CN114890892B - Method for degrading polyester through film-falling flow alcoholysis - Google Patents

Abstract

The invention relates to the technical field of polyester recycling. The invention discloses a method for falling film flow alcoholysis polyester. Pretreated polyester waste and solvent are added to a stirring device, and part of the catalyst is added after reaching a set temperature. , and then transport the obtained reaction liquid to the falling film kettle for reaction. The reaction liquid further alcoholyzes the polyester while performing falling film flow. After the reaction, the obtained alcoholysis liquid is discharged from the discharge port at the bottom of the falling film kettle and undergoes post-processing. , to obtain high-purity recyclable polyester reaction raw materials. According to the method of the present invention, the alcoholysis reaction of polyester is high, the reaction temperature is low, the reaction time is short, the product purity is high, it is easy to refine and purify, and the alcoholysis liquid can be recycled and reused after treatment.

Description

A method for falling film flow alcoholysis polyester

Technical field

The invention relates to the technical field of polyester recycling, and in particular to a method for falling film flow alcoholysis of polyester.

Background technique

Polyester prepared based on the principle of stepwise polymerization of acids and alcohols is widely used in plastics, packaging containers, films, fibers, fabrics, and pipes due to its easy availability of production raw materials, mature large-scale production technology, low cost, and outstanding product comprehensive properties. and sheet materials and other fields. Since the 21st century, new production capacity has continued to increase. According to statistics, in 2020, the world's polyester consumption in the textile, clothing and drinking bottle flakes sectors alone will reach about 80 million tons. While polyester materials provide convenience to people's lives, the solid waste pollution caused by their use is becoming more and more serious. The refractory nature of polyester materials has caused increasing damage to the earth's ecological environment. The recycling of polyester materials has become an important issue in global sustainable development.

At present, most of the recycling of polyester materials involves simple physical or mechanical treatment and then downgraded use, mainly entering the market cycle as low-end products such as filling and coating. Chemical recycling can completely degrade low-molecular compounds of polyester materials, and the degradation products can be reused as raw materials for synthetic polyester after treatment, achieving material recycling in the true sense.

Existing polyester chemical recovery methods mainly include hydrolysis, alcoholysis, ammonolysis and other methods according to the type of decomposition agent. The hydrolysis method consumes a lot of acid and alkali and produces a large amount of waste liquid. The depolymerization product of the ammonolysis method cannot be directly used as a raw material for polyester regeneration. The alcoholysis method has natural advantages because it is the same or similar to the raw materials used in the polyester synthesis process, especially The alcoholysis method based on monomer diols in polyester synthesis has received widespread attention from the industry. However, the existing alcoholysis method has low reaction efficiency and low purity of the target product. It is very necessary to develop an efficient alcoholysis method with less impurities in the polyester material product.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of low reaction efficiency and product purity that need to be improved in the existing alcoholysis method of polyester materials, and provide a method for alcoholysis of polyester by falling film flow. According to the method of the present invention, the polyester is alcoholyzed. , the alcoholysis reaction has high efficiency, low reaction temperature, short reaction time, high product purity, easy to refine and purify, and the alcoholysis liquid can be recycled and reused after treatment.

The specific technical solution of the present invention is: a method for falling film flow alcoholysis of polyester, adding pretreated polyester waste and solvent into a stirring device, adding part of the catalyst after reaching the set temperature, and then reacting the resulting The liquid is transported to the falling film kettle for reaction. The reaction liquid further alcoholyzes the polyester while performing falling film flow. After the reaction, the alcoholysis liquid obtained is discharged from the outlet at the bottom of the falling film kettle. After post-processing, high purity can be obtained. Recycled polyester reaction raw materials.

Compared with the traditional method of alcoholysis reaction that relies entirely on the stirring blades in the reaction kettle to promote the flow of materials, in the present invention, the reaction liquid relies on gravity to form a film on the liquid film support in the falling film kettle and flows for alcoholization. The decomposition reaction greatly reduces the energy consumption of the driving force while improving the film-forming efficiency and surface renewal of the material flow. The material moves in a plug flow without backmixing, and the solution residence time can be effectively controlled by changing the process, greatly reducing the alcoholysis. time and improve the uniformity of alcoholysis reaction. The stirring device designed at the bottom not only provides discharging power, but also can further promote the further reaction of a small amount of incomplete alcoholysis materials and improve the alcoholysis effect.

Preferably, the polyester waste is any one of waste polyester plastics, bottle flakes, films, fibers, fabrics, melt discharge materials, pipes and sheets with a molecular weight exceeding 10,000 and an ester-based structure on the molecular main chain. species or several species.

Preferably, the solvent is a glycol compound.

Preferably, the catalyst is a two-component catalyst, including a metal salt and a nitrogen-containing polycyclic organic compound; wherein: the nitrogen-containing polycyclic organic compound is selected from cycloalkanes containing two nitrogen elements and a ring number of 2 or 3, One or more of the cyclic olefin compounds; the metal salt is selected from one or more of the metal alkoxides, metal carboxylates, and metal phosphates of potassium, zinc, aluminum, and titanium.

Compared with other types of nitrogen-containing polycyclic organic compounds under the above-mentioned limiting conditions of the present invention, two or more nitrogen-containing cyclic compounds can stabilize the protonation site and enhance the attack on the ester bonds on the polyester structure. And compared with monocyclic hydrocarbons, it has a better boiling point and less loss in the reaction. Furthermore, the team of the present invention accidentally discovered during the research process that the above-mentioned types of nitrogen-containing polycyclic organic compounds and specific types of metal salts can be used as a two-component catalyst to catalyze the alcoholysis of polyester, which can produce synergistic effects. The catalytic effect after compounding is far greater than that of a single component. In order to further analyze this synergistic mechanism, we conducted in-depth research and finally concluded that nitrogen-containing polycyclic organic compounds and hydroxyl groups in the solvent can form hydrogen bond donors, which in turn interact with functional groups in metal salts (such as zinc acetate). Carbonyl groups) combine to form a complex and jointly attack the ester bonds on the polyester, thereby effectively increasing the protonation of the carbon base on the polyester molecular chain and promoting the cleavage of the ester bonds. Therefore, the combination of metals and nitrogen-containing polycyclic organic compounds can greatly accelerate the process of ester bond cleavage and significantly improve the alcoholysis efficiency of polyester.

Furthermore, the nitrogen-containing polycyclic organic compound is selected from one or more of six-membered bicyclic guanidines, diazabicycloalkanes, and diazabicycloalkenes; the metal salt is selected from potassium, One or more of the metal carboxylates of zinc.

Preferably, the metal salt is added in a stirring device; the nitrogen-containing polycyclic organic matter is divided into two batches and added to the stirring device and the falling film kettle respectively, or added to the falling film kettle all at once.

Adding part of the catalyst to the stirring device can achieve primary alcoholysis of polyester waste. Adding the stirring device can improve the alcoholysis efficiency in the first stage, reduce the viscosity of the solution entering the falling film reactor, and improve solution transportation and falling film flow. rate.

On the other hand, during more in-depth research, the team of the present invention found that the timing of adding nitrogen-containing polycyclic organic compounds has a significant impact on the catalytic effect. For example, in our experiments in which nitrogen-containing polycyclic organic compounds were added to the reaction system together with metal salts, we found that nitrogen-containing polycyclic organic compounds are easily hydrolyzed and ring-decomposed, forming primary amines and then undergoing nucleophilic reactions, resulting in a significant reduction in polymerization. Ester degradation rate and monomer/prepolymer yield. For this reason, the present invention can effectively avoid the above technical problems by adding nitrogen-containing polycyclic organic matter to the stirring device or falling film kettle in batches or adding nitrogen-containing polycyclic organic matter to the falling film kettle all at once.

Preferably, the top of the falling film kettle is equipped with a material chamber, the bottom plate of the material chamber is a cloth template, the bottom of the cloth template is provided with a falling film support structure, and the cloth template is provided with pores that allow the reaction liquid to flow downward into the falling film support structure; The bottom of the falling film kettle is equipped with a stirring transmission device, which can further react and homogenize the alcoholysis liquid.

Preferably, the falling film kettle is provided with a jacket structure, and the jacket structure is provided with a thermal insulation system, a heat medium flow inlet and a heat medium flow outlet.

The above settings can further improve production efficiency and are suitable for large-scale industrial applications.

Preferably, the pre-treatment steps include but are not limited to one or more operations of crushing, cleaning, quality removal, drying and compression; the post-treatment steps include but are not limited to filtration, cleaning, crystallization and drying. One or more operations.

Preferably, the molar ratio of the polyester's ester group, solvent, metal salt and nitrogen-containing polycyclic organic matter is 1:2~30:0.0001~0.1:0.0001~0.05.

Preferably, the temperature of the stirring device is 150~220 ^° C, and the stirring time is 10~120 min; the temperature of the falling film kettle is 150~190 ^° C, and the material residence time is 2~60 min.

Compared with the existing technology, the present invention has the following technical effects:

(1) The present invention uses a falling film kettle flow method to alcoholyze polyester, which consumes less power and has no dead zone in material flow. The reaction process and effect are easy to control. The alcoholysis reaction is more efficient and is more conducive to obtaining high-purity products.

(2) Compared with the existing alcoholysis recovery polyester method, the alcoholysis method of the present invention is simple, using diol, one of the polyester polymerization monomers, as the solvent, and using nitrogen-containing polycyclic rings prepared without the need for reaction steps. Organic matter and metal salt are two-component catalysts with low catalyst cost, low alcoholysis reaction temperature, short reaction time, fast alcoholysis rate, wide applicability to raw materials, high product purity, and easy refining and purification.

Detailed ways

The present invention will be further described below in conjunction with examples.

Example 1

After crushing, cleaning, removing impurities and drying the waste PET material containing 1 mol of ester groups, put it into a stirring tank, add 10 mol of ethylene glycol, raise the temperature in the stirring tank to 190 ^° C, then add 0.001 mol of acetic acid Zinc and 0.0005 mol of 1,8-diazabicyclo[5.4.0]undec-7-ene. After reacting for 30 minutes, the reaction solution was transported to the material chamber of the falling film kettle through a pump, and 0.0015 was injected into the material chamber at the same time. Mol of 1,8-diazabicyclo[5.4.0]undec-7-ene completes the alcoholysis of the polyester molecular chain while performing the falling film flow of the solution. The reaction temperature in the falling film kettle is 175 ^o C, the alcoholysis liquid after 20 minutes of reaction is discharged from the bottom of the falling film kettle, and the alcoholysis rate reaches 100%. The alcoholysis liquid is filtered, washed, crystallized, and dried to obtain the alcoholysis product terephthalic acid with a purity of 81%. Bishydroxyethyl ester BHET.

The top of the falling film kettle is equipped with a material chamber. The bottom plate of the material chamber is a cloth template. The bottom of the cloth template is provided with a falling film support structure. The cloth template is provided with pores that allow the reaction liquid to flow downward into the falling film support structure; the falling film kettle There is a stirring transmission device at the bottom. In addition, the falling film kettle is provided with a jacket structure, and the jacket structure is provided with a thermal insulation system, a heat medium flow inlet and a heat medium flow outlet.

Example 2

After crushing, cleaning, removing impurities and drying the waste PTT material containing 1 mol of ester groups, put it into a stirring tank, add 8 mol of propylene glycol, raise the temperature in the stirring tank to 180 ^o C, then add 0.001 mol of ethylene glycol Aluminum, after reacting for 30 minutes, transport the reaction solution to the material chamber of the falling film kettle via a pump, and at the same time inject 0.003 mol of six-membered bicyclic guanidine into the material chamber to complete the alcoholysis of the polyester molecular chain while performing the falling film flow of the solution. , the reaction temperature in the falling film kettle is 170 ^o C, the alcoholysis liquid after 17 minutes of reaction is discharged from the bottom of the falling film kettle, the alcoholysis rate reaches 96%, the alcoholysis liquid can be filtered, washed, crystallized and dried. The alcoholysis product bishydroxypropyl terephthalate BHTT was obtained with a purity of 76%.

The top of the falling film kettle is equipped with a material chamber. The bottom plate of the material chamber is a cloth template. The bottom of the cloth template is provided with a falling film support structure. The cloth template is provided with pores that allow the reaction liquid to flow downward into the falling film support structure; the falling film kettle There is a stirring transmission device at the bottom. In addition, the falling film kettle is provided with a jacket structure, and the jacket structure is provided with a thermal insulation system, a heat medium flow inlet and a heat medium flow outlet.

Example 3

After crushing, cleaning, removing impurities and drying the waste PBT material containing 1 mol of ester groups, put it into a stirring tank, add 15 mol of butanediol, raise the temperature in the stirring tank to 170 ^o C, then add 0.003 mol of phosphoric acid Potassium and 0.001 mol of 1,4-diazabicyclo[2.2.2]octane were reacted for 30 minutes. The reaction solution was transported to the material chamber of the falling film reactor of the falling film reactor through a pump, and 0.005 mol was injected into the material chamber at the same time. 1,4-diazabicyclo[2.2.2]octane completes the alcoholysis of the polyester molecular chain material while performing the falling film flow of the solution. The reaction temperature in the falling film reactor of the falling film reactor is 160 ^o C, the alcoholysis liquid after 16 minutes of reaction is discharged from the bottom of the falling film reactor of the falling film reactor. The alcoholysis rate reaches 98%. The alcoholysis liquid can be filtered, washed, crystallized, and dried to obtain an alcoholysis product with a purity of 80%. Bishydroxybutyl terephthalate BHBT.

The top of the falling film kettle is equipped with a material chamber. The bottom plate of the material chamber is a cloth template. The bottom of the cloth template is provided with a falling film support structure. The cloth template is provided with pores that allow the reaction liquid to flow downward into the falling film support structure; the falling film kettle There is a stirring transmission device at the bottom. In addition, the falling film kettle is provided with a jacket structure, and the jacket structure is provided with a thermal insulation system, a heat medium flow inlet and a heat medium flow outlet.

Comparative Example 1 (using traditional stirred reactor)

After crushing, cleaning, removing impurities and drying the waste PET material containing 1 mol of ester groups, put it into a stirring tank, add 10 mol of ethylene glycol, raise the temperature in the stirring tank to 190 ^° C, then add 0.001 mol of acetic acid Zinc and 0.002 mol of 1,8-diazabicyclo[5.4.0]undec-7-ene were reacted for 50 minutes and the reaction liquid was discharged. The alcoholysis rate was 85%. The alcoholysis liquid was filtered and washed. , crystallize and dry to obtain the alcoholysis product bishydroxyethyl terephthalate BHET with a purity of 48%.

Comparative Example 2 (Add all catalysts in the stirred tank at one time)

After crushing, cleaning, removing impurities and drying the waste PET material containing 1 mol of ester groups, put it into a stirring tank, add 10 mol of ethylene glycol, raise the temperature in the stirring tank to 190 ^° C, then add 0.001 mol of acetic acid Zinc and 0.002 mol of 1,8-diazabicyclo[5.4.0]undec-7-ene. After reacting for 30 minutes, the reaction solution is transported to the material chamber of the falling film kettle through a pump, and the solution is allowed to fall film. At the same time, the alcoholysis of the polyester molecular chain is completed. The reaction temperature in the falling film kettle is 175 ^o C. After 20 minutes of reaction, the alcoholysis liquid is discharged from the bottom of the falling film kettle. The alcoholysis rate is 90%. The alcoholysis liquid is then passed through After filtration, cleaning, crystallization and drying, the alcoholysis product BHET with a purity of 58% can be obtained.

The top of the falling film kettle is equipped with a material chamber. The bottom plate of the material chamber is a cloth template. The bottom of the cloth template is provided with a falling film support structure. The cloth template is provided with pores that allow the reaction liquid to flow downward into the falling film support structure; the falling film kettle There is a stirring transmission device at the bottom. In addition, the falling film kettle is provided with a jacket structure, and the jacket structure is provided with a thermal insulation system, a heat medium flow inlet and a heat medium flow outlet.

Comparative Example 3 (single use of metal salt catalyst)

After crushing, cleaning, removing impurities and drying the waste PET material containing 1 mol of ester groups, put it into a stirring tank, add 10 mol of ethylene glycol, raise the temperature in the stirring tank to 190 ^° C, then add 0.003 mol of acetic acid Zinc, after reacting for 30 minutes, the reaction solution is transported to the material chamber of the falling film kettle through a pump, and the alcoholysis of the polyester molecular chain is completed while the solution falls into film. The reaction temperature in the falling film kettle is 175 ^o C. After 20 minutes, the alcoholysis liquid is discharged from the bottom of the falling film kettle. The alcoholysis rate is 68%. The alcoholysis liquid is filtered, washed, crystallized, and dried to obtain the alcoholysis product bishydroxyethyl terephthalate with a purity of 24%. Ester BHET.

The top of the falling film kettle is equipped with a material chamber. The bottom plate of the material chamber is a cloth template. The bottom of the cloth template is provided with a falling film support structure. The cloth template is provided with pores that allow the reaction liquid to flow downward into the falling film support structure; the falling film kettle There is a stirring transmission device at the bottom. In addition, the falling film kettle is provided with a jacket structure, and the jacket structure is provided with a thermal insulation system, a heat medium flow inlet and a heat medium flow outlet.

Comparative Example 4 (Single use of nitrogen-containing polycyclic organic catalysts)

After crushing, cleaning, removing impurities and drying the waste PET material containing 1 mol of ester groups, put it into a stirring tank, add 10 mol of ethylene glycol, raise the temperature in the stirring tank to 190 ^° C, stir for 30 minutes and then add the solution It is transported to the material chamber of the falling film kettle through a pump, and 0.002 mol of 1,8-diazabicyclo[5.4.0]undec-7-ene is injected into the material chamber at the same time to complete the falling film flow of the solution. For the alcoholysis of the polyester molecular chain, the reaction temperature in the falling film kettle is 175 ^° C. After 20 minutes of reaction, the alcoholysis liquid is discharged from the bottom of the falling film kettle. The alcoholysis rate is 88%. The alcoholysis liquid is then filtered and washed. , crystallize and dry to obtain the alcoholysis product bishydroxyethyl terephthalate BHET with a purity of 59%.

The top of the falling film kettle is equipped with a material chamber. The bottom plate of the material chamber is a cloth template. The bottom of the cloth template is provided with a falling film support structure. The cloth template is provided with pores that allow the reaction liquid to flow downward into the falling film support structure; the falling film kettle There is a stirring transmission device at the bottom. In addition, the falling film kettle is provided with a jacket structure, and the jacket structure is provided with a thermal insulation system, a heat medium flow inlet and a heat medium flow outlet.

It can be seen from the comparison of the data of the above-mentioned examples and comparative examples that the two-component catalyst of nitrogen-containing polycyclic organic matter and metal salt of the present invention can achieve efficient and rapid alcoholysis of polyester by adopting falling film flow mode, and can be recycled The purity of the regenerated products can reach a high level. The traditional stirred tank alcoholysis method (Comparative Example 1) has a low alcoholysis rate and low product purity; the method of adding two catalysts to the stirred tank at the same time and then performing falling film outflow alcoholysis (Comparative Example 2), alcoholysis The effects are also significantly lower than adding catalyst in the falling film kettle. Furthermore, the single-component catalyst of metal salt (Comparative Example 3) and the single-component catalyst of nitrogen-containing heterocyclic compound (Comparative Example 4) have low alcoholysis rate and low BHET yield. The above results show that the implementation effects obtained by the present invention cannot be achieved by using single-component catalysts, two-component catalysts without special processing, and traditional flow methods.

The above are only preferred embodiments of the present invention and do not limit the present invention in any way. Any simple modifications, changes and equivalent transformations made to the above embodiments based on the technical essence of the present invention still belong to the technical solution of the present invention. scope of protection.

Claims (10)

1. A method for falling film flow alcoholysis polyester, characterized in that: adding pretreated polyester waste and solvent into a stirring device, adding part of the catalyst after reaching the set temperature, and then transporting the resulting reaction liquid The reaction is carried out in the falling film kettle. The reaction liquid is further alcoholyzed to the polyester while flowing into the falling film. After the reaction, the alcoholysis liquid obtained is discharged from the outlet at the bottom of the falling film kettle. After post-processing, a high-purity recyclable solution is obtained. Polyester reaction raw materials utilized; The catalyst is a two-component catalyst, including metal salts and nitrogen-containing polycyclic organic matter; wherein: the nitrogen-containing polycyclic organic matter is selected from cycloalkanes and cycloalkenes containing two nitrogen elements and with a ring number of 2 or 3. One or more compounds; the metal salt is selected from one or more metal alkoxides, metal carboxylates, and metal phosphates of potassium, zinc, aluminum, and titanium; The top of the falling film kettle is equipped with a material chamber. The bottom plate of the material chamber is a cloth template. The bottom of the cloth template is provided with a falling film support structure. The cloth template is provided with pores that allow the reaction liquid to flow downward into the falling film support structure. 2. The method according to claim 1, characterized in that: the polyester waste is waste polyester plastic, bottle flakes, films, fibers, fabrics, melts with a molecular weight exceeding 10,000 and an ester group structure on the molecular main chain. Any one or more of waste materials, pipes and sheets. 3. The method of claim 1, wherein the solvent is a glycol compound. 4. The method of claim 1, characterized in that: the metal salt is added in a stirring device; the nitrogen-containing polycyclic organic matter is divided into two batches and added to the stirring device and the falling film kettle respectively, or in one go Add to falling film kettle. 5. The method of claim 1, wherein the nitrogen-containing polycyclic organic compound is selected from one of six-membered bicyclic guanidines, diazabicycloalkanes, diazabicycloalkenes, or Several kinds; The metal salt is selected from one of the metal carboxylates of potassium and zinc. 6. The method according to claim 1, characterized in that: the bottom of the falling film kettle is provided with a stirring transmission device. 7. The method of claim 1, wherein the falling film kettle is provided with a jacket structure, and the jacket structure is provided with a thermal insulation system, a heat medium flow inlet and a heat medium flow outlet. 8. The method according to claim 1, characterized in that: the pre-treatment step includes one or more operations of crushing, cleaning, quality removal, drying and compression; the post-treatment step includes filtering, cleaning , one or more operations of crystallization and drying. 9. The method according to claim 1, characterized in that: the molar ratio of the ester group, solvent, metal salt and nitrogen-containing polycyclic organic matter of the polyester is 1:2~30:0.0001~0.1:0.0001~0.05 . 10. The method according to claim 1, characterized in that: the temperature of the stirring device is 150~220 ^° C, and the stirring time is 10~120 min; the temperature of the falling film kettle is 150~190 ^° C, The material residence time is 2 ~ 60 minutes.