Device and process for gas induced mixing

Abstract

The invention is directed to a device (1) for sucking in and compressing a gas (3) and mixing it with a liquid (5), comprising a central propellant nozzle (7) for the supply of a first portion (9) of the liquid (5), wherein the central propellant nozzle (7) has an outlet (11) reaching into a first mixing chamber (13) with an inlet tube (14) for the supply of the gas (3), a mixing nozzle (15) for the supply of a second portion (17) of the liquid (5), wherein the mixing nozzle (15) has a central opening (19) from the first mixing chamber (13) into a proximal end (21) of a tubular second mixing chamber (23) and a diffusor (25) being arranged on a distal end (27) of the tubular second mixing chamber (23), wherein the central propellant nozzle (7) comprises a twist guide (29) with at least three twisted channels (31), preferably six twisted channels (31), and wherein the twist guide (29) has a solid center part (37) with a ratio between an internal diameter (41) of the twist guide (29) and the diameter (39) of the solid center part (37) in a range from 5 to 25, in particular from 10 to 22. The invention is further directed to a vessel comprising the device, a process for mixing a liquid and a process for manufacture of the device.

Description

[0001] Device and process for gas induced mixing

[0002] Description

[0003] The present invention relates to a device for sucking in and compressing a gas and mixing the gas with a liquid, wherein the device comprises a central propellant nozzle for the supply of a first portion of the liquid, a mixing nozzle for the supply of a second portion of the liquid and a diffusor and wherein the central propellant nozzle comprises a twist guide. The invention further relates to a process for mixing a liquid, which particularly comprises a polymerizable compound such as a (meth)acrylate, (meth)acrylic acid and / or styrene, and further to a vessel comprising the device and a process for manufacture of the device.

[0004] (Meth)acrylates, also referred to as (meth)acrylic esters, are generally produced by esterification of (meth)acrylic acid with alcohols in the presence of esterification catalysts. Such processes are known for example from the articles Acrylic Acid and Derivatives in Kirk-Othmer Encyclopedia of Chemical Technology, Wiley, 2002, https: / / doi.org / 10.1002 / 0471238961.0103182502012105.a01.pub2 and Methacrylic Acid and Derivatives in Kirk- Othmer Encyclopedia of Chemical Technology, Wiley, 2003, https: / / doi.org / 10.1002 / 0471238961.1305200807181519.a01.pub2.

[0005] Alkyl esters of (meth)acrylic acid are well known and are of significance, for example, as starting monomers for the preparation of aqueous polymer dispersions which find use, for example, as adhesives, paints or textile, leather and paper auxiliaries.

[0006] Handling and storage of polymerizable compounds such as (meth)acrylates, (meth)acrylic acid and / or styrene require specialized devices and processes as spontaneous polymerization must be avoided.

[0007] Stored liquids are often homogenized in storage tanks by jet mixers. Gas induced mixing provides an effective mixing, whereas in continuous operation, typically an exhaust gas flow is generated or a circular gas compressor is applied. By using a jet pump, a circular gas mode of operation can be established. An ejector jet nozzle, which sucks in and compresses gas with a high degree of efficiency, is particularly suitable for mixing as described by Zehner et al. in "Gasinduziertes Tankmischen fiir Acrylsaure und deren Derivate”, Chemie Ingenieur Technik, 2007, 79, No.7. The gas is dispersed by the ejector jet nozzle and partly dissolved in the liquid. The presence of oxygen, which can be additionally fed to storage tanks, stabilizes acrylic monomers and their derivatives.

[0008] The contents of storage tanks are usually mixed either batchwise or continuously. This may be necessary, for example, to compensate for slight fluctuations in the concentration e.g. of different product batches. But also for the compensation of temperature differences, it may be necessary to mix the tank contents. Jet mixers with liquid jet are often used for these tasks. Hereby, liquid is extracted from the tank near the bottom via a pump and fed back in via a nozzle at high speed. The free jet generated in this way sucks in liquid along the flow path, so that the contents of the tank are circulated and mixed. The nozzle can be directed upwards to ensure effective mixing for higher fill-levels, but which might imply safety risks due to formation of fine liquid droplets and potential electrostatic discharge in an explosive regime.

[0009] Gas induced tank mixing is an alternative to pumps operated with an only liquid jet stream. Gas induced mixing is mainly used in large vessels. Here, mixing of the contents of the container is carried out according to the so-called airlift principle. A gaseous stream is injected into the liquid and the rising gas bubbles entrain liquid from their surroundings, which is transported upwards with them. A vertical circulation flow is generated that promotes the mixing. This mixing principle is also suitable for continuous mixing in storage tanks and particularly advantageous for the mixing of acrylic monomers and their derivatives, as dissolved oxygen is often used to stabilize these chemicals. Further, gas-induced mixing can also be used for slim upright orientated containers, where liquid jet stream pumps are limited.

[0010] The suction and compression of circulating gas for gas induced tank mixing can be effectuated by jet compressors. In principle, standard ejectors are suitable for this task. However, ejector jet nozzles show higher efficiencies. As explained above, the rising gas bubbles entrain the surrounding fluid and thus generate the vertical circulation flow required for mixing.

[0011] DE 2410570 C2 discloses a multi-stream jet pump with mixing nozzle and impulse exchange tube to provide a two- phase liquid / gas mixture. The gas is dispersed in the field of shear forces between a very fast jet of liquid and liquid flowing slowly through an impulse exchange chamber, by which means a large interfacial area is produced. A liquid pump produces a propulsive jet and an ejector is used for compressing and conveying the gas. In the ejector, also referred to as jet pump, gas is drawn in by a fast jet of liquid and is mixed with the liquid in a cylindrical tube. Compression of the gas takes place both in the cylindrical mixing tube and in a diffuser connected thereto. The mixing is effected by a jet showing a twist produced by means of a twist guide dividing the propulsive liquid into a number of individual jets.

[0012] However, due to conventional manufacturing methods, typically implying long lead time in production due to several workshop steps, the optimization of the internal design of multi-stream jet pumps was still limited as the selection of fabricable structures was restricted by for example mechanical constraints. For example twist guides, which are individually formed and then installed in the device, possess a metal core with large diameter and a central straight bore. The central straight bore ensures a sufficient open flow through surface area for the liquid to avoid large pressure-drops induced by the large core part, but the central straight bore constitutes a by-pass for the liquid without twist. This results in a reduced rotation and therefore in a reduced mixing efficiency. Limited performances due to limits in conventional manufacturing processes and thus limits in design optimization have to be overcome. It is an object of the present invention to provide a device and a process for an improved mixing of a gas with a liquid and further to provide a manufacturing process which enable higher production efficiency and an improved design of the device.

[0013] This object is achieved by a device for sucking in and compressing a gas and mixing it with a liquid, comprising a central propellant nozzle for the supply of a first portion of the liquid, wherein the central propellant nozzle has an outlet reaching into a first mixing chamber with an inlet tube for the supply of the gas, a mixing nozzle for the supply of a second portion of the liquid, wherein the mixing nozzle has a central opening from the first mixing chamber into a proximal end of a tubular second mixing chamber and a diffusor being arranged on a distal end of the tubular second mixing chamber, wherein the central propellant nozzle comprises a twist guide with at least three twisted channels, preferably six twisted channels, and wherein the twist guide has a solid center part with a ratio between an internal diameter of the twist guide and the diameter of the solid center part in a range from 5 to 25, preferably from 10 to 22 and more preferably from 15 to 20.

[0014] The invention is also directed to a vessel comprising the device for sucking in and compressing the gas.

[0015] And the object is further achieved by a process for mixing a liquid, in particular comprising a polymerizable compound such as a (meth)acry late, (meth)acry I ic acid and / or styrene, wherein the liquid is present in a vessel under an atmosphere comprising a gas and the gas is dispersed in the liquid by means of the device.

[0016] The invention is further directed to a process for manufacture of the device for sucking in and compressing the gas, wherein the device is produced by an additive manufacturing method, in particular 3D-printing.

[0017] The device according to the present invention is a multi-stream jet pump with delicate geometries of the twist guide. The twist guide provides a slim solid center part with a defined ratio between the internal diameter of the twist guide and the diameter of the solid center part. Due to the solid center part all liquid, which passes through the twist guide, is imposed with the twist and thus the mixing between the liquid and the gas within the device is enforced. With the improved rotation of the liquid, an accurate and optimized dimensioning of the device is supported. Further, the defined ratio between the internal diameter of the twist guide and the diameter of the solid center part allows a wide open through-flow area of the twist guide causing only small pressure losses, and at the same time a robust fixation of the internal structure within the twist guide.

[0018] The device is able to suck the gas into the liquid, provides an excellent mixing between the gas and the liquid, and improves the compression of the gas, wherein the gas suction is optimized. With the device a homogenous temperature is provided in the vessel, hot spots are avoided, and a save handling of the liquid and vessel is ensured. The sucked gas is premixed with a divided liquid jet stream, which leaves the twist guide. The fast flowing resulting premixture comprising the gas and the first portion of the liquid causes a slower stream of the liquid, which is the second portion of the liquid, to be drawn into the mixing nozzle and to be mixed with the premixture. Due to the second stream of the liquid drawn in, there is a sudden interchange of the disperse phases and the gas is entrained in form of fine bubbles. Subsequently, the gas is compressed by conversion of kinetic energy into compression energy in the diffusor. Large interfacial areas between the gas and the liquid are generated. The advantages of multistream ejectors in terms of a high specific interfacial area are combined with the advantages of jet pumps in terms of gas drawing and compression.

[0019] Preferably, a jet of the first portion of the liquid is propelled from the central propellant nozzle and premixed with the gas in the first mixing chamber. The resulting premixture is preferably passed through the mixing nozzle, which is arranged downstream of the central propellant nozzle, into the tubular second mixing chamber, where the premixture is admixed with the second portion of the liquid being drawn in. The jet from the central propellant nozzle has preferably a speed in a range from 10 to 70 m / sec.

[0020] The device according to the present invention provides gas bubbles distributed in the liquid, which possess a smaller size and the coverage of the device as mixing means for the total inner volume of the vessel is enlarged.

[0021] Preferably, the twist guide, the central propellant nozzle, the mixing nozzle and the tubular second mixing chamber are arranged coaxially, more preferably along a same center axis. In particular, the twist guide, the central propellant nozzle, the first mixing chamber, the mixing nozzle and the tubular second mixing chamber are arranged coaxially, more preferably along the same center axis. More particularly, the twist guide, the central propellant nozzle, the mixing nozzle and the tubular second mixing chamber are arranged coaxially in downstream direction consecutively in this order, even more preferably along the same center axis. Particularly, the twist guide, the central propellant nozzle, the first mixing chamber, the mixing nozzle and the tubular second mixing chamber are arranged in the given order. The central propellant nozzle is typically at least partly located within the first mixing chamber.

[0022] Preferably the first mixing chamber has a conical shape in a region extending from the outlet of the central propellant nozzle to an entry of the mixing nozzle, wherein an inner diameter of the first mixing chamber is continuously reduced in this region. By a smooth inner design of the first mixing chamber providing a form in line with an optimal flow path of the gas, the flow resistance and pressure loss coefficient of the device are minimized. Sharp-edged support within the first mixing chamber to mechanically stabilize the central propellant nozzle or the mixing nozzle to keep a central position are dispensable.

[0023] In a preferred embodiment, the inlet tube for the supply of the gas is connected to the first mixing chamber by a rounded joint. By the rounded joint the bend of the gas stream is smoothed, and the gas suction is optimized. The rounded joint possesses a radius of curvature. Preferably, a ratio between the radius of curvature and an inner inlet diameter of the inlet tube is more than 1, more preferably more than 1.15. The ratio between the radius of curvature and the inner inlet diameter of the inlet tube is preferably in a range from 1 to 2, more preferably from 1.15 to 1.55, even more preferably from more than 1.15 to 1.55. For example, the rounded joint has a radius of curvature in a range from 50 mm to 150 mm at least at a part of an inner wall of the rounded joint. The inner inlet diameter of the inlet tube is preferably in a range from 35 mm to 105 mm, for example 40 mm, 50 mm, 65 mm, 80 mm or 100 mm.

[0024] The device according to the invention particularly has a pressure loss coefficient of less than 1.4, preferably less than 1.2, more preferably 1.1 or less. The pressure loss coefficient characterizes the pressure loss of a certain hydraulic system or of a part of a hydraulic system. It can be measured for example in hydraulic loops. The pressure loss coefficient can be determined based on DIN EN 1267:2012-04. The pressure loss coefficient is typically defined by the following equation, wherein is the pressure loss coefficient, Ap is the pressure loss, p is the density and V is the volume.

[0025] Preferably, a cross-sectional area of a feed-opening of the inlet tube and a cross-sectional area of the entry of the mixing nozzle are inclined to each other by a deflection angle in a range from 60° to 120°, in particular from 80° to 100°, for example by a deflection angle of 90°. Preferably, an inlet stream of the gas being passed through the inlet tube is deflected in the device by a deflection angle in a range from 60° to 120°, in particular from 80° to 100°, for example by a deflection angle of 90°.

[0026] The inner inlet diameter of the inlet tube preferably differs from the internal diameter of the twist guide by less than 50% more preferably, less than 20% and most preferably by less than 10%, referring to the inner inlet diameter of the inlet tube. Thus, the outer dimension of the inlet tube and the twist guide are essentially of the same size in a preferred embodiment.

[0027] Preferably, the device is mounted in the vessel in a horizontal orientation. The gas is let in the liquid preferably downwards, against gravity, into the device and ejected from the device essentially in parallel to the bottom of the vessel. In a preferred embodiment, the device is arranged in a lowest third of a total height of the vessel. More preferably, the device is arranged at the bottom of the vessel. Thus, by the rising gas bubbles all liquid stored in the vessel is agitated and homogenization of the liquid is improved in the vessel.

[0028] Typically, the device comprises a feed entry for the supply of the first portion of the liquid into the device. The feed entry diameter is preferably in a range from 35 mm to 105 mm, for example 40 mm, 50 mm, 65 mm, 80 mm or 100 mm. More preferably, the feed entry is of the same diameter as the inner inlet diameter of the inlet tube for the gas. Preferably, the feed entry, the twist guide, the central propellant nozzle, the mixing nozzle and the tubular second mixing chamber are arranged coaxially in downstream direction consecutively in this order, even more preferably along the same center axis, in particular in this given order. Preferably, the mixing nozzle comprises the central opening from the first mixing chamber and preferably at least eight exterior openings, in particular at least twelve exterior openings, for the supply of the second portion of the liquid. The exterior openings are arranged in particular on an outer circumference of the mixing nozzle. The exterior openings preferably have triangular cross-sections, more preferably with curved sidelines. In a preferred embodiment, the exterior openings have an aperture ratio in a range from 2 to 8, more preferred from 3 to 6. The aperture ratio is the ratio between the open flow-through area of the sum of all exterior openings on an outer lateral area of the mixing nozzle to the open flow-through area of an annual clearance surrounding the central opening of the mixing nozzle. In particular with regard to the annual clearance, the central opening is understood as being located at the tip of the mixing nozzle.

[0029] The twisted channels of the twist guide are in particular wounded around a center axis of the twist guide and along the twist guide with a slope, preferably a progressive slope, particularly in flow direction thus in direction to the central propellant nozzle. The twisted channels are characterized by their form of a spiral also referred to as screw. Preferably, all channels present in the twist guide are twisted. Preferably, all channels of the twist guide possess a slope, more preferably a progressive slope. In particular, all channels of the twist guide possess the same slope that can vary over the length of the center axis.

[0030] Preferably, a ratio between an open flow through cross-sectional area and a total cross-sectional area of the twist guide is more than 0.75, more preferably more than 0.8 and most preferably more than 0.9. The large open flow through cross-sectional area is achieved due to the slim solid center part of the twist guide, which can be produced by means of the additive manufacturing method.

[0031] In a preferred embodiment, the twist guide is formed integrally with the central propellant nozzle. Thus, the position of the twist guide is fixed and a risk of slipping or shifting of the twist guide within the device, in particular within the central propellant nozzle, is prevented. In particular, an outer cylinder of the twist guide is the outermost wall of the device, more particularly in a position upstream of the inlet tube. In a lateral cross-sectional view, the twist guide is preferably arranged outside of the first mixing chamber. Thereby dead-volumes in the first mixing chamber located at a side of the inlet tube facing away from the mixing nozzle, where trapped liquid might be replaced only irregularly, are avoided.

[0032] Preferably the liquid consists to more than 90 wt.-%, more preferably to more than 95 wt.-%, even more preferably to more than 99 wt.-%, of the polymerizable compound, based on the total liquid. Preferably the liquid consists to more than 90 wt.-%, more preferably to more than 95 wt.-%, even more preferably to more than 99 wt.-%, of the (meth)acrylate, (meth)acrylic acid and / or styrene, in particular the (meth)acrylate and / or (meth)acrylic acid, based on the total liquid. Unless otherwise stated, the parts, percentages and ppm data given herein relate to parts by weight, % by weight and ppm by weight. Here and throughout the specification, the terms "wt.-%" and "% by weight" are used synonymously.

[0033] The terms "(meth)acrylic acid", "(meth)acrylic ester" or "(meth)acrylate" relate to acrylic acid or the corresponding acrylic esters or acrylates and also to methacrylic acid or the corresponding methacrylic esters or methacrylates.

[0034] Preferably, the (meth)acrylate is a Ci-Cs alkyl (meth) acrylate. More preferably, the (meth)acrylate is selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, tertiarbutyl (meth)acrylate, n-butyl and isobutyl (meth)acrylate and 2-octyl (meth)acrylate. Even more preferably, the (meth)acrylate is selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, tertiarbutyl (meth)acrylate, n-butyl (meth)acrylate and isobutyl (meth)acrylate.

[0035] In a preferred embodiment the liquid comprises a polymerisation inhibitor, in particular the polymerisation inhibitor is selected from the group consisting of alkylphenols, for example o-, m- or p-cresol (methylphenol), 2-tert-butyl-4- methylphenol, 6-tert-butyl-2,4-dimethylphenol, 2,6-di- tert-butyl-4-methylphenol, 2-tert-butylphenol, 4-tert-butylphenol, 2,4-di-tert-butylphenol, 2-methyl-4-tert-butylphenol, 4-tert-butyl-2,6-dimethylphenol, 2,2'-methylene-bis-(6-tert-butyl-4- methylphenol), hydroxyphenols, for example hydroquinone, 2-methylhydroquinone, 2,5-di-tert-butylhydroquinone, catechol (1,2-dihydroxybenzene) or benzoquinone, aminophenols, such as para-aminophenol, nitrosophenols, such as para-nitrosophenol, alkoxyphenols, for example 2-methoxyphenol (guaiacol, pyrocatechol monomethyl ether), 2- ethoxyphenol, 2-isopropoxyphenol, 4-methoxyphenol (hydroquinone monomethyl ether), mono- or di-tert-butyl-4- methoxyphenol, tocopherols, such as e.g. alpha-tocopherol and 2,3-dihydro-2,2-dimethyl-7-hydroxybenzofuran (2,2- dimethyl-7-hydroxycoumaran), N-oxyls such as 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-oxo-2, 2,6,6- tetramethyl-piperidine-N-oxyl, 4-acetoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 2,2, 6,6-tetramethyl-piperidine-N-oxyl, 4,4',4"-tris (2,2,6,6-tetramethyl-piperidine-N-oxyl) phosphite or 3-oxo-2,2, 5,5-tetramethyl-pyrrolidine-N-oxyl, aromatic amines or phenylenediamines, such as N, N-diphenylamine, N-nitrosodiphenylamine, N, N'-dialkyl-para- phenylenediamine, where the alkyl radicals may be the same or different and each independently consist of 1 to 4 carbon atoms and may be straight-chain or branched, hydroxylamines, such as N, N-diethylhydroxylamine, phosphorus-containing compounds, such as triphenylphosphine, triphenylphosphite, hypophosphorous acid or triethylphosphite, sulfur-containing compounds, such as diphenyl sulfide or phenothiazine, optionally in combination with metal salts, such as the chlorides, dithiocarbamates, sulfates, salicylates or acetates of copper, manganese, cerium, nickel or chromium. Mixtures of polymerization inhibitors can also be used. Typically, one or more, for example two or three, of the aforementioned polymerization inhibitors are used. Preference is given to using one or two of the aforementioned polymerization inhibitors. Phenothiazine, methylene blue, hydroquinone, hydroquinone monomethyl ether, alkyl-substituted phenols or N-oxyl compounds or mixtures thereof are more preferably used. Most preferably, the polymerisation inhibitor is phenothiazine and / or hydroquinone monomethyl ether. Preferably, the gas consists to more than 90 vol .-%, more preferably to more than 95 vol .-%, and even more preferably to more than 99 vol .-%, of nitrogen and oxygen, based on the total gas. More preferably, the gas contains 4 vol.-% to 23 vol .-%, even more preferably 5 vol.-% to 8 vol.-%, of oxygen, based on the total gas. Oxygen is known as stabilizer or co-stabilizer for (meth)acrylic acid and (meth)acrylates. The term vol.-% relate to percentages by volume. Preferably, the gas is provided in the vessel partly as a continuous phase, more preferably in form of a gaseous layer. In a preferred embodiment, the feed opening of the inlet tube is arranged inside of the vessel and within the continuous phase of the gas, in particular in the gaseous layer. In particular, all parts of the device, including the inlet tube in full length, are located within the vessel. Oxygen can be fed from outside of the vessel to the continuous phase of the gas in the vessel in a continuous or stepwise manner. Thereby a minimum oxygen concentration for stabilization is ensured.

[0036] Preferably, a ratio between the total height of the vessel and a diameter of the vessel is in a range from 0.3 to 4, more preferably from 0.4 to 2.

[0037] Due to the device according to the invention the liquid present in the vessel is reliably homogenized at variable heights and fill levels. A ratio of the total height of the vessel or a liquid fill level in the vessel to the diameter of the vessel can be more than 2, even more than 3. Preferably, the vessel comprises a pump for liquid circulation.

[0038] An absolute pressure in the vessel is preferably in a range from 950 hPa to 1100 hPa, more preferably from 1000 hPa to 1050 hPa. A temperature of the liquid in the vessel is preferably in a range from 0°C to 40°C, more preferably from 15°C to 40°C.

[0039] The residence or storage time of the liquid in the vessel is preferably more than 6 hours, more preferably more than 12 hours, even more preferably more than 24 hours. The residence or storage time is understood to mean the duration for which the liquid is mixed by the device of the invention.

[0040] The vessel has preferably an inner volume in a range from 150 m3to 40000 m3, more preferably from 150 m3to 6000 m3, in particular in a range from 150 m3to 500 m3or in a range from 550 m3to 6000 m3.

[0041] Preferably, the liquid is circulated, in particular by the pump, with a flow rate of more than 20 m3 / h, more preferably of more than 40 m3 / h and even more preferably of more than 43 m3 / h, for example with a flow rate in a range from 40 m3 / h to 60 m3 / h. Thus, the jet from the central propellant nozzle is preferably provided with a flow rate of more than 20 m3 / h, more preferably of more than 40 m3 / h and even more preferably of more than 43 m3 / h, for example with a flow rate in a range from 40 m3 / h to 60 m3 / h.

[0042] The device is preferably made of a metallic material. The metallic material preferably comprises or consists of austenitic steel and / or black steel. The metallic material can be coated with a second material. The additive manufacturing method to manufacture the device is preferably a powder based method. The powder provides in particular particles sizes in a range from 5 m to 100 pm, more preferably from 10 pm to 60 pm, even more preferably from 20 pm to 50 pm. Material, in particular the metallic material in powder form, is preferably applied in layers with a layer thickness in a range from 10 pm to 100 pm, more preferably from 25 pm to 50 pm.

[0043] The device is preferably produced by 3D-pri nting, in particular by application of Selective Laser Melting (SLM), Laser Powder Bed Fusion (LPBF), Direct Metal Laser Sintering (DMLS), LaserCUSING, Laser Metal Fusion, Direct Metal Printing, Laser-based powder bed fusion of metals (PBF-LB / M) according to ISO / ASTM 52911-1 :2019 or electronbeam melting (EBM). Details of these additive manufacturing methods are known by the person skilled in the art.

[0044] With the process for manufacturing according to the invention, the production lead time is reduced, less manual activities are needed in workshops and devices with a better performance can be produced. In particular, delicate internal parts can be formed, wherein a function led design optimization can be realized with less production limits. The additive manufacturing method provides the creation of delicate geometries of the twist guide such as the slim solid center part. The design and optimization of the inner structure of the twist guide is no longer limited by constraints of for example metal-cutting or casting techniques. Thus, devices with improved mixing efficiencies can be manufactured.

[0045] Embodiments of the invention and comparative embodiments are illustrated in the figures and further described in the following.

[0046] The figures show:

[0047] Figure 1 a schematic view of a vessel comprising a device for sucking in and compressing a gas,

[0048] Figure 2 an enlarged schematic view of a device for sucking in and compressing a gas,

[0049] Figure 3 a detailed cross-sectional view of a device for sucking in and compressing a gas,

[0050] Figure 4 a lateral view of a section of the device for sucking in and compressing a gas,

[0051] Figure 5 a back view of a cross-section of the device for sucking in and compressing a gas,

[0052] Figure 6 a back view of a cross-section of a twist guide according to the state of the art and

[0053] Figure 7 experimental data of a comparison between two devices for sucking in and compressing a gas. Figure 1 shows a schematic view of a vessel 2 comprising a device 1 for sucking in and compressing a gas 3, which is provided in the vessel 2 in form of a gaseous layer 6 being a continuous phase of the gas 3. A liquid 5 comprising a polymerizable compound is stored in the vessel 2 under an atmosphere comprising the gas 3. The device 1 is emerged in the liquid 5. A feed opening 18 of the device 1 is arranged inside of the vessel 2 and within the gaseous layer 6 of the gas 3. The gas 3 is dispersed in the liquid 5 by means of the device 1. The liquid 5 comprises acrylic monomers and the gas 3 comprises oxygen which is partly dissolved in the liquid 5 to ensure stabilization of the acrylic monomers.

[0054] The device 1 is mounted in the vessel 2 in a horizontal orientation and disperses the gas 3 in the liquid 5. The liquid 5 is withdrawn from the vessel 2 near the bottom via a pump 4 and fed back in the vessel 2 via the device 1 at high speed. The free jet generated in this way sucks in the gas 3 and more of the liquid 5 along the flow path, so that the liquid 5 is circulated and mixed according to the airlift principle. The gas 3 is injected into the liquid 5 and the rising gas bubbles entrain the liquid 5 from their surroundings, which is transported upwards with them. A vertical circulation flow is generated in the vessel 2 that promotes continuous mixing. The gas 3 is circulated from the gaseous layer 6 into the liquid 5.

[0055] Figure 2 shows an enlarged schematic view of a multi-stream jet pump depicted as the device 1 for sucking in and compressing the gas 3 in figure 1 . A first portion 9 of the liquid 5 is fed into the device 1 and through a twist guide 29, which causes the liquid 5 to rotate at a point just upstream of a central propellant nozzle 7. The resulting jet of the liquid 5 is premixed in a first mixing chamber 13 with the gas 3 sucked in through an inlet tubel 4 with an inner inlet diameter 20. A resulting premixture is fed to a tabular second mixing chamber 23 and to a diffusor 25 located in the liquid 5 contained in the vessel 2, as a result of which a second portion 17 of the liquid 5 is drawn into the tabular second mixing chamber 23 from the liquid 5 in the vessel 2. In the coaxial diffuser 25, downstream of the tabular second mixing chamber 23, the compression of the mixture of the liquid 5 and the gas 3 to the pressure in the vessel 2 is completed.

[0056] Figure 3 shows a detailed lateral cross-sectional view of a device 1 for sucking in and compressing a gas 3. In the device 1 the gas 3 is mixed with a liquid 5. The device 1 comprises a central propellant nozzle 7 for the supply of a first portion 9 of the liquid 5, which is fed into the device 1 through a feed entry 8. The central propellant nozzle 7 has an outlet 11, which reaches into a first mixing chamber 13, which has an inlet tube 14 for the supply of the gas 3. The inlet tube 14 for the supply of the gas 3 is connected to the first mixing chamber 13 by a rounded joint 43.

[0057] A jet of the first portion 9 of the liquid 5 is propelled from the central propellant nozzle 7 and premixed with the gas 3 in the first mixing chamber 13. The device 1 further comprises a mixing nozzle 15 for the supply of a second portion 17 of the liquid 5. The resulting premixture of the first portion 9 of the liquid 5 and the gas 3 is passed through the mixing nozzle 15, which is arranged down-stream of the central propellant nozzle 7, into the tubular second mixing chamber 23, where the premixture is admixed with the second portion 17 of the liquid 5 being drawn in trough the mixing nozzle 15.

[0058] The first mixing chamber 13 has a conical shape in a region 22 extending from the outlet 11 of the central propellant nozzle 7 to an entry 33 of the mixing nozzle 15. And an inner diameter 35 of the first mixing chamber 13 is continuously reduced in this region 22. A cross-sectional area of a feed-opening 18 of the inlet tube 14 and a cross- sectional area of the entry 33 of the mixing nozzle 15 are inclined to each other by an angle of 90°. Accordingly, an inlet stream of the gas 3 being passed through the inlet tube 14 is deflected in the device 1 by a deflection angle of 90°.

[0059] The mixing nozzle 15 has a central opening 19 from the first mixing chamber 13 into a proximal end 21 of the tubular second mixing chamber 23. The central opening 19 of the mixing nozzle 15 is surrounded by an annual clearance 24. A diffusor 25 is arranged on a distal end 27 of the tubular second mixing chamber 23. The mixing nozzle 15 further comprises twelve exterior openings 47 for the supply of the second portion 17 of the liquid 5.

[0060] The central propellant nozzle 7 comprises a twist guide 29 with six twisted channels 31 . The twisted channels 31 are wounded around a center axis 34 in a spiral form. The twist guide 29 has an internal diameter 41 at an outer cylinder 42 and a slim solid center part 37 with a diameter 39. The central propellant nozzle 7, the twist guide 29, the mixing nozzle 15 and the tubular second mixing chamber 23 are arranged coaxially along the center axis 34.

[0061] The device 1 was produced by a 3D-printing method.

[0062] Figure 4 shows a lateral view of a section of the device 1 for sucking in and compressing a gas according to figure 3. The inlet tube 14 for the supply of the gas 3 is connected to the first mixing chamber 13 by the rounded joint 43. The exterior openings 47 at an outer lateral area 48 of the mixing nozzle 15 are visible. The exterior openings 47 are designed with triangular cross-sections and curved sidelines and they provide a high aperture ratio.

[0063] Figure 5 shows a back view of a cross-section of the twist guide 29 of the device 1 for sucking in and compressing a gas according to figure 3. Four of the six twisted channels 31 are at least partly shown. The twist guide 29 possesses the internal diameter 41 and has the slim solid center part 37.

[0064] Figure 6 shows a back view of a cross-section of a twist guide 29 according to the state of the art. The known twist guide possesses six twisted channels 31 . The center of the twist guide 29 is formed by a hollow center part 37 comprising a straight central bore 32. The hollow center part 37 has a large diameter 39.

[0065] Examples and comparative examples Gas suction as a function of liquid volumetric flow was measured for two different devices for sucking in and compressing a gas. A first device corresponded to the device shown in figure 3. A comparative device, in contrast to the device according to figure 3, was equipped with a twist guide as shown in figure 6 and possessed an inlet tube, which was connected to the first mixing chamber by a sharp 90°-edge. The exterior openings were of a rectangular slit shape and the comparative device comprised a mechanically produced first mixing chamber with stepwise tapering of the inner cross-section in flow direction due to fitting requirements of the mixing nozzle in the device. The first device was manufactured by 3D-printing and the comparative device was manufactured by conventional means of machining shops.

[0066] Both devices were operated, respectively, in a tank with water at a liquid temperature of 21 ,6°C and air at a gas temperature of 19°C, and at a pressure of 1011 hPa. The tank had a length of 10.0 m and a width of 3.3 m. The fill level in the tank accounted to 0.4 m. Both devices had a feed entry with a diameter of 76.1 mm. Liquid circulation was effectuated by means of a rotary pump with a nominal delivery rate of 5000 l / min at 8000 hPa and a back pressure of 2500 hPa.

[0067] Figure 7 shows experimental data of a comparison between two devices for sucking in and compressing a gas. On an abscissa 49 the liquid volumetric flow is represented in m3 / h. On a first ordinate 51 on the left the gas volumetric flow is represented in m3 / h. On a second ordinate 53 on the right the ratio gas to liquid is represented [-].

[0068] A first graph 55 and a second graph 57 represent data obtained for the first, 3D-printed device. A third graph 59 and a fourth graph 61 represent data obtained for the comparative device. With the first device a higher gas volumetric flow was achieved, thus more gas was sucked in, for the respective same liquid volumetric flow, resulting in improved ratios of gas to liquid. A higher gas flow improved the mixing quality and reduced the required mixing time, the demand in pump head can be reduced. Thus, the first device was more efficient in mixing and could be operated with lower pressure loss than the comparative device. For the same mixing result a weaker pump or smaller device for sucking in and compressing a gas is sufficient. Further, the performance of the first device is more stable.

[0069] List of reference numerals

[0070] 1 device

[0071] 2 vessel

[0072] 3 gas

[0073] 4 pump

[0074] 5 liquid

[0075] 6 gaseous layer

[0076] 7 central propellant nozzle

[0077] 8 feed entry

[0078] 9 first portion

[0079] 11 outlet

[0080] 13 first mixing chamber

[0081] 14 inlet tube

[0082] 15 mixing nozzle

[0083] 16 deflection angle

[0084] 17 second portion

[0085] 18 feed opening

[0086] 19 central opening

[0087] 20 inner inlet diameter

[0088] 21 proximal end

[0089] 22 region

[0090] 23 tubular second mixing chamber

[0091] 24 annual clearance

[0092] 25 diffusor

[0093] 27 distal end

[0094] 29 twist guide

[0095] 31 channel

[0096] 32 central bore

[0097] 33 entry

[0098] 34 center axis

[0099] 35 inner diameter

[0100] 37 center part

[0101] 39 diameter

[0102] 41 internal diameter

[0103] 42 outer cylinder

[0104] 43 joint 45 inner wall

[0105] 47 exterior opening

[0106] 48 lateral area

[0107] 49 abscissa 51 first ordinate

[0108] 53 second ordinate

[0109] 55 first graph

[0110] 57 second graph

[0111] 59 third graph 61 fourth graph

Claims

Claims1. Device (1) for sucking in and compressing a gas (3) and mixing it with a liquid (5), comprising a central propellant nozzle (7) for the supply of a first portion (9) of the liquid (5), wherein the central propellant nozzle (7) has an outlet (11) reaching into a first mixing chamber (13) with an inlet tube (14) for the supply of the gas (3), a mixing nozzle (15) for the supply of a second portion (17) of the liquid (5), wherein the mixing nozzle (15) has a central opening (19) from the first mixing chamber (13) into a proximal end (21) of a tubular second mixing chamber (23) and a diffusor (25) being arranged on a distal end (27) of the tubular second mixing chamber (23), wherein the central propellant nozzle (7) comprises a twist guide (29) with at least three twisted channels (31), preferably six twisted channels (31), and wherein the twist guide (29) has a solid center part (37) with a ratio between an internal diameter (41) of the twist guide (29) and the diameter (39) of the solid center part (37) in a range from 5 to 25, in particular from 10 to 22.

2. Device (1) according to claim 1, wherein the first mixing chamber (13) has a conical shape in a region extending from the outlet (11) of the central propellant nozzle (7) to an entry (33) of the mixing nozzle (15), wherein an inner diameter (35) of the first mixing chamber (13) is continuously reduced in this region.

3. Device (1) according to claim 1 or 2, wherein all channels (31) present in the twist guide (29) are twisted.

4. Device (1) according to any of claims 1 to 3, wherein a cross-sectional area of a feed-opening (18) of the inlet tube (14) and a cross-sectional area of the entry (33) of the mixing nozzle (15) are inclined to each other by a deflection angle in a range from 60° to 120°, in particular from 80° to 100°.

5. Device (1) according to any of claims 1 to 4, wherein the inlet tube (14) for the supply of the gas (3) is connected to the first mixing chamber (13) by a rounded joint (43).

6. Device (1) according to claim 5, wherein the rounded joint (43) has a radius of curvature in a range from 50 mm to 150 mm at an inner wall (45) of the rounded joint (43).

7. Device (1) according to any of claims 1 to 6, wherein the mixing nozzle (15) comprises the central opening (19) from the first mixing chamber (13) and at least eight exterior openings (47), in particular at least twelve exterior openings (47), for the supply of the second portion (17) of the liquid (5).

8. Device (1) according to claim 7, wherein the exterior openings (47) have an aperture ratio in a range from 2 to 8, in particular from 3 to 6.

9. Device (1) according to any of claims 1 to 8, wherein the twist guide (29), the central propellant nozzle (7), the mixing nozzle (15) and the tubular second mixing chamber (23) are arranged coaxially.

10. Vessel (2) comprising a device (1) according to any of claims 1 to 9.11 . A process for mixing a liquid (5), in particular comprising a polymerizable compound such as a (meth)acrylate, (meth)acrylic acid and / or styrene, wherein the liquid (5) is present in a vessel (2) under an atmosphere comprising a gas (3) and the gas (3) is dispersed in the liquid (5) by means of a device (1) according to any of claims 1 to 9.

12. A process according to claim 11, wherein a jet of the first portion (9) of the liquid (5) is propelled from the central propellant nozzle (7) and premixed with the gas (3) in the first mixing chamber (13), the resulting premixture is passed through the mixing nozzle (15), which is arranged downstream of the central propellant nozzle (7), into the tubular second mixing chamber (23), where the premixture is admixed with the second portion (17) of the liquid (5) being drawn in.

13. A process according to claim 11 or 12, wherein an inlet stream of the gas (3) being passed through the inlet tube (14) is deflected in the device (1) by the deflection angle (16) in a range from 60° to 120°, in particular from 80° to 100°.

14. A process according to any of claims 11 to 13, wherein the gas (3) consists to more than 90 vol.-% of nitrogen and oxygen, based on the total gas (3).

15. A process according to any of claims 11 to 14, wherein the feed opening (18) of the inlet tube (14) is arranged inside of the vessel and within a continuous phase of the gas (3).

16. A process for manufacture of a device (1) according to any of claims 1 to 9, wherein the device (1) is produced by an additive manufacturing method, in particular 3D-printing.

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