JP3475526B2 - Filtration method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filtration method for removing coarse particles from a dispersion liquid containing a large amount of fine particles, which prevents clogging of a filter medium and allows stable filtration.

[0002]

2. Description of the Related Art A dispersion liquid containing a large amount of fine particles such as a vinyl chloride polymer latex obtained by emulsion polymerization or fine suspension polymerization is filtered to separate and remove coarse particles in the dispersion liquid. As a method for this, a method of treating using a double cylindrical filter is known. However, in this method, the filter medium was clogged from the beginning of operation, and so-called filterability such as filtration speed and operation stability was not always sufficient. Therefore, a method of performing filtration using a liquid to be filtered as a pulsating flow has been proposed (JP-A-63-294916).
issue). Although this method improves the filterability, it is not economical because the apparatus for continuously giving pulsation to the liquid to be filtered becomes industrially large-scale, and the pulsation causes deformation of the filter medium. Since it is necessary to use a flexible filter medium in order to easily peel off the filter cake, there is a possibility that the filter medium may be damaged by repeated stress.

[0003]

DISCLOSURE OF THE INVENTION An object of the present invention is to industrially obtain good filterability without giving pulsation to a liquid to be filtered when filtering a dispersion containing many fine particles. It is to provide an advantageous method.

[0004]

The summary of the present invention is as follows.
A dispersion liquid containing coarse particles in a large amount of fine particles is used as a liquid to be filtered, and this is filtered by a cylindrical filter having a rigid hollow body as a filter material to obtain a dispersion liquid containing no coarse particles as a filtrate. in the filtration method to obtain the liquid to be filtered 25
Circulate in the filter medium with a Reynolds number of 00 or more
It exists in the filtration method characterized by supplying . The present invention will be described in detail below.

Liquid to be filtered The liquid to be filtered suitable for applying the method of the present invention is a dispersion liquid containing a large amount of fine particles and in which it is desirable to remove a small amount of coarse particles. The weight average particle diameter of the dispersoid therein is preferably 0.01 to 50 μm, more preferably 0.1 to 30 μm. The weight average particle size can be measured by, for example, an optical centrifugal sedimentation type particle size distribution measuring device or a laser diffraction particle size distribution measuring device.

Among these, vinyl chloride monomers are emulsion-polymerized in an aqueous medium in the presence or absence of an emulsifier with a water-soluble polymerization initiator, or homogenized and then oil-soluble. Vinyl chloride-based polymer latex obtained by fine suspension polymerization using a polymerization initiator generally has poor filterability and has the property that coarse particles are likely to adversely affect the quality of the final product. Therefore, it is particularly suitable for applying the filtration method of the present invention.

The vinyl chloride monomer in the present invention means
It refers to a mixture of vinyl chloride monomer alone and a copolymerizable monomer mainly containing vinyl chloride monomer. As the other monomer copolymerizable with the vinyl chloride monomer, those conventionally used can be used without particular limitation, and examples thereof include vinyl acetate, vinyl propionate, and stearic acid. Vinyl esters such as vinyl, methyl vinyl ether, ethyl vinyl ether, octyl vinyl ether, lauryl vinyl ether, alkyl vinyl ethers such as cetyl vinyl ether, ethylene, α-olefins such as propylene, acrylic acid, monounsaturated acids such as methacrylic acid, These monounsaturated acid methyl esters, ethyl esters and other alkyl esters, maleic acid, fumaric acid, itaconic acid and other divalent unsaturated acids, these divalent unsaturated acid methyl esters and ethyl esters, etc. Vinylidene compounds such as alkyl esters and vinylidene chloride, One or a mixture of two or more such unsaturated nitriles such as acrylonitrile and the like. These other monomers are used in a proportion of usually 30% by weight or less, preferably 20% by weight or less, with respect to the vinyl chloride monomer, but there is no particular limitation.

Filtration device In the method of the present invention, a cylindrical filtration device is used, which usually has a structure in which a hollow cylindrical filtering material is also installed in a cylinder. The number of filter media may be determined according to the required filtration area and the size of the filter, but usually 1 to
About 10 are used. FIG. 1 shows an example of a filter that can be used in the method of the present invention. In filtration, the liquid to be filtered is circulated and fed into a cylindrical filter medium, and the filtrate is discharged to the shell (mantle) side of the filter. It is suitable for preventing liquid retention.

[0009] filter media used in the filter media present invention method is of hollow bodies of rigid, generally, a hollow cylindrical structure, it is common around the cylindrical portion is constituted by the filter body. The inner diameter of the cylinder is usually about 10 to 50 mm, and the thickness of the filter is 0.5 to
The length is about 3 mm and the length is about 0.5 to 2 m. The rigidity of the filter medium means that the filter material is not deformed or is not deformed under the pressure that is received along with the flow of the liquid to be filtered, and is not deformed at the pressure of 0.1 kg / cm ² , for example. It is said to have rigidity.

As such a filter medium, for example, a sintered metal is preferably laminated in 2 to 5 layers and has a thickness of 0.5 to
A material of 3 mm may be mentioned, and it may be fixed on a support material in order to maintain rigidity and improve strength. Alternatively, a plurality of thin porous mesh-like metal plates such as punch metal may be laminated to form a rigid body as a whole. When the filter medium is not rigid but flexible, if the liquid to be filtered is supplied with a high Reynolds number as in the method of the present invention, the filter medium is deformed due to the pressure difference between the inside and outside of the filter body, and good filterability is maintained. I will not drip.

The mesh size of the filter medium may be selected depending on the diameter of the coarse particles to be removed. In the filtration of the vinyl chloride polymer latex, the mesh size is preferably about 100 μm to 50 μm, for example 145. Approximately 350 mesh is preferable.

Reynolds Number The method of the present invention is characterized in that the liquid to be filtered has a Reynolds number of 2500 or more and is circulated and supplied to the filter medium. When the Reynolds number of the liquid to be filtered is less than 2,500, the filter material is clogged early and stable operation cannot be performed.

The range of Reynolds numbers used is 250.
It is 0 or more, preferably 5000 or more, and the upper limit is not particularly specified, but it is generally 15000 or less or 10000 or less from the viewpoint of the capability of the supply device, the strength of the filter, and the like. The Reynolds number is a value at the time of filtration and can be calculated from the density and viscosity of the liquid to be filtered at the treatment temperature, the inner diameter of the filter medium, and the flow rate of the liquid to be filtered in the filter medium. In addition, the Reynolds number can be usually adjusted by controlling the flow rate of the liquid to be filtered.

Circulation Method As shown in FIG. 2, a method is generally used in which a liquid to be filtered contained in a tank is circulated using a pump such as a centrifugal pump and is supplied to a filter medium so that a predetermined Reynolds number is obtained. .
Here, particularly in the filtration of the vinyl chloride polymer latex, the return pipe to the tank of the liquid to be filtered is preferably opened in the liquid phase portion of the tank in order to prevent foaming due to the emulsifier contained therein. It is effective to reduce the suction of coarse particles accumulated by the filtration process by opening the extraction pipe of No. 2 at a position slightly higher than the bottom of the tank instead of the bottom.

Treatment Conditions The conditions for the filtration treatment in the method of the present invention may be appropriately determined depending on the physical properties of the liquid to be filtered, the required treatment speed and treatment amount, the capacity of the circulation pump, the pipe diameter and the like. In the filtration treatment of the vinyl chloride polymer latex, the circulation speed is 1 to 10 m / sec (Reynolds number of 2,500.
Assuming the above is the case), the filtration speed is 10 to 40 m
It can be said that it is preferable to use conditions of ³ / hour / m ² and a treatment temperature of 20 to 80 ° C. in terms of the efficiency of equipment and the stability of the liquid to be filtered.

[0016]

EXAMPLES Next, specific embodiments of the method of the present invention will be described with reference to Examples, but the present invention is not limited as long as the gist thereof is not exceeded.
The present invention is not limited to the examples below.

(1) Operating conditions A filtering treatment was carried out using the filtering device of FIG. 2 including the cylindrical filter shown in FIG. 1 to evaluate the stability and continuity of the operation. The detailed operating conditions are as follows. Liquid to be filtered: Vinyl chloride polymer latex (those obtained by emulsion polymerization, weight average particle diameter 1.2 μm, 100
Content of coarse particles of μm or more 1.4% by weight) Density ρ = 1170 kg / m ³ (25 ° C.) Viscosity μ = 0.02 kg / m · sec (25 ° C.) Circulation method: Continuous circulation filter by centrifugal pump: 150 mesh / 16 mesh / 8mmφ
Three-layer punched metal mesh of punched metal (D) 34 mm cylindrical installation number: 6 Filtering purpose: Removal of coarse particles of 100 μm or more Treatment temperature: 25 ° C

(2) Evaluation method Reynolds number: Reynolds number (Re) = ρuD / μ In the above equation, the density ρ of the liquid to be filtered described in (1), the viscosity μ, the inner diameter D of the filter medium, and each test It was calculated by substituting the flow velocity u of the liquid to-be-filtrated in the filter medium portion. Weight-average particle size: From the particle size distribution measured using a laser diffraction particle size distribution measuring device (LA-700, manufactured by Horiba, Ltd.) calibrated with polystyrene particles having a standard particle size, the weight-average particle size and 100 μm The above particle contents were determined. Filtration continuity: Initial filtration rate (20 m ³ / hr / m
² ) is shown by the continuous operation time until it decreases by 10% to 18 m ³ / hr / m ² . However, since the test was carried out for up to 50 hours, when the filtration rate was maintained after 50 hours, it was displayed as> 50. Coarse particles: 500 ml of the filtrate was sampled every 30 minutes, and this was filtered through a 150-mesh (100 μm) filter to visually confirm whether or not the coarse particles remained on the filter.

(3) Results A filtration experiment was conducted by changing the circulation rate (flow rate u) of the liquid to be filtered so that the Reynolds number (Re) would be the value shown in the table, and the continuity of the filtration was evaluated. The results are summarized in the table.

[0020]

[Table 1]

[0021]

The Reynolds number of the liquid to be filtered circulated and supplied to the cylindrical filter having a rigid hollow body as a filter medium is 250.
By performing the filtration treatment at 0 or more, coarse particles can be removed without causing clogging and maintaining the filtration rate at the initial stage of filtration for a long time.

By using the above-mentioned method of the present invention, it becomes possible to stably remove coarse particles of the vinyl chloride polymer latex, and the obtained product (vinyl chloride resin) is obtained.
It can be expected to improve the quality.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a cylindrical filter used for carrying out the method of the present invention.

FIG. 2 is a flow sheet showing an example of a filtration device including a cylindrical filter used for carrying out the method of the present invention.

[Explanation of symbols]

1 Cylindrical filter shell 2 Filter material (filter element) 3 upper flange 4 Filter element presser 5 Upper partition plate 6 Lower partition plate 7 Filtered liquid inlet 8 Filtered liquid outlet 9 Filtrate outlet 10 Filtered liquid tank 11 pumps 12 Cylindrical filter

Continuation of the front page (56) Reference JP-A-6-154515 (JP, A) JP-A-2-58510 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01D 29 / 92 C08F 14/06

Claims (5)

(57) [Claims] 1. A dispersion liquid in which coarse particles are mixed in a large amount of fine particles is used as a liquid to be filtered, and the liquid to be filtered is filtered by a cylindrical filter having a rigid hollow body as a filter material to contain the coarse particles. in the filtration method of acquiring free dispersion as the filtrate, so that a Reynolds number of 2500 or more to be filtrate
And a method of circulating and supplying the same to the filter medium . 2. The liquid to be filtered has a weight average particle diameter of the dispersoid of 0.
The filtration method according to claim 1, which is a dispersion liquid of 01 to 50 μm. 3. The filtration method according to claim 1, wherein the liquid to be filtered is a vinyl chloride polymer latex obtained by emulsion polymerization or fine suspension polymerization. 4. The flow velocity in the filter medium is 1 to 10 m / sec,
The filtration method according to claim 3, wherein the filtration rate is 10 to 40 m ³ / hour / m ² . 5. The liquid to be filtered is laid in a layer of 5000 to 10000 .
The filtration method according to any one of claims 1 to 4, wherein the filter is circulated and supplied into the filter medium so as to have a Nords number .