Monomer removal method and device

Abstract

[Problem] The present invention addresses the problem of providing a method capable of removing, in an efficient and simple manner, residual monomer from a reaction solution after polymerization, particularly a latex solution after emulsion polymerization, while avoiding generation of undesirable polymer aggregate. [Solution] The present inventors discovered that residual monomer in a post-reaction polymer solution, such as a latex solution, can be efficiently removed by irradiating the solution with microwaves.

Description

Monomer removal method and apparatus

[0001] The present invention relates to a method for efficiently removing residual monomers from a latex solution obtained by an emulsion polymerization reaction by irradiating the latex solution with microwaves, and to an apparatus suitable for the method.

[0002] In a chemical reaction in which a polymer is obtained by polymerizing a monomer compound in a solution, even if the reaction yield is high, a certain amount of unreacted monomer remains in the reaction solution after the desired polymer is produced. If such residual monomer is contained in a final polymer product such as a latex, it is undesirable from the viewpoint of the working environment when the product is used or processed. For this reason, purification treatments such as removing the residual monomer from the reaction solution after the polymerization have been performed (for example, Patent Document 1).

[0003] Generally, synthesis of polymers such as rubbery polymers is carried out using emulsion polymerization, solution polymerization, suspension polymerization, or the like. For example, emulsion polymerization, which is a type of radical polymerization, is a technique in which an emulsifier is added to a reaction solution and a polymerization reaction is carried out in the state of an emulsion solution in which a monomer that is poorly soluble in the solvent is dispersed in the solvent. In such emulsion polymerization, when removing residual monomers after the reaction, jacket heating, in which the solution after the reaction is heated using a jacket connected to the reactor, or steam heating, in which high-temperature steam is applied to the reaction solution, has been used.

[0004] However, these conventional methods have the problem that undesirable polymer aggregates are generated on the jacket wall where the temperature locally becomes high, and also that the hot steam is entrapped in the emulsion solution, reducing the solid concentration, which requires an additional purification step such as dehydration in the downstream process.

[0005] JP 2003-147016

[0006] Therefore, an object of the present invention is to provide a method for efficiently and simply removing residual monomers from a reaction solution after a polymerization reaction, particularly from a latex solution after emulsion polymerization.

[0007] As a result of intensive research to solve the above-mentioned problems, the inventors have found that by irradiating a polymer solution after a reaction, such as a latex solution, with microwaves, unreacted monomers remaining in the solution can be efficiently removed, and have thus completed the present invention.

[0008] That is, in one aspect, the present invention relates to a method for removing residual monomers, and more specifically, <1> a method for removing residual monomers in a latex solution resulting from an emulsion polymerization reaction, comprising a step of irradiating the latex solution with microwaves, wherein the latex solution contains a polymer, the monomers, and an emulsifier; <2> the method according to <1> above, wherein the microwave irradiation step is carried out under reduced pressure; <3> the method according to <1> above, comprising reducing the monomers in the latex solution to 0.1% by weight or less by the microwave irradiation step; <4> the method according to <1> above, wherein after the microwave irradiation step, the recovery rate of the polymer in the latex solution is more than 90%; <5> the method according to <1> above, wherein the monomers include one or more monomers having a vinyl group; <6> the method according to <1> above, wherein the monomers include butadiene monomers, acrylonitrile monomers, styrene monomers, or a combination thereof; <7> the method according to <1> above, wherein the polymer is a synthetic rubber or elastomer; <8> The method according to the above item <1>, wherein the polymer is a butadiene-based rubber; and <9> The method according to the above item <1>, wherein the microwave frequency is within a range of 0.4 GHz to 6 GHz.

[0009] In another aspect, the present invention also relates to a method for producing a polymer material, and more specifically, <10> a method for producing a polymer material, comprising a step of carrying out emulsion polymerization in an aqueous solution containing raw material monomers and an emulsifier, and a step of irradiating a latex solution containing the polymer obtained by the emulsion polymerization with microwaves; <11> the method according to the above <10>, wherein the step of irradiating with microwaves is carried out before the step of drying the latex solution; <12> the method according to the above <10>, wherein the step of irradiating with microwaves is carried out under reduced pressure conditions; <13> the method according to the above <10>, comprising reducing unreacted monomers in the latex solution to 0.05% by weight or less by the step of irradiating with microwaves; <14> the method according to the above <10>, wherein after the step of irradiating with microwaves, the recovery rate of the polymer in the latex solution is more than 95%; <15> the method according to the above <10>, wherein the raw material monomers include one or more monomers having a vinyl group; <16> The manufacturing method according to the above <10>, wherein the raw material monomer includes a butadiene monomer, an acrylonitrile monomer, a styrene monomer, or a combination thereof; <17> The manufacturing method according to the above <10>, wherein the polymer material is a synthetic rubber or an elastomer; <18> The manufacturing method according to the above <10>, wherein the polymer is a butadiene-based rubber; and <19> The manufacturing method according to the above <10>, wherein the microwave frequency is within a range of 0.4 GHz to 6 GHz.

[0010] In a further aspect, the present invention also relates to an apparatus suitable for the above-mentioned method for removing a monomer, and more specifically, provides: <20> an apparatus for removing a monomer, comprising: a container for containing a latex solution obtained by an emulsion polymerization reaction, a microwave oscillator for generating microwaves, and a microwave irradiation unit for irradiating the latex solution with microwaves; <21> the apparatus according to the above <20>, wherein the container is made of a material that transmits or reflects microwaves; <22> the apparatus according to the above <20>, further comprising a pressure control unit for controlling the pressure inside the container and / or a temperature control unit for controlling the temperature inside the container; and <23> the apparatus according to the above <20>, further comprising a condenser for cooling or liquefying the monomer vaporized by the microwave irradiation.

[0011] According to the present invention, by using a simple method of irradiating a reaction solution after a polymerization reaction, particularly a latex solution after emulsion polymerization, with microwaves, it is possible to efficiently remove monomers remaining in the solution. Furthermore, according to the present invention, when removing the monomers, it is possible to suppress the generation of undesirable polymer aggregates and / or the decrease in solid content concentration, which have been problems in conventional methods.

[0012] The following describes embodiments of the present invention. The scope of the present invention is not limited to these descriptions, and other than the following examples, the present invention can be implemented with appropriate modifications within the scope that does not depart from the spirit of the present invention.

[0013] 1. Monomer Removal Method of the Present Invention The monomer removal method of the present invention is a method for removing monomers remaining in a latex solution resulting from an emulsion polymerization reaction, and is characterized in that it includes a step of irradiating the latex solution with microwaves, and the latex solution contains a polymer, the monomers, and an emulsifier.

[0014] In this specification, the term "latex solution" refers to a colloidal or emulsion-like solution in which polymer molecules produced by emulsion polymerization are dispersed as fine particles in an aqueous solution. Depending on the desired application, the polymer obtained by emulsion polymerization can be used as the latex solution as is, or can be used in the form of a powder or crumb-like solid obtained by dehydrating / drying the latex solution.

[0015] The polymer contained in the latex solution is not particularly limited as long as it is generally a polymer known to be synthesized by emulsion polymerization, but typically may be an elastomer such as a thermoplastic elastomer, a synthetic rubber, or any copolymer thereof.

[0016] Non-limiting examples of the polymer contained in the latex solution include nitrile butadiene rubber (NBR) and styrene butadiene rubber (SBR).

[0017] Emulsion polymerization can typically be carried out in a reaction vessel containing raw material polymerizable monomers, an emulsifier, a polymerization initiator, and the like. Polymerizable monomers used in such emulsion polymerization include conjugated dienes having 4 or more carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene; and non-conjugated dienes having 5 to 12 carbon atoms, such as 1,4-pentadiene and 1,4-hexadiene. Examples include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile and ethacrylonitrile. Examples of aromatic vinyl monomers include styrene, α-methylstyrene, and vinylpyridine. Examples include combinations of one or more of these.

[0018] As described above, unreacted polymerizable monomers remain in the solution after the polymerization reaction, and such residual monomers can be said to be unreacted monomers remaining in the latex solution of the emulsion polymerization reaction. The monomers to be removed by the present invention are preferably one or more monomers having a vinyl group, and more preferably include conjugated diene monomers, aromatic vinyl compound monomers, nitrile monomers, or combinations thereof. Specific examples of unreacted monomers include butadiene monomers, acrylonitrile monomers, styrene monomers, or combinations thereof.

[0019] Examples of emulsifiers used in emulsion polymerization include alkali metal salts of fatty acids, alkaline earth metal salts of fatty acids, alkali metal salts of sulfonic acids, alkaline earth metal salts of sulfonic acids, alkali metal salts of rosin acids, alkaline earth metal salts of rosin acids, etc. These may be used alone or in combination of two or more.

[0020] The polymerization initiator used in emulsion polymerization is not particularly limited as long as it is a radical initiator, and examples thereof include inorganic peroxides such as potassium persulfate, sodium persulfate, ammonium persulfate, potassium perphosphate, and hydrogen peroxide; organic peroxides such as t-butyl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, dibenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, and t-butylperoxyisobutyrate; and azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, and methyl azobisisobutyrate.

[0021] Radical polymerization can be mainly used as the form of emulsion polymerization, and batch polymerization, semi-batch polymerization, etc. can be used as the method.

[0022] In the present invention, the latex solution is heated by irradiating it with microwaves, and unreacted monomers can be removed from the solution by vaporizing them. Heating by microwave irradiation can heat the latex solution more uniformly and gently than conventional jacket heating or steam heating methods, and therefore can reduce the occurrence of undesired polymer condensates.

[0023] In a preferred embodiment, the amount of unreacted monomer in the latex solution can be reduced to 0.1% by weight or less, more preferably 0.05% by weight or less. The vaporized monomer component can then be recovered by cooling or liquefaction.

[0024] From another perspective, in one aspect of the present invention, the generation of undesirable polymer condensates can be reduced, and therefore the loss of polymer content in the latex solution can be minimized by the step of removing monomers by microwave irradiation. Therefore, in one aspect of the present invention, the recovery rate of the polymer in the latex solution after the step of irradiating with microwaves is preferably greater than 90%, more preferably greater than 95%. In other words, in one aspect of the present invention, the reduction rate of the polymer in the latex solution due to the step of irradiating with microwaves is preferably less than 10%, more preferably less than 5%. Here, the "polymer recovery rate" is a value calculated by B / A, where (A) is the weight of the polymer present in the latex solution before the step of removing monomers by microwave irradiation and (B) is the weight of the polymer present in the latex solution after the step of irradiating with microwaves. Furthermore, the "reduction rate of the polymer" is a value calculated by (A-B) / A.

[0025] As described below, microwave irradiation can be performed by generating microwaves using a microwave oscillator and irradiating the latex solution with the microwaves from a microwave irradiation unit. The frequency of the microwaves to be irradiated is not particularly limited, but can be within a range of 0.4 GHz to 6 GHz, more specifically, 0.433 to 5.98 GHz. The frequency may be 2.5 GHz or less, such as 2.45 GHz, or 0.8 GHz or more, such as 915 MHz. Microwaves of a single frequency may be irradiated, or microwaves of multiple frequencies may be irradiated. In the latter case, for example, microwaves of multiple frequencies may be irradiated simultaneously or at different times.

[0026] The microwave irradiation may be performed continuously or intermittently by repeating irradiation and pauses. When microwaves are irradiated, the temperature of the latex solution to be irradiated increases, and the microwave irradiation intensity may be adjusted so that the temperature remains constant, or the microwave irradiation intensity may be kept constant while the temperature is varied, or the microwave irradiation intensity may be changed in small increments.

[0027] The temperature of the latex solution to be irradiated with microwaves may be measured using a known thermometer, such as a thermocouple thermometer or an infrared fiber optic thermometer. The measured temperature may be used to control the output (intensity) of the microwaves.

[0028] The step of irradiating the latex solution with microwaves can be carried out under normal pressure or reduced pressure conditions. In a preferred embodiment, the step of irradiating with microwaves can be carried out under reduced pressure conditions. This allows the target monomer component to be vaporized and removed while preventing the latex solution from becoming excessively hot. For example, microwave irradiation can be carried out under normal pressure, and then the pressure can be changed to reduced pressure before microwave irradiation. When reduced pressure conditions are used, the pressure is preferably reduced to 1 to 90 kPa, more preferably to 1 to 10 kPa, and even more preferably to 1 to 4 kPa.

[0029] The monomer vaporized by microwave irradiation and removed from the latex solution can be cooled or liquefied by a condenser or the like provided downstream of the vessel storing the latex volume, and then recovered.

[0030] The monomer removal method according to one aspect of the present invention is not limited to the latex solution obtained in the above-described emulsion polymerization, but can also be applied to a solution obtained after a reaction in any other polymerization method, as long as the monomer component to be removed remains.

[0031] 2. Polymer Material Production Method of the Present Invention In another aspect, the present invention can also provide a polymer material production method comprising carrying out the above-mentioned monomer removal step. More specifically, the production method of the present invention is characterized by comprising: i) a step of carrying out emulsion polymerization in an aqueous solution containing raw material monomers and an emulsifier; and ii) a step of irradiating a latex solution containing the polymer obtained by the emulsion polymerization with microwaves.

[0032] Here, the type of polymer obtained by emulsion polymerization in step i), the types of raw material monomers and emulsifiers used in emulsion polymerization, etc. are as described above. Step ii) corresponds to the above-mentioned monomer removal method, and the details thereof have also been described above.

[0033] In a preferred embodiment, the step of irradiating with microwaves in step ii) is carried out before the step of drying the latex solution, because it is efficient to remove the remaining monomer components by irradiating with microwaves in a solution state.

[0034] 3. Apparatus of the Present Invention In a further aspect, the present invention also relates to an apparatus suitable for the above-mentioned method for removing monomers. That is, the apparatus for removing monomers of the present invention is characterized by comprising: a) a container for containing a latex solution obtained by an emulsion polymerization reaction; b) a microwave oscillator that generates microwaves; and c) a microwave irradiation unit that irradiates the latex solution with microwaves.

[0035] The container a) for containing the latex solution is preferably made of a material that transmits or reflects microwaves. Examples of such materials that can be used include stainless steel, ceramic, glass, and chemical-resistant resins such as fluororesins. The size and thickness of the container can be adjusted appropriately depending on the amount of the latex solution.

[0036] The microwave oscillator b) can be a magnetron, a klystron, a gyrotron, a semiconductor oscillator, etc. As described above, the frequency of the microwave is not particularly limited, but can be a frequency in the range of 0.4 GHz to 6 GHz, and may be, for example, 2.45 GHz, 5.8 GHz, or 915 MHz.

[0037] The microwave irradiating unit c) is for irradiating the container with microwaves, and may include one or more microwave irradiating units.

[0038] The microwave output can be determined depending on the scale of the apparatus, etc., and is not particularly limited. In a preferred embodiment, the apparatus of the present invention can include an output control unit including a computer or the like for controlling the microwave output.

[0039] As described above, the monomer vaporized by microwave irradiation and removed from the latex solution can be cooled or liquefied by a condenser or the like provided downstream of the vessel a) and recovered. Therefore, the apparatus according to one aspect of the present invention can further include a condenser for cooling or liquefying the monomer vaporized by microwave irradiation.

[0040] As described above, the step of irradiating the latex solution with microwaves can be carried out under normal pressure or reduced pressure. Therefore, the apparatus according to one aspect of the present invention can also include a pressure control unit for adjusting the pressure inside the container. For example, the pressure control unit can include a pressure reducing means such as a vacuum pump.

[0041] Furthermore, the apparatus according to one aspect of the present invention can include a temperature control unit for controlling the temperature inside the container. This allows the temperature of the latex solution in container a) to be cooled and / or heated to a desired range. The temperature control unit preferably includes a temperature measuring unit for measuring the temperature inside container a).

[0042] As a specific configuration of an apparatus equipped with a microwave oscillator, for example, the apparatus disclosed in Japanese Patent Application Laid-Open No. 2023-26212 can be referred to. It is believed that a person skilled in the art can fully understand the configuration of the apparatus of the present invention from this.

[0043] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0044] Example 1: A stainless steel reactor was charged with 80 kg of a latex aqueous solution with a latex solids concentration of approximately 22.9 to 25.0 wt %, 1 kg of an antifoaming agent to suppress foaming, 20 kg of water, and 1 kg of acrylonitrile as simulated residual monomer. The contents were stirred with a stirrer for at least 8 hours to ensure uniform dispersion of the monomer. The liquid in the reactor was then heated from room temperature to 70°C at a heating rate of 1°C / min using 2450 MHz microwaves, heat transfer from a jacket, or by blowing steam into the liquid. After reaching 70°C, the pressure was gradually reduced from atmospheric pressure to approximately 66 kPa at a rate of 0.1 to 1.0 kPa / min. If severe foaming occurred, the pressure was stopped and maintained constant until foaming subsided. The monomer (acrylonitrile) and water in the reactor evaporated due to the reduced pressure, and the liquid temperature dropped due to the loss of latent heat. Therefore, the liquid was heated by microwaves, heat transfer from the jacket, or by blowing steam into the liquid under temperature feedback control to maintain a temperature of 70°C. The evaporated monomer and water were cooled and liquefied in a condenser installed downstream and collected in a catch tank installed below the condenser. The experiment was continued until the monomer concentration in the liquid in the reactor reached 100 ppm or less (approximately 12 hours).

[0045] Example 2 An experiment similar to that of Example 1 was carried out, except that the microwave frequency was changed from 2450 MHz to 915 MHz.

[0046] Comparative Example 1 An experiment similar to that of Example 1 was carried out, except that heating was performed using heat transfer from a jacket instead of microwaves.

[0047] Comparative Example 2 An experiment similar to that of Example 1 was carried out, except that the heating method was changed from microwave heating to steam heating.

[0048] The experimental conditions and the results of monomer removal for Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1 below.

[0049]

[0050] As a result, it was confirmed that in Examples 1 and 2, which are microwave heating methods of the present invention, the monomer could be removed to the target value of 100 ppm or less. As shown in Table 1, in Examples 1 and 2, the solid content yield of the charged latex was 100%, and the entire amount was recovered. However, in Comparative Example 1, when jacket heating was used, the latex aggregated and adhered to the high-temperature wall surface, and the solid content yield of the latex was 90%, a decrease of about 10%. Furthermore, in Comparative Example 2, steam injection heating significantly reduced the solid content concentration of the aqueous latex solution due to the injection of steam into the liquid. Therefore, it is considered that the steam injection heating of Comparative Example 2 requires a subsequent step such as dehydration. However, in the case of the microwave heating of the present invention shown in Examples 1 and 2, such a decrease in solid content was not observed, demonstrating the effect that a subsequent step such as dehydration is not necessary.

Claims

1. A method for removing residual monomers in a latex solution of an emulsion polymerization reaction, comprising the step of irradiating the latex solution with microwaves, the latex solution comprising a polymer, the monomers and an emulsifier.

2. The method according to claim 1, wherein the step of irradiating with microwaves is carried out under reduced pressure conditions.

3. The method of claim 1, further comprising reducing said monomer in said latex solution to 0.1% by weight or less by said microwave irradiating step.

4. The method of claim 1, wherein the recovery rate of the polymer in the latex solution after the microwave irradiating step is greater than 90%.

5. The method of claim 1, wherein the monomers include one or more monomers having a vinyl group.

6. The method of claim 1, wherein the monomers comprise butadiene monomers, acrylonitrile monomers, styrene monomers, or combinations thereof.

7. The method of claim 1, wherein the polymer is a synthetic rubber or elastomer.

8. The method of claim 1, wherein the polymer is a butadiene-based rubber.

9. The method of claim 1, wherein the microwave frequency is in the range of 0.4 GHz to 6 GHz.

10. A method for producing a polymer material, comprising: a step of carrying out emulsion polymerization in an aqueous solution containing raw material monomers and an emulsifier; and a step of irradiating a latex solution containing the polymer obtained by the emulsion polymerization with microwaves.

11. The method of claim 10, wherein the step of irradiating with microwaves is carried out before the step of drying the latex solution.

12. The method according to claim 10, wherein the step of irradiating with microwaves is carried out under reduced pressure conditions.

13. The method of claim 10, further comprising reducing the amount of unreacted monomer in the latex solution to 0.05% by weight or less by the step of irradiating with microwaves.

14. The method of claim 10, wherein after the step of irradiating with microwaves, the recovery rate of the polymer in the latex solution is greater than 95%.

15. The method according to claim 10, wherein the starting monomers include one or more monomers having a vinyl group.

16. The process of claim 10, wherein the feed monomers include butadiene monomers, acrylonitrile monomers, styrene monomers, or combinations thereof.

17. The method of claim 10, wherein the polymeric material is a synthetic rubber or elastomer.

18. The process of claim 10, wherein the polymer is a butadiene-based rubber.

19. The manufacturing method according to claim 10, wherein the microwave frequency is within the range of 0.4 GHz to 6 GHz.

20. A monomer removal apparatus comprising: a container for containing a latex solution obtained by an emulsion polymerization reaction; a microwave oscillator for generating microwaves; and a microwave irradiation unit for irradiating the latex solution with microwaves.

21. The apparatus of claim 20, wherein the container is constructed of a material that is either transparent or reflective to microwaves.

22. The apparatus of claim 20, further comprising a pressure control for controlling the pressure within the vessel and / or a temperature control for controlling the temperature within the vessel.

23. The apparatus according to claim 20, further comprising a condenser for cooling or liquefying the monomer vaporized by the microwave irradiation.

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