JPS6154322B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for polymerizing formaldehyde substantially in the gas phase using a novel polymerization reactor.

As a formaldehyde polymerization method, a slurry polymerization method using a diluent is mainly adopted. This slurry polymerization method requires diluent recovery and purification steps, but in the so-called gas phase polymerization method, which involves reacting in a gas phase, the above steps are virtually unnecessary, simplifying the process and reducing the need for steam, electricity, etc. It is possible to reduce the amount of utility used.

In this gas phase polymerization method, the particulate polymer is kept in a fluidized and agitated state. The contact between the gas phase monomer and the catalyst, and in some cases the comonomer, is greatly influenced by the fluidized and agitated state of the powder. The heat of the polymerization reaction of formaldehyde is extremely large, about 12 Kcal/mol, and if the fluid stirring conditions are not good, local overheating will occur, leading to problems in carrying out the polymerization reaction and problems with the quality of the produced polymer.

In addition, it is necessary to efficiently remove the heat of polymerization that is generated in such a large amount, and if the heat removal is not sufficient, problems will occur in temperature control, which will also cause problems in the execution of the reaction and problems in the quality of the produced polymer. occurs. Therefore, in the gas phase polymerization method, uniform heat removal from such a fluidized bed is a major problem as well as the contact state between the gas phase and the solid phase, that is, the fluidized stirring state of the powder and granules.

Generally, the following proposals have been made regarding reactors for gas phase polymerization.

(1) Fluidized bed reactor (Special Publication No. 47-13962, Special Publication No. 13962, Special Publication No. 13962)
52-40350, Japanese Patent Application Laid-open No. 54-139983) A large capacity compressor is required due to the circulation of a large amount of gas (several tens of times the reaction amount), which consumes a large amount of electricity. Catalysts and equipment to prevent scattering of active fines are also required.

(2) Fluidized bed reactor with stirrer (Special Publication No. 1977-597)
In this method, a stirrer is installed inside the fluidized bed reactor in order to reduce the flow rate of gas blown into the reactor.
However, even with this method, it is still necessary to supply gas at a rate of 5 to 15 cm/sec from the bottom of the reactor, which has the same drawback as (1).

(3) Horizontal stirred bed reactor (Japanese Patent Publication No. 45-2019, 86584-1984, 159205-1987) A horizontal hollow cylindrical reactor equipped with a single-shaft stirrer is used to generate air. This is a method of carrying out phase polymerization, in which the heat of polymerization is removed by injecting a low boiling point liquid into the apparatus and using its latent heat of vaporization, thereby reducing the amount of fluidizing gas blown into the apparatus. This method requires a lot of equipment for recovering and circulating the low-boiling point liquid, and also consumes a lot of electricity, steam, etc.

(4) Horizontal twin-shaft stirring tank (JP-A-55-157605, JP-A-57-73011) A stirring fluidized bed of powdered olefin polymer is formed by the twin-shaft stirring blades installed at the bottom of the reaction tank. death,
This is an apparatus for carrying out gas phase polymerization reactions.

The heat of polymerization is removed by cooling pipes fixedly provided in this fluidized bed. As the cooling tube, a loop-shaped thin tube such as a U-shape, a V-shape, or a spiral shape is used. The above-mentioned Japanese Patent Application Publication No. 1987-
Publication No. 73011 states that the heat transfer surface of the cooling pipe is renewed by the collision of powder in a fluid state. However, when this reactor is used for formaldehyde polymerization, the resulting formaldehyde polymer has a strong adhesive force, and once it adheres to the cooling tube, it is difficult to peel off due to powder collision, and it gradually accumulates on the surface of the cooling tube. go. As a result,
As the polymerization reaction progresses, it becomes difficult to remove the polymerization reaction heat, making it impossible to continue the polymerization reaction smoothly within a short period of time. Further, since the cooling pipe has a loop-like structure, it is difficult to forcibly scrape off the polymer adhering to the surface of the cooling pipe.

As described above, the reactors proposed so far cannot be said to be fully satisfactory as reactors for gas phase polymerization of formaldehyde.

In the present invention, by polymerizing formaldehyde using a reactor that is an improved version of the horizontal twin-screw stirring tank in the first half (4), the adhesion of the polymer to the cooling member is extremely small, and the heat of the polymerization reaction is efficiently dissipated. Provided is a method for polymerizing formaldehyde that can be removed.

That is, in the present invention, a plurality of stirring shafts equipped with stirring blades are provided in the lower part of the container, penetrating the side wall of the container, and the bottom of the container is constituted by a partial cylinder along the locus of the tips of the stirring blades. on the top of the container.
Formaldehyde and a polymerization catalyst are supplied to a horizontal reactor in which a rotating shaft equipped with a disc-shaped cooling member through which a cooling medium flows passes through the side wall of the container. This is a formaldehyde polymerization method characterized by polymerizing formaldehyde.

According to the present invention, the following excellent effects are achieved.

(1) A fluidized state comparable to that of a conventional fluidized bed reactor can be provided substantially only by mechanical stirring.

(2) Good dispersion and mixing inside the reactor, uniform reaction temperature, easy temperature control, and a homogeneous polymer.

(3) Since almost 100% of the heat of polymerization is removed by the cooling member inside the reactor, the amount of gas blown into the reactor is essentially the same as the amount of polymer produced, and the excess gas is circulated. Alternatively, deterioration of the monomer due to circulation of the cooling liquid can be prevented.

(4) By making the cooling member for removing polymerization heat into a rotary disk shape, the sliding force of the powder can be increased, adhesion can be reduced, and the heat transfer area can be increased. Furthermore, a scraping device can be easily installed, and the heat transfer surface can be forced to be cleaned.

Next, the present invention will be explained with reference to the drawings.

At the bottom of the container 1 are two stirring shafts 2 and 3.
are provided through the side walls 4 and 5 of the container 1. Stirring shafts 2 and 3 are supported by bearings 6 and 7. It is preferable that the stirring shafts 2 and 3 are provided substantially horizontally and parallel to each other. The spacing between the stirring shafts 2 and 3 is determined by the support 8 on the shaft.
It is preferable that the trajectories (rotating circles) of the tips of the stirring blades 9 provided through the stirring blades 9 touch or overlap. Note that three or more stirring shafts may be provided, but since there is no significant difference in mixing performance, two stirring shafts are practically sufficient.

There are no particular restrictions on the shape of the stirring blades 9, but
In order to stir the powder in the container 1 upwards, paddle blades are generally used. For the purpose of stirring the powder upward, it is preferable to place the paddle blades parallel to the stirring shafts 2 and 3. However, in order to create a gentle circulation flow throughout the container 1, the paddle blades may be tilted or horizontal blades may be used. It is also possible to combine the blade with an inclined blade.

A plurality of stirring blades 9 are mounted symmetrically on the stirring shaft. Three blades or four blades can also be used, but usually
Two blades with a spacing of 180°C are sufficient. The spacing between the stirring blades 9 in the axial direction is also arbitrary, but from the point of view of the stirring effect, it is preferable that they be close to each other, and they are usually installed at intervals of 1.1 to 3 times the width of the blades. The relative position of the stirring blades 9 between the two shafts is such that both blades do not come into contact with each other due to rotation.

The bottom of the container 1 is formed of a partial cylinder along the trajectory of the tip of the stirring blade 9. The limit of the partial cylinder is
Up to 1/2 cylinder. That is, when the tips of the stirring blades 9 are spaced apart from each other, a chevron-shaped connection part is provided at the bottom of the container 1 in the middle thereof to prevent the powder from stagnation. The gap between the bottom of the container 1 and the tip of the stirring blade 9 is preferably as small as possible, and is generally 10 mm or less.

It is desirable that the height of the container 1 is greater than the height of the powder that has been stirred and floated, and is therefore at least 1.2 times the diameter of the maximum rotation circle drawn by the stirring blades 9, preferably 1.5 to 1.5.
It is 3.5 times. The length of the container 1 in the axial direction is arbitrary, but it is usually 1 to 7 times the diameter of the rotation circle, especially 1.5 to 7 times the diameter of the rotation circle.
5 times is appropriate.

Inside the container 1, there is a rotating shaft 11 on which a disc-shaped cooling member 10 for removing polymerization heat is attached to the upper part of the stirring blade 9.
and 12 are provided through the side walls 4 and 5 and supported by bearings 13 and 14. Rotating shafts 11 and 12 are installed parallel to stirring shafts 2 and 3. The rotating shafts 11 and 12 are provided such that the lower end of the cooling member 10 attached to them is near the highest point of the trajectory of the stirring blade 9. The size, number, etc. of the cooling member 10 can be easily determined by those skilled in the art, taking into consideration the amount of polymerization reaction heat to be removed.

The interiors of the cooling member 10 and the rotating shafts 11 and 12 have a structure through which a cooling medium flows, as shown in FIG. 3, for example. Rotating shafts 11 and 12
A rotary joint 15 is attached to one end of the rotary joint 15, and the cooling medium is supplied to the cooling member 10, and after heat exchange, is discharged through the rotating shafts 11 and 12.

Although it is not normally necessary, as shown in FIG.
can also be fixed to the support shaft 19.

Formaldehyde supply pipe 20, catalyst supply pipe 2
1. An exhaust gas discharge pipe 22 and, if necessary, a comonomer supply pipe 23 are provided to penetrate the top wall 16 of the container 1, respectively. A polymer discharge pipe 24 is also provided in the lower part of the container 1, for example in the bottom wall 17. The polymer outlet pipe 24 can also be provided on the side wall of the container 1.

Formaldehyde, catalyst and optionally comonomer are introduced into vessel 1 via tubes 20, 21 and 23, respectively.

The stirring shafts 2 and 3 are rotated at a constant speed by a drive device (not shown). The rotation directions of the stirring shafts 2 and 3 may be arbitrary, but from the viewpoint of uniformity of stirring,
Preferably, both shafts are rotated in opposite directions. The rotational speed of the stirring blades 9 is determined in consideration of the size of the container 1, the size and number of blades, etc. In order to obtain a sufficient stirring effect, the height of the pulverized polymer in the container 1 is generally set at a height higher than that of the stirring blade 9.
A rotation speed is adopted such that the height from the top of the stirring blade is approximately 0.5 to twice the rotational diameter of the stirring blade.
This is generally 1 to 5 at the tip of the stirring blade 9.
Corresponds to a linear velocity of m/s.

The amount of powdery polymer in the container 1 may be any amount as long as a sufficient stirring effect can be obtained, but the amount below the highest point drawn by the stirring blade 9 when the stirring blade 9 is stopped is sufficient. It is preferable that there be.

Inside the container 1, the particulate polymer is stirred up by the stirring blades 9 to form a fluidized bed. The upper surface of this fluidized bed is preferably located above the highest point of the cooling member 10 in order to efficiently remove the polymerization reaction heat.

The rotating shafts 11 and 12 are rotated by a drive device (not shown). There is no particular restriction on the direction of rotation of the rotating shafts 11 and 12. Further, there is no particular restriction on their rotational speed, but in order to increase the apparent collision speed between the powdery polymer and the cooling member 10, the linear velocity at the tip of the cooling member is set to 0.3~
Preferably, the speed is 3 m/sec.

The heat of the polymerization reaction is removed by a jacket and a cooling member 10 provided around the outer periphery of the container 1.
Particularly, in the present invention, by installing the cooling member 10 in the fluidized bed generated by the violent stirring or splashing effect by the stirring blades 9, the particulate polymer violently collides with the entire cooling member 10. Furthermore, by rotating the heat transfer surface itself,
The sliding force of the powder increases, and the heat transfer surface uniformly contacts the fluid. As a result, there is less adhesion of granular polymer to the heat transfer surface, the heat transfer surface can be updated easily, the heat transfer coefficient can be increased by disturbing the boundary surface, and polymerization heat can be effectively removed. It is.

The resulting polymer is withdrawn from the tube 24 in such a way as to maintain the height of the fluidized bed within the vessel 1 substantially constant and to avoid sudden changes in the pressure within the vessel 1 .

As the catalyst, all compounds known as formaldehyde polymerization catalysts can be used.
Specific examples include boron fluoride, its ether complexes, metal chelate compounds and organotin compounds. In addition, when producing a formaldehyde copolymer, boron fluoride or a mixture of boron fluoride and a metal chelate compound is preferably employed as a catalyst.

Specific examples of the copolymer include cyclic ethers or cyclic formals such as ethylene oxide, dioxane, dioxolane, and trioxocane.

The polymerization reaction is carried out substantially in the gas phase.
"Substantially in a gaseous state" refers to aliphatic hydrocarbons such as pentane, hexane, heptane, benzene,
A state in which an inert organic solvent such as an aromatic hydrocarbon such as toluene is not present in the polymerization system, and a state in which the inert organic solvent is present in at most an equal weight to the polymer in the polymerization system. do.

The polymerization temperature is 0 to 110°C, and the polymerization pressure is usually normal pressure.

Next, Examples and Comparative Examples will be shown.

Example 1 It has the shape shown in Figures 1 to 3 and has a height of 400 mm.
mm, width 300mm, length 300mm, internal volume approx. 32mm
A reactor made of SUS304 was used. Inside the reactor, as an internal cooler, five disc-shaped cooling members (outer diameter 145 mm, made of SUS304) shown in Fig. 3 are installed in series on two rotating shafts arranged in parallel. Each is designed to allow water to flow through it. Temperature-controlled water was passed through it as a coolant. The reactor was also equipped with a jacket for heat removal, which was used in the same way as the internal cooler to remove reaction heat.

The length of the stirring blade from one tip to the tip of the other blade 180 degrees apart is 185 mm.

This apparatus was charged with 4 kg of polyoxymethylene copolymer which had been dried under reduced pressure at 60°C for 10 hours.

The rotation speed of the stirring blade was 320 rpm, and the rotation direction was as shown in FIG.

The rotation speed of the disk-shaped cooling member was 160 rpm, and the rotation direction was the direction shown in FIG.

A solution containing bis(acetylacetone) copper at a concentration of 3.5 μmol/ml was added to a mixed solution of equal weights of 1,3,6-trioxocane (hereinafter referred to as TOC) and toluene at a rate of 114 ml/H to 0.1 mmol/ml. ml
A toluene solution of boron trifluoride diethyl ether was continuously fed into the reactor at a rate of 25 ml/H.
The disk-shaped cooling member, the amount of water passed through the reactor wall jacket, and the water temperature were adjusted so as to maintain the temperature at 75°C.

The copolymer was continuously discharged from the discharge port at a rate of 1.0 kg/H.

It operated continuously for 100 hours, but it was running smoothly. The properties of the obtained copolymer are shown below.

Intrinsic viscosity 1.58 dl/g Base stability 91.8% Average particle size 177 μm The intrinsic viscosity of the oxymethylene copolymer was measured at 60° C. using p-chlorophenol containing 2% by weight of α-pinene as a solvent.

The base stability of the oxymethylene copolymer was measured at 160°C at a copolymer concentration of 10% in a benzyl alcohol solution containing 1% tri-n-butylamine.
This is the recovery rate of the copolymer after heat treatment for 1 hour, and is a measure of the base stability of the copolymer.

Comparative Example 1 Instead of the rotating cooling disk of Example 1, a
Uses a 1/4in diameter SUS304 tube, approximately 1500mm
Five vertical loops were formed with a length of , and such loops were arranged in five rows parallel to the stirring axis. Polymerization was carried out under the same conditions as in Example 1, except that temperature-controlled water was passed therein as a coolant. About 6 hours after the start of polymerization, it became difficult to remove heat from the cooling tube, so polymerization was stopped. When the reactor was opened after stopping, a thick layer of polymer was found to have adhered between the cooling tube and the loops of the cooling tube.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a cross section perpendicular to the stirring axis of the reaction vessel used in the present invention, FIG. 2 is a schematic diagram corresponding to the cross section of FIG. FIG. 4 is a schematic cross-sectional view showing the relative relationship between the powder scraping tool and the cooling member. 1... Container, 2, 3... Stirring shaft, 9... Stirring blade, 1
1, 12... Rotating shaft, 10... Cooling member.

Claims (1)

[Claims] 1 A plurality of stirring shafts equipped with stirring blades are provided at the bottom of the container, penetrating the side wall of the container, and the bottom of the container is composed of a partial cylinder that follows the trajectory of the tips of the stirring blades. Formaldehyde and a polymerization catalyst are supplied to a horizontal reactor, which has a rotating shaft attached to the upper part, which passes through the side wall of the container and has a disk-shaped cooling member through which a cooling medium flows, and
A method for polymerizing formaldehyde, which comprises polymerizing formaldehyde substantially in a gas phase.