RU2811205C1 - Method of producing perfluorinated copolymer with sulfogroups - Google Patents

Abstract

FIELD: producing high-molecular compounds.

SUBSTANCE: invention relates to a method of producing a perfluorinated copolymer with sulfo groups by water-emulsion copolymerization of perfluoro-4-methyl-3,6-dioxaoct-7-ensulfonyl fluoride (SF) and tetrafluoroethylene (TFE). Polymerization is carried out in a steel reactor equipped with an overhead anchor mixer, in the presence of an initiator — a redox system — potassium persulfate — sodium metabisulfite and an emulsifier — a salt of perfluorononanoic acid. The process takes place at elevated temperatures (65–70°C) and pressure of 4.5–6 atm. Molar ratio of components in the polymerization system: perfluoro-4-methyl-3,6-dioxaoct-7-ensulfonyl fluoride: potassium persulfate: sodium metabisulfite: perfluorononanoic acid salt, equal to 1.000:1.092:(0.5–1.055):(25–40) respectively. Tetrafluoroethylene is fed into the reaction mixture containing perfluoro-4-methyl-3,6-dioxaoct-7-ensulfonyl fluoride, potassium persulfate, sodium metabisulfite and an emulsifier into the lower part of the reactor under the layer of the reaction mixture until a pressure of 6 atm is reached, then the resulting mixture is stirred at a speed of 1,000 rpm at a temperature of 70°C, after reducing the pressure in the reactor to~ 4.5 atm, a new portion of TFE is delivered until a pressure of 6 atm and a temperature of 65°C are reached with subsequent 4–5 repetitions of this cycle.

EFFECT: proposed method makes it possible to increase the yield of the target copolymer to 86% and the degree of sulfomonomer conversion to 95%, as well as to improve the quality of the copolymer due to the absence of reactive amide end groups in the resulting target product as a result of using an alkaline salt of perfluorononanoic acid as an emulsifier.

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Description

The present invention relates to the field of production of high-molecular compounds, namely, to a method for producing a perfluorinated copolymer with sulfo groups by copolymerization of perfluoro(3,6-dioxa-4-methyl-7-octene)sulfonyl fluoride (SF) and tetrafluoroethylene (TFE). The resulting copolymer is widely used in the production of membranes, in particular, for the production of proton-conducting membranes for fuel cells (A.P. Koskin, Yu.V. Larichev, A.I. Lysikov, O.N. Primachenko, S.S. Ivanchev, Synthesis and study of the physicochemical and catalytic properties of composites of the composition sulfated perfluoropolymer-carbon nanofibers, Kinetics and Catalysis, 2017, 58, No. 5, pp. 668-675; S.S. Ivanchev, S.V. Myakin, Polymer membranes for fuel cells: obtaining structure, modification, properties, Advances in Chemistry, 79 (2), 2010, 117-134).

There is a known method for producing the target copolymer by solution copolymerization of TFE with SF in perfluorodimethylcyclobutane, but this solvent is expensive (US 3282875 A1, 01.11.1966) and difficult to obtain.

There is a known method for producing (US 3528954, 09.15.1970) the target copolymer in a medium of 1,1,2-trifluorotrichloroethane (freon-113 or R113), by copolymerization of TFE with SF according to a radical mechanism, carried out at a temperature of 40-50°C. Perfluorodiacyl peroxide, preferably bis(perfluoropropionyl) peroxide, is used as a polymerization initiator. The pressure in the reactor is maintained constant up to 20 atm due to TFE replenishment during the polymerization process. The disadvantages of this method are that 1,1,2-trifluorotrichloroethane (freon-113 or R 113) is used as a solvent, which is an ozone-depleting compound, the release of which is prohibited, and also that expensive bis( perfluoropropionyl) peroxide. In addition, the process is carried out at a relatively high pressure of 20 atm, which makes production particularly dangerous.

There is a known method for obtaining a perfluorinated copolymer by copolymerizing TFE with SF in an organic solvent - 1,2-dichlorohexafluorocyclobutane using bis(perfluorocyclohexanoyl) peroxide as an initiator at a pressure of 2.5-5 atm (RU 2412208 C1, 02/20/2011). The disadvantage of this method is the use of an expensive solvent and initiator, as well as technical difficulties associated with the removal of high-boiling solvent and initiator residues using chloroform at the purification stage.

There is a known method for producing a perfluorinated copolymer with sulfo groups by copolymerizing TFE with SF in an organic solvent - perfluoromethyldiethylamine at a temperature of 50°C and a pressure of 2.5-5 atm using bis(perfluorocyclohexanoyl) peroxide as an initiator. The disadvantage of this method is the use of an expensive solvent and initiator, as well as technical difficulties associated with removing a high-boiling solvent and residual initiator using chloroform at the purification stage (RU 2412948 C1, 02/27/2011).

The closest to the proposed method is (S.S. Ivanchev, V.S. Likhomanov, O.N. Primachenko, S.Ya. Khaikin, V.G. Barabanov, A.Yu. Menshikova, N.N. Shevchenko, Features copolymerization of tetrafluoroethylene with perfluoro(3,6-dioxa-4-methyl-7-octene)sulfonyl fluoride in a water-emulsion system, Reports of the Academy of Sciences, 2011, volume 437, No. 3, pp. 344-346) obtaining a perfluorinated copolymer with sulfonic groups water-emulsion copolymerization of TFE and SF under thermostatic conditions at 40°C in a steel reactor equipped with a standard top-drive anchor mixer, with an operating pressure supplied to the TFE system of 0.5 MPa, controlled automatically. Ammonium perfluorononanoate was used as an emulsifier at a concentration of 7.8 mmol/l of the aqueous phase, and the redox system potassium persulfate - sodium metabisulfite was used as an initiator (potassium persulfate concentration 4.6 mmol/l of the aqueous phase). Phosphate buffer was introduced to stabilize the pH. Before copolymerization, the reaction system was subjected to preliminary dispersion using a rotor-stator type dispersant at 10,000 rotor rpm for 15 min at room temperature. The method makes it possible to obtain a copolymer with an equivalent molecular weight optimal for membrane systems in the range of 950-1100 g/mol with a molecular weight of the order of hundreds of thousands (Melt flow index (MFI) = 5-50 g/10 min, 270°C, load 21.2 N with a capillary diameter of 2.095 mm). The isolation of the target copolymer is not described in the source; the yield of the copolymer is not indicated. However, as can be seen from comparative example 5 given in the description of the invention, in the control experiments the copolymer yield did not exceed 70% at a relatively low degree of SF conversion. In this case, the expensive initial product of SF is lost irretrievably. The disadvantages of this known method are the insufficiently high yield of the target product and the unproductive use of SF.

The technical objective of the present invention is to create a method for producing a perfluorinated copolymer with sulfo groups, which makes it possible to increase the yield of the target product and the degree of conversion of SF.

The stated technical problem is achieved by the proposed method for producing a perfluorinated copolymer with sulfo groups by water-emulsion copolymerization of perfluoro-4-methyl-3,6-dioxaoct-7-ensulfonyl fluoride and tetrafluoroethylene in a steel reactor equipped with an overhead anchor mixer, in the presence of an oxidizing agent as an initiator. reducing system potassium persulfate-sodium metabisulfite and emulsifier - salts of perfluorononanoic acid at elevated temperature and pressure of 4.5-6 atm, and characterized in that the copolymerization process is carried out at a temperature of 65-70°C and the molar ratio of perfluoro-4-methyl-3 ,6-dioxaoct-7-ensulfonyl fluoride: potassium persulfate: sodium metabisulfite: perfluorononanoic acid salt, equal to 1000: 1.092: (0.5-1.055): (25-40), respectively, while supplying tetrafluoroethylene to the reaction mixture containing perfluorine -4-methyl-3,6-dioxaoct-7-ensulfonyl fluoride, potassium persulfate, sodium metabisulfite and emulsifier are introduced into the lower part of the reactor under the layer of the reaction mixture until a pressure of 6 atm is reached, then the resulting mixture is stirred at a speed of 1000 rpm at temperature 70°C, after reducing the pressure in the reactor to ~ 4.5 atm, a new portion of TFE is supplied until a pressure of 6 atm and a temperature of 65°C are reached, followed by repeating this cycle 4-5 times.

Isolation of the target product is carried out by precipitation with hydrochloric acid.

An alkaline salt of perfluorononanoic acid, preferably a sodium salt, is used as a salt of perfluorononanoic acid.

The yield of the target product is 80-86%, the degree of conversion is 90-95%.

The proposed set of distinctive features is the implementation of the copolymerization process at a molar ratio of perfluoro-4-methyl-3,6-dioxaoct-7-ensulfonyl fluoride: potassium persulfate: sodium metabisulfite: perfluorononanoic acid salt equal to 1000: 1.092: (0.50-1.55 ):(25-40), at a process temperature of 65-70°C, as well as supplying tetrafluoroethylene to the lower part of the reactor under the layer of the reaction mixture until a pressure of 6 atm is reached, stirring at a speed of 1000 rpm at a temperature of 70°C, then after reducing the pressure to ~ 4.5 atm and supplying a new portion of TFE until a pressure of 6 atm and a temperature of 65°C was reached, followed by repeating this cycle 4-5 times, made it possible to increase the yield of the target product and the degree of conversion of the original perfluoro-4-methyl-3, 6-dioxaoct-7-ensulfonyl fluoride compared to the prototype, and also improve the quality of the copolymer due to the absence of reactive amide end groups in the resulting copolymer (examples 1-4).

The molar ratio of perfluoro-4-methyl-3,6-dioxaoct-7-ensulfonyl fluoride: potassium persulfate: sodium metabisulfite: perfluorononanoic acid salt, equal to 1000: 1.092: (0.50-1.055): (25-40), provides high yield of the target copolymer.

Maintaining the temperature of the copolymerization process within 65-70°C ensures a stable course of the copolymerization process. At temperatures below 65°C, the duration of the process increases; at temperatures above 70°C, the amount of by-products increases and the quality of the target copolymer decreases.

The supply of TFE to the lower part of the steel reactor ensures effective dissolution of TFE in the reaction mixture, which helps to increase the conversion of perfluoro-4-methyl-3,6-dioxaoct-7-ensulfonyl fluoride. The use of an alkaline salt of perfluorononanoic acid, preferably a sodium salt, as an emulsifier ensures the necessary homogeneity of the reaction mixture and improves the quality of the target copolymer, since it is known (US 4743658) that the presence of ammonium ions (usually introduced as part of the emulsifier surfactant or components buffer solution, for example, ammonium perfluorooctanoate) leads to the presence of undesirable amide (-CONH ₂ ) end groups in the resulting product, which reduces the quality of the target copolymer.

The proposed method for producing a perfluorinated copolymer with sulfo groups is carried out as follows:

A. Reactor preparation (surface passivation)

The inner surface of a stainless steel reactor (autoclave), for example grade 12Х18Н10Т, in which copolymerization will be carried out, is treated with a 5% solution of potassium persulfate in water at a temperature of 90±5°C.

b. Preparation of sulfomonomer emulsion.

To obtain a water-emulsion system, the sodium salt of perfluorononanoic acid was used as an emulsifier at a concentration of 0.38 wt. % (relative to the amount of water), while a phosphate buffer was introduced to stabilize the pH, for example, a mixture of sodium dihydrogen phosphate and sodium hydrogen phosphate. Next, a sulfomonomer, perfluoro(3,6-dioxa-4-methyl-7-octene)sulfonyl fluoride, was added to the resulting solution. This mixture was subjected to preliminary dispersion using a “rotor-stator” type dispersant at 10,000 rotor rpm and a temperature of 15-60°C in an argon atmosphere; for this purpose, argon was supplied at a speed of 100 cm ³ /min above the surface of the liquid in the dispersant glass.

V. Preparation of copolymer.

The resulting emulsion was loaded into a steel reactor purged with argon and an initiating system was added - freshly prepared solutions of potassium persulfate and sodium metabisulfite. The molar ratio of perfluoro(3,6-dioxa-4-methyl-7-octene)sulfonyl fluoride: potassium persulfate: sodium metabisulfite: perfluorononanoic acid salt is 1000: 1.092: (0.5-1.055): (25-40) .

The reaction mixture, which is an emulsion of a sulfomonomer - perfluoro(3,6-dioxa-4-methyl-7-octene)sulfonyl fluoride, in an aqueous phase containing an emulsifier - a salt of perfluorononanoic acid, for example, sodium perfluorononanoate in a concentration of 0.38 wt. %, phosphate buffer and initiating system are placed in a prepared steel reactor equipped with a standard overhead drive anchor stirrer. The reactor is filled with argon to a pressure of 6 atm, then the pressure is released to atmospheric pressure. This operation is repeated 2-3 more times. Then the SPE supply is turned on. The production of perfluorinated copolymer with sulfo groups by water-emulsion copolymerization of TFE and SF was carried out under thermostatic conditions at a temperature of 65-70°C in a steel reactor at an excess pressure of 4.5 - 6 atm, while tetrafluoroethylene was supplied into the reaction system into the lower part of the reactor under the layer reaction system until a pressure of 6 atm is reached, then the mixture is stirred at a speed of 1000 rpm at a temperature of 70°C, after reducing the pressure in the reactor to ~ 4.5 atm, a new portion of TFE is fed until an excess pressure of 6 atm is reached and a temperature of 65°C with followed by repeating this cycle 4-5 times until the target amount of TFE is absorbed. The amount of absorbed TFE can be controlled in various ways (based on pressure changes, by mass, using gas flow sensors, etc.). After the absorption of the target amount of TFE, determined from the desired ratio of copolymer units, the supply of TFE was stopped, stirring was stopped, the pressure was released, and the reactor was unloaded. The target product is in the form of a fairly stable aqueous dispersion (latex); to precipitate a compact polymer from it, it was coagulated by adding hydrochloric acid. The precipitated product was thoroughly washed with water. After washing, the product is centrifuged (5 minutes at 6000 rpm), which makes it possible to partially separate the water retained in the pores of the gel. The product is then dried to remove excess moisture. The resulting copolymer has a melt flow index (MFR)=5-50 g/10 min, 270°C, load 21.2 N with a capillary diameter of 2.095 mm), which is in the range of values of the copolymer according to the prototype.

Example 1.

190 mg (0.391 mmol) of sodium perfluorononanoate, 144 mg (0.923 mmol) of sodium dihydrogen phosphate dihydrate and 290 mg (0.81 mmol) of sodium hydrogen phosphate dodecahydrate are dissolved in 50 ml of deionized water with moderate heating. 4.0 ml (6.92 g, 15.52 mmol) of sulfomonomer perfluoro(3,6-dioxa-4-methyl-7-octene)sulfonyl fluoride was added to the resulting solution and the mixture was dispersed 2 times for 10 minutes with a break in the atmosphere argon. The resulting emulsion is placed in a prepared steel reactor equipped with a standard overhead anchor stirrer and purged with argon, and freshly prepared solutions of potassium persulfate and sodium metabisulfite (with a concentration of -1%) are added at the rate of 4.58 mg (0.017 mmol) of potassium persulfate and 4.58 mg (0.024 mmol) sodium metabisulfite. The reactor is closed and filled with argon, then the pressure is slowly released to atmospheric pressure). After this, the reactor is filled with tetrafluoroethylene until a pressure of 2 atm is reached, the pressure is released and the operation is repeated again. This is necessary in order to displace the inert gas - argon or nitrogen - from the system. Then the reactor is filled with TFE until a pressure of 6 atm is reached, while the TFE is fed into the lower part of the reactor under a layer of the reaction system containing perfluoro-4-methyl-3,6-dioxaoct-7-ensulfonyl fluoride, potassium persulfate, sodium metabisulfite and an emulsifier - sodium perfluorononanoate , then the mixture is stirred at a speed of 1000 rpm and at the same time the reactor is heated to 70°C. After the pressure is reduced to ~ 4.5 atm, a new portion of TFE is fed into the reactor until a pressure of 6 atm and a temperature of 65°C are reached. The amount of TFE required to obtain the target copolymer is achieved through 4-5 dosing cycles. Synthesis time is approximately 5.5 hours. After this, the reactor is cooled and the pressure is released. 20 ml is added to the resulting solution. 35% hydrochloric acid, the reaction mixture is stirred for 1 hour, during which a gel-like mass precipitates, which is washed with distilled water until neutral, dried in a vacuum (<0.1 mm Hg), while gradually increasing the temperature to 130°C. The yield of perfluorinated copolymer is 10.12 g (86%), the degree of sulfomonomer conversion is 95%.

Example 2.

The process is carried out similarly to example 1, but using a sample of 1% sodium metabisulfite solution corresponding to 1.46 mg (0.0077 mmol) Na ₂ S ₂ O ₅ . Synthesis time ~8 hours. The yield of the target product is 9.41 g (80%), the degree of sulfomonomer conversion is 90%.

Example 3.

The process is carried out similarly to example 1, but using a sample of sodium perfluorononanoate of 304 mg (0.626 mmol). Synthesis time ~7 hours. The yield of the target product is 9.64 g (82%), the degree of sulfomonomer conversion is 92%.

Example 4.

The process is carried out similarly to example 1, but using a load of sodium perfluorononanoate of 304 mg (0.626 mmol) and a sample of 1% sodium metabisulfite solution corresponding to 1.46 mg (0.0077 mmol) of Na ₂ S ₂ O ₅ . Synthesis time -7.2 hours. The yield of the target product is 9.76 g (83%), the degree of sulfomonomer conversion is 94%.

Example 5 (comparative to the prototype).

Before copolymerization, the reaction system is subjected to preliminary dispersion using a rotor-stator type dispersant at 10,000 rotor rpm for 15 minutes at room temperature under a protective argon atmosphere. Ammonium perfluorononanoate is used as an emulsifier in a concentration of 3.75 g/l (7.8 mmol/l) of the aqueous phase, and the redox system potassium persulfate-sodium metabisulfite is used as an initiator (potassium persulfate concentration is 1.25 g/l (4 .6 mmol/l) aqueous phase). To stabilize the pH, a phosphate buffer is introduced - sodium dihydrogen phosphate and sodium hydrogen phosphate in the same concentrations as in example 1. Copolymerization of TFE and SF is carried out under thermostatic conditions at 40 ° C in a steel reactor equipped with an overhead anchor mixer, at the operating pressure supplied to the system TFE 0.5 MPa. The resulting polymer is then precipitated using hydrochloric acid. The deposited product is thoroughly washed with water. After washing, the product is centrifuged (5 minutes at 6000 rpm), which makes it possible to partially separate the water retained in the pores of the gel. The product is then dried to remove excess moisture.

The polymer yield was 8.14 g (69%), and the degree of sulfomonomer conversion was 76%.

The technical result of the present invention is the creation of a method for producing a perfluorinated copolymer with sulfo groups by water-emulsion copolymerization of tetrafluoroethylene and perfluoro(3,6-dioxa-4-methyl-7-octene)sulfonyl fluoride, which allows increasing the yield of the target product to 86% and the degree of sulfomonomer conversion to 95%, as well as the quality of the copolymer due to the absence of reactive amide end groups in the resulting target product as a result of the use of an alkaline salt of perfluorononanoic acid as an emulsifier.

Claims (2)

1. A method for producing a perfluorinated copolymer with sulfo groups by water-emulsion copolymerization of perfluoro-4-methyl-3,6-dioxaoct-7-ensulfonyl fluoride and tetrafluoroethylene in a steel reactor equipped with an overhead anchor mixer, in the presence of a persulfate redox system as an initiator potassium - sodium metabisulfite and emulsifier - salts of perfluorononanoic acid at elevated temperature and pressure of 4.5-6 atm, characterized in that the copolymerization process is carried out at a temperature of 65-70 ° C and the molar ratio of perfluoro-4-methyl-3,6-dioxaoct -7-ensulfonyl fluoride: potassium persulfate: sodium metabisulfite: perfluorononanoic acid salt, equal to 1000: 1.092: (0.5-1.055): (25-40), respectively, while supplying tetrafluoroethylene to the reaction mixture containing perfluoro-4-methyl- 3,6-dioxaoct-7-ensulfonyl fluoride, potassium persulfate, sodium metabisulfite and an emulsifier are introduced into the lower part of the reactor under the layer of the reaction mixture until a pressure of 6 atm is reached, then the resulting mixture is stirred at a speed of 1000 rpm at a temperature of 70°C, after After reducing the pressure in the reactor to ~4.5 atm, a new portion of TFE is supplied until a pressure of 6 atm and a temperature of 65°C are reached, followed by repeating this cycle 4-5 times. 2. A method for producing a perfluorinated copolymer with sulfo groups according to claim 1, characterized in that the sodium salt of perfluorononanoic acid is used as a salt of perfluorononanoic acid.