DEVICE AND METHOD FOR SEPARATING LIQUID DROPS FROM A GAS FLOW BY MEANS OF A CENTRIFUGAL DROP SEPARATOR

Description

[0001] The invention relates to a centrifugal droplet separator for separating liquid droplets from a gas stream, comprising a circular shell with a vertical longitudinal axis, an upper hood bounding the shell upwards with a gas outlet nozzle for the gas stream cleaned in the centrifugal droplet separator, a drip tray arranged below the gas outlet nozzle, a lower hood bounding the shell downwards with a liquid outlet nozzle for discharging the separated liquid droplets, and an inlet opening tangentially into the shell for supplying the gas stream.

[0002] Furthermore, the invention also relates to a method for separating liquid droplets from a gas stream in such a centrifugal droplet separator.

[0003] In processes for the production of acrylates, which are formed by the acid-catalytic esterification of (meth)acrylic acid with C4 to C10 alcohols, high-boiling process stabilizers, such as phenothiazine (PTZ), or liquid solutions or liquid mixtures containing process stabilizers, are typically used. These process stabilizers must be separated from the acrylate vapor produced during the process to ensure product quality. Depending on the alcohol used, these acrylate processes can also produce, among others, n-butyl acrylate (nBA), 2-ethylhexyl acrylate (2-EHA), isobutyl acrylate, 2-propylheptyl acrylate, or octyl acrylate.

[0004] In such processes, a droplet separator, such as a lamellar separator or demister, also known as a wire mesh separator, is typically used. However, these droplet separators suffer from fouling or polymer formation caused by liquid droplets contained in the gas stream.

[0005] Over time, the liquid droplets that form clog the pores of the lamellae or wire mesh. In this case, the system must be shut down to allow for cleaning or replacement. Problems of this kind are described, for example, in document DE 19604253 A1 (BASF AG), which discloses a 2-ethylhexyl acrylate (2-EHA) manufacturing process using a demister. As another example, document DE 10063510 A1 (BASF AG) discloses a process for the production of n-butyl acrylate (nBA), which also uses a demister to separate the liquid droplets.

[0006] The components contained in the liquid droplets are determined by the specific process. For example, the liquid droplets contain high-boiling components, which originate from the reactor, or the actual product of interest, such as nBA or 2-EHA.

[0007] As an alternative to a separate droplet separator, a rising film evaporator (Ralf Goedecke, "Fundamentals, Methodology, Technology, Practice", Fluid Process Engineering, WILEY-VCH Verlag, Weinheim, 2006) is also known, in which a droplet separator is integrated in the upper part of the rising film evaporator.

[0008] A centrifugal droplet separator does not require a porous structure, such as a demister. Therefore, a centrifugal droplet separator is less susceptible to blockages caused by polymers and impurities compared to the wire mesh described above. Consequently, a longer system lifespan, reduced maintenance costs, and increased production rates can be expected.

[0009] General separators that utilize centrifugal forces to separate solid or liquid particles are also disclosed in the prior art. Document EP 2 076 335 B1 (Vortex Ecological Technologies Ltd) describes how impurities can be removed from flue gases. Another separator is disclosed, for example, in document DE 2137128 A1 (Siemens AG), which removes solid or liquid particles from raw gas.

[0010] However, these types of separators either do not separate liquid droplets or serve only the purpose of processing raw gas. Furthermore, these separators are not used for chemical processes that produce polymers as the target product.

[0011] In general, a centrifugal droplet separator provides a comparable separation efficiency to a wire mesh screen. The majority of small droplets are separated from the steam within the separator.

[0012] The disadvantage of centrifugal droplet separators is that their use in chemical processes can often lead to polymer formation on the separator walls. This frequently necessitates cleaning. A spray system is typically used for this purpose. The walls are moistened with a liquid to ensure the centrifugal droplet separator functions properly for a certain period.

[0013] Disclosure EP 2512683 B1 (BASF SE) describes the injection of a rinsing liquid into a centrifugal droplet separator, where the injection is described as tangential and circumferential to the wall of a gas outlet nozzle.

[0014] The disadvantage of this method is that, in many applications or under certain operating conditions, the formation of polymers on the walls of the centrifugal droplet separator or on the walls of internal components cannot be prevented by flushing. The deposits resulting from polymer formation impair the functionality of the centrifugal droplet separator.

[0015] As a result, such centrifugal droplet separators must be regularly maintained and cleaned in the corresponding processes.

[0016] The task was to develop a centrifugal droplet separator for chemical processes that would prevent polymer formation of liquid droplets on its wall surfaces and on the wall surfaces of its internal components during operation, or at least significantly reduce polymer formation during operation, thus reducing maintenance intervals. The small liquid droplets should also be efficiently separated from the gas stream during operation.

[0017] Another task was to provide such a centrifugal droplet separator, which can be used in chemical processes for the production of, in particular, n-butyl acrylate (nBA) or 2-ethylhexyl acrylate (2-EHA) and is particularly well suited for this purpose.

[0018] These problems were solved according to the invention by a centrifugal droplet separator according to claim 1 and by a method for separating liquid droplets from a gas stream according to claim 10. Advantageous embodiments of the centrifugal droplet separator according to the invention are specified in claims 2 to 9. Advantageous embodiments of the method according to the invention are set out in claims 11 to 14.

[0019] The centrifugal droplet separator according to the invention for separating liquid droplets from a gas stream comprises a circular shell with a vertical longitudinal axis, an upper hood bounding the shell upwards with a gas outlet nozzle for the gas stream cleaned in the centrifugal droplet separator, a drip tray arranged below the gas outlet nozzle, a lower hood bounding the shell downwards with a liquid outlet nozzle for discharging the separated liquid droplets, and an inlet opening tangentially into the shell for supplying the gas stream.According to the invention, at least two nozzles are provided for supplying a stabilizer liquid into the interior of the centrifugal droplet separator, the nozzle outlet of each nozzle is located above the tangential inlet and below the drip tray in the centrifugal droplet separator, and the main spray direction for each individual nozzle is directed upwards at an internal angle in the range of 0 to 60° to the vertical longitudinal axis, whereby all walls in the interior of the centrifugal droplet separator can be completely wetted.

[0020] Due to the direction of gravity, the stabilizer fluid, which was sprayed towards the upper hood, flows downwards and thus also wets the other surface areas of the centrifugal droplet separator. Similarly, the surfaces of internal components located in the spray jet of the nozzles are also wetted. Therefore, the arrangement according to the invention effectively prevents polymer formation on the surfaces of the centrifugal droplet separator and its internal components.

[0021] The arrangement of the nozzles below the drip tray according to the invention ensures that all wall surfaces of the casing and internal components of the centrifugal droplet separator are sufficiently wetted with stabilizer fluid. Even in so-called dead zones, also known to those skilled in the art as backflow areas, the wall surfaces, such as in the edge regions of the upper centrifugal droplet separator area, can be wetted. Internal components within the centrifugal droplet separator, such as the drip tray, are also completely and sufficiently wetted on the outside.

[0022] Surprisingly, the gas flow is not significantly disturbed by the injection in the opposite direction of gravity, so that the separation performance of the centrifugal droplet separator is not significantly reduced with this method according to the invention.

[0023] In a preferred embodiment of the centrifugal droplet separator, the length ratio between the axial distance of the nozzle outlet of the uppermost nozzle to the drip tray and the height of the centrifugal droplet separator is in the range of 0.03 to 0.15. Thus, with a typical height of the centrifugal droplet separator in the range of 1 to 10 m, a suitable distance to the drip tray is ensured, allowing the drip tray to be sufficiently wetted with stabilizer fluid using conventional nozzles.

[0024] In a further preferred embodiment of the centrifugal droplet separator, the length ratio between the radial distance of the nozzle outlet from the inner shell surface and the height of the centrifugal droplet separator is no more than 0.06. This ensures that the stabilizer fluid is injected close to the wall, which ensures that the impact of the stabilizer fluid on the shell surface is sufficiently flat, and thus only a small amount of stabilizer fluid is sprayed back from the shell surface.

[0025] In a preferred embodiment of the centrifugal droplet separator, the inner angle of the respective nozzle is in the range of 0 to 50°, particularly preferably in the range of 0 to 40° and most preferably in the range of 0 to 30°.

[0026] In another preferred embodiment of the centrifugal droplet separator, the respective main spray directions of the nozzles are inclined away from the jacket.

[0027] In another preferred embodiment of the centrifugal droplet separator, an open apex cone is mounted on vortex breakers at the liquid outlet nozzle to stabilize the gas flow.

[0028] In a further preferred embodiment of the centrifugal droplet separator, the gas outlet nozzle is located at least partially above the casing on the outer surface of the casing. This prevents or significantly reduces polymer formation at the gas outlet nozzle, as fewer dead zones are present.

[0029] In a preferred embodiment, the lower half of the centrifugal droplet separator has a temperature control device on the outer surface of the jacket. The temperature control device is preferably a heater. By heating the jacket, polymer formation can be further reduced using suitable chemical processes.

[0030] In a preferred embodiment of the centrifugal droplet separator, the nozzles are fixed in the centrifugal droplet separator by at least one plug-in element, wherein each plug-in element has a lance and at least one retaining element for at least one nozzle. The plug-in element allows the nozzles to be inserted into the separator and removed again as needed.

[0031] In a further embodiment of the centrifugal droplet separator, at least one nozzle extends through an opening element in the casing, preferably through a nozzle, wherein the opening element is sealed by an openable retaining element, preferably a flange. Nozzles and flanges are easy to obtain and inexpensive.

[0032] In a further embodiment of the centrifugal droplet separator, at least one sealing element, preferably a rubber ring, is provided, which seals the opening elements. This reliably prevents leakage of the gas flow by means of an elastic element.

[0033] In a further embodiment of the centrifugal droplet separator, the lower and upper hoods are created by mounting a flange at the top and bottom ends of the separator, respectively. This allows the use of standard and readily available components.

[0034] The method according to the invention for separating liquid droplets from a gas stream is carried out in a centrifugal droplet separator which comprises a jacket which is circular in cross-section and has a vertical longitudinal axis, an upper hood which delimits the jacket at the top and has a gas outlet nozzle for the gas stream purified in the centrifugal droplet separator, a drip tray arranged below the gas outlet nozzle, a lower hood which delimits the jacket at the bottom and has a liquid outlet nozzle for removing the separated liquid droplets, and an inlet which opens tangentially into the jacket and through which the gas stream is supplied.According to the invention, a stabilizer liquid is supplied to the interior of the centrifugal droplet separator through at least two nozzles, the nozzle outlet of each nozzle is located above the tangential inlet and below the drip tray in the centrifugal droplet separator, and the main spray direction of each nozzle is directed upwards with an internal angle in the range of 0 to 60° to the vertical longitudinal axis, whereby all walls in the interior of the centrifugal droplet separator are completely wetted with the stabilizer liquid.

[0035] A stabilizer is generally a substance that reduces the polymerization of chemical compounds. In particular, a suitable stabilizer reduces the polymerization of chemical compounds in the 2-EHA or nBA processes.

[0036] In a preferred embodiment of the method, the stabilizer liquid is continuously fed to the centrifugal droplet separator. This ensures approximately constant wetting of the walls.

[0037] In a preferred embodiment of the process according to the invention, the stabilizer liquid contains 4-methoxyphenol (MeHQ). This particularly effectively prevents polymer formation on the walls without negatively affecting the quality of the target product. This is especially true for substances containing acrylates.

[0038] Other preferred stabilizers that may be included in the stabilizer liquid are, for example, 2,4-dimethyl-6-tert-butylphenol (Topanol A), hydroquinone, and / or butylhydroxytoluene (2,6-di-tert-butyl-p-cresol). In principle, any number of stabilizers can be included in the stabilizer liquid in the form of a mixture.

[0039] The stabilizer liquid preferably comprises, in addition to the stabilizer(s), the target product obtained from the process. In this document, the target product is the gas stream exiting the centrifugal droplet separator. No impurities are added to such stabilizer liquids. The target product can also advantageously serve as a solvent and / or diluent for the stabilizer(s).

[0040] In a preferred embodiment of the process, the stabilizer liquid is provided to the nozzles by branching off a partial stream of the target product, collecting it in a batch tank, mixing it there with the stabilizer(s) and then feeding it to the nozzles.

[0041] In a further preferred embodiment of the method, the supplied gas stream contains droplets of substances that, due to their chemical properties, tend to polymerize on the walls of the centrifugal droplet separator. The complete and sufficient wetting of the shell of the centrifugal droplet separator, as well as the internal components within the separator, prevents polymer formation on the walls and thus extends the maintenance intervals of the centrifugal droplet separator.

[0042] In a particularly preferred embodiment, the gas stream supplied to the centrifugal droplet separator contains acrylates produced by acid-catalytic esterification of (meth)acrylic acid with C4 to C10 alcohols, in particular n-butyl acrylate by esterification of acrylic acid with n-butanol or 2-ethylhexyl acrylate by esterification of acrylic acid with 2-ethylhexanol. These processes typically also contain small amounts of undesirable components, such as phenothiazine (PTZ). These undesirable components are mainly contained in the liquid droplets present in the gas stream and are to be separated in the centrifugal droplet separator so that the target product retains its quality. Furthermore, the liquid droplets contain other components, which preferably arise from the target product itself.

[0043] In a preferred embodiment of the method, the centrifugal droplet separator is designed such that the length ratio between the axial distance of the nozzle outlet of the uppermost nozzle to the drip tray and the height of the centrifugal droplet separator is in the range of 0.03 to 0.15.

[0044] In a preferred embodiment of the method, the centrifugal droplet separator is designed such that the length ratio between the radial distance of the nozzle outlet to the inner shell surface and the height of the centrifugal droplet separator is not more than 0.06.

[0045] In a preferred embodiment of the method, the centrifugal droplet separator is designed such that the internal angle of the respective nozzle is in the range from 0 to 50°, preferably in the range from 0 to 40° and particularly preferably in the range from 0 to 30°.

[0046] In a preferred embodiment of the method, the centrifugal droplet separator is designed such that an open apex cone is mounted on vortex breakers at the liquid outlet nozzle to stabilize the gas flow.

[0047] In a preferred embodiment of the method, the centrifugal droplet separator is designed such that the gas outlet nozzle in the centrifugal droplet separator is located at least partially above the jacket on the side of the outer surface of the jacket.

[0048] In a preferred embodiment of the method, the centrifugal droplet separator is designed such that the lower half of the centrifugal droplet separator has a temperature control device, in particular a heater, on the outer side of the jacket.

[0049] In a preferred embodiment of the method, the centrifugal droplet separator is designed such that the nozzles are fixed in the centrifugal droplet separator by at least one plug-in element, wherein the respective plug-in element has a lance and at least one retaining element for at least one nozzle.

[0050] In a preferred embodiment of the method, the centrifugal droplet separator is designed such that at least one nozzle passes through an opening element in the jacket, preferably through a nozzle, wherein the opening element is sealed by an openable retaining element, preferably a flange.

[0051] The invention is explained in more detail below with reference to the drawings. The drawings are to be understood as schematic representations. They do not represent any limitation of the invention, for example with regard to specific dimensions or embodiments.

[0052] They show: Fig. 1 : Example of an embodiment of a centrifugal droplet separator according to the invention in longitudinal and cross-sectional view. Fig. 2 : Main spray direction of the nozzle, which is normal to the nozzle outlet. Fig. 3 : Cutting plane determined for a nozzle. Fig. 4 The angle between the main spray direction of the nozzle and the opposite gravity vector. In this case, the nozzle is tilted away from the mantle surface. Fig. 5 : Interior angle between the main spray direction of the nozzle and the opposite gravity vector. In this case, the nozzle is inclined towards the mantle surface. Fig. 6 : Plug-in element for the respective nozzle. Fig. 7 : State-of-the-art droplet separator with demister. List of reference symbols used:

[0053] 1 Shell 2 Upper hood 3 Inlet 4 Liquid outlet nozzle 5 Open apex cone 6 Vortex breaker 7 Gas outlet nozzle 8 Drip tray 9 Nozzle(s) 10 Lower hood 11 Vertical longitudinal axis 12 Main spray direction or normal vector of the cross-sectional area 13 14 Gravity direction, gravity vector Vertical section plane 15 Nozzle outlet or cross-sectional area of ​​the nozzle through which the liquid flows out of the respective nozzle 16 Interior angle 17 Plug-in element 18 Lance 19 Retaining element 20 Opening elements 23 Demister 25 Opposite gravity direction, opposite gravity vector 26 Height of the centrifugal droplet 27 Diameter of the centrifugal droplet 28 Spray device

[0054] Fig. 1schematically illustrates an example of an embodiment of a centrifugal droplet separator according to the invention. On the left, a longitudinal section of the centrifugal droplet separator along its vertical longitudinal axis is shown. On the right, a cross-section perpendicular to the direction of gravity 13 is shown, showing the arrangement of the nozzles 9 relative to the casing 1.

[0055] The centrifugal droplet separator is defined by its outer shell 1 which is circular in cross-section, its upper hood 2 which borders it upwards and has a gas outlet nozzle 7 for the gas flow cleaned in the centrifugal droplet separator, its drip plate 8 which is arranged below the gas outlet nozzle for collecting smaller liquid droplets, its lower hood 10 which borders the shell 1 downwards and has a liquid outlet nozzle 4 for removing the separated liquid droplets, and by its dimensions such as the height 26 and the diameter 27.

[0056] A gas stream laden with liquid droplets is fed into the centrifugal droplet separator through a tangential inlet 3. This induces a vortex along the shell 1. Due to gravity 13, the liquid droplets move downward toward a liquid outlet 4. For more efficient droplet separation, an open apex cone 5 with a vortex breaker 6 is installed. The purified gas stream flows out of the separator through a gas outlet 7.

[0057] In the illustrated embodiment, the stabilizer liquid is sprayed into the interior of the centrifugal droplet separator via six nozzles 9.

[0058] The nozzle outlet of the respective nozzle 9 is located above the tangential inlet 3 and below the drip tray 8 in the centrifugal droplet separator.

[0059] The main spray direction for each individual nozzle 9 is directed upwards at an internal angle 16 in the range of 0 to 60° to the vertical longitudinal axis, thereby ensuring that all walls inside the centrifugal droplet separator are fully wetted.

[0060] Fig. 2 Figure 1 shows a main spray direction 12 of a nozzle 9, which is defined by a normal vector on a cross-sectional area, the nozzle outlet 15. The liquid is sprayed through the nozzle outlet 15 of the nozzle 9.

[0061] Fig. 3 sketches a section plane 14 for each individual nozzle 9, which defines a vertical longitudinal axis 11 of the mantle 1 and a geometric center of the cross-sectional area (nozzle outlet 15 according to Fig.2 ) of the nozzle 9. The gravity vector 13, the opposite gravity vector 25, and the main spray direction 12, or normal vector, of the nozzle 9 are also shown.

[0062] Fig. 4This shows that an interior angle 16 can be defined in the section plane 14 along the vertical longitudinal axis 11, which lies between the opposite gravity vector 25 and the vector of the main spray direction 12, or the normal vector, of the respective nozzle 9. Here, the two vectors are projected onto the section plane 14. In this case, the main spray direction 12 is inclined away from the surface of the casing 1.

[0063] Fig.5 This represents a case in the section plane 14 along the vertical longitudinal axis 11, in which the main spray direction 12, or the normal vector, is inclined towards the surface of the casing 1. An interior angle 16 is defined between the opposite gravity vector 25 and the vector of the main spray direction 12 of the respective nozzle 9. Here, the two vectors are projected onto the section plane 14.

[0064] Fig. 6Figure 1 schematically shows a plug-in element 17 for a nozzle 9. Here, a nozzle 9 is fixed to a lance 18. The lance 18 extends through an opening element 20 in the casing 1, the opening element 20 being sealed by an openable retaining element 19. In this example, the opening element is a nozzle and the openable retaining element 19 is a flange.

[0065] Fig. 7This represents a prior art droplet separator with a demister. A gas stream laden with liquid droplets is fed into the separator through an inlet 3 on the jacket 1. Due to gravity, the liquid droplets move downwards towards a liquid outlet nozzle 4, which is located on a lower hood 10. The purified gas stream flows out of the separator through a gas outlet nozzle 7, which is located on an upper hood 2. A demister 23 ensures that smaller liquid droplets are collected. A spray device 28 wets the demister to prevent rapid clogging caused by polymerization of the liquid droplets. Examples: Comparison example 1 for nBA system:

[0066] The substance n-butyl acrylate (nBA) can be produced on an industrial scale by acid-catalytic esterification of (meth)acrylic acid with n-butanol. A corresponding process is disclosed, inter alia, in document DE 10063510 A1 (BASF AG). One process step in such processes is the separation of liquid droplets from a gas stream, wherein the liquid droplets contain the component to be separated, phenothiazine (PTZ). In comparative example 1 according to the prior art, the separation of the droplets was carried out in a continuously operated droplet separator with demister 23 according to Fig. 7 .

[0067] The droplet separator had a height of 4 m and a diameter of 1.0 m, whereby neither the gas outlet nozzle 7 nor the liquid outlet 4 were taken into account when determining the height. The height of the demister was 1470 mm. The demister used was the "Euroform DV270" manufactured by Munters Euroform GmbH (Philipsstraße 8, 52068 Aachen).

[0068] The feed rate was 10,000 kg / h of product. The pressure in the droplet separator was set to 420 mbar above normal pressure. The temperature was 118°C.

[0069] The composition of the product fed into the droplet separator via inlet 3 was: n-butanol 0.04 wt.% n-Butyl acetate 0.07 wt.% n-Dibutyl ether 0.10 wt.% Isobutylacrylate 0.07 wt.% n-butyl acrylate 99.68 wt.% Phenothiazin 10 ppm by weight 4-Methoxyphenol 0 ppm Nitrogen 0.04 wt.%

[0070] 400 kg / h of liquid at a temperature of 34°C was sprayed onto the top of the demister 23 via the spraying device 28. The liquid had the following composition: n-butanol 0.04 wt.% n-Butyl acetate 0.07 wt.% n-Dibutyl ether 0.10 wt.% Isobutylacrylate 0.07 wt.% n-butyl acrylate 99.72 wt.% Phenothiazin < 1 ppm by weight 4-Methoxyphenol 15 ppm by weight

[0071] The gas flow of 9657 kg / h exiting gas outlet 7 had the following composition: n-butanol 0.04 wt.% n-Butyl acetate 0.07 wt.% n-Dibutyl ether 0.10 wt.% Isobutylacrylate 0.07 wt.% n-butyl acrylate 99.68 wt.% Phenothiazin 2 wt.-ppm 4-Methoxyphenol 1 wt.-ppm Nitrogen 0.04 wt.%

[0072] The liquid flowing from liquid outlet nozzle 4 at a rate of 743 kg / h had the following composition: n-butanol 0.04 wt.% n-Butyl acetate 0.07 wt.% n-Dibutyl ether 0.10 wt.% Isobutylacrylate 0.07 wt.% n-butyl acrylate 99.71 wt.% Phenothiazin 110 ppm by weight 4-Methoxyphenol 1 wt.-ppm

[0073] After 120 days of operation, the droplet separator had to be cleaned due to contamination. It was discovered that polymers had formed, contaminating demister 23 and the inner wall of the droplet separator, necessitating the shutdown of the entire system. Example 1 for nBA system:

[0074] For Example 1 according to the invention, the droplet separator of Comparative Example 1 was replaced by a centrifugal droplet separator according to the invention Fig. 1 replaced.

[0075] The dimensions of the centrifugal separator were: Diameter 27: 1500 mm Height 26: 3278 mm Height of nozzle plane relative to the lower hood: 2039 mm Gas inlet 3: DN500 Gas outlet 7: DN600 Liquid outlet 4: DN150 Distance between nozzle and drip tray 8: 500 mm Distance between the outer nozzles and the wall of the centrifugal droplet separator: 7.5 mm Apex cone 5: Diameter: 1050 mm, Height: 300 mm Drip tray 8: Diameter: 1000 mm, Height: 300 mm

[0076] Neither the gas outlet nozzle 7 nor the liquid outlet 4 were taken into account when determining the height.

[0077] The centrifugal droplet separator contained six full cone nozzles from the company Lechler, type 490.404.1Y.CA.00.0, according to the data sheet "Lechler_Axial-Vollkegeldüsen_490_491.pdf" ( https: / / www.lechler.com / fileadmin / media / kataloge / pdfs / industrie / katalog / DE / 03 full-cone / lechler full-cone nozzles series 490 491.pdf ) installed. The inner angle of the main spray direction was 15° and was inclined inwards, i.e. away from the mantle 1.

[0078] A stabilizer liquid was continuously added through the upward-facing nozzles. The total volume flow through all nozzles 9 was 200 to 600 l / h.

[0079] In this example, the gas outlet nozzle 7 was located above the shell 1 on the outer surface of the shell 1, whereby the centrifugal droplet eliminator provided fewer dead zones.

[0080] The feed rate of the gas stream loaded with liquid droplets was 10,000 kg / h. The pressure in the centrifugal droplet separator was set to 420 mbar above normal pressure. The temperature was 118°C.

[0081] The composition of the product fed into the centrifugal droplet separator via inlet 3 was: n-butanol 0.04 wt.% n-Butyl acetate 0.07 wt.% n-Dibutyl ether 0.10 wt.% Isobutylacrylate 0.07 wt.% n-butyl acrylate 99.68 wt.% Phenothiazin 10 ppm by weight 4-Methoxyphenol 0 ppm Nitrogen 0.04 wt.%

[0082] A liquid stream of stabilizer fluid totaling 400 kg / h at a temperature of 34°C was sprayed onto the wall of the centrifugal droplet separator via nozzles 9.

[0083] The stabilizer fluid had the following composition: n-butanol 0.04 wt.% n-Butyl acetate 0.07 wt.% n-Dibutyl ether 0.10 wt.% Isobutylacrylate 0.07 wt.% n-butyl acrylate 99.72 wt.% Phenothiazin < 1 ppm by weight 4-Methoxyphenol 15 ppm by weight

[0084] The gas flow of 9657 kg / h exiting gas outlet 7 had the following composition: n-butanol 0.04 wt.% n-Butyl acetate 0.07 wt.% n-Dibutyl ether 0.10 wt.% Isobutylacrylate 0.07 wt.% n-butyl acrylate 99.68 wt.% Phenothiazin < 1 ppm by weight 4-Methoxyphenol 1 wt.-ppm Nitrogen 0.04 wt.%

[0085] The liquid flowing from liquid outlet nozzle 4 at a rate of 743 kg / h had the following composition: n-butanol 0.04 wt.% n-Butyl acetate 0.07 wt.% n-Dibutyl ether 0.10 wt.% Isobutylacrylate 0.07 wt.% n-butyl acrylate 99.71 wt.% Phenothiazin 130 ppm by weight 4-Methoxyphenol 1 wt.-ppm

[0086] In this example, a runtime of more than 180 days was achieved without shutdown due to contamination in the centrifugal droplet separator. Irreversible polymer clogging or deposits in the centrifugal droplet separator were not observed even after 180 days of operation.

[0087] Furthermore, thanks to its efficient separation, the centrifugal droplet separator achieved a reduction of the mass fraction of phenothiazine to less than 1 ppm by weight in the target product. The target product here is the gas stream exiting the centrifugal droplet separator. In the droplet separator with demister according to Comparative Example 1, phenothiazine could only be reduced to 2 ppm by weight. Comparison example 2 for a 2-EHA system:

[0088] The substance 2-ethylhexyl acrylate (2-EHA) can be produced industrially by acid-catalytic esterification of (meth)acrylic acid with 2-ethylhexanol. A corresponding process is disclosed, among others, in document DE 19604253 A1 (BASF AG). One step in such processes is the separation of liquid droplets from a gas stream, wherein the liquid droplets contain the component to be separated, phenothiazine (PTZ).

[0089] In Comparative Example 2 according to the prior art, the droplets were separated in a continuously operated droplet separator with demister 23 according to Fig. 7 .

[0090] The droplet separator was 4 m high and 1.2 m in diameter. The demister 23 was 790 mm high. The demister used was the "Euroform DV270" manufactured by Munters Euroform GmbH (Philipsstraße 8, 52068 Aachen).

[0091] The feed rate was 10,000 kg / h of product. The pressure in the droplet separator was set to 140 mbar above atmospheric pressure and the temperature to 148°C.

[0092] The composition of the product fed into the droplet separator via inlet 3 was: 2-Ethylhexanol 0.08 wt.% n-Ethylhexyl acetate 0.15 wt.% n-Diethylhexyl ether 0.01 wt.% 2-Ethylhexyl acrylate 99.71 wt.% 3-(2-Ethylhexoxy)-propionic acid 2-ethylhexyl ester 0.03 wt.% Phenothiazin 10 ppm by weight 4-Methoxyphenol 0 ppm Nitrogen 0.02 wt.%

[0093] A liquid flow of 490 kg / h at a temperature of 34°C was sprayed onto the top of the demister 23 via the spray device 28. The liquid had the following composition: 2-Ethylhexanol 0.08 wt.% n-Ethylhexyl acetate 0.15 wt.% n-Diethylhexyl ether 0.01 wt.% 2-Ethylhexyl acrylate 99.73 wt.% 3-(2-Ethylhexoxy)-propionic acid 2-ethylhexyl ester 0.03 wt.% Phenothiazin < 1 ppm by weight 4-Methoxyphenol 15 ppm by weight

[0094] The gas flow of 9623 kg / h exiting from the gas outlet nozzle 7 had the following composition: 2-Ethylhexanol 0.08 wt.% n-Ethylhexyl acetate 0.15 wt.% n-Diethylhexyl ether 0.01 wt.% 2-Ethylhexyl acrylate 99.72 wt.% 3-(2-Ethylhexoxy)-propionic acid 2-ethylhexyl ester 0.02 wt.% Phenothiazin 4 ppm by weight 4-Methoxyphenol 1 ppm by weight Nitrogen 0.02 wt.%

[0095] The liquid flowing from the liquid outlet nozzle 4 at 867 kg / h had the following composition: 2-Ethylhexanol 0.03 wt.% n-Ethylhexyl acetate 0.09 wt.% n-Diethylhexyl ether 0.01 wt.% 2-Ethylhexyl acrylate 99.70 wt.% 3-(2-Ethylhexoxy)-propionic acid 2-ethylhexyl ester 0.16 wt.% Phenothiazin 70 ppm by weight 4-Methoxyphenol 10 ppm by weight

[0096] After 80 days of operation, the droplet eliminator required cleaning due to contamination. It was discovered that polymers had formed, contaminating demister 23 and the inner wall of the droplet eliminator, and resulting in the entire system being shut down. Example 2 for a 2-EHA system:

[0097] For Example 2 according to the invention, the droplet separator of Comparative Example 2 was replaced by a centrifugal droplet separator according to the invention Fig. 1 replaced.

[0098] The dimensions of the centrifugal separator were: Diameter 27: 1800 mm Height 26: 3700 mm Height of the nozzle level relative to the lower hood: 2370 mm Gas inlet 3: DN600 Gas outlet 7: DN600 Liquid outlet (4): DN150 Distance between nozzle and drip tray 8: 500 mm Distance between the outer nozzles and the wall of the centrifugal droplet separator: 7.5 mm Apex cone 5: Diameter: 1260 mm, Height: 360 mm Drip tray 8: Diameter: 1200 mm, Height: 400 mm

[0099] Neither the gas outlet nozzle 7 nor the liquid outlet 4 were taken into account when determining the height.

[0100] The centrifugal droplet separator contained six nozzles. The nozzles were manufactured by Lechler. Specifically, the full cone nozzle type 490.404.1Y.CA.00.0 was used, as described in the datasheet "Lechler_Axial-Vollkegeldüsen_490_491.pdf", which can be accessed via the following link: "https: / / www.lechler.com / fileadmin / media / kataloge / pdfs / industrie / katalog / DE / 03_vollkegel / lechler_vollkegelduesen_baureihe_490_491.pdf". The inner angle of the main spray direction was 15° and was inclined inwards, away from the casing 1.

[0101] In this example, the gas outlet nozzle 7 was located above the shell 1 on the outer surface of the shell 1, whereby the centrifugal droplet eliminator provided fewer dead zones.

[0102] The feed rate of the gas stream loaded with liquid droplets was 10,000 kg / h. The pressure in the centrifugal droplet separator was set to 140 mbar above normal pressure. The temperature was 148°C.

[0103] The composition of the product fed into the centrifugal droplet separator via inlet 3 was: 2-Ethylhexanol 0.08 wt.% n-Ethylhexyl acetate 0.15 wt.% n-Diethylhexyl ether 0.01 wt.% 2-Ethylhexyl acrylate 99.71 wt.% 3-(2-Ethylhexoxy)-propionic acid 2-ethylhexyl ester 0.03 wt.% Phenothiazin 10 ppm by weight 4-Methoxyphenol 0 ppm Nitrogen 0.02 wt.%

[0104] A flow rate of 490 kg / h of stabilizer fluid at a temperature of 34°C was sprayed onto the wall of the centrifugal droplet separator via nozzles 9. The stabilizer fluid had the following composition: 2-Ethylhexanol 0.08 wt.% n-Ethylhexyl acetate 0.15 wt.% n-Diethylhexyl ether 0.01 wt.% 2-Ethylhexyl acrylate 99.73 wt.% 3-(2-Ethylhexoxy)-propionic acid 2-ethylhexyl ester 0.03 wt.% Phenothiazin < 1 ppm by weight 4-Methoxyphenol 15 ppm by weight

[0105] The gas flow of 9623 kg / h exiting gas outlet 7 had the following composition: 2-Ethylhexanol 0.08 wt.% n-Ethylhexyl acetate 0.15 wt.% n-Diethylhexyl ether 0.01 wt.% 2-Ethylhexyl acrylate 99.72 wt.% 3-(2-Ethylhexoxy)-propionic acid 2-ethylhexyl ester 0.02 wt.% Phenothiazin < 2 ppm by weight 4-Methoxyphenol 1 wt.-ppm Nitrogen 0.02 wt.%

[0106] The liquid flow of 867 kg / h leaving the liquid outlet nozzle 4 had the following composition: 2-Ethylhexanol 0.03 wt.% n-Ethylhexyl acetate 0.09 wt.% n-Diethylhexyl ether 0.01 wt.% 2-Ethylhexyl acrylate 99.70 wt.% 3-(2-Ethylhexoxy)-propionic acid 2-ethylhexyl ester 0.16 wt.% Phenothiazin 100 ppm by weight 4-Methoxyphenol 10 ppm by weight

[0107] In this example, a runtime of more than 150 days was achieved without shutdown due to contamination in the centrifugal droplet separator. Irreversible polymer clogging or deposits in the centrifugal droplet separator were not observed even after 150 days of operation.

[0108] Furthermore, thanks to its efficient separation, the centrifugal droplet separator achieved a reduction of the mass fraction of phenothiazine to less than 2 ppm by weight in the target product. The target product here is the gas stream exiting the centrifugal droplet separator. In the droplet separator with demister (Comparative Example 2), phenothiazine could only be reduced to 4 ppm by weight.

Claims

1. A centrifugal droplet separator for separating liquid droplets out of a gas stream, comprising a shell (1) having a circular cross section and a vertical longitudinal axis (11), an upper hood (2) that bounds the shell (1) at the top and has a gas exit port (7) for the gas stream cleaned in the centrifugal droplet separator, a drip plate (8) disposed beneath the gas exit port (7), a lower hood (10) that bounds the shell (1) at the bottom and has a liquid exit port (4) for removal of the deposited liquid droplets and an inlet (3) that opens tangentially into the shell (1) for supply of the gas stream, wherein there are at least two nozzles (9) for feeding a stabilizer liquid into the interior of the centrifugal droplet separator, the nozzle outlet (15) of the respective nozzle (9) is above the tangential inlet (3) and below the drip plate (8) in the centrifugal droplet separator, the main spraying direction (12) for each individual nozzle (9) is directed upward at an internal angle (16) in the range from 0 to 60° relative to the vertical longitudinal axis (11) and hence all walls in the interior of the centrifugal droplet separator are fully wettable.

2. The centrifugal droplet separator according to claim 1, wherein the length ratio between the axial distance of the nozzle outlet (15) of the uppermost nozzle from the drip plate (8) and the height (26) of the centrifugal droplet separator is in the range from 0.03 to 0.15.

3. The centrifugal droplet separator according to either of claims 1 and 2, wherein the length ratio between the radial distance of the nozzle outlet (15) from the inner shell surface and the height (26) of the centrifugal droplet separator is not more than 0.06.

4. The centrifugal droplet separator according to any of claims 1 to 3, wherein the internal angle (16) of the respective nozzle (9) is in the range from 0 to 50°, preferably in the range from 0 to 40° and more preferably in the range from 0 to 30°.

5. The centrifugal droplet separator according to any of claims 1 to 4, wherein an open apex cone (5) for stabilization of the gas stream is mounted on baffles (6) in the liquid exit port (4).

6. The centrifugal droplet separator according to any of claims 1 to 5, wherein the gas exit port (7) in the centrifugal droplet separator is at least partly above the shell (1) on the side of the outer face of the shell (1).

7. The centrifugal droplet separator according to any of claims 1 to 6, wherein the lower half of the centrifugal droplet separator has a temperature control unit, especially a heater, on the outside of the shell.

8. The centrifugal droplet separator according to any of claims 1 to 7, wherein the nozzles (9) are fixed in the centrifugal droplet separator by at least one insert element (17), where the respective insert element (17) has a lance (18) and at least one holding element (19) for at least one nozzle (9).

9. The centrifugal droplet separator according to any of claims 1 to 7, wherein at least one nozzle (9) in each case runs through an opening element (20) in the shell (1), preferably through a port, where the opening element is sealed by an openable holding element (19), preferably a flange.

10. A method of separating liquid droplets out of a gas stream in a centrifugal droplet separator comprising a shell (1) having a circular cross section and a vertical longitudinal axis (11), an upper hood (2) that bounds the shell (1) at the top and has a gas exit port (7) for the gas stream cleaned in the centrifugal droplet separator, a drip plate (8) disposed beneath the gas exit port (7), a lower hood (10) that bounds the shell (1) at the bottom and has a liquid exit port (4) for removal of the deposited liquid droplets, and an inlet (3) that opens tangentially into the shell (1), through which the gas stream is fed in, wherein a stabilizer liquid is fed into the interior of the centrifugal droplet separator through at least two nozzles (9), the nozzle outlet (15) of the respective nozzle (9) is above the tangential inlet (3) and below the drip plate (8) in the centrifugal droplet separator, the main spraying direction (12) of the respective nozzle (9) is directed upward at an internal angle (16) in the range from 0 to 60° relative to the vertical longitudinal axis (11), and hence all walls in the interior of the centrifugal droplet separator are fully wetted by the stabilizer liquid.

11. The method according to claim 10, wherein the stabilizer liquid is fed continuously to the centrifugal droplet separator.

12. The method according to either of claims 10 and 11, wherein the stabilizer liquid comprises 4-methoxyphenol (MeHQ).

13. The method according to any of claims 10 to 12, wherein the gas stream fed to the centrifugal droplet separator comprises droplets of substances which, because of their chemical properties, have a tendency to polymerize on walls of the centrifugal droplet separator.

14. The method according to claim 13, wherein the gas stream fed to the centrifugal droplet separator comprises acrylates that have formed as a result of an acid-catalyzed esterification of (meth)acrylic acid with C4 to C10 alcohols, especially n-butyl acrylate (nBA) or 2-ethylhexyl acrylate (2-EHA).