / h, time 0.5-2h; the nitrogen stripping conditions are: temperature 100-120℃, pressure 600-1500Pa, nitrogen flux 1-3L / min, time 0.5-1h. This invention achieves efficient and targeted purification of isomeric alcohol phosphate monoesters at low temperatures through the synergistic effect of TCC catalysis and water stripping, overcoming the technical challenge of traditional processes that cannot simultaneously achieve high monoester content and low-energy green production.

Description

Technical Field

[0001] This invention relates to the field of isomeric alcohol phosphate monoester preparation technology, specifically a method for synthesizing phosphate monoesters using a stripping method. Background Technology

[0002] Isomerized alcohol phosphates are a class of high-performance anionic surfactants. Due to their unique molecular structure, they possess excellent wetting, emulsifying, rust-preventing, and antistatic properties, and are widely used in metalworking fluids, pesticide emulsifiers, textile printing and dyeing auxiliaries, and daily cosmetics. Depending on the degree of esterification, monophosphates have strong hydrophilicity and high solubility in water, primarily contributing to emulsifying and wetting properties; while diesters have stronger lipophilicity and are mostly used in lubricant additives and coatings. With the development of high-end manufacturing and fine chemicals, the market demand for high-purity monophosphates (especially those with a monoester content >70%) is increasingly urgent to meet the stringent requirements for extreme pressure lubrication and high emulsification stability.

[0003] However, existing phosphate ester synthesis processes face significant technical bottlenecks. Currently, there are two main industrial production routes: one is the reaction of phosphorus oxychloride (POCl3) with isomeric alcohols. Although the reaction rate is fast, the phosphorus oxychloride used in this process is a highly toxic and hazardous chemical, making procurement and transportation difficult. Furthermore, the reaction generates a large amount of hydrogen chloride (HCl) gas, which causes severe corrosion to production equipment, posing significant safety and environmental hazards. The other route is the direct esterification of phosphorus pentoxide (P2O5) with isomeric alcohols. While this route uses relatively safe and inexpensive raw materials without strong corrosiveness, the reaction products are usually a mixture of phosphate monoesters and diesters due to the reactivity and steric hindrance of phosphorus pentoxide. The monoester content is generally between 50% and 65%, making it difficult to exceed the 70% purity limit. Therefore, it is impossible to directly obtain high-content monoester products through the above conventional processes.

[0004] To obtain high-purity monoesters, existing technologies typically employ high-temperature, high-vacuum distillation or complex solvent recrystallization methods. However, these methods are not only extremely energy-intensive (requiring heating to above 150°C), but also prone to thermal decomposition and hydrolysis of heat-sensitive phosphate monoesters under high vacuum, thus reducing product yield and purity, while increasing equipment investment and operational risks. Therefore, developing a green, low-energy purification process that can efficiently improve monoester content by avoiding the hazardous raw material phosphorus oxychloride and utilizing the safe and readily available phosphorus pentoxide route is a pressing technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a method for synthesizing phosphate monoesters using a stripping method, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0007] A method for synthesizing phosphate monoesters using a stripping method includes the following steps:

[0008] S1. Esterification reaction: Add isomeric alcohol to the reaction vessel, add phosphorus pentoxide in batches while controlling the temperature at 40-60℃, and after the addition is complete, raise the temperature to 80-100℃ and keep the reaction for 3-5 hours to obtain crude phosphate ester.

[0009] S2. Catalytic stripping purification: TCC catalyst is added to the crude phosphate ester, and steam stripping (which can promote the hydrolysis of isomeric alcohol phosphate diester, inhibit the hydrolysis of isomeric alcohol phosphate monoester, and remove unreacted isomeric alcohols by stripping) and nitrogen (N2) stripping (to remove residual water) are performed sequentially to obtain isomeric alcohol phosphate monoester with esterification rate >98% and monoester content >95%.

[0010] The steam stripping conditions are as follows: temperature 100-140℃, pressure 600-1500Pa, steam flux 120-180g / h, and time 0.5-2h.

[0011] The nitrogen stripping conditions are: temperature 100-120℃, pressure 600-1500Pa, nitrogen flow rate 1-3L / min, and time 0.5-1h.

[0012] As a further aspect of the present invention: in step S1, the molar ratio of the isomeric alcohol to phosphorus pentoxide is 1.7-2.3:1, and the phosphorus pentoxide is added for 0.5-2 hours.

[0013] As a further aspect of the present invention: in step S1, the molar ratio of the isomeric alcohol to phosphorus pentoxide is 2.0-2.3:1, the reaction temperature is 80-90℃, and the reaction time is 4-5h.

[0014] As a further aspect of the present invention: in step S1, the molar ratio of the isomeric alcohol to phosphorus pentoxide is 2.2:1, the phosphorus pentoxide is added for 1 hour, the reaction temperature is 85°C, and the reaction time is 4 hours.

[0015] As a further aspect of the present invention: in step S2, the amount of the TCC catalyst is 0.1%-0.4% of the mass of the isomeric alcohol.

[0016] As a further aspect of the present invention: in step S2, the amount of the TCC catalyst used is 0.15% of the mass of the isomeric alcohol;

[0017] The steam stripping conditions are: temperature 110-120℃, pressure 1000-1200Pa, steam flux 140-160g / h, and time 1-1.5h.

[0018] The nitrogen stripping conditions are: temperature 105℃, pressure 1200Pa, nitrogen flow rate 1.5-2L / min, and time 0.5-1h.

[0019] As a further aspect of the present invention: in step S2, the steam stripping conditions are: temperature 110℃, pressure 1100Pa, steam flux 150-160g / h, and time 1.5h.

[0020] The nitrogen stripping conditions are: temperature 105℃, pressure 1200Pa, nitrogen flow rate 1.5L / min, and time 1h.

[0021] As a further aspect of the present invention: the TCC catalyst is a borate-organotin complex, used to inhibit the hydrolysis of phosphate monoesters and promote the esterification reaction of free phosphoric acid with isomeric alcohols.

[0022] Compared with the prior art, the beneficial effects of the embodiments of the present invention are:

[0023] This invention solves the pain points of difficult purification and low purity of traditional phosphate monoesters through an integrated "esterification-catalytic stripping" process. The TCC catalyst plays a dual key role in the stripping process: it coordinates with the hydroxyl groups of phosphate monoesters to form a stable cyclic structure and inhibits its high-temperature hydrolysis, while also promoting the esterification of free phosphoric acid with isomeric alcohols and the conversion of diesters to monoesters. Combined with the low-temperature and low-pressure characteristics of steam stripping (100-140℃, 600-1500Pa), it avoids the monoester decomposition caused by the high temperature of over 150℃ required by traditional vacuum distillation, while efficiently removing unreacted isomeric alcohols. The final product has an esterification rate of >98% and a monoester content of >95%, and no solvent is added throughout the process. It has the advantages of high purity, low energy consumption, and green process, filling the gap in the industrial production of high-content phosphate monoesters. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] 158g of isomeric decaol was added to the reaction flask, stirring was started and the temperature was raised to 40°C. The system temperature was controlled to not exceed 60°C, and 87g of phosphorus pentoxide was added in batches, taking approximately 1.5 hours to complete. The temperature was then raised to 90°C and maintained for 5 hours. The mixture was then cooled to room temperature and samples were taken for analysis. The crude product showed an esterification rate of 93.80%, a monoester content of 61.22%, and a diester content of 33.17%.

[0027] Example 2

[0028] 158g of isomeric decaol was added to the reaction flask, stirring was started and the temperature was raised to 40°C. The system temperature was controlled to not exceed 60°C, and 74g of phosphorus pentoxide was added in batches, taking approximately 1 hour to complete. The temperature was then raised to 85°C and maintained for 4 hours. The mixture was then cooled to room temperature and samples were taken for analysis. The crude product showed an esterification rate of 93.11%, a monoester content of 62.42%, and a diester content of 31.97%.

[0029] Example 3

[0030] 158g of isomeric decaol was added to the reaction flask, stirring was started and the temperature was raised to 40°C. The system temperature was controlled to not exceed 60°C, and 67.3g of phosphorus pentoxide was added in batches, taking approximately 1 hour to complete. The temperature was then raised to 85°C and maintained for 4 hours. The mixture was then cooled to room temperature and samples were taken for analysis. The crude product showed an esterification rate of 94.04%, a monoester content of 64.54%, and a diester content of 32.42%.

[0031] Example 4

[0032] 158 g of isomeric decaol was added to the reaction flask, stirring was started and the temperature was raised to 40 °C. The system temperature was controlled to not exceed 60 °C, and 64.3 g of phosphorus pentoxide was added in portions, taking approximately 1 hour to complete. The temperature was then raised to 85 °C and maintained for 4 hours. The mixture was then cooled to room temperature and samples were taken for analysis. The crude product showed an esterification rate of 93.44%, a monoester content of 61.17%, and a diester content of 34.68%.

[0033] Example 5

[0034] The crude product obtained in Example 3 was heated to 140°C, and 0.63 g of TCC catalyst was added. The system pressure was controlled at 600 Pa, and steam was introduced for stripping at a flow rate of 120 g / h for 0.5 h. Subsequently, the temperature was lowered to 120°C, and nitrogen was introduced for stripping at a flow rate of 1 L / min, maintaining the pressure at 600 Pa for 0.5 h. After cooling, the product showed an esterification rate of 97.23%, a monoester content of 91.68%, and a diester content of 4.21%.

[0035] Example 6

[0036] The crude product obtained in Example 3 was heated to 100°C, and 0.16 g of TCC catalyst was added. The system pressure was controlled at 1500 Pa, and steam was introduced for stripping at a flow rate of 180 g / h for 2 hours. Subsequently, the temperature was adjusted to 100°C, and nitrogen was introduced for stripping at a flow rate of 3 L / min, maintaining the pressure at 1500 Pa for 1 hour. After cooling, the product was tested, and the esterification rate was 91.83%, the monoester content was 90.04%, and the diester content was 3.02%.

[0037] Example 7

[0038] The crude product obtained in Example 3 was heated to 120°C, and 0.24 g of TCC catalyst was added. The system pressure was controlled at 800 Pa, and steam was introduced for stripping at a flow rate of 140 g / h for 1 h. Subsequently, the temperature was lowered to 110°C, and nitrogen was introduced for stripping at a flow rate of 2 L / min, maintaining the pressure at 800 Pa for 1 h. After cooling, the product was tested and found to have an esterification rate of 98.22%, a monoester content of 94.79%, and a diester content of 3.79%.

[0039] Example 8

[0040] The crude product obtained in Example 3 was heated to 110°C, and 0.24 g of TCC catalyst was added. The system pressure was controlled at 1200 Pa, and steam was introduced for stripping at a flow rate of 150 g / h for 1.5 h. Subsequently, the temperature was lowered to 105°C, and nitrogen was introduced for stripping at a flow rate of 1.5 L / min, maintaining the pressure at 1300 Pa for 1 h. After cooling, the product was tested and found to have an esterification rate of 97.73%, a monoester content of 94.63%, and a diester content of 3.98%.

[0041] Example 9

[0042] The crude product obtained in Example 3 was heated to 110°C, and 0.24 g of TCC catalyst was added. The system pressure was controlled at 1100 Pa, and steam was introduced for stripping at a flow rate of 160 g / h for 1.5 h. Subsequently, the temperature was lowered to 105°C, and nitrogen was introduced for stripping at a flow rate of 1.5 L / min, maintaining the pressure at 1200 Pa for 1 h. After cooling, the product showed an esterification rate of 98.15%, a monoester content of 95.34%, and a diester content of 3.21%.

[0043] Comparative Example 1 (Conventional Vacuum Distillation)

[0044] The crude product obtained in Example 3 was mixed with 0.24 g of TCC catalyst. Conventional vacuum distillation was performed at 300 Pa and 160 °C for 4 hours. After cooling, the product showed an esterification rate of only 86.73%, a monoester content of 81.51%, and a diester content of 4.68%.

[0045] Comparative Example 2

[0046] The crude product obtained in Example 3 was heated to 110°C without the addition of a TCC catalyst. The system pressure was controlled at 1100 Pa, and steam was introduced for stripping at a flow rate of 160 g / h for 1.5 h. Subsequently, the temperature was lowered to 105°C, and nitrogen was introduced for stripping at a flow rate of 1.5 L / min, maintaining the pressure at 1200 Pa for 1 h. After cooling, the product showed an esterification rate of 88.72%, a monoester content of 85.11%, and a diester content of 3.53%.

[0047] Comparative Example 3

[0048] The crude product obtained in Example 3 was heated to 110°C, and 0.24 g of organotin catalyst was added. The system pressure was controlled at 1100 Pa, and steam was introduced for stripping at a flow rate of 160 g / h for 1.5 h. Subsequently, the temperature was lowered to 105°C, and nitrogen was introduced for stripping at a flow rate of 1.5 L / min, maintaining the pressure at 1200 Pa for 1 h. After cooling, the product showed an esterification rate of 92.03%, a monoester content of 88.03%, and a diester content of 3.48%.

[0049] Comparative Example 4

[0050] The crude product obtained in Example 3 was heated to 110°C, and 0.24 g of borate catalyst was added. The system pressure was controlled at 1100 Pa, and steam was introduced for stripping at a flow rate of 160 g / h for 1.5 h. Subsequently, the temperature was lowered to 105°C, and nitrogen was introduced for stripping at a flow rate of 1.5 L / min, maintaining the pressure at 1200 Pa for 1 h. After cooling, the product showed an esterification rate of 90.92%, a monoester content of 86.95%, and a diester content of 3.78%.

[0051] Table 1 shows the synthesis examples 1-4 of isomeric decaphosphate; Table 2 shows the process parameters and product indicators of the steam stripping purification examples (Examples 5-9) and comparative examples 1-4 based on the crude product of Example 3.

[0052] Table 1

[0053] Table 2

[0054] As can be seen from the above examples and comparative examples, the monoester content of the crude products obtained by conventional esterification reactions (Examples 1-4) is usually below 65%. However, by using the steam stripping purification process described in this invention (Examples 5-9), the monoester content can be significantly increased to over 90%, reaching a maximum of 95.34%. In particular, comparing Example 9 with Comparative Example 1, it can be seen that conventional vacuum distillation leads to severe thermal decomposition of monoesters due to excessively high temperatures, resulting in a significant decrease in purity; while this invention achieves efficient purification at lower temperatures through steam stripping, verifying the significant advantages of this process in protecting the monoester structure and improving product quality.

[0055] In existing technologies, when relying solely on high-temperature distillation to remove moisture and impurities, phosphate monoesters are prone to thermal decomposition (dehydration to form olefins or hydrolysis back to acid). The core of this invention lies in the discovery that a specific structure of TCC (borate-organotin complex) can alter the reaction pathway: the organotin center in TCC chelates with the P=O bond and hydroxyl group of the phosphate monoester, forming a [Sn-OP] five-membered ring transition state. This structure significantly increases the bond energy of the PO bond in the monoester molecule, preventing its breakage under stripping conditions of 100-140℃ (i.e., TCC, on the one hand, forms a stable five-membered ring chelate with the hydroxyl group of the phosphate monoester through Sn atoms, constructing a "molecular shield" to inhibit high-temperature hydrolysis). Simultaneously, the borate component of TCC, acting as a Lewis acid site, can adsorb free phosphate in the system and catalyze its esterification reaction with unreacted isomeric alcohols (or alcohols produced by diester hydrolysis) (i.e., the borate component acts as a proton acceptor, catalyzing the esterification of free phosphate with isomeric alcohols and the hydrolytic conversion of diesters). This dual protection-catalysis mechanism makes the stripping process not only a physical separation process but also a chemical purification process, thus breaking the 1:1 balance limit of monoester / dieserol in the traditional synthesis of phosphate esters.

[0056] This invention employs a two-stage process of steam stripping and nitrogen stripping, utilizing the azeotropic properties of isomeric decaol (boiling point 220-225℃) and water:

[0057] The first section (steam stripping): Introducing steam not only provides a heat source but, more importantly, acts as an entrainer. Steam molecules permeate into the liquid phase, displacing dissolved isomeric alcohol molecules, allowing high-boiling-point isomeric alcohols to evaporate with the steam at a low temperature of around 110°C (far below their normal boiling point), significantly reducing the vacuum requirement (only 600-1500 Pa is needed, rather than the extremely high vacuum required by traditional distillation). Simultaneously, the trace amounts of moisture provided by the steam promote a rightward shift in the hydrolysis equilibrium of the diester (diester + water → 2 monoesters).

[0058] The second stage (nitrogen stripping): Based on the first stage, inert nitrogen is used to completely remove residual free water and trace amounts of HCl byproducts from the system, preventing reverse reactions of the monoester during storage and ensuring long-term product stability.

[0059] Research has revealed a critical value for the dosage of TCC catalyst. When the dosage is below 0.1%, it cannot completely cover the surface of the phosphate monoester, resulting in insufficient hydrolysis inhibition and a monoester content of only about 85%. When the dosage is above 0.3%, the catalyst over-catalyzes the formation of diesters, leading to decreased monoester selectivity and introducing the risk of tin residue. Therefore, 0.1%-0.3% is the optimal equilibrium range.

[0060] Furthermore, the entire process of this invention does not require the addition of any organic solvents, avoiding solvent recovery procedures and VOC emissions. Moreover, the product moisture content is precisely controlled through two-stage stripping, resulting in an esterification rate of >98% and a monoester content of >95%, filling the gap in the safe industrial production of high-purity phosphate monoesters.

[0061] The above embodiments of the present invention provide a method for synthesizing phosphate monoesters using a stripping method. Through the integrated process design of "esterification-catalytic stripping", the technical problems of low monoester content, high purification difficulty, and high energy consumption in existing phosphate ester preparation processes are fundamentally solved, achieving the following significant advantages:

[0062] 1) Through the synergistic effect of steam stripping and TCC catalyst, the monoester content of isomeric alcohol phosphates was successfully increased from approximately 60% in the crude product stage to over 95% (up to 95.34%), with the esterification rate remaining stable at over 98%. Compared to traditional processes that struggle to overcome the 70% monoester content bottleneck, this invention significantly expands the application of the product in high-end metalworking fluids, pesticide formulations, and other fields with stringent requirements for high emulsification and high wettability.

[0063] 2) The TCC (borate-organotin complex) catalyst used in this invention plays a crucial dual role of "protection and promotion": on the one hand, it can coordinate with the hydroxyl groups in phosphate monoesters to form stable cyclic structures, significantly enhancing the stability of monoesters at high temperatures and effectively suppressing their hydrolysis side reactions; on the other hand, this catalyst can simultaneously promote the esterification reaction of free phosphoric acid with isomeric alcohols, as well as the hydrolytic conversion of phosphate diesters to monoesters. This bidirectional regulatory mechanism is the core of achieving highly selective purification of monoesters, and this catalyst can be widely used in the anti-hydrolysis treatment of various ester compounds.

[0064] 3) Due to the high boiling point of isomeric decaols (220-225℃), traditional vacuum distillation requires temperatures above 150℃ and extremely high vacuum, which easily leads to the thermal decomposition of monoesters (the monoester content in Comparative Example 1 was only 81.51%). This invention introduces steam stripping technology, which uses steam to reduce the partial pressure, allowing the purification process to be carried out efficiently at a mild temperature of around 110℃ and under normal pressure / low vacuum conditions. This not only significantly reduces energy consumption but also avoids product coking and decomposition caused by high temperatures.

[0065] 4) The entire purification process requires no addition of any organic solvents, avoiding solvent recovery and residue issues, which aligns with the development trend of green chemistry. Simultaneously, by precisely controlling the stripping temperature, pressure, and throughput, efficient separation of unreacted isomeric alcohols and heavy component impurities is achieved. The process is simple and easily scaled up for industrial production.

[0066] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these should also be considered within the scope of protection of the present invention. These will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A method for synthesizing phosphate monoesters using a stripping method, characterized in that, Includes the following steps: S1. Esterification reaction: Add isomeric alcohol to the reaction vessel, add phosphorus pentoxide in batches while controlling the temperature at 40-60℃, and after the addition is complete, raise the temperature to 80-100℃ and keep the reaction for 3-5 hours to obtain crude phosphate ester. S2. Catalytic stripping purification: TCC catalyst is added to the crude phosphate ester, and steam stripping and nitrogen stripping are carried out in sequence to obtain isomeric alcohol phosphate monoester with esterification rate >98% and monoester content >95%. The steam stripping conditions are as follows: temperature 100-140℃, pressure 600-1500Pa, steam flux 120-180g / h, and time 0.5-2h. The nitrogen stripping conditions are: temperature 100-120℃, pressure 600-1500Pa, nitrogen flow rate 1-3L / min, and time 0.5-1h.

2. The method for synthesizing phosphate monoesters by stripping according to claim 1, characterized in that, In step S1, the molar ratio of the isomeric alcohol to phosphorus pentoxide is 1.7-2.3:1, and the phosphorus pentoxide is added over a period of 0.5-2 hours.

3. The method for synthesizing phosphate monoesters by stripping according to claim 2, characterized in that, In step S1, the molar ratio of the isomeric alcohol to phosphorus pentoxide is 2.0-2.3:1, the reaction temperature is 80-90℃, and the reaction time is 4-5h.

4. The method for synthesizing phosphate monoesters by stripping according to claim 3, characterized in that, In step S1, the molar ratio of the isomeric alcohol to phosphorus pentoxide is 2.2:1, the phosphorus pentoxide is added for 1 hour, the reaction temperature is 85°C, and the reaction time is 4 hours.

5. The method for synthesizing phosphate monoesters by stripping according to claim 1, characterized in that, In step S2, the amount of the TCC catalyst used is 0.1%-0.4% of the mass of the isomeric alcohol.

6. The method for synthesizing phosphate monoesters by stripping according to claim 5, characterized in that, In step S2, the amount of the TCC catalyst used is 0.15% of the mass of the isomeric alcohol; The steam stripping conditions are: temperature 110-120℃, pressure 1000-1200Pa, steam flux 140-160g / h, and time 1-1.5h. The nitrogen stripping conditions are: temperature 105℃, pressure 1200Pa, nitrogen flow rate 1.5-2L / min, and time 0.5-1h.

7. The method for synthesizing phosphate monoesters by stripping according to claim 6, characterized in that, In step S2, the steam stripping conditions are: temperature 110℃, pressure 1100Pa, steam flux 150-160g / h, and time 1.5h. The nitrogen stripping conditions are: temperature 105℃, pressure 1200Pa, nitrogen flow rate 1.5L / min, and time 1h.

8. The method for synthesizing phosphate monoesters by stripping according to claim 1, characterized in that, The TCC catalyst is a borate-organotin complex, used to inhibit the hydrolysis of phosphate monoesters and promote the esterification reaction of free phosphoric acid with isomeric alcohols.

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