Process for the preparation of aqueous polymer dispersions in a tube reactor

Abstract

The invention relates to a process for the preparation of a vinyl acetate ethylene copolymer in the form of an aqueous dispersion by free-radically initiated emulsion polymerization in a continuously operated tubular reactor, characterized in that one or more separation plates with liquid-permeable openings are provided in the tubular reactor perpendicular to the flow direction of the reactor contents (polymerization mixture).

Description

[0001] The present invention relates to a process for the preparation of vinyl acetate-ethylene copolymers in the form of aqueous dispersions by radical-initiated emulsion polymerization in a continuously operated tubular reactor and the use of the process product thus obtained.

[0002] Aqueous polymer dispersions are used in various fields of application, for example, in adhesive applications, in coating applications as binders; in carpet, textile and paper applications as binders; and also in chemical building products such as tile adhesives, renders and plasters. Such dispersions are typically prepared by aqueous emulsion polymerization in stirred batch reactors or in continuously operated stirred tank cascades, as described in EP 1 323 752 B1. However, the space-time yield and process efficiency of these processes is limited by the restricted removal of the reaction heat from the reactor through, for example, cooling coils or reactor walls. In order to increase the cooling efficiency, reactors with a relatively large surface-to-volume ratio can be used, an example being a tubular reactor.

[0003] However, in the case of emulsion polymerization in a tubular reactor, there is a problem with the production of polymers having a particle size distribution, in particular a narrow particle size distribution or a particle size distribution which remains the same during the implementation of the process, which is established in batch reactors or stirred tank cascade processes. In a tubular reactor, this problem is envisaged to be further exacerbated in the case of polymerization of gaseous monomers such as ethylene.

[0004] Furthermore, in tubular reactors, the formation of deposits (so-called fouling (polymer fouling)) also causes particular problems and can even lead to a blockage of the tubular reactor, and in any case significantly reduces the operating time and efficiency of the plant when such deposits are removed after the reactor has been shut down. It is also not possible to avoid polymer fouling by installing a stirrer in the tubular reactor, for example, as in the case of the specific helical stirrer for tubular polymerization reactors described in US 4,383,093. Polymer fouling also occurs in stirred tanks, but is less severe due to the smaller cooling surface area and the different reactor geometry. The build-up of fouling is actually reduced sufficiently in stirred tanks using a fouling-resistant coating, as described in EP 3 256 497 B1, but not in tubular reactors. DE 1137216, US 2015 / 9068031, WO 2015 / 089823 and EP 2471594 describe tubular reactors with close-clearance stirrers and / or scrapers. However, this is not a prevention of the build-up of fouling, but rather a mechanical removal thereof, which constitutes a mechanical exposure and furthermore can lead to blockages, and which affects the polymer particle size distribution. EP 0029701 teaches the removal of wall fouling from tubular reactors by pulsatile flow. For this purpose, PCT / EP2019 / 061017 (application number) recommends a reversal of the flow direction in the tubular reactor.

[0005] In this context, it was the object to provide an improved process for the preparation of vinyl acetate-ethylene copolymers in the form of aqueous dispersions by aqueous emulsion polymerization, in which the space-time performance (process efficiency) can be increased and at the same time a high level of plant availability can be ensured. Furthermore, during the continuous emulsion polymerization in a tubular reactor, a vinyl acetate-ethylene copolymer having a very highly constant particle size distribution should be formed. The polymer dispersion obtained by continuous emulsion polymerization in a tubular reactor should also have a distribution of properties (such as particle size distribution, morphology or viscosity) as far as possible as obtained in the case of conventional emulsion polymerization in a stirred batch reactor or continuous stirred tank cascade.

[0006] This object has surprisingly been achieved for vinyl acetate-ethylene copolymers by continuous aqueous emulsion polymerization in a tubular reactor comprising one or more partitions with liquid-permeable openings and installed transverse to the flow direction of the reactor contents.

[0007] Pipe reactors or stirred columns with partitions are known per se from, for example, "Rührtechnik - Theorie und Praxis", Marko Zlokarnik, Springer-Verlag, 1999, ISBN: 3-540-64639-6, pages 305-308, but not in connection with the production of vinyl acetate-ethylene copolymer dispersions.

[0008] The subject of the present invention is a process for the production of vinyl acetate-ethylene copolymers in the form of aqueous dispersions by means of a free-radically initiated emulsion polymerization in a continuously operated pipe reactor, characterized in that one or more partitions with liquid-permeable openings are installed in the pipe reactor transversely to the flow direction of the reactor contents (polymerization mixture).

[0009] The partitions of the present invention with liquid-permeable openings are also referred to hereinafter as partitions.

[0010] The flow direction of the reactor contents is also referred to hereinafter as flow direction or transport direction. In this context, the flow direction generally means the net flow direction of the reactor contents, i.e. generally the overall flow direction of the reactor contents as a whole. The net direction of flow provides a general description of the overall or overriding flow direction of the reactor contents, rather than any local flow, such as turbulent flow or other non-directional flow. The term "reactor contents" generally means the polymerization mixture comprising monomers, initiator and water, i.e. generally the emulsion polymerization mixture contained in the pipe reactor.

[0011] The partitions are preferably flat components, preferably in the form of a plate, a sheet, a flat cylinder or a ring. Thus, generally the partitions are area or planar bodies, whose areal diameter is substantially greater than their height. Generally, the extent of the partitions in one dimension is significantly smaller than the extent (edge) in two other dimensions (flat sides). The partitions generally do not have a spiral or screw-like form. The design of the partitions is preferably guided by the form of the cross-section at the specific point in the pipe reactor at which the respective partition is installed.

[0012] The one or more partitions, preferably all the partitions, are installed in the pipe reactor transversely to the transport direction (preferably radially or perpendicularly or substantially perpendicularly to the transport direction). The one or more partitions, preferably all the partitions, are arranged with their flat sides parallel or substantially parallel to one another.

[0013] The partitions are preferably stationary. The partitions are preferably immovable or fixed throughout the emulsion polymerization.

[0014] The tube reactor preferably contains 3 to 30 baffles, more preferably 7 to 20 baffles, and most preferably 10 to 15 baffles.

[0015] The baffles preferably stand with their edges in contact with the inner wall of the tube reactor, more preferably all around the edges of the baffles. Alternatively, there can also be one or more seals (examples are rubber, silicone or PTFE seals) or rings (examples are metal rings or metal washers) mounted between the baffles and the inner wall of the tube reactor. It is preferred that there is no free, liquid permeable gap between the baffles and the inner wall of the tube reactor. It is preferred that the reactor contents are not allowed to flow between the baffles and the inner wall of the tube reactor.

[0016] The baffles can be fixed firmly to the tube reactor, more particularly to the reactor cover, the reactor floor or the inner wall of the tube reactor, for example welded to or fixed by mounting pieces optionally equipped with seals, for example. The baffles are preferably not fixed to the inner wall of the tube reactor, more particularly not by their edges to the inner wall of the tube reactor.

[0017] It is preferred that one or more, preferably all adjacent baffles are connected to each other by one or more rods. The rods are preferably mounted on the flat side of the baffles, more particularly outside the area swept by the stirrer. The rods are generally used for static stabilization of the baffles and / or the tube reactor.

[0018] The construction consisting of the baffles and the rods is also called a cage. The cage is preferably fastened to the reactor floor and / or more preferably to the reactor cover. This type of cage assembly has the advantage that all baffles can be removed from the tube reactor at the same time and thus time-efficiently, without having to disassemble the tube reactor into individual components at cost and effort. It is also possible to introduce or replace the stirrer in this way simply and time-efficiently.

[0019] The or each baffle divides the reactor interior into a plurality of chambers, also called compartments. The number of chambers is preferably one more than the number of baffles. Two adjacent chambers are connected to each other by preferably 2 to 8, more preferably 2 to 6 and most preferably 3 to 4 rods. The reactor contents are able to flow from one chamber into the adjacent chamber, more particularly in the direction of transport, through the liquid-permeable openings in the baffles. The different chambers exchange communication with each other in the reactor contents, especially in the direction of transport, preferably exclusively through the liquid-permeable openings in the baffles.

[0020] The diameter of the chamber divided by the height of the chamber is preferably 0.25 to 4, more preferably 0.33 to 3, and most preferably 0.5 to 2. The diameter of the chamber corresponds to the inner diameter (preferably the average inner diameter) of the tubular reactor at the point of the respective chamber. The height of the chamber is the net distance between the two partitions delimiting the chamber. Preferably, all chambers have the same height and / or the same diameter. For all chambers, the above-mentioned ratio of diameter to height is preferably within the above-mentioned range. It is particularly preferred that all chambers have the same ratio of diameter to height, more particularly at all points of all chambers.

[0021] The liquid-permeable openings in the partitions can also be referred to as holes. The holes preferably extend through the entire partition. The holes preferably extend from one flat side of the partition to the opposite flat side. The holes are preferably located in the middle of or substantially in the middle of the flat side of the partition. Thus, the partitions are preferably perforated partitions or hole plates. The partitions can have one or more holes. The partitions preferably have 1 to 1000 holes, more preferably 1 to 100 holes, still more preferably 1 to 10 holes, very preferably 1 to 5 holes, and most preferably one hole.

[0022] The holes can themselves take any desired shape. The holes preferably have a circular or substantially circular shape.

[0023] In general, the reactor contents flow through the holes in the partitions in the course of the flow transport through the tubular reactor. The reactor contents preferably cross the partitions exclusively through the hole or holes in the partitions.

[0024] The average flow velocity V of the reactor contents at the point of the free diameter of the aperture is preferably > 0.05 %, more preferably > 0.5 % and most preferably > 1 % of the peripheral stirrer speed. The average flow velocity V is preferably < 50 %, more preferably < 10 % and most preferably < 5 % of the peripheral stirrer speed. The peripheral stirrer speed is calculated as follows: pi times the stirrer diameter times the stirrer speed. The stirrer diameter is typically the widest radius of the stirrer radially to the stirrer shaft - thus, in the case of a blade stirrer, typically the distance between the two opposite stirrer blade tips that are furthest apart from each other. The average flow velocity V of the reactor contents is typically obtained by dividing the volumetric flow through the pipe reactor by the free passage area of the aperture. The free passage area of the aperture is typically the smallest free area present radially with respect to the main flow direction in the aperture. In the case of a circular aperture, and in particular in the case of a circular aperture in which the passage is unobstructed over the entire aperture area, the free diameter typically corresponds to the aperture diameter. In the case of a non-circular aperture, the free diameter is typically obtained by dividing the free passage area of the aperture by the perimeter of the aperture and multiplying the result by 4. The volumetric flow through the reactor is obtained by dividing the mass flow through the reactor by the density of the flow. In the case of a multiphase flow, the general approach is to determine the mass flow and the density of each phase and to add the resulting volumetric flows. For example, the mass flow and the density of a single-phase or multiphase fluid can be measured by means of Coriolis flow meters at the inlet and outlet of the reactor. The free diameter of the aperture and / or the peripheral stirrer speed are preferably chosen such that the average flow velocity of the reactor contents is within the above-mentioned ranges.

[0025] In the partition, at one or more apertures, preferably all apertures, a guide plate can be installed. The guide plate is preferably located at the edge of the aperture and preferably extends over the entire edge of the aperture. The guide plate is preferably installed perpendicular to the partition. The guide plate is preferably oriented parallel to the stirrer shaft. A guide plate that extends over the entire edge of the aperture is preferably installed at the aperture. For example, the guide plate can protrude into both chambers separated by the partition. The guide plate preferably protrudes into only one chamber. The guide plate is preferably installed on the side of the partition that is upstream and / or more preferably downstream in the flow direction or main flow direction. The guide plate facilitates the production of a copolymer having a desired particle size and particle size distribution.

[0026] The guide plate preferably protrudes into both chambers separated by the partition with a length L. The ratio of the length L of the guide plate to the free diameter of the aperture is preferably > 0.25, more preferably > 0.5 and most preferably > 1. The above-mentioned ratio is preferably < 10, more preferably < 5 and most preferably < 2.

[0027] As an alternative to a guide plate, a thick partition can also be used. The thickness L of the partition preferably achieves the above-mentioned ratio of L of the guide plate to the free diameter of the aperture.

[0028] A tubular reactor without a stirrer can be used. Preferred is a tubular reactor with a stirrer, examples are a blade stirrer, a disc stirrer, a rod stirrer or a Rushton turbine. The direction of action of the stirrer or the direction of displacement of the stirrer is preferably radial or perpendicular to the flow direction of the reactor contents. The direction of action of the stirrer is preferably not in the flow direction of the reactor contents. Two or more or preferably one stirrer can be installed per chamber.

[0029] Particularly preferred is a tubular reactor with a stirring assembly comprising a stirrer shaft, at which one or more stirrers, more particularly stirrer blades, are installed. The stirrer shaft is preferably oriented in the direction of the transport direction. The stirrer shaft is preferably arranged parallel or substantially parallel to the transport direction and / or concentric or substantially concentric to the diameter of the tubular reactor. The stirrer shaft preferably extends over one or more chambers and more preferably over all chambers. The stirrer shaft preferably extends from one longitudinal end of the tubular reactor to the other longitudinal end. The stirrer shaft preferably runs through a hole in the partition, more preferably the stirrer shaft runs through a hole in each partition located in the tubular reactor. The stirrer shaft preferably does not completely fill the hole. The stirrer shaft located in the hole preferably leaves a free gap between the stirrer shaft and the partition. One or more stirrers, in particular stirrer blades, are installed at the stirrer shaft, preferably in one or more chambers, more preferably in all chambers. The tubular reactor preferably comprises a stirring assembly or a stirrer shaft.

[0030] The total net flow velocity U of the reactor contents along the stirrer shaft is preferably at least 2 orders of magnitude, more preferably at least 3 orders of magnitude and most preferably at least 4 orders of magnitude smaller than the peripheral stirrer velocity. These data preferably refer to any desired point on the stirrer shaft in the tubular reactor. The total net flow velocity U can be calculated by the volume flow through the reactor divided by the cross-sectional area of the reactor.

[0031] The speed of the stirrer or stirrer shaft is also determined by the overall size of the tubular reactor and is preferably 100 to 10,000 revolutions per minute and more preferably 200 to 2,000 revolutions per minute. One revolution means one revolution of the stirrer or stirrer shaft around its longitudinal axis or around an axis parallel to the transport direction. The stirrer or stirring assembly can be driven in a conventional manner, for example by mechanical transmission, or by magnetic coupling and optionally sealed by a sliding ring seal.

[0032] One feature of a tubular reactor is the ratio of its length to its diameter. The length usually corresponds to the dimension of the tubular reactor in the direction of transport and the diameter usually corresponds to the dimension of the tubular reactor transversely to the direction of transport. Here, the length and the diameter of the tubular reactor preferably refer to the respective net width inside the tubular reactor. The ratio of the length to the diameter is preferably 8:1 to 40:1, more preferably 10:1 to 25:1. The use of this parameter can also influence the particle size distribution of the polymer particles.

[0033] The tubular reactor can be arranged vertically or horizontally with respect to its longitudinal direction or with respect to the direction of transport or at a position between these two directions. The longitudinal direction of the tubular reactor is usually the section from the reactor floor to the reactor cover. A vertical arrangement is preferred. If the tubular reactor is not arranged horizontally, the reactor contents can flow through the tubular reactor from top to bottom under the influence of gravity or, preferably, against the force of gravity from bottom to top.

[0034] During the implementation of the inventive process, the direction of transport in the tubular reactor can be reversed or changed, for example. Alternatively or preferably, during the implementation of the inventive process, the direction of transport in the tubular reactor is not reversed or changed.

[0035] The tubular reactor can be configured in other ways in a conventional manner. The tubular reactor can take any desired form. Preferred tubular reactors are those having a tubular or cylindrical geometry, more preferably having a uniform cylindrical geometry. Examples of tubular reactors are flow tubes, tubular reactors with internals, for example static mixers, tube bundle reactors, loop reactors, Taylor reactors and tube-in-tube reactors.

[0036] The average residence time of the reactor contents in the tubular reactor is preferably 10 minutes to 5 hours, more preferably 15 minutes to 3 hours, most preferably 20 minutes to 2 hours and absolutely most preferably 30 minutes to 90 minutes. The average residence time can be adjusted, for example, by the flow rate of the reactor contents, the rate of metered addition or the dimensions of the tubular reactor.

[0037] The residence time distribution of the reactor contents in the tubular reactor can be characterised, for example, by the Bodenstein number Bo. The Bodenstein number Bo is preferably > 15, more preferably > 20 and most preferably > 25. The Bodenstein number Bo is preferably < 200, more preferably < 150 and most preferably < 100.

[0038] The Bodenstein number Bo can be calculated, for example, with the following formula:

[0039]

[0040] Eθ (0) is a dimensionless residence time distribution and is obtained using the following equation: E θ (0) = E(t) · T;

[0041] T is the residence time and is calculated from the reactor volume divided by the volume flow. The volume flow through the reactor can be calculated by dividing the mass flow through the reactor by its density. Both values can be measured in a conventional manner (e.g. using Coriolis flow meters at the reactor inlet and outlet). When different volume flows are obtained at the inlet and outlet, the arithmetic mean value is preferably used for the calculation. The dimensionless time 0 = t / T is calculated from the residence time by dividing the dominant time t by the residence time T. The residence time distribution E(t) can be determined experimentally in a conventional manner, for example by means of the so-called step response. The step response can be measured, for example, by means of a stepwise change in the concentration of a dissolved salt (such as sodium chloride) in the feed to the tubular reactor and a time-resolved measurement (for example by means of a conductivity probe) of the subsequent change in the concentration of the dissolved salt at the reactor outlet.

[0042] In addition, the tubular reactor can also comprise internal components, such as static mixing elements. One or more baffles can be installed in the tubular reactor, for example axial to the flow direction of the reactor contents. The tubular reactor preferably contains two, more preferably three and most preferably four baffles per chamber. This can also contribute to more efficient achievement of the objects according to the application.

[0043] In addition, the tubular reactor is usually equipped with one or more metering lines, which are optionally connected to an upstream mixing unit. Through the metering lines, the reactants or other starting materials can usually be introduced into the tubular reactor, preferably continuously. The reactants or other starting materials can usually be mixed in the mixing unit. The one or more metering lines can be installed on one or more chambers. By metered addition at different points in the tubular reactor, it is possible to influence the particle size distribution of the copolymer as well as the fouling of the tubular reactor and the space-time yield.

[0044] For example, the tubular reactor can be equipped with 1 to 100, preferably 2 to 75, more preferably 3 to 50 and most preferably 5 to 30 metering lines.

[0045] The temperature of the tube reactor can generally be adjusted with conventional cooling and / or heating devices, such as, for example, with a jacketed cooler or jacketed heater. The cooling and / or heating devices can be installed, for example, on the tube reactor, on the wall, or on installed cooling coils. For example, the reactor outer wall can carry a cooling or heating jacket (jacket tube) with an intermediate space carrying a flow of a conditioning fluid. For example, tubular coils can be installed in the reactor volume, with a conditioning fluid flowing through these coils. The use of a tube reactor with tube coils is preferred.

[0046] The conditioning can be divided into a plurality of zones, in which the conditioning fluid is used at different inlet temperatures and / or mass flows. Thus, a targeted influence on the temperature profile during the reaction can be made. In this way, it is also possible to influence the particle size distribution of the copolymer and the fouling and the space-time yield of the tubular reactor.

[0047] The tube reactor can contain a closed cleaning stirrer, a scraper and / or a wiper blade. The tube reactor preferably does not contain any closed cleaning stirrer, any scraper and / or any wiper blade. These types of auxiliary components can be used to remove accumulated deposits, but are advantageously not required according to the application.

[0048] For example, the tube reactor, the baffles, the guide plates, the stirrers, the stirring assemblies or other components of the tube reactor can be constructed from conventional materials, such as stainless steel.

[0049] A preferred configuration of a tube reactor for carrying out the method according to the application is illustrated diagrammatically in Figure 1 with reference to a tube reactor (1). Figure 1 The embodiments in

[0050] The tube reactor (1) in which the emulsion polymerization takes place consists of a steel tube, preferably a double-jacketed tube (2), which has an axially arranged stirrer shaft (3) inside, which is equipped with a plurality of stirrers (4). The tube reactor (1) is divided into 10 chambers by nine partitions (10). The tube reactor (1) is equipped with a metering line (5) which is connected to an upstream mixing unit (6) for mixing the reactants. The tube reactor (1) is connected by a discharge line (7) to a downstream vessel (8) in which the polymerization product is collected and optionally post-processed.

[0051] The starting materials can be introduced into the tube reactor (1) preferably continuously via the metering line (5). The polymerization product can be removed from the tube reactor (1) preferably continuously via the discharge line (7). Further substances, preferably initiators, can be supplied to the tube reactor along the tube reactor via one or more further metering devices (9a) to (9e).

[0052] Figure 3 Two preferred embodiments A) and B) are illustratively shown. In these embodiments, a partition (10) separates two chambers (11a) and (11b). Through liquid permeable openings (13) in the partition (10), reactor contents (12) can flow from chamber (11a) into chamber (11b) or vice versa from chamber (11b) into chamber (11a). A guide plate (14) is mounted around the entire edge of the liquid permeable opening (13). The liquid permeable opening (13) equipped with the guide plate (14) can be positioned at any desired point on the partition (10). The stirrer shaft (3) preferably runs through the liquid permeable opening (13) equipped with the guide plate (14), as shown in embodiment B) of Figure 3 . Alternatively, the stirrer shaft (3) does not run through the liquid permeable opening (13) equipped with the guide plate (14), as shown in embodiment A) of Figure 3 .

[0053] The polymerization is carried out in the aqueous medium by emulsion polymerization process - preferably without using organic solvents. The polymerization temperature of the polymerization mixture in the tube reactor is preferably 40 to 140°C and more preferably 50 to 120°C. The pressure in the tube reactor depends on whether the monomers to be polymerized are in liquid form or in gaseous form at the prevailing polymerization temperature and is preferably 1 to 110 bar 绝压 . The polymerization takes place under pressure in the case of copolymerization of gaseous comonomers such as ethylene, 1,3-butadiene or vinyl chloride and more preferably 10 to 80 bar 绝压 .

[0054] One or more components of the reaction mixture or polymerization mixture (starting materials) can be pre-blended in a mixing unit to form a preliminary emulsion and continuously supplied into the tube reactor. The components of the reaction mixture are preferably continuously blended in the mixing unit to form a preliminary emulsion which is fed into the tube reactor. In the case of thermal initiation, the procedure is preferably such that no oxidation catalyst is added to the preliminary emulsion. In the case of initiation using a redox initiator combination, the procedure is preferably such that the reducing initiator is added to the preliminary emulsion and the oxidizing initiator is added to the tube reactor, preferably separately from the preliminary emulsion. When the mixing unit is completely filled, the feed is by pump or by pure mass flow. The mixing unit can comprise, for example, a stirred tank or a static mixing section. The mixing unit can be jacketed for optional cooling or heating during mixing.

[0055] A preferred mixture (pre-emulsion) comprises one or more ethylenically unsaturated monomers, one or more protective colloids and / or one or more emulsifiers and optionally one or more initiators, especially reducing initiators, more particularly not oxidative initiators. The total amount of ethylenically unsaturated monomers, protective colloids and / or emulsifiers is preferably introduced into the pre-emulsion. The pre-emulsion can be introduced into the tube reactor via one or more metering lines. The pre-emulsion is preferably introduced at the end of the tube reactor (opposite to the point of withdrawal). Preferably, one or more initiators, especially oxidative initiators, are added via one or more further metering lines, preferably into at least two chambers, more preferably into at least three chambers and most preferably into at least four chambers. Oxidative initiators are also preferably metered into the chamber(s) into which the pre-emulsion is introduced, the initiator(s) being metered in, especially via separate metering lines. These measures are also useful for better achieving the objects according to the present application.

[0056] The starting materials can be adjusted prior to introduction into the tube reactor. For example, one or more starting materials can be adjusted to a temperature just below the polymerization temperature or to the polymerization temperature, preferably between 10°C and the polymerization temperature, at the time of introduction into the tube reactor. The above-mentioned mixture is preferably adjusted to a temperature between the polymerization temperature and 20°C below the polymerization temperature, more particularly 10°C below the polymerization temperature.

[0057] Prior to the start of the polymerization, the tube reactor is preferably charged with a polymer dispersion, which preferably corresponds to the final product of the polymerization, in terms of the polymer composition, the nature and amount of the protective colloid and the particle size and the solid content. Alternatively, the tube reactor can be charged with a mixture comprising the starting materials but not the initiators, more particularly not the oxidative initiators, prior to the start of the process according to the application, meaning prior to the start of the polymerization. Finally, the tube reactor can be charged with water, preferably exclusively with water, prior to the start of the process according to the application.

[0058] The tube reactor is usually operated continuously. In continuous operation, the starting materials, especially the ethylenically unsaturated monomers, the protective colloids and / or the emulsifiers and / or the initiators, are introduced into the tube reactor and the polymerization product is withdrawn from the tube reactor during the emulsion polymerization. In continuous operation, the mass flow that enters corresponds to the mass flow that emerges.

[0059] The polymerization is generally carried out to at least 80 wt% conversion of the monomer liquid, preferably to 85 to 99 wt% conversion, under polymerization conditions. For example, the polymerization product can subsequently be transferred into a collection vessel (pressure reduction vessel). The transport is generally effected by a pump or on the basis of the pressure difference between the tubular reactor and the collection vessel. In the collection vessel, a post-polymerization can optionally be carried out using known methods, for example by means of a post-polymerization initiated with a redox catalyst. Subsequently, the volatile residual monomer fraction is optionally removed by means of an inert carrier gas (for example air, nitrogen or preferably steam) over or through the aqueous polymerization mixture in a manner known to the skilled person (stripping). After its work-up, the polymerization product is removed from the collection vessel and stored, for example, in a silo. Alternatively, the pressure reduction step, any post-polymerization or stripping can also be carried out continuously.

[0060] The ethylenically unsaturated monomers are preferably selected from the group comprising vinyl esters, (meth)acrylates, vinylaromatics, olefins, 1,3-dienes and vinyl halides, and optionally further monomers copolymerizable therewith.

[0061] Suitable vinyl esters are those of carboxylic acids having 1 to 18 carbon atoms. Preference is given to vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, vinyl 1-methyl-ethanoate, vinyl pivalate and vinyl esters of alpha-branched monocarboxylic acids having 9 to 11 carbon atoms, for example or (Hexion's trade name). Particular preference is given to vinyl acetate.

[0062] Suitable monomers from the group of acrylates or methacrylates, for example, are esters of unbranched or branched alcohols having 1 to 15 carbon atoms. Preferred methacrylates or acrylates are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethylhexyl acrylate. Particular preference is given to methyl acrylate, methyl methacrylate, n-butyl acrylate, tert-butyl acrylate and 2-ethylhexyl acrylate.

[0063] Preferred vinylaromatic compounds are styrene, methylstyrene and vinyltoluene. Preferred vinyl halides are vinyl chloride. Preferred olefins are ethylene, propylene and preferred dienes are 1,3-butadiene and isoprene.

[0064] Optionally 0 to 10 wt% of a co-monomer can be co-polymerized, based on the total weight of the monomer mixture. Preferably 0.1 wt% to 5 wt% of a co-monomer is used. Examples of co-monomers are ethylenically unsaturated mono- and di-carboxylic acids, preferably acrylic acid, methacrylic acid, fumaric acid and maleic acid; ethylenically unsaturated carboxamides and nitriles, preferably acrylamide and acrylonitrile; mono- and di-esters of fumaric acid and maleic acid, such as diethyl and diisopropyl ester and maleic anhydride; ethylenically unsaturated sulfonic acids and salts thereof, preferably vinyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid. Further examples are pre-crosslinking co-monomers, such as poly-ethylenically unsaturated co-monomers, examples are diallyl phthalate, diethylenyl adipate, diallyl maleate, allyl methacrylate and triallyl cyanurate; or post-crosslinking co-monomers, examples are acrylamidoglycolic acid (AGA), methyl acrylamidoglycolate (MAGME), N-methylol acrylamide (NMA), N-methylol methacrylamide, N-methylol allyl carbamate, alkyl ethers such as isobutoxy ether or esters of N-methylol acrylamide, N-methylol methacrylamide and N-methylol allyl carbamate. Also suitable are epoxy-functionalized co-monomers, such as glycidyl methacrylate and glycidyl acrylate. Further examples are silicon-functionalized co-monomers, such as acryloyloxypropyl tri(alkoxy)-silane and methacryloyloxypropyl tri(alkoxy)-silane, vinyl trialkoxy silane and vinyl methyl dialkoxy silane, wherein examples of the alkoxyl groups present can be ethoxyl and ethoxypropylene glycol ether groups. Also to be mentioned are monomers with hydroxyl or CO groups, examples are methacrylate and hydroxyalkyl acrylate, such as hydroxyethyl acrylate, hydroxypropyl acrylate or hydroxybutyl acrylate, or hydroxyethyl methacrylate, hydroxypropyl methacrylate or hydroxybutyl methacrylate, and also compounds such as diacetone acrylamide and acetyl acetoxyethyl acrylate.

[0065] Preferred are one or more monomers selected from the group comprising vinyl esters; vinyl ester mixtures containing one or more monomers from the group comprising vinyl esters, olefins, vinyl aromatics, vinyl halides, acrylic esters, methacrylic esters, mono- or diesters of fumaric acid and / or maleic acid; (meth)acrylic esters; (meth)acrylic ester mixtures containing one or more monomers from the group comprising methacrylic esters, acrylic esters, olefins, vinyl aromatics, vinyl halides, mono- or diesters of fumaric acid and / or maleic acid; monomers or monomer mixtures of dienes, such as butadiene or isoprene, and monomers or monomer mixtures of olefins, such as ethylene or propylene, for example, where the dienes can be copolymerized with styrene, (meth)acrylic esters or esters of fumaric acid or maleic acid; monomers or monomer mixtures of vinyl aromatics, such as styrene, methylstyrene, vinyltoluene; monomers or monomer mixtures of vinyl halogens, such as vinyl chloride, where the monomer mixtures can also comprise auxiliary monomers.

[0066] Particularly preferred are monomer mixtures of vinyl acetate with 1 to 50 wt% of ethylene; monomer mixtures of vinyl acetate with 1 to 50 wt% of ethylene and 1 to 50 wt% of one or more further comonomers from the group comprising vinyl esters having 3 to 12 carbon atoms in the carboxylic acid group, such as vinyl propionate, vinyl laurate, vinyl esters of alpha-branched carboxylic acids having 9 to 11 carbon atoms (such as ); monomer mixtures of one or more vinyl esters, 1 to 50 wt% of ethylene and preferably 1 to 60 wt% of (meth)acrylic esters of unbranched or branched alcohols having 1 to 15 carbon atoms, more particularly n-butyl acrylate or 2-ethylhexyl acrylate; monomer mixtures having 30 to 75 wt% of vinyl acetate, 1 to 30 wt% of vinyl laurate or vinyl esters of alpha-branched carboxylic acids having 9 to 11 carbon atoms and 1 to 30 wt% of (meth)acrylic esters of unbranched or branched alcohols having 1 to 15 carbon atoms, more particularly n-butyl acrylate or 2-ethylhexyl acrylate, which monomer mixtures also contain 1 to 40 wt% of ethylene; monomer mixtures having one or more vinyl esters, 1 to 50 wt% of ethylene and 1 to 60 wt% of vinyl chloride; the monomer mixtures mentioned can each additionally contain the stated amounts of the auxiliary monomers and the data in wt% in each case add up to 100 wt%.

[0067] Also particularly preferred are (meth)acrylate monomer mixtures, such as monomer mixtures of n-butyl acrylate or 2-ethylhexyl acrylate, or copolymers of methyl methacrylate with n-butyl acrylate and / or 2-ethylhexyl acrylate; styrene-acrylate monomer mixtures with one or more monomers from the group of methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate; vinyl acetate-acrylate monomer mixtures with one or more monomers from the group of methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate and optionally ethylene; styrene-1,3-butadiene monomer mixtures; the monomer mixtures can also contain specified amounts of auxiliary monomers and in each case the data in wt% add up to 100 wt%.

[0068] Examples of particularly preferred comonomers for vinyl chloride monomer mixtures are alpha-olefins, such as ethylene and propylene, vinyl esters, such as vinyl acetate, acrylic and methacrylic esters of alcohols having 1 to 15 carbon atoms, such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, t-butyl acrylate, n-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl acrylate, mono- or diesters of fumaric acid and maleic acid, such as dimethyl and diethyl maleate and fumarate.

[0069] Most preferred are monomer mixtures with vinyl acetate and 5 to 50 wt% of ethylene; monomer mixtures with vinyl acetate and 1 to 50 wt% of ethylene and 1 to 50 wt% of a vinyl ester of an alpha-branched monocarboxylic acid having 9 to 1 1 carbon atoms; monomer mixtures with 30 to 75 wt% of vinyl acetate, 1 to 30 wt% of a vinyl ester of lauric acid or of an alpha-branched carboxylic acid having 9 to 1 1 carbon atoms, and 1 to 30 wt% of a (meth)acrylate of an unbranched or branched alcohol having 1 to 15 carbon atoms, which monomer mixtures can optionally also contain 1 to 40 wt% of ethylene; monomer mixtures with vinyl acetate, 5 to 50 wt% of ethylene and 1 to 60 wt% of vinyl chloride; and monomer mixtures containing 60 to 98 wt% of vinyl chloride and 1 to 40 wt% of ethylene, where in each case the monomer mixtures can additionally contain specified amounts of auxiliary monomers and in each case the data in wt% add up to 100 wt%.

[0070] The selection of monomers and the selection of the weight fraction of the comonomers are made such that the glass transition temperature Tg of the polymer obtained is generally in the range from -50°C to +50°C, preferably in the range from -20°C to +30°C. The glass transition temperature Tg of the polymer can be determined in a known manner by differential scanning calorimetry (DSC). The Tg can also be calculated in advance using the Fox equation. According to Fox T.G., Bull. Am. Physics Soc. 1, 3, page 123 (1956): 1 / Tg = xi / Tgi + x2 / Tg2 +... + xn / Tgn, wherein xn denotes the mass fraction (wt% / 100) of monomer n, and Tgn is the glass transition temperature of the homopolymer of monomer n in Kelvin. The Tg values of the homopolymers are listed in the Polymer Handbook, 2nd Edition, John Wiley & Sons, New York (1975).

[0071] The polymerization is initiated with the initiators customary for emulsion polymerization, in particular with a combination of an oxidation initiator and a reduction initiator. Examples of suitable oxidation initiators are sodium, potassium and ammonium salts of peroxodisulfuric acid; hydrogen peroxide and azobisisobutyronitrile. Preferred are sodium, potassium and ammonium salts of peroxodisulfuric acid and hydrogen peroxide. The initiators are generally used in an amount of 0.01 to 2.0 wt%, based on the total weight of the monomers.

[0072] Suitable reducing agents (reduction initiators) are alkali metal sulfites and bisulfites and ammonium sulfites and bisulfites, examples being sodium sulfite; derivatives of sulfoxylate, such as zinc or alkali metal formaldehyde-sulfoxylate, examples being sodium hydroxymethanesulfinic acid (Bruggolite) and ascorbic acid, erythorbic acid or salts thereof; or formaldehyde-free reducing agents, such as the disodium salt of 2-hydroxy-2-sulfinatoacetic acid (Bruggolite FF6). The amount of reducing agent is preferably 0.015 to 3 wt%, based on the total weight of the monomers.

[0073] Regulating substances can be used during the polymerization to control the molecular weight. If such a regulator is used, their amount is generally 0.01 to 5.0 wt%, based on the monomers to be polymerized. Examples of such substances are n-dodecyl mercaptan, t-dodecyl mercaptan, mercaptopropionic acid, ethyl mercaptopropionate, isopropyl alcohol and ethyl acetal. Preferably no regulating substances are used.

[0074] The polymerization preferably takes place in the presence of a protective colloid. Suitable protective colloids are partially hydrolyzed polyvinyl alcohol; polyvinylpyrrolidone; polyvinyl alcohols; water-soluble forms of polysaccharides (such as starch (amylose and amylopectin), cellulose and their carboxymethyl, methyl, hydroxyethyl and hydroxypropyl derivatives); proteins (such as casein or caseinate, soy protein, gelatin, lignin sulfonate); synthetic polymers (such as poly(meth)acrylic acid; copolymers of (meth)acrylic acid esters with carboxy-functional comonomer units; poly(meth)acrylamide; polyvinylsulfonic acid; and water-soluble copolymers thereof); melamine-formaldehyde sulfonates, naphthalene-formaldehyde sulfonates, styrene-maleic acid and vinyl ether-maleic acid copolymers; cationic polymers (such as polydiallyldimethylammonium chloride (poly-DADMAC)).

[0075] A preferred protective colloid is partially or completely hydrolyzed polyvinyl alcohol. Particularly preferred is partially hydrolyzed polyvinyl alcohol having a degree of hydrolysis of from 80 to 95 mol% and a viscosity in 4% aqueous solution of from 1 to 30 mPas (at 20°C, method DIN 53015). A particularly preferred protective colloid is partially hydrolyzed, hydrophobically modified polyvinyl alcohol having a degree of hydrolysis of from 80 to 95 mol% and a viscosity in 4% aqueous solution of from 1 to 30 mPas (at 20°C, method DIN 53015). A particularly preferred protective colloid is partially hydrolyzed, hydrophobically modified polyvinyl alcohol having a degree of hydrolysis of from 80 to 95 mol% and a viscosity in 4% aqueous solution of from 1 to 30 mPas (at 20°C, method DIN 53015). Examples thereof are partially hydrolyzed copolymers of vinyl acetate with hydrophobic comonomers such as isopropenyl acetate, vinyl pivalate, vinyl ethylhexanoate, vinyl esters of saturated alpha-branched monocarboxylic acids having 5 or 9 to 11 carbon atoms, dialkyl maleates and dialkyl fumarates (such as diisopropyl maleate and diisopropyl fumarate), vinyl chloride, vinyl alkyl ethers (such as vinyl butyl ether) and olefins (such as ethylene and decene). The fraction of hydrophobic units is preferably from 0.1 to 10% by weight, based on the total weight of the partially hydrolyzed polyvinyl alcohol. Mixtures of the polyvinyl alcohols mentioned can also be used.

[0076] Most preferred is polyvinyl alcohol having a degree of hydrolysis of from 85 to 94 mol% and a viscosity in 4% aqueous solution of from 3 to 15 mPas (at 20°C, method DIN 53015). Most preferred is polyvinyl alcohol having a degree of hydrolysis of from 85 to 94 mol% and a viscosity in 4% aqueous solution of from 3 to 15 mPas (at 20°C, method DIN 53015). The protective colloids mentioned can be obtained by methods known to the person skilled in the art or are commercially available.

[0077] In the polymerization, the protective colloid is generally added in an amount of from 1 to 20% by weight, based on the total weight of monomers.

[0078] For example, based on the total weight of the comonomers, an emulsifier may optionally be used in the polymerization at 0.1 to 2.0 wt%, examples of which are anionic and / or nonionic emulsifiers. Examples of anionic emulsifiers are alkyl sulfates having a chain length of 8 to 18 carbon atoms, alkyl or alkylaryl ether sulfates having 8 to 18 carbon atoms and up to 40 ethyleneoxy or propyleneoxy units in the hydrophobic group, alkyl or alkylaryl sulfonates having 8 to 18 carbon atoms, and sulfosuccinic acid with monohydric alcohols in total esters and monohydric esters. Examples of nonionic emulsifiers are C-type emulsifiers with an ethoxylation degree of 2 to 20 ethyleneoxy units. 12 -C 14 Fatty alcohol ethoxylates.

[0079] The aqueous dispersion obtained by the method of the present invention has a solid content of 30 to 75 wt%, preferably 50 to 60 wt%.

[0080] The Brookfield viscosity of the aqueous dispersion of vinyl acetate-ethylene copolymer is preferably 50 to 5000 mPas, more preferably 100 to 3500 mPas (measured at 23°C and 20 rpm with a dispersion solids content of 49 to 51 wt% using a Brookfield viscometer).

[0081] The vinyl acetate-ethylene copolymer has an average particle size Dw of preferably 100 nm to 10 μm, more preferably 200 nm to 5 μm, and most preferably 500 nm to 3.5 μm. The vinyl acetate-ethylene copolymer has a polydispersity PD of preferably ≤30, more preferably ≤20, even more preferably ≤10, very preferably ≤5, and most preferably ≤2. The polydispersity PD represents the ratio of weight-average particle size Dw to number-average particle size Dn, PD = Dw / Dn. The parameters Dw and Dn are determined by laser diffraction and laser scattering using an LS13320 instrument (optical model PVAC.RF780D, including PIDS, from Beckman-Coulter), using the physical constants of polyvinyl acetate and observing the instrument manufacturer's scheme.

[0082] Aqueous dispersions can be used to produce water-redispersible polymer powders. For this purpose, the aqueous dispersion is optionally dried by fluidized bed drying, freeze drying, or preferably spray drying after the addition of a protective colloid as an atomizing aid.

[0083] The aqueous polymer dispersions and the water-redispersible polymer powders can be used in their typical fields of use. For example, in chemical construction products, optionally in combination with a hydraulically setting binder such as cement, gypsum and water glass, for the production of construction adhesives, more particularly tile adhesives and external insulation and finishing system adhesives, plastering, filling compounds, floor filling compounds, levelling compounds, mortars, jointing mortars and coatings. Furthermore, as binders for coating and adhesive materials or as coating materials or binders for textiles and paper.

[0084] Surprisingly, the process of the present application can also be used during the time profile of a continuous emulsion polymerization to obtain vinyl acetate-ethylene copolymers with a consistent profile of properties such as particle size distribution, morphology or viscosity. Thus, in the present application a dispersion prepared by continuous polymerization can be used instead of a polymer dispersion conventionally produced in a batch reactor, semi-batch reactor or continuous stirred tank cascade. The space-time performance (process efficiency) can be improved in the present application compared to batch, semi-batch or stirred tank cascade processes. With respect to stirred tank cascades, the quality of the copolymer such as particle size distribution, morphology or viscosity can also be improved. Furthermore, the consumption of initiator can be reduced with respect to stirred tank cascades.

[0085] By the process of the present application, the formation of deposits (fouling) is surprisingly reduced compared to conventional tubular reactors, leading to a reduction of the downtime of the tubular reactor for removal of deposits, also having a positive effect on the space-time performance (process efficiency) and thus enabling a higher level of plant availability. According to the present application, also a tight residence time of the reactor contents in the tubular reactor can be advantageously achieved.

[0086] The following examples serve to further illustrate the present application:

[0087] General experimental description:

[0088] The polymerization was carried out in a tubular reactor (1) having a length of 1600 mm and an inner diameter of 100 mm. The reactor volume was 12.5 liters. The reaction mixture was mixed transversely to the longitudinal axis by a stirrer (3) with a plurality of stirrer blades (4) having a size of 50 mm x 50 mm; the stirrer blades were at a distance of 25 mm from the reactor wall and thus avoided contact with the reactor wall. Along the reactor axis, there were a further 5 other addition devices (9a) to (9e) for the initiator.

[0089] The composition for polymerization was continuously fed from an upstream pressure vessel (6) having a volume of 16 liters to the tube reactor (1). The upstream pressure vessel (6) was continuously charged with the respective compounds by means of a pump.

[0090] After exiting from the tube reactor (1), the product was transferred by means of a pressure maintenance valve (7a) to an unpressurized vessel (8) having a volume of 1000 liters in which the product was collected. At the end of the experiment, the product mixture was worked up and discharged.

[0091] Composition for polymerization:

[0092] The following compounds were continuously supplied to the upstream pressure vessel (stirred tank) (6) and premixed:

[0093] 4.4 kg / h of water, 4.0 kg / h of a 20 wt% aqueous solution of partially hydrolyzed polyvinyl alcohol (having a degree of hydrolysis of 88 mol% and a viscosity (determined in accordance with DIN 53015 in a 4 wt% aqueous solution at 20°C) of 4 mPas, 10.4 kg / h of vinyl acetate, 1.15 kg / h of ethylene, 195 g / h of a 5 wt% aqueous ascorbic acid solution, 1.5 g / h of formic acid and 4 g / h of a 1 wt% aqueous iron ammonium sulfate solution.

[0094] The composition for polymerization was transferred into the tube reactor (1) at a rate of 20 kg / h.

[0095] The potassium persulfate as initiator was metered at the metering points (9a) to (9e) (in the form of a 3 wt% aqueous solution).

[0096] The final product exited the tube reactor (1) at a conversion of 92% and was collected in the unpressurized vessel (8) under reduced pressure.

[0097] Thereafter, in order to remove excess ethylene, the dispersion was transferred to a further unpressurized vessel, in which a pressure of 0.7 bar was applied and a post-polymerization was carried out based on 100 kg of dispersion by adding 0.4 kg of a 10 wt% aqueous tert-butyl hydroperoxide solution and 0.8 kg of a 5 wt% aqueous ascorbic acid solution until the value of the residual vinyl acetate was < 1000 ppm. The pH was adjusted to 4.5 by adding a sodium hydroxide solution (10 wt% aqueous solution). Finally, the batch was dispensed from the unpressurized vessel through a 250 pm sieve.

[0098] In the experiment, the mixture for polymerization was introduced at the bottom end of the tube reactor (1) and the product was taken off at the top end.

[0099] The metering rate of the initiator was

[0100] ​(9a) 0.11 kg / h

[0101] (9b) 0.11 kg / h

[0102] (9c) 0.21 kg / h

[0103] (9d) 0.30 kg / h

[0104] (9e) 0.40 kg / h

[0105] The transfer rate was about 20 1 / h. The stirrer speed was 800 rpm. The pressure in the reactor (1) was built up to 55 bar by means of the delivery valve (7a).

[0106] Example 1, comparison:

[0107] The emulsion polymerization was carried out in a plant according to Figure 2 The tubular reactor (1) did not have partitions and was operated with eight stirrer blades (4) in four planes.

[0108] After 30 h, the polymerization was ended and the free volume of the tubular reactor (1) was determined by making up the water and weighing the amount of water. In this way, the reactor volume was determined to be 8.75 1. Thus, after 30 h, the reactor had lost 3.75 1 in volume, which corresponds to the extent that the corresponding wall deposits had accumulated to 30% of the reactor volume.

[0109] During the experiment, samples were taken every hour. In this case, the particle size distribution proved to be highly unstable; unimodal and bimodal distributions were observed, and the Beckmann Coulter Dw values fluctuated between 1000 and 6000 nm. Fluctuations in the solids content and conversion were also observed; the conversion was always < 90%.

[0110] Overall, it was not possible to achieve stable operating conditions or sufficient product quality. Due to the increasingly uneven temperature distribution in the reactor, fouling had already been very severe regionally, and the experiment was interrupted after 30 h.

[0111] Example 2:

[0112] The emulsion polymerization was carried out in a plant according to The tubular reactor (1) was divided into 10 chambers with a height of 160 mm by means of 9 partitions (10). The stirring assembly (3) was implemented using 10 double-blade stirrers (4) with dimensions of 50 x 50 mm, so that the stirrers (4) were centrally positioned in each chamber. The reactor jacket, including the metering points, remained unchanged. The stirrer speed was continuously 800 rpm.

[0113] Figure 1

[0114] The tubular reactor (1) was divided into 10 chambers with a height of 160 mm by means of 9 partitions (10). The stirring assembly (3) was implemented using 10 double-blade stirrers (4) with dimensions of 50 x 50 mm, so that the stirrers (4) were centrally positioned in each chamber. The reactor jacket, including the metering points, remained unchanged. The stirrer speed was continuously 800 rpm. ​

[0115] After 30 h, the polymerization was finished and the free volume of the pipe reactor (1) was determined by water make-up and weighing of the water amount. In this way, the reactor volume was determined to be 11.3 liters, meaning that after 30 h, the pipe reactor (1) lost 1.2 liters volume, corresponding to a wall deposit accumulation of <10% of the vessel volume.

[0116] During the experiment, samples were taken every hour. After a short start-up time, the product quality proved to be very constant. The obtained particle size distribution was monomodal and stable throughout the experiment. The residual monomer content after the pipe reactor (1) was 5%. The end product was obtained with the following properties:

[0117]

[0118] Example 3:

[0119] The emulsion polymerization was performed in the same equipment and according to the same method as in example 2, with the difference that a baffle (14) was installed on both sides of the liquid permeable opening (13) in the partition (10), as shown in Figure 3 The length L of the baffle in the main flow direction was 1.5 times the free diameter of the liquid permeable opening (13) in the partition.

[0120] After 30 h, the polymerization was finished and the free volume of the pipe reactor (1) was determined by water make-up and weighing of the water amount. In this way, the reactor volume was determined to be 11.5 liters, meaning that after 30 h, the pipe reactor (1) lost 1.0 liters volume, corresponding to a wall deposit accumulation of <10% of the vessel volume.

[0121] During the experiment, samples were taken every hour. After a short start-up time, the product quality proved to be very constant. The obtained particle size distribution was monomodal and stable throughout the experiment. The average particle size corresponds to the average particle size of the batch product. The residual monomer content after the pipe reactor (1) was <5%. The end product was obtained with the following properties:

[0122]

Claims

1. A process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion, which process is carried out by free-radically initiated emulsion polymerization in a continuously operated tubular reactor, characterized in that, One or more partitions with liquid-permeable openings are installed in the tubular reactor transverse to the flow direction of the reactor contents.

2. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 1, characterized in that, The tubular reactor comprises 3 to 30 partitions.

3. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 1 or 2, characterized in that, There is no liquid-permeable gap between the partitions and the inner wall of the tubular reactor.

4. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 1 or 2, characterized in that, Adjacent partitions are connected to each other by one or more rods.

5. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 4, characterized in that, The construct consisting of adjacent partitions and one or more rods is fixed to the floor of the reactor and / or to the lid of the reactor.

6. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 1 or 2, characterized in that, The reactor contents pass through the partitions exclusively through the one or more liquid-permeable openings.

7. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 1 or 2, characterized in that, One or more partitions each have only one liquid-permeable opening.

8. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 1 or 2, characterized in that, One or more guide plates are installed at the edge of the one or more liquid-permeable openings in one or more partitions.

9. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 8, characterized in that, The guide plates project only into one or both of the chambers separated by the partitions.

10. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 8, characterized in that, The guide plates are installed on the side of the partitions that is downstream in the flow direction of the reactor contents.

11. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 9, characterized in that, The guide plates project into both chambers separated by the partitions with a length L, and the ratio of the length L of the guide plates to the free diameter of the liquid-permeable openings is ≥ 0.25 and ≤ 10.

12. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 1 or 2, characterized in that, The tubular reactor comprises a stirring assembly, which comprises a stirrer shaft, one or more stirrer blades are installed on the stirrer shaft, and The stirrer shaft runs through the liquid-permeable openings in one or more partitions.

13. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 12, characterized in that, The stirrer shaft does not completely fill the liquid-permeable openings in one or more partitions.

14. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 12, characterized in that, The stirrer shaft extends from one longitudinal end of the tubular reactor to the other longitudinal end.

15. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 1 or 2, characterized in that, One or more baffle plates are installed in the tubular reactor axially to the flow direction of the reactor contents.

16. Process for the preparation of a vinyl acetate-ethylene copolymer in the form of an aqueous dispersion according to claim 1 or 2, characterized in that, The flow direction of the reactor contents is not reversed in the tubular reactor.

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