DEVICE FOR PRODUCING POLY(METH)ACRYLATE IN POWDER FORM

Abstract

The invention relates to an apparatus for producing pulverulent poly(meth)acrylate, comprising a reactor for droplet polymerization having an apparatus for dropletization of a monomer solution for the preparation of the poly(meth)acrylate having holes through which the monomer solution is introduced, an addition point for a gas above the apparatus for dropletization, at least one gas withdrawal point on the circumference of the reactor, a fluidized bed and an apparatus for product discharge from the fluidized bed. The apparatus for product discharge comprises a discharge apparatus, with a backup segment (39) disposed above the discharge apparatus.

Claims

1. An apparatus for producing pulverulent poly(meth)acrylate, comprising a reactor (1) for droplet polymerization having an apparatus (5) for dropletization of a monomer solution for the preparation of the poly(meth)acrylate having holes through which the monomer solution is introduced, an addition point (13) for a gas above the apparatus (5) for dropletization, at least one gas withdrawal point (19) on the circumference of the reactor (1), a fluidized bed (11) and an apparatus (33) for product discharge from the fluidized bed (11), wherein the apparatus (33) for product discharge comprises a discharge apparatus (49), with a backup segment (39) disposed above the discharge apparatus (49).

2. The apparatus according to claim 1, wherein the backup segment (39) has an upper sensor for detecting a maximum fill level (43) and a lower sensor for detecting a minimum fill level (47).

3. The apparatus according to claim 2, wherein a closed-loop fill level control system is included, in which the upper sensor detects a first upper fill level (41) and, when the latter is attained, the feed is reduced, and detects a second upper fill level (43) and, when the latter is attained, the feed is closed, and the lower sensor detects a first lower fill level (45) and, when the latter is attained, the product flow out of the apparatus (33) for product discharge is reduced, and detects a second lower fill level (47) and, when the latter is attained, the apparatus (33) for product discharge is closed, such that no product is withdrawn.

4. The apparatus according to claim 1, wherein a closure element (35) is disposed above the backup segment (39).

5. The apparatus according to claim 1, wherein a solids comminutor (37) is disposed above the backup segment (39).

6. The apparatus according to claim 5, wherein the solids comminutor (37) is a lump breaker.

7. The apparatus according to claim 6, wherein the lump breaker is a finger breaker having a breaking grid and a rotating breaking tool.

8. The apparatus according to claim 1, wherein the discharge apparatus (49) is a star feeder, a flap, a screw conveyor or a segmented ball valve.

9. The apparatus according to claim 1, wherein a gas supply (48) is disposed in the backup segment (39) in order to introduce gas into the backup segment (39).

10. The apparatus according to claim 1, wherein the apparatus (33) for product discharge is heatable.

11. The apparatus according to claim 10, wherein the apparatus (33) for product discharge is heated by virtue of the solids comminutor, the backup segment and/or the discharge apparatus having electrical heating, a jacket or externally mounted heating coils, it being possible for a heating medium to flow through the jacket or the heating coils.

12. The apparatus according to claim 1, wherein the gas withdrawal point (19) is connected to an apparatus for fine dust removal (27) and the apparatus for fine dust removal (27) has a solids discharge comprising a discharge apparatus (53) and, above the discharge apparatus (53), a closure element (51).

13. The apparatus according to claim 12, wherein the discharge apparatus (53) from the solids discharge of the apparatus for fine dust separation (27) is a star feeder, a flap, a conveying screw or a segmented ball valve.

14. The apparatus according to claim 12, wherein the closure element (51) in the solids discharge of the apparatus for fine dust separation (27) is a flap, a slide vane, a segmented ball valve or another valve.

15. The apparatus according to claim 12, wherein at least one fill level sensor (55) is positioned above the closure element (51).

16. The apparatus according to claim 1, wherein the apparatus (33) for product discharge and/or the solids discharge of the apparatus for fine dust removal (27) open(s) into a suction line which pneumatically conveys the pulverulent poly(meth)acrylate onward.

Description

[0036] The sole FIGURE shows a schematic diagram of the apparatus of the invention.

[0037] A reactor 1 for droplet polymerization comprises a reactor head 3 which accommodates 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.

[0038] 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 the 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 site 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 between the individual droplets and coalescence thereof to form larger droplets.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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 part 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.

[0044] 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.

[0045] 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 duct 21 which encloses 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 duct 21.

[0046] The further-reacted polymer particles of the fluidized bed 11 are withdrawn via a product withdrawal point 23 in the region of the fluidized bed.

[0047] In order to remove any particles entrained by the gas withdrawal point 19 from the gas stream, the gas withdrawal point 19 is connected via a gas duct 25 to an apparatus for fine dust removal 27, for example a filter or a cyclone, preferably a cyclone. From the cyclone, it is then possible for the solid particles separated from the gas to be withdrawn via a solids withdrawal, and the gas which has been freed of solids via a gas takeoff 31.

[0048] For homogeneous gas withdrawal from the annular duct 21, it is preferable when several gas withdrawal points 19 are provided in homogeneous distribution over the circumference of the annular duct 21. In this case, it is possible that each gas withdrawal point 19 is connected to an apparatus for fine dust removal 27 or, alternatively, that each of several gas withdrawal points 19 are passed into an apparatus for fine dust removal 27. Preference is given, however, to such a configuration that every gas withdrawal point 19 is connected to a separate apparatus for fine dust removal 27.

[0049] In order to minimize the amount of inert gas which is discharged from the reactor 1 with the product or, according to the pressure gradient that exists, the amount of air which penetrates into the reactor, and thus to reduce the inert gas consumption for the process, the reactor 1 comprises an apparatus 33 for product discharge, comprising a backup segment 39 and a discharge apparatus 49. Product accumulates in the backup segment, and the backup of the product in the backup segment 39 results in compaction and reduction in the gas volume in the interspaces between the product particles. In addition, the backed-up product has a sealing effect, such that the gas volume which can flow out through the discharge apparatus 49 on withdrawal of the product is likewise minimized; suitable discharge apparatuses 49 are, for example, star feeders, flaps, conveying screws, ball valves or segmented ball valves.

[0050] In order to assure the sealing effect of the product in the backup segment 39, the latter has, in the preferred embodiment shown here, sensors for determining a first upper fill level 41, a second upper fill level 43, a first lower fill level 45 and a second lower fill level 47. For this purpose, on attainment of the first upper fill level, the withdrawal is accelerated and, on attainment of the second upper fill level, it is possible, for example with the aid of a closure element 35, to interrupt the supply of product to the backup segment, in order to prevent overfilling. In order, in addition, to prevent the fill level in the backup segment 39 from becoming too low, meaning that the sealing effect by the backed-up product can no longer be assured, on attainment of the first lower fill level 45, the withdrawal is slowed down, for example by reducing the speed of a star feeder used as discharge apparatus 49, and stopped when the second lower fill level 47 is attained. This ensures that product is always present in the backup segment.

[0051] To prevent bridge formation by the product backed up in the backup segment 39, it is possible to introduce gas into the backup segment 39 via a gas supply 48. The gas loosens the product in the backup segment 39, such that it cannot block the backup segment 39. In addition, use of dry gas achieves the effect that the gas atmosphere in the backup segment does not become too moist and hence condensation is prevented.

[0052] In order to comminute large particles which can arise, for example, through agglomeration of the product particles or as a result of caked material falling down, it is advantageous, as shown here, to use a solids comminutor 37, for example a lump breaker, above the backup segment 39. The comminution of lumps and agglomerates in the solids comminutor 37 also prevents the lumps or agglomerates from remaining suspended in the backup segment and blocking it or the discharge apparatus 49. When a solids comminutor 37 is provided, it is preferably positioned between the closure element 35 and the backup segment 39.

[0053] In order, in addition, to prevent inert gas from being able to exit via the solids discharge of the apparatus for fine dust separation 27 or, according to the pressure gradient that exists, air from being able to penetrate into the reactor, the solids discharge preferably likewise has a closure element 51 and a discharge apparatus 53. As long as the fill level in the apparatus for fine dust separation 27 is low, the closure element 51 remains closed. This prevents solids from being discharged and inert gas from being able to escape with the solids discharged or, according to the pressure gradient that exists, air and oxygen from being able to penetrate into the reactor. In addition, the effect of the closure element 51 is that the solids are backed up in the apparatus for fine dust removal 27, such that it likewise has a sealing effect. Only on attainment of a particular fill level, which can be detected, for example, with a fill level sensor 55, does the closure element 51, for example a valve, a slide vane, a ball valve, a segmented ball valve or a flap, open, and the solids can arrive at the discharge apparatus 53. The discharge apparatus 53 is, like the discharge apparatus 49 of the apparatus 33 for product withdrawal as well, preferably a star feeder, a flap, a conveying screw, a ball valve or a segmented ball valve.

[0054] As a result of the additional use of the closure element, the solids removed in the apparatus for fine dust removal 27 arrive in compacted form at the discharge apparatus 53, and so this minimizes the proportion of gas which can escape via the solids discharge of the apparatus for fine dust removal 27 in the solids withdrawal.

LIST OF REFERENCE NUMERALS

[0055] 1 reactor [0056] 3 reactor head [0057] 5 apparatus for dropletization [0058] 7 middle region [0059] 9 lower region [0060] 11 fluidized bed [0061] 12 monomer feed [0062] 13 addition point for gas [0063] 15 position of the outermost holes in relation to the fluidized bed 11 [0064] 17 gas distributor [0065] 19 gas withdrawal point [0066] 21 annular duct [0067] 23 product withdrawal point [0068] 25 gas duct [0069] 27 apparatus for fine dust removal [0070] 29 solids withdrawal [0071] 31 gas takeoff [0072] 33 apparatus for product discharge [0073] 35 closure element [0074] 37 solids comminutor [0075] 39 backup segment [0076] 41 first upper fill level [0077] 43 second upper fill level [0078] 45 first lower fill level [0079] 47 second lower fill level [0080] 48 gas supply [0081] 49 discharge apparatus [0082] 51 closure element [0083] 53 discharge apparatus [0084] 55 fill level sensor