Apparatus for Production of Pulverulent Poly(Meth)Acrylate

Abstract

An apparatus for production of pulverulent poly(meth)acrylate, comprising a reactor or droplet polymerization, having an apparatus for dropletization of a monomer solution for the production of the poly(meth)acrylate, having holes through which the solution is dropletized, an addition point for a gas above the apparatus for dropletization, at least one gas withdrawal point on the periphery of the reactor and a fluidized bed. The outermost holes through which the solution is dropletized are positioned such that a droplet falling vertically downward falls into the fluidized bed and the hydraulic diameter at the level of the midpoint between the apparatus for dropletization and the gas withdrawal point is at least 10% greater than the hydraulic diameter of the fluidized bed.

Claims

1. An apparatus for production of pulverulent poly(meth)acrylate, comprising a reactor (1) for droplet polymerization, having an apparatus for dropletization (5) of a monomer solution for the production of the poly(meth)acrylate, having holes through which the solution is dropletized, an addition point for a gas (13) above the apparatus for dropletization (5), at least one gas withdrawal point (19) on the periphery of the reactor (1) and a fluidized bed (11), wherein the outermost holes through which the solution is dropletized are positioned such that a droplet falling vertically downward falls into the fluidized bed (11) and the hydraulic diameter at the level of the midpoint between the apparatus for dropletization (5) and the gas withdrawal point (19) is at least 10% greater than the hydraulic diameter of the fluidized bed (11), wherein the reactor (1) widens conically above the fluidized bed (11) to its maximum hydraulic diameter and the at least one gas withdrawal point (19) is positioned at the transition from the conical widening above the fluidized bed (11) to the cylindrical wall of the reactor (1), wherein at the upper end of the widening the diameter of the conical widening above the fluidized bed (11) is greater than the diameter of the reactor wall above the conical widening, wherein the reactor wall projects into the conical widening so as to form an annular gap in which the gas withdrawal point is positioned between the conical widening and the reactor wall.

2. The apparatus according to claim 1, wherein the head (3) of the reactor (1) takes the form of a frustocone and the apparatus for dropletization (5) is positioned in the frustoconical head (3) of the reactor (1).

3. The apparatus according to claim 1 or 2, wherein the ratio of the area in the reactor (1) covered by the apparatus for dropletization (5) relative to the area enclosed by a line connecting the outermost holes is less than 50%.

4. The apparatus according to claim 1, wherein the apparatus for dropletization (5) of the monomer solution has channels (25) arranged in a star shape, with the holes formed at the base thereof.

5. The apparatus according to claim 4, wherein at least the holes at the edge of the channel (25) are formed in such a way that the monomer solution exits from the holes at an angle relative to the axis (29) of the reactor (1).

6. The apparatus according to claim 4, wherein the channel (25) is connected at its base to at least one dropletizer plate in which the holes for addition of the monomer solution are formed.

7. The apparatus according to claim 6, wherein the dropletizer plates are angled along their longitudinal axis at the base thereof.

8. The apparatus according to claim 6, wherein the holes of the dropletizer plates along the longitudinal axis are lower in the middle than at the edges.

9. The apparatus according to claim 6, wherein the holes of the dropletizer plates are arranged in a plurality of rows of holes.

10. The apparatus according to claim 1, wherein the holes in the dropletizer plates have a diameter in the range from 25 to 500 μm.

11. (canceled)

12. (canceled)

13. (Cancellled)

14. The apparatus according to claim 5, wherein the channel (25) is connected at its base to at least one dropletizer plate in which the holes for addition of the monomer solution are formed.

15. The apparatus according to claim 7, wherein the dropletizer plates are angled along their longitudinal axis at the base thereof.

16. The apparatus according to claim 7, wherein the holes of the dropletizer plates are arranged in a plurality of rows of holes.

17. The apparatus according to claim 8, wherein the holes of the dropletizer plates are arranged in a plurality of rows of holes.

Description

[0038] Working examples of the invention are shown in the figures and are more particularly described in the description which follows.

[0039] The figures show:

[0040] FIG. 1 a longitudinal section through a reactor for droplet polymerization,

[0041] FIG. 2 a longitudinal section through the reactor head,

[0042] FIG. 3 an arrangement of dropletizer channels in a first embodiment,

[0043] FIG. 4 an arrangement of dropletizer channels in a second embodiment,

[0044] FIG. 5 an arrangement of dropletizer channels in a third embodiment,

[0045] FIG. 6 a cross section through a dropletizer channel in a first embodiment,

[0046] FIG. 7 a cross section through a dropletizer channel in a second embodiment,

[0047] FIG. 8 a cross section through a dropletizer channel in a third embodiment.

[0048] FIG. 1 shows a longitudinal section through a reactor configured in accordance with the invention.

[0049] A reactor 1 for droplet polymerization comprises a reactor head 3 in which there is accommodated an apparatus for dropletization 5, a middle region 7 in which the polymerization reaction proceeds, and a lower region 9 having a fluidized bed 11 in which the reaction is concluded.

[0050] For performance of the polymerization reaction to prepare the poly(meth)acrylate, the apparatus for dropletization 5 is supplied with a monomer solution via a monomer feed 12. When the apparatus for dropletization 5 has a plurality of channels, it is preferable to supply each channel with the monomer solution via a dedicated monomer feed 12. The monomer solution exits through holes, which are not shown in FIG. 1, in the apparatus for dropletization 5 and disintegrates into individual droplets which fall downward within the reactor. Through a first addition point for a gas 13 above the apparatus for dropletization 5, a gas, for example nitrogen or air, is introduced into the reactor 1. This gas flow supports the disintegration of the monomer solution exiting from the holes of the apparatus for dropletization 5 into individual droplets. In addition, the gas flow promotes lack of contact of the individual droplets and coalescence thereof to larger droplets.

[0051] In order firstly to make the cylindrical middle region 7 of the reactor very short and additionally to avoid droplets hitting the wall of the reactor 1, the reactor head 3 is preferably conical, as shown here, in which case the apparatus for dropletization 5 is within the conical reactor head 3 above the cylindrical region. Alternatively, however, it is also possible to make the reactor cylindrical in the reactor head 3 as well, with a diameter as in the middle region 7. Preference is given, however, to a conical configuration of the reactor head 3. The position of the apparatus for dropletization 5 is selected such that there is still a sufficiently large distance between the outermost holes through which the monomer solution is supplied and the wall of the reactor to prevent the droplets from hitting the wall. For this purpose, the distance should at least be in the range from 50 to 1500 mm, preferably in the range from 100 to 1250 mm and especially in the range from 200 to 750 mm. It will be appreciated that a greater distance from the wall of the reactor is also possible. This has the disadvantage, however, that a greater distance is associated with poorer exploitation of the reactor cross section.

[0052] The lower region 9 concludes with a fluidized bed 11, into which the polymer particles formed from the monomer droplets fall during the fall. In the fluidized bed, further reaction proceeds to give the desired product. According to the invention, the outermost holes through which the monomer solution is dropletized are positioned such that a droplet falling vertically downward falls into the fluidized bed 11. This can be achieved, for example, by virtue of the hydraulic diameter of the fluidized bed being at least as large as the hydraulic diameter of the area which is enclosed by a line connecting the outermost holes in the apparatus for dropletization 5, the cross-sectional area of the fluidized bed and the area formed by the line connecting the outermost holes having the same shape and the centers of the two areas being at the same position in a vertical projection of one onto the other. The outermost position of the outer holes relative to the position of the fluidized bed 11 is shown in FIG. 1 with the aid of a dotted line 15.

[0053] In order, in addition, to avoid droplets hitting the wall of the reactor in the middle region 7 as well, the hydraulic diameter at the level of the midpoint between the apparatus for dropletization and the gas withdrawal point is at least 10% greater than the hydraulic diameter of the fluidized bed.

[0054] The reactor 1 may 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.

[0055] Above the fluidized bed 11, the diameter of the reactor 1 increases in the embodiment shown here, such that the reactor 1 widens conically from the bottom upward in the lower region 9. This has the advantage that polymer particles formed in the reactor 1 that hit the wall can slide downward into the fluidized bed 11 along the wall. To avoid caking, it is additionally possible to provide tappers, not shown here, on the outside of the conical section of the reactor, with which the wall of the reactor is set in vibration, as a result of which adhering polymer particles are detached and slide into the fluidized bed 11.

[0056] For gas supply for the operation of the fluidized bed 11, a gas distributor 17 present beneath the fluidized bed 11 blows the gas into the fluidized bed 11.

[0057] Since gas is introduced into the reactor 1 both from the top and from the bottom, it is necessary to withdraw gas from the reactor 1 at a suitable position. For this purpose, at least one gas withdrawal point 19 is disposed at the transition from the middle region 7 having constant cross section to the lower region 9 which widens conically from the bottom upward. In this case, the wall of the cylindrical middle region 7 projects into the lower region 9 which widens conically in the upward direction, the diameter of the conical lower region 9 at this position being greater than the diameter of the middle region 7. In this way, an annular chamber 21 which surrounds the wall of the middle region 7 is formed, into which the gas flows and can be drawn off through the at least one gas withdrawal point 19 connected to the annular chamber 21.

[0058] The further-reacted polymer particles of the fluidized bed 11 are withdrawn by a product withdrawal point 23 in the region of the fluidized bed.

[0059] FIG. 2 shows a longitudinal section through the reactor head.

[0060] In the embodiment shown here, the reactor head 3 is conical. The apparatus for dropletization 5 comprises individual channels 25 which project into the reactor 3 in a star shape from the outside to the middle of the reactor head 3. In order to promote lack of impact of the droplets leaving the apparatus for dropletization 5 with the wall of the reactor 1, the channels in the embodiment shown here are arranged in the reactor head 3 at an angle 13 to the horizontal. The angle β is preferably in the range from 0° to 20°, more preferably in the range from 0° to 15°, especially preferably in the range from 0° to 10° and especially in the range from 0° to 5°. By virtue of the corresponding alignment of the channels, the droplets exit from the channels at an angle pointing toward the middle of the reactor, such that the risk of droplets being able to arrive at the wall of the reactor 1 and cake thereon is minimized further.

[0061] A corresponding star-shaped arrangement of the channels 25 is shown in FIG. 3. Further possible arrangements of the channels are shown in FIGS. 4 and 5. In these, however, an arrangement with an angle β to the horizontal can be achieved only with difficulty, such that the channels 25 in this case preferably run horizontally. FIG. 4 shows an arrangement in rectangular pitch, in which the individual channels 25 each arranged at an angle of 90° to one another, such that the points of intersection 27 of the channels each form rectangles, preferably squares.

[0062] FIG. 5 shows an arrangement in triangular pitch. The channels 25 here are each arranged at an angle of 60° relative to one another, such that the points of intersection 27 of the channels 25 each form equilateral triangles. However, this additionally requires the channels that run parallel in each case always to have an equal separation.

[0063] As an alternative to the embodiments shown here, it is of course also possible to arrange the channels such that the distance between channels arranged in parallel varies, or the distance between the channels arranged in parallel is equal in each case but the distances between the channels that are arranged in parallel and run in different directions are different. In addition, it is also possible to arrange the channels at any other angle relative to one another.

[0064] Especially in the case of a circular reactor cross section, however, the star-shaped arrangement shown in FIG. 3 is preferred. In this case, however, the number of channels may vary as a function of the circumference of the reactor. In addition, it is possible to configure the channels with different lengths, such that they project into the reactor 1 to different extents. However, a rotationally symmetrical arrangement is always preferred.

[0065] The position of dropletizer plates 26 which conclude the channels for supply of the monomer solution at the base thereof, and in which the holes through which the monomer solution is dropletized into the reactor are formed, is shown in FIGS. 3 to 5 by the dotted areas.

[0066] FIGS. 6, 7 and 8 show cross sections through the channels 25 in different embodiments.

[0067] In order to obtain a homogeneous droplet distribution over the reactor cross section, it is preferable when at least the droplets that are formed in a channel in the outer holes exit at an angle to the vertical, i.e. to the reactor axis. For this purpose, it is possible, for example, to configure the region of the channel in which the holes are formed, as shown in FIG. 6, in the form of a circle segment. As a result of this, the angle a at which the monomer solution exits in relation to the reactor axis 29 increases from the middle of the channel outward.

[0068] Alternatively, it is also possible, as shown in FIG. 7, to align the channel base in which the holes are formed at an angle to the horizontal, in which case, for holes at right angles to the channel base 31, the angle a at which the droplets exit relative to the reactor axis corresponds to the angle a of the channel base to the horizontal. Another possibility is a configuration in which, in addition to the angled regions of the channel base 31, a middle base region 33 runs horizontally.

[0069] In order to enable simple cleaning of the holes, it is advantageous when the holes are formed in dropletizer plates which are positioned at correspondingly configured orifices in the base of the channels 25. The dropletizer plates can then be deinstalled for cleaning and replaced by clean dropletizer plates. In this case, the dropletizer plates are preferably configured either in the form of a circle segment or in angled form, in order that a base profile of the channel 25 as shown in FIGS. 6 to 8 can be achieved.

[0070] Especially in the case of a star-shaped arrangement of the channels, it is additionally preferable when the angle at which the monomer solution exits increases from the middle of the reactor outward.

[0071] As well as the circular cross section shown here, it is also possible to configure the channels 25 with any other cross section. Especially when dropletizer plates are used, it is particularly preferable to form the channels 25 with a rectangular cross section. In this case, the channel may be sealed at the top by a removable lid, and the dropletizer plates may be removed and exchanged in a simple manner after removal of the lid.

LIST OF REFERENCE NUMERALS

[0072] 1 reactor [0073] 3 reactor head [0074] 5 apparatus for dropletization [0075] 7 middle region [0076] 9 lower region [0077] 11 fluidized bed [0078] 12 monomer feed [0079] 13 addition point for gas [0080] 15 position of the outermost holes in relation to the fluidized bed 11 [0081] 17 gas distributor [0082] 19 gas withdrawal point [0083] 21 annular chamber [0084] 23 product withdrawal point [0085] 25 channel [0086] 26 dropletizer plate [0087] 27 point of intersection [0088] 29 reactor axis [0089] 31 channel base [0090] 33 middle region of base