Method for producing (meth)acrylic monomer

Abstract

To provide a production method of a (meth)acrylic monomer for suppressing nonuniformity of a depolymerization system of a (meth)acrylic resin, and making microwaves easily reach the inside of the system efficiently.SOLUTION: A production method of a (meth)acrylic monomer includes steps of: a step 1 of irradiating a charged (meth)acrylic resin with microwaves followed by mixing so as to obtain a molten material containing a (meth)acrylic resin reduced in its molecular weight; a step 2 of adding an additional (meth)acrylic resin to the molten material followed by mixing so as to obtain a mixture containing the additional (meth)acrylic resin in the molten material; and a step 3 of irradiating the mixture with microwaves followed by mixing so as to obtain the (meth)acrylic monomer. With the production method, it is possible to suppress nonuniformity of a depolymerization system of the (meth)acrylic resin, and make microwaves easily reach the inside of the system efficiently.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a (meth)acrylic monomer. More specifically, the present invention relates to a technique for recovering a (meth)acrylic monomer from a (meth)acrylic resin.

Background Art

[0002] Acrylic resin and methacrylic resin (hereinafter, “acrylic” and “methacrylic” are collectively referred to as “(meth)acrylic”).) are amorphous thermoplastic plastics having high transparency and impact resistance. Since (meth)acrylic resins are easy to process and color, they are used as substitutes for inorganic glass in a wide range of applications such as light guide plates for liquid crystal televisions and liquid crystal displays, covers for lighting fixtures, window materials for buildings and vehicles, windshields for bicycles, canopies for aircraft, windshields for watches, and aquariums.

[0003] The production volume of (meth)acrylic resins is expected to increase in the future. On the other hand, from the perspective of resource conservation, techniques for recycling monomers by depolymerizing waste (meth)acrylic resins without producing monomers from fossil raw materials are being studied.

[0004] For example, Patent Document 1 describes a method for decomposing a (meth)acrylic resin by heating a solution in which the (meth)acrylic resin is dissolved, characterized in that heating is carried out while supplying an inert gas and / or water vapor into the solution. Specifically, it is described that heating is carried out using a method in which a heat medium flows through a jacket type, electric heater heating, or a burner method by fuel combustion.

[0005] Further, Patent Document 2 describes a method for recovering a (meth)acrylic acid ester in which a (meth)acrylic resin containing 50% by mass or more of a (meth)acrylic acid ester unit is irradiated with microwaves to decompose the (meth)acrylic resin in a resin-containing liquid dissolved or swollen in a solvent having a boiling point of 250° C. or higher under atmospheric pressure, and the obtained (meth)acrylic acid ester is separated. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-232966 [Patent Document 2] Japanese Patent Publication No. 2007-230905 [Overview of the project] [Problems that the invention aims to solve]

[0007] The technology described in Patent Document 1 requires a means to supply a predetermined gas in addition to a heating means, resulting in a complicated setup. The technology in Patent Document 2 is a simple depolymerization system that uses microwaves as a heating means, but it also requires the use of a solvent, which has the problem of producing undesirable byproducts due to the heating of the solvent.

[0008] (Meth)acrylic resin has the characteristic of having low microwave absorption capacity at room temperature, but increasing microwave absorption capacity as the temperature rises. Since the microwave absorption capacity is high near the depolymerization temperature of (meth)acrylic resin (generally 280°C or higher), it is expected that (meth)acrylic resin can be efficiently heated and decomposed by microwaves. For this reason, the inventors attempted depolymerization using microwaves as a heating means and a molten system of the raw material (meth)acrylic resin without using a solvent. However, in actual investigation, the inventors unexpectedly encountered a problem in that the high microwave absorption capacity of (meth)acrylic resin, which should be inherently advantageous in depolymerization, locally absorbs microwaves at the surface of the molten resin, preventing microwaves from penetrating deeply into the molten material. As a result, microwaves do not easily reach the (meth)acrylic resin inside, making uniform depolymerization difficult. Furthermore, these problems became even more pronounced as the scale of the depolymerization system increased.

[0009] Therefore, the present invention aims to provide a method for producing (meth)acrylic monomers that can suppress the heterogeneity of the depolymerization system of (meth)acrylic resin and efficiently promote depolymerization throughout the molten material. [Means for solving the problem]

[0010] As a result of diligent research, the inventors have found that by adding (meth)acrylic resin from outside the system to a molten material containing components with reduced microwave absorption capacity obtained by irradiating and mixing (meth)acrylic resin with microwaves, and then irradiating the dispersed (meth)acrylic resin with microwaves, the heterogeneity of the depolymerization system of (meth)acrylic resin is suppressed, and microwaves can efficiently reach the interior of the system. The present invention was completed by further research based on this finding.

[0011] In other words, the present invention provides inventions in the following embodiments. Item 1. Step 1 involves irradiating a prepared (meth)acrylic resin with microwaves and mixing it to obtain a molten product containing a component with lower microwave absorption capacity than the prepared (meth)acrylic resin at the depolymerization temperature, Step 2 involves adding and mixing additional (meth)acrylic resin to the molten material to obtain a molten mixture containing additional (meth)acrylic resin in the molten material. A method for producing a (meth)acrylic monomer, comprising step 3 of irradiating the molten mixture with microwaves and mixing to obtain a (meth)acrylic monomer. Item 2. The manufacturing method according to Item 1, wherein the amount of the prepared (meth)acrylic resin prepared in step 1 is 2.5 kg or more. Item 3. The manufacturing method according to item 1 or 2, wherein in step 1, the amount of (meth)acrylic resin prepared is 80 kg or more. Item 4. The manufacturing method according to any one of Items 1 to 3, wherein steps 2 and 3 are repeated. Item 5. The manufacturing method according to any one of Items 1 to 4, wherein in step 2, the additional (meth)acrylic resin has not had a thermal history of being subjected to a depolymerization temperature. Item 6. The manufacturing method according to any one of Items 1 to 5, wherein in step 2, the amount of the additional (meth)acrylic resin added is 5 to 20 parts by weight per 100 parts by weight of the prepared (meth)acrylic resin. Item 7. The manufacturing method according to any one of Items 1 to 6, wherein in step 2, the additional (meth)acrylic resin is added when the amount of the prepared (meth)acrylic resin decreases by 1 to 20 parts by weight from 100 parts by weight. Item 8. The manufacturing method according to any one of Items 1 to 7, wherein step 3 is carried out under temperature conditions of 300 to 360°C. Item 9. The manufacturing method according to any one of Items 1 to 8, wherein the frequency of the microwave is 0.8 to 6 GHz. Item 10. The manufacturing method according to any one of items 1 to 9, wherein steps 1 to 3 are carried out in a container having a side wall with an inverted cone-shaped bottom. [Effects of the Invention]

[0012] The present invention provides a method for producing (meth)acrylic monomer that suppresses heterogeneity in the depolymerization system of (meth)acrylic resin and facilitates the efficient penetration of microwaves into the interior of the system. [Brief explanation of the drawing]

[0013] [Figure 1] A schematic diagram of an example of the apparatus used in the method for producing (meth)acrylic monomer of the present invention is shown. [Figure 2] A schematic diagram of another example of the apparatus used in the method for producing (meth)acrylic monomer of the present invention is shown. [Modes for carrying out the invention]

[0014] 1.Basic process The method for producing a (meth)acrylic monomer according to the present invention comprises: Step 1 of irradiating a charged (meth)acrylic resin with microwaves for mixing to obtain a melt containing a component having a lower microwave absorption ability than the charged (meth)acrylic resin at the depolymerization temperature; Step 2 of adding and mixing an additional (meth)acrylic resin to the melt to obtain a molten mixture containing the additional (meth)acrylic resin in the melt; and Step 3 of irradiating the molten mixture with microwaves for mixing to obtain a (meth)acrylic monomer.

[0015] Step 2 is carried out after Step 1, and Step 3 is carried out after Step 2. Step 2 can be carried out without irradiating with microwaves or while irradiating with microwaves, and is preferably carried out while irradiating with microwaves. The additional (meth)acrylic resin added in Step 2 is depolymerized into a low-molecular-weight (meth)acrylic resin (a (meth)acrylic resin having a smaller molecular weight than the additional (meth)acrylic resin) in the melt at a time difference from the charged (meth)acrylic resin prepared in Step 1, and is decomposed into a (meth)acrylic monomer as the depolymerization progresses.

[0016] It is preferable that Steps 2 and 3 are repeated. In the repetition of Steps 2 and 3, for example, when a molten mixture to which an additional (meth)acrylic resin is added is prepared in the previous Step 2, and the additional (meth)acrylic resin is depolymerized into a low-molecular-weight (meth)acrylic resin and decomposed into a (meth)acrylic monomer as the depolymerization progresses, a molten mixture to which a newly added additional (meth)acrylic resin is added in the subsequent Step 2 is prepared. That is, in the repetition of Steps 2 and 3, the state in which a molten mixture containing a new (meth)acrylic resin is dispersed in the depolymerization system can be continuously updated.

[0017] In a particularly preferred embodiment of the present invention, while irradiating with microwaves for mixing, an additional (meth)acrylic resin is continuously or intermittently added and mixed to a melt containing a component having a low microwave absorption ability obtained by irradiating and mixing a charged (meth)acrylic resin with microwaves, so that depolymerization progresses, and a (meth)acrylic monomer can be obtained.

[0018] The depolymerization system used in the manufacturing method of the present invention is usually in a sealed state, and the monomer product is in gaseous form. The generated monomer is liquefied and recovered by a cooling device provided in communication with the depolymerization system atmosphere.

[0019] In one embodiment of the present invention, from the viewpoint of suppressing an increase in the amount of impurities in the recovered monomer, it is preferable that the process does not further include the step of depolymerizing without adding an additional (meth)acrylic resin and / or the step of depolymerizing without stirring.

[0020] 2.Process 1 In step 1, the prepared (meth)acrylic resin is irradiated with microwaves and mixed to obtain a molten product containing a component with lower microwave absorption capacity than the prepared (meth)acrylic resin at the depolymerization temperature.

[0021] In step 1, "mixing by irradiating with microwaves" includes both a mode in which the mixture is mixed while irradiating with microwaves and a mode in which the mixture is mixed after irradiating with microwaves.

[0022] The initial (meth)acrylic resin refers to the (meth)acrylic resin used as the material initially subjected to the depolymerization system. Specific examples of this (meth)acrylic resin include, preferably, a plastic material containing (meth)acrylic resin, and more preferably, a waste plastic material containing (meth)acrylic resin. The initial (meth)acrylic resin may be added all at once, or it may be added in multiple stages, depending on the need for temperature uniformity throughout the (meth)acrylic resin. When adding in multiple stages, the remaining (meth)acrylic resin should be added until the desired amount is reached, once the previously added (meth)acrylic resin reaches or is about to reach the depolymerization system temperature. For example, when adding the (meth)acrylic resin in two stages, the remaining second (meth)acrylic resin should be added once the first (meth)acrylic resin reaches or is about to reach the depolymerization system temperature. For example, when adding the (meth)acrylic resin in three or more stages, the remaining (meth)acrylic resin should be added sequentially in multiple stages until the desired amount is reached, once the amount added in the first stage has reached or is about to reach the depolymerization temperature. Similarly, when adding the remaining (meth)acrylic resin in multiple stages, the next stage of (meth)acrylic resin should be added once the entirety of the (meth)acrylic resin added in the first stage and the subsequent stages has reached or is about to reach the depolymerization temperature.

[0023] Specifically, the prepared (meth)acrylic resin includes polymers having (meth)acrylic monomers selected from the group consisting of acrylic acid, methacrylic acid, and their esters as constituent units. Examples of acrylic acid esters include methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate, and examples of methacrylic acid esters include methyl methacrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate. The prepared (meth)acrylic resin may contain constituent units derived from any one of the above (meth)acrylic monomers alone, or it may contain constituent units derived from two or more different types of the above (meth)acrylic monomers in a combined state.

[0024] The constituent units derived from (meth)acrylic monomers contained in the prepared (meth)acrylic resin are preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and even more preferably 95% by weight or more, with the most preferred being 100% by weight. If the prepared (meth)acrylic resin contains constituent units derived from monomers other than (meth)acrylic monomers, the other monomers may be selected from the group consisting of maleic anhydride, styrene, α-methylstyrene, and acrylonitrile.

[0025] The weight-average molecular weight of the prepared (meth)acrylic resin is not particularly limited, but examples include 80,000 to 2,000,000, preferably 100,000 to 2,000,000. The weight-average molecular weight (Mw) is a value measured on a standard polystyrene basis by gel permeation chromatography (GPC).

[0026] In the above-mentioned plastic material containing the prepared (meth)acrylic resin, the blending ratio of (meth)acrylic resin is not particularly limited, but is preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and even more preferably 95% by weight or more. Furthermore, in the above-mentioned plastic material containing the (meth)acrylic resin, the proportion of (meth)acrylic resin in the total resin is not particularly limited, but is preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, even more preferably 95% by weight or more, and most preferably 100% by weight. In the above-mentioned plastic material containing the (meth)acrylic resin, additive components that may be included other than the resin include dyes, pigments, inorganic fillers, etc.

[0027] The amount of (meth)acrylic resin to be added is not particularly limited. On the other hand, the manufacturing method of the present invention can heat the depolymerization system with high uniformity and efficiently allow microwaves to reach the inside of the system. Therefore, even in large-scale depolymerization systems where the heating of the depolymerization system tends to be uneven and the problem of microwaves not reaching the inside of the system becomes significant, the effects of the present invention can be obtained well. From this viewpoint, preferred examples of the amount of (meth)acrylic resin to be added in one embodiment of the present invention include 2.5 kg or more, 2.8 kg or more, 3.2 kg or more, more preferably more than 50 kg, even more preferably 80 kg or more, and even more preferably 100 kg or more. There is no particular upper limit to the amount of (meth)acrylic resin to be added in the present invention, but examples include 2000 kg or less or 1000 kg or less. Furthermore, when the amount of methacrylic resin to be added is added in multiple stages, it refers to the total amount of methacrylic resin added from the first to the subsequent stages (i.e., the target amount). When adding methacrylic resin in multiple stages, a preferred amount is over 50 kg. In this case, the amount added in the first stage should be 50 kg or less, and the remaining methacrylic resin can then be added as needed until the target amount is reached.

[0028] By irradiating the prepared (meth)acrylic resin with microwaves, the resin is heated and melted. When it reaches the depolymerization temperature, depolymerization proceeds partially at the microwave-irradiated areas, resulting in the formation of low-molecular-weight (meth)acrylic resin (i.e., (meth)acrylic resin with a smaller molecular weight than the prepared (meth)acrylic resin) in the molten (meth)acrylic resin, which is then dispersed in the molten material by mixing.

[0029] In step 1, the microwave irradiation output is appropriately selected to heat the prepared (meth)acrylic resin to a temperature at which its depolymerization proceeds. In step 2, the temperature at which the depolymerization of the (meth)acrylic resin proceeds is, for example, 280°C or higher, specifically 300-390°C, preferably 320-390°C, more preferably 325-370°C, even more preferably 330-360°C, and even more preferably 335-350°C.

[0030] The specific irradiation output of the microwaves irradiated onto the depolymerization system in step 1 can be set appropriately according to the set temperature and the amount of (meth)acrylic resin to be prepared, but the effective output (value obtained by subtracting the reflected wave (kW) from the incident wave (kW)) can be, for example, 1 kW or more, preferably 1.2 kW or more, and more preferably 1.5 kW or more. There is no particular upper limit to the irradiation output (effective output), but for example, it can be 200 kW or less.

[0031] The frequency of the microwave irradiated onto the depolymerization system in step 1 is not particularly limited, but examples include 0.8 to 6 GHz. From the viewpoint of making it easier to get the microwave into the interior of the molten material, the frequency is preferably 0.8 to 2.5 GHz, more preferably 0.8 to 1.5 GHz, and even more preferably 0.8 to 1 GHz or 0.9 to 0.95 GHz. In the manufacturing method of the present invention, since the microwave can reach the interior of the molten material, it is possible to get the microwave into the interior of the molten material even when using microwaves with frequencies that are not inherently advantageous in terms of deep penetration, such as those between 2.5 GHz and 6 GHz or between 1.5 GHz and 6 GHz, particularly 4 to 6 GHz.

[0032] The mixing method in step 1 is not particularly limited and may include, for example, mixing with a stirring bar, rotating the container holding the molten material, or a combination of both methods. The degree of mixing should be such that the composition of the molten material becomes uniform.

[0033] The molten material obtained in step 1 contains components with lower microwave absorption capacity than the input (meth)acrylic resin at the depolymerization temperature. These components with lower microwave absorption capacity are generated by microwave irradiation of the input (meth)acrylic resin molten material and are not specifically known, but they could be the low molecular weight (meth)acrylic resin and / or by-products other than the low molecular weight (meth)acrylic resin (for example, components that are not converted to (meth)acrylic monomers and remain as residue). The presence of components with lower microwave absorption capacity than the input (meth)acrylic resin at the depolymerization temperature can be confirmed by measuring the real and imaginary parts of the complex dielectric constant at the same temperature (but within the depolymerization temperature range) for the molten material to be checked and the input (meth)acrylic resin, and then calculating the microwave power half-depth based on these measurements.

[0034] 3.Process 2 In step 2, additional (meth)acrylic resin is added to the molten material obtained in step 1 and mixed to obtain a molten mixture containing the additional (meth)acrylic resin.

[0035] In step 2, "adding and mixing additional (meth)acrylic resin" includes both adding and mixing the additional (meth)acrylic resin while adding it, and adding and mixing the additional (meth)acrylic resin after it has been added.

[0036] The molten material obtained in step 1 contains components that have lower microwave absorption capacity compared to the input (meth)acrylic resin at the depolymerization temperature. Therefore, the molten material itself has lower microwave absorption capacity compared to the input (meth)acrylic resin at the depolymerization temperature. In step 2, additional (meth)acrylic resin is added to the molten material with low microwave absorption capacity and mixed, dispersing it within the molten material. This allows microwaves to reach the interior of the molten mixture.

[0037] In this invention, the "additional (meth)acrylic resin" specified as being added in step 2 is added to a melt that has lower microwave absorption capacity than the molten (meth)acrylic resin being prepared. However, it is also permissible to add another additional (meth)acrylic resin in a step other than step 2, separate from the "additional (meth)acrylic resin" added in step 2. An example of adding another additional (meth)acrylic resin in a step other than step 2 is to add the other additional (meth)acrylic resin once or multiple times before obtaining a "molten material containing a component with lower microwave absorption capacity than the prepared (meth)acrylic resin at the depolymerization temperature" in step 1.

[0038] Specific embodiments of the additional (meth)acrylic resin include, preferably, plastic materials containing (meth)acrylic resin, and more preferably, waste plastic materials containing (meth)acrylic resin.

[0039] The type of additional (meth)acrylic resin, the content ratio of constituent units derived from (meth)acrylic monomers, the types of other monomers, and the weight-average molecular weight can be selected from the examples described for the pre-filled (meth)acrylic resin. Furthermore, the blending ratio of (meth)acrylic resin in the plastic material containing the additional (meth)acrylic resin, and any additive components other than resin that may be included, can also be selected from the examples described for the plastic material containing the pre-filled (meth)acrylic resin. The additional (meth)acrylic resin or the plastic material containing it may be the same as or different from the pre-filled (meth)acrylic resin or the plastic material containing it.

[0040] The specific properties of the additional (meth)acrylic resin may be that it is solid or molten.

[0041] Furthermore, it is preferable that the additional (meth)acrylic resin does not have a thermal history of being subjected to the depolymerization temperature, from the viewpoint of further suppressing the non-uniformity of the (meth)acrylic resin depolymerization system and promoting more efficient depolymerization throughout the molten material. In other words, from this viewpoint, it is preferable that the additional (meth)acrylic resin is not one that has been previously subjected to the depolymerization system and is newly added, rather than one that has been previously subjected to the depolymerization system and is being reintroduced.

[0042] Regarding specific examples of the timing and amount (per addition) of additional (meth)acrylic resin, it is preferable to add an amount of additional (meth)acrylic resin equivalent to the amount of decrease when the amount of (meth)acrylic resin added decreases by 20 parts by weight or less, more preferably 1 to 20 parts by weight, more preferably 2 to 18 parts by weight, and even more preferably 3 to 15 parts by weight, per 100 parts by weight of the initial (meth)acrylic resin.

[0043] More specifically, when the amount of (meth)acrylic resin prepared is 1 kg or more but less than 50 kg, it is preferable to replenish with an additional amount of (meth)acrylic resin equivalent to the amount decreased by 1 to 15 parts by weight, preferably 3 to 15 parts by weight, from 100 parts by weight; when the amount of (meth)acrylic resin prepared is 50 kg or more but less than 80 kg, it is preferable to replenish with an additional amount of (meth)acrylic resin equivalent to the amount decreased by 1 to 5 parts by weight, preferably 2.5 to 5 parts by weight, from 100 parts by weight. When the amount of (meth)acrylic resin prepared is 80 kg or more and less than 400 kg, it is preferable to replenish with an additional amount of (meth)acrylic resin equivalent to the amount decreased by 1 to 4 parts by weight, preferably 2 to 4 parts by weight, more preferably 3 to 4 parts by weight, from 100 parts by weight; when the amount of (meth)acrylic resin prepared is 400 kg or more, it is preferable to replenish with an additional amount of (meth)acrylic resin equivalent to the amount decreased by 1 to 3 parts by weight, preferably 1.5 to 3 parts by weight, from 100 parts by weight.

[0044] Step 2 can be carried out without microwave irradiation or while irradiating with microwaves, but from the viewpoint of avoiding the complexity of manufacturing control, it is preferable to carry it out while irradiating with microwaves.

[0045] The temperature in step 2 should be such that the additional (meth)acrylic resin melts at least, and may also be such that depolymerization can proceed as described in step 1. From the viewpoint of avoiding the complexity of control in the manufacturing process, the same temperature conditions as in step 1 can be used. Temperature control can be achieved by microwave irradiation.

[0046] The mixing method in step 2 is not particularly limited and may include, for example, mixing with a stirring bar, rotating the container containing the molten mixture, or a combination of both methods. The degree of mixing should be such that the composition of the molten mixture becomes uniform, that is, that the additional (meth)acrylic resin is uniformly dispersed in the molten mixture.

[0047] 4.Process 3 In step 3, the molten mixture obtained in step 2 is irradiated with microwaves and mixed to obtain (meth)acrylic monomer.

[0048] In step 3, "mixing by irradiating with microwaves" includes both a mode in which the mixture is mixed while irradiating with microwaves and a mode in which the mixture is mixed after irradiating with microwaves.

[0049] In the molten mixture obtained in step 2, additional (meth)acrylic resin is dispersed in the molten material, where local microwave absorption on the surface of the molten mixture is suppressed and microwaves can reach the interior. Therefore, it is thought that the depolymerization reaction can proceed throughout the entire molten material. The additional (meth)acrylic resin undergoes depolymerization with a time lag, after the initial (meth)acrylic resin. Furthermore, since step 3 is performed while mixing, the occurrence of areas that are excessively heated locally is suppressed, thereby reducing unwanted by-products in the recovered monomer.

[0050] The microwave irradiation output in step 3 is appropriately selected to heat the material to a temperature at which depolymerization can proceed. Examples of temperatures at which depolymerization proceeds in step 3 include 280°C or higher, specifically 300-390°C, and preferably 320-390°C.

[0051] From the viewpoint of further improving the recovery rate of (meth)acrylic monomer, the temperature at which depolymerization proceeds in step 3 is preferably 325 to 390°C, more preferably 330 to 390°C, even more preferably 335 to 390°C, even more preferably 340 to 390°C, even more preferably 345 to 390°C, and particularly preferably 350 to 390°C.

[0052] On the other hand, from the viewpoint of further improving the purity of the target (meth)acrylic monomer in the recovered monomer liquid, the temperature at which depolymerization proceeds in step 3 is preferably 320 to 380°C, more preferably 320 to 370°C, even more preferably 320 to 360°C, even more preferably 320 to 355°C, even more preferably 320 to 345°C, particularly preferably 320 to 342°C, and most preferably 320 to 340°C. The improvement in the purity of the target (meth)acrylic monomer in the recovered monomer liquid can also be confirmed by an increase in the weight ratio of (meth)acrylic monomer in the recovered monomer liquid, and / or a reduction in the amount of trace components, which may not be easily reflected in the said weight ratio. Examples of the above trace components include coloring components that can be confirmed by visual inspection or chromosome measurement, and / or methyl isobutyrate, which can be confirmed by chromatography.

[0053] From the perspective of avoiding the complexity of control in the manufacturing process, the temperature at which depolymerization proceeds in step 3 can be the same as the temperature conditions in step 1 and / or step 2. Temperature control can be achieved by microwave irradiation.

[0054] In step 3, the specific microwave irradiation output to the depolymerization system can be set appropriately according to the set temperature and the scale of the depolymerization system, but the effective output (value obtained by subtracting the reflected wave (kW) from the incident wave (kW)) can be, for example, 1 kW or more, preferably 1.2 kW or more, and more preferably 1.5 kW or more. There is no particular upper limit to the irradiation output (effective output), but for example, it can be 200 kW or less.

[0055] The frequency of the microwave irradiated onto the depolymerization system in step 2 is not particularly limited, but examples include 0.8 to 6 GHz. From the viewpoint of making it easier to get the microwave into the interior of the molten mixture, the frequency is preferably 0.8 to 2.5 GHz, more preferably 0.8 to 1.5 GHz, and even more preferably 0.8 to 1 GHz or 0.9 to 0.95 GHz. In the manufacturing method of the present invention, since the microwave can reach into the interior of the molten mixture, it is possible to get the microwave into the interior of the molten mixture even when using microwaves with frequencies that are not inherently advantageous in terms of deep penetration, such as those between 2.5 GHz and 6 GHz or between 1.5 GHz and 6 GHz, particularly 4 to 6 GHz.

[0056] The mixing method in step 3 is not particularly limited and may include, for example, mixing with a stirring blade, rotating the container holding the molten mixture, or a combination of both methods. The degree of mixing should be such that the composition of the molten mixture becomes uniform.

[0057] 5. Repeat steps 2 and 3. In the configuration in which steps 2 and 3 are repeated, the state in which the molten mixture containing additional (meth)acrylic resin is dispersed in the molten material, where local microwave absorption is suppressed and microwaves can reach the interior, can be continuously renewed. In other words, in the configuration in which steps 2 and 3 are repeated, uniform depolymerization that allows microwaves to reach the interior of the system efficiently can be maintained, so that the metabolism of the material to be depolymerized occurs efficiently throughout the entire molten material, and efficient depolymerization is possible even when the depolymerization system is on a large scale.

[0058] In a configuration where steps 2 and 3 are repeated, the timing of step 2 in which additional (meth)acrylic resin is added again is not particularly limited.

[0059] For example, the timing for adding additional (meth)acrylic resin in step 2 could be the time when an amount of monomer equivalent to the additional (meth)acrylic resin added in the preceding step 2 has been recovered. Specifically, if x parts by weight of additional (meth)acrylic resin were added per 100 parts by weight of the initial (meth)acrylic resin in the nth step 2, then when an amount of monomer roughly equivalent to x parts by weight has been liquefied and recovered, an additional x parts by weight of (meth)acrylic resin can be added again as the (n+1)th step 2.

[0060] Furthermore, from the viewpoint of improving the accuracy of temperature control within the container and making it easier to proceed with decomposition at the desired depolymerization temperature, the timing and amount of the additional (meth)acrylic resin to be added in step 2 are as follows: If the total amount of (meth)acrylic resin in the container at the time of the previous addition of additional (meth)acrylic resin was 100 parts by weight, it is preferable to replenish with an amount of additional (meth)acrylic resin equivalent to the amount decreased by 1 to 20 parts by weight from the total amount of 100 parts by weight. More specifically, if the total amount of (meth)acrylic resin in the container at the time of the previous addition of additional (meth)acrylic resin was 1 kg or more but less than 50 kg, it is preferable to replenish with an amount of additional (meth)acrylic resin equivalent to the amount decreased by 1 to 15 parts by weight from the total amount of 100 parts by weight; if the total amount of (meth)acrylic resin in the container at the time of the previous addition of additional (meth)acrylic resin was 50 kg or more but less than 80 kg, it is preferable to replenish with an amount of additional (meth)acrylic resin equivalent to the amount decreased by 1 to 5 parts by weight from the total amount of 100 parts by weight. It is preferable that; if the total amount of (meth)acrylic resin in the container at the time of the previous addition of additional (meth)acrylic resin was 80 kg or more but less than 400 kg, it is preferable to replenish with an amount of additional (meth)acrylic resin equivalent to the amount of the decrease when the total amount has decreased by 1 to 4 parts by weight from 100 parts by weight; if the total amount of (meth)acrylic resin in the container at the time of the previous addition of additional (meth)acrylic resin was 400 kg or more, it is preferable to replenish with an amount of additional (meth)acrylic resin equivalent to the amount of the decrease when the total amount has decreased by 1 to 3 parts by weight from 100 parts by weight.

[0061] 6. (Meth)acrylic monomer manufacturing apparatus The configuration of the apparatus that can be used in the method for producing (meth)acrylic monomer of the present invention is not particularly limited as long as it has a configuration that enables the carrying out of steps 1 to 3 described above.

[0062] Figure 1 shows an example of an apparatus that can be used in the method for producing (meth)acrylic monomer of the present invention. The apparatus shown in Figure 1 includes: a container 10 that provides a site for the depolymerization reaction; a stirring device 20 for stirring the reaction molten material inside the container 10 with stirring blades 211, 212; a waveguide 30 for injecting microwaves in the R1 direction, which is connected to the inside of the container 10 and sealed with an airtight window 31; a container 40 for containing plastic material to be added to the container 10 (in the R2 direction), which is connected to the inside of the container 10; a thermometer 50 for measuring the temperature of the reaction molten material inside the container 10; a cooling device 60 (specifically a spiral condenser is used, and the chiller setting temperature is 0°C) for cooling the monomer vaporized inside the container 10 via a flexible hose 61, which is connected to the inside of the container 10; and a container 70 for recovering the liquefied monomer cooled by the cooling device 60. In the example shown in Figure 1, the bottom of the container 10 is rounded (a curved, dish-shaped structure that is convex in the depth direction), and the stirring blades 211 and 212 are paddle-shaped on both sides (however, for the stirring blade 211, the surface direction of both paddles is parallel to the axis of rotation, and for the stirring blade 212, the surface directions are perpendicular to each other), and are arranged vertically (up and down in Figure 1) at different heights, and are also arranged perpendicularly when viewed vertically. The lower stirring blade 211 has a shape that follows the shape of the inner wall of the bottom when viewed horizontally, enabling efficient stirring, while the upper stirring blade 211 has an arbitrary shape (for example, a rectangular flat plate shape).

[0063] Another example of an apparatus that can be used in the method for producing (meth)acrylic monomer of the present invention is shown in Figure 2. The apparatus shown in Figure 2 differs from the apparatus shown in Figure 1 in at least the shape of the container 10a and the stirring blade 211a. The container 10a has an inverted cone-shaped bottom with side walls. Due to this bottom shape, compared to the container 10 in the apparatus of Figure 1, the charge accumulates at the bottom (tip) of the container 10a, and the electric field strength is higher in that area, so microwaves can penetrate deeper and a more uniform reaction can be carried out. [Examples]

[0064] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0065] [Example 1] (1) Plastic material Polymethyl methacrylate (hereinafter also referred to as PMMA) was used as the plastic material containing (meth)acrylic resin for depolymerization. This PMMA is a polymer obtained by polymerizing methyl methacrylate (MMA) and methyl acrylate (MA) in a ratio of MMA:MA = 98:2 (by weight), and its weight-average molecular weight was 114,190 (measured by GPC method using tetrahydrofuran as the developing solvent and in terms of standard polystyrene). This plastic material is composed of 100% PMMA. This plastic material was also used as the initial (meth)acrylic resin and as additional (meth)acrylic resin.

[0066] (2) Monomer production apparatus Figure 1 shows a schematic diagram of the apparatus used for monomer production from plastic material. The apparatus includes: a container 10 that provides a site for the depolymerization reaction; a stirring device 20 for stirring the reaction molten material inside the container 10 with stirring blades 211 and 212; a waveguide 30 for injecting microwaves in the R1 direction, which is connected to the inside of the container 10 and sealed with an airtight window 31; a container 40 for containing plastic material to be added to the container 10 (in the R2 direction), which is connected to the inside of the container 10; a thermometer 50 for measuring the temperature of the reaction molten material inside the container 10; a cooling device 60 (specifically a spiral condenser is used, and the chiller setting temperature is 0°C) for cooling the monomer vaporized inside the container 10 via a flexible hose 61, which is connected to the inside of the container 10; and a container 70 for recovering the liquefied monomer cooled by the cooling device 60. The bottom of the container 10 is rounded (a curved dish shape that is convex in the depth direction), and the stirring blades 211 and 212 are paddle-shaped on both sides (however, for the stirring blade 211, the surface direction of both paddles is parallel to the axis of rotation, and for the stirring blade 212, the surface directions are perpendicular to each other), and are set at different heights in the vertical direction (up and down direction in Figure 1), and are set to be perpendicular when viewed in the vertical direction. The paddle of the lower stirring blade 211 has a shape that follows the shape of the inner wall of the bottom when viewed in the horizontal direction, and the paddle of the upper stirring blade 211 has a rectangular flat plate shape.

[0067] (3) Operating Procedure 2.8 kg of PMMA (the first batch of PMMA) was placed into an empty container 10. While stirring with a stirring device 20, microwaves (microwaves with a frequency of 2.45 GHz; the same applies hereafter) generated by a microwave oscillator (not shown) were introduced into the PMMA in container 10 via a waveguide 30, causing the PMMA to melt. Stirring and microwave irradiation were continued while measuring the temperature with a thermometer 50, and the temperature was raised to 340°C. While continuing stirring and microwave irradiation, 0.4 kg of PMMA (the second batch of PMMA) was added to container 10 from container 40. The monomer gas generated in container 10 was cooled and liquefied in a cooling device 60 via a flexible hose 61 and collected in container 70. While continuing stirring and microwave irradiation, the operation of adding approximately 0.4 kg of PMMA (additional PMMA) from container 40 was repeated each time the weight of monomer collected in container 70 increased by approximately 0.4 kg. The monomers recovered in container 70 were taken out (parately) in approximately 0.4 kg increments at the time of adding additional PMMA, analyzed as described in (5) below, and then pooled. The operation of adding additional PMMA was carried out at a frequency of approximately once every 10 minutes and continued until approximately 300 minutes after the melting of the initial PMMA. The total amount of additional PMMA added was 11.2 kg. Throughout the process, stirring was also continued while irradiating with microwaves to maintain a uniform temperature of the reaction molten material in container 10 and to facilitate the microwaves reaching the interior of the reaction molten material. During depolymerization, the effective output of the microwaves was 1.5 to 2.3 kW (average 1.7 kW). Furthermore, since the addition of additional PMMA was carried out at a nearly constant frequency of approximately once every 10 minutes until approximately 300 minutes after the melting of the initial PMMA, good reaction efficiency was maintained throughout the process.

[0068] (4) Analysis of the decomposition rate The decomposition rate (%), i.e., (AR) / R × 100, was calculated when the total weight of the prepared PMMA and added PMMA was A (g), and the weight of the residue in container 10 was R (g). The decomposition rate in this example was 80.4%.

[0069] (5) Analysis of recovered materials The monomer solution collected in container 70 was diluted 100-fold with acetone solvent to a concentration of 1.0% by weight. The resulting diluted solution was subjected to an absolute calibration curve method using a gas chromatograph (GC-FID, Shimadzu GC-2010) to measure the methacrylic monomer (methyl methacrylate; MMA) content in the collected monomer solution. Of the MMA content in the monomer solution collected in container 70, the first monomer solution collected (parately) contained 99.19% by weight. As decomposition progressed, the MMA content in the monomer solution collected (parately) in container 70 decreased, and at a decomposition rate of 80.4%, the monomer solution collected (parately) in container 70 contained 96.35% by weight.

[0070] Furthermore, in GC analysis using the above-mentioned dilution, the peak area value of methyl isobutyrate (MIBA), one of the by-products in the monomer solution recovered in container 70, was read as the MIBA content. Of the MIBA content in the monomer solution recovered in container 70, the MIBA content in the first recovered (parately) monomer solution was 625 in terms of peak area value. As decomposition progressed, the MIBA content in the monomer solution recovered (parately) in container 70 increased, and at a decomposition rate of 80.4%, the MIBA content in the monomer solution recovered (parately) in container 70 was 1,184 in terms of peak area value.

[0071] Furthermore, using 0.40 g of residue obtained by depolymerizing to a decomposition rate of 80.4%, the real part e' and imaginary part e'' of the complex dielectric constant, as well as the microwave power half-end depth derived from them, were calculated under the following measurement conditions. The results are shown in Table 1. In Table 1, the results measured under the same conditions for the initial PMMA are also shown for comparison. The weight-average molecular weight of the residue was 27,263.

[0072] (Measurement conditions) Equipment used: Cavity resonator (Linghe Electronics) Frequency: 915MHz Measurement temperature: 340℃ Quartz tube: f 10 mm × 8 mm N2: 100 mL / min

[0073] [Table 1]

[0074] As shown in Table 1, the residue components produced by depolymerization had a lower imaginary part e'' of the complex dielectric constant compared to the initial PMMA, and it was confirmed that the microwave power half-end depth was deeper. From this, it can be reasonably inferred that, from the point at which any of the additional PMMAs repeatedly added to the depolymerization system were added, the molten material accumulated these residue components with low microwave absorption capacity, reducing the microwave absorption capacity of the molten material itself. This allowed microwaves to penetrate deeper into the molten material, suppressing heterogeneity in the depolymerization system and enabling efficient depolymerization.

[0075] [Example 2] The same materials and apparatus as in Example 1 were used, and the same amount of PMMA was added in the same manner. The heating temperature using microwaves (frequency 2.45 GHz) was 350°C, the effective output of the microwaves during depolymerization was 2.1-2.5 kW (average 2.2 kW), and additional PMMA (0.4 kg per addition) was added approximately once every 8 minutes. This process continued until approximately 250 minutes after the melting of the initial PMMA, and the total amount of additional PMMA added was 12.8 kg. The same procedure as in Example 1 was followed. The decomposition rate and recovered material were analyzed in the same manner as in Example 1. The temperature of the reaction molten material in container 10 was kept uniform, and the microwaves were made more likely to reach the interior of the reaction molten material. In addition, since the addition of additional PMMA was done at a nearly constant frequency of approximately once every 8 minutes until approximately 250 minutes after the melting of the initial PMMA, good reaction efficiency was maintained throughout.

[0076] The decomposition rate in this embodiment was 80.0%. Of the monomer liquids recovered in container 70, the MMA content in the first recovered (parsed) monomer liquid was 98.81% by weight. As decomposition progressed, the MMA content in the monomer liquids recovered (parsed) in container 70 decreased, and at the point of 80.0% decomposition, the MMA content in the monomer liquids recovered (parsed) in container 70 was 95.34% by weight. Furthermore, when all the monomer liquids recovered from the first recovered to the point of 80.0% decomposition were combined, the average MMA content was 97.26% by weight.

[0077] Of the MIBA content in the monomer liquid recovered in container 70, the MIBA content in the first recovered (parsed) monomer liquid was 672. As decomposition progressed, the MIBA content in the monomer liquid recovered (parsed) in container 70 increased, and at a decomposition rate of 80.0%, the MIBA content in the monomer liquid recovered (parsed) in container 70 was 1,475. Furthermore, when all the monomer liquids recovered from the first recovered to the monomer liquids recovered at a decomposition rate of 80.0% were combined, the average MIBA content was 1,063.

[0078] [Example 3] In Example 2, additional PMMA was continuously added from the melting of the initial PMMA until approximately 250 minutes later. Then, depolymerization was continued without adding any further PMMA while stirring and microwave irradiation (frequency 2.45 GHz) was continued until a decomposition rate of 95.4% was achieved. The decomposition rate and recovered material were analyzed in the same manner as in Example 1.

[0079] In this embodiment, the MMA content in the monomer liquid collected (separated) in container 70 at a decomposition rate of 95.4% was 78.28% by weight. Furthermore, when all of the monomer liquids collected at the 95.4% decomposition rate were combined from the initially collected monomer liquid, the average MMA content was 96.25% by weight.

[0080] In this example, the MIBA content in the monomer liquid collected (separated) in container 70 at a decomposition rate of 95.4% was 24,916. Furthermore, when all the monomer liquids collected at a decomposition rate of 95.4% were combined from the initially collected monomer liquid, the average MIBA content was 1778.

[0081] [Example 4] 50 kg of PMMA (the first batch of PMMA), the same material as in Example 1, was placed into an empty container 10. While stirring with a stirring device 20, microwaves (915 MHz frequency) generated by a microwave oscillator (not shown) were introduced into the PMMA in container 10 via a waveguide 30, causing the PMMA to melt. Stirring and microwave irradiation were continued while measuring the temperature with a thermometer 50, and the temperature was raised to 350°C. While continuing stirring and microwave irradiation, 40 kg of PMMA (the second batch of PMMA) was added to container 10 from container 40, bringing the total amount of PMMA to 90 kg (the target amount). The monomer gas generated in container 10 was cooled and liquefied in a cooling device 60 via a flexible hose 61 and collected in container 70. While continuing stirring and microwave irradiation, approximately 3 kg of PMMA (additional PMMA) was added from container 40 each time the weight of PMMA in container 70 decreased by approximately 3 kg. The monomer recovered in container 70 was removed (parately) when it accumulated to approximately 40 kg, and after the analysis described in (5) above, it was pooled. The operation of adding additional PMMA was performed at a frequency of approximately once every 5 minutes and continued until approximately 360 minutes after the melting of the initial PMMA. The total amount of additional PMMA added was 250 kg. Throughout the process, stirring was also continued while microwave irradiation was performed to maintain a uniform temperature of the reaction molten material in container 10 and to facilitate the microwaves reaching the interior of the reaction molten material. During depolymerization, the effective output of the microwaves was 20-24 kW (average 22 kW). Furthermore, from the melting of the initial PMMA to approximately 360 minutes later, additional PMMA was added at a nearly constant frequency of about once every 5 minutes, thus maintaining good reaction efficiency throughout. In addition, the decomposition rate and recovered material were analyzed in the same manner as in Example 1.

[0082] The decomposition rate in this embodiment was 95.1%. Of the monomer liquid recovered in container 70, the MMA content in the first recovered (parsed) monomer liquid was 91.67% by weight. As decomposition progressed, the MMA content in the monomer liquid recovered (parsed) in container 70 decreased, and at the point of a 95.1% decomposition rate, the MMA content in the monomer liquid recovered (parsed) in container 70 was 89.46% by weight.

[0083] In this embodiment, the MIBA content in the monomer liquid recovered in container 70 was 0.06% by weight in the monomer liquid that was first recovered (paritted). As decomposition progressed, the MIBA content in the monomer liquid recovered (paritted) in container 70 increased, and at a decomposition rate of 95.1%, the MIBA content in the monomer liquid recovered (paritted) in container 70 was 0.14% by weight.

[0084] [summary] The conditions and results for Examples 1 to 4 described above are shown in Table 2 below.

[0085] [Table 2]

[0086] As shown in Examples 1-4, a high monomer recovery rate was achieved by depolymerizing PMMA by microwave heating while adding additional PMMA. Furthermore, as shown in Example 3, which includes a depolymerization step without additional PMMA, in contrast to Example 2 in which additional PMMA was constantly added until the end of depolymerization, adding a depolymerization step without additional PMMA resulted in increased byproducts, although PMMA decomposition progressed. In other words, it was found that by performing PMMA depolymerization by microwave heating while adding additional PMMA, the heterogeneity of the PMMA depolymerization system is suppressed, and microwaves can be efficiently delivered to the interior of the system, resulting in suppression of byproduct generation and improvement of the yield of the target product. Furthermore, because the effect of performing the depolymerization step of PMMA by microwave heating while adding additional PMMA is significantly superior, as shown in Comparative Example 3, even when an additional depolymerization step without adding additional PMMA is added, an excellent yield of the target product can be achieved overall (although not as good as in Example 2). Also, as shown in Example 4, even when the reaction scale is drastically increased, the amount of by-products is kept to a very low level relative to the reaction scale, and an excellent yield of the target product can be achieved.

[0087] [Example 5] The same procedure as in Example 1 was followed, except that the same materials were used as in Example 1, the container was a 100 mL container, the amount of PMMA added was 10 g, the amount of additional PMMA added was 1 g per addition, the total number of additions was 100, and the heating temperature for depolymerization by microwave (frequency 915 MHz) was changed in the following order: 350°C (at additions 1 to 60), 375°C (at additions 61 to 90), and 360°C (at additions 91 to 100). The monomer liquid collected (separated) in container 70 at additions 40, 50, and 60; at additions 70, 80, and 90; and at addition 100 was measured to determine the saturation c as follows. * We measured it.

[0088] The monomer solution collected in container 70 was subjected to measurement using a 1 cm quartz cell with a UV-Vis-Infrared spectrophotometer (JASCO Corporation, V-600), and the chromaticity value (L) was determined. * a * b * The chroma c of yellow was measured using the following formula. * Converted to saturation c * The larger the value, the stronger the coloration. The results are shown in Table 3.

[0089]

number

[0090] [Table 3]

[0091] As is clear from Table 3, a significant decrease in saturation was observed at a depolymerization temperature of 360°C compared to 375°C. Furthermore, a decrease in saturation was also observed at 350°C compared to 360°C. In other words, it was observed that the coloration decreased in the order of 375°C, 360°C, and 350°C, indicating that the formation of by-components related to coloration was suppressed in this order.

Claims

1. Step 1 involves irradiating a prepared (meth)acrylic resin with microwaves and mixing it to obtain a molten material containing a component with lower microwave absorption capacity than the prepared (meth)acrylic resin at the depolymerization temperature. Step 2 involves adding and mixing an additional (meth)acrylic resin to the molten material to obtain a molten mixture containing the additional (meth)acrylic resin in the molten material. The process includes step 3, in which the molten mixture is irradiated with microwaves and mixed to obtain a (meth)acrylic monomer. A method for producing (meth)acrylic monomer, wherein steps 2 and 3 are repeated.

2. The manufacturing method according to claim 1, wherein in step 1, the amount of the prepared (meth)acrylic resin prepared is 2.5 kg or more.

3. The manufacturing method according to claim 1, wherein in step 1, the amount of the prepared (meth)acrylic resin prepared is 80 kg or more.

4. The manufacturing method according to claim 1, wherein in step 2, the additional (meth)acrylic resin does not have a thermal history of being subjected to a depolymerization temperature.

5. The manufacturing method according to claim 1, wherein in step 2, the amount of the additional (meth)acrylic resin added is 20 parts by weight or less per 100 parts by weight of the prepared (meth)acrylic resin.

6. The manufacturing method according to claim 1, wherein in step 2, the additional (meth)acrylic resin is added at a timing when the amount of the prepared (meth)acrylic resin decreases from 100 parts by weight to 1 to 20 parts by weight.

7. The manufacturing method according to claim 1, wherein steps 1 to 3 are carried out in a container having a side wall and a bottom shaped like an inverted cone.

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