JPH0118083B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for granulating thermoplastic polymer fine particles suspended in a liquid medium and continuously obtaining a suspension of uniform granulated particles having porous properties. As a method for recovering thermoplastic polymers, for example, an appropriate amount of a coagulant is added to a thermoplastic polymer latex produced by emulsion polymerization to coagulate the latex, and after washing with water and separating it from water, it is heated and dried. Therefore, methods for recovering polymers are often employed in polymer manufacturing processes. In the process of recovering this polymer, the polymer often becomes suspended in the liquid medium as fine particles. In such a case, if you try to recover the polymer fine particles from that state, the productivity will decrease due to clogging of the cloth during the dehydration process, the fine powder will scatter during the drying process and the recovery rate will decrease due to this, and furthermore, the obtained powder will be pelletized. Since various problems occur, such as poor penetration into the ruder during oxidation, it is necessary to granulate the fine particles to a certain size before recovering them. A common method for granulating such fine particles is to add a certain type of binder to solid particles to moisten the surface of the fine particles, and then use a rolling or other granulation device to granulate the particles to a desired particle size. . However, if the target fine particles are supplied in a suspended state in a liquid medium, it is necessary to reduce the liquid medium to an appropriate amount by solid-liquid separation operation in advance in order to granulate using the general equipment described above. There is. In that case, the addition of pretreatment steps such as separation, concentration, or drying complicates the apparatus system, and the economic burden becomes industrially unacceptably large. In particular, the finer the particle size, the more technically difficult the pretreatment becomes, and the higher the cost required. On the other hand, there is a method of drying slurry using a dryer known as a spray dryer. According to this method, the solvent of the object to be supplied as a homogeneous solution is turned into droplets, and the solvent is evaporated by flowing countercurrently or cocurrently with a high-temperature gas flow in the device, and granulation and drying can be performed simultaneously. However, in order to obtain porous granules, a post-processing step of humidification, granulation, and re-drying is required, and granules cannot be obtained if the fine particles are suspended in a liquid medium. However, the method using a spray dryer cannot be applied to the granulation of fine polymer particles suspended in a solvent body, which is the object of the present invention. It is widely known that the surface of thermoplastic polymers softens above the thermal deformation temperature of the polymer, and that when solid particles in the form of particles are brought into contact with each other, adhesion and fusion occur. However, in the case of fine particles in a suspended state, their weight is small and it is difficult for them to have inertial force, and due to the resistance of the intervening liquid medium, it is not possible to simply stir them in a stirring tank and raise the temperature in the system. If there are not enough grains and the temperature is raised too much in an attempt to obtain a sufficient granulation effect, large lumps will occur, making it impossible to discharge them from the tank. The present inventors stably granulated particles to a desired particle size by blowing high-temperature steam into a suspension in a piping system and raising the temperature in the system to a temperature higher than the heat distortion temperature of the polymer. We focused on the fact that if we could do this, it would be much easier to achieve the goal than installing a stirring tank, and as a result of intensive consideration of the various conditions for realizing this process, we found that: The present invention was achieved by discovering that when a suspension of a thermoplastic polymer is brought into contact with steam under appropriate conditions, moderately uniform granulated particles with extremely uniform porous properties can be obtained even without a stirring tank. That is, the present invention provides a method for continuously granulating thermoplastic polymer fine particles suspended in a liquid medium, in which the temperature in a mixing system of a suspension of thermoplastic polymer fine particles and high-temperature steam is controlled to Maintained above heat distortion temperature and in gas/liquid/solid state, gas/(liquid + solid)
The polymer suspension and the high-temperature steam are brought into continuous contact for at least 0.05 seconds so that the volume ratio of This is a method for continuous granulation of thermoplastic polymer particles, characterized by: The present invention will be explained in detail below. The thermoplastic polymer to which the present invention is applicable can be of any type as long as its fine particles can be obtained in a suspended state. Specific examples include polymers of aromatic vinyl compounds such as styrene and styrene substituted with nuclear halogens, copolymers of these with one or more unsaturated monomers such as acrylonitrile or methyl methacrylate, and α-methyl α such as styrene, nuclear halogen substituted α-methylstyrene, etc.
-A polymer of an alkyl-substituted aromatic vinyl compound or a copolymer of the same with one or more unsaturated monomers such as an aromatic vinyl compound, acrylonitrile or methyl methacrylate, a copolymer of acrylonitrile and methyl methacrylate,
Copolymers of styrene and maleic anhydride or their copolymers with acrylonitrile, rubber-reinforced polymers of these polymers or copolymers (e.g. HIPS resins, ABS resins, AAS resins, AES resins), polycarbonates, polyvinyl chloride, vinyl chloride and vinyl acetate copolymers. In particular, the method of the present invention exhibits its effects when applied to a polymer whose liquid medium has a heat deformation temperature higher than a temperature where the vapor pressure exceeds atmospheric pressure. The high-temperature steam used in the present invention is the same type of medium vapor as the liquid medium of the suspension and water vapor. Both dry steam and wet steam are used, but the conditions are such that the steam has sufficient enthalpy to raise the temperature of the suspension above the desired temperature, and that an appropriate amount of steam remains in the suspension and condensate at the desired temperature. It needs to be supplied with The amount is determined in relation to the chemical and physical properties of the target thermoplastic polymer particles, the flow rate in the mixing zone after contact, and the retention time. If the amount of steam supplied is appropriate, the frequency of particle collisions will increase due to the turbulent state during contact between the suspension and high-temperature steam and the subsequent mixing zone, which will advance granulation and produce granulated particles with a uniform particle size distribution. is obtained, but
If the amount of steam supplied is inappropriate, granulation will be insufficient or agglomerates will be generated, making it impossible to continue operation. The conditions depend on the pipe diameter and length of the mixing zone, but as a mixed phase state, the volume ratio of gas/(liquid + solid) is 0.5~
A range of 100 is appropriate. If this ratio is less than 0.5, sufficient granulation cannot be expected at an acceptable temperature in terms of deterioration of the thermoplastic polymer;
On the other hand, if it exceeds 100, the equipment will become larger in industrial terms, and although the equipment cost will be high, no improvement in the granulation effect can be expected. Preferably, the above ratio is selected to be 4 to 30. Under these conditions, operation is stable even in the face of disturbances such as flow rate fluctuations, and sufficient granulation is possible. The contact residence time between the polymer suspension and high-temperature steam is affected by temperature deterioration of the thermoplastic polymer, granulation properties, and the size of the equipment, but it is necessary to allow contact to occur for at least 0.05 seconds or longer. If it is less than 0.05 seconds, the desired particle size cannot be obtained unless the treatment is performed at a temperature considerably higher than the heat distortion temperature of the thermoplastic polymer, and thermal deterioration of the polymer may become a problem. This is disadvantageous in terms of stable operation. Even if the upper limit of the residence time is 100 seconds or more, the granulation performance will not be fatally degraded, but the granulation will be excessive and there will be a strong tendency to form small lumps, and the equipment will become larger, making it uneconomical. Undesirable. From the viewpoint of uniformity of particle size distribution, the preferred residence time is 0.1~
It is 10 seconds. The injection of the cooling medium condenses the vapor present in the mixing zone, lowers the temperature of the polymer, prevents the polymers from adhering to each other, and blocks the mixing zone, and is also effective in preventing deterioration of the polymer. The cooling medium is not particularly limited as long as it has a suitable heat capacity, but water is usually used because it is easily available and has a large heat capacity. The amount used is from the same amount to 1000 times, preferably from 1 to 10 times, the amount of steam blown. It is of course possible to improve the granulation properties by mixing a binder into the polymer fine particle suspension in the method of the present invention. By adding, for example, a polymer monomer or a solvent with good compatibility as a binder, the same granulation effect as when no binder is used can be obtained while shifting the polymer granulation processing conditions to, for example, a lower temperature side. You can also do that. Also, types that do not adversely affect the quality of the polymer suspension.
It is also possible to use a quantity of polymer latex as a binder to obtain a granulating effect. An embodiment of the present invention will be described with reference to the drawings. The suspension of thermoplastic polymer fine particles is passed through the flow control valve 1.
It enters the system via. High-temperature steam is introduced into the system through a flow rate control valve 2 while retaining an appropriate enthalpy, causes appropriate granulation to occur in a mixing zone 3, and is cooled and condensed by a cooling medium introduced through a valve 4. 5
This is a crusher for producing large lumps, and is not necessary depending on the operating conditions. The valve 6 sets the pressure within the system and controls the temperature of the mixing zone. The shape of the mixing zone is not particularly limited as long as it can maintain the desired residence time, but a cylindrical shape is generally preferred from the viewpoint of ease of manufacturing the device, and the diameter (D)
and length (L) (L/D) of 0.01 to 10,000, preferably 1 to 1,000. Further, stirring blades may be inserted into the mixing zone to increase the number of times the slurry particles come into contact with each other or to maintain good gas-liquid contact. According to the method of the present invention, (1) the resulting granulated particles have a porous property and therefore have low residual volatile matter;
(2) Particles with uniform particle size can be obtained, (3) Separation in post-processing steps and loss during drying operations are significantly reduced, and (4) granulation can be performed using relatively simple equipment. has. Next, the present invention will be explained with reference to examples. Example 1 A suspension of ABS resin, which was obtained by adding a coagulant to ABS resin latex having a heat deformation temperature of 87° C. and coagulating it, passing 100% by weight through a 200-mesh wire gauze, was granulated according to the apparatus shown in the figure. The ABS resin suspension (volume ratio of 12.5 particles, 37.5 water, and 50 air) taken out from tank A was pumped to 1/2 diameter using pump B at a temperature of 75°C and a flow rate of 500/Hr.
The steam was supplied to piping 3 with a length of 2.0 m and 71.0 kg/hr of steam was supplied from valve 2 at the same time, so that the temperature of piping 3 was 142°C. Gas phase at this time/
The suspension volume ratio was 26 and the residence time was 0.12 seconds.
In pipe 3, the fine particles of ABS resin soften under high temperatures and collide with each other, increasing the particle size and increasing the particle size to 200 mm.
The percentage of particles passing through the mesh wire mesh is 4.6% by weight
It became. Cooling medium D is installed at the outlet of pipe 3 to cool the ABS resin particles, harden them, and stabilize the particle size.
Water was injected as The amount of water is 500/Hr with valve 4.
was controlled. cooled by cooling medium D
The slurry of ABS resin particles and water is discharged to the outside of the system through a crusher 5 and a pressure control valve 6. The particle size distribution of the ABS resin particles discharged from the system was measured using a Tyler standard sieve. As a result, all particles passed through a 5-mesh sieve. The proportion of particles that passed through 5 meshes but did not pass through 100 meshes was 93.0% by weight of the total. Passed 100 meters
The percentage of particles that do not pass through 200 meshes is 2.4% by weight.
It was hot. The percentage of particles passing through 200 meshes is
It was 4.6% by weight. Comparative Example 1 The ABS resin suspension used in Example 1 was used, the steam supply amount was 123.2 Kg/Hr, and the length of the pipe 3 of the pressure granulation device was 0.2 m, but no changes were made. , Pressure granulation was carried out in the same manner as in Example 1. The residence time at this time was 0.01 seconds. Regarding the particle size distribution of the obtained ABS resin particles, the proportion of particles passing through 200 meshes was 19.0% by weight, which was a larger amount of fine particles than in Example 1. Example 2 The volume ratio of air in the ABS resin suspension used in Example 1 was changed from 50% to 8%. Further, the diameter of the pipe 3 of the pressure granulation device was not changed, and the length was set to 3.1 m. Pressure granulation was performed with a steam supply rate of 50.1 Kg/Hr. At this time, the gas phase/suspension volume ratio was 4.0,
The residence time was 1.0 seconds. The particle size distribution of the obtained particles was such that the proportion of particles passing through 200 meshes was 8.2% by weight. Example 3 The volume ratio of air in the ABS resin suspension used in Example 1 was changed to 2%. Furthermore, the length of the pipe 3 of the pressure granulation device was set to 1.4 m without changing the diameter. Pressure granulation was performed with a steam supply rate of 47.3 Kg/Hr. At this time, the gas phase/suspension volume ratio is 1.0,
The residence time was 1.1 seconds. The particle size distribution of the obtained particles was such that the proportion of particles passing through 200 meshes was 9.5% by weight. Comparative Example 2 The volume ratio of air in the ABS resin suspension used in Example 1 was changed to 0.5%. The length of the pipe 3 of the pressure granulation device was set to 1.4 m without changing the diameter. Pressure granulation was performed with a steam supply rate of 46.5 Kg/Hr. At this time, the gas phase/suspension volume ratio was 0.27 and the residence time was 1.7 seconds. The particle size distribution of the obtained particles was such that the proportion of particles passing through 200 meshes was 30.3% by weight. The results of Examples 1 to 3 and Comparative Examples 1 to 2 are summarized in the table. Example 4 A suspension (100% by weight of a suspension (fine particles 12.5,
Pressure granulation was carried out in the same manner as in Example 1, with a volume ratio of 37.5% water and 50% air (volume ratio) 500/Hr, a steam supply rate of 120 Kg/Hr, and a length of the piping 3 of the pressure granulation device to 3 m. At this time, the gas phase/suspension volume ratio was 41,
The residence time was 0.5 seconds. The particle size distribution of the obtained α-methylstyrene-methyl methacrylate-acrylonitrile copolymer particles was such that the proportion of particles passing through 200 meshes was 3.5% by weight.
It was hot. 【table】

[Brief explanation of drawings]

The figure shows a flow sheet of an example of implementing the method of the present invention. A... Suspension tank, B... Pump, C... High temperature steam, D... Refrigerant, 1, 2, 4, 6... Flow rate control valve,
5...Crushing machine.

Claims (1)

[Claims] 1 In a method of continuously granulating thermoplastic polymer fine particles suspended in a liquid medium, the temperature in the mixed system of a suspension of thermoplastic polymer fine particles and high-temperature steam is set to the heat distortion temperature of the polymer. It holds gas, liquid,
In the solid state, the polymer suspension and the high temperature steam are brought into continuous contact for at least 0.05 seconds so that the volume ratio of gas/(liquid + solid) is 0.5 to 100, and then the cooling medium is added to the mixture. A method for continuous granulation of thermoplastic polymer particles, characterized by injecting the vapor into a system and condensing the vapor.