Method for preparing rubbers

Abstract

The invention relates to a method for preparing rubbers from a dispersion (1) containing the rubber, said method comprising: (a) feeding the dispersion (1), that contains the rubber, and a precipitation solution (3) into a precipitation tank (5), an aqueous suspension (9) that contains rubber particles being produced; (b) optionally sintering the rubber particles contained in the aqueous suspension (9) that contains rubber particles to form larger particles; (c) mechanically dewatering the aqueous suspension (9) that contains rubber particles, rubber particles (33) that contain residual moisture and a liquid phase (35) that contains fine-particle rubber being obtained, the liquid phase (35) that contains fine-particle rubber being returned to the precipitation tank (5).

Description

[0001] Process for processing rubber

[0002] Description

[0003] The invention is based on a process for the preparation of rubbers from a dispersion containing the rubber, in which the dispersion containing the rubber and a precipitation solution are fed into a precipitation container so that an aqueous suspension containing rubber particles is produced, the rubber particles contained in the aqueous suspension containing rubber particles are optionally sintered to form larger particles and the aqueous suspension containing rubber particles is mechanically dewatered so that rubber particles containing residual moisture and a liquid phase containing finely divided rubber are obtained.

[0004] Particulate rubbers that can be prepared using the process according to the invention are frequently used as impact modifiers in the production of thermoplastic polymers or other plastics, particularly in the production of styrene-based copolymers such as acrylonitrile-butadiene-styrene copolymers (ABS) or acrylonitrile-styrene-acrylate copolymers (ASA). These thermoplastic products can then be used in a variety of ways in molding compounds and molded parts.

[0005] The particulate rubbers, in particular butyl acrylate graft rubbers or butadiene graft rubbers, are generally produced by emulsion polymerization in an aqueous system and subsequently precipitated using a precipitation solution. The particles thus obtained are then typically dewatered, for example by filtration, sieving, decanting, pressing out the water, or centrifugation, optionally washed with water during or after dewatering, and optionally subsequently freed of further water by thermal drying.

[0006] Processes for producing the particulate rubbers as a component in the production of ASA or ABS molding compounds are described, for example, in EP-A 0734825, WO-A 2020 / 043690, WO-A 2015 / 000873, or WO-A 2015 / 004112. To maximize space-time yields, the dispersions are generally prepared with a solids content of 30 wt. % or higher.

[0007] The disadvantage of all known processes is that the water separated during dewatering still contains rubber particles, which are usually disposed of with the separated water. Furthermore, fine-particle rubber, which is not retained during dewatering due to the mesh size of sieves or the pore size of filters, enters the wastewater and must be removed during wastewater treatment and subsequently disposed of. The precipitating salt contained in the separated water is also completely disposed of with the wastewater. Likewise, the precipitation of dispersions with a high solids content easily leads to blockages in the precipitation and / or sintering process.

[0008] An object of the present invention is therefore to provide a process for processing rubbers from a dispersion containing the rubber, which process provides a better yield and in which the amount of product and precipitation salt removed from the process with the water can be minimized and at the same time the risk of blockages in the process part of the precipitation and / or sintering is minimized.

[0009] This object is achieved by a process for the preparation of rubbers from a dispersion containing the rubber, comprising:

[0010] (a) feeding the dispersion containing the rubber and a precipitation solution into a precipitation container, whereby an aqueous suspension containing rubber particles is produced,

[0011] (b) optionally sintering the rubber particles contained in the aqueous suspension containing rubber particles to form larger particles;

[0012] (c) mechanically dewatering the aqueous suspension containing rubber particles, yielding rubber particles containing residual moisture and a liquid phase containing finely divided rubber. The liquid phase containing finely divided rubber is returned to the precipitation vessel. At the same time, it was found that by reducing the solids content of dispersions with solids contents above 30 wt.% to below 25 wt.% during precipitation and / or sintering, the tendency toward clogging can be significantly reduced.

[0013] By returning the liquid phase containing finely divided rubber to the precipitation tank, the finely divided rubber returned with the liquid phase is typically subjected to thermal stress several times, at least twice, since the precipitation in the precipitation tank or the sintering in the sintering vessel is generally carried out at elevated temperatures. Surprisingly, it has been shown that the repeated thermal stress on the plastic particles returned to the precipitation tank with the liquid phase containing the finely divided rubber does not adversely affect the mechanical properties of products containing the rubber processed according to the method according to the invention. This means that the recirculation can increase the rubber yield while maintaining the same product quality and simultaneously minimize the amount of rubber removed from the process with the wastewater.Likewise, the amount of wastewater and thus also the amount of precipitating salt required is minimized, while precipitation and / or sintering can be carried out simultaneously with a reduced solids content, thus reducing the risk of blockage in this process step.

[0014] The rubber processed by the process according to the invention can be a grafted rubber. Preferred is a rubber having one or more grafted shells made of other, generally non-elastomeric polymers. For this purpose, the single- or multi-stage elastomeric base stages are obtained by polymerizing one or more of the monomers butadiene, isoprene, chloroprene, styrene, alkylstyrene, C1- to C8-alkyl esters of acrylic acid or methacrylic acid, as well as small amounts of other, including crosslinking, monomers. The hard graft stages are polymerized from one or more of the monomers styrene, alkylstyrene, acrylonitrile, and methyl methacrylate. It is also possible to produce the basic stage using a seed obtained on the basis of the monomers butadiene, isoprene, chloroprene, styrene, alkylstyrene, Ci- to Cw-alkyl esters of acrylic acid or methacrylic acid as well as small amounts of other, also crosslinking, monomers.

[0015] Preferred rubbers are those based on butadiene / styrene / acrylonitrile, n-butyl acrylate / styrene / acrylonitrile, butadiene / n-butyl acrylate / styrene / acrylonitrile, n-butyl acrylate / styrene / methyl methacrylate, butadiene / styrene / acrylonitrile / methyl methacrylate, and butadiene / n-butyl acrylate / methyl methacrylate / styrene / acrylonitrile. Up to 10 wt.% of polar monomers carrying functional groups or crosslinking monomers can be polymerized into the seed and / or core and / or shell.

[0016] Examples of the rubbers processed by the process according to the invention are polymers of conjugated dienes such as butadiene, with an outer graft shell, in particular based on a vinylaromatic compound, such as SAN copolymers. The rubbers can also be graft rubbers based on crosslinked polymers of C1- to C12-alkyl esters of acrylic acid, such as n-butyl acrylate or ethylhexyl acrylate, grafted with polymers based on vinylaromatic compounds, such as SAN copolymers. Furthermore, the process is also suitable for graft rubbers that essentially contain a copolymer of conjugated dienes and C1- to C12-alkyl acrylates, for example a butadiene-n-butyl acrylate copolymer, and one or more graft stages of SAN copolymer, polystyrene, or PMMA. Butadiene graft rubbers and butyl acrylate graft rubbers are particularly preferred.

[0017] The rubber is usually produced in an aqueous system, for example by emulsion polymerization as described, for example, in WO-A 2020 / 043690.

[0018] In emulsion polymerization, an aqueous dispersion is formed with water as the continuous phase and rubber particles produced during polymerization as the disperse phase.

[0019] For processing, the dispersion is introduced into a precipitation tank. A peristaltic pump is preferably used to convey the dispersion from the emulsion polymerization if the dispersion storage tank does not have sufficient gradient for pump-free dosing via gravity.

[0020] The dispersion fed to the precipitation tank preferably has a solids content in the range of 10 to 50 wt.%, more preferably 20 to 45 wt.%, and particularly preferably 30 to 40 wt.%. The solid contained in the dispersion is the particulate rubber.

[0021] In the precipitation tank, the dispersion is converted into an aqueous suspension containing rubber particles by adding a precipitating salt solution which preferably contains at least one salt and / or one acid.

[0022] For the purposes of the present invention, a dispersion is understood to mean a mixture of particles with a volume-average particle diameter Dv of 20 to 999 nm, preferably in the range of 50 to 800 nm, in a liquid phase. The volume-average particle diameter Dv (or the average particle diameter according to De Broucker) is an average size relative to the unit volume of the particles. The volume-average particle diameter of the particles in the dispersion can be determined, for example, by means of light scattering (laser diffraction), for example, using a Beckman Coulter device.

[0023] A suspension is understood to be a mixture of particles in a liquid phase whose particles are larger than the particles of the dispersion. To determine the particle size of the suspension, the D10 value, the D50 value or the D90 value can be used, depending on the type of particle size determination and the size distribution, where the D10 value indicates the particle size up to which 10 wt.% are smaller, the D50 value accordingly indicates the particle size up to which 50 wt.% of the particles are smaller and the D90 value indicates the particle size up to which 90 wt.% of the particles are smaller. The particles in the suspension usually have a D10 value in the range of 50 to 400 pm, a D50 value in the range of 200 to 2000 pm and / or a D90 value in the range of 500 to 4000 pm. Particularly preferably, the particles in the suspension have a D10 value of 50 to 400 pm, a D50 value of 200 to 2000 pm and a D90 value of 500 to 4000 pm.

[0024] The particle size of the suspension particles is preferably determined by wet sieving, using sieve towers with sieves of different mesh sizes. After sieving, the mass of the particles on each sieve is determined, resulting in the D10, D50, and D90 values.

[0025] Preferably, the precipitation solution contains a divalent salt or a trivalent salt and in particular the precipitation solution contains at least one alkaline earth metal salt, preferably a magnesium salt and / or calcium salt, particularly preferably at least one magnesium salt.

[0026] In particular, the at least one alkaline earth metal salt is selected from alkaline earth metal halides, such as chlorides, alkaline earth metal sulfates, alkaline earth metal phosphates, such as orthophosphates or pyrophosphates, alkaline earth metal acetates, and alkaline earth metal formates. Preferably, the at least one alkaline earth metal salt is selected from chlorides and sulfates.

[0027] Preferred alkaline earth metal salts are magnesium sulfate (such as kieserite (Mg[SÜ4] • H2O), pentahydrite (Mg[SÜ4] • 5H2O), hexahydrite (Mg[SÜ4] • 6H2O) and Epsom salt (Mg[SÜ4] • 7H2O)), magnesium chloride, calcium chloride, calcium formate, magnesium formate or mixtures thereof. The use of magnesium sulfate is particularly preferred.

[0028] If the precipitation solution contains a trivalent salt, anhydrous aluminum sulfate or aluminum sulfate with water of crystallization are particularly preferred.

[0029] The amount of salt added depends on the amount of water contained in the dispersion and is preferably in a range of 0.1 to 3 wt.%, more preferably in a range of 0.5 to 3 wt.% and in particular in a range of 0.5 to 2 wt.% salt, in each case based on the amount of water in the dispersion.

[0030] The pH of the mixture of dispersion and precipitation solution obtained in step (a) is preferably in the range from 5 to 10, more preferably in the range from 6 to 9, and in particular in the range from 8 to 9. The pH can be adjusted, for example, by the addition of buffer salts, acids and / or bases, for example sulfuric acid, phosphoric acid, solutions of sodium hydroxide, potassium hydroxide, sodium salts and potassium salts of carbonates (e.g. sodium carbonate Na2CO3 and / or sodium hydrogen carbonate NaHCCh or mixtures thereof), sulfates or phosphates (e.g. tetrasodium pyrophosphate).

[0031] Preferably, for example, at least one buffer salt from the group of sodium salts, in particular from the group of sodium carbonates, sodium sulfates and sodium phosphates, preferably from the group of sodium carbonates Na2COs and sodium hydrogen carbonates NaHCOs, is added.

[0032] The buffer salts, acids, and / or bases can be added during the production of the rubber in the emulsion polymerization or mixed into the precipitation vessel in step (a). Preferably, the addition takes place during the production of the rubber in the emulsion polymerization.

[0033] In order to precipitate the rubber from the dispersion and to obtain the aqueous suspension containing rubber particles, the precipitation solution and the dispersion are usually mixed for a period of time in the range of 5 to 50 minutes, preferably 5 to 40 minutes.

[0034] The precipitation in step (a) can be carried out in a temperature range from 20 to 150°C, preferably from 40 to 100°C, particularly preferably from 45 to 99°C, likewise preferably from 60 to 95°C. Preferably, the dispersion is mixed with the at least one precipitation solution at a temperature in the range from 30 to 95°C, preferably from 40 to 95°C, particularly preferably from 40 to 90°C.

[0035] To obtain larger particles, the rubber particles contained in the aqueous suspension containing rubber particles obtained in step (a) can be agglomerated to form larger particles in a subsequent sintering step (b). For this purpose, the aqueous suspension containing rubber particles obtained in step (a) is preferably conveyed into a sintering vessel in which the aqueous suspension containing rubber particles is maintained at a temperature in the range of 70 to 150°C, preferably in the range of 75 to 140°C, and particularly preferably in the range of 85 to 140°C. In particular, the aqueous suspension containing rubber particles is maintained at this temperature for a period of 10 to 90 minutes, preferably 15 to 90 minutes, particularly preferably 15 to 80 minutes.

[0036] Particularly preferably, the mixing of the dispersion and the precipitation solution in step (a) is carried out at a temperature in the range of 30 to 95°C and preferably in the range of 40 to 90°C, and, when step (b) is carried out, the sintering in step (b) is carried out for at least 5 minutes at a temperature in the range of 70 to 120°C, preferably 80 to 100°C.

[0037] The precipitation of the rubber particles in step (a) and the sintering in step (b) can be carried out in different containers or in the same container. Precipitation and sintering in the same container are particularly possible when the process is operated batchwise, since in this case the dispersion is first mixed with the precipitation solution at a lower temperature and the rubber particles are then sintered at a higher temperature. It is therefore preferred to use a precipitation container for step (a) and a sintering container for step (b), the sintering container and the precipitation container being two different containers. To transport the aqueous suspension containing rubber particles, the sintering container and the precipitation container are connected by a connecting line in which a pump is accommodated.

[0038] In order to achieve the most uniform size distribution possible of the resulting agglomerated particles during sintering, it is advantageous if both the precipitation of the rubber particles in the precipitation container and the sintering are carried out continuously.

[0039] In order to keep the suspension containing the rubber particles in motion and to prevent sedimentation of the rubber particles, especially when the supply of the suspension to a subsequent part of the plant is not possible, for example due to a malfunction, a pumping circuit is provided in the connecting line between the precipitation tank and the sintering tank, in which the aqueous suspension containing the rubber particles is pumped in a ring line.

[0040] For continuous operation, it is also advantageous to make the sintering container larger than the precipitation container if the necessary residence time in the sintering container is longer than the residence time in the precipitation container.

[0041] After precipitation, or, if step (b) is carried out, after sintering, the aqueous suspension containing rubber particles is dewatered to obtain rubber particles containing residual moisture and a liquid phase containing finely divided rubber.

[0042] The water content of the residual moisture-containing rubber particles is preferably a maximum of 60 wt.%, more preferably a maximum of 50 wt.%, and in particular a maximum of 40 wt.%, each based on the total mass of the residual moisture-containing rubber particles. The water content can be determined in particular using suitable analytical devices, for example, drying and weighing devices, whereby a sample is dried until a constant sample weight is reached over a certain period of time. For example, the water content of the residual moisture-containing rubber particles can be determined in a Mettler Toledo HR73 Halogen Moisture Analyzer at 180°C for 30 seconds until constant weight is reached.

[0043] In particular, the water content of the rubber particles containing residual moisture obtained in step (c) is in the range from 10 to 50 wt.%, preferably in the range from 20 to 45 wt.% and in particular in the range from 20 to 40 wt.%, in each case based on the total mass of the rubber particles containing residual moisture.

[0044] Mechanical dewatering is typically achieved by continuous or batch centrifugation and / or filtration. Preferably, mechanical dewatering is achieved by continuous centrifugation. For this purpose, the aqueous suspension containing rubber particles is subjected to a centripetal acceleration of 200 g to 2000 g, with gravitational acceleration g = 9.81 m / s. 2 , preferably with a centripetal acceleration of 500 g to 1300 g, for a period of 1 second to 5 minutes, preferably 1 to 120 seconds.

[0045] To prevent sedimentation of the rubber particles, particularly in the event of a failure of a continuously operating mechanical dewatering system, it is also advantageous here if a pumping circuit is provided in the connection between the sintering vessel and the continuously operating mechanical dewatering system, in particular at least one centrifuge or at least one filter device, in which the suspension containing the sintered rubber particles can be temporarily stored before being fed to the centrifuge and / or the filter device. If a batch centrifuge is used that is emptied discontinuously, a buffer tank is required in which the suspension containing the rubber particles is collected.

[0046] The rubber particles containing residual moisture can then be washed with water and / or a mixture of water and a polar, water-miscible solvent and then dried, as described, for example, in WO 2020 / 043690.

[0047] Since the liquid phase separated from the residual moisture-containing rubber particles during mechanical dewatering of the aqueous suspension containing rubber particles still contains finely divided rubber, the liquid phase containing the finely divided rubber is returned to the precipitation tank according to the invention. To buffer fluctuations in throughput in the individual process steps, it is preferred if the liquid phase containing the finely divided rubber is first collected in a return water tank before being returned to the precipitation tank. This also allows for control of the amount of liquid phase containing finely divided rubber that is added to the dispersion in the precipitation tank, for example, to establish a desired solids content in the mixture of the dispersion originating from the emulsion polymerization fed to the precipitation tank and the liquid phase containing the finely divided rubber.

[0048] Since the amount of finely divided rubber in the liquid phase containing the finely divided rubber is very small, generally not exceeding 2 wt.% and in particular in the range of 0.01 to 1 wt.%, based in each case on the total mass of the liquid phase containing the finely divided rubber, it is further preferred if the return water tank is a settling tank in which a rubber-rich phase and a rubber-poor phase form. Depending on the density of the rubber, the rubber-rich phase can be the upper phase or the lower phase.

[0049] To prevent the liquid phase contained in the return water tank from being disturbed and mixed by the introduction of additional finely particulate rubber-containing liquid phase obtained in subsequent mechanical dewatering steps, and to further prevent foam formation in the return water tank, it is preferable for the liquid phase containing the finely particulate rubber to be introduced into the return water tank via a dip tube. Particularly if the return water tank is a settling tank, this can prevent the already forming rubber-rich phase and the rubber-poor phase from mixing again.

[0050] The proportion of rubber in the rubber-rich phase is sufficiently large that the rubber-rich phase can be returned directly from the return water tank to the precipitation tank. The rubber content in the rubber-poor phase is preferably a maximum of 0.5 wt.%, more preferably in the range of 0.001 to 0.1 wt.%, and in particular in the range of 0.001 to 0.07 wt.%, each based on the total mass of the rubber-poor phase.

[0051] Since the water of the returned rubber-rich phase contains not only the finely divided rubber but also dissolved salt and / or acid from the precipitation solution fed into the precipitation tank, it is further preferred if the rubber-rich phase returned directly to the precipitation tank is mixed with the precipitation solution also introduced into the precipitation tank before being introduced into the precipitation tank. Mixing the precipitation solution with the returned rubber-rich phase before being introduced into the precipitation tank has the further advantage of preventing the formation of undesirably large rubber particles due to high local concentrations of the precipitation solution in the precipitation tank and the very rapid precipitation.

[0052] The salt content can be determined, for example, by conductivity measurement or titration. The acidity can be determined by pH measurement, and the flow rates can be determined by installing a suitable flow meter known to those skilled in the art in the lines upstream of the mixing point. To adjust the desired concentration of salt and / or acid for precipitation, the mass flows of the supplied precipitation solution and the returned rubber-rich phase are determined separately, and the desired amount of precipitation solution is added via a ratio control.

[0053] To recover the rubber from the low-rubber phase and prevent it from being disposed of with the wastewater, the low-rubber phase is preferably concentrated and then fed to the precipitation tank. The wastewater generated during the concentration is disposed of, with the amount of wastewater preferably corresponding to the amount of water introduced with the dispersion and the precipitation solution, less the amount of water removed from the process at other points, particularly the water still contained in the residual moisture in the rubber particles. This enables a continuous process without the amount of water in the process continually increasing due to recirculated water.

[0054] To concentrate the rubber particles contained in the rubber-poor phase, any method known to those skilled in the art for separating solids from a solids-containing liquid can be used. Particularly preferably, the rubber particles from the rubber-poor phase are concentrated by filtration. Upon filtration of the rubber-poor phase, a rubber-rich retentate and a substantially rubber-free filtrate are produced, and the rubber-rich retentate is returned to the precipitation vessel.

[0055] The filtration of the rubber-poor phase can be operated continuously. In this case, the rubber-poor phase is concentrated by forcing liquid through the filter as it flows through the filter apparatus. This produces a rubber-rich retentate, which is returned to the precipitation tank, and a substantially rubber-free filtrate, which can be disposed of as wastewater. To adjust the rubber content in the retentate, for example, the volume flow through the filter, the pressure difference across the filter, and / or the filter surface can be adjusted. It is possible to use just one filter or two or more filters, with the filters being connected in parallel and / or in series.

[0056] Alternatively, and preferably, the filtration is carried out in such a way that the rubber contained in the rubber-poor phase accumulates as a filter cake on the filter of the filtration apparatus, and the liquid is withdrawn from the filter as a substantially rubber-free filtrate. In this case, the resulting filter cake is discontinuously rinsed into the precipitation tank with filtered backwater.

[0057] Filters that can be used to concentrate the rubber from the rubber-poor phase include edge-gap filters. Suitable filter materials include edge-gap filters, with the gap size of the filter preferably being in the range of 10 to 500 μm, more preferably in the range of 50 to 250 μm, and especially in the range of 75 to 200 μm.

[0058] During filtration, solids typically settle on the filter, forming a filter cake. Depending on the volume flow of the rubber-poor phase passing through the filter apparatus, at least a portion of the filter cake can be rinsed from the filter with the rubber-poor phase, in which the rubber accumulates during filtration, and returned to the precipitation tank with the retentate.

[0059] If a filter cake forms that cannot be rinsed away with the retentate, it is preferable to rinse the filter regularly. The time at which the filter is rinsed can be determined, for example, by the increase in the pressure difference required to force the filtrate through the filter. Even if the filtration is carried out in such a way that the rubber is separated from the low-rubber phase so that a filter cake forms, the resulting filter cake is regularly rinsed from the filter as described above, and the rinsing liquid, containing the rubber, is returned to the precipitation tank.

[0060] When using a filter that does not require the application of overpressure on the retentate side and / or underpressure on the filtrate side, the time at which filter flushing is required can also be determined based on the filtrate volume flow or the solids content in the retentate.

[0061] To rinse the filter, a rinsing liquid can be passed through the filter from the filtrate side to the retentate side, thereby rinsing the filter cake from the filter. Alternatively, it is also possible to feed the rinsing liquid to the filter instead of the rubber-poor phase. Since the filter cake essentially contains rubber, it is preferred if the rinsing liquid, with the rubber contained therein, is introduced from the filter cake into the precipitation tank. In order to be able to introduce the rinsing liquid, with the rubber contained therein, into the precipitation tank, it is preferable to use a rinsing liquid that contains only those components that are also contained in the liquid in the precipitation tank. Water is therefore particularly preferably used as the rinsing liquid.

[0062] The essentially rubber-free filtrate is removed from the process and preferably subjected to wastewater treatment before the wastewater is released into the environment.

[0063] In the event that the amount of liquid phase containing finely divided rubber that is fed to the return water tank from the mechanical dewatering is greater than the amounts of rubber-rich phase and rubber-poor phase that are removed from the return water tank and thus the filling level in the return water tank can exceed a maximum filling level, the return water tank preferably comprises an overflow through which a wastewater stream can flow out of the return water tank.

[0064] If the rubber has a lower density than the liquid, it floats in the return water tank, so that the rubber-rich phase is located in the upper area of ​​the return water tank. For this reason, the overflow is preferably arranged in the lower area of ​​the return water tank in this case, so that in the event that the fill level in the return water tank exceeds a maximum fill level, only the rubber-poor phase is removed. To allow the liquid to flow out without providing an additional valve, it is preferred if the line forming the overflow initially runs upwards to the height of the maximum fill level and has a bend of at least 90° there, so that the rubber-poor phase can only flow out through the overflow due to hydrostatic pressure when the maximum fill level is reached.

[0065] Accordingly, the rubber will sink if it has a higher density than the liquid. In this case, the rubber-rich phase is located at the bottom of the return water tank, and the rubber-poor phase is located at the top. This means that if the overflow is located in the upper area of ​​the return water tank, preferably at the position where the maximum fill level is, the rubber-poor phase will flow into the overflow when the fill level in the return water tank becomes too high.

[0066] Particularly when using the return water tank in a swing system in which both rubber with a lower density and rubber with a higher density than the liquid are produced, it is preferred to arrange an overflow at the top of the return water tank, preferably at the position of the maximum fill level, and an overflow at the bottom of the return water tank, wherein for a rubber with a density that is lower than the density of the liquid, the overflow at the top of the return water tank is closed and for a rubber with a density that is higher than the density of the liquid, the overflow at the bottom of the return water tank is closed.It is further preferred if the overflow at the bottom is connected via a line to the overflow at the top of the return water tank, wherein the line opens into the overflow downstream of a shut-off device and the opening of the line into the overflow is preferably at the same height as the connection of the overflow to the return water tank.

[0067] As soon as the fill level in the return water tank exceeds the maximum fill level, the rubber-rich phase flows into the overflow. To prevent the rubber-rich phase, which then flows into the overflow, from being directed to a wastewater disposal facility and the rubber contained in the rubber-rich phase being lost, a return line is preferably provided in this case. This line branches off from the overflow and flows into the line through which the rubber-poor phase flows for concentration, particularly filtration. This prevents the liquid removed through the overflow, which still contains rubber, from being directed to a disposal facility, thus removing the rubber it contains from the process as waste.

[0068] A centrifugal pump designed as a free-flow pump is preferably used as the pump used to convey the liquid phase containing the sintered rubber particles or, if the separate sintering step was not performed, the suspension containing rubber particles obtained in step (a) to the mechanical dewatering stage. A progressive cavity pump is preferably used as the pump used to convey the low-rubber phase to the filtration stage.

[0069] The use of a centrifugal pump designed as a free-flow pump or an eccentric screw pump allows the transport of the liquid phase containing the rubber particles without the pump becoming clogged by the rubber particles contained in the liquid phase, since a sufficiently large flow channel is included through which the liquid can flow without contact with the impeller of the pump.

[0070] In order to prevent wear or blockage of the eccentric screw pump due to swelling of the plastic due to any residual monomers still present, and thus to enable uniform conveyance of the liquid phase containing the rubber particles, it is further preferred if the stator and / or the rotor of the eccentric screw pump is made of chlorosulfonated polyethylene rubber (CMS), for example available as Hypalon® from DuPont Performance Elastomers. Since the rubber particles continue to agglomerate and thus become larger with increasing residence time, it is further preferred if the particle size of the rubber particles precipitated in step (a) and / or sintered in step (b) can be controlled. For this purpose, it is possible, for example, to use a pump that contains a cutting tool for particle comminution and / or to connect a particle comminutor upstream of the pump.

[0071] Suitable particle size reducers include wet grinding machines, through which the liquid phase containing the rubber particles flows. These typically contain cutting tools. The cutting tools can be rigidly integrated into the particle size reducer or can be designed as a rotor and stator. Suitable particle size reducers include Siefer TrigonalO machines.

[0072] Pumps that contain rotor-stator tooth mixing elements for particle comminution are available, for example, under the name Supraton® inline homogenizers from BWS Technologie GmbH.

[0073] Embodiments of the invention are illustrated in the figures and are explained in more detail in the following description and the claims.

[0074] They show:

[0075] Figure 1 is a flow diagram of the process according to the invention;

[0076] Figure 2 is a schematic representation of a return water tank for rubber particles with a density greater than the density of the liquid,

[0077] Figure 3 is a schematic representation of a return water tank for rubber particles with a density lower than the density of the liquid,

[0078] Figure 4 is a schematic representation of a return water tank for a swing plant in which rubber particles with a density lower than the density of the liquid and rubber particles with a density higher than the density of the liquid are produced alternately.

[0079] Figure 1 shows a flow diagram of the process according to the invention.

[0080] To process rubbers from a rubber-containing dispersion, the rubber-containing dispersion 1, which originates, for example, from an emulsion polymerization, is introduced into a precipitation tank 5 together with a precipitation solution 3. The dispersion 1 is preferably conveyed into the precipitation tank 5 solely by gravity. If conveying by gravity is not possible, particularly if the dispersion storage tank in which the dispersion is temporarily stored is too low, the dispersion 1 is preferably conveyed into the precipitation tank 5 using a peristaltic pump. To adjust the concentration in the precipitation tank 5, additional water can be fed via a line 6 either directly into the precipitation tank 5 or alternatively into the line through which the precipitation solution 3 is introduced.

[0081] In the precipitation tank, the rubber-containing dispersion 1 and the precipitation solution 3 are mixed with a mixing unit 7, for example, a stirrer, resulting in an aqueous suspension containing rubber particles. The aqueous suspension 9 containing rubber particles is removed from the precipitation tank and fed to an optional sintering tank 11, in which the rubber particles agglomerate into larger particles. To prevent the rubber particles from settling, the rubber-particle-containing suspension contained in the sintering tank 11 is also mixed with the aid of a mixing unit 13, for example, a stirrer.

[0082] In order to convey the aqueous suspension 9 containing the rubber particles from the precipitation tank 5 into the sintering tank 11, a first pump 15 is accommodated in the line connecting the precipitation tank 5 and the sintering tank 11. Preferably, the first pump 15 is part of a circulation circuit 17, in which, particularly in the event of a failure of the removal from the sintering tank 11, for example, in the event of a failure of system components downstream of the sintering tank, the suspension 9 containing the rubber particles is kept in motion, thus preventing sedimentation of the particles. The first pump 15 is preferably a centrifugal pump designed as a free-flow pump.

[0083] From the sintering tank 11, the suspension 18, now containing larger rubber particles, is fed to a mechanical dewatering system 19. The mechanical dewatering 19 can be carried out, for example, by centrifugation or filtration, with centrifugation being preferred. For emptying the sintering tank 11, a drain line 20 is preferably provided at the bottom of the sintering tank. During normal operation, the drain line 20 is closed, and the aqueous suspension 18 containing larger rubber particles produced in the sintering tank is removed via the removal line at the top of the sintering tank 11.

[0084] Particularly in batch mechanical dewatering 19, it is necessary for the aqueous suspension containing rubber particles fed to the mechanical dewatering 19 to be temporarily stored. For this purpose, for example, a buffer tank 21 can be provided in which the aqueous suspension 18 containing rubber particles is temporarily stored. To prevent rubber particles from settling out of the suspension, it is preferred for the buffer tank 21 to have a mixing unit, for example, a stirrer, with which the suspension can be stirred.

[0085] Alternatively or additionally, it is further preferred if, as shown here, a second pumping circuit 23 is provided, in which the aqueous suspension containing rubber particles can be pumped. In the second pumping circuit 23, the aqueous suspension containing rubber particles is thoroughly mixed so that the rubber particles do not precipitate. The second pumping circuit 23 is particularly advantageous when mechanical dewatering is carried out continuously.

[0086] If the mechanical drainage 19 is operated continuously, it is sufficient to provide the second pumping circuit 23, but the buffer tank 21 can also be additionally or alternatively connected upstream of the mechanical drainage 19.

[0087] If the mechanical dewatering 19 is operated batchwise, the buffer tank 21 is necessary to temporarily store the suspension before it is fed to the mechanical dewatering 19. However, it is also possible here, as shown in Figure 1, to connect the second pumping circuit 23 upstream of the buffer tank 21.

[0088] A second pump 25 is accommodated in the second pumping circuit 23 both for transporting the aqueous suspension containing rubber particles from the sintering vessel 11 into the mechanical dewatering system 19 and for the circulation in the second pumping circuit 23. Furthermore, it is preferred if a bypass 27 is provided, with which the second pump 25 can be bypassed, wherein a third pump 29 is accommodated in the bypass 27.

[0089] As an alternative to the embodiment shown here, the second pump 25 and the third pump 29 can also be connected in series. This is particularly advantageous if the third pump 29 cannot build up a sufficiently high pressure relative to the second pump 25, since this would result in a circular flow from the pressure side to the suction side.

[0090] The second pump 25 and the third pump 29 are preferably, like the first pump 15, each a centrifugal pump designed as a free-flow pump.

[0091] Since the particles can continue to agglomerate in the second circulation circuit 23, it is further preferred if the second pump 25 and / or the third pump 29 are equipped with a cutting tool for particle comminution. By using the cutting tool, the particle size of the rubber particles can be adjusted to a desired size, and particles that reach an undesirable size due to agglomeration are comminuted. In particular, when the suspension 18 containing rubber particles is conveyed directly into the mechanical dewatering 19, it is preferred if the second pump 25 and the third pump 29 are connected in series, in which case the second pump 25 preferably does not have a cutting tool and builds up the necessary pressure, and the third pump 29 with the cutting tool is connected downstream of the second pump.If a buffer tank 21 is present, no significant pressure build-up is necessary and the second pump 25 and the third pump 20 can run in parallel.

[0092] Alternatively or in addition to a pump with a cutting tool, a particle crusher can also be incorporated into the second circulation circuit 23 to prevent the formation of excessively large rubber particles. The particle crusher is preferably a wet grinder.

[0093] The sintering of the rubber particles in the sintering tank 11 generally takes place at a temperature above the temperature at which the mechanical dewatering 19 is carried out. To cool the aqueous suspension containing rubber particles, a heat exchanger 31 is therefore preferably provided in the connecting line from the sintering tank 11 to the mechanical dewatering 19.

[0094] If a second pumping circuit 23 is provided between the sintering tank 11 and the mechanical dewatering system 19, the heat exchanger 31 is preferably located at a position in the second pumping circuit 23 through which the aqueous suspension containing rubber particles flows even when it is introduced directly from the sintering tank 11 into the mechanical dewatering system 19 and does not flow in a circuit in the second pumping circuit 23. When using a buffer tank 21, it is alternatively also possible to temperature-control the buffer tank 21 with a cooling system, for example, through a double jacket or cooling pipes running through the buffer tank.

[0095] In mechanical dewatering, the rubber particles are separated from the aqueous suspension containing rubber particles, yielding rubber particles 33 containing residual moisture and a liquid phase 35 containing finely divided rubber. The rubber particles 33 containing residual moisture are removed from the processing process as a raw product and fed, for example, to an extruder for the production of ABS or ASA.

[0096] The liquid phase 35 containing finely divided rubber is introduced into a return water tank 37. The return water tank 37 is preferably a settling tank in which the finely divided rubber accumulates from the liquid phase containing the finely divided rubber, forming a rubber-rich phase and a rubber-poor phase. The proportion of rubber in the rubber-rich phase 39 is preferably so large that the rubber-rich phase can be removed directly from the return water tank 37 and returned to the precipitation tank 5.

[0097] In order to convey the rubber-rich phase 39 from the return water tank 37 into the precipitation tank 5, a pump 41 can be incorporated into the connecting line from the return water tank 39 to the precipitation tank 5. However, it is preferred if the return water tank 37 is positioned higher than the precipitation tank 5, so that the rubber-rich phase 39 can flow into the precipitation tank 5 purely by gravity, thus eliminating the need for the pump 41.

[0098] Furthermore, it is preferred if the recycled, rubber-rich phase 39 is mixed with the precipitation solution 3 before being introduced into the precipitation container 5.

[0099] In order to also retain the rubber contained in the low-rubber phase 43 as a product and not dispose of it with the process wastewater, the low-rubber phase 43 is fed from the return water tank 37 to a filtration 45. In the filtration 45, the rubber from the low-rubber phase is concentrated, producing a rubber-rich retentate 47, which is fed into the precipitation tank 5.

[0100] If the filtration 45 is carried out in such a way that a filter cake forms on the filter in the filtration apparatus, this filter cake is preferably rinsed regularly, and the rinsing solution with the rubber contained therein is introduced into the precipitation tank 5 as a rubber-rich retentate 47. In order to avoid introducing any undesirable components into the precipitation tank 5, backwashing is preferably carried out with water, in particular with demineralized water 49. Alternatively, filtrate 51 can also be used for backwashing.

[0101] The pore size of the filter used for filtration 45 is preferably selected such that substantially all of the finely divided rubber contained in the rubber-poor phase is separated, so that a substantially rubber-free filtrate 51 is produced, which can be discharged as wastewater and fed to a wastewater treatment plant and then disposed of.

[0102] A fourth pump 53 is preferably used to convey the low-rubber phase 43 into the filtration 45. Any pump capable of conveying a liquid phase containing only a low solids content can be used. Suitable pumps include centrifugal pumps or eccentric screw pumps. When using an eccentric screw pump, it is particularly preferred if the stator and / or rotor of the eccentric screw pump are made of chlorosulfonated polyethylene rubber (CMS).

[0103] Figure 2 shows a return water tank 37 designed as a settling tank in a first embodiment.

[0104] The liquid phase 35 containing finely divided rubber is fed to the return water tank 37 via a dip pipe 55. By feeding the liquid phase 35 containing the finely divided rubber via the dip pipe 55, the upper region of the return water tank 37 is prevented from becoming enriched with a rubber-depleted phase containing rubber from the liquid phase 35 containing the finely divided rubber. At the same time, the inflow of the liquid phase 35 containing the finely divided rubber into the bottom region ensures that the sedimenting rubber does not form deposits in the bottom region of the return water tank 37. In this way, the return water tank 37 can be used as a settling tank, even if the liquid phase containing finely divided rubber is introduced into the return water tank 37 continuously or, in the case of batchwise mechanical dewatering, at regular intervals.

[0105] In the return water tank 37, designed as a settling tank, the rubber contained in the liquid phase containing finely particulate rubber accumulates, forming a rubber-rich phase and a rubber-poor phase. If the rubber has a greater density than the liquid of the liquid phase containing finely particulate rubber, the rubber sinks, so that the rubber-rich phase is at the bottom and the rubber-poor phase is at the top. Accordingly, if the density of the rubber is lower than the density of the liquid of the liquid phase containing finely particulate rubber, the rubber floats, so that in this case the rubber-rich phase is at the top and the rubber-poor phase is at the bottom.

[0106] In the embodiment shown in Figure 2, the return water tank is particularly preferably used when the rubber has a density that is greater than the density of the liquid. In this case, the dip tube 55 preferably ends near the bottom 57 of the return water tank 37, so that the newly added liquid phase containing finely divided rubber is fed into the lower region of the rubber-rich phase. This achieves mixing of the rubber-rich phase with the newly added liquid phase containing finely divided rubber near the bottom 57 of the return water tank 37, thereby minimizing the amount of rubber that can sediment and form a coating on the bottom 57 of the return water tank 37.

[0107] The rubber-rich phase which forms in the lower region of the return water tank 37 is preferably removed via an outlet 59 at the bottom 57 of the return water tank and fed to the precipitation tank 5.

[0108] The low-rubber phase forms the upper phase in the filling tank and is preferably removed via an outlet 61 in the upper region of the return water tank 37 and fed to the filter 45, possibly via a pump 53. It is particularly preferred if the outlet 61 for the low-rubber phase is arranged at a height corresponding to a desired maximum filling level 63.

[0109] To prevent overfilling of the return water tank 37, particularly when the amount of liquid phase containing finely divided rubber that is fed to the return water tank 37 is greater than the amounts of rubber-rich phase and rubber-poor phase that are removed from the return water tank via the outlets 59, 61, an overflow 65 is provided. Since the rubber-poor phase is located in the upper region of the return water tank 37, only a very small amount of rubber is removed from the return water tank 37 when removed via the overflow 65, so that the loss of product is very low. The rubber-poor liquid flowing out via the overflow 65 is then usually fed to a wastewater treatment plant so that after treatment the wastewater can be released into the environment.

[0110] Figure 3 shows a return water tank 37 in a second embodiment, as it is preferably used when the rubber has a density which is lower than the density of the liquid phase containing the finely divided rubber, so that the rubber floats in the return water tank and the rubber-rich phase forms at the top and the rubber-poor phase at the bottom.

[0111] Unlike the return water tank shown in Figure 2, in a return water tank used in a process in which the rubber-rich phase forms at the top of the return water tank 37, the dip tube 55 ends already in the middle region of the return water tank, so that the rubber supplied from the liquid phase containing finely divided rubber introduced through the dip tube 55 rises and the rubber-rich phase forms above the mouth of the dip tube 55 in the return water tank 37 and the rubber-poor phase below the mouth of the dip tube 55. Accordingly, the rubber-rich phase is removed via an outlet 67 in the upper region of the return water tank 37, wherein here too the outlet 67 is preferably arranged at the position of the desired maximum filling height 63.As a result, the rubber-rich phase in the region of the phase boundary, where the largest proportion of rubber is found as the rubber rises, is removed from the return water tank 37. Accordingly, the proportion of rubber in the rubber-poor phase at the bottom 57 of the return water tank 37 is lowest, so that the rubber-poor phase is removed via an outlet 69 at the bottom 57 of the return water tank 37.

[0112] In the embodiment shown in Figure 3, the return water tank 37 also comprises an overflow 65 to prevent the return water tank 37 from overfilling. Since the rubber-poor phase, in the case of light rubber, is located in the lower region of the return water tank 37, the overflow 65 branches off from the outlet 69 at the bottom 57 of the return water tank 37 and preferably runs upwards outside the return water tank 37 to a height of the maximum fill level in the return water tank. At the height of the maximum fill level, the overflow 65 has a bend of at least 90° so that the liquid can flow horizontally or downwards again after the bend. The bend represents the highest point of the overflow. In this way, the rubber-poor phase can flow out of the return water tank 37 without the need for an additional shut-off device as soon as the maximum fill level is reached.

[0113] Figure 4 shows a return water tank 37 which can be used in a swing plant in which rubber is alternately produced which has a density which is lower than the density of the liquid of the liquid phase containing the finely divided rubber, and rubber which has a density which is higher than the density of the liquid of the liquid phase containing the finely divided rubber.

[0114] In order to avoid having to use two different return water tanks in a swing system depending on the density of the rubber produced, the return water tank 37, which can be used in a swing system, in contrast to the embodiments shown in Figures 2 and 3, has an overflow 65 which branches off at the position of the maximum fill level and which can be closed with a first shut-off device 71A, as well as a line 73 which branches off from the outlet 69 at the bottom 57 of the return water tank, can be closed with a second shut-off device 71B and opens into the overflow 65 downstream of the first shut-off device 71A at the same height at which the overflow 65 branches off from the return water tank 37. The shut-off devices 71A, 71B can be independent of one another, for example a valve, a cock or a slide valve.When a rubber is produced with a density that is greater than the density of the liquid phase containing the finely divided rubber, the first shut-off device 71 A is opened and the second shut-off device 71 B is closed. In this way, when the maximum liquid level is exceeded, the rubber-poor phase can drain from the return water tank 37 via the overflow 65. Since the rubber-rich phase collects in the lower area of ​​the return water tank 37, the rubber-rich phase is removed from the return water tank 37 via the outlet 69. The rubber-poor phase can be withdrawn from the return water tank 37 via the outlet 67.

[0115] For use with a rubber with a density that is lower than the density of the liquid phase containing the finely divided rubber, the first shut-off device 71A is closed and the second shut-off device 71B is opened. In this case, when the maximum fill level is exceeded, the rubber-poor phase flows via line 73 into the overflow 65. The rubber-rich phase is removed via the outlet 67 in the upper area of ​​the return water tank 37, and the rubber-poor phase via the outlet 69.

[0116] Since, depending on the density of the rubber produced, the rubber-rich phase is removed either via the outlet 67 in the upper area of ​​the return water tank 37 or via the outlet 69 at the bottom 57 of the return water tank 37, and the rubber-poor phase is correspondingly removed via the other outlet 69, 67, the outlet 67, 69, via which the rubber-rich phase is removed, is connected to the system in such a way that the rubber-rich phase is led into the precipitation tank 5, and the outlet 67, 69, via which the rubber-poor phase is removed, is connected to the filtration 45. For this purpose, for example, 3 / 2-way valves can be used, in which the inlet is connected to the outlet 67, 69, one of the outlets to a line to the precipitation tank 5 and the other outlet to a line to the filtration 45. Alternatively, the respective line to the precipitation tank 5 or to the filtration 45 can also be connected to the corresponding outlet 67, 69.This can be achieved, for example, with a hose that is connected to the respective outlet 67, 69 via a coupling.

[0117] Examples

[0118] In all examples and comparative examples, an aqueous dispersion containing butyl acrylate graft rubber (hereinafter referred to as "dispersion") was used. The butyl acrylate graft rubber in the dispersion had an average particle size of 95 nm, and the proportion of graft rubber in the dispersion was 35 wt.%. All examples and comparative examples were carried out in a processing plant as shown in Figure 1, but without the buffer tank 21 and with a backwater tank 37 as shown in Figure 2.

[0119] The temperature in the precipitation tank 5 was maintained at 60 °C, with the temperature being adjusted by direct steam supply. From the precipitation tank, the resulting suspension was pumped into the sintering tank 11 via the circulation circuit 17, with a temperature of 92 °C being maintained in the sintering tank 11. The pump 15 in the circulation circuit 17 was operated with a flow rate of 11 m 3 / h. Through the second pumping circuit 23, the suspension obtained in the sintering tank 11 was fed to a continuously operated centrifuge for mechanical dewatering 19. The flow rate in the pumping circuit 23 was 85 m 3 / h. The gap size of the filter in the continuously operated centrifuge 19 and in the filter 45 was 100 pm each.

[0120] Comparison example 1

[0121] 1.4 m 3 / h of the dispersion, 160 kg / h of a 14% magnesium sulfate solution and 1 .9 m 3 / h of demineralized water was introduced. Neither the retentate obtained in filter 45 nor the rubber-rich phase 39 obtained in the return water tank were returned to the precipitation tank.

[0122] From the return water tank 2.8 m 3 / h of rubber-containing phase flowed out and was discharged directly as wastewater. The loss of rubber via the wastewater was 2.8 kg / h. Furthermore, 22 kg / h of magnesium sulfate was removed via the wastewater.

[0123] Comparison example 2

[0124] To reduce losses via the wastewater, the concentration in the precipitation tank was increased by reducing the amount of demineralized water added. In Comparative Example 2, neither the retentate obtained in filter 45 nor the rubber-rich phase obtained in the return water tank were returned to the precipitation tank.

[0125] In the precipitation container 1 ,4 m 3 / h of the dispersion, 160 kg / h of a 14% magnesium sulfate solution and 0.9 m 3 / h of demineralized water is introduced.

[0126] From the return water tank there are now only 1.5 m 3 / h of liquid flowed away as wastewater. The loss of rubber via the wastewater was 1.5 kg / h, and 12 kg / h of magnesium sulfate was excreted via the wastewater. Example 1

[0127] Unlike in the comparative examples, both the rubber-rich phase 39 and the retentate 47 obtained in the filter 45 were returned to the precipitation vessel.

[0128] For the example, 1.4 m 3 / h of the dispersion was introduced into the precipitation tank. The amount of 14% magnesium sulfate solution added was 51.4 kg / h.

[0129] From the return water tank 1.9 m 3 / h of rubber-rich phase 39 was returned to the precipitation tank and the amount of recycled retentate 47 was 50 kg / h, which was introduced discontinuously into the precipitation tank.

[0130] The amount of filtrate 51 withdrawn from the filter 45 as wastewater was 0.7 m 3 / h. No rubber loss was detectable, and the amount of magnesium sulfate removed from the process via the filtrate was 5.5 kg / h.

[0131] It is thus shown that the process according to the invention can maximize the yield of rubber, since no rubber is removed from the process with the wastewater and, in addition, the amount of magnesium sulfate removed from the process with the wastewater can be minimized.

[0132] This provides a process that is also improved from an ecological point of view.

Claims

Patent claims 1 . A process for the preparation of rubbers from a dispersion (1) containing the rubber, comprising: (a) feeding the dispersion (1) containing the rubber and a precipitation solution (3) into a precipitation container (5), whereby an aqueous suspension (9) containing rubber particles is produced, (b) optionally sintering the rubber particles contained in the aqueous suspension (9) containing rubber particles to form larger particles; (c) mechanically dewatering the aqueous suspension (9) containing rubber particles, whereby rubber particles (33) containing residual moisture and a liquid phase (35) containing finely divided rubber are obtained, characterized in that the liquid phase (35) containing finely divided rubber is returned to the precipitation container (5).

2. Process according to claim 1, characterized in that the liquid phase (35) containing finely divided rubber is collected in a return water tank (37).

3. Process according to claim 2, characterized in that the liquid phase (35) containing the finely divided rubber is introduced into the return water tank (37) via a dip tube (55).

4. Method according to claim 2 or 3, characterized in that the return water tank (37) is a settling tank in which a rubber-rich phase (39) and a rubber-poor phase (43) are formed.

5. Process according to claim 4, characterized in that the rubber-rich phase (39) is returned directly to the precipitation tank (5).

6. Process according to claim 4, characterized in that the rubber-rich phase (39) is mixed with the precipitation solution (3) before being introduced into the precipitation container (5).

7. Process according to one of claims 4 to 6, characterized in that the rubber-poor phase (43) is concentrated and then returned to the precipitation tank (5).

8. The method according to claim 7, characterized in that the rubber-poor phase (43) is filtered for concentration, whereby a rubber-rich retentate (47) and a substantially rubber-free filtrate (51) are produced and the rubber-rich retentate (47) is returned to the precipitation tank (5).

9. The method according to claim 8, characterized in that the rubber-rich retentate (47) collects as a filter cake in the filter and is fed into the precipitation tank (5) with a rinsing liquid (49).

10. Method according to one of claims 2 to 9, characterized in that a waste water stream can flow out of the return water tank (37) via an overflow.

11. The method according to any one of claims 1 to 10, characterized in that a centrifugal pump designed as a free-flow pump is used to convey the aqueous suspension (9) containing rubber particles from step (a) or the suspension containing larger particles from step (b).

12. Method according to one of claims 4 to 11, characterized in that an eccentric screw pump is used to convey the rubber-poor phase (43).

13. The method according to claim 12, characterized in that the stator and / or the rotor of the eccentric screw pump is made of chlorosulfonated polyethylene rubber.

14. Method according to one of claims 11 to 13, characterized in that the centrifugal pump designed as a free-flow pump comprises cutting tools for particle comminution and / or a particle comminutor is connected upstream of the eccentric screw pump or the centrifugal pump designed as a free-flow pump.

15. A process according to any one of claims 1 to 13, characterized in that the rubber is a butyl acrylate graft rubber or a butadiene graft rubber.

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