WO1997045184A1

WO1997045184A1 - Column and process for deodorising dispersions

Info

Publication number: WO1997045184A1
Application number: PCT/EP1997/002639
Authority: WO
Inventors: Wolfgang HÜBINGER; Peter Keller; Rudolf Kaiser; Wolfgang Heider; Ulrich Eiden
Original assignee: Basf Aktiengesellschaft
Priority date: 1996-05-24
Filing date: 1997-05-22
Publication date: 1997-12-04
Also published as: EP0907393A1; TR199802417T2; CO4990982A1; CN1226181A; BR9709367A; ID16979A; KR20000015969A; AU3091697A

Abstract

In the counterflown column for lowering the residual volatile substance content of dispersions, having 5 to 50 vertical and/or transverse flow filter bases, the specific free aperture area in the vertical flow filter bases is 2 to 25 % and in the transverse flow filter bases 1 to 10 %, and the mean aperture diameter is 10 to 50 mm in the vertical and 2 to 10 mm in the transverse flow filter bases.

Description

Column and process for the deodorization of dispersions

The invention relates to a column and a process for reducing the residual volatile content in dispersions (deodorization of dispersions), and to a device for producing polymer dispersions and the polymer dispersions obtained and their use.

It is known to produce polymer dispersions or polymer suspensions by so-called suspension or emulsion polymerizations. The products usually still contain undesired volatile organic components, such as residual monomers resulting from incomplete conversion, impurities from the starting materials, decomposition products of the initiators or low molecular weight products from side reactions. These compounds are referred to below with the collective term "residual volatile". In the decision of the Commission 96/13 / EG on the definition of environmental criteria for the award of the EC eco-label for interior paints and varnishes of December 15, 1995 these residual volatiles are divided into volatile organic compounds (VOC) and volatile aromatic hydrocarbons . In both cases, these are organic compounds with a boiling point (or start of boiling) of at most 250 ° C under normal pressure conditions. The volatile aromatic hydrocarbons have at least one aromatic nucleus in the structural formula. The collective term "residual volatiles" used here denotes all such organic compounds with a boiling point (or start of boiling point) of at most 250 ° C. The residual volatiles are undesirable in many applications of dispersions or suspensions, for example in the food or cosmetics sector or in interior applications, and efforts are made to remove them as completely as possible. Dispersions or suspensions are therefore subjected to a treatment which removes the volatile organic constituents. This treatment is mostly referred to as deodorization. Various methods and devices are known for this purpose: in addition to chemical methods, which, however, mostly only influence the unsaturated compounds, these are predominantly stripping methods in which a stripping gas is passed through the suspension or dispersion. Air, nitrogen, supercritical carbon dioxide, ozone or water vapor are used as stripping gas. Apparatus in which the suspension or dispersion is treated with the stripping gas can have different forms. In the simplest version, the apparatus consists of a container which receives the suspension or dispersion and through which the stripping gas is introduced by means of lances or valves on the bottom of the container. However, today deodorization can also be carried out continuously in so-called deodorization columns or degassing columns.

DE-A 25 50 023 discloses a degassing column with a plurality of trays one above the other. An essential feature of this column is that a gap that is uniform over the circumference is left between each tray and the column jacket. This feature, however, greatly reduces the efficiency of the entire column, since the liquid phase can be trickled past the open edges without the desired stripping effect occurring.

DE-C 27 59 097 describes a process for removing monomers from dispersions, in which the column used is almost completely filled with liquid. As a result, however, the hold-up in the column is undesirably increased, and regularly necessary cleaning work is complex, so that, for example, when changing products problems occur again and again. The specific free hole area is 1.6%.

From DE-C 28 55 146 a process for the removal of monomers is known, in which a sieve plate column is operated in countercurrent with water vapor, the aqueous dispersion being allowed to flow through channel-like paths which are formed by side plates. The hole diameter is 0.5 to 2 mm, the specific free hole area is 0.04 to 0.0004%. This column structure is also complex, the hold-up in the column is enlarged, and the cleaning work is complex.

DE-C 25 21 780 discloses a process for removing monomers with the aid of a column equipped with sieve plates, in which water vapor at a temperature of 100 to 150 ° C. under a pressure of 0.8 to 1.6 bar is used. However, the method described here has the disadvantage that the relatively high temperatures can damage the products. One tries to counter this problem by reducing the dwell time. Water vapor is introduced in amounts of 1 to 5% by weight, based on the amount of dispersion added. DE-A 27 33 679 describes a similar process for separating monomers by means of a column with perforated plates, in which the temperature in the column is 90 to 150 ° C. In order to reach the temperatures, the pressure in the column usually has to be raised. In addition to generally applicable disadvantages such as relatively high energy costs, this relatively high temperature level in the column also has the disadvantage that relatively temperature-sensitive products cannot be processed. Furthermore, no polymers can be used in the process mentioned here, which soften at temperatures below 90 ° C. Only relatively small plate Distances described in the column, otherwise the polymer is feared to back up on the column wall. The hole diameter is 10 mm, the specific free hole area 5.5 to 7.5%.

The object was to find an improved process which remedies the disadvantages mentioned and enables a technically simple and economical separation of the residual volatiles from aqueous suspensions or dispersions. It should also be possible to use relatively high amounts of steam in the process and it should also be possible to use relatively temperature-sensitive products, with high purities being achieved without the residence time in the column having to be increased appreciably. In addition, a countercurrent column is to be provided which allows the process to be carried out in such a way that separate storage containers in front of the column can be dispensed with, and the cleaning of the column is simplified, so that product changes are easily possible.

The object is achieved by providing a countercurrent column for reducing the volatile content in dispersions which has 5 to 50 rain sieve trays and / or crossflow sieve trays, the specific free perforated area in the rain sieve trays 2 to 25% and in the crossflow sieve trays 1 to 10% is, in the rain screen trays the average hole diameter is 10 to 50 mm and in the cross-flow tray trays the average hole diameter is 2 to 10 mm.

Furthermore, the object is achieved by a process for the preparation of dispersions with a low residual volatile content by treating the dispersion with water vapor in a countercurrent column comprising rain sieve trays and / or crossflow sieve trays, the steam being added to a pressure of 0.1 to 0.7 bar in the column in countercurrent to the dispersion.

The dispersion feed, based on the free perforated area, is preferably 4 to 15 kg / cm ² h for rain sieve trays and 15 to 25 kg / cm ² h for cross-flow sieve trays.

The collective term "residual volatiles" has the meaning given at the beginning. The measurement of residual volatiles is carried out according to DRAFT International Standard ISO / DIS 13741, Part 1 by gas chromatography. They are referred to in this standard as remaining monomers and other organic components. Examples include acrylic acid esters such as n-butyl acrylate and isobutyl acrylate, methacrylic acid esters such as methyl methacrylate, acrylonitrile, butadiene, styrene, vinyl acetate, vinyl chloride, and also by-products, for example acetaldehydes and ethylbenzene. Propionitrile, ethyl acrylate and 4-vinylcyclohexene are also listed.

The process according to the invention offers the possibility of separating monomers from aqueous suspensions or dispersions in a technically simple and economical manner with a relatively simple construction. Due to the simple design, the column is reliable and easy to clean in practical operation, and a product change is also easy due to the relatively low hold-up in the column. Furthermore, relatively high plate efficiencies can be achieved, whereby the number of plates in the column can be reduced. Due to the reduced pressure in the column, the temperatures in the column are relatively low, so that temperature-sensitive dispersions can also be used. The method also enables the use of relatively high amounts of steam, and it can soften the polymers in the suspension or Dispersion in the column can be reduced so far that the separation process is not affected.

First, the countercurrent column according to the invention and a device containing it are described, then the process according to the invention and the dispersions according to the invention obtained therewith, and their use.

Counterflow column

In contrast to known countercurrent columns, the countercurrent column according to the invention can be operated with a very high throughput, so that the column itself can be designed to be small. This makes cleaning the column easier. Since the countercurrent columns are increasingly used not only for deodorization of a certain type of dispersions, but are also operated as part of multi-product systems with frequently changing products or dispersions, simple cleaning of the column used is desirable. The intensity of the cleaning of the column determines the quality of the dispersion obtained. Cleaning is simplified and accelerated by the column designed according to the invention, with smaller amounts of cleaning liquid being required. This enables the column to be operated much more economically and can be used in multi-product plants with frequently changing products. Because of the particularly simple cleaning, columns with rain sieve trays (also referred to as dual-flow trays) are preferred in multi-product systems over the cross-flow sieve trays that can also be used.

The columns according to the invention can comprise rain screen trays, cross-flow screen trays or combinations of rain screen trays and cross-flow screen trays exhibit. They preferably have either rain sieve trays or cross-flow sieve trays. The number of trays is 5 to 50, preferably 8 to 40, particularly preferably 15 to 30. The distance between the trays is preferably 250 to 800, particularly preferably 300 to 700, in particular 400 to 600 mm. The column height is preferably 6 to 25, particularly preferably 10 to 20 m. The diameter of the column, preferably with a circular cross section, is preferably 400 to 2500 mm, particularly preferably 800 to 1600 mm. The rain screen trays have average hole diameters of 10 to 50, preferably 12 to 25 mm. In the crossflow sieve trays, the average hole diameter is 2 to 10, preferably 4 to 8 mm. The holes are preferably circular. The specific free perforated area, that is to say the percentage of each area filled by holes, is expediently 2 to 25% in the rain sieve trays, preferably 5 to 20%, particularly preferably 10 to 18%, expediently 1 to in the cross-flow sieve trays 10%, preferably 3 to 8%, particularly preferably 4 to 7%.

The specific free perforated area is preferably selected so that the following dispersion feeds, based on the free perforated area, are accessible with the stated amounts of steam.

Both the cross-sectional shape of the column and the shape of the holes can be adapted to the respective requirements. They are preferably circular cross sections or holes, although other shapes can also be suitable for special applications.

Cross-flow sieve trays and rain sieve trays and their structure are described in general in Klaus Sattler, "Thermal Separation Processes", VCH 1988 (page 172, Figure 2-59; page 174, Table 2-19). The column diameter of the column according to the invention is preferably enlarged in the upper region for gravity separation of dispersion droplets from the steam. The diameter of this extension is at least 1 meter, in particular in the case of smaller columns. It can be up to 4 meters, especially for larger columns. As a rule, the head widening is approximately 1.5 times the diameter of the column trays.

In addition, the column preferably has an extension of 1 to 3 m, preferably 2 to 3 m, in the lower region, which represents the column bottom. The deodorized dispersion is taken up in this column bottom. It serves as a pump template for subsequent process stages.

The dispersion is fed in in the upper region (head) of the column, preferably in the enlarged upper region (head extension) of the column.

A column with rain sieve trays is preferably used according to the invention, since it has no construction-related dead zones, which means reduced cleaning effort and allows higher efficiencies. As a result, the column size, in particular the column height and the number of trays, can be reduced. The column preferably has 15 to 30 trays, which are arranged at a distance of 400 to 600 mm. The column diameter is 800 to 1600 mm, especially 1000 to 1500 mm. The specific free perforated area and the diameter of the column are selected so that a dispersion throughput in the range of in particular 5 to 30 t / h is possible with a dispersion feed of 4 to 15 kg / cm ² h based on the free perforated area. A crossflow sieve tray column preferably has the same external dimensions and number of trays as the rain sieve tray column. The specific free perforated area and the diameter of the column are selected so that a dispersion addition in the range of in particular 10 to 30 t / h is possible with a dispersion feed of 15 to 25 kg / m ² h based on the free perforated area.

The column according to the invention preferably has a discharge weir. The weir height is preferably 50 to 200 mm. The height of the column exit from the column is preferably 20 to 50 mm, particularly preferably 25 to 40 mm. The specific hole area is about 6%. The number of holes per floor is 2000 to 9000.

The column according to the invention can be integrated into a device for producing polymer dispersions. A corresponding device according to the invention for producing polymer dispersions comprises a reactor (A), optionally a post-reactor (B), a column (C), as described above, a heat exchanger (D) for the evaporation, and, if appropriate, an expansion device (E) , a filter (F) and a conditioning device (G). The outlet of the reactor (A) or of the secondary reactor (B) is preferably connected directly to the inlet of the column (C) without the interposition of a separate feed tank. Corresponding devices are in the

Shown in the drawing

1 shows a device with a rain sieve tray column in a schematic representation and Figure 2 shows a device with a cross-flow sieve tray column in a schematic representation.

The reference symbols used in the figures have the following meaning:

A: Polymerization reactor with agitator

B: Post reactor

C: countercurrent column with

Cl: head extension of the column

C2: Rain sieve trays (Figure 1) or cross-flow sieve trays

(Figure 2)

C3: Column sump

D: Exchanger heat exchanger

E: relaxation level with

El: steam outlet and

E2: dispersion outlet

F: filter

G: conditioning device.

Dispersion preparation is generally carried out batchwise in the reactor (A), the content of which is usually transferred to the after-reactor after, incompletely, the reaction. According to previous processes, the dispersion had to be transferred from the after-reactor (B) into a separate storage container from which the deodorization column was fed. This was necessary because the throughput of the column was significantly lower than the pumping throughput from the after-reactor (B). The column (C) according to the invention preferably allows such a high throughput that when the after-reactor (B) is emptied the dispersion can be fed directly into the column, since the column has the same throughput may have, which occurs when emptying the post-reactor (B). By dispensing with a separate storage container, the entire device can be simplified and thus constructed more cost-effectively. The operation is also less expensive because there is no need to control a separate storage container. In the parts of the plant which are not directly influenced by the column (s), the aim is to be able to pump at rates of 20 to 50 t / h. In the case of column throughputs of around 10 t / h and above, a separate storage container or intermediate buffer upstream of the column can be dispensed with and the column can be fed directly from the after-reactor.

The relaxation stage (E) is generally provided in order to be able to adjust the water content of the dispersion discharged from the column bottom. Part of the introduced steam often condenses in the column, so that the water content of the dispersion in the column bottom is increased. In order to reduce the water content, the dispersion obtained can be expanded further (by reducing the pressure with the aid of vacuum equipment), as a result of which some of the water can be discharged as steam (El). The dispersion (E2) discharged from the relaxation stage (E) can thus be adjusted to a desired water content.

The procedure

The columns and devices described above are advantageously used in the process according to the invention for producing dispersions with a low residual volatile content. In the process according to the invention, the dispersion obtained from the reaction, generally a polymer dispersion, preferably an aqueous polymer dispersion, is passed through the column in countercurrent to the water vapor. The water vapor is passed at a pressure of 0.1 to 0.7 bar in the column in countercurrent to the dispersion. When using polymer dispersions, the pressure in the Column preferably adjusted so that the temperature at the top of the column is above the glass transition temperature of the polymer and the temperature in the bottom of the column is below the temperature at which the polymer dispersion loses its stability and, for example, decomposes or agglomerates or coagulates.

The pressure in the column is preferably 0.2 to 0.7 bar, particularly preferably 0.2 to 0.5 bar at the top of the column.

The temperature in the column is preferably from 50 to 90 ^C C, particularly preferably 60-82 ° C. Due to the pressure drop in the column, the temperature at the top of the column is lower than in the bottom of the column. The inlet temperature of the dispersions is preferably 50 to 90 ° C, particularly preferably 60 to 80 ° C. The temperature in the column bottom is preferably 70 to 90 ° C. The outlet temperature of the dispersion corresponds to this temperature. The pressure at the top of the column is 0.2 to 0.5 bar, above the bottom of the column 0.3 to 0.7 bar.

Design data for a rain sieve tray column are, for example: hole diameter 15 to 25 mm, surface loading 8 to 15 m ³ / m ² h, specific loading, based on the hole cross section, 10 to 12 kg / cm ² h, pressure at the column head 0.2 to 0.5 bar (absolute).

A cross-flow sieve tray column is designed, for example, as follows: hole diameter approximately 4 mm, surface loading 8 to 15 m ³ / m ² h, specific free perforated area 5 to 10%, weir height 100 to 200 mm, pressure at the column head 0.2 to 0.5 bar, specific load, based on the hole cross section, 15 to 22 kg / cm ² h. The specific steam requirement in the process according to the invention is preferably 10 to 50%, particularly preferably 20 to 30% by weight, measured as water, based on the amount of dispersion introduced.

The steam throughput is preferably about 0.1 to 10 t / h, particularly preferably 1 to 8 t / h. The throughput of dispersion is preferably 1 to 50 t / h, particularly preferably 5 to 30 t / h. In a column used in production, the throughput of dispersion is preferably 20 t / h or more, with lower production 5 to 10 t / h, on a pilot plant scale (test stage) about 1 to 2 t / h. The throughput depends on the column diameter.

The specific surface loading of the column is 1.6 to 25, preferably 8 to 15, m ^{3 of} dispersion per m ^{2 of} cross-sectional area of the column and hour.

The inflow, based on the free area, is preferably 4 to 15, particularly preferably 10 to 13 kg / cm ² h for rain sieve trays, preferably 15 to 25, particularly preferably 15 to 22 kg / cm ² h for cross-flow sieve trays.

The procedure according to the invention allows high specific throughputs in the column. Therefore, the dimensions of the column can be kept small, which on the one hand leads to an inexpensive construction and on the other hand reduces the inner surface of the column, which in turn reduces the cleaning effort when changing batches.

With a given weight ratio of stripping steam to dispersion, a high specific liquid load (dispersion load) leads to high gas loads and thus high flow velocities in the gas space. The formation of stable foams on the floors can thereby be made more difficult, preferably largely avoided. Foams often lead to faults in the column and the downstream separators and vacuum equipment and are therefore undesirable. The formation of foam can be suppressed by the column according to the invention and the method according to the invention, so that the use of additional foam separators or foam breakers can be dispensed with.

With the method according to the invention using the column according to the invention it is possible to reduce the sum of all contents of residual volatiles to a value of less than 100 ppm, often even less than 50 ppm, in favorable cases even less than 25 ppm to reduce the total weight of the dispersion. The degree of reduction can be adapted to the corresponding requirements by the design of the column and the procedure. In the preferred continuous operation of the column, the residence time in the column is preferably 100 to 2000 s, particularly preferably 200 to 1000 s, in particular 400 to 800 s, depending on the dispersions used. By adjusting the throughput, the steam load and the steam temperature or pressure, and the number of column plates provided, it is possible to achieve the desired purity of the dispersion. A particularly preferred combination of process parameters for a cross-flow tray column is as follows:

Throughput dispersion 10 to 25 t / h with a column diameter of 1 to 1.5 m,

Throughput steam 2.5 to 7.5 t / h, gas velocity in the holes 40 to 140 m / s, gas velocity in the tube 2.5 to 10 m / s. In the method according to the invention, high soil efficiencies can be used. When using rain screen trays, the achievable soil efficiency depends on the throughput related to the free cross-section. The soil efficiency is preferably in the range from 7.0 to over 30%. In the case of crossflow sieve trays, the bottom efficiency is preferably up to 20%. The determination of the soil efficiency is explained in the examples.

The invention also relates to the dispersions which can be prepared by the process according to the invention. These are dispersions, in particular polymer dispersions, with a residual volatile content of less than 100 ppm, often even less than 50 ppm, in favorable cases even less than 25 ppm, which can be prepared by the above process. The structure of the preferred dispersions is given below.

dispersions

The dispersions used in the process according to the invention can be any dispersions which have removable levels of residual volatiles. Examples of such dispersions can be dispersions of contaminated soil, dispersions of inorganic particles, dispersions of biomolecules and preferably dispersions of organic compounds, in particular polymer dispersions. The dispersions are preferably aqueous dispersions.

The aqueous polymer dispersions which are preferably suitable for the process according to the invention are fluid systems which, as a disperse phase in the aqueous dispersion medium, contain polymer particles in a stable disperse distribution. The diameter of the polymer particles is generally mainly in the range from 0.01 to 5 μm, often mainly in the range of 0.01 to 1 μm. The stability of the disperse distribution often extends over a period of at least one month, in many cases even over a period of at least 6 months.

Just like polymer solutions when the solvent is evaporated, aqueous polymer dispersions have the property of forming polymer films when the aqueous dispersion medium is evaporated, which is why aqueous polymer dispersions are used in many ways as binders, e.g. for paints or compositions for coating leather.

In principle, a distinction is made between aqueous polymer dispersions into aqueous secondary and aqueous primary dispersions. The aqueous secondary dispersions are those in the production of which the polymer is produced outside of the aqueous dispersion medium, for example in solution of a suitable non-aqueous solvent. This solution is then transferred to the aqueous dispersion medium and the solvent is separated off, generally by distillation, with dispersion. In contrast, aqueous primary dispersions are those in which the polymer is itself produced in disperse distribution in the aqueous dispersion medium. It is essentially common to all production processes that monomers which have at least one ethylenically unsaturated group are used for the synthesis of the polymer, or that the polymer is constructed exclusively from such monomers.

Such monomers having at least one ethylenically unsaturated group are usually incorporated by initiated polyreaction, the type of initiation used being determined in particular by the desired performance properties of the target product and therefore being adapted to this. For example, an ionic or a radical initiation can be considered. Installation can also be done by catalytically initiated polymer-analogous reaction take place. Radical initiation is used particularly frequently, which is why the incorporation of monomers having ethylenically unsaturated groups in the case of aqueous primary dispersions is generally by the method of free-radical aqueous emulsion polymerization and in the case of aqueous secondary dispersions is is generally the method the radical solution polymerization takes place.

The polyreaction conditions are chosen so that the desired properties of the polymer, such as molecular weight, molecular weight distribution and degree of branching, are obtained. In order to conduct the reaction rapidly, it is generally not sensible to carry out the reaction until conversion is complete. Therefore, the aqueous polymer dispersions obtained after the reaction normally still have, in particular ethylenically unsaturated, monomers. Due to the increased reactivity of the ethylenically unsaturated double bond, residual monomers such as acrylonitrile and vinyl acetate are not completely harmless from a toxicological point of view and should therefore be removed from the dispersion. The present method serves this purpose. The method can be used for all polymers dispersed in an aqueous medium, regardless of the type of polymer. The term "polymer" here therefore encompasses both polycondensates such as polyesters, polyadducts such as polyurethanes and polymers which are accessible by ionic or radical polymerization. Mixed variants of the syntheses mentioned, as well as copolymers, likewise result in dispersions which can be used according to the invention.

The preparation of aqueous polymer dispersions of the aforementioned various types of polymer is known, for example from Encyclopedia of Polymer Science and Engineering, Volume 8, page 659ff (1987); DC Blackley, in High Polymer Latices, Volume 1, page 35ff (1966); H. Warson, The Application of Synthetic Resin Emulsions, page 246ff, Chapter 5 (1972); [Publisher?] D. Diederich, Chemistry in our time 24, pages 135 to 142 (1990); Emulsion Polymerization, Interscience Publishers, New York (1965); DE-A 40 03 422 and dispersions of synthetic high polymers, F. Hölscher, Springer-Verlag, Berlin (1969).

Suitable monomers having at least one monoethylenically unsaturated group for the process according to the invention are in particular, in a simple manner, radically polymerizable monomers, such as the olefins, for example ethylene, vinylaromatic monomers such as styrene, α-methylstyrene, o-chlorostyrene or vinyl toluenes, esters of vinyl alcohol and monocarboxylic acids having 1 to 18 carbon atoms, such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl laurate, vinyl pivalate and vinyl stearate, and commercially available monomers VEOVA 9 to 11 (VEOVA is a trade name of Shell and stands for vinyl esters of carboxylic acids, which are also referred to as Versatic ^® X acids), esters of α, /? - mono-ethylenically unsaturated mono- and dicarboxylic acids, such as acrylic acid, preferably having 3 to 6 carbon atoms. Methacrylic acid, maleic acid, fumaric acid and itaconic acid, with generally 1 to 12, preferably 1 to 8 and in particular 1 to 4 carbon atoms a pointing alkanols, such as acrylic acid and methacrylic acid methyl, ethyl, n-butyl, isobutyl, tert-butyl and -2-ethylhexyl ester, dimethyl maleate or n-butyl maleate, nitriles α.jS monoethylenically unsaturated carboxylic acids, such as acrylonitrile, and C ₄ . _8- conjugated dienes such as 1,3-butadiene and isoprene. In the case of aqueous polymer dispersions produced exclusively by free-radical aqueous emulsion polymerization, the monomers mentioned generally form the main monomers which, based on the total amount of the monomers to be polymerized by the free-radical aqueous emulsion polymerization process, normally account for more than 50% by weight unite. As a rule, these monomers have Water at normal conditions (25 ° C, 1 atm) only has a moderate to low solubility.

Monomers which have an increased water solubility under the abovementioned conditions are, for example, α, / J-monoethylenically unsaturated mono- and dicarboxylic acids and their amides, such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, acrylamide and methacrylamide, and also vinylsulfonic acid and their water-soluble salts, as well as N-vinyl pyrrolidone.

In the case of aqueous polymer dispersions produced exclusively by free-radical aqueous emulsion polymerization, the abovementioned monomers, which have increased water solubility, are normally only used as modifying monomers in amounts, based on the total amount of the monomers to be polymerized, of less than 50% by weight. , usually 0.5 to 20, preferably 1 to 10 wt .-%, with copolymerized.

Monomers which usually increase the internal strength of the films of the aqueous polymer dispersions normally have at least one epoxy, hydroxy, N-methylol, carbonyl or at least two non-conjugated ethylenically unsaturated double bonds. Examples include N-alkylamides of 3 to 10 carbon atoms, a, β-monoethylenically unsaturated carboxylic acids and their esters with 1 to 4 carbon atoms, among which the N-methylol acrylamide and the N-methylol methacrylamide are particularly preferred , two vinyl-containing monomers, two vinylidene-containing monomers and two alkenyl-containing monomers. The di-esters of dihydric alcohols with α, β-monoethylenically unsaturated monocarboxylic acids are particularly advantageous, among which acrylic and methacrylic acid are preferred. Examples of such two nonconjugated ethylenically unsaturated double bonds are alkylene monomers lenglykolacrylate diacrylates and dimethacrylates, such as ethylene glycol diacrylate, butylene glycol diacrylate 1,3-, 1, 4-butylene glycol diacrylates and propylene glycol diacrylate, divinylbenzene, vinyl methacrylate, vinyl acrylate, allyl methacrylate, allyl acrylate, diallyl maleate, Diallyl fumarate, methylenebisacrylamide, cyclopentadienyl acrylate or triallyl cyanurate. Of particular importance in this connection are also the methacrylic acid and acrylic acid-C _j -Cg-hydroxyalkyl esters, such as n-hydroxyethyl, n-hydroxypropyl or n-hydroxybutyl acrylate and methacrylate, and compounds such as diacetone acrylamide and acetylacetoxyethyl acrylate, respectively -methacrylate, ureidoethyl methacrylate and acrylamidoglycolic acid. In the case of aqueous polymer dispersions produced exclusively by the free-radical aqueous emulsion polymer method, based on the total amount of the monomers to be polymerized, the above monomers are also copolymerized in amounts of from 0.5 to 10% by weight.

Dispersants which ensure the stability of the aqueous polymer dispersion produced are usually also used in the course of the free-radical aqueous emulsion polymerization.

Both the protective colloids usually used to carry out free-radical aqueous emulsion polymerizations and emulsifiers come into consideration as such.

Suitable protective colloids are, for example, polyvinyl alcohols, cellulose derivatives or copolymers containing vinylpyrrolidone. A detailed description of other suitable protective colloids can be found in the Houben Weyl, Methods of Organic Chemistry, Volume XIV / 1, Macromolecular Substances, Georg-Thieme-Verlag, Stuttgart, 1969, pages 411 to 420. Of course, mixtures of emulsifiers and / or protective colloids can also be used. Preferably only emulsifiers are used as dispersants, the relative molecular weights of which, in contrast to the protective colloids, are usually below 1000. They can be anionic, cationic or nonionic in nature. Of course, if mixtures of surface-active substances are used, the individual components must be compatible with one another, which in the case of doubt can be checked using a few preliminary tests. In general, anionic emulsifiers are compatible with one another and with nonionic emulsifiers.

The same applies to cationic emulsifiers, while anionic and cationic emulsifiers are usually incompatible with one another. Common emulsifiers are, for example, ethoxylated mono-, di- and tri-alkylphenols (EO grade: 3 to 100, alkyl radical: C ₄ to C ₁₂ ), ethoxylated fatty alcohols (EO grade: 3 to 100, Alkyl radical: C ₈ to C ₁₈ ), and alkali and ammonium salts of alkyl sulfates (alkyl radical: C ₈ to C ₁₆ ), of sulfuric acid half-ethers of ethoxylated alkylphenols (EO degree: 3 to 100, alkyl radical: C ₄ to C ₁₂ ), of alkylsulfonic acids (alkyl radical: C ₁₂ to C ₁₈ ) and of alkylarylsulfonic acids (alkyl radical: C ₉ to C ₁₈ ). Further suitable emulsifiers such as sulfosuccinic acid esters can be found in Houben-Weyl, Methods of Organic Chemistry, Volume XIV / 1, Macromolecular Substances, Georg-Thieme Verlag, Stuttgart, 1961, pages 192 to 208.

As a rule, the amount of dispersant used is 0.5 to 6, preferably 1 to 3,% by weight, based on the weight of the monomers to be polymerized by free radicals. Of course, the aforementioned dispersants are generally suitable for stabilizing the process products according to the invention. However, the process products according to the invention also comprise aqueous polymer dispersions of self-emulsifying polymers, that is to say of polymers which have ionic groups which, owing to the repulsion of charges of the same sign, are able to bring about stabilization. The direct process products according to the invention preferably have anionic stabilization (in particular anionic dispersants).

If the aqueous polymer dispersion, the residual monomer content of which is to be reduced in the manner according to the invention, is prepared by radical aqueous emulsion polymerization from monomer compositions of monomers having at least one ethylenically unsaturated group, monomer compositions are of particular importance with regard to the process according to the invention. which comprise at least two different monomers which have at least one ethylenically unsaturated group, and for the rest

70 to 99.9% by weight of esters of acrylic and / or methacrylic acid with alkanols and / or styrene having 1 to 12 carbon atoms, or

70 to 99.9% by weight of styrene and / or butadiene, or

70 to 99.9% by weight of vinyl chloride and / or vinylidene chloride, or

40 to 99.9% by weight vinyl acetate, vinyl propionate and / or ethylene

included, the total amount being 100% by weight. The polymeric solids content in the suspension or dispersion is usually about 20 to 75% by weight, preferably about 40 to 70% by weight, particularly preferably 50 to 60% by weight.

The viscosities of the suspensions or dispersions used are at a temperature of 25 ° C. at about 10 to 5000 mPas, preferably 20 to 2000 mPas, particularly preferably 50 to 1000 mPas.

The viscosity of the dispersions used is preferably low. It can be in the range from 30 to 1000 mPas. The density of the dispersions is preferably around 1 g / cm ³ .

Definition and determination of relevant measurands

Glass transition temperature

The glass transition temperature is preferably determined from the temperature dependency of the specific heat in a differential thermal analysis (G. Goldbach in: Plastics, Order States and Properties in: Ulimanns Encyklopadie der Technische Chemie, Volume 15, pages 219 to 222, Weinheim, 1980).

The glass transition temperature of copolymers can also be calculated from the glass transition temperatures of the respective homopolymers, weighted according to the mass fractions of the monomers and the expansion coefficients of the polymers. Minimum imaging temperature

The minimum film bifunction temperature of the polymer is the lowest temperature at which a dispersion just forms a coherent film after the water has evaporated. It is close to the glass transition temperature of the polymer (H. Gerrens in: Polymerisationstechnik in: Ullmann Encyklopadie der Technische Chemie, Volume 19, page 141, Weinheim, 1989).

A metal plate on which a temperature gradient is applied serves as the measuring device. The temperature at which the film begins to crack is observed (E. Penzel in: Polyacrylic and Polymethacrylic Compounds in: Ullmanns Encyklopadie der Technische Chemie, Volume 19, pages 17 to 18, Weinheim, 1980).

The glass transition temperature of the acrylates which are preferably used as the dispersion in the process according to the invention is between -62 and + 6 ° C. (see Table 8 from E. Penzel in: Polyacrylic and Polymethacryl Compounds in: Ullmanns Encyklopadie der Technische Chemie, Volume 19, page 17 to 18, Weinheim, 1980). The resulting minimum film image temperatures of the polymers in the dispersions are therefore often far below the preferred operating temperature of the process according to the invention. The dispersions to be treated are therefore often soft at the process temperature and easily form films.

viscosity

Dispersions with those frequently used in the process according to the invention

The range of the solids content of 20 and 75%, preferably 50 to 70%, show a broad spectrum of theological behavior. The flow behavior depends on the solids content, the particle size, the particle size division and of the auxiliary system that was used in the manufacture. Structural viscosity and dilatancy are frequently observed flow anomalies.

The viscosity is measured under standardized measuring conditions in a capillary viscometer, Couette viscometer or cone-plate viscometer (C. Gerth: Rheometrie, Ullmanns Encyklopadie der Technische Chemie, Volume 19, pages 17 to 18, Weinheim 1980).

The invention further relates to a process for the preparation of these polymer dispersions with a low residual volatile content by the above process.

The method is particularly suitable for shear-sensitive dispersions, for example low-emulsifier or emulsifier-free formulations, sterically (with protective colloid or with starch) stabilized dispersions or self-dispersing systems (such as polyurethane dispersions), for thermosensitive dispersions.

The method is preferably carried out in the device described above. In stage a), the reactor (A) comes to

Use, stage b) of the after-reactor (B), in stage c) the column (C), the vapor being removed in stage d) through the heat exchanger (D).

Stage e) is carried out in the relaxation stage (E), stage f) in the filter

(F) and stage g) in the assembly device (G). The assembly includes all the necessary steps that are necessary to complete the

Process obtained polymer dispersion in the commercial product.

For example, stabilizers, antioxidants,

Biocides, protective polymers, acids, alkalis, anti-foaming agents, thickeners,

Solvents, dispersants such as water, and other suitable substances can be added. The polymer dispersions according to the invention are preferably used as adhesive raw materials, in sealing compounds, paper coating dispersions, plastering compounds, fillers, coatings, as lacquer and paint raw materials, binders or thickeners, in particular for interior applications. Due to the low content of residual volatiles, safe use in indoor applications is possible, with no or minimal evaporation of the remaining minimal amounts of residual volatiles.

They serve as adhesive raw materials, for example for the lamination of foils, such as glossy, metal or composite foils made of copper and / or aluminum and paper, for technical laminations, for example in vehicle construction, for foams or furniture foils, as packaging adhesives, as pressure sensitive adhesives, for example for paper labels and envelopes, as sealants and floor adhesives, as well as for special coatings and as binders.

They can be used as paper coating dispersions for the finishing of offset printing paper, gravure printing paper and cardboard. They can also be used as thickeners for printing inks and coating slips.

As paint and varnish raw materials, they are used for wood coatings, for the graphic industry, for technical paint applications such as corrosion protection, for emulsion paints and emulsion paints, for example for interior and exterior paints, especially for interior paints, for plasters and fillers for interior use. for cement coatings such as primers, facade paints and concrete roof tiles.

In addition, they can be used as nonwoven coating compositions, such as tufting, needle fleece and floor coverings or the carpet backing, as well as for molded foams and diving articles. These applications preferably relate to interior applications, that is to say applications within closed buildings or vehicles.

The invention is illustrated by the examples below.

Examples

example 1

Column with crossflow sieve trays (comparative example)

The column (diameter 0.4 m) contains 8 cross-flow sieve trays at a distance of 50 cm from each other. The sieve trays have holes with a diameter of 4 mm at a uniform distance. The holes make up 1.0% of the floor area. The floors are connected to one another via laterally arranged shafts. The respective drain shaft extends 40 mm above the floor. This creates a dispersion layer of this height (40 mm) on the floor during operation caused by the water vapor. This column was fed with 0.2 t / h of a 50% aqueous polymer dispersion which was conveyed to the top sieve tray by means of an eccentric screw pump. In countercurrent, 40 kg / h of 4 bar steam were introduced into the column below the bottom tray.

After the top floor has filled with dispersion, dispersion runs over the 40 mm high overflow weir through the shaft to the next floor and so on. The steam flows through the holes in the bottom floor, flows through the dispersion layer and thereby accumulates with the substances to be separated from the dispersion. The floors above are flowed through in the same way. The loaded one is at the top of the column Steam is drawn off using a vacuum (approx. 200 mbar) and condensed in a downstream condenser. The dispersion is collected in a sump below the bottom floor and pumped from there for conditioning.

With the test settings mentioned (corresponds to an area load of 1.6 m ³ dispersion / m ² column cross section and h) butyl acrylate is depleted from 415 ppm initial concentration to 140 ppm (tray 5). This corresponds to a depletion of 66% or a soil efficiency of around 14% of a thermodynamic equilibrium.

Example 2

Column with cross-flow sieve trays

The column (diameter 0.4 m) contains 8 cross-flow sieve trays at a distance of 50 cm from each other. The sieve trays have holes with a diameter of 4 mm at a uniform distance. The holes make up 5.3% of the floor area. The floors are connected to each other via shafts. The shafts protrude 100 mm into the floor and form the drain weir.

1500 kg / h of dispersion (corresponding to an area load of 12 m ³ / m ² ) were introduced into the column on the top tray and 375 kg / h steam as stripping medium below the bottom tray. The pressure was 330 mbar.

The butyl acrylate content was reduced from 219 ppm at the beginning to 16 ppm, which corresponds to a depletion of 93%. The efficiency the cross-flow sieve plates each amounted to around 11% of a thermodynamic equilibrium.

With this high surface load, the soil efficiency is only reduced by about 25% compared to the comparative example. This makes it possible to build a column with such a high dispersion throughput that it behaves like a piece of pipe in a line of equipment and there is no need for intermediate buffers during the transition from discontinuous process steps to continuous column deodorization.

Example 3 Column with rain sieve trays

The column (diameter 0.4 m) contains 8 trays at a distance of 50 cm from each other. The sieve trays have holes with a diameter of 10 mm at a uniform distance. The holes make up 2.1% of the floor area. The floors are not connected to one another via manholes. The dispersion flows in countercurrent to the steam through the same holes.

For this purpose, the column was charged with 200 kg / h of dispersion (corresponds to a surface load of 1.6 m ³ / m ² h) from above and stripped with 40 kg / h of steam. The pressure was 285 mbar.

The butyl acrylate content was reduced from 477 ppm at the beginning to 5 ppm, which corresponds to a depletion of 99%. The efficiency of these rain screen trays was around 31% of a thermodynamic equilibrium. A significantly better depletion and a considerably higher soil efficiency were found with the preferred rain sieve trays than with the crossflow sieve trays.

When using rain screen trays, the soil efficiency η achieved depends on the throughput related to the free cross-section. At low values (example 12) the efficiency can drop to 7.0%. At high throughputs, over 30% soil efficiency can be achieved regardless of the pressure (Examples 13 to 15). The hole diameter in the crossflow sieve trays (example 4 to 11) is preferably 4 mm. Soil efficiency is affected by weir height and pressure. The column diameter is 400 mm in all examples.

The efficiency in the individual tests is calculated according to equations 1, 2, 3, 4 and 5. Here mean:

iri _j equilibrium coefficient of component i (see equation 3)

Y _GGW equilibrium concentration in the gas phase (% based on the solid) ^ GGW equilibrium concentration in the liquid phase (% based on the solid)

D desorption factor (see equation 4) n Practical number of trays r ^ Theoretical number of trays X _a Concentration in the running dispersion

X _e concentration in the incoming dispersion

M _{jjpf amount of} steam, kg / h

M _{Disp amount of} dispersion, kg / h

α = X _a / X _e (1) V = n ^ / n (2)

"^ ^{= Y} GGW ^ GGW (3)

D = m _i * M _Dpf / M _Disp (4) n ^ = ln (D / α-l / α + l) / lnD-l (5)

The evaluation of the deodorization experiments was carried out for butyl propionate (α), styrene (ß) and vinyl acetate (γ). The equilibrium value ^m _BP r was determined experimentally. It is 8.4 for butyl propionate (concentration based on the solid in the dispersion).

Table 1: Further tests with crossflow sieve trays

1 ro

10th

Table 2: Further experiments with rain sieve trays

I OJ co ι

10

The product α is an adhesive dispersion based on butyl acrylate and acrylonitrile with a solids content of 55%. 15 The product ß is a styrene / butadiene dispersion for paper coating, 50% solids content, 40 mPas viscosity.

The product γ is a vinyl acetate-containing PSA dispersion, 70% solids content, 150 to 900 mPas viscosity. 17 is based on butylpropionate for a, ß on styrene and γ on vinyl acetate.

20th

FB means the surface loading of the floors with dispersion.

Claims

claims

1. countercurrent column for lowering the residual volatile content in dispersions, which has 5 to 50 rain sieve trays and / or crossflow sieve trays, characterized in that the specific free perforated area in the rain sieve trays is 2 to 25% and in the crossflow sieve trays 1 to 10%, in the Rain sieve trays the average hole diameter is 10 to 50 mm and in the cross-flow sieve trays the average hole diameter is 2 to 10 mm.

2. Column according to claim 1, characterized in that it has one or more of the following features:

Inside diameter of the column in the range from 400 to 2500 mm, height of the column in the range from 6 to 25 m, number of trays in the range from 5 to 50, tray distance in the range from 250 to 800 mm, - column in the lower range by 1 to 3 m extended as a column sump,

Column diameter increased in the upper area for gravity separation of dispersion droplets from the steam, feeding the dispersion in the enlarged upper area of the column.

3. Device for producing polymer dispersions, comprising a reactor (A), optionally a post-reactor (B), a column (C) as defined in claim 1 or 2, a heat exchanger (D) for the exhaust steam, and optionally a flash device (E), a filter (F) and a conditioning device (G).

4. The device according to claim 3, characterized in that the output of the reactor (A) or the post-reactor (B) is connected directly to the input of the column (C) without the interposition of a separate storage container.

5. A process for the preparation of dispersions with a low residual volatile content by treating the dispersion with water vapor in a countercurrent column comprising rain sieve trays and / or crossflow sieve trays, characterized in that the water vapor is at a pressure in the column of 0.1 to 0. 7 bar in countercurrent to the dispersion.

6. The method according to claim 5, characterized in that the dispersion is a polymer dispersion and the pressure in the column is adjusted so that the temperature at the top of the column above the glass transition temperature of the polymer and the temperature in the bottom of the column is below the temperature at which the polymer dispersion their

Stability loses.

7. The method according to claim 5 or 6, characterized in that a column is used as countercurrent column as defined in claim 1 or 2.

8. The method according to any one of claims 5 to 7, characterized in that it has one or more of the following features:

Pressure in the column in the range from 0.2 to 0.7 bar, Temperature in the column in the range from 50 to 90 ° C., surface loading of the trays in the range from 2 to 25 m ³ / m ² h, specific steam requirement in the range from 10 to 50%, dispersion feed based on the free perforated area in the range from 4 to 15 kg / cm ² h for the rain sieve trays and 15 to 25 kg / cm ² h for the cross-flow sieve trays dispersion throughput in the range from 1 to 50 t / h.

9. Process for the preparation of polymer dispersions with a low residual volatile content

a) polymerization, b) optionally post-reaction, c) treating the dispersion with steam in a countercurrent column, d) removing the steam from the countercurrent column, and if appropriate e) releasing the polymer dispersion obtained from the countercurrent column, f) filtering the polymer dispersion, g) assembly of the polymer dispersion,

characterized in that the treatment in step c) is carried out by a method as defined in one of claims 5 to 8.

10. The method according to claim 9, characterized in that it is carried out in a device as defined in claim 3 or 4.

11. Dispersion, in particular polymer dispersion with a residual volatile content of less than 100 ppm, can be produced by a process according to one of claims 5 to 10.

12. Use of polymer dispersions as claimed in claim 11 as adhesive raw materials, in sealing compounds, paper coating dispersions, plastering compounds, fillers, coatings, as paint and coating raw materials, binders or thickeners, in particular for interior applications.