A process and system for the enzymatic hydrolysis of waste PET to co-produce high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide.

Abstract

This invention relates to the field of waste PET degradation and recycling technology, specifically to a process and system for the enzymatic hydrolysis of waste PET to co-produce high-purity diammonium terephthalate (PTA), purified terephthalic acid (TPA), and terephthalamide (TPD). The process provided by this invention mainly includes the steps of enzymatic hydrolysis of waste PET, primary freeze crystallization, secondary freeze crystallization, preparation of purified terephthalic acid (PTA), and preparation of terephthalamide (TPD). PET is gently degraded using PET hydrolytic enzymes, and pH is controlled using ammonia water / ammonia gas to generate diammonium terephthalate (PTA). After multi-stage freeze crystallization and membrane filtration purification, diammonium terephthalate crystals with a purity >99.5% are obtained. The diammonium terephthalate crystals can be split to prepare two high-value-added aromatic monomers: purified terephthalic acid (PTA) (99.9% purity) and terephthalamide (TPD) (99.5% purity). This is a complete, continuous, and green production process.

Description

Technical Field

[0001] This invention relates to the field of waste PET degradation and recycling technology, specifically to a process and system for enzymatically hydrolyzing waste PET to co-produce high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide. Background Technology

[0002] Polyethylene terephthalate (PET), with its excellent mechanical properties, high transparency, good barrier properties, and processability, has become one of the most widely used thermoplastic polyesters in beverage packaging, synthetic fibers, sheets, and engineering plastics. With the continuous increase in annual PET production, the improper disposal of large quantities of waste PET products (especially disposable beverage bottles and textiles) will pose a serious threat to terrestrial and marine ecosystems. PET molecules are rich in aromatic benzene ring structures, have high crystallinity, and possess extremely strong resistance to hydrolysis, light, and microbial attack.

[0003] The recycling of waste PET mainly includes two methods: physical melt recycling and chemical depolymerization. Physical recycling is simple, but the intrinsic viscosity and molecular weight distribution of the recycled material are significantly degraded, making high-value recycling difficult. Chemical recycling (such as ethylene glycol alcoholysis, methanol alcoholysis, and hydrolysis) can depolymerize PET into monomers such as diethyl terephthalate (BHET) or terephthalic acid (TA), but it usually requires high temperature and high pressure conditions, demanding reaction conditions, large equipment investment, and the use of organic solvents or acid / base catalysts can lead to secondary pollution and equipment corrosion.

[0004] In recent years, enzymatic degradation has attracted widespread attention due to its mild reaction conditions and environmental friendliness. However, traditional bio-enzymatic hydrolysis processes require the use of sodium hydroxide or phosphate buffer to maintain the pH of the hydrolysis system, and the degradation product is sodium terephthalate, introducing a large number of sodium ions into the system. A subsequent acidification step is needed to convert the sodium salt into free TA, inevitably generating high-salt organic wastewater and resulting in high costs for salt residue treatment. Furthermore, due to the difficulty in crystallizing and purifying the sodium salt form, impurities such as pigments, oligomers, and residual enzyme proteins are difficult to remove effectively, leading to a final TA purity that fails to meet polymerization-grade standards, thus limiting the direct application of recycled TA in high-end polyester products. Summary of the Invention

[0005] In view of this, the present invention provides a process and system for the enzymatic hydrolysis of waste PET to co-produce high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide. Under mild bio-enzymatic hydrolysis conditions, the process generates diammonium terephthalate in situ using ammonia as a pH adjuster. After multi-stage low-temperature freezing crystallization and membrane filtration for deep impurity removal, high-purity diammonium terephthalate (DAT) is obtained. It can also simultaneously co-produce two high-value-added aromatic monomers, purified terephthalic acid (PTA) and terephthalamide (TPD), making it a complete, continuous, and green production process.

[0006] To solve the above technical problems, this invention provides a process for the enzymatic hydrolysis of waste PET to co-produce high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide, comprising the following steps: Waste PET enzymatic hydrolysis: Waste PET material is mixed with water and crude PET hydrolysis enzyme solution to carry out enzymatic hydrolysis reaction. During the enzymatic hydrolysis process, ammonia water or ammonia gas is introduced to adjust the pH of the system to 6-10. The terephthalic acid continuously generated during the enzymatic hydrolysis process reacts with ammonia to generate diammonium terephthalate. After the diammonium terephthalate reaches supersaturation in the enzymatic hydrolysate solution, a solid is precipitated. After solid-liquid separation, solid diammonium terephthalate and enzymatic hydrolysate containing ethylene glycol and diammonium terephthalate are obtained. First-stage freeze-crystallization: The solid diammonium terephthalate is dissolved in water to obtain a first aqueous solution. The solution is filtered to remove insoluble impurities. The filtrate is then frozen and kept warm to crystallize. After solid-liquid separation, crude diammonium terephthalate and a first-stage filtrate containing diammonium terephthalate are obtained. Secondary freeze-crystallization: The crude diammonium terephthalate is dissolved in water to obtain a second aqueous solution. The solution is filtered to remove colored impurities and oligomers. The filtrate is then frozen and crystallized. After solid-liquid separation, purified diammonium terephthalate crystals and a secondary filtrate containing diammonium terephthalate are obtained. Preparation of purified terephthalic acid: Dissolve the purified terephthalic acid diammonium crystals in water, add acid to adjust the pH to 2.0~3.5 to precipitate terephthalic acid, separate the solid and liquid, wash and dry the solid to obtain purified terephthalic acid, and add alkali to the filtrate to distill ammonia and recover ammonia gas; Preparation of terephthalamide: The purified diammonium terephthalate crystals were pyrolyzed at a constant temperature in a pyrolysis reactor to generate terephthalamide. During the pyrolysis process, the pressure inside the reactor was maintained at 0.4~0.6MPa. After the pyrolysis was completed, the reactor was cooled, and the gaseous free ammonia was absorbed by water and reused for enzymatic hydrolysis. The solid phase was washed and dried to obtain terephthalamide.

[0007] The present invention also provides a system for enzymatically hydrolyzing waste PET to co-produce high-purity diammonium terephthalate, purified terephthalic acid and terephthalamide, comprising a waste PET enzymatic hydrolysis unit, a first purification unit, a second purification unit and a co-production conversion unit connected in sequence; The waste PET enzymatic hydrolysis unit includes an enzymatic hydrolysis device and a filtration device connected in sequence. The enzymatic hydrolysis device is equipped with an ammonia water or ammonia gas inlet, a PET hydrolysis crude enzyme liquid inlet, a waste PET feeding port, and a liquid outlet connected to the filtration device. The filtration device separates diammonium terephthalate solid from the enzymatic hydrolysis liquid containing ethylene glycol and diammonium terephthalate. The first refining unit includes a first heating and dissolving device, a first filtering device, a first freezing and crystallization device, and a first membrane filtering device connected in sequence. The first heating and dissolving device is used to dissolve the diammonium terephthalate obtained from the waste PET enzymatic hydrolysis unit, and the first filtering device filters out insoluble impurities to obtain a first filtrate. The first freezing and crystallization device precipitates the crude diammonium terephthalate solid from the first filtrate. The crude diammonium terephthalate enters the second refining unit, and the obtained freezing filtrate is heated and filtered by the first membrane filtering device before being reused in the first heating and dissolving device. The structure of the second refining unit is the same as that of the first refining unit, including a second heating and dissolving device, a second filtering device, a second freezing crystallization device, and a second membrane filtering device connected in sequence. Diammonium terephthalate crystals are precipitated through the second freezing crystallization device. The obtained diammonium terephthalate crystals enter the co-production conversion unit. The co-production conversion unit includes a terephthalic acid conversion device and a terephthalamide conversion device, which are respectively connected to the second refining unit via branches, to obtain refined terephthalic acid and terephthalamide, respectively. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the process of the system for the enzymatic hydrolysis of waste PET to co-produce high-purity diammonium terephthalate, purified terephthalic acid and terephthalamide according to the present invention. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0010] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art and should not be interpreted in an idealized or overly formal sense unless specifically defined.

[0011] In existing technologies, there are also processes that use chemical ammonolysis of PET under high temperature conditions. However, these processes require a high-temperature, high-pressure, and closed environment above 120°C, which places high demands on equipment and requires large investments. Furthermore, they can only produce terephthalamide and cannot simultaneously produce high-purity terephthalic acid. In addition, the purification of conventional salts only uses a single cooling crystallization process, resulting in severe impurity inclusion and significant color differences in the product.

[0012] In view of this, the present invention provides a process and system for the enzymatic hydrolysis of waste PET to co-produce high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide. The process uses ammonia water or ammonia gas as a pH adjuster to generate diammonium terephthalate in situ. After multi-stage low-temperature freezing crystallization and membrane filtration for deep impurity removal, it can simultaneously co-produce two high-value-added aromatic monomers, purified terephthalic acid and terephthalamide. This is a complete and green preparation process.

[0013] The process for co-producing high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide through enzymatic hydrolysis of waste PET provided by this invention includes the following steps: Waste PET enzymatic hydrolysis: Waste PET material is mixed with water and crude PET hydrolysis enzyme solution to carry out enzymatic hydrolysis reaction. During the enzymatic hydrolysis process, ammonia water or ammonia gas is introduced to adjust the pH of the system to 6~10. The terephthalic acid continuously produced during the enzymatic hydrolysis process reacts with ammonia to generate diammonium terephthalate. After the diammonium terephthalate reaches supersaturation in the enzymatic hydrolysate solution, a solid is precipitated. After the enzymatic hydrolysis reaction is completed, the solid and liquid are separated to obtain solid diammonium terephthalate and enzymatic hydrolysate containing ethylene glycol and diammonium terephthalate. First-stage freeze-crystallization: Solid diammonium terephthalate is dissolved in water to obtain a first aqueous solution. The solution is filtered to remove insoluble impurities. The filtrate is then frozen and kept warm to crystallize. After solid-liquid separation, crude diammonium terephthalate and a first-stage filtrate containing diammonium terephthalate are obtained. Secondary freeze-crystallization: Crude diammonium terephthalate is dissolved in water to obtain a second aqueous solution. The solution is filtered to remove colored impurities and oligomers. The filtrate is then frozen and crystallized. After solid-liquid separation, purified diammonium terephthalate crystals and a secondary filtrate containing diammonium terephthalate are obtained. Preparation of purified terephthalic acid: Dissolve diammonium terephthalate crystals in water, add acid to adjust the pH to 2.0~3.5 to precipitate terephthalic acid, separate the solid and liquid, wash and dry the solid to obtain purified terephthalic acid, and add alkali to the filtrate to distill ammonia and recover ammonia gas; Preparation of terephthalamide: Purified diammonium terephthalate crystals are pyrolyzed at a constant temperature in a pyrolysis reactor to generate terephthalamide. During the pyrolysis process, the pressure inside the reactor is maintained at 0.4~0.6MPa. After the pyrolysis is completed, the reactor is cooled, and the gaseous free ammonia is absorbed by water and reused for enzymatic hydrolysis. The solid phase is washed and dried to obtain terephthalamide.

[0014] The process provided by this invention for the enzymatic hydrolysis of waste PET to co-produce high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide mainly includes several steps: enzymatic hydrolysis of waste PET, primary freeze-crystallization, secondary freeze-crystallization, preparation of purified terephthalic acid, and preparation of terephthalamide. In the enzymatic hydrolysis process of waste PET, this invention uses ammonia water / ammonia gas instead of the traditional sodium hydroxide or potassium hydroxide buffer system, and the entire process does not introduce sodium. + K + The process removes metallic impurities, and the acidified wastewater from the subsequent terephthalic acid production contains only ammonium ions. After alkali removal and ammonia distillation, the ammonia gas is absorbed by water to obtain ammonia water, which can be reused for pH adjustment. The entire process generates no high-salt solid waste, demonstrating significant environmental advantages. Furthermore, the process employs two freeze-crystallization steps, including hot water dissolution, filtration, and freeze crystallization. This combination of hot water dissolution, atmospheric pressure filtration / membrane filtration, and freeze crystallization effectively removes pigments, enzymes, and oligomers, resulting in purified terephthalic acid diammonium crystals with a purity ≥99.9%. The purified terephthalic acid product co-produced using these crystals meets polyester grade standards, and the terephthalamide co-produced has a purity ≥99.5%. Moreover, this process can produce two high-value-added products by using a single refined intermediate, diammonium terephthalate crystals, taking into account both the polyester raw material PTA and the organic synthesis intermediate terephthalamide, greatly improving the comprehensive utilization rate of waste PET raw materials, and realizing the closed-loop circulation of ammonia throughout the entire process. The entire production process has no ammonia-containing waste gas emissions, low raw material loss, and lower industrial production costs.

[0015] In some possible embodiments, the enzymatic hydrolysate containing ethylene glycol and diammonium terephthalate obtained in the enzymatic hydrolysis step of waste PET can be reused multiple times in the enzymatic hydrolysis reaction of waste PET materials, so that ethylene glycol is enriched in the enzymatic hydrolysate. After the concentration of ethylene glycol reaches the preset requirement, the diammonium terephthalate solid is precipitated by evaporation and dehydration. After solid-liquid separation, the mother liquor is distilled to obtain ethylene glycol, and the diammonium terephthalate solid is recovered for subsequent freeze crystallization purification steps.

[0016] In some possible embodiments, in the enzymatic hydrolysis step of waste PET, the temperature of the enzymatic hydrolysis reaction is 50~70℃, the enzymatic hydrolysis time is 5~48h, and the stirring speed during the enzymatic hydrolysis process is 80~150r / min.

[0017] The enzymatic hydrolysis process of waste PET in this invention is carried out under mild conditions throughout, and the degradation of waste PET can be achieved under normal pressure at 50~70℃. It does not require a high-temperature and high-pressure reactor, and the required equipment investment and energy consumption are far lower than those of chemical ammonolysis and supercritical hydrolysis processes.

[0018] In some possible embodiments, the concentration of ammonia used to adjust the pH of the system is 0.1~3 mol / L.

[0019] In some possible embodiments, the mass ratio of waste PET material to water in the enzymatic hydrolysis step is 1:2 to 4. This ratio ensures both complete degradation of the waste PET material and maximizes the precipitation of diammonium terephthalate solids during the enzymatic hydrolysis process.

[0020] In some possible embodiments, in the primary and secondary freeze-crystallization steps: the temperature of the water used is 50~95℃, the temperature of the freeze-crystallization is 0~5℃, and the holding time is 1~3h.

[0021] In some possible embodiments, in the first freeze-crystallization step: solid diammonium terephthalate is dissolved in water to obtain a first aqueous solution, which is filtered to remove insoluble impurities. The crude diammonium terephthalate obtained by solid-liquid separation is used for a second freeze-crystallization. The first filtrate containing diammonium terephthalate is heat-exchanged with the influent of the freeze-crystallization and filtered. It is then heat-exchanged again with the influent of the freeze-crystallization and then combined into the first aqueous solution.

[0022] Specifically, in the first freeze-crystallization step, an atmospheric pressure filtration device can be used to filter the first aqueous solution to remove insoluble impurities from the filtrate. After exchanging heat with the feed water for freeze-crystallization, the temperature of the first filtrate containing diammonium terephthalate can be increased from 0~5℃ to 15~25℃. Then, it is filtered through a 1000Da membrane filtration device to remove trace impurities from the filtrate. After exchanging heat with the feed water for freeze-crystallization again, a first filtrate containing diammonium terephthalate with a temperature of 75~80℃ is obtained. This first filtrate is then mixed with the first aqueous solution for subsequent steps.

[0023] In some possible embodiments, in the secondary freeze-crystallization step: crude diammonium terephthalate is dissolved in water to obtain a second aqueous solution, which is filtered to remove insoluble impurities, and solid-liquid separation is performed to obtain refined diammonium terephthalate crystals and a secondary filtrate containing diammonium terephthalate. The obtained secondary filtrate containing diammonium terephthalate is heat-exchanged with the influent of the freeze-crystallization and filtered, and then heat-exchanged again with the influent of the freeze-crystallization, and then combined into the second aqueous solution.

[0024] Specifically, in the secondary freeze-crystallization step, an ultrafiltration membrane filtration system is used to filter the second aqueous solution, removing colored impurities, trace amounts of oligomers, and other impurities. The ultrafiltration membrane can be an organic membrane with a molecular weight cutoff of 300-3000 Da, and the operating pressure is 1.0-2.5 MPa. After exchanging heat with the feed water for freeze-crystallization, the temperature of the secondary filtrate containing diammonium terephthalate can be increased from 0-5℃ to 15-25℃. Then, it passes through a 500 Da membrane filtration device to remove trace impurities. After another heat exchange with the feed water for freeze-crystallization, a secondary filtrate containing diammonium terephthalate at a temperature of 75-80℃ is obtained. This secondary filtrate is then mixed with the second aqueous solution for subsequent steps.

[0025] In some possible embodiments, the preparation step of terephthalamide involves isothermal pyrolysis at a temperature of 180-260°C for 1-3 hours.

[0026] In the preparation of terephthalamide, purified diammonium terephthalate crystals are pyrolyzed in a pressure-controlled pyrolysis reactor. By controlling the pressure inside the reactor at 0.4~0.6 MPa, the pyrolysis of diammonium terephthalate into terephthalamide is ensured. The trace amounts of terephthalic acid inevitably generated during pyrolysis can be removed by sequentially washing the pyrolysis products with alkali and water. The washed terephthalamide is then dried to obtain pure solid terephthalamide.

[0027] The present invention also provides a system for enzymatically hydrolyzing waste PET to co-produce high-purity diammonium terephthalate, purified terephthalic acid and terephthalamide. The system includes a waste PET enzymatic hydrolysis unit, a first purification unit, a second purification unit and a co-production conversion unit connected in sequence. The waste PET enzymatic hydrolysis unit includes an enzymatic hydrolysis device and a filtration device connected in sequence. The enzymatic hydrolysis device is equipped with an ammonia water or ammonia gas inlet, a PET hydrolysis crude enzyme solution inlet, a waste PET feeding port, and a liquid outlet connected to the filtration device. The filtration device separates diammonium terephthalate solid from the enzymatic hydrolysis solution containing ethylene glycol and diammonium terephthalate. The first refining unit includes a first heating and dissolving device, a first filtering device, a first freezing and crystallization device, and a first membrane filtering device connected in sequence. The first heating and dissolving device is used to dissolve the diammonium terephthalate obtained from the waste PET enzymatic hydrolysis unit, and the first filtering device filters out insoluble impurities to obtain a first filtrate. The first freezing and crystallization device precipitates the crude diammonium terephthalate solid from the first filtrate. The crude diammonium terephthalate obtained enters the second refining unit, and the obtained freezing filtrate is heated and filtered by the first membrane filtering device before being reused in the first heating and dissolving device. The structure of the second refining unit is the same as that of the first refining unit, including a second heating and dissolving device, a second filtering device, a second freezing crystallization device, and a second membrane filtering device connected in sequence. Diammonium terephthalate crystals are precipitated through the second freezing crystallization device. The obtained diammonium terephthalate crystals enter the co-production conversion unit. The co-production conversion unit includes a terephthalic acid conversion unit and a terephthalamide conversion unit, which are respectively connected to the second purification unit via branch lines, to obtain purified terephthalic acid and terephthalamide, respectively.

[0028] The system provided by this invention includes a waste PET enzymatic hydrolysis unit, a first purification unit, a second purification unit, and a co-production conversion unit connected in sequence. The waste PET enzymatic hydrolysis unit degrades PET, which then reacts with ammonia to produce diammonium terephthalate, continuously precipitating solids from the hydrolysate. These solids are then sequentially processed through the first and second purification units to obtain purified diammonium terephthalate crystals. These diammonium terephthalate crystals are then processed through the co-production conversion unit to obtain purified terephthalic acid and terephthalamide, respectively.

[0029] In some possible embodiments, the waste PET enzymatic hydrolysis unit also includes an evaporation device and a distillation device. The resulting enzymatic hydrolysate containing ethylene glycol and diammonium terephthalate can be recycled back into the waste PET enzymatic hydrolysis unit to achieve ethylene glycol enrichment. When the ethylene glycol content reaches a preset concentration, the enzymatic hydrolysate containing ethylene glycol and diammonium terephthalate is evaporated by the evaporation device, and the solid diammonium terephthalate is recovered after precipitation. The mother liquor is used to recover ethylene glycol through the distillation device.

[0030] In some possible embodiments, the first refining unit and the second refining unit each independently include a primary heat exchange device and a secondary heat exchange device. The primary heat exchange device is located upstream of the corresponding membrane filtration device, and the secondary heat exchange device is located downstream of the corresponding membrane filtration device. The heat source medium for both the primary and secondary heat exchange devices is supplied by the hot solution in the heating and dissolving device.

[0031] In some possible embodiments, in the co-production conversion unit, the terephthalic acid conversion device is configured to dissolve diammonium terephthalate crystals in water and precipitate terephthalic acid after pH adjustment; the terephthalamide conversion device is configured to pyrolyze diammonium terephthalate crystals into terephthalamide in a pressure-controlled pyrolysis reactor.

[0032] In some possible embodiments, the cogeneration conversion unit also includes an ammonia recovery device, which is used to absorb ammonia released during the production process of the terephthalic acid conversion unit with water, and the resulting ammonia water is fed back to the enzymatic hydrolysis unit to adjust the pH of the system.

[0033] The continuous production process and system of the present invention will be further described below through a specific embodiment.

[0034] The process for co-producing high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide through enzymatic hydrolysis of waste PET provided in this embodiment includes the following steps: Enzymatic hydrolysis of waste PET: 200g of waste PET material crushed to less than 2mm is added to a 2L enzymatic hydrolysis vessel, along with 200mL of deionized water and crude enzyme solution. The mixture is stirred at 60℃ and 100r / min for 10h. During this time, 1mol / L dilute ammonia is continuously added dropwise to maintain the pH of the system at 8.5. After the enzymatic hydrolysis reaction is completed, solid and liquid are separated to obtain diammonium terephthalate solid. The filtrate containing ethylene glycol and diammonium terephthalate is recycled back to the enzymatic hydrolysis vessel.

[0035] First-stage freeze-crystallization: The solid diammonium terephthalate obtained in the previous step was added to 65 mL of 90 °C hot water to completely dissolve it to obtain the first aqueous solution. The solution was filtered with filter paper to remove insoluble impurities. The filtrate was transferred to a crystallization vessel and kept at 0 °C for 3 h to precipitate crude diammonium terephthalate. After filtration, 75.5 g of crude diammonium terephthalate and a filtrate containing diammonium terephthalate were obtained. The filtrate was then returned to the first aqueous solution for recycling after heat exchange and filtration through a 1000 Da membrane.

[0036] Secondary freeze-crystallization: 75.5g of crude diammonium terephthalate obtained in the previous step was added to 100mL of 90℃ hot water to completely dissolve it to obtain a second aqueous solution. The solution was filtered through a 1000Da organic membrane at 20MPa pressure to remove colored impurities and oligomers. The permeate was transferred to a crystallization vessel and frozen at 0℃ for 3h for secondary freeze-crystallization. After filtration, 40.5g of purified diammonium terephthalate crystals (purity 99.6%) and a secondary filtrate containing diammonium terephthalate were obtained. The filtrate was then returned to the second aqueous solution for recycling after heat exchange and filtration through a 500Da membrane.

[0037] Preparation of purified terephthalic acid: 20g of purified terephthalic acid diammonium crystals were dissolved in 230mL of water, and the pH was adjusted to <3 with 20% dilute sulfuric acid. White terephthalic acid crystals precipitated. After filtration, the filter cake was washed with hot water and dried at 110℃ to obtain 16.5g of purified terephthalic acid with a purity of 99.9%. Alkali solution was added to the obtained filtrate and ammonia gas was distilled off. The ammonia gas was absorbed by water to obtain ammonia water, which was then reused.

[0038] Preparation of terephthalamide: 20.5g of purified diammonium terephthalate crystals were dried at 80-90℃ and then pyrolyzed at 210℃ for 2h in a pyrolysis reactor, during which the pressure inside the reactor was maintained at 0.4-0.6MPa. After pyrolysis, the mixture was cooled, and the gaseous free ammonia was absorbed by water and reused for enzymatic hydrolysis. The solid phase was washed with hot sodium hydroxide solution and water and then dried to obtain 16.8g of terephthalamide with a purity of 99.5%.

[0039] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A process for the enzymatic hydrolysis of waste PET to co-produce high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide, characterized in that, Includes the following steps: Waste PET enzymatic hydrolysis: Waste PET material is mixed with water and crude PET hydrolysis enzyme solution to carry out enzymatic hydrolysis reaction. During the enzymatic hydrolysis process, ammonia water or ammonia gas is introduced to adjust the pH of the system to 6-10. The terephthalic acid continuously generated during the enzymatic hydrolysis process reacts with ammonia to generate diammonium terephthalate. After the diammonium terephthalate reaches supersaturation in the enzymatic hydrolysate solution, a solid is precipitated. After solid-liquid separation, solid diammonium terephthalate and enzymatic hydrolysate containing ethylene glycol and diammonium terephthalate are obtained. First-stage freeze-crystallization: The solid diammonium terephthalate is dissolved in water to obtain a first aqueous solution. The solution is filtered to remove insoluble impurities. The filtrate is then frozen and kept warm to crystallize. After solid-liquid separation, crude diammonium terephthalate and a first-stage filtrate containing diammonium terephthalate are obtained. Secondary freeze-crystallization: The crude diammonium terephthalate is dissolved in water to obtain a second aqueous solution. The solution is filtered to remove colored impurities and oligomers. The filtrate is then frozen and crystallized. After solid-liquid separation, purified diammonium terephthalate crystals and a secondary filtrate containing diammonium terephthalate are obtained. Preparation of purified terephthalic acid: Dissolve the purified terephthalic acid diammonium crystals in water, add acid to adjust the pH to 2.0~3.5 to precipitate terephthalic acid, separate the solid and liquid, wash and dry the solid to obtain purified terephthalic acid, and add alkali to the filtrate to distill ammonia and recover ammonia gas; Preparation of terephthalamide: The purified diammonium terephthalate crystals were pyrolyzed at a constant temperature in a pyrolysis reactor to generate terephthalamide. During the pyrolysis process, the pressure inside the reactor was maintained at 0.4~0.6MPa. After the pyrolysis was completed, the reactor was cooled, and the gaseous free ammonia was absorbed by water and reused for enzymatic hydrolysis. The solid phase was washed and dried to obtain terephthalamide.

2. The process for co-producing high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide by enzymatic hydrolysis of waste PET as described in claim 1, characterized in that, The enzymatic hydrolysate containing ethylene glycol and diammonium terephthalate obtained in the enzymatic hydrolysis step of the waste PET is repeatedly reused in the enzymatic hydrolysis reaction of waste PET materials, so that ethylene glycol is enriched in the enzymatic hydrolysate. Then, the enzymatic hydrolysate is evaporated and dehydrated, and diammonium terephthalate solid is precipitated. After solid-liquid separation, the mother liquor is distilled to obtain ethylene glycol. The obtained diammonium terephthalate solid is recovered by the first and second freeze crystallization.

3. The process for co-producing high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide by enzymatic hydrolysis of waste PET as described in claim 1, characterized in that, In the enzymatic hydrolysis step of the waste PET, the temperature of the enzymatic hydrolysis reaction is 50~70℃, the hydrolysis time is 5~48h, and the stirring speed during the hydrolysis process is 80~150r / min; and / or The concentration of the ammonia solution is 0.1~3 mol / L; and / or The mass ratio of the waste PET material to water is 1:2~4.

4. The process for co-producing high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide by enzymatic hydrolysis of waste PET as described in claim 1, characterized in that, In the first and second freeze-crystallization steps: the temperature of the water used to dissolve the diammonium terephthalate solid is 50~95℃, the temperature of the freeze-crystallization is 0~5℃, and the holding time is 1~3h.

5. The process for co-producing high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide by enzymatic hydrolysis of waste PET as described in claim 1, characterized in that, In the first freeze-crystallization step: the solid diammonium terephthalate is dissolved in water to obtain a first aqueous solution. The first aqueous solution is filtered to remove insoluble impurities. Solid-liquid separation is performed to obtain crude diammonium terephthalate and a first filtrate. The crude diammonium terephthalate enters the second freeze-crystallization step. In the secondary freeze-crystallization step: the crude diammonium terephthalate is dissolved in water to obtain a second aqueous solution, which is then filtered to remove insoluble impurities, and solid-liquid separation is performed to obtain purified diammonium terephthalate crystals and a secondary filtrate.

6. The process for co-producing high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide by enzymatic hydrolysis of waste PET as described in claim 5, characterized in that, The first freezing crystallization step is a continuous processing step. The resulting first filtrate is recycled to the first aqueous solution after first-stage heat exchange heating, first membrane filtration and second-stage heat exchange heating. The heat source medium for the first-stage heat exchange heating and the second-stage heat exchange heating steps is supplied by the hot solution obtained from the filtration of the first aqueous solution. The secondary freezing and crystallization step is a continuous processing step. The resulting secondary filtrate is recycled to the second aqueous solution after primary heat exchange and heating, primary membrane filtration, and secondary heat exchange and heating. The heat source medium for both the primary and secondary heat exchange and heating steps is supplied by the hot solution obtained from the filtration of the second aqueous solution.

7. The process for co-producing high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide by enzymatic hydrolysis of waste PET as described in claim 1, characterized in that, In the step of preparing terephthalamide: the temperature of the isothermal pyrolysis is 180~260℃, and the pyrolysis time is 1~3h.

8. A system for the enzymatic hydrolysis of waste PET to co-produce high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide, characterized in that, The system is used to implement the process of enzymatic hydrolysis of waste PET to co-produce high-purity diammonium terephthalate, purified terephthalic acid and terephthalamide as described in any one of claims 1 to 7, comprising a waste PET enzymatic hydrolysis unit, a first refining unit, a second refining unit and a co-production conversion unit connected in sequence; The waste PET enzymatic hydrolysis unit includes an enzymatic hydrolysis device and a filtration device connected in sequence. The enzymatic hydrolysis device is equipped with an ammonia water or ammonia gas inlet, a PET hydrolysis crude enzyme liquid inlet, a waste PET feeding port, and a liquid outlet connected to the filtration device. The filtration device separates diammonium terephthalate solid from the enzymatic hydrolysis liquid containing ethylene glycol and diammonium terephthalate. The first refining unit includes a first heating and dissolving device, a first filtering device, a first freezing and crystallization device, and a first membrane filtering device connected in sequence. The first heating and dissolving device is used to dissolve the diammonium terephthalate obtained from the waste PET enzymatic hydrolysis unit, and the first filtering device filters out insoluble impurities to obtain a first filtrate. The first freezing and crystallization device precipitates the crude diammonium terephthalate solid from the first filtrate. The obtained crude diammonium terephthalate enters the second refining unit, and the obtained freezing filtrate is heated and filtered by the first membrane filtering device before being reused in the first heating and dissolving device. The structure of the second refining unit is the same as that of the first refining unit, including a second heating and dissolving device, a second filtering device, a second freezing crystallization device, and a second membrane filtering device connected in sequence. Diammonium terephthalate crystals are precipitated through the second freezing crystallization device. The obtained diammonium terephthalate crystals enter the co-production conversion unit. The co-production conversion unit includes a terephthalic acid conversion device and a terephthalamide conversion device, which are respectively connected to the second refining unit via branches, to obtain refined terephthalic acid and terephthalamide, respectively.

9. The system for co-producing high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide by enzymatic hydrolysis of waste PET as described in claim 8, characterized in that, The waste PET enzymatic hydrolysis unit also includes an evaporation device and a distillation device. The resulting enzymatic hydrolysate containing ethylene glycol and diammonium terephthalate is recycled. When the ethylene glycol content reaches a preset concentration, the enzymatic hydrolysate containing ethylene glycol and diammonium terephthalate is sequentially passed through the evaporation device to recover the solid diammonium terephthalate, and through the distillation device to recover the ethylene glycol; and / or The first refining unit and the second refining unit each independently include a primary heat exchange device and a secondary heat exchange device. The primary heat exchange device is located upstream of the corresponding membrane filtration device, and the secondary heat exchange device is located downstream of the corresponding membrane filtration device. The heat source medium for both the primary and secondary heat exchange devices is supplied by the hot solution obtained from the filtration of the heating and dissolving device.

10. The system for co-producing high-purity diammonium terephthalate, purified terephthalic acid, and terephthalamide by enzymatic hydrolysis of waste PET as described in claim 8, characterized in that, In the co-production conversion unit, the terephthalic acid conversion device is configured to dissolve diammonium terephthalate crystals in water and precipitate terephthalic acid after pH adjustment; the terephthalamide conversion device is configured to pyrolyze diammonium terephthalate crystals into terephthalamide in a pressure-controlled pyrolysis reactor; and / or The co-production conversion unit also includes an ammonia recovery device, which is used to absorb the ammonia released during the production process of the terephthalic acid conversion device and the terephthalamide conversion device with water, and the resulting ammonia water is fed back to the enzymatic hydrolysis device.

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