JP4187979B2 - Method for treating ethylene glycol recovered distillation residue - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating an ethylene glycol recovery distillation still residue. More specifically, crude ethylene glycol, in particular, bis (2-hydroxyethyl) terephthalate ester of diethylene glycol contained in the distillation distillation residue of crude ethylene glycol generated in the process of producing bis (2-hydroxyethyl) terephthalate from polyethylene terephthalate. ) It relates to a processing method for converting to terephthalate.
[0002]
[Prior art]
Polyethylene terephthalate is used in various molded product fields such as bottles, fibers, and films because it is excellent in mechanical properties, thermal properties, chemical properties, and the like. Polyethylene terephthalate is usually a reaction product mainly composed of bis (2-hydroxyethyl) terephthalate and its oligomer by esterification of terephthalic acid and ethylene glycol or transesterification of dimethyl terephthalate and ethylene glycol. Further, it is produced by polycondensation. At that time, for the purpose of satisfying the required properties according to the application, the third component is copolymerized, or a property-imparting agent such as a colorant, a stabilizer, an antistatic agent, an ultraviolet absorber or the like is added. ing.
[0003]
In recent years, the disposal of polyethylene terephthalate molded articles, particularly polyethylene terephthalate bottles (hereinafter referred to as PET bottles), has become a social problem as it deteriorates the environment, and studies on recovery and reuse are underway.
[0004]
As one of the methods, a polyethylene terephthalate molded product, particularly a PET bottle, is collected, pulverized into chips or flakes, depolymerized (glycolysis) using ethylene glycol, and separated and purified from the resulting reaction product. Thus, there is a method of obtaining polyethylene terephthalate by obtaining high-purity bis (2-hydroxyethyl) terephthalate and further polycondensing this high-purity bis (2-hydroxyethyl) terephthalate.
[0005]
As a result of studying this method, the present inventors have found that the reaction product obtained by glycolysis of polyethylene terephthalate has impurities as the above-mentioned property-imparting agent (for example, a colored product), mainly an ion or polymer produced by a reaction catalyst or a stabilizer. Including diethylene glycol by-produced at the time of glycolysis, terephthalic acid ester of diethylene glycol, and other resin (for example, bottle cap, label, etc.) that is attached to or adhered to the molded product. It has been found that high-purity bis (2-hydroxyethyl) terephthalate can be produced by removing by combining purification techniques such as ion, crystallization, molecular distillation, etc. (JP 2000-169623 A, International Publication WO01 / 10812).
[0006]
In this purification process, crude ethylene glycol containing impurities and active ingredients is generated, but this crude ethylene glycol is subjected to distillation purification, and a distillation residue consisting mainly of purified ethylene glycol and high-boiling components (residue remaining in the ethylene glycol recovery distillation kettle). ). This purified ethylene glycol is usually recycled as a raw material for the glycolysis.
[0007]
Most of the distillation residue is bis (2-hydroxyethyl) terephthalate (hereinafter sometimes referred to as BHET), oligomer, terephthalic acid ester of diethylene glycol (hereinafter sometimes referred to as DEG ester), monoethylene glycol terephthalate (hereinafter referred to as “DEH ester”). , Sometimes referred to as MHET ester), ethylene glycol, diethylene glycol, and impurities accompanying the raw material.
[0008]
By the way, when the DEG ester is contained in the product bis (2-hydroxyethyl) terephthalate, it directly affects the content of diethylene glycol in the polyethylene terephthalate polycondensed from the product bis (2-hydroxyethyl) terephthalate. Become. Polyethylene terephthalate having a high content of diethylene glycol is not preferable because it decreases physical properties such as a decrease in melting point, coloring, and crystallization speed.
[0009]
Therefore, the residue containing DEG ester and free diethylene glycol is difficult to return to the production process of bis (2-hydroxyethyl) terephthalate as it is, and has been disposed as industrial waste until now. There was only a way to do it.
[0010]
However, since the residue contains a large amount of active ingredients, discarding it as it is leads to a decrease in the yield of the product bis (2-hydroxyethyl) terephthalate, an increase in production cost, and the like, which is extremely uneconomical.
[0011]
[Problems to be solved by the invention]
If the present inventors can convert the DEG ester contained in the residue into bis (2-hydroxyethyl) terephthalate as an active ingredient and remove free diethylene glycol, the residue does not need to be disposed of, and bis ( The inventors have paid attention to the fact that the yield of 2-hydroxyethyl) terephthalate can be remarkably increased, and as a result of intensive studies on the method, the present invention has been achieved.
[0012]
Accordingly, an object of the present invention is to provide a method for converting DEG ester contained in an ethylene glycol recovery distillation residue into bis (2-hydroxyethyl) terephthalate as an active ingredient and effectively utilizing the distillation residue. .
[0013]
Another object of the present invention is to subject the crude ethylene glycol generated in the production process of bis (2-hydroxyethyl) terephthalate to distillation purification, and distilling the residue in the distillation kettle, the DEG ester contained therein as an active ingredient. After converting to bis (2-hydroxyethyl) terephthalate, return to the manufacturing process of bis (2-hydroxyethyl) terephthalate to provide a method that contributes to increasing the yield of product bis (2-hydroxyethyl) terephthalate There is to do.
[0014]
Still other objects and advantages of the present invention will become apparent from the following description.
[0015]
[Means for Solving the Problems]
According to the present invention, the above-mentioned objects and advantages of the present invention are as follows. The ethylene glycol recovery distillation kettle residue containing at least diethylene glycol terephthalic acid ester as the solid content is from 2 to 20 based on the total solid content in the distillation kettle residue. Add ethylene glycol by weight and 0.1 to 1.0% by weight of a transesterification catalyst, and carry out a transesterification reaction of the terephthalic acid ester with ethylene glycol under heating to obtain bis (2-hydroxyethyl) terephthalate and diethylene glycol. This is achieved by a method for treating a residue of an ethylene glycol recovery distillation kettle characterized by evaporating and distilling the produced diethylene glycol together with ethylene glycol under a pressure of normal pressure to 0.5 MPa.
[0016]
In a further preferred embodiment of the present invention, during the transesterification reaction, ethylene glycol in an amount substantially equal to the distillate amount is continuously added while diethylene glycol is distilled together with ethylene glycol while adjusting the pressure to normal pressure to 0.5 MPa. Or a new supply intermittently to keep the solid content concentration of the reaction liquid substantially constant; the content of terephthalic acid ester of diethylene glycol in the residue of the distillation still is 10 to 30% by weight; The time for the exchange reaction is 0.5 to 3 hours, and the ethylene glycol in which the recovered distillation kettle residue is generated by the distillation purification process is obtained from the reaction product obtained by depolymerizing polyethylene terephthalate using ethylene glycol. (Hydroxyethyl) terephthalate was produced in the process of purification and separation, etc. For free.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The distillation still residue in the present invention is a distillation residue containing at least diethylene glycol terephthalic acid ester (DEG ester) as a solid content, which is taken out by distillation purification of crude ethylene glycol. The content of DEG ester in the distillation residue is preferably 10 to 30% by weight. This crude ethylene glycol is generated, for example, in the process of purifying and separating bis (2-hydroxyethyl) terephthalate from a reaction product obtained by glycolysis of polyethylene terephthalate with ethylene glycol.
[0018]
The polyethylene terephthalate is a used molded product made of polyethylene terephthalate, for example, a bottle, fiber, film, or the like, or a collection of polyethylene terephthalate that did not become a product due to poor molding or poor quality, for example, a small amount, for example, 10 mol% or less, Preferably, it may be copolymerized with 7 mol% or less of a third component such as isophthalic acid or produced by adding a property-imparting agent.
[0019]
Examples of a method for depolymerizing the polyethylene terephthalate with an excess of ethylene glycol include methods described in, for example, JP 2001-48837 A, JP 2000-53802 A, and International Publication WO 01/10812. Can be used. And, as a method for obtaining purified bis (2-hydroxyethyl) terephthalate by subjecting the reaction product obtained by this depolymerization to purification treatment such as decolorization treatment, deionization treatment, crystallization purification treatment, distillation treatment, etc. For example, methods described in JP 2001-48837 A, International Publication WO 01/10812, and the like can be used.
[0020]
For example, 3 to 10 times by weight of ethylene glycol is added to polyethylene terephthalate, and the mixture is heated and reacted (depolymerized) at a temperature of 220 to 270 ° C. and a pressure of normal pressure to 0.7 MPa. High-purity purified bis (2-hydroxyethyl) terephthalate can be obtained by performing decolorization adsorption treatment for removing components, deionization treatment for removing cations and anions, crystallization purification treatment, and purification treatment for molecular distillation. In this purification process, ethylene glycol acts as a solvent. The crude ethylene glycol generated by this treatment is usually purified and recycled to the production process of the bis (2-hydroxyethyl) terephthalate. During this time, a part of ethylene glycol is converted to diethylene glycol by thermal history, and a part of it is present as a DEG ester by transesterification with bis (2-hydroxyethyl) terephthalate.
[0021]
In the process of producing bis (2-hydroxyethyl) terephthalate, some discharge to the outside of the system is necessary to prevent accumulation of impurities in the production process. It is also used as a solvent for the removal operation, and a part of it needs to be subjected to a purification treatment of ethylene glycol to remove diethylene glycol having a boiling point higher than that of ethylene glycol.
[0022]
Thus, in the glycolysis and purification treatment step, diethylene glycol is by-produced by heat condensation of ethylene glycol. This diethylene glycol is combined with a terephthalic acid component to form a DEG ester. For this reason, the crude ethylene glycol generated in the purification process contains the DEG ester produced in the above step in a concentrated form, and it is necessary to remove it.
[0023]
Here, the terephthalic acid ester (DEG ester) of diethylene glycol is one in which diethylene glycol is ester-bonded to at least one carboxyl group of terephthalic acid, and diethylene glycol is mainly ester-bonded to one carboxyl group of terephthalic acid. It consists of an ester in which ethylene glycol is ester-bonded to a carboxyl group (ethylene glycol / diethylene glycol terephthalate).
[0024]
Crude ethylene glycol generated in this purification treatment is subjected to distillation purification treatment to be divided into purified ethylene glycol and distillation residue as the residue of the kettle, and the purified ethylene glycol is again produced in a bis (2-hydroxyethyl) terephthalate production process, for example, Returned to the polymerization process. The crude ethylene glycol can be distilled and purified by a conventionally known method such as a vacuum distillation method. For example, crude ethylene glycol can be distilled and purified by a method in which low-boiling components such as moisture are first distilled off and then ethylene glycol is distilled off using the same distillation column or another distillation column. In this case, the residue taken out as a residue can be used as it is in the method of the present invention. However, in some cases, the residue may be further subjected to a treatment for evaporating and removing free diethylene glycol before being used in the method of the present invention. Good.
[0025]
The distillation residue depends on distillation conditions, but usually 15 to 25% DEG ester, 50 to 60% BHET, 10 to 20% ethylene glycol, 5 to 10% diethylene glycol, 2 to 5% by weight. And 0.1 to 0.5% of isophthalic acid ester and the like. Among these, components other than diethylene glycol, DEG ester and isophthalate ester (ie, BHET, oligomer and ethylene glycol) can be used as active ingredients, and even if they are returned to the bis (2-hydroxyethyl) terephthalate production process, there will be no effect on product quality. It is something that does not give.
[0026]
In the present invention, the DEG ester present in the distillation residue is transesterified with an excess of ethylene glycol in the presence of a transesterification catalyst, and the diethylene glycol component of the DEG ester is replaced with the ethylene glycol component to liberate diethylene glycol. By evaporating (DEG) together with ethylene glycol (EG), distilling it out of the system, and supplying new EG instead, ethylene glycol ester of terephthalic acid (hereinafter, referred to as BHET having a small amount of DEG as a main component) EG ester), and by recycling to the bis (2-hydroxyethyl) terephthalate production process, waste can be reduced and process yield can be improved.
[0027]
The transesterification reaction in the present invention is preferably 2 to 20 times by weight, more preferably 3 to 10 times by weight, and further preferably 4 to 8 times by weight of ethylene glycol (EG) with respect to the total solid weight in the distillation residue. ) And preferably 0.1 to 1.0% by weight, more preferably 0.2 to 0.5% by weight of transesterification catalyst, these are mixed with the distillation residue and heated under, for example, atmospheric pressure to EG is boiled and evaporated under a pressure of 0.5 MPa, preferably 0.1 to 0.2 MPa. At that time, it is preferable to maintain an almost constant solid content concentration in the reaction solution by adding an amount of EG corresponding to the evaporation amount. Thereby, transesterification can be performed efficiently. In addition, by this evaporation, free diethylene glycol is also evaporated together with ethylene glycol at a rate proportional to the partial pressure and distilled out of the system. The reaction time is preferably 0.5 to 3 hours, more preferably 1 to 2 hours. This transesterification reaction may be carried out batchwise or continuously. When it is carried out continuously, the residence time of the reaction solution is preferably 0.5 to 3 hours, more preferably 1 to 2 hours. By this transesterification reaction, the content of the DEG ester can be preferably 5% by weight or less, more preferably 4% by weight or less.
[0028]
As the transesterification catalyst, a known catalyst can be used. Preferred examples include acetates such as cobalt acetate, zinc acetate and manganese acetate, and alkali metal compounds such as sodium hydroxide and sodium methylate. The activity of these catalysts varies depending on the type, but the amount used corresponding to the catalyst activity may be determined in the range of 0.1 to 1.0% by weight. In addition, it is desirable in terms of process control to use the same type of catalyst as the depolymerization catalyst used in the bis (2-hydroxyethyl) terephthalate production process. Further, those that greatly increase the load of decation treatment and those that have low deionization properties are not preferred. Incidentally, a catalyst in which the conversion of the DEG ester into bis (2-hydroxyethyl) terephthalate smoothly proceeds is desirable, and the use of heavy metals must naturally be avoided.
[0029]
The amount of DEG ester in the distillation residue varies depending on the amount of free diethylene glycol (DEG) in crude ethylene glycol subjected to distillation purification, pH, residence time of the ethylene glycol recovery and purification system, etc. Increases when the acidity is low and the acidity is high, or when the residence time is long.
[0030]
In this connection, crude ethylene glycol is supplied to the first distillation column to remove low-boiling substances such as moisture from the top of the column, and the bottom of the column is supplied to the second distillation column and purified from the top of the second distillation column. In the method of supplying the liquid extracted from the bottom of the column to the concentrator and evaporating and recovering the remaining ethylene glycol and diethylene glycol, diethylene glycol having a boiling point higher than that of ethylene glycol is bis (2-hydroxyethyl) in the residue. Due to the transesterification reaction with terephthalate, the DEG ester content is increased due to the transition to DEG ester.
[0031]
In the present invention, it is necessary to carry out the transesterification using a transesterification catalyst and a large amount of ethylene glycol in order to advance this DEG ester production reaction in the reverse direction.
[0032]
In the present invention, the transesterification reaction may be carried out batchwise or continuously, and the vapor evaporated from the transesterification reactor is directly supplied to an ethylene glycol distillation column or once condensed by a condenser. After that, it may be mixed with crude ethylene glycol and used as a purified ethylene glycol feed solution.
[0033]
The transesterification reaction is desirably carried out continuously if the purification of the crude ethylene glycol is carried out continuously, and batchwise if it is carried out batchwise.
[0034]
In the present invention, the transesterification product in an amount commensurate with the remaining amount of the ethylene glycol recovery distillation kettle supplied to the transesterification reactor is withdrawn from the reactor to produce bis (2-hydroxyethyl) terephthalate. It is preferable to return to the step before the deionization treatment step in the method described in International Publication WO01 / 10812. In particular, it is preferable to return to the depolymerization reaction step. In this case, the transesterification catalyst can also be used as the depolymerization catalyst.
[0035]
In the present invention, the transesterification reaction product taken out from the reactor is further purified by subjecting it to a crystallization purification treatment, thereby producing bis (2-hydroxyethyl) terephthalate of diethylene glycol, DEG ester and isophthalic acid ester. Recycling amount can be greatly reduced. This is due to the fact that the solubility of diethylene glycol, DEG ester and isophthalic acid ester in ethylene glycol is several times higher than that of bis (2-hydroxyethyl) terephthalate or oligomer.
[0036]
This crystallization treatment is preferably performed for 3 to 7 hours, more preferably 3.5 to 5 hours while cooling the reaction solution to 0 to 40 ° C, more preferably 10 to 30 ° C. Filtration can be performed by a conventionally known method. In this crystallization treatment, diethylene glycol, DEG ester and isophthalic acid ester are mainly present on the filtrate side, and the content of DEG ester in the filtered cake can be 3% by weight or less, further 2% by weight or less. The filtered cake is preferably returned to the step before the deionization treatment step of the bis (2-hydroxyethyl) terephthalate production step. In particular, it is preferable to return to the depolymerization reaction step.
[0037]
According to the present invention, DEG ester in the distillation residue can be converted into EG ester, particularly bis (2-hydroxyethyl) terephthalate, and the amount of diethylene glycol can be reduced. Therefore, the efficiency of the method for producing a high purity bis (2-hydroxyethyl) terephthalate from a polyethylene terephthalate molded article, particularly a PET bottle, can be further enhanced.
[0038]
【Example】
The present invention will be further described below using examples. The characteristics in the examples were measured by the following methods.
(1) Composition analysis of distillation residue and reaction solution 1) Separation of components, quantity measurement 5 mg of a sample was dissolved in chloroform to prepare a solution of about 1,000 ppm, which was measured with an HPLC LC-6 model manufactured by Shimadzu Corporation. .6 mm ^ID × 250 mm ^L silica-60 column, temperature 40 ° C., flow rate 1.0 ml / min, injection volume 5 μl, mobile phase using dichloromethane / dioxane, measurement wavelength 240 nm, UV spectrophotometer detector Measured.
2) Identification by LC / MS LC / MS measurement was performed to identify the HPLC peak.
[0039]
Using JEOL SX-102A type, measurement and identification were performed under the same conditions as described above.
(2) Amount of diethylene glycol 1 g of a sample, 30 ml of methanol and 2 mg of zinc acetate were chromatographed using a solution obtained by methanolysis at 200 ° C. in a 100 ml Carius tube.
[0040]
Example 1
65 kg of polyethylene terephthalate recovered from the bottle, 430 kg of ethylene glycol and 225 g of caustic soda are charged into a 1 m ³ depolymerization tank, depolymerized at a pressure of 0.13 MPa and a temperature of 220 ° C. for 2 hours, cooled to 85 ° C. and decolorized by activated carbon. Then, a deionization operation with a cation exchanger and an anion exchanger was performed at 120 liter / hour, followed by crystallization at 15 ° C. for 5 hours, solid-liquid separation, and distillation at 140 ° C. and 133 Pa in a falling film evaporator. Purified bis (2-hydroxyethyl) terephthalate (BHET) was produced by molecular distillation at 205 ° C. and 12 Pa. The crude ethylene glycol generated from this production process was recovered and subjected to distillation at a tower top temperature of 143 ° C. and a pressure of 13.3 KPa, and a distillation residue was taken out from the bottom of the tower as a kettle residue.
[0041]
This distillation residue, ie, 55% by weight of BHET, 23% by weight of DEG ester, 9% by weight of oligomer, 1 kg of distillation residue containing 6% by weight of diethylene glycol and 7% by weight of ethylene glycol, 5 kg of ethylene glycol and 3 g of caustic soda as a catalyst is jacketed. Charge into autoclave, start transesterification at pressure of 0.15 MPa and temperature of 224 ° C, boil evaporate while adjusting pressure to 0.5 MPa, condense vapor from outlet of pressure control valve with condenser The amount was adjusted to 500 kg / hour by heating, and at the same time, new ethylene glycol was added at 500 kg / hour and reacted for 90 minutes, and then the reaction was stopped.
[0042]
When the total solid content in the obtained reaction product was analyzed, results of 94% by weight of BHET, 3.0% by weight of DEG ester, and 2.7% by weight of oligomer were obtained. A significant decrease in esters and an increase in BHET were confirmed.
[0043]
Subsequently, while stirring the reaction product at a rate of 2 ° C./min, the reaction product was cooled to 15 ° C., and crystallization was performed for 4.2 hours. A lubricating cake containing 36% by weight of the filtrate component was obtained by suction filtration through 5A filter paper. Analysis of the total solid content in this cake gave results of 96.7 wt% BHET, 1.6 wt% DEG ester, 1.1 wt% oligomer, and 0.6 wt% MHET.
It was confirmed that the DEG ester was further greatly reduced by crystallization of the reaction product.
[0044]
Comparative Example 1
10 kg of the distillation residue used in Example 1, 65 kg of polyethylene terephthalate recovered from the bottle, 430 kg of ethylene glycol and 225 g of caustic soda were charged into a 1 m ³ depolymerization tank and subjected to a depolymerization reaction at a pressure of 0.13 MPa and a temperature of 220 ° C. for 2 hours. , Cooled to 85 ° C., decolorized and deionized at 120 liters / hour, then crystallized at 15 ° C. for 5 hours, separated into solid and liquid, distilled off at 140 ° C. and 133 Pa in a falling film evaporator, Molecular distillation was performed at 205 ° C. and a pressure of 12 Pa to obtain BHET.
[0045]
When the composition analysis of the obtained BHET was conducted, the results were as follows: BHET 86.3% by weight, DEG ester 9.6% by weight, oligomer 2.3% by weight, and MHET 1.8% by weight. It was confirmed that when the distillation residue taken out by distillation purification of crude ethylene glycol was returned to the BHET production process without transesterification, only BHET with extremely low purity was obtained.
[0046]
【The invention's effect】
According to the present invention, crude ethylene glycol generated in the production process of bis (2-hydroxyethyl) terephthalate is subjected to distillation purification, and terephthalic acid ester of diethylene glycol contained in the resulting residue is converted to bis (2- By converting to hydroxyethyl) terephthalate, it is possible to recycle the residue to the production process of bis (2-hydroxyethyl) terephthalate and to provide a method for increasing the yield of product bis (2-hydroxyethyl) terephthalate be able to.

Claims (5)

The ethylene glycol recovery distillation kettle residue containing at least diethylene glycol terephthalic acid ester as a solid content, 2 to 20 times by weight of ethylene glycol and 0.1 to 1.0% by weight with respect to the total solid content in the distillation kettle residue The terephthalic acid ester and ethylene glycol are subjected to a transesterification reaction under heating to produce bis (2-hydroxyethyl) terephthalate and diethylene glycol, and the generated diethylene glycol is subjected to normal pressure to 0.5 MPa. A method for treating the residue of an ethylene glycol recovery distillation kettle characterized by evaporating and distilling together with ethylene glycol below. During the transesterification reaction, while adjusting the pressure to normal pressure to 0.5 MPa, diethylene glycol is evaporated together with ethylene glycol, and ethylene glycol in an amount substantially equal to the distillate amount is continuously or intermittently supplied. The method according to claim 1, wherein the solid content concentration of the reaction solution is kept substantially constant. The method according to claim 1 or 2, wherein the content of terephthalic acid ester of diethylene glycol in the residue of the distillation still is 10 to 30% by weight. The method according to any one of claims 1 to 3, wherein the transesterification time is 0.5 to 3 hours. The ethylene glycol in which the recovered distillation still residue is generated by the distillation purification treatment is produced in the process of purifying and separating bis (2-hydroxyethyl) terephthalate from the reaction product obtained by depolymerizing polyethylene terephthalate using ethylene glycol. The method according to claim 1.