JP2013028687A - Method of liquefying waste plastic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of liquefying a waste plastic, which can crack and separate the waste plastic by a simple method without using a catalyst, thereby obtaining an industrially practicable fuel oil.SOLUTION: The method of liquefying the waste plastic includes: a step of introducing the waste plastic into a reaction vessel; a step of introducing water vapor into the reaction vessel and then melting the waste plastic while heating the waste plastic to maintain the temperature in the reaction vessel at 180-300°C; a step of discharging the water vapor from the reaction vessel and then raising the temperature in the reaction vessel to 350-450°C to pyrolyzing the waste plastic thus melted; and a step of discharging the pyrolyzed products of the waste plastic as a gas from the reaction vessel and then cooling them to recover them as a liquid.

Description

  The present invention relates to a method for converting waste plastics into oil.

  Conventionally, as one method of reusing waste plastic, there is a method of thermally decomposing at high temperature and using it as fuel oil.

  As a technology for reusing waste plastic as fuel oil, after the waste plastic is pyrolyzed at high temperature and gasified, the generated gas is secondarily pyrolyzed with a solid acid catalyst, and the organic acid contained in the gas There is disclosed a method for oily treatment of waste plastics that removes with a transition metal catalyst (see, for example, Patent Document 1).

JP-A-6-298994

  However, in the method of Patent Document 1, since the catalyst is used, the cost and maintenance of the catalyst are required, and the hydrocarbon mixture which is a decomposition product obtained by the method has a large molecular weight distribution. In addition, since it contains a long-chain hydrocarbon having a large number of carbon atoms, it may solidify when the liquid temperature is lowered, and the kinematic viscosity is also high. Therefore, when using as fuel oil, a load was applied to the liquid feed pump and piping, and there was a problem in industrial use.

  The present invention has been made in view of the above, and waste plastic can be decomposed and separated by a simple method without using a catalyst to obtain industrially practical fuel oil. An object of the present invention is to provide a method for converting waste plastic to oil.

In order to solve the above-described problems and achieve the object, an introduction step of introducing waste plastic into the reaction vessel, water vapor is introduced into the reaction vessel, and a material temperature in the reaction vessel is set to 180 ° C. to 300 ° C. While heating so as to maintain the temperature range, a melting step for melting the waste plastic, and water vapor is discharged from the reaction vessel, and the temperature of the material in the reaction vessel is raised to a temperature range of 350 ° C. to 450 ° C. A thermal decomposition step of thermally decomposing the waste plastic melted, and a recovery step of discharging the thermal decomposition product of the waste plastic from the reaction vessel as a gas, cooling it and recovering it as a liquid And
By providing the melting step in this manner, the molecular weight of the hydrocarbon in the pyrolysis product can be made smaller than when the melting step is not provided.

  Moreover, in the above-described invention, the method for converting waste plastic into oil according to the present invention is such that the water vapor introduced into the reaction vessel in the melting step is overheated in a temperature range of 180 ° C to 300 ° C and a pressure range of 0.1 MPa to 4 MPa. It is water vapor.

  Moreover, the oil plasticization method for waste plastics of the present invention is characterized in that, in the above invention, the water vapor introduced into the reaction vessel in the melting step is saturated water vapor in a temperature range of 180 ° C to 300 ° C.

  Moreover, the oil plasticizing method for waste plastics according to the present invention is characterized in that, in the above invention, the melting step heats and maintains the temperature in the reaction vessel in a temperature range of 200 ° C to 250 ° C.

  Moreover, the oil plasticizing method for waste plastics according to the present invention is characterized in that, in the above invention, the thermal decomposition step heats and maintains the temperature in the reaction vessel in a temperature range of 380 ° C to 420 ° C.

  In the melting step, the temperature in the reaction vessel is heated and held in a temperature range of 200 ° C. to 250 ° C. for 1 to 2 hours.

  Moreover, the method for converting oil into waste plastic according to the present invention is characterized in that, in the above invention, the waste plastic is a mixed waste plastic from which chlorine-containing plastic has been removed.

  The method for converting waste plastic into oil according to the present invention is a hydrocarbon that is industrially practical by heating and melting the waste plastic in the presence of water vapor, then discharging the water vapor and raising the temperature to thermally decompose the waste plastic. There is an effect that fuel oil composed of a mixture can be easily obtained.

FIG. 1 is a schematic diagram showing an oil plasticizing apparatus for waste plastic according to Embodiment 1 of the present invention. FIG. 2 is a flowchart of the waste plastic oiling step according to Embodiment 1 of the present invention. FIG. 3 is a diagram showing the relationship between the time of the oil plasticizing step for waste plastic according to Embodiment 1 of the present invention and the superheating temperature. FIG. 4 is a schematic diagram showing an oil plasticizing apparatus for waste plastic according to Embodiment 2 of the present invention.

  Hereinafter, a method for converting waste plastic into oil according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a schematic diagram showing a waste plastic oiling apparatus 100 according to Embodiment 1 of the present invention. The waste plastic oil converting apparatus 100 includes a rotary kiln 1 as a reaction vessel for introducing and processing waste plastic, a heater 2 as a heating means for heating the rotary kiln 1 to a predetermined temperature, and steam for supplying water vapor to the reaction vessel. A boiler 3 as supply means and a drive unit 4 that is a motor that rotates the rotary kiln 1 are provided.

  The waste plastic to be treated by the waste plastic oiling apparatus 100 of the present invention is a mixture of thermoplastic resins such as polyethylene, polypropylene, and styrene. Polyesters such as polyethylene terephthalate produce sublimable substances such as terephthalic acid and benzoic acid by thermal decomposition, and the sublimable substances cause corrosion and clogging of piping, so waste plastics should not contain polyester if possible. preferable. In addition, waste plastics preferably do not contain or remove chlorine-containing plastics such as polyvinyl chloride and polyvinylidene chloride if possible, but when waste plastics containing chlorine-containing plastics are oiled, the generated hydrogen chloride A means for processing / recovering may be provided separately. The waste plastic may contain a thermosetting resin such as polyurethane or phenol resin as long as the amount is small.

  The rotary kiln 1 which is a reaction vessel preferably has a built-in grinding aid such as a ceramic ball, a metal piece, or a metal ball. The rotary kiln 1 is rotated by the drive unit 4. The waste plastic introduced into the rotary kiln 1 is rotated and stirred together with the pulverization aid by rotating the rotary kiln 1 in the presence of water vapor supplied by a boiler 3 described later.

  The heater 2 is provided in the outer peripheral part of the rotary kiln 1, and heats the introduced waste plastic to a predetermined temperature by heating the rotary kiln 1. The heater 2 heats the waste plastic introduced into the rotary kiln 1 at two stages of temperature. The temperature in the rotary kiln 1 is measured by the temperature sensor 5, and the heater 2 is switched on and off according to the temperature in the rotary kiln 1. The heating temperature in the melting step for melting the waste plastic in the presence of water vapor is preferably in the range of 180 ° C to 300 ° C. When the heating temperature is lower than 180 ° C, polypropylene, which is a high melting point plastic contained in the waste plastic, is difficult to melt. When the heating temperature is higher than 300 ° C, polystyrene that starts decomposition at the lowest temperature is thermally decomposed. is there. The melting step is particularly preferably held by heating in a temperature range of 200 ° C. to 250 ° C., but a suitable temperature can be changed depending on the proportion of the plastic contained in the waste plastic. When the waste plastic contains chlorine-containing plastic, it can be desorbed from the chlorine-containing plastic by heating to 200 ° C. to 250 ° C. in the melting step.

  The heating temperature in the pyrolysis step for pyrolyzing the molten waste plastic is preferably in the range of 350 ° C to 450 ° C. When the heating temperature is lower than 350 ° C., the polyethylene contained in the waste plastic is difficult to be thermally decomposed, and when the heating temperature is higher than 450 ° C., there is a possibility of decomposing even a substance having a low molecular weight such as carbon dioxide and thermal efficiency is lowered. Because. The heating temperature in the pyrolysis step is particularly preferably 380 ° C to 420 ° C. The preferred range of the heating temperature in the pyrolysis step can be changed depending on the proportion of plastic contained in the waste plastic.

  A boiler 3 as a water vapor supply means supplies water vapor at a predetermined temperature to the rotary kiln 1. The supplied water vapor is preferably saturated water vapor at a temperature of 180 ° C. to 300 ° C. (0.5 MPa to 3.6 MPa), which is the heating temperature of the waste plastic in the melting step. Then, the temperature in the rotary kiln 1 may be raised to a predetermined temperature by the heater 2.

  In Embodiment 1, the waste plastic is not pyrolyzed in one stage, but is first heated in the temperature range of 180 ° C. to 300 ° C. in the presence of steam to melt the waste plastic, and then the steam is discharged. The heating temperature is raised to a temperature range of 350 ° C. to 450 ° C., and the waste plastic is pyrolyzed into a hydrocarbon mixture having a small molecular weight distribution. In this way, waste plastic is first heated and melted in the temperature range of 180 ° C to 300 ° C in the presence of saturated water vapor, so that the plastic having a molecular weight of several hundreds of thousands can be decomposed into a size of several tens of thousands. Can do. The waste plastic is once decomposed to a molecular weight of about 1/10, whereby a hydrocarbon mixture having a relatively small molecular weight distribution can be obtained in the subsequent random decomposition.

  Note that the hydrocarbon mixture obtained in the first embodiment is a mixture of hydrocarbons that is liquid at room temperature. For example, it is a chain saturated hydrocarbon having about 4 to 19 carbon atoms, a chain unsaturated hydrocarbon, a cyclic saturated hydrocarbon, or a mixture of cyclic unsaturated hydrocarbons. Since unsaturated hydrocarbons other than aromatic compounds are not excellent in storage stability, it is preferable that the content is small. Even when solid hydrocarbons are contained at room temperature, other hydrocarbons may be contained in the hydrocarbon mixture as long as they dissolve as a solvent and exhibit fluidity at room temperature as a hydrocarbon mixture. .

  Next, the oil plasticizing process for waste plastic according to the first embodiment will be described with reference to the drawings. FIG. 2 is a flowchart of the waste plastic oiling step according to Embodiment 1 of the present invention.

  First, as shown in FIG. 2, waste plastic is introduced into the rotary kiln 1 (step S101).

  After the waste plastic is introduced into the rotary kiln 1, saturated steam at a predetermined temperature is supplied into the rotary kiln 1 by the boiler 3. And while rotating the rotary kiln 1 with the drive part 4, the rotary kiln 1 is heated to 180 to 300 degreeC with the heater 2, and a waste plastic is fuse | melted (step S102). Although the melting step can be changed depending on the amount of waste plastic introduced into the rotary kiln 1, as shown in FIG. 3, the waste plastic is melted by heating and holding at a temperature of 180 ° C. to 300 ° C. for 1 to 2 hours. In addition, the one-dot chain line of FIG. 3 shows the relationship between the time and temperature during heating of the rotary kiln 1 when there is no melting step, and the solid line represents the time during heating of the rotary kiln 1 of the oiling method according to the first embodiment. The relationship of temperature is shown.

  After the melting step, the rotation of the rotary kiln 1 is stopped, and the saturated water vapor in the rotary kiln 1 is discharged through the steam discharge port 6. The saturated water vapor is discharged by forcibly replacing it by supplying an inert gas such as nitrogen into the rotary kiln 1. When the waste plastic contains a chlorine-containing plastic, hydrogen chloride is recovered by the recovery device because the discharged saturated water vapor contains hydrogen chloride. After discharge of saturated water vapor, the rotary kiln 1 is further heated to a temperature range of 350 ° C. to 450 ° C. by the heater 2 to thermally decompose the waste plastic melted (step S103). The pyrolysis step can be changed depending on the amount of waste plastic introduced into the rotary kiln 1, but as shown in FIG. 3, the waste plastic is heated and held at a temperature of 350 ° C. to 450 ° C. for 2 to 8 hours. Pyrolysis to a hydrocarbon mixture of Thus, if melting and thermal decomposition are performed in the same container (rotary kiln 1) without taking out the waste plastic from the container, there is an advantage that transportation between the containers becomes unnecessary. However, melting and pyrolysis may be performed in separate containers.

  The waste plastic (low molecular weight hydrocarbon mixture) that has been pyrolyzed and reduced in molecular weight is vaporized in the rotary kiln 1. The vaporized hydrocarbon mixture is introduced into the cooling device through the gas discharge port 7, and is cooled and liquefied by the cooling device (step S104). The low molecular weight gas component that is not liquefied is incinerated by an off-gas furnace, and the oiling process is completed.

  In the waste plastic oil conversion method according to the first embodiment, the waste plastic oil conversion treatment is performed in a melting step of heating in the temperature range of 180 ° C. to 300 ° C. in the presence of saturated steam, and a temperature range of 350 ° C. to 450 ° C. By performing the gasification step by heating in two stages, hydrocarbons having 4 to 19 carbon atoms can be efficiently obtained while reducing the mixing ratio of other high molecular weight hydrocarbons. .

  In addition, the waste plastic oil conversion method according to the first embodiment is simplified by performing final pyrolysis of the waste plastic after discharging saturated water vapor using the gas discharge port / steam discharge port. In addition, a hydrocarbon mixture having a low pour point and industrially practical as a fuel oil can be obtained.

(Embodiment 2)
FIG. 4 is a schematic diagram showing a waste plastic oiling apparatus 200 according to Embodiment 2 of the present invention. The oil refiner 200 according to Embodiment 2 of the present invention is the same as the oil refiner 100 except that the boiler 3 that is the steam supply means of the oil refiner 100 according to Embodiment 1 is replaced with the superheated steam supply device 8. It has the composition of. The superheated steam supply device 8 only needs to be able to supply superheated steam in a temperature range of 180 ° C. to 300 ° C., and a boiler with a built-in superheater may be used. The superheated steam to be used can be either superheated steam at normal pressure (about 0.1 MPa) or superheated steam at high pressure (pressure range of about 0.1 MPa to 4 MPa) in the temperature range of 180 ° C to 300 ° C. May be.

  The oil converting apparatus 200 according to the second embodiment introduces waste plastic and superheated steam into the rotary kiln 1 and rotates the rotary kiln 1 by the drive unit 4 while heating the rotary kiln 1 to 180 ° C. to 300 ° C. by the heater 2. Then, heat and stir the waste plastic. By this treatment, the waste plastic is melted. The melting temperature of the waste plastic is preferably in the temperature range of 200 ° C to 250 ° C.

  After the waste plastic is heated and held at a predetermined temperature in the presence of superheated steam and melted, the rotation of the rotary kiln 1 is stopped and the superheated steam in the rotary kiln 1 is discharged through the steam discharge port 6. The superheated steam is discharged by, for example, forcibly replacing the steam through the steam discharge port 6 by supplying an inert gas such as nitrogen into the rotary kiln 1. After discharging the superheated steam, the rotary kiln 1 is further heated to 350 ° C. to 450 ° C. by the heater 2 to thermally decompose the molten waste plastic. The thermal decomposition temperature of the waste plastic is preferably in the temperature range of 380 ° C to 420 ° C.

  The waste plastic (low molecular weight hydrocarbon mixture) that has been pyrolyzed and reduced in molecular weight is vaporized in the rotary kiln 1. The vaporized hydrocarbon mixture is introduced into the cooling device through the gas discharge port 7 and is cooled and liquefied by the cooling device. By the oil refiner 200 according to the second embodiment, the waste plastic is thermally decomposed, and a hydrocarbon mixture having a small molecular weight distribution can be obtained.

  In the waste plastic oil conversion method according to the second embodiment, the waste plastic oil conversion process is performed in a temperature range of 180 ° C. to 300 ° C. in the presence of superheated steam, and a temperature range of 350 ° C. to 450 ° C. By performing the gasification step by heating in two stages, hydrocarbons having 4 to 19 carbon atoms can be efficiently obtained while reducing the mixing ratio of other high molecular weight hydrocarbons. .

  In addition, the method for converting waste plastic into oil according to the second embodiment is simplified by performing final thermal decomposition of the waste plastic after discharging superheated steam using the gas outlet / steam outlet. In addition, a hydrocarbon mixture having a low pour point and industrially practical as a fuel oil can be obtained.

Example 1
A rotary kiln was used as a reaction vessel, 180 ° C. saturated steam was introduced into the rotary kiln into which the waste plastic was introduced, and the waste plastic was melted by heating at 180 ° C. for 1 hour. Thereafter, nitrogen gas was purged and saturated water vapor was discharged from the rotary kiln. The rotary kiln was heated and held at 400 ° C. for 8 hours, and the waste plastic was pyrolyzed and gasified. The gas obtained by pyrolysis was cooled to obtain a hydrocarbon mixture.

(Example 2)
A rotary kiln was used as a reaction vessel, and superheated steam at normal pressure (0.1 MPa) and 180 ° C. was introduced into the rotary kiln into which waste plastic was introduced, and heated at 180 ° C. for 1 hour to melt the waste plastic. Thereafter, nitrogen gas was purged to discharge superheated steam from the rotary kiln, and the rotary kiln was heated and held at 400 ° C. for 8 hours to thermally decompose and gasify the waste plastic. The gas obtained by pyrolysis was cooled to obtain a hydrocarbon mixture.

(Comparative Example 1)
A rotary kiln was used as a reaction vessel, waste plastic was introduced, and the rotary kiln filled with nitrogen gas was heated and held at 400 ° C. for 8 hours to thermally decompose and gasify the waste plastic. The gas obtained by pyrolysis was cooled to obtain a hydrocarbon mixture.

Table 1 shows the results of measuring the flash point and pour point of the hydrocarbon mixtures obtained in Examples 1 and 2 and Comparative Example 1. The flash point was measured according to JIS K2265, and the pour point was measured according to JIS K2269.

  As shown in Table 1, both the flash point and pour point were smaller in Example 1 and Example 2 than in Comparative Example 1. In the hydrocarbon mixture produced by thermal decomposition of waste plastics, especially polyethylene and polypropylene, it is presumed that the flash point increases when the molecular weight of the generated hydrocarbon increases, and the flash point decreases when the molecular weight decreases. In Examples 1 and 2 having a low flash point, it is estimated that a hydrocarbon mixture having a low average molecular weight is obtained.

  Similarly, in hydrocarbon mixtures generated by pyrolysis of waste plastics, especially polyethylene and polypropylene, it is estimated that the pour point increases as the molecular weight of the generated hydrocarbon increases, and the pour point decreases as the molecular weight decreases. In Examples 1 and 2, which have a very low pour point compared to Example 1, it is estimated that a hydrocarbon mixture having a low average molecular weight is obtained. In Examples 1 and 2 and Comparative Example 1, not only the pour point differs by 30 ° C. or more, but Examples 1 and 2 are very practical as fuel oils in that the pour point is below room temperature. Is.

  As described above, the method for converting waste plastic into oil according to the present invention is useful as a method for recycling waste plastic.

DESCRIPTION OF SYMBOLS 1 Rotary kiln 2 Heater heating part 3 Boiler 4 Drive part 5 Temperature sensor 6 Steam exhaust port 7 Gas exhaust port 8 Superheated steam supply apparatus 100, 200 Oil refiner

Claims (7)

An introduction step of introducing waste plastic into the reaction vessel;
A melting step of melting the waste plastic while introducing water vapor into the reaction vessel and heating the material temperature in the reaction vessel to maintain a temperature range of 180 ° C. to 300 ° C .;
A thermal decomposition step of discharging steam from the reaction vessel, raising the temperature in the reaction vessel to a temperature range of 350 ° C. to 450 ° C., and thermally decomposing the molten waste plastic;
A recovery step of discharging the thermal decomposition product of the waste plastic as a gas from the reaction vessel, cooling and recovering as a liquid;
A method for converting oil into waste plastic, comprising:   2. The waste plastic according to claim 1, wherein the steam introduced into the reaction vessel in the melting step is superheated steam having a temperature range of 180 ° C. to 300 ° C. and a pressure range of 0.1 MPa to 4 MPa. Oiling method.   2. The method according to claim 1, wherein the water vapor introduced into the reaction vessel in the melting step is saturated water vapor in a temperature range of 180 ° C. to 300 ° C. 3.   The waste plastic oil conversion method according to claim 1, wherein in the melting step, the temperature in the reaction vessel is heated and held in a temperature range of 200 ° C to 250 ° C.   2. The method according to claim 1, wherein in the thermal decomposition step, the temperature in the reaction vessel is heated and held in a temperature range of 380 ° C. to 420 ° C. 3.   2. The method according to claim 1, wherein in the melting step, the temperature in the reaction vessel is heated and held in a temperature range of 200 ° C. to 250 ° C. for 1 to 2 hours.   2. The method of converting waste plastic into oil according to claim 1, wherein the waste plastic is mixed waste plastic from which chlorine-containing plastic has been removed.

Images