Continuous production system and process for efficiently recovering and refining PTA (pure terephthalic acid) from waste PET (polyethylene terephthalate) and application

Abstract

The invention belongs to the technical field of waste PET (Polyethylene Terephthalate) recovery, and particularly relates to a continuous production system and process for efficiently recovering and refining PTA (Purified Terephthalic Acid) from waste PET and application. According to the continuous production system and process for efficiently recovering and refining the PTA from the waste PET, through mutual cooperation of the enzymolysis unit, the first solid-liquid separation unit, the filter cake dissolving and decolorizing unit, the electrolysis unit, the second solid-liquid separation unit and the recrystallization unit, continuous production of'obtaining the refined PTA by taking the waste PET as a raw material 'is realized; besides, by adjusting the runner structure in the electrolysis assembly of the electrolysis unit, the situation of electrolysis interruption caused by the fact that TA generated by electrolysis is prone to being deposited on the surface of the anode plate is avoided, guarantee is provided for continuous proceeding of the whole degradation and recovery process, and the system and the process have important significance on efficient degradation and recovery of waste PET.

Description

Technical Field

[0001] The invention belongs to the technical field of waste PET recovery, and particularly relates to a continuous production system, process and application for efficiently recovering refined PTA from waste PET. Background Art

[0002] Polyethylene terephthalate (PET) is widely used in many fields such as plastic bottles, food packaging and textiles due to its excellent transparency, strength and chemical resistance. However, the widespread use of PET materials has put great pressure on the ecological environment. Therefore, achieving green recycling and effective utilization of PET is of vital importance to promoting green environmental protection and sustainable development.

[0003] In order to promote the recycling of resources, discarded PET products are usually recycled into raw material monomer terephthalic acid (TA) through a degradation process. The current process is mostly intermittent processing. For example, the waste PET is first degraded into terephthalate and ethylene glycol by chemical methods, and then the terephthalate is decolorized, acidified and filtered to obtain purified terephthalic acid (PTA) with higher purity. However, this series of operation steps is complicated and the production efficiency is not high. There are also studies to obtain higher purity TA by electrolyzing terephthalate solution, but the process used is still intermittent processing, that is, it is necessary to use terephthalate solution as raw material for electrolysis, and waste PET cannot be directly used as the initial raw material of the entire process. Moreover, in the actual electrolysis process, the TA precipitated by electrolysis is easily deposited on the electrode surface, affecting the continuous progress of the electrolysis reaction, and may even cause the electrolysis reaction to be interrupted, and the continuity of the electrolysis process cannot be guaranteed, and the electrolysis efficiency is low.

[0004] Therefore, there is an urgent need for a process that can continuously recover high-purity PTA directly from waste PET, thereby realizing the continuous recovery of "waste PET to refined PTA". Summary of the invention

[0005] The object of the present invention is to provide a process capable of efficiently recovering refined PTA from waste PET in a single step. The process comprises an enzymatic hydrolysis unit, a solid-liquid separation unit, an electrolysis unit, a recrystallization unit and an ethylene glycol recovery unit. Through specific connection and coordination between the units and special design of the electrolytic cell structure in the electrolysis unit, continuous production from waste PET to refined PTA is achieved, and ethylene glycol is recovered at the same time.

[0006] In view of this, the first aspect of the present invention provides a continuous production system for efficiently recovering refined PTA from waste PET, the system comprising: A plurality of enzymatic hydrolysis units are configured to sequentially perform enzymatic hydrolysis reactions on PET to obtain a slurry containing TA alkaline salt; a processing unit, the processing unit comprising a first solid-liquid separation unit, a filter cake dissolving and decolorizing unit, an electrolysis unit, a second solid-liquid separation unit and a recrystallization unit connected in sequence; the processing unit is used to perform solid-liquid separation, dissolve and decolorize, and electrolyze the TA alkaline salt slurry to obtain a TA crude product slurry, and then perform solid-liquid separation and recrystallization on the TA crude product slurry to obtain a PTA fine product; and The switching control unit is configured as follows: when the first enzymolysis unit completes the enzymolysis reaction, the processing unit is connected to the first enzymolysis unit to start the processing operation; during the processing operation of the processing unit on the first enzymolysis unit, the second enzymolysis unit performs an enzymolysis reaction; in response to the processing unit completing the processing operation on the first enzymolysis unit, the processing unit is switched to be connected to the second enzymolysis unit, so that the processing unit cyclically connects the enzymolysis units to achieve continuous processing.

[0007] The present invention provides a continuous production system for efficiently recovering refined PTA from waste PET, comprising a plurality of enzymolysis units, which are respectively connected to a first solid-liquid separation unit to continuously provide the first solid-liquid separation unit with slurry containing TA alkaline salt by enzymolysis of PET, so as to ensure that the system can achieve continuous production; after the enzymolysis unit is connected to the first solid-liquid separation unit, the slurry enters the first solid-liquid separation unit for solid-liquid separation, the TA alkaline salt solid obtained by separation enters a filter cake dissolution and decolorization unit for dissolution, decolorization, impurity removal and filtration, the TA alkaline salt solution obtained by filtration enters an electrolysis unit, the TA crude product slurry is recovered in an anode plate tank in the electrolysis unit, and the alkaline solution is recovered in the cathode plate tank; the obtained TA crude product slurry is filtered by a second solid-liquid separation unit, and solid TA crude product is collected, and the TA crude product is refined by a recrystallization unit to obtain refined PTA.

[0008] In combination with the first aspect, the first solid-liquid separation unit is used to separate the TA alkaline salt in the slurry; the filter cake dissolution and decolorization unit is used to dissolve, decolorize and filter the TA alkaline salt to obtain a TA alkaline salt solution; the electrolysis unit is composed of a plurality of electrolysis components in parallel, each electrolysis component is separated into an anode chamber and a cathode chamber by a cation exchange membrane, wherein the anode chamber is equipped with an anode plate and a plate frame arranged on both sides of the anode plate to form an anode plate slot, and the cathode chamber is equipped with a cathode plate and a plate frame arranged on both sides of the cathode plate to form a cathode plate slot, the TA alkaline salt solution enters the electrolysis unit from the anode chamber, the TA crude product slurry is recovered in the anode plate slot, and the alkaline solution is recovered in the cathode plate slot; the second solid-liquid separation unit is used to separate the TA crude product from the TA crude product slurry, and the recrystallization unit is used to refine the TA crude product.

[0009] In combination with the first aspect, the continuous production system further includes a distillation unit, which is connected to the solution side of the first solid-liquid separation unit and is used to recover and reuse ethylene glycol in the solution.

[0010] In combination with the first aspect, the anode plate slot or cathode plate slot is a hollow plate slot, and two or more flow channels are arranged along the fluid flow direction, each flow channel is respectively provided with a pair of fluid inlet and outlet, wherein the flow channels are separated by arc-shaped corrugated isolation strips.

[0011] The second aspect of the present invention provides a continuous production process for efficiently recovering refined PTA from waste PET, comprising: The enzymatic hydrolysis step includes a plurality of enzymatic hydrolysis units, wherein the enzymatic hydrolysis step uses a PET degrading enzyme, the enzymatic hydrolysis temperature is 40-70° C., the enzymatic hydrolysis process pH is 8-10, and a TA alkaline salt slurry is obtained; A first solid-liquid separation step is used to separate the TA alkaline salt in the TA alkaline salt slurry; The filter cake dissolving and decolorizing step comprises adding 5-10 times the weight of water to the TA alkaline salt to dissolve the TA alkaline salt, adding a decolorizing agent, and filtering to obtain a TA alkaline salt solution; The electrolysis step includes a plurality of electrolysis components arranged in parallel, each electrolysis component is divided into an anode chamber and a cathode chamber by a cation exchange membrane, the TA alkaline salt solution enters the electrolysis component from the anode, TA slurry is obtained at the anode, the alkaline solution is recovered at the cathode, and oxygen and hydrogen are collected respectively; The second solid-liquid separation step is used to filter the TA slurry to obtain a crude TA product; A refining step, wherein the crude TA product is recrystallized to obtain a fine PTA product; Among them, when the first enzymatic hydrolysis unit performs the first solid-liquid separation step after completing the enzymatic hydrolysis reaction, the second enzymatic hydrolysis unit performs the enzymatic hydrolysis step. After completing the processing operation of the first enzymatic hydrolysis unit, the second enzymatic hydrolysis unit continues the first solid-liquid separation step to complete the continuity.

[0012] The present invention provides a continuous production process for efficiently recovering refined PTA from waste PET, which realizes the continuous production of refined PTA using waste PET as raw material through an enzymatic hydrolysis step, a first solid-liquid separation step, a filter cake dissolving and decolorizing step, an electrolysis step, a second solid-liquid separation step and a refining step in sequence. Specifically, the pre-treated waste PET is hydrolyzed with PET degrading enzyme to obtain a slurry containing TA alkaline salt. Since the solubility of TA alkaline salt in the crude enzyme solution used for hydrolysis is low, the TA alkaline salt will gradually precipitate as the degree of hydrolysis increases. The slurry containing TA alkaline salt is separated by the first solid-liquid separation step to obtain solid TA alkaline salt; the TA alkaline salt filter cake is dissolved with a soluble amount of water, and then a decolorant is added for decolorization and impurity removal, and the decolorant is removed. The obtained TA alkaline salt solution is electrolyzed to obtain TA slurry at the anode of the electrolysis component and an alkaline solution at the cathode. The TA slurry generated at the anode of each electrolysis component is separated by the second solid-liquid separation step, and the solid is collected to obtain a TA crude product. The TA crude product is further recrystallized to obtain refined PTA. Wherein, when the first enzymolysis unit performs the first solid-liquid separation step after completing the enzymolysis reaction, the second enzymolysis unit performs the enzymolysis step. After completing the treatment operation of the first enzymolysis unit, the second enzymolysis unit continues the first solid-liquid separation step to complete the continuous process.

[0013] In combination with the second aspect, the continuous production process further includes a distillation step, in which the solution obtained in the first solid-liquid separation step is distilled to recover ethylene glycol.

[0014] In combination with the second aspect, the enzymatic hydrolysis step is specifically as follows: prepare 10-1000mmol / L sodium phosphate buffer, add 100-1000g of waste PET per liter of buffer, add 0.1%-1% of the mass of the buffer solution of PET degradation enzyme crude enzyme, and react for enzymatic hydrolysis for 5-25h; the refining step is specifically as follows: transport the crude TA product to a pulping tank, add a mixed solvent to make the mass concentration of the crude TA product 20%-35wt%, wherein the mixed solvent is a mixture of water and at least one of dimethylformamide, diethylformamide and dimethyl sulfoxide; increase the temperature to 265-280°C and the pressure to 6.0-8.0MPa to dissolve the crude TA product; pass the obtained solution through an adsorption column for decolorization and removal of metal impurities, and then pass through 1-6 stage cooling and pressure reduction flash crystallizers for step-by-step crystallization, wash and dry to obtain refined PTA.

[0015] Exemplarily, at least one of dimethylformamide, diethylformamide and dimethyl sulfoxide is prepared with deionized water to form a mixed solvent, wherein the mass proportion of deionized water in the mixed solvent is 80% to 95%.

[0016] In combination with the second aspect, each of the electrolytic components is separated into an anode chamber and a cathode chamber by a cation exchange membrane, and an anode plate and a plate frame are arranged in the anode chamber, and a cathode plate and a plate frame are arranged in the cathode chamber. The plate frames are arranged on both sides of the anode plate and the cathode plate, respectively, to form an anode plate slot and a cathode plate slot, and TA crude slurry is recovered in the anode plate slot, and alkaline solution is recovered in the cathode plate slot; the plate frame is rectangular, and at least one arc-shaped corrugated isolation strip is arranged along the long side of the plate frame, and the curvature diameter of the arc-shaped corrugated isolation strip is not less than the narrow side size of the plate slot; the ratio of the long side to the narrow side of the plate slot is 2-5:1, and the depth of the plate slot is 2-20mm; the distance between the upstream edge of the plate and the upper edge of the plate slot is greater than 1 / 8 of the length of the plate slot, and the distance between the downstream edge of the plate and the lower edge of the plate slot is not less than 1 / 4 of the length of the plate slot.

[0017] The third aspect of the present invention provides a refined PTA, which is produced by using the above-mentioned continuous production system for efficiently recovering refined PTA from waste PET or according to the above-mentioned continuous production process for efficiently recovering refined PTA from waste PET.

[0018] A fourth aspect of the present invention provides an application of the above-mentioned refined PTA in the preparation of PET products, wherein the PET products include films, fibers and / or bottle flakes made of PET material.

[0019] Illustratively, films made of PET prepared from refined PTA can be used in multiple fields and industries, such as food packaging films, heat-sealing films and stretch films in the packaging industry, electronic protective films, light diffusion films and anti-reflective films in the electronics and optics fields, industrial and functional films such as antistatic films, high temperature resistant films and electrical insulation films, and can also be biaxially stretched films or uniaxially stretched films.

[0020] Illustratively, fibers made of PET prepared from refined PTA can also be used in multiple fields and industries, for example: they can be polyester filaments or polyester staple fibers produced by the textile industry, they can also be high-strength fibers, low-elasticity fibers or high-modulus fibers commonly used in the industrial field, or they can be some functional fibers such as moisture wicking fibers, antistatic fibers, anti-ultraviolet fibers or flame retardant fibers, or they can be pre-oriented yarns, fully stretched yarns or stretched deformed yarns obtained according to different production processes.

[0021] Illustratively, PET bottle flakes prepared from refined PTA can also be used in multiple fields and industries, for example: they can be used to produce food packaging bottles, beverage packaging bottles, medicine packaging bottles, cosmetic packaging bottles or industrial chemical bottles, and can also be used to produce PET bottles with different structures such as single-layer PET bottles, multi-layer PET bottles or composite PET bottles, and can also be used to produce PET bottles with specific functions such as UV-resistant PET bottles, high-temperature resistant PET bottles, low-temperature resistant PET bottles or high-barrier PET bottles.

[0022] The above-mentioned system and process provided by the present invention can realize the continuous production of "refined PTA obtained by using waste PET as raw material"; moreover, by adjusting the flow channel structure in the electrolysis component, the occurrence of electrolysis interruption caused by the easy deposition of TA produced by electrolysis on the surface of the anode plate is avoided, thereby providing a guarantee for the continuous progress of the entire degradation and recycling process. The system and process are of great significance for realizing the efficient degradation and recycling of waste PET. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic flow chart of a continuous production process for efficiently recovering refined PTA from waste PET provided by the present invention; Figure 2 A schematic diagram of an electrolysis unit and a second solid-liquid separation unit of a continuous production process for efficiently recovering refined PTA from waste PET provided by the present invention; Figure 3 A schematic diagram of the structure of an electrolytic component in an electrolytic unit of a continuous production process for efficiently recovering refined PTA from waste PET provided by the present invention; Figure 4 is a schematic cross-sectional view of an electrolytic component of an electrolytic unit, wherein: Figure 4 (a) is a schematic cross-sectional view of the anode chamber in the electrolysis assembly. Figure 4 (b) is a schematic cross-sectional view of the cathode chamber in the electrolysis assembly; Figure 5 A schematic flow chart of the refining step of a continuous production process for efficiently recovering and refining PTA from waste PET provided by the present invention.

[0024] In the figure: 021, cathode chamber; 022, anode chamber; 023, cation exchange membrane; 024, cathode plate; 025, anode plate; 026, plate frame; 027, sealing gasket; 028, end plate; 301, upstream edge of the plate; 302, downstream edge of the plate; 400, arc-shaped corrugated isolation strip; 401, first flow channel; 402, second flow channel; 601, anode chamber fluid inlet; 602, anode chamber fluid outlet; 701, anode plate frame upstream edge fluid conduit; 702, anode plate frame downstream edge fluid conduit; 801, cathode chamber fluid inlet; 802, cathode chamber fluid outlet; 901, cathode plate frame upstream edge fluid conduit; 902, cathode plate frame downstream edge fluid conduit. DETAILED DESCRIPTION

[0025] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] See also Figure 1 , the continuous production system for efficiently recovering refined PTA from waste PET provided by the present invention is now described. The system includes: a plurality of enzymolysis units, configured to sequentially perform enzymolysis reactions on PET to obtain a slurry containing TA alkaline salts; a processing unit, the processing unit including a first solid-liquid separation unit, a filter cake dissolving and decolorizing unit, an electrolysis unit, a second solid-liquid separation unit and a recrystallization unit connected in sequence; the processing unit is used to perform solid-liquid separation, dissolution and decolorization, and electrolysis of the slurry of TA alkaline salts to obtain a crude TA slurry, and then the crude TA slurry is subjected to solid-liquid separation and recrystallization to obtain a fine PTA product; and a switching control unit, configured to: when the first enzymolysis unit completes the enzymolysis reaction, connect the processing unit with the first enzymolysis unit to start the processing operation; during the processing operation of the processing unit on the first enzymolysis unit, the second enzymolysis unit performs an enzymolysis reaction; in response to the processing unit completing the processing operation on the first enzymolysis unit, the processing unit is switched to connect with the second enzymolysis unit, so that the processing unit circulates and connects each enzymolysis unit to achieve continuous processing.

[0027] The present invention provides a continuous production system for efficiently recovering refined PTA from waste PET, comprising a plurality of enzymolysis units, which are respectively connected to a first solid-liquid separation unit to continuously provide the first solid-liquid separation unit with slurry containing TA alkaline salt by enzymolysis of PET, so as to ensure that the system can achieve continuous production; after the enzymolysis unit is connected to the first solid-liquid separation unit, the slurry enters the first solid-liquid separation unit for solid-liquid separation, the TA alkaline salt solid obtained by separation enters a filter cake dissolution and decolorization unit for dissolution, decolorization, impurity removal and filtration, the TA alkaline salt solution obtained by filtration enters an electrolysis unit, the TA crude product slurry is recovered in an anode plate tank in the electrolysis unit, and the alkaline solution is recovered in a cathode plate tank; the obtained TA crude product slurry is filtered by a second solid-liquid separation unit, and solid TA crude product is collected, and the TA crude product is refined by a recrystallization unit to obtain refined PTA.

[0028] As a specific embodiment of the continuous production system for efficiently recovering refined PTA from waste PET of the present invention, the continuous production system also includes a control unit, which is respectively connected to the liquid outlet control ends of multiple enzymatic hydrolysis units; when the enzymatic hydrolysis liquid of one of the enzymatic hydrolysis units is processed, the control unit controls the liquid outlet end of another enzymatic hydrolysis unit to be connected to the first solid-liquid separation unit.

[0029] A control unit is provided to control the connection between the enzymatic hydrolysis unit and the first solid-liquid separation unit, thereby ensuring that the enzymatic hydrolysis liquid produced by the enzymatic hydrolysis unit is sufficient to supply the processing of subsequent units, thereby ensuring that the entire system can produce continuously.

[0030] As a specific embodiment of the continuous production system for efficiently recovering and refining PTA from waste PET of the present invention, the continuous production system also includes a distillation unit, which is connected to the solution side of the first solid-liquid separation unit and is used to recover and utilize ethylene glycol in the solution.

[0031] As a specific implementation of the continuous production system for efficiently recovering refined PTA from waste PET of the present invention, the plate frames are respectively arranged on both sides of the anode plate and the cathode plate, and respectively constitute the anode plate slot and the cathode plate slot; the anode plate slot or the cathode plate slot is a hollow plate slot, and 2 or more flow channels are arranged along the fluid flow direction, and each flow channel is respectively provided with a pair of fluid inlet and outlet, wherein the flow channels are separated by arc-shaped corrugated isolation strips.

[0032] See also Figure 2 As a specific embodiment of the continuous production system for efficiently recovering refined PTA from waste PET of the present invention, the electrolysis unit includes at least two groups of electrolysis components, which are composed of alternating anodes and cathodes in the electrolysis components. The TA alkaline salt solution (i.e., decolorizing solution) generated by the filter cake dissolving decolorization unit enters the electrolysis unit from the anode, and the generated alkaline solution flows out from the cathode.

[0033] See also Figure 3 As a specific embodiment of the continuous production system for efficiently recovering and refining PTA from waste PET of the present invention, sealing gaskets 027 are provided between the cation exchange membrane 023 and the plate frame 026 in each group of electrolytic components, between the plate frame 026 and the cathode plate 024 or the anode plate 025, and between the plate frame 026 and the end plate 028, and each component is fixed by a penetrating screw and nuts at both ends.

[0034] See also Figure 4 As a specific embodiment of the continuous production system for efficiently recovering refined PTA from waste PET of the present invention, please refer to Figure 4(a) In the hollow anode plate slot formed by the anode plate 025 and the plate frame 026, at least two flow channels (a first flow channel 401 and a second flow channel 402) are arranged along the fluid flow direction, and the flow channels are separated by arc-shaped corrugated isolation strips 400. Each flow channel is provided with a pair of anode chamber fluid inlet 601 and anode chamber fluid outlet 602, and a pair of anode plate frame upstream edge fluid pipelines 701 and anode plate frame downstream edge fluid pipelines 702 are respectively arranged at the upstream edge and downstream edge of the plate frame corresponding to each flow channel. Figure 4 (b) In the hollow cathode plate groove formed by the cathode plate 024 and the plate frame 026, at least two flow channels (a first flow channel 401 and a second flow channel 402) are arranged along the fluid flow direction, and the flow channels are separated by arc-shaped corrugated isolation strips 400. Each flow channel is provided with a pair of cathode chamber fluid inlet 801 and cathode chamber fluid outlet 802, and a pair of cathode plate frame upstream edge fluid conduits 901 and cathode plate frame downstream edge fluid conduits 902 are respectively arranged at the upstream edge and downstream edge of the plate frame corresponding to each flow channel.

[0035] The arc-shaped corrugated isolation strips 400 are used to separate the flow channels. When the liquid flows in the electrode plate groove, it collides with the flow channel with a certain curvature separated by the arc-shaped corrugated isolation strips 400, thereby increasing its own flow velocity. The fluid with increased flow velocity has a greater impact force on the TA generated on the surface of the anode plate 025, thereby preventing it from being stably deposited on the surface of the anode plate 025.

[0036] When electrolysis is performed using an electrolysis unit formed by connecting two electrolysis components in parallel, the TA alkaline salt solution (i.e., decolorizing solution) first enters the anode chamber through the anode chamber fluid inlet 601, or first flows through the cathode plate frame upstream edge fluid pipeline 901 and then enters the anode chamber through the anode chamber fluid inlet 601. The TA alkaline salt combines with the hydrogen ions produced by anode electrolysis in the anode chamber to form a TA crude product. The slurry containing the TA crude product flows out from the anode chamber fluid outlet 602 and flows through the cathode plate frame downstream edge fluid pipeline 902 to the TA crude product from the other electrolysis component. The TA crude slurry flowing out of the anode chamber is mixed and then enters the main pipeline, and oxygen escapes and is collected; at the same time, the water required for electrolysis enters the cathode chamber through the cathode chamber fluid inlet 801 and the downstream edge fluid pipeline 702 of the anode plate frame, and the hydroxide ions produced by the cathode electrolysis of water react with the sodium ions or potassium ions that enter the cathode chamber through the cation exchange membrane to form an alkaline solution, which then flows out from the cathode chamber fluid outlet 802 and passes through the upstream edge fluid pipeline 701 of the anode plate frame and is mixed with the alkaline solution flowing out of the cathode chamber of another electrolysis component before entering the main pipeline.

[0037] The second aspect of the present invention provides a continuous production process for efficiently recovering refined PTA from waste PET, comprising: The enzymatic hydrolysis step includes a plurality of enzymatic hydrolysis units, wherein the enzymatic hydrolysis step uses a PET degrading enzyme, the enzymatic hydrolysis temperature is 40-70° C., the enzymatic hydrolysis process pH is 8-10, and a TA alkaline salt slurry is obtained; A first solid-liquid separation step is used to separate the TA alkaline salt in the TA alkaline salt slurry; The filter cake dissolving and decolorizing step is to add 5-10 times the weight of water to the TA alkaline salt to dissolve the TA alkaline salt, add a decolorizing agent, and filter to obtain a TA alkaline salt solution; The electrolysis step includes a plurality of electrolysis components arranged in parallel, each electrolysis component is divided into an anode chamber and a cathode chamber by a cation exchange membrane, a TA alkaline salt solution enters the electrolysis component from the anode, a TA slurry is obtained at the anode, an alkaline solution is recovered at the cathode, and oxygen and hydrogen are collected respectively; The second solid-liquid separation step is used to filter the TA slurry to obtain a crude TA product; In the refining step, the crude TA product is recrystallized to obtain the fine PTA product.

[0038] The present invention provides a continuous production process for efficiently recovering refined PTA from waste PET, which realizes the continuous production of refined PTA using waste PET as raw material through an enzymatic hydrolysis step, a first solid-liquid separation step, a filter cake dissolving and decolorizing step, an electrolysis step, a second solid-liquid separation step and a refining step in sequence. Specifically, the pretreated waste PET is hydrolyzed with PET degrading enzyme to obtain a slurry containing TA alkaline salt. Since the solubility of TA alkaline salt in the crude enzyme solution used for enzymatic hydrolysis is relatively low, the TA alkaline salt will gradually precipitate as the degree of enzymatic hydrolysis increases. The slurry containing TA alkaline salt is separated through a first solid-liquid separation step to obtain solid TA alkaline salt; the TA alkaline salt filter cake is dissolved with a soluble amount of water, and then a decolorizing agent is added to decolorize and remove impurities, the decolorizing agent is removed, and the obtained TA alkaline salt solution is electrolyzed to obtain TA slurry at the anode of the electrolytic component and an alkaline solution at the cathode. The TA slurry generated at the anode of each electrolytic component is separated through a second solid-liquid separation step, and the solid is collected to obtain a crude TA product. The crude TA product is further recrystallized to obtain refined PTA.

[0039] As a specific embodiment of the continuous production process for efficiently recovering refined PTA from waste PET of the present invention, the continuous production process also includes a TA alkaline salt slurry control step. After the TA alkaline salt slurry of one enzymatic hydrolysis unit is treated, the TA alkaline salt slurry in another enzymatic hydrolysis unit is controlled to perform a first solid-liquid separation step.

[0040] As a specific embodiment of the continuous production process for efficiently recovering and refining PTA from waste PET of the present invention, the continuous production process also includes a distillation step, in which the solution obtained in the first solid-liquid separation step is distilled to recover ethylene glycol.

[0041] As a specific embodiment of the continuous production process for efficiently recovering refined PTA from waste PET of the present invention, the enzymatic hydrolysis step is specifically as follows: preparing 10-1000mmol / L sodium phosphate buffer, adding 100-1000g of waste PET per kilogram of buffer, adding 0.1%-1% of the mass of the buffer solution of PET degrading enzyme crude enzyme, and reacting enzymatic hydrolysis for 5-25h.

[0042] After the enzymatic hydrolysis step is completed, in order to precipitate more TA alkaline salt, the slurry can be appropriately cooled according to the actual temperature before the first solid-liquid separation step.

[0043] As a specific implementation method of the continuous production process for efficiently recovering refined PTA from waste PET of the present invention, each electrolytic component is divided into an anode chamber and a cathode chamber by a cation exchange membrane, an anode plate and a plate frame are arranged in the anode chamber, and a cathode plate and a plate frame are arranged in the cathode chamber, the plate frames are arranged on both sides of the anode plate and the cathode plate, respectively, to form an anode plate slot and a cathode plate slot, the TA crude slurry is recovered in the anode plate slot, and the alkaline solution is recovered in the cathode plate slot; the plate frame is rectangular, at least one arc-shaped corrugated isolation strip is arranged along the long side of the plate frame, and the curvature diameter of the arc-shaped corrugated isolation strip is not less than the narrow side size of the plate slot; the ratio of the long side to the narrow side of the plate slot is 2-5:1, and the depth of the plate slot is 2-20mm; the distance between the upstream edge of the plate and the upper edge of the plate slot is greater than 1 / 8 of the length of the plate slot, and the distance between the downstream edge of the plate and the lower edge of the plate slot is not less than 1 / 4 of the length of the plate slot.

[0044] As a specific implementation mode of the continuous production process for efficiently recovering refined PTA from waste PET of the present invention, the long side length of the pole plate frame is 30 cm, the narrow side length is 10 cm, the length of the pole plate slot space is 26 cm, the width is 6 cm, the depth is 5 mm, the curvature diameter of the arc-shaped corrugated isolation strip is 6 cm, the distance between the upstream edge of the pole plate and the upper edge of the pole plate slot is 3.5 cm, and the distance between the downstream edge of the pole plate and the lower edge of the pole plate slot is 6.5 cm.

[0045] As a specific implementation of the continuous production process for efficiently recovering refined PTA from waste PET of the present invention, the cathode plate or the anode plate is at least one of titanium plated with ruthenium, titanium plated with iridium or titanium plated with platinum; the voltage between the cathode plate and the anode plate is 1.5-5V.

[0046] See also Figure 5As a specific embodiment of the continuous production process for efficiently recovering and refining PTA from waste PET of the present invention, the refining steps of the process are specifically as follows: transporting the crude TA product to a pulping tank, preparing a PTA slurry with a concentration of 20% to 35% with at least one of dimethylformamide, diethylformamide and dimethyl sulfoxide and deionized water, raising the temperature to 265 to 280°C and the pressure to 6.0 to 8.0 MPag to dissolve the crude TA product, passing the obtained solution through an adsorption column for decolorization and removal of metal impurities, and then passing through a 1 to 6 stage temperature and pressure reduction flash crystallizer for step-by-step crystallization, filtering the crystallized slurry through a filtration system, and washing and drying the obtained solid to obtain refined PTA.

[0047] As a specific embodiment of the continuous production process for efficiently recovering refined PTA from waste PET of the present invention, the specific parameters of the step-by-step crystallization step are: the temperature of the first-stage crystallizer is controlled at 250-260°C, and the pressure is controlled at 4.0-4.5MPag, the temperature of the second-stage crystallizer is controlled at 200-210°C, and the pressure is controlled at 3.0-4.0MPag, the temperature of the third-stage crystallizer is controlled at 160-185°C, and the pressure is controlled at 0.7-1.1MPag, and the temperature of the fourth-stage crystallizer is controlled at 130-155°C, and the pressure is controlled at 0.3-0.65MPag.

[0048] As a specific embodiment of the continuous production process for efficiently recovering refined PTA from waste PET of the present invention, the obtained solution is decolorized and demetallized by passing through an adsorption column. Specifically, the decolorization and demetallization treatment can be carried out by: a combination of one or more processes such as fixed bed continuous adsorption, precision filtration and membrane separation to remove colored substances and metal impurities in the crude TA solution. The adsorption material can be selected from at least one of coconut shell activated carbon, zeolite molecular sieve, diatomaceous earth or chitosan, and other adsorption materials with the functions of decolorization and adsorption of metal impurities can also be selected.

[0049] As a specific implementation of the continuous production process for efficiently recovering and refining PTA from waste PET of the present invention, in the refining step, the flash steam generated by the temperature-reducing and pressure-reducing flash crystallizer can be introduced into the preheating, dissolving and pulping process at the front end to achieve energy recovery and utilization.

[0050] The following is a description of the continuous production process and system for efficiently recovering refined PTA from waste PET provided by the present invention through specific embodiments: A 1000 mmol / L sodium phosphate buffer solution with a pH of 9.0 was prepared, 1000 g of pre-crushed waste PET was added per kilogram of the buffer solution, 1 wt% of the buffer solution mass of PET degradation enzyme crude enzyme solution was added for enzymolysis, the reaction temperature was controlled at 40-70°C, the reaction was carried out for 5-25 hours, and during the reaction process, a 5%-50% mass fraction of sodium hydroxide solution was added dropwise to maintain the system pH always between 8 and 10.

[0051] After the enzymolysis reaction is completed, the enzymolysis solution is naturally cooled to room temperature and then filtered. The filtrate enters the distillation unit to recover ethylene glycol to obtain 1531g of TA alkaline salt filter cake. 11kg of water is added to dissolve the TA alkaline salt, and then 30g of decolorant is added and stirred for 1h for decolorization and impurity removal. The decolorant and other insolubles are filtered to remove the decolorant, and the filtrate enters the electrolysis unit. During the electrolysis process, the plate voltage is set to 2V and the current is 77.0A. The current is kept unchanged during the electrolysis process. After 9h of electrolysis reaction, the plate voltage rises to 2.2V, indicating that the amount of TA generated on the surface of the anode plate 025 is very small and will not affect the electrolysis reaction. The crude TA slurry produced by electrolysis was filtered, and the obtained solid crude TA was recrystallized, specifically: 1200g of the crude TA was transported to the TA pulping tank through a spiral pipeline, 2369g of a mixed solvent was added to obtain a TA slurry (the mixed solvent used was obtained by mixing deionized water and dimethylformamide in a mass ratio of 85:15), the temperature was raised to 280°C and the pressure was raised to 6.4MPa to dissolve the crude TA, and then the crude TA solution was decolorized and demetallated by an adsorption column filled with coconut shell activated carbon. The 4-stage cooling and pressure-reducing flash crystallizer is used for step-by-step crystallization. The parameters of step-by-step crystallization are set as follows: the temperature of the first-stage crystallizer is controlled at 250-260°C and the pressure is controlled at 4.0-4.5MPa; the temperature of the second-stage crystallizer is controlled at 200-210°C and the pressure is controlled at 3.0-4.0MPa; the temperature of the third-stage crystallizer is controlled at 160-185°C and the pressure is controlled at 0.7-1.1MPa; the temperature of the fourth-stage crystallizer is controlled at 130-155°C and the pressure is controlled at 0.3-0.65MPa. The crystallized slurry is filtered and washed through a filtration system and finally dried to obtain 811g of refined PTA with a purity of 99.91% and a recovery rate of 93.8%. Among them, the recovery rate (%) = 811 / (1000 / 192*166) = 93.8%.

[0052] However, when the mixed solvent used for recrystallization and dissolution in the refining step is replaced with a mixed solution of water: ethanol: isopropanol in a mass ratio of 80:10:10, the yield of the obtained refined PTA is reduced to 91.5% and the purity is reduced to 98.4%, indicating that the recrystallization solvent used in the present invention can ensure that the obtained PTA has high purity and higher yield.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A continuous production system for efficiently recovering and refining PTA from waste PET, characterized in that: include: A plurality of enzymatic hydrolysis units are configured to sequentially perform enzymatic hydrolysis reactions on PET to obtain a slurry containing TA alkaline salt; a processing unit, the processing unit comprising a first solid-liquid separation unit, a filter cake dissolving and decolorizing unit, an electrolysis unit, a second solid-liquid separation unit and a recrystallization unit connected in sequence; the processing unit is used to perform solid-liquid separation, solution decolorization and electrolysis of TA alkaline salt slurry to obtain TA crude slurry, and then perform solid-liquid separation and recrystallization of the TA crude slurry to obtain PTA fine product; and The switching control unit is configured as follows: when the first enzymolysis unit completes the enzymolysis reaction, the processing unit is connected to the first enzymolysis unit to start the processing operation; during the processing operation of the processing unit on the first enzymolysis unit, the second enzymolysis unit performs an enzymolysis reaction; in response to the processing unit completing the processing operation on the first enzymolysis unit, the processing unit is switched to be connected to the second enzymolysis unit, so that the processing unit cyclically connects the enzymolysis units to achieve continuous processing.

2. The continuous production system for efficiently recovering refined PTA from waste PET as claimed in claim 1, characterized in that: The first solid-liquid separation unit is used to separate the TA alkaline salt in the slurry; The filter cake dissolving and decolorizing unit is used to dissolve, decolorize and filter the TA alkaline salt to obtain a TA alkaline salt solution; The electrolysis unit is formed by connecting a plurality of electrolysis components in parallel, and each electrolysis component is divided into an anode chamber and a cathode chamber by a cation exchange membrane, wherein the anode chamber is equipped with an anode plate and a plate frame arranged on both sides of the anode plate to form an anode plate slot, and the cathode chamber is equipped with a cathode plate and a plate frame arranged on both sides of the cathode plate to form a cathode plate slot, and the TA alkaline salt solution enters the electrolysis unit from the anode chamber, and the TA crude product slurry is recovered in the anode plate slot, and the alkaline solution is recovered in the cathode plate slot; The second solid-liquid separation unit is used to separate the crude TA product from the crude TA product slurry, and the recrystallization unit is used to refine the crude TA product.

3. The continuous production system for efficiently recovering refined PTA from waste PET as claimed in claim 1, characterized in that: It also includes a distillation unit, which is connected to the solution side of the first solid-liquid separation unit and is used to recover and reuse the ethylene glycol in the solution.

4. The continuous production system for efficiently recovering refined PTA from waste PET as claimed in claim 2, characterized in that: The anode plate slot or cathode plate slot is a hollow plate slot, and two or more flow channels are arranged along the fluid flow direction, each flow channel is respectively provided with a pair of fluid inlet and outlet, wherein the flow channels are separated by arc-shaped corrugated isolation strips.

5. A continuous production process for efficiently recovering refined PTA from waste PET, characterized in that: include: The enzymatic hydrolysis step includes a plurality of enzymatic hydrolysis units, wherein the enzymatic hydrolysis step uses a PET degrading enzyme, the enzymatic hydrolysis temperature is 40-70° C., the enzymatic hydrolysis process pH is 8-10, and a TA alkaline salt slurry is obtained; A first solid-liquid separation step is used to separate the TA alkaline salt in the TA alkaline salt slurry; The filter cake dissolving and decolorizing step comprises adding 5-10 times the weight of water to the TA alkaline salt to dissolve the TA alkaline salt, adding a decolorizing agent, and filtering to obtain a TA alkaline salt solution; The electrolysis step includes a plurality of electrolysis components arranged in parallel, each electrolysis component is divided into an anode chamber and a cathode chamber by a cation exchange membrane, the TA alkaline salt solution enters the electrolysis component from the anode, TA slurry is obtained at the anode, the alkaline solution is recovered at the cathode, and oxygen and hydrogen are collected respectively; The second solid-liquid separation step is used to filter the TA slurry to obtain a crude TA product; A refining step, wherein the crude TA product is recrystallized to obtain a fine PTA product; Among them, when the first enzymatic hydrolysis unit performs the first solid-liquid separation step after completing the enzymatic hydrolysis reaction, the second enzymatic hydrolysis unit performs the enzymatic hydrolysis step. After completing the processing operation of the first enzymatic hydrolysis unit, the second enzymatic hydrolysis unit continues the first solid-liquid separation step to complete the continuity.

6. The continuous production process for efficiently recovering refined PTA from waste PET as claimed in claim 5, characterized in that: The method further comprises a distillation step of distilling the solution obtained in the first solid-liquid separation step to recover ethylene glycol.

7. The continuous production process for efficiently recovering refined PTA from waste PET as claimed in claim 5, characterized in that: The enzymatic hydrolysis step is specifically as follows: preparing a 10-1000 mmol / L sodium phosphate buffer, adding 100-1000 g of waste PET per liter of buffer, adding 0.1%-1% of the mass of the buffer to a crude PET degradation enzyme solution, and performing enzymatic hydrolysis for 5-25 hours; The refining steps are specifically as follows: The crude TA product is transported to a pulping tank, and a mixed solvent is added to make the mass concentration of the crude TA product be 20% to 35wt%, wherein the mixed solvent is a mixture of water and at least one of dimethylformamide, diethylformamide and dimethyl sulfoxide; Raise the temperature to 265-280°C and the pressure to 6.0-8.0 MPa to dissolve the crude TA; The obtained solution is decolorized and demetallized by an adsorption column, and then crystallized step by step by 1 to 6 temperature-reducing and pressure-reducing flash crystallizers, washed and dried to obtain refined PTA.

8. The continuous production process for efficiently recovering refined PTA from waste PET as claimed in claim 5, characterized in that: Each of the electrolytic components is divided into an anode chamber and a cathode chamber by a cation exchange membrane, an anode plate and a plate frame are provided in the anode chamber, and a cathode plate and a plate frame are provided in the cathode chamber, the plate frames are provided on both sides of the anode plate and the cathode plate, respectively, to form an anode plate slot and a cathode plate slot, the anode plate slot is used to recover TA crude slurry, and the cathode plate slot is used to recover alkaline solution; The plate frame is rectangular, and at least one arc-shaped corrugated isolation strip is arranged along the long side of the plate frame, and the curvature diameter of the arc-shaped corrugated isolation strip is not less than the narrow side size of the plate slot; the ratio of the long side to the narrow side of the plate slot is 2-5:1, and the depth of the plate slot is 2-20mm; the distance between the upstream edge of the plate and the upper edge of the plate slot is greater than 1 / 8 of the length of the plate slot, and the distance between the downstream edge of the plate and the lower edge of the plate slot is not less than 1 / 4 of the length of the plate slot.

9. A refined PTA, characterized in that: The method is prepared by using the continuous production system for efficiently recovering and refining PTA from waste PET as described in any one of claims 1 to 4 or the continuous production process for efficiently recovering and refining PTA from waste PET as described in any one of claims 5 to 8.

10. Use of the refined PTA according to claim 9 in preparing PET products, characterized in that: The PET products include films, fibers and / or bottle flakes made of PET material.

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