System and method for recovering polyester to prepare bis(2-hydroxyethyl) terephthalate

Abstract

The present invention relates to the field of organic synthesis, and in particular relates to a system and method for recovering a polyester to prepare bis(2-hydroxyethyl) terephthalate. The system sequentially comprises, along a feeding direction, a polyester pretreatment system, a polyester alcoholysis system, a solid matter filtering system, a solvent recovery system, a diethyl terephthalate refining system and a bis(2-hydroxyethyl) terephthalate preparation system. In the present invention, by optimizing the process route for recovering a polyester to prepare bis(2-hydroxyethyl) terephthalate, i.e., first degrading a polyester into an intermediate product diethyl terephthalate and then preparing bis(2-hydroxyethyl) terephthalate from the diethyl terephthalate, the costs for recovering the polyester to prepare bis(2-hydroxyethyl) terephthalate can be reduced, and the yield of bis(2-hydroxyethyl) terephthalate can be improved, thereby making the method more suitable for industrial application.

Description

System and method for recycling polyester to prepare bis-hydroxyethyl terephthalate TECHNICAL FIELD

[0001] The present application relates to the field of organic synthesis, and in particular to a system and method for recycling polyester to prepare bis-hydroxyethyl terephthalate. BACKGROUND

[0002] Polyester is one of the most commonly used polymers at present, and is mainly used for preparing fibers, films and bottles, etc. According to statistics, since 2003, the global polyester production capacity has expanded at an average annual rate of about 9%, and the polyester production capacity in China reached 29 million tons in 2010, becoming the world's largest producer and consumer of polyester. Due to the increasing social demand, the global polyester production is growing rapidly, and most of the polyester products are disposable consumer goods, which leads to the generation of a large amount of polyester waste. Waste polyester materials are not easily degraded by air or microorganisms in a short period of time due to their strong chemical inertness, which causes great pressure on the protection of the ecological environment. Therefore, there are many related researches on the degradation of waste polyester materials at home and abroad, but the intermediate product diethyl terephthalate obtained by alcoholysis of waste polyester materials has no direct application in the market, so that the existing various recycling methods cannot meet the industrial application.

[0003] CN117430506A discloses a method for degrading and recycling polyester. The method mixes polyester, solvent and catalyst, and then heats and reacts to degrade the polyester into bis-hydroxyethyl terephthalate. The catalyst is an ionic liquid functionalized magnetic nanoparticle, and the solvent is a binary organic alcohol (specifically, any one of ethylene glycol, propylene glycol, butylene glycol and pentanediol). However, the catalyst used for polyester degradation in this method needs to be specially prepared, the degradation process is complicated, many reagents are needed, the overall scheme has poor economic value, and the yield of bis-hydroxyethyl terephthalate obtained is low. TECHNICAL PROBLEM

[0004] Therefore, how to reduce the cost of recycling polyester to prepare bis-hydroxyethyl terephthalate and improve the yield of bis-hydroxyethyl terephthalate is a technical problem to be solved. TECHNICAL SOLUTION

[0005] To solve the above technical problems, the present application provides a system and method for recycling polyester to prepare bis-hydroxyethyl terephthalate. The system and method optimize the process route of recycling polyester to prepare bis-hydroxyethyl terephthalate, which can simultaneously solve the problems of high cost and low yield of the product, and make it more suitable for industrial application.

[0006] The application provides a polyester recovery system for preparing bis-hydroxyethyl terephthalate, which comprises, in sequence in the feeding direction, a polyester pretreatment system, a polyester alcoholysis system, a solid filtering system, a solvent recovery system, a diethyl terephthalate refining system and a bis-hydroxyethyl terephthalate preparation system, wherein,

[0007] The polyester pretreatment system comprises, in sequence in the feeding direction, a crusher and a vibrating screen.

[0008] The polyester alcoholysis system comprises a depolymerization reactor.

[0009] The solid filtering system comprises, in sequence in the feeding direction, a centrifuge and a filter.

[0010] The solvent recovery system comprises an ethanol recovery tower.

[0011] The diethyl terephthalate refining system comprises, in sequence in the feeding direction, a diethyl terephthalate distillation tower and a diethyl terephthalate crystallizer.

[0012] The bis-hydroxyethyl terephthalate preparation system comprises, in sequence in the feeding direction, a beater, an ester exchange reactor, a bis-hydroxyethyl terephthalate crystallizer and an ethylene glycol recovery tower.

[0013] Further, the crusher is used for crushing the polyester to obtain polyester fragments, and the polyester fragments continue to enter the vibrating screen.

[0014] Further, the vibrating screen is used for removing the fragments with a large particle size from the polyester fragments to obtain polyester fragments with a uniform particle size, and the polyester fragments with a uniform particle size continue to enter the depolymerization reactor.

[0015] Further, the depolymerization reactor is used for making the polyester fragments with a uniform particle size to perform a depolymerization reaction to obtain a depolymerization solution, and the depolymerization solution continues to enter the centrifuge.

[0016] Further, the depolymerization reactor is additionally provided with an electric agitator, and the electric agitator is used for stirring the material.

[0017] Further, the centrifuge is used for centrifuging the depolymerization solution to obtain a depolymerization centrifugal liquid, and the depolymerization centrifugal liquid continues to enter the filter.

[0018] Further, the filter is used for filtering the depolymerization centrifugal liquid to obtain a depolymerization filtered liquid, and the depolymerization filtered liquid continues to enter the ethanol recovery tower.

[0019] Further, the ethanol recovery tower is used for recovering the ethanol in the depolymerization filtered liquid to obtain crude diethyl terephthalate, and the crude diethyl terephthalate continues to enter the diethyl terephthalate distillation tower.

[0020] Further, the terephthalic acid diethyl ester distillation column is used for distilling the crude terephthalic acid diethyl ester, to obtain a distillation terephthalic acid diethyl ester, which continues to enter the terephthalic acid diethyl ester crystallizer.

[0021] Further, the terephthalic acid diethyl ester crystallizer is used for crystallizing the distillation terephthalic acid diethyl ester, to obtain terephthalic acid diethyl ester crystals, which continue to enter the beater.

[0022] Further, the beater is used for mixing the terephthalic acid diethyl ester crystals and ethylene glycol uniformly, to obtain terephthalic acid diethyl ester slurry, which continues to enter the ester exchange reactor.

[0023] Further, the ester exchange reactor is used for performing ester exchange reaction on the terephthalic acid diethyl ester slurry, to obtain crude bis-hydroxyethyl terephthalate, which continues to enter the bis-hydroxyethyl terephthalate crystallizer.

[0024] Further, the bis-hydroxyethyl terephthalate crystallizer is used for crystallizing the crude bis-hydroxyethyl terephthalate, to obtain bis-hydroxyethyl terephthalate crystals, and the filtrate after crystallization continues to enter the ethylene glycol recovery column.

[0025] Further, the ethylene glycol recovery column is used for recovering ethylene glycol in the filtrate.

[0026] The present application provides a method for preparing bis-hydroxyethyl terephthalate from polyester, which comprises a polyester pretreatment method, a polyester alcoholysis method, a solid filtration method, a solvent recovery method, a terephthalic acid diethyl ester refining method, and a bis-hydroxyethyl terephthalate preparation method.

[0027] Further, in the polyester pretreatment method, the following steps are included in sequence:

[0028] Step 1.1: the polyester is subjected to crushing treatment in the crusher, to obtain polyester fragments;

[0029] Step 1.2: the polyester fragments are subjected to removal of larger particle size fragments in the vibrating screen, to obtain polyester fragments with uniform particle size.

[0030] Further, in the polyester alcoholysis method, the following steps are included:

[0031] Step 2.1: the polyester fragments with uniform particle size, anhydrous ethanol, and a depolymerization catalyst are subjected to the depolymerization reaction in the depolymerization reactor, to obtain the depolymerization solution.

[0032] Further, in the solid filtering method, sequentially comprising the following steps:

[0033] Step 3.1: the depolymerization solution is subjected to centrifugal treatment in the centrifuge to obtain the depolymerization centrifugal liquid;

[0034] Step 3.2: the depolymerization centrifugal liquid is subjected to filtering treatment in the filter to obtain the depolymerization filtered liquid.

[0035] Further, in the solvent recovery method, comprising the following steps:

[0036] Step 4.1: the depolymerization filtered liquid is subjected to ethanol recovery treatment in the ethanol recovery tower to obtain the crude diethyl terephthalate, and the recovered ethanol is returned to the depolymerization reactor through a pipeline.

[0037] Further, in the diethyl terephthalate refining method, sequentially comprising the following steps:

[0038] Step 5.1: the crude diethyl terephthalate is subjected to distillation treatment in the diethyl terephthalate distillation tower to obtain the distillation diethyl terephthalate;

[0039] Step 5.2: the distillation diethyl terephthalate is subjected to crystallization treatment in the diethyl terephthalate crystallizer to obtain the diethyl terephthalate crystal.

[0040] Further, in the preparation method of the bis-hydroxyethyl terephthalate, sequentially comprising the following steps:

[0041] Step 6.1: the diethyl terephthalate crystal and ethylene glycol are uniformly mixed in the beater to obtain diethyl terephthalate slurry;

[0042] Step 6.2: the diethyl terephthalate slurry and the transesterification catalyst are subjected to the transesterification reaction in the transesterification reactor to obtain the crude bis-hydroxyethyl terephthalate;

[0043] Step 6.3: the crude bis-hydroxyethyl terephthalate is subjected to crystallization treatment in the bis-hydroxyethyl terephthalate crystallizer to obtain the bis-hydroxyethyl terephthalate crystal;

[0044] Step 6.4: the filtrate after the crystallization treatment is subjected to ethylene glycol recovery treatment in the ethylene glycol recovery tower, and the recovered ethylene glycol is returned to the transesterification reactor through a pipeline.

[0045] Further, in the step 1.1, the polyester is one or a mixture of both of polyethylene terephthalate and polyethylene terephthalate-1,4-cyclohexane dimethanol.

[0046] Further, in the step 2.1, the mass ratio of the uniformly sized polyester fragments to the anhydrous ethanol is 1: (5-10).

[0047] Further, in the step 2.1, the depolymerization catalyst is one of zinc acetate, manganese acetate, sodium hydroxide, or sulfuric acid, and the amount of the depolymerization catalyst is 2-5% of the total mass of the uniformly sized polyester fragments.

[0048] Further, in the step 2.1, the temperature of the depolymerization reactor is 200-260°C, and the time of the depolymerization reaction is 1-3h.

[0049] Further, in the step 2.1, the pressure of the depolymerization reactor is 2.0-2.5MPa.

[0050] Further, in the step 2.1, the depolymerization rate of the uniformly sized polyester fragments is 97-99%.

[0051] Further, in the step 4.1, the temperature of the ethanol recovery column is 80-120°C.

[0052] Further, in the step 5.1, the temperature of the diethyl terephthalate distillation column is 200-250°C.

[0053] Further, in the step 5.1, the pressure of the diethyl terephthalate distillation column is 1-5MPa.

[0054] Further, in the step 5.2, the distilled diethyl terephthalate is subjected to a crystallization process using anhydrous ethanol, and the mass ratio of the distilled diethyl terephthalate to the anhydrous ethanol is 1: (0.5-1).

[0055] Further, in the step 5.2, the temperature of the crystallization process is 0-10°C.

[0056] Further, in the step 5.2, the purity of the diethyl terephthalate crystals is 99.9%.

[0057] Further, in the step 6.1, the mass ratio of the diethyl terephthalate crystals to the ethylene glycol in the diethyl terephthalate slurry is 1: (3-8).

[0058] Further, in the step 6.2, the transesterification catalyst is one of calcium oxide, titanium dioxide, aluminum oxide or vanadium oxide, and the amount of the transesterification catalyst is 2-5% of the mass of the terephthalic acid diethyl ester crystals.

[0059] Further, in the step 6.2, the initial temperature of the transesterification reactor is 150-200℃, and the initial reaction time is 1-3h, and then the transesterification reactor is heated to 200-240℃, and the reaction is continued for 1-3h.

[0060] Further, in the step 6.2, the pressure of the transesterification reactor is (-0.002)-0.006MPa.

[0061] Further, in the step 6.3, the crude bis-hydroxyethyl terephthalate is crystallized using ethylene glycol, and the mass ratio of the crude bis-hydroxyethyl terephthalate to the ethylene glycol is 1:(3-5).

[0062] Further, in the step 6.3, the temperature of the bis-hydroxyethyl terephthalate crystallizer is 10-20℃.

[0063] Further, in the step 6.3, the yield of the bis-hydroxyethyl terephthalate crystals is 94-95%.

[0064] Further, in the step 6.4, the temperature of the ethylene glycol recovery tower is 100-120℃. Advantages

[0065] 1. The prior art generally adopts a method of directly degrading polyester into bis-hydroxyethyl terephthalate, and the degradation process is complicated, and sometimes the catalyst used for degradation needs to be specially prepared, so the prior art has poor economy; and the present application unexpectedly optimizes the process route of polyester recovery and preparation of bis-hydroxyethyl terephthalate by adopting an unexpected preparation system and method, first degrading polyester into intermediate product terephthalic acid diethyl ester, and then preparing bis-hydroxyethyl terephthalate from terephthalic acid diethyl ester, so that the present application unexpectedly optimizes the process route of polyester recovery and preparation of bis-hydroxyethyl terephthalate, reduces the cost of polyester recovery and preparation of bis-hydroxyethyl terephthalate, and at the same time improves the yield of bis-hydroxyethyl terephthalate, making it more suitable for industrial application.

[0066] 2. The present application recovers after degrading waste polyester, which is beneficial to resource recycling and sustainable development of society.

[0067] 3. The present application reduces waste polyester pollution by degrading waste polyester, which is beneficial to ecological environment protection. BRIEF DESCRIPTION OF DRAWINGS

[0068] Fig. 1 is a flow chart of a polyester recycling system for preparing bis-hydroxyethyl terephthalate according to the present application,

[0069] 1-polyester pretreatment system; 2-polyester alcoholysis system; 3-solid filtering system; 4-solvent recovery system; 5-diethyl terephthalate refining system; 6-bis-hydroxyethyl terephthalate preparation system; 1-1-crusher; 1-2-vibrating screen; 2-1-depolymerization reactor; 3-1-centrifuge; 3-2-filter; 4-1-ethanol recovery column; 5-1-diethyl terephthalate distillation column; 5-2-diethyl terephthalate crystallizer; 6-1-beater; 6-2-ester exchange reactor; 6-3-bis-hydroxyethyl terephthalate crystallizer; 6-4-ethylene glycol recovery column. Best mode of the present application

[0070] A polyester recycling system for preparing bis-hydroxyethyl terephthalate, the system comprises, in sequence in the feeding direction, a polyester pretreatment system 1, a polyester alcoholysis system 2, a solid filtering system 3, a solvent recovery system 4, a diethyl terephthalate refining system 5 and a bis-hydroxyethyl terephthalate preparation system 6, wherein, as shown in Fig. 1, the polyester pretreatment system 1 comprises, in sequence in the feeding direction, a crusher 1-1 and a vibrating screen 1-2; the polyester alcoholysis system 2 comprises a depolymerization reactor 2-1; the solid filtering system 3 comprises, in sequence in the feeding direction, a centrifuge 3-1 and a filter 3-2; the solvent recovery system 4 comprises an ethanol recovery column 4-1; the diethyl terephthalate refining system 5 comprises, in sequence in the feeding direction, a diethyl terephthalate distillation column 5-1 and a diethyl terephthalate crystallizer 5-2; and the bis-hydroxyethyl terephthalate preparation system 6 comprises, in sequence in the feeding direction, a beater 6-1, an ester exchange reactor 6-2, a bis-hydroxyethyl terephthalate crystallizer 6-3 and an ethylene glycol recovery column 6-4.

[0071] The polyester enters the crusher 1-1 to obtain polyester fragments, which continue to enter the vibrating screen 1-2 to obtain polyester fragments with uniform particle size. The polyester fragments with uniform particle size continue to enter the depolymerization reactor 2-1, and an electric agitator is also arranged in the depolymerization reactor 2-1 to obtain a depolymerization solution. The depolymerization solution continues to enter the centrifuge 3-1 to obtain a depolymerization centrifugal liquid, which continues to enter the filter 3-2 to obtain a depolymerization filtered liquid, which continues to enter the ethanol recovery column 4-1 to obtain crude diethyl terephthalate. The crude diethyl terephthalate continues to enter the diethyl terephthalate distillation column 5-1 to obtain refined diethyl terephthalate, which continues to enter the diethyl terephthalate crystallizer 5-2 to obtain diethyl terephthalate crystals.

[0072] The terephthalic acid diethyl ester crystals continue to enter the beater 6-1 to obtain terephthalic acid diethyl ester slurry, and the terephthalic acid diethyl ester slurry continues to enter the ester exchange reactor 6-2 to obtain crude terephthalic acid bis-hydroxyethyl ester, and the crude terephthalic acid bis-hydroxyethyl ester continues to enter the terephthalic acid bis-hydroxyethyl ester crystallizer 6-3 to obtain terephthalic acid bis-hydroxyethyl ester crystals, and the filtrate after the crystallization treatment continues to enter the ethylene glycol recovery tower 6-4. Embodiments of the present application

[0073] Example 1

[0074] A system for recovering and preparing terephthalic acid bis-hydroxyethyl ester from polyester, the system comprises in sequence in the feeding direction: a polyester pretreatment system 1, a polyester alcoholysis system 2, a solid filter system 3, a solvent recovery system 4, a terephthalic acid diethyl ester refining system 5, and a terephthalic acid bis-hydroxyethyl ester preparation system 6, wherein, as shown in FIG. 1, the polyester pretreatment system 1 comprises in sequence in the feeding direction: a crusher 1-1, a vibrating screen 1-2; the polyester alcoholysis system 2 comprises a depolymerization reactor 2-1; the solid filter system 3 comprises in sequence in the feeding direction: a centrifuge 3-1, a filter 3-2; the solvent recovery system 4 comprises an ethanol recovery tower 4-1; the terephthalic acid diethyl ester refining system 5 comprises in sequence in the feeding direction: a terephthalic acid diethyl ester rectifying tower 5-1, a terephthalic acid diethyl ester crystallizer 5-2; the terephthalic acid bis-hydroxyethyl ester preparation system 6 comprises in sequence in the feeding direction: a beater 6-1, an ester exchange reactor 6-2, a terephthalic acid bis-hydroxyethyl ester crystallizer 6-3, an ethylene glycol recovery tower 6-4.

[0075] The polyester enters the crusher 1-1 to obtain polyester fragments, and the polyester fragments continue to enter the vibrating screen 1-2 to obtain polyester fragments with uniform particle size. The polyester fragments with uniform particle size continue to enter the depolymerization reactor 2-1, and an electric agitator is also arranged in the depolymerization reactor 2-1 to obtain a depolymerization solution. The depolymerization solution continues to enter the centrifuge 3-1 to obtain a depolymerization centrifugal liquid, and the depolymerization centrifugal liquid continues to enter the filter 3-2 to obtain a depolymerization filtrate, and the depolymerization filtrate continues to enter the ethanol recovery tower 4-1 to obtain crude terephthalic acid diethyl ester. The crude terephthalic acid diethyl ester continues to enter the terephthalic acid diethyl ester rectifying tower 5-1 to obtain rectified terephthalic acid diethyl ester, and the rectified terephthalic acid diethyl ester continues to enter the terephthalic acid diethyl ester crystallizer 5-2 to obtain terephthalic acid diethyl ester crystals.

[0076] The terephthalic acid diethyl ester crystals continue to enter the beater 6-1 to obtain terephthalic acid diethyl ester slurry, and the terephthalic acid diethyl ester slurry continues to enter the ester exchange reactor 6-2 to obtain crude terephthalic acid bis-hydroxyethyl ester, and the crude terephthalic acid bis-hydroxyethyl ester continues to enter the terephthalic acid bis-hydroxyethyl ester crystallizer 6-3 to obtain terephthalic acid bis-hydroxyethyl ester crystals, and the filtrate after the crystallization treatment continues to enter the ethylene glycol recovery tower 6-4. Embodiment

[0077] A method for preparing bis-hydroxyethyl terephthalate by polyester recycling, comprising the following steps:

[0078] Step 1: polyester pretreatment: the polyester is subjected to crushing treatment in a crusher 1-1 to obtain polyester fragments, and the polyester fragments are subjected to treatment for removing fragments with large particle sizes in a vibrating screen 1-2 to obtain polyester fragments with uniform particle sizes.

[0079] Step 2: polyester alcoholysis: 10 kg of the polyester fragments with uniform particle sizes obtained in step 1, 50 kg of anhydrous ethanol, and 0.4 kg of a depolymerization catalyst zinc acetate are subjected to depolymerization reaction in a depolymerization reactor 2-1 to obtain a depolymerization solution, the temperature of the depolymerization reactor 2-1 is 260 ℃, the pressure is 2 MPa, the time of the depolymerization reaction is 1 h, and the depolymerization rate of the polyester is 99%.

[0080] Step 3: solid filtration: the depolymerization solution obtained in step 2 is subjected to centrifugal treatment in a centrifuge 3-1 to obtain a depolymerization centrifugal solution, and the depolymerization centrifugal solution is subjected to filtration treatment in a filter 3-2 to obtain a depolymerization filtrate.

[0081] Step 4: solvent recovery: the depolymerization filtrate obtained in step 3 is subjected to anhydrous ethanol recovery treatment in an ethanol recovery tower 4-1 to obtain crude diethyl terephthalate, the temperature of the ethanol recovery tower 4-1 is 100 ℃, and the recovered anhydrous ethanol is returned to the depolymerization reactor 2-1 through a pipeline to continue to participate in the depolymerization reaction as a solvent.

[0082] Step 5: diethyl terephthalate refining: the crude diethyl terephthalate obtained in step 4 is subjected to rectification treatment in a diethyl terephthalate rectification tower 5-1 to obtain rectified diethyl terephthalate, the temperature of the diethyl terephthalate rectification tower 5-1 is 200 ℃, and the pressure is 3 MPa, and then 5 kg of the rectified diethyl terephthalate and 2.5 kg of anhydrous ethanol are subjected to crystallization treatment in a diethyl terephthalate crystallizer 5-2, the temperature of the crystallization treatment is 5 ℃, and diethyl terephthalate crystals with a purity of 99.9% are obtained.

[0083] Step 6: bis-hydroxyethyl terephthalate preparation: 1 kg of the diethyl terephthalate crystals obtained in step 5 and 5 kg of ethylene glycol are uniformly mixed in a beater 6-1 to obtain diethyl terephthalate slurry, and the diethyl terephthalate slurry and 20 g of an ester exchange catalyst calcium oxide are subjected to ester exchange reaction in an ester exchange reactor 6-2 to obtain crude bis-hydroxyethyl terephthalate, the initial temperature of the ester exchange reactor 6-2 is 150 ℃, the initial reaction time is 2 h, then the ester exchange reactor 6-2 is heated to 240 ℃, and the reaction is continued for 2 h, and the pressure of the ester exchange reactor 6-2 is -0.002 MPa.

[0084] Then, 0.5 kg of the crude bis-hydroxyethyl terephthalate and 1.5 kg of ethylene glycol were subjected to crystallization treatment in the bis-hydroxyethyl terephthalate crystallizer 6-3 at a temperature of 15°C, and 95% of bis-hydroxyethyl terephthalate crystals were obtained, the color index of the bis-hydroxyethyl terephthalate crystals being L value 93, a value 0.12, and b value 0.51. The filtrate after the crystallization treatment was subjected to ethylene glycol recovery treatment in the ethylene glycol recovery tower 6-4 at a temperature of 100°C, and the recovered ethylene glycol was returned to the ester exchange reactor 6-2 through a pipe to participate in the ester exchange reaction as a solvent. Example

[0085] A method of recovering and preparing bis-hydroxyethyl terephthalate from polyester, comprising the following steps:

[0086] Step 1: Polyester pretreatment: The polyester was subjected to crushing treatment in the crusher 1-1 to obtain polyester fragments, and the polyester fragments were subjected to removal of large-size fragments in the vibrating screen 1-2 to obtain polyester fragments with uniform particle size.

[0087] Step 2: Polyester alcoholysis: 10 kg of the polyester fragments with uniform particle size obtained in Step 1, 80 kg of anhydrous ethanol, and 0.2 kg of a depolymerization catalyst zinc acetate were subjected to depolymerization reaction in the depolymerization reactor 2-1, and a depolymerization solution was obtained, the temperature of the depolymerization reactor 2-1 being 230°C, the pressure being 2.5 MPa, the time of the depolymerization reaction being 2 h, and the depolymerization rate of the polyester being 97%.

[0088] Step 3: Solid filtration: The depolymerization solution obtained in Step 2 was subjected to centrifugal treatment in the centrifuge 3-1 to obtain a depolymerization centrifugal liquid, and the depolymerization centrifugal liquid was subjected to filtration treatment in the filter 3-2 to obtain a depolymerization filtrate.

[0089] Step 4: Solvent recovery: The depolymerization filtrate obtained in Step 3 was subjected to anhydrous ethanol recovery treatment in the ethanol recovery tower 4-1 to obtain crude bis-ethyl terephthalate, the temperature of the ethanol recovery tower 4-1 being 80°C, and the recovered anhydrous ethanol was returned to the depolymerization reactor 2-1 through a pipe to participate in the depolymerization reaction as a solvent.

[0090] Step 5: Bis-ethyl terephthalate purification: The crude bis-ethyl terephthalate obtained in Step 4 was subjected to distillation treatment in the bis-ethyl terephthalate distillation tower 5-1 to obtain distilled bis-ethyl terephthalate, the temperature of the bis-ethyl terephthalate distillation tower 5-1 being 250°C and the pressure being 5 MPa, and then 5 kg of the distilled bis-ethyl terephthalate and 4 kg of anhydrous ethanol were subjected to crystallization treatment in the bis-ethyl terephthalate crystallizer 5-2 at a temperature of 0°C to obtain bis-ethyl terephthalate crystals with a purity of 99.9%.

[0091] Step 6: Preparation of bis-hydroxyethyl terephthalate: Take the terephthalic acid diethyl ester crystals 1 kg obtained in step 5 and ethylene glycol 3 kg, mix them uniformly in a beater 6-1 to obtain terephthalic acid diethyl ester slurry, take the terephthalic acid diethyl ester slurry and ester exchange catalyst calcium oxide 35 g, and carry out ester exchange reaction in an ester exchange reactor 6-2 to obtain crude bis-hydroxyethyl terephthalate, the initial temperature of the ester exchange reactor 6-2 is 180°C, the initial reaction time is 3 h, then the ester exchange reactor 6-2 is heated to 200°C, and the reaction is continued for 1 h, the pressure of the ester exchange reactor 6-2 is 0.002 MPa.

[0092] Then take the crude bis-hydroxyethyl terephthalate 0.5 kg and ethylene glycol 2 kg, and carry out crystallization treatment in a bis-hydroxyethyl terephthalate crystallizer 6-3, the temperature of the crystallization treatment is 20°C, to obtain bis-hydroxyethyl terephthalate crystals with a yield of 94%, the color index of the bis-hydroxyethyl terephthalate crystals is: L value is 92, a value is 0.11, and b value is 0.46, the filtrate after the crystallization treatment is subjected to ethylene glycol recovery treatment in an ethylene glycol recovery tower 6-4, the temperature of the ethylene glycol recovery tower 6-4 is 110°C, and the recovered ethylene glycol is returned to the ester exchange reactor 6-2 through a pipeline to continue to participate in the ester exchange reaction as a solvent. Example

[0093] A method for preparing bis-hydroxyethyl terephthalate by recycling polyester, comprising the following steps:

[0094] Step 1: Pre-treatment of polyester: The polyester is subjected to crushing treatment in a crusher 1-1 to obtain polyester fragments, and the polyester fragments are subjected to removal of large-size fragments in a vibrating screen 1-2 to obtain polyester fragments with uniform particle size.

[0095] Step 2: Alcoholysis of polyester: Take the polyester fragments with uniform particle size obtained in step 1 10 kg, anhydrous ethanol 100 kg, and depolymerization catalyst zinc acetate 0.5 kg, and carry out depolymerization reaction in a depolymerization reactor 2-1 to obtain a depolymerization solution, the temperature of the depolymerization reactor 2-1 is 200°C, the pressure is 2.5 MPa, the time of the depolymerization reaction is 3 h, and the depolymerization rate of the polyester is 99%.

[0096] Step 3: Filtration of solid: Take the depolymerization solution obtained in step 2 and carry out centrifugal treatment in a centrifuge 3-1 to obtain a depolymerization centrifugal liquid, and carry out filtration treatment in a filter 3-2 to obtain a depolymerization filtrate.

[0097] Step 4: Recovery of solvent: Take the depolymerization filtrate obtained in step 3 and carry out recovery of ethanol in an ethanol recovery tower 4-1 to obtain crude terephthalic acid diethyl ester, the temperature of the ethanol recovery tower 4-1 is 120°C, and the recovered anhydrous ethanol is returned to the depolymerization reactor 2-1 through a pipeline to continue to participate in the depolymerization reaction as a solvent.

[0098] Step 5: Diethyl terephthalate purification: the crude diethyl terephthalate obtained in step 4 is first subjected to distillation treatment in a diethyl terephthalate distillation column 5-1 to obtain distilled diethyl terephthalate, the temperature of the diethyl terephthalate distillation column 5-1 being 220℃, and the pressure being 1 MPa, and then the distilled diethyl terephthalate 5 kg and anhydrous ethanol 5 kg are subjected to crystallization treatment in a diethyl terephthalate crystallizer 5-2, the temperature of the crystallization treatment being 10℃, to obtain diethyl terephthalate crystals with a purity of 99.9%.

[0099] Step 6: Bis-hydroxyethyl terephthalate preparation: 1 kg of the diethyl terephthalate crystals obtained in step 5 and 8 kg of ethylene glycol are uniformly mixed in a beater 6-1 to obtain diethyl terephthalate slurry, and the diethyl terephthalate slurry and 50 g of ester exchange catalyst calcium oxide are subjected to ester exchange reaction in an ester exchange reactor 6-2 to obtain crude bis-hydroxyethyl terephthalate, the initial temperature of the ester exchange reactor 6-2 being 200℃, and the initial reaction time being 1 h, and then the ester exchange reactor 6-2 is heated to 220℃, and the reaction is continued for 3 h, the pressure of the ester exchange reactor 6-2 being 0.006 MPa.

[0100] Then, 0.5 kg of the crude bis-hydroxyethyl terephthalate and 2.5 kg of ethylene glycol are subjected to crystallization treatment in a bis-hydroxyethyl terephthalate crystallizer 6-3, the temperature of the crystallization treatment being 10℃, to obtain bis-hydroxyethyl terephthalate crystals with a yield of 94%, the colorimetric index of the bis-hydroxyethyl terephthalate crystals being: L value 94, a value 0.11, and b value 0.49, and the filtrate after the crystallization treatment is subjected to ethylene glycol recovery treatment in an ethylene glycol recovery column 6-4, the temperature of the ethylene glycol recovery column 6-4 being 120℃, and the recovered ethylene glycol is returned to the ester exchange reactor 6-2 through a pipeline to continue to participate in the ester exchange reaction as a solvent. Industrial applicability

[0101] By adopting the unexpected preparation system and method, the polyester is first degraded into the intermediate product diethyl terephthalate, and then the bis-hydroxyethyl terephthalate is prepared from the diethyl terephthalate, so that the process route of the polyester recovery and preparation of the bis-hydroxyethyl terephthalate is unexpectedly optimized, the cost of the polyester recovery and preparation of the bis-hydroxyethyl terephthalate is reduced, the yield of the bis-hydroxyethyl terephthalate is improved, and the bis-hydroxyethyl terephthalate is more suitable for industrial application.

Claims

1. A system for the recovery production of bis-hydroxyethy! terephthalate from a polyester, characterized in that, The system sequentially comprises, in the feeding direction: a polyester pretreatment system (1), a polyester alcoholysis system (2), a solid filtering system (3), a solvent recovery system (4), a diethyl terephthalate refining system (5), and a bis-hydroxyethyl terephthalate preparation system (6), wherein, The polyester pretreatment system (1) sequentially comprises, in the feeding direction: a crusher (1-1), a vibrating screen (1-2); The polyester alcoholysis system (2) comprises: a depolymerization reactor (2-1); The solid filtering system (3) sequentially comprises, in the feeding direction: a centrifuge (3-1), a filter (3-2); The solvent recovery system (4) comprises: an ethanol recovery tower (4-1); The diethyl terephthalate refining system (5) sequentially comprises, in the feeding direction: a diethyl terephthalate rectifying tower (5-1), a diethyl terephthalate crystallizer (5-2); The bis-hydroxyethyl terephthalate preparation system (6) sequentially comprises, in the feeding direction: a beating kettle (6-1), an ester exchange reactor (6-2), a bis-hydroxyethyl terephthalate crystallizer (6-3), and an ethylene glycol recovery tower (6-4).

2. The system of claim 1, wherein, The depolymerization reactor (2-1) is used for making the polyester undergo a depolymerization reaction to obtain a depolymerization solution, which continues to enter the centrifuge (3-1).

3. The system of claim 2, wherein, The centrifuge (3-1) is used for centrifuging the depolymerization solution to obtain a depolymerization centrifugal liquid, which continues to enter the filter (3-2); The filter (3-2) is used for filtering the depolymerization centrifugal liquid to obtain a depolymerization filtered liquid, which continues to enter the ethanol recovery tower (4-1).

4. The system of claim 3, wherein, The ethanol recovery tower (4-1) is used for recovering ethanol in the depolymerization filtered liquid to obtain crude diethyl terephthalate, which continues to enter the diethyl terephthalate rectifying tower (5-1).

5. The system of claim 4, wherein, The diethyl terephthalate rectifying tower (5-1) is used for rectifying the crude diethyl terephthalate to obtain rectified diethyl terephthalate, which continues to enter the diethyl terephthalate crystallizer (5-2).

6. The system of claim 5, wherein, The diethyl terephthalate crystallizer (5-2) is used for crystallizing the rectified diethyl terephthalate to obtain diethyl terephthalate crystals, which continue to enter the beating kettle (6-1).

7. The system of claim 6, wherein, The beating kettle (6-1) is used for uniformly mixing the diethyl terephthalate crystals with ethylene glycol to obtain diethyl terephthalate slurry, which continues to enter the ester exchange reactor (6-2).

8. The system of claim 7, wherein, The ester exchange reactor (6-2) is used for making the diethyl terephthalate slurry undergo an ester exchange reaction to obtain crude bis-hydroxyethyl terephthalate, which continues to enter the bis-hydroxyethyl terephthalate crystallizer (6-3).

9. The system of claim 8, wherein, The terephthalic acid bishydroxyethyl ester crystallizer (6-3) is used for crystallizing the crude terephthalic acid bishydroxyethyl ester to obtain terephthalic acid bishydroxyethyl ester crystals, and the filtrate after the crystallization treatment continues to enter the ethylene glycol recovery tower (6-4).

10. A method for the production of bis-hydroxyethy! terephthalate from the recovery of polyester using the system of any one of claims 1 to 9, characterized in that, The method comprises a polyester pretreatment method, a polyester alcoholysis method, a solid filtration method, a solvent recovery method, a terephthalic acid diethyl ester refining method, and a terephthalic acid bishydroxyethyl ester preparation method.

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