KR20240005392A - Waste plastic treatment method - Google Patents

Abstract

The present invention relates to a process for treating waste plastic containing polymers, chemical foreign substances and physical foreign substances, an aging step of supplying the waste plastic to a container storing the aging solution to prepare a first solution containing the aged waste plastic. ; A first filtration step of separating the aging solution and the aged waste plastic; A first drying step of drying the waste plastic separated from the aging solution; A dissolution step of stirring the dried waste plastic with a solvent to prepare a second solution in which the polymer and the chemical foreign substances are dissolved and the physical foreign substances are dispersed; a second filtration step of preparing a lysate from which the physical foreign substances contained in the second solution are removed; A separation step of centrifuging the lysate to separate a first lysate containing the polymer and a second lysate containing the chemical foreign substances; A concentration step of concentrating the first lysate; It relates to a waste plastic treatment process including a second drying step of drying the concentrated first lysate and a pulverization step of pulverizing the dried polymer.

Description

Waste plastic treatment process {WASTE PLASTIC TREATMENT METHOD}

The present invention relates to a waste plastic treatment process. Specifically, the present invention relates to a waste plastic treatment process that can recycle waste plastic using a single solvent.

In general, when recycled plastic waste is received at a collection point for recycling, the recycled plastic waste has largely different characteristics as flame retardant and non-flammable, and various materials are mixed for flame retardancy and non-flammability, and in terms of color, it is white, Recycled plastic waste of various colors such as black and red is received in a mixed state.

In the process of recycling plastic, impurities are removed through the steps of crushing, dissolving, settling (or precipitating), and drying the plastic.

More specifically, the conventional process of recycling plastic is to precipitate and precipitate the polymer by supplying a solution in which the plastic is dissolved to a container storing the non-solvent, then collecting and drying the precipitated polymer to remove the non-solvent to produce recycled plastic. Manufactured.

In the conventional process of recycling plastic, the non-solvent stored in the container must be contained in a sufficient amount so that the solubility of the solution is reduced so that the plastic contained in the solution can precipitate. Therefore, the conventional plastic recycling process used an excessive amount of non-solvent, resulting in an increase in the cost of recycled plastic.

Korean Patent Publication No. 10-2010-7025766

The present invention is intended to solve the problems of the prior art, and seeks to provide a waste plastic treatment process that uses a single solvent to precipitate polymers contained in waste plastic.

One embodiment of the present invention is a process for treating waste plastic containing polymers, chemical foreign substances, and physical foreign substances, by supplying the waste plastic to a container storing the aging solution to prepare a first solution containing the aged waste plastic. Aging step of manufacturing; A first filtration step of separating the aging solution and the aged waste plastic; A first drying step of drying the waste plastic separated from the aging solution; A dissolution step of stirring the dried waste plastic with a solvent to prepare a second solution in which the polymer and the chemical foreign substances are dissolved and the physical foreign substances are dispersed; A dissolution step of stirring the dried waste plastic with a solvent to prepare a second solution in which the polymer and the chemical foreign substances are dissolved and the physical foreign substances are dispersed; a second filtration step of preparing a lysate from which the physical foreign substances contained in the second solution are removed; A separation step of centrifuging the lysate to separate a first lysate containing the polymer and a second lysate containing the chemical foreign substances; A concentration step of concentrating the first lysate; It provides a waste plastic treatment process including a second drying step of drying the concentrated first lysate and a pulverization step of pulverizing the dried polymer.

One embodiment of the present invention provides a waste plastic treatment process in which the first drying step of drying the aged waste plastic and the second drying step of drying the first melt have different drying methods.

In one embodiment of the present invention, the first drying step is to dry the waste plastic by any one of a thin film drying method, a drum drying method, a fluidized bed drying method, a silo drying method, and a belt drying method. Provides a waste plastic processing process.

In one embodiment of the present invention, the second drying step is a waste plastic treatment process in which the polymer is dried by any one of a thin film drying method, a drum drying method, a fluidized bed drying method, a silo drying method, and a belt drying method. to provide.

One embodiment of the present invention provides a waste plastic treatment process in which the first drying step dries the aged waste plastic at a temperature of 65°C to 200°C.

One embodiment of the present invention provides a waste plastic treatment process in which the second drying step dries the first melt at a temperature of 50°C to 200°C.

One embodiment of the present invention provides a waste plastic treatment process in which the separation step is centrifugal separation based on a difference in molecular weight between the polymer and the chemical foreign matter.

One embodiment of the present invention provides a waste plastic treatment process in which the pulverizing step pulverizes the dried polymer to a diameter of 500 ㎛ or less.

One embodiment of the present invention provides a waste plastic treatment process further comprising the step of pulverizing the waste plastic before the aging step.

One embodiment of the present invention provides a waste plastic treatment process in which the aging step creates voids in the waste plastic to first remove the chemical foreign substances.

One embodiment of the present invention provides a waste plastic treatment process in which the aging step involves stirring the waste plastic in the container storing a methyl isobutyl ketone, acetone, ethyl acetone or acetylacetone solution.

One embodiment of the present invention provides a waste plastic treatment process in which the concentration step concentrates the first melt by heating the first melt in a vacuum state.

According to the waste plastic treatment process according to the embodiments of the present invention, an economic effect can be generated by lowering the cost of recycled plastic by using one solvent when precipitating polymers contained in waste plastic.

1 is a flowchart of a waste plastic treatment process according to an embodiment of the present invention.

The detailed description of the present invention is intended to completely explain the present invention to those skilled in the art. Throughout the specification, when a part is said to “include” a certain component or is “characterized” by a certain structure and shape, this means excluding other components or excluding other structures and shapes unless specifically stated to the contrary. It does not mean that it does, but that it can include other components, structures, and shapes.

Since the present invention can be modified in various ways and can have various embodiments, specific embodiments will be presented and explained in detail in the detailed description. However, this is not intended to limit the content of the invention by examples, and should be understood to include all transformations, equivalents, and substitutes included in the spirit and technical scope of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings. However, the drawings are for illustrating the present invention, and the scope of the present invention is not limited by the drawings.

1 is a flowchart of a waste plastic treatment process according to an embodiment of the present invention.

The waste plastic treatment process includes an aging step (S10), a first filtration step (S20), a first drying step (S30), a dissolution step (S40), a second filtration step (S50), a separation step (S60), and a concentration step ( It may include a second drying step (S70), a second drying step (S80), and a grinding step (S90).

Waste plastic according to the present invention may contain polymers, chemical foreign substances, and physical foreign substances. Chemical foreign substances are substances that can dissolve in solvents or non-solvents, and physical foreign substances are substances that are dispersed without dissolving in solvents or non-solvents.

For example, polymers include High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE), Polyethylene terephthalate PET, Polystyrene (PS), polypropylene (PP), It may include any one of polyvinyl chloride (PVC), polycarbonate (PC), and acrylonitrile butadiene styrene copolymer (ABS).

Chemical foreign substances may include plasticizers, thermosetting agents, and other additives, and physical foreign substances may include fiber, iron, and rubber.

The aging step (S10) is a step of preparing a first solution containing aged waste plastic by supplying waste plastic to a container in which the aging solution is stored. Here, aged waste plastic may mean that waste plastic has swelled. And, the first solution may include aged waste plastic and an aging solution.

In the aging step (S10), an aging solution sufficient to submerge the waste plastic may be stored in a container, and the waste plastic and aging solution may be stored in a container and stirred to age the waste plastic.

Aging in the aging step (S10) means that pores of waste plastic or polymer are created by the aging solution, and the size of the generated pores is accelerated to expand.

In the aging step (S10), the additives contained in the waste plastic can easily escape from the polymer structure in the dissolution step (S40) performed after the aging step (S10) and enhance diffusion into the solution. Here, the additive refers to various additives applied to plastic manufacturing, and in the present invention, it may specifically be CaCO ₃ , a plasticizer, or a stabilizer.

The aging solvent is a solvent between a good solvent and a non-solvent, and although it is difficult to completely dissolve waste plastic, it is a solvent that can cause swelling. The aging solvent refers to a compound having a Hansen Solubility Parameter (HSP) of 6 to 10 for polymers contained in waste plastic. For example, an aging solvent refers to a compound having a Hansen Solubility Parameter (HSP) of 6 or more and 10 or less for polyvinyl chloride.

At this time, the Hansen solubility factor of waste plastic refers to the difference in Hansen parameters between two substances, a solute and a solvent. The Hansen solubility factor is a value proportional to the solubility of the two substances, through which the solubility of the two substances can be calculated. The more similar the properties of two substances are, the lower the HSP value is because the Hansen parameter values are similar. It can be predicted that these two substances will dissolve well in each other through the HSP value.

The Hansen solubility factor can be calculated using the formula below. When using HSPip software, which easily calculates this, δd, δp, and δh of the two substances can be obtained. By applying the values to the formula below, the HSP value with the corresponding solvent can be calculated. .

The aging solution may include a solution containing methyl isobutyl ketone, acetone, ethyl acetone, or acetylacetone. Preferably, the solvent applied in the aging step (S10) may be an acetone solution.

The aging step (S10) may be performed for 1 to 12 hours at a stirring speed of 50 rpm to 300 rpm, and may be stirred to prepare a solution at room temperature to 85°C. Preferably, it may be performed for 1 hour to 2 hours at a stirring speed of 100 rpm to 200 rpm, and a first solution of 50°C to 65°C may be prepared by stirring.

However, the stirring time, speed, and temperature conditions are not limited to the above, and can be appropriately selected under conditions that can sufficiently create voids in the waste plastic.

And, in the present invention, room temperature may be 15°C to 25°C.

In another embodiment of the present invention, after the aging step, the step of cooling the aging solution by adding a cooling solvent of a lower temperature than the aging solution may be further included. The aging solvent is a solvent between the good solvent and the non-solvent of waste plastic, and has low solubility in waste plastic. However, if the residence time is sufficiently long, the probability of contact through stirring increases, or the temperature rises, some of the waste plastic is absorbed by the aging solvent. Since the bond becomes loose and the amount of waste plastic lost increases, the amount of waste plastic lost by being dissolved in the aging solvent can be reduced by adding the cooling solvent.

The temperature of the aging solution may be 30°C to 130°C, and the temperature of the cooling solvent lower than the aging solution may be 20°C to 40°C. However, since the temperature of the cooling solvent is lower than the temperature of the aging solution and is a solution that cools the aging solution, when the temperature of the aging solution is 30°C, the temperature of the cooling solvent is selected in the range of 20°C or more and less than 30°C.

The step of cooling the aging solution by adding a cooling solvent of a lower temperature than the aging solution may be performed by adding the cooling solvent to the transfer line while transferring the aging solution through the transfer line.

The cooling solvent may be one or more selected from the group consisting of alcohol, ether, cycloalkane, ester, carboxylic acid, nitrile, acetone, and acetylacetone.

The method for producing recycled polyvinyl chloride according to an exemplary embodiment of the present invention may further include a third filtration step of filtering out the polyvinyl chloride that has been aged in the aging step.

When filtering polyvinyl chloride by removing the solvent applied in the aging step, an 80 mesh (177 ㎛) filter can be used, but is not limited to this.

The waste plastic treatment process according to the present invention may further include a pretreatment step (S0) of pulverizing the waste plastic before the aging step (S10).

The pretreatment step (S0) is a step that reduces the size of the waste plastic and increases the contact area where the waste plastic comes into contact with the aging solution. As the area in contact with the aging solution increases, waste plastic's void creation rate increases and the time it takes for voids to be created may decrease.

The pretreatment step (S0) can crush waste plastic to a size of 5 mm to 15 mm. Here, the size of waste plastic refers to the straight line distance between both ends of a piece of waste plastic in the form of pulverized particles.

The first filtration step (S20) is a step of separating the aging solution and aged waste plastic. That is, the first filtration step (S20) may separate the aging solution and waste plastic by filtering the first solution.

The first filtration step (S20) may include compressing the first solution (S20-1).

For example, in the first filtration step (S20), the first solution is supplied to a filter unit including a filter net, and the aging solution contained in the first solution passes through the hole provided in the filter net to be separated from the aged waste plastic. You can. The diameter of the holes included in the filter net used in the first filtration step (S20) is not particularly limited as long as the aging solution can pass through.

Alternatively, in the first filtration step (S20), the aging solution may be filtered by supplying the first solution to a filter unit including a filter net and pressing the surface on which the first solution containing the aged waste plastic is mounted. In the first filtration step (S20), compression can remove the aging solution remaining in the aged waste plastic without being removed by gravity, thereby increasing the rate of decrease in water content of the aged waste plastic.

The first drying step (S30) is a step of drying the waste plastic separated from the aging solution through the first filtration step (S20). The first drying step (S30) is a step of removing the residual aging solution contained in the aged waste plastic.

In the first drying step (S30), aged waste plastic can be dried by any one of the thin film drying method, drum drying method, fluidized bed drying method, silo drying method, drum drying method, and belt drying method. .

In the first drying step (S30), the first solution contains aged waste plastic of a certain size dispersed in the aging solution, rather than the waste plastic dissolved in the aging solution, preferably using a fluidized bed drying method, a silo drying method, or a drum. Aged waste plastic can be dried using either a drying method or a belt drying method.

The first drying step (S30) may dry the aged waste plastic using a method different from the drying method used in the second drying step (S80). In the first drying step (S30), aged waste plastic may be dried using any one of a fluidized bed drying method, a silo drying method, and a belt drying method.

For example, if the aged waste plastic is dried using a fluidized bed drying method in the first drying step (S30), the first melt can be dried using a drum drying method in the second drying step (S80).

And, the first drying step (S30) may dry the aged waste plastic at a temperature of 65°C to 200°C. Preferably, the first drying step (S30) may dry the aged waste plastic at a temperature of 75°C to 180°C, more preferably at a temperature of 85°C to 150°C.

The first drying step (S30) is to evaporate the aging solution, and when the temperature range is met, the aging solution can be effectively converted from liquid to gas and evaporated relative to the energy supplied.

The dissolution step (S40) is a step of stirring the dried waste plastic with a solvent to prepare a second solution in which the polymer and chemical foreign substances are dissolved in the solvent, and the physical foreign substances are dispersed in the solvent.

The second solution may mean that the polymer contained in the waste plastic is dissolved by mixing the waste plastic with a positive solvent (or solvent) that has high solubility for the polymer contained in the waste plastic. When the polymer contained in waste plastic dissolves in a solvent, physical bonds such as dipole moment bonds and hydrophobic bonds between chains are weakened, the chain is released, and the degree of freedom increases, and additives such as plasticizers trapped in the chain are released.

Accordingly, in the second solution, the polymer and the polymer chain are released and the chemical foreign substances trapped in the chain are dissolved in the good solvent, and the physical foreign substances separated by the dissolution of the polymer and chemical foreign substances can be dispersed and included in the good solvent.

Dissolution step (S40) The solubility of the polymer in the solvent can be controlled by the amount of solvent, temperature, size of waste plastic, stirring speed, etc. In addition, the dissolution step (S40) dissolves the waste plastic in which voids were created by the aging step (S10) in a solvent. The contact area between the waste plastic and the solvent increases due to the voids, thereby increasing the dissolution rate of the polymer. .

In the dissolution step (S40), a solvent may be supplied to the dissolution reactor to the extent that the waste plastic is submerged in the solvent. In one embodiment, in the dissolution step (S40), the amount of solvent and waste plastic may be supplied to the dissolution reactor at a mass ratio of 1:1 to 2:1.

The dissolution step (S40) can increase the solubility of the polymer by increasing the temperature of the solvent. The temperature of the solvent may be 25°C to 130°C. The dissolution step (S40) may include heating the solvent. And, in the dissolution step (S40), the waste plastic may be stirred with the solvent for 0.5 to 3 hours.

In the dissolution step (S40), the solubility of the polymer can be adjusted by controlling the rotation speed of the solvent. In the dissolution step (S40), the solvent flows as the stirrer rotates, and the solvent and waste plastic can be stirred. The dissolution step (S40) may be stirred under conditions of 100 rpm to 1,500 rpm.

The second filtration step (S50) is a step of filtering out physical foreign substances contained in the second solution. In other words, the second filtration step (S50) is a step of secondarily removing physical foreign substances that were not removed in the aging step (S10).

The second solution contains dissolved polymers and chemical foreign substances and physical foreign substances, and the second filtration step (S50) can separate the dissolved substances and physical foreign substances.

In the second filtration step (S50), like the first filtration step (S20), a second solution is supplied to a filter net and filter, and the dissolved polymer and chemical foreign substances can be separated from physical foreign substances through the holes of the filter net. . The filter network may include a plurality of holes with a diameter smaller than the physical foreign matter. The diameter of the hole may be 500 μm to 1 mm, preferably 100 μm to 1 mm, and more preferably 1 μm to 1 mm.

The separation step (S60) is a step of centrifuging polymers and chemical foreign substances. In the separation step (S60), the polymer and chemical foreign substances may be separated by centrifuging the dissolved material filtered in the second filtration step (S50).

The separation step (S60) may be centrifuged due to the difference in molecular weight between the polymer and chemical foreign substances. For example, in the separation step (S60), the lysate may be centrifuged by storing the lysate in a beaker and rotating it. The centrifuged lysate may be separated into a first lysate in which polymers are dissolved and a second lysate in which chemical foreign substances are dissolved. The first melt has a greater weight or density than the second melt, so it moves to the bottom of the beaker, and the second melt has a weight or density less than the first melt, so it can move to the top of the beaker. At this time, the centrifuge used may be an ultra-high-speed centrifuge.

In the separation step (S60), polymers and chemical foreign substances can be centrifuged under conditions of 2,000 rpm to 20,000 rpm for 10 to 60 minutes.

The concentration step (S70) is a step of concentrating the first melt, and is a step of increasing the polymer concentration of the first melt by evaporating part of the solvent contained in the first melt. By first removing the solvent contained in the first melt before the second drying step (S80), the energy consumed in the second drying step (S80) can be reduced.

In the concentration step (S70), the solvent contained in the first melt may be evaporated by heating the first melt in a vacuum. For example, the concentration step (S70) includes supplying the first dissolved substance inside a sealed housing, connecting the housing and a vacuum pump to remove all gas inside the housing to form a vacuum inside the housing, and forming the housing in a vacuum state. It may include the step of evaporating the solvent contained in the first melt by heating.

The concentration step (S70) may concentrate the first lysate at a lower temperature than the second drying step (S80). For example, the concentration step (S70) may control the internal temperature of the housing to 45°C to 65°C, preferably 45°C to 55°C, more preferably 45°C to 50°C.

The second drying step (S80) is a step of drying the separated polymer. In more detail, the second drying step (S80) is a step of drying the first melt in which the polymer separated by centrifugation is dissolved.

In the second drying step (S80), the solvent may be evaporated by drying the first melt, and as the solvent evaporates, the polymer may be crystallized to produce polymer particles.

In the second drying step (S80), the first melt may be dried using any one of a thin film drying method, a drum drying method, a fluidized bed drying method, a silo drying method, a drum drying method, and a belt drying method.

Preferably, the second drying step (S80) may use a drum drying method or a thin film drying method. The second drying step (S80) is a step of drying the solution to precipitate the polymer dissolved in the solution.

For example, in the second drying step (S80), the washed polymer may be dried using a drum dryer equipped with a rotating part with a plurality of wings inside the housing. A drum dryer can dry polymers by directly heating the housing, heating the rotating part by supplying high-temperature air inside the rotating part, or supplying heated air inside the housing.

The second drying step (S80) may heat the housing or the air inside the housing to a temperature that can evaporate the solvent (or good solvent) contained in the first melt. In one embodiment, the second drying step (S80) may dry the first melt by increasing the temperature of the housing or the air inside the housing to a temperature of 50°C to 200°C. Preferably, in the second drying step (S80), the housing or the air temperature inside the housing may be 55°C to 150°C, more preferably 85°C to 120°C.

The pulverizing step (S90) is a step of pulverizing the dried polymer. The dried polymer can be processed to make recycled plastic. Therefore, polymers undergo processing steps such as extrusion and molding depending on the intended use of recycled plastic. The pulverizing step (S90) may pulverize the polymer to increase the processing rate of the polymer in the processing step.

In the pulverizing step (S90), the dried polymer can be pulverized to a diameter of 500 μm or less. Preferably, the grinding step (S90) may grind the polymer to a diameter of 400 ㎛ or less, more preferably 300 ㎛ or less.

Although the present invention has been described above with reference to preferred embodiments, those skilled in the art may make various modifications and changes to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. You will understand that you can do it.

Claims (12)

In the process of treating waste plastic containing polymers, chemical foreign substances, and physical foreign substances,
An aging step of supplying the waste plastic to a container storing an aging solution to prepare a first solution containing the aged waste plastic;
A first filtration step of separating the aging solution and the aged waste plastic;
A first drying step of drying the waste plastic separated from the aging solution;
A dissolution step of stirring the dried waste plastic with a solvent to prepare a second solution in which the polymer and the chemical foreign substances are dissolved and the physical foreign substances are dispersed;
A second filtration step of preparing a lysate from which the physical foreign substances contained in the second solution are removed;
A separation step of centrifuging the lysate to separate a first lysate containing the polymer and a second lysate containing the chemical foreign substances;
A concentration step of concentrating the first lysate;
a second drying step of drying the concentrated first lysate; and
Grinding step of pulverizing the dried polymer
Waste plastic processing process including. The waste plastic treatment process according to claim 1, wherein the first drying step of drying the aged waste plastic and the second drying step of drying the first melt have different drying methods. The method according to claim 1, wherein the first drying step is to dry the aged waste plastic by any one of a thin film drying method, drum drying, fluidized bed drying method, silo drying method, and belt drying method. Plastic processing process. The waste plastic treatment process according to claim 1, wherein the second drying step is to dry the first melt by any one of a thin film drying method, a drum drying method, a fluidized bed drying method, a silo drying method, and a belt drying method. The waste plastic treatment process according to claim 1, wherein the first drying step dries the aged waste plastic at a temperature of 65°C to 200°C. The waste plastic treatment process according to claim 1, wherein the second drying step is to dry the first melt at a temperature of 50°C to 200°C. The process of claim 1, wherein the separation step is centrifugation based on a difference in molecular weight between the polymer and the chemical foreign matter. The method according to claim 1, wherein the pulverizing step is pulverizing the dried polymer to a diameter of 500㎛ or less. The waste plastic treatment process according to claim 1, further comprising the step of pulverizing the waste plastic before the aging step. The waste plastic treatment process according to claim 1, wherein the aging step creates voids in the waste plastic to first remove the chemical foreign substances. The process of claim 1, wherein the aging step involves stirring the waste plastic in the container storing a methyl isobutyl ketone, acetone, ethyl acetone, or acetylacetone solution. The process of claim 1, wherein the concentration step concentrates the first melt by heating the first melt in a vacuum.