JP2005060471A - Method and apparatus for recovering solvent and styrene from polystyrene solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently recover a solvent and styrene from a polystyrene solution. <P>SOLUTION: In recovering a solvent and styrene from a polystyrene solution prepared by dissolving polystyrene in the solvent, the solvent is recovered by evaporating and separating it from the solution and then the polystyrene separated from the solvent is thermally decomposed to recover styrene. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and an apparatus for recovering a solvent and styrene from a polystyrene solution obtained by dissolving polystyrene having a low bulk density such as polystyrene foam in a solvent.

  Most plastics discharged from factories and households, so-called waste plastics, are thermally decomposed and recovered as monomers for fuel and chemical raw materials. Since various types of waste plastics are mixed, usually, these various types of waste plastics are sorted by type and subjected to thermal decomposition. As a conventionally known thermal decomposition method, for example, techniques described in Patent Document 1 and Patent Document 2 are known.

  As the types of waste plastics to be discharged, there are many styrene-based resins (hereinafter simply referred to as polystyrene) such as polystyrene and copolymers of styrene and butadiene, acrylic, or the like. Waste polystyrene includes hard or soft non-expanded polystyrene that has been injection-molded or blow-molded and expanded polystyrene that has been foam-molded.

  Hard or soft non-expanded polystyrene has a large bulk density, so there is no problem in transportation, storage, or handling to the primary collection site or pyrolysis facility. Very low. Therefore, conventionally, foamed polystyrene is often dissolved in a solvent in a container installed in a primary collection site or the like to reduce the volume, and the resulting polystyrene solution is transported to a thermal decomposition facility for thermal decomposition.

  Solvents that can dissolve polystyrene include styrene, benzene, toluene, xylene, and the like, but recently, a solvent mainly composed of limonene is frequently used because of its dissolving ability and cost advantage. This limonene has the ability to dissolve polystyrene in the same volume as the solvent weight, and the polystyrene solution in which a large amount of polystyrene is dissolved exhibits a highly viscous gel.

  A polystyrene solution obtained by dissolving polystyrene in a solvent can be pyrolyzed with a pyrolyzer. A general pyrolysis apparatus is composed of a pyrolyzer, a condenser, a distillation apparatus, and the like, but the cracked gas obtained in the pyrolyzer is condensed by cooling in the condenser, and two oil components, for example, are condensed components. The styrene monomer is recovered by distillation with a distillation apparatus constituted by a distillation column.

  Since the solvent used for reducing the volume of polystyrene is relatively expensive, it is finally desirable to recover and reuse it by some method. Usually, when a polystyrene solution is supplied to a thermal decomposer, the solvent contained therein evaporates in the thermal decomposer, flows out together with the decomposition gas, and is condensed in the condenser. The condensed solvent is supplied to the distillation apparatus together with the styrene monomer component, where it is recovered by distillation operation.

JP 2001-302563 A JP 2001-335658 A

  When styrene is used as the solvent, the distillation operation is easy because the distillation apparatus can be distilled under the same conditions as the styrene monomer component. However, when limonene or the like is used as the solvent, two additional distillation columns different from the separation and recovery of styrene are required, which is disadvantageous in terms of cost. Accordingly, an object of the present invention is to solve such a problem, and an object thereof is to provide a new solvent and styrene recovery method and recovery apparatus therefor.

  The recovery method according to the present invention for solving the above problems is a method of recovering a solvent and styrene from a polystyrene solution obtained by dissolving polystyrene in a solvent. And this method is characterized by recovering styrene by evaporating and separating the solvent from the polystyrene solution and thermally decomposing the polystyrene from which the solvent has been separated (Claim 1).

  In the above recovery method, cracked gas obtained by thermally decomposing polystyrene can be condensed, and the oil can be distilled to recover high-purity styrene.

  Moreover, the collection | recovery apparatus which concerns on this invention which solves the said subject is an apparatus which collect | recovers a solvent and styrene from the polystyrene solution which melt | dissolved the polystyrene in the solvent. The apparatus comprises a solvent evaporator for evaporating and recovering the solvent from the polystyrene solution, and a thermal decomposing apparatus for thermally decomposing the polystyrene from which the solvent has been separated (Claim 3).

  In the recovery apparatus, the thermal decomposition apparatus recovers styrene by pyrolyzing polystyrene, a condenser for condensing cracked gas obtained by pyrolysis, and distilling the oil obtained by condensation. A distillation apparatus can be provided (Claim 4).

  According to the recovery method of the present invention, it is possible to efficiently recover the solvent and styrene from the polystyrene solution without complicating the distillation apparatus. At that time, high-purity styrene monomer can be recovered by condensing the cracked gas and distilling the oil. Moreover, the said collection | recovery method can be implemented efficiently by using the collection | recovery apparatus which concerns on this invention.

  Next, the best embodiment of the collection method and collection apparatus of the present invention will be described with reference to the drawings. 1 and 2 are process flow diagrams of an apparatus for carrying out a recovery method according to the present invention. First, in FIG. 1, a storage tank 1 for a polystyrene solution obtained by dissolving polystyrene with a solvent is installed in a thermal decomposition facility. A pipe 2 a provided with a transfer pump 2 for high viscosity such as a gear pump is connected to the storage tank 1, and the tip of the pipe 2 a is connected to the solvent evaporator 3.

  An upper part of the solvent evaporator 3 is provided with a discharge part for discharging the separated solvent, and the discharge part communicates with a condenser (condenser) 5 through a pipe 4. A pipe 6 for collecting the condensed solvent and a pipe 7 for discharging the non-condensed gas are connected to the condenser 5, and decompression means 8 such as a vacuum pump is provided in the middle of the pipe 7.

  A discharge pipe 9 for discharging the polystyrene from which the solvent has been separated is connected to the bottom of the solvent evaporator 3, and the tip of the discharge pipe 9 communicates with the inlet of the supply device 10. An outlet portion of the supply device 10 is connected to a pipe 11 covered with a heat insulating material, and a tip of the pipe 11 is connected to an inlet portion 12 a of a tubular pyrolyzer 12.

  Further, a pipe 13 is connected to the outlet 12 b of the pyrolyzer 12, and the tip of the pipe 13 communicates with a condenser (condenser) 14. A pipe 15 for discharging the condensed oil is connected to the bottom of the condenser 14, and the tip of the pipe 15 communicates with the distillation apparatus shown in FIG. A pipe 16 for discharging non-condensable gas is connected to the upper part of the condenser 14, and a decompression means 17 such as a vacuum pump is provided in the middle of the pipe 16.

  Next, in FIG. 2, a pump 16 is provided in the pipe 15 from the condenser 14, and the outlet side thereof communicates with the middle stage of the first distillation column 21 constituting the distillation apparatus 20. A reboiler 22 heated by steam is provided at the lower portion of the first distillation column 21, and a pipe 24 provided with a pump 23 is connected to the reboiler 22 portion, that is, near the bottom of the first distillation column 21. A pipe 25 is connected to the top of the first distillation column 21, and the tip of the pipe 25 communicates with the first condenser 26.

  A pipe 28 provided with a pump 27 is connected to the bottom of the first condenser 26, the leading end of a reflux pipe 29 branched from the pipe 28 communicates with the upper portion of the first distillation column 21, and a recovery pipe 30 branched from the pipe 28. A check valve 31 is provided. The tip of the collection pipe 30 communicates with the heavy oil collection tank 41. On the other hand, a pipe 33 provided with a pressure regulating valve 32 is connected to the upper part of the first condenser 26, and the tip of the pipe 33 communicates with a decompression means 34 such as a vacuum pump.

  The tip of the pipe 24 from the first distillation column 21 communicates with the middle stage of the second distillation column 35. A reboiler 36 heated by steam is provided at the lower part of the second distillation column 35, and a pipe provided with a cooler 37, a pump 38 and a check valve 39 in this order in the reboiler 36 portion, that is, near the bottom of the second distillation column 35. 40 is connected, and the tip of the pipe 40 communicates with the heavy oil recovery tank 41. A pipe 42 is connected to the top of the second distillation column 35, and the tip of the pipe 42 communicates with the second condenser 43.

  A pipe 44 is connected to the bottom of the second condenser 43, a pump 46 is provided in the middle of the reflux pipe 45 branched from the pipe 44, and the tip communicates with the upper part of the second distillation column 35. Furthermore, a cooler (for example, SM cooler) 48 is provided in the recovery pipe 47 branched from the pipe 44, and the tip thereof communicates with the monomer recovery tank 49. On the other hand, a pipe 50 provided with a pressure regulating valve 51 is connected to the upper part of the second condenser 43, and the tip of the pipe 50 communicates with a decompression means 34 such as a vacuum pump.

  Next, each device constituting the recovery apparatus will be described in detail. The solvent evaporator 3 can be a centrifugal thin film evaporator. As shown in FIG. 1, the centrifugal thin film type evaporator is provided with a scraper 60 having rotating blades in a cylindrical container, and the axis of the scraper 60 is a drive unit 61 such as a motor with a speed reducer disposed on the upper part of the container. Connected to the drive shaft. A heating unit (not shown) is provided around the container so that the container is heated to about 200 ° C. from the outside. The gel-like polystyrene solution supplied from the upper part of the container descends in a thin film shape on the inner wall of the container by centrifugal force by the scraper 60, and during that time, the solvent which is a low boiling point component evaporates by heating from the outside.

  As the supply apparatus 10, an extrusion apparatus generally used for plastic injection molding can be used. The extrusion apparatus includes a melt extrusion unit 63 that heats and melts polystyrene with a heater and extrudes the molten polystyrene. The melt extrusion unit 63 includes a cylinder 64 with a heater and a screw 65 disposed therein, and the screw 65 is a drive unit. 66 is driven to rotate.

  The heat exchanger 12 includes a tank type and a pipe type as illustrated. The tank-type pyrolyzer 12 is provided with a scraper for stirring and scraping residue on a cylindrical tank body having a conical bottom, and thermally decomposes polystyrene in a tank heated from the surroundings. It is suitable for batch pyrolysis of large quantities of polystyrene at once over a period of time.

  On the other hand, as shown in the figure, the tubular pyrolyzer 12 is composed of a long and narrow reaction tube 67, which is heated from the surroundings while the polystyrene passes through it and thermally decomposed, and a smaller amount than in the case of the tank type. Suitable for continuous pyrolysis of polystyrene. In addition, when using the tubular pyrolyzer 12, the method of supplying molten polystyrene from the supply apparatus 10 as described above is preferable.

  The tubular pyrolyzer 12 as shown in the figure is a slender reaction tube made of a metal tube having good heat resistance and heat conductivity such as stainless steel and having a diameter of about 50 mm to 200 mm and a length of about 5 m to several tens of meters. 67 and a heating unit 68 provided so as to cover the periphery of the reaction tube 67. The diameter and length of the reaction tube 67 are not limited to the above ranges, and can be changed according to the required processing amount.

  The higher the temperature during the thermal decomposition, the higher the thermal decomposition efficiency of the thermal decomposer 12, and further, the generation of by-products such as ethylbenzene and toluene is suppressed during the thermal decomposition, and a high-purity styrene monomer as a chemical raw material is increased. In order to obtain a high yield, it is desirable to perform thermal decomposition under reduced pressure. The polystyrene is heated and thermally decomposed by the heating gas flowing through the heating unit 68, but as a heating gas supply source to the heating unit 68, a heating gas that burns liquid fuel or gaseous fuel to generate high-temperature combustion gas. A generator (not shown) is provided separately.

  Cooling pipes (not shown) are arranged inside the condensers 5, 14, the first condenser 26 and the second condenser 43, and the cooling water flows through the cooling pipes. The supplied gas component exchanges heat on the surface of the cooling pipe, the high boiling point component condenses and becomes an oil component and stays at the bottom, and the low boiling point component stays at the top as a non-condensed gas. As the first distillation column 21 and the second distillation column 35, a general distillation column filled with multistage shelves or lashing can be used. In order to separate and recover styrene monomer and the like with high efficiency, It is preferable to carry out the distillation operation at.

  Next, a method for recovering the solvent and styrene from the polystyrene solution by the recovery device will be described. First, the solvent evaporator 3, the supply device 10, the thermal decomposition system, and the distillation system are brought into an operable state. That is, the decompression means 8 is operated to place the condenser 5, the solvent evaporator 3 and the piping system connecting them into a decompressed state, and the temperature of the solvent evaporator 3 is raised to about 200 ° C. Moreover, the melting part of the supply apparatus 10 is heated.

  Further, the decompression means 17 is operated, and an inert gas such as nitrogen is introduced from a gas introduction part (not shown) provided in the pipe 11, and the inside of the pyrolyzer 12, the condenser 14, and the piping system that communicates them The oxygen is replaced with an inert gas. When the thermal decomposition system is in the absence of oxygen, the introduction of the inert gas is stopped, and a pressure reducing valve (not shown) provided in the pressure reducing means 17 is adjusted to adjust the internal pressure of the thermal decomposer 12 to 3 to 20 kpa, preferably The pressure is reduced to about 10 kpa. Further, a heating gas from a heating gas generator (not shown) is introduced into the heating unit 68, and the temperature of the reaction tube 67, that is, the thermal decomposition temperature is raised to a range of about 500 ° C to 800 ° C.

  Further, the decompression means 34 is operated to replace the first distillation column 21 and the second distillation column 35 and the piping system connecting them with an inert gas in the same manner as described above, and to reduce the pressure to about 5 to 10 kpa. . Further, a heating source such as steam is supplied to the reboilers 22 and 36 to raise the temperature of the first distillation column 21 and the second distillation column 35 to a predetermined distillation temperature. The reduced pressure level of the first distillation column 21 is adjusted by the pressure adjustment valve 32, and the reduced pressure level of the second distillation column 35 is adjusted by the pressure adjustment valve 51.

  Next, the thermal decomposition operation of polystyrene will be described. Limonene is used as a solvent to dissolve the expanded polystyrene, and the resulting gel-like polystyrene solution is transported to a thermal decomposition facility by a transport means such as a tank truck and temporarily stored in the storage tank 1. The polystyrene solution in the storage tank 1 is supplied to the solvent evaporator 3 by the transfer pump 2, where it is heated to a temperature of about 200 ° C. to evaporate and separate the solvent from the polystyrene. The solvent separated in a gaseous state flows out to the condenser 5 through the pipe 4 and is cooled, and the condensed solvent is recovered in a solvent recovery tank (not shown).

  On the other hand, the polystyrene from which the solvent has been separated by the solvent evaporator 3 flows down the pipe 9 and is supplied to the melting part 62 of the supply device 10 arranged at the lower part. In the melting part 62, polystyrene is heated and melted at a temperature of about 150 ° C. to 200 ° C., and is extruded from the melt extrusion part 63 to the pipe 11. The molten polystyrene extruded into the pipe 11 flows into the inlet 12a of the pyrolyzer 12, that is, the tip of the reaction tube 67, and is heated from the surroundings and thermally decomposed while passing through the reaction tube 67.

  The cracked gas produced in the reaction tube 67 flows out from the outlet portion 12b of the thermal cracker 12, that is, the rear end portion of the reaction tube 67 together with the cracked residue, and the cracked residue is a staying portion (not shown) provided at the rear end portion. And the cracked gas flows out into the pipe 13. Maintaining the temperature and pressure reduction level of the reaction tube 67 in the above-described state and thermally decomposing molten polystyrene made of styrene polymer, 70% by weight of styrene monomer, about 10% by weight of styrene dimer, about 10% by weight of styrene trimer, toluene, ethylbenzene, Decomposition gas of about 2% by weight of α-methylstyrene and other by-products can be obtained.

  The cracked gas that has flowed out to the pipe 13 is supplied to the condenser 14 where it is cooled to condense relatively high-boiling components including the styrene monomer, and is supplied as an oil component from the pipe 15 to the distillation apparatus 20. The low boiling point component that is not condensed by the condenser 14 is sucked by the decompression means 17 and recovered as a gas component from the pipe 16 to a recovery tank (not shown). This gas component can be supplied as fuel for the heated gas generator.

  Next, a method for recovering high purity styrene by distillation will be described. The oil content from the condenser 14 is supplied to the middle stage of the first distillation column 21 by operating the pump 16 in the pipe 15 and distilled there. The low boiling point component separated by the distillation operation of the first distillation column 21 flows out from the top of the column through the pipe 25 to the first condenser 26. This low-boiling component contains about 3 to 5% by weight of toluene, ethylbenzene, α-methylstyrene, etc., supplied to the first distillation column 21 and is cooled by the first condenser 26 and relatively contained therein. Components with a high boiling point condense as oil. Further, the relatively low boiling point component that does not condense is recovered from the pipe 33 through the pressure reducing means 34 to a recovery tank (not shown).

  The oil produced in the first condenser 26 flows out of the pipe 28 by operating the pump 27, part of it is returned to the upper part of the first distillation column 21 from the reflux pipe 29, and the rest is recovered from the pipe 30 with heavy oil. Collected in the tank 41. The reflux ratio of the first distillation column 21 is set to, for example, about 20 to 100 by adjusting an adjustment valve (not shown) provided in the pipe 29.

  At the bottom of the first distillation column 21, a high-boiling component containing styrene monomer that has been separated by distillation stays, and the high-boiling component is supplied from the pipe 24 to the middle stage of the second distillation column 35 by operating the pump 23. There it is further distilled. The low boiling point component separated by the distillation operation of the second distillation column 35 flows from the top of the column through the pipe 42 to the second condenser 43, where it is cooled and condensed with a relatively high boiling point component as oil. Further, the relatively low boiling point component that does not condense is recovered from the pipe 50 through the pressure reducing means 34 to a recovery tank (not shown).

  The oil produced in the second condenser 43 flows out from the pipe 44, and a part of the oil is refluxed from the reflux pipe 45 to the upper part of the second distillation column 35 by operating the pump 46. The reflux ratio of the second distillation column 35 is set to, for example, about 2 to 5 by adjusting an adjustment valve (not shown) provided in the pipe 45. The remaining oil flowing out of the pipe 44 is cooled by a cooler 48 provided in the pipe 47 and recovered in the monomer recovery tank 49. The styrene monomer recovered in the monomer recovery tank 49 has a high purity of about 99.9%, and the recovery rate is approximately 70% by weight of the molten polystyrene supplied to the thermal cracker 12.

  The high-boiling components separated by distillation stay at the bottom of the second distillation column 35, and the high-boiling components flow out of the pipe 40 by operating the pump 38, and are cooled by the cooler 37 to recover heavy oil. Collected in the tank 41. The heavy oil recovered in the heavy oil recovery tank 41 is about 20 to 30% by weight of the molten polystyrene supplied to the pyrolyzer 12, and generates steam that is a heat source of the reboilers 22 and 36. It can be used as a fuel for the generator and the heated gas generator.

  The recovery method and recovery apparatus according to the present invention can be effectively used for efficiently recovering a solvent and styrene from a polystyrene solution obtained by dissolving foamed polystyrene with a solvent.

The process flow figure which shows the thermal decomposition part of the apparatus which enforces the collection | recovery method concerning this invention. The process flow figure which shows the distillation part of the apparatus which enforces the collection | recovery method concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Storage tank 2 Transfer pump 2a Piping 3 Solvent evaporator 4 Piping 5 Condenser 6, 7 Piping 8 Pressure reducing means 9 Draining pipe 10 Supply device

DESCRIPTION OF SYMBOLS 11 Piping 12 Pyrolyzer 12a Inlet part 12b Outlet part 13 Piping 14 Condenser 15,16 Piping 17 Decompression means 20 Distillation device

21 First distillation column 22 Reboiler 23 Pump 24, 25 Piping 26 First condenser 27 Pump 28 Piping 29 Reflux pipe 30 Recovery pipe

31 Check Valve 32 Pressure Regulating Valve 33 Piping 34 Depressurizing Means 35 Second Distillation Column 36 Reboiler 37 Cooler 38 Pump 39 Check Valve 40 Piping

41 Heavy Oil Recovery Tank 42 Piping 43 Second Condenser 44 Piping 45 Reflux Pipe 46 Pump 47 Recovery Pipe 48 Cooler 49 Monomer Recovery Tank 50 Piping

51 Pressure Adjusting Valve 60 Scraper 61 Drive Unit 62 Melting Unit 63 Melting Extrusion Unit 64 Cylindrical Body 65 Screw 66 Drive Unit 67 Reaction Tube 68 Heating Unit

Claims (4)

  In the method of recovering a solvent and styrene from a polystyrene solution in which polystyrene is dissolved in a solvent, the solvent is evaporated and recovered from the polystyrene solution, and the polystyrene from which the solvent is separated is thermally decomposed to recover styrene. To recover solvent and styrene from polystyrene solution.   The method for recovering a solvent and styrene from a polystyrene solution according to claim 1, wherein the cracked gas obtained by thermally decomposing polystyrene is condensed and the oil is distilled to recover high-purity styrene.   In an apparatus for recovering a solvent and styrene from a polystyrene solution in which polystyrene is dissolved in a solvent, a solvent evaporator 3 for recovering the solvent by evaporating and separating the solvent from the polystyrene solution, and a thermal decomposition apparatus for thermally decomposing the polystyrene from which the solvent has been separated A collection device characterized by comprising. 4. The thermal decomposition apparatus according to claim 3, wherein the thermal decomposition apparatus includes a thermal decomposer 12 for thermally decomposing polystyrene, a condenser 14 for condensing a cracked gas obtained by thermal decomposition, and distilling an oil component obtained by condensation. A recovery device comprising a distillation device 20 for recovery.

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