Plastic recovery method of polyvinyl chloride

Abstract

The invention provides a plastic recovery method of polyvinyl chloride, which comprises the following steps: dissolving polyvinyl chloride by adopting a solvent and a dissolving step, and separating the solvent and recovering the polyvinyl chloride through negative pressure. The plastic recovery method of polyvinyl chloride has high plastic recovery rate and high recovery efficiency, and the solvent can be recycled, so that the cost is reduced, and the derivative environmental problem can be avoided.

Description

Technical Field

[0001] The invention relates to a method for recycling polyvinyl chloride plastics. Background Art

[0002] The invention of plastics began in the 19th century. Due to its advantages of high quality, low price and versatility, it has become a common raw material for various products. For example, polyvinyl chloride (PVC) has the advantages of acid and alkali resistance, flame retardancy and durability, so it is widely used in bank cards, doors and windows, plastic wrap, imitation leather and cable insulators.

[0003] Since plastics are not easily decomposed in nature, the plastic products that can be seen everywhere in daily life have gradually become a serious environmental problem in the process of gradual replacement. Current plastic recycling methods include: (1) Melt Regeneration Method: Recycling clean scraps left over from processing plants and reshaping them into recycled plastics; or recycling mixed plastic products for composite recycling; and (2) Thermal Cracking Method: Recycling specific plastics into fuels, for example: Taiwan Patent Publication No. TWI254115B: Cracking waste plastics into liquid oil and combustible gas.

[0004] Although countries are gradually implementing plastic reduction policies, the environmental problems caused by plastic waste still need to be solved urgently, so it is necessary to develop new plastic recycling methods. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for recycling polyvinyl chloride plastics, comprising:

[0006] (1) Preparation step: preparing a plastic-containing material, wherein the plastic-containing material comprises a plastic, and the plastic comprises polyvinylchloride (PVC);

[0007] (ii) a mixing step of mixing the plastic-containing material and a solvent to obtain a first mixture, wherein the plastic is soluble in the solvent;

[0008] (iii) a dissolving step: stirring the first mixture at a temperature of 20° C. to 110° C. to dissolve the plastic in the solvent to obtain a solution; and

[0009] (iv) Separation step: filtering the second mixture through a filter.

[0010] According to the present invention, first, a solvent is used to dissolve the plastic as the recycling target, which has a high plastic recycling rate. Second, stirring can prevent the plastic-containing materials from sticking to each other or adhering to the surface of the container containing the first mixture, and helps dissolution, thereby improving the plastic recycling efficiency. Third, the solvent is evaporated in a negative pressure environment. In addition to effectively separating the solvent and the plastic as the recycling target, it can also prevent the solvent or plastic from deteriorating due to excessive heating, so that the recovered solvent can also be reused to further reduce the recycling cost. In addition to attracting more manufacturers to invest in the plastic recycling industry, this can also avoid the cost increase and potential environmental problems caused by the discharge of solvents, so it can double reduce environmental problems.

[0011] The plastic-containing material of the present invention comprises a polymer, a mixture or a combination thereof.

[0012] In one embodiment, if the plastic-containing material includes a material other than polyvinyl chloride, the dissolving solution includes not only the polyvinyl chloride dissolved in the solvent but also a portion insoluble in the solvent, such as a precipitate or a suspended substance.

[0013] Preferably, the temperature of the dissolving step is 25°C to 105°C, for example, 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C or 105°C.

[0014] In one embodiment, the separation step further comprises a heat preservation step: the solution is kept warm at a temperature of 40° C. to 110° C., for example, 40° C., 50° C., 60° C., 70° C., 80° C., 90° C., 100° C. or 110° C. The present invention reduces the boiling point of the solvent by creating a negative pressure environment, and keeps the solvent in a boiling state through heat preservation, so as to accelerate and stabilize the recovery of the solvent, and has the advantage of reducing energy consumption.

[0015] In one embodiment, in the separation step, after the heat preservation step is completed to obtain a recycled semi-finished product, a drying step is further performed: the recycled semi-finished product is dried at a temperature of 70° C. to 90° C., for example, 70° C., 75° C., 80° C., 85° C. or 90° C. to obtain the plastic. The present invention further removes the solvent that may remain in the recycled semi-finished product through the drying step.

[0016] In one embodiment, in the separation step, the pressure of the negative pressure environment is greater than or equal to 0 mbar and less than or equal to 90 mbar, for example, 1 mbar, 10 mbar, 30 mbar, 50 mbar, 70 mbar or 90 mbar. Preferably, the pressure of the negative pressure environment is greater than or equal to 0 mbar and less than or equal to 20 mbar. More preferably, the pressure of the negative pressure environment is the pressure of the insulation step. The drying step can be performed under normal atmospheric pressure.

[0017] In one embodiment, the insulation step lasts for 5 minutes to 1 hour. Preferably, when the pressure of the negative pressure environment is greater than or equal to 0 mbar and less than or equal to 20 mbar, the insulation step lasts for 10 minutes to 20 minutes.

[0018] In one embodiment, the polyvinyl chloride plastic recycling method of the present invention does not use a precipitant to separate the plastic.

[0019] In one embodiment, the solvent comprises any one of butanone, cyclohexanone and tetrahydrofuran (THF) or a combination thereof.

[0020] Preferably, when the solvent comprises butanone, the temperature in the dissolving step is 60°C to 80°C, for example, 60°C, 65°C, 70°C, 75°C or 80°C; and / or the temperature in the keeping step is 40°C to 70°C, for example, 40°C, 50°C, 60°C or 70°C.

[0021] Preferably, when the solvent comprises cyclohexanone, the temperature in the dissolving step is 20°C to 100°C, for example 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C; and / or the temperature in the keeping step is 70°C to 110°C, for example 70°C, 80°C, 90°C, 100°C or 110°C.

[0022] Preferably, when the solvent comprises tetrahydrofuran, the temperature in the dissolving step is 20°C to 60°C, for example, 20°C, 30°C, 40°C, 50°C or 60°C; and / or the temperature in the keeping step is 40°C to 70°C, for example, 40°C, 50°C, 60°C or 70°C.

[0023] In one embodiment, the solvent comprises butanone and cyclohexanone.

[0024] In one embodiment, the solvent comprises butanone and tetrahydrofuran.

[0025] In one embodiment, the solvent comprises cyclohexanone and tetrahydrofuran.

[0026] Preferably, when the solvent comprises butanone and cyclohexanone, the temperature in the dissolving step is 60°C to 80°C, for example, 60°C, 63°C, 66°C, 69°C, 72°C, 75°C, 78°C or 80°C; and / or the temperature in the heat preservation step is 70°C to 110°C, for example, 70°C, 80°C, 90°C, 100°C or 110°C. More preferably, when the solvent comprises butanone and cyclohexanone, the temperature in the dissolving step is 68°C to 72°C, and / or the temperature in the heat preservation step is 80°C to 100°C.

[0027] Preferably, when the solvent comprises butanone and tetrahydrofuran, the temperature in the dissolving step is 20°C to 80°C, for example, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C or 80°C; and / or the temperature in the heat preservation step is 40°C to 70°C, for example, 40°C, 50°C, 60°C or 70°C. More preferably, based on the total volume of the solvent, the content of butanone is 40 volume percent to 60 volume percent, and the content of tetrahydrofuran is 40 volume percent to 60 volume percent.

[0028] Preferably, when the solvent comprises cyclohexanone and tetrahydrofuran, the temperature in the dissolving step is 20° C. to 80° C., for example, 20° C., 30° C., 40° C., 50° C., 60° C., 70° C. or 80° C., and / or the temperature in the heat preservation step is 70° C. to 110° C., for example, 70° C., 80° C., 90° C., 100° C. or 110° C. More preferably, based on the total volume of the solvent, the content of cyclohexanone is 40 volume percent to 60 volume percent, and the content of tetrahydrofuran is 40 volume percent to 60 volume percent.

[0029] In one embodiment, the volume ratio of butanone to cyclohexanone is 0.28 to 3.5; for example, 0.28, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8, 2.1, 2.4, 2.7, 3.0, 3.3 or 3.5. For example, when the butanone is 60 ml and the cyclohexanone is 20 ml, the volume ratio of butanone to cyclohexanone is 3. Preferably, the volume ratio of butanone to cyclohexanone is 0.28 to 3.05. More preferably, the volume ratio of butanone to cyclohexanone is 0.28 to 1.6.

[0030] In one embodiment, based on the total volume of the solvent, the content of butanone is 20 volume percent to 80 volume percent, for example, 20 volume percent, 30 volume percent, 40 volume percent, 50 volume percent, 60 volume percent, 70 volume percent or 80 volume percent, and the content of cyclohexanone is 20 volume percent to 80 volume percent, for example, 20 volume percent, 30 volume percent, 40 volume percent, 50 volume percent, 60 volume percent, 70 volume percent or 80 volume percent. Preferably, the content of butanone is 20 volume percent to 62 volume percent, and the content of cyclohexanone is 38 volume percent to 80 volume percent.

[0031] In one embodiment, the preparation step further includes a classification step: preparing classification solutions with different specific gravities to float out plastic-containing materials with different specific gravities.

[0032] Preferably, the classification step is to float out plastic-containing materials of different specific gravity ranges in the order of low to high specific gravity.

[0033] In one embodiment, the specific gravity is 0.8 to 1.6, for example, 0.8, 1.0, 1.2, 1.4 or 1.6. For example, flotation is performed in the order of specific gravity of 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 and 1.6. Preferably, the specific gravity is 1.3 to 1.5. More preferably, the specific gravity is 1.35 to 1.45. The present invention can effectively screen out non-polyvinyl chloride materials through flotation to improve the recovery efficiency of polyvinyl chloride.

[0034] In one embodiment, the plastic-containing material is in granular form.

[0035] Preferably, the average diameter of the plastic-containing material is greater than 0 mm and less than or equal to 5 mm. More preferably, the average diameter of the plastic-containing material is greater than 0 mm and less than or equal to 3.1 mm, for example: 0.5 mm, 1 mm, 2 mm, 3 mm or 3.1 mm.

[0036] In one embodiment, the stirring speed of the dissolving step is 150 rpm to 200 rpm, for example, 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm or 200 rpm. The present invention can maintain the plastic-containing material continuously suspended in the solvent by stirring, so as to improve the dissolving efficiency and recovery rate.

[0037] In one embodiment, the dissolution step takes 15 to 120 minutes, for example, 15 minutes, 30 minutes, 45 minutes, 60 minutes, 90 minutes or 120 minutes.

[0038] In one embodiment, the weight of the plastic-containing material is greater than 0 g and less than or equal to 8 g, for example, 0.05 g, 0.1 g, 0.5 g, 1 g, 2 g, 3 g, 4 g, 5 g, 6 g, 7 g or 8 g, based on 100 ml of the solvent. Preferably, the weight of the plastic-containing material is 6.8 g to 7.2 g, based on 100 ml of the solvent. According to the present invention, the ratio of the volume of the solvent to the weight of the plastic-containing material can avoid the problem of too high viscosity and difficulty in stirring in the process of forming the first mixture into a dissolving solution, so as to improve the efficiency of plastic recycling.

[0039] In one embodiment, the dissolving step (III) comprises: (III-1): stirring the first mixture at a temperature of 20°C to 110°C to dissolve the plastic in the solvent to obtain a second mixture; and (III-2): filtering the second mixture with a filter to obtain a dissolved liquid. The present invention can remove impurities insoluble in the solvent to improve the purity of the recyclables.

[0040] In one embodiment, the step (three of two) further comprises a precipitation step, that is, after obtaining the second mixture, the second mixture is allowed to stand to obtain a second mixture that has been allowed to stand; wherein the temperature of the second mixture that has been allowed to stand is lower than that of the first mixture, and the mixture comprises a supernatant and a precipitate, and the impurities in the supernatant are filtered through a filter to obtain the solution. In other words, the present invention can remove impurities by using a precipitation step, that is, by standing the second mixture without heating, and by using a filter to remove undissolved components and suspended matter.

[0041] Preferably, in the precipitation step, the second mixture is allowed to stand for 2 to 3 hours. The present invention allows the second mixture to stand at room temperature, and after the second mixture has obvious precipitation, the supernatant is filtered through a filter. Compared with directly filtering the second mixture, the filtration time can be shortened and the impurity content of the solution can be reduced.

[0042] In one embodiment, the separation step can obtain a recovered solvent.

[0043] Preferably, the recovery solvent comprises a first solvent and a second solvent, and after the separation step, further comprises a solvent separation step: placing the recovery solvent in a recovery negative pressure environment, first boiling the recovery solvent at a first solvent recovery temperature, and condensing to obtain a first recovery liquid, and obtaining a first recovery residual liquid; then boiling the first recovery residual liquid at a second solvent recovery temperature, and condensing to obtain a second recovery liquid; wherein the first solvent recovery temperature is lower than the second solvent recovery temperature, and the first recovery liquid comprises the first solvent, and the second recovery liquid comprises the second solvent.

[0044] Preferably, the pressure of the recycling negative pressure environment is greater than or equal to 0 mbar and less than or equal to 90 mbar, for example: 1 mbar, 10 mbar, 30 mbar, 50 mbar, 70 mbar or 90 mbar. Preferably, the pressure of the recycling negative pressure environment is greater than or equal to 0 mbar and less than or equal to 20 mbar.

[0045] Preferably, the first solvent comprises butanone, and the second solvent comprises cyclohexanone, and the first solvent recovery temperature is 70°C to 80°C, and the second solvent recovery temperature is 90°C to 100°C.

[0046] Preferably, the first recovery liquid and / or the second recovery liquid is used as a recovery solvent, and the solvent separation step is performed again. According to the present invention, performing the solvent separation step again can improve the purity of the first recovery liquid and / or the second recovery liquid.

[0047] In summary, the polyvinyl chloride plastic recycling method of the present invention has a high plastic recycling rate and a high recycling efficiency, and the solvent can be recycled and reused, which not only reduces costs but also avoids derivative environmental problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 and Figure 2 The present invention is a flow chart of the polyvinyl chloride plastic recycling method. DETAILED DESCRIPTION

[0049] Several operation modes are provided below to illustrate the implementation methods of the present invention. Those skilled in the art can easily understand the advantages and effects that can be achieved by the present invention through the contents of this specification, and make various modifications and changes without departing from the spirit of the present invention to implement or apply the contents of the present invention.

[0050] like Figure 1 As shown, the plastic recycling method of polyvinyl chloride of the present invention first performs step S1: preparation step: a plastic-containing material is prepared, the plastic-containing material includes a plastic, and the plastic includes polyvinyl chloride. Specifically, the plastic-containing material is a powder obtained by crushing and sieving industrial waste containing polyvinyl chloride, for example, sieving through a 10-mesh screen to obtain plastic-containing material particles with a diameter of less than 2 mm.

[0051] Next, S2: a mixing step is performed: the plastic-containing material and a solvent are mixed to obtain a first mixture, wherein the plastic is soluble in the solvent. Specifically, the solvent is selected from butanone and cyclohexanone, and the plastic-containing material, butanone and cyclohexanone are mixed to obtain the first mixture.

[0052] Then, S3: dissolving step is performed: stirring the first mixture at a temperature of 20° C. to 110° C. to dissolve the plastic in the solvent to obtain a solution. Specifically, the temperature of the dissolving step is 70° C., the stirring speed is 150 rpm to 200 rpm, and the time is 20 minutes to 40 minutes.

[0053] Finally, S4: separation step is performed: the dissolved liquid is placed in a negative pressure environment to separate the solvent, and the plastic is obtained. Specifically, the dissolved liquid is sealed in a vacuum concentration device, and a negative pressure is formed by pumping air to boil the dissolved liquid to separate butanone and cyclohexanone, so as to obtain polyvinyl chloride in the form of flakes or particles.

[0054] Please refer to Figure 1 and Figure 2When the plastic-containing material is industrial waste containing polyvinyl chloride, since it contains components that are insoluble in the solvent, the S3 dissolution step includes: S3-1: stirring the first mixture at a temperature of 20°C to 110°C to dissolve the plastic in the solvent to obtain a second mixture; and S3-2: filtering the second mixture with a filter to obtain a dissolved liquid. Specifically, the filter is used to remove undissolved solids to remove impurities. In addition, before removing the undissolved solids with the filter, the second mixture can be allowed to stand at room temperature, and after the second mixture that has been allowed to stand shows obvious precipitation, the supernatant can be filtered.

[0055] Example 1 to Example 14

[0056] like Figure 1 As shown, the polyvinyl chloride plastic recycling method of the present invention first performs step S1: preparation step: prepare a plastic-containing material, the plastic-containing material includes a plastic, and the plastic includes polyvinyl chloride. Specifically, the plastic-containing materials used in Examples 1 to 14 are all commercially available polyvinyl chloride particles (volume is about 0.5 cubic centimeters).

[0057] Next, S2: a mixing step is performed: the plastic-containing material and a solvent are mixed to obtain a first mixture, wherein the plastic is soluble in the solvent. Specifically, each set of solvents is as shown in Table 1, and 7 grams of commercially available polyvinyl chloride particles and 100 milliliters of solvent are weighed with a measuring cylinder and mixed in a vacuum concentration bottle to obtain a first mixture.

[0058] After that, S3: dissolution step: stirring the first mixture at a temperature of 20°C to 110°C, so that the plastic is dissolved in the solvent to obtain a solution. Specifically, the vacuum concentration bottle containing the first mixture is connected to a vacuum concentration device, and the pressure is maintained at normal atmospheric pressure, and then the vacuum concentration bottle containing the first mixture is placed in a water bath and stirred. The stirring speed of each group is 170rpm, and the temperature of each group during the stirring process is as shown in Table 1: wherein the room temperature is 25°C. After the commercially available polyvinyl chloride particles are completely dissolved, the dissolution time of each group (i.e., the time required to obtain the solution) is recorded, and the results are shown in Table 1.

[0059] Finally, S4: separation step is performed: the dissolving solution is placed in a negative pressure environment to separate the solvent, and the plastic is obtained. Specifically, the dissolving solution is allowed to stand, and when the temperature of the dissolving solution is approximately the same as the room temperature, the vacuum pump is turned on to decompress the vacuum concentration device, so that the pressure in the vacuum concentration bottle is reduced to 0 mbar to 20 mbar, so as to perform the separation step; wherein the stirring speed of the dissolving solution is set to 20 rpm, and the dissolving solution is heated through a water bath to accelerate the evaporation of the solvent. After the boiling of the dissolving solution is observed, the heating temperature, i.e., the temperature of the insulation step, is maintained, as shown in Table 1, and the vacuum pump is turned off, and the solvent vapor is condensed through a condenser to recover the solvent, so as to keep the pressure in the system from rising at the same time.

[0060] After the solvent is completely evaporated and condensed, the volume of the recovered solution is recorded to calculate the solvent recovery rate, and the results are shown in Table 2. In addition, when no solvent is seen in the vacuum concentration bottle and the film-shaped recovery semi-finished product is approximately dry, the recovery semi-finished product is moved to an oven and set at 80°C for drying for about 1 hour to completely remove possible residual solvents and obtain a polyvinyl chloride film. After the polyvinyl chloride film is cooled at room temperature, its weight is measured to calculate the plastic recovery rate, and the results are shown in Table 2. Fourier transform infrared spectroscopy (FTIR) analysis is also performed to confirm the purity of the plastic, and the results are shown in Table 2.

[0061] Table 1: Solvents used in Examples 1 to 14, temperature of the dissolution step (referred to as dissolution temperature), dissolution time, and temperature of the insulation step (referred to as insulation temperature)

[0062]

[0063] As can be seen from Table 1, first, the dissolution time of each group ranges from 15 minutes to 120 minutes; among them, the dissolution time of Example 5 is the shortest, which takes only 15 minutes, indicating that using tetrahydrofuran as a solvent and using 50° C. as a temperature in the dissolution step can dissolve polyvinyl chloride the fastest and has the highest dissolution efficiency.

[0064] Second, from the comparison between Example 2 and Example 3, Example 4 and Example 5, Example 6 and Example 7, and Example 13 and Example 14, it can be seen that, under the premise of using the same solvent, increasing the temperature of the dissolution step can greatly reduce the dissolution time; among them, the difference in the temperature of the dissolution step between Example 2 and Example 3 is 65°C, and the difference in the dissolution time is 80 minutes; the difference in the temperature of the dissolution step between Example 4 and Example 5 is 25°C, and the difference in the dissolution time is 25 minutes; the difference in the temperature of the dissolution step between Example 6 and Example 7 is 45°C, and the difference in the dissolution time is 100 minutes; the difference in the temperature of the dissolution step between Example 13 and Example 14 is 45°C, and the difference in the dissolution time is 40 minutes. In addition, the degree of shortening of the dissolution time by increasing the temperature of different solvents in the dissolution step is different, and when the solvent is 50 weight percent of butanone and tetrahydrofuran, increasing the temperature of the dissolution step can obtain the highest degree of shortening of the dissolution time.

[0065] Third, considering that tetrahydrofuran is relatively expensive, Example 7 mixes the solvents of Example 1 and Example 5 to further understand the feasibility of mixing solvents to reduce costs. From the comparison of Example 1, Example 5 and Example 7, it can be seen that when Example 5 only uses tetrahydrofuran as a solvent, the required dissolution time is the shortest, that is, the dissolution efficiency of Example 7 mixing butanone and tetrahydrofuran is only better than that of Example 1 (using only butanone). Similarly, Example 14 mixes the solvents of Example 3 and Example 5. From the comparison of Example 3, Example 5 and Example 14, it can be seen that the dissolution efficiency of Example 14 mixing cyclohexanone and tetrahydrofuran is also only better than that of Example 3 (using only cyclohexanone). It can be seen that although mixing butanone or cyclohexanone with tetrahydrofuran can reduce costs, the dissolution efficiency is reduced accordingly.

[0066] In contrast, from the comparison of Example 1, Example 3 and Example 8, it can be seen that when Example 8 mixes butanone of Example 1 and cyclohexanone of Example 3, the temperature (70°C) of the dissolution step of Example 8 is the same as 70°C of Example 1, and the dissolution time of Example 8 is only 40 minutes, which is significantly shorter than 120 minutes of Example 1. At the same time, the temperature (70°C) of the dissolution step of Example 8 is lower than 90°C of Example 3, and the dissolution time of Example 8 is the same as 40 minutes of Example 3. It can be seen that when the solvent is mixed with butanone and cyclohexanone, an unexpected effect of improving the dissolution efficiency can be produced.

[0067] Finally, from the comparison between Example 8 and Example 9 to Example 12, it can be seen that, under the premise that the temperature of the dissolution step is the same, the dissolution time of Example 8 is 40 minutes, and the dissolution time of Example 9 to Example 12 is only 20 minutes, which is half of the dissolution time of Example 8. It can be seen that when the content of butanone is 25 volume percent to 60 volume percent and the content of cyclohexanone is 40 volume percent to 75 volume percent based on the total volume of the solvent, the dissolution efficiency can be further improved.

[0068] Table 2: Plastic recovery rate, plastic purity and solvent recovery rate of Examples 1 to 14

[0069]

[0070]

[0071] As can be seen from Table 2, the plastic recovery rate of each group is about 100%, and the FTIR spectrum has no other noise, indicating that the recovered product (i.e., polyvinyl chloride film) has high purity. In addition, the solvent recovered by each group is a clear liquid without impurities, which shows that the recovered solvent is also of high purity. Finally, the solvent recovery rates of Examples 6 to 14 are relatively low, which shows that mixing solvents will lead to a slight decrease in the solvent recovery rate.

[0072] In summary, the polyvinyl chloride plastic recycling method of the present invention does have a high plastic recycling rate and high recycling efficiency, and the solvent can be recycled and reused, which not only reduces costs but also avoids derivative environmental problems.

Claims

1. A method for recycling polyvinyl chloride plastics, comprising: (1) Preparation step: preparing a plastic-containing material, wherein the plastic-containing material comprises a plastic, and the plastic comprises polyvinyl chloride; (ii) a mixing step of mixing the plastic-containing material and a solvent to obtain a first mixture, wherein the plastic is soluble in the solvent; (iii) a dissolving step: stirring the first mixture at a temperature of 20° C. to 110° C. to dissolve the plastic in the solvent to obtain a solution; and (iv) Separation step: placing the dissolved liquid into a negative pressure environment to separate the solvent, thereby obtaining the plastic.

2. The method for recycling polyvinyl chloride plastic according to claim 1, wherein the separation step further comprises a heat preservation step: the dissolved liquid is kept warm at a temperature of 40°C to 110°C.

3. The method for recycling polyvinyl chloride plastics according to claim 1, wherein the solvent comprises any one of butanone, cyclohexanone and tetrahydrofuran or a combination thereof.

4. The method for recycling polyvinyl chloride plastics according to claim 3, wherein the solvent comprises butanone and cyclohexanone.

5. The method for recycling polyvinyl chloride plastics according to claim 4, wherein the temperature in the dissolving step is 68°C to 72°C.

6. The method for recycling polyvinyl chloride plastics according to claim 4, wherein the volume ratio of butanone to cyclohexanone is 0.28 to 3.

5.

7. The method for recycling polyvinyl chloride plastic according to claim 4, wherein based on the total volume of the solvent, the content of butanone is 20 volume percent to 80 volume percent, and the content of cyclohexanone is 20 volume percent to 80 volume percent.

8. The method for recycling polyvinyl chloride plastic according to claim 1, wherein the plastic-containing material is in granular form, and the average diameter of the plastic-containing material is greater than 0 mm and less than or equal to 5 mm, the stirring speed of the dissolving step is 150 rpm to 200 rpm, and the time of the dissolving step is 15 minutes to 120 minutes.

9. The method for recycling polyvinyl chloride plastics according to claim 1, wherein the pressure of the negative pressure environment is greater than or equal to 0 mbar and less than or equal to 90 mbar.

10. The method for recycling polyvinyl chloride plastics according to claim 1, wherein the weight of the plastic-containing material is greater than 0 g and less than or equal to 8 g based on 100 ml of the solvent.

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