Resin decomposition gas recovery method, reusable liquefied gas production method, and resin decomposition gas recovery device

Abstract

The present invention improves the operation rate of a resin treatment recirculation system. In the present disclosure, a gas that solidifies when cooled to a final temperature is recovered as a liquid at a stage of cooling to an intermediate temperature higher than the final temperature, on the other hand, a gas that is not liquefied at the intermediate temperature is liquefied and recovered by cooling from the intermediate temperature to the final temperature.

Description

Technical Field

[0001] The present invention relates to a resin decomposition gas recovery technology, a reusable liquefied gas production technology and a resin decomposition gas recovery device, for example, to a technology effectively applied in the technology of liquefying and recovering various gases generated by thermal decomposition of resin. Background Art

[0002] Japanese Patent Application Laid-Open No. 2005-349838 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2008-302555 (Patent Document 2) describe technologies for discharging gas generated inside an extruder to the outside through a vent provided in the extruder when a resin is thermally decomposed using an extruder.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2005-349838

[0006] Patent Document 2: Japanese Patent Application Publication No. 2008-302555 Summary of the invention

[0007] Problems to be solved by the invention

[0008] In recent years, research known as "ESG" has received attention.

[0009] “ESG” stands for “Environment,” “Social,” and “Governance,” and is known as the following research.

[0010] (1) Environment: Research on environmental issues such as global warming and environmental pollution.

[0011] (2) Contribution to improving the working environment, protecting human rights, and local activities, etc.

[0012] (3) Implementation of proactive information disclosure, legal compliance, and the appointment of external management personnel

[0013] What is important in ESG research is that it is necessary to consider not only customers, shareholders, clients, but also stakeholders in the local community, and it must be clearly positioned in the management policy and handled as a key task.

[0014] Management that incorporates "ESG" into its main business is called "ESG management." The advantages of companies focusing on "ESG management" include obtaining new business opportunities, strengthening risk management, and improving corporate value through the concentration of human resources and funds.

[0015] In the study of "ESG", if we focus on environmental issues, it is important to achieve a circular economy to solve environmental problems. In addition, when achieving a circular economy, it is useful to strive for recycling as much as possible.

[0016] In this regard, for example, plastic products are used in a very wide range of fields, and their usage is huge. On the other hand, the disposal of plastic products costs money, and since they are left in the natural environment, their components flow into rivers and oceans, and the impact on the environment has also become a problem. Therefore, in order to achieve an environmentally friendly circular economy through "ESG" research, it is necessary to establish a mechanism for efficiently recycling plastic products. Therefore, for resins that are plastic components, research has been ongoing on how to effectively utilize them by recycling them. In particular, it is hoped that the operating rate of recycling systems that process resins represented by waste plastics will be increased.

[0017] It should be noted that the concept of "recycling" in this specification is not only a method of thermally decomposing resins constituting waste products and resynthesizing resins as product raw materials, but also widely includes, for example, a method of thermally decomposing waste resins and reusing the generated components as fuel.

[0018] Means for solving problems

[0019] A method for recovering resin decomposition gas in one embodiment includes the steps of: (a) liquefying the first decomposition gas of a first decomposition gas and a second decomposition gas generated by thermally decomposing a resin; and (b) liquefying the second decomposition gas after the step (a).

[0020] A method for recovering a resin decomposition gas in one embodiment includes a step of liquefying and recovering a plurality of gases respectively by utilizing the difference in boiling points of the plurality of gases generated by thermally decomposing a resin.

[0021] A method for producing a reusable liquefied gas in one embodiment includes the steps of: (a) liquefying the first decomposition gas of a first decomposition gas and a second decomposition gas generated by thermally decomposing a resin; and (b) liquefying the second decomposition gas after the step (a).

[0022] A method for producing a reusable liquefied gas in one embodiment includes a step of liquefying and recovering a plurality of gases respectively by utilizing the difference in boiling points of the plurality of gases generated by thermal decomposition of a resin.

[0023] A resin decomposition gas recovery device in one embodiment includes: a first cooling unit configured to liquefy and recover the first decomposition gas of a first decomposition gas and a second decomposition gas generated by thermally decomposing the resin; and a second cooling unit configured to liquefy and recover the second decomposition gas.

[0024] A resin decomposition gas recovery device in one embodiment includes a plurality of liquefaction recovery sections configured to liquefy and recover a plurality of gases generated by thermally decomposing a resin, respectively, using differences in boiling points of the gases.

[0025] Effects of the Invention

[0026] According to one embodiment, the operation rate of the recycling system that performs resin processing can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a block diagram illustrating the conceptual structure of a recycling system.

[0028] Figure 2 This is a block diagram showing an example of a method of realizing the basic concept.

[0029] Figure 3 This is a block diagram showing another example of a method of realizing the basic concept.

[0030] Figure 4 It is a diagram showing the configuration of a recycling system in a concrete form.

[0031] Figure 5 It is a diagram showing a configuration example of a resin decomposition gas recovery device.

[0032] Figure 6 is a table showing the melting points and boiling points of various hydrocarbon compounds.

[0033] Figure 7 This is a diagram showing a recycling system including a resin decomposition gas recovery device in Modification 1. DETAILED DESCRIPTION

[0034] In all the drawings for explaining the embodiments, the same reference numerals are attached to the same components in principle, and their repeated descriptions are omitted. It should be noted that, in order to facilitate understanding of the drawings, hatching is sometimes also attached to the top views.

[0035] <Research for improvement>

[0036] First, the related art will be described, and then the room for improvement in the related art will be described.

[0037] The “related technology” in this specification is not a publicly known technology, but a technology with a problem discovered by the inventor of the present application, and is a technology that is a premise of the present invention.

[0038] For example, a recycling system for recycling resin constituting plastics includes: a heat treatment device for thermally decomposing the resin; a tank for accumulating decomposition products discharged from the heat treatment device; and a cooling unit for liquefying the decomposition gas discharged from the heat treatment device. For example, an extruder is used as the heat treatment device, and a heat exchanger is used as the cooling unit.

[0039] When a resin represented by waste plastic fragments is introduced into an extruder, the resin is thermally decomposed inside the extruder. As a result, gas (decomposition gas), liquid (melt), solid, etc. are discharged from the extruder according to the resin (raw material) and its decomposition reaction mode. At this time, the solid and liquid are discharged and recovered in a tank. On the other hand, the decomposition gas can be recovered as a gas, but it is difficult to handle due to its low density and large volume. Considering this situation, it is usually desired to recover the decomposition gas as a liquid. Thus, the decomposition gas discharged from the extruder is recovered after being cooled by a heat exchanger.

[0040] Here, there are usually multiple types of decomposition gases generated by thermally decomposing the resin. Therefore, the decomposition gases whose melting points are lower than the cooling temperature of the heat exchanger among the multiple decomposition gases can be liquefied and recovered by the heat exchanger. In contrast, the decomposition gases whose melting points are higher than the cooling temperature of the heat exchanger among the multiple decomposition gases solidify when cooled to the cooling temperature by the heat exchanger. If the decomposition gases solidify in this way, the passage of the decomposition gases in the heat exchanger may be blocked. In this case, the recycling system cannot operate continuously, resulting in a decrease in the operating rate of the recycling system.

[0041] The following is a specific description.

[0042] Consider putting a polyolefin resin into an extruder for thermal decomposition. For example, if the heating temperature of the polyolefin resin is set to 400°C, the alkanes with a boiling point of more than 400°C among the chain saturated hydrocarbons (alkanes) produced by the thermal decomposition of the polyolefin resin are alkanes with a carbon number greater than 25. Therefore, alkanes with a carbon number exceeding 25 exist in the state of solution inside the extruder. On the other hand, alkanes with a carbon number of 25 or less exist in the state of gas inside the extruder. Here, it is assumed that the cooling temperature of the heat exchanger for recovering the generated decomposition gas is 15°C. As for the melting points of gasified alkanes with a carbon number of less than 25, pentadecane with a carbon number of 15 is 9.9°C, and hexadecane with a carbon number of 16 is 18°C.

[0043] Thus, alkanes with less carbon atoms than pentadecane, which has 15 carbon atoms, can be liquefied and recovered by a heat exchanger because their melting points are lower than the cooling temperature (15°C) of the heat exchanger. In contrast, alkanes with more carbon atoms than hexadecane, which has 16 carbon atoms, solidify inside the heat exchanger because their melting points are higher than the cooling temperature of the heat exchanger. Therefore, among the alkanes obtained by thermal decomposition at 400°C, if an attempt is made to liquefy and recover the gasified decomposition gas by a heat exchanger, the alkanes with a melting point higher than the temperature of the heat exchanger solidify, and thus the passage of the decomposition gas in the heat exchanger may be clogged. In this case, the recycling system cannot be operated continuously, resulting in a decrease in the operating rate of the recycling system.

[0044] As described above, from the perspective of suppressing the decrease in the operating rate of the recirculation system, there is room for improvement in the related art. Therefore, in this embodiment, efforts are made to overcome the room for improvement in the related art. The following describes the technical idea in this embodiment that is aimed at this point.

[0045] <Basic concept of implementation>

[0046] The basic idea of ​​this embodiment is to utilize the difference in boiling points of the various gases generated by thermal decomposition of the resin to liquefy and recover the various gases separately. In other words, the basic idea is not to cool the various gases together to the final temperature, but to cool the various gases to an intermediate temperature higher than the final temperature, and after a part of the gases included in the various gases are liquefied and recovered, the other part of the gases included in the various gases that are not liquefied at the intermediate temperature are liquefied and recovered by cooling to the final temperature. In other words, the basic idea is that the gas that solidifies when cooled to the final temperature is recovered as a liquid at the stage of cooling to the intermediate temperature higher than the final temperature, and the gas that is not liquefied at the intermediate temperature is liquefied and recovered by cooling from the intermediate temperature to the final temperature.

[0047] According to this basic concept, solidification of gas in the heat exchanger can be avoided, and as a result, clogging of the gas passage caused by accumulation of solidified gas can be suppressed. Thus, according to the basic concept, the inability of the recirculation system to operate continuously due to clogging of the gas passage can be prevented, and as a result, the reduction in the operating rate of the recirculation system can be suppressed.

[0048] Hereinafter, contents capable of suppressing gas solidification will be described based on the basic concept.

[0049] For example, the plurality of gases include a decomposition gas G1 and a decomposition gas G2. Here, the boiling point of the decomposition gas G1 is set to a temperature T1, and the boiling point of the decomposition gas G2 is set to a temperature T2 lower than the temperature T1. In addition, the melting point of the decomposition gas G1 is set to a temperature T3 lower than the temperature T2, and the melting point of the decomposition gas G2 is set to a temperature T4 lower than the temperature T3.

[0050] First, consider not applying the basic concept, and cooling the decomposition gas G1 and the decomposition gas G2 together to a final temperature lower than the temperature T3 and higher than the temperature T4. In this case, the final temperature is higher than the melting point (temperature T4) of the decomposition gas G2, so the decomposition gas G2 liquefies without solidifying. In contrast, the final temperature is lower than the melting point (temperature T3) of the decomposition gas G1, so the decomposition gas G1 further solidifies after liquefaction. Therefore, it can be seen that if the basic concept is not applied, and the decomposition gas G1 and the decomposition gas G2 are cooled together to a final temperature lower than the temperature T3 and higher than the temperature T4, the decomposition gas G1 solidifies.

[0051] In contrast, applying the basic concept, first, consider cooling the decomposition gas G1 and the decomposition gas G2 together to an intermediate temperature lower than the temperature T1 and higher than the temperature T2 (first stage). In this case, the intermediate temperature is lower than the boiling point of the decomposition gas G1, that is, the temperature T1, and higher than the melting point of the decomposition gas G1, that is, the temperature T3, so the decomposition gas G1 is liquefied but not solidified.

[0052] Therefore, in the first stage, the liquefied decomposition gas G1 can be recovered. That is, the decomposition gas G1 can be recovered in a liquid state before solidification.

[0053] Furthermore, since the intermediate temperature is higher than the temperature T2 which is the boiling point of the decomposition gas G2, the decomposition gas G2 maintains a gaseous state.

[0054] Next, consider cooling the decomposition gas G2 in a gaseous state from the intermediate temperature to a final temperature lower than the temperature T3 and higher than the temperature T4 (the second stage). In this case, the final temperature is lower than the melting point of the decomposition gas G1, that is, the temperature T3, but in the first stage described above, the liquefied decomposition gas G1 has been recovered and removed. Therefore, there is no case where the decomposition gas G1 solidifies. On the other hand, the final temperature is lower than the boiling point of the decomposition gas G2, that is, the temperature T2, and higher than the melting point of the decomposition gas G2, that is, the temperature T4, so the decomposition gas G2 liquefies but does not solidify.

[0055] Therefore, in this second stage, the liquefied decomposition gas G2 can be recovered. In other words, the decomposition gas G2 can also be recovered in a liquid state before solidification.

[0056] As described above, according to the basic concept of having the first stage and the second stage, the decomposition gas G1 and the decomposition gas G2 can be cooled to the final temperature without cooling them together to the final temperature. After the decomposition gas G1 and the decomposition gas G2 are cooled to an intermediate temperature higher than the final temperature and only the decomposition gas G1 is liquefied and recovered, the decomposition gas G2 that has not been liquefied at the intermediate temperature can be cooled to the final temperature to be liquefied and recovered. That is, according to the basic concept, the boiling point difference between the decomposition gas G1 and the decomposition gas G2 can be used to liquefy and recover the decomposition gas G1 and the decomposition gas G2 separately without solidifying. Therefore, according to the basic concept, the solidification of the decomposition gas G1 and the decomposition gas G2 can be avoided, and as a result, the clogging of the gas channel caused by the accumulation of the solidified gas can be suppressed. Therefore, according to the basic concept, it is possible to prevent the recycling system from being unable to operate continuously due to the clogging of the gas channel, and as a result, the reduction in the operating rate of the recycling system can be suppressed.

[0057] Next, the conceptual structure of the recycling system that realizes the above-mentioned basic concept will be described.

[0058] Figure 1 1 is a block diagram illustrating the conceptual structure of the recycling system 100 .

[0059] exist Figure 1 In the embodiment, the recycling system 100 includes a heat treatment device 110 , a tank 120 , a cooling unit 130 , and a cooling unit 140 .

[0060] The heat treatment device 110 is, for example, a device configured to thermally decompose a resin constituting a plastic product, and is connected to a tank 120 storing a decomposition product after thermal decomposition. Decomposition products including a melt (liquid), gas (decomposition gas), or solid generated by thermal decomposition of the resin are discharged from the heat treatment device 110.

[0061] At this time, the solid and the melt are cooled and discharged and recovered in the tank 120. On the other hand, the decomposition gas is also discharged into the tank 120. The decomposition gas can also be recovered as a gas, but the density is low and the volume is large, and it is difficult to handle. Therefore, it is desired to recover the decomposition gas as a liquid. Therefore, the recycling system 100 is provided with a cooling unit that liquefies the decomposition gas discharged into the tank 120.

[0062] Here, the cooling unit provided in the recycling system includes the cooling unit 130 and the cooling unit 140. Thus, the basic idea can be realized. That is, according to the recycling system 100, instead of cooling the high boiling point gas and the low boiling point gas together to the final temperature, the high boiling point gas and the low boiling point gas are first cooled to an intermediate temperature higher than the final temperature in the cooling unit 130, and after only the high boiling point gas is liquefied and recovered, the low boiling point gas that has not been liquefied at the intermediate temperature is cooled to the final temperature in the cooling unit 140, thereby being liquefied and recovered. That is, according to the recycling system 100, by utilizing the boiling point difference between the high boiling point gas and the low boiling point gas, the high boiling point gas and the low boiling point gas can be liquefied and recovered separately without solidifying.

[0063] Thus, according to the recirculation system 100, it is possible to prevent the high-boiling point gas and the low-boiling point gas from solidifying, and as a result, it is possible to suppress the clogging of the gas passage due to the accumulation of the solidified gas. Thus, according to the recirculation system 100, it is possible to prevent the recirculation system 100 from being unable to operate continuously due to the clogging of the gas passage, and as a result, it is possible to suppress the reduction in the operating rate of the recirculation system 100.

[0064] In the above-mentioned recycling system 100, if Figure 2 As shown, the cooling unit 130 and the cooling unit 140 can be assembled into the resin decomposition gas recovery device 200A. In this case, the high boiling point gas and the low boiling point gas generated by the heat treatment device 110 are discharged into the tank 120 and then supplied from the tank 120 to the resin decomposition gas recovery device 200A. For example, the high boiling point gas and the low boiling point gas are supplied from the tank 120 to the cooling unit 130 and cooled to an intermediate temperature. As a result, the liquefied high boiling point gas is recovered from the cooling unit 130. On the other hand, the low boiling point gas that is not liquefied by the cooling unit 130 is supplied from the cooling unit 130 to the cooling unit 140 in a gaseous state. Then, in the cooling unit 140, the low boiling point gas is cooled from the intermediate temperature to the final temperature and liquefied, and the liquefied low boiling point gas is recovered.

[0065] In addition, in the recycling system 100, if Figure 3 As shown in FIG. 1 , the cooling unit 130 and the cooling unit 140 can also be incorporated into the resin decomposition gas recovery device 200B. Figure 2The resin decomposition gas recovery device 200A shown is different, and includes a tank 120 as a component, and the cooling unit 130 is configured to cool the tank 120. In this case, the high boiling point gas and the low boiling point gas generated by the heat treatment device 110 are discharged into the tank 120. At this time, the tank 120 is cooled to an intermediate temperature by the cooling unit 130. As a result, the high boiling point gas and the low boiling point gas supplied to the tank 120 are cooled to an intermediate temperature in the tank 120. Thus, the liquefied high boiling point gas is recovered from the tank 120. On the other hand, the low boiling point gas that is not liquefied in the tank 120 is supplied from the tank 120 to the cooling unit 140 in a gaseous state. Then, in the cooling unit 140, the low boiling point gas is cooled from the intermediate temperature to the final temperature and liquefied. Thus, the low boiling point gas is recovered from the cooling unit 140.

[0066] As described above, the recycling system 100 that implements the basic concept takes into account Figure 2 The method shown and Figure 3 Therefore, the following description adopts Figure 2 The embodiment of the recycling system 100 shown in the embodiment of FIG. Figure 3 The recirculation system 100 of the embodiment shown is described in Modification 1.

[0067] <Method of realization>

[0068] <<Composition of the recycling system>>

[0069] Figure 4 It is a diagram showing the configuration of a recycling system in a concrete form.

[0070] exist Figure 4 In the embodiment, the recycling system includes an extruder 110A, a tank 120, and a resin decomposition gas recovery device 200A. Figure 2 As an example of the heat treatment apparatus 110 shown, an extruder 110A is used.

[0071] The extruder 110A has a cylinder 10, a hopper 20 and a rotary drive mechanism 30. The cylinder 10 includes a plurality of cylinder blocks. A screw is disposed inside the cylinder 10, and the screw is configured to be rotatable by the rotary drive mechanism 30. In addition, a tank 120 is installed at the front end of the cylinder 10. The tank 120 is connected to the resin decomposition gas recovery device 200A via a pipe, for example. In addition, the cylinder 10 is connected to the hopper 20, and the hopper 20 functions as a raw material supply port for supplying raw materials to the inside of the cylinder 10.

[0072] In the extruder 110A configured as above, when the raw material is supplied to the hopper 20, the raw material is fed into the cylinder 10. The raw material fed into the cylinder 10 is kneaded by the screw provided inside the cylinder 10. Specifically, the raw material fed into the cylinder 10 by the screw rotated by the rotary drive mechanism 30 is kneaded, and the kneaded material is conveyed from the upstream of the cylinder 10 toward the downstream.

[0073] At this time, the kneaded material is decomposed into solid, liquid or gaseous decomposition products. After the decomposition products flow into the tank 120 installed at the front end of the cylinder 10, the gas contained in the decomposition products is discharged from the tank 120.

[0074] The resin decomposition gas recovery device 200A includes a heat exchanger 40 and a heat exchanger 50 .

[0075] Here, Figure 2 An example of the cooling unit 130 shown is a heat exchanger 40. Figure 2 An example of the cooling unit 140 shown is a heat exchanger 50 .

[0076] The heat exchanger 40 is connected to the tank 120 and is configured to allow the gas discharged from the extruder 110A to flow into the tank 120. The heat exchanger 40 is configured to cool the gas flowing into the tank 120 to an intermediate temperature.

[0077] On the other hand, the heat exchanger 50 is connected to the heat exchanger 40 and is configured to allow the gas exhausted from the heat exchanger 40 to flow in. Furthermore, the heat exchanger 50 is configured to cool the gas exhausted from the heat exchanger 40 to a final temperature lower than the intermediate temperature.

[0078] For example, the heat exchanger 40 is configured to be able to cool to an intermediate temperature higher than the temperature T2 and lower than the temperature T1. As a result, the heat exchanger 40 is configured to introduce a high-boiling-point gas having a boiling point higher than the temperature T1 and a low-boiling-point gas having a boiling point lower than the temperature T1 at the temperature T2, thereby liquefying and recovering only the high-boiling-point gas.

[0079] On the other hand, the heat exchanger 50 is configured to be able to cool to a final temperature that is lower than or equal to the temperature T2, and is configured to liquefy and recover the low-boiling-point gas by introducing the low-boiling-point gas.

[0080] The recirculation system is constructed in the above-mentioned manner.

[0081] <<Operation of the recirculation system>>

[0082] Next, the operation of the recirculation system will be described.

[0083] exist Figure 4In the process, resin is fed into the hopper 20 of the extruder 110A. When the resin is fed into the hopper 20, the resin is fed into the cylinder 10. The resin fed into the cylinder 10 is kneaded by the screw provided inside the cylinder 10. Specifically, the raw material fed into the cylinder 10 by the rotating screw is kneaded by the rotary drive mechanism 30, and the kneaded material is transported from the upstream to the downstream of the cylinder 10.

[0084] Decomposition products including a melt (liquid), gas (gas), or solid generated by thermal decomposition of the resin are discharged from the extruder 110A into the tank 120 .

[0085] Here, the decomposition gas includes multiple gases. For example, in order to simply and clearly explain the technical significance of the technical idea, the multiple gases include two types: high boiling point gas A (g) and low boiling point gas B (g). The high boiling point gas A (g) and the low boiling point gas B (g) flow from the tank 120 into the resin decomposition gas recovery device 200A.

[0086] Figure 5 It is a diagram showing a configuration example of a resin decomposition gas recovery device 200A.

[0087] like Figure 5 As shown, the high boiling point gas A(g) and the low boiling point gas B(g) flowing into the resin decomposition gas recovery device 200A are supplied to the heat exchanger 40. In the heat exchanger 40, the high boiling point gas A(g) and the low boiling point gas B(g) are cooled to an intermediate temperature by the circulating refrigerant R1. At this time, the intermediate temperature is a temperature lower than the boiling point of the high boiling point gas A(g) and higher than the boiling point of the low boiling point gas B(g). In addition, the intermediate temperature is a temperature higher than the melting point of the high boiling point gas A(g). Therefore, if the high boiling point gas A(g) is cooled to the intermediate temperature, the high boiling point gas A(g) is liquefied to become a liquefied gas A(l) but is not solidified. The liquefied gas A(l) falls into the tank 120 due to gravity, for example, and is thereby accumulated inside the tank 120. As a result, the liquefied gas A(l) can be recovered from the tank 120.

[0088] It should be noted that the resin decomposition gas recovery device 200A may not be configured to allow the liquefied gas A(l) to fall into the tank 120 for recovery, and the tank 120 may be configured to store the liquefied gas A(l) and recover it in another storage unit.

[0089] When the low boiling point gas B(g) is cooled to the intermediate temperature, the low boiling point gas B(g) does not liquefy but maintains the gas state (gas state). Figure 5 As shown, the low boiling point gas B(g) cooled to the intermediate temperature is discharged from the heat exchanger 40 and then supplied to the heat exchanger 50 .

[0090] In the heat exchanger 50, the low boiling point gas B(g) is cooled to the final temperature by the circulating refrigerant R2. At this time, the final temperature is a temperature lower than the intermediate temperature, which is a temperature lower than the boiling point of the low boiling point gas B(g) and higher than the melting point of the low boiling point gas B(g). Therefore, when the low boiling point gas B(g) is cooled to the final temperature, the low boiling point gas B(g) is liquefied into liquefied gas B(l) without solidifying. The liquefied gas B(l) is recovered after being discharged from the heat exchanger 50. As described above, the method for recovering the resin decomposition gas in the embodiment is realized by the action of the recycling system.

[0091] The above-mentioned method for recovering the resin decomposition gas is summarized as follows.

[0092] That is, the method for recovering resin decomposition gas includes the steps of: (a) liquefying the high-boiling-point gas among the high-boiling-point gas and the low-boiling-point gas generated by thermal decomposition of the resin; and (b) liquefying the low-boiling-point gas after the step (a).

[0093] In addition, the boiling point of the high boiling point gas is above the temperature T1, and the boiling point of the low boiling point gas is at a temperature T2 lower than the temperature T1. In the step (a), the high boiling point gas and the low boiling point gas are introduced into the heat exchanger 40 which can be cooled to an intermediate temperature higher than the temperature T2 and lower than the temperature T1, so that the high boiling point gas is liquefied and recovered. On the other hand, in the step (b), the low boiling point gas is introduced into the heat exchanger 50 which can be cooled to a final temperature lower than the temperature T2, so that the low boiling point gas is liquefied and recovered.

[0094] In the method for recovering resin decomposition gas by the above-mentioned operation of the recycling system, liquefied high-boiling point gas and liquefied low-boiling point gas are recovered. As a result, for example, resin as a product raw material can be synthesized again by reusing the liquefied high-boiling point gas and the liquefied low-boiling point gas.

[0095] However, the method of reusing the liquefied high-boiling point gas and the liquefied low-boiling point gas includes not only a method of resynthesizing the resin as a product raw material, but also a method of reusing the liquefied high-boiling point gas and the liquefied low-boiling point gas as fuel. In this case, the method of recovering the resin decomposition gas by operating the recycling system can also be expressed as a method of manufacturing a liquefied gas that can be reused. That is, the technical idea in the embodiment can have one aspect as a method of recovering the resin decomposition gas and another aspect as a method of manufacturing a liquefied gas that can be reused.

[0096] <<Specific examples of resin>>

[0097] The resin to be thermally decomposed in the recycling system is not particularly limited, and examples thereof include polyethylene resin, polypropylene resin, polyamide 6 resin, polycarbonate resin, polyethylene terephthalate resin, and polybutylene terephthalate resin.

[0098] Hereinafter, application examples of the technical concept will be described using representative resins.

[0099] 1. Polycarbonate resin

[0100] When the resin to be thermally decomposed is a polycarbonate resin, water is added as a reaction aid or additive and thermal decomposition is performed in the extruder 110A. At this time, the internal temperature of the extruder 110A (the temperature of the cylinder 10) is, for example, 260°C to 320°C.

[0101] When the polycarbonate resin is thermally decomposed, bisphenol A (melting point: 159°C, boiling point: 220°C) and phenol (melting point: 40.5°C, boiling point: 182°C) are generated. Here, the high-boiling-point gas is bisphenol A, and the low-boiling-point gas is phenol. It should be noted that the gas discharged from the extruder 110A contains the above-mentioned bisphenol A and phenol and unreacted water (melting point: 0°C, boiling point: 100°C).

[0102] Therefore, for example, the intermediate temperature as the cooling temperature in the heat exchanger 40 is set to 182° C. or higher and lower than 220° C. to liquefy bisphenol A, while the final temperature as the cooling temperature in the heat exchanger 50 is set to lower than 182° C. to liquefy phenol. At this time, for example, by setting the temperature of the heat exchanger 50 to 100° C. or higher and lower than 182° C., phenol can be recovered as a liquid and water (water vapor) can be released into the atmosphere.

[0103] 2. Polyamide 6 resin

[0104] When the resin to be thermally decomposed is polyamide 6 resin, water is added as a reaction aid or additive, and thermal decomposition treatment is performed in the extruder 110A. At this time, the internal temperature of the extruder 110A is, for example, 230°C to 350°C.

[0105] When polyamide 6 resin is thermally decomposed, caprolactam (melting point: 69° C., boiling point: 267° C.) is generated. Here, the gas discharged from the extruder 110A contains caprolactam and unreacted water (melting point: 0° C., boiling point: 100° C.). Here, the high-boiling-point gas is caprolactam, and the low-boiling-point gas is water vapor.

[0106] Therefore, for example, the intermediate temperature as the cooling temperature in the heat exchanger 40 is set to 100° C. or higher and lower than 267° C. to liquefy caprolactam, while the final temperature as the cooling temperature in the heat exchanger 50 is set to lower than 100° C. to liquefy water vapor.

[0107] 3. Polyethylene terephthalate resin

[0108] When the resin to be thermally decomposed is polyethylene terephthalate resin, water or ethylene glycol is added as a reaction aid or additive, and thermal decomposition treatment is performed in the extruder 110A. At this time, the internal temperature of the extruder 110A is, for example, 255°C to 320°C.

[0109] When ethylene glycol is added to polyethylene terephthalate resin, bis(2-hydroxyethyl)terephthalate (melting point: 106°C, boiling point: 317°C or higher) is generated when the polyethylene terephthalate resin is thermally decomposed. Here, the gas discharged from the extruder 110A contains bis(2-hydroxyethyl)terephthalate and unreacted ethylene glycol (melting point: -10°C, boiling point: 244°C). Here, the high-boiling-point gas is bis(2-hydroxyethyl)terephthalate, and the low-boiling-point gas is ethylene glycol.

[0110] Therefore, the intermediate temperature as the cooling temperature in heat exchanger 40 is set to 244°C or higher and lower than 317°C to liquefy bis(2-hydroxyethyl)terephthalate, while the final temperature as the cooling temperature in heat exchanger 50 is set to lower than 244°C to liquefy ethylene glycol.

[0111] 4. Polyolefin resin (chain hydrocarbon resin)

[0112] When the resin to be thermally decomposed is a polyolefin resin, the thermal decomposition treatment is performed in the extruder 110A. At this time, the internal temperature of the extruder 110A is, for example, 300°C to 430°C.

[0113] The polyolefin resin is decomposed into a plurality of hydrocarbon compounds having different carbon atoms by the thermal decomposition. Examples of the gasified hydrocarbon compounds include Figure 6 The hydrocarbon compounds shown are also shown along with the melting points and boiling points of these hydrocarbon compounds.

[0114] In this case, the gas discharged from the extruder 110A includes Figure 6 The gases shown are a plurality of hydrocarbon compounds having carbon numbers of 1 to 21. Although depending on the temperature conditions, hydrocarbon compounds having a large carbon number are not vaporized in the extruder 110A but are molten, discharged from the front end of the extruder 110A, and recovered in the tank 120 .

[0115] And, the generated gas is introduced into the heat exchanger 40. At this time, the high boiling point gas to be liquefied can be any hydrocarbon compound, and can be determined in consideration of the control temperature in the subsequent heat exchanger 50. For example, when the control temperature in the heat exchanger 50 is set to 15°C (room temperature), as the gas cooled in the heat exchanger 50, if the melting point is 15°C or above, solid matter will precipitate in the heat exchanger 50. Therefore, in this case, if hydrocarbons having more carbon atoms than pentadecane having a carbon number of 15 (melting point: 9.9°C) (hydrocarbons having a carbon number of 16 or more) are contained, solid matter will adhere to the inside of the heat exchanger 50, and if the treatment is continued, the efficiency of the thermal decomposition treatment will decrease. If the adhesion of the solid matter further develops and accumulates, the passage of the gas will be blocked, and it may develop into a situation where it is difficult to continue the thermal decomposition treatment.

[0116] Therefore, under the above conditions, it is desirable to set the high boiling point gas to be liquefied in the heat exchanger 40 to a hydrocarbon having 16 carbon atoms (hexadecane, chemical formula: C 16 H 34 ). In this case, since hexadecane is liquefied in the heat exchanger 40, the gas introduced into the heat exchanger 50 does not contain hexadecane. Therefore, even if the control temperature of the heat exchanger 50 is set to 15°C, since the gas having a melting point of 15°C or higher and not solidified in the heat exchanger 50 is not contained, the above-mentioned inconvenience can be suppressed.

[0117] When treating like this, the control temperature of the heat exchanger 40 can be set to a temperature above its melting point and below the low boiling point (above 18°C ​​and below 287°C), for example. Here, in this thermal decomposition treatment, compounds with similar molecular weights and similar melting points and boiling points are included. Therefore, it is desirable to efficiently liquefy the target compound, not to include compounds with boiling points lower than those of the target compound as much as possible, and not to mix unnecessary compounds. Therefore, it is desirable to set the control temperature of the heat exchanger 40 when performing thermal decomposition based on the above conditions to about 230 to 260°C.

[0118] <<Characteristics of the materialization method>>

[0119] Next, the characteristic points in the embodiment will be described.

[0120] The characteristic point in the actual form is that the resin decomposition gas recovery technology has a first stage of cooling the high boiling point gas and the low boiling point gas together to an intermediate temperature and a second stage of cooling the low boiling point gas in a gaseous state from the intermediate temperature to the final temperature.

[0121] According to this characteristic point, the high-boiling-point gas and the low-boiling-point gas can be cooled to an intermediate temperature higher than the final temperature instead of being cooled together to the final temperature. After only the high-boiling-point gas is liquefied and recovered, the low-boiling-point gas that has not been liquefied at the intermediate temperature is cooled to the final temperature, thereby being liquefied and recovered.

[0122] That is, according to the characteristic point, the high boiling point gas and the low boiling point gas can be liquefied and recovered respectively without solidifying by utilizing the boiling point difference between the high boiling point gas and the low boiling point gas. Thus, according to the characteristic point, solidification of the high boiling point gas and the low boiling point gas can be avoided, and as a result, clogging of the gas channel caused by accumulation of solidified gas can be suppressed.

[0123] Thus, according to the characteristic point, it is possible to prevent the recirculation system from being unable to operate continuously due to clogging of the gas passage. As a result, according to the characteristic point, it is possible to suppress a decrease in the operating rate of the recirculation system.

[0124] <Variation 1>

[0125] In the above-mentioned embodiment, for example, Figure 4 As shown in FIG. 1 , the resin decomposition gas recovery device 200A is configured to include the heat exchanger 40 and the heat exchanger 50. That is, the resin decomposition gas recovery device 200A in the embodiment includes the following: Figure 2 The method shown will Figure 1 The basic idea shown is embodied in the structure. However, Figure 1 The basic idea shown is that even Figure 3 The method shown can also be realized. This structure is the first variation of this invention. Figure 7 1 is a diagram showing a recycling system including the resin decomposition gas recovery device 200B in the first modification.

[0126] exist Figure 7 In the embodiment, the resin decomposition gas recovery device 200B includes a tank 120 connected to the front end (downstream) of the extruder 110A, a cooling unit 45 for cooling the inside of the tank 120, and a heat exchanger 50 connected to the tank 120. Specifically, the cooling unit 45 is configured to cool the tank 120 provided at the discharge port of the heat treatment device (extruder 110A) for thermally decomposing the resin to an intermediate temperature, and the high boiling point gas and the low boiling point gas are discharged from the discharge port. On the other hand, the heat exchanger 50 is configured to be connectable to the tank 120.

[0127] According to the resin decomposition gas recovery device 200B constructed as described above, since the tank 120 is cooled to the intermediate temperature by the cooling unit 45, only the high-boiling-point gas is liquefied among the high-boiling-point gas and the low-boiling-point gas discharged from the extruder 110A into the tank 120. On the other hand, the low-boiling-point gas in a gaseous state is introduced from the tank 120 into the heat exchanger 50, and is cooled to the final temperature and liquefied in the heat exchanger 50. In this way, Figure 1 The basic idea shown adopts Figure 7 The resin decomposition gas recovery device 200B in the present modification 1 shown can also be realized.

[0128] <Variation 2>

[0129] In the above-mentioned embodiment, for example, Figure 4 As shown, the resin decomposition gas recovery device 200A is connected to the tank 120, but the present invention is not limited thereto. A vent portion may be provided in the extruder 110A, and the resin decomposition gas recovery device 200A may be connected to the vent portion.

[0130] For example, in a configuration in which the resin decomposition gas recovery device 200A is connected to the tank 120, the high boiling point gas liquefied in the heat exchanger 40 falls into and is accumulated in the tank 120. Here, when the resin is a polyolefin resin, the high boiling point gas liquefied in the heat exchanger 40 is a gas with a large number of carbon atoms. Therefore, when it is desired to use such a gas with a large number of carbon atoms, it is desirable to configure the resin decomposition gas recovery device 200A to be connected to the tank 120.

[0131] On the other hand, when it is desired to improve the acquisition rate of the gas with a small number of carbon atoms compared to the gas with a large number of carbon atoms, it is desirable to connect the resin decomposition gas recovery device 200A to the vent portion as in this modification 2, rather than connecting the resin decomposition gas recovery device 200A to the tank 120. The reason is that in this configuration, the gas with a large number of carbon atoms liquefied in the heat exchanger 40 is returned to the inside of the extruder 110A via the vent portion instead of the tank 120, and is decomposed into the gas with a small number of carbon atoms again in the extruder 110A.

[0132] As mentioned above, the invention proposed by the inventors of the present application has been specifically described based on the embodiments. However, the present invention is not limited to the above-mentioned embodiments, and various modifications can be made without departing from the gist of the invention.

[0133] Description of Reference Numerals

[0134] 10 cylinder block

[0135] 20 Hopper

[0136] 30 Rotation drive mechanism

[0137] 40Heat exchanger

[0138] 50 heat exchanger

[0139] 100 Recirculation System

[0140] 110 Heat treatment device

[0141] 110A Extruder

[0142] 120 cans

[0143] 130 Cooling unit

[0144] 140 Cooling unit

[0145] 200A resin decomposition gas recovery device

[0146] 200B resin decomposition gas recovery device

[0147] A(g) High boiling point gas

[0148] A(l) Liquefied gas

[0149] B(g) Low boiling point gas

[0150] B(l) Liquefied gas

[0151] R1 refrigerant

[0152] R2 refrigerant

Claims

1. A method for recovering resin decomposition gas, characterized in that: The following steps are included: (a) liquefying the first decomposition gas of the first decomposition gas and the second decomposition gas generated by thermally decomposing the resin; and (b) After the step (a), the second decomposed gas is liquefied.

2. The method for recovering resin decomposition gas according to claim 1, wherein: The boiling point of the first decomposition gas is higher than the first temperature, The boiling point of the second decomposition gas is a second temperature lower than the first temperature, In the step (a), the first decomposition gas and the second decomposition gas are introduced into a first cooling unit capable of cooling the first decomposition gas to a temperature higher than the second temperature and lower than the first temperature, thereby liquefying and recovering the first decomposition gas. In the step (b), the second decomposed gas is introduced into a second cooling unit capable of cooling the second decomposed gas to a temperature lower than the second temperature, thereby liquefying and recovering the second decomposed gas.

3. The method for recovering resin decomposition gas according to claim 2, wherein: The first cooling unit includes a first heat exchanger, The second cooling unit includes a second heat exchanger.

4. The method for recovering resin decomposition gas according to claim 2, wherein: The first cooling unit is configured to cool a tank provided at an outlet of a heat treatment device for thermally decomposing the resin to the first temperature, and the first decomposition gas and the second decomposition gas are discharged from the outlet. The second cooling unit includes a heat exchanger connected to the tank.

5. The method for recovering resin decomposition gas according to claim 4, wherein: The heat treatment device is an extruder.

6. A method for recovering resin decomposition gas, characterized in that: The method includes a step of liquefying and recovering a plurality of gases generated by thermally decomposing the resin by utilizing the difference in boiling points of the gases.

7. A method for producing a reusable liquefied gas, characterized in that: The following steps are included: (a) liquefying the first decomposition gas of the first decomposition gas and the second decomposition gas generated by thermally decomposing the resin; and (b) After the step (a), the second decomposed gas is liquefied.

8. The method for producing reusable liquefied gas according to claim 7, wherein: The boiling point of the first decomposition gas is higher than the first temperature, The boiling point of the second decomposition gas is a second temperature lower than the first temperature, In the step (a), the first decomposition gas and the second decomposition gas are introduced into a first cooling unit capable of cooling the first decomposition gas to a temperature higher than the second temperature and lower than the first temperature, thereby liquefying and recovering the first decomposition gas. In the step (b), the second decomposed gas is introduced into a second cooling unit capable of cooling the second decomposed gas to a temperature lower than the second temperature, thereby liquefying and recovering the second decomposed gas.

9. The method for producing a reusable liquefied gas according to claim 8, wherein: The first cooling unit includes a first heat exchanger, The second cooling unit includes a second heat exchanger.

10. The method for producing reusable liquefied gas according to claim 8, wherein: The first cooling unit is configured to cool a tank provided at an outlet of a heat treatment device for thermally decomposing the resin to the first temperature, and the first decomposition gas and the second decomposition gas are discharged from the outlet. The second cooling unit includes a heat exchanger connected to the tank.

11. The method for producing reusable liquefied gas according to claim 10, wherein: The heat treatment device is an extruder.

12. A method for producing reusable liquefied gas, characterized in that: The method includes a step of liquefying and recovering a plurality of gases generated by thermally decomposing the resin by utilizing the difference in boiling points of the gases.

13. A resin decomposition gas recovery device, characterized in that: include: a first cooling unit configured to liquefy and recover the first decomposition gas of the first decomposition gas and the second decomposition gas generated by thermally decomposing the resin; and The second cooling unit is configured to liquefy and recover the second cracked gas.

14. The resin decomposition gas recovery device according to claim 13, characterized in that: The boiling point of the first decomposition gas is higher than the first temperature, The boiling point of the second decomposition gas is a second temperature lower than the first temperature, The first cooling unit is configured to be able to cool to an intermediate temperature that is higher than the second temperature and lower than the first temperature. The first cooling unit is configured to cool the first cracked gas and the second cracked gas to the intermediate temperature, thereby liquefying and recovering the first cracked gas. The second cooling unit is configured to be able to cool to a final temperature lower than the second temperature. The second cooling unit is configured to liquefy and recover the second cracked gas by cooling the second cracked gas to the final temperature.

15. The resin decomposition gas recovery device according to claim 14, characterized in that: The second decomposed gas discharged from the first cooling part is introduced into the second cooling part and cooled to the final temperature, thereby liquefying and recovering the second decomposed gas.

16. The resin decomposition gas recovery device according to claim 13, characterized in that: The first cooling unit includes a first heat exchanger, The second cooling unit includes a second heat exchanger.

17. The resin decomposition gas recovery device according to claim 13, characterized in that: The first cooling unit is configured to cool a tank provided at an outlet of a heat treatment device for thermally decomposing the resin to the first temperature, and the first decomposition gas and the second decomposition gas are discharged from the outlet. The second cooling unit includes a heat exchanger connected to the tank.

18. The resin decomposition gas recovery device according to claim 17, characterized in that: The heat treatment device is an extruder.

19. A resin decomposition gas recovery device, characterized in that: A plurality of liquefaction recovery units are provided, each of which is configured to liquefy and recover the plurality of gases generated by thermal decomposition of the resin using the difference in boiling points of the plurality of gases.

20. The resin decomposition gas recovery device according to claim 19, characterized in that: The plurality of gases are recyclable gases.

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