Process for the preparation of cyclic formals

Abstract

To provide a method for producing a cyclic formal, capable of simply producing the cyclic formal by using a polyacetal resin as a raw material.SOLUTION: The method for producing a cyclic formal includes a step of adding (A) a polyacetal resin, (B) a polyhydric alcohol having a plurality of hydroxyl groups in one molecule, and (C) a silicate mineral to one selected from the group consisting of 1, 4-dioxane, nitrobenzene, and acetonitrile as a reaction medium, and heating the mixture at a temperature of 125 to 160 °C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a process for the preparation of cyclic formals. [Background technology]

[0002] Polyacetal resin has an excellent balance of mechanical properties, chemical resistance, and sliding properties, and is easy to process, making it widely used as an engineering plastic, primarily for electrical and electronic components, automotive parts, and various other mechanical components.

[0003] Meanwhile, in recent years, there has been a demand for recycling used resins in order to prevent environmental destruction and make effective use of resources. Examples of resin recycling include chemical recycling, in which resins are chemically decomposed and reused as raw materials. For the recycling of polyacetal resins, a recycling method is known in which polyacetal resins are decomposed in water under heat and pressure in the presence of an acid to obtain formaldehyde (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 93 / 24439 Summary of the Invention [Problem to be solved by the invention]

[0005] The decomposition product of the recycling method described in Patent Document 1 is formaldehyde, which cannot be used as is to regenerate polyacetal resin. In other words, formaldehyde must be converted into 1,3,5-trioxane as a main monomer or a cyclic formal as a comonomer. Cyclic formals are known as excellent solvents and can be used for purposes other than recycling polyacetal resin. Therefore, it would be useful to be able to directly produce cyclic formals from polyacetal resin. Furthermore, since an acidic aqueous solution is used, the reaction vessel is prone to corrosion, so a corrosion-resistant vessel is required, which raises concerns about increased costs.

[0006] The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a method for producing a cyclic formal by which a cyclic formal can be easily produced using a polyacetal resin as a raw material. [Means for solving the problem]

[0007] One aspect of the present invention that solves the above problem is as follows. (1) As a reaction medium, one selected from the group consisting of 1,4-dioxane, nitrobenzene, and acetonitrile is used. A method for producing a cyclic formal, comprising the steps of adding (A) a polyacetal resin, (B) a polyhydric alcohol having multiple hydroxyl groups in one molecule, and (C) a silicate mineral, and heating the mixture at a temperature of 125 to 160°C.

[0008] (2) The method for producing a cyclic formal according to (1) above, wherein the silicate mineral (C) is montmorillonite.

[0009] (3) The method for producing a cyclic formal according to (1) above, wherein the silicate mineral (C) is montmorillonite obtained by acid treatment.

[0010] (4) The method for producing a cyclic formal according to any one of (1) to (3) above, wherein the reaction medium is 1,4-dioxane. [Effects of the Invention]

[0011] According to the present invention, a method for producing a cyclic formal can be provided that uses a polyacetal resin as a raw material and enables a cyclic formal to be produced simply and easily. DETAILED DESCRIPTION OF THE INVENTION

[0012] The method for producing a cyclic formal of this embodiment includes the steps of adding (A) a polyacetal resin (hereinafter also referred to as "POM resin"), (B) a polyhydric alcohol having multiple hydroxyl groups in one molecule, and (C) a silicate mineral to a reaction medium selected from the group consisting of 1,4-dioxane, nitrobenzene, and acetonitrile, and heating the mixture at a temperature of 125 to 160°C.

[0013] In the method for producing a cyclic formal according to this embodiment, a silicate mineral (C) is used as a decomposing agent, and (B) a polyhydric alcohol having multiple hydroxyl groups per molecule is added and decomposed at a predetermined temperature to obtain a cyclic formal. In other words, the cyclic formal can be obtained directly without going through formaldehyde. Furthermore, the silicate mineral (C) used as the decomposing agent has the following advantages: (1) it does not corrode metals, so there is no need to use a corrosion-resistant reaction vessel; (2) it is nonvolatile, so it remains in the distillation residue after distillation, making it easy to separate from other components; and (3) it can be reused many times. On the other hand, in this embodiment, the (A) POM resin and (C) silicate mineral, which are the decomposition targets, are a heterogeneous reaction that does not dissolve in the system. Therefore, the unreacted (A) POM resin and (C) silicate mineral are easily separated from the reaction medium, allowing the (C) silicate mineral and reaction medium to be reused. Furthermore, since the (A) POM resin reacts in an unmolten state, the (C) silicate mineral and the (A) POM resin can be easily separated. Furthermore, while the recycling method described in Patent Document 1 requires neutralization of the reaction system, the manufacturing method of this embodiment does not require neutralization.

[0014] Examples of cyclic formals produced by decomposing POM resin using the cyclic formal production method of this embodiment include 1,3-dioxolane, diethylene glycol formal, 1,4-butanediol formal, and 1,3-dioxane.

[0015] Each component used in the method for producing a cyclic formal of this embodiment will be described below.

[0016] [Reaction medium] In this embodiment, the reaction medium is one selected from the group consisting of 1,4-dioxane, nitrobenzene, and acetonitrile, of which 1,4-dioxane is most preferred.

[0017] In this embodiment, the amount of the reaction medium used is preferably 50 to 2000 parts by mass, and more preferably 300 to 1000 parts by mass, per 100 parts by mass of the (A) POM resin.

[0018] [(A) Polyacetal resin] In this embodiment, (A) polyacetal resin (POM resin) is the resin to be decomposed. POM resins are broadly classified into two types: homopolymers having only oxymethylene units (-CHO-) as their unit structure, and copolymers having oxyethylene units (-CHCHO-) in addition to oxymethylene units. In this embodiment, both homopolymers and copolymers are targeted for decomposition. In this embodiment, the POM resin is decomposed to produce the cyclic formal described above.

[0019] [(B) Polyhydric alcohols with multiple hydroxyl groups per molecule] Examples of polyhydric alcohols having multiple hydroxyl groups per molecule (hereinafter simply referred to as "polyhydric alcohols") used in this embodiment include ethylene glycol, diethylene glycol, 1,3-propanediol, and 1,4-butanediol. The polyhydric alcohol contributes to the structure of the cyclic formal produced. For example, when ethylene glycol is used, 1,3-dioxolane, a five-membered ring, is obtained, and when 1,3-propanediol is used, 1,3-dioxane, a six-membered ring, is obtained. Therefore, the polyhydric alcohol to be used is determined depending on the structure of the desired cyclic formal.

[0020] In this embodiment, the amount of (B) polyhydric alcohol added is preferably 30 to 300 parts by mass, and more preferably 70 to 150 parts by mass, per 100 parts by mass of (A) POM resin.

[0021] [(C) Silicate minerals] In this embodiment, the silicate mineral (C) functions as a decomposing agent. Specific examples include phyllosilicate minerals (layered), inosilicate minerals (fibrous), and tectosilicate minerals (network-like). Among these, montmorillonite, which is a type of phyllosilicate mineral, is preferred. The silicate mineral (C) is preferably used as a fine powder. (C) Silicate minerals are solid decomposing materials and have the advantages mentioned above.

[0022] (C) It is preferable to subject the silicate mineral to an acid treatment. For example, when montmorillonite obtained by acid treatment is used as the montmorillonite, the interlayer cations are converted to Na by the acid treatment. + From H + It is exchanged with HCl and shows high activity.

[0023] In this embodiment, the amount of (C) silicate mineral added is preferably 10 to 200 parts by mass, and more preferably 50 to 120 parts by mass, per 100 parts by mass of (A) POM resin.

[0024] [Other ingredients] In this embodiment, in addition to the above components, other components may be used to decompose the POM resin, such as known substances that are added when decomposing the POM resin and that do not inhibit the effect of the silicate mineral (C).

[0025] In this embodiment, the above components are mixed and then heated at a predetermined temperature. The components can be mixed, for example, by preparing a reaction medium and adding components (A) to (C) into it. Alternatively, the solid POM resin (A) and silicate mineral (C) can be mixed first, and then the resulting mixture and the polyhydric alcohol (B) can be added to the reaction medium separately.

[0026] In this embodiment, the above components are mixed and then heated at a temperature of 125 to 160°C to decompose the (A) POM resin. If the heating temperature is below 125°C, the decomposition reaction is slow and the cyclic formal cannot be obtained in high yield. If the heating temperature exceeds 160°C, the yield of the cyclic formal decreases, or the (A) POM resin melts, making it difficult for the reaction to occur in a heterogeneous system. The heating temperature is preferably 125 to 160°C, and more preferably 125 to 140°C.

[0027] In this embodiment, the cyclic formal can be obtained as described above. The produced cyclic formal can then be separated and recovered according to a standard method. [Example]

[0028] The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to the following examples.

[0029] [Examples 1 to 9, Comparative Examples 1 to 9] In each example and comparative example, as shown in Tables 1 to 3, (A) POM resin pellets, (B) polyhydric alcohol, and (C) silicate mineral (other substances in Comparative Examples 4 to 9) were added in the amounts (g) shown in Tables 1 to 3 to 2 mL of reaction medium (1,4-dioxane). The mixture was then heated at the decomposition temperature and for the decomposition time shown in Tables 1 to 3 to decompose the (A) POM resin and obtain a cyclic formal. The yield of the resulting cyclic formal was calculated using the following formula. Yield = (amount of HCHO-derived substance in the obtained cyclic formal) / amount of POM resin The components used are as follows:

[0030] (A)POM resin POM resin 1 (copolymer): DURACON (registered trademark) M90-44, manufactured by Polyplastics Co., Ltd. POM resin 2 (homopolymer): Delrin (registered trademark) 500P, manufactured by DuPont (B) Polyhydric alcohol 1,3-propanediol ethylene glycol 1,4-butanediol All reagents used were manufactured by Sigma-Aldrich. (C) Silicate minerals Mont K-10: Sigma-Aldrich, reagent H-Mont: A mixture of 3.0 g of the following Na-Mont (sodium-type montmorillonite) and 200 mL of 1.1 wt% hydrochloric acid was stirred at 90°C for 24 hours. The reaction mixture (slurry) was filtered, washed with 1 L of distilled water, and dried in air at 110°C to obtain whitish-gray powdery proton-type montmorillonite (H-Mont). The acid content (Amount of Acid Sites) of the proton-type montmorillonite was measured and found to be 0.86 mmol / g. The conversion rate of sodium ions to protons was 98.9%. Na-Mont: sodium-type montmorillonite [manufactured by Kunimine Kogyo Co., Ltd., trade name "Kunipia F", elemental analysis values: Na 2.69%, Mg 1.97%, Al 11.8%, Fe 1.46%] (C) Substances other than silicate minerals Sulfuric acid: Reagent H-mordenite: Catalysis Society reference catalyst JRC-Z-HM-20(5) Amberlyst® 36: Reagent manufactured by Sigma-Aldrich H-ZSM-5: Zeolite 822HOA manufactured by Tosoh Corporation Nafion: NAFION (registered trademark, manufactured by Fisher Scientific) SO4·ZrO2 (sulfated zirconia): Fujifilm Wako Pure Chemical Industries, Ltd., reagent

[0031] [Table 1]

[0032] [Table 2]

[0033] [Table 3]

[0034] It can be seen from Tables 1 to 3 that cyclic formals were obtained in high yields in Examples 1 to 9. In contrast, in Comparative Examples 1 to 9, cyclic formals were not obtained, or even if they were obtained, the yield was low. In particular, in Comparative Examples 1 to 3, silicate mineral (C) was used, but the heating temperature was outside the range of 125 to 160°C, so cyclic formals were not obtained or the yield was low.

Claims

1. As a reaction medium, one selected from the group consisting of 1,4-dioxane, nitrobenzene, and acetonitrile is used. A method for producing a cyclic formal, comprising the steps of: adding (A) a polyacetal resin; (B) a polyhydric alcohol having multiple hydroxyl groups in one molecule; and (C) a silicate mineral; and heating the mixture at a temperature of 125 to 160°C.

2. 2. The method for producing a cyclic formal according to claim 1, wherein the silicate mineral (C) is montmorillonite.

3. 2. The method for producing a cyclic formal according to claim 1, wherein the silicate mineral (C) is montmorillonite obtained by acid treatment.

4. The method for producing a cyclic formal according to any one of claims 1 to 3, wherein the reaction medium is 1,4-dioxane.

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