JPH1190387A - Waste plastic dechlorination method and dechlorination equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously and stably obtain molten plastics which are low in chlorine concn. and are low in the contents of foreign matter and residues as well by maintaining the waste plastics while agitating and mixing the waste plastics under a specific pressure, temp. and time in a reducing atmosphere. SOLUTION: The waste plastics P1 contg. polyvinyl chloride, etc., are pulverized and are fed into a hopper 8. The waste plastics P1 are dropped into a screw feeder 9, are sent toward an outflow end. and are introduced to a waste plastic feeding port 2, from which the waste plastics are dropped into a reaction vessel 1. The dropped waste plastics P1 are heated to about 200 to 320 deg.C by hot medium oil 25 passed into a heat medium jacket 6 under the pressure below 1 kgf/cm<2> G controlled by a pressure control means 11 in a reduction atmosphere to which oxygen is not supplied. The waste plastics are held for a prescribed time of >=1 hour under agitating and mixing. As a result, the acidic gases, such as hydrogen chloride, formed by the pyrolysis of the PVC, etc., are removed and the gravity settled foreign matter and residues are easily discharged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for dechlorinating waste plastics containing polyvinyl chloride.

[0002]

2. Description of the Related Art The enactment of the Containers and Packaging Recycling Law requires the reuse of waste plastics. Currently proposed recycling methods include a method in which the material is blown into a blast furnace to be used as a reducing agent, a method in which the material is used as a raw material for cement or the like, and a method in which oil is used as a fuel.

[0003] However, if polyvinyl chloride is contained in waste plastics, the chlorine content is converted into hydrogen chloride in the heating step, causing corrosion of the reactor and air pollution, and obtaining products containing chlorine content. Various measures against chlorine have been taken in order to cause corrosion of equipment using the product and generation of toxic gas.

[0004] For example, in the waste disposal method and apparatus described in Japanese Patent Application Laid-Open No. 55-121875, waste containing waste plastic or waste plastic is put into a closed container together with an alkali agent, and the container is heated from the outside. To melt the waste and neutralize acidic gas such as hydrogen chloride generated with the melting of the waste with an alkaline agent, thereby preventing corrosion of equipment and air pollution by the acidic gas, Agglomerates obtained by cooling the melt are reused as construction blocks and the like.

In the waste plastic dechlorination / separation apparatus described in Japanese Patent Application Laid-Open No. 6-65582, as a pretreatment for converting waste plastic into fuel (solid fuel, oil, gasification), the waste plastic is heated and melted. Into the tank, dechlorination is performed by holding the melt in the tank at about 300 ° C. by heating from the outside, and the resulting carbide is taken out of the tank.
It is intended to obtain a molten plastic which is dechlorinated and free of carbides.

In the waste plastic pyrolysis reaction apparatus described in Japanese Patent Application Laid-Open No. H8-120285, waste plastic introduced into a reaction tube from a waste plastic input port is mixed with molten plastic returned to the vicinity of the input port through a return flow path. The molten plastic is heated and melted by mixing, and the molten plastic is sent out in the direction toward the molten plastic outlet by the blades.At this time, the mixture is heated from the inside and outside by the external heating means and the internal heating means and kneaded by the blades, so that the temperature is uniform. To promote the thermal decomposition reaction to obtain molten plastic with low chlorine concentration.

[0007]

However, in the above-mentioned Japanese Patent Application Laid-Open No. 55-121875, the use of the product is limited to that described above because an alkali agent is added. Japanese Patent Application Laid-Open No. 6-65582 is a method of heating from the outside, so that a sharp temperature gradient is generated, and not only a region where low temperature corrosion is caused by touching the generated hydrogen chloride is generated, but also foreign substances and residues are sufficiently removed. I can't pull it out.
The method described in JP-A-8-120285 cannot sufficiently remove an acidic gas such as hydrogen chloride generated due to a short residence time in a reaction tube, not only leaving a problem of apparatus corrosion, but also a waste of raw materials. If foreign matter such as metal is mixed in the plastic, there is a drawback that the device is easily damaged and maintenance in such a case is not easy.

The present invention solves the above-mentioned problems, and can continuously and stably produce a molten plastic having a low chlorine concentration and a small content of foreign substances and residues, and can prevent corrosion of the apparatus due to generated acidic gas. It is an object of the present invention to provide a method and apparatus for dechlorinating waste plastic.

[0009]

In order to solve the above-mentioned problems, the present invention is a method for dechlorinating waste plastics containing polyvinyl chloride, wherein the waste plastics are reduced to 1 kgf / cm ² in a reducing atmosphere. By maintaining the temperature at about 200 to 320 ° C. for 1 hour or more while stirring and mixing under a pressure of less than G, the waste plastic is melted,
It is an object of the present invention to provide a method for dechlorinating waste plastics, in which a gas such as hydrogen chloride gas generated by thermally decomposing polyvinyl chloride is discharged and a dechlorinated molten plastic is taken out.

Under a low pressure of less than 1 kgf / cm ² G,
At a temperature of 0 to 320 ° C., polyvinyl chloride and polyethylene terephthalate are thermally decomposed in a high temperature range, but other waste plastics, that is, plastics such as polyolefin resin such as polystyrene used for containers are not thermally decomposed.

For this reason, if the waste plastic is maintained for one hour or more under the above conditions, the polyvinyl terephthalate and the polyethylene terephthalate may be heated to a high temperature in a state where a sufficient pyrolysis reaction time is secured. Pyrolysis in the area, other waste plastics melt without pyrolysis, gases such as hydrogen chloride gas generated by the pyrolysis are discharged, and molten plastics with extremely low chlorine concentration can be obtained, as well as reaction equipment etc. Corrosion is prevented.

In order to more effectively prevent corrosion of a reaction device or the like due to generated acidic gas such as hydrogen chloride gas,
Maintain the waste plastic above 250 ° C. When the obtained molten plastic is used for oiling, the waste plastic is maintained at about 320 ° C. so that polyethylene terephthalate which generates sublimate is sufficiently thermally decomposed in the oiling apparatus.

The present invention is also a dechlorination apparatus for performing the above-described method for dechlorinating waste plastic, wherein a waste plastic inlet and a gas outlet are formed in the upper part, and a molten plastic collector is formed in the cone-shaped lower part. Stirring having a sealed reaction vessel in which an outlet and a residue discharge port are formed vertically in this order, a heating means for heating the reaction vessel from the outside, and a stirring blade moving circumferentially near the inner surface of the reaction vessel. Waste plastic dechlorination apparatus comprising: means, a temperature adjusting means for adjusting the contents of the reaction vessel to a predetermined temperature via the heating means, and a pressure adjusting means for adjusting the gas pressure in the reaction vessel to a predetermined pressure. I will provide a.

According to the above configuration, when the waste plastic is charged into the reaction vessel through the waste plastic charging port, the waste plastic is heated indirectly by the heating means outside the vessel and is rotated by the stirring blade. Melts in a state where it is stirred and mixed in the direction.

At this time, the gas pressure in the reaction vessel is adjusted to a predetermined pressure by the pressure adjusting means, and the content of the reaction vessel is adjusted to the predetermined temperature via the heating means by the temperature adjusting means. Only the resin that thermally decomposes under a predetermined pressure and temperature is thermally decomposed, and the generated gas flows out from the gas outlet with stirring and mixing.

The waste plastic that has been melted without being thermally decomposed is taken out of the lower molten plastic outlet as molten plastic, and foreign substances mixed in the waste plastic and residues generated by thermal decomposition of the waste plastic are removed by a stirring blade. It settles without being scraped up, moves along the slope of the lower inner surface, gathers at the bottom, and is appropriately extracted from the residue extraction outlet.

[0017] The stirring blade may be provided with a scraping plate for slidingly contacting the inner surface of the reaction vessel to scrape off the deposits.
In this case, carbon residues generated by thermal decomposition of the waste plastic and attached to the inner surface of the reaction vessel are also effectively removed.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a waste plastic dechlorination apparatus according to an embodiment of the present invention includes a closed reaction vessel 1 having an upper part having a cylindrical shape and a lower part having a cone shape. A waste plastic inlet 2 and a gas outlet 3, and a lower part of a molten plastic outlet 4 and a residue outlet 5 at a lower part in this order.
A heat medium jacket 6 covering substantially the entire outer peripheral surface;
And a stirrer 7 for stirring and mixing the contents.

Above the waste plastic inlet 2, the outflow end of a horizontally arranged screw feeder 9 having a hopper 8 at one end is located. The gas outlet 3 is connected to a gas extraction pipe 10 which has been subjected to anticorrosion treatment. The gas extraction pipe 10 has a pressure adjusting means 11 for adjusting the gas pressure in the reaction vessel 1 to a predetermined pressure. A sublimate separation device 12 having a cooling means (not shown) and a neutralization device 13 having an acid gas neutralizing means such as an aqueous caustic soda solution (not shown) are interposed. The pressure adjusting means 11 is, for example,
The pressure gauge 11a for detecting the gas pressure inside the gas extraction pipe 10 communicating with the inside of the reaction vessel 1 is compared with the detected gas pressure and a predetermined pressure in the reaction vessel to be maintained. A flow valve 11 is provided so as to pass an amount of gas corresponding to the difference.
and a control device 11c for controlling b.

At the side of the molten plastic outlet 4, the inflow end of a horizontally disposed molten plastic extracting device 15 having an outlet 14 at one lower end is located.
Below, is located an inflow end of a residue removing device 17 which is provided with a discharge port 16 at one end lower portion and is disposed in a horizontal direction. Each of the extraction devices 15 and 17 has a double pipe structure, in which guide means 18 and 19 are disposed inside the inner pipe, and cooling water flow paths 20 and 21 are formed between the inner pipe and the outer pipe. I have.

Outside the heat medium jacket 6, there is provided a heat medium circulation path 24 which connects an inflow port 22 formed at a lower part of the heat medium jacket 6 and an outflow port 23 formed at an upper part thereof. Is provided with a heating device 26 for heating the heating medium oil 25 as a heating fluid to a predetermined temperature.

The stirrer 7 has a vertical shaft 29 connected to a motor 27 above the reaction vessel 1 via a drive shaft 28, and a V-shape along the inner surface of the reaction vessel 1. 1 support members 30, 31 arranged in the radial direction
Blades 3 fixed to shaft 29 through
2 and a scraping plate 33 fixed to each stirring blade 32 and slidably provided on the inner surface of the reaction vessel 1.

The operation of the above configuration will be described. When the waste plastic P1 containing polyvinyl chloride or polyethylene terephthalate is pulverized and put into the hopper 8, the waste plastic P1 in the hopper 8 falls into the screw feeder 9, is sent toward the outflow end, and is put into the waste plastic. The liquid is guided to the port 2 and falls into the reaction vessel 1.

Waste plastic P dropped into reaction vessel 1
1 is a heating medium oil 25 flowing through the inside of the heating medium jacket 6 under a pressure of less than 1 kgf / cm ² G adjusted by the pressure adjusting means 11 in a reducing atmosphere to which oxygen is not supplied.
To about 320 ° C., and is held for a predetermined time of one hour or more while being stirred and mixed in the circumferential direction by the stirring blade 32.

As a result, polyvinyl chloride and polyethylene terephthalate are thermally decomposed at a low pressure of less than 1 kgf / cm ² G and at a temperature of about 320 ° C., and an acid gas such as hydrogen chloride generated by the pyrolysis or a decomposition product of polyethylene terephthalate. A gas such as (terephthalic acid) flows out through the gas outlet 3, and the other waste plastic P1 is melted without being thermally decomposed.

The molten plastic P2 thus dechlorinated and from which polyethylene terephthalate has been removed is taken out through the molten plastic take-out port 4 after a predetermined time, introduced into the inflow end of the molten plastic take-out device 15, and flows through the cooling water flow path 20. While being cooled by the cooling water w, it is guided toward the discharge port 14 by the guide means 18, solidified during that time, and discharged as solid plastic P3 from the discharge port 14 onto a carry-out device (not shown).

The gas flowing out from the gas outlet 3 is guided to the outside of the reaction vessel 1 through a gas extraction pipe 10, and is cooled in a sublimate separation device 12 in the middle of the pipe, thereby decomposing polyethylene terephthalate. Is sublimated and separated, and an acid gas such as hydrogen chloride is neutralized and removed by a caustic soda aqueous solution in the neutralization device 13.

Foreign substances such as glass, metal, calcium compound and the like mixed in the waste plastic P1 are removed by the stirring blade 32.
The carbon residue generated by thermal decomposition and attached to the inner surface is scraped off by the scraping plate 33 and moved to the bottom along the inclined surface. Then, it is appropriately extracted as a residue R from the residue discharge port 5, and
It is guided to the discharge port 16 by the guide means 19 while being guided by the cooling water w flowing through the cooling water flow path 21 while being guided to the inflow end of the residue removing device 17, and the discharge device (not shown) is discharged from the discharge port 16. Discharged up.

In the above, assuming that the obtained molten plastic P2 (solid plastic P3) is converted to oil, the temperature of the waste plastic P1 is raised to about 320 ° C. so that polyethylene terephthalate is thermally decomposed together with polyvinyl chloride. To prevent coking and the formation of sublimates in the oiling device, but when oiling is not used, there is no need to thermally decompose polyethylene terephthalate. 200 ° C. or higher, preferably 25 ° C. or more, in which corrosion of the reaction vessel 1 and the like due to generated acidic gas can be avoided.
The temperature may be maintained at 0 ° C. or higher and about 290 ° C. or lower.

Although the batch type operation method has been described above, a continuous type operation in which waste plastics are continuously charged and molten plastics are continuously taken out may be employed. Although somewhat inferior,
A product having a sufficiently low chlorine concentration can be obtained continuously and stably.

[0031]

As described above, according to the dechlorination method and the dechlorination apparatus of the present invention, by maintaining the waste plastic at a predetermined temperature lower than the thermal decomposition temperature of the polyolefin resin or the like for one hour or more, In a state where the reaction time is secured, the polyvinyl chloride contained in the waste plastic is selectively and completely thermally decomposed, the generated acidic gas such as hydrogen chloride is removed, and foreign substances and residues that settle down with specific gravity are easily discharged. Thus, a product having a low chlorine concentration and a low content of foreign substances and residues can be obtained. At the above-mentioned predetermined temperature, corrosion due to the generated acidic gas does not occur, so that it is not necessary to use a special material for the reaction vessel, the stirrer and the like.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a schematic overall configuration of a waste plastic dechlorination apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 reaction vessel 2 waste plastic inlet 3 gas outlet 4 molten plastic outlet 5 residue discharge outlet 6 heating medium jacket 11 pressure control means 25 heating medium oil 26 heating device 32 stirring blade 33 scraping plate P1 waste plastic P2 molten plastic P3 Solid plastic R residue

Claims (5)

[Claims] 1. A method for dechlorinating waste plastics containing polyvinyl chloride, wherein said waste plastics are stirred at about 200-320 ° C. in a reducing atmosphere under a pressure of less than 1 kgf / cm ² G. By maintaining the temperature of at least 1 hour, the waste plastic is melted,
A method for dechlorinating waste plastics, which comprises decomposing polyvinyl chloride by pyrolysis, discharging gas such as hydrogen chloride gas produced, and taking out dechlorinated molten plastic. 2. The method for dechlorinating waste plastic according to claim 1, wherein the waste plastic is maintained at 250 ° C. or higher. 3. The method of claim 1 wherein the waste plastic is maintained at about 320 ° C. 4. A hermetically sealed reaction vessel having a waste plastic inlet and a gas outlet formed in the upper part, a molten plastic outlet and a residue outlet formed in the lower part in a cone shape in this order. Heating means for heating the reaction vessel from the outside, stirring means having stirring blades moving in the circumferential direction near the inner surface of the reaction vessel, and a temperature for adjusting the contents of the reaction vessel to a predetermined temperature via the heating means. An apparatus for dechlorinating waste plastics, comprising: an adjusting means; and a pressure adjusting means for adjusting a gas pressure in a reaction vessel to a predetermined pressure. 5. The apparatus for dechlorinating waste plastic according to claim 4, wherein a scraping plate for slidingly contacting the inner surface of the reaction vessel and scraping off the adhered substance is mounted on the stirring blade.