JPS59111815A - Thermal decomposition of thermoplastics - Google Patents

Abstract

PURPOSE:To thermally decompose thermoplatics stably and effectively without causing any slugging phenomenon by contacting the thermoplastics with a fluidized layer consisting of heated specific solid particles. CONSTITUTION:Heat-resistant porous spherical substances, having a fine pore volume of 0.2-1.5cm<2>1g, a specific surface area of 5-1,500m<2>/g, a bulk density of 0.3-1.5g/cm<3>, and a weight average diameter of 0.025-0.5mm., (e.g., fine porous alumina particles by a particle circulation method, silica-alumina catalyst for fluidized catalytic decomposition by internal heating method, etc.) are used solid perticles for forming a fluidized layer. As a gas for fluidization in the thermal decomposition process, a gas containing oxygen in an amount anough to only a part of thermoplastics to be treated is preferably used. The thermal decomposition can be more effectively performed by a particle circulation method.

Description

BACKGROUND OF THE INVENTION TECHNICAL FIELD This invention relates to a method for pyrolyzing thermoplastics in a fluidized bed of solid particles. More specifically, the invention relates to a pyrolysis process characterized by the properties of the solid particles used.

Since large quantities of thermoplastics have been used, the disposal of their waste has also become an important issue.

A method of thermally decomposing thermoplastics has been proposed as a method for processing thermoplastics, and among these methods, the method of thermally decomposing in a fluidized bed of heated solid particles is an effective method due to the following advantages: .

(a) There is no need to melt the raw materials in advance.

(b) Decomposition rate is high.

(Easy to drive/operate.

) It is relatively easy to increase the size.

However, in the conventional fluidized bed method, non-porous sand with large particle size and bulk density, coke generated by thermal decomposition, etc., have been used as fluidized particles, and it is difficult to form a uniform fluid state or to form particles by melting. No special measures were taken to prevent the adhesive from sticking. As a result, the following drawbacks were avoided.

(r) The residence time of the thermoplastic to be thermally decomposed in the layer must be shortened, resulting in insufficient thermal decomposition and the formation of wax-like substances.

(b) At low temperatures, particles tend to stick together, making fluidization impossible.

(c) At high temperatures, thermal decomposition progresses well and a large amount of fluid oil is produced, but a large amount of gas is also generated.

SUMMARY OF THE INVENTION The present invention aims to provide a solution to the above-mentioned problems, and attempts to achieve this aim by using fluidized particles with specific properties.

Therefore, the method of pyrolyzing thermoplastics according to the present invention is a method of pyrolyzing thermoplastics by bringing them into contact with a fluidized bed of heated solid particles, in which the solid particles form a heat-resistant porous body having the following properties. It is characterized by being a spherical object.

Pore volume 0.2-1.5cm/g Specific surface area 5-1500m/g Bulk density
0.3-1.5g/cm3 weight average diameter
0.025 to 0.5mm Another method of pyrolyzing thermoplastics according to the present invention includes a pyrolysis step in which thermoplastics are brought into contact with a heated fluidized bed of solid particles and pyrolyzed. In a method in which a regeneration step consisting of heating the solid particles from this step in a fluidized state to gasify the deposit-resistant combustible material is carried out while circulating the solid particles between both steps, the solid particles are as follows: It is characterized by being a spherical heat-resistant porous material having the following properties.

Pore volume 0.2-1, 5cm/g Specific surface area 5-1500m 1g bulk density
0.3-1.5g/cm3 weight average diameter
0.025 to 0.5 mm effect The fluidized particles used in the present invention have a pore size of 10 to 5 mm because their pore volume and specific surface area are as described above.
Since there are many fine pores of 1,000 angstroms in diameter, the thermoplastic plastic, which becomes liquid at the thermal decomposition temperature, is quickly absorbed into the pores by surface tension. Since the particles in the fluidized bed can be given an arbitrary residence time, the molten thermoplastic can be occluded by the particles and retained in the fluidized bed for a long time to allow the thermal decomposition reaction to proceed sufficiently. .

Since the molten thermoplastic plastic is occluded within the pores of the particles, the liquefied plastic remains within the pores and does not wet the surface of the particles, thus preventing deterioration of the fluid state due to adhesion of the particles.

The fluidized particles used in the present invention are fine and lightweight spherical objects, as is clear from the above-mentioned weight-average diameter and bulk density specifications, so such particles have good fluidity like a low-viscosity liquid. Not only is it easy to transport and handle, but it exhibits an extremely uniform fluidized state, allowing sufficient contact between the particles and the fluidizing gas, and the fluidized bed does not cause slagging phenomena, making it easy to operate the fluidized bed. Extremely easy to operate. The fact that the present invention can fully enjoy the advantages of using such fine and lightweight particles is closely related to the fact that these particles are porous. This is because fine, lightweight particles tend to stick to liquids that wet their surfaces.

Basic Steps The process for pyrolysis of thermoplastics according to the invention consists in contacting the plastic with a fluidized bed of heated solid particles. As mentioned above, this basic process itself is known.

In the case of thermal decomposition of organic substances using heated solid particles in a fluidized state as a heat source, combustible substances such as coke adhere to the particles, but in order to remove them, the particles from the thermal decomposition process are fluidized. A regeneration process consisting of gasifying and removing adhesion-resistant combustible materials by heating in a heated state is also generally known, but in the present invention, this regeneration process can also be carried out while circulating particles between the pyrolysis process and the pyrolysis process. .

The products of the pyrolysis process are mainly oils, gases and residues at room temperature. Their composition and generation rate vary depending on the type of raw plastic. When plastics such as polyethylene and polypropylene are made from carbon and hydrogen, the calorific value of the oil is approximately 950.
It is a hydrocarbon oil of 0 kcal/kg. The main components of the gaseous substances are ethylene and propylene, respectively. Tasoshi,
When a molecular oxygen-containing gas is used in addition to water vapor as the fluidizing gas, the oily substance contains a small amount of an oxygen-containing compound, and the gaseous substance contains carbon monoxide, carbon dioxide, and the like. Furthermore, when plastics containing elements other than carbon and hydrogen, such as polymethacrylic acid and polyvinyl chloride, are used as raw materials, oily and gaseous substances containing elements other than carbon and hydrogen are produced along with hydrocarbons.

The residue is mainly composed of carbon and also contains trace amounts of hydrogen and the like. When water vapor is used as the fluidizing gas,
Most of the residue is retained within the pores of the fluidized particles. When a molecular oxygen-containing gas is used as the fluidizing gas, part or all of the residue becomes gaseous substances such as carbon dioxide and carbon monoxide due to combustion and gasification reactions.

The product in the regeneration step is a gas containing carbon dioxide gas and carbon monoxide, which are obtained by burning or gasifying the residue in the fluidized particles described above, and may also contain nitrogen, water, hydrogen, etc.

Thermoplastics The thermoplastics targeted for thermal decomposition in the present invention are:
It can be anything that becomes liquid at the pyrolysis temperature.

Some thermoplastics are decomposed into corresponding monomers when heated, and such plastics also fall within the scope of the thermoplastics targeted by the present invention.

Specific examples of such thermoplastics include:
Examples include polyethylene, polypropylene, polystyrene, polymethacrylate, polyvinyl chloride, polyamino polyethylene terephthalate, and others.

These may be in the form of various molded products that have become waste, or may be defective products generated during polymerization or molding.

When introduced into the pyrolysis process, these plastics are preferably in the form of granules that are as uniform as possible.

Solid Particles The fluidized bed particles used in the present invention are heat-resistant porous spherical particles having the following properties.

(a) Pore volume 0.2-1.5cm 7g
Preferably 0.3-1.2cm 7g (b) Specific surface area 5-1500m 7g Preferably 10-1000m /g 0→Bulk density 0, 3-1, 5g/cm
(preferably 0.4 to 1.3 g/cm2) Weight average diameter 0.025 to 0.5 mm, preferably 0.03 to 0.25 mm Here, "heat resistance" means that these properties are This means that it remains stable at least during the operating period (preferably for one month or more). Also, "spherical objects"
This means that even if the individual particles have slight irregularities, the overall appearance is spherical, and moreover, such particles account for about 90% by weight or more of the total particles.

Specific examples of particles that meet these requirements include silica-alumina fluidized catalysts for catalytic cracking of kerosene, zeolite fluidized catalysts, alumina microspherical particles used as carriers for fluidized catalysts, and waste materials. Microscopic spherical particles used in gas and wastewater treatment, etc. Since these are not necessarily the same in terms of heat resistance, the most suitable one should be selected depending on the operating temperature (details will be described later).

EXAMPLE An example of an embodiment of the invention is shown in FIGS. 1 and 2. Figure 1 shows the process of thermally decomposing thermoplastic plastics and the particle regeneration process of burning or gasifying combustible materials that adhere to the fluidized particles and become young through thermal decomposition. This shows an example of a method carried out while circulating.

FIG. 2 shows an example of the pyrolysis method in which thermal decomposition of thermoplastics and combustion or gasification of combustible particles adhering to the particles are carried out using a single fluidized bed. Here, we will refer to the former as the "particle circulation type" and the latter as the "internal heating type."

Most conventional embodiments are internally heated. This is because the apparatus is simple and easy to operate since no particle circulation is required.

However, in this internal heating method, the component gases in the oxygen-containing gas such as air to burn or gasify the combustible materials adhering to particles, and the oily substance generated by the thermal decomposition of thermoplastics by the combustion or gasified gas. Since the oil and gaseous substances are diluted, recovery by cooling the oily substances becomes a burden, and the calorific value of the gas decreases. Furthermore, even when oxygen compounds are not contained in the raw material plastic, organic oxygen compounds are contained in the produced oil, and there is a drawback that it is necessary to separate and recover appropriate fractions.

On the other hand, the particle circulation type has a complicated device, but the gas for combustion or gasification of particle adhesion is separated from the products of thermal decomposition of thermoplastics.
The oil can be easily cooled, the generated gas has a high calorific value, and the oil does not contain organic oxygen compounds.

Even when applied internally, the method of the present invention provides many advantages over conventional methods. In other words, the fluidized bed of the present invention exhibits an extremely uniform fluid state and does not cause unstable slagging phenomena, making operation extremely easy and preventing molten combustibles from entering the pores of the particles. By holding the fluid for a long time and increasing the height of the fluidized bed, the contact time between the pyrolyzed product and the particles can be increased, so the 11 pyrolysis reaction can proceed sufficiently without causing deterioration of fluidity due to adhesion of particles. I can do it. Furthermore, troubles due to particle abrasion and device wear rarely occur.

However, the method of the present invention can be more effective when applied to a particle circulation method. When relatively coarse and heavy particles such as conventional sand are used, the particles have poor fluidity and are difficult to move and transport for particle circulation, and are prone to equipment failures such as wear. . On the other hand, since the method of the present invention has good particle fluidity, it does not cause the above-mentioned difficulties and failures, and is extremely easy to operate. This is because the advantage of the case is added.

Now, in Fig. 1, numeral 1 is a fluidized bed reaction tower (pyrolysis tower) for thermally decomposing thermoplastic plastics, and the raw material plastic is fed through a screw feeder 3 from the hole ξ- of 2, for example, as shown in the figure. is fed into the fluidized bed from the top of the column. From the bottom of the tower, a water vapor-containing gas, that is, pure water vapor or water vapor and N
2 or a mixture with an inert or non-oxidizing gas such as CO2, N2, etc. The fluidizing gas in the pyrolysis step may be a molecular oxygen-containing gas. Such a gas preferably contains molecular oxygen in an amount that causes only a portion of the raw plastic to be combusted.

The upper part of the cracking tower is enlarged, and a cyclone installed inside the tower separates entrained particles from the gas and returns them to the fluidized bed.

Thermal decomposition temperature varies depending on the type of meltable combustible material, but
The temperature is approximately 300-500°C. The velocity of the fluidizing gas is typically about 10-100 cm/sec based on the sky column.

The raw material plastic is usually pulverized into pieces of several millimeters or less.

The products of thermal decomposition pass through a pipe 6, are cooled to room temperature or lower in a cooler 7, and are separated into an oily substance (cracking oil) in a receiver 8 and a gaseous substance (cracking gas) in a pipe 9. It will be done.

The particles are discharged from the pipe 10 at the bottom of the decomposition tower, reach the ejector 11, and pass through the pipe 13 with water vapor 12 to a fluidized bed reaction tower (regeneration tower) for burning and gasifying the particle-resistant combustibles. Transported to 14.

A molecular oxygen-containing gas, i.e., air or pure oxygen, a mixture of both, or a mixture thereof with water vapor, or water vapor or a non-oxidizing gas containing water vapor is fed from the pipe 15 at the bottom of the regeneration tower. Ru. The upper part of the regeneration tower is enlarged, and a gas (regeneration gas) from which entrained particles are separated by a cyclone 16 installed therein is discharged to the outside of the system through a pipe 17. The particles that have been heated and heated in the regeneration tower are twisted to the decomposition tower through a pipe 18.

The regeneration temperature is determined for the purpose of sufficiently promoting combustion or gasification of particle adhering particles and further supplying the heat necessary for thermal decomposition. Usually it is about 650-850°C. The superficial velocity of the fluidizing gas in the regeneration tower is typically 10 to 100 cm/sec.

The original reaction atmosphere of the fluidized bed in the regeneration tower is mixed with C01 into the regeneration gas.
The regeneration temperature, fluidized bed height, and , the amount of oxygen-containing gas, and other conditions.

On the other hand, in the embodiment shown in FIG. 2, reference numeral 1' is a fluidized bed reaction tower for simultaneously proceeding with the thermal decomposition of raw plastic and the combustion or gasification of particle adhering particles.

2 is a hopper for raw plastic, and 3 is a screw feeder. A molecular oxygen-containing gas is fed as a fluidizing gas from a pipe 4 at the bottom of the tower.

This gas is usually air, but may also be pure oxygen or a mixture of air or pure oxygen with water, steam, CO2, etc. Note that it is desirable to feed less molecular oxygen in the fluidizing gas than the required theoretical amount in order to cause the raw material plastic to burn.

The thermal decomposition products and combustion or gasification gas thus generated are separated from the entrained particles by a cyclone 5 housed in the enlarged section at the top of the tower, and then passed through a pipe 6 in a similar manner to that shown in Fig. 1. It is led to a cooler and receiver, where it is separated into oily and gaseous substances. In this method, the temperature of the fluidized bed needs to be about 400 to 600°C, which is higher than in the previous example, since it is necessary to advance the combustion gasification reaction simultaneously with thermal decomposition. In addition, the superficial velocity of the fluidizing gas is approximately 10 to 100 cm.
/second is appropriate.

In the particle circulation type, the temperature in the regeneration step is as high as about 650 to 850°C, so thermally stable particles of alumina, carbon, etc. are preferable. The operating temperature for internal heating type is approximately 40℃.
Since the temperature is about 0 to 600°C, silica/alumina catalysts or zeolite catalysts for fluid catalytic cracking of kerosene and gas oil, which are thermally unstable than the previous particles, can be used.

An apparatus similar to that shown in FIG. 1 attached to the Example was used. The pyrolysis tower has an inner diameter of 5.
It is a stainless steel tube with a diameter of 4 cm and an effective height of approximately 2 m, with the top of the column expanded to an inner diameter of 10.6 cm.

The raw material supply port is located at the top of the fluidized bed, and the inlet for return particles from the regeneration tower is located approximately in the middle of the fluidized bed. The regeneration tower has an inner diameter of 5.4 cm, an enlarged top section of 10.6 cm, and an effective height of about 1 m.

Four liters of alumina porous material in the form of fine powder and spheres for use as a fluidized catalyst carrier was filled as fluidized particles.

The properties of the fluidized particles are as follows.

Pore volume 0.70cm3/g, specific surface area 300m
27g bulk density 0, 42g/am3, weight average diameter 0
．． As a 060mm raw plastic, the size is approximately 2
~3 mm polyethylene waste pellets were fed to the pyrolysis tower at 6 oog/hour. At this time, steam preheated to about 400°C was supplied from the bottom of the column at a rate of 250 g/hour, and the fluidized bed temperature was maintained at 450°C.

In addition, room temperature air was fed into the regeneration tower at 21 ONIJ liter/hour to maintain the fluidized bed temperature at 800°C.

The particle circulation rate between the cracking tower and the regeneration tower was approximately 2.5 liters/hour. The pyrolysis product was cooled at about o'ct using water and dry ice and separated into cracked oil and cracked gas.

Thermal decomposition was carried out stably for a long time under the above conditions, and when the operation was continued for about 5 hours or more, the following constant results were obtained (value per gram of polyethylene).

Cracking oil yield 91 g/g l Specific gravity 0.872 Decomposition gas amount 44Ncm/g composition Co21vo1% C2H614〃 C2H429I ”3H814g C3H621〃 Regeneration gas amount 35ONcm/g composition Co217vo1% Co 3. , r O□　　〃〃 N27’8#

[Brief explanation of the drawing]

1-2 are flow sheets illustrating two embodiments of the method of the present invention. 1... Pyrolysis tower, 1'... Pyrolysis/regeneration tower, 2...
- Raw material plastic hole - ξ-14... Gas supply pipe for fluidization, 13.17... Particle circulation pipe, 14... Regeneration tower.

Claims (1)

[Claims] 1. A method of thermally decomposing a thermoplastic plastic by bringing it into contact with a fluidized bed of heated solid particles, wherein the solid particles are spherical heat-resistant porous bodies having the following properties. A method for pyrolyzing thermoplastics, characterized by: Pore volume 0, 2-1, 50m/g Specific surface area 5-1500m/g Bulk density
0.3-1.5g/cm3 weight average diameter
2. The method according to claim 1, wherein the fluidizing gas in the pyrolysis step contains an amount of molecular oxygen that causes only a portion of the thermoplastic to be combusted. 3. A thermal decomposition process consisting of bringing the thermoplastic plastic into contact with a fluidized bed of heated solid particles to thermally decompose it, and heating the solid particles from this process in a fluidized state to gasify the adhesion-resistant combustibles. A method of carrying out a regeneration step consisting of Pyrolysis of plastics. Pore volume 0.2-1.5cm/g Specific surface area 5”-1500m/g Bulk density
0.3~1,5 g/cm3 weight average diameter
0, 025-0, 5mm4, the fluidizing gas in the pyrolysis step is a water vapor-containing gas, and the fluidizing gas in the regeneration step is a molecular oxygen-containing gas, Claim 3
The method described in section. 5. The method according to claim 3, wherein the fluidizing gas in the pyrolysis step contains molecular oxygen in an amount that causes only a portion of the thermoplastic to be combusted.