JPH0789900A - Method for recovering high-quality monomer from plastic - Google Patents

Abstract

PURPOSE:To efficiently recover high-quality monomer(s) from plastics in high yield in good operability by feeding feedstock plastics into a reactor heated to specified temperatures followed by pyrolyzing the plastics under dry distillation and then conducting a distillation of the resultant monomer(s). CONSTITUTION:Feedstock plastics such as acrylic synthetic resin or styrenic synthetic resin is continuously fed into a reactor heated to >=300 deg.C in advance and packed with a heating medium comprising spherical granules 0.1-100mm in diameter and/or aspherical granules 0.1-100mm in size consisting of inorganic material selected from sand, alumina, glass, agate zirconia, silicon nitride and ceramics and/or metallic material selected from aluminum, iron, stainless steel and titanium; In the reactor, the plastics are pyrolyzed under dry distillation into crude monomer(s), which is, in turn, distilled to separate and eliminate impurity compounds higher and lower in boiling point than the aimed monomer(s), thus recovering the objective high-quality monomer(s) from the platics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering and refining a thermoplastic material such as an acrylic synthetic resin or a styrene synthetic resin (hereinafter abbreviated as plastic) by dry distillation. The present invention relates to a method of recovering a high-quality monomer by decomposing methyl methacrylate (hereinafter abbreviated as PMMA), polystyrene (hereinafter abbreviated as PS) and the like into a crude monomer by dry distillation pyrolysis and then distilling the crude monomer.

[0002]

2. Description of the Related Art It is known that plastics such as acrylic synthetic resins and styrene synthetic resins are relatively easily decomposed into monomers by dry distillation pyrolysis as compared with other thermoplastics. Therefore, various methods of industrially recovering the monomer by the dry distillation pyrolysis method have been studied for the polymer, the molded product, the waste material generated at the time of molding, or the waste material recovered after being used as a product.

For example, in JP-A-54-154710, waste material of PMMA is mixed with one or more additives selected from an inorganic material having a small particle size and a low bulk specific gravity or a metal powder. A method of continuously carrying out dry distillation pyrolysis using a rotary kiln to recover a methyl methacrylate monomer (hereinafter abbreviated as MMA) is disclosed. However, in this method, the PMMA waste material is likely to be aggregated together with the additive, so that it is difficult to control the thermal decomposition temperature, and as a result, the recovery rate of the MMA monomer is low. There is a high risk of explosion due to the entry of outside air into the equipment, and it is difficult to ensure the safety of the entire equipment.
There is a problem that it is easily clogged with waste material A, and it cannot be said to be an industrially completed method.

Further, Japanese Patent Publication No. 47-41886 discloses a method of continuously contacting a PMMA waste material and a PMMA waste material maintained at or above the PMMA depolymerization temperature with an inert atmosphere. However, this method also has a drawback that the MMA recovery rate decreases with time due to the accumulation of carbides and ash (hereinafter abbreviated as ash) produced by carbonization in the system, and that molten metal components are mixed in the carbonization liquid. Yes, this is also not a completed industrial method.

[0005]

DISCLOSURE OF THE INVENTION The present invention uses a polymer of a plastic such as PMMA or PS, a molded product, a waste material produced at the time of molding, and a waste material recovered after being used as a raw material as a raw material for dry distillation heat. It is an object of the present invention to provide a method of decomposing and then industrially obtaining a high quality monomer by a distillation method with good operability and in a high yield.

[0006]

As a result of repeated studies for solving the above-mentioned problems, the inventors of the present invention have conducted a dry distillation in an inert atmosphere using a reactor which can be internally stirred and which is filled with a specific heat medium. By pyrolyzing and then condensing the vapor generated at that time, the crude monomer corresponding to the plastic is recovered, and at the same time, the ash produced by dry distillation pyrolysis is continuously discharged from the lower part of the reactor, and then the crude monomer is discharged. By the distillation method
The inventors have found that high-quality monomers can be recovered by separating and removing the impure compound having a low boiling point and the impure compound having a high boiling point as compared with the monomer, and arrived at the present invention.

That is, according to the present invention, the first step of continuously supplying the raw material plastic to a reactor filled with a heating medium preheated to 300 ° C. or higher and pyrolyzing it to decompose it into a crude monomer And a second dry distillation pyrolysis crude monomer that has undergone the first step is distilled to separate and remove an impure compound having a lower boiling point and an impure compound having a higher boiling point than the monomer.
The present invention provides a method for recovering high quality monomers from plastics, which comprises the steps of

The present invention will be described in detail below. Examples of the acrylic synthetic resin as the raw material of the present invention include polymethyl acrylate, polyethyl acrylate, polypropyl acrylate, polybutyl acrylate, PMMA, polypropyl methacrylate, polybutyl methacrylate and the like.

Examples of styrene synthetic resins include PS, polymethylstyrene, polyethylstyrene, polybutylstyrene, polydimethylstyrene and the like. Moreover, as these copolymers, MMA-styrene copolymers,
Examples thereof include MMA-dimethylstyrene copolymer. Although the above plastics may be used alone or in combination, it is preferable to subject the individual plastics to dry distillation pyrolysis because the purification process in the subsequent step is facilitated.

The plastic to be fed into the reactor for the pyrolysis by dry distillation may have any shape, such as shavings, flakes, granules, powder, chips and sheets, which may be used alone. They may be used in combination or with contaminated or uncontaminated liquid monomers. However, it is preferable to crush a large plastic such as a sheet or a molded product in its original shape into an easy-to-use piece having a size of 20 mm or less in order to facilitate charging into a reactor.

Next, the method of the present invention will be described with reference to the flow sheet shown in FIG. Pyrolysis is continuously performed using the above plastic as a raw material and using an external heat type vertical reactor (1) as shown in FIG. That is, the plastic is put in a hopper (2) of a supply device, and a closed structure is provided so as to prevent invasion of outside air and backflow and leakage of gas from inside the reactor, and an inert gas for purging is appropriately supplied from a conduit (13). While being introduced, the plastic in the hopper (2) is supplied to the reactor (1) by the constant quantity supply device (3).

The supply pipe (14) connected to the reactor (1) and the plastic have a structure in which the temperature can be adjusted to 250 ° C. or lower, preferably 50 to 100 ° C. Prevents blockage due to, and provides stable supply with good operability. The plastic supply rate is determined by the size of the plastic, the size of the reactor (1), the amount of heated heating medium and the holding temperature, and the like. Further, as the inert gas, nitrogen, argon, carbon dioxide, and non-condensable gas produced during pyrolysis of carbon are used.

The reactor (1) was filled with a heat medium in an amount of 5 to 95%, preferably 40 to 80% of the reactor volume, and heated to a temperature of 300 ° C to 700 ° C, preferably 350 ° C to 450 ° C. Under the conditions, the heat medium and the plastic are efficiently contacted with each other while stirring at a constant speed. In addition, the ash content generated by dry distillation pyrolysis and adhered to the inside and walls of the reactor is crushed by the heat medium stirred at the same time, and then the ash is separated by the wire mesh-like separation plate (4) provided at the bottom of the reactor. After separating the ash from the ash, the ash that interferes with heat transfer is removed from the reactor lower valve (5).
The temperature inside the reactor is stabilized by continuously discharging through the reactor.

As the heat medium, sand, alumina, glass,
One or more selected from inorganic materials such as meno, zirconia, silicon nitride, and ceramics, and metal materials such as aluminum, iron, stainless steel, and titanium may be used in combination, and the shape of the heating medium has a diameter of 0.1 to 0.1. A sphere having a diameter of 100 mm or a lump having a side of 0.1 to 100 mm is used alone or in combination. The heat medium is selected in consideration of thermal conductivity, density, heat resistance strength, wear resistance, corrosion resistance, and economic efficiency.

The gas containing the monomer produced by dry distillation pyrolysis is introduced from the top of the reactor through a conduit (15) into a cooling tower (6) where the monomer is condensed and stored in a crude monomer storage tank (7). To do. The non-condensable gas is introduced into the conduit (16) by the blower (8), and the intermediate nozzle (1
7) and hopper (2) are recycled to the reactor. In addition, the surplus gas is passed through the conduit (18) to the gas treatment device (9).
To be processed. The gas produced in the reactor is preferably expelled from the reactor as quickly as possible in order to prevent secondary decomposition. Therefore, in addition to the circulating gas, an inert gas for purging is appropriately introduced from the conduit (13). .

As a heating method for the reactor, direct heating using electric heat or gas fuel, or an indirect heating method in which a heating medium such as a molten salt is passed through a jacket of the reactor is used. Preferably, an indirect heating method is used, which has a uniform heat distribution and is easy to ensure safety. The molten salt in the molten salt tank (11) heated in the heating furnace (10) is circulated in the reactor jacket by the circulation pump (12). The temperature of this reactor is controlled by a thermocouple (19). Furthermore, the gas temperature is measured with a thermocouple (20) and used as an index for operation management of dry distillation pyrolysis. The surplus gas treatment device (9) is treated by a gas washing tower device or a gas incinerator device using water or alkaline water.

Next, the low-boiling point impure compound and the high-boiling point impure compound produced in the course of the above-mentioned dry distillation pyrolysis are separated by distillation from the crude monomer liquid to obtain a high-quality monomer as an intermediate fraction. This distillation may be carried out in two columns, a low boiling point impure compound separation distillation column and a high boiling point impure compound separation distillation column, or a single distillation column may simultaneously separate a low boiling point impure compound and a high boiling point impure compound, The desired high quality monomer may be withdrawn as a sidestream of this distillation column. These are operated either batchwise or continuously.

These operations can be carried out by any of depressurization, normal pressure and pressurization. However, in order to ensure high quality monomers in consideration of polymerization of monomers, suppression of decomposition of impurities, etc. It is preferable to carry out distillation under reduced pressure while adding a polymerization inhibitor. As described above, high quality monomers can be recovered from plastic at a high recovery rate.

[0019]

EXAMPLES Next, the present invention will be described with reference to Examples and Comparative Examples.

Example 1 A stainless steel reactor having an internal capacity of 3 L was charged with 1 L of iron balls (having a diameter of 3 mm) as a heat medium, and 5 L of nitrogen gas for purging.
/ Hr, and the temperature was adjusted to 400 ° C. while stirring the inside of the reactor at 60 RPM. Next, PMMA crushed into 7 mm square was supplied from a supply port kept at 70 ° C. at a supply rate for maintaining the temperature inside the reactor at 400 ° C., and the produced gaseous MMA monomer was promptly introduced into the condenser.

PMMA was supplied at a rate of 400 g per hour, and at the same time, ash was added from the bottom of the reactor at 4 g per hour.
Discharged. This operation was continuously carried out for 1000 hours, but the fluctuation of the gas temperature in the reactor was extremely small, the ash could be easily extracted, and the continuous dry distillation pyrolysis of PMMA could be stably carried out. . Further, the recovery rate of the crude MMA at this time was as high as 99% of the supplied PMMA.

Next, using the above-mentioned crude MMA as a raw material, 5 m
The column top pressure was reduced to 80 mmHg by a distillation apparatus having a diameter of 15 mm, which was filled with m Raschig rings at a height of 1000 mm, and was completely refluxed. When 90% was distilled off, MMA concentration of 99.8 wt% was obtained.
MA monomer was obtained. The recovery rate of MMA monomer in one operation from dry distillation pyrolysis to distillation is 89% of the supplied PMMA.
%Met.

Example 2 In Example 1, 1 L of zirconia ceramic balls having the same size and quantity were put in place of the iron balls, and pyrolysis was continuously carried out for 2 days. It was possible to operate stably as in Example 1. At this time, the PMMA supply rate was 380 g per hour, and the ash content was about 4 g per hour.
The recovery of the crude MMA discharged was as high as 98% of the feed PMMA.

Then, using the same apparatus and operation as in Example 1, a coarse M
MA was distilled to obtain a colorless and high-quality MMA monomer having an MMA concentration of 99.6 wt%. The recovery rate of MMA monomer in one operation from dry distillation pyrolysis to distillation is
It was 88% of MA.

Example 3 In Example 1, 1 L of alumina balls of the same size and amount were put in place of the iron balls, and pyrolysis was continuously carried out over 20 hours, and stable operation was possible. At this time, PMMA was supplied at a rate of 390 g per hour, ash was discharged at about 4 g per hour, and the recovery rate of crude MMA was a high yield of 97% of the supplied PMMA. Then, Example 1
Crude MMA was distilled using the same equipment and operation as in MMA concentration 9
9.5 wt% colorless and transparent high quality MMA monomer was obtained. In addition, MMA in one operation from dry distillation pyrolysis to distillation
Monomer recovery was 87% of the feed PMMA.

Comparative Example 1 In Example 1, dry distillation pyrolysis was continuously carried out for 16 hours at a feed rate for keeping the temperature inside the reactor at 400 ° C. without adding a heat medium. PMMA supply at this time is 1
At a rate of 100 g per hour, the recovery of crude MMA was 92% of the feed PMMA. Further, as the operating time passed, the ash content in the reactor increased, and the gas temperature became unstable, making stable operation impossible. Furthermore,
The MMA was a crude MMA having a high degree of coloring and a large amount of impurities.

Then, using the same apparatus and operation as in Example 1, a coarse M
MA was distilled to obtain a colorless and transparent MMA monomer having an MMA concentration of 96.5 wt%. The recovery rate of MMA monomer in one operation from dry distillation pyrolysis to distillation is 8
It was 3%. Compared with Example 1, the PMMA supply rate is reduced to 1/4, the crude MMA recovery rate is reduced by 3%, the MMA monomer recovery rate in a single operation is reduced to 83%, and the operation is further reduced. It is difficult to carry out industrially because it is difficult.

Comparative Example 2 In Example 1, the heat medium was zeolite (dimension diameter 3 m).
m) and charged to the reactor by 1 L. Then, dry distillation pyrolysis could be carried out continuously and stably over 10 hours at a feed rate maintaining the temperature in the reactor at 400 ° C. At this time, the amount of PMMA supplied was 400 g per hour, and at the same time, 4 g of ash was discharged from the lower part of the reactor per hour. The recovery rate of the crude MMA was as low as 56% of the supplied PMMA, and contained a large amount of impurities in the crude MMA as compared with Examples 1 to 3, and also generated a large amount of non-condensable gas.

Then, using the same apparatus and operation as in Example 1, a coarse M
MA was distilled to obtain a colorless and transparent MMA monomer having an MMA concentration of 85.2 wt%. In addition, the recovery rate of MMA monomer in one operation from dry distillation pyrolysis to distillation is 5 for PMMA supplied.
It was 0%. Compared with Example 1, the recovery rate of crude MMA is 4
It can be seen that it is difficult to carry out industrially, because the MMA monomer recovery rate is reduced by 3% and the MMA monomer recovery rate per operation is drastically reduced to 50%.

Comparative Example 3 In Example 1, dry distillation pyrolysis was continuously carried out for 10 hours at a feed rate maintaining the temperature in the reactor at 290 ° C. The amount of PMMA supplied at this time was 50 g per hour, and the recovery rate of crude MMA was 10% of the supplied PMMA.
It was low, and almost no pyrolysis was carried out, and it was deposited in the system.

Then, using the same apparatus and operation as in Example 1, a coarse M
MA was distilled to obtain a colorless and transparent MMA monomer having an MMA concentration of 96.4 wt%. In addition, the recovery rate of MMA monomer in one operation from dry distillation pyrolysis to distillation is 9 for PMMA supplied.
%Met. Compared to Example 1, the recovery rate of crude MMA was 89.
%, And the MMA monomer recovery rate per operation is drastically reduced to 9%, which indicates that the method cannot be industrially implemented.

Comparative Example 4 In Example 1, dry distillation pyrolysis was continuously carried out for 10 hours at a feed rate maintaining the temperature in the reactor at 750 ° C. The amount of PMMA supplied at this time is 600 g per hour
At the same time, 6 g of ash was discharged from the lower part of the reactor per hour. The recovery rate of crude MMA is 6 for PMMA supplied.
It was as low as 1% and contained a large amount of impurities. Also, a large amount of non-condensable gas was generated.

Then, using the same apparatus and operation as in Example 1, a coarse M
MA was distilled to obtain a colorless and transparent MMA monomer having an MMA concentration of 92.0 wt%. In addition, the recovery rate of MMA monomer in one operation from dry distillation pyrolysis to distillation is 5 for PMMA supplied.
It was 5%. Compared to Example 1, the recovery rate of crude MMA is 3
It can be seen that it is difficult to carry out the process industrially, because it is decreased by 8% and the recovery rate of the MMA monomer in one operation is drastically reduced to 55%.

Example 4 In Example 1, the plastic was replaced by P instead of PMMA.
20% S at a feed rate for maintaining the temperature in the reactor at 400 ° C.
Pyrolysis was carried out continuously over Hr. At this time, the PS feed rate was 270 g per hour, and at the same time, ash was discharged from the lower part of the reactor at 5.4 g per hour. The recovery rate of crude PS was as high as 96% of the supplied PS, but it contained a large amount of impurities. Then, the crude PS was distilled using the same apparatus and operation as in Example 1 to obtain a colorless and transparent styrene monomer having a styrene concentration of 88.5 wt%. The styrene monomer recovery rate in one operation from dry distillation pyrolysis to distillation was 86% of the supplied PS.

[0035]

Industrial Applicability According to the present invention, it is possible to obtain a high quality monomer from a plastic such as PMMA or PS with good operability and a high yield industrially.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an example of a dry distillation pyrolysis apparatus used in the method of the present invention.

[Explanation of symbols]

 1 Reactor 2 Hopper 3 Fixed-quantity Supply Device 4 Separation Plate 5 Reactor Lower Valve 6 Cooling Tower 7 Crude Monomer Storage Tank 8 Blower 9 Gas Treatment Device 10 Heating Furnace 11 Molten Salt Tank 12 Circulation Pump 13 Conduit 14 Supply Pipe 15 Conduit 16 Conduit 16 17 middle stage nozzle 18 conduit 19 thermocouple 20 thermocouple

Claims (7)

[Claims] 1. A first step in which a raw material plastic is continuously supplied to a reactor filled with a heating medium previously heated to 300 ° C. or higher, and pyrolysis is carried out to decompose it into a crude monomer. The high-quality monomer is obtained from the plastic, which comprises the second step of distilling the dry distillation pyrolysis crude monomer that has undergone the first step to separate and remove the impure compound having a lower boiling point and the impure compound having a higher boiling point than the monomer. How to collect. 2. A method for recovering high-quality monomers from a plastic according to claim 1, wherein the raw material is a plastic containing an acrylic synthetic resin and / or a styrene synthetic resin. 3. The diameter of the heat medium is 0.1, which is made of an inorganic material selected from sand, alumina, glass, meno, zirconia, silicon nitride and ceramics and / or a metal material selected from aluminum, iron, stainless steel and titanium. ~ 100
The method for recovering high-quality monomers from plastics according to claim 1, wherein the heat medium has a spherical shape of mm and / or a lump shape having a side of 0.1 to 100 mm. 4. The method for recovering high-quality monomers from plastic according to claim 1, wherein the temperature of the plastic and the supply pipe are kept at 250 ° C. or lower when the plastic is supplied to the reactor. 5. The method for recovering high-quality monomers from a plastic according to claim 1, wherein the heat medium is stirred in the reactor of the first step. 6. The method for recovering high-quality monomers from plastic according to claim 1, wherein an inert gas is circulated in the carbonization pyrolysis apparatus in the first step. 7. The method for recovering high-quality monomers from plastics according to claim 1, wherein charcoal and ash produced by dry distillation pyrolysis in the first step are continuously discharged.