JP5529498B2 - Process for producing dimethyl terephthalate from polyester - Google Patents

Description

  The present invention relates to a method for producing dimethyl terephthalate in polyester production from a polyester product.

  Polyester, such as polyethylene terephthalate, is widely used as a fiber, film, resin, etc. due to its excellent properties, but effective utilization of polyester waste such as fiber, film, resin, etc. generated in these manufacturing processes is costly. It is a big issue not only from the aspect but also from environmental issues. Various proposals have been made by material recycling, thermal recycling, and chemical recycling. Among these, polyester resin waste such as PET bottles is collected and actively reused mainly by local governments in material recycling.

  In addition, thermal recycling that converts polyester waste into fuel has the advantage of reusing the combustion heat of polyester waste, but the calorific value is relatively low, and it is nothing but burning a large amount of polyester waste. There is a problem of polyester raw material loss, which is not preferable from the viewpoint of resource saving. On the other hand, in chemical recycling, polyester waste is regenerated as a raw material monomer. Therefore, since it is regenerated, there is little deterioration in quality due to regeneration, and it is excellent as closed-loop recycling.

  Most of the chemical recycling targets resin waste and film waste. For example, polyester waste was obtained after depolymerization with excess ethylene glycol (hereinafter sometimes abbreviated as EG). A method of obtaining a regenerated polyester by directly polycondensation of bis (β-hydroxyethyl) terephthalate has been proposed (see, for example, Patent Documents 1 and 2). Since the depolymerization is performed by batch charging into the depolymerization reaction system, the charged polyester waste may become a lump inside the reactor and may not be stirred. For this reason, the depolymerization system becomes non-uniform and the depolymerization time becomes long, and the amount of EG used is not only economically disadvantageous, but also impurities such as diethylene glycol are by-produced, and the resulting polyester The physical properties, particularly the softening point, are significantly reduced, and only low-quality polyesters can be obtained. Thus, in the prior art, the technique which processes polyester waste efficiently is not completed.

JP-A-48-61447 (Claims) JP 2005-330444 A

  The present invention has been made in view of the above-mentioned background art, and is to establish a method for efficiently and economically producing polyester, particularly dimethyl terephthalate used in the production of polyalkylene terephthalate.

According to the studies by the present inventors, a polyester having an alkylene terephthalate unit is depolymerized with alkylene glycol to obtain a depolymerization solution containing bis ( ω -hydroxyalkyl) terephthalate, and then calcium oxide is used as a catalyst. It has been clarified that the above-mentioned problem can be achieved by a method for producing dimethyl terephthalate by transesterification with methanol.

  INDUSTRIAL APPLICABILITY The present invention provides a method for efficiently and economically producing a useful component in polyester production from a product containing polyester. Specifically, since the reaction rate of the transesterification reaction is high, the yield can be increased in a short time, and when producing a specific amount of dimethyl terephthalate, it can be manufactured with smaller equipment, and the amount of capital investment Can be suppressed. Moreover, since the production amount of hydroxymethyl terephthalate, which is a reaction intermediate, is small, both the yield and purity of dimethyl terephthalate can be increased. Moreover, since calcium oxide as a catalyst exists as a solid even after the transesterification reaction, it can be easily removed from the solution after the reaction. Finally, the catalyst remaining in the residue after removal of dimethyl terephthalate, alkylene glycol, and methanol by distillation purification is still active, so it can be used as a catalyst for repeated transesterification reactions. .

Hereinafter, embodiments of the present invention will be specifically described. In the method for producing dimethyl terephthalate of the present invention, the polyester used as the raw material is required to be mainly a polyester having a polyalkylene terephthalate unit. Specific examples of the polyalkylene terephthalate include polyethylene terephthalate, polytrimethylene terephthalate, and polytetramethylene terephthalate. More specifically, it is preferable that the product contains polyethylene terephthalate, and the polyester may contain a different material. For example, in a textile product, a dye used for dyeing polyethylene terephthalate fiber. In addition, other fiber materials such as nylon and cotton, which are included in the form of blends, and other plastic components used for purposes such as surface modification may be included. Here, “mainly” represents 80% by weight or more, preferably 90% by weight or more. Further, alkylene glycol, which is another raw material, specifically includes ethylene glycol, trimethylene glycol, 1,2-propanediol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, triethylene glycol, bis (trimethylene) glycol , [bis (3-hydroxypropyl) ether], bis (tetramethylene) glycol , and [bis (4-hydroxybutyl) ether]. Among these, it is preferable to use an alkylene glycol corresponding to the alkylene portion of the above polyalkylene terephthalate unit, and it is more preferable to use ethylene glycol. The alkylene glycol used in the depolymerization step is preferably used 0.5 to 20 times the weight of the polyalkylene terephthalate. More preferably, it is 1.0 to 10 times by weight.

In the present invention, an excess molar amount of alkylene glycol is added to a product (polyester) containing polyalkylene terephthalate, depolymerized, and a depolymerized solution containing bis ( ω -hydroxyalkyl) terephthalate (BHAT) and oligomer components thereof is obtained. Can be obtained. In the depolymerization reaction, it is preferable to use a known depolymerization catalyst within a known catalyst concentration range and perform the depolymerization reaction in excess alkylene glycol heated to 120 to 200 ° C. When the temperature of the alkylene glycol is less than 120 ° C., the depolymerization time becomes very long and it is not efficient. On the other hand, when the temperature exceeds 200 ° C., the thermal decomposition of the different materials contained in the fiber waste becomes remarkable, and the nitrogen compounds generated by the decomposition are dispersed in the recovered useful components, and the subsequent process for recovering the useful components Then it becomes difficult to separate. The pressure during the reaction can be maintained at 0.1 to 0.5 MPa.

  Furthermore, in the present invention, a known depolymerization catalyst may be used at a known catalyst concentration. Types of depolymerization catalysts include lithium acetate, sodium acetate, potassium acetate, rubidium acetate, zinc acetate, manganese acetate, lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, Rubidium bicarbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, lithium alkoxide, sodium alkoxide, potassium alkoxide, rubidium alkoxide, magnesium carbonate, calcium carbonate, magnesium hydroxide, calcium hydroxide, magnesium alkoxide, calcium It is preferable to use at least one compound selected from the group consisting of alkoxides. The addition amount of these depolymerization catalysts is preferably from 0.01 to 10% by weight, and preferably from 0.05 to 5% by weight, based on the polyalkylene terephthalate.

  Further, the depolymerization liquid can be concentrated by distilling and evaporating a part of the alkylene glycol from the depolymerization liquid obtained after the completion of the depolymerization reaction. By performing this operation, the amount of methanol used in the subsequent transesterification reaction can be reduced. Further, the recovered alkylene glycol can be effectively used, for example, again in the depolymerization reaction. Further, the amount of alkylene glycol distilled / evaporated in this step is 0.1 to 1.0 times the amount of alkylene glycol added during the depolymerization reaction, or the alkylene glycol and alkylene terephthalate units are It is preferable to carry out until the weight ratio of the polyester to 0.5 to 2.0 times. In addition, it is preferable to carry out the distillation / evaporation step at a temperature in the range of 120 to 180 ° C. in terms of high purity and the ability to obtain an alkylene glycol that can be used later in a depolymerization reaction or the like. .

  Subsequently, the depolymerization liquid obtained by the depolymerization reaction can be reacted with methanol using calcium oxide as a catalyst to perform a transesterification reaction. Calcium oxide can increase the reaction rate compared to other known alkaline earth metal compounds or alkali metal compounds, etc., so that it can be realized with a smaller facility for certain production, As a result, capital investment can be reduced, which is preferable. Here, commercially available calcium oxide having a purity, shape, and size can be used as the catalyst, but a specific surface area is preferably large in order to achieve sufficient catalytic activity. The size of calcium oxide is preferably 3 mm or less, particularly preferably 1 mm or less. In addition, since calcium oxide is hardly soluble in methanol and alkylene glycol, it remains in a solid state after completion of the transesterification reaction, so that solid-liquid separation can be easily performed. For this reason, the size of the calcium oxide to be used is preferably a particle size of 10 micrometers or more, and particularly preferably a size of 100 micrometers or more. When the reaction temperature increases, the temperature during the transesterification reaction becomes difficult to carry out the reaction at normal pressure, and a high-pressure facility is required in the transesterification reaction. Therefore, the temperature of the transesterification reaction at normal pressure is preferably 85 ° C. or lower. Moreover, as a usage-amount of a catalyst, it is preferable to add 0.5-10 wt% with respect to the weight of the product (polyester) containing a polyethylene terephthalate. More preferably, it is added in the range of 0.05 to 5 wt%. In addition to calcium oxide, other known alkaline earth metal compounds or alkali metal compounds may be used in combination as a catalyst for the transesterification reaction. Specifically, zinc acetate, manganese acetate, lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, rubidium bicarbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide And at least one compound selected from the group consisting of rubidium hydroxide, lithium alkoxide, sodium alkoxide, potassium alkoxide, rubidium alkoxide, magnesium carbonate, calcium carbonate, magnesium hydroxide, calcium hydroxide, magnesium alkoxide, and calcium alkoxide. Is preferred. The addition amount of these compounds is preferably the above-mentioned use amount including calcium oxide. Then, dimethyl terephthalate can be produced by solid-liquid separation of the produced dimethyl terephthalate crystals by solid-liquid separation means such as centrifugation. When a high-purity product is desired, the purity of dimethyl terephthalate can be increased by purification by distillation. At this time, since calcium oxide is more reactive than the other known alkaline earth metal compounds or alkali metal compounds shown above, crystals of dimethyl terephthalate that have been transesterified with calcium oxide are used. Has a small amount of hydroxyethyl methyl terephthalate (hereinafter sometimes abbreviated as HMT) as a reaction intermediate. For this reason, the yield in distillation purification can be increased and the distillation residue can be reduced.

  In addition, after the transesterification reaction, by adding a residue obtained by removing methanol and ethylene glycol from the residual liquid from which dimethyl terephthalate (DMT) has been separated, calcium flowing out into the residual liquid Ingredients and active ingredients such as BHAT and dimethyl terephthalate can be recovered. In particular, the ability to repeatedly use a calcium component as a catalyst for the transesterification reaction contributes to carrying out the transesterification reaction efficiently and at low cost, and has great industrial significance.

Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to these examples. Moreover, each numerical value in an Example was calculated | required with the following method.
(A) (Dimethyl terephthalate production)
The production amount of dimethyl terephthalate was calculated by the following formula (1).
(Cake weight after solid-liquid separation) x (Purity of dimethyl terephthalate in cake) x 100
(1)
(A) (Dimethyl terephthalate [DMT] purity in cake, HMT concentration)
It was determined by gas chromatography (apparatus: GC-17A manufactured by Shimadzu Corporation, capillary column: NB-1 0.25 mm × 30 m).
(C) (Bishydroxyethyl terephthalate [BHET] and BHET oligomer components)
The BHET and BHET oligomer components contained in the depolymerization solution were measured with a gel permeation analyzer (HLC-8220 manufactured by Tosoh Corporation).

[Example 1]
100 g of polyethylene terephthalate, 400 g of EG, and 0.5 g of potassium carbonate as a depolymerization catalyst were added, and a depolymerization reaction was performed in a reactor at normal pressure and a temperature of 185 ° C. for 6 hours to obtain a depolymerization solution containing BHET. Thereafter, 300 g of ethylene glycol was distilled off under the conditions of a temperature of 140 to 160 ° C. and a pressure of 13.3 kPa in the same reactor to obtain 200 g of a concentrated depolymerization solution.
Next, 0.7 g of calcium oxide (separated by pulverizing in a mortar and passing through a 1-mm sieve) and 175 g of methanol as a transesterification reaction catalyst and adding 175 g of methanol, 1 at normal pressure, 75-80 ° C. Reacted for hours. The precipitation of DMT crystals could be confirmed immediately after the addition of calcium oxide and methanol. After completion of the reaction, the reaction solution is cooled to 10 ° C. and separated by solid-liquid separation into a cake containing dimethyl terephthalate as a main component and a residual solution containing methanol and ethylene glycol as main components by separation by filtration, and dimethyl terephthalate from the cake. Manufactured. At this time, the production amount of dimethyl terephthalate was 91 g (HMT concentration: 0.3 wt%).

[Example 2]
In the same manner as in Example 1, 100 g of polyethylene terephthalate was depolymerized, and then EG was distilled off to obtain a concentrated depolymerization solution. Then, as an ester exchange reaction catalyst, calcium oxide (pulverized in a mortar with an opening of 1 0.7 g and 175 g of methanol were added, and the mixture was reacted at normal pressure at 75-80 ° C. for 10 minutes. The precipitation of DMT crystals could be confirmed immediately after the addition of calcium oxide and methanol. Then, operation similar to Example 1 was performed and dimethyl terephthalate was manufactured. At this time, the production amount of dimethyl terephthalate was 70 g.

[Example 3]
After transesterification in Example 1, 20 g of a residue obtained by removing methanol and ethylene glycol from the solid-liquid separated residue was added to 100 g of polyethylene terephthalate. Thereafter, the same operation as in Example 1 was performed, and dimethyl terephthalate was added. Manufactured. At this time, the total of BHET and BHET oligomer components contained in the residue was 1.7 g. The production amount of dimethyl terephthalate was 85 g.

[Example 4]
Dimethyl terephthalate was produced in the same manner as in Example 1 except that the transesterification reaction temperature was 50 ° C. At this time, the production amount of dimethyl terephthalate was 88 g.

[Example 5]
Dimethyl terephthalate was produced in the same manner as in Example 1 except that calcium oxide (2 cm square) was used as the transesterification reaction catalyst, and the transesterification time was changed to 2 hours. At this time, the production amount of dimethyl terephthalate was 87.6 g.

[Comparative Example 1]
Dimethyl terephthalate was produced in the same manner as in Example 1 except that sodium carbonate was used as the transesterification reaction catalyst. At this time, precipitation of DMT crystals in the transesterification reaction was confirmed 12 minutes after the addition of calcium oxide and methanol. The production amount of dimethyl terephthalate was 89 g (HMT concentration: 1.2 wt%).

[Comparative Example 2]
Dimethyl terephthalate was produced in the same manner as in Example 2 except that sodium carbonate was used as the transesterification reaction catalyst. At this time, the production amount of dimethyl terephthalate was 49 g.

[Comparative Example 3]
After the transesterification reaction in Comparative Example 1, 20 g of a residue obtained by removing methanol and ethylene glycol from the solid-liquid separated residue was added to 100 g of polyethylene terephthalate. Thereafter, the same operation as in Comparative Example 1 was performed, and dimethyl terephthalate was added. Manufactured. At this time, the total of BHET and BHET oligomer components contained in the residue was 1.7 g. The production amount of dimethyl terephthalate was 83 g.

  According to the present invention, dimethyl terephthalate can be produced from a product containing polyethylene terephthalate more efficiently and economically than the conventional method. This is very significant in terms of industry.

Claims (5)

  A polyester having an alkylene terephthalate unit is subjected to a depolymerization reaction with alkylene glycol to obtain a depolymerization solution containing bis (ω-hydroxyalkyl) terephthalate, and then subjected to a transesterification reaction with methanol using calcium oxide as a catalyst. Production method. 2. The production of dimethyl terephthalate according to claim 1, wherein after the transesterification reaction, a residue obtained by further removing methanol and alkylene glycol from the residue obtained by separating dimethyl terephthalate in the obtained reaction solution is used in addition to the depolymerization reaction. Method. The method for producing dimethyl terephthalate according to claim 1 or 2, wherein a particle diameter of the calcium oxide is 3 millimeters or less. The method for producing dimethyl terephthalate according to any one of claims 1 to 3, wherein an amount of the calcium oxide used is 0.5 to 10 wt% with respect to the polyester. The method for producing dimethyl terephthalate according to any one of claims 1 to 4, wherein a temperature of the transesterification reaction is 85 ° C or lower.