JP2697182B2 - Washing and dewatering apparatus and method for recovering polymer using the same - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a washing and dewatering apparatus and a method for recovering a polymer using the same, and more particularly, to simultaneously washing and dewatering a polymer slurry. The present invention relates to a washing / dehydrating apparatus capable of removing water and a washing / dehydrating method for efficiently and continuously recovering a polymer by dehydrating a polymer slurry to a sufficiently low water content using the same.

b. Conventional technology When a polymer obtained by emulsion polymerization is coagulated and recovered, many impurities such as an emulsifier used in the polymerization remain in the polymer and deteriorate the physical properties of the polymer. For this reason, after coagulation, it is important that the slurry is sufficiently washed with water and then dried to obtain a product.

Further, when the slurry is dewatered and dried, the latent heat of evaporation of water is very large. Therefore, it is important to reduce the amount of water carried into the dryer as much as possible to reduce the energy required for drying.

The same applies to the case where the polymer obtained by solution polymerization, suspension polymerization, or bulk polymerization other than emulsion polymerization is converted into a slurry to recover the polymer.

The simplest method of washing slurry that has been used in the past is to wash the slurry by diluting the slurry with water in a stirring tank, or to arrange two or more stirring tanks and slit screen at the outlet of the stirring tank. After once separating the water by
In this method, the slurry is mixed again with water in the next stirring tank to form a slurry, and this is repeated several times for washing.

As another washing method, there is a method of washing while spin-drying using a vacuum belt filter or a drum type filter.

The above method and the above method are described in, for example, a styrene butadiene rubber production system diagram of Chemical Process Assembly (Tokyo Kagaku Dojin).

c. Problems to be Solved by the Invention However, in the former method, a sufficient cleaning effect cannot be obtained, and in the latter method, several stirring tanks are required.
There is a problem that the equipment cost is high and the installation space of the apparatus requires a large area.

The method is for cleaning while draining dirty water,
It is better than the method in terms of cleaning effect. However, the polymer obtained by this method has a high water content of about 40% by weight, and if it is dried as it is, the required energy becomes very large. It was necessary to separately dehydrate using a dehydrator such as a dehydrator.

c. Means for Solving the Problems The present inventors have conducted intensive studies to solve these problems at once, and as a result, have reached the present invention.

That is, the present invention provides a washing region in the middle of the screw of the screw type squeezing and dewatering machine, forms a through hole in the screw shaft and provides a washing water injection hole in the middle of the shaft, A low-moisture content polymer is recovered by simultaneously performing washing and dehydration of a polymer slurry using the washing and dewatering device, wherein the washing solution is supplied to the washing region, and the washing and dewatering device. It provides a method.

Hereinafter, a washing and dewatering apparatus of the present invention and a method for recovering a polymer using the same will be described with reference to FIG.

The washing and dewatering apparatus 1 of the present invention comprises a feed barrel 2 for supplying a material to be dewatered, a dewatering barrel 3 connected thereto, a discharge box 4 at the tip of the apparatus, and a screw 5 penetrating these.
It is composed of

The feed barrel 2 and the dewatering barrel 3 are provided with a discharge port constituted by a perforated plate, a slit bar, a wedge wire, and the like.

The screw 5 is rotated by a motor 7 via a speed reducer 6, and these may be further connected therebetween via a belt or a chain.

The screw 5 includes a screw shaft 8 and a screw flight 9 formed on the outer periphery thereof. In FIG. 1, the depth of the groove of the flight 9 in the A zone and the B zone is the same, but may be different. . Further, a through hole 10 through which washing water passes is provided inside the screw shaft 8, and a washing water injection hole is provided in the B zone of the screw shaft 8 so that water can be sprayed in the barrel direction through the through hole 10. 11
Is provided.

A cone-shaped disturb bar 12 is provided at the outlet of the discharge box 4 as a resistor for maintaining the internal pressure.

The washing and dewatering apparatus 1 has L / D = 4 to 15 (L: length of a dewatering part to an outlet including an inlet part, D: inner diameter of a barrel), and a screw pitch of 0.5D to 1.5D, preferably 0.7D to 1.2D. The length of each zone (A zone, B zone, C zone) is not particularly limited, but preferably, when the length of the B zone is 1, 0.5 to 2.0 for the A zone and 2.0 for the C zone.
4.04.0, and if it is in this range, the more excellent effect of the present invention can be obtained.

The screw 5 in the dewatering zone (C zone)
Is preferably 1.1 to 4.0. The polymer slurry can be dehydrated to a target water content of 5 to 25% by weight (wet base) by selecting an optimum value within this range depending on the type of the dewatering object.

In the present specification, the “compression ratio” is a value represented by a flight valley volume for one pitch at the entrance / a flight valley volume for one pitch at the exit.

In recovering the polymer using the washing and dewatering apparatus 1, a polymer slurry is first supplied to the feed barrel 2 as indicated by an arrow 13. At this time, the solid content concentration of the slurry is preferably 10 to 40% by weight, and more preferably 20 to 35% by weight. When the content is less than 10% by weight, the dewatering ability is reduced, and when the content is more than 40% by weight, the bite at the inlet is deteriorated.

The fed slurry is first filtered in zone A, followed by a screw flight 9 rotating at 0.5-20 RPM.
To move to zone B.

The zone B is a zone for washing the slurry after dehydration lightly. The longer this zone or the larger the amount of washing water, the more the washing effect is improved.

In the zone B, the washing water supplied to the through hole 10 of the screw 5 is jetted from the washing water jetting hole 11 in the barrel direction as shown by the arrow 14.

The number of washing water injection holes 11 depends on the amount of washing water, but generally the number is large and it is preferable that the washing water injection holes 11 are provided uniformly in the axial direction.

The temperature of the supplied washing water should be selected within the temperature range from the room temperature to the glass transition point of the polymer to be treated, like the operating temperature of the washing and dewatering apparatus 1, but more preferably from the viscosity of water. Considering that the temperature is high, improvement of the cleaning effect can be expected.

The polymer slurry washed in the B zone is sent to a C zone (a dewatering zone), where it is compressed and dewatered to a target water content of 5 to 25% by weight (wet base).

Since a disturb bar 12 is provided at the outlet of the discharge box 4, the internal pressure is maintained, and a favorable throttling effect is obtained by the resistance. In addition, disturb bar
12 may be fixed to a shaft or may be supported from behind the outlet discharge box.

The wet cake dehydrated in the dewatering zone is discharged from the outlet of the discharge box 4 as indicated by an arrow 15.

On the other hand, the squeezed water is discharged from the feed barrel 2 and the dewatering barrel 3 as shown by an arrow 16.

The polymer that can be recovered from the polymer slurry by the method of the present invention is not particularly limited, and examples thereof include a rubbery polymer, a thermoplastic elastomer, and a thermoplastic resin.

Examples of the rubbery polymer include conjugated diene-based polymer rubbers such as polyisoprene rubber and polybutadiene rubber, hydrogenated products of the conjugated diene-based polymer rubber, conjugated diene-based copolymer rubbers such as SBR and NBR, and the conjugated diene. Examples include hydrogenated copolymer rubbers, acrylic rubbers, and ethylene-propylene rubbers.

Examples of the thermoplastic elastomer include a block copolymer of a conjugated diene and an aromatic vinyl, a hydrogenated product of the block copolymer, a hydrogenated product of a random copolymer of a conjugated diene and an aromatic vinyl, and at least one aromatic compound. Examples include a block copolymer comprising a vinyl polymer block and a random copolymer block of at least one aromatic vinyl and a conjugated diene, or a hydrogenated product thereof.

Examples of the thermoplastic resin include aromatic vinyl polymers such as polystyrene and (meth) such as polymethyl methacrylate.
Acrylic acid alkyl ester polymer, aromatic vinyl,
(Meth) alkyl acrylate, copolymer of two or more selected from vinyl cyanide and N-substituted maleimide compound, at least one polymer selected from the above rubber polymers and thermoplastic elastomers In the presence, polymerization of two or more monomers selected from aromatic vinyl or alkyl (meth) acrylate, or aromatic vinyl, alkyl (meth) acrylate, or N-substituted maleimide compound The resulting graft copolymer (for example, HIPS, ABS, AES, AAS, etc. is exemplified).

According to the method of the present invention, a polymer latex is obtained by an emulsion polymerization method, and a polymer slurry obtained by coagulating the polymer latex, or a polymer slurry obtained by a suspension polymerization method, a solution polymerization, and a bulk polymerization method are used. The polymer can be recovered from a polymer slurry obtained by dispersing the polymer in water.

e. Examples Hereinafter, the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

First, a coagulated slurry of the ABS resin used in the following Examples 1 and 2 and Comparative Example 1 was prepared in the following manner.

27 parts by weight of polybutadiene latex, 1 part by weight of sodium stearate, 200 parts by weight of distilled water and 0.3 parts by weight of sodium pyrophosphate, 0.35 parts by weight of glucose, 0.005 parts by weight of ferrous sulfate
Parts by weight and 0.6 parts by weight of cumene hydroperoxide, and a mixture of 50 parts by weight of styrene and 23 parts by weight of acrylonitrile was added dropwise thereto.
Emulsion polymerization with a reaction time of 5 hours gives a polymerization conversion rate.
A 98% polymer latex was obtained. H ₂ as a coagulant
2 parts of SO ₄ was added and coagulated at 95 ° C. to finally obtain a thermoplastic resin water slurry having a slurry concentration of 25%.

Example 1 The following test was performed using the above-mentioned coagulated slurry and using the washing and dewatering apparatus 1 shown in FIG.

<Specifications of washing and dewatering device 1> <Test Method> The temperature of the slurry whose solid content concentration in the slurry was adjusted to 25% by weight was raised to 80 ° C., and the slurry was continuously supplied from the feed barrel 2. At the same time, washing water at 80 ° C. was continuously supplied from the through hole 10 of the screw 5. The screw of the washing apparatus 1 was of a type having a different inclination between the B zone and the C zone, and had a compression ratio of 1.9. The feed barrel 2 and the dewatering barrel 3 were provided with slit bars having a clearance of 0.3 mm.

 The operating conditions of the washing and dewatering apparatus 1 are as follows.

Shaft rotation speed = 6 rpm Washing water amount = 1000 kg / hr Subsequently, the water content of the wet cake obtained from the washing / dewatering apparatus 1 was measured, and after drying with a dryer, the resin was molded and the color tone was evaluated.

<Test Results> The water content of the ABS resin cake at the outlet of the washing and dewatering device 1 was 18.8% by weight (wet base), and the whiteness of the ABS resin molded product showing the cleaning effect was 33 at the inlet. At the exit, it improved by 6 points to 39.

The whiteness and the water content were measured by the following methods, and DRY FLOW was calculated by multiplying the wet cake amount at the outlet of the washing and dehydrating apparatus 1 by the water content.

Measurement of whiteness: As a method of measuring whiteness, a washing and dehydrating apparatus 1 is used.
Was crushed by a crusher to make a wet powder. Subsequently, the wet powder was dried with a hot air drier and then pelletized, and a test piece for color tone measurement 80 m / m × 40 m / m was formed using a SHIBAURAIS80A injection molding machine. Using this test piece, it was measured by a reflection measurement method using an automatic colorimeter of 45 ° diffusion method (according to JIS Z8722).

Measurement of moisture content: The wet cake was finely crushed, and this solid was taken in an aluminum dish whose weight was accurately measured, and weighed accurately together with the aluminum dish. This was placed in an electric constant temperature drier and dried at 110 ° C. for 1 hour. The weight after drying was again accurately measured. The water content is determined by the following equation.

A: Weight of aluminum dish (g) B: Weight of aluminum dish and sample before drying C: Weight of aluminum dish and sample after drying Example-2 Using the coagulated slurry of ABS resin described above, FIG. The following test was performed using the cleaning / dewatering apparatus 17 shown below.

Since the basic structure of the cleaning and dewatering device 17 shown in FIG. 2 is the same as that of the cleaning and dewatering device 1, the same members and the same portions are denoted by the same reference numerals.

The screw 5 of the washing and dewatering device 17 temporarily raises the compression ratio of the screw so that the mother liquor can be dehydrated as much as possible in zone A in order to further enhance the washing effect (part indicated by E in FIG. 2). ), The compression ratio is reduced again in zone B.

<Specifications of washing and dehydrating equipment> <Test Method> The latex of the ABS resin was coagulated with sulfuric acid, the solid content of the slurry was adjusted to 25% by weight, the temperature was raised to 80 ° C., and the slurry was continuously supplied from the feed barrel 2. At the same time, washing water at 80 ° C. was continuously supplied from the through hole 10 of the screw. As the screw 5 in the washing and dewatering device 17, a screw having a compression ratio of zone A of 1.5, a gradient of zone B and zone C being the same, and a final compression ratio of 2.5 is also used.
After preliminary dehydration in the zone, washing and dehydration were performed in the B and C zones.

As the feed barrel 2 and the dewatering barrel 3, those having a slit bar with a clearance of 0.3 mm were used.

 The operating conditions of the washing and dewatering device 17 are as follows.

Shaft rotation speed = 9 rpm Washing water amount = 500 kg / hr Subsequently, the obtained cake was treated in the same manner as in Example 1, analyzed and evaluated.

<Test Results> The water content of the ABS cake at the outlet of the washing and dewatering device 20 was 16.0% by weight (wet base), and the whiteness of the ABS resin molded product showing the washing effect was 33 at the inlet.
At the exit, it improved by 8 points to 41.

The methods for measuring the water content and whiteness were the same as in Example 1.

Comparative Example 1 A test was performed using a reslurry type washing / dewatering apparatus 18 according to a flow sheet shown in FIG.

In FIG. 3, reference numeral 19 denotes a first centrifugal dehydrator, 20 denotes a second centrifugal dehydrator, 21 denotes a reslurry tank, and 22 denotes a motor for driving the centrifugal dehydrator.

<Specifications and operating conditions of the washing and dewatering device 18> (1) First and second centrifugal dehydrators (batch method) Rotor 400mm dia Number of rotations 1700rpm Dehydration time 5min (2) Reslurry tank Tank volume 100L Input ABS amount 30kg dry Input amount of washing water 90kg Stir time 5min <Test method> As shown in Fig. 3, latex of ABS resin was coagulated with sulfuric acid, and the solid content in the slurry was adjusted to 25.0% by weight. The temperature was raised and the ABS resin slurry was supplied to the first centrifugal dehydrator 19 as shown by the arrow 23. ABS resin slurry is dewatered, dewatered water is arrow 2
Discharged as shown at 4. The moisture content of the wet powder after dehydration is 30.
It was 5% by weight (wet base). Arrow 25 of the wet powder after dehydration
Is supplied to the reslurry tank 21 as shown by the arrow, reslurry washing is performed by adding washing water as shown by the arrow 26, dewatered again by the second dehydrator 20 as shown by the arrow 27, and shown by the arrow 28 A wet powder of 29.5% by weight (wet base) was thus obtained.

Subsequently, the obtained cake was treated in the same manner as in Example 1, and analyzed and evaluated.

<Test results> The whiteness indicating the washing effect was increased by 6 points from 33 to 39, but the water content was 29.5% by weight.

The methods for measuring the water content and whiteness were the same as in Example 1.

f. Effects of the Invention The washing and dehydrating apparatus of the present invention incorporates a washing mechanism in a screw-type squeezing and dehydrating machine, and can achieve washing and a high dehydration rate with one machine. It is a very economical device in terms of installation area.

Further, according to the method for recovering a polymer of the present invention, it is possible to greatly improve the dehydration rate while maintaining the cleaning effect at or above the conventional level. Therefore, it is possible to significantly reduce energy in the subsequent drying step.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a washing / dehydrating apparatus according to the present invention, FIG. 2 is a longitudinal sectional view of another washing / dehydrating apparatus according to the present invention, and FIG. 3 is a reslurry type washing / dehydrating apparatus of Comparative Example-1. It is a flow sheet. DESCRIPTION OF SYMBOLS 1 ... Washing dehydration apparatus, 2 ... Feed barrel, 3 ... Draining barrel, 4 ... Discharge box, 5 ... Screw, 6 ... Reducer, 7 ... Motor, 8 ... Screw shaft, 9 ... Flight, 10: Through-hole, 11: Wash water injection hole, 12: Disturber bar.

Claims (2)

(57) [Claims] 1. A screw-type squeezing and dehydrating machine having a washing area in the middle of the screw, a through hole in the screw shaft, and a washing water injection hole in the middle of the screw shaft. A cleaning and dewatering apparatus characterized in that a cleaning liquid is supplied to a cleaning area. 2. A method for recovering a polymer having a low water content by simultaneously performing washing and dehydration of a polymer slurry using the washing and dehydrating apparatus according to claim 1.