JPH0971608A - Spray dryer and spray drying method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spray dryer that prevents back flow of drying gas caused inside the dryer and formation of coarse particles by the back flow of the drying gas to obtain fine dried particles stably in spray-drying a solution or dispersion of solid material, particularly a vinyl chloride-based polymer latex. SOLUTION: The spray dryer is constructed as a parallel-flow type that has a cylindrical part, conical parts on the top and bottom of the cylindrical part under the conditions that the opening angle (α) of the upper conical part and the ratio (DIN/D) of the inlet diameter (DIN) of the upper conical part to the diameter of the cylindrical part of the dryer (D) satisfy the relationships: 10 deg.<=α<=60 deg.; 0.3<= DIN/D<=0.7.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a spray dryer capable of obtaining fine spray-dried particles and a spray-drying method using the same, and more particularly to a spray-drying method of latex in which vinyl chloride polymer particles are emulsified and dispersed. .

[0002]

2. Description of the Related Art A spray dryer has been widely used to obtain fine dry particles from a solid solution, emulsion, dispersion or the like. However, depending on the conventional dryer,
It has been difficult to industrially stably produce particles having a fine particle size of 50 μm or less, particularly 30 μm or less.

For example, even in a spray dryer using a two-fluid nozzle which is suitable for obtaining fine spray droplets, the gas flow rate for spraying and the flow rate of the liquid to be sprayed are varied for the purpose of atomizing the spray droplets. Even if the ratio is increased, a backflow of the drying gas (hereinafter simply referred to as "backflow") occurs in the dryer, resulting in spray droplets or collision between spray droplets and dried particles.
In many cases, coalescence occurred, resulting in the formation of particles much larger than the intended particle size.

As a method for preventing the formation of coarse particles in spray drying, for example, JP-A-54-4195 is known.
As disclosed in Japanese Patent Laid-Open No. 1, a method is disclosed in which the spray direction of a nozzle is adjusted to cause a rotating motion of a dry air flow in a drying tower to give an appropriate heat history to the obtained dry particles. However, even with this method, it may not be possible to obtain sufficiently fine particles depending on the spray drying conditions.

Further, Japanese Patent Publication No. 51-46299 proposes a method of obtaining fine dry particles by introducing an upward swirling flow along the cylinder wall from the cylinder wall. However, in order to carry out this method, equipment for introducing the gas for swirling flow is required, which makes maintenance complicated and increases equipment cost. On the other hand, as a method of suppressing backflow by improving the method of introducing drying air into the dryer, "Practice of the latest granulation technology", No. 1
Although a hot-air rectification type dryer as described on pages 44 to 145 has been proposed, it is not so general because of high equipment cost.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to carry out spray drying of a solid solution or dispersion by backflow of a drying gas in a dryer so that sprayed droplets and dried particles rise up. Due to the collision and coalescence of the particles, it is possible to prevent the formation of particles that are much larger than the intended particle size, and to stabilize fine dry particles that do not require crushing or sieving process or can be simplified. It is to provide a spray dryer that can be obtained and a spray drying method using the same. Another object of the present invention is to obtain fine dry particles from a latex (hereinafter abbreviated as "latex") in which vinyl chloride polymer particles are emulsified and dispersed using the above spray dryer. An object of the present invention is to provide a spray drying method that can be performed.

[0007]

Means for Solving the Problems The inventors of the present invention have studied the shape of a spray dryer, particularly the shape of the upper cone portion and the relative size of the upper cone portion and the straight body portion, and as a result,
In a spray dryer in which those values are within a specific range, it is possible to reduce the backflow of the drying gas and significantly reduce the generation of coarse particles due to collision / coalescence of spray droplets and particles. Heading, completed the present invention.

That is, the gist of the present invention is to provide a parallel flow type spray dryer having a cylindrical body and cone portions above and below,
The opening angle of the upper cone portion of the dryer (hereinafter referred to as “α”, unit: degree), the inlet diameter of the upper cone portion (hereinafter referred to as “D _IN ”), and the diameter of the dryer straight body portion (hereinafter referred to as “D”). The ratio (D _IN / D)) is in the following range.

[0009]

Equation 3 10 ≦ α ≦ 60 (degrees)

[0010]

[Formula 4] 0.3 ≦ D _IN /D≦0.7

Another subject of the present invention resides in a spray dryer using a one-fluid nozzle or a two-fluid nozzle as an atomizer (sprayer) of the above spray dryer. Another gist of the present invention resides in a spray drying method in which the solid solution or dispersion is dried using the above spray dryer, and further,
The above-mentioned spray-drying method also exists in which the liquid to be sprayed is a latex in which vinyl chloride polymer particles are emulsified and dispersed. Another subject matter of the present invention resides in the above spray drying method, wherein the vinyl chloride polymer particles are produced by an emulsion polymerization method or a fine suspension polymerization method.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in more detail. (1) Spray Dryer A parallel flow type spray dryer having cone portions above and below a cylindrical straight body portion is used. As for the size, it is usually preferable to use a straight body having a diameter of 1 to 15 m and a height of 0.5 to 50 m.

The parallel-flow type spray dryer is a spray dryer which performs drying under the condition that the spray direction and the flow direction of the drying gas are substantially the same. The cone portion of this spray dryer preferably has a truncated cone shape, and the opening angle (α) of the upper cone portion is 10 degrees or more and 60
Use less than one degree. Here, the opening angle (α) of the cone portion is the apex angle of the truncated cone, assuming that the cone portion has a perfect cone shape.

The opening angle (α) of the upper cone portion is 10
If it is less than 100 ° C., the length (height) of the upper cone portion becomes extremely high, or the diameter (D _IN ) of the inlet becomes too large, and the flow rate of the drying gas tends to be non-uniform, resulting in a non-dry state It becomes uniform, and collisions between particles easily occur. On the other hand, when α is larger than 60 degrees, backflow of the drying gas is likely to occur around the connecting portion between the upper cone portion and the straight body portion, and fine dry particles cannot be obtained.

The ratio (D _IN / D) between the inlet diameter (D _IN ) of the upper cone portion and the diameter (D) of the straight body portion is 0.3 or more and 0.7 or less. If this value is less than 0.3, the reverse flow of the drying gas occurs as described above, while if it exceeds 0.7, the upper cone becomes large and the flow rate of the drying gas is uneven. It is also economically disadvantageous because it requires a large rectifier.

The value of the ratio of the length (L) to the diameter (D) of the straight body portion is usually in the range of 0.5 to 5, but it may be selected depending on the type of atomizer used. For example, it is generally 0.5 to 1 for a rotary disk type (disk type) atomizer, 1 to 2 for a two-fluid nozzle type atomizer, and 2 to 5 for a one-fluid nozzle type atomizer, but it is particularly limited. Not a thing.

The dryer is a vertical type, the drying gas is introduced from the top of the dryer, and the vertical downward flow type in which the drying gas flows downward is suitable for the present invention. is there. The outlet for the dried powder and the drying gas may be of the type discharged from the bottom of the dryer or the type discharged from the side wall of the lower cone portion. Further, it is preferable that a rectifier (disperser) for uniformly rectifying the flow direction and flow velocity of the gas is provided at the inlet of the drying gas. This rectifier is preferably a metal plate having a large number of holes and having several layers of so-called punch metal (perforated plate), but is not particularly limited as long as it can rectify the air flow.

(2) Atomizer As the atomizer (sprayer), a one-fluid nozzle (pressure nozzle), a two-fluid nozzle, a rotary disk type atomizer, etc. are often used. The dryer of the present invention is for drying. It is preferable to use a one-fluid nozzle or a two-fluid nozzle capable of matching the gas flow direction and the atomization direction. As a type of one-fluid nozzle, a type capable of fine spray such as a hollow cone type or a fan type is suitable. The type in which the spray angle is narrow and the spray is performed in a rod shape is not so preferable because the straight body portion needs to have a long length. The type of the two-fluid nozzle includes an external mixing type and an internal mixing type, both of which can be used, but the external mixing type is preferable because clogging is less likely to occur.

(3) Spray drying conditions Suitable liquids to be sprayed using the spray dryer of the present invention are atomized into fine droplets by an atomizer (atomizer) to volatilize the solvent and dispersion medium, and then dried and granulated. There is no particular limitation as long as it can be applied, for example, a solution, dispersion or melt of a thermoplastic resin such as polyester, polystyrene, polyamide, polyurethane, polyolefin, polyvinyl chloride, polyphenol, urea resin. , Melamine resin, silicone resin, epoxy resin,
Dispersion of thermosetting resin such as unsaturated polyester resin, detergent / soap, dye / pigment, insecticide, herbicide, fungicide, other agricultural chemicals, skim milk, instant coffee,
Cocoa, malt extract, starch, other foods, natural and synthetic flavors, antibiotics, serum, plasma, various vitamins,
Examples thereof include solutions or dispersions of drugs such as penicillin, glucose and various amino acids. Among these, it is preferable to spray a polymer dispersion or solution to collect fine and uniform powder and granules. Particularly, an emulsion dispersion of vinyl chloride polymer particles (latex ) Suitable for spray drying.

The type of drying gas is selected according to the properties of the substance to be sprayed, and air is usually used because it is easily available. However, an inert gas such as nitrogen is used in the spray drying of the combustible substance. Is preferable for safety. The flow rate may be determined from the heat balance in the dryer in consideration of the drying temperature, but normally a flow rate in the range of 200 to 100,000 kg / hour is used.

The flow rate of the drying gas is 0.1 to 5 (m / sec), preferably as a flow rate at the inlet of the dryer upper cone portion (drying gas flow rate / inlet cross-sectional area of the upper cone portion). It is preferably 0.2 to 2 (m / sec). If the flow velocity here is less than 0.1 (m / sec), backflow is likely to occur, while if it exceeds 5 (m / sec), the residence time of the drying gas in the dryer is short. And the drying may not be performed sufficiently.

The drying temperature needs to be adjusted according to the properties of the material to be dried, but the conditions are usually set according to the target drying efficiency, the heat resistance of the material to be dried, and the temperature of the supply heat source.
Generally, the hot air temperature for drying is 50 to 50 at the dryer inlet.
Often, 450 ° C and 25-200 ° C at the outlet are used.
When the outlet temperature is 25 ° C. or lower, it is difficult to keep the temperature stable in relation to the outside air temperature, and water-based spraying may result in insufficient drying.

When a nozzle type atomizer is used, the flow rate of the liquid to be sprayed per nozzle is usually 1
It is good to be ~ 200 kg / hour, preferably 10 to 100 kg / hour. If it is less than 1 kg / hour, the treatment efficiency of the dryer tends to be low, whereas if it exceeds 200 kg / hour, fine spraying tends to be difficult. When using a plurality of nozzles, it is preferable that the flow rate of the sprayed liquid in each nozzle be uniform.

In the case of a one-fluid nozzle, the pressure of the liquid to be sprayed is 0.5 to 500 kg / cm ² (gage pressure, the same applies below), preferably 1 to 200 kg / cm ² . If this pressure is too low, fine atomization becomes difficult,
If it is too high, the wear of the nozzle becomes severe, and the cost for pressurizing increases, and further, in spray drying of the dispersion liquid, the dispersion stability thereof may be impaired and the nozzle portion may be clogged. For a two-fluid nozzle, -1 to 50 kg /
The pressure is preferably cm ² and preferably −0.5 to 5 kg / cm ² . In the two-fluid nozzle, due to the suction force of the gas for atomization, atomization may be possible without particularly increasing the supply pressure.

In particular, air, an inert gas (nitrogen, helium, neon, argon, etc.) or water vapor is used as the atomizing gas, especially when the two-fluid nozzle is used. You may use the mixture of 2 or more types of these. The flow rate of the atomizing gas depends on the optimum load amount of the two-fluid nozzle used, but is generally 0.1 to 200 per nozzle.
0 kg / piece ・ hour, preferably 1-1000 kg / piece ・
Hour, more preferably 1 to 500 kg / piece / hour. At a flow rate of less than 0.1 kg / hour / hour, it becomes difficult to make the liquid droplets fine, while at a flow rate of more than 2000 kg / hour / hour, the wear of the nozzle gas flow path becomes severe.

The ratio (mass ratio) of the total flow rate of the gas for atomization and the flow rate of the liquid to be atomized is a main operating condition in atomization using a two-fluid nozzle, and this value is 0.1 to 20, preferably 0. The range of 0.5 to 10, more preferably 1 to 5 is preferable. If this value is smaller than 0.1, the spray droplets themselves become large, making it difficult to obtain fine dry particles, and if this value exceeds 20 it becomes difficult to atomize the spray droplets. Although effective, the consumption of the atomizing gas increases, and the cost for the compressed gas manufacturing facility and the facility operating cost increase, which is economically disadvantageous.

(4) Spray Drying of Vinyl Chloride Polymer Latex A latex in which vinyl chloride polymer particles are emulsified and dispersed in water is dried by the spray dryer of the present invention to obtain a vinyl chloride resin for paste having excellent quality. It is possible to manufacture This will be described below, but the above description may be followed except for special notes. As the latex in which vinyl chloride polymer particles are emulsified and dispersed in water, vinyl chloride or a mixture of vinyl chloride and a comonomer copolymerizable therewith in an aqueous medium in the presence of an emulsifier and a water-soluble polymerization initiator. Those containing vinyl chloride polymer particles having a particle size of 0.01 to 20 μm, which are produced by an emulsion polymerization method or a fine suspension polymerization method in the presence of an emulsifier and an oil-soluble polymerization initiator, are preferable. is there.

Examples of comonomers copolymerizable with vinyl chloride include vinyl esters such as vinyl acetate, vinyl propionate and vinyl steanate, acrylic acid, methacrylic acid,
Mono-unsaturated acids such as itaconic acid, alkyl esters of these mono-unsaturated acids, vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, octyl vinyl ether, lauryl vinyl ether, di-unsaturated acids such as maleic acid, fumaric acid, etc. Alkyl ester of diunsaturated acid, vinylidene halide such as vinylidene chloride,
Examples thereof include one kind or a mixture of two or more kinds such as unsaturated nitrile.

As the polymerization initiator used for the production of the vinyl chloride polymer latex, in the case of emulsion polymerization, for example, persulfates (sodium salts, potassium salts, ammonium salts, etc.), water-soluble hydrogen peroxide, etc. Peroxides, or water-soluble redox initiators comprising these water-soluble peroxides and water-soluble reducing agents (eg sodium sulfite, sodium pyrosulfite, sodium bisulfite, ascorbic acid, sodium formaldehyde sulfoxylate, etc.), In the case of fine suspension polymerization, azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile,
Examples thereof include monomer-soluble (oil-soluble) initiators such as lauroyl peroxide and t-butylperoxypivalate, or redox initiators composed of a combination of these oil-soluble initiators and the above water-soluble reducing agent.

Examples of emulsifiers used for producing latex include higher alcohol sulfate ester salts (alkali metal salts, ammonium salts), alkylbenzene sulfonates (alkali metal salts, ammonium salts), higher fatty acid salts (alkali metal salts, ammonium salts). Salt), other anionic surfactants, nonionic surfactants, and cationic surfactants. These surfactants may be used alone or in combination of two or more. Particularly preferred are anionic surfactants. Further, the anionic surfactant and / or nonionic surfactant may be added separately from the emulsifier for polymerization during or after preparation of the latex.

Further, in the production of latex, a polymerization degree adjusting agent and other auxiliaries may be used. Examples of the polymerization degree adjusting agent include trichloroethylene, carbon tetrachloride, and 2-
Examples thereof include chain transfer agents such as mercaptoethanol and octyl mercaptan, and crosslinking agents such as diallyl phthalate, triallyl isocyanurate, ethylene glycol diacrylate and trimethylolpropane trimethacrylate.

Other auxiliaries other than the above are, for example, cupric chloride which acts as an activator of a redox initiator,
Water-soluble transition metal salts such as ferrous sulfate and ferric nickel nitrate,
Alternatively, a pH adjusting agent such as an alkali metal salt of mono- or dihydrogen phosphate, potassium hydrogen phthalate, sodium hydrogen carbonate, etc. may be mentioned. The solid content in the vinyl chloride polymer latex is not particularly limited and is usually 20-80.
The latex after the polymerization reaction may be used as it is or may be concentrated by a method such as ultrafiltration. The viscosity of latex is usually 0.1 Pa · sec or less.

[0033]

EXAMPLES Hereinafter, specific embodiments of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. "Parts" and "%" in the examples mean "parts by weight" and "% by weight", respectively, unless otherwise specified.

<Examples, Comparative Examples 1 to 3> (1) Production of Vinyl Chloride Polymer Latex A vinyl chloride polymer latex was produced by polymerizing a vinyl chloride monomer by a seeded emulsion polymerization method. The polymerization initiator used was a redox initiator of potassium persulfate-sodium pyrosulfite, and the main emulsifier was sodium lauryl sulfate. The reaction temperature was 55 ° C., the solid content of the obtained latex was 46% by weight, and the average particle size of the polymer particles in the latex was 1.1 μm. The average degree of polymerization of the produced polyvinyl chloride was 1200. The following spray drying was performed using this latex.

(2) Dryer A dryer having a straight body portion having a diameter (D) of 4 m and a length of 4 m and a lower cone portion having a length of 3.1 m is used. The opening angle (α) of the upper cone portion is The above-mentioned latex was spray-dried using a dryer having specifications such that the inlet diameter (D _IN ) and the length (L _TOP ) are shown in the table. As the atomizer, the material is stainless steel, and the cross-sectional area of the opening is 95 mm in the liquid flow path (inner cylinder).
^2. Six external mixing type two-fluid nozzles having a gas flow path (outer sleeve-inner cylinder gap) of about 48 mm ² were installed on the same circumference on the upper part of the straight body part of the dryer via an arm. The spray angles of the nozzles were all directed vertically downward. Further, air is used as a drying gas, and this airflow is rectified by a rectifier (air disperser) mounted on the upper cone portion of the dryer and supplied as a downflow.

(3) Spray drying conditions In spray drying, the inlet temperature of the drying air is 160 ° C., the outlet temperature is 55 ° C., and the latex flow rate is 70 kg per nozzle.
/ Hour, the amount of gas (air) for spraying was 630 kg / hour (mass ratio = 1.5), and the flow rate of the drying air was 6500 kg / hour. The air flow velocity at the inlet of the upper cone portion of the dryer was measured at three points on the diameter of the circle forming the cone portion cross section using an anemometer.

(4) Measurement of particle size distribution of dry vinyl chloride resin A laser diffraction particle size distribution measuring device (manufactured by Horiba, Ltd.,
LA-500) is set with a flow cell holder, and about 200 ml of 0.1% polyoxyethylene sorbitan monolaurate aqueous solution as a dispersion medium is put in a bath and stirred and circulated. The blank of the diffraction pattern was measured, and a small amount of vinyl chloride resin obtained by spray drying was added to the bath, and
After dispersing for 0 seconds, the particle size distribution of the sample is measured. From the obtained particle size distribution, the average particle size (median size) and the content ratio of coarse particles having a particle size of more than 70 μm are calculated.

(5) Evaluation of results The results are summarized in the table. As can be seen from this table, by drying using the spray dryer of the present invention, the average particle size of the obtained dry vinyl chloride resin becomes 50 μm or less, and the number of coarse particles exceeding 70 μm is small. Has become.

[0039]

[Table 1] *: Content ratio of coarse particles exceeding 70 μm

[0040]

By carrying out the drying using the spray drying of the method of the present invention, it is possible to reduce the backflow of the drying gas in the dryer, especially in the vicinity of the connecting portion between the upper cone portion and the straight body portion. Therefore, it is possible to prevent coarse particles from being generated due to collision or coalescence of spray droplets and dry particles, and it is possible to stably obtain fine dry particles. Further, by applying the present dryer to spray drying, particularly spray drying of vinyl chloride polymer latex, the generation of coarse particles can be reduced, whereby the steps such as crushing and sieving can be omitted or simplified.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining a spray dryer of the present invention.

[Explanation of symbols] 1 rectifier (disperser) 2 upper cone portion 3 straight body portion 4 lower cone portion 5 drying gas inlet 6 dryer outlet duct D _IN upper cone portion inlet diameter D straight body portion diameter L _TOP upper cone portion length L Length of straight body L _BOT Length of lower cone α Angle of upper cone

Claims (5)

[Claims] 1. A parallel flow spray dryer having a cylindrical straight body having cones above and below, and an opening angle (hereinafter referred to as "α", unit: degree) and an upper portion of an upper cone of the dryer. The ratio (D _IN / D) of the inlet diameter of the cone portion (hereinafter referred to as “D _IN ”) to the diameter of the dryer straight body portion (hereinafter referred to as “D”) is in the following range: Spray dryer. [Equation 1] 10 ≦ α ≦ 60 (degrees) [Equation 2] 0.3 ≦ D _IN /D≦0.7 2. The spray dryer according to claim 1, wherein a one-fluid nozzle or a two-fluid nozzle is used as an atomizer. 3. A spray drying method in which the solid solution or dispersion is dried using the spray dryer according to claim 1. 4. The spray drying method according to claim 3, wherein the liquid to be sprayed is a latex in which vinyl chloride polymer particles are emulsified and dispersed. 5. The spray drying method according to claim 4, wherein the vinyl chloride polymer particles are produced by an emulsion polymerization method or a fine suspension polymerization method.