JP2011236342A - Thermal decomposition method for acrylic resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal decomposition method capable of continuously, stably and easily performing thermal decomposition of an acrylic resin for a long period of time under an inert gas atmosphere by a fluidized bed.SOLUTION: In the thermal decomposition method for the acrylic resin, a step (a) of fluidizing a fluidization medium by continuously feeding a fluidized gas containing an inert gas from a lower part of a decomposition tank to the decomposition tank filled with the fluidization medium and forming the fluidized bed, a step (b) of continuously feeding an acrylic resin to the fluidized bed to perform thermal decomposition, cooling the generated gaseous decomposition product and recovering it as a liquid, and a step (c) of continuously discharging the fluidization medium in the decomposition tank from a position at a lower side than the height of a feeding position of the acrylic resin and heating it and thereafter continuously feeding it to the decomposition tank are performed in parallel. At this time, a feeding speed of the fluidized gas fed to the decomposition tank, a feeding speed of the acrylic resin, a feeding speed of the fluidization medium and the temperature thereof are made constant, and a height of the fluidized bed at the thermal decomposition is controlled to a constant height by only control of a discharge speed of the fluidization medium discharged from the decomposition tank in the step (c).

Description

  The present invention relates to a thermal decomposition method for an acrylic resin in which an acrylic resin is thermally decomposed by a fluidized bed in an inert gas atmosphere, and a gaseous decomposition product to be generated is cooled and recovered as a liquid.

Conventionally, there has been known a method in which a resin for waste plastic is thermally decomposed in an inert gas atmosphere, and a generated gaseous decomposition product (monomer, oil, etc.) is cooled and recovered as a liquid. In particular, when the resin is an acrylic resin, by using this method, the monomer can be recovered as a liquid and can be recycled for the production of the acrylic resin, so that the amount of crude oil used and the environmental load during the resin production can be reduced. Is useful.
One of the thermal decomposition methods of resin is a method using a fluidized bed. In this method, a high-temperature fluid medium (solid particles such as sand) heated to a temperature equal to or higher than the thermal decomposition temperature of the resin is caused to flow in the decomposition tank, and the resin is charged therein. The required amount of heat is supplied by the sensible heat of the fluidized medium. Therefore, thermal decomposition can be carried out more efficiently than when heating only on the wall surface of the decomposition tank, the scale-up of the decomposition tank is easy, the heated fluid medium is continuously supplied to the decomposition tank, and the decomposition tank Continuous thermal decomposition treatment is possible by continuously discharging the fluid medium from the lower part, the thermal decomposition residue of the resin can be attached to the fluid medium and discharged from the lower part of the decomposition tank, the discharged fluid medium is heated, etc. This method is industrially advantageous because it can be recycled and reused. For example, in Patent Document 1, a heated fluid medium, fluidized gas, and resin are continuously supplied to the decomposition tank, and the fluid medium is continuously discharged from the lower part of the decomposition tank, and the discharged fluid medium is heated. A method is described in which after being introduced into the apparatus and heated, it is again supplied to the decomposition vessel.

However, in the method of continuously performing thermal decomposition in a fluidized bed under an inert gas atmosphere as described in Patent Document 1, when an acrylic resin is used as the resin, it is relatively about 24 hours. Although operation for a short time is possible, it tends to be difficult to carry out thermal decomposition stably for a long time of several days or longer. For example, in this method, normally, the supply speed of the fluid medium supplied to the decomposition tank is the same as the discharge speed of the fluid medium discharged from the lower part of the decomposition tank so that the staying amount of the fluid medium in the decomposition tank is constant. Driving. However, during pyrolysis, part of the fluidized medium jumps out from the fluidized bed together with the fluidized gas to the gas phase part at the top of the cracking tank and is discharged from the top of the cracking tank. There is a problem that the height of the fluidized medium decreases. Thus, when the fluidized bed height of the decomposition tank changes, the reaction conditions of the decomposition tank change, and the amount and quality of the recovered monomer tend to become unstable. In addition, since the reaction of thermally decomposing an acrylic resin under an inert atmosphere is an endothermic reaction, there is a problem that the temperature of the fluidized bed fluctuates when the resin is not properly dispersed in the fluidized bed. Specifically, the resin is fused in the fluidized bed, the reaction time until the resin is completely decomposed is increased, or a large amount of heat is required locally for the fluidized bed. This causes a local temperature drop. If the temperature drop exceeds the limit, the temperature may be lowered to a temperature at which the resin cannot be decomposed locally and the decomposition efficiency may decrease, or the fluidized bed may solidify and the thermal decomposition reaction may not be performed.
The fluctuation of fluidized bed height and fluidized bed temperature may cause fluctuations in pressure, temperature, etc. when the recovered liquid is purified by distillation in order to obtain high quality monomer, and the quality of the obtained monomer is not stable. Because it is also a cause, improvement is required.

On the other hand, it is not a method of thermally decomposing a resin using sensible heat of a fluid medium in an inert gas atmosphere, but various solid fuels such as coal, coke, waste plastic, RDF, and shredder dust in an air atmosphere The methods described in Patent Documents 2 to 4 shown below have been proposed as methods for making the fluidized bed height in the decomposition tank (fluidized bed furnace) constant when thermally decomposing solid waste or the like.
Patent Documents 2 and 3 disclose a method in which the fluidized bed height is detected by a detector value (pressure) or a tilt switch to control both the amount of fluid flowing into and out of the decomposition tank.
In Patent Document 4, the supply amount of combustible materials, the discharge amount of furnace bottom ash, and the supply amount of gasified air (fluidized gas) are controlled.

JP 2008-214320 A Japanese Utility Model Publication No. 57-10639 JP 2006-68656 A Japanese Patent Laid-Open No. 2003-165982

However, even if the methods described in Patent Documents 2 to 4 are used in a method of thermally decomposing a resin using sensible heat of a fluid medium in an inert gas atmosphere, the thermal decomposition of the acrylic resin is performed for a long time. It is difficult to carry out continuously and stably. For example, in the methods of Patent Documents 2 and 3, when the acrylic resin is thermally decomposed under an inert atmosphere, the fluidized bed temperature fluctuates. There is also a problem that the setting of control methods and control parameters becomes complicated. In the method of Patent Document 4, the dispersion state of the resin in the decomposition tank becomes unstable, and the temperature of the fluidized bed fluctuates as described above.
The present invention has been made in view of the above circumstances, and provides a thermal decomposition method capable of continuously and stably carrying out thermal decomposition of an acrylic resin under an inert gas atmosphere by a fluidized bed for a long period of time. For the purpose.

As a result of intensive studies, the present inventors have found that the fluidized gas supply rate, the acrylic resin supply rate, the fluidized medium supply rate, and the temperature are the conditions affecting the fluidized bed height. Of the discharge speed of the fluid medium discharged from the lower part of the decomposition tank, fluctuations in conditions other than the fluid medium discharge speed are caused by a lack of heat required for the thermal decomposition of the acrylic resin, the acrylic resin and the flow in the fluidized bed. It has been found that the dispersibility of the medium is deteriorated, and the quality of the recovered liquid (particularly, the monomer that is recovered by the purification treatment, which is a raw material for the acrylic resin) is unstable. As a result of further investigation based on this knowledge, the conditions that affect the fluidized bed height and its temperature are kept constant, and the fluidized bed height during thermal decomposition is controlled to be constant only by the discharge rate of the fluidized medium. The inventors have found that the above problems can be solved and have completed the present invention.
The present invention for solving the above problems has the following aspects.
[1] A method for thermally decomposing an acrylic resin in which the following steps (a) to (c) are performed in parallel, the supply rate of a fluidizing gas supplied to the decomposition tank, the supply rate of an acrylic resin, and a fluid medium The heat for controlling the fluidized bed height during the thermal decomposition to a constant height by controlling only the discharge speed of the fluidized medium discharged from the decomposition tank in the step (c). Disassembly method.
Step (a): A step of forming a fluidized bed by continuously supplying a fluidizing gas containing an inert gas from the lower part of the decomposition tank to the decomposition tank filled with the fluidizing medium to cause the fluidizing medium to flow.
Step (b): A step of continuously supplying an acrylic resin to the fluidized bed for thermal decomposition, cooling a gaseous decomposition product generated by the thermal decomposition, and recovering it as a liquid.
Step (c): The fluid medium in the decomposition tank is continuously discharged from a position below the height of the acrylic resin supply position, introduced into a heating device, heated, and then into the decomposition tank. The process of supplying continuously.
[2] The thermal decomposition method according to [1], wherein in the step (b), the recovered liquid is further purified, and the monomer of the acrylic resin raw material contained in the liquid is recovered.

  According to the thermal decomposition method of the present invention, it is possible to provide a thermal decomposition method in which the thermal decomposition of an acrylic resin in an inert gas atmosphere by a fluidized bed can be carried out continuously and stably for a long time.

It is the schematic which shows one Embodiment of the thermal decomposition apparatus used for the thermal decomposition method of this invention.

In the thermal decomposition method of the present invention, an acrylic resin (hereinafter sometimes simply referred to as “resin”) is thermally decomposed by a fluidized bed in an inert gas atmosphere, and a gaseous decomposition product generated by the thermal decomposition is obtained. Is cooled and recovered as a liquid.
Hereinafter, the thermal decomposition method of the present invention will be described with reference to an embodiment thereof. However, the present invention is not limited to the following embodiments.
FIG. 1 is a schematic view showing an embodiment (hereinafter sometimes referred to as a first embodiment) of a thermal decomposition apparatus used in the thermal decomposition method of the present invention.
A thermal decomposition apparatus 100 according to the present embodiment includes a decomposition tank 1 that performs thermal decomposition of a resin, a fluidizing gas supply channel 2 that supplies a fluidizing gas containing an inert gas to the decomposition tank 1, and a resin that is supplied to the decomposition tank 1. A resin supply screw 3 for supplying a fluid, a fluid medium supply screw 4 for supplying a fluid medium to the decomposition tank 1, and a fluid medium discharge screw 5 disposed below the decomposition tank 1 for discharging the fluid medium in the decomposition tank 1. A hopper 6 that stores the fluid medium discharged from the fluid medium discharge screw 5, a heating device 7 that heats the fluid medium discharged from the hopper 6, and a fluid medium that is heated by the heating device 7 is supplied to the fluid medium. A fluid medium supply flow path 8 for supplying to the screw 4, a gas discharge flow path 9 for discharging the gas in the decomposition tank 1, and a gas discharge flow path 9 installed downstream of the gas discharge flow path 9 to cool the gas discharged from the decomposition tank 1. And collect the condensate A retirement unit 10 comprises a mist collecting device 11 for collecting the mist in the discharged gas from the cooling device 10, a purifier 12 for purifying the recovered liquid in the cooling device 10 and the mist collecting device 11, the.
A blower 13 is installed in the fluidizing gas supply flow path 2 so that the fluidizing gas supply speed can be controlled.
The resin supply screw 3 includes a screw part 3 a and a hopper part 3 b installed on the upper upstream side of the screw part 3 a, and an outlet of the screw part 3 a is connected to the decomposition tank 1.
The fluid medium supply screw 4 is composed of a screw part 4 a and a hopper part 4 b installed on the upper upstream side of the screw part 4 a, and an outlet of the screw part 4 a is connected to the decomposition tank 1.
The fluid medium discharge screw 5 includes a screw part 5 a and a hopper part 5 b installed on the upper upstream side of the screw part 5 a, and an outlet of the screw part 5 a is connected to the hopper 6.
Rotation speed control devices 3c, 4c, and 5c (for example, inverters) that control the screw rotation speed are attached to the resin supply screw 3, the fluid supply screw 4, and the fluid discharge screw 5, respectively.

The decomposition tank 1 has a main body 1a, a dispersing device 1b installed above the position where the fluidizing gas is supplied by the fluidizing gas supply channel 2, and dividing the inside of the main body 1a up and down, and the dispersing device 1b A fluid medium layer 1c made of a packed fluid medium, a fluid medium discharge passage 1d having one end opened in the lowermost layer of the fluid medium layer 1c and the other end connected to the inlet of the fluid medium discharge screw 5, and a dispersion A fluidizing gas chamber 1e disposed under the device 1b and for uniformly feeding the supplied fluidizing gas to the entire surface of the dispersing device 1b.
Examples of the dispersing device 1b include a perforated plate, a slit plate, a mesh plate, a sintered filter, a nozzle, and a nozzle with a cap.

Although there is no restriction | limiting in particular in the height (fluidized bed height) of the fluidized medium layer 1c, The range whose ratio of the fluidized bed height of the stationary state / representative length of the decomposition tank 1 is 0.5-3.5. It is preferable to be within.
Here, the stationary state refers to a state before the resin is supplied and the fluidized gas is not supplied and the stirring device is not stirred.
The fluidized bed height means a distance from the lowermost end of the fluidized medium layer 1c to the height of the uppermost surface of the fluidized medium layer 1c. “The lowest end of the fluidized medium layer 1c” is the position of the lowermost surface when the lowermost surface of the fluidized medium layer 1c is flat as shown in FIG. 1, and the lowermost surface of the fluidized medium layer 1c is the apex. When is a conical shape on the lower side, it is a position corresponding to the apex of the cone.
The representative length of the decomposition tank 1 is the diameter of the circle when the horizontal cross-sectional shape of the decomposition tank 1 is a circle, and the length of one side when the horizontal cross-sectional shape of the decomposition tank 1 is a square. When the horizontal sectional shape is rectangular, the length is one half of the sum of the short side and the long side. In the case of other cross-sectional shapes, the cross-sectional area is first calculated, and the diameter of a circle having the same area as the cross-sectional area is obtained.
By setting the ratio of the height of the fluidized bed in the stationary state / the representative length of the decomposition tank 1 to 0.5 or more, the spots of flow of the fluidized medium are reduced. Also. By setting the ratio of the height of the fluidized bed in a stationary state / the representative length of the decomposition tank to 3.5 or less, the pressure loss of the fluidized bed is reduced, and the power required for supplying the fluidized gas can be reduced. it can.

It is preferable to provide a space in the decomposition tank 1 and above the fluidized medium layer 1c.
The length of the space portion in the stationary state is preferably within a range where the ratio of the length of the space portion in the stationary state / the representative length of the decomposition tank 1 is 0.5 to 5.
Here, the length of the space portion refers to the distance from the height of the uppermost surface of the fluidized medium layer 1c in a stationary state to the height of the uppermost surface of the decomposition tank 1.
The representative length of the decomposition tank is as described above.
By setting the ratio of the length of the space in the stationary state / the representative length of the decomposition tank 1 to 0.5 or more, the gas discharged from the decomposition tank 1 (the fluidized gas and the decomposition product of the resin When the mixed gas) is sent to the cooling device 10, the amount of the fluid medium discharged along with the gas can be reduced. Further, by setting the ratio of the length of the space portion in the stationary state / the representative length of the decomposition tank 1 to 5 or less, the total height of the decomposition tank 1 can be lowered, and the equipment cost of the decomposition tank 1 is reduced. it can.

The total height of the decomposition tank 1 is preferably in a range where the ratio of the total height of the decomposition tank 1 / the representative length of the decomposition tank 1 is 1 to 8.5.
The total height of the decomposition tank 1 means the distance from the lowermost end of the decomposition tank 1 to the height of the uppermost surface of the decomposition tank 1. The “lowermost end of the decomposition tank 1” means the position of the lowermost surface when the lowermost surface of the decomposition tank 1 is flat as shown in FIG. In the case of a conical shape, the position corresponds to the apex of the cone.
By setting the ratio of the total height of the decomposition tank 1 to the representative length of the decomposition tank 1 to be 1 or more, the spots of flow of the fluid medium are reduced, and a sufficient space can be easily secured. By setting the ratio of the total height of the cracking tank 1 to the representative length of the cracking tank to 8.5 or less, the pressure loss of the fluidized bed can be reduced, the total height of the cracking tank 1 is reduced, and the equipment cost of the cracking tank 1 is reduced. Can be reduced.

A stirring device (not shown) is installed in the decomposition tank 1 so that the fluidized medium layer 1c can be stirred. When the fluidizing gas is supplied, the flow in the horizontal direction and the vertical direction of the fluid medium and the resin in the decomposition tank is improved by performing the stirring using the stirring device in parallel.
There is no restriction | limiting in the number of the stirring shafts of a stirrer, One may be sufficient and two or more may be sufficient. When the number of stirring shafts is 2 or more, the horizontal and vertical flow in the decomposition tank is further improved.
The shape of the stirring blade of the stirrer is not particularly limited, and examples thereof include a paddle blade, an anchor blade, a ribbon blade, a helical blade, a propeller blade, and a turbine blade.
Note that the stirring device is not essential, and when the fluidized medium layer 1c sufficiently flows only by the fluidized gas supplied through the dispersion device 1b, it is not always necessary to provide the stirring device.

A fluidizing gas supply channel 2 is connected to the lower part of the main body 1 a of the decomposition tank 1.
Here, the “lower part” of the decomposition tank 1 means a range from the lowest end of the decomposition tank 1 to the height of the connection position (resin supply position) of the resin supply screw 3. As described above, the “lowermost end of the decomposition tank 1” is the position of the lowermost surface when the lowermost surface of the decomposition tank 1 is flat as shown in FIG. When the apex has a conical shape on the lower side, it is a position corresponding to the apex of the cone.
By connecting the fluidizing gas supply channel 2 to this position, when the fluidizing gas is supplied to the decomposition tank 1 through the fluidizing gas supply channel 2, the fluidizing medium layer 1c can be easily flowed, The resin supplied into the layer can be uniformly dispersed.

A gas discharge passage 9 is connected to the upper surface of the main body 1a of the decomposition tank 1, and gas (fluidized gas and gas generated by thermal decomposition of resin) existing in the decomposition tank 1 from the space above the decomposition tank 1. In the form of a decomposition product in the form of a product). By taking out the gas from the space, it is possible to reduce the amount of the fluid medium discharged accompanying the gas, which is preferable.
Here, the “upper part” of the decomposition tank 1 means a portion between the uppermost surface of the fluidized medium layer 1 c and the uppermost end of the decomposition tank 1. "The uppermost end of the decomposition tank 1" is the position of the uppermost surface when the uppermost surface of the decomposition tank 1 is flat as shown in FIG. In the case of a certain cone shape, it is the position corresponding to the apex of the cone.
In addition, although the gas discharge flow path 9 is connected to the upper surface of the main body 1a here, this invention is not limited to this, For example, you may connect to the side surface of the upper part of the decomposition tank 1. FIG.

The resin supply screw 3 and the fluid medium supply screw 4 are respectively connected to the lower part of the intermediate part of the main body 1a of the decomposition tank 1, and supply the resin and the fluid medium from the lower part of the fluid medium layer 1c.
Here, the “intermediate portion” of the decomposition tank 1 means a portion from the lowermost end to the uppermost surface of the fluidized medium layer 1c in a stationary state. As described above, the “lowermost end of the fluid medium layer 1c” is the position of the lowermost surface when the lowermost surface of the fluid medium layer 1c is flat as shown in FIG. When the lower surface has a conical shape with the apex on the lower side, the position corresponds to the apex of the cone.
The “lower part of the intermediate part” means a lower side than the height of the intermediate position between the position of the lowermost end and the position of the uppermost surface of the fluidized medium layer 1c in the stationary state.
The connection position of the resin supply screw 3, that is, the supply position of the resin is not necessarily limited to the lower part of the fluid medium layer 1c, but supplying the resin and the fluid medium from the lower part of the fluid medium layer 1c is the thermal decomposition efficiency of the resin. This is advantageous in terms of the dispersibility of the resin and the fluidized medium in the fluidized bed.
The connection position of the fluid medium supply screw 4, that is, the fluid medium supply position is not necessarily limited to the lower part of the fluid medium layer 1c. In the decomposition tank 1, the fluidized medium is fluidized by supplying a fluidizing gas or in addition to stirring by a stirrer, so that the fluidized medium flows uniformly in the decomposition tank 1 no matter where it is supplied. Can do.
The screws used as the resin supply screw 3 and the fluid medium supply screw 4 are not particularly limited, and known screws used for supplying and discharging powder can be used. From the viewpoint of quantitative supply, a single screw or a twin screw is preferable. A uniaxial screw is preferred in that the device cost can be reduced.

The fluid medium discharge screw 5 is installed below the decomposition tank 1, and a fluid medium discharge channel 1d is connected to the inlet of the fluid medium discharge screw 5 from the lowermost layer of the fluid medium layer 1c via the fluid medium discharge channel 1d. The fluid medium can be discharged.
Here, the fluid medium discharge flow path 1d is connected to the lowermost layer of the fluid medium layer 1c, but the present invention is not limited to this, and may be connected to, for example, the lower side surface of the decomposition tank 1. However, also in this case, it is preferable that the connection position of the fluid medium discharge flow path 1d is lower than the height of the connection position (resin supply position) of the resin supply screw 3.
The fluid medium discharged from the lower side than the height of the resin supply position contains almost no resin, ensures fluidity of the fluid medium, and is a raw material for the acrylic resin that is finally recovered. The amount of monomer increases. On the other hand, if the fluid medium is discharged from the same height as the resin supply position or from above, a large amount of resin is mixed in the fluid medium to be discharged, so the fluidity is poor and the fluid medium is discharged. There is a problem. Also, the amount of monomer recovered is reduced.
The screw used as the fluid medium discharge screw 5 is not particularly limited, and a known screw used for supplying and discharging powder can be used. From the viewpoint of quantitative supply, a single screw or a twin screw is preferable.

The cracking tank 1 is provided with fluidized bed height detecting means (not shown) so that the fluidized bed height in the cracking tank 1 can be detected.
As the fluidized bed height detecting means, there are a contact type such as a switch and a non-contact type calculated from a differential pressure between the lower part and the upper part of the fluidized bed, and any one of them can be used. From the viewpoint that the thermal decomposition is performed under a high temperature condition and the control width can be easily changed, a non-contact type calculated from the differential pressure between the lower part and the upper part of the fluidized bed is preferable. Since the differential pressure between the lower part and the upper part of the fluidized bed is proportional to the fluidized bed height, a calibration curve indicating the relationship between the fluidized bed height and the differential pressure is prepared in advance for the decomposition tank 1 to be used. The height of the fluidized bed at the time of decomposition can be determined from the differential pressure.
As a non-contact type fluidized bed height detection means, more specifically, a position (first pressure measurement unit) higher than the position of the uppermost surface of the fluidized solid particle layer 1c in the decomposition tank 1, Examples include a differential pressure gauge that measures a pressure difference with a position (second pressure measurement unit) lower than the lowermost surface of the solid particle layer 1c, such as in the fluidizing gas chamber 1e.
In the detecting means, the vicinity of the first and second pressure gauge measuring parts can be purged with an inert gas so that a problem that the fluid medium is mixed into the pressure gauge and cannot be measured accurately does not occur. Is preferred.

The thermal decomposition apparatus 100 further includes a control device (not shown) that is electrically connected to the fluidized bed height detection means (not shown) of the decomposition tank 1 and the rotational speed control device 5c of the fluid medium discharge screw 5.
The control device controls the screw rotation speed of the fluid medium discharge screw 5 based on information from the fluidized bed height detection means, and controls the discharge speed of the fluid medium. By controlling the discharge speed of the fluidized medium, the fluidized bed height can be controlled to a constant height.
In the control device, examples of the control method for controlling the fluidized bed height by the discharge speed of the fluidized medium include PID control, cascade control, and feedforward control. Among these, PID control is preferable in terms of simple design and setting of control parameters.
PID control is a kind of feedback control, and is a method in which control of an input value is performed by three elements: a deviation between an output value and a target value, its integration, and differentiation. The parameters for PID control may be auto-tuning, or may be set in advance by adjusting the response time and the swing width by trial operation of the thermal decomposition apparatus 100. It is preferable in terms of responsiveness and stability to determine parameters for PID control by trial operation.

The cooling device 10 cools the gas discharged from the decomposition tank 1 through the gas discharge channel 9. When the gas is cooled, the gaseous decomposition product contained in the gas is condensed (liquefied) and recovered as a liquid.
The cooling device 10 is not particularly limited as long as it can cool a gaseous thermal decomposition product and condense it as a liquid. For example, a tubular heat exchanger, a plate heat exchanger, a scrubber, a spray tower, etc. Is mentioned.
A container is installed under the cooling device 10 so as to accommodate the generated condensate (liquid containing decomposition products). There is no restriction | limiting in the magnitude | size and shape of this container.

The mist collecting device 11 collects mist in the gas discharged from the cooling device 10. In the gas discharged from the cooling device 10, decomposition products that have not been condensed by the cooling device 10 may exist as mist. For this purpose, the yield of the monomer can be further increased by introducing the gas into the mist collecting device 11 and collecting the mist.
Examples of the mist collecting device 11 include a cyclone mist collecting device and a mesh mist collecting device.
A container is installed under the mist collecting device 11 so that the collected mist (liquid containing decomposition products) can be accommodated. There is no restriction | limiting in the magnitude | size and shape of this container.

The liquid recovered by the cooling device 10 and the mist recovery device 11 may contain impurities and mixed fluid medium in addition to the monomer of the acrylic resin raw material.
The refining device 12 is for removing those impurities and fluid medium in the liquid collected by the cooling device 10 and the mist collecting device 11.
As the purification apparatus 12, a known purification apparatus can be used depending on the object to be removed. Specific examples include a filter and a distillation column. For example, when a monomer as a raw material for an acrylic resin is recovered, a distillation column is preferably used.
A plurality of purification apparatuses may be used in combination as the purification apparatus 12.

The thermal decomposition of the acrylic resin and the recovery of the decomposition products using the thermal decomposition apparatus 100 shown in FIG. 1 can be performed by performing the following steps (a ′) to (c ′) in parallel.
Step (a ′): Fluidizing gas is continuously supplied to the cracking tank 1 filled with the fluidizing medium to form the fluidizing medium layer 1c through the fluidizing gas supply channel 2 to flow the fluidizing medium. Forming a fluidized bed.
Step (b ′): Resin is continuously supplied to the fluidized medium layer 1c by the resin supply screw 3 for thermal decomposition, and the gaseous decomposition product generated by the thermal decomposition is passed through the gas discharge passage 9. The process which sends to the cooling device 5 through and cools and collects as a liquid.
Step (c ′): The fluid medium in the decomposition tank 1 is continuously discharged through the fluid medium discharge channel 1d and the fluid medium discharge screw 5, introduced into the heating device 7, heated, and then supplied with the fluid medium. A step of feeding the fluid medium supply screw 4 through the flow path 8 and continuously supplying the fluid medium supply screw 4 to the decomposition tank 1 again.

When the fluidizing gas is supplied from the fluidizing gas supply channel 2 in the step (a ′), the fluidizing gas diffused in the fluidizing gas chamber 1e is blown up through the dispersing device 1b, and the fluidized medium layer 1c is formed. To flow. When the resin is supplied thereto in the step (b ′), the specific gravity of the resin is lower than that of the fluidized medium, and therefore the fluid rises in the fluidized medium layer 1c together with the fluidizing gas. At this time, the resin comes into contact with a high-temperature fluid medium and is thermally decomposed.
The gaseous decomposition product generated by the thermal decomposition of the resin is discharged from the decomposition tank 1 together with the fluidizing gas, and is sent to the cooling device 5 via the gas discharge passage 9. When the gas (mixed gas of fluidized gas and gaseous decomposition products generated by thermal decomposition) sent from the decomposition tank 1 to the cooling device 5 is cooled, the gaseous decomposition products contained in these gases Condenses and is recovered as a liquid.
Hereinafter, each process will be described in more detail.

[Step (a ′)]
Examples of the fluid medium include sand, ceramic particles, metal particles, metal hydroxide particles, and metal halide particles. In particular, sand is preferable because it is inexpensive, easy to handle, hardly undergoes side reactions due to thermal decomposition, and does not easily reduce the yield of the entire process. There is no restriction | limiting in particular in the kind of this sand, River sand, mountain sand, sea sand, etc. can be used. Among them, river sand is preferable from the viewpoint of good fluidity.
The size of the fluid medium is not particularly limited, but from the viewpoint of handleability, the average particle size is preferably 0.01 mm to 1 mm, more preferably 0.05 mm to 0.8 mm.

The fluidizing gas includes an inert gas.
Examples of the inert gas include nitrogen, carbon dioxide, and argon. Among these, nitrogen is preferable because it is low in price, easy to handle, hardly causes side reactions due to thermal decomposition, and hardly reduces the yield of the entire process.
The fluidizing gas may contain a gas other than the inert gas as long as the effects of the present invention are not impaired. For example, the mixed gas discharged from the cooling device 10 in the step (b ′) to be described later, or the mixed gas discharged from the mist collecting device 11 arbitrarily provided downstream of the cooling device 10 may be reused.

The supply rate (kg / hour (hr)) of the fluidizing gas may be within a range in which the fluidizing medium layer 1c can be fluidized.
In this embodiment, the fluidizing gas is supplied using a blower 13. Use of the blower 13 is preferable from the viewpoint of quantitative supply. However, the present invention is not limited to this, and various blowers other than the blower 13 can be used.
Measurement and control of the supply speed of the fluidized gas can be performed, for example, by a gas flow controller such as a vortex flow meter. In this case, the rotational speed of the blower can be PID controlled from the difference between the current value of the flow rate controller and the flow rate set value.
In this step, it is necessary to make the supply rate of the fluidizing gas to the decomposition tank 1 constant.
“Fixed” of the supply speed of the fluidizing gas means that the set value of the blowing amount of the blower or the like (for example, the set value of the rotational speed of the blower) is not changed, and the actual supply speed and its set value are Means that the difference is less than 0.1% with respect to the set value (100%).

The temperature of the fluidizing gas supplied to the decomposition tank 1 (hereinafter sometimes referred to as supply temperature) is preferably not lower than the temperature of the resin supplied to the decomposition tank 1 in step (b ′) and not higher than 500 ° C. If the temperature of the fluidizing gas is equal to or higher than the temperature of the resin, an excessive temperature drop of the fluidized medium layer 1c can be suppressed. When the supply temperature of the fluidizing gas is 500 ° C. or lower, the quality of the recovered liquid is improved.
The supply temperature of the fluidizing gas is controlled by installing a heat exchanger that can heat or cool the fluidizing gas up to a blower or other blower and the decomposition tank 1, measuring the temperature discharged from the heat exchanger, The fluid temperature for heating and cooling the exchanger and the fluid flow rate can be controlled by controlling the PID or the like.
The supply temperature of the fluidizing gas can be measured by a thermometer such as a thermocouple installed in the fluidizing gas chamber 1e.
The supply temperature of the fluidizing gas is preferably constant.
“Fixed” supply temperature of fluidized gas means that the fluid temperature for heating and cooling of the heat exchanger and the set value of the fluid flow rate are not changed, and the difference between the actual supply temperature and the set value is , Within ± 0.5 ° C.

  Fluidization of the fluidized medium layer 1c may be performed only by supplying the fluidizing gas, or may be performed by supplying the fluidizing gas and stirring using a stirring device (not shown) disposed in the decomposition tank 1. Good. The method using agitation with a stirrer is preferred in that the flow of the fluid medium or acrylic resin in the decomposition tank 1 in the horizontal direction and the vertical direction is improved.

[Step (b ′)]
In the step (b ′), first, a resin is continuously supplied to the fluid medium layer 1 c fluidized in the step (a ′) by the resin supply screw 3.
In the present invention, an acrylic resin is used as the resin.
The “acrylic resin” is a polymer having (meth) acrylic acid ester units as monomer units (repeating units constituting the polymer). Here, “(meth) acryl” means “acryl” or “methacryl”. The (meth) acrylic acid ester has a general formula: CH ₂ ═C (R ¹ ) —CO—O—R ² [wherein R ¹ is a hydrogen atom or a methyl group, and R ² is an organic group. It is a compound represented by this.
R ¹ is preferably a methyl group. That is, as the (meth) acrylic acid ester, a methacrylic acid ester is preferable.
Examples of the organic group for R ² include an alkyl group. That is, as the (meth) acrylic acid ester, an alkyl (meth) acrylate is preferable.
Specific examples of the alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate.
The acrylic resin preferably contains at least a methyl methacrylate unit. In particular, from the viewpoint of recovering the monomer in high yield, it is preferable that 50% by mass or more of methyl methacrylate units are contained in 100% by mass of all the structural units, and 70% by mass or more of methyl methacrylate units are contained. Is more preferable.

The acrylic resin may contain other monomer units other than the (meth) acrylic acid ester unit.
The other monomer may be any copolymerizable with (meth) acrylic acid ester, such as (meth) acrylic acid, maleic anhydride, styrene, α-methylstyrene, acrylonitrile, polyfunctional monomer and the like. It is done.
Examples of the polyfunctional monomer include polyfunctional (meth) acrylic acid esters. Examples of the polyfunctional (meth) acrylic acid ester include ethylene glycol diacrylate, propylene glycol diacrylate, 1,4 butanediol diacrylate, 1,6 hexanediol diacrylate, neopentyl glycol diacrylate, ethylene glycol dimethacrylate, propylene Examples include glycol dimethacrylate, 1,4 butanediol dimethacrylate, 1,6 hexanediol dimethacrylate, neopentyl glycol dimethacrylate, and the like.
Crosslinked acrylic resin is mentioned as an acrylic resin containing a polyfunctional monomer unit.
The acrylic resin may be mixed with other resins.

The acrylic resin may contain a filler. Examples of the filler include aluminum hydroxide, silica, calcium carbonate, glass fiber, talc, and clay.
The acrylic resin may contain additives other than the filler. Examples of the additive include pigments, dyes, reinforcing agents, antioxidants, stabilizers and the like.

  As for the magnitude | size of the acrylic resin to supply, 1-20 mm is preferable as an average particle diameter, and 3-10 mm is more preferable. When the average particle diameter is 1 mm or more, adhesion and fusion between resins can be suppressed. If the average particle diameter of the resin pulverized pieces is 20 mm or less, the dispersibility of the resin and the fluid medium is good. The average particle diameter is a weight average diameter calculated from an average weight of resin crushed pieces obtained by taking 100 resin crushed pieces and a resin density, assuming that the crushed pieces are spherical.

The resin supply rate (kg / hr) to the decomposition tank 1 is the ratio of the fluidization gas supply rate (kg / hr) to the decomposition tank 1 and the resin supply rate (kg / hr) to the decomposition tank 1. It is preferable that the fluidizing gas / resin ratio be a speed within a range of 0.4 to 3.0. If the fluidizing gas / resin ratio is 0.4 or more, the fluidity of the fluidized medium layer 1c can be maintained. If the fluidizing gas / resin ratio is 3.0 or less, the load on the cooling device 10 can be reduced.
The measurement of the resin supply speed to the decomposition tank 1 can be performed by using a mass measuring device (not shown) such as a load cell attached to the hopper 3b of the resin supply screw 3. The supply speed can be controlled by controlling the screw rotation speed of the resin supply screw 3 with the rotation speed control device 3c.
In this step, it is necessary to keep the resin supply speed to the fluid medium layer 1c (resin supply speed to the decomposition tank 1) constant.
The “constant” of the resin supply speed means that the set value for the supply amount control in the resin supply means, such as the set value of the rotation speed of the resin supply screw 3, is not changed, and the actual supply speed is This means that the difference from the set value is less than 0.1% with respect to the set value (100%).

The temperature of the resin supplied to the decomposition tank 1 (hereinafter sometimes referred to as supply temperature) is preferably 0 ° C. or higher and (glass transition temperature of resin or melting point −50 ° C.) or lower. When the supply temperature of the resin is 0 ° C. or higher, the temperature drop of the fluid medium layer 1c is suppressed, and the fluidity of the fluid medium layer 1c is improved. If the supply temperature of the resin is (the glass transition temperature of the resin or the melting point −50 ° C.) or less, the adhesion between the resins is suppressed, and the mixing of the resin and the fluid medium is good.
The supply temperature of the resin can be controlled by installing a mechanism capable of heating or cooling the resin upstream of the resin supply screw.
The resin supply temperature can be measured by a thermometer such as a thermocouple installed in the resin supply line.
The resin supply temperature is preferably constant.
“Constant” resin supply temperature means that the electrical output in the mechanism that can heat or cool the resin, the heating and cooling fluid temperature and flow rate settings are not changed, and the actual supply temperature and its set value are This means that the difference is within ± 0.5 ° C.

The temperature of the fluidized medium layer 1c (the temperature of the fluidized bed) when supplying the resin (when performing thermal decomposition) is preferably 350 ° C. or higher, and more preferably 350 to 500 ° C. When the temperature is 350 ° C. or higher, the thermal decomposition rate of the resin is increased. When the temperature is 500 ° C. or lower, the quality of the recovered liquid is improved. The temperature of the fluidized bed can be adjusted by adjusting the temperature of the fluidized medium or fluidized gas supplied to the fluidized bed.
The temperature of the fluid medium layer 1c can be measured by installing it in a thermocouple (not shown) where the fluid medium in the decomposition tank 1 exists.
The temperature of the fluid medium layer 1c can be controlled by adjusting the temperature of the fluid medium supplied to the decomposition tank 1 in the step (c ′), and the temperature of the fluid medium is the temperature of the fluid medium installed in the heating device 7. It can be controlled by the control device. Specifically, it can be controlled by installing a thermocouple where the fluid medium of the heating device 7 is present and measuring the temperature, and adjusting the fuel supply amount so that the temperature becomes a predetermined temperature.

  When the resin is supplied to the decomposition tank 1 as described above, the resin is thermally decomposed by the heat of the fluid medium, and a gaseous decomposition product (for example, a monomer such as (meth) acrylic ester) is generated. Therefore, when the gas in the decomposition tank 1 (mixed gas of fluidized gas and gaseous decomposition product generated by thermal decomposition) is sent to the cooling device 10 through the gas discharge passage 9 and cooled, Gaseous decomposition products contained in the gas are condensed and recovered as a liquid.

From the cooling device 10, a mixed gas of the fluidized gas and the decomposition product that has not been liquefied is discharged. This mixed gas may be exhausted out of the system after the detoxification process such as the combustion process, or may be supplied to the decomposition tank 1 again.
By supplying this mixed gas to the decomposition tank 1 again, the amount of monomers recovered from the acrylic resin material can be increased.
The detoxification treatment can be carried out, for example, by sending the mixed gas to the heating device 7 and burning it.

In the present invention, in order to recover the decomposition product in the mixed gas discharged from the cooling device 10, the mixed gas is preferably introduced into the mist collecting device 11 installed downstream of the cooling device 10. Thereby, the decomposition product which exists as mist in the mixed gas discharged | emitted from the cooling device 10 is collect | recovered, and the yield of a monomer can further be raised.
From the mist recovery device 11, a mixed gas of the fluidized gas, the decomposition product that has not been liquefied, and the separation gas is discharged. Like the mixed gas discharged from the cooling device 10, this mixed gas may be exhausted outside the system after the detoxification process, or may be supplied again to the decomposition tank 1.

When the mixed gas discharged from the cooling device 10 or the mist collecting device 11 is supplied again to the decomposition tank 1, an inert gas may be mixed with the mixed gas.
Examples of the inert gas mixed with the mixed gas include the same inert gases listed as the fluidizing gas.
The mass ratio of the inert gas to be mixed with respect to the mixed gas coming out of the cooling device 10 or the mist collecting device 11 is preferably inert gas / mixed gas = 0 to 5, preferably 0.01 to 5. Is more preferable. The ratio of 0 means that only the gas that has not been liquefied by the cooling device 10 among the decomposition products of the resin is used as the fluidizing gas for the decomposition tank 1. By setting this ratio to 5 or less, the amount of gas supplied from another process can be reduced, and the cost associated with the use of gas can be reduced.
The gas mixed with the inert gas (hereinafter sometimes referred to as dilution gas) is separated from the gas supplied to the decomposition tank 1 by the flow control device, the control valve, etc. It is divided into exhaust gas.
By exhausting a part of the dilution gas from the flow rate control device and then discharging it out of the system, the concentration of oxygen contained in the gas supplied to the decomposition tank can be reduced.
The oxygen concentration in the mixed gas or dilution gas supplied to the decomposition tank 1 is preferably 3% by volume or less from the viewpoint of ensuring the stability of resin decomposition, increasing the amount of liquid to be recovered, and improving the quality of the liquid. 1% by volume or less is particularly preferable.
The temperature of the mixed gas supplied to the decomposition tank 1 or its dilution gas is the same as the temperature of the fluidized gas described above.

In the step (b ′), it is preferable that the liquid recovered by the cooling device 10 and the mist recovery device 11 is further introduced into the purification device 12 to perform the purification process.
In the liquid recovered by the cooling device 10 or the mist recovery device 11, impurities or a fluid medium discharged from the decomposition tank 1 together with the gas may be mixed. By removing these, the recovered liquid has a higher quality.
Examples of the purification treatment include filtration with a filter and distillation.
In the present invention, it is particularly preferable to perform a purification treatment for recovering the monomer of the acrylic resin material contained in the liquid. Such a purification treatment can be carried out, for example, by performing distillation using a distillation apparatus such as a distillation tower as the purification apparatus 13.
For example, when distillation is performed as a purification treatment, the purification apparatus is combined with a distillation column that separates components having a lower boiling point than the monomer that is the raw material of the acrylic resin, and two or more distillation columns that separate components having a higher boiling point than the monomer. Is preferred in order to increase the purity of the recovered monomer.
An apparatus for collecting the fluid medium discharged from the decomposition tank 1 accompanying the gas from the decomposition tank 1 may be installed upstream of the cooling device 10, and the fluid medium may be removed in advance. A cyclone is illustrated as an example of the device.

[Step (c ′)]
In the step (c ′), the fluid medium in the decomposition tank 1 is continuously discharged through the fluid medium discharge channel 1 d and the fluid medium discharge screw 5, stored in the hopper 6, and then introduced into the heating device 7. After the heating, the fluid is supplied to the fluid medium supply screw 4 through the fluid medium supply flow path 8 and continuously supplied from the fluid medium supply screw 4 to the decomposition tank 1 again.
When there is an undecomposed product of resin in the fluid medium layer 1c, the undecomposed product is discharged from the decomposition tank 1 together with the fluid medium. Even if the undecomposed material is accompanied by the discharged fluid medium, the fluid medium is heated by the heating device 7 to thermally decompose or burn the undegraded material and remove it from the fluid medium. It can be used for thermal decomposition.

There is no particular limitation on the discharge rate (kg / hr) of the fluid medium from the decomposition tank 1. It depends on the kind of resin / processing speed and the temperature of the solid particles supplied to the decomposition tank 1.
The discharge speed of the fluid medium can be calculated by determining the weight change per unit time by using a mass measuring device such as a load cell attached to the hopper 5b of the fluid medium discharge screw 5.
Control of the discharge speed of the fluid medium can be performed by controlling the screw rotation speed of the fluid medium discharge screw 5 by the rotation speed controller 5c.

In this step, it is necessary to control the discharge rate of the fluidized medium so that the fluidized bed height during pyrolysis, that is, the height of the fluidized medium layer 1c during the step (b ′) is constant. is there. When such a control is not performed and the discharge speed is constant, the effect of the present invention cannot be obtained. Here, “constant” of the discharge speed of the fluid medium does not change the set value of the screw rotation speed of the fluid medium discharge screw 5 and the difference between the actual discharge speed and the set value is the set value ( 100%) means less than 0.1%.
As described above, the control can be performed by a control device (not shown) electrically connected to the fluidized bed height detecting means (not shown) of the decomposition tank 1 and the rotation speed control device 5c of the fluid medium discharge screw 5. .

Examples of the heating device 7 include a fluidized bed furnace and a rotary kiln.
When using a fluidized bed furnace, for example, while supplying a fluidized medium to the fluidized bed furnace and supplying fluidized gas, combustion gas of fuel or a mixture thereof as a fluidized gas, Increase temperature. When a rotary kiln is used, the temperature of the fluidized medium is raised while rotating the apparatus itself while supplying air, a combustion gas of fuel or a mixture thereof, and flowing the fluidized medium therein. Thus, by raising the temperature of the fluidized medium, the undecomposed product of the resin discharged accompanying the fluidized medium can be thermally decomposed or burned.

Although there is no restriction | limiting in particular in the fuel used with the heating apparatus 7, For example, heavy oil, light oil, kerosene, the collection liquid (liquid containing a decomposition product) collect | recovered at the said process (b ') etc. are mentioned. In particular, the use of the recovered liquid is preferable from the viewpoints of environment and cost because it is not necessary to purchase a new fuel. In addition, the use of the recovered liquid provides a closed system and a process with a low environmental load because the recovered liquid covers the amount of heat necessary for resin decomposition.
The heating temperature in the heating device 7 may be appropriately set in consideration of the temperature of the fluid medium supplied to the decomposition tank 1 and the like.
The heating temperature (fluid medium temperature) in the heating device 7 can be controlled by controlling the amount of fuel supplied to the heating device 7.

The fluid medium heated by the heating device 7 is supplied to the decomposition tank 1 via the fluid medium supply screw 4.
The temperature of the fluidized medium supplied to the decomposition tank 1 (hereinafter sometimes referred to as supply temperature) is preferably (fluidized bed temperature + 50 ° C.) or more and (fluidized bed temperature + 250 ° C.) or less. When the supply temperature of the fluid medium is equal to or higher than the lower limit value of the range, the thermal decomposition rate of the resin is increased, and when it is equal to or lower than the upper limit value, the quality of the recovered liquid is improved.
The supply temperature of the fluid medium can be measured by installing a thermometer such as a thermocouple where the fluid medium in the fluid medium supply channel 8 is present.
The supply temperature of the fluid medium is controlled by setting the temperature in the heating device 7, that is, controlling the amount of fuel supplied to the heater 7 and controlling the temperature of the fluid medium in the heater 7. it can.
In this step, it is necessary to keep the supply temperature of the fluid medium constant.
“Fixed” of the supply temperature of the fluid medium does not change the set value of the amount of fuel to be supplied to the heating device 7 that is set to be the predetermined supply temperature, and the actual supply temperature and the predetermined supply temperature. It means that the difference between is within ± 0.5 ° C.

There is no restriction | limiting in particular in the supply speed (kg / hr) of the fluid medium from the fluid medium supply screw 4 to the decomposition tank 1 in a process (c '). It depends on the type of resin / processing speed and the temperature of the fluid medium supplied to the decomposition tank 1.
It is preferable that the ratio (fluid medium / resin) of the fluid medium supply rate (kg / hour) to the decomposition tank 1 with the resin supply rate (kg / hour) is in the range of 1-20. If the fluid medium / resin is 1 or more, the resin can be efficiently thermally decomposed. If the fluid medium / resin is 20 or less, the circulation amount of the fluid medium between the decomposition tank 1 and the fluid medium heating device 12 can be suppressed, and an increase in cost due to an increase in the size of the heating device 12 can be suppressed.
The supply speed of the fluid medium can be measured by using a mass measuring device (not shown) such as a load cell attached to the hopper 4b of the fluid medium supply screw 4.
In addition, the supply speed of the fluid medium is controlled by a method in which the rotational speed of the fluid medium supply screw 4 is controlled by the rotational speed control device 4c, and a quantitative supply means such as a rotary valve is attached to the hopper 4b, and the rotational speed is controlled. It can be performed by the method to do.
In this step, it is necessary to make the supply speed of the fluid medium to the decomposition tank 1 constant.
“Fixed” of the supply speed of the fluid medium means that the set value for controlling the supply amount in the fluid medium supply means, such as the set value of the rotational speed of the fluid medium supply screw 4, is not changed, and This means that the difference between the supply speed and the set value is less than 0.1% with respect to the set value (100%).

  In the present embodiment, an example in which a screw is used as a method for supplying the heated fluid medium to the decomposition tank 1 has been shown. However, the present invention is not limited to this, and for example, a method based on the falling of the fluid medium by its own weight is used. Also good. The method of dropping the fluid medium by its own weight is a simple method and has the advantage that the equipment cost is low. However, the screw method is advantageous from the viewpoint of quantitative supply.

As described above, the above steps (a ′) to (c ′) are performed in parallel, and the supply speed of the fluidizing gas supplied to the decomposition tank 1 in the step (a ′), the step (b ′). In step (c ′), the supply speed of the resin supplied to the decomposition tank 1 in step, the supply speed of the fluid medium supplied to the decomposition tank 1 in step (c ′), and the temperature thereof are set constant. By controlling the fluidized bed height (height of the fluidized medium layer 1c) at the time of thermal decomposition to a constant height by controlling only the discharge speed of the fluidized medium to be discharged, acrylic in an inert gas atmosphere by the fluidized bed Thermal decomposition of the resin can be carried out continuously for a long time in a stable and simple manner.
This is because not only the height of the fluidized bed during pyrolysis but also the occurrence of local temperature fluctuations in the fluidized bed is suppressed, the thermal decomposition reaction conditions in the decomposition tank are constant, and the amount of resin supplied This is considered to be because the stability of the thermal decomposition reaction is high, and the acrylic resin is favorably decomposed into the raw material monomer.
In addition, this improves the concentration of the monomer in the gas discharged from the decomposition tank, and the concentration is stable, thereby stabilizing the amount of liquid (condensate) recovered by the cooling device, The monomer purity in the liquid is also improved.
For this reason, in step (b ′), the recovered liquid is further sent to the purifier 13 and the load when the purification process such as distillation is performed to recover the resin raw material monomer contained in the liquid is increased. And the fluctuation of the purification conditions (temperature, pressure, etc. in the distillation column) is also suppressed.
Although the present invention has been described with reference to the first embodiment, the present invention is not limited to the embodiment.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to a present Example.
The fluid medium, resin, controllable items during continuous operation, control method thereof, and evaluation method (operation stability) used in the following examples are as follows.
(Fluid medium)
As the fluid medium, sand (natural river sand, manufactured by Changei Material Co., Ltd., trade name: Ebaralozuna, average particle diameter (diameter) 0.3 mm, bulk density 1600 kg / m ³ ) was used.

(resin)
Resin 1: Resin (polymethyl methacrylate) comprising 100% by mass of methyl methacrylate (hereinafter abbreviated as “MMA”). The weight average molecular weight of the resin 1 was 400,000, and the glass transition temperature was 100 ° C. The thing of the magnitude | size which passes a sieve with an opening of 5.6 mm, and does not pass a sieve with an opening of 4.75 mm was used.

(Fluidized bed height)
In advance, a predetermined amount of fluid medium was put into the decomposition tank 1 to form a solid particle layer 1c, and the height (fluid bed height) was measured. At the same temperature as the thermal decomposition conditions, the pressure difference between the pressure in the space (the position above the uppermost surface of the solid particle layer 1c) in the decomposition tank 1 and the pressure in the fluidizing gas chamber 1e was measured. The same operation was repeated while changing the amount of the fluid medium, and a calibration curve of the fluidized bed height with respect to the differential pressure was obtained.
From the differential pressure during pyrolysis, the fluidized bed height during pyrolysis was determined using the calibration curve.

  The measurement location is a height of 250 mm, 500 mm, 750 mm, and 1000 mm away from the surface on the fluidized bed side of the plate-like dispersion apparatus 1b, and 3 cm in the horizontal direction from the center of the fluidized medium layer 1c and the inner wall surface of the decomposition tank 1. , A total of 12 positions 30 cm apart.

(Controllable items and control method during continuous operation)
-Supply speed of resin 1 to decomposition tank 1 (kg / hr): Controlled by screw rotation speed of resin supply screw 3.
-Feeding rate of fluidized gas to the decomposition tank 1 (kg / hr): Controlled by the rotational speed of the blower 13.
Feed rate of fluid medium to decomposition tank 1 (kg / hr): Controlled by screw rotation speed of fluid medium supply screw 4.
-Supply temperature (° C) of the fluid medium to the decomposition tank 1: Controlled by the set temperature of the heating device 7.
-Discharge rate (kg / hr) of the fluid medium from the decomposition tank 1: Controlled by the screw rotation speed of the fluid medium discharge screw 5.

(Operation stability)
The height of the fluidized bed during 100 hours of operation, the fluidized bed temperature, the amount of condensate recovered by the cooling device 10, and the condition fluctuation during purification in the purification device 13 were determined according to the following criteria.
[Fluidized bed height] The differential pressure during pyrolysis was measured every 5 minutes, and all values were summed to determine the average value of the fluidized bed height. A state of ± 1% or less with respect to the average value was judged as ◯, and other cases were judged as ×.
[Fluidized bed temperature] As a result of the measurement of the local temperature in the fluidized medium layer 1c in the above procedure, the case where the temperature of all the measurement points is within ± 1% of the average value is ○, otherwise X was judged. The average value is an average value of the temperatures at all measurement locations.
[Amount of condensate] A liquid flow meter was installed on the outlet side of the condenser, and the value was measured every 5 minutes, and all values were summed to obtain an average value of the amount of condensate. A state of ± 1% or less with respect to the average value was judged as ◯, and other cases were judged as ×.
[Conditions during purification] The pressure in the distillation column was measured by installing a pressure gauge at the bottom of the column. The temperature in the distillation column was measured by installing thermometers at the top and bottom of the column. Since the top of the pressure was operated under reduced pressure in the distillation column, the top pressure was controlled to be constant by a vacuum pump. The average value was measured every 5 minutes for both pressure and temperature, and all values were summed to obtain an average value of pressure and temperature. A state where the pressure and temperature in the distillation column were ± 1% or less with respect to the average value was judged as ◯, and other cases were judged as x.

[Example 1]
It implemented using the thermal decomposition apparatus 100 of the structure shown in FIG.
The diameter of the decomposition tank 1 was 350 mm and the height was 1400 mm.
For the flow of the fluidized medium layer 1c, a fluidizing gas and a stirring device provided with a stirring blade were used. Nitrogen gas was used as the fluidizing gas. The stirrer blade uses two inclined paddle blades in 5 stages. The diameter of the two paddle blades is 310 mm, width 20 mm, inclination angle 45 degrees, pitch between paddles (the distance between the center of the paddle blades in the upper and lower stages) ) Was 140 mm. The upper and lower stage paddle blades were made to be orthogonal. The stirring speed was 25 revolutions per minute (25 rpm).
In the lower part of the decomposition tank 1, as a dispersing device 1b, a dispersing device (thickness 1.6 mm, made of stainless steel, hereinafter referred to simply as “dispersing device 1b”) is used. It is sometimes called "dispersion plate"). A pipe for discharging sand (fluid medium discharge channel 1d) was installed at the lower part of the dispersing device 1b.

First, 70 kg of a fluid medium was placed in the decomposition tank 1 to form a fluid medium layer 1c. The height of the sand layer in a stationary state was 520 mm. Thereafter, the inside of the decomposition tank 1 was replaced with nitrogen.
The fluid medium was continuously discharged from the decomposition tank 1 by the fluid medium discharge screw 5 and sent to the heating device 7. A uniaxial screw was used as the fluid medium discharge screw 5, and the discharge speed was measured by a load cell of a hopper 5 b installed between the decomposition tank 1 and the fluid medium discharge screw 5.
As the heating device 7, a fluidized bed furnace for fluidizing sand with hot air was used. In the heating device 7, 600 kg of the same sand as the above was put as a fluid medium. In the heating device 7, the temperature of the sand is controlled to be a predetermined temperature by controlling the temperature of the hot air.
The set temperature of the heating device 7 was set to 400 ° C., and the heated fluid medium was continuously supplied to the decomposition tank 1 by the fluid medium supply screw 4 at a supply rate of 120 kg / hr. A uniaxial screw was used as the fluid medium supply screw 4. The supply position was 850 mm above the apex of the cone of the dispersion plate. The supply speed was calculated by measuring the weight with a load cell of the hopper 6 installed between the heating device 7 and the decomposition tank 1.
Nitrogen gas (20 ° C.) was continuously supplied from the fluidizing gas supply passage 2 into the decomposition tank 1 at a supply rate of 20 kg / hr. The supply speed of the fluidizing gas was measured by a vortex flow meter installed between the blower 12 and the dispersion chamber 1e of the decomposition tank 1 in FIG.
Further, the resin 1 was continuously supplied from the resin supply screw 3 to the decomposition tank 1 at 20 ° C. at a supply rate of 10 kg / hr. The supply position was 0.7 m above the dispersing device 1b. The supply speed of the resin 1 was calculated by measuring the weight with a load cell of the hopper 3b installed on the resin supply screw 3.

After the start of the supply of the resin 1, a mixed gas of the decomposition product of the resin 1 coming out of the decomposition tank 1 and a gas containing nitrogen gas was sent to the cooling device 10. The gaseous decomposition product sent to the cooling device 10 was cooled and recovered as a liquid. The cooling device 10 is a multi-tube condenser, and a −10 ° C. refrigerant was passed through the jacket. The temperature of the gas coming out of the multi-tube condenser was 3 ° C., and it was sent to the mist collecting device 11 to collect the liquid mist contained in the gas. As the mist collecting device 11, a cyclone type device was used. Containers for recovering the liquid were respectively installed under the cooling device 10 and the mist recovery device 11, and the liquid recovered by each device was accommodated.
The liquid collected from the cooling device 10 and the mist collecting device 11 was sent to the purifying device 12, and a purification process was performed. As the purification apparatus 12, a distillation tower was used.

The fixed items and controlled items in Example 1 are as follows.
-Supply speed of resin 1 to decomposition tank 1: 10 kg / hr
-Feeding rate of fluidized gas to the decomposition tank 1: 20 kg / hr
-Feed rate of fluid medium to decomposition tank 1: 120 kg / hr
-Supply temperature of fluid medium to decomposition tank 1: 400 ° C
・ Discharge rate of fluid medium from decomposition tank 1: Control (parameters are determined by auto-tuning)
In Example 1 and Comparative Examples 1 to 4 below, “control” was performed by PID control so that the measured value of the fluidized bed height was constant.

  When continuous operation was performed for 100 hours under the above conditions, the fluidized bed height, fluidized bed temperature, and the amount of condensate recovered by the cooling device 10 were all very stable, and the fluctuation of conditions during purification also occurred. There wasn't.

[Comparative Example 1]
As shown below, the same operation as in Example 1 was performed except that the discharge speed of the fluid medium from the decomposition tank 1 was constant (120 kg / hr).
-Supply speed of resin 1 to decomposition tank 1: 10 kg / hr
-Feeding rate of fluidized gas to the decomposition tank 1: 20 kg / hr
-Feed rate of fluid medium to decomposition tank 1: 120 kg / hr
-Supply temperature of fluid medium to decomposition tank 1: 400 ° C
-Discharge rate of fluid medium from decomposition tank 1: 120 kg / hr

  When continuous operation was performed under the above conditions, the fluidized bed height gradually decreased in the decomposition tank 1. For this reason, during the continuous operation for 100 hours, it is necessary to adjust the screw rotation speed of the fluid medium discharge screw 5 in such a direction that the discharge speed of the fluid medium from the decomposition tank 1 is often reduced.

[Comparative Example 2]
As shown below, the same operation as Example 1 was implemented except having controlled the fluid supply speed to the decomposition tank 1. FIG.
-Supply speed of resin 1 to decomposition tank 1: 10 kg / hr
-Feeding rate of fluidized gas to the decomposition tank 1: 20 kg / hr
-Feed rate of fluid medium to cracking tank 1: Control (parameters are determined by auto tuning)
-Supply temperature of fluid medium to decomposition tank 1: 400 ° C
・ Discharge rate of fluid medium from decomposition tank 1: Control (parameters are determined by auto-tuning)

  When continuous operation was performed for 100 hours under the above conditions, when the supply rate of the fluidized medium decreased, the temperature of the fluidized bed decreased, the decomposition reaction of the resin 1 slowed, and the resin 1 stayed in the decomposition layer 1 The amount increased and it took time for the fluidized bed temperature to rise, and the fluidized bed temperature was not stable.

[Comparative Example 3]
As shown below, the same operation as in Example 1 was performed except that the discharge speed of the fluid medium from the decomposition tank 1 was constant (120 kg / hr) and the acrylic resin supply speed to the decomposition tank 1 was controlled.
-Supply speed of resin 1 to decomposition tank 1: Control (parameters are determined by auto tuning)
-Feeding rate of fluidized gas to the decomposition tank 1: 20 kg / hr
-Feed rate of fluid medium to decomposition tank 1: 120 kg / hr
-Supply temperature of fluid medium to decomposition tank 1: 400 ° C
-Discharge rate of fluid medium from decomposition tank 1: 120 kg / hr

  When continuous operation was performed for 100 hours under the above conditions, the fluidized bed temperature was not stable because the supply rate of the resin 1 changed. Further, the condensate obtained by the cooling device 10 also changed depending on the supply speed of the resin 1, and accordingly, a fluctuation of conditions during the purification by the purification device 13 also occurred.

[Comparative Example 4]
As shown below, the same operation as in Example 1 was performed except that the discharge speed of the fluid medium from the decomposition tank 1 was constant (120 kg / hr) and the fluidizing gas supply speed to the decomposition tank 1 was controlled. .
-Supply speed of resin 1 to decomposition tank 1: 10 kg / hr
・ Supply speed of fluidized gas to decomposition tank 1: Control (parameters are determined by auto-tuning)
-Feed rate of fluid medium to decomposition tank 1: 120 kg / hr
-Supply temperature of fluid medium to decomposition tank 1: 400 ° C
-Discharge rate of fluid medium from decomposition tank 1: 120 kg / hr

  When continuous operation was performed under the above conditions, when the fluidizing gas supply rate decreased, the dispersion state of the resin in the fluidized bed deteriorated, and the reaction time significantly increased due to melting of the resins. As a result, the fluidized bed temperature locally decreased and the operation was stopped when 10 hours had elapsed.

  Control conditions for the acrylic resin supplied to the decomposition tank in Example 1 and Comparative Examples 1 to 4 above, the supply speed of the fluidizing gas and the fluid medium, the supply temperature of the fluid medium, the supply speed of the fluid medium discharged from the decomposition tank, Table 1 shows the evaluation results. As shown in these results, the supply speed of the resin 1 (acrylic resin), fluidizing gas and fluidized medium supplied to the decomposition tank, the supply temperature of the fluidized medium are fixed, and only the supply speed of the fluidized medium is controlled. The stable operation of the pyrolysis apparatus 100 for a long time was possible.

  As described above, according to the present invention, thermal decomposition of an acrylic resin in an inert gas atmosphere by a fluidized bed can be carried out continuously for a long time in a stable and simple manner.

  DESCRIPTION OF SYMBOLS 1 ... Decomposition tank, 2 ... Fluidization gas supply channel, 3 ... Resin supply screw, 4 ... Fluid medium supply screw, 5 ... Fluid medium discharge screw, 6 ... Hopper, 7 ... Heating device, 8 ... Fluid medium supply channel , 9 ... Gas discharge flow path, 10 ... Cooling device, 11 ... Mist recovery device, 12 ... Purification device, 13 ... Blower, 100 ... Pyrolysis device

Claims (2)

A method for thermally decomposing an acrylic resin in which the following steps (a) to (c) are performed in parallel, the supply speed of a fluidizing gas supplied to the decomposition tank, the supply speed of an acrylic resin, and the supply speed of a fluid medium And the thermal decomposition method which controls the fluidized bed height at the time of the said thermal decomposition to fixed height by controlling only the discharge speed of the fluidized medium discharged | emitted from a decomposition tank in the said process (c) by making each the temperature constant.
Step (a): A step of forming a fluidized bed by continuously supplying a fluidizing gas containing an inert gas from the lower part of the decomposition tank to the decomposition tank filled with the fluidizing medium to cause the fluidizing medium to flow.
Step (b): A step of continuously supplying an acrylic resin to the fluidized bed for thermal decomposition, cooling a gaseous decomposition product generated by the thermal decomposition, and recovering it as a liquid.
Step (c): The fluid medium in the decomposition tank is continuously discharged from a position below the height of the acrylic resin supply position, introduced into a heating device, heated, and then into the decomposition tank. The process of supplying continuously.   2. The thermal decomposition method according to claim 1, wherein in the step (b), the recovered liquid is further purified, and the monomer of the acrylic resin material contained in the liquid is recovered.

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