EP1631538A1

EP1631538A1 - Depolymerization method and device

Info

Publication number: EP1631538A1
Application number: EP04722182A
Authority: EP
Inventors: Egbert Schöla; Mojmir Ruzicka
Original assignee: Roehm GmbH Darmstadt
Current assignee: Roehm GmbH Darmstadt
Priority date: 2003-06-03
Filing date: 2004-03-20
Publication date: 2006-03-08
Also published as: CA2527969A1; WO2004106277A1; CN1812957A; CN100415708C; JP2006526582A; BRPI0411093A; ZA200509808B; KR20060021342A; RU2355675C2; DE10325251A1; MXPA05013109A; RU2005141291A

Abstract

The invention concerns the recovery of monomeric esters of substituted or unsubstituted acrylic acid or of monomers containing styrene from polymer material (66) containing corresponding structural units. According to the invention, the polymer material is brought into contact with a heat transfer medium inside a heated reactor (51). The heat transfer medium and the polymer material (66) are agitated inside the reactor (51), and gas, which forms inside the reactor (51) and which contains the monomer, is drawn out of the reactor (51). The heat transfer medium contains a multitude of spherical particles (67), which has been proven to be particularly advantageous for achieving high yields and purity of the monomer to be recovered.

Description

Process and arrangement for depolymerization

description

The invention relates to a method and an arrangement for the recovery of monomeric esters of substituted or unsubstituted acrylic acid, of styrene and / or of monomeric styrene derivatives from polymer material having corresponding structural units.

Acrylate polymers, which mainly include acrylic glasses made from polymethyl methacrylate (PMMA), are used, among other things, to manufacture durable consumer goods. Molding processes are often used for this purpose, in the course of which waste polymer is obtained. For this reason, but also for the recycling of used polymeric waste materials, it makes sense to process it. The same applies to polystyrene and to styrene-containing copolymers and to their processing. Acrylate polymers, especially PMMA, polystyrene and styrene-containing copolymers can advantageously be completely broken down into corresponding monomers again at certain temperatures and pressures.

In the introduction to the description of DE 198 43 112 A1, a continuous process for PMMA depolymerization is described, in which the plastic is placed in a hot extruder in which two closely intermeshing screws rotate with a self-cleaning effect. The PMMA depolymerizes due to the thermal and mechanical shear in the extruder. The resulting methyl methacrylate (MMA) is drawn off and condensed in the gas phase via a degassing dome. The MMA content in the condensate fluctuates between 89 percent and 97 percent with this process, the yield of MMA is less than 97 percent. In this process, the PMMA is heated in the extruder via jacket walls. However, as the reactor volume increases, the ratio between the outer surface (and thus the heatable wall surface) and the reactor volume to be heated deteriorates. For large systems on an industrial scale, very high wall temperatures are required, or it has to be done with one Decline in yield can be expected. High wall temperatures can lead to local overheating, which in turn can lead to the formation of undesirable by-products which affect the purity of the monomer.

Furthermore, it is also known from the introduction to DE 198 43 112 A1 to depolymerize PMMA by means of fluidized bed pyrolysis. Quartz sand with a grain size of 0.3 to 0.7 mm is used as the eddy material. To maintain the fluidized bed flow, however, an elaborate fluidic system is required.

In DE 198 43 112 A1 it is proposed to bring the polymer material in contact with hot mechanically swirled solid (heat transfer medium) in a reactor and to discharge and condense the vapors produced. The already hot heat transfer medium is fed continuously at one end of the reactor and the cooled heat transfer medium is discharged at the other end. Inorganic fine-grained solids with a grain size between 0.1 and 5 millimeters or naturally occurring or synthetically produced oxides based on silicon, aluminum, magnesium, zirconium or also mixtures of these elements are proposed as heat carriers.

In this process, therefore, a separate heating device, separate from the reactor, and a device for introducing and discharging the heat transfer medium into and out of the reactor are required. The discharge of the heat transfer medium from the reactor must also be coordinated with the residence time of the polymer material and thus with the dynamics of the depolymerization in order to obtain the desired yield of monomer.

It is an object of the present invention to provide a method and an arrangement for the recovery of monomeric esters of substituted or unsubstituted acrylic acid, of styrene and / or of monomeric styrene derivatives from polymer material having corresponding structural units, which make it possible with little outlay in terms of process technology to obtain an effective heat transfer to the polymer material and a largely homogeneous temperature distribution at least in partial areas of the reactor space.

In the process according to the invention, the polymer material is brought into contact with a heat transfer medium in a heated reactor, the heat transfer medium and the polymer material are moved in the reactor and gas produced in the reactor is discharged from the reactor which contains the monomer. Surprisingly, it has been found that the depolymerization leads to good results even without complex fluidized bed technology if the heat transfer medium has a large number of spherical particles.

Accordingly, it is proposed in the arrangement according to the invention to provide such a large number of spherical particles in a heatable reactor for generating the monomer gas. In this case, a movement device is provided for moving a material to be moved that has the spherical particles and the polymer material in the reactor.

The surprising effect of the spherical particles to the depolymerization is probably due to the fact that the balls (z. B. Heating and / or moving means) particularly easily against each other, against ⁰ surfaces of the reactor and any disposed therein means against differently shaped particles as well as against the polymeric material are displaceable and therefore mix particularly well with one another and with parts of the polymer material. Therefore, an effective heat transfer from the heater to the polymer material and a largely homogeneous temperature distribution can be achieved at least in some areas of the reactor space.

In experiments, it has proven advantageous for the size of the balls if the diameter is in the range from 0.075 mm to 0.25 mm, preferably in the range from 0.1 to 0.2 mm. The individual has in this size range Ball on the one hand still has a considerable heat capacity for depolymerization and on the other hand - like a particle of a liquid - it is particularly easy to move.

The movement device can have different configurations. In particular, all variants familiar to the person skilled in the art come into consideration, such as, for. B. moving or rotating walls or moving other parts of the reactor. The movement device can also have, for example, a part or more parts which carry out a mechanical oscillation and / or a continuously continued linear (also curved) movement and thereby generate and / or maintain a movement of the material to be moved in the reactor. Movement devices with one or more rotating shafts, which are in particular provided with blade-like curved and / or other mixing tools, are preferred. The wave (s) can be z. B. extend in the horizontal or vertical direction. Favorable for a good mixing result is e.g. B. a mixer with a shaft extending in the vertical direction in a reactor vessel to which at least one mixing tool protruding in the radial direction of the shaft is attached. This embodiment allows a continuous movement of at least part of the goods to be moved, a constant mixing movement taking place within the goods to be moved due to the spherical particles.

The spherical particles preferably remain in the reactor during the depolymerization and are not - as described in DE 198 43 112 A1 - fed to one end of the reactor and discharged at an opposite end. Remaining in the reactor considerably simplifies the process. In this case, too, the relatively complex and loss-prone heating of the heat carrier outside the reactor described in DE 198 43 112 A1 can be avoided (see the following paragraph). However, the invention is not limited to the fact that the spherical particles remain in the reactor. With other embodiments of the invention, thorough mixing can be achieved in a simple manner compared to conventional heat transfer media or the same mixing can be achieved with simpler means. In particular, lower drive energies and a correspondingly less powerful movement device and a lower heating output are sufficient. Local overheating with the negative effects mentioned above is avoided.

In a preferred embodiment there is direct, preferably electrical heating of the reactor or at least parts of the reactor. For example, an inwardly facing surface of an outer wall of the reactor and / or at least part of a movement device arranged in the reactor is heated. In particular, at least a part of the reactor or within the reactor is connected in a heat-conducting manner to a heater, the part repeatedly coming into contact with individual particles during the movement process of the spherical particles. In this way, good heat transfer to the polymer material is achieved with the aid of the particles.

If the polymer material has acrylic compounds, the average temperature of the particles of the heat carrier in the reactor is in particular in the range from 250 to 600 degrees Celsius, in the case of recovery of MMA preferably below 425 ° C., the autoignition temperature of MMA. Experiments explained later have shown that high yields and also high purity of the monomer can be achieved with the process according to the invention even at such low temperatures.

In one embodiment of the process according to the invention, the polymer material is heated and depolymerized in the same reactor vessel during its dwell time. It is not necessary - as is known, for example, from DE 31 46 194 A1 - to preheat the polymer material in a heating space upstream of the actual reactor space, since, because of the spherical particles, heat transfer from the heat source to the polymer material is particularly rapid, and there is a particular one uniform temperature distribution can be realized. However, the invention is not restricted to such one-stage heating. Rather, the polymer material can, for example, already be heated in a supply container assigned to the reactor or can be introduced into such a supply container already heated.

The spherical particles preferably consist of a material that is not reactively involved in the recovery of the monomer. In this way, work-up of the heat transfer medium can be simplified or even avoided. For example, steel is well suited as a material for the spherical particles. Stainless steel is particularly preferred, in particular steel containing chromium and nickel, approximately 18/10 Cr / Ni steel (V2A steel) or 17/12/2 Cr / Ni / Mo steel (V4A steel). Even simple steel has a pronounced elasticity, so that - with the appropriate mechanical excitation by the movement device - there are also sudden movements of the individual particles, which accelerate the heat distribution, in addition to the ease of movement. In addition, stainless steel is particularly well suited as a material because it is resistant to chemical reactions with a large number of the substances introduced into or together with the polymer material in the reactor. Balls made of V2A steel or V4A steel can also be manufactured inexpensively.

The depolymerization preferably takes place in a protective gas atmosphere, e.g. B. in a nitrogen atmosphere. The pressure in the reactor can be below, at or above ambient pressure (generally equal to the atmospheric pressure of the earth's atmosphere). In the case of overpressure, this is, for. B. up to 133.3 hPa (100 torr). Although higher overpressures are also included in the invention, in practice they mean an additional expenditure in terms of equipment. The overpressure is preferably in the range from 50 to 80 hPa (37.5 to 60 torr), in particular from 65 to 70 hPa (48.75 to 52.5 torr). In the case of a negative pressure, this can, for. B. 80 to 133.3 hPa (60 to 100 Torr) under ambient pressure. Higher pressures (i.e. lower absolute pressures) are also possible here.

In a special embodiment of the invention, a lock device is provided for introducing the polymer material into the reactor, the lock device having a lock chamber. Furthermore, one there is a first closing device arranged on an entry side of the lock chamber and a second closing device arranged on an exit side of the lock chamber. An evacuation device and a gas filling device are combined with the lock chamber, so that when the first and second locking devices are closed, gas can be evacuated from the lock chamber and the lock chamber can be filled with the protective gas. In this way, a quantity of polymer material can be repeatedly introduced into the lock chamber with the first locking device open, the lock chamber evacuated, the protective gas introduced into the lock chamber, and then after opening the second locking device, the polymer material can be introduced into the reactor.

Because the polymer material is already in a protective gas atmosphere immediately before it is introduced into the reactor, direct filling of the reactor with protective gas can be omitted. In particular, the reactor can thereby be better insulated against heat loss.

The invention is explained in more detail below by way of example with reference to the accompanying drawing. However, the invention is not restricted to the exemplary embodiments. The individual figures of the drawing show schematically:

Fig. 1 a plant for the recovery of monomeric substances

Polymer material,

Fig. 2 shows a heated reactor for the production of monomer

Gas from the polymer material from above,

Fig. 3 shows an arrangement of spherical particles by a

Mixing tool to be moved

Fig. 4 shows the arrangement of FIG. 3 at a later time

movement and FIG. 5 shows a lock device which is connected upstream of the reactor shown in FIG. 1 and serves to introduce polymer material into the reactor.

The plant shown in FIG. 1 is used, for example, for the depolymerization and the recovery of MMA. However, it can be used alternatively for the recovery of other monomeric esters of substituted or unsubstituted acrylic acid, of styrene and / or of monomeric styrene derivatives, if appropriate by adjusting the pressure and the temperature in a reactor 1 of the plant.

As already mentioned, the system described below is an exemplary embodiment. Individual or multiple system components can be replaced by other components. In particular, the feed of the polymer material into the reactor described below, the reactor itself and / or the processing of the monomer gas derived from the reactor can be carried out in another way.

The polymer material to be depolymerized is located in a storage container 23, at the outlet of which a dosing device 21 is attached. The polymer material reaches a lock chamber 19 via the metering device 21. An example of a lock device is explained in more detail with reference to FIG. 5. The lock device and the lock chamber 19 serve to introduce the polymer material into the reactor 1, so that the depolymerization process can take place in a protective gas atmosphere.

The polymer material is introduced into the reactor 1 via a filling opening 14 in the reactor 1. The reactor 1 shown in FIG. 1 is a heated reactor with a continuously driven shaft 3 oriented in the horizontal direction, from which a plurality of arms 11 protrude in the radial direction of the shaft 3. From the perspective of wave 3 A mixing tool 13 is arranged opposite the opposite end of the arms 11, which has, for example, a triangular shape as shown in cross section. The mixing tools, to which the arms can also be counted, can also have a different design, e.g. B. a blade shape and / or a variety of mixing elements starting at the end of the respective arm. The appropriate mixing tool is selected depending on the type and size of the spherical particles used (heat transfer medium) and / or on the type and size of parts of the polymer material. For example, the polymer material can be processed in different ways before being introduced into the reactor, in particular divided into pieces and / or shapes of different sizes. A common and suitable process is the shredding of larger parts of the polymer material into pieces with dimensions of a few millimeters to several centimeters. Due to the spherical particles, the depolymerization can be carried out with good yields and high purity with different sizes and shapes of the polymer material.

2 shows an alternative embodiment of the reactor, namely a reactor 51 with a vertically oriented rotating shaft 53 and with a plurality (here three) of shovel-shaped mixing tools 63 which attach directly to the shaft 53 and project from the shaft 53 in the radial direction. The linear rectilinear representation of the mixing tools 63 is to be understood schematically. In embodiments, the mixing tool 63 can be curved in the vertical and / or horizontal direction.

FIG. 2 shows (for reasons of clarity of illustration only in one of the three sectors of the reactor 51 subdivided by the mixing tools 63) a moving material 65 moved by the mixing tools 63 with pieces of polymer material 66 and balls 67. Because of their shape, the balls 67 can easily move move against each other and relative to the pieces of polymer material 66. There is therefore no mechanical snagging or jamming within the material to be moved 67. In order to ensure particularly good mobility within the goods to be moved, it is preferred that the total volume of the balls in the reactor is greater than the total volume the still solid pieces of polymer material, in particular at least twice as large. Baking or snagging of the pieces of polymer material together is thus largely avoided.

It is also preferred to use stainless steel balls, since PMMA does not cause the polymer material to bake on the balls. The high mobility of the balls helps in any case to prevent the polymer material from baking on the mixing tools, on other parts of the movement device and / or on the reactor walls.

As indicated in FIG. 2, the reactor 51 has an electrical heater 59 at least on the side of the reactor wall. The lateral reactor walls and the base are preferably heated essentially over the entire surface and / or by means of a heating device distributed uniformly along the wall surface. Not only in this specific example can e.g. B. a conventional electrical resistance heater and / or an inductively acting heating device.

In the reactor 1 shown in FIG. 1, the circular outer jacket of the reactor 1, for example, is heated over the entire surface by a heating device 9. In order to maintain good running properties of the shaft 3 over the long term, the shaft 3 can be combined with a shaft cooling 5.

In the reactor 1, the polymer material is heated and depolymerized in a short time due to the mixing movement and due to the balls present in the reactor 1. The time that a piece of PMMA typically takes until the complete transition to the monomeric gas phase is in the range from five to sixty seconds, depending on the average ball temperature.

The gaseous MMA is discharged through a gas opening 15 of the reactor 1 and a monomer gas line 25 into a separating device 27, in which additives, such as. B. color pigments. As shown in FIG. 1, the separating device 27 is in particular a cyclone. The aggregates can be discharged from the separating device 27 by means of a pump 29 via a discharge line 28. In addition to the MMA and the Aggregates also receive protective gas (here nitrogen) in the separating device 27. The protective gas is later separated from the MMA or discharged together with the MMA.

Via a line connection 31, the MMA / protective gas mixture is passed into a cooling device 33 (for example a quencher), in which the still hot gas mixture is sprayed with a portion of previously cooled and recirculated condensate by means of a nozzle as in a shower and in a very short time Time is cooled. This can further increase the yield and purity of the monomer. Solid deposits that can occur on otherwise conventional coolers are significantly reduced. For the return, the cooling device 33 is connected via a monomer drain 35 to a monomer container 37, into which the cooled monomer is drained. By means of a pump 41, part of the monomer located in the monomer container 37 is returned via a return line 40 to the nozzle of the height device. A continuous cooling device 43 is located in the return line 40.

Via a further line 38 attached to the monomer container 37, the monomer is driven out of the system by a pump 39. An additional return to the cooling device 33 is possible through a connecting line connected to the line 38, which can be shut off by means of a valve 47. For this purpose, the other end of the connecting line 46 is connected to that part of the return line 40 which lies in the flow direction beyond the continuous cooling device 43. The resulting temperature at the nozzle of the cooling device 33 can be controlled via the control of the valve 47 and a corresponding mixture of recycled monomer of different temperatures.

FIGS. 3 and 4 again illustrate an essential effect of the spherical shape of the heat transfer particles according to the invention. As indicated by a double-line arrow pointing downward in the illustration, a ball 68 resting on a mixing tool 63 is moved and transfers the movement to two further balls 69, 70 resting on it. The resulting movement of the balls 69, 70 is by two Arrows shown. in the As a result, the balls 69, 70 diverge with very little movement resistance and allow the ball 68 to pass easily (as shown in FIG. 4). Corresponding movements of the balls are also possible with just as little movement resistance relative to pieces of polymer material.

FIG. 5 shows a lock device 22 which can be connected upstream of the reactor 1, for example in the arrangement according to FIG. 1. A filler neck 20, which, for example, is attached to the metering device 21 shown in FIG. 1, opens into the lock chamber 19 of the lock device 22 can close the filler neck 20 by means of a reciprocating closure part 80. In general, the locking device 71 is designed such that the lock chamber can be closed gas-tight on the entry side. On the outlet side of the lock chamber 19, here below the lock chamber, there is a second closing device 72 which, for example, can also close a polymer feed line 17 to the reactor via a back and forth movable closure part 81. The second closing device 72 is also designed such that it can close the container 19 (here on the outlet side) in a gas-tight manner.

A gas line 74, which is combined with a main valve 78, also attaches to the lock chamber 19. From the view of the lock chamber 19, beyond the main valve 78, there is a T-piece 75, on which the gas line 74 branches into an upper branch and a lower branch. A pump 76 is arranged in the upper branch. A protective gas valve 79 is arranged in the lower branch. The lower branch opens, for example, into the protective gas feed line shown in FIG. 1. The upper and lower branches do not have to lead up or down as shown in the figure, but can lead in any suitable direction.

During the depolymerization process, in particular during the operation of the plant shown in FIG. 1 or another plant, the reactor is repeatedly filled with a quantity of polymer material. This will first the amount of polymer material is filled into the lock chamber 19 through the filler neck 20. The second, lower closing device 72 is closed. After the introduction of the polymer material, the first, upper closing device 71 is also closed. The main valve 78 is then opened (if it is not already open) and gas (in particular air) is evacuated from the lock chamber 19 by means of the pump 76. The protective gas valve 79 is closed. The pump 76 is then switched off and, if necessary, the upper branch of the gas line 74 is additionally shut off. Furthermore, with the main valve 78 open and with the protective gas valve 79 open, protective gas is then introduced into the lock chamber 19 up to a desired pressure. In this case, a final pressure in the lock chamber 19 is preferably reached which is higher than the pressure of the protective gas in the reactor. In this way, losses of protective gas from the reactor can be compensated for by discharging the monomer / protective gas mixture from the reactor and, on the other hand, the monomer / protective gas mixture can be prevented from flowing out through the polymer feed line into the lock chamber 19.

After the final pressure in the lock chamber 19 has been reached, the second, lower closing device 72 is opened and the quantity of polymer material is thus introduced into the reactor.

Test examples for the design and implementation of the depolymerization process in a reactor are described below.

Example 1: A vane reactor with a diameter of 280 mm and a length of 400 mm was chosen. Twelve kilograms of steel balls with a diameter of 0.2 mm were filled into this reactor as a heat transfer medium. During the depolymerization, the mean sphere temperature was 456 degrees Celsius, the excess pressure of the protective gas in the reactor (nitrogen in the example), based on atmospheric pressure at sea level, and 66.7 hPa (approx. 50 Torr), and the speed of the shaft of the blade reactor 100 rpm. With a plant structure as shown in FIG. 1, a yield of MMA of 97% with a purity of 98.5% was achieved. Example 2: The procedure was as in Example 1, but twenty kilograms of the steel balls were introduced into the reactor and an average ball temperature of 380 degrees Celsius was set. The MMA yield was 98% with a purity of 99%.

Example 3: The test was carried out as described in Example 2, but the process was carried out at an average ball temperature of only 320 degrees Celsius. The MMA yield was 98.5% with a purity of 99%.

Claims

claims

1. A process for the recovery of monomeric esters of substituted or unsubstituted acrylic acid, of styrene and / or of monomeric styrene derivatives from corresponding structural units polymer material, the polymer material in a heated reactor (1; 51) with a

Heat transfer medium is brought into contact, the heat transfer medium and the polymer material in the reactor (1; 51) are moved and in the reactor (1; 51) resulting, containing the monomer

Gas is discharged from the reactor (1; 51), the heat transfer medium having a large number of spherical particles (67).

2. The method according to claim 1, wherein the polymer material comprises acrylic compounds and wherein the average temperature of the particles (67) of the heat carrier in the reactor (1; 51) is in the range of 250 to 600 degrees Celsius.

3. The method according to claim 1 or 2, wherein the reactor (1; 51) is electrically heated.

4. The method according to any one of claims 1 to 3, wherein the spherical particles (67) consist of a material which is not reactively involved in the recovery of the monomer.

5. The method according to claim 4, wherein the spherical particles (67) made of stainless steel, in particular chromium and nickel-containing steel.

6. The method according to any one of claims 1 to 5, wherein the spherical particles (67) have a diameter in the range from 0.075 mm to 0.25 mm, in particular in the range from 0.1 to 0.2 mm.

7. The method according to any one of claims 1 to 6, wherein the spherical particles (67) are moved by a continuously driven mixing tool and remain in the reactor (1; 51).

8. The method according to any one of claims 1 to 7, wherein the polymer material and the spherical particles are moved in a protective gas atmosphere.

9. The method according to any one of claims 1 to 8, wherein the polymer material is in a protective gas atmosphere immediately before it is introduced into the reactor (1; 51).

10.An arrangement for the recovery of monomeric esters of substituted or unsubstituted acrylic acid or of styrene-containing monomers from corresponding structural units polymer material, the arrangement comprising the following: a heatable reactor (1; 51) for generating the monomer-containing gas from the polymer material and a moving device ( 3, 11, 13; 53, 63) for moving goods (65) contained in the reactor (1; 51), which is combined with the reactor (1; 51) or is part of the reactor, the goods (65) comprising the polymer material and a heat carrier, and wherein the heat carrier has a plurality of spherical particles (67).

1. Arrangement according to claim 10, characterized by a

Lock device (22) for introducing the polymer material into the reactor (1; 51), the lock device (22) comprising a lock chamber (19), a first closing device (71) arranged on an entry side of the lock chamber (19), and a second, has a locking device (72) arranged on an outlet side of the lock chamber (19) and an evacuation device (74, 75, 76) and a gas filling device (18, 74, 75, 79) are combined with the lock chamber (19), so that at closed first and second closing device (71, 72), gas can be evacuated from the lock chamber (19) and the lock chamber (19) can be filled with a protective gas.