How to dechlorinate plastics

Abstract

A method for dechlorinating plastics with a high dechlorination rate is provided. [Solution] In a reactor 10 consisting of a pressure vessel, plastics to be treated are heated in the presence of water at a temperature of 200°C to 350°C for 8 to 240 minutes, thereby carrying out hydrothermal treatment on the plastics to be treated in the reactor 10, and the oil phase portion of the reaction product 30 present in the reactor 10 after the hydrothermal treatment is recovered as dechlorinated organic components 32. The recovered dechlorinated organic components 32 are converted into oil by pyrolysis or the like using a known method, making it possible to recover oil with a low chlorine concentration of 100 ppm or less.

Description

[Technical Field]

[0001] The present invention relates to a method for dechlorinating plastics, and more particularly to a method for dechlorinating plastics suitable for use as a pretreatment for oiling waste plastics and the like when the waste plastics and the like are chemically recycled by oiling. [Background technology]

[0002] Due to a growing sense of crisis about environmental issues such as climate change and global warming, there is a need to reduce the consumption of limited resources and reduce the burden on the environment by recycling resources in a circular manner.

[0003] Due to these demands, the importance of recycling waste plastics, which are used as packaging containers and are discarded in large quantities, is increasing.

[0004] Currently, approximately 60% of plastic recycling in Japan is carried out as so-called "thermal recycling," which reuses waste plastic as fuel for the purpose of energy recovery, such as using waste incineration heat, waste incineration for power generation, conversion into cement raw materials and fuel, and conversion into solid fuels such as RPF (Refuse Paper & Plastic Fuel) and RDF (Refuse Derived Fuel).

[0005] However, plastics that have been subjected to thermal recycling are lost through combustion and can no longer be recycled.

[0006] Therefore, from the perspective of recycling resources, it is desirable to recycle waste plastics by subjecting them to "material recycling," in which they are recycled while remaining in their plastic state, or "chemical recycling," in which they are decomposed using chemical methods and reused.It is desirable that only the remaining waste plastics that cannot be recycled in this way be subjected to "thermal recycling," in which energy is recovered as a final recycling method.

[0007] One such chemical recycling method is the conversion of plastics into oil.

[0008] Plastic oil recycling involves converting plastics, which are made from petroleum, back into the original oil and reusing it, so it can be said to be the recycling method that is most in line with the perspective of cyclical use of resources.

[0009] Some plastics, such as polyvinyl chloride (PVC), contain chlorine, and if such chlorine-containing plastics are directly converted into oil, the resulting oil will also contain chlorine and chlorine compounds.

[0010] Furthermore, the aforementioned polyvinyl chloride (PVC) is widely used as a wrap for food packaging, and is therefore consumed in large quantities. Therefore, even plastics recovered through separate collection as chlorine-free plastics (PE, PP, PS, etc., known as the "3Ps") may contain PVC. If these plastics are converted directly into oil, there is a risk that chlorine or chlorine compounds may be contaminated in the recovered oil.

[0011] As a result, if plastics containing chlorine or waste plastics mixed with chlorine-containing plastics are directly converted into oil using methods such as thermal decomposition, not only will the quality of the recovered oil be reduced due to the inclusion of chlorine or chlorine compounds, but if the recovered oil is used as fuel, for example, fuel containing chlorine or chlorine compounds can cause corrosion of equipment such as combustion furnaces and engines, and may also produce harmful gases when burned.

[0012] Therefore, when converting chlorine-containing plastics such as polyvinyl chloride (PVC) or waste plastics that have been mixed with such chlorine-containing plastics into oil, dechlorination is required as a pretreatment process.

[0013] As a method for dechlorinating such plastics, Patent Document 1, listed below, proposes that waste plastics be heated to 300 to 350°C in the cylinder of a screw extruder and extruded in a molten state, as shown in Figure 9, and that this be made possible by a dehydrochlorination reaction that occurs as a result of thermal decomposition. The vaporized hydrogen chloride is then discharged from the cylinder of the screw extruder, thereby separating chlorine from the molten plastic (see Figure 3 of Patent Document 1). [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-344934 Summary of the Invention [Problem to be solved by the invention]

[0015] As introduced in the aforementioned Patent Document 1, the dechlorination method in which waste plastics are thermally decomposed at high temperatures of 300°C or higher to separate the vaporized hydrogen chloride requires a large-scale processing device such as a screw extruder to carry out the dechlorination process, which requires a significant initial investment.In addition, the hydrogen chloride produced by the thermal decomposition of PVC reacts with oil to produce organic chlorine compounds, which degrades the quality of the oil.

[0016] Furthermore, heating waste plastics under atmospheric pressure to pyrolyze them requires a large amount of energy consumption, so when dechlorinating using the method described in Patent Document 1, not only do running costs increase, but problems also arise, such as the unpleasant odor that occurs during pyrolysis and the noise that is generated when the treatment equipment is operating.

[0017] Furthermore, not only is hydrogen chloride produced and separated from the waste plastic being treated, but some of the reusable organic components are also lost during gasification, which may reduce the yield of oil obtained from the subsequent oilification process.

[0018] On the other hand, if the treatment is carried out at a temperature lower than the above-mentioned temperature in order to suppress the gasification of organic components and improve the oil yield, the dechlorination cannot be carried out sufficiently, which reduces the quality of the recovered oil, or the treatment takes a long time, which reduces workability.

[0019] One possible reason why the chlorine concentration of the recovered oil does not decrease even after dechlorination is that the hydrogen chloride produced by the dechlorination of plastics causes the plastics to be rechlorinated.

[0020] Therefore, the present invention has been made to eliminate the drawbacks of the above-mentioned conventional technologies, and aims to provide a method for dechlorinating plastics that can achieve dechlorination at relatively low cost, in a relatively short time, and with little generation of unpleasant odors or noise, and preferably to provide a method for dechlorinating plastics that can perform dechlorination at a high dechlorination rate, and that, when the obtained dechlorinated plastic is used to produce oil, can produce oil with a low content of chlorine and chlorine compounds (for example, a chlorine concentration of 100 ppm or less).

[0021] Another object of the present invention is to provide a method for dechlorinating plastics that can suppress rechlorination of plastics by hydrogen chloride generated during dechlorination. [Means for solving the problem]

[0022] The means for solving the problems are described below together with the reference numerals used in the description of the embodiment of the invention. These reference numerals are intended to clarify the correspondence between the claims and the description of the embodiment of the invention, and needless to say, are not used to restrict the interpretation of the technical scope of the present invention.

[0023] In order to achieve the above object, the method for dechlorinating plastics of the present invention comprises the steps of: For example, plastics containing chlorine such as PVC, or mixed plastics such as PVC and PP, PE, PS, etc., which contain chlorine-containing plastics in part, are treated as plastics. In a reactor 10 consisting of a pressure vessel, the plastic to be treated is heated in the presence of water at a temperature of 200°C to 350°C, preferably 250°C to 300°C, for 8 to 240 minutes, preferably 15 to 240 minutes, thereby carrying out a hydrothermal treatment on the plastic to be treated, and The method is characterized in that the oil phase portion of the reaction product 30 present in the reactor 10 after the hydrothermal treatment is recovered as a dechlorinated organic component (hereinafter referred to as "dechlorinated organic component 32") (Claim 1).

[0024] The water may be present in the reactor in the form of an alkaline aqueous solution such as an NaOH aqueous solution (claim 2).

[0025] Furthermore, the reaction pressure during the hydrothermal treatment is preferably 16.5 MPa or less, more preferably 8.6 MPa or less (claim 3).

[0026] The method for dechlorinating plastics of the present invention can be carried out as a pretreatment for oilification to recover recycled heavy oil (JIS K 2170).

[0027] Another method for dechlorinating plastics according to the present invention includes the steps of: The method is characterized by the fact that the rechlorination of plastics by the generated hydrogen chloride is inhibited by dechlorinating plastics in high-temperature water or alkaline water (claim 5).

[0028] In addition, "rechlorination" as referred to here does not only include the rechlorination of chlorine-containing plastics such as PVC, but also includes chlorination in which hydrogen chloride produced by the chlorine-containing plastic reacts with the chlorine-free plastics such as the 3Ps to form new chlorine compounds when the object to be treated is a mixed plastic of chlorine-containing plastics such as PVC and chlorine-free plastics such as PP, PE, and PS. [Effects of the Invention]

[0029] With the configuration of the present invention described above, the plastic dechlorination method of the present invention performs dechlorination by hydrothermal treatment, which makes it possible to perform dechlorination using a relatively simple device configuration, with relatively little energy consumption, and with little generation of unpleasant odors or noise.

[0030] In particular, when the heating temperature was set to 250°C or higher, dechlorination with a high dechlorination rate (88% or higher in the examples) was achieved in a relatively short time of less than 240 minutes. Furthermore, the hydrogen chloride generated in the dechlorination process dissolved in water, significantly reducing its reactivity, so that rechlorination of PVC and chlorination of coexisting plastics could be almost completely suppressed.

[0031] As a result, by converting the dechlorinated organic matter component 32 obtained by the dechlorination method of the present invention into oil, it was possible to recover oil with an extremely low chlorine concentration of 100 ppm or less.

[0032] This chlorine concentration is sufficiently small compared to the chlorine content of recycled heavy oil specified in JIS K 2170 (2013) (500 ppm for Type 1, 1000 ppm for Type 2). By dechlorinating using the method of the present invention and converting the recovered dechlorinated organic matter component 32 into oil to recover heavy oil, it was possible to recover recycled heavy oil that meets the chlorine content specified in JIS K 2170 (2013).

[0033] In addition, in the dechlorination method of the present invention, in which plastics are dechlorinated in high-temperature water or alkaline water, the hydrogen chloride produced by the dechlorination reaction dissolves in water and, in the presence of alkali, is further neutralized by the alkali, reducing its reactivity to chlorination, thereby suppressing the rechlorination of plastics. [Brief explanation of the drawings]

[0034] [Figure 1]1 is an explanatory diagram of a process for recycling waste plastics including the dechlorination method of the present invention. [Figure 2] FIG. 1 is an explanatory diagram showing the separation state of a reaction product in a reactor into which a filtrate has been introduced. [Figure 3] This is an explanatory diagram of the dechlorination equipment used in the dechlorination test. (A) is the reactor, and (B) is an overall diagram of the dechlorination equipment consisting of the reactor and heating tank. [Figure 4] Graph showing the results of a dechlorination test using PVC as the treatment target. [Figure 5] This is a graph showing the results of a dechlorination test on mixed plastics (PVC + 3P). [Figure 6] This graph shows the measurement results of the chlorine concentration (ppm) in the solid residue obtained when mixed plastic (PVC + 3P) was dechlorinated at 250°C, and in each product obtained by oiling the dechlorinated organic components. [Figure 7] This graph shows the measurement results of the chlorine concentration (ppm) in the solid residue obtained when mixed plastic (PVC + 3P) was dechlorinated at 300°C, and in each product obtained by oiling the dechlorinated organic components. [Figure 8] This is a graph showing the measurement results of the chlorine concentration (ppm) in each product obtained by oiling mixed plastics (PVC + 3P) without dechlorination. [Figure 9] FIG. 1 is an explanatory diagram of a conventional dechlorination device (corresponding to FIG. 3 of Patent Document 1). DETAILED DESCRIPTION OF THE INVENTION

[0035] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0036] [Overall structure] The plastic dechlorination method of the present invention treats chlorine-containing plastics such as polyvinyl chloride (PVC) or plastic mixtures that partially contain chlorine-containing plastics, and as shown in Figure 1, includes a "hydrothermal treatment step" in which the treatment target is subjected to hydrothermal treatment, and a "recovery step" in which dechlorinated organic components (dechlorinated organic components 32: see Figure 2) are recovered from the reaction product 30 obtained by this hydrothermal treatment step (see Figure 2), and preferably can further include a "pretreatment step" that is performed on the treatment target before the aforementioned "hydrothermal treatment step" is performed.

[0037] [Pretreatment process] 1 illustrates an example in which discarded waste plastics used as packaging containers, etc., are treated. The recovered waste plastics may be subjected to removal of PET by rough separation, etc., as needed, and the mixed plastics of PVC and 3P (PP, PE, PS) obtained in this way can be treated. However, since the method of the present invention can deoxidize PET and the like in addition to dechlorination, waste plastics containing PET may also be treated.

[0038] Mixed plastics of PVC and 3P (PP, PE, PS) can be crushed into appropriate sizes using a shredding machine or similar, and then washed to remove any attached matter. If necessary, the plastic to be treated that has been pre-treated in this way can be subjected to the "hydrothermal treatment process" described below.

[0039] Furthermore, even when waste plastics are to be treated, they may be subjected to the dechlorination method of the present invention without undergoing the above-mentioned rough separation, crushing, washing, etc.

[0040] In this embodiment, the dechlorination method of the present invention will be explained using an example in which mixed plastics (PVC + 3P) are treated, but the plastics to be treated in this invention may also be chlorine-containing plastics such as PVC, which are treated alone.

[0041] [Hydrothermal treatment process] The plastic to be treated (PVC + 3P) that has undergone the pretreatment process described above is subjected to a "hydrothermal treatment process" in which it is heated in the presence of water in a reactor 10 at a predetermined temperature for a predetermined time, thereby carrying out hydrothermal treatment in the reactor 10.

[0042] The reactor 10 mentioned above is a pressure vessel that has pressure resistance capable of withstanding the increase in internal pressure due to the water vapor pressure generated during the hydrothermal treatment process, and various types of reactor 10 can be used as long as they have heat resistance properties that allow the internal temperature to be heated to the heating temperature described below.

[0043] In the hydrothermal treatment device 1 (see Figure 3) described below as an experimental device, a small stainless steel reactor 10 is immersed in molten salt 22 heated in a heating tank 20, thereby raising the internal temperature of the reactor 10 to the required heating temperature.However, instead of this configuration, the inside of the reactor may be heated by, for example, a band heater wrapped around the outer periphery of a cylindrical reactor, although this is not shown in the figure, and the configurations of the hydrothermal treatment device 1 and the reactor 10 are not limited to those of the experimental device described below.

[0044] Furthermore, in the experimental apparatus described below, the reactor 10 is configured as a batch type, but the reactor 10 may be of a continuous type as long as it is possible to carry out hydrothermal treatment under the treatment conditions described below.

[0045] The heating temperature in the reactor 10 can be in the range of 200°C to 350°C, but if the heating temperature is below 250°C, dechlorination is possible, but the reaction rate is slow and it is difficult to increase the dechlorination rate (%) to a high value within the heating time described below, so the lower limit of the heating temperature is preferably 250°C.

[0046] Furthermore, in the hydrothermal treatment carried out by the dechlorination method of the present invention, as is clear from the experimental data shown below, the higher the heating temperature, the faster the reaction rate and the higher the dechlorination rate (%) can be achieved in a short period of time, so the upper limit of the heating temperature can be selected within a range below 374°C, which is the critical temperature of water.

[0047] However, an increase in the heating temperature results in an increase in pressure inside the reactor 10, and therefore a reactor 10 with high pressure resistance performance must be used. Therefore, the practical upper and lower limits of the heating temperature are approximately 350°C (reaction pressure 16.5 MPa), preferably approximately 300°C (reaction pressure 8.6 MPa).

[0048] The time for the hydrothermal treatment is 8 to 240 minutes, preferably 15 to 240 minutes.

[0049] By extending the hydrothermal treatment time, it is possible to improve the dechlorination rate (%) even when the hydrothermal treatment is performed at a low heating temperature, but treatment for longer than 240 minutes reduces the workability of the dechlorination treatment.

[0050] On the other hand, in order to achieve a high dechlorination rate (%) in a shorter time, it is necessary to increase the heating temperature, and since the internal pressure of the reactor 10 increases with the increase in heating temperature, it is necessary to use a reactor 10 with high pressure resistance, so it is preferable that the hydrothermal treatment time (heating time) be 8 minutes or more, preferably 15 minutes or more.

[0051] In order to carry out the above-mentioned hydrothermal treatment, the plastic to be treated needs to be heated in the presence of water in the reactor 10 .

[0052] In order to have water present in the reactor 10, "water" may be introduced into the reactor 10 together with the plastic to be treated and heated, or this water may be introduced into the reactor 10 in the form of an alkaline aqueous solution, which makes it possible to neutralize the hydrogen chloride produced by the dechlorination reaction within the reactor 10.

[0053] As the alkaline aqueous solution to be put into the reactor 10 together with the plastic to be treated, an aqueous NaOH solution, an aqueous ammonia solution, lime water, sodium bicarbonate water, etc. can be used, and in this embodiment, an aqueous NaOH solution was used.

[0054] After such a dechlorination reaction is carried out for a predetermined time, heating is stopped and the reactor 10 is cooled or the like to lower the internal temperature, thereby completing the dechlorination reaction by hydrothermal treatment.

[0055] [Recovery process] After the hydrothermal treatment step is completed as described above, a "recovery step" is carried out in which the oil phase portion is recovered as dechlorinated organic matter components 32 from the post-reaction product 30 present in the reactor 10.

[0056] When water is added to the reaction product 30 by, for example, introducing water into the reactor after the hydrothermal treatment described above, the dechlorinated organic matter components 32, which are the oil phase portion of the reaction product 30, float on the water (NaCl aqueous solution in this embodiment) as shown in Figure 2, while the solid residue 31 combined with chlorine or chlorine compounds sinks in the water, so that the dechlorinated organic matter components 32 can be easily separated and recovered by known methods such as gravity separation.

[0057] In the above-mentioned hydrothermal treatment step, in this embodiment, an alkaline aqueous solution (NaOH aqueous solution) was placed in the reactor 10 together with the plastic to be treated and hydrothermal treatment was carried out, and water was added directly to the reaction product 30 and gravity separation was carried out. However, if the hydrothermal treatment step involves placing simple water in the reactor 10 instead of an alkaline aqueous solution, the reaction product 30 may be neutralized by adding an alkaline aqueous solution, and then the above-mentioned gravity separation or the like may be carried out to recover the oil phase portion as the dechlorinated organic matter component 32.

[0058] Furthermore, in this embodiment, a method of introducing water into the reactor 10 and carrying out gravity separation has been described, but the post-reaction product 30 taken out from the reactor 10 may also be subjected to gravity separation or the like.

[0059] Furthermore, the recovery of the dechlorinated organic matter components 32 is not limited to the above-mentioned gravity separation, and can be carried out by various known methods as long as the method is capable of recovering the oil phase portion from the reaction product 30.

[0060] In this way, the dechlorinated organic matter components 32 recovered in the recovery process can then be converted into oil using known methods such as thermal decomposition, allowing oil with a low chlorine concentration (for example, oil with a chlorine concentration of 100 ppm or less) to be recovered.

[0061] The oils recovered from the dechlorinated organic matter components 32 by such oilification include naphtha, kerosene, light oil, heavy oil, as well as SAF (Sustainable Aviation Fuel), and the type is not particularly limited. [Example]

[0062] [Dechlorination test] The following shows the test results of dechlorinating plastics using the dechlorination method of the present invention.

[0063] 1. Purpose of the test It has been confirmed that the dechlorination method of the present invention can dechlorinate both chlorine-containing plastics such as PVC, and mixed plastics consisting of chlorine-containing plastics and chlorine-free plastics such as 3P (PP, PE, PS), and the treatment conditions under which dechlorination can be carried out effectively are sought.

[0064] 2. Hydrothermal treatment equipment An example of the configuration of the hydrothermal treatment device 1 used in this test example is shown in FIG.

[0065] The hydrothermal treatment device 1 shown in Figure 3 consists of a reactor (batch type) 10 (see Figures 3(A) and (B)), which is a stainless steel pressure vessel, and a heating tank 20 (see Figure 3(B)).The reactor 10 is configured so that the inside of the reactor 10 can be heated uniformly by immersing it in molten salt 22 that is heated and stirred by stirring blades 21 in the heating tank 20 to achieve a uniform temperature.

[0066] 3. Test Method (1) Dechlorination test using PVC as the treatment target 4.5 g of PVC was placed in a 27.48 cm3 container with 12 mL of a 3 mol / L NaOH solution.3 After the mixture was placed in the reactor 10, the lid 10a of the reactor 10 was closed and sealed, and the reactor 10 was immersed in the molten salt 22 in the heating tank 20 and heated at temperatures of 200°C, 220°C, 250°C, 275°C, and 300°C (all of which were the temperatures of the molten salt), and the change in the dechlorination rate (%) with respect to the heating time at each heating temperature was measured.

[0067] The reaction pressure at each temperature is the saturated water vapor pressure of 1.5 MPa at 200°C, 2.31 MPa at 220°C, 4.0 MPa at 250°C, 5.8 MPa at 275°C, and 8.6 MPa at 300°C.

[0068] In addition, the dechlorination rate (%) was measured by removing the reactor 10 from the heating tank 20 after heating for a predetermined time, pouring cooling water (distilled water) onto the outer surface of the reactor 10 to rapidly cool it and stop the reaction, and then performing the following procedure.

[0069] Distilled water was introduced into the reactor 10 as the filtrate 50, and the post-reaction product 30 in the reactor 10 was separated into a solid residue 31 that settled in the filtrate 50 and a dechlorinated organic matter component 32, which was an oil phase portion that floated on the filtrate 50, due to the difference in specific gravity, as shown in Figure 2.

[0070] The dechlorinated organic matter component 32 that floated to the surface and the filtrate 50 were removed from the reactor 10, and the components remaining in the reactor 10 were recovered as a solid residue 31.

[0071] The filtrate 50 and dechlorinated organic matter components 32 removed from the reactor 10 were separated into the filtrate 50 and the dechlorinated organic matter components 32, and the weight (mg) of chlorine contained in the filtrate 50 after removing the dechlorinated organic matter components 32 was measured.

[0072] Based on the measured weight (mg) of chlorine in the filtrate 50 and the weight (mg) of chlorine contained in the PVC plastic to be treated, the dechlorination rate (%) was calculated using the following formula. Dechlorination rate (%) = [weight of chlorine in the filtrate (mg) / weight of chlorine contained in the PVC plastic to be treated (mg)] × 100 (Equation 1)

[0073] As described above, the dechlorination rate (%) is the weight of chlorine contained in the filtrate 50 divided by the weight of chlorine contained in the PVC, and is expressed as a percentage. Therefore, the weight of chlorine contained in the solid residue 31 of the post-reaction product 30 obtained by hydrothermal treatment is not taken into account in the dechlorination rate (%).

[0074] (2) Dechlorination test using PVC+3P as treatment target 4.5 g of a mixed plastic of PVC and 3P (PE, PP, PS) was placed in a 27.48 cm3 container with 12 mL of a 3 mol / L NaOH solution. 3 After the mixture was placed in the reactor 10, the lid 10a was put on and the reactor 10 was sealed, and the reactor 10 was immersed in the molten salt 22 in the heating tank 20 and heated at temperatures of 250°C and 300°C (both of which were the temperatures of the molten salt), and the change in the dechlorination rate (%) with respect to the heating time at each heating temperature was measured.

[0075] The reaction pressure when the heating temperature was 250°C was approximately 4.0 MPa, and when the heating temperature was 300°C, the reaction pressure was approximately 8.6 MPa.

[0076] In addition, the breakdown of each resin in 4.5g of mixed plastic (PVC + 3P) is 0.5g of PVC, and the weight ratio of each is PE:PP:PS:PVC = 3:2:1:0.75 ≒ 2.0g:1.33g:0.67g:0.5g.

[0077] 4. Test Results (1) Results of dechlorination tests using PVC as the treatment target In a dechlorination test using PVC as the treatment target, the change in dechlorination rate (%) versus the change in treatment time (min) at each heating temperature was measured. The results are shown in Figure 4.

[0078] In dechlorination tests using PVC as the treatment target, it was confirmed that dechlorination occurred over the entire range of heating conditions from 200°C to 300°C, and in particular, when the heating temperature was in the range of 275°C to 300°C, the dechlorination rate exceeded 90% in an extremely short treatment time of 15 minutes.

[0079] Furthermore, even when heating at 250°C, the dechlorination rate increased to approximately 95% by extending the treatment time to 240 minutes.

[0080] From the above results, it was confirmed that the dechlorination method of the present invention can dechlorinate PVC over the entire range of heating conditions from 200°C to 300°C, and in particular, by setting the heating temperature to 250°C or higher, dechlorination can be achieved at a high dechlorination rate (%) of 90% or more in a treatment time of 240 minutes or less.

[0081] In this test example, the maximum heating temperature was set to 300°C, and dechlorination tests were not conducted at temperatures higher than that. However, as is clear from the experimental results shown in Figure 4, as the heating temperature increases, the dechlorination rate (%) can be increased in a shorter time (the dechlorination reaction can be promoted), and therefore it is thought that as long as the heating temperature is in the range below 374°C, which is the critical temperature of water, a high improvement in the dechlorination rate (%) can be obtained in a short time even at temperatures above 300°C.

[0082] Furthermore, under heating conditions of 250°C, the dechlorination rate can be increased to over 95% with a heating time of 240 minutes. Therefore, by carrying out hydrothermal treatment for dechlorination at a temperature of 250°C or higher, it is possible to complete the hydrothermal treatment in a relatively short time of 240 minutes or less under any temperature conditions.

[0083] (2) Results of dechlorination tests on mixed plastics (PVC + 3P) Figure 5 shows the results of measuring the change in dechlorination rate (%) versus treatment time when hydrothermal treatment was performed on mixed plastic (PVC + 3P) at heating temperatures of 250°C and 300°C.

[0084] For comparison, Figure 5 also shows the results of the dechlorination test using the aforementioned PVC as the treatment target, with heating temperatures of 250°C and 300°C.

[0085] The test results shown in Figure 5 confirm that dechlorination can be achieved at both 250°C and 300°C, even in tests using mixed plastics (PVC + 3P), and that the dechlorination rate (%) increases with increasing heating time.

[0086] Furthermore, the graph shown in Figure 5 confirms that the maximum dechlorination rate (%) in the test results in which mixed plastics (PVC + 3P) were treated was approximately 10% lower than the test results in which only PVC was treated.

[0087] However, as a result of the oilification test described below, even when oilification was performed on the dechlorinated organic matter component 32 obtained by the dechlorination process using mixed plastic (PVC + 3P) as the processing target, the chlorine concentration (ppm) of the obtained oil was significantly below the target value of 100 ppm, confirming that the dechlorination method of the present invention is effective as a dechlorination method performed as a pretreatment for oilification not only when PVC is the processing target alone, but also when mixed plastic (PVC + 3P) is the processing target.

[0088] [Oil-making test] 1. Purpose of the test It is confirmed that oil with a low chlorine content (target chlorine concentration of 100 ppm or less) can be obtained by subjecting the dechlorinated organic matter component 32 obtained by the dechlorination method of the present invention to oilification.

[0089] 2. Test Method Among the dechlorinated organic matter components 32 obtained by the dechlorination method of the present invention, the dechlorinated organic matter components 32 obtained by the dechlorination treatment of mixed plastics (PVC + 3P) with a low dechlorination rate (%) were subjected to oilification.

[0090] The dechlorinated organic matter components 32 targeted for oilification were those obtained by dechlorination treatment at a heating temperature of 250°C and those obtained by dechlorination treatment at a heating temperature of 300°C.

[0091] These dechlorinated organic components 32 were each heated at 475°C under a pressure of 0.1 MPa (atmospheric pressure) for 10 minutes, and the pyrolysis gas produced by this heating was cooled to condense and recover the oil.

[0092] The chlorine concentration (ppm) was measured for the oil recovered by the above method, the gas after the oil was recovered, and the components (char) that remained ungasified during pyrolysis (however, the chlorine concentration in the gas was not measured for the oilification of the dechlorinated organic component 32 obtained by dechlorination at 300°C).

[0093] The chlorine concentration (ppm) of the solid residue 31 generated during dechlorination by hydrothermal treatment was also measured.

[0094] As a comparative example, a mixed plastic (PVC + 3P) of the same composition was directly heated at 475°C and 0.1 MPa (atmospheric pressure) for 10 minutes without undergoing dechlorination treatment, and the oil content was recovered from the resulting pyrolysis gas. The chlorine concentrations in the oil, char, and gas were also measured.

[0095] 3. Test Results The chlorine concentrations of the oil, gas, char, and solid residue obtained from the above-mentioned oilification test are shown in Figures 6 and 7.

[0096] Figure 6 shows the chlorine concentration when the dechlorinated organic matter component 32 obtained by dechlorination at 250°C is oiled, and Figure 7 shows the chlorine concentration when the dechlorinated organic matter component 32 obtained by dechlorination at 300°C is oiled.

[0097] Figure 8 also shows the chlorine concentrations in the oil, char, and gas when mixed plastics (PVC + 3P) that had not been subjected to dechlorination treatment were directly converted to oil.

[0098] As can be seen from Figure 6, the chlorine concentration of the oil obtained by oilifying the dechlorinated organic component 32 obtained by dechlorination at 250°C was 67.13 ppm, and as can be seen from Figure 7, the chlorine concentration of the oil obtained by oilifying the dechlorinated organic component 32 obtained by dechlorination at 300°C was 53.71 ppm. In both cases, oil with chlorine concentrations well below the target value of 100 ppm was recovered.

[0099] When mixed plastics (PVC+3P) that have not been subjected to dechlorination treatment are directly oiled, the chlorine concentration in the oil obtained is 8099 ppm. Therefore, by performing the dechlorination treatment of the present invention and then oiling, the chlorine concentration in the oil obtained by oiling can be reduced to less than 1% of the chlorine concentration in the oil obtained when oiling is performed without dechlorination treatment, and it has been confirmed that the dechlorination method of the present invention is extremely effective as a dechlorination method performed as a pretreatment for oiling.

[0100] Furthermore, in this oilification test, it was confirmed that the dechlorination rate (%) was lower than when PVC was used as the processing target. Even when the dechlorinated organic matter component 32 obtained by dechlorinating PVC+3P was oilified, the chlorine concentration of the oil obtained by oilification could be kept below 100 ppm. Therefore, it can be reasonably inferred that if the dechlorinated organic matter component 32 obtained by the dechlorination treatment using PVC as the processing target, which showed a higher dechlorination rate (%), is oilified, it will be possible to recover oil with an even lower chlorine concentration (ppm).

[0101] As such, the chlorine concentration of the oil recovered by dechlorination using the method of the present invention is sufficiently small compared to the chlorine content of recycled heavy oil specified in JIS K 2170 (2013) (500 ppm for Type 1, 1000 ppm for Type 2). Therefore, by using the dechlorination method of the present invention as a pretreatment for oilification to recover heavy oil, it is possible to recover recycled heavy oil specified in JIS K 2170 (2013).

[0102] As shown in Figure 8, in an example where mixed plastic (PVC + 3P) was directly converted to oil without undergoing dechlorination treatment, the chlorine concentration in the gas was extremely high, whereas when the dechlorinated organic matter component 32 obtained by the dechlorination method of the present invention was converted to oil, the chlorine concentration in the gas was reduced to a low value of 24.68 ppm (see Figure 6).Even if the gas after oil recovery is used as fuel, it is possible to suppress corrosion of equipment such as combustion furnaces and the emission of harmful substances associated with combustion. [Explanation of symbols]

[0103] 1 Hydrothermal treatment equipment 10. Reactor 10a Lid (of reactor) 20 Heating tank 21 Stirring blade 22 Molten Salt 30 Reaction products 31 Solid residue 32 Dechlorinated organic components 50 Filtrate (water)

Claims

1. The plastics to be treated are plastics containing chlorine or plastics that partially contain plastics containing chlorine, In a reactor consisting of a pressure vessel, the plastic to be treated is heated in the presence of water at a temperature of 200 ° C to 350 ° C for 8 to 240 minutes, thereby performing hydrothermal treatment on the plastic to be treated in the reactor; A method for dechlorinating plastics, characterized in that an oil phase portion of the reaction product present in the reactor after the hydrothermal treatment is recovered as a dechlorinated organic component.

2. 2. The method for dechlorinating plastics according to claim 1, wherein the water is present in the reactor in the form of an alkaline aqueous solution.

3. 3. The method for dechlorinating plastics according to claim 1, wherein the reaction pressure during the hydrothermal treatment is 16.5 MPa or less.

4. 3. The method for dechlorinating plastics according to claim 1 or 2, wherein the method is carried out as a pretreatment for oilification in order to recover recycled heavy oil.

5. A method for dechlorinating plastics, characterized by the fact that the rechlorination of plastics by the generated hydrogen chloride is suppressed by dechlorinating plastics in high-temperature water or alkaline water.

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