EP3589398A1

EP3589398A1 - Device and method for producing powdered polymers

Info

Publication number: EP3589398A1
Application number: EP18708946.1A
Authority: EP
Inventors: Stephan Bauer; Markus Toennessen; Christophe Bauduin; Katrin Baumann; Marco Krueger; Andreas Daiss; Markus Muehl
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2017-03-01
Filing date: 2018-02-26
Publication date: 2020-01-08
Also published as: WO2018158191A1; CN110352092A; JP2020509130A; US20200231711A1; CN110352092B; JP7143315B2; US11332550B2

Abstract

The invention relates to a device for producing powdered polymers, comprising a reactor (1) for droplet polymerization with a device for dropletizing (5) a monomer solution for the production of the polymer, wherein the device for dropletizing (5) has holes through which the monomer solution is introduced, a feed point (13) for a gas above the device for dropletizing (5), at least one gas removal point (19) at the circumference of the reactor (1) and a fluidized bed (11), wherein at least one of the following features is satisfied: - in the region of the device for dropletizing (5) the monomer solution there is arranged a device for increasing the turbulence (31) in the gas flow, - in the region of the feed point (13) for the gas there is arranged a device for increasing the turbulence in the gas flow, - the feed point (13) for gas is designed such that increased turbulence is produced. The invention also relates to a method for producing powdered polymers, wherein an increase in the flow turbulence takes place in the gas flow in the region of the device for dropletizing (5).

Description

Apparatus and process for the preparation of powdered polymers

description

The invention is based on a device for the production of pulverulent polymers comprising a droplet polymerization reactor with a device for dropping a monomer solution for the production of the polymer with holes through which the monomer solution is introduced, a point of addition for a gas above the device for dripping , at least one gas sampling point on the circumference of the reactor and a fluidized bed. The invention further relates to a process for the preparation of pulverulent polymers in such a device.

The apparatus used and the process are suitable, for example, for producing water-absorbing polymers, in particular poly (meth) acrylates, which are used in the production of diapers, tampons, sanitary napkins and other hygiene articles or as water-retaining agents in agricultural horticulture.

The properties of the water-absorbing polymers can be adjusted via the degree of crosslinking. As the degree of crosslinking increases, the gel strength increases and the absorption capacity decreases. This means that with increasing absorption under pressure, the centrifuge retention capacity decreases, and at very high degrees of crosslinking the absorption under pressure also decreases again. In order to improve the application properties, for example the liquid conductivity in the diaper and the absorption under pressure, water-absorbing polymer particles are generally postcrosslinked. As a result, only the degree of crosslinking at the particle surface increases, whereby the absorption under pressure and the centrifuge retention capacity can be at least partially decoupled. This postcrosslinking can be carried out in aqueous gel phase. In general, however, ground and sieved polymer particles are coated on the surface with a postcrosslinker, thermally postcrosslinked and dried. Crosslinkers suitable for this purpose are compounds which contain at least two groups which can form covalent bonds with the carboxylate groups of the hydrophilic polymer. Various processes are known for the preparation of the water-absorbing polymer particles. Thus, for example, the monomers used for the preparation of poly (meth) acrylates and optionally additives may be added to a mixing kneader in which the monomers react to form the polymer. By rotating shafts with kneading bars in the mixing kneader, the resulting polymer is torn into chunks. The polymer removed from the kneader is dried and ground and fed to a post-processing. In an alternative variant, the monomer is introduced into a reactor for droplet polymerization in the form of a monomer solution, which may also contain further additives. When the monomer solution is introduced into the reactor, it decomposes into drops. The mechanism of dripping may be to act turbulent or laminar jet decay or even dripping. The mechanism of droplet formation depends on the entry conditions and the material properties of the monomer solution. The drops fall down the reactor, with the monomer reacting to the polymer. In the lower part of the reactor there is a fluidized bed into which the polymer particles formed by the reaction from the droplets fall. In the fluidized bed then takes place a post-reaction. Corresponding methods are described, for example, in WO-A 2006/079631, WO-A 2008/086976, WO-A 2007/031441, WO-A 2008/040715, WO-A 2010/003855 and WO-A 201 1/026876 described. A droplet polymerization reactor with different devices for introducing the monomer solution is described, for example, in WO-A 2015/197571 or WO-A 2015/197359.

In the known reactors, the droplet concentrations and gas temperatures over the reactor cross section may be subject to fluctuations due to the flow conditions. These fluctuations lead to incomplete utilization of the gas used for drying. This has the consequence that the monomer solution in the individual drops reacts to the polymer at different speeds. The object of the present invention is therefore to provide an apparatus and a method for the production of pulverulent polymers in which an improved mixing of the drying gas and the dripped-in monomer solution is ensured and, moreover, that the droplets are distributed more homogeneously over the reactor cross section. The object is achieved by a device for the production of powdery polymers, comprising a dropwise polymerization reactor with a device for dropping a monomer solution for the preparation of the polymer, wherein the device for dropping (5) has holes through which the monomer solution is introduced, a Loading point for a gas above the device for dripping, at least one gas sampling point at the periphery of the reactor and a fluidized bed, wherein at least one of the following features is fulfilled:

in the region of the device for dropping the monomer solution, a device for turbulence increase in the gas flow is arranged,

in the region of the point of addition of the gas, a device for turbulence increase in the gas flow is arranged,

the gas addition point is designed to produce increased turbulence.

The object is further achieved by a process for the preparation of polymers in such a device, comprising the following steps:

(a) dripping a monomer solution in the device for dripping, wherein the generated monomer droplets fall through the reactor and the monomer at least partially reacts with the polymer to form particles, (b) supplying gas via the gas addition point above the dropper to produce gas flow in the reactor from top to bottom; (c) collecting the particles produced in step (a) in the fluidized bed, wherein in the fluidized bed the reaction to the polymer in the individual particles is completed and optionally a post-crosslinking takes place,

(D) removal of the particles from the fluidized bed, wherein in the gas flow in the region of the device for dripping an increase in the flow turbulence takes place.

In the following description, the gas flow generated from top to bottom in the reactor is also referred to as the drying gas flow and the gas supplied via the gas addition point is also referred to as the drying gas.

By increasing the turbulence of flow, which is achieved by the use of the device for turbulence increase or the design of the gas addition point in the gas flow, compared to the known reactors improved mixing of the drying gas, which is added via the gas addition point, with the Drops from the monomer solution reached. Due to the good mixing, the drying gas is better utilized, so that the drying gas can be added at a lower gas inlet temperature. Due to the lower gas inlet temperature, the energy required for heating the gas is reduced, so that less energy is needed overall for the production of the polymer than when using the known reactors.

Depending on the design of the device for dropletizing the monomer solution, the drops produced are already distributed relatively homogeneously over the reactor cross-section and thus also mixed with the drying gas. Nevertheless, variations in the droplet concentration and the gas temperature, which lead to incomplete utilization of the drying gas, generally result locally above the reactor cross section. Taking advantage of the drying gas is understood here as the water absorption and heat emission of the gas, which sets a fully homogeneous temperature and a largely homogeneous water concentration in the gas in a full utilization of the drying gas over the reactor cross-section. In the case of incomplete utilization of the drying gas, by contrast, the temperature distribution and the water concentration are not homogeneous over the reactor cross-section. In order to minimize this effect, a defined flow turbulence is generated in the gas phase, which increases the homogeneity of the distribution of the droplets over the reactor cross section and thus ensures an even better mixing of the drying gas with the droplets from the monomer solution. The flow turbulence must neither be too small, because the homogenizing effect is otherwise negligible, nor too large, because otherwise drops or Particles can get too fast to the reactor wall and lead there to a deposit formation.

As a device for turbulence increase, any device can be used with which the turbulence of the gas flow can be increased. As an apparatus for turbulence increase, for example, flow obstacles can be used, which are arranged above or below the device for dropping. Alternatively, it is also possible to use gas nozzles, gas / liquid nozzles or liquid nozzles to increase turbulence.

If flow obstacles are used, the circulation of the flow obstacles swirls the drying gas and in this way increases the turbulence. In order to prevent the monomer solution leaving the device for dripping from being caused by the generated turbulence to deposit at the flow obstacles, the flow obstacles are preferably placed so that they are always at a gap between the individual when placed below the device for dripping in an imaginary vertical projection Vertropfereinrichtungen the device for dripping sitting and are not taken directly from the droplets formed at the Vertropfereinrichtungen. By size and number of flow obstacles, the degree of flow turbulence can be adjusted. Suitable flow obstacles are, for example, arbitrarily shaped, vertically or substantially perpendicular to the vertical plates arranged, for example, round, rectangular or polygonal plates, or any other body that cause a significant separation of the flow and thus generation of flow turbulence. Furthermore, as flow obstacles also perforated plates can be used or the Vertropfereinrichtungen can be modified in their geometry so that thereby an additional increase in turbulence takes place.

Alternatively, the flow obstructions may also include a perforated bottom having holes with a hydraulic diameter of 5 to 200 cm, preferably 10 to 100 cm. The holes may be arbitrarily shaped, for example, be circular, polygonal or elliptical. Preferably, the holes are circular. The size of the holes in the hole bottom prevents - unlike very fine free jets, which emerge from small holes with a few millimeters in diameter, as they are formed in conventional hole bottoms, the induced flow turbulence is immediately dissipated by friction. The turbulence thus generated leads, as with the flow obstacles, to a homogenization of the gas phase temperature and of the particle concentration. Since the hole bottom must necessarily be arranged above the device for dripping, otherwise impact the drops of monomer solution on the hole bottom and thus lead to a coating, is already at the level of Vertropfereinrichtungen an increased level of turbulence, resulting in collisions of droplets with each other and thus Coalescence can lead. This can lead to an undesirably wide droplet size distribution.

The gas addition point may for example have one or more perforated plates and is usually designed so that a sufficient uniform distribution of the in the reactor inflowing drying gas is achieved. Reference is made to technical literature such as Keith Masters, Spray Drying Handbook, 5th Edition (1991), or WO-A 91/04776 for reference to possible embodiments, where the gas addition site is designed to produce increased turbulence, Thus, it is possible, for example, to design at least one perforated bottom, in particular the last perforated bottom in the flow direction of the gas, as described above for the flow obstacles, namely that it has holes with a hydraulic diameter in the range of 5 to 200 cm, preferably 10 Alternatively, the gas addition site may also include one or more gas nozzles that generate flow turbulence.

Increased turbulence in the context of the present invention means that the local turbulence of the gas flow in the area of the dropletizing devices or below the dropletizing devices is greater than the mean turbulence which the incoming gas would have solely due to the mean gas velocity in the reactor.

As Vertropfereinrichtungen be understood in the context of the present invention, the parts of the device for dropping, in which the droplets are generated. As Vertropfer- devices such as spray nozzles can be used. However, it is preferred if the dropletizing devices each comprise a dropletizing channel which has holes on its underside through which the monomer solution is dripped. The holes are particularly preferably formed in perforated plates which form the underside of the Vertropferkanals. A possible configuration of the reactor as well as possible forms of the apparatus for the dripping are exemplified in WO-A 2015/197359.

Alternatively or additionally, preferably alternatively, nozzles can also be used to increase the turbulence. For this purpose, the device for turbulence increase gas nozzles,

Gas / liquid nozzles or liquid nozzles. If the nozzles used to increase the turbulence are gas / liquid nozzles or liquid nozzles, in one embodiment they are part of the device for dropping the monomer solution. For this purpose, an increased turbulence can be achieved, for example, by increasing the entry momentum of the droplet jets of the dropletizing devices or by using spray nozzles to produce the droplets. However, both can also lead to an undesirably wide droplet size distribution. The use of spray nozzles or increasing the droplet jet velocity also entail the risk that droplets reach the reactor wall at an early stage and as a result deposit formation occurs.

Particular preference is given to using gas nozzles as nozzles for increasing the turbulence. Gas nozzles induce turbulence downstream of the nozzle free jet depending on nozzle diameter and gas exit velocity. By changing the gas flow rate, the turbulence level and thus the homogenization of drop concentration and gas phase temperature can be easily adjusted. Like the flow obstacles, the nozzles can at the height of the droppers or slightly below or above the droppers. In a vertical projection, the nozzles preferably also sit on the gap between the Vertropfereinrichtungen to avoid that drop jets hit the nozzles and lead to a rapid deposit formation on the nozzles.

The turbulence induced by the nozzles is essentially determined by the pulse current I _{D introduced} by the nozzles. The momentum flow is the product of mass flow and gas velocity of the free jet at the outlet of the nozzles:

I _D = rh _D - v _D

I _D : total momentum of all turbulence generating nozzles [kg ^* m / s ² ]

rh _D : mass flow of all turbulence generating nozzles [kg / s]

v _D : Mean flow velocity of the free jet at the nozzle outlet [m / s] Decisive for influencing the flow turbulence through the nozzles is the ratio rrc = I _D / I _{TG of} the momentum flow introduced through the nozzles to the momentum flow of the drying gas flow in the reactor and the ratio r _r = I _D / I _R of the momentum current introduced by the nozzles is introduced to the momentum current supplied by the monomer solution supplied through the device for drowning.

The pulse stream of the drying gas is here

I _TG : momentum flow of the drying gas [kg ^* m / s ² ]

rh _TG : mass flow of the drying gas [kg / s]

v _TG : mean flow rate of the drying gas in the part of the reactor of constant hydraulic diameter [m / s]

The registered by the Vertropfereinrichtungen pulse current is l _v = u _v v _v ^■.

I _v : momentum flow introduced by all dropletizers [kg ^* m / s ² ] rh _v : total mass flow of the monomer solution introduced via the dropletizers

[Kg / s]

v _v : Mean flow velocity of the monomer solution at the exit of the dropletizer

[M / s]

In order to achieve a sufficient but not excessive influence of the flow turbulence by the nozzles, the ratio r _{TG is} preferably in the range of 0.1 to 50, more preferably in the range of 0.2 to 20 and particularly preferably in the range of 0.5 to 10. Likewise the ratio r _{r is} preferably in the range of 0.1 to 100, more preferably in the range of 0.2 to 50, and particularly preferably in the range of 0.5 to 20.

The desired pulse I _{D of} the turbulence-generating nozzles can be adapted both by the mass flow and by the nozzle exit speed. In the case of very high exit velocities, for example with multiple sound velocities, the locally generated turbulence is very high, but this is very fine-scale and is immediately dissipated by friction, so that it is no advantage to choose particularly high exit velocities. On the contrary, very high exit velocities result in high noise loading and higher power required to produce nozzle flow. The nozzle exit velocity is therefore preferably selected in a range between 5 and 1000 m / s, more preferably between 10 and 500 m / s and particularly preferably between 20 and 300 m / s. From the desired pulse current is then obtained when selecting the speed of the required mass flow. This finally results in the required nozzle cross-section.

The shape of the nozzle cross-section is of minor importance. Can be used round, slot-like, elliptical or optionally also nozzles with multiple openings.

Depending on the size of the reactor for droplet polymerization, one or more turbulence-generating nozzles are used to obtain the total momentum. Since it is desirable that the turbulence be generated evenly over the reactor cross-section, it is advantageous to use more nozzles as the reactor size increases. The reactor cross-sectional area per turbulence generation nozzle in the region of the reactor having a constant hydraulic diameter is preferably between 0.5 and 50 m ² , preferably between 1 and 25 m ² and particularly preferably between 2 and 10 m ² . This means that the number of gas nozzles used for turbulence increase, gas / liquid nozzles or liquid nozzles, in particular gas nozzles, in the range of 0.02 to 2 per square meter reactor cross-sectional area, more preferably 0.04 to 1 and in particular 0.1 to 0.5.

When the dropwise polymerization reactor comprises a central region of constant hydraulic diameter, a conically shaped reactor head of downward increasing hydraulic diameter, and a lower region which is also conical, in which case the hydraulic diameter decreases from top to bottom, and the device for Dropper and the device for turbulence increase are arranged in the reactor head, the above sizes refer to the reactor cross-sectional area in the central region with a constant hydraulic diameter. When the turbulence increasing device is located in the area of the monomer solution dripping device, the turbulence increasing device is preferably arranged in a range between 2 m above and 2 m below the dripping device. Preferably, the device for turbulence increase is 1 m above to 1 m below arranged the device for Vertropfung. If the device for dripping comprises drip devices at different heights, the height of the device for dripping, which is used to determine the distance of the device for turbulence increase, the middle level, in which the Vertropfereinrichtungen are arranged, is used.

When the turbulence increasing device is located in the vicinity of the gas addition point, the turbulence increasing device is located up to 2 m below the gas addition point, and more preferably in a range between 10 cm and 1 m below the gas addition point.

The devices for turbulence increase, that is, the gas nozzles, gas / liquid nozzles or liquid nozzles or the flow obstacles can be arranged at different heights. This is particularly advantageous when the Vertropfereinrichtungen are arranged at different heights or when mounting reasons make a different height required.

Alternatively, all flow obstacles, gas nozzles, gas / liquid nozzles or liquid nozzles of the device for turbulence increase can be arranged at a height in the reactor. This is particularly advantageous when the Vertropfereinrichtungen are also arranged at a height.

When using nozzles, that is to say gas nozzles, gas / liquid nozzles or liquid nozzles, in particular when using gas nozzles as a device for increasing the turbulence, the orientation of the nozzles can take place vertically downwards or vertically upwards, other orientations are conceivable. For example, a slight adjustment of the nozzles can take place in the direction of the reactor axis or also to the outside. Likewise, the nozzles may also have a partial tangential orientation. However, it must always be borne in mind that, as in the case of a tangential orientation, for example, there is the danger that particles will be entrained by the nozzle streams, reach the reactor wall at an early stage and lead to deposit formation. It is particularly preferred if the nozzles are aligned vertically upwards, that is, that the gas flow exiting through the gas nozzles is directed counter to the flow of the drying gas. Such an orientation causes the largest turbulence increase.

The distribution of the nozzles used as a device for turbulence increase over the reactor cross section depends on the arrangement of the Vertropfereinrichtungen. In principle, it is advantageous to distribute the nozzles as uniformly as possible over the reactor cross-section in order to produce the most uniform flow turbulence possible. It is also advantageous to gap the nozzles with respect to the horizontal position of the dropletizers so as not to cause direct jet-to-droplet jet interaction. Likewise, it is advantageous to arrange the nozzles as symmetrically as possible relative to the dropletizing devices. In the case of a strongly asymmetrical arrangement, there is the danger that the flow field in the area of the dropletizing device will be greatly deflected and the droplet jets will not only be expand due to the induced turbulence of the nozzles, but are strongly deflected and this can also lead to the collision of radiation.

So that enough gas can flow past the device for dropping the monomer solution, so that a uniform gas velocity can be achieved in the reactor and there is no excessive acceleration and turbulence of the gas when flowing around the device, it is further preferred if the ratio of that of the device the area covered by dripping in the reactor, based on the area enclosed by the line connecting the outermost holes, is less than 50% and preferably in the range between 3 and 30%.

The device according to the invention and the method according to the invention are preferably used for the production of water-absorbing polymers, in particular for the preparation of poly (meth) acrylates. In the context of the present invention, poly (meth) acrylates are understood as meaning polyacrylates, polymethacrylates and any desired mixture of polyacrylates and polymethacrylates.

Embodiments of the invention are illustrated in the figures and are explained in more detail in the following description.

1 shows a longitudinal section through a droplet polymerization reactor with a device for turbulence elevation below the device for dripping, a longitudinal section through a droplet polymerization reactor with a device for turbulence elevation above the device for dripping, an arrangement of radially extending droplet channels of different lengths and between the droplets Channels arranged turbulence increasing device, an arrangement of star-shaped Vertropferkanälen and arranged between the channels turbulence increasing devices, an array of Vertropferkanälen in rectangular pitch and arranged between the channels devices for turbulence increase,

FIG. 6 shows an arrangement of dropletizing channels in triangular division and turbulence-increasing devices arranged between the channels.

FIG. 7 shows an upper section of a drop polymerization reactor in which the gas addition point is designed to generate increased turbulence. FIG. 8 shows an upper section of a drop polymerization reactor with gas nozzles pointing upwards as a device for turbulence increase,

9 shows a profile of the standard deviation of the particle temperature as a function of the particle residence time with and without the use of a device for turbulence increase, wherein the dashed curve shows the case with and the solid curve represents the case without turbulence increase,

10 shows a profile of the total temperature as a function of the particle residence time with and without the use of a device for turbulence increase, wherein the dashed curve represents the case with and the solid curve represents the case without turbulence increase.

Figure 1 shows a longitudinal section through a reactor for droplet polymerization, as it is preferably used for the preparation of poly (meth) acrylate particles.

A droplet polymerization reactor 1 comprises a reactor head 3, in which a device for dripping 5 is accommodated, a central region 7, in which the polymerization reaction takes place, and a lower region 9 with a fluidized bed 11, in which the reaction is completed.

To carry out the polymerization reaction for the preparation of the poly (meth) acrylate, the device for dropping 5 is supplied with a monomer solution via a monomer feed 12. If the device for dripping 5 has a plurality of channels, it is preferable to supply the monomer solution to each channel via its own monomer feed 12. The monomer solution exits through holes, not shown in FIG. 1, in the dropletizing device 5 and breaks down into individual drops which fall downwards in the reactor. Via a first addition point for a gas 13 above the device for dropping 5, a gas, for example nitrogen or air, is introduced into the reactor 1. The gas flow thereby supports the disintegration of the monomer solution emerging from the holes of the device for dropping 5 into individual drops. In addition, the gas flow assists that the individual drops do not touch each other and coalesce into larger drops.

In order to make the cylindrical central region 7 of the reactor as short as possible and also to prevent droplets from bouncing against the wall of the reactor 1, the reactor head 3 is preferably conical, as shown here, wherein the device for dripping 5 in FIG conical reactor head 3 is located above the cylindrical portion. Alternatively, it is also possible to make the reactor in the reactor head 3 cylindrical with a diameter as in the central region 7. However, a conical configuration of the reactor head 3 is preferred. The position of the dropletizing device 5 is selected so that a collision occurs between the outermost holes, through which the monomer solution is supplied and the wall of the reactor, is still a sufficiently large distance to prevent the drop to the wall. For this purpose, the distance should be at least in the range of 50 to 1500 mm, preferably in the range of 100 to 1250 mm and in particular in the range of 200 to 750 mm. Of course, a greater distance to the wall of the reactor is possible. However, this has the disadvantage that with a greater distance is associated with a poorer utilization of the reactor cross-section.

In order to further obtain a better utilization of the gas supplied via the addition point 13, according to the invention a device for increasing the turbulence 31 is used in the region of the device 5 for dripping the monomer solution. By the device for turbulence increase the turbulence of the gas is increased, so that a better mixing of gas and drops generated with the device for dropletizing 5 is realized. This allows the drops to deliver even water to the gas. In addition, a more uniform temperature distribution over the residence time of the droplets is obtained in the reactor. The turbulence generated by the device for turbulence increase 31 is shown here by arrows 33. For example, flow obstructions or nozzles, in particular gas nozzles, gas / liquid nozzles or liquid nozzles can be used as the device for turbulence increase 31. In the embodiment illustrated here, 31 gas nozzles 35 are used as the device for increasing turbulence. These are arranged in the embodiment shown in Figure 1 below, preferably at most 2 m below the device for dropping 5. As a result of the gas jet 37 emerging from the gas nozzles 35, the gas supplied via the gas injection point 10 is accelerated. At the same time, the gas emerging from the gas nozzles 35 is decelerated, whereby the gas jet 37 is deflected and deformed, so that an additional turbulence is induced. It should be noted here that the difference in velocity between the gas added by the gas addition point 13 and the gas added through the gas nozzles 35 is not too great, so that the generated turbulence is not dissipated by the friction that occurs.

The lower region 9 terminates with a fluidized bed 11 into which the polymer particles formed during the fall from the monomer droplets fall. The post-reaction to the desired product takes place in the fluidized bed. According to the invention, the outermost holes through which the monomer solution is dripped are positioned such that a drop falling vertically downwards falls into the fluidized bed 1 1. This can be realized, for example, in that the hydraulic diameter of the fluidized bed is at least as large as the hydraulic diameter of the area enclosed by a line connecting the outermost holes in the device 5, the cross-sectional area of the fluidized bed and that of the surface forming the outermost holes has the same shape and the centers of the two surfaces are in a perpendicular projection at the same position. The outermost position of the outer holes with respect to the position of the fluidized bed 1 1 is shown in Figure 1 by means of a dashed line 15.

In order to further prevent drops from hitting the wall of the reactor even in the middle region 7, the hydraulic diameter is at the level of the middle between the device. dripping and the gas sampling point at least 10% greater than the hydraulic diameter of the fluidized bed.

The reactor 1 can have any desired cross-sectional shape. However, the cross section of the reactor 1 is preferably circular. In this case, the hydraulic diameter corresponds to the diameter of the reactor 1.

Above the fluidized bed 1 1, the diameter of the reactor 1 increases in the embodiment shown here, so that the reactor 1 widens conically in the lower region 9 from bottom to top. This has the advantage that in the reactor 1 resulting polymer particles that hit the wall, can slide down the wall in the fluidized bed 1 1. To avoid caking additionally not shown knockers may be provided, with which the wall of the reactor is vibrated, thereby dissolving adhering polymer particles and slip into the fluidized bed 1 1.

For gas supply for the operation of the fluidized bed 1 1, located below the fluidized bed 1 1, a gas distributor 17, through which the gas is injected into the fluidized bed 1 1.

Since gas is introduced into the reactor 1 both from above and from below, it is necessary to remove gas from the reactor 1 at a suitable position. For this purpose, at least one gas sampling point 19 is arranged at the transition from the central region 7 with a constant cross-section to the conically extending from bottom to top lower portion 9. In this case, the cylindrical central portion 7 protrudes with its wall in the upwardly conically widening lower portion 9, wherein the diameter of the conical lower portion 9 at this position is greater than the diameter of the central region 7. In this way, the wall of the middle Area 7 circumferential annular chamber 21 is formed, into which the gas flows and can be withdrawn through the at least one gas sampling point 19 which is connected to the annular chamber 21. The post-reacted polymer particles of the fluidized bed 1 1 are removed via a product removal point 23 in the fluidized bed.

Figure 2 shows a reactor for drop polymerization in an alternative embodiment. In contrast to the reactor for droplet polymerization 1 shown in FIG. 1, in the reactor 1 shown in FIG. 2 the device for turbulence elevation 31 is positioned above the device 5 for dropletizing the monomer solution. FIG. 2 also shows, by way of example, gas nozzles 35 for increasing the turbulence. By the gas jet 35 emerging from the gas jet 35, the turbulence in the gas flow is increased, the turbulence increasing at above the device for dropping 5 arranged gas nozzles 35 used at a higher position than in the variant shown in Figure 1 with gas nozzles 35 below the device for Dropping 5. When adjusting the turbulence, care must therefore be taken to ensure that the drops of monomer leaving the dropping device 5 do not violate the Dropping device 5 bounce and thus lead to a deposit formation. In particular, when using gas nozzles 35, the turbulence can be adjusted in a simple manner by changing the velocity of the gas leaving the gas nozzles 35. In order, in particular, to prevent a device for turbulence enhancement 31 from forming on the turbulence-increasing device 31 below, when the turbulence-increasing device 31 is arranged underneath the device for dripping 5, the individual flow obstacles or nozzles of the device for turbulence-increasing 31 are positioned such that they are interposed between the individual dropletizing devices. conditions of the device for dropping 5 are arranged. This is illustrated by way of example for the use of gas nozzles 35 as a device for turbulence increase 31 and dropletizing channels 25 as dripping devices of the device for dripping 5 in FIGS. 3 to 6.

FIG. 3 shows an arrangement of radially extending droplet channels of different lengths.

In a first embodiment, the device for dripping has radially extending channels 25. In this case, a portion of the channels 25 extends into the middle of the reactor 1. Another portion of channels 24 projects less far into the reactor 1, so that in particular in the outer regions of the reactor, where the distance between the radially extending to the center the reactor 1 protruding channels 25 is large, further channels 24 are provided, can be introduced through the monomer solution in the reactor 1. This allows a more uniform distribution of the drops over the entire reactor cross-section.

The individual gas nozzles 35, which are used to increase the turbulence, are positioned between the channels 24, 25. Here, the gas nozzles 25 are evenly distributed over the reactor cross-section for a uniform turbulence and thus a uniform gas flow in the reactor.

A corresponding star-shaped arrangement of the channels 25 is shown in FIG.

Both in the embodiment shown in Figure 3 and in that shown in Figure 4, it is possible to align the channels 24, 25 with an angle ß to the horizontal. For this purpose, it is particularly advantageous if the channels 24, 25 rise toward the center of the reactor. This orientation results in a more even distribution of the droplets in the reactor 1 and prevents premature contact of the droplets with the reactor wall.

Further possible arrangements of the channels are shown in FIGS. 5 and 6. In these, however, an arrangement having an angle β to the horizontal is difficult to realize, so that in this case the channels 25 preferably extend horizontally. Figure 5 shows an arrangement in rectangular division, in which the individual channels 25 are each arranged at an angle of 90 ° to each other, so that each rectangles, preferably squares are formed by the intersections 27 of the channels. FIG. 6 shows an arrangement in triangular division. Here, the channels 25 are each arranged at an angle of 60 ° to each other, so that 25 each equilateral triangles are formed by the intersections 27 of the channels. However, this also requires that the respective parallel channels always have the same distance.

Regardless of the arrangement of the channels 25 used as dropletizers, the flow obstacles or nozzles, for example the gas nozzles 35, are evenly distributed over the reactor cross-section between the dropletizers. In the case of a rectangular division or a triangular division, the position of the flow obstacles or nozzles is preferably in each case in the center of the rectangles or triangles formed by the channels 25.

The necessary supply of gas and / or liquid preferably takes place via lines 39, which in an arrangement as shown in FIGS. 3 and 4 extend between the channels 24, 25 or in the case of an arrangement as shown in FIGS 5 or 6, above the channels 25 run to prevent drops generated in the device 5 drops fall on the lines 39 and lead there to a deposit formation.

As an alternative to the embodiments shown here, it is of course also possible to arrange the channels so that the distance between parallel channels varies or the distance between the parallel channels is the same size, but the distances between the parallel channels arranged in different Direction, are different. In addition, it is also possible to arrange the channels at any other angle to each other.

However, in particular with a circular reactor cross section, the arrangements shown in FIGS. 3 and 4 are preferred. However, the number of channels may vary depending on the size of the reactor. In addition, it is possible to make the channels of different lengths, as shown in FIG. 3, so that they project into the reactor 1 at different distances. However, a rotationally symmetrical arrangement is always preferred.

The position of dropletizing plates 26, with which the channels for supplying the monomer solution are closed on its underside, and in which the holes are formed, through which the monomer solution is dropped into the reactor, is shown in Figures 3 to 6 by the dotted areas ,

According to the invention, the number of channels 24, 25 is chosen such that the ratio of the area covered by the channels 24, 25 or the droplet head in the reactor relative to the area defined by the circumference of a line along the outermost holes is smaller than 50%. This ensures that sufficient gas can flow past the channels 24, 25 and a sufficient contact between the gas and the channels 24, 25 leaving drops is realized. Another possibility for generating an increased turbulence in the gas flow is shown in FIG. Here, in contrast to the embodiments in Figures 1 to 6, the addition point for gas 13 is designed so that an increased turbulence is generated. For this purpose, the addition point for gas 13 comprises at least one perforated bottom 41, through which the gas is passed. The hole bottom has holes that have a hydraulic diameter of 5 to 200 cm, preferably from 10 to 100 cm. It is particularly advantageous if a plurality of perforated plates are arranged one above the other and at least the last hole bottom in the flow direction of the gas as described above has holes with a hydraulic diameter of 5 to 200 cm. The arrangement of the perforated plates is preferably carried out so that the holes of the individual perforated plates are not exactly on top of each other. This means that the centers of superimposed holes are not on a vertical axis.

The shape of the holes can be chosen arbitrarily. However, preferred are circular holes. In the design of the gas addition point 13 such that increased turbulence is generated, the gas flow already above the device 5 for dropletizing turbulence 33, which leads to a more homogeneous distribution of drops generated in the device 5 for droplet over the reactor cross-section , However, the turbulence increase should be localized and preferably act only in the region or below the dropletizing units. As a result, the desired improved mixing of the drying gas with the dripped monomer solution is ensured and the droplets are distributed more homogeneously over the reactor cross-section, without resulting in undesirable effects such as scale formation on the reactor wall.

A preferred embodiment of the device for turbulence increase is shown in FIG.

In contrast to the turbulence-increasing devices shown in FIGS. 1 and 2 with gas nozzles 35 directed downwards, in FIG. 8 the gas nozzles 35 are oriented vertically upwards. The gas nozzles 35 thus each leaves a gas jet 37 which is directed against the flow direction of the drying gas supplied via the point of addition of the gas 13. Due to the gas emerging from the gas nozzles 35 in the opposite direction to the flow direction of the drying gas, the turbulence 33 is generated in the region of the dropletizing device 5. Since the drying gas is the main gas flow, the total gas flow is directed downwards and the drying gas flow remains turbulent in the flow direction of the drying gas as it flows past the device 5 for dripping. Due to the orientation of the gas nozzles 35 vertically upwards, the flow turbulence is induced farther upstream of the device for dripping 5. As a result, the flow turbulence in the drying gas stream up to the device for dropping 5 can spread better across and thus more effectively and uniformly affect the exiting from the device for dropping 5 monomer solution.

Regardless of the arrangement of the dispensing devices, the flow obstructions or nozzles of the turbulence-increasing device 31 are always positioned so that no droplets are present. can fall on the flow obstacles or nozzles. Furthermore, the flow obstacles or nozzles are evenly distributed over the reactor cross-section to obtain a uniform gas flow and turbulence throughout the reactor cross-section to produce a uniform product.

example

The following example shows a comparison for the operation of the droplet polymerization reactor with and without turbulence generation in the gas flow. Results were used for the comparison, which were calculated using numerical flow simulation. In comparison, two cases are considered:

(1) Operation of a droplet polymerization reactor, as shown in FIG. 1, with 16 gas nozzles for turbulence elevation, wherein the gas nozzles are distributed uniformly over the circumference on two imaginary concentric circles with diameters of 3.8 and 5.8 m and arranged symmetrically with respect to the dropletizer channels are, and on each of the concentric circles 8 gas nozzles are positioned. For this purpose, 8 Vertropferkanäle are provided, which are arranged in a star shape according to the embodiment shown in Figure 4. The gas volume flow through all the nozzles together is 7500 Nm ³ / h. The nozzles have an opening diameter of 45 mm. The diameter in the middle part of the reactor with a constant hydraulic diameter is 10.3 m. The diameter of the reactor at the level of the Vertropfereinrichtungen is 7.2 m. The gas volume flow, which is fed in via the addition point for gas 13, is 175,000 Nm ³ / h. (2) Operation of the droplet polymerization reactor under the same conditions as in the first case but without turbulence nozzles and the additional gas flow supplied thereto.

FIG. 9 shows the course of the standard deviation of the particle temperature as a function of the particle residence time for the two calculated cases, wherein the course for the first case with gas nozzles for turbulence increase is shown with a dashed line and the profile for the second case without turbulence increase with a solid line. For this purpose, the particle dwell time in seconds and the ordinate the standard deviation are shown on the abscissa. The higher the standard deviation, the more heterogeneous is the particle heating up. In the residence time range of 0 to 6 s, the standard deviation in the case of operation with turbulence nozzles is up to 5 K lower than in the case without turbulence nozzles. The residence time of 6 seconds corresponds to the time it takes for the particles to reach the fluidized bed at the lower end of the reactor.

FIG. 10 shows the gas temperature of the gas surrounding the particles along their trajectory as a function of the particle residence time. Again, the particle residence time is shown in seconds on the abscissa. The ordinate shows the temperature of the gas surrounding the particles in ° C. Again, the first case with gas nozzles for turbulence increase with a dashed line and the second case without additional turbulence increase with a solid line shown. In the case of operation with gas nozzles for turbulence increase, the gas temperature decreases faster, which means that the particles are heated on average faster. Both the standard deviation of the particle temperature and the gas temperature of the gas surrounding the particles along their trajectory show that the drying of the particles during operation with gas nozzles to increase the turbulence is more uniform and faster, which causes the particles to the fluidized bed at the bottom Reach the end of the reactor in a drier state and thus have a lower tendency to agglomerate.

LIST OF REFERENCE NUMBERS

I reactor for drop polymerization

3 reactor head

5 device for dripping

7 middle range

9 lower area

I I fluidized bed

12 monomer feed

13 addition point for gas

15 Position of the outermost holes in relation to the fluidized bed

17 gas distributor

19 gas sampling point

21 annular chamber

23 product delivery point

24 channel

25 channel

26 droplet plate

27 Intersection of the channels

29 reactor axis

31 device for turbulence increase

33 turbulence

35 gas nozzles

37 gas jet

39 line

41 hole bottom

Claims

claims

Apparatus for the preparation of powdery polymers, comprising a drop polymerization reactor (1) with a device for dropping (5) a monomer solution for the preparation of the polymer, the dropping device (5) having holes through which the monomer solution is introduced Loading point (13) for a gas above the device for dripping (5), at least one gas sampling point (19) at the periphery of the reactor (1) and a fluidized bed (1 1), characterized in that at least one of the following features is fulfilled: im A device for turbulence increase (31) in the gas flow is arranged in the region of the device for atomizing (5) of the monomer solution, a device for turbulence increase in the gas flow is arranged in the region of the point of addition (13) for the gas,

the gas addition point (13) is designed to produce increased turbulence.

Apparatus according to claim 1, characterized in that the device for turbulence increase (31) comprises flow obstacles.

Apparatus according to claim 2, characterized in that the flow obstacles comprise a hole bottom having holes with a diameter of 5 to 200 cm.

Device according to one of claims 1 to 3, characterized in that the device for turbulence increase (31) comprises gas nozzles (35), gas / liquid nozzles or liquid nozzles.

Apparatus according to claim 4, characterized in that the gas / liquid nozzles or liquid nozzles used for turbulence increase are part of the device for dropping (5) the monomer solution.

Apparatus according to claim 4, characterized in that the gas nozzles (35) used for turbulence increase are aligned in the direction of the addition point (13) for gas, so that from the gas nozzles (35) effluent gas flow of the gas flow from the addition point (13) for gas is opposite.

Device according to one of claims 4 to 6, characterized in that the An¬ Number of gas nozzles used for turbulence increase (35), gas / liquid nozzles or

Liquid nozzles is 0.02 to 2 per square meter reactor cross-sectional area.

8. Vornchtung according to one of claims 1 to 7, characterized in that the device for turbulence increase (31) in a range between 2 m above and 2 m below the device for dripping (5) and / or up to 2 m below the point of addition (13) is arranged for gas.

9. Device according to one of claims 1 to 8, characterized in that the

Flow obstacles, gas nozzles (35), gas / liquid nozzles or liquid nozzles of the device for turbulence increase (31) are arranged at different heights in the reactor (1).

10. Device according to one of claims 1 to 9, characterized in that the addition point (13) for gas comprises at least one perforated bottom having holes with a diameter of 5 to 200 cm. 1 1. Process for the preparation of pulverulent polymers in a device according to one of Claims 1 to 10, comprising the following steps:

(a) dropping a monomer solution in the dropper device (5), wherein the generated monomer droplets fall through the reactor (1) and the monomer at least partially reacts with the polymer to form particles,

(b) supplying gas via the gas addition point (13) above the dropper device (5) so as to generate a gas flow in the reactor (1) from top to bottom,

(C) collecting the particles produced in step (a) in the fluidized bed (1 1), wherein in the fluidized bed (1 1) the reaction to the poly (meth) acrylate in the individual particles is completed and optionally post-crosslinking, (i ) Removal of the particles from the fluidized bed (1 1), characterized in that in the gas flow in the region of the device for dripping (5) an increase in the flow turbulence takes place. 12. The method according to claim 1 1, characterized in that to increase turbulence gas nozzles (35) are used and the ratio of the pulse current of the gas through all nozzles (35) gas supplied to the pulse stream of the addition point (13) for gas supplied gas in the range of 0.1 to 50 lies. 13. The method according to claim 1 1, characterized in that the turbulence increase

Gas / liquid nozzles or liquid nozzles are used and the ratio of the pulse current generated by all nozzles, to the pulse current generated in the device for dropping (5) is in the range between 0.1 and 100.

14. The method according to claim 1 1 or 12, characterized in that for increasing the turbulence gas nozzles (35) are used and the exit velocity of the gas from the gas nozzles (35) in the range of 5 to 1000 m / s.

15. The method according to claim 14, characterized in that one of the gas nozzles (35) exiting gas flow of the gas flow generated in step (b) in the reactor (1) is directed opposite. 16. The method according to any one of claims 1 1 to 15, characterized in that the gas addition point (13) comprises at least one perforated bottom having holes with a diameter of 5 to 200 cm, so that the gas with increased turbulence from the point of addition (13) for gas leaks. 17. The method according to any one of claims 1 1 to 16, characterized in that the powdery polymer is a poly (meth) acrylate.