JP3426730B2 - Plastic recycling method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment of waste plastics contained in industrial wastes, especially plastics containing polyvinyl chloride resin.

[0002]

2. Description of the Related Art In recent years, a method of thermally decomposing waste plastics to produce fats and oils has been developed, and it is regarded as a promising method for recycling a large amount of waste plastics.
In this liquefaction process, if the waste plastic contains halogen-containing resin such as polyvinyl chloride (PVC) resin, the decomposition apparatus is damaged by halogen-containing gas such as hydrogen chloride gas generated by thermal decomposition, and decomposition product is generated. Hazardous organochlorine compounds are also mixed in things. The proportion of PVC resin in commonly used plastics is high, and the amount of PVC resin contained in waste plastics is not at a negligible level. As a measure to solve this problem, a method of thermally decomposing by adding a metal hydroxide, especially an alkali is effective. The addition of alkali also improves the oil conversion rate in thermal decomposition.

[0003]

However, whether or not the recycling method can actually function effectively depends on whether all the products produced by the implementation can be recycled or treated without causing environmental problems. It depends on how you do it. In the case of thermal decomposition of the above-mentioned plastics, solid carbonaceous decomposition residue is generated in addition to oil and fat, and the residue itself can be used for land reclamation and road paving. However, if alkali remains in the decomposition residue, it remains for land reclamation as it is. Use causes environmental pollution. Therefore, it is necessary to develop an application for separating the residual alkali from the decomposition residue and reusing it. In addition, it is necessary to develop a wide variety of applications for the produced oils and fats.

The present invention has been made in order to solve the problems of the prior art as described above, and it is an object of the present invention to provide a method and an apparatus for recycling plastics which can effectively utilize all of those generated by thermal decomposition of plastics. It is intended.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the inventors of the present invention have conducted extensive studies, and as a result, the metal hydroxide separated from the decomposition residue is saponified with oil and fat which is a decomposition product to produce soap. It was found that the use of surplus metal hydroxide can be effectively utilized and the use of fats and oils can be widened by forming the above-mentioned structure. Thus, the inventors have invented the recycling method and apparatus of the present invention.

The plastic recycling method of the present invention is
A pyrolysis step of generating and including decomposition residues of the pyrolysis products and the metal hydroxide of the plastic by heating the plastic with a metal hydroxide, separation step of separating said metal hydroxides from said decomposition residues And a saponification step of producing a saponified product by using the separated metal hydroxide and the decomposition product.

[0007] In addition, recycling apparatus of the plastic of the present invention, the thermal decomposition apparatus for heating the plastic with a metal hydroxide to produce a including decomposition residues of the pyrolysis products and the metal hydroxide of the plastic And a separation device for separating the metal hydroxide from the decomposition residue, and a saponification device for forming a saponified product using the separated metal hydroxide and the decomposition product.

As the compound serving as a source of the above hydroxyl group,
A metal hydroxide is used.

The metal hydroxide is a basic hydroxide composed of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, barium hydroxide, lithium hydroxide, aluminum hydroxide and zirconium hydroxide. , Amphoteric hydroxides such as cerium hydroxide.

[0010]

The plastic is heated together with the metal hydroxide to be thermally decomposed, and oil is obtained as a thermal decomposition product, and a solid decomposition residue remains. The solid decomposition residue contains metal hydroxide and / or its metal salt, and the solid decomposition residue is separated by washing and removing them with water or the like. The soap is obtained by reacting the removed metal hydroxide and / or its metal salt with the oil obtained by thermal decomposition to saponify the oil. The solid decomposition residue has a higher adsorption capacity due to the coexistence of a metal hydroxide during thermal decomposition, and is used as a gas-phase or liquid-phase purification adsorbent.

The present invention will be described in more detail below.

As shown in FIG. 1, when the plastic 1 is pyrolyzed in the presence of the metal hydroxide 3 (step A), a decomposition product of the plastic is obtained, but at the same time, excess metal hydroxide and excess metal hydroxide and Carbonaceous solid decomposition residue mixed with salt 7
Remain in the reaction vessel. In order to handle the decomposition residue safely, it is necessary to separate the metal hydroxides and salts from the decomposition residue. In this respect, the metal hydroxide and salt can be separated from the decomposition residue 11 by eluting and washing the metal hydroxide and salt with warm water or water 9 (step B). It can be removed by washing with a dilute aqueous solution. If the metal hydroxide recovered by such a method is contained in the cleaning liquid at a high concentration, it will be relatively easy to recycle it in the thermal decomposition process of plastics, but from the viewpoint of cleaning the residue. However, in reality, it is difficult to recover at a concentration suitable for recycling in the thermal decomposition process.

However, when the oil or fat which is the decomposition product 5 is added to the cleaning liquid 13 containing the metal hydroxide and the salt, the metal component can be converted into soap by the saponification reaction (step C). The soap 15 is widely used in industry and general households, and has various product forms. In particular, as industrial soap, there are many applications that do not require the aesthetics required for household soap and the like, and in such applications, even if coloring is caused by using the washing liquid of the decomposition residue as a raw material. It does not hinder the use. Further, recently, from the viewpoint of environmental protection, it is said that it is preferable to use soap instead of a synthetic surfactant or the like, so that recovery as soap also meets social demand.

The composition of the decomposition product 5 obtained by the thermal decomposition of the plastic 1 (step A) will, of course, vary depending on the starting plastic and the decomposition reaction conditions.
Generally, it is composed of aliphatic and aromatic components having about 5 to 22 carbon atoms, and organic acid components such as fatty acids and esters are, for example, 60 to 80 in the thermal decomposition product of polyolefin.
wt%, 40 to 60 wt% for PVC resin decomposition products
% Included. Therefore, by reacting the solution 13 of metal hydroxide obtained by washing the decomposition residue 7 and the thermal decomposition product 5, these acid components and esters can be saponified (C1). At this time, the salt of the same metal contained together with the metal hydroxide in the washing liquid for washing the decomposition residue exerts a salting-out (C2) effect to enhance the formation of soap. In order to make the saponification reaction more reliable, it is preferable to heat the reaction system, and after the saponification, additives are appropriately mixed depending on the use of the soap and cooled (C3) to recover the solidified soap.

Examples of metal hydroxides used in the thermal decomposition of plastics include sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide,
Examples thereof include basic hydroxides such as barium hydroxide and lithium hydroxide, and amphoteric hydroxides such as aluminum hydroxide, zirconium hydroxide and cerium hydroxide. Of these, sodium hydroxide and potassium hydroxide are preferable in terms of neutralization of hydrogen halide gas, promotion of decomposition reaction, and cost, and are highly applicable in practice. When sodium hydroxide is used during thermal decomposition, the soap obtained from the residue washing liquid and the decomposition product becomes hard soap, and when potassium hydroxide or the like is used, soft soap is obtained. Further, when the decomposition product contains a large amount of a saponifying component having a relatively low molecular weight, the saponifying component does not precipitate and solidify from the liquid even if a salt is present. In such a case, it can be used as salt water soap. The oil component that is not saponified and not recovered as soap can be separated and recovered from the salt-containing water 19 and used as the fuel oil 17. When the metal hydroxide used in the thermal decomposition reaction is poorly soluble in water, it is difficult to wash the decomposition residue with water, but the decomposition residue is washed by eluting the metal component with a dilute aqueous acid solution. can do. This cleaning liquid can be used to produce metallic soap. In this case, the decomposition residue is preferably washed with water.

When the metal hydroxides given above as examples are used during the thermal decomposition of plastics, a high adsorption capacity can be imparted to the carbonaceous solid residue, so that the decomposed residue is a gas or liquid purification adsorbent. It becomes possible to use it as etc. When the thermal decomposition is sufficiently performed at a temperature of about 400 to 600 ° C. and the residue is further heated, the adsorption ability of the decomposition residue is improved.

FIG. 2 shows an embodiment of an apparatus for carrying out the above plastic recycling method. In this example, pyrolysis is performed in two steps. That is, the recycling device 21 includes an atmospheric decomposition tank 23 and a pressure decomposition tank 25, each of which is provided with a heating device (not shown). An additive tank 27 for appropriately supplying alkali and water is connected to the atmospheric decomposition tank 23 via a control valve 29. The atmospheric decomposition tank 23 and the pressurized decomposition tank 25 are connected via a primary condenser 31, a pump 33 and a check valve 35. The pressure decomposition tank 25 is connected to the secondary condenser 39 via the pressure control valve 37. The primary condenser 31 is the secondary condenser 39.
Is also connected. The secondary condenser 39 is connected to the oil recovery tank 41 and the exhaust gas processing tank 43. Further, a residue cleaning tank 45 is provided, and water is supplied from a water tank 47 via a control valve 49. Also, the saponification tank 51
Is provided and is connected to the residue cleaning tank 45 and the oil recovery tank 41 via the control valves 53 and 55.

In the above-mentioned apparatus 21, a predetermined amount of alkali and water are added from the additive tank 27 to the plastic put in the atmospheric decomposition tank 23, and the plastic is heated to about 450.degree.
Gaseous decomposition products generated by thermal decomposition are the primary condenser 31.
At about 250 ° C., the heavy components of the decomposition products are condensed and sent to the pressure decomposition tank 25 via the check valve 35 by the pump 33. The heavy components are heated to about 450 ° C. in the pressure decomposition bed. The internal pressure of the pressure decomposition tank 25 is set to about 4 kgf / cm ² by the pressure control valve 37, and further decomposed into lighter components. When the internal pressure exceeds this pressure, the decomposition products are sent to the secondary condenser 39. The decomposition products and the light components not condensed in the primary condenser are cooled to about 50 ° C. in the secondary condenser and liquefied, and then stored in the oil recovery tank 41. The gas containing components that are not condensed is the exhaust gas treatment tank 4
3 is processed. When the decomposition operation is performed in multiple stages as described above, it is possible to set the purpose of each stage and the reaction conditions for achieving it individually,
It becomes easy to control the composition of the product, and it becomes possible to obtain a higher quality product. Further, in this configuration, the decomposition residue is mainly generated in the first atmospheric pressure decomposition tank, and the residue is hardly generated in the second-stage pressure decomposition tank 25.

On the other hand, the carbonaceous decomposition residue remaining in the atmospheric decomposition tank 23 is finely crushed, discharged from the bottom of the tank 23, and charged into the residue cleaning tank 45. Water is supplied from the water tank 47 to the residue cleaning tank 45, and the salt and excess metal hydroxide in the residue are eluted into the water. The water for washing the residue is sent to the saponification tank 51 through the valve 53. Furthermore, the oil and fat which is a decomposition product is supplied from the oil recovery tank 41 to the saponification tank 51 through the valve 55. The fats and oils are saponified with the metal components in the wash water to produce soap. If necessary, the saponification tank 51 is heated to stir the contents in order to accelerate the saponification reaction. The decomposed residue after cleaning is taken out from the cleaning tank 45 and used as a landfill material, an adsorbent, or the like.

Of course, the thermal decomposition step in the above configuration is
There may be only stages or multiple stages. Furthermore, various changes can be made as needed. For example, the gas that is not liquefied in the secondary condenser 39 may be passed through the wash water in the saponification tank 51. In this case, the saponifiable component and the inorganic acid component contained in the light component which is difficult to liquefy are saponified.
Can be captured with. Alternatively, the first condenser 3
The gaseous components that pass without being condensed in 1 and the decomposition products released from the pressure decomposition tank 25 are introduced into the saponification tank 51 without passing through the secondary condenser, and the components that move to the aqueous phase by saponification are It may be separated into oily components.

[0021]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples. In addition, the following examples and comparative examples,
The primary condenser 31, the pump 33, the pressure decomposition tank 25, and the valves 35 and 37 were omitted from the apparatus shown in FIG.

(Embodiment 1) Decomposition tank 23 of recycling device
Then, 5 kg of waste plastic containing PVC resin (PVC ratio: about 20% by weight) and 1.1 kg of sodium hydroxide were charged and heated to 450 ° C. for thermal decomposition. The generated decomposition product gas was cooled by the condenser 39, and 3 kg of the liquid oil and fat condensed in the oil recovery tank 41 was collected. On the other hand, 2 kg of a black solid decomposition residue remained in the decomposition tank 23. This residue is washed with water 2
After dipping in 000 ml and boiling to wash the residue, the residue was separated from water and dried, and the amount of the residue was reduced to 1.5 kg. Therefore, the salt or sodium hydroxide contained in the water after washing the residue is about 0.5 kg.

Next, 3 kg of oil / fat in the oil recovery tank 41 and water from which the residue was washed were mixed, boiled, and cooled with water.
kg of soap solidified.

Example 2 Example 1 except that 1.54 kg of potassium hydroxide was used instead of sodium hydroxide.
When thermal decomposition was performed under the same conditions as above, 3 kg of fats and oils were collected in the oil recovery layer 41, and 2.5 kg of black solid decomposition residue remained in the decomposition layer 23. When this decomposed residue was washed in the same manner as in Example 1, the amount of the residue was reduced to 1.5 kg. Therefore, the salt or potassium hydroxide contained in the water after washing the residue is about 1.0 kg.

Next, 3 kg of the oil / fat in the oil recovery tank 41 and water from which the residue was washed were mixed, boiled, and cooled with water.
4 kg of soap solidified.

[0026]

Industrial Applicability As described above, the method and apparatus for recycling plastics according to the present invention enables detoxification of decomposition residues due to thermal decomposition of plastics and recycling of excess metal hydroxide, which causes problems. Does not give rise to such end products. Therefore, its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a flow chart showing an example of work of a plastic recycling method of the present invention.

FIG. 2 is a schematic view showing an example of the plastic recycling apparatus of the present invention.

[Explanation of symbols]

21 Recycling device 23 Atmospheric pressure decomposition tank 25 Pressure decomposition layer 27 Additive layer 31 first condenser 39 Second condenser 41 Oil recovery layer 45 Residue cleaning tank 51 Saponification tank

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukishige Maesawa 8 Shinsitata-cho, Isogo-ku, Yokohama, Kanagawa Prefecture Yokohama Works, Toshiba Corp. (72) Inoue Yoji 3-7-1, Nishishinbashi, Minato-ku, Tokyo Toshiba Plant Construction Co., Ltd. (58) Fields surveyed (Int.Cl. ⁷ , DB name) C08J 11/00-11/28 B29B 17/00-17/02 C10G 1/10 C11D 1/00-19/00

Claims (2)

(57) [Claims] 1. A plastic is heated together with a metal hydroxide to contain a thermal decomposition product of the plastic and the metal hydroxide.
A pyrolysis step of generating a non-decomposed residue, a separation step of separating said metal hydroxides from the decomposition residues, the saponification step of producing saponified using a separate metal hydroxide and the decomposition products A method for recycling plastics, which comprises: 2. A plastic is heated together with a metal hydroxide to contain a thermal decomposition product of the plastic and the metal hydroxide.
A pyrolyzer to produce a non-decomposition residue, saponifying apparatus for generating a saponified with a separating device for separating the metal hydroxide from the decomposition residues, the a separate metal hydroxide and the decomposition products An apparatus for recycling plastics characterized by comprising: