Waste mulching film recovery device and method

Abstract

The invention provides a waste mulching film recycling device and method, and belongs to the technical field of plastic waste recycling. The waste mulching film recycling device comprises a dissolving unit used for dissolving a waste mulching film in a dissolving solvent and discharging a crude polymer solution, a recycling unit used for recycling the waste mulching film, and a recycling unit used for recycling the waste mulching film, the filtering unit is used for receiving the crude polymer solution from the dissolving unit, filtering the crude polymer solution and discharging the filtered polymer solution; the washing unit is used for receiving the filtered polymer solution from the filtering unit, sequentially performing static mixing, stirring mixing and standing separation on the filtered polymer solution and a washing solution, and discharging the washed polymer solution; the adsorption unit is used for carrying out adsorption treatment on the washed polymer solution and discharging a refined polymer solution; and the devolatilization unit is used for removing volatile matters in the refined polymer solution to obtain a purified polymer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of plastic waste recycling, in particular, the present application relates to a waste mulch recycling device and method. BACKGROUND

[0002] With the acceleration of agricultural modernization, mulching technology has been widely used in agricultural production. Mulching film has many advantages such as improving soil temperature, maintaining soil moisture, inhibiting weed growth, etc., which can significantly improve crop yield and play an important role in ensuring food security. However, the large-scale use of mulching film has also brought serious environmental problems. Because most of the mulching film is difficult to degrade naturally, it remains in the soil for a long time, leading to soil structure damage, fertility decline, affecting crop root growth and water and nutrient absorption, and thus reducing crop yield and quality. At the same time, waste mulching film also pollutes water, air and other environments, harming the ecological balance and human health.

[0003] Plastic recycling has become a solution to alleviate the problems related to the widespread use of plastics in their life cycle, which ends with their leakage into the environment.

[0004] In related technologies, the waste mulch recycling device involves many devices and complex systems. The ash content and volatile content of the polymer recovered by the waste mulch recycling device are high. SUMMARY

[0005] Therefore, in order to at least partially solve the above-mentioned technical problems, the present application provides a waste mulch recycling device and method.

[0006] According to an embodiment of the first aspect of the present application, a waste mulch recycling device is provided, comprising in sequence: a dissolving unit for dissolving waste mulch in a dissolving solvent, and discharging a crude polymer solution, wherein the waste mulch includes a polymer used as a raw material for mulching film; a filtering unit for receiving the crude polymer solution from the dissolving unit and filtering the crude polymer solution, and discharging a filtered polymer solution; a washing unit for receiving the filtered polymer solution from the filtering unit, and sequentially performing static mixing, stirring mixing and static separation of the filtered polymer solution with a washing solution, and discharging a washed polymer solution; an adsorption unit for receiving the washed polymer solution from the washing unit and performing adsorption treatment on the washed polymer solution, and discharging a refined polymer solution; and a devolatilization unit for receiving the refined polymer solution from the adsorption unit and removing volatiles in the refined polymer solution to obtain a purified polymer.

[0007] According to the embodiments of the present application, the washing unit comprises: a static mixer, which is internally provided with fixed mixing elements, for receiving the filtered polymer solution from the filtering unit and the washing solution from the washing solution feeding device, and for statically mixing the washing solution with the filtered polymer solution, and discharging the statically mixed polymer solution; a mixing stirred tank, for receiving the statically mixed polymer solution from the static mixer, and for stirring and mixing the statically mixed polymer solution, and discharging the stirred and mixed polymer solution; and a standing separation tank, for receiving the stirred and mixed polymer solution from the mixing stirred tank, and for standing and treating the stirred and mixed polymer solution, and discharging the washed polymer solution.

[0008] According to the embodiments of the present application, the mixing elements are helical mixing units or sheet mixing units, which are arranged in sequence along the axial direction of the internal pipeline of the static mixer.

[0009] According to the embodiments of the present application, the filtering unit comprises: a first filter, for receiving the crude polymer solution from the dissolving unit, and for primary filtering the crude polymer solution, and discharging the primary filtered polymer solution; and a second filter, for receiving the primary filtered polymer solution from the first filter, and for secondary filtering the primary filtered polymer solution, and discharging the filtered polymer solution; wherein the pore size of the filter element of the first filter is larger than the pore size of the filter element of the second filter.

[0010] According to the embodiments of the present application, the pore size of the filter element of the first filter is 100-300 mesh, and the pore size of the filter element of the second filter is 500-800 mesh.

[0011] According to the embodiments of the present application, the devolatilization unit comprises: a primary devolatilizer, for receiving the refined polymer solution from the adsorption unit, and for primary devolatilization treatment of the refined polymer solution under reduced pressure of 0.05-0.2 MPa, and discharging the primary devolatilized polymer melt; and a secondary devolatilizer, for receiving the primary devolatilized polymer melt from the primary devolatilizer, and for secondary devolatilization treatment of the primary devolatilized polymer melt under the condition of -0.4 bar to -0.6 bar, to obtain the purified polymer.

[0012] According to the embodiments of the present application, the waste mulch recycling device further comprises: a condensation recovery unit, for receiving the volatiles removed from the devolatilization unit, and for condensing and recovering the volatiles and incorporating the volatiles into the dissolving solvent.

[0013] According to the embodiments of the present application, the temperature of the dissolving unit, the filtering unit, the washing unit and / or the adsorbing unit is adjustable in the range of 100℃ to 200℃, and the pressure is adjustable in the range of 1.0MPa to 5.0MPa.

[0014] According to the embodiments of the second aspect of the present application, a waste mulch recycling method is provided, comprising: dissolving waste mulch in a dissolving solvent to obtain a crude polymer solution, wherein the waste mulch comprises a polymer used as a raw material of the mulch; filtering the crude polymer solution to obtain a filtered polymer solution; sequentially performing static mixing, stirring mixing and standing separation of the filtered polymer solution and a washing solution to obtain a washed polymer solution; performing adsorption treatment on the washed polymer solution to obtain a refined polymer solution; and removing volatile substances in the refined polymer solution to obtain a purified polymer.

[0015] According to the embodiments of the present application, the washing solution comprises a flocculating agent; and the flocculating agent comprises at least one of dicyandiamide formaldehyde resin, cationic starch, sulfourea dioxide, polymeric ferric sulfate, polymeric aluminum sulfate, polymeric aluminum chloride, and polyacrylamide.

[0016] According to the embodiments of the present application, the washing solution further comprises an anionic surfactant, a metal ion complexing agent and nano Fe3O4.

[0017] According to the embodiments of the present application, the mass content of the flocculating agent is 0.005% to 1% based on the mass of the washing solution.

[0018] According to the embodiments of the present application, the mass content of the anionic surfactant is 0.001% to 0.01% based on the mass of the washing solution.

[0019] According to the embodiments of the present application, the mass content of the metal ion complexing agent is 0.001% to 0.005% based on the mass of the washing solution.

[0020] According to the embodiments of the present application, the mass content of the nano Fe3O4 is 0.001% to 0.005% based on the mass of the washing solution.

[0021] According to the embodiments of the present application, the anionic surfactant comprises sodium dodecyl benzene sulfonate, sodium fatty alcohol ether sulfate, alpha-sulfo monocarboxylic acid and its derivatives, and alkyl phosphate ester salt.

[0022] According to the embodiments of the present application, the metal ion complexing agent comprises at least one of ethylenediaminetetraacetic acid, polyacrylic acid and citric acid.

[0023] The waste plastic film recycling device provided in this application includes a dissolving unit, a filtering unit, a washing unit, an adsorption unit, and a devolatilization unit connected in sequence. The device has a simple structure and is economically feasible. By using this waste plastic film recycling device to sequentially dissolve, filter, wash, adsorb, and devolatilize waste plastic film, purified polymer can be obtained. The purified polymer has low ash and volatile matter content, and the process is time-efficient, highly efficient, and requires less chemical consumption, making it suitable for industrial production and possessing strong practical value. Furthermore, by sequentially statically mixing, stirring, and separating the filtered polymer solution with the washing solution in the washing unit, the washing effect of the polymer is further improved, reducing the ash and volatile matter content in the purified polymer. Attached Figure Description

[0024] The above and other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0025] Figure 1 A schematic diagram of a waste plastic film recycling device according to an embodiment of this application;

[0026] Figure 2 This is a schematic diagram of a waste plastic film recycling device according to another embodiment of this application;

[0027] Figure 3 A flowchart illustrating a method for recycling waste plastic film according to an embodiment of this application;

[0028] Figure 4 A flowchart of a waste plastic film recycling method according to another embodiment of this application;

[0029] [Explanation of Labels in the Attached Image]

[0030] 100-Dissolution unit;

[0031] 110 - Screw feeding equipment;

[0032] 120 - Dissolving vessel;

[0033] 130 - Solvent delivery pump;

[0034] 200-Filter Unit;

[0035] 210 - First Filter;

[0036] 220 - Second filter;

[0037] 300-washing unit;

[0038] 310 - Static Mixer;

[0039] 320 - Mixing and stirring vessel;

[0040] 330 - Static Separation Tank;

[0041] 340 - Washing solution feeding equipment;

[0042] 400-Adsorption unit;

[0043] 410 - First adsorption filter column;

[0044] 410 - Second adsorption filter column;

[0045] 500-devouring unit;

[0046] 510 - First-stage devourer;

[0047] 520-Secondary devourer;

[0048] 530 - Vacuum screw extruder. Detailed Implementation

[0049] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0050] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The term "comprising" as used herein indicates the presence of features, steps, or operations, but does not exclude the presence or addition of one or more other features.

[0051] When using expressions such as "at least one of A, B, and C," the expression should generally be interpreted in accordance with the meaning commonly understood by a person skilled in the art (e.g., "a system having at least one of A, B, and C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.). When using expressions such as "at least one of A, B, or C," the expression should generally be interpreted in accordance with the meaning commonly understood by a person skilled in the art (e.g., "a system having at least one of A, B, or C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0052] Mechanical recycling uses equipment such as crushers, washing and sorting equipment, screw extruders, and granulators to turn plastic waste into valuable recyclables.

[0053] In related technologies, the recycled granules obtained through mechanical recycling still contain a considerable amount of impurities such as grease, pesticide residues, dyes, pigments, and other substances that contribute to the dark appearance of the final product. While there are some applications that are not sensitive to color contamination, such as logistics pallets, wood-plastic composites, drip irrigation tape, bumper liners, and chassis guards, most applications require colorless granules. Although the widespread implementation of mechanical recycling technology has improved the quality of recycled plastic polymers, including mulch films, to some extent, mechanical purification methods still have fundamental limitations, such as the inability to remove coloring impurities. Therefore, these limitations restrict their application in the plastics industry.

[0054] To overcome the fundamental limitations of mechanical recycling, contaminated polymers can be purified through chemical recycling and solvent-based recycling, the latter utilizing solvents to dissolve the polymer and extract impurities, further achieving optional separation effects.

[0055] For example, soluble components can be removed from plastic mixtures by solid-liquid extraction under conditions below the dissolution temperature, followed by dissolution and subsequent separation steps to obtain the polymer. Polyolefin mixtures or waste can also be extracted from the alkane fraction of gasoline or diesel fuels with boiling points above 90°C at temperatures between 90°C and the boiling point of the hydrocarbon solvent. Hot polyolefin solutions can also be contacted with bleaching clay and / or activated carbon to remove foreign components from the solution. Alternatively, the solution can be cooled to below 70°C to crystallize the polyolefin, then heated above its melting point, the solvent evaporated in a vacuum, a gas stream passed through the polyolefin to precipitate it, or the solvent can be removed by extraction with alcohols or ketones with boiling points below the melting point of the polyolefin.

[0056] Solvent-based methods for purifying contaminated polyolefin plastics (especially agricultural mulch films with complex contamination), as described above, do not produce “naïve” polymers because they do not address the problem of adequately and effectively removing contaminants from plastics, thus hindering their application in fields with stringent requirements for raw material quality.

[0057] In addition, the waste plastic film recycling device also has the problems of involving a large number of devices and complex systems; and the high ash and volatile content of the polymer after recycling using the waste plastic film recycling device.

[0058] Therefore, there is a need for a solvent-based waste plastic film recycling device for purifying contaminated recycled polyolefin polymers, wherein the method: 1) uses a solvent that can be easily and economically removed from the polymer; 2) removes surface contamination and overall contamination in an efficient manner; 3) is easy and simple in terms of the number of unit operations, suitable for large-scale operation; and 4) the final product is similar in properties to the virgin polymer, is essentially free of contaminants, colorless, and odorless.

[0059] This application aims to overcome adverse factors such as pollutants and participate in the recycling of polyolefin plastics, and proposes an effective, simple and economically feasible apparatus and method for processing polyethylene-based plastic raw materials (especially those obtained from waste mulch film) in order to at least partially eliminate the impurities contained therein, so as to improve the economic efficiency of plastic raw materials (more specifically plastic waste).

[0060] Specifically, this application aims to provide a device and method for recycling waste plastic film (plastic raw materials obtained from plastic film waste) in order to effectively remove at least some impurities, especially pollutants (soil colloid-organic complexes, pesticide / fertilizer residues, microbial biofilms, inorganic stubborn impurities, etc.) that cannot be completely removed by conventional recycling processes such as straw, drip irrigation tape, or even multi-stage washing such as water washing and friction washing. More particularly, impurities that are significantly soluble in organic solvents are also included. This allows for the upgrading of plastic raw materials and, more specifically, plastic waste by separating and recycling polymers, enabling their use, for example, as polymer base materials for new plastic articles.

[0061] In view of this, this application provides a waste plastic film recycling device. Figure 1 This is a schematic diagram of a waste plastic film recycling device according to an embodiment of this application, as shown below. Figure 1 As shown, the waste plastic film recycling device includes a dissolving unit 100, a filtering unit 200, a washing unit 300, an adsorption unit 400, and a devolatilization unit 500 connected in sequence.

[0062] The dissolving unit 100 is used to dissolve the waste plastic film in a dissolving solvent and discharge the crude polymer solution. The waste plastic film includes polymers used as raw materials for plastic film.

[0063] The filtration unit 200 is used to receive the crude polymer solution from the dissolving unit 100, filter the crude polymer solution, and discharge the filtered polymer solution.

[0064] The washing unit 300 is used to receive the filtered polymer solution from the filtration unit 200, and to sequentially perform static mixing, stirring mixing and static separation of the filtered polymer solution and the washing solution, and then discharge the washed polymer solution.

[0065] The adsorption unit 400 is used to receive the washed polymer solution from the washing unit 300, perform adsorption treatment on the washed polymer solution, and discharge the purified polymer solution.

[0066] The devolatilization unit 500 is used to receive the purified polymer solution from the adsorption unit 400 and remove the volatiles from the purified polymer solution to obtain the purified polymer.

[0067] The waste plastic film recycling device provided in this application includes a dissolving unit, a filtering unit, a washing unit, an adsorption unit, and a devolatilization unit connected in sequence. The device has a simple structure and is economically feasible. By using this waste plastic film recycling device to sequentially dissolve, filter, wash, adsorb, and devolatilize waste plastic film, purified polymer can be obtained. The purified polymer has low ash and volatile matter content, and the process is time-efficient, highly efficient, and requires less chemical consumption, making it suitable for industrial production and possessing strong practical value. Furthermore, by sequentially statically mixing, stirring, and separating the filtered polymer solution with the washing solution in the washing unit, the washing effect of the polymer is further improved, reducing the ash and volatile matter content in the purified polymer.

[0068] The waste plastic film recycling device provided in this application has a particularly good application effect in processing waste plastic film and other plastic raw materials (especially polyethylene) containing a variety of impurities such as straw, soil, drip irrigation tape and pesticide residues, which are difficult to remove by conventional mechanical methods.

[0069] The waste plastic film recycling device in this application embodiment can be used for the recycling of waste polyolefin base films, such as waste polyethylene base films, waste polypropylene base films, etc., and has a particularly good recycling effect on waste polyethylene base films.

[0070] Waste plastic film can include waste plastic film raw materials containing straw, roots, soil, drip irrigation tape, etc., processed by wet and dry methods. Waste plastic film can be classified as Class I waste plastic film, Class II waste plastic film, etc. (refer to DB 65 / T 3834-2003). By using a waste plastic film recycling device to sequentially dissolve, filter, wash, adsorb, and devolatilize the waste plastic film, the aforementioned foreign matter and commonly used additives in the plastic film (such as dyes, pigments, organic fillers, and inorganic fillers) are separated, thereby purifying the polyolefin raw materials to achieve the purpose of repeated and efficient utilization.

[0071] The following is for reference. Figure 2 In conjunction with specific embodiments Figure 1 The waste plastic film recycling device shown will be further explained. Among other things, Figure 2 This is a schematic diagram of a waste plastic film recycling device according to another embodiment of this application.

[0072] In some embodiments of this application, such as Figure 2 As shown, the dissolving unit 100 may include a screw feeder 110, a dissolving vessel 120, and a solvent delivery pump 130. The screw feeder 110 and the dissolving vessel 120 may be connected by a shut-off valve, and the solvent delivery pump 130 may be connected to the dissolving vessel 120 via a pipeline. Dissolving solvent can be pumped into the dissolving vessel 120 from both the bottom and top.

[0073] This application does not impose any particular limitation on the screw feeding device 110, as long as it achieves the purpose of this application. Exemplarily, the screw feeding device 110 can be a single-screw extruder, and the screw of the single-screw extruder can be a threaded screw. The screw feeding device 110 may also be equipped with a screen changer device for preliminary filtration of physical impurities. The mesh size of the filter device is 10 micrometers to 1 millimeter, preferably 20 micrometers to 200 micrometers.

[0074] This application does not impose any particular limitation on the dissolving vessel 120, as long as it achieves the purpose of this application. Exemplarily, the dissolving vessel 120 can be a jacketed vessel reactor, and a stirring paddle can be installed inside the vessel. The dissolving vessel 120 can preferably be a combination of a propeller-type and a paddle-type or ribbon-type agitator.

[0075] According to embodiments of this application, the temperature of the dissolving unit 100 is adjustable within the range of 100°C to 200°C, and the pressure is adjustable within the range of 1.0 MPa to 5.0 MPa. Exemplarily, the temperature of the dissolving unit 100 can be adjusted within the range of 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, or any two of the above values. The dissolving solvent can be selected from at least one organic solvent with a boiling point of -50°C to 250°C. The dissolving solvent can be a solvent capable of dissolving polymers in waste mulch film. When the polymer is polyethylene, the solvent may include one or more solvents selected from the following: 0-dichlorobenzene; 1,2,3,4-tetrahydronaphthalene; 1,2-dichloroethane; chlorobenzene; chloroform; cyclohexane; cyclohexanone; decahydronaphthalene; dibutoxymethane; methyl ethyl ketone; methyl isobutyl ketone; methyl cyclohexane; dichloromethane; methyl n-pentyl ketone; n-decane; n-heptane; n-hexane; n-hexane; p-xylene; pyridine; 1,1,2,2-tetrachloroethane; tetrachloroethane; and carbon tetrachloride; toluene, etc.

[0076] This application does not impose any particular limitation on the type of filter used in the filter unit 200, as long as it can achieve the purpose of this application. For example, the filter unit in this application may consist of a basket filter, a T-type filter, or a dual-switching filter, etc., and the filter element pore size may be 100-500 mesh. Specifically, the basket filter may be a hot oil jacketed type.

[0077] The bottom of the filtration unit 200 and the top of the dissolving vessel 120 in the dissolving unit 100 can be connected via a pipe valve. The filtration unit 200 may include multiple filters connected in series. The pore size of each filter element can be set according to the actual impurities in the waste mulch film to be treated. Optionally, multiple filters can be arranged sequentially, and the pore size of the filter elements can be progressively reduced. For example, the filtration unit 200 can be a series-connected dual-switch filter, that is, a filtration device consisting of two filter units connected in series and having a switching function.

[0078] In some embodiments of this application, such as Figure 2 As shown, the filter unit 200 may include a first filter 210 and a second filter 220. The first filter 210 may be one or more, and the second filter 220 may be one or more.

[0079] The first filter 210 receives the crude polymer solution from the dissolving unit 100, performs a first filtration on the crude polymer solution, and discharges the pre-filtered polymer solution. The second filter 220 receives the pre-filtered polymer solution from the first filter 210, performs a second filtration on the pre-filtered polymer solution, and discharges the filtered polymer solution. The pore size of the first filter is larger than that of the second filter. This improves the filtration efficiency of the dissolving unit 100 for the crude polymer solution. The pore size of the first filter 210 and the second filter 220 can be set according to the actual impurities in the waste plastic film to be treated. For example, the pore size of the first filter 210 can be 100 mesh to 300 mesh; the pore size of the second filter 220 can be 500 mesh to 800 mesh. Exemplarily, the pore size of the first filter 210 can be any two values ​​between 100 mesh, 150 mesh, 200 mesh, 250 mesh, and 300 mesh. The filter element pore size of the second filter 220 can be any two values ​​between 500 mesh, 550 mesh, 600 mesh, 650 mesh, 700 mesh, 750 mesh, 800 mesh or more.

[0080] The bottom of the primary filter in the filtration unit 200 of this application, such as the bottom of the first filter 210, can be connected to the top of the dissolving vessel 120 in the dissolving unit 100. Each filter may have a drain port at its lowest point, which can be controlled by a double ball valve and externally connected to a mobile electrostatic discharge waste collection tank.

[0081] According to embodiments of this application, the temperature of the filter unit 200 is adjustable within the range of 100°C to 200°C, and the pressure is adjustable within the range of 1.0 MPa to 5.0 MPa. Exemplarily, the temperature of the filter unit 200 can be adjusted within the range of any two values ​​between 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, and 200°C, and the pressure can be adjusted within the range of any two values ​​between 1.0 MPa, 2.0 MPa, 3.0 MPa, 4.0 MPa, and 5.0 MPa.

[0082] In some embodiments of this application, the washing unit 300 may consist of a stirred reactor, a static mixer, a decanter mixer, a co-current or counter-current washing tower, a plate tower, a stirred tower, a packed tower, a pulse tower, etc., and may be further equipped with a stratified storage tank. Each type of equipment may include one or more devices used alone or in combination with another type of equipment. The number of devices in series in the washing unit 300 may be increased or decreased according to the washing effect. Preferably, as shown in the following embodiments... Figure 2 As shown, the washing unit 300 may include a static mixer 310, a mixing and stirring vessel 320, and a settling and separating tank 330. The static mixer 310 may have a fixed mixing element inside, used to receive the filtered polymer solution from the filtration unit 200 and the washing solution from the washing solution feed device 340, and statically mix the washing solution with the filtered polymer solution, discharging the statically mixed polymer solution. The mixing and stirring vessel 320 can receive the statically mixed polymer solution from the static mixer 310, stir and mix the statically mixed polymer solution, and discharging the stirred and mixed polymer solution. The settling and separating tank 330 can receive the stirred and mixed polymer solution from the mixing and stirring vessel 320, and allow the stirred and mixed polymer solution to settle before discharging the washed polymer solution.

[0083] According to embodiments of this application, the mixing elements of the static mixer 310 can be spiral mixing units or plate mixing units, and the mixing elements are arranged sequentially along the axial direction of the internal pipes of the static mixer 310. Laminar mixing can be achieved by cutting the fluid with spirals or multi-stage plates, resulting in high uniformity. Among these, the spiral type is preferred as it can balance mixing efficiency and shear sensitivity.

[0084] In this application, such as Figure 2As shown, the washing unit 300 may further include a washing solution feeding device 340. The front end of the static mixer 310 may be connected to a washing solution storage tank via a check valve and the washing solution feeding device 340. The washing solution is pumped into the front end of the static mixer 310 via a diaphragm pump, and the flow rate of the washing solution entering the static mixer 310 is adjustable within the range of 5~15 kg / h. For example, the flow rate of the washing solution entering the static mixer 310 may be adjustable within the range of any two of the following values: 5 kg / h, 8 kg / h, 10 kg / h, 12 kg / h, 15 kg / h, or more.

[0085] This application does not impose any particular limitation on the mixing vessel 320, as long as it achieves the purpose of this application. Exemplarily, the mixing vessel 320 can be a jacketed vessel reactor, and the vessel may contain an agitator. Optionally, the mixing vessel 320 can be a high-shear and high-circulation combined agitator, for example, the main impeller can be a serrated disc turbine, and the auxiliary impeller can be a slanted blade impeller (such as a 45° slanted blade turbine) or a propeller impeller.

[0086] This application does not impose any particular limitation on the settling separation tank 330, as long as it can achieve the purpose of this application. For example, the settling separation tank 300 can be a vertical cylindrical jacketed stainless steel tank, and the tank can be equipped with an interface meter for monitoring the position of the interface layer and the separation effect. The bottom of the tank can be equipped with a drain port, which can be connected to a condensation device through a ball valve or a needle valve. Wastewater mixed with flocculent solid impurities can be discharged in a timely manner by monitoring the interface through the interface meter.

[0087] According to embodiments of this application, the temperature of the washing unit 300 is adjustable within the range of 100°C to 200°C, and the pressure is adjustable within the range of 1.0 MPa to 5.0 MPa. Exemplarily, the temperature of the washing unit 300 can be adjusted within the range of any two values ​​between 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, and 200°C, and the pressure can be adjusted within the range of any two values ​​between 1.0 MPa, 2.0 MPa, 3.0 MPa, 4.0 MPa, and 5.0 MPa.

[0088] In some embodiments of this application, the adsorption unit 400 may include one or more adsorption filter columns. When the adsorption unit 400 includes multiple adsorption filter columns, the multiple adsorption filter columns may be arranged in series and / or in parallel. Arranging multiple adsorption filter columns in series can improve adsorption efficiency; arranging multiple adsorption filter columns in parallel can improve adsorption effect. For example, as... Figure 2 As shown, the filtration unit 400 may include a first adsorption filter column 410 and a second adsorption filter column 420 connected in parallel.

[0089] In this application, the adsorption filter column, such as the first adsorption filter column 410 and the second adsorption filter column 420, may include one or more combinations of molecular sieves, alumina, silica, silica-alumina, activated carbon or diatomaceous earth, and organobentonite, preferably molecular sieves, decolorizing sand, or mixtures thereof. Optionally, the adsorption filter column may also contain one or more combinations of detachable random-stacking adsorption balls, Johnson mesh material liquid phase channels, and variable-diameter liquid phase channels.

[0090] According to embodiments of this application, the temperature of the adsorption unit 400 is adjustable within the range of 100°C to 200°C, and the pressure is adjustable within the range of 1.0 MPa to 5.0 MPa. Exemplarily, the temperature of the adsorption unit 400 is adjustable within the range of any two values ​​between 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, and 200°C, and the pressure is adjustable within the range of any two values ​​between 1.0 MPa, 2.0 MPa, 3.0 MPa, 4.0 MPa, and 5.0 MPa.

[0091] In some embodiments of this application, the devolatilization unit 500 may include one or more devolatilizers. When the devolatilization unit 500 includes multiple devolatilizers, the multiple devolatilizers may be connected in series to improve the devolatilization effect of the devolatilization unit 500 on the purified polymer solution.

[0092] Optionally, such as Figure 2 As shown, the devolatilization unit 500 may include a primary devolatilizer 510 and a secondary devolatilizer 520. Optionally, the primary devolatilizer 510 and the secondary devolatilizer 520 may be flash evaporators.

[0093] The primary devolatilizer 510 can be used to receive the purified polymer solution from the adsorption unit 400 and depressurize the purified polymer solution to 0.05 MPa to 0.2 MPa for a first devolatilization treatment, discharging the initially devolatilized polymer melt. Exemplarily, the purified polymer solution can be depressurized to 0.05 MPa, 0.08 MPa, 0.10 MPa, 0.12 MPa, 0.15 MPa, 0.18 MPa, 0.20 MPa, or any two of these values ​​for a single devolatilization treatment.

[0094] The secondary devolatilizer 520 can be used to receive the polymer melt that has undergone preliminary devolatilization from the primary devolatilizer (510) and perform a secondary devolatilization treatment on the polymer melt at a temperature of -0.4 bar to -0.6 bar to obtain a purified polymer. For example, the polymer melt that has undergone preliminary devolatilization can be subjected to a secondary devolatilization treatment at a temperature between any two of the following values: -0.4 bar, -0.45 bar, -0.5 bar, -0.55 bar, -0.6 bar, or higher.

[0095] The primary devolatilizer 510 may also be equipped with a melt pump to deliver the polymer melt that has undergone preliminary devolatilization. The secondary devolatilizer 520 may also be equipped with a melt pump to deliver the purified polymer.

[0096] This application does not impose any particular limitation on the devolatilization device, as long as it can achieve the purpose of this application. For example, the devolatilization device can be a flash evaporator, a strip devolatilization device, a fluidized bed degassing chamber, etc.

[0097] The devolatilization unit 500 may also include a vacuum screw extruder 530. The bottom of the secondary devolatilizer 520 may be connected to the vacuum screw extruder granulator 530 for further devolatilization and pelletizing to collect the final product.

[0098] According to an embodiment of this application, the temperature of the devolatilization unit 500 can be adjusted within the range of 100°C to 200°C. Exemplarily, the temperature of the devolatilization unit 500 can be adjusted within the range of any two values ​​between 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, and 200°C.

[0099] According to embodiments of this application, the aforementioned waste plastic film recycling device may further include a condensation recovery unit for receiving volatiles removed from the devolatilization unit 500, such as the primary devolatilizer 510 and the secondary devolatilizer 520, and condensing and recovering the volatiles before incorporating them into the dissolving solvent. Further, the aforementioned waste plastic film recycling device may also include a recovery solvent storage tank for storing the condensed and recovered volatiles and incorporating them into the dissolving solvent.

[0100] According to an embodiment of the second aspect of this application, a method for recycling waste plastic film is provided. Figure 3 Here is a flowchart of a waste plastic film recycling method according to an embodiment of this application, as shown below. Figure 3 As shown, the waste plastic film recycling method includes steps S310 to S350.

[0101] In step S310, the waste plastic film is dissolved in a dissolving solvent to obtain a crude polymer solution, wherein the waste plastic film includes polymers used as raw materials for plastic film.

[0102] In step S320, the crude polymer solution is filtered to obtain the filtered polymer solution.

[0103] In step S330, the filtered polymer solution and the washing solution are statically mixed, stirred and mixed, and allowed to stand for separation in sequence to obtain the washed polymer solution.

[0104] In step S340, the washed polymer solution is subjected to adsorption treatment to obtain a purified polymer solution.

[0105] In step S350, volatiles in the purified polymer solution are removed to obtain the purified polymer.

[0106] According to embodiments of this application, purified polymers can be obtained by sequentially dissolving, filtering, washing, adsorbing, and devolatilizing waste plastic film. The purified polymers have low ash and volatile matter content, and the process is time-efficient, highly efficient, and requires minimal chemical consumption, making them suitable for industrial production and possessing strong practical value. Furthermore, by sequentially statically mixing, stirring, and separating the filtered polymer solution with the washing solution in the washing unit, the washing effect of the polymer is further improved, reducing the ash and volatile matter content in the purified polymers.

[0107] A further advantage of this application is that it allows the recycled plastic film collected from the field to participate in the recycling of its products and the recovery of fossil resources by improving the quality of the film. Specifically, this application enables the purification of waste plastic film to obtain purified polymers with extremely low impurity content, significantly decolorized and deodorized, making them reusable to form new plastic products. Therefore, to obtain plastic products with both aesthetic appeal and processability, the resulting purified plastic film polymers can be used directly in product manufacturing, either as a mixture with additives such as dyes, pigments, or other polymers, replacing virgin polymer resins or as a mixture with virgin polymer resins.

[0108] The waste plastic film recycling method provided in this application can be implemented using the aforementioned waste plastic film recycling device. (Refer to...) Figure 1 , Figure 2 Step S310 can be achieved by dissolving unit 100, step S320 can be achieved by filtering unit 200, step S330 can be achieved by washing unit 300, step S340 can be achieved by adsorption unit 400, and step S350 can be achieved by devolatilization unit 500.

[0109] In step S310, the waste plastic film can be contacted with a dissolving solvent at a dissolution temperature of 100℃~200℃ and a dissolution pressure of 1.0~5.0MPa to obtain a crude polymer solution. The waste plastic film can be Class I waste plastic film, Class II waste plastic film, etc. (refer to DB 65 / T 3834-2003). The dissolving solvent can be selected from at least one organic solvent with a boiling point of -50℃ to 250℃. The dissolving solvent can be a solvent capable of dissolving the polymer in the waste plastic film. When the polymer is polyethylene, the solvent may include one or more solvents selected from the following: 0-dichlorobenzene; 1,2,3,4-tetrahydronaphthalene; 1,2-dichloroethane; chlorobenzene; chloroform; cyclohexane; cyclohexanone; decahydronaphthalene; dibutoxymethane; methyl ethyl ketone; methyl isobutyl ketone; methyl cyclohexane; dichloromethane; methyl n-pentyl ketone; n-decane; n-heptane; n-hexane; n-hexane; p-xylene; pyridine; 1,1,2,2-tetrachloroethane; tetrachloroethane; and carbon tetrachloride; toluene, etc.

[0110] In step S320, the crude polymer solution can be filtered using the filtration unit 200 at a dissolution temperature of 100°C to 200°C and a dissolution pressure of 1.0 to 5.0 MPa to obtain the filtered polymer solution.

[0111] In step S330, the filtered polymer solution can be contacted with a washing solution at a dissolution temperature of 100°C to 200°C and a dissolution pressure of 1.0 to 5.0 MPa using the washing unit 300 to obtain a filtered polymer solution. The washing solution can be an aqueous solution with a density higher than that of the polymer solution or a high-density organic solvent such as dimethyl sulfoxide, γ-butyrolactone, or triethyl phosphate. The pH of the aqueous solution can be adjusted using acid or alkali, or inorganic or organic water-soluble flocculants can be added to prepare a suitable aqueous solution. The washing solution may include a flocculant, which may include at least one of dicyandiamide-formaldehyde resin, cationic starch, thiourea dioxide, polyferric sulfate, polyaluminum sulfate, polyaluminum chloride, and polyacrylamide to further improve the washing effect. The flow rate of the washing solution entering the static mixer 310 can be adjusted within the range of 5 to 15 kg / h. For example, the flow rate of the washing solution entering the static mixer 310 can be adjusted within any two of the following values: 5 kg / h, 8 kg / h, 10 kg / h, 12 kg / h, 15 kg / h, or more.

[0112] According to embodiments of this application, the washing solution also includes anionic surfactants, metal ion complexing agents, and nano-Fe3O4.

[0113] The flocculant content is 0.005% to 1% based on the mass of the washing solution. For example, the flocculant content is within any two values ​​of 0.005%, 0.01%, 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, or more.

[0114] The mass content of the anionic surfactant is 0.001% to 0.01% based on the mass of the washing solution. For example, the mass content of the anionic surfactant is 0.001%, 0.002%, 0.003%, 0.005%, 0.008%, 0.009%, 0.01%, or any two of the above values ​​based on the mass of the washing solution.

[0115] The mass content of the metal ion complexing agent is 0.001% to 0.005% based on the mass of the washing solution. For example, the mass content of the metal ion complexing agent is 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, or any two of the above values ​​based on the mass of the washing solution.

[0116] Based on the mass of the washing solution, the mass content of nano-Fe3O4 is 0.001% to 0.005%. For example, based on the mass of the washing solution, the mass content of nano-Fe3O4 is 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, or any two of the above values.

[0117] According to embodiments of this application, the anionic surfactant includes sodium dodecylbenzenesulfonate, sodium fatty alcohol ether sulfate, α-sulfonyl monocarboxylic acid and its derivatives, and alkyl phosphate salts. The metal ion complexing agent includes at least one selected from ethylenediaminetetraacetic acid, polyacrylic acid, and citric acid.

[0118] In step S340, the washing unit 400 can be used to contact and filter the washed polymer solution with at least one adsorbent at a dissolution temperature of 100°C to 200°C and a dissolution pressure of 1.0 to 5.0 MPa to remove residual flocculated impurities in the washed polymer solution, thereby obtaining a refined polymer solution. Optionally, the adsorbent used is one or more combinations of molecular sieves, alumina, silica, silica-alumina, activated carbon or diatomaceous earth, and organobentonite, preferably molecular sieves, decolorizing sand, or mixtures thereof.

[0119] In step S350, the purified polymer solution can be depressurized to 0.05 MPa to 0.2 MPa by the devolatilization unit 500 for a first devolatilization treatment, and the initially devolatilized polymer melt is discharged. The initially devolatilized polymer melt is then subjected to a second devolatilization treatment under conditions of -0.4 bar to -0.6 bar to obtain the purified polymer. Specifically, the purified polymer solution can be depressurized to 0.05 to 0.2 MPa through a back pressure valve and the gas phase outlet valve of the first-stage devolatilizer 510. The initially devolatilized polymer melt is transferred to the second-stage devolatilizer 520 by a melt pump, where the solvent is further removed under a negative pressure of -0.4 to -0.6 bar. The purified polymer is then transported to a vacuum screw extruder by a melt pump at the bottom of the second-stage devolatilizer 520 for final devolatilization, and the product is pelletized and collected.

[0120] Figure 4 Here is a flowchart of a waste plastic film recycling method according to another embodiment of this application, as shown below. Figure 4 As shown, the waste plastic film recycling method includes steps S410 to S450.

[0121] In step S410, the recycled mulch film 1 containing impurities such as straw and soil is dissolved in the dissolving solvent 2 to obtain a crude polymer solution 3.

[0122] In step S420, the insoluble impurities doped in the crude polymer solution 3 are separated by filtration to obtain the filtered polymer solution 5 and the insoluble impurities 4.

[0123] In step S430, the filtered polymer solution 5 is washed by contacting the washing solution 6 to obtain washed deposited flocculents 7 and washed polymer solution 8.

[0124] In step S440, the washed polymer solution 8 is contacted with the adsorbent and further separated to remove insoluble impurities 9, thereby obtaining a refined polymer solution 10.

[0125] In step S450, the purified polymer solution 10 is subjected to a devolatilization process to obtain a solvent 11 and a purified polymer 12.

[0126] The technical solutions and advantages of this application will be further described in detail below with reference to specific embodiments.

[0127] Test methods and equipment:

[0128] Before testing, the granular or powdered mulch film samples were molded into square specimens of 80mm x 80mm x 0.5mm thickness using a thermoforming machine. Each specimen was visually evaluated for voids and air bubbles; only specimens with no defects in the measurement area (minimum diameter 18mm) were used for measurement. The color and opacity / transparency of the polymer are important parameters determining whether the polymer can produce products with the desired visual appeal. Recycled mulch films, especially post-consumer derived films, are typically dark and opaque due to residues of soil, plant straw, pigments, fillers, and other contaminants. Therefore, color and opacity measurements are important parameters for determining the effectiveness of polymer purification methods.

[0129] Opacity: Place the square sample tightly against the test aperture of the spectrophotometer (equipped with a projection / reflection module) to avoid light leakage; measure the reflectance of the sample against a black background (R0) and a white background (R) (typically using a D65 light source, wavelength 550nm), and calculate the opacity (%) using the following formula = R0 is the reflectance of the sheet against a black background, R is the reflectance of the same sample against a white background, 100% opacity means completely opaque, and 0% means completely transparent.

[0130] Whiteness and color difference are characterized using the CIE (International Commission on Illumination) L*, a*, b* three-dimensional color space. Dimension L* is a measurement of the sample's brightness, where L* = 0 corresponds to the darkest black sample, and L* = 100 corresponds to the brightest white sample.

[0131] Odor sensory testing: 3g of samples from each example and comparative example were placed in 20ml glass bottles and allowed to stand at room temperature for at least 30 minutes. After standing, olfactory-trained raters smelled each sample bottle to determine the odor intensity and a simple descriptive term. Odor intensity was graded on the following scale: 5, very strong; 4, strong; 3, moderate; 2, weak to moderate; 1, weak; 0, odorless.

[0132] Gel content test: Weigh 2-3g of sample and wrap it sequentially with stainless steel mesh and filter paper. Accurately weigh the sample packet, isolate the sample packets with stainless steel mesh, wrap them together, and place them in the middle of a Soxhlet extractor. Extract with xylene as the extractant for 24 hours. Then, drain the sample packets and place them in a vacuum drying oven to dry to constant weight. Accurately weigh the sample packets after extraction.

[0133] Gel content calculation: In the formula, W is the weight of the sample package, W1 is the weight of the sample package after extraction, and G is the weight of the sample. This test characterizes the degree of cross-linking of the polymer in the recycled mulch film after aging.

[0134] Number of black spots: An optical microscope with a certain magnification is used to clearly observe the surface and interior of the plastic particles. A white background and suitable lighting equipment are required to ensure uniform light and a brightness between 500 and 1000 lumens. Avoid reflections that may affect the test results.

[0135] Ash content: Cool the crucible, which has been preheated to constant weight in a muffle furnace, to room temperature and weigh it accurately (~0.1 mg). Place the sample into the crucible and weigh it accurately (~0.1 mg). Then, slowly ignite it with a Bunsen burner or other heating source. Repeat the above operation until the sample is completely burned. Place the crucible in a muffle furnace preheated to the specified temperature and calcine for 30 minutes. Repeat the operation until constant weight is achieved.

[0136] In the formula, m0 is the weight of the dried sample and m1 is the weight of the obtained ash content.

[0137] Volatile matter: Take 10g of sample (accurate to 0.1mg) and place it in a dry weighing dish, weigh the initial total mass, heat to constant weight in an oven at 105℃, cool to room temperature in a drying oven, and record the remaining mass. Volatile matter calculation: In the formula, M1 is the initial mass and M2 is the mass after drying.

[0138] Example 1

[0139] like Figure 2 As shown in the figure, this embodiment discloses a waste plastic film recycling device, which includes a dissolving unit 100, a filtering unit 200, a washing unit 300, an adsorption unit 400, and a devolatilization unit 500 connected in sequence. The dissolving unit 100 includes a screw feeder 110 and a dissolving kettle 120, which are connected by a shut-off valve. The dissolving solvent is pumped into the dissolving kettle 120 through a dissolving pump 130. The dissolving unit 100 and the filtering unit 200 are connected by a ball valve. For ease of maintenance and process continuity, the filtering unit 200 can be connected in series or parallel. The filtering unit 200 includes two first filters 210 and two second filters 220. The filtering unit 200 and the washing unit 300 are connected by a ball valve. The washing unit consists of a static mixer 310, a mixing and stirring kettle 320, and a settling and separating tank 330. The washing unit 300 is externally connected to a washing solvent storage tank, which is pumped into the front end of the static mixer 310 through a washing solution feeding device 340. Similarly, the adsorption unit 400 is connected to the devolatilization unit 500 via a back pressure valve. The devolatilization unit 500 consists of a primary devolatilizer 510, a secondary devolatilizer 520, a vacuum screw extruder 530, and a corresponding solvent recovery system.

[0140] Based on the above-mentioned waste plastic film recycling device, sheet-like waste plastic film is added from the feed port of the screw extruder, melts at high temperature, and enters the dissolving tank 320 in molten form. The dissolving solvent is pumped into the dissolving tank 320 from the solvent storage tank. The pumped dissolving solvent and the internal pressure serve as the main power source of this system. The polymer solution dissolved in the dissolving tank 320 enters the filtration unit 200 through pipeline valves. Larger physical impurities are intercepted by the filter element and can be discharged and separated through the drain port at the bottom of the filter. The filtered polymer solution is transferred to the static mixer 310 in the washing unit 300. Washing solution is pumped into the inlet of the static mixer 310 to mix and wash with the filtered polymer solution. The polymer solution after further static mixing is transferred to the stirred reaction vessel 320 for stirring, mixing, and washing. After continuous stirring and mixing, the polymer solution enters the settling tank 330 from the top of the stirred reactor 320 for settling and stratification. The lower layer, containing impurities, is the washing solution, which is periodically discharged from the bottom of the settling tank 330. The upper layer, after washing, is discharged from the top of the settling tank 330 and transferred to the adsorption unit 400. After the polymer passes through the adsorption unit 400, residual impurities are adsorbed and filtered out. Then, it enters the first-stage devolatilizer 510 of the devolatilization unit 500 through a back pressure valve. Most of the solvent is recycled after condensation, recovery, and purification. The polymer melt is pumped from the bottom of the first-stage devolatilizer 510 into the second-stage devolatilizer 520 through a melt pump. Under high temperature and negative pressure, the solvent is further removed. The polymer melt is then pumped from the bottom of the second-stage devolatilizer 530 into the screw extruder 530 for devolatilization and granulation or directly pelletized and collected.

[0141] More specifically, the molten waste plastic film raw material can optionally be filtered at the extruder outlet of the dissolving unit 100 using a filtration device such as a screen changer to remove the coarsest impurity particles; typically, the sieve size of this filtration device is 100 micrometers. Further, for continuous production, the filtration unit 200 can be a dual-stage switching filter, and two sets of filters can be connected in series to improve the purification efficiency of the plastic film polymer solution, namely two sets of first filters 210 and second filters 220 connected in series respectively. Depending on the particle size of the polymer and impurities, the filter element pore size of the first filter 210 is 300 mesh, and the filter element pore size of the second filter 220 is 500 mesh. The washing solution is pumped into the front end of the static mixer 310 via a diaphragm pump; the static mixer 310 is selected as a single-channel left- and right-hand torsional spiral mixing unit based on the multiphase media characteristics of the polymer solution. The stirring impeller of the stirred reactor 320 is a combination of a large-blade axial flow impeller and a dispersion disc. The settling separation tank 330 is equipped with an interface level monitoring device, including a float-type interface meter, a guided wave radar (TDR) interface meter, a differential pressure interface meter, and a radio frequency admittance interface meter. To further improve purification efficiency, the washing step can be repeated twice according to the above steps. The adsorption unit 400 uses a gradient combination of molecular sieves, alumina, and decolorizing sand to achieve both adsorption and filtration effects. To further improve production efficiency, the adsorption unit 400 uses a dual-switching adsorption column. The primary devolatilizer 510 uses a paddle agitator based on the medium viscosity, and a back pressure valve is installed in the gas phase pipeline to regulate the devolatilizer pressure and ensure normal solvent recovery.

[0142] Example 2

[0143] This embodiment provides a method for recycling waste plastic film, which utilizes the waste plastic film recycling device described in Embodiment 1, and specifically includes the following steps:

[0144] (1) The recycled Class I mulch film (refer to standard DB 65 / T 3834-2023 "Classification and Grading Specification for Waste Mulch Film") is fed into a screw extruder preheated to 140~180℃ through the feed barrel. The recycled waste film is then conveyed to a 40L high-pressure dissolving kettle 120 in a molten state through the screw. The dissolving kettle 120 is sealed and heated to 170~180℃. At the same time, the polymer is uniformly dispersed by stirring at a speed of 500 rpm to obtain a crude polymer solution. The extruder feeding speed is controlled at 700~800g / h. At the same time, the preheated solvent is pumped into the kettle from the bottom to the top of the solvent tank through the solvent feed pump. The solvent flow rate is controlled at 10~20kg / h.

[0145] (2) The crude polymer solution is filtered sequentially through the top of the dissolving vessel 120 and then through filters with 100μm and 25μm pore sizes (arranged in sequence) to obtain the filtered polymer solution. The pressure drop of each filter is about 0.2~0.3MPa (when the pressure drop of a single filter is >0.8MPa, the filter is considered to be blocked and can be switched to a standby filter).

[0146] (3) The filtered polymer solution was mixed with washing solvent in a static mixer 310 at a flow rate of 10 kg / h. The mixture was then transferred to a stirred reactor 320 for further mixing and washing. After stratification, the polymer was placed in a settling tank 330 to separate some of the evaporated water, yielding the washed polymer solution. Polyaluminum sulfate and polyacrylamide flocculant were added to the washing solution in a 1:1 ratio. Based on the mass of the washing solution, the flocculant content was 1%.

[0147] (4) After washing, the polymer solution is adsorbed, decolorized, and filtered by the adsorption column of the devolatilization unit and then enters the first-stage devolatilizer 510. The pressure is controlled at 0.05~0.25MPa. The solvent is recovered to the solvent recovery tank through the gas phase pipe and condenser, and then transferred to the crude and refined product tank for recycling via the diaphragm pump. The polymer melt that has undergone preliminary devolatilization is pumped into the second-stage devolatilizer 520 by the melt pump at the bottom of the first-stage devolatilizer 510. The temperature is controlled at 190~200℃ and the pressure is controlled at -0.4~-0.6bar. After deodorizing and further removing solvent from the polymer melt, the purified polymer is pumped from the bottom of the second-stage devolatilizer 520 into the vacuum screw extruder for extrusion granulation, and the product is collected.

[0148] Example 3

[0149] This embodiment provides a method for recycling waste plastic film, which is carried out using the waste plastic film recycling device described in Embodiment 1. The specific steps are the same as those in Embodiment 2. The difference is that in this embodiment, no flocculant is added to the washing solvent in step (3).

[0150] Example 4

[0151] This embodiment provides a method for recycling waste plastic film, using the waste plastic film recycling device described in Embodiment 1. The specific steps are the same as in Embodiment 2, except that in this embodiment, the washing solvent in step (3) further includes sodium dodecylbenzenesulfonate, ethylenediaminetetraacetic acid, and nano-Fe3O4. The mass content of sodium dodecylbenzenesulfonate is 0.005% based on the mass of the washing solution. The mass content of ethylenediaminetetraacetic acid is 0.001% based on the mass of the washing solution. The mass content of nano-Fe3O4 is 0.001% based on the mass of the washing solution.

[0152] Comparative Example 1

[0153] The waste plastic film recycling device provided in this comparative example is the same as that in Example 1, except that the washing unit 300 in this comparative example does not include the static agitator 310.

[0154] The waste plastic film recycling method provided in this comparative example refers to Example 2, except that step (3) is as follows:

[0155] (3) The filtered polymer solution is mixed with washing solvent in a stirred reactor 320 and washed. The flow rate of the washing solution is 10 kg / h. After washing and stratification, the polymer is put into a static separation tank 330 to separate part of the evaporated water, and the washed polymer solution is obtained.

[0156] Comparative Example 2

[0157] The waste plastic film recycling device provided in this comparative example is the same as that in Example 1, except that the waste plastic film recycling device in this comparative example does not include the washing unit 300.

[0158] The waste plastic film recycling method provided in this comparative example refers to Example 2, except that this comparative example does not include step (3).

[0159] Samples obtained from Examples 2, 3, 4, Comparative Example 1, and Comparative Example 2 were sampled and analyzed. The test results are detailed in Table 1.

[0160] Table 1

[0161]

[0162] Analysis of Examples 2 and 3, and Comparative Examples 1 and 2, shows that the waste mulch film recycling device and method provided in this application have good purification effects on waste mulch film, especially with low color difference and a significant reduction in the number of black spots compared to virgin material. The aged cross-linked portion of the polymer is removed (gel content is significantly reduced), meeting the standards for the reuse of agricultural mulch film. Comparative examples show that the combined washing unit of static mixer + stirred reactor is more conducive to improving purification efficiency. Comparative examples 2 and 3 show that adding flocculant to the washing unit helps improve purification efficiency and yield. The table above shows that the waste mulch film recycling device and method provided in this application can efficiently purify and recycle waste mulch film. The purified product has properties close to that of virgin material and can be used in high-value-added applications such as recycled agricultural film or other film sheets where the appearance, texture, and color of the product are critical.

[0163] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A waste plastic film recycling device, comprising: connected in sequence: A dissolving unit is used to dissolve waste plastic film in a dissolving solvent and discharge a crude polymer solution, wherein the waste plastic film includes polymers used as raw materials for plastic film. A filtration unit is used to receive a crude polymer solution from a dissolving unit, filter the crude polymer solution, and discharge the filtered polymer solution. The washing unit is used to receive the filtered polymer solution from the filtration unit, and to sequentially perform static mixing, stirring and mixing and static separation of the filtered polymer solution and the washing solution, and then discharge the washed polymer solution. An adsorption unit is used to receive the washed polymer solution from the washing unit, and to adsorb the washed polymer solution to discharge the purified polymer solution. The devolatilization unit is used to receive the purified polymer solution from the adsorption unit and remove the volatiles from the purified polymer solution to obtain the purified polymer.

2. The waste plastic film recycling device according to claim 1, wherein, The washing unit includes: A static mixer, wherein a fixed mixing element is provided inside the static mixer, for receiving the filtered polymer solution from the filtration unit and the washing solution from the washing solution feeding device, and statically mixing the washing solution with the filtered polymer solution, and discharging the statically mixed polymer solution. A mixing vessel is used to receive a statically mixed polymer solution from a static mixer, to stir and mix the statically mixed polymer solution, and to discharge the stirred and mixed polymer solution. A settling separation tank is used to receive the polymer solution after stirring and mixing from a mixing vessel, and to set the polymer solution after stirring and mixing for settling treatment, and to discharge the washed polymer solution.

3. The waste plastic film recycling device according to claim 2, wherein, The mixing element is a spiral mixing unit or a plate mixing unit, and the mixing elements are arranged sequentially along the axial direction of the internal pipe of the static mixer.

4. The waste plastic film recycling device according to claim 1, wherein, The filtering unit includes: The first filter is used to receive the crude polymer solution from the dissolving unit, and to filter the crude polymer solution once, and to discharge the polymer solution after preliminary filtration. The second filter is used to receive the polymer solution after preliminary filtration from the first filter, and to perform secondary filtration on the polymer solution after preliminary filtration, and to discharge the filtered polymer solution. The filter element pore size of the first filter is larger than that of the filter element of the second filter.

5. The waste plastic film recycling device according to claim 4, wherein, The filter element of the first filter has a pore size of 100 mesh to 300 mesh; The filter element of the second filter has a pore size of 500 mesh to 800 mesh.

6. The waste plastic film recycling device according to claim 1, wherein, The devouring unit includes: The first-stage devolatilizer is used to receive the refined polymer solution from the adsorption unit and depressurize the refined polymer solution to 0.05MPa~0.2MPa for a first devolatilization treatment, and discharge the polymer melt that has undergone preliminary devolatilization. The secondary devolatilizer is used to receive the polymer melt that has undergone preliminary devolatilization from the primary devolatilizer, and to perform a secondary devolatilization treatment on the polymer melt under conditions of -0.4 bar to -0.6 bar to obtain the purified polymer.

7. The waste plastic film recycling device according to claim 1 further includes: The condensation recovery unit is used to receive the volatiles removed from the devolatilization unit, and to condense and recover the volatiles and incorporate them into the dissolving solvent.

8. The waste plastic film recycling device according to any one of claims 1 to 7, wherein, The temperature of the dissolving unit, filtering unit, washing unit, and / or the adsorption unit is adjustable within the range of 100℃ to 200℃, and the pressure is adjustable within the range of 1.0MPa to 5.0MPa.

9. A method for recycling waste plastic film, comprising: Waste plastic film is dissolved in a dissolving solvent to obtain a crude polymer solution, wherein the waste plastic film includes polymers used as raw materials for plastic film. The crude polymer solution is filtered to obtain the filtered polymer solution. The filtered polymer solution and the washing solution were sequentially statically mixed, stirred, and allowed to stand for separation to obtain the washed polymer solution. The washed polymer solution is subjected to adsorption treatment to obtain a refined polymer solution; The volatiles in the refined polymer solution are removed to obtain the purified polymer.

10. The method for recycling waste plastic film according to claim 9, wherein, The washing solution includes flocculants, anionic surfactants, metal ion complexing agents, and nano-Fe3O4; Based on the mass of the washing solution, the mass content of the flocculant is 0.005%~1%; Based on the mass of the washing solution, the mass content of the anionic surfactant is 0.001%~0.01%; Based on the mass of the washing solution, the mass content of the metal ion complexing agent is 0.001%~0.005%; Based on the mass of the washing solution, the mass content of the nano-Fe3O4 is 0.001%~0.005%; The flocculant includes at least one of dicyandiamide-formaldehyde resin, cationic starch, thiourea dioxide, polyferric sulfate, polyaluminum sulfate, polyaluminum chloride, and polyacrylamide. The anionic surfactants include sodium dodecylbenzenesulfonate, sodium fatty alcohol ether sulfate, α-sulfonyl monocarboxylic acid and its derivatives, and alkyl phosphate salts; The metal ion complexing agent includes at least one of ethylenediaminetetraacetic acid, polyacrylic acid, and citric acid.

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