JP2012116779A - Method for producing polyester monomer from polyester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably producing a structural monomer from a polyester with a high yield and a low energy load.SOLUTION: The method for producing a constituent monomer of a polyester includes subsequent steps of: (a) making a polyester containing polyethylene terephthalate directly react, or after depolymerization by a polyhydric alcohol, react with a monohydric alcohol to obtain a reaction product; (b) carrying out solid-liquid separation of the reaction product into a solid component and a liquid component; (c) recovering a polyhydric alcohol and a monohydric alcohol from the liquid component; (d) making the residue of the step (c) react with a monohydric alcohol; (e) carrying out solid-liquid separation of the reaction product into a polyester constituent monomer as a solid component and a liquid component; and (f) recovering a polyhydric alcohol and a monohydric alcohol from the liquid component of the step (e). In the method, the amount of the residue of the step (f) to be charged again to the steps (a) to (e) is controlled to be less than 50 wt.% of the whole residue amount.

Description

  The present invention relates to a method for stably producing a polyester comprising polyethylene terephthalate as a main component, preferably from polyester waste, at a high yield and with a low energy load.

  Polyester, such as polyethylene terephthalate, is prone to defective products, scraps, etc. in the polymerization process, or in the process of forming into yarns or films. Therefore, it is economically preferable to collect and reuse the polyester waste), which is necessary from the viewpoint of global environmental measures. These recovered polyester wastes contain dyes, flame retardants, general waste and other plastics, and are often difficult to melt and reuse as they are. For this reason, it is preferable to separate and recover raw material monomers such as terephthalic acid, dimethyl terephthalate, and bis (2-hydroxyethyl) terephthalate, which are raw materials of the polyester, from these recovered polyester wastes. As a method for producing the raw material from polyester waste, polyester was depolymerized with ethylene glycol (hereinafter sometimes abbreviated as EG) to obtain a composition containing bis (2-hydroxyethyl) terephthalate. Thereafter, this is reacted with methanol to produce dimethyl terephthalate (hereinafter sometimes abbreviated as DMT) (see, for example, Patent Documents 1 and 2), or polyester is reacted with methanol to dimethyl terephthalate. Is known (for example, see Patent Documents 3 and 4). In these examination processes, since the reaction product becomes a slurry property, the monomer (for example, DMT) constituting the recovered polyester is solid-liquid separated from the solvent (for example, methanol or EG) and recovered on the solid side. The process to do is needed. However, on the other hand, active ingredients such as monomers and reaction intermediates for solubility are mixed into the liquid (hereinafter also abbreviated as reaction filtrate) after solid-liquid separation, which causes a decrease in yield. . In addition, it is preferable from the viewpoint of cost to recover the solvent from the reaction filtrate. However, in the known method, when the solvent is recovered from the reaction filtrate, the active component and the catalyst component are concentrated and the recovery operation causes a relatively high temperature. As a result of the progress of the polycondensation reaction, the viscosity of the reaction filtrate increases and the operability deteriorates, and the heat transfer efficiency of the heat exchanger decreases due to precipitation and adhesion of active ingredients. It is necessary to reduce the recovery rate. Further, since unnecessary components in the reaction filtrate need to be discharged out of the system, there are various problems that a large amount of active components must be discharged out of the system.

JP-A-11-302443 Japanese Patent No. 40656657 Japanese Patent No. 4008214 Japanese Patent No. 4183548

  The present invention has been made in view of the above-described background art, and its purpose is to provide a method for stably producing a monomer constituting polyethylene terephthalate from a polyester mainly composed of polyethylene terephthalate at a high yield and a low energy load. Is to provide.

According to the study by the present inventors, “in producing a monomer constituting polyethylene terephthalate from a polyester containing polyethylene terephthalate, the following steps (a) to (f):
Step (a): Either a step of obtaining a reaction product by reacting a substance obtained by depolymerizing the polyester with a polyhydric alcohol with a monohydric alcohol or a step of obtaining a reaction product by reacting the polyester with a monohydric alcohol. One reaction step Step (b): Step of separating the reaction product in Step (a) into a solid component and a liquid component Step (c): Liquid component recovered by solid-liquid separation in Step (b) Step (d) for recovering part or all of the polyhydric alcohol and monohydric alcohol from the liquid component recovered by solid-liquid separation in step (b), and part or all of the polyhydric alcohol and monohydric alcohol. Step (e) for reacting the residue after recovering the monohydric alcohol with the monohydric alcohol: Step (f) for separating the reaction product in step (d) into a solid component and a liquid component Step (e) ) Solid-liquid separation From yield the liquid component, the method comprising sequentially subjecting to a step of recovering a part or the whole of the polyhydric alcohol and monohydric alcohol,
From the liquid component recovered by the solid-liquid separation in step (f), the total amount of the residue remaining after recovering part or all of the polyhydric alcohol and monohydric alcohol to steps (a) to (e) is: The manufacturing method of the monomer which comprises the polyethylene terephthalate which uses polyester as a raw material characterized by being less than 50 weight% of the residual residue. It became possible to produce the active ingredient from the residue after recovering the solvent from the transesterification filtrate that had been conventionally discarded, and to achieve the above-mentioned object.

  According to the method for producing a monomer that constitutes a polyester using the polyester of the present invention as a raw material, the active ingredient is produced at a low energy load to improve the yield, as well as impurities contained in the reaction filtrate. Can be concentrated. By these effects, the monomer which comprises polyester from the polyester which has polyethylene terephthalate as a main component can be manufactured, suppressing a waste generation amount with a high yield and a low energy load.

  Hereinafter, an embodiment of the present invention will be described using an example, but the present invention is not limited to this example. In order to carry out the production method according to the present invention, first, a substance obtained by depolymerizing a polyester containing polyethylene terephthalate as a main component with a polyhydric alcohol is subjected to a transesterification reaction with a monohydric alcohol, It is necessary to carry out a transesterification reaction with a monohydric alcohol (step (a)). Here, containing polyethylene terephthalate as a main component means that the ratio of the weight of polyethylene terephthalate to the total weight of the polyester is preferably 80% by weight or more. More preferably, the content of polyethylene terephthalate relative to the total weight of the polyester is 90% by weight. Moreover, about polyester, the polyester obtained by collect | recovering the polyester molding products used in the manufacturing process or the market may be included. As the depolymerization reaction condition and the transesterification reaction condition, any known condition may be adopted as long as the reaction proceeds. As the polyhydric alcohol, ethylene glycol which is a raw material of polyethylene terephthalate is used. Is preferable from the viewpoint of solvent recovery. If necessary, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol (tetramethylene glycol) may be used in combination or these compounds may be used alone. As the monohydric alcohol, it is preferable to use a monohydric lower alcohol having 1 to 6 carbon atoms, more preferably methanol, ethanol or propanol, and the separation and purification as a monomer is easy and economically valuable. From the viewpoint of producing a high DMT, it is most preferable to use methanol.

  Furthermore, as a depolymerization reaction catalyst, alkali metal carbonate, alkali metal acetate, alkali metal alkoxide, alkali metal hydroxide, alkaline earth metal carbonate, alkaline earth metal acetate, alkaline earth The addition of at least one substance selected from the group consisting of metal oxides, alkaline earth metal alkoxides and alkaline earth metal hydroxides, accelerates the depolymerization reaction rate, produces a depolymerization reaction From the viewpoint of improving the yield of the product. That is, it is preferable from the viewpoint of capital investment and operability to select a catalyst species that is active even under normal pressure reaction conditions. In addition, it is preferable to use an alkali metal carbonate because it can be easily obtained at a low cost and there are few concerns about side reactions and the above-mentioned purpose can be achieved at a high numerical level. Furthermore, it is preferable to use a transesterification catalyst when performing the transesterification reaction in order to increase the reaction rate and improve the yield. Also in the transesterification reaction catalyst, it is preferable to use an alkali metal carbonate from the viewpoint that it can be easily obtained at low cost and has few concerns such as side reactions and can achieve the above-mentioned object at a high numerical level. .

  Next, the reaction product obtained by the transesterification reaction with the monohydric alcohol obtained by the above operation is solid-liquid separated into a solid component and a liquid component (step (b)). As a method of solid-liquid separation, any known condition may be adopted as long as it can be separated into a solid component and a liquid component. Examples of solid-liquid separation operations include, for example, filtration operations and centrifugation operations. The reaction filtrate component obtained by solid-liquid separation contains surplus monohydric alcohol and polyhydric alcohol used in the depolymerization reaction and transesterification reaction, as well as polyhydric alcohol produced by the depolymerization reaction. It is preferable in terms of cost to recover these solvents (step (c)). Polyhydric alcohol can also be used as a raw material for polyester. Examples of the recovery method include membrane separation and distillation, but it is preferable to perform a distillation operation because miscellaneous impurities are often mixed in the recycling process. In addition to unnecessary components that need to be discharged (discarded) out of the system, the residue obtained by recovering the solvent from the reaction filtrate contains monomer components and active components such as reaction intermediates in depolymerization and transesterification reactions. Therefore, it is preferable to recover the active ingredient from these residues. Specifically, these residues are reacted with a monohydric alcohol to produce a monomer component (step (d)). The active ingredients (reaction intermediates, etc.) in these residues show good reactivity with monohydric alcohols, so that monomers are formed only by mixing with monohydric alcohols. From the viewpoint of reaction equilibrium, 1 part by weight of residue It is preferable to mix and react with a monohydric alcohol of 0.5 parts by weight or more, more preferably 1 part by weight or more. From the viewpoint of equipment, the reaction is preferably carried out at normal pressure, and the reaction temperature is preferably 50 ° C. or higher from the viewpoint of reaction rate. Furthermore, from the viewpoint of promoting the reaction, as a reaction catalyst, alkali metal carbonate, alkali metal acetate, alkali metal alkoxide, alkali metal hydroxide, alkaline earth metal carbonate, alkaline earth metal acetate It is preferable to add at least one substance selected from the group consisting of an alkaline earth metal oxide, an alkaline earth metal alkoxide, and an alkaline earth metal hydroxide.

  The reaction filtrate, which is the liquid component separated in step (b), is particularly preferably used as a method for adding the catalyst from the viewpoint of avoiding an increase in unnecessary substances (waste) such as metal salts due to the addition of a new catalyst. The residue is mixed, and the reaction is promoted by the action of a non-deactivated catalyst remaining in the reaction filtrate. The reaction product produced by this reaction has a slurry property, and the solid main component is DMT. Therefore, it is preferable to recover the DMT by solid-liquid separation of the reaction product (step (e)). Examples of this solid-liquid separation operation include, for example, a filtration operation and a centrifugation operation. In addition, the mother liquor components after solid-liquid separation include solvent components such as monohydric alcohols and polyhydric alcohols and unnecessary materials such as metal salts such as catalyst residues. Therefore, it is preferable to recover part or all of the solvent component from the mother liquor component (step (f)). These solvents are monohydric alcohols or polyhydric alcohols used or generated in the previous step, and it is preferable in terms of cost to recover these solvents. Polyhydric alcohol can also be used as a raw material for polyester. Examples of the recovery method include membrane separation and distillation. In addition, the residue after recovering the solvent contains a small amount of active ingredients. However, since unnecessary substances are concentrated due to the effects of this report, from the viewpoint of maintaining product quality and ensuring reactivity, It is preferable to remove part or all of the system outside the system and discard it. That is, it is preferable that the total amount of residue to be recharged in any of steps (a) to (f) is less than 50 weight percent, particularly preferably less than 30 weight percent of the generated residue. Moreover, there is no problem even if all of these residues are removed from the system. Here, the total amount of residue is, for example, 2 parts by weight in the step (a) and 3 parts by weight in the case of 3 parts by weight in the step (b).

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

[Example 1]
200 g of polyethylene terephthalate (hereinafter sometimes abbreviated as PET) chip, EG: 800 g, 4 g of sodium carbonate are added and reacted in a separable flask with stirring at 190 to 200 ° C. under normal pressure for 4 hours. (A) was obtained. After completion of the reaction, the pressure was reduced to 40.0 kPa (300 mmHg), and 602 g of a light boiling component (A) containing EG as a main component was distilled off from the reaction product (A). Next, 400 g of methanol was gradually added to the residue (c) obtained by distilling off the light boiling component (a) from the product (a). Furthermore, after adding 1.4 g of sodium carbonate as a catalyst, it was made to react for 1.0 hour on 70-80 degreeC and the conditions of a normal pressure. After completion of the reaction, the mixture was allowed to cool and the temperature of the transesterification product (d) was adjusted to 40 ° C. The product (d) at 40 ° C. was subjected to solid-liquid separation by filtration to obtain a solid (cake) and a filtrate (e), respectively. Thereafter, 400 g of the filtrate (e) was collected and heated in a distillation apparatus having 10 theoretical plates under normal pressure until the bottom temperature reached 180 ° C., and 262 g of the first fraction containing methanol as a main component. Was recovered. Furthermore, after cooling the tower bottom temperature to 120 ° C., the pressure was changed to 13.3 kPa (100 mmHg), heating was started again, and 32.2 g of the second fraction mainly composed of methanol and ethylene glycol was recovered. Further, heating was continued, and 128 g of the third fraction containing ethylene glycol as a main component was recovered. Here, 20 g was collected from the residue (g) remaining at the bottom of the tower, 20 g of methanol and 0.2 g of sodium carbonate as a catalyst were added thereto, and then 1.0 to 1.0 at 70 to 80 ° C. under normal pressure. Reacted for hours. After completion of the reaction, the mixture was allowed to cool and the temperature of the transesterification product (ki) was adjusted to 40 ° C. The product (ki) having a temperature of 40 ° C. was subjected to solid-liquid separation by filtration to obtain a cake and a filtrate, respectively. When cake (ku) was dried with a steam dryer at 90 to 100 ° C. for 1 day, 2.1 g of DMT was recovered.

[Example 2]
In Example 1, 20 g was collected from the recovered residue (f), 50 g of the filtrate (e) recovered in Example 1 was added thereto, and then 1.0 hour under conditions of 75 to 85 ° C. and normal pressure. Reacted. After completion of the reaction, the mixture was allowed to cool and the temperature of the transesterification product (ki) was adjusted to 40 ° C. The product (ku) having a temperature of 40 ° C. was subjected to solid-liquid separation by filtration to obtain a cake (ke) and a filtrate, respectively. When cake (ke) was dried with a steam dryer at 90 to 100 ° C. for 1 day, 2.9 g of DMT was recovered.

  According to the method for producing a monomer constituting polyethylene terephthalate from the polyester of the present invention, the monomer component can be recovered with a low energy load to improve the yield. In addition, it is possible to concentrate impurities contained in the reaction filtrate. By these effects, the monomer which comprises polyester from the polyester which has polyethylene terephthalate as a main component can be collect | recovered, suppressing a waste generation amount with a high yield and a low energy load. This is very significant in terms of industry.

Claims (2)

When manufacturing the monomer which comprises a polyethylene terephthalate from the polyester containing a polyethylene terephthalate, the following process (a)-(f):
Step (a): Either a step of obtaining a reaction product by reacting a substance obtained by depolymerizing the polyester with a polyhydric alcohol with a monohydric alcohol or a step of obtaining a reaction product by reacting the polyester with a monohydric alcohol. One reaction step Step (b): Step of separating the reaction product in Step (a) into a solid component and a liquid component Step (c): Liquid component recovered by solid-liquid separation in Step (b) Step (d) for recovering part or all of the polyhydric alcohol and monohydric alcohol from the liquid component recovered by solid-liquid separation in step (b), and part or all of the polyhydric alcohol and monohydric alcohol. Step (e) for reacting the residue after recovering the monohydric alcohol with the monohydric alcohol: Step (f) for separating the reaction product in step (d) into a solid component and a liquid component Step (e) ) Solid-liquid separation From yield the liquid component, the method comprising sequentially subjecting to a step of recovering a part or the whole of the polyhydric alcohol and monohydric alcohol,
From the liquid component recovered by the solid-liquid separation in step (f), the total amount of the residue remaining after recovering part or all of the polyhydric alcohol and monohydric alcohol to steps (a) to (e) is: The manufacturing method of the monomer which comprises the polyethylene terephthalate which uses polyester as a raw material characterized by being less than 50 weight% of the residual residue.   2. Polyethylene terephthalate using polyester as a raw material according to claim 1, wherein part or all of the monohydric alcohol to be reacted with the residue in step (d) is a liquid component separated in step (b) The manufacturing method of the monomer which comprises.