JP2003321571A - Method for recovering monomer from acrylic resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering high purity monomer which produces an acrylic resin product with extremely reduced impurity and high transparency, without decomposition of the monomer gas produced by pyrolysis in a recovery process recovering the monomer from an acrylic resin waste or the like mainly comprising methyl methacrylate monomer in dry distillation using a heating vessel with an agitator. <P>SOLUTION: The method comprises thermally decomposing the acrylic resin into a gas state by dry distillation in the heating vessel with the agitator, liquefying the gas state pyrolysis product, and then purifying the liquefied pyrolysis product by distillation to recover the monomer, where the tip speed of the agitator is set at 0.1 to 35 m/min. <P>COPYRIGHT: (C)2004,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an acrylic resin product having a very high degree of transparency from waste acrylic resin or offcuts during processing. The present invention relates to a method for recovering a purity monomer. 2. Description of the Related Art In recent years, there has been a strong demand for recycling plastic waste from the standpoint of protecting the global environment and saving resources. Recycling of plastic waste is carried out by various methods, but one of the most effective methods is dry distillation, that is, in the absence of oxygen, the plastic is thermally decomposed and reduced to low molecular weight monomers, and the recovered monomers are recovered. Reusing has been done. [0003] An acrylic resin containing methyl methacrylate as a main component can be recovered in a high yield as a raw material monomer constituting the resin by dry distillation. Therefore,
Industrial methods for recovering monomers by dry distillation are used for defective molded products made of acrylic resin, scraps generated during molding, or waste materials collected after using the molded products as products. Have been done. Here, the dry distillation of an acrylic resin for monomer recovery is generally carried out by charging a resin raw material into a heating kettle,
If necessary, heating is performed at a temperature of 350 to 800 ° C. in an inert gas atmosphere in a state in which substantially no oxygen is present. The condensed liquid is condensed and liquefied by an exchanger type cooler or the like, and the condensed liquefied product is purified by distillation to recover the monomer. [0005] However, in dry distillation using a heating oven, the monomer gas generated by the thermal decomposition is further subjected to a thermal history to further decompose, thereby lowering the recovery rate of the monomer and at the same time deteriorating the quality due to an increase in impurities. Alternatively, even the carbon reaches the carbon and adheres to the inner wall of the dry still to lower heat conduction, thereby deteriorating the overall thermal efficiency. [0006] Generally, in an acrylic resin containing methyl methacrylate as a main component, methyl isobutyrate, which is converted into a saturated bond due to a monomer having an unsaturated bond generated by thermal decomposition and further subjected to heat history, is mainly produced as an impurity. I do. Since methyl isobutyrate does not contribute to polymerization, it remains in the resin product obtained from the recovered monomer containing a large amount of it and lowers the heat distortion temperature, lowers the solvent resistance, or easily foams during heat molding. And many other problems. Further, methyl isobutyrate has a similar boiling point to that of methyl methacrylate and thus has a small difference in boiling point, and it is substantially impossible to completely remove it by distillation or the like. Therefore, various studies have been made on a monomer recovery apparatus based on the dry distillation method of resin waste material in order to suppress further decomposition of the decomposition product gas. For example, Japanese Patent Application Laid-Open No. Sho 60-49086 discloses a dry distillation tank structure having a jacket structure, in which a heating medium is filled in the jacket, and heating is performed through the heating medium to reduce the temperature difference between the inside and the side surface of the drying tank. A method for reducing overheating to prevent overheating is disclosed. However, in this method, the cost required for the equipment is increased, and extra energy for heating the heat medium is required, which is economically difficult. Japanese Patent Application Laid-Open No. 3-285987 discloses that an upper portion of a dry distillation tank is prevented from being directly heated by a flame of a heating furnace by a heat insulating material, and a cooling fin protruding outside is provided at an upper portion of the heating furnace. A method is disclosed in which the temperature in the upper part of the heating still is kept low. However,
If the temperature in the upper part of the still is kept low, the gas generated by thermal decomposition is cooled unnecessarily and liquefied and refluxed inside the still. , And the quality of the recovered monomer obtained by receiving a large amount of heat history is reduced, which is not preferable. Furthermore, the heat radiation from the cooling fins is greatly affected by the surrounding environmental temperature, and it is difficult to keep the temperature at an appropriate temperature. Japanese Patent Application Laid-Open No. 4-50293 discloses that an internal agitator attached to a dry still has not only a lower stirring blade for stirring a molten resin but also an upper gas portion for suppressing overheating of gas generated by thermal decomposition. A method is disclosed in which an upper stirring blade for stirring is provided to prevent partial overheating of a gaseous gas phase portion and to suppress excessive decomposition. However, if one stirring shaft is provided with a stirring blade for upper stirring and a stirring blade for lower stirring, stirring can be performed only at a certain rotation, so that a viscous material such as a molten resin is stirred. It is difficult to simultaneously obtain a stirring rotation speed suitable for the above and a stirring rotation speed sufficient to realize overheating prevention of the upper gas portion. Also,
If the stirring shaft is duplicated and individual stirring blades are attached to separate drive systems, it is possible to obtain a suitable stirring rotation speed, but complicated equipment is required, so a large amount of cost is required and economical It is inferior to. In addition, all of the conventional methods focus on recovery as an oil component, and there is also a problem in that the viewpoint of recovering high-purity monomers that can be reused as resin raw materials is thin. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for recovering monomers from waste acrylic resin containing a methyl methacrylate unit as a main component in a dry distillation system using a heating kettle having a stirring device. It is another object of the present invention to provide a method for recovering a high-purity monomer capable of producing an acrylic resin product having a very high degree of transparency and having a small amount of impurities without further changing the monomer gas generated by thermal decomposition. Means for Solving the Problems The present inventors pyrolyze an acrylic resin into a gaseous state by dry-distilling it in a heating kettle having a stirrer, and then liquefy the gaseous heat-decomposed product. Then, when recovering the monomer by distilling and purifying the liquefied heat decomposition product, the tip speed of the stirring blade at the time of heating and distillation is within the range of 0.1 to 35 m / min. The inventors have found that a monomer having high purity can be recovered, and have completed the present invention. Hereinafter, preferred embodiments of the present invention will be described in detail. The acrylic resin used in the present invention comprises a polymer containing at least 40% by mass of a methyl methacrylate unit which returns to a monomer which is a raw material before polymerization in a high yield during thermal decomposition by dry distillation. From the viewpoint of monomer recovery efficiency, a homopolymer of methyl methacrylate is most preferable, but a copolymer containing another monomer unit may be used. In this case, it is preferable to use a copolymer of 80% by mass or more of methyl methacrylate and 20% by mass or less of alkyl methacrylate or alkyl acrylate, and 90% by mass or more of methyl methacrylate and 10% by mass or less of alkyl methacrylate or alkyl acrylate. And those comprising a copolymer of These resins may contain about 10% by mass or less of a stabilizer or a coloring agent. Further, a physical property improving agent such as an acrylic rubber may be contained. In the present invention, the shape of the acrylic resin to be put into a heating pot having a stirrer is preferably crushed to a size within 20 mm square or 20 mm cubic from the viewpoint of handling. , Flakes, granules, powders, chips, etc.
Further, they may have a single shape or a combination of different shapes. In the dry distillation, an acrylic resin is charged into a heating pot,
Heating is performed in an inert gas atmosphere in a state where oxygen is not substantially present. In that case, the oxygen concentration is preferably 1% by volume or less. In addition, it is also possible to dry-distill by heating in a state where oxygen is not substantially present by reducing the pressure in the heating pot. In that case, the oxygen partial pressure is more preferably 1 kPa or less. The method of charging the acrylic resin into the heating pot is as follows.
The acrylic resin may be charged in the heating pot in advance, or may be continuously charged into the heating pot. In the present invention, the heating pot may be any heating pot having a stirring function. In the present invention, the temperature of the heating kettle may be maintained at a temperature suitable for dry distillation, generally at a temperature of 350 to 800 ° C.
A range of 50 ° C is preferable, and a range of 450 to 700 ° C is more preferable. When the temperature is too low, the carbonization speed is slow and the decomposition takes a long time, so that not only is the economy inferior, but also
If the temperature is too high, the generated gaseous heat decomposition product undergoes thermal history and is further decomposed, resulting in a decrease in the recovery rate and an increase in the impurities in the recovered monomer. There is a risk of inviting. As for the heating at the time of carbonization, the entire inner wall of the heating pot may be heated, but it is sufficient that the inner wall in contact with the acrylic resin is heated, and only the lower surface of the heating pot may be heated. The tip speed of the stirring blade of the present invention is 0.1 to
It is 35 m / min, preferably 0.7 to 30 m / min. 3
At a blade tip speed exceeding 5 m / min, the monomer gas generated by thermal decomposition is more susceptible to heat history, and the progress of decomposition proceeds, resulting in an increase in impurities in the recovered monomer. On the other hand, when the blade tip speed is low, the carbonization speed tends to decrease. When the blade tip speed is less than 0.1 m / min, impurities in the recovered monomer do not increase due to the progress of decomposition due to heat history. Pyrolysis residues accumulate on the bottom of the kettle,
A sharp decrease in the yield of the gaseous thermal decomposition product causes a difficulty in economically recovering the monomer. The gaseous thermally decomposed product generated by heating the acrylic resin as described above is taken out of the heating pot, and then used with a heat exchanger type cooler or the like.
The condensed liquid is condensed and liquefied by a known method, and the condensed liquid is purified by distillation or the like, and the monomer is recovered. Next, the present invention will be described with reference to examples and comparative examples, but the present invention is not limited to these examples. Pulverized Acrylic Resin In Examples 1 to 3 and Comparative Examples 1 to 3, a homopolymer of methyl methacrylate (weight average molecular weight 700,00
0 (polystyrene equivalent value), an acrylic sheet having a thickness of 3 mm was pulverized, and an acrylic resin pulverized product A passed through a sieve having 20 mm square openings was used. In Example 4, an acrylic sheet having a thickness of 3 mm made of a copolymer of methyl methacrylate and n-butyl acrylate (weight ratio: 95/5, weight average molecular weight: 200,000 (in terms of polystyrene)) was prepared. Acrylic resin pulverized body B that had been pulverized and passed through a sieve having an opening of 20 mm square was used. Analysis of Recovered Monomer Purity of the obtained recovered methyl methacrylate monomer was measured by gas chromatography. In addition, impurities are multi-component, and there are unknown components.
The content of methyl isobutyrate, which is a main component, was measured by gas chromatography and defined as the impurity content. Example 1 As shown in FIG. 1, a height of 250 mm and an inner diameter of 200 mm
A stainless steel cylindrical vertical heating pot having a rotating radius of 95 mm, a blade height of 20 mm, and a two-blade type anchor-type stirring blade was prepared. The tip speed of the stirring blade is adjusted to 30 m / min and rotated, and the heating surface temperature of the heating pot is set to 600 ° C.
Supply nitrogen gas for purging at 5 L / hr into the heating kettle,
The oxygen concentration in the heating pot was set to 1% by volume or less. Next, 2 kg of the acrylic resin pulverized material A is charged from the raw material charging port on the upper surface of the heating furnace, and thereafter, the monomer vapor generated by the decomposition of the acrylic resin is recovered from the monomer vapor outlet on the upper lid surface of the heating furnace. And then condensed and liquefied in an external cooling condenser through which cold water at -5 ° C is passed, and the crushed acrylic resin A having a weight corresponding to the weight of the obtained dry distillation liquid.
Was charged at a rate of 100 g / time, and the amount kept in the heating kettle was kept substantially constant. This carbonization operation was continued for 8 hours to obtain a carbonized liquid. The total amount of the crushed acrylic resin A was 17.5 kg. Moreover, the obtained dry distillation liquid is 1
The weight was 5.1 kg. Next, the dry distillate was used for an inner diameter of 46 m.
Then, the mixture was charged into a 30-stage glass-made Oldershaw distillation column, and distilled under a reduced pressure of 40 kPa at a reflux ratio of 3.
After cutting the first distillate 5% by weight, the recovery of methyl methacrylate monomer was started, and finally the distillation was terminated leaving 15% by weight of high-boiling substances. 12.1 kg of a high-purity methyl methacrylate monomer having a purity of 99.7% and an impurity (methyl isobutyrate) of 0.20% could be recovered. Example 2 The same operation as in Example 1 was performed except that the tip speed of the stirring blade was changed to 10 m / min. The total input amount of the crushed acrylic resin A was 16.8 kg. Further, the obtained dry distillate was 14.4 kg. By distillation, purity 99.8%, impurity (methyl isobutyrate) 0.1
7% high purity methyl methacrylate monomer 11.5
kg was collected. Example 3 The same operation as in Example 1 was performed, except that the tip speed of the stirring blade was changed to 1.0 m / min. The total amount of the crushed acrylic resin A was 17.3 kg.
Further, the obtained dry distillate was 14.9 kg. High-purity methyl methacrylate monomer 1 having a purity of 99.8% and an impurity of methyl isobutyrate 0.16% by distillation
1.9 kg could be recovered. Example 4 In Example 1,
The same operation as in Example 1 was performed except that the acrylic resin pulverized body B was used instead of the acrylic resin pulverized body A. The total amount of the crushed acrylic resin B was 16.9 kg. Further, the obtained dry distillate was 14.5 kg. By distillation, 11.6 kg of a high-purity methyl methacrylate monomer having a purity of 99.7% and methyl isobutyrate of 0.19% as impurities was recovered. Comparative Example 1 The same operation as in Example 1 was performed except that the tip speed of the stirring blade was changed to 40 m / min. The total input amount of the crushed acrylic resin A was 18.1 kg. Further, the obtained dry distillate was 15.6 kg. By distillation, purity: 99.3%, impurity (methyl isobutyrate): 0.5
12.5 kg of 3% methyl methacrylate monomer could be recovered. The purity of the recovered methyl methacrylate monomer is not sufficiently satisfactory, and it is necessary to further cut the initial fraction. Comparative Example 2 The same operation as in Example 1 was performed, except that the tip speed of the stirring blade was changed to 50 m / min. The total input amount of the crushed acrylic resin A was 18.1 kg. Further, the obtained dry distillate was 15.5 kg. By distillation, purity 99.0%, impurity (methyl isobutyrate) 0.8
12.4 kg of 6% methyl methacrylate monomer could be recovered. The purity of the recovered methyl methacrylate monomer is further worse than in Comparative Example 1, and it is necessary to further increase the cut of the first fraction. Comparative Example 3 The same operation as in Example 1 was performed, except that the stirring blade was not rotated at all. The total input amount of the crushed acrylic resin A was 13.6 kg. Further, the obtained dry distillate was 11.4 kg. By distillation, 9.1 kg of a methyl methacrylate monomer having a purity of 99.7% and an impurity (methyl isobutyrate) of 0.19% could be recovered.
The recovered methyl methacrylate monomer was of high purity, but the recovered amount was reduced. The results of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1. [Table 1] According to Table 1, in the method of recovering monomers by pyrolysis by dry distillation in a heating kettle having a stirrer, the speed of the stirring blade tip is set to 0.1 to 35 m / min. It can be seen that high-purity methyl methacrylate monomer can be recovered. According to the present invention, a monomer capable of producing an acrylic resin product having extremely high transparency can be recovered from waste acrylic resin and the like. This promotes the effective use of waste materials discharged from factories and the like and waste materials used in signboards and the like, and contributes to the protection of the global environment by the resource saving effect.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view showing an example of a heating and drying still. [Description of Signs] 1 Heating pot 2 Acrylic resin inlet 3 Monomer vapor outlet 4 Pot lid 5 Anchor-type stirring blade 6 Mirror unit 7 Heating furnace

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Hiroshi Amitani             Mitsubishi Rayon 3 Kaigandori, Toyama City, Toyama Prefecture             Toyama Works Co., Ltd. F term (reference) 4F301 AA20 CA09 CA27 CA34 CA52                       CA71                 4H006 AA02 AC91 AD11 BC50 KC14                       KE00

Claims (1)

Claims 1. An acrylic resin is pyrolyzed into a gaseous state by dry distillation in a heating vessel having a stirrer, and then the gaseous thermally decomposed product is liquefied and then liquefied. A method for recovering a monomer by distillation and purification from the heat decomposed product, wherein a tip speed of a stirring blade at the time of heating and distillation is 0.1 to 35 m / min.