Polymerization method of PTFE dispersion resin for filter membrane

Abstract

The invention relates to the technical field of PTFE (Polytetrafluoroethylene) polymerization, in particular to a polymerization method of PTFE dispersion resin for a filter membrane. The polymerization method comprises the following steps: pre-mixing deionized water heated to 70-80 DEG C with a part of an emulsifier and molten paraffin under the condition of air isolation to obtain a pre-mixed solution; and introducing a gas-phase TFE (tetrafluoroethylene) monomer into the premixed liquid to carry out polymerization reaction to obtain PTFE dispersion resin, and adding the residual emulsifier in batches in the polymerization process. According to the polymerization method, the stability of the addition amount of the deionized water, the stabilizer and the emulsifier is controlled in a premixing manner, and the difference of materials among batches is reduced. Meanwhile, adding an emulsifier step by step, and adding part of the emulsifier during premixing so as to reduce the number of polytetrafluoroethylene particles generated at the initial stage of polymerization; in the polymerization reaction process, an emulsifier is gradually added to generate a polytetrafluoroethylene micronucleus, and a resin product with narrow particle size distribution is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of PTFE polymerization, and in particular to a polymerization method of PTFE dispersed resin for filter membrane. Background Art

[0002] Polytetrafluoroethylene (PTFE) dispersion resin is produced by emulsion polymerization, using fluorinated surfactant as emulsifier and liquid paraffin as dispersion stabilizer. Polymerization is initiated by peroxide initiators such as persulfate and hydrogen peroxide in an aqueous medium to produce polytetrafluoroethylene dispersion resin.

[0003] The common preparation method of polytetrafluoroethylene dispersion resin for filtration membrane is as follows: deionized water, paraffin and ammonium persulfate are added to a polymerization reactor, the gas phase in the reactor is replaced with nitrogen to remove oxygen in the reactor, and gas phase tetrafluoroethylene monomer is introduced to cause polymerization reaction under stirring to obtain polytetrafluoroethylene dispersion resin.

[0004] The above production process has the following disadvantages: 1. Fluororesin particles easily collide with each other to form large particles, which affects the micropore shape, porosity and air permeability of the filter membrane; 2. The viscosity of the polymerization system is high, and the amount of emulsifier in the polymerization system cannot meet the growth needs of the polytetrafluoroethylene micronuclei, and only a dispersed resin with a wide particle size distribution can be obtained. When this type of dispersed resin is used in the production of filter membranes, it has the disadvantages of high shrinkage and easy breakage in the paste extrusion and biaxial stretching processes; 2. During the polymerization preparation process, deionized water is pre-added to the reactor, and then steam is introduced to increase the temperature. Due to the different temperatures of the pre-added water, when the temperature is raised to the reaction temperature again, the amount of deionized water in each batch of the reaction system is different, resulting in a large difference in the particle size of the primary particles formed during the polymerization process, affecting the stability of the product between batches. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a polymerization method for PTFE dispersed resin for filter membrane with good batch stability.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a polymerization method of PTFE dispersed resin for filter membrane, comprising the following steps: Deionized water heated to 70-80°C is pre-mixed with a portion of the emulsifier and melted paraffin in an airtight state to obtain a premixed liquid; gaseous TFE (tetrafluoroethylene) monomer is introduced into the premixed liquid for polymerization to obtain a PTFE dispersed resin, and the remaining emulsifier is added in batches during the polymerization process.

[0007] The beneficial effects of the present invention are as follows: the polymerization method of the present invention uses a pre-mixing method to control the stability of the amount of deionized water, stabilizer, and emulsifier added, thereby reducing the difference between batches of materials. At the same time, the emulsifier is added step by step, and part of the emulsifier is added during pre-mixing to reduce the number of polytetrafluoroethylene particles generated in the initial stage of polymerization; during the polymerization reaction, the emulsifier is gradually added to generate polytetrafluoroethylene micronuclei, thereby obtaining a resin product with a narrow particle size distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a process flow chart of the polymerization method of Example 1 of the present invention. DETAILED DESCRIPTION

[0009] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in combination with the implementation modes and the accompanying drawings.

[0010] A polymerization method for a PTFE dispersed resin for a filter membrane comprises the following steps: Deionized water heated to 70-80°C is pre-mixed with a portion of the emulsifier and melted paraffin in an airtight state to obtain a premixed liquid; gas-phase TFE monomer is introduced into the premixed liquid for polymerization reaction to obtain a PTFE dispersed resin, and the remaining emulsifier is added in batches during the polymerization process.

[0011] From the above description, it can be seen that the beneficial effects of the present invention are as follows: the polymerization method of the present invention pre-modulates the polymerization raw materials, pre-mixes the deionized water heated to a temperature close to the initial polymerization temperature with part of the emulsifier and the melted paraffin stabilizer in an airtight state, controls the stability of the amount of materials added, and reduces the difference in materials between batches. During pre-mixing, the temperature of the deionized water is close to the initial polymerization temperature, avoiding the phenomenon of different water amounts after heating due to different initial temperatures of each batch of deionized water, and improving the stability of products between batches.

[0012] The present invention also adopts a step-by-step method of adding an emulsifier, wherein part of the emulsifier is added before the reaction and pre-mixed with auxiliary agents such as deionized water to reduce the number of polytetrafluoroethylene particles generated in the initial polymerization stage; during the operation of the polymerization system, the emulsifier is gradually added so that the amount of the emulsifier in the polymerization system can meet the growth requirements of the polytetrafluoroethylene micronuclei, thereby obtaining a resin product with a narrow particle size distribution, which is suitable for preparing a filter membrane.

[0013] Furthermore, the paraffin wax is refined and then pre-mixed.

[0014] From the above description, it can be seen that after refined treatment, the impurities and activation performance of paraffin can be removed, and the product quality and stability between batches can be improved.

[0015] Furthermore, the gas phase TFE monomer is adsorbed by silica gel and then polymerized.

[0016] From the above description, it can be seen that the use of silica gel adsorption to purify the raw material TFE monomer can effectively remove the inhibitor and improve the quality of polytetrafluoroethylene used in the filter membrane.

[0017] Furthermore, the oxygen content of the environment during premixing is less than 30 ppm.

[0018] From the above description, it can be seen that the reaction between oxygen and tetrafluoroethylene will form explosive oxides. For safety reasons, the oxygen content in the environment must be strictly controlled.

[0019] Furthermore, the mass of the partial emulsifier is 7-9% of the mass of the emulsifier.

[0020] Furthermore, the mass ratio of the remaining emulsifier to the gas phase TFE monomer is 1:326.

[0021] From the above description, it can be known that the growth requirement of polytetrafluoroethylene micronuclei can be met by controlling the mass ratio of the remaining emulsifier to the gas phase TFE monomer.

[0022] Furthermore, the premix solution also includes at least one of ammonium persulfate, succinic acid and oxalic acid.

[0023] Furthermore, the stirring speed of the polymerization reaction is 50-70 rpm.

[0024] Furthermore, the stirring speed in the initial stage of the polymerization reaction was 50 rpm.

[0025] From the above description, it can be seen that as the concentration of the dispersion liquid in the polymerization reaction system increases, the reaction stirring speed is gradually increased by frequency conversion to improve the dispersion effect.

[0026] Furthermore, the reaction temperature of the polymerization reaction is 81-87°C.

[0027] Furthermore, the starting temperature of the polymerization reaction is 81-83°C.

[0028] From the above description, it can be seen that the polymerization reaction is carried out at a lower starting temperature to increase the number of tetrafluoroethylene micronuclei.

[0029] Furthermore, the introduction rate of gas phase TFE monomer is 355-365 kg / h.

[0030] Furthermore, the reaction pressure of the polymerization reaction is 1.8~2.2MPa.

[0031] From the above description, it can be seen that by strictly controlling the introduction rate of gas phase TFE monomer and the reaction pressure of the polymerization reaction, the pressure fluctuation can be reduced and the stability of the production process can be improved.

[0032] Furthermore, when the reaction liquid in the reactor reaches 28-32% of the reactor capacity, the reaction is stopped.

[0033] From the above description, we can see that Furthermore, the polymerization reaction is carried out in a reactor, and the materials adhering to the stirring in the reactor are cleaned once every 45 to 55 batches of PTFE dispersion resin are produced.

[0034] From the above description, it can be seen that large particles can be reduced to prevent large particles from affecting the particle size.

[0035] Furthermore, the reactor thermometer is cleaned and calibrated every 45 to 55 batches of PTFE dispersion resin are produced.

[0036] From the above description, it can be seen that the batch-to-batch differences caused by inaccurate temperature measurement can be reduced.

[0037] Furthermore, after the polymerization reaction is completed, the polymerization liquid is separated, and the polymerization liquid is successively condensed, washed and dried to obtain a PTFE dispersed resin.

[0038] Please refer to Figure 1 Embodiment 1 of the present invention is: a polymerization method of PTFE dispersed resin for filter membrane, the steps are as follows: S1: refining the paraffin in a paraffin refining tank, and then placing the refined paraffin in a paraffin storage tank for jacket heating to obtain melted paraffin; The gas phase TFE monomer is subjected to silica gel adsorption in a silica gel adsorber; Steam is introduced into the deionized water heating tank to heat the deionized water to 75°C; S2: 2000 kg of heated deionized water, 2.4 kg of emulsifier, 80 kg of melted paraffin, 0.5 kg of oxalic acid and 0.13 kg of succinic acid are added into a mixing tank with an oxygen content of less than 30 ppm, and pre-mixed in an airtight state to obtain a premixed liquid.

[0039] S3: adding the premixed liquid into a 4000 L nitrogen-substituted polymerization kettle, and nitrogen-substituted again, introducing gas-phase TFE monomer at a rate of 360 kg / h for polymerization reaction, adding 27.6 kg of emulsifier in batches during the polymerization process, and stopping the reaction when the reaction liquid in the reactor reaches 30% of the reactor capacity to obtain a PTFE dispersed resin; During the polymerization reaction, the initial stirring speed was 50 rpm, and as the reaction progressed, the speed was increased by 5 rpm every 10 minutes to 70 rpm and then maintained; the reaction initial speed was 82°C, and as the reaction progressed, the temperature was increased by 1°C every 10 minutes to 87°C and then maintained; the reaction pressure was 2.0 MPa; Every time 50 batches of PTFE dispersion resin are produced, the materials adhering to the stirring in the reactor are cleaned and the thermometer in the reactor is cleaned and calibrated.

[0040] S4: After the polymerization reaction is completed, the polymerization liquid is separated and the monomer is recovered. The polymerization liquid is successively condensed, washed and dried to obtain a PTFE dispersed resin.

[0041] The PTFE dispersed resin prepared in Example 1 was tested. The resin particle size was measured according to the method specified in Appendix A of HG / T2901-1997. The particle size distribution was measured to be: median diameter D50 = 448.9 μm, span 0.959.

[0042] Embodiment 2 of the present invention is: a polymerization method of PTFE dispersed resin for filter membrane, the steps are as follows: S1: refining the paraffin in a paraffin refining tank, and then placing the refined paraffin in a paraffin storage tank for jacket heating to obtain melted paraffin; The gas phase TFE monomer is subjected to silica gel adsorption in a silica gel adsorber; Steam is introduced into the deionized water heating tank to heat the deionized water to 70°C; S2: 2000 kg heated deionized water, 2.1 kg emulsifier, 80 kg melted paraffin, 0.5 kg oxalic acid and 0.13 kg succinic acid are added into a mixing tank with an oxygen content of less than 30 ppm, and pre-mixed in an airtight state to obtain a premixed liquid.

[0043] S3: adding the premixed liquid into a 4000 L nitrogen-substituted polymerization kettle, and nitrogen-substituted again, introducing gas-phase TFE monomer at a rate of 355 kg / h for polymerization reaction, adding 27.9 kg of emulsifier in batches during the polymerization process, and stopping the reaction when the reaction liquid in the reactor reaches 28% of the reactor capacity to obtain a PTFE dispersed resin; During the polymerization reaction, the initial stirring speed was 50 rpm, and as the reaction progressed, the speed was increased by 5 rpm every 10 minutes to 70 rpm and then maintained; the reaction initial speed was 81°C, and as the reaction progressed, the temperature was increased by 1°C every 10 minutes to 87°C and then maintained; the reaction pressure was 1.8 MPa; Every time 45 batches of PTFE dispersion resin are produced, the stirring materials adhering to the reactor are cleaned and the thermometer of the reactor is cleaned and calibrated.

[0044] S4: After the polymerization reaction is completed, the polymerization liquid is separated and the monomer is recovered. The polymerization liquid is successively condensed, washed and dried to obtain a PTFE dispersed resin.

[0045] Embodiment 3 of the present invention is: a polymerization method of PTFE dispersed resin for filter membrane, the steps are as follows: S1: refining the paraffin in a paraffin refining tank, and then placing the refined paraffin in a paraffin storage tank for jacket heating to obtain melted paraffin; The gas phase TFE monomer is subjected to silica gel adsorption in a silica gel adsorber; Steam is introduced into the deionized water heating tank to heat the deionized water to 80°C; S2: 2000 kg heated deionized water, 2.7 kg emulsifier, 80 kg melted paraffin, 0.5 kg oxalic acid and 0.13 kg oxalic acid are added into a mixing tank with an oxygen content of less than 30 ppm, and pre-mixed in an airtight state to obtain a premixed liquid.

[0046] S3: adding the premixed liquid into a 4000 L nitrogen-substituted polymerization kettle, and nitrogen-substituted again, introducing gas-phase TFE monomer at a rate of 365 kg / h for polymerization reaction, adding 27.3 kg of emulsifier in batches during the polymerization process, and stopping the reaction when the reaction liquid in the reactor reaches 32% of the reactor capacity to obtain a PTFE dispersed resin; During the polymerization reaction, the initial stirring speed was 50 rpm, and as the reaction progressed, the speed was increased by 5 rpm every 10 minutes to 70 rpm and then maintained; the reaction initial speed was 83°C, and as the reaction progressed, the temperature was increased by 1°C every 10 minutes to 87°C and then maintained; the reaction pressure was 2.2MPa; Every time 55 batches of PTFE dispersion resin are produced, the stirring materials adhering to the reactor are cleaned and the thermometer of the reactor is cleaned and calibrated.

[0047] S4: After the polymerization reaction is completed, the polymerization liquid is separated and the monomer is recovered. The polymerization liquid is successively condensed, washed and dried to obtain a PTFE dispersed resin.

[0048] In summary, the polymerization method of PTFE dispersed resin for filter membrane provided by the present invention improves the stability of products between batches and obtains a resin product with a narrow particle size distribution by regulating the ratio of reaction materials, the cleanliness of materials, reaction stirring speed, polymerization temperature, and the addition method of emulsifier during the polymerization process, and is suitable for preparing filter membranes, as follows: 1. Reduce the difference between batches of materials by controlling the amount of materials added in advance, refining paraffin, adsorbing TFE monomer on silica gel, strictly controlling the introduction rate of gas phase TFE monomer and the reaction conditions of polymerization reaction, etc.

[0049] 2. The method of adding emulsifier in steps is adopted to reduce the number of polytetrafluoroethylene particles generated in the initial stage of polymerization and at the same time meet the growth requirements of polytetrafluoroethylene micronuclei to obtain a resin product with a narrow particle size distribution.

[0050] 3. Clean the equipment regularly to prevent large particles from affecting particle size and reduce batch differences caused by inaccurate temperature measurement.

[0051] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for polymerizing a PTFE dispersed resin for a filter membrane, characterized in that: The following steps are involved: Deionized water heated to 70-80°C is pre-mixed with a portion of the emulsifier and melted paraffin in an airtight state to obtain a premixed liquid; gas-phase TFE monomer is introduced into the premixed liquid for polymerization reaction to obtain a PTFE dispersed resin, and the remaining emulsifier is added in batches during the polymerization process.

2. The method for polymerizing a PTFE dispersed resin for a filtration membrane according to claim 1, characterized in that: The paraffin wax is refined and then pre-mixed.

3. The polymerization method of PTFE dispersed resin for filtration membrane according to claim 1, characterized in that: The gas phase TFE monomer is adsorbed by silica gel and then polymerized.

4. The method for polymerizing a PTFE dispersed resin for a filtration membrane according to claim 1, characterized in that: The oxygen content of the environment during the premixing is less than 30 ppm.

5. The polymerization method of PTFE dispersion resin for filtration membrane according to claim 1, characterized in that: The mass of the partial emulsifier is 7-9% of the mass of the emulsifier.

6. The method for polymerizing a PTFE dispersed resin for a filtration membrane according to claim 1, characterized in that: The premix solution also includes at least one of ammonium persulfate, succinic acid and oxalic acid.

7. The method for polymerizing a PTFE dispersed resin for a filtration membrane according to claim 1, characterized in that: The stirring speed of the polymerization reaction is 50-70 rpm.

8. The method for polymerizing a PTFE dispersed resin for a filtration membrane according to claim 1, characterized in that: The reaction temperature of the polymerization reaction is 81-87°C.

9. The method for polymerizing a PTFE dispersed resin for a filtration membrane according to claim 1, characterized in that: The introduction rate of the gas phase TFE monomer is 355-365 kg / h.

10. The method for polymerizing a PTFE dispersed resin for a filtration membrane according to claim 1, characterized in that: The reaction pressure of the polymerization reaction is 1.8-2.2 MPa.

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