JP4071655B2 - How to remove different plastics - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for recovering an active ingredient from a polyester waste containing polyethylene terephthalate as a main component. More specifically, the different plastics contained in the polyester waste are separated and removed in a depolymerization tank, and the next step of foreign matter is performed. The present invention relates to a method for preventing the trouble of the process in the recycling process by suppressing the feed.
[0002]
[Prior art]
Since polyethylene terephthalate is excellent in chemical stability, its use in food fields such as life-related materials such as fibers, films and resins, drinking water, bottles for carbonated beverages and the like is rapidly increasing.
[0003]
However, used polyethylene terephthalate (especially used beverage bottles) generated in large quantities due to the increase in the amount used as described above, or quality ineligible products generated in the polyethylene terephthalate manufacturing stage (hereinafter referred to as polyester waste) Is a big social problem.
[0004]
In order to solve the above problems, so-called chemical recycling in which polyester waste is converted and recovered into a monomer and polyethylene terephthalate is produced and reused by a polymerization reaction using this monomer as a raw material has been studied. In this method, there is basically no loss, the compound can be reused and the resources can be reused.
[0005]
These recovered polyester wastes are depolymerized with ethylene glycol, then transesterified with methanol, and further separated and purified to dimethyl terephthalate (hereinafter sometimes abbreviated as DMT) and ethylene glycol. (Hereinafter, it may be abbreviated as EG.), Leading to effective use of resources and a reduction in total cost.
[0006]
As these recovery methods, an excess of ethylene glycol is added to polyethylene terephthalate and heated to obtain a mixture of bis (β-hydroxyethyl) terephthalate and a low polymer containing a β-hydroxyethyl ester group at the terminal by a depolymerization reaction. A method of recovering dimethyl terephthalate by adding an excess of methanol (hereinafter sometimes abbreviated as MeOH) to the mixture and carrying out a substitution esterification reaction in the presence of a catalyst has been proposed (for example, patents). Reference 1).
[0007]
The present inventors previously proposed a method for separating and recovering dimethyl terephthalate and ethylene glycol from polyester waste (see Patent Document 2). The patent proposed a method of recovering dimethyl terephthalate and ethylene glycol by depolymerizing polyester waste containing foreign components with alkylene glycol and then transesterifying with methanol. Further, the patent proposed a method for removing solid foreign matters floating on the surface of the solution, for example, polyolefin, by solid-state selection, among solid foreign matters contained in the obtained depolymerization reaction solution. . However, there is no description of a method for feeding the reaction solution from the depolymerization reaction tank to the next step, and there is a possibility of feeding polyolefin or the like to the next step, which may cause a process trouble.
[0008]
As described above, when polyester waste is processed by chemical recycling, it is important to remove foreign matters contained in the polyester waste, particularly beverage bottles. Conventionally, foreign substances such as caps and labels contained in beverage bottles have been removed by manual gravity or specific gravity separation using water, but if it is manual labor, mass processing is difficult and economically undesirable, In the specific gravity separation method using water, a substance having a specific gravity greater than that of water cannot be substantially separated.
[0009]
On the other hand, if the foreign matter cannot be completely removed, foreign matter will be mixed in the recycling process, and the foreign matter may partially melt at a solid or high temperature condition, thereby causing adhesion to equipment in the recycling process or blockage of piping. Trouble occurs.
[0010]
[Patent Document 1]
Japanese Patent Publication No. 43-2088 [0011]
[Patent Document 2]
International Publication No. 01/30729 Pamphlet [0012]
[Problems to be solved by the invention]
The object of the present invention is to eliminate the problems of the prior art described above, to separate and remove the different plastics contained in the polyester waste in the depolymerization tank, and to suppress the sending of foreign substances to the next process, The object is to provide a method for preventing troubles in the chemical recycling process.
[0013]
[Means for Solving the Problems]
As a result of intensive studies in view of the above-described prior art, the present inventors have completed the present invention. That is, the object of the present invention is to
In a depolymerization reaction vessel in which polyalkylene terephthalate is depolymerized with alkylene glycol, polyester waste containing polyalkylene terephthalate as the main component and a different plastic other than polyalkylene terephthalate is added, and the depolymerization reaction vessel is stirred. depolymerization reaction was carried out to obtain a depolymerization reaction while, among the heterologous plastic, a light plastic specific gravity than the depolymerization reaction liquid of alkylene glycols and polyalkylene terephthalate is floated on the liquid surface, the depolymerization reaction tank after removing at least a portion of the light plastic in specific gravity from the depolymerization reaction tank by withdrawing the stopped light plastic specific gravity stirring the upper layer portion of the depolymerization reaction vessel together with the depolymerization reaction liquid obtained by the depolymerization reaction solution The polymerization reaction liquid is moved downward in the depolymerization reaction tank. For feeding to the next step from the bottom of the depolymerization reaction vessel while suppressing by stopping the stirring of the feeder included flow depolymerization reaction vessel can be achieved by different plastic removal method from polyester waste.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail, but it goes without saying that other embodiments may also belong to the category of the present invention as long as they match the gist of the present invention.
[0015]
In the method of the present invention, the polyester waste is generally subjected to pretreatment such as washing with water and coarse pulverization to form a shape suitable for the depolymerization reaction, and then charged into the depolymerization reaction tank. The present invention can be applied to either continuous or batch systems. In the case of carrying out in a batch system, the polyester waste is put into a solution containing ethylene glycol containing a polyester depolymerization catalyst as a main component to cause a depolymerization reaction. In the depolymerization reaction tank, a stirrer, a self-circulation line of the depolymerization reaction tank, and the like are installed in order to promote the reaction.
[0016]
During this depolymerization reaction, among the different types of plastics contained in the polyester waste, plastics mainly composed of polyolefin or polystyrene having a light specific gravity with respect to the reaction solution float on the liquid surface. These floating foreign substances are removed by drawing out at the same time as the upper layer reaction solution. This removal can be carried out even in a stage where the depolymerization reaction is not completely completed, even in a slurry state in which foreign matter is sufficiently floated to be separated or unreacted polyester remains. About the method of extracting simultaneously with this reaction liquid, it is difficult to completely remove foreign substances contained in the polyester waste, and it is inevitable that some foreign substances remain in the depolymerization tank.
[0017]
For this reason, when the depolymerization reaction liquid is taken out from the batch-type depolymerization tank to the next process, the downward entrainment flow in the depolymerization reaction tank is suppressed, and the feed of foreign substances to the next process is suppressed. It is necessary to prevent troubles after the process. In the depolymerization reaction tank, it is generally necessary to circulate the liquid in the reaction tank using a stirrer, a circulation pump, or the like in order to promote the reaction. However, the specific gravity difference between the liquid in the depolymerization tank and the polyolefin or polystyrene is small. For this reason, at the time of taking out the liquid, it is necessary to adjust the stirring speed and to suppress the downward liquid flow. Further, in order to minimize the influence of the downward entrainment flow, the possibility of sending to the next process becomes lower when the amount of liquid remaining in the depolymerization tank is increased as much as possible.
[0018]
The foreign matter partially melts in a solid state or at a high temperature, which causes troubles such as adhesion to equipment and blockage of piping. As a corresponding method, in the process after the depolymerization reaction tank, it is necessary to handle not sending foreign substances, and a method of suppressing the downward entrainment flow in the depolymerization reaction tank, specifically, when taking out, It is necessary to temporarily stop the rotation of the stirrer or reduce the rotation speed. Or when sending liquid, it is necessary to send to the next process in the state which kept the liquid in the tank more than a fixed capacity | capacitance in a depolymerization reaction tank.
[0019]
Further, in the depolymerization reaction tank, it is not always necessary to carry out the depolymerization reaction completely. Therefore, the present invention can be applied even in a state where unreacted polyester remains at the time of taking out. Furthermore, if the depolymerization reaction has progressed for a certain level or more, it is possible to install a device such as a filtration or strainer at a location where the liquid is transferred from the depolymerization reaction tank to the next process.
[0020]
【Example】
Hereinafter, the content of the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.
[0021]
[Example 1]
50 parts of polyethylene terephthalate, 2 parts of polystyrene, 2 parts of polyethylene, 200 parts of ethylene glycol and 1.5 parts of sodium carbonate as a depolymerization catalyst were added, and the temperature was maintained at 180 ° C. for 1 hour while stirring at 100 rpm. At this point, a part of the charged polyethylene terephthalate reacted, the unreacted part floated in the liquid, and polystyrene and polyethylene floated on the liquid surface. Stirring was once stopped in this state, and 20 parts of the upper liquid was extracted together with polystyrene and polyethylene. As a result, polystyrene and polyethylene could be completely extracted and remained in the 0.2 part depolymerization tank.
[0022]
Further, the remaining mixture was heated to 185 ° C. and held for 4 hours with stirring at 100 rpm. As a result, polyethylene terephthalate was dissolved and the depolymerization reaction was completed.
[0023]
Stirring was stopped again, and 190 parts of the reaction solution was extracted from the bottom of the depolymerization tank. At this time, 0.2 parts of polyethylene and polystyrene remained on the surface of the liquid remaining in the depolymerization tank, while polystyrene and polyethylene were not contained at all in the extracted liquid.
[0024]
[ Reference Example 2]
In Example 1, the same operation was performed except that 120 parts were extracted from the bottom of the depolymerization tank after completion of the depolymerization reaction in a stirring state of 100 rpm. At this time, 0.2 parts of polyethylene and polystyrene remained in the liquid remaining in the depolymerization tank, while polystyrene and polyethylene were not contained at all in the extracted liquid.
[0025]
[Comparative Example 1]
In Example 2, when the same operation was performed except that the extraction amount was 190 parts, 0.1 part of polyethylene and polystyrene remained in the liquid remaining in the depolymerization tank, and also in the extracted liquid. Further, 0.1 part of polystyrene and polyethylene were contained, and the entrainment flow could not be suppressed in the depolymerization tank.
[0026]
【The invention's effect】
According to the removal method of the present invention, when recovering an active ingredient from a polyester waste containing polyethylene terephthalate as a main component, different plastics contained in the polyester waste are separated and removed in a depolymerization tank, and the next step of foreign matter is performed. Therefore, it is possible to prevent process troubles in the chemical recycling process.

Claims (4)

In a depolymerization reaction vessel in which polyalkylene terephthalate is depolymerized with alkylene glycol, polyester waste containing polyalkylene terephthalate as the main component and a different plastic other than polyalkylene terephthalate is added, and the depolymerization reaction vessel is stirred. depolymerization reaction was carried out to obtain a depolymerization reaction while, among the heterologous plastic, a light plastic specific gravity than the depolymerization reaction liquid of alkylene glycols and polyalkylene terephthalate is floated on the liquid surface, the depolymerization reaction tank after removing at least a portion of the light plastic in specific gravity from the depolymerization reaction tank by withdrawing the stopped light plastic specific gravity stirring the upper layer portion of the depolymerization reaction vessel together with the depolymerization reaction liquid obtained by the depolymerization reaction solution The polymerization reaction liquid is moved downward in the depolymerization reaction tank. For feeding to the next step from the bottom of the depolymerization reaction vessel while suppressing by stopping the stirring of the feeder included flow depolymerization reaction tank, heterogeneous plastic removal method from polyester waste.   The removal method according to claim 1, wherein the downward entrainment flow is suppressed by maintaining a liquid storage amount in the depolymerization reaction tank at a certain level or more.   The removal method according to claim 1, wherein the polyalkylene terephthalate is polyethylene terephthalate.   The removal method according to claim 1, wherein the alkylene glycol is ethylene glycol.