Method for separating organic zinc catalyst and method for producing aliphatic polycarbonate

Abstract

A method for separating an organic zinc catalyst, the method comprising a step for adding at least one organic acid selected from the group consisting of formic acid and acetic acid to a reaction solution containing a solvent, an organic zinc catalyst, and an aliphatic polycarbonate polymerized in the presence of the organic zinc catalyst.

Description

Method for separating organozinc catalysts and method for producing aliphatic polycarbonates

[0001] This invention relates to a method for separating organozinc catalysts and a method for producing aliphatic polycarbonates.

[0002] Aliphatic polycarbonates possess excellent mechanical strength, heat resistance, and transparency, and are widely used in various industrial fields such as electrical and electronics, automotive, and optics. Aliphatic polycarbonates are produced, for example, by polymerizing alkylene oxides and carbon dioxide in the presence of a polymerization catalyst.

[0003] Metal catalysts, such as organozinc catalysts, are used as polymerization catalysts in the production of aliphatic polycarbonates. When an organozinc catalyst is used as a polymerization catalyst to produce aliphatic polycarbonates, if the organozinc catalyst remains present with the aliphatic polycarbonate after the reaction is complete, depolymerization of the polymerized aliphatic polycarbonate occurs via a back-biting reaction. Therefore, it is necessary to separate and remove the organozinc catalyst after polymerization. Methods for removing the organozinc catalyst include, for example, centrifuging the reaction solution containing the aliphatic polycarbonate and the organozinc catalyst, or filtering it.

[0004] Patent Document 1 discloses a method for separating an organozinc catalyst, which includes the step of introducing an aliphatic polycarbonate resin solution containing an aliphatic polycarbonate resin and an organozinc catalyst into a composite filtration membrane, wherein the composite filtration membrane is a composite material containing a hydroxyl group-containing substance and a polyolefin, and the hydroxyl group-containing substance is coated on one or both sides of the polyolefin.

[0005] Special Publication No. 2021-526579

[0006] However, conventional methods for separating organozinc catalysts, such as centrifugation and filtration, required the use of a large amount of solvent to sufficiently lower the viscosity of the reaction solution and reduce the solid content. In such cases, a step was needed to remove a large amount of solvent after removing the organozinc catalyst from the reaction solution, resulting in high energy consumption and poor productivity. Therefore, there is a need for a method that can separate organozinc catalysts without using a large amount of solvent.

[0007] This invention has been made in view of the above circumstances, and aims to provide a method for separating an organozinc catalyst that can efficiently separate the organozinc catalyst from a reaction solution, and a method for producing an aliphatic polycarbonate using this separation method.

[0008] As a result of diligent research, the present inventors have found that the above problems can be solved by a method using a specific organic acid, and have completed the present invention as follows. That is, the present invention relates to the following [1] to [9]. [1] A method for separating an organozinc catalyst, comprising the step of adding one or more organic acids selected from the group consisting of formic acid and acetic acid to a reaction solution containing a solvent, an organozinc catalyst, and an aliphatic polycarbonate polymerized in the presence of the organozinc catalyst. [2] The method for separating an organozinc catalyst according to [1], wherein the organozinc catalyst is aliphatic zinc dicarboxylate. [3] The method for separating an organozinc catalyst according to [2], wherein the aliphatic zinc dicarboxylate is one or more selected from the group consisting of zinc glutarate and zinc adipate. [4] The method for separating an organozinc catalyst according to any one of [1] to [3], wherein the molar ratio of the organic acid to the organozinc catalyst [organic acid / organozinc catalyst] is 0.01 to 20. [5] The method for separating an organozinc catalyst according to any one of [1] to [4] above, wherein the aliphatic polycarbonate is polybutylene carbonate. [6] The method for separating an organozinc catalyst according to any one of [1] to [5] above, wherein the solvent is one or more selected from the group consisting of ethyl acetate, toluene, chloroform, propylene glycol monomethyl ether acetate, diethylene glycol dimethyl ether, propylene glycol diacetate, butyl carbitol acetate, butylene carbonate, propylene carbonate, and xylene. [7] The method for separating an organozinc catalyst according to any one of [1] to [6] above, further comprising the step of adding the organic acid, followed by the step of precipitating the organozinc catalyst or filtering the organozinc catalyst. [8] The method for separating an organozinc catalyst according to [7] above, wherein the content of the organozinc catalyst in the solution obtained by separating the organozinc catalyst by the step of precipitating the organozinc catalyst or filtering the organozinc catalyst is 1.5% by mass or less. [9] A method for producing an aliphatic polycarbonate, comprising the step of separating an organozinc catalyst from a reaction solution containing a solvent, an organozinc catalyst, and an aliphatic polycarbonate polymerized in the presence of the organozinc catalyst, by the organozinc catalyst separation method described in any of [1] to [8] above.

[0009] According to the present invention, a method for separating an organozinc catalyst from a reaction solution that can efficiently separate the organozinc catalyst, and a method for producing an aliphatic polycarbonate using the separation method can be provided.

[0010] In this specification, the lower and upper limits described in steps for a preferred numerical range can be combined independently. For example, from the description "preferably 10 to 90, more preferably 30 to 60," the "preferred lower limit (10)" and the "more preferred upper limit (60)" can be combined to arrive at "10 to 60."

[0011] Furthermore, the mechanism of action described herein is speculative and does not limit the mechanism by which the present invention achieves its effects.

[0012] [Method for separating organozinc catalysts] The method for separating organozinc catalysts according to this embodiment is a method for separating organozinc catalysts that includes the step of adding one or more organic acids selected from the group consisting of formic acid and acetic acid to a reaction solution containing a solvent, an organozinc catalyst, and an aliphatic polycarbonate polymerized in the presence of the organozinc catalyst.

[0013] Hereinafter, in this specification, "one or more organic acids selected from the group consisting of formic acid and acetic acid" will also be simply referred to as "organic acid." Furthermore, in this specification, "a reaction solution comprising a solvent, an organozinc catalyst, and an aliphatic polycarbonate polymerized in the presence of the organozinc catalyst" will also be simply referred to as "reaction solution." In this specification, when simply referred to as "reaction solution," it means the reaction solution before the addition of the organic acid, and if the solid content concentration of the reaction solution is adjusted before the addition of the organic acid, it means the reaction solution after the adjustment of the solid content concentration. Furthermore, in the following description, the step of adding one or more organic acids selected from the group consisting of formic acid and acetic acid to the reaction solution may be referred to as the "organic acid addition step."

[0014] <Organic Acid Addition Step> The organic acid addition step is a step of adding one or more organic acids selected from the group consisting of formic acid and acetic acid to a reaction solution containing a solvent, an organozinc catalyst, and an aliphatic polycarbonate polymerized in the presence of the organozinc catalyst. In this embodiment, the organozinc catalyst can be efficiently separated from the reaction solution by adding an organic acid to the reaction solution in the organic acid addition step. The reason for this is not clear, but it is presumed to be as follows: In the reaction solution containing an aliphatic polycarbonate polymerized in the presence of the organozinc catalyst, the organozinc catalyst exists in a stably dispersed state in the solvent, and is in a state where sedimentation and aggregation are unlikely to occur. This is thought to be due to the aliphatic polycarbonate being bound to or adsorbed on the surface of the organozinc catalyst, and its surfactant effect. In the separation method of this embodiment, by adding one or more organic acids selected from the group consisting of formic acid and acetic acid, aliphatic polycarbonate is detached from the surface of the organozinc catalyst, improving the sedimentation and cohesiveness of the organozinc catalyst, and thus it is presumed that the organozinc catalyst can be efficiently separated from the reaction solution.

[0015] (Composition of reaction solution) The reaction solution to which the organic acid is added comprises a solvent, an organozinc catalyst, and an aliphatic polycarbonate polymerized in the presence of the organozinc catalyst.

[0016] Examples of solvents include aliphatic hydrocarbons such as pentane, hexane, octane, decane, and cyclohexane; aromatic hydrocarbons such as benzene, toluene, and xylene; halogenated hydrocarbons such as chloromethane, dichloromethane, chloroform, carbon tetrachloride, 1,1-dichloroethane, chlorobenzene, and bromobenzene; carboxylic acid esters such as ethyl acetate, propyl acetate, butyl acetate, and isobutyl acetate; carbonate esters such as dimethyl carbonate, diethyl carbonate, propylene carbonate, and butylene carbonate; lactams such as N-methylpyrrolidone; glycol ethers or glycol ether acetates such as propylene glycol monomethyl ether acetate, diethylene glycol dimethyl ether, propylene glycol diacetate, and butyl carbitol acetate; and the like. Among these, one or more selected from the group consisting of toluene, chloroform, propylene glycol monomethyl ether acetate, diethylene glycol dimethyl ether, propylene glycol diacetate, butyl carbitol acetate, butylene carbonate, propylene carbonate, and xylene are preferred, with toluene being more preferred from the viewpoint of the ease with which the organozinc catalyst precipitates. The solvent contained in the reaction solution may be a single solvent or two or more solvents. The solvent content in the reaction solution is not particularly limited, but for example, it may be 60 to 99% by mass, 70 to 90% by mass, or 75 to 85% by mass of the total amount of the reaction solution.

[0017] Examples of organozinc catalysts include zinc aliphatic dicarboxylates such as zinc adipate and zinc glutarate; Zn ３ (Co[CN] ６ ) ２Examples include zinc-containing complex metal cyanide catalysts (DMC catalysts); and so on. Among these, zinc aliphatic dicarboxylate is preferred from the viewpoint of exhibiting high polymerization activity, one or more selected from the group consisting of zinc glutarate and zinc adipate is more preferred, and zinc glutarate is even more preferred. The organozinc catalyst contained in the reaction solution may be a single type or two or more types. The content of the organozinc catalyst in the reaction solution is not particularly limited, but for example, it may be 0.1 to 5.0% by mass, 1.0 to 4.0% by mass, or 2.0 to 3.0% by mass of the total amount of the reaction solution.

[0018] Aliphatic polycarbonates are aliphatic polycarbonates polymerized in the presence of the organozinc catalyst described above. Examples of aliphatic polycarbonates include those obtained by polymerizing alkylene oxides such as ethylene oxide, propylene oxide, 1,2-butylene oxide, isobutylene oxide, 1-pentene oxide, 2-pentene oxide, 1-hexene oxide, 1-octen oxide, 1-decene oxide, cyclopentene oxide, cyclohexene oxide, and their derivatives, with carbon dioxide. Specific examples of aliphatic polycarbonates include polyethylene carbonate, polypropylene carbonate, and polybutylene carbonate, among which polypropylene carbonate and polybutylene carbonate are preferred, and polybutylene carbonate is more preferred. The aliphatic polycarbonate contained in the reaction solution may be a single type or two or more types. The content of aliphatic polycarbonate in the reaction solution is not particularly limited, but may be, for example, 1 to 40% by mass, 10 to 30% by mass, or 15 to 20% by mass of the total amount of the reaction solution.

[0019] The reaction solution may or may not contain components other than the solvent, organozinc catalyst, and aliphatic polycarbonate (hereinafter also referred to as "other components"). Examples of other components include co-catalysts used with the organozinc catalyst and unreacted monomers. Examples of co-catalysts include bis(triphenylphosphoranylidene)ammonium chloride, 4-dimethylaminopyridine, tetrabutylammonium chloride, tetrabutylammonium bromide, triphenylphosphine, 1,5,7-triazabicyclo[4.4.0]deca-5-ene, and 1,4-diazabicyclo[2.2.2]octane. One type of co-catalyst may be used alone, or two or more types may be used in combination.

[0020] (Method of adding organic acid) The method of adding organic acid is not particularly limited; the organic acid may be added to the reaction solution all at once or sequentially. The organic acid may also be added directly to the reaction solution or diluted with a solvent before addition. The temperature of the reaction solution when adding the organic acid is not particularly limited, but may be, for example, 10 to 80°C, 15 to 60°C, or 20 to 30°C. After adding the organic acid, it is preferable to stir the reaction solution as needed. Stirring of the reaction solution can be done using a known stirrer.

[0021] (Amount of organic acid added) The molar ratio of organic acid to organozinc catalyst [organic acid / organozinc catalyst] is preferably 0.01 to 20, more preferably 0.02 to 15, even more preferably 0.04 to 10, even more preferably 0.06 to 5, even more preferably 0.08 to 3, even more preferably 0.10 to 1, even more preferably 0.12 to 0.5, and even more preferably 0.14 to 0.25. When the above molar ratio [organic acid / organozinc catalyst] is above the lower limit, the organozinc catalyst tends to be easier to separate. Also, when the molar ratio [organic acid / organozinc catalyst] is below the upper limit, it tends to be easier to suppress the use of more organic acid than necessary.

[0022] <Step of settling the organozinc catalyst or filtering the organozinc catalyst> The separation method of this embodiment preferably includes, after the step of adding the organic acid, a step of settling the organozinc catalyst or a step of filtering the organozinc catalyst.

[0023] In the process of settling the organozinc catalyst, methods for settling the organozinc catalyst include, for example, centrifugation of the reaction solution and standing of the reaction solution. For example, the conditions for centrifugation can be set to a rotation speed of 100 to 10,000 rpm and a centrifugation time of 30 seconds to 60 minutes. After settling the organozinc catalyst, the supernatant liquid can be collected to separate the settled organozinc catalyst from the aliphatic polycarbonate contained in the supernatant liquid.

[0024] The process of filtering the organozinc catalyst allows for the separation of the organozinc catalyst residue from the aliphatic polycarbonate contained in the filtrate by filtering the reaction solution. Conventional known methods can be used to filter the organozinc catalyst.

[0025] In the step of precipitating the organozinc catalyst or filtering the organozinc catalyst, a solvent may or may not be added to the reaction solution. As described above, the organozinc catalyst separation method of this embodiment can efficiently separate the organozinc catalyst from the reaction solution, so the organozinc catalyst can be easily precipitated or filtered without adding a large amount of solvent as in the conventional technology. Therefore, even when a solvent is added to the reaction solution when performing the step of precipitating the organozinc catalyst or filtering the organozinc catalyst, the amount of solvent added can be kept low. From this viewpoint, in the step of precipitating the organozinc catalyst or filtering the organozinc catalyst, the solvent content in the reaction solution may be, for example, 90% by mass or less, 85% by mass or less, or 80% by mass or less. Also, in the step of precipitating the organozinc catalyst or filtering the organozinc catalyst, the solvent content in the reaction solution may be 10% by mass or more, 20% by mass or more, or 30% by mass or more.

[0026] The content of the organozinc catalyst in the solution obtained by separating the organozinc catalyst by the steps of settling the organozinc catalyst or filtering the organozinc catalyst is preferably 1.5% by mass or less, more preferably 1.0% by mass or less, even more preferably 0.8% by mass or less, even more preferably 0.5% by mass or less, even more preferably 0.3% by mass or less, even more preferably 0.1% by mass or less, even more preferably 0.05% by mass or less, and even more preferably 0% by mass. For example, the solution obtained by separating the organozinc catalyst by the step of settling the organozinc catalyst is the supernatant, and the solution obtained by separating the organozinc catalyst by the step of filtering the organozinc catalyst is the filtrate. The content of the organozinc catalyst in the solution obtained by separating the organozinc catalyst can be measured by the method described in the examples.

[0027] [Method for producing aliphatic polycarbonate] The method for producing aliphatic polycarbonate according to this embodiment is a method for producing aliphatic polycarbonate that includes the step of separating the organozinc catalyst from a reaction solution containing a solvent, an organozinc catalyst, and aliphatic polycarbonate polymerized in the presence of the organozinc catalyst, using the method for separating the organozinc catalyst according to this embodiment.

[0028] The method for producing aliphatic polycarbonate according to this embodiment may include a step of separating the organozinc catalyst by the organozinc catalyst separation method of this embodiment, but it is preferable to include the following steps 1 and 2. Step 1: A step of polymerizing alkylene oxide and carbon dioxide in a solvent in the presence of an organozinc catalyst. Step 2: A step of separating the organozinc catalyst by the organozinc catalyst separation method of this embodiment.

[0029] <Step 1> Step 1 involves mixing alkylene oxide with carbon dioxide (CO2). ２ This step involves polymerizing the alkylene oxide and the organic zinc catalyst in a solvent using an organozinc catalyst as the polymerization catalyst. The alkylene oxide, solvent, and organozinc catalyst used in step 1 are described in the description of the reaction solution configuration to which the organozinc catalyst separation method of this embodiment is applied.

[0030] The amount of the organozinc catalyst used as the polymerization catalyst is preferably 0.001 to 50 parts by mass, more preferably 0.01 to 45 parts by mass, still more preferably 0.1 to 40 parts by mass, and even more preferably 1 to 35 parts by mass, per 100 parts by mass of the alkylene oxide used.

[0031] The method for carrying out the polymerization reaction is not particularly limited as long as the target product can be obtained. For example, a method may be mentioned in which alkylene oxide, an organozinc catalyst, a solvent, and optionally used a cocatalyst or the like are charged into an autoclave, after mixing, carbon dioxide is injected under pressure into the obtained mixture to allow the reaction to proceed. The amount of the solvent used is preferably 50 to 2,000 parts by mass, more preferably 60 to 1,500 parts by mass, still more preferably 70 to 1,000 parts by mass, and even more preferably 80 to 500 parts by mass, per 100 parts by mass of the alkylene oxide used.

[0032] The pressure at the time of injecting carbon dioxide in the polymerization reaction is preferably 0.1 to 20 MPa, more preferably 0.1 to 10 MPa, and still more preferably 0.1 to 5 MPa. When the pressure at the time of injecting carbon dioxide is not less than the above lower limit, the polymerization reaction proceeds more easily. Further, when the pressure at the time of injecting carbon dioxide is not more than the above upper limit, excessive use of carbon dioxide is suppressed, and economic efficiency is improved.

[0033] The reaction temperature during the polymerization reaction is preferably 20 to 100°C, more preferably 25 to 80°C, from the viewpoints of reaction rate and suppression of side reactions. The reaction time of the polymerization reaction may be appropriately adjusted according to the reaction temperature, and is preferably 2 to 40 hours.

[0034] <Step 2> Step 2 is a step of separating the organozinc catalyst by the method for separating an organozinc catalyst of the present embodiment. The description of the method for separating an organozinc catalyst of the present embodiment is as described above.

[0035] <Other Steps> The method for producing an aliphatic polycarbonate of the present embodiment may include a step of purifying the aliphatic polycarbonate after performing Step 2. The step of purifying the aliphatic polycarbonate is not particularly limited, and known purification methods such as washing, distillation, and drying can be applied.

[0036] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0037] [Synthesis of Metal Catalysts] Production Example 1 (Synthesis of Zinc Glutarate) 2.0 g of zinc oxide and 3.12 g of glutaric acid were placed in a 50 mL cylindrical glass container (outer diameter 27 mm) with a lid in air, and the container was sealed with the lid without adding any solvent or grinding media. The cylindrical glass container was placed on the rotating roller of a mix rotor (manufactured by AS ONE Corporation, product name "MIX ROTOR VMR-5R", with a rotating roller that has a seesaw motion function) which was set on a horizontal stand, and the reaction was carried out by rotating it for 24 hours at room temperature (23°C) under the conditions of a set rotation speed of 100 rpm and a container rotation speed of 119 rpm. The rotation axis of the cylindrical glass container is perpendicular to the bottom surface of the cylindrical glass container and passes through the center of gravity of the bottom surface, and the angle of the rotation axis (maximum tilt angle of the seesaw motion) is ±2.5° with respect to the horizontal. The resulting white powder was dried in a vacuum dryer at 120°C for 5 hours to obtain zinc glutarate.

[0038] [Synthesis of Aliphatic Polycarbonates] Production Example 2 100 parts by mass of 1,2-butylene oxide as a raw material monomer and 20 parts by mass of zinc glutarate prepared in Production Example 1 as a polymerization catalyst were mixed with 257 parts by mass of toluene to obtain a mixture. Next, the system of a 4 L autoclave equipped with a stirrer, gas inlet pipe and thermometer was pre-filled with a nitrogen atmosphere, and the above mixture was charged in. Subsequently, while stirring the mixture in the autoclave, carbon dioxide gas was filled into the reaction system until the pressure reached 4 MPa. After that, the temperature was raised to 70°C, and the polymerization reaction was carried out for 4 hours while replenishing the carbon dioxide consumed by the reaction. After the reaction was completed, the autoclave was cooled and depressurized to obtain a post-polymerization reaction solution containing 32.3% by mass of polybutylene carbonate as a polymerization product, 4.6% by mass of zinc glutarate as a polymerization catalyst, and 63.1% by mass of toluene as a solvent and unreacted raw materials. This was further diluted with toluene to obtain a reaction solution containing 16.2% by mass of polybutylene carbonate, 2.3% by mass of zinc glutarate, and 81.5% by mass of toluene and unreacted raw materials.

[0039] [Catalyst Separation Step] Examples 1 to 8, Comparative Example 2 An organic acid of the type and in the amount shown in Table 1 was added to the reaction solution obtained in Production Example 2, and the mixture was stirred for 20 seconds with a vortex stirrer. Subsequently, centrifugation was performed at 3000 rpm for 10 minutes using a centrifuge (manufactured by Kokusan Co., Ltd., product name "Small Desktop Centrifuge H-19F") to separate the supernatant and the precipitate.

[0040] Comparative Example 1 In Example 1, a supernatant and a precipitate were separated in the same manner as in Example 1, except that no organic acid was added.

[0041] [Method for Measuring Content of Organozinc Catalyst in Supernatant] Using the supernatant obtained in each Example and Comparative Example as a measurement sample, the sample was heated in air in an oven at 270°C for 2 hours to volatilize volatile components such as the solvent and unreacted monomers in the measurement sample, and to thermally decompose polybutylene carbonate, which is a polymerization product. Let the weight of the measurement sample before the above heating be W １ , and let the weight of the residue after the above heating be W ２ , then the content C １ (mass%) of the organozinc catalyst in the supernatant was calculated by the following formula (1). C １ =W ２ ×100 / W １ (1)

[0042] [Method for Measuring Residual Ratio of Organozinc Catalyst] The residual ratio of the organozinc catalyst after the catalyst separation step was measured by the following method. (1) Quantification of each component in the reaction solution before the catalyst separation step The reaction solution obtained in Production Example 2 was analyzed by nuclear magnetic resonance spectroscopy ( １ H-NMR, Biospin Avance 500, manufactured by Bruker) using CDCl ３ (containing 0.03 vol% tetramethylsilane) as a solvent, and the obtained １In the 1H-NMR spectrum, the molar ratios of the peaks originating from the unreacted monomer (1,2-butylene oxide), the polymer (polybutylene carbonate), and the polymer decomposition products were calculated from the integrated values ​​of the peaks originating from the unreacted monomer (1,2-butylene oxide), the polymer, and the polymer decomposition products in the reaction solution. Furthermore, the weights of the unreacted monomer, polymer, and polymer decomposition products in the reaction solution were calculated from the amount (number of moles) of 1,2-butylene oxide charged as the raw material monomer and the molar ratios calculated above. (2) Calculation of the residual ratio of the organozinc catalyst Next, the concentration of zinc glutarate in the reaction solution before the catalyst separation step C was calculated from the weights of each component in the reaction solution calculated above and the weights of zinc glutarate and solvent charged at the start of the reaction using the following formula (2). ０ C was calculated. ０ = (Weight of zinc glutarate used in the reaction) × 100 / (Weight of zinc glutarate used in the reaction + Weight of solvent used in the reaction + Weight of unreacted monomer in the reaction solution + Weight of polymer in the reaction solution + Weight of polymer decomposition products in the reaction solution + Weight of toluene added as diluent) (2) 　 The zinc glutarate concentration C in the reaction solution before the catalyst separation step, calculated using the above formula (2) ０ , and the zinc glutarate concentration C in the supernatant liquid calculated by formula (1) above. １ Therefore, the residual ratio of the organozinc catalyst was calculated using the following formula (3): Residual ratio of organozinc catalyst (%) = C １ ×100 / C ０ (3)

[0043]

[0044] As shown in Table 1, in Examples 1 to 8, which are methods for separating the organozinc catalyst according to this embodiment, the residual ratio of the organozinc catalyst in the supernatant is low, indicating that the organozinc catalyst can be efficiently separated from the reaction solution.

Claims

1. A method for separating an organozinc catalyst, comprising the step of adding one or more organic acids selected from the group consisting of formic acid and acetic acid to a reaction solution containing a solvent, an organozinc catalyst, and an aliphatic polycarbonate polymerized in the presence of the organozinc catalyst.

2. The method for separating an organozinc catalyst according to claim 1, wherein the organozinc catalyst is aliphatic dicarboxylate zinc.

3. The method for separating an organozinc catalyst according to claim 2, wherein the aliphatic dicarboxylate zinc is one or more selected from the group consisting of zinc glutarate and zinc adipate.

4. The method for separating an organozinc catalyst according to any one of claims 1 to 3, wherein the molar ratio of the organic acid to the organozinc catalyst [organic acid / organozinc catalyst] is 0.01 to 20.

5. The method for separating organozinc catalysts according to any one of claims 1 to 3, wherein the aliphatic polycarbonate is polybutylene carbonate.

6. The method for separating an organozinc catalyst according to any one of claims 1 to 3, wherein the solvent is one or more selected from the group consisting of ethyl acetate, toluene, chloroform, propylene glycol monomethyl ether acetate, diethylene glycol dimethyl ether, propylene glycol diacetate, butyl carbitol acetate, butylene carbonate, propylene carbonate, and xylene.

7. A method for separating an organozinc catalyst according to any one of claims 1 to 3, further comprising the step of precipitating the organozinc catalyst or filtering the organozinc catalyst after the step of adding the organic acid.

8. The method for separating an organozinc catalyst according to claim 7, wherein the content of the organozinc catalyst in the solution obtained by separating the organozinc catalyst by a step of settling the organozinc catalyst or a step of filtering the organozinc catalyst is 1.5% by mass or less.

9. A method for producing an aliphatic polycarbonate, comprising the step of separating an organozinc catalyst from a reaction solution containing a solvent, an organozinc catalyst, and an aliphatic polycarbonate polymerized in the presence of the organozinc catalyst, by the method for separating an organozinc catalyst described in any one of claims 1 to 3.

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