CN118812354A - A new continuous process for preparing BHET by alcoholysis of recycled polyester - Google Patents

Abstract

The invention discloses a new continuous process for preparing BHET by recycled polyester alcoholysis, belongs to the technical field of waste polyester recycling, solves the problems of high energy consumption, poor cycle performance and inconvenient glycol treatment in the prior art, the method comprises the steps of carrying out alcoholysis on waste polyester materials, a catalyst and dihydric alcohol, filtering to obtain dihydric alcohol alcoholysis liquid, then allowing the dihydric alcohol alcoholysis liquid to enter an evaporation chamber, and carrying out thin film evaporation to enable steam generated by the dihydric alcohol alcoholysis liquid to be used as an alcoholysis raw material to participate in alcoholysis reaction again, and purifying BHET by sublimation. The invention adopts the thin film evaporation alcoholysis liquid, avoids the problem of high energy consumption caused by the need of adding a heat source and circulating cooling water during the dissolution, crystallization and purification of hot water, ensures that low molecules in the dihydric alcohol alcoholysis liquid are separated and then are used as alcoholysis raw materials for recycling reaction again, solves the problem of difficult dihydric alcohol treatment in the conventional polyester alcoholysis reaction, and realizes the recycling of steam.

Description

A new continuous process for preparing BHET by alcoholysis of recycled polyester

Technical Field

The invention belongs to the technical field of recycling waste polyester, and in particular relates to a new continuous process for preparing BHET by alcoholysis of recycled polyester.

Background Art

Using waste textiles (polyester-based clothing, scraps, etc.) and low-value and low-quality old polyester bottles to synthesize polyester melts through alcoholysis and repolymerization to spin recycled polyester fibers is a new method for high-value recycling of waste polyester materials. This method is different from the purely physical method of selecting, sorting, crushing, cleaning, dehydrating and drying recycled polyester. The method is to put the waste polyester raw materials into an alcoholysis kettle, add 2 to 8 times the mass of the raw materials and a small amount of initiator, alcoholyze at 170 to 245 ° C for 1 to 5 hours, cool and filter out insoluble matter, remove excess ethylene glycol, and then condense into a polyester melt with a characteristic viscosity of 0.63 to 0.65 and send it to the box to spin recycled polyester fibers. It can be seen from the above process for preparing regenerated polyester fiber that the amount of ethylene glycol is large and necessary, and the following methods are used to treat the alcoholysis solution after spinning the polyester fiber: 1) collect the ethylene glycol in the alcoholysis solution and directly use it for depolymerization; 2) purify the ethylene glycol in the alcoholysis solution and then use it for depolymerization; 3) use a reverse osmosis membrane to recover part of the ethylene glycol contained in the water after water crystallization, that is, pass most of the water from the water-ethylene glycol mixture after most of the water crystallization through a reverse osmosis membrane to remove most of the water, send the concentrated solution in the reverse osmosis membrane to a dehydration tower to remove water, and then purify the ethylene glycol; the above treatment methods either have no specific implementation plan or bring other problems.

When PET is depolymerized during the spinning process of recycled polyester fiber, there is no special limit on the amount of ethylene glycol used. The amount ranges from 10% to 800% to achieve the depolymerization and repolymerization of waste gas PET into valuable polyester, but it will affect the quality, yield and cost of polyester. Advantages of 10% ethylene glycol depolymerization of waste PET: very low production and operation costs, because very little ethylene glycol needs to be evaporated and refined, and low energy consumption; Disadvantages: alcoholysis temperature is above 240°C, alcoholysis will produce diethylene glycol, alcoholysis products have high viscosity, difficult to filter, and large waste, mainly in the waste of 95% of alcoholysis products solidified and attached to the filter screen during slag unloading, and the filter screen can only be regenerated by high-temperature calcination, and the filter screen will be scrapped after calcination for 10 to 15 times, which also indirectly increases the cost, and calcination will also increase environmental pressure. Therefore, in order to reduce the depolymerization cost of alcoholysis solution, it is necessary to treat the alcoholysis solution and realize the recycling of alcoholysis raw materials.

Summary of the invention

The purpose of the present invention is to provide a new continuous process for preparing BHET by alcoholysis of recycled polyester with low energy consumption, good circulation performance and convenient diol treatment in view of the shortcomings of the prior art.

In order to achieve the above technical objectives, the technical solution adopted by the new continuous process for preparing BHET by alcoholysis of recycled polyester is as follows:

A novel continuous process for preparing BHET by alcoholysis of recycled polyester comprises the following steps:

S1 Put appropriate amount of waste polyester material, catalyst and diol into alcoholysis reactor through screw extruder according to mass ratio, heat to appropriate temperature, stir alcoholysis for a period of time, cool the reacted solution to 80-160℃ and filter it while hot;

S2: separating the undepolymerized PET, washing the filtered solid with deionized water, drying it, and weighing it to obtain the mass of the undepolymerized PET;

S3: The diol alcoholysis liquid enters the evaporation chamber, and the diol alcoholysis liquid is evaporated by thin film, and low molecular weight is evaporated and purified by sublimation. The low molecular weight steam generated by the alcoholysis liquid is recycled as the alcoholysis raw material;

S4: The BHET product in step S3 is further refined to obtain refined-grade BHET.

Preferably, the mass ratio of each component in step S1 is based on the mass of the waste polyester, the amount of ethylene glycol is 0.5-10.0% (wt%) of the waste polyester, and the amount of catalyst is 0.1-10.0% (wt%) of the waste polyester.

Preferably, the waste polyester in step S1 is diethylene glycol terephthalate (PET), including bottle flakes, foam materials and textiles.

Preferably, the ethylene glycol in step S1 is industrial grade ethylene glycol, and its water content and diethylene glycol content are both less than 100 ppm.

Preferably, the alcoholysis reaction catalyst in step S1 is zinc acetate or hydrated zinc acetate.

Preferably, in step S1, the reaction temperature of the alcoholysis reactor is raised to 190-220° C., the temperature is maintained and the pressure is controlled to be 0.01-1.0 MPa, and the reaction is stirred for 2-3 hours.

Preferably, in step S3, the evaporation temperature of the evaporation chamber is 150-260°C.

Compared with the prior art, the present invention has the following beneficial effects:

The invention firstly alcoholizes waste polyester material, catalyst and diol, obtains diol alcoholysis liquid after filtering, then puts the diol alcoholysis liquid into an evaporation chamber, performs thin film evaporation, makes steam generated by the diol alcoholysis liquid participate in alcoholysis reaction again as low-molecular weight raw material of alcoholysis, sublimates and purifies BHET, avoids the problem of high energy consumption caused by adding heat source and circulating cooling water during hot water dissolution, crystallization and purification; utilizes thin film evaporation alcoholysis liquid, makes low-molecular weight in the diol alcoholysis liquid be removed and then used as alcoholysis raw material for recycling reaction again, solves the problem of difficult diol treatment in conventional polyester alcoholysis reaction, and realizes the recycling of steam; the whole process is simple, and effectively realizes the recycling of mother liquor.

DETAILED DESCRIPTION

The invention is further described below in conjunction with specific embodiments:

A novel continuous process for preparing BHET by alcoholysis of recycled polyester comprises the following steps:

S1 Put appropriate amount of waste polyester material, catalyst and diol into alcoholysis reactor through screw extruder according to mass ratio, heat the reaction temperature of alcoholysis reactor to 190-220℃, keep warm and control the pressure to 0.01-1.0MPa, stir alcoholysis reaction for 2-3h, cool the solution after reaction to 80-160℃ and filter it while hot;

S2: separating the undepolymerized PET, washing the filtered solid with deionized water, drying it, and weighing it to obtain the mass of the undepolymerized PET;

S3: The diol alcoholysis liquid enters the evaporation chamber, and the diol alcoholysis liquid is evaporated by thin film, and low molecular weight is evaporated and purified by sublimation. The low molecular weight steam generated by the alcoholysis liquid is recycled as the alcoholysis raw material;

S4: The BHET product in step S3 is further refined to obtain refined-grade BHET.

In the present invention, the mass ratio of each component in step S1 is based on the mass of the waste polyester, the amount of ethylene glycol is 0.5-10.0% (wt%) of the waste polyester, and the amount of catalyst is 0.1-10.0% (wt%) of the waste polyester.

In the present invention, the waste polyester in step S1 is diethylene glycol terephthalate (PET), including bottle flakes, foam materials and textiles, the ethylene glycol is industrial grade ethylene glycol, the water content and diethylene glycol content of which are both less than 100 ppm, and the alcoholysis reaction catalyst is zinc acetate or hydrated zinc acetate.

In the present invention, the evaporation temperature of the evaporation chamber in step S3 is 150-260°C.

The present invention not only has a simple process, but also provides a method for removing excess diol in an alcoholysis solution. In this method, low molecular weight ethylene glycol removed by thin film evaporation is put back into the alcoholysis solution for alcoholysis, thereby realizing the recycling of ethylene glycol, sublimating and purifying BHET, and further improving the quality of BHET.

Example

In a 1000mL stirred reactor, 300 grams of ethylene glycol and 6 grams of catalyst were added in sequence, the temperature was raised to 100°C and stirred for 30 minutes, and then 60 grams of waste polyester was added, stirring was maintained, and the temperature was controlled between 200°C±2°C. At this time, the reaction pressure was 0.05MPa±0.01MPa. After 2 hours of reaction, the solution was cooled to 160°C and filtered. Insoluble matter above 15 microns was removed by a dynamic continuous filter. The filtrate was transferred to an evaporation chamber under heat preservation. The ethylene glycol alcoholysis solution was evaporated at a high temperature of 200°C in the film to evaporate low molecular weight ethylene glycol. After being discharged from the evaporation chamber, it was added to the alcoholysis solution for alcoholysis again, and the BHET product was sublimated and purified. At this time, the conversion rate of PET was 100%, and the yield of BHET was 86%.

Example

In a 1000mL stirred reactor, 300 grams of ethylene glycol and 6 grams of catalyst were added in sequence, the temperature was raised to 100°C and stirred for 30 minutes, and then 60 grams of waste polyester was added, stirring was maintained, and the temperature was controlled between 200°C±2°C. At this time, the reaction pressure was 0.05MPa±0.01MPa. After 2 hours of reaction, the solution was cooled to 160°C and filtered. Insoluble matter above 15 microns was removed by a dynamic continuous filter. The filtrate was transferred to an evaporation chamber under heat preservation. The ethylene glycol alcoholysis solution was evaporated at a high temperature of 180°C in the film to evaporate low molecular weight ethylene glycol. After being discharged from the evaporation chamber, it was added to the alcoholysis solution for alcoholysis again, and the BHET product was sublimated and purified. At this time, the conversion rate of PET was 88% and the yield of BHET was 75%.

Example

In a 1000mL stirred reactor, 300 grams of ethylene glycol and 6 grams of catalyst were added in sequence, the temperature was raised to 100°C and stirred for 30 minutes, and then 60 grams of waste polyester was added, stirring was maintained, and the temperature was controlled between 200°C±2°C. At this time, the reaction pressure was 0.05MPa±0.01MPa. After 2 hours of reaction, the solution was cooled to 160°C and filtered. Insoluble matter above 15 microns was removed by a dynamic continuous filter. The filtrate was transferred to the evaporation chamber under heat preservation. The ethylene glycol alcoholysis solution was evaporated at a high temperature of 170°C in the film to evaporate the low molecular weight ethylene glycol. After being discharged from the evaporation chamber, it was added to the alcoholysis solution for alcoholysis again, and the BHET product was sublimated and purified. At this time, the conversion rate of PET was 68% and the yield of BHET was 69%.

Example

In a 1000mL stirred reactor, 300 grams of ethylene glycol and 6 grams of catalyst were added in sequence, the temperature was raised to 100°C and stirred for 30 minutes, and then 60 grams of waste polyester was added, stirring was maintained, and the temperature was controlled between 200°C±2°C. At this time, the reaction pressure was 0.05MPa±0.01MPa. After 2 hours of reaction, the solution was cooled to 150°C and filtered. Insoluble matter above 15 microns was removed by a dynamic continuous filter. The filtrate was transferred to an evaporation chamber under heat preservation. The ethylene glycol alcoholysis solution was evaporated at a high temperature of 200°C in the film to evaporate low molecular weight ethylene glycol. After being discharged from the evaporation chamber, it was added to the alcoholysis solution for alcoholysis again, and the BHET product was sublimated and purified. At this time, the conversion rate of PET was 93% and the yield of BHET was 78%.

Example

In a 1000mL stirred reactor, 300 grams of ethylene glycol and 6 grams of catalyst were added in sequence, the temperature was raised to 100°C and stirred for 30 minutes, and then 60 grams of waste polyester was added, stirring was maintained, and the temperature was controlled between 200°C±2°C. At this time, the reaction pressure was 0.05MPa±0.01MPa. After 2 hours of reaction, the solution was cooled to 140°C and filtered. Insoluble matter above 15 microns was removed by a dynamic continuous filter. The filtrate was transferred to an evaporation chamber under heat preservation. The ethylene glycol alcoholysis solution was evaporated at a high temperature of 200°C in the film to evaporate low molecular weight ethylene glycol. After being discharged from the evaporation chamber, it was added to the alcoholysis solution for alcoholysis again, and the BHET product was sublimated and purified. At this time, the conversion rate of PET was 90% and the yield of BHET was 75%.

In summary, the above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. All equivalent changes and modifications in the shape, structure, characteristics and spirit of the claims of the present invention should be included in the scope of the claims of the present invention.

Claims (7)

1. A new continuous process for preparing BHET by alcoholysis of recycled polyester, characterized in that it comprises the following steps: S1 Put appropriate amount of waste polyester material, catalyst and diol into alcoholysis reactor through screw extruder according to mass ratio, heat to appropriate temperature, stir alcoholysis for a period of time, cool the reacted solution to 80-160℃ and filter it while hot; S2: separating the undepolymerized PET, washing the filtered solid with deionized water, drying it, and weighing it to obtain the mass of the undepolymerized PET; S3: The diol alcoholysis liquid enters the evaporation chamber, and the diol alcoholysis liquid is evaporated by thin film, and low molecular weight is evaporated and purified by sublimation. The low molecular weight steam generated by the alcoholysis liquid is recycled as the alcoholysis raw material; S4: The BHET product in step S3 is further refined to obtain refined-grade BHET. 2. The novel continuous process for preparing BHET by alcoholysis of recycled polyester according to claim 1 is characterized in that: the mass ratio of each component in step S1 is based on the mass of the waste polyester, the amount of ethylene glycol is 0.5-10.0% (wt%) of the waste polyester, and the amount of catalyst is 0.1-10.0% (wt%) of the waste polyester. 3. The novel continuous process for preparing BHET by alcoholysis of recycled polyester according to claim 1, characterized in that: the waste polyester in step S1 is diethylene glycol terephthalate (PET), including bottle flakes, foam materials and textiles. 4. The novel continuous process for preparing BHET by alcoholysis of recycled polyester according to claim 1, characterized in that the ethylene glycol in step S1 is industrial grade ethylene glycol, and its water content and diethylene glycol content are both less than 100 ppm. 5. The novel continuous process for preparing BHET by alcoholysis of recycled polyester according to claim 1, characterized in that the alcoholysis reaction catalyst in step S1 is zinc acetate or hydrated zinc acetate. 6. The novel continuous process for preparing BHET by alcoholysis of recycled polyester according to claim 1, characterized in that: in the step S1, the reaction temperature of the alcoholysis reactor is raised to 190-220°C, the temperature is maintained and the pressure is controlled to be 0.01-1.0 MPa, and the reaction is stirred for 2-3 hours. 7. The novel continuous process for preparing BHET by alcoholysis of recycled polyester according to claim 1, characterized in that the evaporation temperature of the evaporation chamber in step S3 is 150-260°C.