JP3804197B2 - Method for recovering fluorinated monomers - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for recovering the unreacted monomer from a latex obtained by emulsion polymerization of a fluorinated monomer having a boiling point of 20 to 300 ° C.
[0002]
[Prior art]
Fluoropolymers are manufactured by methods such as emulsion polymerization, suspension polymerization, solution polymerization, bulk polymerization, etc., but emulsion polymerization has high volumetric efficiency of the polymerization tank, low heat during polymerization and low torque during stirring, etc. It is preferably employed because of its advantages.
[0003]
In emulsion polymerization, a monomer that is gaseous at room temperature such as ethylene tetrafluoride is easily recovered by purging after polymerization. On the other hand, an unreacted fluorinated monomer having a boiling point of 20 to 300 ° C. is contained in the latex after polymerization. If the monomer has a functional group as it is, the latex is denatured at the time of agglomeration and the recovery rate is increased. May be reduced. Therefore, it is preferable to collect the monomer before aggregation.
[0004]
Conventionally, as a method for recovering a fluorinated monomer having a boiling point of 20 to 300 ° C., a latex and a fluorinated chlorinated saturated hydrocarbon solvent are mixed and allowed to stand, and then separated into two layers and extracted into the solvent. A method for recovering the monomer was employed (Japanese Examined Patent Publication No. 62-56886). However, chlorofluorocarbons (CFCs) such as trichlorotrifluoroethane, which has been used in the past, are supposed to destroy the ozone layer, and their use has been discontinued.
[0005]
Examples of the solvent that replaces the CFC include perfluorocarbon (PFC) such as perfluorohexane, perfluorodimethylcyclobutane, perfluoro (2-butyltetrahydrofuran), perfluorotributylamine, 1,1-dichloro-1,1,2, Hydrochlorofluorocarbon (HCFC) such as 2,3-pentafluoropropane, 1,1-dichloro-2,2,3,3,3-pentafluoropropane, perfluorobutylethane, 3H, 4H-perfluoro (2- It is known that hydrochlorocarbon (HFC) such as methylpentane) and 1H-perfluorohexane can be used (JP-A-6-930912).
[0006]
However, although these have little influence on the ozone layer destruction, there is a concern that the contribution to global warming is large.
[0007]
[Problems to be solved by the invention]
The present invention seeks to solve the aforementioned problems. That is, it is a method for efficiently recovering the unreacted fluorinated monomer from a latex obtained by emulsion polymerization of a fluorinated monomer having a boiling point of 20 to 300 ° C., and there is no possibility of destroying the ozone layer. Provide a method with less impact on global warming.
[0008]
[Means for Solving the Problems]
The present invention is a method for recovering unreacted fluorinated monomer from a latex obtained by emulsion polymerization of a fluorinated monomer having a boiling point of 20 to 300 ° C., wherein the hydrofluoroether compound and the latex are brought into contact with each other. This provides a method for recovering the fluorinated monomer, wherein the unreacted fluorinated monomer is extracted.
[0009]
Here, the boiling point is a boiling point at atmospheric pressure.
[0010]
The hydrofluoroether compound (hereinafter referred to as HFE compound) in the present invention is a hydrofluorocarbon having an ether bond.
[0011]
The HFE compound preferably has a boiling point of 10 to 250 ° C., particularly 20 to 200 ° C. from the viewpoints of recyclability and ease of handling at room temperature. In addition, from the viewpoint of ease of separation and recovery by distillation after extraction of the fluorinated monomer, those having a boiling point difference from the fluorinated monomer of 20 ° C. or more are preferable.
[0012]
Specifically, the HFE compound preferably has 4 to 12 carbon atoms, and the structure may be linear, branched, or cyclic. In particular, C ₄ F ₉ OCH ₃ , C ₄ F ₉ OC ₂ H ₅ , CF ₃ CF ₂ CF ₂ OCH ₃ , (CF ₃ ) ₂ CFOCH ₃ , and CF ₃ CFHCF ₂ OCH ₃ are characteristically and industrially produced. Is preferable in that it is easy.
[0013]
These HFE compounds may be used alone or as a mixed solvent of two or more.
[0014]
The extraction operation is usually performed by adding the above-mentioned HFE compound to the latex and allowing it to stand after stirring or shaking. The fluorinated monomer is extracted into the HFE compound, and the HFE compound is separated into the lower layer. After extracting this lower layer, a new HFE compound is added and the above operation is repeated several times, whereby unreacted monomers can be completely recovered.
[0015]
The mixing ratio of latex and HFE compound during the extraction operation is a weight ratio in the range of latex / HFE compound = 20/1 to 1/10. However, if the mixing ratio of HFE compound is increased, the number of extractions can be reduced. This is not preferable because the volume of the apparatus during the distillation recovery of the fluorinated monomer needs to be increased. On the other hand, if the mixing ratio of the fluorinated solvent is too small, the number of extractions is undesirably increased. The ratio is particularly preferably in the range of 10/1 to 1/2.
[0016]
The recovery method of the present invention is applied to a latex obtained by emulsion polymerization of a fluorinated monomer having a boiling point of 20 to 300 ° C. Examples of the fluorinated monomer include various ones, and fluorinated monomers containing a functional group such as a carboxylic acid group, a sulfonic acid group, and a phosphoric acid group in the pendant side chain are preferable. Other than the above, monomers having a perfluoro structure are suitable.
[0017]
The emulsion polymerization is generally a copolymerization of a specific fluorinated monomer as described above and a fluoroethylenically unsaturated monomer that is gaseous at room temperature.
[0018]
Examples of the fluorinated monomer to which the present invention is preferably applied include fluorinated functional monomers having a carboxylic acid type functional group or a sulfonic acid type functional group. As the fluorinated functional monomer, a fluorovinyl compound, particularly a perfluorovinyl compound, is preferably used from the viewpoint of the use and performance of the produced polymer.
[0019]
Among them, the general formula _{CF 2 = CF (OCF 2 CF} (CF 3)) a O (CF 2) b COOCH 3 ( wherein, a is an integer of 0 to 3, b is an integer of from 1 to 5) are represented by that fluorovinyl compound of the general formula _{CF 2 = CF (OCF 2 CF} (CF 3)) c O (CF 2) d SO 2 F ( wherein, c is an integer of 0 to 3, d is an integer of from 1 to 5) The fluorovinyl compound represented by these is preferably used.
[0020]
Next, examples of the fluoroethylene unsaturated monomer include ethylene tetrafluoride, ethylene trifluoride chloride, propylene hexafluoride, ethylene trifluoride, vinylidene fluoride, and vinyl fluoride. ₂ = CZY (Z and Y are fluorine atoms, chlorine atoms, hydrogen atoms, or trifluoromethyl groups). Of these, perfluoroolefin compounds are preferable, and tetrafluoroethylene is particularly preferable.
[0021]
In the present invention, the fluorinated functional monomer and the fluoroethylenically unsaturated monomer can each be used in a mixture of two or more. In addition, olefin compounds represented by other components such as CH ₂ ═CR ⁴ R ⁵ (R ⁴ and R ⁵ represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms or an aromatic nucleus), a general formula CF ₂ = CFOR ^f (R ^f represents a perfluoroalkyl group having 1 to 10 carbon atoms and may contain an ether bond), CF ₂ = CFCF = CF ₂ , general formula CF ₂ = One or more kinds of divinyl monomers such as CFO (CF ₂ ) _e OCF═CF ₂ (e is an integer of 1 to 6) can be used in combination.
[0022]
Specific examples of the olefin compound include ethylene, propylene, butene-1, isobutylene, styrene, α-methylstyrene, pentene-1, hexene-1, heptene-1, 3-methyl-butene-1, 4-methyl- Examples include pentene-1. Of these, the use of ethylene, propylene, isobutylene and the like is particularly preferred from the viewpoint of production and performance of the produced polymer.
[0023]
Further, for example, it is possible to improve the mechanical strength when a polymer obtained by the combined use of a divinyl monomer is crosslinked to form a molded product such as a film.
[0024]
The composition ratio of the fluorinated functional monomer, the fluoroethylenically unsaturated monomer, the olefin compound, and other components in the produced polymer in the latex in the present invention is important because it is related to performance.
[0025]
The content ratio of the fluorinated functional monomer is directly related to the ion exchange capacity, but is preferably 1 to 50 mol%, preferably 3 to 35 mol% in the polymer. When the content ratio of the fluorinated functional monomer is too large, when it is formed into an ion exchange membrane or the like, the mechanical strength is lowered, and further, the ion exchange performance is lowered due to the increase in the water content, and too little. The content is not preferable because the ion exchange function is not exhibited.
[0026]
Further, the content of the olefin compound is important because it is largely related to properties such as electrical, mechanical and chlorine resistance. When the olefin compound is used in combination, the ratio of the olefin compound and the fluoroethylenically unsaturated monomer is a molar ratio, olefin compound / fluoroethylenically unsaturated monomer = 5/95 to 70/30, particularly 10/90 to 60 / 40 is preferable.
[0027]
When fluorovinyl ether or divinyl ether is used in combination, the vinyl ether is preferably 30 mol% or less, preferably 2 to 20 mol% in the polymer.
[0028]
In the present invention, the ion exchange capacity of the polymer in the latex is preferably selected from a wide range of 0.5 to 2.2 meq / g dry resin, but the characteristic point is that the ion exchange capacity is increased. However, the molecular weight of the polymer can be increased, and the mechanical properties and durability of the polymer are not lowered. Although the ion exchange capacity varies depending on the type of polymer, it is preferably 0.7 meq / g dry resin or more, particularly 0.9 meq / g dry resin or more as a mechanical ion exchange membrane. And preferable in terms of electrochemical performance.
[0029]
In addition, the molecular weight of the polymer obtained in the present invention is important because it is related to the mechanical performance and film-forming property as an ion exchange membrane, and expressed as a TQ value of 150 ° C. or higher, preferably 170 to 340 ° C., In particular, the temperature is preferably about 180 to 300 ° C.
[0030]
The ion exchange capacity was determined as follows. That is, the H-type cation exchange resin membrane was left in 1N hydrochloric acid at 60 ° C. for 5 hours, completely converted to H-type, and thoroughly washed with water so that no hydrochloric acid remained. Thereafter, the H-shaped membrane 0.5g, water solution comprising in addition 25 cm ³ sodium hydroxide 0.1 N 25 cm ^3, and allowed to stand at room temperature for 2 days. The membrane was then removed and the sodium hydroxide in the solution was determined by back titration with 0.1N hydrochloric acid.
[0031]
In the present specification, “TQ” is defined as a temperature indicating a volume flow rate of 100 mm ³ / sec, which is related to the molecular weight of the polymer. The volume flow rate indicates the amount of polymer flowing out in the unit of mm ³ / sec when the polymer is melted and flowed out from an orifice having a diameter of 1 mm and a length of 1 mm under a constant pressure of 30 kg / cm ² .
[0032]
In the present invention, emulsion polymerization is carried out in an aqueous medium. Usually, the amount of the aqueous medium used is controlled by controlling the ratio of the aqueous medium to the fluorinated functional monomer at a weight ratio of aqueous medium / fluorinated functional monomer = 20/1 or less, preferably 10/1 or less. It is preferable to do this. If the amount of the aqueous medium used is too large, problems such as disadvantages in work operation such as an increase in the size of the reaction apparatus or polymer separation and recovery occur.
[0033]
In the present invention, it is preferable to employ a reaction pressure of 1 kg / cm ² or more in emulsion polymerization. If the reaction pressure is too low, the reaction rate cannot be maintained at a practically satisfactory level, and there are difficulties in forming a high molecular weight polymer. On the other hand, if the reaction pressure is too low, the ion exchange capacity of the polymer to be produced becomes extremely high, resulting in a decrease in mechanical strength due to an increase in water content and a decrease in ion exchange performance.
[0034]
Further, the reaction pressure is preferably selected from 50 kg / cm ² or less from the viewpoint of the reaction apparatus or work operation in industrial implementation. Although it is possible to employ a reaction pressure higher than the above range, the object of the present invention is not proportionally improved. Accordingly, in the present invention, the reaction pressure is optimally selected from the range of 1 to 50 kg / cm ² , preferably 3 to 30 kg / cm ² .
[0035]
In the emulsion polymerization in the present invention, other conditions and operations of the reaction conditions are not particularly limited and can be employed over a wide range. For example, the reaction temperature is selected depending on the type of polymerization initiation source, the reaction molar ratio, and the like. Usually, too high and low temperatures are disadvantageous for industrial implementation, and therefore 10 to 90 ° C., preferably 20 to About 80 ° C is selected.
[0036]
As the polymerization initiation source, it is desirable to select one that exhibits high activity at the above-mentioned suitable reaction temperature. For example, highly active ionizing radiation can be employed even at room temperature or lower, but a method employing an azo compound or a peroxy compound is usually advantageous for industrial implementation.
[0037]
Specifically, diacyl peroxides such as disuccinic acid peroxide, benzoyl peroxide, lauroyl peroxide, dipentafluoropropionyl peroxide, which exhibit high activity at about 10 to 90 ° C. under reaction pressure, 2,2 ′ -Azo compounds such as azobis (2-amidinopropane) hydrochloride, 4,4'-azobis (4-cyanovaleric acid), azobisisobutyronitrile, t-butylperoxyisobutyrate, t-butylper Peroxyesters such as oxypivalate, peroxydicarbonates such as diisopropylperoxydicarbonate, di-2-ethylhexylperoxydicarbonate, hydroperoxides such as diisopropylbenzene hydroperoxide, potassium persulfate, ammonium persulfate Inorganic Oxides thereof, and the like redox systems.
[0038]
In the present invention, a preferable polymerization initiator concentration is about 0.0001 to 3% by weight, particularly about 0.001 to 2% by weight, based on the total amount of monomers. If the polymerization initiator concentration is too low, the polymerization rate is practically too low. Conversely, if the polymerization initiator concentration is too high, the polymerization rate becomes too high and it becomes difficult to control the reaction.
[0039]
In addition, surfactants, dispersants, buffers, molecular weight regulators, and the like used in normal emulsion polymerization can be added.
[0040]
In the present invention, it is suitable to control the concentration of the produced polymer to 40% by weight or less, preferably 30% by weight or less. If the concentration is too high, problems such as increased stirring load, insufficient heat removal, and poor diffusion of the fluoroethylenically unsaturated monomer occur.
[0041]
The latex obtained as described above is added with an HFE compound to extract and separate a fluorinated monomer having an unreacted boiling point of 20 to 300 ° C. Note that the unreacted gaseous monomer such as tetrafluoroethylene is easily separated and recovered by a purge method or the like. After recovering the unreacted monomer, an acid such as hydrochloric acid or sulfuric acid is added to the latex to aggregate the polymer. In addition, you may use well-known or well-known aggregation methods, such as salting out, freeze aggregation, and mechanical aggregation.
[0042]
The agglomerated polymer is thoroughly washed with water, and then water is replaced with a water-soluble organic solvent such as methanol or acetone. After air-drying the polymer, 100 cm ³ preferably based on 100 parts by weight of the polymer added 400～600Cm ³ or more methanol, preferably it to 1 to 50 hours at the addition of sulfuric acid while stirring 20 ° C. or higher. Next, when the polymer and methanol are separated and sulfuric acid is added, after washing with methanol to remove this, the polymer is obtained by drying at 40-80 ° C. under reduced pressure.
[0043]
According to the present invention, an ion exchange group-containing fluoropolymer having a high ion exchange capacity and a high molecular weight and excellent in moldability by heating and melting can be obtained smoothly and advantageously. For example, the fluoropolymer after emulsion polymerization has a TQ of over 300 ° C. even when a fluorinated monomer containing a carboxyl group is used, but the TQ is about 220 ° C. by heat contact treatment with methanol or the like. Can be lowered.
[0044]
Fluoropolymers having a TQ of 300 ° C. or higher are extremely difficult to heat and melt and cannot be formed into a film or sheet, but the fluoropolymer according to the present invention can be easily formed into a film or sheet by extrusion.
[0045]
The fluoropolymer obtained in a preferred embodiment of the present invention is formed by appropriate means. For example, if necessary, the functional group is converted to a carboxylic acid group by hydrolysis. This hydrolysis treatment can be performed before or after film formation. Usually, it is preferable to perform a hydrolysis treatment after film formation. Various methods can be adopted as the film forming means, and for example, known or well-known methods such as heat-melt molding, latex molding, and casting by dissolving in an appropriate solution can be appropriately employed.
[0046]
Since the ion exchange membrane made of the fluoropolymer obtained from the present invention has various excellent performances, it is widely used in various fields, purposes and applications. For example, it is suitably used in fields requiring heat resistance and corrosion resistance, such as diffusion dialysis, electrolytic synthesis, and fuel cell membranes. In particular, when used as a cation-selective membrane for alkaline electrolysis, high performance that cannot be obtained with conventional ion exchange membranes can be exhibited.
[0047]
For example, in the cation exchange resin film made of the fluoropolymer of the present invention, the anode and the cathode are partitioned to form an anode chamber and a cathode chamber, and an alkaline chloride aqueous solution is supplied to the anode chamber for electrolysis and from the cathode chamber Even in the case of a so-called two-chamber tank for obtaining alkali hydroxide, high concentration water of 30% or more can be obtained by electrolysis at a current density of 5 to 100 A / dm ² using a sodium chloride aqueous solution having a concentration of ² N or more as a raw material. Sodium oxide can be stably produced over a long period of time with a high current efficiency of 90% or more. Furthermore, electrolysis at a low cell voltage of 4.5 volts or less is possible.
[0048]
【Example】
Hereinafter, the present invention will be described with reference to Examples (Examples 1, 2 and 5) and Comparative Examples (Examples 3 and 4).
[0049]
[Example 1]
0.2 l stainless steel autoclave in deionized water 100g, C ₈ F ₁₇ COONH ₄ and _{0.2g, Na 2 HPO 4 · 12H} 2 O to 0.5g, a _{NaH 2 PO 4 · 2H 2 O} 0.3g _{, (NH 4) 2 S 2} O 8 to 0.026g and _{CF 2 = CFO (CF 2)} 3 COOCH 3 were thoroughly degassed 20g were charged, under liquid nitrogen. Thereafter, the temperature was raised to 55 ° C., and ethylene tetrafluoride was introduced into the system and maintained at 10.4 kg / cm ² . After stirring for 3.5 hours, unreacted ethylene tetrafluoride was purged to complete the reaction. The produced polymer was a latex having a composition containing 20 mol% of copolymerized CF ₂ ═CFO (CF ₂ ) ₃ COOCH ₃ , and the produced amount was 15.5 g.
[0050]
The latex contains unreacted CF ₂ ═CFO (CF ₂ ) ₃ COOCH ₃ , but is impregnated with polymer particles in the latex to form a uniform layer. 30 g of C ₄ F ₉ OCH ₃ (boiling point 60 ° C.) was added to 100 g of the latex, shaken in a separatory funnel for 10 minutes, and then allowed to stand for 30 minutes. After separating the lower C ₄ F ₉ OCH ₃ layer, the same amount of C ₄ F ₉ OCH ₃ was added again, and the same extraction operation was repeated. When the extraction operation was performed 6 times and analyzed by gas chromatography, CF ₂ ═CFO (CF ₂ ) ₃ COOCH ₃ was not detected in the C ₄ F ₉ OCH ₃ layer and the aqueous layer. C ₄ F ₉ and the extracted layer was collected distillation OCH _3, were recovered _{CF 2 = CFO (CF 2)} 3 COOCH 3 12.0g.
[0051]
[Example 2]
When extraction operation was performed in the same manner as in Example 1 except that C ₄ F ₉ OC ₂ H ₅ (boiling point 78 ° C.) was used instead of C ₄ F ₉ OCH ₃ , unreacted CF ₂ ═CFO (CF ₂ ) ₃ 11.5 g of ₃ COOCH ₃ was recovered.
[0052]
[Example 3]
When except for the use of CF ₂ ClCFCl ₂ instead of C ₄ F ₉ OCH ₃ was subjected to extraction with the same manner as Example 1, unreacted _{CF 2 = CFO (CF 2)} 3 COOCH 3 is 11.1g recovered It was.
[0053]
[Example 4]
Where except using CH ₂ Cl ₂ was subjected to extraction in the same manner as in Example 1, after standing also not sufficient to separate the aqueous layer is clouded The CH ₂ Cl ₂ layer, CH ₂ Cl ₂ to the aqueous layer Was found to partially dissolve.
[0054]
[Example 5]
In a 0.2 liter stainless steel autoclave, 120 g of ion exchange water, 0.42 g of C ₈ F ₁₇ CONH ₄ , 0.6 g of Na ₂ HPO ₄ .12H ₂ O, and NaH ₂ PO ₄ .2H ₂ O of 0. 35 g, 0.064 g of (NH ₄ ) ₂ S ₂ O ₈ and 12 g of CF ₂ ═CFO (CF ₂ ) ₂ SO ₂ F were charged and sufficiently deaerated under liquid nitrogen. Thereafter, the temperature was raised to 60 ° C., ethylene tetrafluoride was introduced into the system, and the pressure was maintained at 11.7 kg / cm ² . After stirring for 5.5 hours, unreacted ethylene tetrafluoride was purged to complete the reaction. The produced polymer was a latex having a composition containing 13.6 mol% of copolymerized CF ₂ ═CFO (CF ₂ ) ₂ SO ₂ F, and the produced amount was 19.4 g.
[0055]
The latex contains unreacted CF ₂ ═CFO (CF ₂ ) ₂ SO ₂ F, but is impregnated with polymer particles in the latex to form a uniform layer. 30 g of C ₄ F ₉ OCH ₃ was added to 100 g of the latex, and the extraction operation was performed in the same manner as in Example 1 to collect an unreacted CF ₂ ═CFO (CF ₂ ) ₂ SO ₂ F extraction layer, and CF by distillation. ₂ = CFO (CF ₂ ) ₂ SO ₂ F was recovered in an amount of 4.2 g. Note that after repeated extraction operation six times, was analyzed aqueous and C ₄ F ₉ OCH ₃ Tier by gas _{chromatography, CF 2 = CFO (CF 2} ) 2 SO 2 F is not detected from either It was.
[0056]
【The invention's effect】
The fluorinated monomer having an unreacted boiling point of 20 to 300 ° C. remaining in the latex is easily recovered with high efficiency by the HFE compound having a small ozone depletion coefficient and a global warming coefficient.

Claims (5)

A method for recovering unreacted fluorinated monomer from a latex obtained by emulsion polymerization of a fluorinated monomer having a boiling point of 20 to 300 ° C., wherein the unreacted fluorinated monomer is brought into contact with the latex by contacting the latex with a hydrofluoroether compound. A method for recovering a fluorinated monomer, comprising extracting the fluorinated monomer in the reaction. The recovery method according to claim 1, wherein the fluorinated monomer is a fluorinated functional monomer having a carboxylic acid type functional group or a sulfonic acid type functional group. The monomer having a carboxylic acid type functional group is represented by the general formula CF ₂ ═CF (OCF ₂ CF (CF ₃ )) _a O (CF ₂ ) _b COOCH ₃ (wherein, a is an integer of 0 to 3, b is 1 to The recovery method according to claim 2, which is a fluorovinyl compound represented by an integer of 5. A monomer having a sulfonic acid type functional group is represented by the general formula CF ₂ ═CF (OCF ₂ CF (CF ₃ )) _c O (CF ₂ ) _d SO ₂ F (wherein c is an integer of 0 to 3, d is 1) The recovery method according to claim 2, which is a fluorovinyl compound represented by an integer of ˜5. Hydrofluoroether _{compounds, C 4 F 9 OCH 3,} C 4 F 9 OC 2 H 5, CF 3 CF 2 CF 2 OCH 3, selected from the group consisting of _{(CF 3) 2 CFOCH 3,} CF 3 CFHCF 2 OCH 3 The recovery method according to claim 1, 2, 3 or 4.