JPH0549821A - Dehydrating separation of vinyl chloride base polymer - Google Patents

Abstract

(57) [Summary] [Structure] In a method for dehydrating and separating a vinyl chloride polymer by suction filtration of an aqueous medium from a vinyl chloride polymer slurry, (1) the filtration surface of a filtration dehydrator is immersed in the polymer slurry. The step of putting in and sucking and adhering the solid content in the slurry to the filtration surface (2) the step of sucking and dehydrating the adhering solid content outside the slurry and (3) the step of peeling the adhering solid content from the filtration surface A method for dehydrating and separating a vinyl chloride-based polymer, characterized in that [Effect] The dehydration efficiency is good, and heat energy can be saved during drying.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dehydrating and separating a vinyl chloride polymer from a vinyl chloride polymer slurry, and particularly to a vacuum dehydrator for a vinyl chloride polymer slurry obtained by a suspension polymerization method. And a dehydration method for obtaining a dehydrated cake having a low water content.

[0002]

2. Description of the Related Art Vinyl chloride polymers are generally mass-produced by suspension-polymerizing vinyl chloride or a monomer containing vinyl chloride as a main component in an aqueous medium in a polymerization vessel. In this suspension polymerization method, the vinyl chloride polymer slurry produced in the polymerization vessel is subjected to heat treatment under reduced pressure or heat treatment with steam to recover unreacted vinyl chloride monomer, and then stored in a slurry tank. Then
From here, the polymer slurry is continuously supplied to a dehydrator for dehydration, and the dehydrated polymer cake is transferred to a drying step and dried to obtain a product.

Centrifugal separators are generally widely used for the dehydration operation in the dehydrator. In this dehydrator, it is advantageous to increase the dehydration efficiency as much as possible in order to reduce the heat energy cost in the drying step, but industrially, as the dehydration efficiency, the water content in the polymer cake is about 30%. It is near. It is industrially difficult to further improve the dehydration efficiency because there are problems such as the performance of the centrifugal separator and the prolonged dehydration operation.

[0004]

In view of the above problems relating to the dehydration method of a vinyl chloride polymer slurry, the present inventors have made earnest studies to establish an industrially advantageous dehydration method with good dehydration efficiency. As a result of stacking, the vinyl chloride polymer slurry was dehydrated with a vacuum filtration dehydrator having, for example, a rotor, and the dehydration efficiency was significantly increased by subjecting the filtered surface of the rotor to a specific thickness of the solid adhered on the filtration surface. They have found that they can be improved and have completed the present invention.

That is, the gist of the present invention is that a vinyl chloride-based polymer is obtained by suction filtration of an aqueous medium from a polymer slurry obtained by polymerizing vinyl chloride or a monomer containing vinyl chloride as a main component in the aqueous medium. In the method of dehydrating and separating the coalescence,
(1) a step of putting the filtration surface of the filtration dehydrator into the polymer slurry and suction-adhering the solid content in the slurry to the filtration surface; (2) a step of suction-dehydrating and drying the solid content adhering outside the slurry; 3) A method for dehydrating and separating a vinyl chloride-based polymer, and a dehydrating apparatus for the same, which are characterized by sequentially performing a step of peeling off the adhered solids from the filtration surface.

The present invention will be described in more detail below. The vinyl chloride-based monomer used in the method of the present invention includes, in addition to the vinyl chloride monomer itself, a vinyl chloride monomer as a main component, and a vinyl chloride monomer and a copolymerizable monomer. It may be a mixture of bodies. Examples of the copolymerizable monomer include olefins such as ethylene and propylene, vinyl esters such as vinyl acetate and vinyl stearate, vinyl ethers such as ethyl vinyl ether and cetyl vinyl ether, acrylic acid esters, maleic acid and fumaric acid. Any of the conventionally known vinyl chloride-copolymerizable monomers such as unsaturated carboxylic acid derivatives such as esters and anhydrides, aromatic vinyl compounds such as styrene, and unsaturated nitrile compounds such as acrylonitrile. Can be used.

For the polymerization of vinyl chloride-based monomers, all of the commonly known polymerization recipes for vinyl chloride-based monomers in an aqueous medium are adopted, and the dispersants, emulsifiers, polymerization initiators, etc. used. Does not need to be special, and a widely used dispersant, emulsifier, or polymerization initiator can be used. For example, as the dispersant and the emulsifier, a partially saponified product of polyvinyl acetate, an acrylic acid copolymer, a maleic anhydride copolymer, a cellulose derivative, gelatin, a protective colloidal drug such as den powder, or a natural high Molecular compounds, esters of higher fatty acids and polyhydric alcohols, nonionic surfactants such as polyoxyethylene derivatives, metal salts of higher fatty acids, and anionic surfactants such as alkali salts of higher alcohol sulfates are used. The amount of these dispersants and emulsifiers used is not particularly limited, and varies depending on the type, stirring efficiency, polymerization temperature, type and composition of other copolymerizable monomers, and particle size of the vinyl chloride polymer, Generally, it is used within a range of 0.01 to 2% by weight, preferably 0.03 to 1% by weight, based on the total amount of vinyl chloride-based monomers.

As the polymerization initiator, benzoyl peroxide, lauroyl peroxide, t-butyl peroxypivalate, α-cumyl peroxy neodecanoate,
Organic peroxides such as dioctyl peroxydicarbonate, t-butyl peroxydicarbonate, diisopropyl peroxydicarbonate, acetylcyclohexylsulfonyl peroxide, azo compounds such as azobisisobutyronitrile and dimethylvaleronitrile, potassium persulfate, Persulfates such as ammonium persulfate are used. The amount of these polymerization initiators used is generally in the range of 0.01 to 1% by weight based on the total amount of vinyl chloride-based monomers.

Further, in the polymerization reaction of vinyl chloride type monomers, generally known polymerization aids such as trichlorethylene, dodecyl mercaptan, 2-mercaptoethanol, propionaldehyde and other chain transfer agents, antioxidants, etc. It does not matter at all to use. The polymerization method of the vinyl chloride-based monomer is not particularly limited, mainly vinyl chloride monomer, or vinyl chloride monomer,
A mixture of this and a copolymerizable monomer may be charged all at once at the start of the polymerization, or a part of the vinyl chloride monomer may be charged at the start of the polymerization and the rest may be continuously charged after the start of the polymerization. You can also The polymerization temperature varies depending on the kind of the polymerization initiator used, the polymerization method and the like, but it is preferably in the range of 0 to 90 ° C, particularly 40 to 70 ° C.

The vinyl chloride polymer slurry produced by the above suspension polymerization reaction is subjected to a heat treatment under reduced pressure, a heat treatment with steam or the like to recover the unreacted vinyl chloride monomer, and then a blowdown tank or Is transferred to a slurry tank such as a blend tank and temporarily stored. In the present invention, the vinyl chloride polymer slurry produced as described above is supplied to a suction filtration dehydrator to be dehydrated. As the suction filtration dehydrator used in the present invention, for example, a rotary body having a compartment capable of being depressurized or pressurized inside is used as a filter dehydrator, and the rotary body enters the polymer slurry. The solid content in the slurry adheres to the filtration surface of the rotating body due to the negative pressure in the rotating body during the filtration process, and the solid content adhered to the surface of the rotating body due to the negative pressure inside the rotating body during the dehydration process when the rotating body comes out of the slurry. Water in the vacuum is dehydrated and dried by aeration to form an adhered cake, and the adhered cake is separated by a pressurized gas purge in the rotor during the cake removing process before entering the slurry of the rotor, and the vinyl chloride polymer and the aqueous medium are removed. It is composed of a process of separating the. The polymer slurry may be supplied to the filtration / dehydration apparatus continuously or intermittently, though it depends on the type of the filtration / dehydration machine.

The method of the present invention will be described with reference to the drawings. Figure 1
Is an explanatory view showing an outline of the dehydrating apparatus of the present invention, FIG. 2 is an explanatory view illustrating each step of filtration dehydration separation in the apparatus shown in FIG. 1, and FIG. 3 is for setting operating conditions of the apparatus of the present invention. It is an experimental device. In the figure, reference numeral 1 is a filter dehydrator having a part thereof immersed in a slurry tank 2 (rotating body, hereinafter referred to as a vacuum drum), 3 is an endless filter cloth wound around the vacuum drum 1, and 4 is a vinyl chloride system. Stirrer for polymer slurry, 5 scraper (scraping plate) for peeling cake, 6 cake receiver, 7 pump for supplying vinyl chloride polymer slurry, 8
Is a tank for receiving the filtrate from the vacuum drum 1, 9 is a vacuum pump,
Reference numeral 10 is a filtrate extracting pump, and 11 is an air compressor for purging compressed air to a vacuum drum during a cake removing process.

The operation of the apparatus of the present invention will be described in detail. First, the vinyl chloride polymer slurry supplied to the slurry tank 2 is rotated with the vacuum drum 1 while the vacuum pump 9 is operating. The solid content in the slurry (vinyl chloride polymer) due to the negative pressure in the vacuum drum 1 while the vacuum drum 1 enters the slurry of vinyl chloride polymer in the slurry tank 2 and passes through the slurry. Is attached to the filter cloth 3 on the filtering surface of the vacuum drum 1 (filtering step). Then, when the vacuum drum 1 comes out of the slurry water surface to the outside, the negative pressure inside the vacuum drum 1 sucks the water in the solid content to vacuum dehydrate, and the air is sucked to dry by aeration to form a cake (dehydration step. ), And before the vacuum drum 1 enters the slurry in the slurry tank 2 again, the adhered cake is separated by the back purge air by the compressed air in the vacuum drum 1 and by the scraping plate 5, and the separated cake is received as a cake receiver. 6 (collecting step). On the other hand, by depressurizing the vacuum drum 1,
The filtrate having passed through the filter cloth is transferred from the vacuum drum 1 to the filtrate receiving tank 8 and discharged from the filtrate extracting pump 10.

The number of revolutions of the vacuum drum 1 is 1 to 1.
The rpm is 0 rpm, preferably 2 to 6 rpm, and the retention time is 0.1 to 3 seconds in the filtration step, 1 to 20 seconds in the dehydration step, and 0.5 to 2 seconds in the cake peeling step. The operating pressure is 50 to 500 mmH in the filtration process.
g, 50 to 750 mmHg in the dehydration step, and 0.5 to 1.0 kg / cm ² G as the purge pressure in the cake stripping step.

Further, as the filter cloth 3, polypropylene, po
Of woven fabrics of various fibers such as polyethylene, nylon, vinylon
A filter medium is used, and its permeability is 1500 to 2000 (c
c / cm ²sec) range, as a commercial product PP303
(Polypropylene), PO801 (Polyethylene), N
Y201 and NY202 (nylon) are preferably used
It

The vinyl chloride polymer (PVC) slurry concentration is usually in the range of 20 to 40% by weight, and the particle size of PVC in the polymer slurry is 0.1 to 250 μm, preferably. It is in the range of 100 to 250 μm. The slurry temperature during the filtration step is usually 10
It is in the range of -80 ° C. In the present invention, the thickness of the attached cake on the surface of the filter cloth of the vacuum drum is preferably 20 mm or less, preferably 5 to 20 mm. When the thickness of the attached cake is larger than the upper limit, the water content of the PVC cake is significantly high. It is not preferable because it becomes high. The thickness of the attached cake is adjusted by selecting and adjusting the PVC slurry concentration, the type of filter cloth, the pressure during the filtration step, and the like.

Further, the filter dehydrator usable in the present invention may be of a disc type or a belt type other than the drum type described above.

【Example】

Examples 1 to 8 A vinyl chloride monomer was polymerized in an aqueous medium in a polymerization vessel according to a known method to produce a PV having a concentration of 28.6 wt%.
C slurry (average degree of polymerization 1100, average particle size 150μ
m) was obtained. The PVC slurry was heated to a slurry temperature of 50 ° C.
Then, a vacuum dehydration test was conducted using the experimental apparatus (leaf test apparatus) shown in FIG. That is, in FIG. 3, a leaf tester 31 (filtering area 0.005 m ² ) using NY202 (nylon) as the filter cloth 33 is put downward in the PVC slurry 32 and vacuumed for a predetermined time under the conditions shown in Table 1. Pressure is applied to carry out constant pressure filtration, and then the leaf tester 31 is taken out from the slurry while being kept under reduced pressure, and suctioned for a predetermined time to perform aeration dehydration, and then the vacuum pressure is cut off. 0.5 kg / cm ² G) was fed to peel off the adhered cake. The results are shown in Table 1.

[0017]

[Table 1]

COMPARATIVE EXAMPLE 1 In Example 1, a screw discharge type centrifugal dehydrator (centrifugal force 3000 G) was used in place of the vacuum filtration dehydrator, and P was used.
The VC slurry was dehydrated. The water content of the obtained dehydrated cake was 30 wt%.

Comparative Example 2 The PVC slurry was dehydrated for 20 minutes at a pressure of 100 kg / cm ² G using a pressure dehydrator (filter press) instead of the vacuum filtration dehydrator in Example 1. The water content of the obtained dehydrated cake was 25 wt%.

[0020]

The method of the present invention employs a vacuum (vacuum) filter dehydrator for dehydrating and separating the vinyl chloride polymer and the aqueous medium from the vinyl chloride polymer slurry. By selecting a cloth or the like, the thickness of the vinyl chloride polymer adhering to the filtration surface can be adjusted, and as a result, the dehydration efficiency can be increased. In particular, by setting the thickness to 20 mm or less, the dehydration efficiency is more remarkable than that using the centrifugal separator. Therefore, the heat energy can be reduced also in the subsequent drying step.

The vacuum filtration dehydrator consumes less power than the centrifugal separator, and the thickness of the vinyl chloride polymer adhering to the filtration surface is more than 20 mm, and the water content is centrifugal separator. Even if it is the same as the case of, the adoption has a great industrial utility value from the viewpoint of energy saving. Further, according to the method of the present invention, since suction is performed in a vacuum, there is an effect that the vinyl chloride monomer in the filtered and dehydrated vinyl chloride polymer is reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the outline of a dehydrator of the present invention.

FIG. 2 is an explanatory view illustrating each step of filtration dehydration separation in the apparatus shown in FIG.

FIG. 3 is an experimental device for setting operating conditions of the device of the present invention.

[Explanation of symbols]

 1,31 Filtration and dehydrator 2,32 Polymer slurry tank 3,33 Filter cloth 5 Scraper 11 Air compressor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display area C08F 6/24 MFP 8016-4J

Claims (6)

[Claims] 1. A method for dehydrating and separating a vinyl chloride polymer by suction filtration of an aqueous medium from a polymer slurry obtained by polymerizing vinyl chloride or a monomer containing vinyl chloride as a main component in an aqueous medium. In (1) the step of putting the filtration surface of the filtration / dehydration machine into the polymer slurry and suction-adhering the solid content in the slurry to the filtration surface, (2) the step of suction-dehydrating and drying the solid content adhering outside the slurry And (3) A method for dehydrating and separating a vinyl chloride polymer, which comprises sequentially performing a step of peeling the attached solid content from the filtration surface. 2. The method for dehydration separation of a vinyl chloride polymer according to claim 1, wherein the solid content concentration of the polymer slurry is 20% by weight or more. 3. The dehydration separation method for a vinyl chloride polymer according to claim 1 or 2, wherein the thickness of the solid matter attached to the filtration surface is 20 mm or less. 4. The method for dehydrating and separating a vinyl chloride polymer according to claim 1, wherein a pressurized gas is purged from the back surface of the filtration when the adhered solids are removed. 5. The method for dehydrating and separating a vinyl chloride polymer according to claim 1, wherein the filter dehydrator is a rotating body having compartments capable of depressurizing or pressurizing each inside. 6. A vacuum drum type filter dehydrator which rotates around a horizontal shaft having a filter surface formed by winding a filter cloth having an endless end portion, wherein the filter dehydrator is partially filtered. It is arranged so that it enters into the slurry, and the rotation causes the filtration surface to adhere the vinyl chloride polymer, which is the solid content in the slurry when passing through the slurry, and to the solid content when it goes out from the water surface of the slurry. The water is sucked and dehydrated, and the cake is dried by aeration and drying, and then the back-purge air by the compressed air in the filter dehydrator and the scraping plate are used to peel and collect the attached cake from the filtration surface. Dewatering device for combined slurry.