A continuous process for the preparation of hexafluoropropylene oligomers

Abstract

The present application relates to the technical field of fluorinated chemical industry, in particular to a continuous preparation method of hexafluoropropylene oligomer, comprising the following steps: step 1, adding a catalyst and an aprotic polar solvent into a liquid tank, mixing thoroughly and keeping constant temperature to a reaction temperature to obtain a catalyst liquid; step 2, the catalyst liquid enters a falling film reactor through a metering pump and a buffer tank; meanwhile, hexafluoropropylene gas enters the falling film reactor through a pressure reducing valve and a mass flow meter, and fully reacts with the catalyst liquid; step 3, the catalyst liquid and the reaction product are separated efficiently through a liquid separation device to obtain the hexafluoropropylene oligomer, and the separated catalyst liquid is recycled. The present application solves the problem of "flying temperature" in the existing method using a kettle reactor, and improves the reaction efficiency and the purity of the product.

Description

Technical Field

[0001] This invention relates to the field of fluorochemical technology, and more specifically to a continuous preparation method for hexafluoropropylene oligomers. Background Technology

[0002] Hexafluoropropylene dimers / trimers are important fluorinated intermediates from which a variety of chemical products can be derived. Due to their branched nature, various hydrophilic groups can be introduced to prepare fluorocarbon surfactants. Furthermore, the fact that hexafluoropropylene oligomers are free of bromine and chlorine makes them a good alternative to ozone-depleting substances (ODS). In addition, hexafluoropropylene oligomers are widely used in polymer additives, foaming agents, and polymer monomers.

[0003] Existing hexafluoropropylene oligomerization processes generally employ batch reactors, most of which use coil cooling. These reactors have inherent limitations in temperature control for strongly exothermic reactions, easily causing "temperature runaway" within the reactor. Furthermore, the small internal heat exchange area of ​​batch reactors results in inconsistent residence times of raw materials within the reactor, leading to low product purity and low yield. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and propose a continuous preparation method for hexafluoropropylene oligomers to solve the problem of "temperature runaway" in the reactor caused by the use of a batch reactor in the existing method, thereby improving the reaction efficiency and product purity.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] A continuous preparation method for hexafluoropropylene oligomers includes:

[0007] Step 1: Add the catalyst and aprotic polar solvent to a liquid tank, mix thoroughly and keep the temperature constant to the reaction temperature to obtain the catalyst liquid;

[0008] Step 2: The catalyst liquid enters the falling film reactor through a metering pump and a buffer tank; at the same time, hexafluoropropylene gas enters the falling film reactor through a pressure reducing valve and a mass flow meter to fully react with the catalyst liquid.

[0009] Step 3: The catalyst liquid and reaction products are efficiently separated by a liquid separator to obtain hexafluoropropylene oligomer, while the separated catalyst liquid is recycled.

[0010] The above technical solution uses a falling film reactor as the synthesis reaction vessel. Because the liquid film is in full contact with the wall and has a large specific surface area, the heat generated is promptly carried away by the refrigerant in the cooling jacket. This allows for instantaneous response to temperature changes within the reactor, enabling precise temperature control during the hexafluoropropylene polymerization process, avoiding the "runaway temperature" problem, and improving product purity. Simultaneously, it efficiently separates the catalyst liquid and reaction products, achieving efficient reuse of the catalyst liquid and realizing efficient, automated, and continuous production.

[0011] Furthermore, the catalyst is catalyst one, or a mixture of catalyst one and catalyst two; catalyst one is selected from thiocyanates, cyanates, and alkali metal fluorides; catalyst two is selected from molecules with a hole structure, preferably calixarene-6 or gamma-cyclodextrin. Using this catalyst combination results in high catalytic efficiency, effectively catalyzing the oligomerization of hexafluoropropylene with a half-reaction time of 1-30 s; this catalyst combination has high solubility in the target solvent, and during the reaction, the catalyst does not precipitate on the inner wall of the falling film reactor, thus preventing blockage of the liquid distribution system and reactor pipelines; this catalyst combination directionally generates the target product, in which the dimer has a D1 structure and no isomerized D2 structure.

[0012] Furthermore, the molar ratio of catalyst one to catalyst two is 1:0.01-1:10; more preferably 1:0.1-1:3. The vacant molecular structure of catalyst two can capture positive ions in catalyst one, increase the solubility of catalyst one, and avoid catalyst precipitation during the reaction. Adding catalyst two to catalyst one according to the molar ratio of the present invention can enhance the nucleophilicity of catalyst one and increase the reaction rate.

[0013] Furthermore, the catalyst is one or more of sodium cyanate, ammonium cyanate, potassium cyanate, sodium thiocyanate, sodium thiocyanate, potassium thiocyanate, sodium fluoride, and potassium fluoride.

[0014] Furthermore, the aprotic polar solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, and ethylene glycol diethyl ether.

[0015] Furthermore, the concentration of catalyst one is 0.01 mol / L-12 mol / L, preferably 0.5-3 mol / L, and catalyst one can catalyze the reaction rapidly and efficiently within this concentration range; the concentration of catalyst two is 0.01 mol / L-12 mol / L, preferably 0.1-2 mol / L.

[0016] Furthermore, in step 1, the reaction temperature is 10-80℃.

[0017] Furthermore, in step 2, the reaction pressure between the gas in the reaction cylinder and the catalyst liquid is preferably 0.2-3 MPa, more preferably 0.8-2 MPa; the reaction temperature between hexafluoropropylene gas and the catalyst liquid is preferably -20-150℃, more preferably -10-80℃. The reaction rate is correlated with pressure and temperature. Low reaction pressure and temperature result in a slow reaction rate or even no reaction; high reaction pressure and temperature can lead to the formation of polymers with no application value. The synergistic combination of reaction pressure and reaction temperature in this invention not only improves the reaction rate but also avoids the formation of polymers with no application value.

[0018] Furthermore, in step 2, the catalyst liquid and gas enter the falling film reactor per unit time, wherein the mass ratio of catalyst liquid to gas is 0.5-40:1, such as 0.5:1, 2:1, 8:1, 10:1, 15:1, 22:1, 35:1, 38:1, 40:1, etc.

[0019] This invention also provides another technical solution:

[0020] An apparatus for implementing the continuous preparation method includes a liquid storage tank, a gas cylinder, a falling film reactor, and a liquid separator. The liquid storage tank is connected to the top of the falling film reactor, the gas cylinder is connected to the bottom of the falling film reactor, the discharge port at the bottom of the falling film reactor is connected to the liquid separator, and the liquid separator is connected to a catalyst recovery valve pipeline and a discharge pipe. A catalyst recovery valve and a discharge valve are respectively installed on the catalyst recovery valve pipeline and the discharge pipe. Hexafluoropropylene gas enters from the bottom of the falling film reactor, and the catalyst liquid is evenly distributed to each reaction tube from the top through the falling film reactor liquid distribution system. The liquid descends along the wall to form a uniform film and flows countercurrently with the gas, increasing the gas-liquid contact area, enhancing mass transfer, increasing the reaction rate, and significantly shortening the reaction time. The residence time of the catalyst liquid in the falling film reactor is only tens of seconds to several minutes, thus maintaining catalyst activity. Simultaneously, the catalyst liquid can be recycled, resulting in a high degree of automation and enabling continuous production.

[0021] Furthermore, a filter, a metering pump, and a buffer tank are sequentially installed on the connecting pipeline between the liquid storage tank and the falling film reactor, and a pressure reducing valve and a mass flow meter are sequentially installed on the connecting pipeline between the gas cylinder and the falling film reactor, enabling precise feeding.

[0022] Technical effects of the present invention:

[0023] Compared with the prior art, the continuous preparation method of hexafluoropropylene oligomer of the present invention has the following advantages:

[0024] (1) The present invention uses a falling film reactor to prepare hexafluoropropylene oligomers. Because the internal channel size of the falling film reactor is small and the specific surface area is large, the catalyst solution is in full contact with the wall during the reaction process, and it can respond to temperature changes instantaneously, realize precise temperature control of the hexafluoropropylene polymerization process, and avoid the phenomenon of "temperature runaway".

[0025] (2) The falling film reactor of the present invention has a large contact area between hexafluoropropylene gas and catalyst solution, resulting in good mass transfer and fast reaction rate. Therefore, the reaction can be completed within tens of seconds to several minutes, thus solving the problem of isomerization of hexafluoropropylene dimer products caused by the long residence time of materials in existing batch reactors. The experimental products of the present invention are hexafluoropropylene dimer, hexafluoropropylene trimer or a mixture of the two, depending on the polarity of the different types of solvents used. The hexafluoropropylene dimer has a D1 structure and no isomerization product D2 structure or polymer products are generated.

[0026] (3) Compared with the batch reactor, the residence time of the catalyst liquid in the falling film reactor can be reduced from several hours to tens of seconds to several minutes. Therefore, the catalytic activity of the catalyst is maintained. The catalyst can be used directly more than 25 times without purification, and the catalytic activity does not decay significantly, thus reducing the cost.

[0027] (4) The falling film reactor is equipped with a mass flow meter, mechanical pump and other metering devices, which can accurately and automatically feed and accurately proportion the material; at the same time, the catalyst liquid can be recycled, which makes the automation level high, the process simpler, and can realize continuous production, solving the problem that the batch reactor cannot produce continuously. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the apparatus used to implement the continuous preparation method of the present invention.

[0029] In the diagram, 1. Liquid storage tank; 2. Filter; 3. Metering pump; 4. Buffer tank; 5. Gas cylinder; 6. Pressure reducing valve; 7. Mass flow meter; 8. Falling film reactor; 9. Separator; 10. Catalyst recovery valve; 11. Discharge valve; 12. Catalyst recovery valve pipeline; 13. Discharge pipe. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0031] Example 1:

[0032] This embodiment relates to a continuous preparation method of hexafluoropropylene oligomers, comprising:

[0033] Step 1: Set the liquid tank to a preheating temperature of 50°C, add the catalyst and aprotic polar solvent to the liquid tank, mix thoroughly and keep the temperature constant to 45°C to obtain a catalyst liquid; wherein, the catalyst is potassium thiocyanate with a concentration of 0.5 mol / L; the aprotic polar solvent is N,N-dimethylformamide;

[0034] Step 2: Undissolved catalyst is filtered out by filter 2. The catalyst liquid enters the falling film reactor 8 at a rate of 140 g / min through metering pump 3 and buffer tank 4. Simultaneously, hexafluoropropylene gas from reaction cylinder 5 enters the falling film reactor 8 through pressure reducing valve 6 and mass flow meter 7 to fully react with the catalyst liquid. The reaction pressure between hexafluoropropylene gas and catalyst liquid is 1 MPa. The reaction temperature between gas and catalyst liquid in reaction cylinder 5 is 45°C. The mass ratio of catalyst liquid to gas is 15:1.

[0035] Step 3: The catalyst liquid and reaction product are efficiently separated by the liquid separator 9. The catalyst liquid is recycled after separation, and the product is purified by distillation. The purified product is hexafluoropropylene trimer with a yield of 97.6%.

[0036] Example 2:

[0037] The continuous preparation method of hexafluoropropylene oligomers involved in this embodiment is basically the same as that in Example 1, except that:

[0038] The catalyst described in this embodiment is a mixture of catalyst one and catalyst two; catalyst one is sodium thiocyanate with a concentration of 0.5 mol / L; catalyst two is calixarene-6 with a concentration of 0.5 mol / L; the molar ratio of catalyst one to catalyst two is 1:1.

[0039] The purified product in this example is hexafluoropropylene trimer, with a yield of 95.8%.

[0040] Example 3:

[0041] The continuous preparation method of hexafluoropropylene oligomers involved in this embodiment is basically the same as that in Example 1, except that:

[0042] The catalyst described in this embodiment is a mixture of catalyst one and catalyst two; catalyst one is potassium thiocyanate with a concentration of 1 mol / L; catalyst two is gamma-cyclodextrin with a concentration of 1 mol / L; the molar ratio of catalyst one to catalyst two is 1:1; and the aprotic polar solvent is acetonitrile.

[0043] The purified products in this embodiment are hexafluoropropylene dimer D1 structure and hexafluoropropylene trimer, with yields of 76.2% and 22.5%, respectively.

[0044] Example 4:

[0045] The continuous preparation method of hexafluoropropylene oligomers involved in this embodiment is basically the same as that in Example 1, except that:

[0046] The catalyst described in this embodiment is a mixture of catalyst one and catalyst two; catalyst one is potassium fluoride with a concentration of 0.01 mol / L; catalyst two is gamma-cyclodextrin with a concentration of 0.02 mol / L; the molar ratio of catalyst one to catalyst two is 1:1; and the aprotic polar solvent is acetonitrile.

[0047] The purified product in this example is a hexafluoropropylene dimer with a D1 structure and a yield of 98.3%.

[0048] Example 5:

[0049] like Figure 1 As shown, this embodiment provides an apparatus for implementing the continuous preparation method, including a liquid storage tank 1, a gas cylinder 5, a falling film reactor 8, and a liquid separator 9. The liquid storage tank 1 is connected to the top of the falling film reactor 8, the gas cylinder 5 is connected to the bottom of the falling film reactor 8, the bottom outlet of the falling film reactor 8 is connected to the liquid separator 9, and the liquid separator 9 is connected to a catalyst recovery valve pipeline 12 and a discharge pipe 13. A catalyst recovery valve 10 and a discharge valve 11 are respectively installed on the catalyst recovery valve pipeline 12 and the discharge pipe 13. A filter 2, a metering pump 3, and a buffer tank 4 are sequentially installed on the connecting pipeline between the liquid storage tank 1 and the falling film reactor 8, and a pressure reducing valve 6 and a mass flow meter 7 are sequentially installed on the connecting pipeline between the gas cylinder 5 and the falling film reactor 8, which can achieve precise feeding.

[0050] In this invention, hexafluoropropylene gas enters from the bottom of the falling film reactor 8, while the catalyst liquid is evenly distributed to each reaction tube from the top through the liquid distribution system of the falling film reactor 8. The liquid descends along the wall to form a uniform film and flows counter-currently with the gas, increasing the gas-liquid contact area, enhancing mass transfer, increasing the reaction rate, and significantly shortening the reaction time. The residence time of the catalyst liquid in the falling film reactor 8 is only tens of seconds to several minutes, thus maintaining the catalyst activity. Simultaneously, the catalyst liquid can be recycled, resulting in a high degree of automation and enabling continuous production.

[0051] The above-described specific embodiments are merely specific examples of the present invention. The patent protection scope of the present invention includes, but is not limited to, the above-described specific embodiments. Any appropriate changes or modifications made by a person skilled in the art that conform to the claims of the present invention should fall within the patent protection scope of the present invention.

Claims

1. A continuous preparation method for hexafluoropropylene oligomers, characterized in that: include: Step 1: Add the catalyst and aprotic polar solvent to a liquid tank, mix thoroughly and keep the temperature constant to the reaction temperature to obtain the catalyst liquid; Step 2: The catalyst liquid enters the falling film reactor (8) through the metering pump (3) and buffer tank (4); at the same time, hexafluoropropylene gas enters the falling film reactor (8) through the pressure reducing valve (6) and mass flow meter (7) to fully react with the catalyst liquid; Step 3: The catalyst liquid and reaction products are efficiently separated by the liquid separator (9) to obtain hexafluoropropylene oligomer, while the separated catalyst liquid is recycled. The catalyst is catalyst one, or a mixture of catalyst one and catalyst two; catalyst one is selected from thiocyanates, cyanates, and alkali metal fluorides; catalyst two is selected from molecules with a hole structure. The aprotic polar solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, and ethylene glycol diethyl ether. The concentration of catalyst one is 0.01 mol / L-12 mol / L; the concentration of catalyst two is 0.01 mol / L-12 mol / L. In step 2, the reaction pressure of the hexafluoropropylene gas and the catalyst liquid is 0.2-3 MPa; the reaction temperature of the gas in the reaction cylinder (5) and the catalyst liquid is -20-150℃. In step 2, the catalyst liquid and gas enter the falling film reactor per unit time, wherein the mass ratio of catalyst liquid to gas is 0.5-40:

1.

2. The continuous preparation method of hexafluoropropylene oligomer according to claim 1, characterized in that: The molar ratio of catalyst one to catalyst two is 1:0.01-1:

10.

3. The continuous preparation method of hexafluoropropylene oligomer according to claim 1, characterized in that: The catalyst is one or more of sodium cyanate, ammonium cyanate, potassium cyanate, sodium thiocyanate, potassium thiocyanate, sodium fluoride, and potassium fluoride.

4. The continuous preparation method of hexafluoropropylene oligomer according to any one of claims 1-3, characterized in that: The apparatus for implementing the continuous preparation method includes a liquid storage tank (1), a gas cylinder (5), a falling film reactor (8), and a liquid separator (9); the liquid storage tank (1) is connected to the top of the falling film reactor (8), the gas cylinder (5) is connected to the bottom of the falling film reactor (8), the discharge port at the bottom of the falling film reactor (8) is connected to the liquid separator (9), the liquid separator (9) is connected to the pipeline of the catalyst recovery valve (10) and the discharge pipe (13), and the catalyst recovery valve (10) and the discharge pipe (13) are respectively provided with a catalyst recovery valve (10) and a discharge valve (11).

5. The continuous preparation method of hexafluoropropylene oligomer according to claim 4, characterized in that: A filter (2), a metering pump (3), and a buffer tank (4) are sequentially installed on the connecting pipeline between the liquid storage tank (1) and the falling film reactor (8). A pressure reducing valve (6) and a mass flow meter (7) are sequentially installed on the connecting pipeline between the gas cylinder (5) and the falling film reactor (8).

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