Method for producing oxymethylene polymer

Abstract

To provide a production method of an oxymethylene polymer capable of producing an oxymethylene polymer in a polymerization vessel continuously and stably.SOLUTION: A method for continuously producing an oxymethylene polymer includes an introduction step of introducing a raw material and a liquid containing a catalyst into a polymerization vessel using a double pipe composed of an inner pipe and an outer pipe, and a reaction step of reacting the raw material and the catalyst in the polymerization vessel to produce an oxymethylene polymer. In the introduction step, the raw material flows between the inner pipe and the outer pipe of the double pipe, whereas the liquid containing the catalyst flows inside the inner pipe of the double pipe. The inner pipe has an appearance of the tip part getting thinner toward the tip end.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing an oxymethylene polymer. [Background technology]

[0002] Oxymethylene polymers have the advantage of being excellent in processability and productivity, and therefore can be efficiently produced into products or parts of desired shapes by molding methods such as melt injection molding and melt extrusion molding. Taking advantage of these advantages, oxymethylene polymers are widely used in the fields of electric and electronic materials, automobiles, and various other industrial materials, food packaging, and parts materials. In manufacturing products for these applications, there is a demand for a method for producing an oxymethylene polymer, which includes a polymerization step in which raw materials and a polymerization catalyst are mixed to continuously and stably obtain an oxymethylene polymer.

[0003] Among the methods for obtaining oxymethylene polymers, various methods have been proposed in which raw materials and a polymerization catalyst are mixed and then fed into a polymerization vessel. For example, there is a method in which the angle of introduction of a polymerization catalyst solution pipe into a monomer and comonomer mixed raw material liquid pipe is changed to enable continuous operation without causing a supply failure to the polymerization reactor due to blockage or narrowing of the pipe by the polymer (see, for example, Patent Document 1), and a method in which the comonomer and polymerization catalyst are mixed in advance, and then in the step of mixing them with the monomer, the comonomer and polymerization catalyst are brought into contact with each other and mixed while being supplied in the same direction (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4092545 [Patent Document 2] Patent No. 3208377 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above Patent Document 1, the polymerization reaction proceeds by mixing the raw materials and the catalyst, and the time required for the raw materials and the catalyst to reach the polymerization vessel from the mixing contact section is specified. However, fluctuations in the supply amounts of the raw materials and the catalyst liquid and fluctuations in the pressure in the polymerization vessel may lengthen the residence time at the contact section, causing the polymer to adhere to the tip of the piping, which may eventually lead to the stop of polymerization due to blockage of the supply section.

[0006] In the above Patent Document 2, the linear velocity of the mixed flow and the mixing time are specified when the catalyst liquid and the comonomer are mixed in advance to prepare a mixture, and then mixed with the raw material trioxane. However, it cannot be denied that there is a possibility that polymerized solids may adhere to the mixture and cause the supply pipe to become clogged when the catalyst liquid, the comonomer, and the trioxane are mixed.

[0007] Therefore, an object of the present invention is to provide a method for producing an oxymethylene polymer, which can continuously and stably produce an oxymethylene polymer in a polymerization vessel. [Means for solving the problem]

[0008] As a result of intensive research by the present inventors to solve the above-mentioned problems of the conventional technology, they found that in the piping for supplying the raw materials to the polymerization vessel and the liquid containing a catalyst (hereinafter also referred to as "catalyst liquid"), polymerization is inhibited by adhesion of polymerized solid matter to the piping caused by retention of a mixed liquid of the raw materials and the catalyst liquid near the piping when the two come into contact.The present inventors then found that the above-mentioned problems can be solved by supplying the raw materials and the catalyst liquid to the polymerization vessel using a double pipe having a specific structure, and arrived at the present invention.

[0009] That is, this embodiment is as follows. [1] A method for continuously producing an oxymethylene polymer, comprising the steps of: an introduction step of introducing the raw material and the liquid containing the catalyst into the polymerization vessel using a double pipe composed of an inner pipe and an outer pipe; a reaction step of reacting the raw material with the catalyst in the polymerization vessel to produce an oxymethylene polymer; having In the introduction step, The raw material passes between the inner tube and the outer tube of the double tube, a liquid containing the catalyst passes through an inside of the inner tube of the double tube; The inner tube has a shape that tapers toward its tip. the law of nature , a ratio of the linear velocity of the raw material divided by the linear velocity of the liquid containing the catalyst in a range of 0.4 to 8.9, the linear velocity being in units of m / s, in a portion where the raw material and the catalyst flow at a constant linear velocity immediately before contacting each other, and where a cross-sectional area of ​​the space inside the inner tube and a cross-sectional area of ​​the space between the inner tube and the outer tube are both constant; In the cross section of the inner pipe, a taper angle formed by a line forming the inner surface of the inner pipe and a straight line connecting a point where the wall thickness of the inner pipe starts to decrease and a point where the wall thickness of the inner pipe is at a minimum is in a range of 10 to 70°. Characterized in that A method for producing an oxymethylene polymer. [2] The method for producing an oxymethylene polymer according to [1], wherein the raw material is contacted with the liquid containing the catalyst and introduced into a polymerization vessel at the same time. [3] The method for producing an oxymethylene polymer according to [1] or [2], wherein the raw material is trioxane. [4] The method for producing an oxymethylene polymer according to any one of [1] to [3], wherein the catalyst is a cationic polymerization catalyst. 。 [5 ] The taper angle is in the range of 10 to 30 degrees. [1] - [4] A method for producing the oxymethylene polymer described in claim 1. Effect of the Invention

[0010] According to the process for producing an oxymethylene polymer of the present invention, an oxymethylene polymer can be obtained continuously and stably. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view of a double pipe used in this embodiment, taken along a plane along its axis. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment for carrying out the present invention (hereinafter, referred to as "the present embodiment") will be described in detail. The present embodiment is an example for explaining the present invention, and the present invention is not limited to the following content. The present invention can be carried out in various modifications within the scope of its gist.

[0013] (Method of producing oxymethylene polymer) The method for producing an oxymethylene polymer of this embodiment includes an introduction step of introducing raw materials and a liquid containing a catalyst into a polymerization vessel using a double tube, and a reaction step of reacting the raw materials and the catalyst in the polymerization vessel to produce an oxymethylene polymer, and is characterized in that in the introduction step, the raw materials pass through the outer flow part (between the inner tube and the outer tube) of the double tube, the catalyst liquid passes through the inner flow part (inside the inner tube) of the double tube, and the inner tube has a shape that appears to taper toward the tip at its tip. Note that the tip does not strictly refer to only the tip of the tube, but includes a reasonable range for grasping the shape of the tube, as shown in Figure 1.

[0014] [Introduction process] The method for producing an oxymethylene polymer of the present embodiment includes an introduction step of supplying the raw material and a liquid containing a catalyst (catalyst liquid) to a polymerization reactor through a double pipe consisting of an inner pipe and an outer pipe. In the introduction step, optional components such as a molecular weight regulator described later may be supplied to the polymerization reactor together with the raw material and the catalyst liquid through the double pipe. In this step, it is preferable that the raw materials come into contact with the catalyst liquid and are introduced into the polymerization vessel at the same time. Here, "the raw materials come into contact with the catalyst liquid and are introduced into the polymerization vessel at the same time" means that the time difference between the time when at least a part of the raw materials come into contact with at least a part of the catalyst liquid and the time when the raw materials are introduced into the polymerization vessel is less than 0.1 seconds. Here, "the time when the raw materials are introduced into the polymerization vessel" means the time when the mixed liquid formed by the contact of the raw materials with the catalyst liquid is located inside the polymerization vessel with respect to the opening of the polymerization vessel (which may be the tip of a double tube).

[0015] <Double pipe> FIG. 1 is a cross-sectional view of a double pipe used in this embodiment taken along a plane along its axis. The double pipe used in this embodiment is a pipe for supplying raw materials and catalyst liquid into a polymerization vessel, and is installed at the front end, upper side, of the polymerization vessel. The double pipe has a structure in which raw materials flow between its inner pipe and outer pipe, and catalyst liquid flows inside the inner pipe. Here, the space inside the inner pipe forms the double pipe inner liquid part, and the space between the inner pipe and outer pipe forms the double pipe outer liquid part (see FIG. 1). The cross-sectional area of ​​the double pipe inner liquid part may be constant over a predetermined extension length of the tip of the inner pipe, and the cross-sectional area of ​​the double pipe outer liquid part may be constant over a predetermined extension length of the tip of the inner pipe (see FIG. 1).

[0016] Specifically, in the case of homopolymers, for example, trioxane and an optional molecular weight modifier are mixed in advance as raw materials, while in the case of copolymers, for example, trioxane and a cyclic ether and / or cyclic formal as comonomers and an optional molecular weight modifier are mixed in advance as raw materials, and the mixture is passed through the outer liquid section of the double tube, while a catalyst solution, which is a mixture of a catalyst and a diluent solvent, is passed through the inner liquid section.

[0017] At least a part of the tip of the double tube, for example, a part where the raw material flows at a constant linear velocity just before contact with the catalytic liquid (a part where the cross-sectional areas of the flow part inside the double tube and the flow part outside the double tube are both constant), the ratio of the linear velocity of the raw material divided by the linear velocity of the catalytic liquid (the ratio of the linear velocity of the raw material to the linear velocity of the catalytic liquid) is in the range of 0.4 to 8.9, and more preferably 0.9 to 8.4. Here, the unit of linear velocity is m / s.

[0018] As shown in FIG. 1, the inner pipe of the double pipe has a tapered shape at its tip. The cross-sectional area of ​​the inner liquid flow part of the double pipe at the tip may be the same as the cross-sectional area of ​​the inner liquid flow part of the double pipe at the non-tip. That is, the wall thickness of the inner pipe of the double pipe at the tip gradually decreases toward the tip. In the cross section of the inner pipe (see FIG. 1), a line forming the inner surface of the inner pipe and a straight line connecting the point where the thickness of the inner pipe wall starts to decrease and the point where the thickness of the inner pipe wall is at its minimum intersect at an angle (taper angle). In the cross section of the inner pipe, the end of the line forming the inner surface of the inner pipe is located further outward in the axial direction of the double pipe than the end of the line forming the outer surface of the inner pipe. The taper angle is preferably 10 to 70°, more preferably 10 to 30°, and even more preferably 10 to 20°. The taper angle may be the smaller angle between a line forming the inner surface of the inner tube and a straight line connecting the point where the wall thickness of the inner tube starts to decrease and the point where the wall thickness of the inner tube is at its minimum.

[0019] In this embodiment, since the range of the ratio of the linear velocity of the raw material divided by the linear velocity of the catalyst liquid and the tip angle of the inner tube are within the above-mentioned ranges, stable continuous polymerization can be carried out without the mixed liquid of the raw material and the catalyst liquid remaining at the tip of the double tube.

[0020] <Raw material> The source material used in this embodiment may be, for example, trioxane. Trioxane can be produced by reacting formaldehyde in the presence of an acidic catalyst. The raw material usually contains water and formic acid as impurities. These impurities act as chain transfer agents, and the polymer end groups of the oxymethylene polymer obtained by polymerization may become thermally unstable, making it difficult to obtain an oxymethylene polymer with high thermal stability. Therefore, it is preferable to purify and remove these impurities to a certain concentration before the start of polymerization. The total content of these impurities in the raw material is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, and even more preferably 30 mass ppm or less, based on the mass of the raw material.

[0021] <Raw material for copolymer> In the present embodiment, when a copolymer of an oxymethylene polymer is produced, a cyclic ether and / or a cyclic formal can be used as a comonomer component added to the raw material. Specifically, the cyclic ether and / or the cyclic formal can be ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxetane, 1,3-dioxolane, ethylene glycol formal, propylene glycol formal, diethylene glycol formal, triethylene glycol formal, 1,4-butanediol formal, 1,5-pentanediol formal, 1,6-hexanediol formal, etc. These can be used alone or in combination of two or more kinds.

[0022] The amount of cyclic ether and / or cyclic formal added during polymerization is preferably in the range of 0.01 to 0.2 mol, more preferably in the range of 0.01 to 0.15 mol, further preferably in the range of 0.01 to 0.1 mol, and particularly preferably in the range of 0.01 to 0.05 mol, per mol of the raw material. If the amount of cyclic ether and / or cyclic formal added is within the above range, the polymerization rate is relatively fast, the polymerization yield is sufficiently high, and the oxymethylene polymer tends to be stably produced.

[0023] <Catalyst> The catalyst used in the production method of the present embodiment is not particularly limited as long as it is a catalyst that can stably produce an oxymethylene polymer, but is preferably a cationic polymerization catalyst. Examples of cationic polymerization catalysts include Lewis acids, protonic acids, and their esters or anhydrides. Examples of Lewis acids include boric acid, tin, titanium, phosphorus, arsenic, and antimonides, and in particular, boron trifluoride, boron trifluoride hydrates, and coordination complexes of organic compounds containing oxygen atoms or sulfur atoms and boron trifluoride are preferred. Examples of protonic acids and their esters or anhydrides include perchloric acid, trifluoromethanesulfonic acid, perchloric acid tertiary butyl ester, acetyl perchlorate, trimethyloxonium hexafluorophosphate, heteropolyacids, isopolyacids, acid salts of heteropolyacids, and acid salts of isopolyacids, and in particular, heteropolyacids are preferred. These may be used alone or in combination of two or more.

[0024] The amount of polymerization catalyst added is 1×10 per 1 mol of raw material from the viewpoint of stable continuous polymerization. -9 ~1×10 -2 mol range is preferred, more preferably 2×10 -9 ~1×10 -2 mol, more preferably in the range of 5×10 -9 ~1×10 -3 The range is mol.

[0025] <Catalyst liquid> The catalyst solution used in the production method of this embodiment is prepared by diluting the above-mentioned catalyst species as a polymerization catalyst with an inactive dilution solvent that does not adversely affect the polymerization reaction. The dilution solvent for diluting the polymerization catalyst is preferably a hydrocarbon compound having no hydroxyl group. Specific examples of the hydrocarbon compound include aromatic hydrocarbon compounds such as benzene, toluene, and xylene; aliphatic hydrocarbon compounds such as n-hexane, n-heptane, and cyclohexane; ether compounds such as diethyl ether, dibutyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol diethyl ether, and 1,4-dioxane; and the like, which can be appropriately selected according to the solubility of the cationic polymerization catalyst used. The above-mentioned hydrocarbon compounds having no hydroxyl group may be used alone or in combination of two or more kinds. By using such a hydrocarbon compound having no hydroxyl group as a dilution solvent, the molecular weight of the oxymethylene polymer can be easily controlled.

[0026] The amount of diluent added during polymerization was 0.1×10 per 1 mol of raw material. -3 The range of 0.2 mol or less is preferable, and 0.2×10 -3 ~0.1 mol, more preferably 0.5 × 10 -3 When the amount of the dilution solvent added is within the above range, it is preferable in that the polymerization reaction is not inhibited and the oxymethylene polymer can be obtained in a higher yield.

[0027] <Molecular weight regulator> In the present embodiment, a low molecular weight acetal compound may be used as the molecular weight regulator. The low molecular weight acetal compound functions as a chain transfer agent during polymerization of the raw material with the cyclic ether and / or cyclic formal, and is an acetal compound having a molecular weight of 200 or less, preferably 60 to 170. Specifically, suitable examples of the molecular weight regulator include methylal, methoxymethylal, dimethoxymethylal, and trimethoxymethylal. These may be used alone or in combination of two or more. The amount of the low molecular weight acetal compound added during polymerization is 0.1×10 per 1 mol of the raw material from the viewpoint of controlling the molecular weight of the polyacetal copolymer within a suitable range. -4 ~0.6×10 -2 It is preferred that the molar ratio is in the range of 1:1.

[0028] [Reaction process] The production method of this embodiment includes a reaction step in which raw materials are reacted with a catalyst in a polymerization vessel to produce an oxymethylene polymer. The oxymethylene polymer is polymerized by cationic polymerization in a bulk method. The shape (structure) of the polymerization reactor used is not particularly limited, but generally, a two-shaft paddle-type or screw-type stirring and mixing polymerization reactor capable of passing a heat transfer medium through a jacket can be suitably used. The polymerization reaction temperature is preferably kept in the range of 63 to 135° C. The polymerization reaction temperature is more preferably in the range of 70 to 120° C., and further preferably in the range of 70 to 100° C. The residence (reaction) time in the polymerization reactor is preferably from 0.1 to 30 minutes, more preferably from 0.1 to 25 minutes, and further preferably from 0.1 to 20 minutes.

[0029] By adjusting the polymerization reaction temperature and the residence time in the polymerization reactor within the above-mentioned ranges, respectively, the thermal decomposition of the oxymethylene polymer can be more effectively suppressed, and a thermally more stable oxymethylene polymer can be produced.

[0030] <Washing, filtration, and drying after polymerization> After the polymerization, for example, the polymerization catalyst can be washed and removed from the obtained oxymethylene polymer. As a method for washing and removing the polymerization catalyst, a method proposed in the past can be used. For example, the oxymethylene polymer discharged from the polymerization reactor is put into an aqueous solution containing only water or at least one deactivator such as amines such as ammonia, triethylamine, and tri-n-butylamine, hydroxides of alkali metals or alkaline earth metals, inorganic salts, and organic acid salts, and the polymerization catalyst can be washed and removed while continuously stirring in a slurry state at room temperature to 100°C or less for several minutes to several hours. When the oxymethylene polymer is in a large lump form, it is preferable to crush the oxymethylene polymer and make it finer to make it easier to wash and remove it, from the viewpoint of increasing the efficiency of washing and removing the polymerization catalyst. After washing and removing the polymerization catalyst, the target oxymethylene polymer can be obtained by filtering with a centrifuge or the like and drying under a nitrogen environment or the like. EXAMPLES

[0031] The following are specific examples. and reference examples The present embodiment will be described in detail with reference to the following examples and comparative examples, but the present embodiment is not limited to the following examples as long as it does not depart from the gist of the present embodiment.

[0032] In addition, in the embodiment , reference example The evaluation methods and raw materials used in the comparative examples are as follows.

[0033] [Driving stability evaluation method] The raw materials and catalyst liquid were supplied to a polymerization reactor through a double-walled pipe and polymerized continuously. The continuous operation time until pressure fluctuations in the raw material supply section and catalyst liquid supply section due to blockage at the tip of the double-walled pipe reached 50% or more of the steady-state value was evaluated.

[0034] [Example 1] As a polymerization reactor, a 2-shaft paddle type continuous polymerization reactor (manufactured by Kurimoto Iron Works Co., Ltd., diameter 2B, L / D=14.8) rotating in the same direction and set at 80°C was used. In order to prevent oxygen from being mixed in, 60 L of nitrogen was flowed per hour from the vicinity of the feed port of the polymerization reactor. A double tube with a tapered tip of the inner tube was used, and the taper angle θ was as described below. Then, trioxane was supplied to the polymerization reactor at 4000 g / hr through the outer liquid part of the double tube. In addition, 0.045 mol (148.0 g / hr) of 1,3-dioxolane as a cyclic ether and / or cyclic formal was fed to the polymerization reactor per mol of trioxane. Thereafter, iron trichloride as a polymerization catalyst was diluted at an appropriate ratio with 1,4-dioxane as a dilution solvent, and the obtained polymerization catalyst liquid was supplied to the polymerization reactor through the inner flow part of the double tube to start polymerization. The time required for the mixture of trioxane and 1,3-dioxolane to come into contact with the 1,4-dioxane solution of iron trichloride and for the mixture to be located inside the opening of the polymerization reactor was less than 0.1 seconds. The results are shown in Table 1.

[0035] [Example 2~ 5, Reference example 6, 7] The same procedure as in Example 1 was carried out, except that the linear velocity ratio of the raw material and the catalyst liquid and the tip angle of the inner tube were set to the conditions shown in Table 1. The results are shown in Table 1.

[0036] [Table 1]

[0037] [Comparative Examples 1 and 2] The same procedure as in Example 1 was carried out, except that the linear velocity ratio of the raw material and the catalyst liquid and the tip angle of the inner tube were set to the conditions shown in Table 2. The results are shown in Table 2.

[0038] [Table 2]

[0039] As shown in Table 1, Examples 1 to 5, Reference example 6, In No. 7, the tip of the inner tube is narrowed toward the tip, so there was no pressure fluctuation in the supply piping and continuous operation for more than 7 hours was possible without any problems. As shown in Table 2, in Comparative Examples 1 and 2, since the tip of the inner tube was not narrowed toward the tip, the pressure fluctuation in the supply pipe was significant, and the operation of the polymerization reactor was stopped soon after the start of polymerization. When the tip of the double pipe was observed after the polymerization reactor was stopped, the pipe was clogged due to polymer precipitation, which was not at a practical level. [Industrial Applicability]

[0040] According to the process for producing an oxymethylene polymer of the present invention, an oxymethylene polymer can be obtained continuously and stably.

Claims

1. A method for continuously producing an oxymethylene polymer, comprising the steps of: an introduction step of introducing the raw material and the liquid containing the catalyst into the polymerization vessel using a double pipe composed of an inner pipe and an outer pipe; a reaction step of reacting the raw material with the catalyst in the polymerization vessel to produce an oxymethylene polymer; having In the introduction step, The raw material passes between the inner tube and the outer tube of the double tube, a liquid containing the catalyst passes through an inside of the inner tube of the double tube; The inner tube has a tip end that appears tapered toward the tip end, a ratio of the linear velocity of the raw material divided by the linear velocity of the liquid containing the catalyst in a range of 0.4 to 8.9, the linear velocity being in units of m / s, in a portion where the raw material and the catalyst flow at a constant linear velocity immediately before contact between the raw material and the liquid containing the catalyst, and where a cross-sectional area of ​​the space inside the inner tube and a cross-sectional area of ​​the space between the inner tube and the outer tube are both constant; In the cross section of the inner pipe, the taper angle formed by a line forming the inner surface of the inner pipe and a straight line connecting the point where the wall thickness of the inner pipe starts to decrease and the point where the wall thickness of the inner pipe is at its minimum is in the range of 10 to 70 degrees. Characterized in that A method for producing an oxymethylene polymer.

2. 2. The method for producing an oxymethylene polymer according to claim 1, wherein the raw materials are contacted with the liquid containing the catalyst and introduced into a polymerization vessel simultaneously.

3. 3. The method for producing an oxymethylene polymer according to claim 1, wherein the raw material is trioxane.

4. The method for producing an oxymethylene polymer according to any one of claims 1 to 3, wherein the catalyst is a cationic polymerization catalyst.

5. The method for producing an oxymethylene polymer according to any one of claims 1 to 4, wherein the taper angle is in the range of 10 to 30°.

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