DE2435704A1 - PROCESS AND DEVICE FOR THE PRODUCTION OF POLYMERIZED DISPERSIONS WITH LOW MONOMER CONTENT - Google Patents

Description

"Process and device for the production of polymer dispersions with low monomer content "

The invention relates to a method and a device for spray treatment of polymer dispersions to reduce their monomer content.

The monomer content of polymer dispersions' should be from
for various reasons. On the one hand, the monomers still present can react in an uncontrolled manner during storage of the dispersion and thereby have an unfavorable effect on the properties of the dispersions themselves and the layers or coatings produced therefrom. On the other hand, the monomers evaporating with the water during the drying of the dispersions can lead to health problems. In particular when working up dispersions to form plastic powders, for example in large-scale production
of polyvinyl chloride, if the monomer content of the dispersions is high, for example above 0.1% by weight, considerable amounts of monomer escape with the drying air, which must be reduced for reasons of environmental protection. Furthermore, coatings produced from dispersions for food packaging with a higher monomer content can affect the smell or taste of the packaged goods and thus make them unsuitable for the intended application.

Various methods are known for reducing the monomer content of aqueous polymer dispersions.

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It is common practice to remove the monomers by releasing the pressure of the polymerization approach.

It is also known that the polymer dispersion of monomers can be achieved by passing steam or inert gases through to free. For this purpose, considerable amounts of steam or gas are used, especially in the case of polymer dispersions that are used for Foaming tend to cause trouble. The addition of defoamers makes the process more expensive and is not always effective and can adversely affect the dispersion properties. To avoid the difficulties, it is also known the foam formed when the water vapor or the inert gases are passed through at steam flow speeds of over 100 m / sec by rapidly lowering the pressure, separating the steam from the broken dispersion foam and the latter returned to the boiling dispersion. The process works discontinuously, has high steam consumption and requires considerable expenditure on equipment.

In a further known method, the dispersion is mixed with water vapor or hot inert gases in a tube and the three-phase mixture formed is separated again shortly thereafter into the dispersion and the gas phase. It is also known to atomize polymer dispersions in steam flowing at high speed, to pass the mixture between heated plates through a relaxation zone, where the dispersion is separated from the gas phase in a cyclone. The last two processes mentioned work continuously, but also require large amounts of steam and considerable expenditure on equipment. Despite the high flow rate, they are sensitive to overheating of the dispersion, coagulation phenomena and caking of the polymer on the walls of the apparatus. In addition, monomers that are included in the polymer core and require a certain diffusion time are only removed very imperfectly. Pre-degassing is usually required.

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In a further known process, the dispersion is passed in a column against a stream of steam. Here too the outlay on equipment is relatively high; at high throughputs, dispersions with low surface tension foam on. In addition, deposits of solid matter can easily lead to clogging.

Finally, it is known that dispersion in a vapor atmosphere to spray so that the sprayed particles fall through the steam by means of gravity. This will be a big, relative expensive container needed.

A continuous process has now been found which requires relatively little expenditure on equipment and low energy consumption allows effective removal of the monomers from polymer dispersions, in particular from those used for The formation of foam and incrustations on the apparatus parts tend to be sensitive to shear and thermal stress and require a longer treatment time, for example more than 30 minutes, in order to largely remove the monomers.

According to this process, a polymer dispersion is produced by emulsion or suspension polymerization of the monomer or monomers in aqueous liquor with subsequent expansion of the polymerization batch and removal and condensation of the gaseous products and is subjected to a treatment which is characterized in that the optionally heated dispersion in a vertical, rotationally symmetrical container radially in the form of a hollow cone or a disk of droplets with a maximum diameter of 6 mm (measured according to Fraser-Eisenklam, Trans. Instn. Chem. Engs. ]> ± (1956), pp. 301 to 302 a 20 ⁰ C warm dispersion at normal pressure) is sprayed against the container wall, deposited there and collected at the container bottom , with gaseous substances being drawn off from the spraying device above the exit of the dispersion.

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A vertical cylindrical container is advantageously used. This can be done in the polymerization plants Anyway, mostly existing dispersion collecting containers are used, and also in several series-connected Containers the treatment can take place.

The container can also consist of two or more superimposed be composed of cylindrical parts, the respective lower part with a smaller diameter being concentric a piece protrudes into the overlying part with a larger diameter (see Figure 5). The resulting ring-shaped The channel (19) should expediently have at least one opening for discharging the liquid (15). Each of the cylindrical Parts can contain a spraying device (6; 17) which can be switched so that the method can be carried out in several stages in a row in one container is possible.

The container jacket can be designed to be temperature-controlled over its entire surface or in partial areas, for example by a double jacket through which a liquid heating or cooling medium flows. In particular, it can be beneficial be to heat or cool the container jacket where the sprayed dispersion hits the inside.

As a spray device for the dispersion it is expedient to use at least a spray nozzle with 'hollow cone-shaped spray jet (hollow cone nozzle) is used, which is mounted in the upper part of the container is that the axis of the hollow cone of sprayed material coincides approximately with the container axis. Is preferred the jet of the nozzle is directed downwards.

The scattering angle of the hollow cone, that is the angle between two opposing surface lines of the cone surface, which represents the main spray direction ■ 'of the nozzle, should be between 30 and 180, the cone surface can therefore also be a horizontally lying disc. A scattering angle of 80 to 120 ° is advantageously chosen.

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A single-fluid nozzle is used as a hollow cone nozzle, for example a spiral or eccentric nozzle, as described in Chemical Eng. Prog. £ 9_, ^s · ¹⁸ 5 to 186, which produces a hollow cone that is as sharply delimited as possible.

It is useful to provide the narrowest passage cross-section of the nozzle about twice as large as the diameter of the largest Solid particles in the dispersion. Generally will For reasons of capacity, a passage cross-section of at least 1 mm is selected; a passage cross-section is preferred from 5 to 100 mm, in particular from 10 to 50 mm.

The spraying device should atomize the dispersion in such a way that the largest droplets have a maximum diameter of 6 mm. Particularly good results are achieved when the mean droplet size, measured according to Fräser and Eisenklam (loc. Cit.) On a ^{dispersion at 20 °} C. at normal pressure, is between 0.05 and 3 mm in diameter.

The exit speed of the particles from the spray device, measured according to H. Hege, processing technology, 1969, S. 142 to 143, is expediently between 5 and 250 m / sec, advantageous the exit speed is set between 10 and 100 m / sec.

In general, the sprayed particles should leave the spraying device until they hit the container wall Cover a distance of at least 20 cm. This distance is upward due to economic considerations regarding the Container dimensions and limited by the size and exit speed of the particles to about 400 cm. One is preferred Path length selected in the range from 40 to 200 cm.

After striking the container wall, the particles collect to form a thin dispersion film which runs down the container wall, collects in the lower part of the container and is drawn off through an opening. The standing height of the given

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if stirred liquid in the container must be regulated so that at most a 'small amount, for example below 5 wt the sprayed dispersion hits the liquid level directly. Half or more of the container can be filled with dispersion be filled and. at the same time as a collection and homogenization vessel to serve.

The contents of the container can be heated during the spraying process, for example by a heated container jacket or by introducing water vapor into the liquid, with the entire Water vapor should condense in the liquid and it should not boil.

The pressure in the container is expediently kept greater than the saturation vapor pressure of the water vapor above that in the lower one Part of the container collected dispersion and should generally not be more than 200 torr, preferably not more than 100 Torr, below the saturation vapor pressure of the water vapor of the sprayed-in dispersion. It can also be equal to the saturation vapor pressure of the water vapor of the sprayed-in dispersion or up to about 500 torr. It should be avoided that during the often necessary longer treatment period to remove the monomers, larger amounts of water evaporate together with the monomers, because this reduces the economy of the process unnecessarily deteriorated, as well as undesirably strong thickening of the dispersion and deterioration in quality of the end product.

The pressure necessary for spraying the dispersion can be generated with a pump or other suitable means, the dispersion under pressure from the polymerization can also be sprayed directly.

The dispersion can be heated indirectly in the feed line to the spraying device, for example with a heat exchanger, or directly by introducing steam , but with at most minor amounts, for example below

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5 vol .- # of a gaseous phase may arise. The amount the gaseous phase should be as small as possible.

The method according to the invention can be carried out in one or more series-connected .Inventive devices are executed, the sprayed and again as a liquid Collected .Dispersion are either fed to the spraying device in the same or a subsequent device can. In certain cases only partial recycling of the dispersion into the same device and continuation can be used of the rest be expedient.

The vapors escaping when the dispersion is sprayed are passed through an opening above the spraying device attached to the container, withdrawn, condensed and optionally a recovery plant for the monomers fed.

In addition to the spraying device already described, you can other embodiments may be advantageous, for example the Arrangement of several nozzles generating hollow cones on the container axis one above the other, whereby the spray cones of the individual nozzles overlap as little as possible (see Fig. 2), or the arrangement of at least two, preferably 3 to 12, one circular segment-shaped flat jet generating nozzles on a concentric ring around the container axis so that as large as possible opposite parts of the container wall, the spray segment surfaces at the same angle of 15 to 90 °, preferably 40 to 60 °, cut (see Fig. 3).

A rotating disk can also be used as the spraying device whose axis of rotation coincides with the axis of the container (see Fig. 4).

The method according to the invention is not susceptible to faults and allows in a simple manner, often using existing equipment by adding less expensive facilities, dis-

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persions with low monomer content, for example of 0.03 wt .- # to prepare. By the impact of the sprayed Dispersion particles on the optionally heated container wall will have a particularly good degassing effect without disadvantageous Foaming achieved. It is particularly advantageous that up to 10% by weight (based on the dispersion) of larger particles up to 5 mm in diameter in the dispersion do not interfere.

The dispersions can either be used as such or by known methods, optionally after centrifugation or other concentration methods, for example by spray, electric or Zontakt drying, processed into solid polymers ^ with no disruptive monomer load on the dry air.

The treatment according to the invention changes the dispersion properties practically not. The dispersions as well as the dry plastics obtained from them can be used like the previous ones be used, with the advantage that disturbances due to the monomer content do not occur or are significantly reduced. The treatment according to the present description is particularly suitable for polymer dispersions that are resistant to shear and Are sensitive to heat, tend to foam and crust on the parts of the apparatus and are reluctant to release the monomers, e.g. for polyvinyl chloride produced by the emulsion or suspension process and its copolymers or graft polymers with up to 30 wt .- ^ comonomers, such as aliphatic Vinyl, acrylic and methacrylic esters, acrylonitrile, butadiene, styrene, vinyl ethers and others copolymerizable with vinyl chloride Monomers.

The usual water- or oil-soluble activators or activator systems can be used in the polymerization, as well as emulsifiers such as alkali or ammonium salts of alkyl sulfonic acids with about 10 to 18 carbon atoms, of acidic fatty alcoholsulfuric acid esters, of sulfosuccinic acid dialkyl esters, of fatty acids and / or epoxidized fatty acids, also partial fatty acids

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acid esters of polyhydric alcohols such as sorbitan monolaurate, polyoxyethylene ether of fatty alcohols or of aromatic hydroxy compounds, as well as polypropylene oxide-polyethylene oxide condensation products.

For the polymerization, may also be used protective colloids, for example water-soluble cellulose derivatives such as Methylcellul'ose, carboxymethylcellulose, hydroxyethylcellulose, polyvinyl alcohol, and optionally also up can contain about 40 $> acetyl, gelatin and copolymers of maleic acid or the half esters with styrene, and optionally other Polymerisation auxiliaries.

Examples 1 to 5 show devices according to the invention in FIGS. 1 to 5.

Figure 1: A standing cylindrical container (1) contains in the lower part an opening (2) for the discharge of liquid and a stirrer (4), in the upper part a gas discharge opening (5) and the spraying device in the form of a spiral nozzle (6), the a hollow cone (7) sprays against the container wall. The container is filled so far with dispersion (8) that the surface of the liquid is not hit by the spray cone. Via a pump (9) the dispersion is fed to the spraying device, at the same time heated by introducing steam through line (10). New dispersion is fed in via line (3) the line (15) drawn off the treated dispersion.

Figure 2: The container contains an opening for the discharge of liquid (2) and gases (5), a stirrer (4) and the spraying device in the form of three axially superposed eccentric nozzles (6) whose spray cones do not overlap and which Practically not hit the surface of the liquid (8). Heated dispersion is fed in via three lines (31 to 33), and each line can come from different stages of the process.

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In Figure 3, the spraying device contains an arrangement of four flat jet nozzles (6), which together form a hollow cone of sprayed material 'produce (7). The container (1) contains a double jacket (11) »which over two lines (20; 21) of a liquid / temperature control medium flows through it. The remaining Designations have the meaning explained in FIG. 1.

Figure 4 shows an arrangement with a rotating spray plate (12) as a spray device, the axis of rotation (13) with the Container axis coincides. The dispersion is fed in via the pipe (14) and sprayed in the form of a disk (7); the remaining Numbers have the meaning explained in FIG. 1.

FIG. 5 shows a device consisting of a cylindrical container, the lower part (1) of which has a smaller inner diameter has than the upper part (25) and protrudes a piece into this upper part, whereby an annular groove (19) is formed which contains an opening for drawing off liquid (15). A spray device (6; 17) is installed in both container parts, whose spray cone (7; 18) hits the container wall above the liquid level of the dispersion (8; 19). In the top area The container has an opening (5) for the withdrawal of gaseous products. The dispersion is over the pipe (3) fed to the lower spray device (6), drawn off through an opening in the bottom of the container (2) and via a pump (9) and a heat exchanger (24) with the line (16) of the upper Verspjjüheinrichtung and fed via the line (15) discharged from the device. The upper part of the container contains a double jacket (11), which over two lines (20; 21) is traversed by a liquid temperature control medium.

Example 6

In a device according to Figure 3 with the following container dimensions: 1.4 m diameter, 2.8 m height, 1500 kg of an aqueous dispersion prepared by continuous emulsion polymerization with a content of 45 wt .- ^

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Polyvinyl chloride (K value 78) and 0.8% by weight of monomeric] vinyl chloride by means of four flat jet nozzles that have a hollow cone a scattering angle of. Generate 120 °, sprayed. The values determined in this way are listed in Table 1. That gaseous Escaping vinyl chloride is discharged at the top of the container, recovered and, after the usual cleaning, again for the polymerization used. The treated dispersion is withdrawn from the bottom of the container. The double jacket of the container is used in this Attempt not used.

That from the dispersion treated according to the invention by drying The polyvinyl chloride powder obtained shows no differences in processing behavior when processed into a rigid film on a calender compared to a powder produced from an untreated dispersion.

Example 7

In the same apparatus as in example 6 in a hour 1500 of an aqueous dispersion prepared by emulsion polymerization kg with a content of 45 wt .- # polyvinylchloride (K-value 59) and 0.6 wt -. $> Monomeric) Vinyl chloride sprayed , the treated dispersion discharged at the bottom and the vinyl chloride escaping in gaseous form at the top of the container. The double jacket of the container is gheizt through a liquid medium at 70 ⁰ C. The values determined are listed in the table.

The polyvinyl chloride powder obtained from the dispersion treated according to the invention by drying shows no differences in processing behavior when processed into hard profiles on an extruder compared to a powder obtained from an untreated Diaper sion.

Example 8

In a device according to FIG. 5 with the following dimensions: container lower part (1) 2 m in diameter, 6 m in height; Container upper part (25) is 2.5 m in diameter, 5 m in height are in kg an hour 6300 by continuous emulsion polymerization aqueous dispersion prepared with a content of 4 parts by weight of monomeric vinyl chloride and 56 42 wt. -F> Vinyl chloride-butadiene-acrylic -

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nitrile copolymer with 93 wt .- ^ polymerized vinyl chloride sprayed by means of a hollow cone spray nozzle (6) with a scattering angle of 90 in the lower part of the container, the dispersion collected at the bottom of the container drawn off, via a pump (9) and a heat exchanger (24) guided and sprayed again by means of a hollow cone spray nozzle (17) with a scattering angle of 90 ° in the upper part of the container. The double jacket (11) of the upper container part is heated ^{to 70 ° C. by a liquid medium.} The values determined are listed in the table.

The monomer vinyl chloride escaping in gaseous form is on the pigtail withdrawn from the container and sent to a recovery plant. The finished dispersion is removed from the collecting channel (19) 'in the middle of the container via the line (15) deducted. ·;

Example 9

In a device according to FIG. 1 with the following container dimensions: 3 m diameter, 10 m height, 10 id of an aqueous dispersion prepared by suspension polymerization and containing 33% by weight of polyvinyl chloride (K value 55) are fed to a circulation system in one hour (3) and together with already treated dispensing, which is drawn off at the bottom of the container (2), ^{heated to a temperature of 75 °} C by introducing saturated steam of up to 1.5 ata, via a pump (9) of a hollow cone Spray nozzle supplied with a 90 ° spray angle and sprayed. 10 r of dispersion are discharged from the circulatory system via line (15) in one hour. The amount of dispersion in the container is kept constant at about 20 nm. The values determined are listed in the table.

Example 10 to 12

The procedure is as in Example 9, except that 20 m of dispersion are fed in or discharged in one hour and the nozzle inlet temperature and pressure in the container are varied, as can be seen from the table.

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Table In the tests according to Examples 6 to 12, the following values were determined:

Examples

6th 7th 8th
Level I. 8th
Stage II 265 13th 13th 9 10 11: 12th untreated nozzle inlet
temperature (C) 70 70 55 0.8 1 75 80 85 90 Dispersion% by weight of monomer
Vinyl chloride 0.8 ¹ ' 0.6 ^ 4 ^. 0.6 ^ 20th 20th 1.5 ⁵ ^ 1.5 ⁵⁾ 2.6 ⁵ -> according to the invention Container exit
treated temperature (CJ_ 55 70 40 70 70 76 79 83 Dispersion _G ew .-% monomeric
• vinyl chloride 0.07 ¹ ^ 0.02 ¹ ' 0.6 ¹ > 0.01 ¹ ^ O, O3 ⁵⁾ 0.02 ⁵ ^ 0.007 ⁵ ^ 0.002 Pressure in the container (Torr) 150 250 330 400 440 565 narrowest passage cross-section
of the nozzle (mm) 46) 46) 30th 30th 30th 30th medium diameter pder
sprayed particles (mm) 0.5 0.5 1.6 1.6 1.6 1-7 Speed of the sprayed \
Particles from the nozzle mouth ■ * '
(m / sec) 24 24 40 40 40 40

1) based on dispersion

2) measured according to milling cutter & iron clamp loc. cit.

3) measured according to H. Hege loc. cit.

4) Values for dispersion pretreated according to the invention in stage I

5) based on centrifuged solid with 20 % moisture

6) each of the four flat fan nozzles has this diameter

Claims (11)

-243S7O4 patent claims; 1.) Process for the preparation of polymer dispersions by emulsion or suspension polymerization of the monomer (s) in aqueous liquor, letting down the Polymer approach and removal and condensation of the gaseous products, characterized in that the optionally heated dispersion in a vertical, rotationally symmetrical container radially, in In the form of a hollow cone or a disk made of droplets not exceeding 6 mm in diameter, sprayed against the container wall. deposited there and collected in the lower part of the container, with gaseous substances above the The exit of the dispersion from the spraying device can be withdrawn. 2.) The method according to claim 1, characterized in that the scattering angle of the hollow cone is 30 to 180 °, preferably 80 to 120 °. 3.) Process according to Claims 1 and 2, characterized in that the mean droplet size of the sprayed dispersion is between 0.05 and 3 mm in diameter. 4.) Process according to claims 1 to 3, characterized in that the path length of the droplets until they hit the wall is about 20 to about 400 cm, preferably 50 to 200 cm _f . 5.) Process according to claims 1 to 4, characterized in that the exit speed of the particles from the Spray device between 5 and 250 m / sec, preferably between 10 and 100 m / sec. 6.) Device for carrying out the method according to claims 1 to 5 »consisting of at least one vertically standing, rotationally symmetrical container with a gas outlet opening in the upper part and at least one liquid outlet in the lower part, which may have means for -15- 609886/1002 Contains temperature control and / or stirring of the container contents, characterized in that in the upper part of the container, a spray device is attached, which consists of at least one of a hollow cone generating There is a spray nozzle, the opening of which is directed downwards so that the axis of the hollow cone consists of sprayed Material coincides approximately with the container axis and that the gas outlet opening above the spraying device is arranged. 7.) Device according to claim 6, characterized in that the spraying device consists of at least two one circular segment-shaped There is a flat jet generating spray nozzles, which are arranged so that as similar as possible large opposite parts of the container wall, the spray segment surfaces at the same angle from 15 to 90 °, preferably 40 to 60 °, cut and that the gas outlet opening is attached above the spray device. 8.) Device according to claim 6 and 7, characterized in that the nozzles have a narrowest passage cross section of at least 1 mm, preferably 5 to 100 mm. 9.) Device according to claim 6, characterized in that the spraying device has a rotary plate atomizer contains, whose axis of rotation coincides approximately with the container axis and that the gas outlet opening above this Spray device is attached. 10.) Device according to claims 6 to 9 »characterized in that the liquid outlet of the container via a Pump and a heating device with the spray device of the same container or a subsequent one Device according to claims 6 to 9 is connected. 11.) Device according to claims 6 to 10, characterized in that the container wall preferably has means for temperature control in the areas in which the sprayed particles impinge . Le e rs e ι te