Depolymerization system

Abstract

This depolymerization system is provided with: a dissolver (11) for dissolving a resin using a solvent; a solid-liquid separator (12) that separates a solution containing the resin and the solvent dissolved in the dissolver (11) into a solid and a liquid; an evaporator (13) that evaporates the solvent contained in the liquid separated from the solution; a depolymerization device (15) that depolymerizes water and a liquid obtained by evaporating the solvent by the evaporator (13); a concentrator (19) for heating and concentrating the reaction product of the depolymerization device (15); a condenser (14) that condenses vapor of the solvent generated in the evaporator (13); and a heat transfer unit that transfers, to the dissolver (11) and the concentrator (19), condensation heat generated when the condenser (14) condenses the vapor of the solvent.

Description

Technical Field

[0001] The present invention relates to a depolymerization system for recovering raw materials from plastics. Background Art

[0002] In recent years, initiatives to significantly reduce waste generation by preventing and reducing waste generation, recycling and reusing waste are being actively developed. As such a technology, it is known in the past that there is a device that converts waste plastics into oil or gas by heating the heat of the combustion gas generated by the combustion reaction of fuel and oxygen-containing gas (see, for example, Patent Document 1). The device described in Patent Document 1 is configured to reuse the waste heat of the combustion gas for heating the oxygen-containing gas before combustion.

[0003] However, in general, when depolymerizing waste plastics to recover raw material monomers, the waste plastics are dissolved with a solvent, and after the foreign matter is separated, the solvent is degassed and put into a depolymerization device. The solvent evaporated in such a degassing process is condensed and reused. However, in order to condense the solvent, energy from the outside is required, and it is preferred to condense the solvent efficiently.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2001-181651 (JP 2001-181651 A). Summary of the invention

[0007] A depolymerization system according to one embodiment of the present invention comprises: a dissolver that dissolves a resin using a solvent; a solid-liquid separator that separates a solution containing a resin and a solvent obtained by dissolving in the dissolver into a solid and a liquid; an evaporator that evaporates the solvent contained in a liquid separated from the solution; a depolymerizer that causes a depolymerization reaction between the liquid obtained by evaporating the solvent in the evaporator and water; a concentrator that heats and concentrates a reaction product of the depolymerizer; a condenser that condenses the vapor of the solvent generated in the evaporator; and a heat transfer unit that transfers condensation heat generated when the vapor of the solvent is condensed in the condenser to the dissolver and the concentrator. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The objects, features and advantages of the present invention will be further clarified through the following description of the embodiments in conjunction with the accompanying drawings.

[0009] Figure 1 This is a diagram showing an example of the configuration of a deaggregation system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0010] Below, refer to Figure 1One embodiment of the present invention is described. A depolymerization system 1 according to an embodiment of the present invention recovers raw material monomers from waste plastics (hereinafter referred to as waste resin) used as vehicle components (interior trim, bumper, etc.). Specifically, the depolymerization system 1 recovers ε-caprolactam (hereinafter referred to as CL) by depolymerizing polyamide 6 (hereinafter referred to as PA6) contained in the waste resin. The waste resin is, for example, polyamide 6 (hereinafter referred to as PA6GF) mixed with glass fiber (hereinafter referred to as GF).

[0011] When CL is recovered from PA6GF, in order to separate GF from PA6GF, first, ethylene glycol (hereinafter referred to as EG) is used as a solvent to dissolve PA6GF, and the solution is separated into solid and liquid to remove GF from the solution. Hereinafter, EG used as a solvent is referred to as EG solution. After that, EG contained in the solution is evaporated and removed, and the solution from which EG has been removed is put into a depolymerizer. At this time, the evaporated EG is condensed and reused in dissolving PA6GF.

[0012] However, since a large amount of waste heat is generated during the condensation of EG, sufficient efficiency cannot be obtained in terms of energy by simply condensing EG for reuse as described above. In order to cope with such a problem, the depolymerization system is configured as follows in the present embodiment.

[0013] Figure 1 : is a diagram showing an example of the structure of a depolymerization system according to an embodiment of the present invention. Figure 1 As shown, the depolymerization system 1 includes: a dissolver 11 that uses EG to dissolve the waste resin; a solid-liquid separator 12 that separates the solution containing the waste resin and EG obtained by dissolving in the dissolver 11 into solid and liquid; an EG evaporator (hereinafter referred to as evaporator) 13 that evaporates EG contained in the liquid (hereinafter referred to as filtrate) separated from the solution; a depolymerizer 15 that causes the filtrate obtained by evaporating EG in the evaporator 13 to undergo a depolymerization reaction with water; and an EG condenser (hereinafter referred to as condenser) 14 that condenses the vapor of EG generated in the evaporator 13 (hereinafter referred to as EG vapor).

[0014] The depolymerization system 1 further includes: a heat exchanger 16 that performs heat exchange between the reaction product of the depolymerizer 15 (hereinafter referred to as the depolymerization liquid) and water; a separator 17 that separates the depolymerization liquid into a gas phase and a liquid phase; a condenser (hereinafter referred to as a water condenser or a gas phase condenser) 18 that condenses the gas phase separated from the depolymerization liquid by the separator 17; a CL concentrator (hereinafter referred to as a concentrator) 19 that concentrates the liquid phase (CL) separated from the depolymerization liquid by the separator 17; a regenerated water tank TK1 that stores the liquid phase (water) obtained by condensing the gas phase by the water condenser 18 and the distillate (water) discharged from the concentrator 19; a hot water tank TK2 that stores the hot water (hereinafter referred to as the discharge liquid) discharged from the concentrator 19; and a regenerated EG tank TK3 that stores the liquid of EG obtained by condensing the EG vapor by the condenser 14 (hereinafter referred to as the regenerated EG).

[0015] In the depolymerization system 1, first, waste resin (PA6GF) and solvent (EG) are put into the dissolver 11 at a predetermined mass ratio (for example, PA6GF:EG=1:5), and PA6GF and EG are heated by the heater 11a. At this time, when the PA6GF and EG in the dissolver 11 are heated at a temperature (for example, 150°C) or higher for a predetermined time (for example, 45 minutes), the PA6GF is dissolved by the EG. It should be noted that the heating temperature and heating time for dissolution vary depending on the crushing size of the PA6GF, the stirring conditions, and the mass ratio of the PA6GF to the EG.

[0016] The solution of PA6GF and EG is transported from the dissolver 11 to the solid-liquid separator 12 which is a centrifugal separator. When the solution reaches a specified temperature (about 150°C) or below, the viscosity begins to gradually increase, and when it reaches a lower temperature (about 130°C or below), it becomes a high viscosity state with almost no fluidity. Therefore, the solid-liquid separator 12 has a structure for keeping the solution warm with heat medium oil (hereinafter referred to as heat medium), so that the solution can be kept at a temperature higher than the temperature (about 150°C). It should be noted that a foreign matter separation filter can be provided instead of the centrifugal separator or on the basis of the centrifugal separator.

[0017] The dissolved liquid is separated into a filtrate and a filter residue (solid matter) by a solid-liquid separator 12. Since the filtrate contains EG, the EG contained in the filtrate is evaporated by an evaporator 13. In addition, the filter residue also contains EG. Specifically, a small amount of EG remains on the surface of the filter residue. The EG contained in the filter residue is evaporated at a predetermined temperature (e.g., 200° C.) using a tube-heated evaporator, a rotary kiln, etc. (not shown). A container rotary dryer, a conical mixer with stirring wings, etc. can also be used to evaporate the EG contained in the filter residue.

[0018] The evaporator 13 includes a first evaporator 131 and a second evaporator 132 provided at a subsequent stage.

[0019] First, the first evaporator 131 reduces the pressure of the filtrate to a predetermined pressure (for example, 0.02 MPa) at a predetermined temperature (about 200° C.) to evaporate EG contained in the filtrate.

[0020] As EG gradually evaporates, the viscosity of the filtrate increases. When the viscosity of the filtrate increases, it becomes difficult to degas the EG. Therefore, the filtrate (i.e., the filtrate with increased viscosity) delivered from the first evaporator 131 sometimes includes residual EG that has not been degassed. Therefore, the filtrate delivered from the first evaporator 131, i.e., the filtrate with increased viscosity, sometimes contains EG that has not been degassed and remains. Therefore, a second evaporator 132 is provided at the subsequent stage of the first evaporator 131, and the EG remaining in the filtrate is degassed by the second evaporator 132. The second evaporator 132 is a twin-screw extruder, which dissolves the filtrate delivered from the first evaporator 131 at a predetermined temperature (e.g., 250 to 300°C) while evaporating the EG remaining in the filtrate. The filtrate (PA6) obtained by evaporating EG from the second evaporator 132 is then sent to the depolymerizer 15 at an equal pressure via a gear pump (not shown).

[0021] The EG vapor generated in the evaporator 13 is condensed and restored to liquid in the condenser 14 and fed into the dissolver 11 as regenerated EG. The condenser 14 includes a first condenser 141 and a second condenser 142 .

[0022] The first condenser 141 cools the EG vapor to condense it. The first condenser 141 uses the regenerated EG put into the dissolver 11 as a solvent as a medium for cooling the EG vapor (hereinafter referred to as a cooling medium). The first condenser 141 condenses the EG vapor by exchanging heat between the EG vapor and the regenerated EG. As a result, the EG vapor at a predetermined temperature T1 (for example, 170°C) is cooled to a predetermined temperature T2 (for example, 149°C). On the other hand, the regenerated EG as the cooling medium is heated from a predetermined temperature T3 (for example, 90°C) to a predetermined temperature T4 (for example, 160°C) by the condensation heat generated when the EG vapor is condensed. The regenerated EG (EG liquid) heated to the predetermined temperature T4 is supplied to the dissolver 11 via a heat transfer section HT1 composed of a pipe connected from the first condenser 141 to the dissolver 11, a pump provided in the pipe, and the like. As a result, the condensation heat of the first condenser 141 is transferred to the dissolver 11.

[0023] It should be noted that all the EG vapor generated in the evaporator 13 cannot be condensed only by heat exchange in the first condenser 141 . Therefore, the EG vapor remaining in the first condenser 141 that has not been completely condensed is further condensed in the second condenser 142 .

[0024] The second condenser 142 condenses the EG vapor (EG vapor partially condensed to become liquid) at a predetermined temperature T2 sent from the first condenser 141 by heat exchange with water at a predetermined pressure (e.g., 0.2 MPaG) and a predetermined temperature T11 (e.g., 70°C). It should be noted that the water is hot water (discharge liquid) discharged from the concentrator 19 (more specifically, the reboiler 192 described later) as described later, and is supplied from the concentrator 19 to the second condenser 142 via the hot water tank TK2. In addition, the water is heated by the above-mentioned heat exchange in the second condenser 142, that is, heated by the condensation heat generated when the EG vapor is condensed, and becomes steam (saturated steam) at a predetermined temperature T12 (e.g., 120°C). The saturated steam is supplied to the concentrator 19 via a heat transfer section HT2 composed of a pipe connected from the second condenser 142 to the concentrator 19 (more specifically, the reboiler 192 described later), a pump provided in the pipe, and the like. Thus, the condensation heat of the second condenser 142 is transferred to the concentrator 19. On the other hand, the EG vapor condensed by the above heat exchange in the second condenser 142 becomes a liquid (regenerated EG) at a predetermined temperature T10 (about 90°C), and is stored in the regenerated EG tank TK3. The regenerated EG stored in the regenerated EG tank TK3 is supplied to the first condenser 141 via the pump PM1, and after being heated by the condensation heat of the first condenser 141, it is reused in the dissolver 11. It should be noted that the EG liquid is replenished to the regenerated EG tank TK3 as needed.

[0025] The depolymerizer 15 is supplied with water (hereinafter referred to as depolymerization water) in an amount that is a predetermined multiple (for example, 3 times) of the amount of the filtrate (PA6) supplied from the second evaporator 132. The depolymerization water is supplied from the regenerated water tank TK1 to the depolymerizer 15 via the heat exchanger 16. The reaction liquid (reaction product) generated by the depolymerization reaction in the depolymerizer 15 is supplied to the heat exchanger 16.

[0026] The heat exchanger 16 performs heat exchange between the depolymerization liquid supplied from the depolymerizer 15 and the depolymerization water of a predetermined temperature (e.g., 50° C.) supplied from the regenerated water tank TK1. The heat exchanger 16 supplies the depolymerization water heated by heat exchange with the depolymerization liquid to the depolymerizer 15. In this way, by heating the depolymerization water before being fed into the depolymerizer 15, the amount of heating when the filtrate (PA6) is depolymerized in the depolymerizer 15 can be reduced. In addition, the heat exchanger 16 supplies the depolymerization liquid cooled by heat exchange with the depolymerization water to the separator 17 via the opening and closing section VL. The opening and closing section VL is a valve for adjusting the amount of the depolymerization liquid supplied to the separator 17.

[0027] The separator 17 separates the depolymerization liquid into a gas phase and a liquid phase. The gas phase is transported to the water condenser 18, condensed by the water condenser 18 to become a liquid phase (specifically, water), stored in the regenerated water tank TK1, and then reused as depolymerization water for the depolymerizer 15. The liquid phase is transported to the concentrator 19. The concentrator 19 concentrates CL, which is the main component of the depolymerization liquid. The depolymerization liquid (hereinafter referred to as concentrated CL solution) concentrated to a specified concentration (about 80%) by the concentrator 19 is then transported to a factory with polymerization equipment, etc. The distillate (water) in the concentrator 19 is stored in the regenerated water tank TK1, and then reused as depolymerization water for the depolymerizer 15. It should be noted that water is supplied to the regenerated water tank TK1 as needed.

[0028] The concentrator 19 includes a concentrating tower 191 and a reboiler 192 for heating the solution (depolymerization liquid) in the concentrating tower 191. The saturated steam of the predetermined temperature T12 obtained by the second condenser 142 is supplied to the reboiler 192 for reboiler heating. The saturated steam used for reboiler heating becomes hot water and is discharged from the reboiler 192. As described above, the hot water (discharge liquid) is supplied to the second condenser 142. Specifically, the hot water discharged from the reboiler 192 is stored in the hot water tank TK2 and is pressure-sent from the hot water tank TK2 to the second condenser 142 via the pump PM2. The hot water supplied to the second condenser 142 is used for heat exchange with EG vapor in the second condenser 142. It should be noted that the heat of the steam discharged from the second condenser 142 is greater than the heat required for reboiler heating, so the hot water discharged from the reboiler 192 becomes high temperature (> predetermined temperature T11). Such high-temperature hot water is not suitable for heat exchange with EG vapor in the second condenser 142. Therefore, an air-cooling cooler AC for cooling the hot water supplied to the second condenser 142 to a predetermined temperature T11 is provided between the pump PM2 and the second condenser 142 .

[0029] The hot water supplied from the concentrator 19 to the second condenser 142 via the hot water tank TK2 and the air-cooled cooler AC is converted again into saturated steam of a specified temperature T12 by the condensation heat of the second condenser 142. The saturated steam is supplied from the second condenser 142 to the concentrator 19 via the heat transfer part HT2 for reboiler heating.

[0030] As mentioned above, in Figure 1 In the depolymerization system 1, waste heat (condensation heat) in the condensation step of EG is used for heating the EG liquid and concentrating the depolymerization liquid by heat exchange.

[0031] According to this embodiment, the following effects can be achieved.

[0032] (1) The depolymerization system 1 includes: a dissolver 11 that dissolves the waste resin (PA6GF) using a solvent (EG); a solid-liquid separator 12 that separates the solution containing the waste resin and the solvent obtained by dissolving in the dissolver 11 into solid and liquid; an evaporator 13 that evaporates the solvent contained in the liquid separated from the solution; a depolymerizer 15 that causes the liquid obtained by evaporating the solvent in the evaporator 13 to undergo a depolymerization reaction with water; a concentrator 19 that heats and concentrates the reaction product (depolymerization liquid) of the depolymerizer 15; a condenser 14 that condenses the vapor of the solvent generated in the evaporator 13; and heat transfer parts HT1 and HT2 that transfer the condensation heat generated when the condenser 14 condenses the vapor of the solvent to the dissolver 11 and the concentrator 19. Thus, the waste heat generated by the condensation of EG can be effectively used for heating EG and concentrating the depolymerization liquid. By reusing the thermal energy in this way, an energy-efficient system can be provided.

[0033] (2) The condenser 14 includes a first condenser 141 and a second condenser 142. The first condenser 141 condenses the vapor of the solvent generated in the evaporator 13 by exchanging heat between the vapor of the solvent generated in the evaporator 13 and the solvent used in the dissolver 11. The second condenser 142 condenses the vapor of the vapor generated in the evaporator 13 that has not been completely condensed in the heat exchange in the first condenser 141 by exchanging heat between the vapor of the vapor generated in the evaporator 13 and a predetermined liquid (discharge liquid of the reboiler 192). The liquid of the solvent obtained from the vapor of the solvent by condensation of the first condenser 141 and the second condenser 142 is supplied to the first condenser 141. The first condenser 141 condenses the vapor of the solvent generated in the evaporator 13 by exchanging heat between the vapor of the solvent generated in the evaporator 13 and the liquid of the supplied solvent. The heat transfer part HT1 transfers the condensation heat to the dissolver 11 by supplying the liquid solvent heated by the condensation heat of the solvent in the first condenser 141 to the dissolver 11. The dissolver 11 dissolves the waste resin using the liquid solvent supplied via the heat transfer part HT1. In this way, by heating the liquid solvent before being put into the dissolver 11 by utilizing the condensation heat of the condenser 14, the amount of heating required when dissolving the waste resin in the dissolver 11 can be reduced.

[0034] (3) The heat transfer section HT2 supplies the vapor (saturated vapor) of the predetermined liquid generated by the heat exchange of the second condenser 142 to the concentrator 19. The concentrator 19 uses the vapor supplied via the heat transfer section HT2 to heat the reaction product of the depolymerizer 15. Thus, the heat of the vapor (saturated vapor) generated by the heat exchange of the second condenser 142 can be effectively used for heating the reboiler of the concentrator 19.

[0035] (4) The concentrator 19 discharges the predetermined liquid cooled by heating the reaction product used in the depolymerizer 15. The second condenser 142 condenses the vapor that has not been condensed by the heat exchange of the first condenser 141 in the vapor by exchanging heat with the predetermined liquid discharged from the concentrator 19.

[0036] (5) The concentrator 19 concentrates the liquid phase separated from the reaction product of the depolymerizer 15. The depolymerization system further includes: a water condenser 18 that condenses the gas phase separated from the reaction product of the depolymerizer 15; and a heat exchanger 16 that heats the water supplied to the depolymerizer 15 by exchanging heat with the liquid (water) obtained by condensing the gas phase in the water condenser 18 and the distillate (water) discharged from the concentrator 19. Thus, the amount of heat when the filtrate (PA6) is depolymerized in the depolymerizer 15 can be reduced.

[0037] The above-described embodiment can be modified in various forms. Modifications will be described below.

[0038] In the above embodiment, the depolymerization system 1 is used as an example to recover CL from PA6GF. However, the waste resin may be a substance other than PA6GF, and the recovered raw material is not limited to CL. That is, the depolymerization system 1 may also depolymerize polymers other than polyamide 6.

[0039] In addition, in the above embodiment, the air-cooled cooler AC cools the hot water discharged from the concentrator 19 to a temperature suitable for heat exchange with the EG vapor in the second condenser 142. However, when the hot water discharged from the concentrator 19 is at a temperature suitable for heat exchange with the EG vapor in the second condenser 142, the cooling by the air-cooled cooler AC may be omitted. In addition, in the above embodiment, the case where the waste resin is fed into the dissolver 11 is taken as an example, but the resin may be fed into the dissolver 11 instead of the waste resin. That is, the present invention can also be applied to the high-purity decomposed resin itself.

[0040] The above description is merely an example, and the above embodiment and modified examples do not limit the present invention unless the features of the present invention are impaired. One or more of the above embodiment and modified examples can be arbitrarily combined, and the modified examples can be combined with each other.

[0041] According to the present invention, raw material monomers can be efficiently recovered from resin.

[0042] The present invention has been described above in conjunction with preferred embodiments, but it should be understood by those skilled in the art that various modifications and changes can be made without departing from the scope of the claims.

Claims

1. A depolymerization system, characterized in that: have: a dissolver (11) which dissolves the resin using a solvent; A solid-liquid separator (12) which separates the solution including the resin and the solvent obtained by dissolving in the dissolver (11) into solid and liquid; an evaporator (13) for evaporating the solvent contained in the liquid separated from the dissolved liquid; a depolymerizer (15) for subjecting the liquid obtained by evaporating the solvent in the evaporator (13) to a depolymerization reaction with water; a concentrator (19) for heating and concentrating the reaction product of the depolymerizer (15); a condenser (14) which condenses the vapor of the solvent generated in the evaporator (13); and A heat transfer portion transfers condensation heat generated when the vapor of the solvent is condensed in the condenser (14) to the dissolver (11) and the concentrator (19).

2. The depolymerization system according to claim 1, characterized in that: The condenser (14) comprises a first condenser (141) and a second condenser (142). The first condenser (141) condenses the vapor of the solvent generated in the evaporator (13) by exchanging heat with the solvent used in the dissolver (11). The second condenser (142) condenses the vapor that has not been completely condensed in the heat exchange in the first condenser (141) by exchanging heat with a predetermined liquid.

3. The depolymerization system according to claim 2, characterized in that: supplying the liquid of the solvent obtained from the vapor of the solvent by condensation in the first condenser (141) and the second condenser (142) to the first condenser (141), The first condenser (141) condenses the vapor of the solvent generated in the evaporator (13) by exchanging heat with the liquid of the supplied solvent. The heat transfer unit supplies the liquid of the solvent heated by the condensation heat generated when the vapor of the solvent is condensed in the first condenser (141) to the dissolver (11). The dissolver (11) dissolves the resin using the liquid of the solvent supplied via the heat transfer portion.

4. The depolymerization system according to claim 2 or 3, characterized in that: The heat transfer unit supplies the vapor of the predetermined liquid generated by heat exchange in the second condenser (142) to the concentrator (19). The concentrator (19) heats the reaction product using the vapor of the predetermined liquid supplied via the heat transfer unit.

5. The depolymerization system according to claim 4, characterized in that: The concentrator (19) discharges the predetermined liquid that has been cooled by heating the reaction product. The second condenser (142) condenses the vapor that has not been completely condensed in the heat exchange in the first condenser (141) by exchanging heat with the predetermined liquid discharged from the concentrator (19).

6. The depolymerization system according to claim 1, characterized in that: It also includes a gas phase condenser (18) and a heat exchanger (16), The concentrator (19) concentrates the liquid phase separated from the reaction product. The gas phase condenser (18) condenses the gas phase separated from the reaction product. The heat exchanger (16) heats the water supplied to the depolymerizer (15) by exchanging heat with a liquid obtained by condensing the gas phase in the gas phase condenser (18) and a distillate discharged from the concentrator (19).

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