Purification process for producing polyolefin reworked material
Through the combination technology of the diaphragm filter and evaporator, the problem of difficult removal of macromolecular pollutants in polyolefins is solved, and high efficiency and low energy consumption purification of recycled materials is achieved, ensuring the high purity and environmental protection of polyolefin recycled materials.
Patent Information
- Application Number
- CN202380039673.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-09-22
- Filing Date
- 2023-05-10
- Publication Date
- 2024-12-20
AI Technical Summary
The prior art cannot effectively remove pollutants with molecular weights between 400 and 800 Daltons in polyolefin recycled materials, resulting in pollutants affecting the quality of regenerated materials and generating odor problems, and common methods consume a large amount of solvent and energy.
The solvent and crude polymer are separated into permeate and retentate by using a diaphragm filter to reduce solvent use and heat energy consumption, and further separate contaminants through multi-stage diaphragm filtration and evaporator to achieve the production of high-purity recycled materials.
It significantly reduces the amount of solvent used and heat energy consumption, improves the purity of polyolefin recycled materials, avoids pollutant migration and odor problems, and achieves an economical and environmentally friendly regeneration process.
Smart Images
Figure CN119173364A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a purification method for producing polyolefin (PO) regenerated material according to the preamble of claim 1 and a method for recycling polyolefin waste according to the preamble of claim 11. Background Art
[0002] Polyolefins, such as high-density polyethylene or polyethylene, are used extensively in the plastics market in particular for the processing of packaging materials. Therefore, efforts are made to recover the materials for reuse. Polyolefins have the property of absorbing substances from the environment during use. In the subsequent use of polyolefin plastics as regrind, these substances can affect the quality, because they can be re-emitted into the filler or, if they are more volatile, cause odors. Contaminants in the polymer material can affect the quality of the recycled material. However, recycling methods have not been able to remove these contaminants from the material sufficiently to economically provide the market with a regrind suitable for food packaging, medical product packaging or high-quality cosmetics packaging.
[0003] Commonly used methods, while economical, are inadequate or incapable of removing large contaminants with molecular weights between about 400 and 800 Daltons that can embed deeply into high-density polyethylene. From a molecular weight of 800 Daltons onwards, the molecules become inert, making it virtually impossible for the contaminants to migrate into the packing. As a result, they no longer pose any risk or contamination to subsequent applications.
[0004] In order to regenerate the solvent, it is known to use a membrane separation step in order to purify the solvent. The purpose of the membrane separation step is to remove the solvent from the polymer matrix after the solid contaminants have been separated by means of a decanter. The solid contaminants are separated from the continuous phase formed by the solvent and the polymer using a decanter. The membrane separation step separates the solvent from the polymer in order to regenerate the polymer. As the polymer concentration increases, the viscosity of the mixture increases, which reduces the permeability.
[0005] This problem is partially solved by selecting carefully inspected raw materials from upstream applications. However, such careful selection is very limited because many separate recycling streams are required. In a general sense, it does not solve the potential contamination problem caused by misuse.
[0006] One solution is based on a solvent approach that removes the contaminants by dissolving the polymer and selectively precipitating it. In another solution, the contaminants are separated by swelling the polymer with a solvent and squeezing it out.
[0007] However, both methods require large amounts of solvent. Furthermore, the purification of the solvent by energy-intensive evaporation is problematic both economically and ecologically. Both methods produce polymers that contain large amounts of solvent, which must be removed in a drying step. Contaminants dissolved in these solvent residues remain in the polymer during the drying process.
[0008] Purpose of the Invention
[0009] In view of the disadvantages of the current technology, the object of the present invention is to better remove contaminants having a molecular weight between about 400 and 800 Daltons in a process for the regeneration of polyolefins in an economical and ecologically friendly manner.
[0010] illustrate
[0011] This object is achieved by a purification method for producing polyolefin (PO) regrinds, which has the features indicated in the characterizing part of patent claim 1. Improvements and / or advantageous embodiments are the subject matter of the dependent claims.
[0012] The preferred feature of the present invention is that the solvent and the crude polymer dissolved therein are added to a membrane filter and separated into a solvent-containing retentate and a solvent-containing permeate in the membrane filter. In this way, the present invention is particularly energy-saving because the amount of solvent to be regenerated can be reduced when removing contaminants from the crude polymer, and it is not necessary to distill a large amount of contaminated solvent. The thermal energy required can be significantly reduced in the present invention. The dissolved polymer is separated into a permeate containing solvent and low-molecular components and a retentate containing solvent and high-molecular components by means of a membrane filter. The low-molecular components contain the contaminants to be separated and can be discarded together with the solvent if necessary. The high-molecular components are the target product. Since the permeate contains low-molecular components in addition to the solvent, the method according to the present invention has good permeability. The permeability of the membrane is designed so that the low-molecular components (including the contaminants to be removed) are part of the permeate and are not blocked by the membrane. According to the current technology, the function of the membrane filter is to remove the solvent from the polymer matrix after the solid contaminants are separated by means of a decanter. Therefore, the separation purpose achieved by the current technology is different from that of the present invention: the solid contaminants are separated from the continuous phase consisting of solvent and polymer using a decanter. The membrane separation method, on the other hand, separates the solvent from the polymer in order to obtain the polymer. However, the contaminants deeply embedded in the polymer matrix continue to remain in the retentate.
[0013] Advantageously, all components with a molecular weight of <2000 Dalton, preferably <1000 Dalton, particularly preferably <800 Dalton are separated as permeate in the first membrane filter. In this way, more components whose molecules are inert will remain in the crude polymer, so that contaminants can hardly migrate into the packing of the regeneration container. In addition, the vapor pressure of such macromolecules is low, so that they do not cause odor problems. The polymer components that have been separated and evaluated as non-contaminants can be replenished by adding them again after purification if they are relevant to the functional properties of the polymer.
[0014] The invention is also preferably characterized in that a second membrane filter is used to separate the solvent containing pollutants and having a molecular weight substantially <400 Daltons, preferably <200 Daltons, from the solvent containing pollutants and having a molecular weight substantially >400 Daltons, preferably >200 Daltons. In this way, the solvent can be further regenerated or purified without consuming heat energy. The number of membrane filters or filter stages and the selected filter area and the associated costs of each filter stage are in competition with the energy costs, especially the heat costs, of the selective distillation on the sieve plate for the purpose of purifying the solvent. Therefore, the purification method is not limited to 2 membrane filters, and the specific number of membrane filters used depends on the purity of the required PO regenerated material and the energy requirements.
[0015] In another preferred embodiment of the present invention, after removing all components with a molecular weight of preferably <= 2000 Dalton, preferably <= 1000 Dalton and particularly preferably <= 800, the polymer solution as retentate after the first membrane filter is separated in a first evaporator into a PO regenerated material containing solvent residues and a purified first solvent, thereby realizing method step (b). In this way, a high-purity PO regenerated material is obtained, which contains only a small amount of solvent residues. In addition to the first evaporator, it is also conceivable to use a further membrane filter in order to separate the PO regenerated material (target product) from the solvent.
[0016] In another preferred embodiment of the present invention, the solvent containing pollutants and substantially >400 Dalton, preferably >200 Dalton, is separated in a second evaporator into a first residue and a purified second solvent. In this way, almost all of the solvent can be regenerated and recovered. The separated pollutants can be disposed of separately.
[0017] The purified first and second solvents can be returned to the mixing step in the first and second recovery devices, so that almost all of the solvents can be reused and their loss is minimized in the present purification process.
[0018] Advantageously, a portion of the polymer solution is returned to the mixing step as a thick solution after the first membrane filter. By returning the thick solution, the content of the remaining contaminants in the plastic pellets can be controlled in the molecular weight range of 400-800 Dalton, preferably 200-800 Dalton.
[0019] Advantageously, a portion of the solvent containing contaminants and having a molecular weight of substantially <400 Dalton and preferably >200 Dalton can also be returned to the mixing step as a dilute solution after the second membrane filter. By returning the amount of dilute solution, the content of contaminants in the PO regenerated material can be controlled within the molecular weight range of <400 Dalton, preferably >200 Dalton.
[0020] In another particularly preferred embodiment, the return amount of the thick solution and the dilute solution to the mixing step is controlled by the first valve and the second valve. In this way, the content of the substance can be conveniently set or controlled in the molecular weight range of <400 Daltons and in the molecular weight range of 400-800 or 200-800.
[0021] Advantageously, the extrusion step is carried out in a vacuum extruder and the solvent residue is separated as a second residue from the PO regenerated material in the vacuum extruder by exhaust gas. In this way, final contaminants with a molecular weight of <400 Daltons or <200 Daltons can be removed from the PO regenerated material.
[0022] Another aspect of the invention relates to a method for recycling polyolefin waste, for which PO recycled material is produced, the method comprising the above-mentioned purification method. In this way, the complete recycling method can be carried out particularly energy-efficiently. Polyolefins are fed to the recycling process in the form of post-consumer fractions together with typical contaminants on and in all polyolefin materials. The fractions can be "rigid" high-density polyethylene bottle materials or "flexible" film materials, but can also contain polypropylene, low-density polyethylene or mixed polyolefin fractions. In addition, there are fractions classified by color and size.
[0023] Advantageously, mechanical cleaning of the waste is carried out before waste cleaning, or vice versa, or both method steps are carried out simultaneously, depending on the waste to be recycled, in order to clean its surface as efficiently as possible.
[0024] Further advantages and features emerge from the following description of three exemplary embodiments of the invention with reference to the schematic drawings. The drawings are not drawn to scale.
[0025] Figure 1 : A flow chart is shown illustrating a purification method for producing PO regenerated material.
[0026] Figure 1 An improved purification method for producing PO regenerated materials is shown in . Surface-cleaned polymers from waste recovery (hereinafter referred to as crude polymers) are added to the dissolution and membrane process and mixed with the solvent in a stirred container a. The dissolved crude polymer enters a temperature-controlled receiver v and is added from there to the first membrane filter c1, which separates the solution into a first fraction containing dissolved components and having a molecular weight <800 Daltons (permeate: fluid passing through the first membrane filter c1) and a second fraction with a molecular weight >800 Daltons (retentate: fluid blocked by the first membrane filter c1). Therefore, the dissolved crude polymer is separated into a permeate containing solvent and dissolved low-molecular components and a retentate containing solvent and dissolved high-molecular components by means of the first membrane filter (c1).
[0027] The fraction with a molecular weight <800 Dalton is added to a second membrane filter c2 which separates it into a third fraction containing dissolved components with a molecular weight <400 Dalton, preferably <200 Dalton, and a fourth fraction with a molecular weight ranging from 400 to 800 Dalton or from 200 to 800 Dalton.
[0028] The diversion product with a flow rate of >800 D will be partially sent back to the receiver v and partially added to the first evaporator g1. The mass ratio can be set by the valve h1.
[0029] Next, the residue of the evaporator g1 is fed into a vacuum extruder f. A second residue e2 is separated off via the exhaust of the extruder f, which contains all polymer components and contaminants <400 Dalton, preferably <200 Dalton.
[0030] The fraction containing dissolved components with molecular weights between 400-800 Dalton or 200-800 Dalton is fed to evaporator 2. The recovered solvent condensate is sent back to receiver v in the second recovery device d2. The first residue e1 contains polymer components and contaminants with molecular weights between 400 and 200 and 800 Dalton that need to be separated.
[0031] The divert containing dissolved components with a molecular weight of <400 Dalton or <200 Dalton (called "dilute solution") is returned partly to the receiver v and partly to the second evaporator g2. The mass ratio can be set by the second valve h2.
[0032] The product of the extruder f is PO regrind in the form of plastic pellets r, from which the polymer components and other substances or contaminants in the molecular weight range of 400 or 200-800 D have been purified in a targeted manner compared to the crude polymer.
[0033] The remaining contaminants in the plastic pellets r with a molecular weight in the range of 400 or 200-800 Daltons are determined by the circulation rate of a "thick solution" added to the receiver v, which is set by means of the first valve h1.
[0034] For the recycled material or plastic pellets added to the extruder, the proportion of substances in the molecular weight range <400D or <200D is determined by the circulation rate of a dilute solution added to the receiver v, which is set by the second valve h2, or separated as the second residue e2 in the vacuum extruder.
[0035] The high energy-consuming solvent regeneration distillation commonly used in the purification method according to the prior art can be replaced in the purification method described in the present invention. As an alternative, a membrane filter can be responsible for the purification of the solvent.
[0036] The part of the used solvent separated by the extruder exhaust gas should be replenished by fresh solvent (I) in the mixer (a).
[0037] Reference Numbers :
[0038] a Mixing container
[0039] v Receiver
[0040] b Recovery of purified polymer
[0041] c1 first membrane filter
[0042] c2 Second membrane filter
[0043] d1 First solvent recovery unit
[0044] d2 Second solvent recovery device
[0045] e1 first residue
[0046] e2 second residue
[0047] f Vacuum Extruder
[0048] g1 First evaporator
[0049] g2 Second evaporator
[0050] h1 First valve
[0051] h2 Second valve
[0052] p Crude polymer, PO waste
[0053] r PO recycled material, granular material
[0054] v Receiver
Claims
1. A purification method for producing polyolefin (PO) recycled material (r), the method comprising the following steps (a) mixing a surface-cleaned PO waste material (p) referred to as a crude polymer (p) with a solvent and dissolving the crude polymer (p) in the solvent, (b) recovering the purified polymer from the solvent, (c) purifying the solvent, (d) returning the solvent to step (a), (e) separation residues (e1, e2) and (f) extruding the purified PO regenerated material (r) to form pellets (r), It is characterized in that The solvent and the crude polymer dissolved therein are added to the first membrane filter (c1) and separated into a retentate containing the solvent and a permeate containing the solvent in the first membrane filter (c1).
2. The purification method according to claim 1, characterized in that In the first membrane filter ( c1 ), all components having a molecular weight of <2000 Dalton, preferably <1000 Dalton, particularly preferably <800 Dalton are separated as permeate.
3. The purification method according to claim 1 or 2, characterized in that The solvent containing contaminants whose molecular weight is substantially <400 Dalton and preferably <200 Dalton is separated from the solvent containing contaminants whose molecular weight is substantially >400 Dalton and preferably >200 Dalton using a second membrane filter (c2).
4. The purification method according to any one of the preceding claims, characterized in that After removing all components with a molecular weight of preferably <= 2000 Dalton, preferably <= 1000 Dalton and particularly preferably <= 800, the polymer solution as retentate is separated in a first evaporator (g1) after the first membrane filter (c1) into PO regenerated material containing solvent residues and a purified first solvent, thereby realizing the method step (b).
5. The purification method according to any one of the preceding claims, characterized in that The solvent containing contaminants and having essentially >400 Daltons and preferably >200 Daltons is separated in the second evaporator (g2) into a first residue (e1) and a purified second solvent.
6. The purification method according to claim 5, characterized in that The purified first and second solvents are returned to the mixing step (a) in first and second recovery devices (d1, d2).
7. The purification method according to any one of the preceding claims, characterized in that After the first membrane filter (c1), a portion of the polymer solution is returned to the mixing step (a) as a thick solution.
8. The purification method according to any one of the preceding claims, characterized in that A portion of the solvent containing contaminants and having a molecular weight substantially <400 Dalton and preferably <200 Dalton is returned to the mixing step (a) as a dilute solution after the second membrane filter (c2).
9. The purification method according to claim 8, characterized in that The return amount of the thick solution and the thin solution to the mixing step (a) is controlled by the first valve (h1) and the second valve (h2).
10. The purification method according to any one of the preceding claims, characterized in that The extrusion step (f) is performed in a vacuum extruder, and the solvent residue as the second residue (e2) is separated from the PO regenerated material (r) by degassing in the vacuum extruder.
11. A method for recycling polyolefin waste to produce PO recycled material, the method comprising the following steps: (A) Pre-sorting of waste materials, (B) mechanical cleaning waste, (C) Washing waste with fluids and (D) producing PO recycled material in a purification process using a solvent that dissolves polyolefin waste, It is characterized in that The purification method (D) is the purification method according to any one of claims 1 to 10.
12. The method according to claim 11, characterized in that The step (B) is performed before the step (C), or the step (C) is performed before the step (B), or the steps (B) and (C) are performed simultaneously.