Dimethyl Phosphite By-Product Hydrolysis Process and Its Microchannel Reactor

Abstract

The present invention provides a hydrolysis process for by-products of dimethyl phosphite, which has a preheating step, a hydrolysis step, and a crystallization step that are carried out continuously in sequence; the vacuum degree of the hydrolysis step system is -31.2 kPa > vacuum degree > -76.1 KPa; the temperature of the crystallization step system is 65 - 74 °C, and the vacuum degree is -76.1 KPa < vacuum degree < -64.2 KPa. Additionally, a microchannel reactor used in this process is provided, which has a preheating module A, a preheating module B, a hydrolysis module, a crystallization module, and a controller; the controller can interlock and adjust the temperature and pressure in the hydrolysis module and the crystallization module. In the present invention, when methanol gas is discharged, it rarely contains water vapor, and when water vapor is discharged, it is purified gas. When phosphorous acid crystallizes, the crystallization rate is fast and the purity is high.

Description

Technical Field

[0001] The present invention relates to a hydrolysis technology and equipment for by-products of dimethyl phosphite. Background Art

[0002] The preparation of dimethyl phosphite usually adopts a solvent-free continuous production process with phosphorus trichloride and methanol as raw materials, and high-content dimethyl phosphite is obtained through rectification. Its by-products include monomethyl phosphite formed by side reactions, trimethyl phosphite, high-boiling substances with P-O-P bonds produced by condensation between phosphorus-containing compounds, and phosphorous acid formed by the hydrolysis reaction of a small amount of water introduced during the production process with dimethyl ester.

[0003] In the traditional process, the by-products of dimethyl phosphite are generally 5% - 10% of the product quantity, among which: monomethyl phosphite is 5% - 10%, dimethyl phosphite is 15% - 20%, phosphorous acid is 40% - 45%, and the rest are some high-boiling substances containing P-O-P bonds.

[0004] Properties of dimethyl phosphite: Colorless mobile liquid. Boiling point 170 - 171 °C, 56.5 °C (1.07 kPa), relative density 1.200 (24 / 4 °C), refractive index 1.4035, flash point 29 °C. Soluble in water and most organic solvents. Dimethyl phosphite undergoes a hydrolysis reaction with water, mainly producing phosphorous acid and methanol.

[0005] Phosphorous acid, an inorganic compound. It has strong hygroscopicity and deliquescence, and is easily soluble in water and alcohol. It is slowly oxidized to orthophosphoric acid in the air. It decomposes into phosphine and orthophosphoric acid at 180 °C. Appearance: Colorless crystals. Density: 1.651 kg / L; Melting point: 74 °C; Boiling point: 200 °C (decomposition).

[0006] Physical properties of methanol: Colorless transparent liquid, with a pungent odor. Melting point (°C): -97.8; Boiling point (°C): 64.7; Relative density (water = 1): 0.79.

[0007] According to empirical data, we also know that: the boiling point of water is related to the vacuum degree. When the vacuum degree is -31.2 kPa, the boiling point of water is 90 °C; when it is -76.1 kPa, the boiling point of water is 65 °C; when it is -64.2 kPa, the boiling point of water is 74 °C. Summary of the Invention

[0008] Object of the Invention:

[0009] To provide a hydrolysis process for by-products of dimethyl phosphite and a microchannel reactor thereof, which have lower temperature and pressure, fast hydrolysis speed, fast crystallization speed, and small equipment investment.

[0010] Technical Solution:

[0011] The hydrolysis process of the by - product of dimethyl phosphite in the present invention has a pre - heating step and a hydrolysis reaction step that are continuously carried out in the following order:

[0012] (1) Pre - heating step: Pre - heat the by - product of dimethyl phosphite to a temperature of 65 - 90°C; pre - heat water to 65 - 90°C;

[0013] (2) Hydrolysis reaction step: The pre - heated by - product of dimethyl phosphite and water at a similar temperature are mixed to form a hydrolysis solution, and the hydrolysis reaction is carried out while maintaining the above temperature; control the vacuum degree of the hydrolysis system to be: - 31.2 kPa > vacuum degree > - 76.1 kPa; obtain phosphorous acid aqueous solution and released formaldehyde gas; the total residence time in the hydrolysis reaction module is 10 s - 20 s, so that the hydrolysis is basically completed and the methanol release is completed;

[0014] (3) Crystallization step: After step (2), control the temperature of the reaction system to be 65 - 74°C and the vacuum degree to be: - 76.1 kPa < vacuum degree < - 64.2 kPa; water vapor is gradually evaporated and removed, and phosphorous acid solid gradually crystallizes out.

[0015] The equipment used in the above reaction is a micro - channel reactor, which has a pre - heating module A (used for pre - heating the by - product of dimethyl phosphite), or a pre - heating module B or a hot water storage and delivery device (used for pre - heating water; or without this pre - heating module, directly take water at an appropriate temperature from the hot water storage and delivery device); and there are also a hydrolysis reaction module and a crystallization module.

[0016] The outlet of the pre - heating module A, the outlet of the pre - heating module B or the hot water storage and delivery device are all connected to the inlet of the hydrolysis reaction module; above the hydrolysis module (not lower than the space of the fluid) there is a methanol gas outlet (for methanol gasification to flow out), and there is also a liquid product outlet; the liquid product outlet is connected to the inlet of the crystallization module, and above the crystallization module there is a water vapor outlet and a solid or liquid outlet (for discharging phosphorous acid crystals, etc.).

[0017] The pre - heating module A, the hydrolysis module, and the crystallization module all have a three - layer sandwich structure. The outer two layers (the upper and lower layers) are used for the flow circulation of the heat - conducting liquid; the middle layer is used for the flow or transfer of reaction substances; the methanol gas outlet has a pipeline connected to the top of the middle layer of the hydrolysis module, and the water vapor outlet has a pipeline connected to the top of the middle layer of the crystallization module, which is convenient for gas release, and liquids and solids cannot flow out through the gas outlet.

[0018] The temperature of the hydrolysis module and the temperature of the crystallization module are respectively heated and controlled, so that the temperature of the hydrolysis module is 65 - 90°C; the temperature of the crystallization module is 65 - 74°C. 65°C is the boiling point temperature of methanol; 74°C is the melting point temperature of phosphorous acid; 90°C is the boiling point temperature of water at a vacuum degree of 31.2 kPa.

[0019] The flow channel of the hydrolysis module is connected to vacuum pump A, and the vacuum degree therein is controlled as: -31.2 kPa > vacuum degree > -76.1 kPa. The flow channel of the crystallization module is connected to vacuum pump B, and the vacuum degree therein is controlled as: -76.1 kPa < vacuum degree < -64.2 kPa.

[0020] Moreover, the temperature and pressure (vacuum degree) of the hydrolysis module are interlocked and controlled (the signals of the temperature measuring instrument and the barometer are collected by the controller, and then the working states of the temperature regulating mechanism - the thermostat and the vacuum degree regulating mechanism - the vacuum pump are controlled), ensuring that methanol gasifies therein while water hardly gasifies.

[0021] The temperature and pressure (vacuum degree) of the crystallization module are interlocked and controlled, ensuring that water gasifies therein while phosphorous acid hardly melts. When the water vapor is discharged, phosphorous acid crystals (solids) gradually crystallize out.

[0022] Beneficial effects:

[0023] Compared with the traditional kettle hydrolysis process, due to its unique internal structure, the microchannel reactor enables the reaction temperature and pressure to be more precisely regulated. When methanol gas is discharged, it contains very little water vapor; when water vapor is discharged, it is basically a purified gas that can be directly discharged. During the crystallization of phosphorous acid, with the evaporation of water vapor, the crystallization speed is faster, the yield is high, and the purity is high. The temperature is lower and the vacuum degree is smaller in the whole system, making it safer to use; the materials are in more sufficient contact, accelerating the reaction rate, greatly shortening the reaction cycle, and reducing the probability of side reactions. The gases are separately recycled and discharged, saving resources and optimizing the environment. Description of the drawings

[0024] Figure 1 is a three-dimensional structural schematic diagram of a microchannel reactor of the present invention;

[0025] In the figure, 1 - preheating module A; 2 - preheating module B; 3 - hydrolysis module; 4 - crystallization module; 5 - phosphorous acid outlet; 6 - controller; 7 - vacuum pump; 8 - thermostat; 9 - wireless temperature measuring instrument; 10 - wireless barometer; 11 - methanol gas outlet; 12 - water vapor outlet. Detailed implementation manners

[0026] As Figure 1 shown, the microchannel reactor has a preheating module A, a preheating module B, a hydrolysis module, and a crystallization module.

[0027] The outlet of preheating module A and the outlet of preheating module B are both connected to the inlet of the hydrolysis reaction module; there is a methanol gas outlet above the hydrolysis module, and there is also a liquid product outlet; the liquid product outlet is connected to the inlet of the crystallization module, and there are a water vapor outlet and a solid outlet above the crystallization module.

[0028] The preheating module A, hydrolysis module, and crystallization module have a three-layer sandwich structure. The outer two layers are used for the recirculation of the heat transfer fluid; the middle layer is used for the flow or transfer of reaction substances, and there are pipelines connecting this layer to facilitate the release of methanol gas and water vapor.

[0029] The hydrolysis module and the crystallization module respectively have a thermostat and a vacuum pump, and each has a controller that can be interlocked and adjusted so that the temperature and pressure of the substances in the hydrolysis module and the crystallization module can be accurately controlled.

Claims

1. A hydrolysis process for by-products of dimethyl phosphite, which has a preheating step and a hydrolysis reaction step that are continuously carried out in the following order, Characterized in that: There is also a crystallization step; (1) Preheating step: Preheat the by-products of dimethyl phosphite to a temperature of 65 - 90°C; preheat water to 65 - 90°C; (2) Hydrolysis reaction step: The preheated by-products of dimethyl phosphite and water at a similar temperature are mixed to form a hydrolysis solution, and the hydrolysis reaction is carried out while maintaining the above temperature; control the vacuum degree of the hydrolysis system to be: -31.2 kPa > vacuum degree > -76.1 kPa; obtain phosphorous acid aqueous solution and released methanol gas; (3) Crystallization step: After step (2), control the temperature of the reaction system to be 65 - 74°C, and the vacuum degree to be: -76.1 kPa < vacuum degree < -64.2 kPa; water vapor is gradually evaporated and removed, and solid phosphorous acid gradually crystallizes out; The temperature and vacuum degree in the hydrolysis reaction step are interlocked and controlled to ensure that methanol gasifies in it and water does not gasify; The temperature and vacuum degree in the crystallization step are interlocked and controlled to ensure that water gasifies in it and phosphorous acid does not melt. When the water vapor is discharged, phosphorous acid crystals are gradually crystallized and precipitated; The hydrolysis process for by-products of dimethyl phosphite uses a microchannel reactor, and the microchannel reactor has a preheating module A, or a preheating module B or a hot water storage and delivery device; there are also a hydrolysis module and a crystallization module; The outlet of the preheating module A, the outlet of the preheating module B or the hot water storage and delivery device are all connected to the inlet of the hydrolysis reaction module; there is a gas outlet above the hydrolysis module, and there is also a liquid product outlet; the liquid product outlet is connected to the inlet of the crystallization module, and there are a water vapor outlet and a solid outlet above the crystallization module; The preheating module A, the hydrolysis module, and the crystallization module have a two-layer or three-layer sandwich structure. The lower layer or the outer two layers are used for the recirculation of the heat transfer fluid; the upper layer or the middle layer is used for the flow or transfer of the reaction substances, and there are pipelines connecting this layer to facilitate the release of gas; The hydrolysis module and the crystallization module respectively have a temperature adjustment mechanism and a vacuum degree adjustment mechanism, and respectively have a controller that can interlock and adjust the temperature and pressure.

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