PROCESS FOR THE DEPOLYMERISATION OF POLYSTYRENE

Abstract

The invention relates to a process for the preparation of styrene monomers by depolymerising polystyrene, to a device for carrying out the process and to the use of a fluidised bed reactor for the depolymerisation of polystyrene. Said process comprising the following steps: a) feeding a polymer composition (A) containing 60 to 99.9 wt. polystyrene, based on the total weight of the polymer composition (A), into the reaction zone (R) of a pyrolysis reactor (P); b) thermally cracking the polystyrene contained in the polymer composition (A) in the reaction zone (R) of the pyrolysis reactor (P) at a temperature of between 400° C. to 1000° C. to obtain a product mixture (G) containing styrene monomers and other components; c) removing the product mixture (G) obtained in step b) from the reaction zone (R) of the pyrolysis reactor (P); d) cooling the product mixture (G) removed in step c) to obtain a condensed product mixture (K) containing styrene monomers and further components; and e) separating the styrene monomers from the further components of the condensed product mixture (K) obtained in step d), wherein the average residence time (Z) of the polymer composition (A) in the reaction zone (R) of the pyrolysis reactor (P) is from 0.01 sec to 10 sec.

Claims

1-15. (canceled)

16. A process for the production of styrene monomers by depolymerization of polystyrene, comprising the steps of: a) feeding a polymer composition (A) containing 60% to 99.9% by weight of a polystyrene, based on the total weight of the polymer composition (A), into the reaction zone (R) of a pyrolysis reactor (P); b) thermally cleaving the polystyrene present in the polymer composition (A) in the reaction zone (R) of the pyrolysis reactor (P) at a temperature of from 400° C. to 1000° C., to obtain a product mixture (G) containing styrene monomers and further components; c) withdrawing the product mixture (G) obtained in step b) from the reaction zone (R) of the pyrolysis reactor (P); d) cooling the product mixture (G) withdrawn in step c), to obtain a condensed product mixture (K) containing styrene monomers and further components; and e) separating the styrene monomers from the further components of the condensed product mixture (K) obtained in step d), wherein the average residence time (Z) of the polymer composition (A) in the reaction zone (R) of the pyrolysis reactor (P) is from 0.01 s to 10 s.

17. The process of claim 16, wherein the temperature in the reaction zone (R) of the pyrolysis reactor (P) is 580° C. to 630° C. and the average residence time (Z) of the polymer composition (A) in the reaction zone (R) of the pyrolysis reactor (P) is 0.4 s to 0.6 s.

18. The process of claim 16, wherein the condensed product mixture (K) obtained in step d) contains from 75% to 99% by weight of styrene and 1% to 25% by weight of the further components, based on the total weight of the condensed product mixture (K).

19. The process of claim 16, wherein the pyrolysis reactor (P) is a fluidized bed reactor.

20. The process of claim 19, wherein the reaction zone (R) of the fluidized bed reactor comprises a silicon carbide fluidized bed.

21. The process of claim 16, wherein at least a portion of the further components obtained in step e) is recycled into the reaction zone (R) of the pyrolysis reactor (P).

22. The process of claim 21, wherein the further components obtained in step e) which are recycled into the reaction zone (R) of the pyrolysis reactor (P) consist essentially of styrene oligomers.

23. The process of claim 21, wherein the recycling of the further components obtained in step e) into the reaction zone (R) of the pyrolysis reactor (P) is continuous.

24. The process of claim 16, wherein the polystyrene component in the polymer composition (A), which in step a) is fed into the reaction zone (R) of the pyrolysis reactor (R), consists essentially of general purpose polystyrene (GPPS).

25. The process of claim 16, wherein in step d), the product mixture (G) withdrawn in step c) is cooled to a temperature of from 0° C. to 50° C.

26. The process of claim 16, wherein the polymer composition (A) containing polystyrene in step a) does not contain any further polymeric components.

27. The process of claim 16, wherein the separation of the styrene monomers in step e) comprises a step of fractional distillation.

28. A process for the depolymerization of a polystyrene comprising the use of a fluidized bed reactor with a temperature in a reaction zone (R) of a pyrolysis reactor of from 400° C. to 1000° C. and with an average residence time (Z) of the polystyrene in the reaction zone (R) of the pyrolysis reactor of from 0.01 s to 10 s.

29. The process of claim 28, wherein the fluidized bed reactor comprises a silicon carbide fluidized bed.

30. The process of claim 28, wherein the temperature in the reaction zone (R) of the pyrolysis reactor is 580° C. to 630° C. and the average residence time of the polymer composition (A) in the reaction zone (R) of the pyrolysis reactor is 0.4 s to 0.6 s.

31. An apparatus for conducting the process of claim 16, wherein the reaction zone (R) and the pyrolysis reactor (P) are configured such that gentle depolymerization of polystyrene is possible.

32. The apparatus of claim 31, wherein the pyrolysis reactor (P) is a fluidized bed reactor.

33. The apparatus of claim 32, wherein the fluidized bed reactor comprises a silicon carbide fluidized bed.

Description

EXAMPLES

[0083] The polymer is metered from an inertized reservoir vessel (B101) via volumetric metering into a gas jet, which conveys the particles pneumatically into the reaction zone of a fluidized bed reactor (R101) containing SiC particles. The heat energy is input into the reaction zone via resistive heating conductors through the metallic reactor wall. The steam for producing the fluidized bed is provided by an evaporator (D101) and is brought to the desired temperature via a steam superheater (E102).

[0084] In the reaction zone, the SiC fluidized bed is produced with the steam and the polymer particles conveyed in pneumatically are mixed in the fluidized bed and ultimately depolymerized.

[0085] The product mixture of the depolymerization process from (R101) is cooled to below 50° C. in the column (K101) in a water mist. In the process, the condensable constituents are condensed according to their vapor pressures and are collected with the water in the cooled bottom. Solid particles are also deposited with the mist according to their coalescence tendency.

[0086] Floating, water-insoluble constituents are transferred into a buffer vessel via a skimmer system. Samples are filled of the concentrated, organic fraction of the condensed product mixture. These are measured by gas chromatography.

[0087] The water from the condensation process is cooled via a heat exchanger and then sent back into the cooling column (K101) using the pump. Solids are optionally removed via a solid-liquid filter.

Examples 1.1 to 1.6

[0088] An amorphous polystyrene (GPPS) (INEOS Styrolution, Frankfurt) with a melt volume-flow rate (Melt Volume Rate 200°/5 kg load, ISO 1133) of around 28 cm.sup.3/10 min was depolymerized in the apparatus described above under various conditions. Here, the temperature in the reaction zone of the fluidized bed reactor (R101) was varied in the range from 550° C. to 650° C. and the residence time was varied in the range from 0.46 to 1 s. Unless stated otherwise, the concentration of the polymer composition in the reaction zone was maintained at 5% by weight, based on the total charge of the reactor, consisting of SiC particles and polymer particles. The yields of pyrolysis oil (condensate oil) and of styrene monomers depending on the reaction conditions are presented in table 1. The compositions of the pyrolysis oil are presented in table 2.

Example 2

[0089] Example 1.2 was repeated with a high impact amorphous polystyrene (HIPS) (INEOS Styrolution, Frankfurt) with a melt volume-flow rate (Melt Volume Rate 200° C./5 kg load, ISO 1133) of around 4 cm.sup.3/10 min. The yield of styrene monomers is presented in table 1. The composition of the pyrolysis oil is presented in table 2.

Example 3

[0090] Example 1.1 was repeated with a polymer composition consisting of 50% by weight of the polymer composition from Example 1 and 50% by weight of the polymer composition from Example 2. The yield of styrene monomers is presented in table 1. The composition of the pyrolysis oil is presented in table 2.

TABLE-US-00001 TABLE 1 Results of the pyrolysis experiments Proportion by mass of the con- Average densate oil Styrene con- Temperature residence based on centration in in the reac- time in mass used the conden- tion zone reaction [% by sate oil [% by Example Polymer [° C.] zone [s] weight] weight] 1.1 GPPS 550 0.54 70.6 74.8 1.2 GPPS 600 0.51 65.9 83.2 1.3 GPPS 550 0.46 64.8 68.2 1.4 GPPS 650 0.48 69.0 76.8 1.5 GPPS 550 0.66 72.3 76.3 1.6 GPPS, 8% 550 0.54 72.5 73.4 by weight in reaction zone 2 HIPS 600 0.51 45.7 70.9 3 50% by 550 0.54 91.9 70.1 weight GPPS/ 50% by weight HIPS

TABLE-US-00002 TABLE 2 Composition of the pyrolysis oil Styrene Dimer Trimer Concentration concentration concen- concentra- of other com- in conden- tration in con- tion in conden- pounds in con- Ex- sate oil [% by densate oil [% sate oil [% by densate oil [% ample weight] by weight] weight] by weight] 1.1 74.8 8.4 8.3 8.6 1.2 83.2 6.0 0.6 10.3 1.3 68.2 10.7 9.8 11.2 1.4 76.8 4.5 0.7 17.9 1.5 76.3 7.0 5.3 11.3 1.6 73.4 8.2 1.1 17.3 2 70.9 7.3 3.3 18.6 3 70.1 6.6 7.5 15.7

EXPLANATION OF THE FIGURES

[0091] FIG. 1 shows a flow diagram of the pilot plant for carrying out the production of styrene monomers by depolymerization of polystyrene

[0092] FIG. 2 shows an overview of the styrene concentration in the condensate oil.

[0093] FIG. 3 shows the dependence of the pyrolysis oil composition on the temperature.

[0094] FIG. 4 shows the dependence of the pyrolysis oil composition on the residence time in the case of pure GPPS.

[0095] FIG. 5 shows the dependence of the pyrolysis oil composition on the concentration of the reaction material in the reactor.

[0096] FIG. 6 shows the dependence of the pyrolysis oil composition on the composition of the reaction material.