JPH026561B2 - - Google Patents

Description

Claim 1: A method of forming a thermoplastic polymer solution in a volatile organic solvent into a large number of relatively uniformly sized, substantially ellipsoidal solidified particles, comprising: (A) passing said solution through a jet nozzle; (B) superheated steam is injected into the above flow to create a suspension of disordered polymer particles in the gas flow consisting of evaporated organic solvent and steam; (C) is passed through a uniformly heated tortuous solidification tube having a uniform diameter and a set of at least six semicircular curvatures, such that said suspension remains in said tube. and (D) separating the fine particles from the gas stream.

2. The method of claim 1, wherein said heated steam is at a temperature in the range from 100°C to 500°C, said heated tube is at a temperature in the range from 80 to 170°C, and said residence time is at a temperature in the range from 80 to 170°C. 0.01 to 60
A method that is in the range of seconds.

3. The method of claim 2, wherein said heated steam is at a temperature in the range from 190°C to 230°C, said heated tube is at a temperature in the range from 125 to 150°C, and said residence time is at a temperature in the range from 125 to 150°C. 0.1 to 2
A method that is in the range of seconds.

4. The method of claim 1, 2 or 3, wherein the thermoplastic polymer is a polycarbonate polymer.

Description The present invention relates to a method of forming a thermoplastic polymer solution in a volatile solvent into a large number of substantially spheroidal compacted granules.

It is known in the art that various liquid foods such as milk, eggs, orange juice, and coffee can be spray dried with steam or hot air. The method of hardening this dry food by contacting it with a spray of untreated liquid food is
It is disclosed in US Pat. No. 3,039,107 issued on June 12, 1962.

Furthermore, it is known from the following patents that finely divided and/or finely divided aqueous slurries of polymers can be obtained by steam precipitation of organic slurries or solutions of various polymers.

US2592814 (4-15-52) US3050113 (8-21-62) US3202647 (8-24-65) US3287301 (11-22-66) US3306342 (2-28-66) US3427370 (2-11-69) US3450184 ( 6-17-69) US3596700 (8-3-71) US3862103 (1-21-75) It is known that steam precipitation of polymer solutions produces dry or substantially dry polymer granules. The following patent shows this.

US3508339 (4-28-70 US3804145 (4-16-74)) US3968003 (7-6-76) US4209912 (7-1-80) US4212967 (7-15-80) In addition, the US Pat. No. 4,252,968 shows that polycarbonate powder can be solidified by heating it to 165-190°C in an agitated, heated tubular dryer.
(1981-2-24).

Although the method of making a water slurry of polymer fines described above appears to be efficient, the need to remove the water after making the slurry and remove the water adsorbed on the polymer is a clear disadvantage. This is a point. Furthermore, the method of US Pat. No. 4,252,968, in which a polymer powder is made and then consolidated by means of rotating mechanical equipment that can be mechanically damaged, is clearly disadvantageous.

The object of the present invention is to form a solution of a thermoplastic polymer in a volatile organic solvent into a large number of relatively uniformly sized, substantially spheroidal solidified granules. The method of the present invention includes the following steps: (A) Passing the aforementioned solution through a jet nozzle to create a high velocity stream; (B) Injecting superheated steam into the aforementioned stream to create a gas stream consisting of evaporated organic solvent and steam. (C) forming a suspension of polymer microparticles in a turbulent state with a uniform diameter and a set of adjacent circular curvatures of at least six semicircular curvatures; through a uniformly heated tortuous solidification tube having a temperature of approximately 100 nm, the residence time of said suspension in said tube being sufficient for substantially complete solidification of said particulates, and (D ) Separating the granules from the gas stream described above.

FIG. 1 shows the equipment used in the process of the invention and includes a steam settling tank 14, a solidification tube 16, and a cyclone 22.

FIG. 2 shows a modification of the solidification tube in which the tortuous tube of FIG. 1 has been modified to include a 360 degree bend.

3 is an isometric view of the tube and container shown in FIG. 1; FIG.

FIG. 4 is an isometric view of the modified tube and container, showing a set of 180 degree bends in the vertical plane and a combined 360 degree transverse bend.

FIG. 5 shows a 5-5 cross section of the steam settling tank of FIG.

FIG. 6 is a side view of the steam settling tank.

In the figure, the steam settling tank is shown at 14. The introduction pipe 10 transfers the polymer solution of organic solvent to the precipitation tank 14.
, where it comes into contact with superheated steam coming from the steam inlet 12 . A connector pipe is shown at 15, which connects the steam settling tank 14 and the solidification tube 16 by screws. Required interlocking couplers not shown.

Tube 16 is supported in heating vessel 17 by a support (not shown). Although the heating container is shown as a rectangular parallelepiped, it can also be cylindrical if desired. The container 17 enters through the entrance 18, and
It is heated to the appropriate drying temperature by low pressure steam from 0.

The fine particles are blown by steam pressure into a cyclone separator 22, which has an upper outlet 2 for water vapor and organic solvent.
4, and has a lower outlet 26 for the solidified granules.

The tube 16 has an upper 180 degree curve 32 and a lower portion all in one vertical plane as shown in FIG.
Not only 180 degree curvature 34 but also upper 360 degree curvature 28 and lower 360 degree curvature 30 and various combinations thereof, e.g. 360 degree curvature followed by 180 degree curvature
Various arrangements can be made, such as sets of degree curvatures or alternating combinations of 180 degree and 360 degree curvatures.

Similarly, as shown in Figure 4, 180 degree curve 3
2 and 34 are in different planes that cross this
Alternating sets of 360 degree curvatures 36 and 37 are also possible.

The polymer solution enters the steam precipitation vessel 14 through the ray inlet 46 and flows through the large bore 48 to the constriction 50 where the flow rate is greatly increased.
The conical slope 5 passes through the internal space 54 from the entrance 12
6 and into the superheated vapor stream flowing into the polymer solution.
The polymer solution is passed through jet nozzle 52 at a rate sufficient to break up the solution into a stream of fine particles suspended in superheated steam.
, and this suspended particulate stream exits through the streaked outlet 60 .

Steam settling tank 14 includes an inner body 40 that is adjustable in position relative to outer body 38 by one or more shims 42 .
Fasteners such as bolts and nuts 44 are used to assemble them. The filler 42 allows the distance between the conical slope 56 and the conical sheet 58 to be properly adjusted, thereby providing a thin layer of superheated steam at a flow rate suitable for breaking down the polymer solution into fine particles. It will be done.

In the process of the present invention, a polymer solution in an organic solvent is pumped into a jet nozzle at a rate in the range of about 1-100 feet/second (0.3-30.5 m/S).
Preferably 10-50 feet/second (3.0-15.2m/
S) Becomes a fluid with a range of speeds. Polymer solutions in methylene chloride, ethylene chloride, or monochlorobenzene are preferred, but thermoplastic polymers such as polyethylene, polystyrene, polybutadiene, and polyisoprene are also suitable, if they are suitable volatile organic It can be processed if it is dissolved in a solvent.

Temperature in the range 100-500℃, preferably 190-230
Superheated steam at a temperature in the range of 0.degree. C. is injected into the polymer stream as a conical stream to decompose the polymer solution into steam and a fine mist of polymer suspended in a volatilized organic solvent.

This suspension is blown into a solidification tube having a set of circular curves where it is heated by rolling contact with the heated inner wall of the tube and becomes sticky and sticks to each other. However, because the flow velocity inside the tube is high, it does not adhere to the walls of the tube. As they pass through the tube, the particles are constantly rotated repeatedly due to the large number of curvatures, becoming substantially larger and somewhat rounded.

The preferred solidification tubes are 6 to 20 in the same plane.
It consists of a curved tube with a set of 180 degree curves at the top and bottom. The actual number of bends is not very important, but generally at least six bends are required to properly round the granules, while more than 20 bends will cause the granules to be tubed or piped. Requires higher gas pressure to flow through the bend in the tube and may partially or completely rupture the tube. Similar criteria apply to the design of more complex arrangements.

The outer wall of the tube is heated by steam and
to 170°C, preferably 125 to 150°C.

Generally, the residence time of particles in the tube is 0.01
to 60 seconds, preferably 0.1 to 2 seconds. It is understood that the residence time is a direct function of several variables, such as the feed rate of the superheated steam and/or polymer solution, the temperature of the superheated steam and the temperature of the steam heating the solidification tube. In any case, the residence time depends on whether the particles are spherical or
The granules are selected to be substantially fully consolidated into larger dimensions of various shapes commonly described as spheroidal, bead-shaped, and the like.

Some granules are oblate spheroids, others are more flat pebble-like, but many appear to be substantially spheroidal. What is important in the present invention is that the granules have a substantially uniform size or mesh range and are low in dust or powder.

The granules are conveyed by a gas stream to a conventional cyclone separator where organic solvent vapors and water vapor are withdrawn from the top and condensed to recover the solvent.
The granules are extracted from the bottom, moisture and solvent removed in an indirect mechanical steam dryer, and processed in a conventional vent extruder and chopper to obtain polycarbonate pellets of suitable purity for molding or external sales. .

The invention will be further illustrated by the following examples.

Example 1 10% methylene chloride at 25℃
of polycarbonate solution at 30lb/hr (37.8g/s)
The mixture was then supplied to the settling tank shown in FIG. 200 psig
(1.38MPa gauge) steam (200℃) is also
115.5 lb/hr (14.55 g/s) was fed to the settling tank.

The internal dimensions of the settling tank are 0.312 inch (7.92 mm) ID for the polycarbonate injection barrel and a mixing slot for
It has a 0.375 inch (9.52mm) ID. The steam flow path was adjusted so that the pressure drop in the annular portion was 30 psi (207 kPa).

The polycarbonate was dispersed into fine particles in a mixer. This particulate was then conveyed to a solidification tube. The microparticles became sticky and recombined into spherical granules. This was accomplished by passing through alternating circular curvatures of the solidification tube. The inner diameter of the tube is
0.305 inches (7.75mm), 7 feet (2.1m) long
Made from 3/8" (9.525mm) stainless steel tube. The tube is 180 similar to Figure 12.
It includes 20 degree bends, which have an inside diameter of about 1 inch.

18lb/hr to control vessel temperature
(2.27 g/s) of 40 psig (276 kPa gauge) steam (132°C) was used. The average heat transfer coefficient of the container is
It was 135BTU/hr.ft ^2. (767w/m ² K).

The polycarbonate granules obtained from the cyclone contained 40% by weight water and 1.5% by weight methylene chloride. The dry bulk density of the polycarbonate granules was 0.2 g/cm ³ . The product is #4-
The distribution was between #12 mesh (4.75 mm and 1.68 mm) (US sieve), and 86% by weight was in the range of #4 to #8 mesh (4.75 and 2.38 mm).

Examples 2-7 A 10% by weight solution of polycarbonate in methylene chloride was fed to the steam precipitation tank of Figure 1 at various different rates expressed in lb/hr (g/s). Process conditions other than speed were almost the same as in Example 1.
Solidification tube has an outside diameter of 0.625 inches (15.875 mm)
It is made from 316 stainless steel and the wall thickness is
It was 18BWG gauge or 0.048 inch (1.22mm). The tube includes 15 180 degree bends with an inside diameter of approximately 2.625 inches (66.675 mm).

The superheated steam feed rate was adjusted to maintain a constant polymer solution to steam ratio of 3.95:1.

Table 1 shows the results of the sieve test of the recovered fine particles.

The results show that the method of the present invention produces fine grains of various sizes, but mostly US sieve #4.
(0.187 inch or 4.76 mm) with very small amounts of fines
2.38mm) finer.

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