JP2005002161A - Method for removing different kind of plastic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preventing troubles in a recycling process, in recovering an effective component from a polyester waste containing as the main component a polyalkylene terephthalate, by separating and removing a different kind of plastic contained in the polyester waste in a depolymerization reaction tank and omitting liquid-feeding to the next process. <P>SOLUTION: The method for removing the different kind of plastic from the polyester waste comprises removing the polyester waste, which is mainly composed of the polyalkylene terephthalate and contains the different kind of plastic from the polyalkylene terephthalate, where the polyester waste is successively subjected to the following steps (1) and (2): (1) a step for throwing the polyester waste into a depolymerization reaction step for depolymerization by a polyalkylene glycol to cause a part or the whole of the polyalkylene terephthalate to be depolymerized to obtain a depolymerization liquid; and (2) a step for drawing out the different kind of plastic which has a smaller specific gravity than the depolymerization liquid and floats in the vicinity of the liquid level of the depolymerization liquid while keeping the temperature of the depolymerization liquid within the range of 120-180°C at the time of removing the different kind of plastic in a solid state contained in the depolymerization liquid out of the system. <P>COPYRIGHT: (C)2005,JPO&NCIPI

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 present invention relates to a method for preventing a process trouble in a recycling process by separating and removing different plastics contained in polyester waste in a depolymerization tank.
[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, the used polyethylene terephthalate (especially used beverage bottles) generated in large quantities with the increase in the amount used as described above, and the quality inadequate products generated in the polyethylene terephthalate manufacturing stage (hereinafter referred to as “polyester”). The process of “waste” may be abbreviated as a big social problem.
[0004]
In order to solve the above problems, so-called chemical recycling is effective, in which polyester waste is converted and recovered into a monomer, and polyethylene terephthalate is produced and reused by a polymerization reaction using the monomer as a raw material. In this method, the compound can be recycled and reused without any loss, and resources can be reused.
[0005]
That is, these recovered polyester wastes are depolymerized with ethylene glycol, then transesterified with methanol, and further separated and purified to be recovered as dimethyl terephthalate and ethylene glycol for effective use of resources, total This leads to cost reduction.
[0006]
For example, an excessive amount of ethylene glycol is added to polyethylene terephthalate and heated, and a depolymerization reaction yields a mixture of bis (β-hydroxyethyl) terephthalate and a low polymer containing a β-hydroxyethyl ester group at the end. A method for recovering dimethyl terephthalate by adding an excess of methanol and carrying out a substitution esterification reaction in the presence of a catalyst is described (for example, see Patent Document 1).
[0007]
However, 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.
[0008]
On the other hand, if the foreign matter cannot be completely removed, the foreign matter will be mixed in the recycling process, and the foreign matter may partially melt at a solid or high temperature condition, causing adhesion to equipment in the recycling process or blockage of piping. Trouble occurs.
[0009]
In addition, a method for separating and recovering dimethyl terephthalate and ethylene glycol from polyester waste has been proposed (see, for example, Patent Document 2). The patent document proposes a method of recovering dimethyl terephthalate and ethylene glycol by depolymerizing a polyester waste containing a foreign component with alkylene glycol and then transesterifying with methanol. Further, the patent document proposes a method of removing solid foreign matters floating on the surface of the solution, for example, polyolefin, by solid-state separation, among solid foreign matters contained in the obtained depolymerization reaction solution. Has been. The present inventors have proposed a foreign matter removal method as in Patent Document 2, but nevertheless, when removing the foreign matter floating on the surface even when the method is used, and when separating the solution from the foreign matter However, there are still problems such as foreign matter adhering to and blocking the device and piping.
[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 with the prior art described above, and eliminate the need to send to the next process when separating and removing different plastics contained in polyester waste in a depolymerization tank. The object is to provide a method for preventing troubles in the 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 present invention
Polyalkylene terephthalate is a main component, and polyalkylene terephthalate is a method for removing different plastics from polyester waste containing different plastics, and sequentially passing the following steps (1) and (2). This is a method for removing different types of plastics.
(1) A step of putting into a depolymerization reaction step of depolymerizing with an alkylene glycol and depolymerizing a part or all of the polyalkylene terephthalate to obtain a depolymerization solution.
(2) When the solid different plastic contained in the depolymerization liquid is removed from the system, the temperature of the depolymerization liquid is controlled in the range of 120 ° C. to 180 ° C. A step of extracting a different kind of plastic having a specific gravity smaller than that of the depolymerization solution floating on the surface.
[0014]
In this invention, the removal method for controlling the temperature of the depolymerization solution in the range of 130 ° C. to 170 ° C., the removal method in which the alkylene glycol is ethylene glycol, and the polyalkylene terephthalate contained as a main component in the polyester waste is polyethylene. A removal method that is terephthalate and a removal method that is derived from a PET bottle recovered from polyethylene terephthalate are preferred.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to examples. In addition, these Examples etc. and description illustrate this invention, and do not restrict | limit the scope of the present invention. It goes without saying that other embodiments may belong to the category of the present invention as long as they match the gist of the present invention.
[0016]
In the removal method of the present invention, polyalkylene terephthalate refers to polyalkylene terephthalate that can be obtained from terephthalic acid or a derivative thereof and alkylene glycol by a usual production method. Further, “based on polyalkylene terephthalate” means that 80% by weight or more of the polyester waste described later is polyalkylene terephthalate. Polyester in the polyester waste includes polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate and the like, but polyethylene terephthalate is often used and preferably used from the viewpoint of market distribution and economy. Furthermore, in the removal method of the present invention, the following two steps can be sequentially passed.
[0017]
That is, the first step is a step in which a polyester waste is depolymerized with alkylene glycol, and the polyalkylene glycol is partially or completely depolymerized to form a depolymerization solution. In general, it is preferable that polyester waste is pretreated such as washing with water and coarsely pulverized to have a shape suitable for the depolymerization reaction and then put into the depolymerization reaction tank. The removal method of the present invention can be applied to either a continuous or batch system. In the case of carrying out in a batch system, the polyester waste is subjected to a depolymerization reaction in a solution containing an alkylene glycol containing a polyester depolymerization catalyst as a main component to obtain a depolymerization solution. The depolymerization catalyst includes at least one selected from the group consisting of alkali metal carbonates, hydroxides or acetates, alkaline earth metal carbonates, hydroxides or acetates, or manganese or zinc acetates. It is preferable to use a compound selected from one kind. Moreover, it is preferable to use ethylene glycol as the alkylene glycol used in this case. In order to promote the reaction, the depolymerization reaction tank is preferably provided with a stirrer or a self-circulation line of the depolymerization reaction tank, and the depolymerization proceeds while circulating the alkylene glycol or the depolymerization liquid.
[0018]
During this depolymerization reaction, among the dissimilar plastics contained in the polyester waste, plastics mainly composed of polyolefin such as polyethylene, polypropylene, polystyrene, etc., which have a low specific gravity with respect to the depolymerization liquid, float near the liquid surface of the depolymerization liquid. To do. Normally, different types of plastics with a specific gravity that is considerably smaller than the depolymerization solution rise and float to the surface of the depolymerization solution to such an extent that it can be easily distinguished by visual observation. It may not be said that it is floating. Further, when the amount of different plastics is larger than the liquid surface area, the different plastics may float in a state where the different plastics are crowded with respect to the narrow liquid surface. In such a case, removing the dissimilar plastic floating on the liquid level will cause the liquid level to rise and float, but because there is a dissimilar plastic on the liquid level, it may not be possible to rise to the liquid level as a result. . “Floating in the vicinity of the liquid surface” is due to these reasons, and as a result, removal of dissimilar plastics that are not floating on the liquid surface is also included in the present invention.
[0019]
These floating dissimilar plastics are removed by drawing out at the same time as the depolymerization solution in the upper layer. About this removal step, even when the depolymerization reaction of the polyalkylene terephthalate is not completely completed, even if it is in a slurry state in which the different plastics float enough to be separated or unreacted polyalkylene terephthalate remains. It can be implemented. That is, it can be carried out even when all of the polyalkylene terephthalate has undergone a depolymerization reaction or a part of the polyalkylene terephthalate has undergone a depolymerization reaction.
[0020]
In the next second step, the surface of the outer depolymerization solution is controlled while controlling the temperature of the external polymerization solution to be in the range of 120 to 180 ° C. when the solid different plastic contained in the depolymerization solution is removed from the system. This is a step of extracting a dissimilar plastic having a specific gravity smaller than that of the depolymerization solution floating in the vicinity. When separating the depolymerization liquid and the foreign matter from the depolymerization reaction tank, it is necessary to keep the temperature of the depolymerization liquid at 120 to 180 ° C. When the temperature exceeds 180 ° C., the viscosity of the different plastic increases, so that fusion occurs and it becomes difficult to extract the suspended matter from the depolymerization reaction tank. Preferably, the temperature of the depolymerization solution is controlled in the range of 130 ° C to 170 ° C. If this temperature range is maintained, the viscosity of dissimilar plastics composed mainly of polyolefin can be reduced, and the dissimilar plastics can be kept in a state that does not decrease the viscosity of the depolymerization solution while curing the dissimilar plastics. It is possible to prevent troubles in the subsequent steps. Also, when the depolymerization solution is sent to the next step, it is preferable to keep this temperature because the solution can be sent easily. In the depolymerization reaction tank, it is generally preferable to circulate the liquid in the depolymerization reaction tank using a stirrer, a circulation pump, or the like in order to promote the reaction.
[0021]
In the depolymerization reaction tank, the depolymerization reaction does not necessarily need to be carried out completely. Therefore, the depolymerization reaction can be applied even when unreacted polyalkylene terephthalate remains at the time of removal. 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.
[0022]
【Example】
The contents of the present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto. In addition, each value in an Example was calculated | required according to the following method.
[0023]
[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 put into a dereaction polymerization tank and heated to 170 ° C. with stirring at 100 rpm. The state was kept for 1 hour. A part of the polyethylene terephthalate charged at this time reacted, the unreacted product was in a state of floating in the depolymerization solution, and polystyrene and polyethylene floated on small particles on the surface of the depolymerization solution. Stirring was once stopped in this state, and when 20 parts of the upper depolymerization liquid close to the liquid surface was extracted together with polystyrene and polyethylene, 3.8 parts of polystyrene and polyethylene were extracted and the liquid remaining in the depolymerization tank was removed. Only 0.2 parts of polyethylene and polystyrene remained. In addition, problems such as polyethylene or polystyrene adhering to the pipe and clogging of the pipe did not occur.
[0024]
[Comparative 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 put into a dereaction polymerization tank and heated to 185 ° C. with stirring at 100 rpm. Furthermore, when the state was kept at 100 rpm with stirring for 4 hours, the polyethylene terephthalate was dissolved and the depolymerization reaction was completed. At this time, the charged polystyrene and polyethylene floated on the surface of the depolymerization solution, but because of their increased viscosity, they fused together to form a large lump. In this state, stirring is once stopped, and when 20 parts of the upper depolymerization liquid close to the liquid surface is extracted together with polystyrene and polyethylene, the depolymerization liquid remaining in the dereaction polymerization tank cannot be extracted completely. Two parts remained.
[0025]
【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 having a small specific gravity contained in the polyester waste are separated and removed in a depolymerization tank. It is possible to eliminate sending to the process and prevent process troubles in the recycling process.

Claims (5)

Polyalkylene terephthalate is a main component, and polyalkylene terephthalate is a method for removing dissimilar plastics from polyester waste containing dissimilar plastics, and sequentially passing the following steps (1) and (2). A method for removing different types of plastics.
(1) A step of putting into a depolymerization reaction step of depolymerizing with an alkylene glycol and depolymerizing a part or all of the polyalkylene terephthalate to obtain a depolymerization solution.
(2) When the solid different plastic contained in the depolymerization liquid is removed from the system, the temperature of the depolymerization liquid is controlled in the range of 120 ° C. to 180 ° C. A step of extracting a different kind of plastic having a specific gravity smaller than that of the depolymerization solution floating on the surface. The removal method according to claim 1, wherein the temperature of the depolymerization solution is controlled in a range of 130 ° C to 170 ° C. The removal method according to claim 1 or 2, wherein the alkylene glycol is ethylene glycol. The removal method according to claim 1, wherein the polyalkylene terephthalate contained as a main component in the polyester waste is polyethylene terephthalate. The removal method according to claim 4, wherein the polyethylene terephthalate is derived from a recovered PET bottle.