JPH0667997B2 - Formaldehyde copolymer manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a formaldehyde copolymer. More specifically, the present invention relates to a method for producing a formaldehyde copolymer capable of efficiently removing the heat of polymerization generated during the production of the formaldehyde copolymer.

(Prior art and its problems) It is known that a formaldehyde copolymer excellent in moldability, heat resistance and mechanical properties can be obtained by copolymerizing formaldehyde and cyclic formal.

The applicant of the present invention, in Japanese Examined Patent Publication No. 62-31727, formaldehyde, cyclic formal and a specific amount of an inert organic solvent are fed to a biaxial mixing stirrer in the presence of boron trifluoride or its ether complex, A method of gas phase copolymerizing formaldehyde and cyclic formal has been disclosed. According to this method, stability in a basic medium is good, and a formaldehyde copolymer having an appropriate molecular weight can be obtained in a high yield.

In the method proposed above, in order to efficiently remove the heat of polymerization, the copolymer discharged from the twin-screw mixing agitator is supplied to an agitation-type cooler and cooled, and the amount of the copolymer corresponding to the amount of the supplied monomer is reduced. A method in which the polymer is taken out of the system as a product and the remaining copolymer is circulated and fed to a biaxial mixing stirrer is preferably adopted.

As a cooling method in the above method, if a direct cooling method of introducing a volatile organic solvent into the cooler and contacting with the copolymer to cool by the latent heat of vaporization of the organic solvent is adopted, the inner wall of the cooler and the stirrer Almost no polymer is attached, and the operation can be continued stably for a long time. In the above direct cooling method, the organic solvent vapor discharged from the cooler is condensed, and the condensed organic solvent is circulated and used,
Industrially preferred. By the way, since this organic solvent vapor contains a small amount of formaldehyde gas, if the organic solvent vapor is condensed as it is, the formaldehyde polymer adheres to the heat transfer surface of the condenser during long-term operation, and the heat transfer efficiency is improved. It causes deterioration and blockage of the condenser.

The present applicant has already proposed as a Japanese Patent Application No. 62-279047 a method for producing a formaldehyde copolymer which solves such a problem. The proposed method is to supply the organic solvent vapor to the lower part of the absorption tower, supply alcohols as the formaldehyde absorbing liquid from the upper part to bring them into contact with each other, and after absorbing and removing the formaldehyde entrained in the organic solvent vapor. In this method, the organic solvent vapor is condensed and circulated and supplied to the cooler.

The present inventors have obtained the following findings when the method proposed above was examined in more detail. That is, the organic solvent vapor discharged from the cooler contains, in addition to formaldehyde, a trace amount of boron trifluoride, which is a copolymerization catalyst, or an ether complex thereof. Promotes the condensation reaction of compounds with formaldehyde, and the water produced by this condensation reaction is brought into the copolymerization reactor via the cooler, and as a result, acts as a chain transfer agent during the copolymerization reaction, It has been found that it becomes difficult to obtain a copolymer having a molecular weight.

(Object of the Invention) It is an object of the present invention to provide a method for producing a formaldehyde copolymer that efficiently removes heat of copolymerization reaction and solves the above-mentioned problems.

(Technical Means for Solving the Problems) According to the present invention, formaldehyde, circulating formal and cooled copolymer circulated from the second step are continuously fed to a twin-screw mixing stirrer, The first step of copolymerizing formaldehyde and cyclic formal in the presence of boron trifluoride or its ether complex, the resulting copolymer and the volatile organic solvent are continuously supplied to a stirrer-type cooler. The copolymer supplied from the first step is contacted and cooled by the latent heat of vaporization of the organic solvent, and the amount of formaldehyde and cyclic formal to be supplied to the first step in the cooled copolymer is adjusted to the system. A second step of extracting the copolymer outside and circulating the remaining copolymer to the first step;
And a third step of bringing the organic solvent vapor discharged from the second step into contact with the synthetic zeolite to remove the accompanying boron trifluoride or its ether complex to obtain a purified organic solvent vapor,
And the organic solvent vapor from the third step is supplied from the pipe 50 to the formaldehyde absorption tower, alcohols as an absorbing liquid are supplied from the upper part to bring them into contact with each other, and formaldehyde entrained in the organic solvent vapor is absorbed and removed, There is provided a method for producing a formaldehyde copolymer, which comprises a fourth step of condensing the organic solvent vapor from which formaldehyde has been removed, and then circulating the same in the second step.

Each step of the present invention will be described below with reference to FIG. 1 showing an example of an apparatus adopted for carrying out the present invention.

First Step A hopper 12 is attached to the biaxial mixing agitator 11 via a screw conveyor 13. Boron trifluoride or its ether complex and an organic solvent as a copolymerization reaction catalyst are continuously supplied into the screw conveyor 13 through pipes 51 and 52, respectively. Formaldehyde is continuously introduced into the twin-screw mixer 1 via pipe 53 and cyclic formal via pipes 54 and 53, respectively. The cooled formaldehyde copolymer, which is circulated from the second step at the same time, is continuously supplied to the twin-screw mixing stirrer 11 through the pipe 55, the hopper 12 and the screw conveyor 13.

The twin-screw mixing stirrer 11 used in the present invention has two horizontal stirring shafts fitted with a large number of elliptical mixing stirrers in an outer case. When the stirring shaft is rotated, In addition, the device has a slight gap between the surface of the mixing and stirring blade and the inner wall of the case which are mutually opposed. Such a twin-screw mixing stirrer 11 is, for example, a KRC from Kurimoto Iron Works Co., Ltd.
It is commercially available as a kneader. The biaxial mixing agitator 11 is 1
It may be configured with only one machine, or may be configured with two or more machines provided in series or in parallel. For example, two twin-screw mixing stirrers 11 can be provided in series to divide the copolymerization reaction.

The water content of formaldehyde is 0.1% by weight or less, especially
It is preferably 0.01% by weight or less. Formaldehyde is supplied to the twin-screw mixing stirrer 11 in the vapor phase.

General formula for cyclic formal The compound represented by In the above formula, R ₁ ,
_{R 2, R 3, R 4} , R 5 and R ₆ are each a hydrogen atom, an alkyl group, an allyl group and a cycloalkyl group, l, m and n is an integer from 1 to 6 respectively and l, At least one of m and n is an integer of 2 or more, and a, b and c are 0 or 1, respectively.

Specific examples of the cyclic formal include ethylene oxide, propylene oxide, butene-1-oxide,
1,3-butadiene-1-oxide, styrene oxide, α-methylstyrene oxide, oxetane, tetrahydrofuran, 1,3-dioxolane, 2-methyl-1,3
-Dioxolane, 2-phenyl-1,3-dioxolane,
4-phenyl-1,3-dioxolane, 1,3-dioxopan, 2-butyl-1,3-dioxopan, 1,3,6-trioxocane, 1,3,5-trioxopane, polyethylene glycol formal can be mentioned. The amount of cyclic formal used is preferably 0.001 to 0.1 mol, particularly 0.01 to 0.04 mol, per mol of formaldehyde supplied. When a cyclic formal that is liquid at room temperature is used, it is preferably preheated to be in the gas phase and used for the reaction.

The presence of an inert organic solvent in the copolymerization reaction system is not essential, but the stability of the produced copolymer in a basic medium is increased, and the molecular weight of the produced copolymer is as high as practically required. To increase, it is preferable to use an inert organic solvent.

Specific examples of the inert organic solvent include aliphatic hydrocarbons such as pentane, hexane and heptane, alicyclic hydrocarbons such as cyclohexane and cyclopentane, aromatic hydrocarbons such as benzene, toluene and xylene, and these hydrocarbons. A halide is mentioned. The amount of inert organic solvent used is
It is preferably 0.1 to 20 parts by weight, particularly 0.5 to 5 parts by weight, per 100 parts by weight of formaldehyde supplied. The inert organic solvent is preferably in liquid form and supplied to the biaxial mixing stirrer 11.

Specific examples of the boron trifluoride ether complex include a complex of boron trifluoride and an aliphatic ether such as dimethyl ether or diethyl ether. The amount of boron trifluoride or its tail complex (hereinafter, both may be collectively referred to as a copolymerization catalyst) used is usually 1 × 10 ⁻⁵ to 1 × 10 ⁻³ mol per mol of feed formaldehyde. In the case of a boron trifluoride ether complex which is liquid at room temperature, it is preferable that the complex is fed into the biaxial mixing stirrer 11 in the vapor phase in advance.

In the biaxial mixing stirrer 11, the copolymerization of formaldehyde and cyclic formal proceeds in the gas phase to form a formaldehyde copolymer.

The copolymerization reaction temperature is usually 40 to 80 ° C. Biaxial mixing agitator
Space velocity of formaldehyde within 11 is usually 300-2000h
^-1 .

The produced copolymer is discharged from the pipe 56 together with the circulating copolymer. The copolymer discharged is heated by the tube 55
It has a higher temperature than the circulating copolymer fed through to the biaxial mixing agitator 11.

Second Step The formaldehyde copolymer produced in the first step is continuously supplied to the stirring type cooler 21 through the pipe 56 together with the circulating copolymer. As the agitating cooler 21, a uniaxial or biaxial agitator provided with a large number of agitating blades known per se can be used.

A volatile organic solvent is supplied to the stirring cooler 21 from a pipe 57 in a liquid phase. As the volatile organic solvent, an organic solvent having a relatively low boiling point is used, and specific examples thereof include aliphatic hydrocarbons such as heptane and hexane, and alicyclic hydrocarbons such as cycloheptane and cyclohexane. Among these volatile organic solvents, those having a boiling point lower than the temperature of the formaldehyde copolymer at the outlet of the stirring-type cooler 21 are preferably used. Although not industrially advantageous, it is also possible to liquefy and use butane, propane, etc., which are gases at room temperature. In this case, the recovery system becomes pressurized and becomes complicated.

In the stirrer cooler 21, the formaldehyde copolymer supplied from the first step comes into contact with the organic solvent, and the organic solvent is heated by the formaldehyde copolymer and evaporated,
The heat of copolymerization reaction is removed by the latent heat of vaporization at that time.

The cooled formaldehyde copolymer is discharged from the pipe 58 and passed through the screw conveyor 22 and the pipe 55 to the hopper 12
Is supplied to. An amount commensurate with the amount of formaldehyde and cyclic formal supplied to the first step is withdrawn as a product from the system through the pipe 59. The remaining copolymer is circulated through the screw conveyor 12 and circulated to the biaxial mixing agitator 11 in the first step. The amount of formaldehyde copolymer circulated and fed varies depending on the heat of the copolymerization reaction to be removed, but it is usually 50 to 200 times the weight of formaldehyde fed.

The evaporated organic solvent is discharged through the pipe 60 and used in the third step. The organic solvent vapor discharged from the pipe 60 is accompanied by 4 to 24 mg and 1 to 30 μg of unreacted formaldehyde and the copolymerization catalyst in the first step per vapor, respectively.

Third step Pipe 60 from the top of adsorption tower 31 filled with synthetic zeolite 32
The organic solvent vapor discharged in the second step is supplied via.

There is no special limitation on the synthetic zeolite used,
A-type, X-type, Y-type, L-type, model knight or chabazite having an average pore size of 3 to 10 Å is preferably used.

The synthetic zeolite used in the present invention is known as an adsorbent for various organic substances together with synthetic hydrosaltite, silica gel and activated alumina. Of these, synthetic hydrotalcite has a large amount of water adsorbed by itself, and reacts with formaldehyde to produce methanol and methyl formate, so the object of the present invention is unsuitable. Further, silica gel has a high adsorption capacity when a single gas of boron trifluoride or its ether complex is circulated, but once it is circulated through the organic solvent vapor discharged from the second step of the present invention, it is once adsorbed. Boron fluoride or its ether complex is desorbed, causing the problems described above. Furthermore, activated alumina has a high adsorption capacity when a single gas of boron trifluoride or its ether complex is passed through, but its remarkable catalytic action changes formaldehyde into methanol, methyl formate, methylal, trioxane and the like. .

On the contrary, the synthetic zeolite used in the present invention is
It has the excellent characteristics that formaldehyde is hardly altered and the adsorbed boron trifluoride or its ether complex is not desorbed.

The organic solvent vapor is a synthetic zeolite filled in the adsorption tower 31.
Upon contact with 32, the contained copolymerization catalyst is adsorbed on the synthetic zeolite 32. The organic solvent vapor from which the copolymerization catalyst has been removed is discharged from the pipe 61 and used in the next fourth step.

Although not shown, it is industrially convenient to provide two or more adsorption towers 31 and use them alternately.

Fourth Step The organic solvent vapor from the pipe 61 is introduced into the lower part of the absorption tower 41. On the other hand, alcohols as a formaldehyde absorbing liquid are introduced from the upper part of the absorption tower 41 through a pipe 62.

As the formaldehyde absorbing liquid, alcohols having a boiling point higher than that of the organic solvent can be used, and polyethylene glycol having a high formaldehyde absorbing performance is preferably used. The molecular weight of polyethylene glycol is 20
It is preferably 0 to 400.

The organic solvent vapor and alcohols come into countercurrent contact in the absorption tower 41, and the formaldehyde entrained in the organic solvent vapor is absorbed by the absorption liquid and discharged from the bottom of the absorption tower 41 through the pipe 63, if necessary. Used for the formaldehyde recovery process. The absorption liquid from which formaldehyde has been collected and removed is the absorption tower 41
Can be circulated to.

The organic solvent vapor from which formaldehyde has been removed is the absorption tower 41
Is discharged from the top of the tube via a pipe 64 and supplied to the condenser 42. The organic solvent condensed and liquefied in the condenser 42 is circulated and supplied to the cooler 21 in the second step through the pipe 57.

As described above, the copolymerization catalyst entrained in the organic solvent vapor discharged from the second step is removed in the adsorption tower 31, and there is no generation of water due to the reaction between alcohols and formaldehyde in the absorption tower. In the copolymerization reaction of the first step, a copolymer having a desired molecular weight can be efficiently obtained. Further, since the formaldehyde entrained in the organic solvent vapor discharged from the second step is removed from the organic solvent vapor in the absorption tower 41, the heat transfer of the condenser 42 when condensing the organic solvent vapor in the condenser 42 is performed. The polymer does not adhere to the surface, and a stable formaldehyde copolymer can be produced.

(Example) An example is shown below.

In the examples, a copolymer of formaldehyde and 1,3,6-trioxocane was produced using the apparatus shown in FIG.

The intrinsic viscosity of the formaldehyde copolymers obtained in the examples was measured at 60 ° C. using p-chlorophenol containing 2% by weight of α-pinene as a solvent. The base stability of a formaldehyde copolymer is the copolymer concentration of 10% in benzyl alcohol containing 1% by weight of tri-n-butylamine.
It is the recovery rate (%) of the copolymer when heat-treated at 160% by weight for 1 hour.

Example 1 With a hopper manufactured by Kurimoto Iron Works Co., Ltd. as a biaxial mixing agitator
KRC Kneader # 4 was used, and a paddle dryer NPD-1.6W manufactured by Nara Machinery Co., Ltd. was used as a stirring type cooler. All the copolymers were transported using a tube containing a screw conveyor.

Using the above apparatus, a copolymerization reaction of formaldehyde (hereinafter referred to as FA) and 1,3,6-trioxocane (hereinafter referred to as TOC) was continuously performed.

Approximately 40 kg of FA-TOC copolymer was placed in the device and 500 kg
/ H. Benzene at 870 g / h and gaseous boron trifluoride (hereinafter referred to as BF) at 17.5 mmol / h, respectively.
It was introduced through an inlet provided between the hopper and the kneader. In addition, 5 kg / h of gaseous FA with a water content of 50-80 ppm
Then, 260 g / h of gaseous TOC was introduced into the vicinity of the inlet of the circulating copolymer in the kneader. A copolymerization reaction between FA and TOC was performed under the above conditions. The copolymer discharged from the kneader outlet was continuously supplied to the cooler.

Simultaneously with the start of the copolymerization reaction, pentane was introduced at a rate of 55 kg / h downstream of the copolymer inlet of the cooler.

Of the cooled copolymer, an amount corresponding to the introduced FA and TOC was extracted from the overflow line of the hopper.

In the evaporated pentane gas, about 4 μg per 1
It contained BF and 8 mg FA. The pentane gas was contacted with synthetic zeolite (A type pore size 10Å) in the adsorption tower to remove BF. The pentane gas at the outlet of the adsorption tower could not be detected by ICPA emission spectrometry. The pentane gas discharged from the adsorption tower was brought into countercurrent contact with polyethylene glycol in the absorption tower to remove entrained FA, then condensed in a condenser, and then circulated and fed to a dryer. The formaldehyde concentration in pentane gas at the outlet of the absorption tower was about 0.8 mg per gas.

The above continuous operation was continued for 336 hours. The kneader inlet temperature of the copolymer was 65 ° C, and the outlet temperature was 38 ° C.

The resulting copolymer has an intrinsic viscosity of 1.7 and a base stability of 87%, 1
The FA yield of the pass was 98%, and the TOC unit content of the copolymer was 1.7 mol%.

Comparative Example 1 The same method as in Example 1 was repeated, except that the pentane gas discharged in the second step was directly supplied to the fourth step without passing through the adsorption tower of the third step. That is, in this example, the synthetic zeolite adsorption tower was used as a bypass.

The intrinsic viscosity and base stability of the resulting copolymer gradually decreased to 0.9 and 79%, respectively. At this time, the water content in the polyethylene glycol in the 4th step is usually 20.
Had doubled.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an apparatus used for implementing the present invention. 11 …… Biaxial mixing stirrer, 12 …… Hopper, 21 …… Stirring cooler, 21 …… Adsorption tower, 41 …… Absorption tower, 42 …… Condenser The abbreviations in Fig. 1 mean the following. To do. FA: Formaldehyde, TOC: Cyclic formal, BF ₃ : Boron trifluoride, IOS: Inert organic solvent

Claims (1)

[Claims] 1. Formaldehyde, cyclic formal and the cooled copolymer recycled from the second step are continuously fed to a biaxial mixing stirrer in the presence of boron trifluoride or its ether complex. The first step of copolymerizing formaldehyde and cyclic formal, the resulting copolymer and the volatile organic solvent are continuously supplied to a stirring type cooler to bring them into contact with each other, and the first step is carried out by latent heat of vaporization of the organic solvent. From the cooled copolymer, the amount corresponding to the amounts of formaldehyde and cyclic formal to be supplied to the first step is extracted out of the system, and the remaining copolymer is cooled in the first step. The second step of circulating
And a third step of bringing the organic solvent vapor discharged from the second step into contact with the synthetic zeolite to remove the accompanying boron trifluoride or its ether complex to obtain a purified organic solvent vapor,
And the organic solvent vapor from the third step is supplied to the lower part of the formaldehyde absorption tower, and alcohols as the formaldehyde absorbing liquid are supplied from the upper part to bring them into contact with each other to absorb and remove the formaldehyde entrained in the organic solvent vapor. A method for producing a formaldehyde copolymer, which comprises a fourth step of condensing the organic solvent vapor from which formaldehyde has been removed, and then circulatingly supplying the vapor to the second step.