A filtration device and a method of filtering pet glycolysis solution

Abstract

The application provides a filtering device and a method for filtering PET alcoholysis solution, the filtering device comprising a tubular filter element, the tubular filter element comprising, in order from outside to inside in the radial direction, an outer tube body, a filler layer and an inner tube body; the outer tube body is sleeved outside the inner tube body, and the filler layer is arranged between the outer tube body and the inner tube body; at least part of the outer wall of the outer tube body is provided with a porous coating; the porous coating comprises a filter aid; the filler layer comprises, in order from outside to inside in the radial direction, a first filler layer and a second filler layer; the first filler layer comprises at least one of diatomite, kaolin, white clay and volcanic ash; the second filler layer comprises at least one of activated carbon, bentonite and diatomite; and the thickness ratio of the first filler layer to the second filler layer is 1:1 to 1:3. The filtering device solves the problems of low filtering rate, easy blocking of deep filter material and poor removal effect on complex impurities of the traditional filtering device.

Description

Technical Field

[0001] This invention relates to the field of chemical recycling and resource utilization of waste textiles, and in particular to a filtration device and a method for filtering PET alcoholysis solution. Background Technology

[0002] With the global textile industry placing greater emphasis on sustainable development, the resource utilization of waste textiles has become a key issue. Polyethylene terephthalate (PET), as the most widely used synthetic fiber material in the textile field, is chemically recycled through ethylene glycol (EG) alcoholysis. This process initially generates a PET alcoholysis solution containing the target product, diethyl terephthalate (BHET), unreacted ethylene glycol, and impurities. After purification and separation, BHET can be obtained, which can then be further polymerized to produce recycled polyester fibers. However, the impurities in the PET alcoholysis solution (such as incompletely depolymerized PET fragments, residual cotton cellulose particles, microcrystalline particles, dye molecules, metal ions, oligomers, and other colored impurities and small molecule pollutants) pose challenges to the filtration process, including high viscosity, deep clogging of filter cartridges, and difficulty in cleaning. This results in a low filtration rate, severely restricting the economic efficiency and continuity of the process.

[0003] To address the filtration issues of PET alcoholysis solutions, existing technologies optimize the alcoholysis solvent system (such as mixing ethylene glycol and propylene glycol) or introduce magnetic fluid adsorption technology (such as FeO magnetic fluid) to remove dissolved or colloidal impurities. However, these technologies have limited effectiveness in filtering incompletely depolymerized solid particles, and the filter cartridges are prone to deep clogging, resulting in persistent low filtration rates. Furthermore, while diatomaceous earth filter aids have been used in the filtration of high-viscosity materials, their adsorption selectivity is insufficient, and they are not optimized for the PET alcoholysis system. This leads to poor filtration of PET alcoholysis solutions containing colored impurities such as dye molecules, metal ions, and oligomers, as well as small-molecule contaminants, making it difficult to meet the color value and crystal quality requirements of BHET products. Summary of the Invention

[0004] Based on this, the present invention provides a filtration device that solves the problems of low filtration rate, easy clogging of deep filter media, and poor removal effect of complex impurities, improves the filtration rate, and can efficiently remove colored impurities and microcrystalline particulate impurities, thereby improving the quality of BHET products.

[0005] The present invention also provides a method for filtering PET alcoholysis liquid. Using the above-mentioned filtration device, a highly efficient gradient filtration system is constructed for PET alcoholysis liquid, which effectively reduces the filtration pressure of the inner layer of the filter element, avoids deep clogging problems, and effectively filters impurities. The process is simple and continuous.

[0006] In a first aspect, the present invention provides a filtration device, comprising a tubular filter element, wherein the tubular filter element comprises, in a radial direction from the outside to the inside, an outer tube body, a packing layer, and an inner tube body; the outer tube body is sleeved on the outside of the inner tube body, and the packing layer is disposed between the outer tube body and the inner tube body; at least a portion of the outer wall of the outer tube body is provided with a porous coating; the porous coating comprises a filter aid.

[0007] The filler layer includes a first filler layer and a second filler layer in sequence from the outside to the inside in the radial direction;

[0008] The first filler layer includes at least one of diatomaceous earth, kaolin, clay, and volcanic ash;

[0009] The second filler layer includes at least one of activated carbon, bentonite, and diatomaceous earth;

[0010] The thickness ratio of the first filler layer to the second filler layer is 1:1 to 1:3.

[0011] Furthermore, the first filler layer comprises diatomaceous earth and kaolin;

[0012] And / or, the second filler layer comprises activated carbon and bentonite.

[0013] Furthermore, the mass ratio of the diatomaceous earth to the kaolin is (2~5):1;

[0014] And / or, the mass ratio of the activated carbon to the bentonite is (2~5):1.

[0015] Furthermore, the thickness of the outer tube is 3mm to 5mm;

[0016] And / or, the thickness of the filler layer is 10mm~20mm;

[0017] And / or, the thickness of the inner tube is 3mm~5mm;

[0018] And / or, the thickness of the porous coating is 1mm to 3mm.

[0019] Furthermore, the filter aid includes at least one of activated carbon, bentonite, volcanic ash, slag powder, kaolin, and activated clay.

[0020] In a second aspect, the present invention provides a method for filtering PET alcoholysis liquid using the filtration device described in the first aspect, comprising the following steps:

[0021] In the filtration device, the PET alcoholysis solution is transported to the outside of the tubular filter element for filtration treatment, and passes sequentially through the porous coating, the outer tube, the first packing layer, the second packing layer and the inner tube.

[0022] Furthermore, it also includes: simultaneously conveying the PET alcoholysis solution to the outside of the tubular filter element and adding the filter aid to the outside of the tubular filter element to participate in the filtration process;

[0023] Alternatively, the solvent is mixed with the filter aid to form a first mixture, and the first mixture is added to the outside of the tubular filter element while the PET alcoholysis solution is being transported to the outside of the tubular filter element to participate in the filtration process.

[0024] Further, in the first mixture, the mass ratio of the solvent to the filter aid is (5~20):1;

[0025] And / or, the volume ratio of the PET alcoholysis solution to the solvent is (4:1) to (9:1);

[0026] And / or, the filter aid is added to the outside of the tubular filter element, specifically including the following process: every 2 min to 4 min, 4 g to 6 g of the filter aid is delivered to the outside of the tubular filter element;

[0027] And / or, the first mixture is added to the outside of the tubular filter element, specifically including the following process: every 2 min to 4 min, 4 g to 6 g of the first mixture is delivered to the outside of the tubular filter element.

[0028] Furthermore, the flow rate of the PET alcoholysis solution delivered to the outside of the tubular filter element is 10 g / s to 25 g / s.

[0029] Furthermore, it also includes: physical regeneration treatment and / or chemical regeneration treatment of the tubular filter element.

[0030] This invention provides a filtration device including a tubular filter element. The filtration device has a layered structure, with a porous coating, an outer tube, a first packing layer, a second packing layer, and an inner tube working synergistically. Each structural layer is functionally adapted to achieve gradient purification of PET alcoholysis liquid. During the filtration process, the PET alcoholysis liquid is first pre-filtered through a porous coating located on at least part of the outer wall of the outer tube. The filter aid in the porous coating, relying on its porous structure and adapted physical properties, efficiently traps large-particle impurities such as incompletely depolymerized PET fragments and cotton cellulose residues, reducing the contamination load on subsequent filter layers and providing a stable foundation for subsequent deep impurity removal. Next, the pre-filtered alcoholysis liquid enters the first packing layer, wherein the components of the first packing layer (including at least one of diatomaceous earth, kaolin, clay, and volcanic ash) are porous. The structure is resistant to compression and shearing, and the self-packing properties between particles give it the integrity to be formed without binders. Therefore, whether used alone or in combination, it can form a stable, interconnected, and non-densifying porous filter layer skeleton in the annular space between the outer and inner tubes. This effectively traps medium-sized impurities and microcrystalline particles, preventing them from entering the second packing layer. Subsequently, the alcoholysis liquid treated by the first packing layer flows through the second packing layer. The components of the second packing layer (including at least one of activated carbon, bentonite, and diatomaceous earth) have strong adsorption properties and ion exchange capacity, which can accurately adsorb colored impurities and small molecule pollutants such as dye molecules, metal ions, and oligomers. Finally, the PET alcoholysis liquid that has passed through the porous coating, the first packing layer, and the second packing layer is collected on the inner wall of the inner tube. This filtration device clearly defines the functional division between the first packing layer (particle retention) and the second packing layer (adsorption and impurity removal), and combines the appropriate thickness ratio of the two to achieve a reasonable radial distribution of the filtration load. This ensures that impurities are progressively retained and adsorbed from the outside to the inside, avoiding deep clogging of the filter element caused by the disordered accumulation of different types of impurities. This effectively reduces the filtration burden on the deep layers of the filter element, significantly lowers the probability of filter element blockage, and greatly improves the filtration rate of PET alcoholysis liquid, ensuring the continuous industrial operation of the PET chemical recycling process. At the same time, the component selection of each structural layer is highly matched with the functional requirements. The filter aid in the porous coating enhances the pre-filtration effect, the inorganic powder in the first packing layer ensures particle retention efficiency, and the adsorption material in the second packing layer improves the selectivity of impurity removal. Combined with the structural support of the outer and inner tubes, the PET alcoholysis liquid can fully contact each filter layer, resulting in a significant improvement in filtration efficiency. This not only lays the foundation for easy deep cleaning of the filter element and improves the filtration rate, but also significantly enhances the purity of the filtered alcoholysis solution, thereby improving the color value and crystal quality of subsequent BHET products and meeting the filtration needs of complex impurity systems in the chemical recycling of waste textiles.

[0031] This invention provides a filtration method for PET alcoholysis solution. This method, combined with the layered structure of the aforementioned filtration device, effectively reduces the filtration pressure on the inner layer of the filter element, avoids deep clogging, and increases the filtration rate. It allows for thorough filtration of the PET alcoholysis solution, thereby achieving efficient removal of solid and soluble impurities, significantly improving product purity, enhancing the color value and crystal quality of BHET products, and ensuring a stable and smooth filtration process. This method is simple and continuous. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic sectional view of the filter device 1 provided in Example 1.

[0034] Explanation of reference numerals in the attached figures

[0035] 1-Filtering device; 10-Tubular filter element; 20-Shell; 11-Outer tube; 12-Packaging layer; 13-Inner tube; 14-Sealing assembly; A-Annular space; 110-Porous coating; First packing layer 121; 122-Second packing layer. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] In a first aspect, the present invention provides a filtration device, including a tubular filter element, the tubular filter element comprising, in a radial direction from the outside to the inside, an outer tube body, a packing layer, and an inner tube body; the outer tube body is sleeved on the outside of the inner tube body, and the packing layer is disposed between the outer tube body and the inner tube body; at least a portion of the outer wall of the outer tube body is provided with a porous coating; the porous coating includes a filter aid.

[0038] The packing layer consists of a first packing layer and a second packing layer in the radial direction from the outside to the inside.

[0039] The first filler layer includes at least one of diatomaceous earth, kaolin, white clay, and volcanic ash;

[0040] The second filler layer includes at least one of activated carbon, bentonite, and diatomaceous earth;

[0041] The thickness ratio of the first filler layer to the second filler layer is 1:1 to 1:3.

[0042] For example, the thickness ratio of the first filler layer and the second filler layer is any value of 1:1, 1:2, 1:3, or any combination of both.

[0043] In this invention, the PET alcoholysis solution to be treated includes BHET, an alcoholysis agent, and impurities; wherein, the impurities include solid impurities and adsorbable impurities. The alcoholysis agent includes, but is not limited to, ethylene glycol and / or methanol.

[0044] In some preferred embodiments, the mass concentration of BHET in the PET alcoholysis solution to be treated is 3% to 15%.

[0045] For example, the mass concentration of BHET is any value or a range of any two of the following: 3%, 6%, 9%, 12%, 15%.

[0046] The solid impurities of this invention include large-particle-size impurities, medium-particle-size impurities, and microcrystalline particles.

[0047] In some embodiments, the median particle size D of large-particle impurities 50 The median particle size D of medium-sized impurities is ≥200 μm. 50 The median particle size D of the microcrystalline particles is 10~200μm. 50 It is <10μm.

[0048] For example, large-particle-size impurities include, but are not limited to, incompletely alcoholyzed polyester fragments, textile accessories (such as button and zipper residues), and at least one of heterogeneous fibers such as cotton / nylon / spandex; the median particle size D of the impurities. 50 For sizes such as ≥200μm, ≥250μm, ≥260μm, and ≥270μm.

[0049] For example, medium-sized impurities include, but are not limited to, at least one of catalyst residues and oligomer particles precipitated during the reaction.

[0050] For example, the microcrystalline particles include, but are not limited to, at least one of the following: precipitated BHET microcrystals, dye aggregates, and metal ion complexes. The precipitated BHET microcrystals may originate from BHET supersaturated crystallization caused by "system state changes" during filtration and subsequent processes.

[0051] The present invention can adsorb at least one of the following impurities, including but not limited to dye molecules, metal ions, oligomers and other colored impurities and small molecule pollutants.

[0052] In some embodiments, the PET alcoholysis solution to be treated is crystallized to obtain BHET crystals with a color value L of 60~80, an a value of -2~2, and a b value of 5~15.

[0053] For example, the color value L of the BHET crystal is any value or a range of any two of the following: 60, 65, 70, 75, 80; the value a is any value or a range of any two of the following: -2, -1, 0, 1, 2; and the value b is any value or a range of any two of the following: 5, 10, 15.

[0054] The filtration device provided by this invention includes a tubular filter element, which adopts a radially layered structure of an outer tube, a packing layer, and an inner tube to form a gradient filtration system. Through the synergistic design of the gradient filtration system and a specialized filter aid, a reasonable radial distribution of the filtration load is achieved, effectively reducing the filtration burden on the deeper layers of the filter element, significantly reducing the probability of filter element clogging, and greatly improving the filtration rate of PET alcoholysis liquid, ensuring the continuous industrial operation of the PET chemical recycling process. Simultaneously, this gradient filtration structure, in synergy with the filter aid compound system, achieves the graded retention and selective adsorption of incompletely depolymerized PET fragments, catalyst residues, and other solid particles, as well as colored and small-molecule impurities such as dye molecules, metal ions, and oligomers in the PET alcoholysis liquid. This effectively improves the purity of the alcoholysis liquid, providing a pure crystallization environment for the subsequent formation of larger-diameter, narrower-size crystals in BHET products, significantly improving the color value and crystal quality of BHET products, and possessing dual industrial value of improved process efficiency and optimized product quality. The porous coating on the outer side of the outer tube serves as a pre-filtration structure. After the filter aid it contains is formed, the porous coating has a porous structure and suitable physical properties, which can effectively intercept large-particle impurities such as incompletely depolymerized PET fragments and cotton cellulose residues, reducing the contamination load of subsequent filter layers. At the same time, it provides a uniform fluid distribution channel for the PET alcoholysis liquid to be treated, guiding the PET alcoholysis liquid to penetrate evenly into the subsequent filter layers along the circumference of the outer tube, avoiding uneven filtration load caused by local fluid concentration, and ensuring the stability of the subsequent process.

[0055] The packing layer between the outer and inner tubes can deeply treat the pre-filtered PET alcoholysis liquid, retaining medium-sized and microcrystalline impurities and adsorbing colored impurities and small molecule pollutants to obtain filtered PET alcoholysis liquid. The components of the first packing layer (including at least one of diatomaceous earth, kaolin, clay, and volcanic ash) have a porous structure and are resistant to compression and shearing. The self-packing characteristics between particles give it the integrity to be formed without binders. Therefore, whether used alone or in combination, it can form a stable, interconnected, and non-densifying porous filter layer framework within the annular space between the outer and inner tubes, specifically retaining medium-sized impurities and microcrystalline particles, preventing these impurities from entering the deeper filter layer (second packing layer). The components of the second packing layer (including at least one of activated carbon, bentonite, and diatomaceous earth) have strong adsorption properties and ion exchange capacity, accurately adsorbing colored impurities and small molecule pollutants such as dye molecules, metal ions, and oligomers.

[0056] The inner tube serves as the collection channel for the filtered PET alcoholysis solution. Together with the outer tube and the packing layer, it forms a complete filtration channel, allowing the PET alcoholysis solution to undergo multi-stage filtration radially from the outside to the inside. Finally, the filtered PET alcoholysis solution is collected on the inner wall of the inner tube. This achieves gradient removal of impurities from the PET alcoholysis solution, significantly improving filtration rate and precision. It provides a suitable crystallization environment for BHET, promoting larger and more concentrated BHET crystals, thereby improving the color value and crystal quality of the BHET product.

[0057] The tubular filter element features clearly defined functional zones and well-fitted assembly for each structural layer (porous coating, outer tube, first packing layer, second packing layer, and inner tube). Impurities are progressively trapped radially from the outside to the inside, preventing disordered accumulation and deep clogging, thus significantly improving the filtration rate. This allows for targeted treatment of each layer during cleaning and maintenance—the outermost porous coating can be cleaned or replaced individually without disassembling the entire filter element. The packing layers can be cleaned, replenished, or replaced as needed, and the inner tube, serving as the filtrate collection channel, can be unblocked separately. This significantly reduces cleaning difficulty and maintenance costs, while ensuring the filter element can quickly restore its filtration performance after maintenance, supporting continuous process operation.

[0058] In addition, the range of thickness / mass ratio of the first and second packing layers can ensure that the filtration accuracy and adsorption capacity are precisely matched, so that when the PET alcoholysis liquid to be treated flows through the first and second packing layers in sequence, the impurities in the PET alcoholysis liquid to be treated are gradually intercepted and adsorbed, effectively improving the overall filtration rate and impurity removal efficiency of the filtration device.

[0059] The filtered PET alcoholysis solution of this invention includes BHET and an alcoholysis agent.

[0060] In some example implementations, such as Figure 1 The filter device 1 shown includes a tubular filter element 10, a housing 20, and a porous coating 110. The tubular filter element 10 includes an outer tube 11, a packing layer 12, and an inner tube 13 in a radial direction from the outside to the inside. The outer tube 11 is sleeved on the outside of the inner tube 13, and an annular space A is formed between the outer tube 11 and the inner tube 13. The packing layer 12 is disposed between the outer tube 11 and the inner tube 13. The packing layer 12 includes a first packing layer 121 and a second packing layer 122 in a radial direction from the outside to the inside. At least a portion of the outer wall of the outer tube 11 is provided with a porous coating 110. The top end of the outer tube 11 and the top end of the inner tube 13 are sealed to the sealing assembly 14.

[0061] The above-mentioned preparation of the tubular filter element 10 includes the following process: inserting the inner tube 13 coaxially into the inner tube 11 using a positioning fixture, and sealing the inner tube 13 at the bottom of the outer tube 11, so that an annular space A is formed between the outer tube 11 and the inner tube 13; filling the annular space A with a corresponding filter aid to form a first packing layer 121 and a second packing layer 122; installing a sealing assembly 14 on the top of the filter element to seal and fix the top ends of the outer tube 11 and the inner tube 13 to the sealing assembly 14; and applying a coating to at least a portion of the surface of the outer wall side of the outer tube 11 to form a porous coating 110.

[0062] In some embodiments, the coating comprises a filter aid and an alcohol solution; the alcohol solution includes, but is not limited to, ethylene glycol, anhydrous ethanol, propylene glycol, and isopropanol.

[0063] All of the above-mentioned alcohol solvents can effectively disperse the filter aid powder and are compatible with the PET alcoholysis solution system. They do not introduce harmful impurities after film formation and are suitable for the filtration process environment of PET alcoholysis solution.

[0064] In some preferred embodiments, the coating comprises a filter aid and a liquid to be filtered.

[0065] It can effectively disperse filter aid powder and is compatible with the PET alcoholysis liquid system to be filtered. After film formation, it does not introduce harmful impurities and is suitable for the filtration process environment of PET alcoholysis liquid.

[0066] In some embodiments, the preparation process of the outer tube 11 includes: loading a first ultra-high molecular weight material into a mold for sintering, and cooling and demolding to obtain the outer tube 11.

[0067] In some embodiments, the preparation process of the inner tube 13 includes: loading a second ultra-high molecular weight material into a mold for sintering, and cooling and demolding to obtain the inner tube 13.

[0068] The present invention does not limit the shape of the mold, and includes, but is not limited to, U-shaped tubular molds, straight tubular molds, S-shaped tubular molds, etc.

[0069] The first ultra-high molecular weight material and the second ultra-high molecular weight material are each independently, including but not limited to, at least one of polyethylene, polypropylene, and nylon. The molecular weight of the first ultra-high molecular weight material and the second ultra-high molecular weight material are each independently 700,000 to 1,500,000 g / mol.

[0070] The prepared tubular filter element has excellent mechanical properties: tensile strength > 30 MPa, flexural strength > 15 MPa, and can withstand a purging pressure of 0.6 MPa to 0.8 MPa.

[0071] For example, the tensile strength is any range of >30 MPa, >600 MPa, >90 MPa, etc.; the flexural strength is any range of >15 MPa, >35 MPa, >75 MPa, etc.; and the tolerable purging pressure is any value of 0.6 MPa, 0.7 MPa, 0.8 MPa, etc., or any combination of both.

[0072] In some embodiments, the first filler layer 121 comprises kaolin and volcanic ash.

[0073] In some preferred embodiments, the mass ratio of kaolin to volcanic ash is 1:1 to 1:3.

[0074] For example, the mass ratio of kaolin to volcanic ash is any value of 1:1, 1:2, 1:3, or any range of both.

[0075] The kaolin in the first packing layer, with its layered structure, can efficiently trap medium-sized impurities and adsorb trace metal ions. The volcanic ash, with its natural porous glassy structure, forms a stable filter skeleton, increasing the slag capacity and filtration throughput of the packing layer. The two work together in proportion to achieve efficient graded trapping of medium-sized impurities.

[0076] In some embodiments, the second filler layer 122 comprises activated carbon and diatomaceous earth.

[0077] In some preferred embodiments, the mass ratio of activated carbon to diatomaceous earth is (2~5):1.

[0078] For example, the mass ratio of activated carbon to diatomaceous earth is any value of 2:1, 3:1, 4:1, 5:1, or any combination of both.

[0079] The activated carbon in the second packing layer adsorbs colored impurities and metal ions with its high specific surface area microporous structure, while diatomaceous earth achieves microcrystalline particle interception and optimizes the filtration channel through its porous structure. The two are compounded in a mass ratio of (2~5):1, and the adsorption purification and precise interception effects complement each other to complete the deep purification of PET alcoholysis liquid.

[0080] In some embodiments, the first filler layer 121 comprises diatomaceous earth and kaolin.

[0081] The combination of the two can form a stable, interconnected, and non-densified porous filter layer framework, which is perfectly suited to the function of the first packing layer in intercepting impurities and microcrystalline particles. At the same time, diatomaceous earth and kaolin can withstand the filtration conditions of PET alcoholysis liquid for a long time, maintaining the porosity and interception efficiency of the filter layer.

[0082] In some preferred embodiments, the diatomaceous earth has a porosity >75%, a particle size distribution of 45μm~150μm, and a specific surface area of ​​10 m². 2 / g~80 m 2 / g.

[0083] For example, the porosity of diatomaceous earth is any range from >75%, >80%, >85%, >90%, >95%, etc. The particle size distribution of diatomaceous earth is any value or a range of any two of the following: 45μm, 75μm, 105μm, 135μm, 150μm, etc.; specific surface area is 10m². 2 / g、30m 2 / g, 50m 2 / g、70m 2 / g、80m 2 Any value in / g, or a range consisting of any two of them.

[0084] In some preferred embodiments, the kaolin has a particle size distribution of 45 μm to 75 μm and a specific surface area of ​​10 m². 2 / g~50 m 2 / g, porosity 40%~70%.

[0085] For example, the particle size distribution of kaolin is any value or a range of any two of the following: 45μm, 55μm, 65μm, 75μm; specific surface area is 10m². 2 / g、20m 2 / g、30m 2 / g、40m 2 / g, 50m 2 / g or any value or a range of any two of them; porosity of 40%, 50%, 60%, 70% or any two of them.

[0086] This parameter range ensures that the kaolin and diatomite blend has excellent particle retention performance and structural stability, and improves the fluid permeability and medium-sized impurity capture effect of the first filler layer 121.

[0087] In some preferred embodiments, the second filler layer 122 comprises activated carbon and bentonite.

[0088] The second filler layer includes activated carbon and bentonite, which work together to exert a combination of physical adsorption and ion exchange, efficiently adsorbing colored and small molecule impurities such as dye molecules, metal ions, and oligomers in the PET alcoholysis solution, improving the purification purity of the alcoholysis solution, and laying the foundation for improving the color value and crystallization quality of subsequent BHET products.

[0089] In some preferred embodiments, the activated carbon has a methylene blue adsorption value ≥180 mg / g, an iodine adsorption value ≥1000 mg / g, and a BET specific surface area of ​​800~1500 m². 2 / g, average particle size 45-150μm, pore volume ≥0.8 m³ 3 / g.

[0090] For example, the activated carbon has a methylene blue adsorption value of ≥180 mg / g, ≥190 mg / g, ≥200 mg / g, etc.; an iodine adsorption value of ≥1000 mg / g, ≥1500 mg / g, ≥2000 mg / g, ≥2500 mg / g, etc.; and a BET specific surface area of ​​800 m². 2 / g, 1000m 2 / g、1200m 2 / g, 1400m 2 / g, 1500 m 2 / g or any value or a range of any two of these; average particle size of any value or a range of any two of these, such as 45μm, 75μm, 105μm, 135μm, 150μm; pore volume ≥0.8m 3 / g, ≥1.6 cm 3 / g, ≥3.2 cm 3 Any range from / g, etc.

[0091] In some embodiments, the bentonite has a cation exchange capacity (CEC) of 50–150 mmol / 100g and a specific surface area of ​​30–80 m². 2 / g, particle size distribution 10~45μm.

[0092] For example, the cation exchange capacity (CEC) of bentonite is any value or a range of any two of the following: 50 mmol / 100g, 100 mmol / 100g, 150 mmol / 100g; specific surface area is 30 m². 2 / g、40 m 2 / g、50 m 2 / g、60m 2 / g、70 m 2 / g、80 m 2 / g or any value or a range of any two of them; particle size distribution of 10μm, 15μm, 30μm, 45μm or any value or a range of any two of them.

[0093] This parameter range ensures that bentonite has a high adsorption capacity for inorganic impurities such as metal ions, and works in synergy with activated carbon to achieve deep removal of complex soluble impurities.

[0094] In some preferred embodiments, the first filler layer 121 comprises diatomaceous earth and kaolin, and the second filler layer 122 comprises activated carbon and bentonite.

[0095] The first packing layer 121 is made of diatomaceous earth and kaolin. Both packing materials have excellent particle retention performance. Their porous structure can efficiently capture medium-sized impurities with a median particle size D50 of 10~200μm after pre-filtration by the porous coating, laying the foundation for subsequent deep filtration. Meanwhile, the second packing layer 122 is made of activated carbon and bentonite. Activated carbon has a strong adsorption capacity for colored impurities, while bentonite can specifically adsorb metal ion impurities. The two work together to achieve deep removal of complex soluble impurities.

[0096] In some preferred embodiments, the mass ratio of diatomaceous earth to kaolin is (2~5):1;

[0097] And / or, the mass ratio of activated carbon to bentonite is (2~5):1.

[0098] For example, the mass ratio of diatomaceous earth to kaolinite is any value of 2:1, 3:1, 4:1, 5:1, or any combination of both.

[0099] For example, the mass ratio of activated carbon to bentonite is any value of 2:1, 3:1, 4:1, 5:1, or any combination of both.

[0100] The mass ratio of diatomaceous earth to kaolin is (2~5):1. The high porosity of diatomaceous earth ensures the fluid permeability of the first filler layer 121, while the high strength structure of kaolin improves the stability of the filler layer. The appropriate ratio of the two can ensure the median particle size D. 50 It effectively retains medium-sized impurities of 10~200μm while maintaining a suitable filtration flow rate.

[0101] When activated carbon and bentonite are mixed in a mass ratio of (2~5):1, the adsorption capacity of bentonite can complement that of activated carbon. When the ratio is within this range, the efficient removal of metal ions and colored impurities can be ensured, and the filter layer can be prevented from becoming saturated due to excessive adsorption of a single impurity. This will improve the overall adsorption capacity and service life of the packing layer and ensure the continuity of the filtration process.

[0102] The packing layer of the present invention is sealed in the annular space A between the outer tube 11 and the inner tube 13. The present invention does not limit its arrangement. For example, it can completely fill the annular space A between the outer tube 11 and the inner tube 13, or a portion of the space A can be reserved according to the actual filtration conditions and fluid characteristics.

[0103] All of the above solutions can ensure that the impurity retention and adsorption functions of the packing layer 12 are properly realized. By fixing the components of the first packing layer 121 and the second packing layer 122 inside the treatment device 1, dust pollution is fundamentally avoided.

[0104] For example, the packing layer 12 reserves some gaps in the annular space. These gaps can serve as a buffer flow area for the fluid, further optimizing the uniformity of the distribution of high-viscosity fluid in the filtration device, reducing filter layer wear or clogging caused by local flow velocity differences, and forming a synergy with the gradient filtration structure of the porous coating 110 and the packing layer 12 to maintain the stability and continuity of the filtration process, while providing flexibility for subsequent process adjustments (such as adjusting the packing amount according to the impurity content).

[0105] For example, during the filling process, vibration compaction or gradient filling methods are used to completely fill the annular space A with the filling layer 12, ensuring that the filling layer 12 is uniform, free of voids, and tightly fitted with the inner wall of the outer tube 11 and the outer wall of the inner tube 13. The complete filling setting maximizes the utilization of the effective space between the outer tube 11 and the inner tube 13, significantly increasing the total filtration area and adsorption capacity of the filling layer 12.

[0106] The ample amount of packing material in this invention can extend the residence time of impurities in the filter layer, allowing solid impurities to be more fully retained, and colored impurities, metal ions, etc. to be more comprehensively adsorbed, thereby further improving the total impurity removal rate.

[0107] In some implementations, the thickness of the outer tube is 3mm to 5mm.

[0108] For example, the thickness of the outer tube is any value of 3 mm, 4 mm, 5 mm, or any combination of both.

[0109] In this invention, the thickness of the outer tube refers to the wall thickness of the outer tube. This thickness range ensures the tube has sufficient mechanical strength to withstand fluid pressure, while avoiding excessive thickness that could increase fluid flow resistance, thus guaranteeing filtration throughput.

[0110] In some embodiments, the thickness of the porous coating is 1 mm to 3 mm.

[0111] For example, the thickness of the porous coating is any value of 1 mm, 2 mm, 3 mm, etc., or a range of any combination of both.

[0112] This range of thicknesses ensures that the coating has sufficient impurity retention capacity while maintaining appropriate permeability, enabling efficient pre-filtration.

[0113] In some implementations, the thickness of the inner tube is 3mm to 5mm.

[0114] For example, the thickness of the inner tube is any value of 3 mm, 4 mm, 5 mm, etc., or a range of any two of them.

[0115] In this invention, the thickness of the inner tube refers to the wall thickness of the inner tube. An inner tube within this thickness range ensures sufficient mechanical strength to withstand fluid pressure, while avoiding excessive thickness that could increase fluid flow resistance, thus guaranteeing filtration throughput.

[0116] In some embodiments, the thickness of the filler layer is 10 mm to 20 mm.

[0117] For example, the thickness of the filler layer is any value of 10 mm, 15 mm, 20 mm, or a range of any combination of both.

[0118] The thickness of the packing layer within this range provides ample space for the interception and adsorption of impurities, ensuring a deep filtration effect. At the same time, it is compatible with the thickness of the outer and inner tubes, making the entire tubular filter element structure compact, easy to install and maintain, and suitable for industrial production needs.

[0119] In some preferred embodiments, the outer tube has a thickness of 3mm to 5mm, the filler layer has a thickness of 10mm to 20mm, the inner tube has a thickness of 3mm to 5mm, and the porous coating has a thickness of 1mm to 3mm.

[0120] The thicknesses of the aforementioned porous coating, outer tube, packing layer, and inner tube form a cohesive thickness matching system, jointly ensuring the stable operation and high-efficiency filtration of the filtration device. The matching thicknesses of the outer and inner tubes provide uniform and sufficient mechanical support for the entire tubular filter element, working together to resist the fluid pressure within the filtration device and providing a stable reference for the assembly of the porous coating and packing layer. The precise matching of the porous coating thickness with the outer tube thickness allows for stable adhesion via the outer tube and provides uniform fluid distribution and pre-filtration conditions for subsequent packing layer filtration. The packing layer thickness connects the thickness characteristics of the porous coating and the inner tube, ensuring sufficient space for impurity retention and adsorption while ensuring smooth radial flow of the PET alcoholysis solution from the outside to the inside, improving filtration speed and avoiding sudden changes in fluid resistance or filtration blind spots caused by imbalances in the thicknesses of the various structural layers. The four components work together in a coordinated manner, with their thicknesses being well-matched. This results in a compact structure and synergistic function for the tubular filter element, ensuring the continuity and stability of the filtration process. Furthermore, the efficient operation of the gradient filtration system significantly improves the filtration rate and impurity removal efficiency, thereby guaranteeing the color value and crystal quality of BHET products.

[0121] The outer tube of this invention has a perforated structure on its wall, which allows fluid to pass through and enter the packing layer, improving the filtration rate. At the same time, it can initially intercept large-diameter impurities, preventing them from impacting and damaging the packing layer, thus protecting the filtration function of the packing layer.

[0122] The inner tube of this invention has a porous structure on its wall, which can efficiently collect PET alcoholysis liquid after filtration through the packing layer, avoid the filtrate from remaining in the packing layer, ensure filtration efficiency, and at the same time prevent substances in the packing layer from entering the filtered PET alcoholysis liquid and causing secondary pollution.

[0123] In some embodiments, the filter aid includes at least one of activated carbon, bentonite, volcanic ash, slag powder, kaolin, and activated clay.

[0124] The aforementioned filter aids are all compatible with the physicochemical system of PET alcoholysis solution. By optimizing the composition of the porous coating, the filtration performance and compatibility of the porous coating are improved. These filter aids are dispersed in the porous coating used to filter PET alcoholysis solution, with their core function being the physical interception of large-particle solid impurities in the PET alcoholysis solution. Simultaneously, each material, based on its own physicochemical properties, also possesses auxiliary functions such as targeted adsorption (of trace impurities such as organic pigments and metal ions), constructing a porous framework support, regulating coating porosity and mechanical strength, and optimizing coating film-forming properties. The combination of these materials creates a synergistic effect of gradient retention and deep purification, further enhancing the filtration flux, residue capacity, and process compatibility of the porous coating while efficiently intercepting large-particle solid impurities.

[0125] When using the above-mentioned filtration device, the porous coating 110, which easily traps impurities, can be cleaned or replaced separately. The packing layer 12 can be cleaned, replenished, or replaced as needed. The inner tube 13, which serves as a filtrate collection channel, can also be unblocked separately, greatly reducing the difficulty of cleaning and maintenance costs. At the same time, it ensures that the tubular filter element 10 can quickly restore its filtration performance after maintenance, achieving the effect of deep and easy cleaning of the tubular filter element 10.

[0126] In a second aspect, the present invention provides a method for filtering PET alcoholysis solution using the filtration device of the first aspect, comprising the following steps:

[0127] In the filtration device, the PET alcoholysis liquid is transported to the outside of the tubular filter element for filtration treatment, passing sequentially through the porous coating, outer tube, first packing layer, second packing layer and inner tube.

[0128] In the above filtration method, the PET alcoholysis liquid to be treated (the above PET alcoholysis liquid) is transported to the filtration device of the first aspect for filtration treatment; since the filtration treatment is a dynamic process, the above-transported PET alcoholysis liquid cannot complete the entire filtration process instantly, and the PET alcoholysis liquid waiting to complete the filtration treatment will accumulate on the outside of the tubular filter element.

[0129] The specific process of the above filtration treatment is as follows: the PET alcoholysis liquid is transported to the outside of the tubular filter element, and the PET alcoholysis liquid passes through the porous coating, the outer tube, the first packing layer, the second packing layer and the inner tube in sequence; while the PET alcoholysis liquid is being filtered, a filter aid is added to the outside of the tubular filter element; the liquid flowing out from the inner wall of the inner tube is collected, and the filtered PET alcoholysis liquid is obtained.

[0130] Utilizing the radially layered structure of the aforementioned filtration device—comprising a porous coating, outer tube, first packing layer, second packing layer, and inner tube—the PET alcoholysis solution is guided to permeate directionally along a pre-defined flow path, allowing impurities to be progressively trapped and adsorbed radially from the outside in. The alcoholysis solution, along with dynamically added filter aids along the porous coating, first efficiently traps large-particle impurities such as incompletely depolymerized PET fragments and cotton cellulose residues, laying a stable foundation for subsequent filtration. The first packing layer specifically traps medium-particle impurities such as catalyst residues and oligomer particles, preventing them from embedding into the deeper filter media. The second packing layer precisely adsorbs fine particles and colored impurities such as dye aggregates, metal ion complexes, and BHET microcrystals, ultimately achieving comprehensive removal of multiple types of impurities and significantly improving the purity of the PET alcoholysis solution.

[0131] Meanwhile, the gradient layered filtration structure ensures that the filtration load is evenly distributed radially, avoiding deep clogging of the filter element caused by disordered accumulation of impurities, significantly extending the stable operation cycle of the filter element, reducing process interruptions caused by frequent replacement of filter media, and ensuring the continuous operation of the PET chemical recycling process.

[0132] The PET alcoholysis solution filtered by this method not only significantly reduces the content of contaminants such as solid particles, colored impurities, and metal ions, but also improves the stability of the system. This provides a pure raw material basis for subsequent BHET crystallization and polymerization processes, effectively avoids the interference of impurities on BHET crystal growth, promotes the formation of BHET products with uniform particle size and high crystallinity, and improves the color value of the product, thereby enhancing the final quality of recycled polyester fibers.

[0133] In some embodiments, the above-described method for filtering PET alcoholysis liquid further includes: while conveying the PET alcoholysis liquid to the outside of the tubular filter element, adding a filter aid to the outside of the tubular filter element to participate in the filtration process;

[0134] Alternatively, the solvent and filter aid are mixed to form a first mixture, and the PET alcoholysis solution is delivered to the outside of the tubular filter element while the first mixture is added to the outside of the tubular filter element to participate in the filtration process.

[0135] In some embodiments, the PET alcoholysis solution to be treated also includes a portion of the PET alcoholysis solution.

[0136] In this invention, the solvents mixed with the filter aid include, but are not limited to, a portion of PET alcoholysis solution and / or ethylene glycol.

[0137] In some embodiments, the mass ratio of solvent to filter aid in the first mixture is (5~20):1;

[0138] And / or, the volume ratio of PET alcoholysis solution to solvent is (4:1) to (9:1);

[0139] And / or, add a filter aid to the outside of the tubular filter element, specifically including the following process: every 2 min to 4 min, deliver 4 g to 6 g of filter aid to the outside of the tubular filter element;

[0140] And / or, a first mixture is added to the outside of the tubular filter element, specifically including the following process: every 2 min to 4 min, 4 g to 6 g of the first mixture is delivered to the outside of the tubular filter element.

[0141] For example, the mass ratio of the solvent to the filter aid is any value or a combination of any two of the following: 5:1, 10:1, 15:1, 20:1, etc.

[0142] The volume ratio range of the PET alcoholysis solution to the solvent is (4:1) to (9:1).

[0143] For example, the volume ratio of PET alcoholysis solution to solvent is any value or a range of any two of the following: 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, etc.

[0144] For example, the mass of filter aid delivered is any value or a range of any two of the following: every 2 minutes, 3 minutes, 4 minutes, etc.

[0145] For example, the mass of the first mixture delivered is any value or a range of any two of the following: every 2 minutes, 3 minutes, 4 minutes, etc.

[0146] This feeding method ensures full contact with each filtration structure of the aforementioned filtration device (porous coating, outer tube, packing layer, inner tube), resulting in efficient retention and adsorption of impurities. Simultaneously, the first mixture contains filter aid; this feeding method continuously refreshes the adsorption sites in the filter cake by adding filter aid material that has not participated in the filtration and adsorption process and is not loaded with impurities. This effectively combats adsorption saturation and increased filtration resistance caused by impurity accumulation, prevents filter cake passivation, and maintains long-term stable high filtration efficiency. It maximizes the auxiliary filtration effect of the filter aid, balancing filtration activity and operating frequency.

[0147] The filter aid dynamically added during the filtration process works synergistically with the porous coating of the tubular filter element. This not only fills the tiny gaps in the coating pores and optimizes the filter cake structure, but also reduces the interfacial resistance between the filter layer and the alcoholysis liquid, effectively alleviating the problem of filtration rate decline caused by high-viscosity alcoholysis liquid.

[0148] This invention provides a method for filtering PET alcoholysis liquid. By combining the layered structure of the filtration device, it enables deep filtration of the PET alcoholysis liquid, fundamentally solving the problem of deep clogging of the filter media. This results in an order-of-magnitude improvement in filtration efficiency and stability, thereby achieving efficient removal of microcrystalline particles and colored impurities, significantly improving product purity, enhancing the color value and crystal quality of BHET products, ensuring a stable and smooth filtration process, and guaranteeing continuous production. Using the aforementioned filtration device, this method significantly improves filtration efficiency and BHET product purity while reducing operating costs, demonstrating promising prospects for industrial application.

[0149] In some embodiments, the PET alcoholysis solution to be treated is filtered, including the following process:

[0150] 1) The PET alcoholysis solution to be treated is divided into PET alcoholysis solution and partial PET alcoholysis solution;

[0151] 2) The PET alcoholysis liquid is transported to the filtration device and, under pressure, first contacts the porous coating on the outer wall of the outer tube. The porous coating preferentially traps large-particle impurities in the PET alcoholysis liquid (such as incompletely depolymerized PET fragments and cotton cellulose residue particles), while allowing the fluid to permeate evenly into the pore channels of the outer tube, achieving pre-filtration and providing a stable fluid distribution for subsequent deep filtration. The pre-filtered PET alcoholysis liquid enters the packing layer located in the annular space through the outer tube and permeates radially inward. The gradient structure of the packing layer (including the first packing layer and the second packing layer) works synergistically: the first packing layer further traps medium-particle impurities; the second packing layer removes colored impurities and metal ions through adsorption, achieving filtration of the PET alcoholysis liquid, obtaining the filtered PET alcoholysis liquid, which then permeates into the pore channels of the inner tube and flows along the central axis of the tubular filter element to a sealing assembly, and is finally discharged through the outlet of the sealing assembly.

[0152] 3) While performing the above filtration process, every 2 to 4 minutes, inject 4 to 6 g of the first mixture into the outside of the outer tube of the filter device to replenish the filter aid and allow this portion of the PET alcoholysis liquid to participate in the filtration process. It mixes with the PET alcoholysis liquid to be treated accumulated on the outside of the outer tube and passes through the porous coating, outer tube, first packing layer, second packing layer and inner tube in sequence, penetrating into the pore channels of the inner tube and flowing along the central axis of the tubular filter element to the sealing assembly, and finally being discharged through the outlet of the sealing assembly.

[0153] 4) Collect the liquid discharged from the outlet of the sealing assembly to obtain the filtered PET alcoholysis solution.

[0154] By optimizing the method parameters, during the dynamic filtration process described above, 4g to 6g of the first mixture is quantitatively added to the accumulation area on the outside of the tubular filter element at process time intervals of 2 to 4 minutes. This allows the first mixture to fully mix with the PET alcoholysis liquid to be filtered accumulated in that area, forming a mixed liquid. This mixed liquid then participates in the filtration process along the same layered path (passing sequentially through the porous coating, outer tube, first packing layer, second packing layer, and inner tube). The final filtered liquid is collected from the inner wall of the inner tube, meaning the liquid collected from the inner wall of the inner tube is the final filtered PET alcoholysis liquid.

[0155] The sealing assembly of this invention is the core connecting structure between the tubular filter element and subsequent pipelines. It is primarily used to uniformly collect the liquid flowing out of the filter element's inner tube, achieving directional and stable discharge, connecting the flow channel and ensuring a leak-proof seal. It is compatible with pressure-driven systems, preventing filtrate retention or leakage, and ensuring continuous and smooth operation of the filtration process. Batch replenishment of filter aid replenishes the adsorption active sites and pore capacity of the filtration device, dynamically maintaining the filtration rate, slowing down the pore clogging process, and further ensuring the continuity and stability of the filtration process.

[0156] This method achieves high-efficiency filtration through simple operation of directional delivery and dynamic filtration aid. At the same time, the synergistic effect of the gradient filtration structure and filter aid reduces the probability of filter cartridge clogging. Combined with the regenerable characteristics of the filter cartridge, it further reduces filter media consumption and waste liquid treatment costs, taking into account both industrial practicality and economy.

[0157] In some embodiments, the first mixture is injected into the filtration device at a flow rate of 4 to 6 g / s and mixed with the PET alcoholysis solution to be treated.

[0158] For example, the flow rate of the first mixture is any value of 4 g / s, 5 g / s, 6 g / s, or a range of any combination of both.

[0159] Rapid injection at a flow rate of 4~6 g / s allows the added filter aid particles to embed into the three-dimensional pore structure of the already formed filter cake through hydrodynamic action, rather than simply accumulating on the surface of the filter cake. At the same time, the physicochemical properties of the filter aid itself determine that it has a large number of adsorption active sites, which can continuously form new adsorption active sites inside the filter cake.

[0160] In addition, rapid injection at a flow rate of 4~6 g / s ensures that the first mixture is evenly dispersed in the unfiltered PET alcoholysis solution, avoiding sudden changes in filtration resistance caused by local aggregation of the filter aid. The parameter setting of 2~4 min intervals and single injection of 4~6 g can accurately replenish the purification capacity of the filter layer that has decreased due to impurity adsorption, ensuring that the filter layer always maintains a high impurity removal efficiency. This parameter combination can effectively slow down the clogging process of the filtration device, ensure the long-term continuity of the filtration process, and further improve the thoroughness of impurity removal, thus providing a guarantee for the preparation of high-quality BHET products.

[0161] In some preferred embodiments, the mass ratio of a portion of the PET alcoholysis solution to the filter aid in the first mixture is (5~20):1.

[0162] For example, the mass ratio of a portion of the PET alcoholysis solution to the filter aid is any value or a range of any two of the following: 5:1, 10:1, 15:1, 20:1, etc.

[0163] This invention mixes a portion of PET alcoholysis liquid with a filter aid at a mass ratio of (5~20):1 to form a first mixture. This ratio, with PET alcoholysis liquid as the main component and the filter aid as a quantitatively added phase, allows the filter aid to quickly form a stable suspension system in the accumulated alcoholysis liquid. The uniformly dispersed filter aid maximizes its adsorption and retention effects, specifically removing minute solid impurities, residual pigments, catalyst metal ions, etc., that have slightly accumulated in the accumulated liquid due to dynamic filtration, achieving the purpose of deep purification through filtration. The accumulated liquid on the outside of the filter element is the PET alcoholysis liquid to be treated. The filtration of the PET alcoholysis liquid to be treated and the addition of the first mixture are carried out simultaneously and dynamically. The ratio of (5~20):1 can strictly control the content of solids in the system. It will not cause the pores of the porous coating, the first packing layer, and the second packing layer to be overfilled or blocked due to excessive filter aid, nor will it increase the filtration resistance due to excessive suspended particles of filter aid. It ensures that the PET alcoholysis liquid to be filtered can pass through the filter element channel normally, and ensures that the filtration treatment and the addition of filter aid are carried out in a coordinated manner without interference, thereby improving the flow rate of the overall filtration process and maintaining stable throughput.

[0164] In addition, the PET alcoholysis liquid accumulated on the outside of the filter element is not a high impurity concentration system. Only a small amount of impurities are locally enriched due to the dynamic process of filtration. The ratio of (5~20):1 can accurately match the impurity load: sufficient filter aid can completely adsorb and retain the enriched impurities, with no purification dead corners, reducing the solid waste separation burden of subsequent filtration stages, and making the purification effect and filtration efficiency of secondary filtration optimal.

[0165] In some embodiments, the solvent is mixed with the filter aid at a temperature of 100°C to 120°C.

[0166] In some preferred embodiments, the temperature at which a portion of the PET alcoholysis solution is mixed with the filter aid is 100°C to 120°C.

[0167] For example, the temperature at which a portion of the PET alcoholysis solution is mixed with the filter aid is any value of 100°C, 110°C, 120°C, or any combination thereof.

[0168] In some preferred embodiments, the volume ratio of PET alcoholysis solution to a portion of PET alcoholysis solution is (4:1) to (9:1).

[0169] For example, the volume ratio of PET alcoholysis solution to a portion of PET alcoholysis solution is any value or a range of any two of the following: 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, etc.

[0170] The aforementioned volume ratio range of PET alcoholysis liquid and partial PET alcoholysis liquid can achieve a two-dimensional process balance while ensuring a sufficient supply of raw materials for porous coating preparation. On the one hand, this volume ratio can provide a sufficient amount of partial PET alcoholysis liquid to mix with the filter aid to form a first mixture, providing a suitable slurry system for the preparation of porous coatings, ensuring uniform pore structure and stable impurity retention performance of the coating. On the other hand, this ratio can effectively balance the material throughput of the main filtration unit, maintaining an appropriate processing scale for PET alcoholysis liquid, thereby ensuring the overall operating efficiency of the filtration device and the stability of product quality.

[0171] In some embodiments, the flow rate of the PET alcoholysis solution delivered to the filtration device is 10 g / s to 25 g / s.

[0172] For example, the flow rate of PET alcoholysis solution delivered to the filtration device is any value of 10 g / s, 15 g / s, 20 g / s, 25 g / s, or any combination thereof.

[0173] By optimizing the flow rate of the PET alcoholysis solution, filtration efficiency and impurity removal are improved. A flow rate of 10–25 g / s ensures sufficient time for the PET alcoholysis solution to come into full contact with each filter unit of the filtration device, enabling effective retention and adsorption of impurities. Simultaneously, it maintains a suitable fluid throughput, ensuring process efficiency. This flow rate range is precisely matched to the pore structure and packing characteristics of the filtration device, preventing excessively high flow rates that could cause impurities to penetrate the filter layer, or excessively low flow rates that could lead to low production efficiency, thus ensuring a highly efficient and stable filtration process.

[0174] In some preferred embodiments, the method for filtering PET alcoholysis further includes: mixing a solvent and a filter aid and coating them onto at least a portion of the outer wall of the housing to form a porous coating, and then conveying the PET alcoholysis to the outside of the tubular filter element for filtration.

[0175] In some preferred embodiments, the solvents mentioned above include, but are not limited to, the PET alcoholysis solution to be treated and / or ethylene glycol.

[0176] The filter aid is compounded with the PET alcoholysis solution to form a porous coating, which makes the composition of the porous coating compatible with the PET alcoholysis solution. During filtration, the material of the porous coating can be prevented from reacting with the PET alcoholysis solution to avoid the introduction of impurities.

[0177] In some preferred embodiments, the PET alcoholysis solution and filter aid are mixed by stirring at a speed of 800-1200 rpm.

[0178] For example, the stirring speed is any value of 800 rpm, 1000 rpm, 1200 rpm, or a range of any two of these values.

[0179] In some embodiments, the porous coating includes PET alcoholysis solution and a filter aid.

[0180] In some embodiments, the porous coating includes ethylene glycol and a filter aid.

[0181] In some embodiments, the mass ratio of PET alcoholysis solution to filter aid in the porous coating is (5~20):1.

[0182] For example, the mass ratio of PET alcoholysis solution to filter aid in the porous coating is any value or a range of any two of the following: 5:1, 10:1, 15:1, 20:1, etc.

[0183] The mass ratio of PET alcoholysis liquid to filter aid in the porous coating is (5~20):1, which enables the porous coating to have both good structural stability and excellent pre-filtration effect. At the same time, it is compatible with the PET alcoholysis liquid to be treated, reduces filtration resistance, increases the flow rate of the filtration process, and further enhances the interception effect of large-particle impurities, providing a good foundation for subsequent deep filtration.

[0184] In some embodiments, the method further includes physical regeneration and / or chemical regeneration of the tubular filter element with attached impurities.

[0185] The regeneration process of this invention is simple to operate and can significantly reduce the cost of filter aid consumables and solid waste treatment costs. This method achieves high-efficiency filtration through simple operation of directional delivery and dynamic filtration; simultaneously, the synergistic effect of the gradient filtration structure and filter aid reduces the probability of filter cartridge clogging. Combined with the regenerable nature of the filter cartridge, it further reduces filter media consumption and wastewater treatment costs, balancing industrial practicality and economy.

[0186] In some preferred embodiments, the physical regeneration process includes the following steps: using air backflushing and / or liquid backwashing, the tubular filter element is backwashed from the inside using the appropriate backflushing / backwashing medium. Because the tubular filter element has sufficient mechanical strength, the filter cake adhering to its outer surface can be detached; simultaneously, the backflushing / backwashing medium agitates and washes the packing layer, allowing the filter aid components within the packing layer to reorganize and regain some of their activity, resulting in a regenerated tubular filter element and the detached filter cake.

[0187] Backflush media include, but are not limited to, air.

[0188] Backwashing media include, but are not limited to, ethylene glycol.

[0189] In some preferred embodiments, the backflush pressure is 0.3 MPa to 0.4 MPa.

[0190] For example, the backflush pressure is any value or a range of any two of 0.3MPa, 0.35MPa, 0.4MPa, etc.

[0191] In some preferred embodiments, the backflushing time is 2 to 3 minutes.

[0192] For example, the backflush time is any value of 2 min, 2.5 min, 3 min, etc., or a range of any two of them.

[0193] The aforementioned detached filter cake contains partially deactivated filter aids and trapped impurities; the filter aids include, but are not limited to, at least one of activated carbon, bentonite, volcanic ash, slag powder, kaolin, and activated clay; the trapped impurities include, but are not limited to, incompletely depolymerized PET fragments and / or residual cotton cellulose particles.

[0194] In some embodiments, the detached filter cake is washed with a first cleaning agent and then calcined at 300°C to 600°C to obtain a regenerated filter aid.

[0195] For example, the calcination temperature is any value or a range of any two of 300°C, 400°C, 500°C, 600°C, etc.

[0196] Regenerated filter aids can be used to prepare the porous coatings and / or filler layers of the present invention.

[0197] In some preferred embodiments, the regenerated filter aid includes, but is not limited to, at least one of activated carbon, bentonite, volcanic ash, slag powder, kaolin, and activated clay.

[0198] In some preferred embodiments, the first cleaning agent includes, but is not limited to, at least one of deionized water, anhydrous ethanol, dilute alcohol solution, and weakly alkaline aqueous solution.

[0199] The detached filter cake, after being cleaned with a first cleaning agent and calcined at 300℃~600℃, yields a regenerated filter aid. The core of this combined process lies in its ability to specifically purify and activate the effective components in the filter cake. The filter cake itself contains partially degraded filter aids and impurities with a potentially porous framework. The first cleaning agent does not damage the structure of the filter aids such as activated carbon, bentonite, and volcanic ash within the filter cake. Simultaneously, it dissolves and removes metal ions and colored impurities that clog the pores, purifying and retaining components with a porous framework. Subsequent low-temperature calcination at 300℃~600℃ preserves the stable porous and layered adsorption structures of the activated carbon and kaolin, while thoroughly removing residual first cleaning agent and the PET alcoholysis liquid to be treated from the filter cake. This exposes the blocked pore channels and adsorption sites, ultimately restoring the filter cake to its core functions as a filter aid: impurity retention, fluid permeation, and adsorption, enabling recycling.

[0200] In some embodiments, the chemical regeneration process includes the following steps: immersing the tubular filter element that has adsorbed impurities in a second cleaning agent to cause a chemical reaction in the impurities, thereby obtaining a regenerated tubular filter element.

[0201] In some preferred embodiments, if the filter cake still fails to detach after 5 to 8 cycles of air backflushing and / or liquid backwashing of the filled filter element that adsorbs impurities, the tubular filter element that adsorbs impurities is chemically regenerated.

[0202] For example, the number of operations is any value of 5, 6, 7, 8, etc., or a range of any two of them.

[0203] The second cleaning agent includes, but is not limited to, acidic and / or alkaline solutions. It can chemically react with stubborn impurities, dissolving them.

[0204] In some preferred embodiments, the concentration of the acid solution is 5% to 20%.

[0205] For example, the concentration of the acid solution is any value or a range of any two of the following: 5%, 10%, 15%, 20%.

[0206] In some preferred embodiments, the acid solution includes, but is not limited to, at least one of hydrochloric acid, acetic acid, and citric acid.

[0207] In some preferred embodiments, the concentration of the alkali solution is 1% to 5%.

[0208] For example, the concentration of the alkali solution is any value or a range of any two of the following: 1%, 2%, 3%, 4%, 5%.

[0209] In some preferred embodiments, the alkaline solution includes, but is not limited to, at least one of sodium hydroxide solution, potassium hydroxide solution, and sodium carbonate solution.

[0210] In some implementations, the actual filtration rate of the tubular filter cartridge used to filter the PET alcoholysis solution to be treated is x, and the initial filtration rate of the tubular filter cartridge is y. When x ≤ 0.6y, the tubular filter cartridge is replaced.

[0211] The initial filtration rate of a tubular filter cartridge refers to the filtration rate when the cartridge first performs filtration, i.e., the calibrated filtration rate. When the actual filtration rate x drops below 60% of the initial filtration rate y, the tubular filter cartridge cannot be regenerated and its recycling process must be stopped.

[0212] To further understand the present invention, the technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0213] Unless otherwise specified, the reagents used in the embodiments and comparative examples of this invention are all commercially available.

[0214] The examples and comparative examples were conducted using the pharmaceuticals shown in Table 1.

[0215] Table 1:

[0216]

[0217] Example 1

[0218] The inner tube 13 is coaxially inserted into the outer tube 11 using a positioning fixture, and the inner tube 13 is sealed and installed at the bottom of the outer tube 11, forming an annular space A between the outer tube 11 and the inner tube 13. A corresponding filter aid is filled into the annular space A to form a first packing layer 121 and a second packing layer 122. A sealing assembly 14 is installed on top of the filter element to seal and fix the top ends of the outer tube 11 and the inner tube 13 to the sealing assembly 14. Coating is applied to at least a portion of the outer wall surface of the outer tube 11 to form a porous coating 110. The result is as follows: Figure 1 The filter device 1 shown.

[0219] The filter device 1 includes a tubular filter element 10 and a housing 20. The tubular filter element includes an outer tube 11, a packing layer 12, and an inner tube 13 in a radial direction from the outside to the inside. The outer tube 11 is sleeved on the outside of the inner tube 13, and the packing layer 12 is disposed between the outer tube 11 and the inner tube 13.

[0220] The PET alcoholysis solution S-1 to be treated is mixed with filter aid (activated carbon) at a mass ratio of 10:1 (M1) and stirred at high speed at 1000 rpm to form a uniform suspension, which is the coating mentioned above.

[0221] The thickness of the porous coating 110 is 2 mm;

[0222] The outer tube 11 and the inner tube 13 are sintered from polyethylene (800,000 g / mol); at least part of the outer wall of the outer tube 11 is provided with a porous coating 110, and the thickness of the outer tube 11 is 3 mm; the thickness of the inner tube 13 is 3 mm.

[0223] The thickness of the filler layer 12 is 10 mm; the filler layer 12 includes a first filler layer 121 and a second filler layer 122 in the radial direction from the outside to the inside. The first filler layer 121 includes diatomaceous earth (200 mesh) and kaolin (200 mesh), with a mass ratio M2 of 2:1; the second filler layer 122 includes activated carbon (200 mesh) and bentonite (white, sodium-based), with a mass ratio M3 of 2:1; the thickness ratio K of the first filler layer 121 and the second filler layer 122 is 1:1.

[0224] Examples 2-9

[0225] Examples 2-9 are basically the same as Example 1, with the only difference being as shown in Table 2.

[0226] Table 2:

[0227]

[0228] Example 10

[0229] The process is essentially the same as in Example 1, except that the porous coating uses only a filter aid (activated carbon) and ethylene glycol. A filter device 10 is thus obtained.

[0230] Example 11

[0231] The process is basically the same as in Example 1, except that: the first filler layer consists of activated clay (industrial grade) and volcanic ash (white, 200 mesh) in a 1:1 mass ratio; the second filler layer consists of activated carbon (200 mesh) and diatomaceous earth (200 mesh) in a 2:1 mass ratio; and the porous coating consists of S-2 and a filter aid (slag powder). A filter device 11 is obtained.

[0232] Example 12

[0233] Ethylene glycol and waste textile raw materials (PET mass percentage 90%) were used to prepare PET alcoholysis solution S-1 (the color values ​​of BHET before filtration were 65, 1.2 and 13, respectively). The BHET mass concentration in the obtained S-1 alcoholysis solution was approximately 20%.

[0234] The PET alcoholysis liquid S-1 to be treated is divided into two parts: PET alcoholysis liquid and a portion of PET alcoholysis liquid. When the temperature drops to about 110°C, the portion of PET alcoholysis liquid is mixed with filter aid (activated carbon) at a mass ratio of 10:1 to form a first mixture. The first mixture is stirred at high speed at 1000 rpm to form a uniform suspension.

[0235] The PET alcoholysis solution was kept at 110°C for later use. A circulating pump continuously fed the PET alcoholysis solution into the filtration device 1 of Example 1 at a flow rate of 10 g / s for filtration. During this process, every 4 minutes, 5 g of the aforementioned uniform suspension (first mixture) was injected into the outside of the tubular filter element 10 of the filtration device 1. This mixture was then mixed with the PET alcoholysis solution to be filtered and passed sequentially through the porous coating, outer tube, first packing layer, second packing layer, and inner tube, allowing this portion of the PET alcoholysis solution to participate in the filtration process. This injection was repeated 3 times.

[0236] The liquid obtained after filtration is collected on the inner wall of the inner tube 13, which is the filtered PET alcoholysis solution (containing dissolved BHET).

[0237] After filtration is completed, the tubular filter element 10 that adsorbs impurities is regenerated by backflushing the inside of the tubular filter element with compressed air (backflushing pressure is 0.3 MPa, time is 2 minutes) to obtain a regenerated tubular filter element that can be recycled; the detached filter cake is collected, washed with ethylene glycol and deionized water, and then dried at 110°C to obtain a recyclable regenerated filter aid (activated carbon).

[0238] Of these, based on the total volume of the PET alcoholysis solution to be treated, the volume percentage of the PET alcoholysis solution is 10%; activated carbon is used as the filter aid.

[0239] The porous coating 110 of the filter device 1 is formed by coating the outer wall surface of the outer tube 11 with the above-mentioned suspension.

[0240] Example 13

[0241] Example 13 is basically the same as Example 12, with the difference shown in Table 3.

[0242] Example 14

[0243] Example 14 is basically the same as Example 12, with the difference shown in Table 3.

[0244] Example 15

[0245] Ethylene glycol and waste textile raw materials to be alcoholyzed (PET mass percentage 77%) were used to prepare PET alcoholysis solution S-2 (the color values ​​of BHET before filtration were 65, 2, and 15, respectively). The BHET mass concentration in the obtained S-2 alcoholysis solution was approximately 16%.

[0246] The PET alcoholysis liquid S-2 to be treated is divided into two parts: PET alcoholysis liquid and a portion of PET alcoholysis liquid. When the temperature drops to about 110°C, the portion of PET alcoholysis liquid is mixed with filter aid (slag powder) at a mass ratio of 10:1 to form the first mixture. The first mixture is stirred at high speed at 1000 rpm to form a uniform suspension.

[0247] The PET alcoholysis solution was kept at 110°C for later use. A circulating pump continuously fed the PET alcoholysis solution into the filtration device 11 of Example 11 at a flow rate of 25 g / s for filtration. During this process, every 2 minutes, 5 g of the above-mentioned uniform suspension (first mixture) was injected into the outside of the tubular filter element of the filtration device 11 and mixed with the PET alcoholysis solution to be filtered. The mixture passed through the porous coating, outer tube, first packing layer, second packing layer and inner tube in sequence, so that this part of the PET alcoholysis solution participated in the above-mentioned filtration process. The injection was repeated 4 times.

[0248] The filtered liquid is collected on the inner wall of the inner tube to obtain the filtered PET alcoholysis solution (containing dissolved BHET).

[0249] After filtration is completed, the tubular filter element that adsorbs impurities is regenerated by backflushing the inside of the tubular filter element with compressed air (backflushing pressure is 0.3MPa, time is 2 minutes) to obtain the regenerated tubular filter element, which can be recycled; the detached filter cake is collected, washed with ethylene glycol and deionized water, and then dried at 110℃ to obtain a recyclable regenerated filter aid (slag powder).

[0250] Of which, based on the total volume of the PET alcoholysis liquid to be treated, the volume percentage of the PET alcoholysis liquid is 10%; the filter aid is slag powder;

[0251] The porous coating of the filter device 11 is formed by coating the outer wall surface of the outer tube with the above-mentioned suspension.

[0252] Example 16

[0253] Example 16 is basically the same as Example 12, with the difference shown in Table 3.

[0254] Table 3:

[0255]

[0256] Comparative Example 1

[0257] Take 250 mL of the PET alcoholysis solution S-1 to be treated and place it in a beaker for later use; select qualitative filter paper with a pore size of 10 μm, spread it in the Buchner funnel, and gently press the edge of the filter paper to make it fit tightly against the inner wall of the funnel without gaps. Connect the Buchner funnel to the vacuum filtration flask and vacuum pump to form a vacuum filtration device; turn on the vacuum pump and adjust the system vacuum to 0.07 MPa, slowly pour the alcoholysis solution into the Buchner funnel, without adding any filter aid, and filter naturally; after all the filtrate has flowed into the vacuum filtration flask, turn off the vacuum pump, collect all the filtrate, record the total filtration time, and take a sample for testing.

[0258] Comparative Example 2

[0259] It is basically the same as Comparative Example 1, except that the PET alcoholysis solution S-2 to be treated is filtered.

[0260] Test Example 1

[0261] Test filtration rate

[0262] The total filtration time and actual filtrate mass collected for Examples 12, 14, 15, 16, Comparative Example 1 and Comparative Example 2 were recorded. The filtration rate (g / min) was calculated using Formula 1. The results are shown in Tables 4 to 8.

[0263] , Formula 1.

[0264] Test Example 2

[0265] The performance of the filtered PET alcoholysis solutions obtained in Examples 12, 14, 15, 16, Comparative Example 1 and Comparative Example 2 was tested using the following methods, and the results are shown in Tables 4 to 8.

[0266] 1) BHET crystallization experiment

[0267] The filtered alcoholysis solutions were concentrated under reduced pressure to BHET saturation, and then slowly cooled to crystallize. After filtration and vacuum drying, the crystal particle size was measured by a laser particle size analyzer, and the crystal morphology was observed by an optical microscope.

[0268] 2) Test the color value of the product

[0269] The color value of BHET crystals was determined according to GB / T 30921.7-2016 standard, using a colorimeter. The filtered PET alcoholysis solution obtained in Example 12 was tested, and the experimental results of 10 cycles of using the tubular filter cartridge were recorded, as shown in Table 4.

[0270] The filtered PET alcoholysis solution obtained in Example 14 was tested, and the experimental results of the tubular filter cartridge being recycled 7 times were recorded, as shown in Table 5.

[0271] The filtered PET alcoholysis solution obtained in Example 15 was tested, and the experimental results of the tubular filter cartridge being recycled 6 times were recorded, as shown in Table 6.

[0272] The filtered PET alcoholysis solution obtained in Example 16 was tested, and the experimental results of the tubular filter cartridge being recycled 10 times were recorded, as shown in Table 7.

[0273] The filtered PET alcoholysis solutions obtained from Comparative Example 1 and Comparative Example 2 were tested, and the results are shown in Table 8.

[0274] Table 4:

[0275]

[0276] Table 5:

[0277]

[0278] Table 6:

[0279]

[0280] Table 7:

[0281]

[0282] Table 8:

[0283]

[0284] As shown in Tables 4 and 7, after 10 cycles of use, the filtration rate of the tubular filter element remained above 75% of its initial value, demonstrating good cycle stability. After 6 cycles of use, the filtration rate of the tubular filter element in Example 15 remained above 75% of its initial value, also demonstrating good cycle stability. The color value improvement of Comparative Examples 1 and 2 was not significant (the L, a, and b values ​​after filtration in Comparative Example 1 were 64.8, 0.4, and 13.1, respectively; the L, a, and b values ​​after filtration in Comparative Example 2 were 64.9, 3.2, and 14.1, respectively). The median particle size of the BHET crystals was relatively small (the median particle size D of the BHET crystals in Comparative Example 1 was...). 50 The median grain size D of the BHET crystal in Comparative Example 2 is 26.266 μm. 50 (33.251 μm).

[0285] The above examples and comparative examples demonstrate that the present invention constructs a highly efficient gradient filtration system through specific filter aid selection, a batch-addition strategy of the PET alcoholysis liquid to be treated, and a filtration device, which effectively solves the problem of alcoholysis liquid filtration and significantly improves the purity and crystal quality of BHET in the product.

[0286] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A filtration device, characterized in that, The filter includes a tubular filter element, which, radially from the outside to the inside, comprises an outer tube, a packing layer, and an inner tube. The outer tube is sleeved on the outside of the inner tube, and the packing layer is disposed between the outer tube and the inner tube. The packing layer has a portion of voids reserved in the annular space between the outer tube and the inner tube, and the voids serve as a buffer flow area for fluid. At least a portion of the outer wall of the outer tube is provided with a porous coating, and the porous coating includes a filter aid. The filler layer includes a first filler layer and a second filler layer in a radial direction from the outside to the inside; The thickness ratio of the first filler layer to the second filler layer is 1:1 to 1:3; The first filler layer comprises diatomaceous earth and kaolin. The second filler layer comprises activated carbon and bentonite; The mass ratio of the diatomite to the kaolin is 2~5:1; The mass ratio of activated carbon to bentonite is 2~5:

1.

2. The filtration device according to claim 1, characterized in that, The thickness of the outer tube is 3mm~5mm; And / or, the thickness of the filler layer is 10mm~20mm; And / or, the thickness of the inner tube is 3mm to 5mm; And / or, the thickness of the porous coating is 1mm to 3mm.

3. The filtration device according to claim 1 or 2, characterized in that, The filter aid includes at least one of activated carbon, bentonite, volcanic ash, slag powder, kaolin, and activated clay.

4. A method for filtering PET alcoholysis liquid using the filtration device as described in any one of claims 1-3, characterized in that, Includes the following steps: In the filtration device, the PET alcoholysis solution is transported to the outside of the tubular filter element for filtration treatment, and passes sequentially through the porous coating, the outer tube, the first packing layer, the second packing layer and the inner tube.

5. The method for filtering PET alcoholysis liquid according to claim 4, characterized in that, Also includes: While the PET alcoholysis solution is being transported to the outside of the tubular filter element, the filter aid is added to the outside of the tubular filter element to participate in the filtration process; Alternatively, the solvent is mixed with the filter aid to form a first mixture, and the first mixture is added to the outside of the tubular filter element while the PET alcoholysis solution is being transported to the outside of the tubular filter element to participate in the filtration process.

6. The method for filtering PET alcoholysis liquid according to claim 5, characterized in that, In the first mixture, the mass ratio of the solvent to the filter aid is 5~20:1; Alternatively, the volume ratio of the PET alcoholysis solution to the solvent is 4:1 to 9:1; Alternatively, the filter aid can be added to the outside of the tubular filter element, specifically including the following process: every 2 min to 4 min, 4 g to 6 g of the filter aid is delivered to the outside of the tubular filter element; Alternatively, the first mixture may be added to the outside of the tubular filter element, specifically including the following process: every 2 min to 4 min, 4 g to 6 g of the first mixture may be delivered to the outside of the tubular filter element.

7. The method for filtering PET alcoholysis liquid according to claim 4, characterized in that, The flow rate of the PET alcoholysis solution delivered to the outside of the tubular filter element is 10 g / s to 25 g / s.

8. The method for filtering PET alcoholysis liquid according to any one of claims 4-7, characterized in that, Also includes: The tubular filter element is subjected to physical regeneration and / or chemical regeneration treatment.

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