JPH06179877A - Method and apparatus for thermal decomposition of waste plastics - Google Patents

Abstract

PURPOSE:To provide a method and apparatus for thermal decomposition of waste plastics which enable efficient recovery of a light fuel oil. CONSTITUTION:The thermal decomposition method comprises the step of thermally decomposing waste plastics under pressure in a decomposition vessel 2 and the step of separating the decomposition product thus obtd. into a relatively heavy oil component and a relatively light oil component in a separation vessel 3. The apparatus has means for carrying out these steps, and the thermal decomposition vessel 2 is pref. made of an iron alloy contg. Ni and Cr.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for thermally decomposing waste plastic and recovering it as fuel oil,
In particular, it relates to a technique for improving the quality and recovery efficiency of fuel oil.

[0002]

2. Description of the Related Art Since plastics are lightweight and have excellent strength, they are often used in products in various fields including home electric appliances. Conventionally, incineration and landfilling methods have been used for waste treatment, but the recycling and recycling of waste plastics has been implemented by the Recycling Promotion Law that came into effect in Japan in 1991 due to the reduction of landfill areas and the movement for effective use of resources. There is a rapid rise in interest in becoming more popular.

However, although there are many kinds of plastics and their processing methods are different from each other, it is common to use a plurality of kinds of plastics for one product, so that separate collection is difficult. This not only reduces the value of the recycled product, but also complicates the recycling itself.

Under the present circumstances, there is a possibility that recycled products having a relatively high commercial value may be obtained. Therefore, a technique for pyrolyzing waste plastics by pyrolysis to recycle them as fuel oil is drawing attention. However, the economy is low and improvement of recovery efficiency is desired. In addition, thermoplastic waste plastics such as polystyrene and polypropylene cannot be rapidly and uniformly heated due to their low thermal conductivity. Therefore, the resulting fuel oil contains various components over a wide boiling point range, which results in poor oil quality. It is also necessary to improve.

Therefore, as a method for improving the oil quality, attempts have been made to reform the oil by using a gas-phase catalytic catalyst such as zeolite, as disclosed in JP-A-63-178195 and JP-A-2-2949.
Although it has been proposed in Japanese Patent Laid-Open No. 2 (1993), there is a problem in that the heat decomposition section and the oil reforming section need to be separately heated, so that the apparatus becomes large-scale and the fuel cost is increased.

When a mixed plastic waste containing a vinyl chloride resin (hereinafter referred to as a PVC resin) is pyrolyzed, hydrogen chloride which is a corrosive gas is generated, which damages the furnace material and decomposes the plasticizer. There is a drawback that the pipe for collecting the fuel oil is blocked by an object.

[0007]

As described above, according to the conventional method of oiling waste plastics, the oil quality and recovery rate of fuel oil are improved, and the damage of the apparatus due to the generation of hydrogen chloride and decomposition products of the plasticizer. Had to be prevented.

The present invention has been made to solve such conventional problems, and an object thereof is to provide a method for thermally decomposing a plastic capable of recovering fuel oil from waste plastic with high efficiency and high quality. Is.

[0009]

In order to achieve the above object, a method for thermally decomposing a plastic according to the present invention comprises a thermal decomposition step of thermally decomposing a plastic under a pressure atmosphere to obtain a thermally decomposed product; A separation step of separating the decomposition product of the step into a relatively heavy oil component and a relatively light oily component;
A refluxing step of refluxing the relatively heavy oil component separated in the separation step to the thermal decomposition step in order to pyrolyze it, and a recovery step of recovering a relatively light oily component separated in the separation step. It is characterized by having.

Further, the apparatus for thermally decomposing plastics according to the present invention comprises a thermal decomposition means for thermally decomposing the plastic under a pressurized atmosphere; the decomposition product obtained by the thermal decomposition means is converted into a relatively heavy oily component. Separation means for separating into relatively light oil components; reflux means for returning to the thermal decomposition means for thermally decomposing the relatively heavy oily matter separated by the separation means; and the separation means It is provided with a recovery means for recovering a relatively light oily component separated by.

The present invention will be described in more detail below.

When the plastic is heated and decomposed at a temperature in the range of 300 to 600 ° C. without supplying oxygen under normal pressure, various gases of light to heavy are simultaneously generated in the produced gas. The oil obtained by condensing is not preferable as a fuel oil, and when polyethylene is decomposed, for example, it may solidify into a wax at room temperature because the proportion of heavy components is large. On the other hand, when the plastic is heated in the closed system, the pressure inside the system naturally increases due to the decomposition of the plastic, the molecular motion becomes active, and the heat transfer property is improved. Moreover, since the boiling point of each component rises due to the increase in pressure, the heavy component easily stays in the liquid phase,
The decomposition rate is improved. The higher the pressure is, the higher the decomposition rate is, but if the pressure is too high, the production rate of the gas component that does not condense at room temperature becomes high, so that the recovery rate of the liquid oil decreases. Therefore, in order to obtain oil with less heavy components, the amount of pressurization is
The gauge pressure is preferably within the range of 1 to 10 kg / cm ² . However, since the effect of pressurization is that the distribution of the produced oil component shifts to the smaller molecular weight, it is unavoidable to mix the heavy component only by the pressurizing operation, and the molecular weight distribution of the produced oil is narrowed, That is, high quality cannot be dealt with.

On the other hand, the method of lowering the temperature of the gas obtained by the thermal decomposition to a certain extent and condensing and separating the heavy components and returning to the decomposition step is to obtain a fuel oil having a narrower molecular weight distribution range than the decomposition product gas. to enable. However, when it is decomposed by heating at atmospheric pressure, even if it is condensed and separated, the amount of heavy components in the produced gas itself is high, so removal of the heavy components is not satisfactory, and the yield of produced oil is also low. Low.

The inventors of the present invention have made earnest studies on the method of oiling waste plastics. As a result, when the thermal decomposition under pressure and the condensation separation of the produced gas are performed in combination, the yield and quality of the oil obtained can be remarkably improved. It has been found that it is possible to obtain an oil having a boiling point of more than 250 ° C and containing almost no heavy components. That is, the plastic thermal decomposition method of the present invention comprises thermally decomposing the plastic under pressure, cooling the gas product obtained by thermal decomposition to a predetermined temperature, condensing and separating heavy oil components, and conducting a thermal decomposition step. And recovering oil containing only light components that do not condense in the separation step.

As described above, the higher the pressure in the thermal decomposition step, the lighter the decomposition products become. Therefore, the degree of pressurization in the thermal decomposition step of the plastic thermal decomposition method according to the present invention depends on the target fuel oil. It is set appropriately according to the quality. When converting to fuel oil of kerosene, the amount of pressurization is preferably in the range of 1 to 6 kg / cm ^{2 in} gauge pressure. In this range, a yield of about 50 to 80 wt% is obtained. Fuel oil can be obtained. About 3-5kg / cm
Within the range of ² , it is more preferable. Under such suitable pressure, the plastic is heated to about 300-600 ° C.

The decomposed gas product is cooled to a predetermined temperature lower than the thermal decomposition temperature in the separation step, the heavy component is condensed and separated from the light component, and is returned to the thermal decomposition step. Light oil is recovered by further cooling the light component gas that has passed through the separation step without condensation to room temperature and liquefied. The oil component that is recovered after passing through the condensing step varies depending on the gas cooling temperature in the condensing step, so the cooling temperature is also appropriately set according to the target fuel oil quality. Boiling point 150
In the case of converting to fuel oil of about kerosene at ~ 250 ° C, about 200 to 350 at a pressure suitable for the above-mentioned thermal decomposition.
C., more preferably about 250-300.degree. When the cooling temperature is lowered, the incorporation of heavy components having a boiling point of 250 ° C. or higher is reduced, but when it is too low, the amount of oil recovered per hour is reduced. Even if the produced gas is cooled at normal pressure, it can be suitably separated, but it is desirable to cool it at a temperature lower than the above temperature range.

The above method is performed by using, for example, an apparatus having a structure shown in FIG. In this configuration,
The apparatus 1 comprises a decomposition tank 2 for thermally decomposing plastic, a separation tank 3 for separating heavy components from generated gas, a pump 4 for refluxing the heavy components from the separation tank 3 to the decomposition tank 2, and a heavy component. The recovery tank 5 is provided for cooling the removed gas through a cooling pipe and recovering an oil component composed of a light component. The decomposition tank 2 and the separation tank 3 are connected via a pressure control valve 6, and by releasing the gas in the decomposition tank to the separation tank 3 when the pressure in the decomposition tank 2 rises by heating and exceeds a predetermined value. It is configured to maintain the internal pressure of the decomposition tank 3 at a predetermined value. The separation tank 3 and the recovery tank 5 are also connected via a pressure control valve 7, and when the pressure in the separation tank 3 exceeds a certain value, gas is discharged to the recovery tank 5 to keep the pressure constant. ing. The separation tank 3 is maintained at a predetermined temperature lower than that of the decomposition tank 2.

When the crushed waste plastics are heated in the decomposition tank 2 according to the above-mentioned constitution, they are thermally decomposed to generate gas and the pressure in the tank rises. When the pressure reaches a predetermined pressure, the gas is discharged to the separation tank 3 and cooled to the temperature in the separation tank 3, so that the heavy component having a high boiling point is condensed among the gas components. This is returned to the decomposition tank 2 by the pump 4 and used again for the decomposition reaction. On the other hand, when the pressure in the separation tank 3 reaches the pressure set by the pressure control valve 7, the light gas component that does not condense is released to the recovery tank 5, is sufficiently cooled to about room temperature and is liquefied, and then is stored in the container 8. Be accommodated. The low boiling point component that is not liquefied in the recovery tank 5 is sent to the gas treatment tank 9 and processed.

When actually handling waste plastics, it is complicated to separate a mixture of various kinds of plastics depending on the type, and therefore it is desirable to decompose the mixture by heating. In this case, the method of cleaving the plastic polymer during thermal decomposition differs depending on the type of plastic.For example, polypropylene, polyethylene, etc. randomly cleave, polystyrene, etc. preferentially monomer cleaving, and polyvinyl chloride, etc. cleave the side chain. Has priority. In any case, the product is mainly composed of an olefinic or aromatic unsaturated hydrocarbon. On the other hand, it is preferable that the fuel oil is, for example, kerosene, which contains a paraffinic component as a main component and a small amount of an aromatic component. Therefore, it is desirable to convert olefinic components to paraffinic components. Catalysts such as activated alumina and zeolites hydrogenate olefinic double bonds and are therefore convenient for achieving this purpose. Such a catalyst 11 can be installed in the separation layer 3 and used as shown in FIG. Alternatively, the function of the catalyst tank and the function of the cooling separation tank can be provided by connecting and using the catalyst tank whose temperature is adjusted to be suitable for the cooling separation, instead of the separation tank.

When polyvinyl chloride is contained in waste plastic, harmful hydrogen chloride gas is generated by thermal decomposition,
Corrodes equipment and contaminates the resulting oil. Further, polyvinyl chloride products often contain a plasticizer such as di (2-ethylhexyl) phthalate (DOP) in a proportion of about 30 wt%, which becomes a sublimable phthalic anhydride by heating as shown in Chemical formula 1. Adheres to the piping of the device and causes blockage of the piping. To solve this problem, it is effective to make an alkaline component coexist when heating the waste plastic.

[0021]

[Chemical 1] Examples of the alkali component include alkali metal hydroxides such as sodium hydroxide and alkaline earth metal hydroxides. The alkali component reacts with hydrogen chloride gas to generate a salt and water vapor. Therefore, as shown in Chemical formula 2, most of the hydrogen chloride gas produced by the primary thermal decomposition of PVC (decomposition of the side chain) remains in the decomposition tank as metal chlorides. Therefore, the produced oil is of high quality containing almost no chlorine compounds.

[0022]

[Chemical 2] Furthermore, in the presence of an alkali component, DOP contained in the PVC resin as a plasticizer becomes a metal salt of phthalic acid by an alkali saponification reaction as shown in Chemical formula 3, and phthalic acid or phthalic anhydride is not produced, so that decomposition gas is generated. It is possible to prevent blockage of the pipe that guides. Also, even if phthalic anhydride or the like is generated and adheres to the pipes, etc., steam generated by the neutralization reaction between the alkali and hydrogen chloride gas dissolves this and recirculates into the tank. There is no fear. Other ester components contained as an additive in the waste plastic are also hydrolyzed. Therefore, the waste plastic is likely to be thermally decomposed, and the decomposition rate of the hardly decomposable waste plastic can be improved.

[0023]

[Chemical 3] Further, since the salt dissolves in water, the decomposition residue (carbon) of the waste plastic attached to the salt in the tank can be easily removed by washing with water after the reaction. Further, since unreacted alkali is also soluble in water, it is easy to clean the device after the reaction.

The amount of alkali added varies depending on the PVC content in the waste plastic, but is about 0.2 to 2.0 in the form of alkali metal hydroxide with respect to PVC plastic.
If the weight part is appropriate and the amount of alkali is insufficient, a large amount of organic chlorine compounds will be produced from the produced hydrogen chloride gas, and the decomposition products of the plasticizer will cause clogging of pipes and the like. If it is too large, the energy cost will increase, the decomposition tank will be corroded by alkali, and the produced oil will contain an alkaline component. The alkaline component is not only in the form of hydroxide, but also metal,
It may be added in the form of an oxide. The supply method is not particularly limited, and a predetermined amount of alkali component can be added directly before heating.

Since the effect of the above-mentioned alkali is further improved by adding an appropriate amount of water, the addition of water is preferable for improving the quality of the produced oil. The effect of preventing the blockage of the pipe becomes remarkable. The appropriate amount of water to be added varies depending on the type of waste plastic and the treatment temperature, but is generally about 0.1 to 1 part by weight with respect to PVC. When the amount of water decreases, the decomposition efficiency decreases. If it is too large, energy efficiency will decrease. Water with less impurities is desirable. The supply method is not particularly limited, and a predetermined amount of water may be directly added to the decomposition tank before heating. You may add as an alkaline aqueous solution. If the waste plastic contains a proper amount of water, it is not necessary to add it.

Although water can be a hydrogen source for reforming oil, it is inefficient if it evaporates and separates during heating. In this regard, however, in the present invention, the inside of the decomposition tank is pressurized, so that the density of water vapor is high and it can be used efficiently. For this reason, the polymer straight chain of the plastic is likely to be fragmented, and the produced oil contains a large amount of components having a small molecular weight such as gasoline, so that the quality is improved.

Furthermore, the above-mentioned alkaline components are PVC, P
It has been found that both plastics other than VC exhibit a catalytic effect of improving the decomposition rate. This effect is exhibited not only by thermal decomposition at normal pressure but also in a pressurized state. Therefore, by adding an alkaline component such as sodium hydroxide and water to waste plastic and heating it under pressure, it is possible to limit the effect to PVC. In addition, the recovery rate of fuel oil from various plastics can be improved, and the component can be made to have a low molecular weight.

The amount of alkali added to obtain the catalytic effect is preferably 5% by weight or more based on the plastic in the case of sodium hydroxide. If the amount of sodium hydroxide is less than 5% by weight, the decomposition rate of the waste plastic will decrease. The supply method is not particularly limited, and a predetermined amount of sodium hydroxide can be directly added before heating. The amount of water added is preferably 10% by weight or more based on the plastic. When the amount of water added is less than 10% by weight, the ratio of heavy oil quality in the produced oil increases. Water with less impurities is desirable. The supply method is not particularly limited, and a predetermined amount of water can be directly added before heating. The pressure of the decomposition tank is preferably 1 atm (≈1.03 kg / cm ² ) or more in gauge pressure.

At this time, it is necessary to use an apparatus capable of withstanding the above-mentioned reaction conditions using a high concentration of alkali under high temperature and pressure. The inventors of the present invention have found that the corrosion-resistant alloy containing nickel and chromium. Was found to be suitable as a material for the decomposition tank. This corrosion-resistant alloy is an iron-based alloy containing 5% or more nickel and 10% or more chromium, such as SUS304 stainless steel. When the amount of nickel decreases, the corrosion resistance deteriorates, making it difficult to use a high-concentration alkali under high temperature and pressure. When the amount of chromium decreases, the mechanical properties at high temperature deteriorate, making it difficult to use under pressure.

The corrosion-resistant alloy containing nickel and chromium is excellent not only in corrosion resistance but also in mechanical strength at high temperatures, and is optimal as a constituent material of a device for carrying out the present invention. Nickel and chromium contained in the alloy also act as a waste plastic decomposition catalyst under pressure.

The waste plastics include thermoplastic plastics such as polyethylene, polystyrene and polypropylene, as well as thermosetting waste plastics such as semiconductor sealing resin. As a result of studying the thermal decomposition of these without separating them, the present inventors have found that the coexistence of a semiconductor sealing resin improves the recovery rate of oil from plastics such as polystyrene and polypropylene. The semiconductor encapsulating resin contains silicon dioxide such as fused silica glass powder and crystalline silica powder. Since such silicon dioxide material has excellent thermal conductivity, it has low thermal conductivity such as polystyrene and polypropylene. It is considered that the temperature of the entire decomposition tank is uniformly and rapidly increased by supplementing the above. Therefore,
In the thermal decomposition of waste plastics, it is not always necessary to separate thermoplastics and thermosetting plastics, but conversely, the recovery rate can be increased by mixing them. When a semiconductor encapsulating resin containing about 70 wt% silicon dioxide is used, it is 10 to 20 wt% with respect to the waste plastic.
Addition increases oil recovery by 8-10%.

In order to improve the thermal conductivity of the reaction system,
It is also effective to use an inert oil such as silicone or a heat medium such as a molten salt. When a heat medium which is a liquid at the thermal decomposition temperature is used, the heat transfer property is enhanced and rapid heating is possible, and since it is uniformly heated, hot spots are eliminated and safety is improved. Further, the heating medium also has an effect of preventing the generated tar content from adhering to the heating furnace. or,
In general, oxygen partially oxidizes plastics, so even if it is used as a decomposition initiator, it adversely affects the properties of the produced oil, so that oxygen is not replenished during thermal decomposition. In particular, when the oxygen concentration exceeds 15%, the viscosity of the fuel oil increases, the amount of tar-like components increases, and the production amount decreases. However, the use of a heating medium is effective because it is possible to cover the waste plastic with a liquid and block oxygen.

The heat medium used has a boiling point of 400.
Examples include, but are not limited to, an inert oil having a melting point of 200 ° C. or higher and a molten salt having a melting point of 200 ° C. or lower, as long as the liquid is a liquid during thermal decomposition and does not react undesirably with a plastic. Specifically, silicone oils, ternary nitrates (eg, 7 mol% NaNO
An inorganic molten salt such as ₃ +44 mol% KNO ₃ +49 mol% NaNO ₂ ) can be used.

Also, according to the properties of the waste plastic,
If one or more of nickel oxide, iron oxide, copper oxide, manganese dioxide, silica, zirconia, and titania is used as a decomposition catalyst for waste plastics in addition to the plastics, low molecular weight oil increases and the molecular weight distribution narrows. Effective in improving oil characteristics. The amount of catalyst is preferably 10 to 200 wt% with respect to the plastic.

Even when a catalyst is used in the decomposition tank,
The addition of water further improves the properties of the fuel oil. The amount of water added in this case varies depending on the type of plastic and the treatment temperature, but is generally about 0.1 to 2 times the weight of waste plastic by weight. When the amount of water decreases,
As the decomposition efficiency decreases, the molecular weight distribution of the fuel oil broadens, and characteristics such as the increase of olefinic hydrocarbons occur. On the other hand, too much increases energy costs. Moreover, it is desirable that the water has few impurities. The supply method is not particularly limited, and generally, a predetermined amount of water is directly added to the decomposition tank before heating.

The above-mentioned heat medium, decomposition catalyst, and water exhibit effects when used alone or in combination, and are more effective when used in combination.

The oil obtained by the above-mentioned thermal decomposition method is
It has a high calorific value of about 10,000 kcal / kg and can be used as a fuel in the process of thermally decomposing waste plastic. Therefore, by adding a means for using a part of the fuel obtained by thermal decomposition for heating the decomposition tank to the above-described thermal decomposition apparatus according to the present invention, the apparatus can be efficiently operated, which is very economical. Target. Moreover, since the oil obtained is light, it is also excellent in terms of ecology.

[0038]

EXAMPLES Preferred examples of the present invention will be described below based on experimental results.

1. Effect of Pyrolysis under Pressure and Separation / Reflux Operation of Heavy Components (Experimental Example 1) 100 g of polyethylene pellets were placed in the stainless steel decomposition tank 2 of the apparatus 1 shown in FIG. 1, and pressure control valves 6 and 7 were respectively provided. The gauge pressure was set to be 4 kg / cm ² . The cooling temperature of the separation tank 3 was set to 300 ° C, and the decomposition tank 2 was heated to 450 ° C.

When the temperature of the plastic increased and reached the decomposition temperature, the internal pressure of the decomposition tank 2 started to increase due to the decomposition gas of the plastic. When the decomposition gas filled both the decomposition tank 2 and the separation tank 3 and the pressure thereof exceeded a gauge pressure of 4 kg / cm ² , a part of the decomposition gas escaped to the recovery tank 5 via the pressure control valve 6. Therefore, the gauge pressures in the decomposition tank 2 and the separation tank 3 were both kept at 4 kg / cm ² . Gas recovery tank 5
The pump 4 was started when it was confirmed that it escaped to. As a result, the process in which the heavy component liquefied in the separation tank 3 was transferred again to the decomposition tank 2 via the pump 4 and further decomposed was repeated. One hour after reaching the decomposition temperature, 80 g of liquid oil can be recovered in the oil recovery container 8, and its components are 20% equivalent to gasoline (boiling point 150 ° C. or lower), kerosene equivalent (boiling point 150 to 250 ° C.) 70%. %, Wax content (boiling point 2
50% or more) 10%.

(Experimental Examples 2 to 11) Under the same conditions as Experimental Example 1 except that the gauge pressure settings of the pressure control valves 6 and 7 and the temperature setting of the separation tank 3 were changed to the values shown in Table 1. The polyethylene pellets were pyrolyzed. The results are shown in Table 1.

(Experimental Example 12) The separation tank 3, the pump 4, and the pressure control valve 6 were removed from the apparatus 1 to remove the decomposition layer from the pressure control valve 7.
Pyrolysis was performed under the conditions shown in Table 1 using the one directly connected to. The results are shown in Table 1.

Table 1 Effects of pressure pyrolysis and separation / reflux operation ---------------------- Conditions Produced oil Separation tank Gauge pressure Component content (wt%) No Cooling temperature (kg / cm ²⁾ Yield Gasoline Kerosene wax (° C) Valve 6 Valve 7 (wt%) −−−−−−−−−−−−−−− −−−−−−−−−−−−−−−−−−−−− Experimental example 1 300 4 4 80 20 70 70 10 2 300 4 0 80 80 20 60 60 20 3 300 2 2 60 60 10 60 30 4 300 6 6 70 40 60 0 5 300 300 10 10 50 70 30 30 0 6 300 300 15 15 40 40 90 10 0 7 200 4 4 4 50 40 50 10 8 8 250 4 4 4 70 30 70 70 0 9 250 4 0 0 70 30 60 60 10 10 350 4 20 50 30 −−−−−−−−−−−−−−− −−−−−−−−−−−−−−−−−−− Experimental example 11 300 0 0 40 20 30 50 50 12 −−− 4−80 20 20 40 40 −−−−−−−−−−−− As shown in Table 1, in Experimental Example 2, 80 g of liquid oil was recovered, but the component was gasoline. Equivalent 20%, kerosene 60%, wax 20%. It is considered that this is because the separability of the heavy cracked gas was lower than that in Experimental Example 1 because the pressure inside the separation tank 3 became normal pressure.

As is clear from Experimental Example 3 and Experimental Example 11, when the gauge pressure in the cracking tank is small, the production rate of heavy components becomes high, and the speed of light oil conversion becomes slow,
As a result, the yield of oil was reduced and the amount of heavy components mixed in the produced oil was increased. However, if the amount of pressurization is made too large, the light gas component that does not condense even in the cooling pipe of the recovery layer 5 increases, so the produced oil becomes light, but the oil yield decreases. From the results of Experimental Examples 4 to 6, Recognize.

In Experimental Example 7, the proportion of light components in the oil was high, but the yield was low, and the decomposition was not completed in 1 hour. Therefore, if the cooling temperature of the separation tank is lowered, the decomposition time becomes longer.

In Experimental Example 11, the product gas was separated, but it was obtained because the product gas itself contained a large amount of heavy components, and at low pressure, the heavy components were difficult to liquefy and the separation efficiency decreased. Oil contains a large amount of heavy components. Further, in Experimental Example 12, although the amount of oil was large due to the pressurization, since the separation and re-decomposition of heavy components were not performed, the oil contained a large amount of wax and had a high viscosity. In either case, the heavy component cannot be sufficiently removed. On the other hand, it is possible to remove the heavy component unexpectedly by combining the thermal decomposition under pressure and the heavy component separation operation. It is understood by comparing the results of -10.

(Experimental Examples 13 to 17) Using the apparatus shown in FIG. 2 in which the catalysts listed in Table 2 are provided in the separation tank 3, the polyethylene pellets are pyrolyzed under the same conditions as in Experimental Example 1. It was The results are shown in Table 2.

Table 2 Effect of catalyst --------------------------------------------------------------------------------------------------------------------------------------------- wt%) (wt%) Gasoline Kerosene wax --------------------------------------------------- Experimental Example 1-80 20 70 10 13 Activated alumina 80 20 80 0 14 Zeolite 80 20 80 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− -Experimental Example 15 Diatomaceous earth 80 20 70 10 16 Silica 80 20 70 10 10 17 Nickel oxide 50 10 60 30 --------------------------------------- When using activated alumina and zeolite as the catalyst, 80 g of oil containing no wax was obtained. In these, the olefinic components are reduced,
Aromatic and paraffinic components increased relatively.

Experimental Examples 15 and 16 using diatomaceous earth and silica
In the case of, the effect of adding the catalyst was not observed. In Experimental Example 17 using nickel, the wax content increased and the oil amount decreased. In each case, the content of olefinic component was hardly reduced.

As is clear from the above results, by mounting activated alumina or zeolite as a catalyst, the produced gas can be reformed and high quality fuel oil can be recovered.

2. Effect of Addition of Alkali and Water (Experimental Example 18) From the apparatus 1 used in Experimental Example 1 to the separation tank 3,
Glass decomposition layer 2 with pump 4 and pressure control valve 6 removed
Was directly connected to the pressure control valve 7. The pressure control valve 7 was set to zero gauge pressure. Sodium hydroxide (18g) was put into the decomposition tank 2 and then soft PVC with a particle size of 1-2 mm
Pellets (18 g) were added and continuous heating was performed at 450 ° C. for 1 hour. As a result, 4 ml of fuel oil was recovered in the oil recovery container 8, and this amount was 20 wt% with respect to the amount of PVC. The obtained fuel oil contains benzene, octene, and 2-ethylhexanol as main components, and has 3 or more components having a boiling point of 250 ° C. or higher.
It was a light oil of 0% or less, and sodium and chlorine were not detected by an ion chromatograph with a detection sensitivity of 1 ppm.

Experimental Example 19 Sodium hydroxide (18
g), PVC pellets (18 g) and water (4 g) were placed in the decomposition tank 2 and the same experiment as in Experimental Example 13 was performed. The results are shown in Table 3.

(Experimental Examples 20 to 38) An experiment was conducted in the same manner as in Experimental Example 19 except that the types of waste plastics, the types and amounts of additives, and the amounts of water were changed as shown in Table 3.
The amount and properties of the fuel oil recovered in the oil recovery container 8 were measured. The results are shown in Table 3. Table 3
In, the amounts of alkali, water and produced oil are the respective weights when the weight of the waste plastic is 1.

Table 3 Effect of Addition of Alkali and Water ------------------------------------------------------------------------- Plastic Additive Addition amount Water Produced oil No addition amount Oil quality Yield of Na and Cl (parts by weight) (parts by weight) (parts by weight) Detection −−−−−−−−−−−−−−−−−−−−−−− −−−−−−−−−−−−− Experimental Example 18 PVC NaOH 1.0 0 Light 0.2 − Experimental Example 19 PVC NaOH 1.0 0.2 Light 0.3 − Experimental Example 20 PVC Ca (OH) ₂ 1.0 0.2 Light 0.2 − Experimental Example 21 PVC Mg (OH) ₂ 1.0 0.2 Light 0.2 − Experimental Example 22 PVC KOH 1.0 0.2 Light 0.2 − Experimental Example 23 PVC NaOH 0.2 0.2 Light 0.2 − Experimental Example 24 PVC NaOH 0.5 0.2 Light 0.3 − Experimental Example 25 PVC NaOH 2.0 0.2 Light 0.3 − Experimental Example 26 PVC NaOH 1.0 0.1 Light 0.3 − Experimental Example 27 PVC NaOH 1.0 0.5 Light 0.3 − Experimental Example 28 PVC NaOH 1.0 1.0 Light 0.2 − Experimental Example 29 PVC + PP (1: 1) NaOH 1.0 0.2 Light 0. 6 − Experimental Example 30 PVC + PS (1: 1) NaOH 1.0 0.2 Light 0.5 − Experimental Example 31 PVC + PE (1: 1) NaOH 1.0 0.2 Light 0.5 − Experimental Example 32 PVC NaOH 3.0 0.2 Heavy 0.3 Na Experimental Example 33 PVC NaOH 5.0 0.2 Heavy 0.3 Na Experimental Example 34 PVC NaOH 1.0 2.0 Heavy 0.2 − −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− −−−−− Experimental Example 35 PVC − − − Heavy 0.2 Cl Experimental Example 36 PVC − − 0.2 Heavy 0.2 Cl Experimental Example 37 PVC Al ₂ O ₃ 1.0 0.2 Heavy 0.2 Cl Experimental Example 38 PVC Fe ₂ O ₃ 1.0 0.2 Heavy 0.1 Cl −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− In Experimental Example 19, 6 ml of fuel oil was used. And, compared with Experimental Example 18, the number is significantly increased. Since the increase rate of 2-ethylhexanol in the fuel oil component is remarkable, it is considered that the decomposition rate of the plasticizer contained in PVC was improved by the addition of water, and therefore the fuel oil yield was increased.

As is clear from the results of Experimental Examples 18 to 28, it is possible to prevent the chlorine compound from being mixed into the produced oil by using the alkaline material. In addition, Experimental Examples 29 to 31
From the results, it can be seen that PVC and other chlorine-free plastics can be pyrolyzed simultaneously without any problems. However, if the amount of alkali added is excessive as in Experimental Examples 32 and 33, chlorine can be prevented from being mixed, but on the other hand, alkali is mixed into the produced oil and the produced oil becomes heavy.

In Experimental Example 35, phthalic acid or phthalic anhydride was crystallized on the wall of the recovery tank 5 immediately after the start of decomposition, and in Experimental Example 36, after the water in the decomposition tank 2 was completely evaporated. The behavior was observed. Then, as shown in Table 3, the amount of oil produced was smaller than that in Experimental Example 19, which indicates that sodium hydroxide and water have the effect of promoting the decomposition of PVC. In Experimental Example 36, 4 ml of water was obtained with respect to the initial filling water amount of 3 g, but this water shows acidity, and it is considered that hydrochloric acid, phthalic acid, etc. were dissolved. Further, in these experimental examples in which no alkali is added, the produced oil contains a large amount of chlorine compounds such as chlorooctane, and is therefore unsuitable as a fuel oil.

As described above, when alkali and water are added when the waste plastic containing vinyl chloride resin is thermally decomposed, generation of hydrogen chloride gas can be prevented, and the pipe of the device can be prevented from being blocked. You can Further, it is possible to obtain a high-quality fuel oil containing no chlorine compound, and the decomposition rate is improved.

In addition, also for waste plastics containing no vinyl chloride resin, fuel oil can be rapidly obtained under the same heating condition in which alkali and water are added, and the treatment of the residue becomes easy.

3. Effect of addition of alkali and water under pressure (Experimental Example 39) The pressure control valve 7, the recovery tank 5 and the recovery container 8 were connected to the decomposition tank 2 made of SUS304 (8% nickel + 18% chromium) having a closed structure. Put polypropylene pellets (20g), sodium hydroxide (1g) and water (2g) in the decomposition tank 2 in advance and cover with
Continuous heating was carried out at 420 ° C. for 1 hour. Since steam pressure is generated in the decomposition tank 2 when the temperature rises, the pressure control valve 7 was adjusted so that the gauge pressure became 1 atm. 20 ml of fuel oil can be obtained, which is 70% based on the amount of polypropylene.
% By weight. Furthermore, the fuel oil is 2-methyl-1-
Pentene, 2,4-dimethyl-1-heptene as a main component, and having 8 or less carbon atoms (boiling point 200 ° C. or less)
It was a gasoline-based oil of 0% or more.

(Experimental Examples 40 to 52) The same as Experimental Example 39 except that the types of waste plastics, the amount of NaOH added, the amount of water, and the gauge pressure in the decomposition tank were changed to the values shown in Table 4. Experiments were conducted to measure the amount and properties of the produced fuel oil. The results are shown in Table 4. In the table, heavy oil means that 20% or more of components have 17 or more carbon atoms (boiling point of 300 ° C. or more).

(Experimental Example 53) The fuel produced in the same manner as in Experimental Example 39 except that a decomposition tank made of martensitic stainless steel (0.14% nickel + 12.95% chromium) was used. The amount and nature of the oil was measured.
The results are shown in Table 4.

(Experimental Example 54) An experiment was conducted in the same manner as in Experimental Example 39 except that a cracking tank made of carbon steel for S35C mechanical structure (0% of both nickel and chromium) was used, and the amount of fuel oil produced. And the properties were measured. The results are shown in Table 4.

Table 4 Effect of addition of alkali and water under pressure ------------------------------------------------------------------------------- −− No Plastic NaOH Water gauge pressure Produced oil (wt%) (wt%) (atm) Oil quality Yield (%) −−−−−−−−−−−−−−−−−−−−−−− −−−−−−−−−−−−− Experimental Example 39 PP 5 10 1 Gasoline 70 Experimental Example 40 PP 0 10 1 Gasoline 30 Experimental Example 41 PP 2 10 1 Gasoline 50 Experimental Example 42 PP 20 10 1 Gasoline 70 Experimental Example 43 PP 50 10 1 gasoline 70 Experimental example 44 PP 5 30 1 gasoline 70 Experimental example 45 PP 5 50 1 gasoline 70 Experimental example 46 PP 5 10 5 gasoline 70 Experimental example 47 PP 5 10 10 gasoline 70 Experimental example 48 PE 5 10 1 Gasoline 70 Experimental Example 49 S 5 10 1 gasoline 80 Experimental example 50 PVC 5 10 1 gasoline 30 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− -Experimental example 51 PP 5 0 1 heavy oil 70 Experimental example 52 PP 5 10 0 heavy oil 80 Experimental example 53 PP 5 10 1 Gasoline 60 Experimental example 54 PP 5 10 1 Gasoline 60 -------------------- In Table 4, the amounts of sodium hydroxide (NaOH), water, and produced oil are based on the weight of waste plastic as 100. Is the weight of each.

From Experimental Examples 40 to 43, it can be seen that when the amount of sodium hydroxide is less than 5% by weight, the decomposition rate of waste plastic is lowered and the amount of fuel oil obtained is reduced. In addition, in Experimental Examples 44 to 47 and Experimental Examples 51 and 52,
It has been shown that fuel oil becomes heavy oil quality when the amount of water decreases or the operating pressure decreases. Under the above experimental conditions, water of 10 wt% or more and a gauge pressure of 1 atm or more are preferable.

From Experimental Examples 48 to 50, it is shown that, although the amount of fuel oil obtained varies depending on the type of plastic, gasoline-quality oil can be obtained in all cases. Therefore,
Light oil can be recovered from waste plastics by adding sodium hydroxide and water and thermally decomposing under pressure. However, in the case of actually thermally decomposing waste plastic, it is expected that the amount of heavy components in the decomposition product gas will increase because it decomposes a mixture of various plastics. Even in such a case, it is obvious that a light oil can be easily obtained by adopting the step of separating / refluxing the heavy component as shown in Experimental Example 1.

Experimental examples 53 and 54 are examples in which the material of the decomposition tank used is changed. In these cases, the amount and quality of the produced fuel oil were good, but the decomposition tank was severely corroded and could not be put to practical use. Experimental example 3
9 and these results, 8% nickel, 18%
It is suggested that chromium-containing stainless steel has a catalytic effect. Therefore, by applying this stainless steel to the decomposition tank, it becomes possible to endure the corrosion and efficiently recover the oil.

4. Pyrolysis of plastic in the presence of thermosetting resin (Experimental Example 55) 100 parts by weight of a crushed waste plastic product of polypropylene and 10 parts by weight of a crushed waste plastic product generated by transfer molding of a semiconductor encapsulating resin are mixed in advance, This mixed product was placed in the decomposition tank 2 having the same apparatus as in Experimental Example 18. Set the gauge pressure to 0, 500 ℃
Heated for 2 hours. As a result, the produced fuel oil was 80 parts by weight, and the amount of polypropylene waste plastic charged (1
(00 parts by weight) and the organic compound (3 parts by weight) such as epoxy resin in the semiconductor encapsulating resin waste plastic (78 parts by weight), the recovery rate of the produced fuel oil was 78%.

(Experimental Examples 56 to 58, 61, 62) A thermal decomposition test was conducted in the same manner as in Experimental Example 55 except that the kinds of plastics and the amount of the semiconductor sealing resin added were changed as shown in Table 5. Then, the amount of the produced fuel oil was measured and the recovery rate was obtained. The results are shown in Table 5.

(Experimental Examples 59, 60, 63, 64) A thermal decomposition test was conducted in the same manner as in Experimental Examples 55, 57, 61, 62 except that the gauge pressure of the pressure control valve 7 was changed to 3 kg / cm ^2. Then, the amount of the produced fuel oil was measured and the recovery rate was obtained. The results are shown in Table 5.

Table 5 Results in the Coexistence of Thermosetting Resins -------------------------- Plastic plastics (Parts by weight) Produced oil PP PS Semiconductor encapsulating resin Yield (parts by weight) Recovery rate (wt%) ------------------------------- --------------- Experimental example 55 100-1080 78 Experimental example 56 100-20 85 80 Experimental example 57-100 100 75 73 Experimental example 58-100 20 20 80 75 Experimental example 59 100-10 85 83 Experimental example 60-100 10080 78 Experimental Example 61 100-70 70 Experimental Example 62-100-65 65 Experimental Example 63 100-83 83 83 Experimental Example 64-100-78 78 -------------- −−−−−−−−−−−−−−−−−−−−−− - As apparent from Table 5, fuel oil towards the case of mixing the waste plastic pulverized product of the semiconductor sealing resin Polypropylene waste plastic ground product is generated much, it can be seen that can improve the collection efficiency.

The oils obtained in Experimental Examples 55 to 60 had a distillation point of 5
It was a component of about 0 to 350 ° C. From this result, it is easily understood that a light oil can be efficiently obtained by using the thermal cracking method including the same separation / reflux step as in Experimental Example 1.

Therefore, even if the thermosetting waste plastic containing silicon oxide such as the semiconductor sealing resin is added to the thermoplastic waste plastic such as polypropylene, there is no problem in the thermal decomposition, and conversely, the recovery of the fuel oil is performed. It is possible to improve efficiency.

5. Effect of Addition of Heating Medium, Decomposition Catalyst and Water (Experimental Example 65) Pressure control valve 7 of the same device as in Experimental Example 13
Is set to a gauge pressure of 0, 2 liters of silicon oil is put into the decomposition tank 2 as a heating medium, 1 kg of waste plastic made of polypropylene crushed to a diameter of about 2 cm, 1 kg of water, and 100 g of nickel oxide as a catalyst are placed in the lid. Did. Then, after burning a small amount of waste plastic to make the oxygen concentration of the air in the decomposition tank 15%, it was heated at 500 ° C. for 2 hours. As a result, the fuel oil produced was 1.0 liter of JIS standard A heavy oil equivalent product, and the amount of gas produced at the same time was 100 cc and the tar content was 100 cc.

(Experimental Examples 66 to 84, 89 to 92) Experimental Example 65 except that the type of heating medium, the type of decomposition catalyst, the amount of water added, and the type of waste plastic material were changed.
A thermal decomposition test was carried out in the same manner as described above, and the properties and amount of the produced fuel oil were measured. The results shown in Table 6 were obtained.

(Experimental Examples 85-88, 93-96) Similar to Experimental Examples 65, 82-84, 93-96, except that the gauge pressure setting of the pressure control valve 7 was changed to 3 kg / cm ^2. A thermal decomposition test was conducted and the properties and amount of the produced fuel oil were measured, and the results shown in Table 6 were obtained.

Table 6 Effect of Addition of Heating Medium, Decomposition Catalyst, and Water --------------------------------------------------------------- − No Plastic medium Catalyst water Produced oil (kg) Oil quality Yield (l) −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− --- Experimental example 65 PP silicone NiO 1.0 A heavy oil 1.0 Experimental example 66 PP silicone --- A heavy oil 0.7 Experimental example 67 PP-NiO-A heavy oil 0.8 Experimental example 68 PP --- 1.0 A Heavy Oil 0.8 Experimental Example 69 PP Silicone NiO-A Heavy Oil 0.9 Experimental Example 70 PP Silicone-1.0 A Heavy Oil 0.9 Experimental Example 71 PP Molten Salt NiO 1.0 A Heavy Oil 1.0 Experimental Example 72 PP Melted salts Fe ₂ O ₃ 1.0 A heavy oil 1.0 experiment 73 PP molten salt Co ₂ O ₃ 1.0 A heavy oil 1.0 experimental example 7 PP silicone CuO 1.0 A heavy oil 1.0 Experiment 75 PP silicone MnO ₂ 1.0 A heavy oil 1.0 Experiment 76 PP silicone SiO ₂ 1.0 A heavy oil 1.0 Experiment 77 PP Silicone ZrO ₂ 1. 0 A heavy oil 1.0 Experimental example 78 PP silicone TiO ₂ 1.0 A heavy oil 1.0 Experimental example 79 PP silicone NiO 0.5 A heavy oil 0.9 Experimental example 80 PP silicone NiO 1.5 A heavy oil 1.0 Experimental Example 81 PP Silicone NiO 2.0 A Heavy Oil 0.9 Experimental Example 82 PE Silicone NiO 1.0 A Heavy Oil 0.3 Experimental Example 83 PS Silicone NiO 1.0 A Heavy Oil 0.9 Experimental Example 84 PVC Silicone NiO 1.0 A heavy oil 0.2 Experimental example 85 PP Silicone NiO 1.0 Kerosene 1.0 Experimental example 86 PE Silicone NiO 1.0 Kerosene 1.0 Experimental example 87 PS Silicone NiO 1.0 Kerosene 1.0 Experimental Example 88 PVC Silicone NiO 1.0 Kerosene 0.2 ---------------------------------------------------------------------------------------------------------------------------- -Experimental Example 89 PP --- C Heavy Oil 0.7 Experimental Example 90 PE ---- C Heavy Oil 0.3 Experimental Example 91 PS ---- C Heavy Oil 0.6 Experimental Example 92 PVC ---- C Heavy Oil 0.2 Experiment Example 93 PP --- gas oil 1.0 Experimental example 94 PE --- Gas oil 0.9 Experimental example 95 PS --- Gas oil 1.0 Experimental example 96 PVC --- Gas oil 0.1 ---------- In the table, as the molten salt, 7 mol% NaNO ₃ -44 mol
% KNO ₃ −49 mol% NaNO ₂ ternary nitrate is used.

Comparing Experimental Examples 89 to 92 and Experimental Examples 65 to 84 in which neither heating medium, catalyst nor water is used, it is apparent that the oil quality is lighter and the yield is also increased. The amount of gas and tar is also reduced. Similar results are obtained in the comparison between Experimental Examples 93 to 96 and Experimental Examples 85 to 88, and the oil quality and the yield can be similarly improved even in the reaction under pressure. Therefore, it is obvious that higher quality oil can be obtained in higher yield by introducing these additives into the thermal cracking step performed in Experimental Example 1 as needed.

(Experimental Example 97) Using the same apparatus as in Experimental Example 1, 100 g of polypropylene crushed product was placed in the decomposition tank 2, the gauge pressure of the pressure control valve was set to 4 kg / cm ₂ , and the temperature was 420 ° C. Was pyrolyzed. A kerosene burner was used as the heat source of the decomposition tank 2. About 30 minutes after heating, when light oil started to be generated, the fuel of the burner was switched from kerosene to the light oil, and heating was continued. As a result, the decomposition was completed in 2 hours, and a total amount of light oil of 80 kg was obtained, and the light oil used after the fuel switching was 30 kg of 80 kg. Also, the amount of kerosene used before switching fuel is 1
It was 0 kg.

As is clear from the above results, by using the light oil obtained by thermal decomposition for self-combustion, it is possible to cover the energy required for the decomposition of plastic.

[0080]

As described above, according to the present invention,
The efficiency of decomposing waste plastics is improved, and the recovery rate of fuel oil is significantly improved compared to the past. Further, it becomes possible to recover good quality fuel oil.

[Brief description of drawings]

FIG. 1 is a flow chart showing the configuration of a first embodiment of a plastic thermal decomposition apparatus of the present invention.

FIG. 2 is a flow chart showing the configuration of a second embodiment of the plastic thermal decomposition apparatus of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI technical display location C08L 77:06 9286-4J (31) Priority claim number Japanese Patent Application No. 4-275763 (32) Priority date Hei 4 (1992) October 14 (33) Priority claiming country Japan (JP) (72) Inventor Hideki Shimada 1 Komukai Toshiba-cho, Komachi, Kawasaki-shi, Kanagawa Toshiba Research & Development Center

Claims (2)

[Claims] 1. A method for thermally decomposing a plastic comprising the following steps: a thermal decomposition step of thermally decomposing a plastic under a pressure atmosphere to obtain a thermally decomposed material; Separation step for separating a relatively heavy oil component and a relatively light oil component; a reflux step for refluxing the relatively heavy oil component separated in the separation step to the thermal decomposition step for thermal decomposition; and the separation A recovery process that recovers relatively light oil components separated in the process. 2. A thermal decomposition apparatus for plastics comprising the following means: thermal decomposition means for thermally decomposing plastics under a pressurized atmosphere; decomposition products obtained by the thermal decomposition means are relatively heavy oils. Separating means for separating components and relatively light oily components; reflux means for returning to the thermal cracking means to thermally decompose the relatively heavy oil components separated by the separating means; and the separating Recovery means for recovering a relatively light oil component separated by the means.