A method of degrading plastic

Abstract

The application discloses a method for degrading plastic, comprising the following steps: step one, preparing an auxiliary solution, which is an acid solution or an alkali solution; step two, degrading, specifically comprising the following steps: step 201, placing plastic in a reaction kettle and adding the auxiliary solution; step 202, purging the reaction kettle with CO2; step 203, continuously introducing CO2 until the initial pressure in the reaction kettle is reached and maintained; step 204, starting a heating furnace, placing the reaction kettle in the heating furnace, increasing the pressure in the reaction kettle as the temperature increases, starting timing when the pressure in the reaction kettle rises to the critical pressure of CO2, and completing plastic degradation until a preset reaction time is reached. The method for mixing the auxiliary solution with plastic and then treating the mixture in supercritical CO2 and a high-temperature environment has the characteristics of high plastic degradation efficiency and good degradation effect, and the degradation efficiency of polystyrene plastic reaches up to 90%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of degradation technology, and particularly relates to a method for degrading plastic. BACKGROUND

[0002] Plastics are widely used due to their outstanding advantages, such as light weight, good ductility, durability, low cost, easy processing and the like. Plastic products have played an important role in protecting people, and the wide application of plastic products has also brought new challenges, such as statistics show that up to 1.6 million tons of plastic waste will be generated every day. Only about 2% of these plastics are recycled, and most (about 92%) are discarded in landfills or natural environments.

[0003] Plastics are highly inert and take about 200-400 years to completely degrade in the natural environment. Waste plastics in the environment not only cause visual "white pollution", but also damage the ecological environment, thereby threatening the survival of animals, plants, microorganisms and even humans.

[0004] Among the methods for treating waste plastics, the most widely used is landfill treatment together with other waste. Although this method is simple to operate and has low investment cost, it will cause secondary pollution to the soil and waste land resources. Incineration is also a commonly used method for treating waste plastics. Compared with the landfill method, the incineration method has the advantages of short treatment period, high efficiency and small land occupation. In addition, the large amount of heat energy released by incineration can be used for power generation and heating. However, burning plastics produces smoke, solid particles and other substances, which are harmful to the environment and humans. Therefore, it is necessary to find a new method for degrading plastics and to recycle the degradation products in order to improve resource utilization. SUMMARY

[0005] The technical problem to be solved by the application is to provide a method for degrading plastics, which has the characteristics of high plastic degradation efficiency and good degradation effect, by mixing an auxiliary solution with plastics and then treating them in supercritical CO2 at high temperature.

[0006] To solve the above technical problems, the technical solution adopted by the application is: a method for degrading plastics, characterized in that it comprises: mixing plastics with an auxiliary solution and then treating them in a supercritical CO2 environment.

[0007] The method for degrading plastics, characterized in that the auxiliary solution is an acid solution or an alkali solution.

[0008] The method for degrading plastic according to any one of the preceding method, wherein the acid solution is hydrochloric acid solution, the base solution is sodium hydroxide solution, the concentration of the hydrochloric acid solution is 1wt%-5wt%, the solubility of the base solution is 1wt%-5wt%; the mass of the plastic is 0.15 times of the volume of the auxiliary solution, the mass of the plastic is g, and the volume of the auxiliary solution is mL.

[0009] The method for degrading plastic according to any one of the preceding method, wherein the plastic is polystyrene plastic.

[0010] The method for degrading plastic according to any one of the preceding method, wherein the supercritical CO2 environment includes that the CO2 pressure in the environment is 7.29MPa.

[0011] The method for degrading plastic according to any one of the preceding method, wherein the temperature of the treatment is 300℃-500℃.

[0012] The method for degrading plastic according to any one of the preceding method, wherein the time of the treatment is 30min-120min.

[0013] The method for degrading plastic according to any one of the preceding method, wherein the method specifically comprises:

[0014] Step one, preparing an auxiliary solution, the auxiliary solution is acid solution or base solution, when the auxiliary solution is acid solution, the method for preparing the auxiliary solution comprises: diluting hydrochloric acid with a concentration of 50wt% to a concentration of 1wt%-5wt% to obtain the acid solution; when the auxiliary solution is base solution, the method for preparing the auxiliary solution comprises: dissolving sodium hydroxide in water to obtain a base solution with a concentration of 1wt%-5wt%;

[0015] Step two, degrading, specifically comprising:

[0016] Step 201, placing the plastic in a reaction kettle and adding the auxiliary solution;

[0017] Step 202, tightening the reaction kettle and purging the reaction kettle with CO2 to remove air in the reaction kettle;

[0018] Step 203, continuing to introduce CO2 to the initial pressure in the reaction kettle and maintaining;

[0019] Step 204, starting the heating furnace to a temperature of 300℃-500℃, placing the reaction kettle in the heating furnace, the pressure in the reaction kettle rises as the temperature rises, when the pressure in the reaction kettle rises to the critical pressure of CO2, start timing, to the preset reaction time, complete the degradation of the plastic; the preset reaction time is 30min-120min.

[0020] The method for degrading plastic has the characteristics that in step 201, the mass of the plastic is 0.15 times the volume of the auxiliary solution, the mass of the plastic is g, and the volume of the auxiliary solution is mL; and in step 203, the initial pressure is 6 MPa.

[0021] The method for degrading plastic has the characteristics that in step 204, the critical pressure of CO2 is 7.29 MPa.

[0022] Compared with the prior art, the method for degrading plastic has the following advantages:

[0023] 1. The method for degrading plastic has the characteristics of high plastic degradation efficiency and good degradation effect, and the degradation efficiency of polystyrene plastic is as high as 90% after the auxiliary solution is mixed with the plastic and then treated in supercritical CO2 and a high-temperature environment.

[0024] 2. In the method, supercritical CO2 is used to provide a homogeneous environment and a solvent for plastic degradation, which can effectively reduce the mass transfer resistance between material interfaces.

[0025] 3. In the method, acid solution and alkali solution are used as auxiliary solutions, which can enhance the solubility of plastic in supercritical CO2, reduce the activation energy of the reaction, and promote the degradation of plastic.

[0026] 4. After the plastic is degraded by the method, the degradation efficiency of polystyrene plastic is 84.96% to 90.34% when the reaction temperature is 400°C, the reaction time is 120 min, and the concentration of the auxiliary solution is 5 wt%, and the total volume of the generated gas is 116.99 to 126.88 mL.

[0027] The technical solutions of the present application will be further described in detail below in combination with the drawings and examples.

[0028] Drawings of the specification

[0029] Figure 1 The degradation efficiency of polystyrene plastic in examples 1 to 6 and comparative examples 1 to 9.

[0030] Figure 2 The gas product after the degradation of polystyrene plastic treated by acid solution.

[0031] Figure 3 The gas product after the degradation of polystyrene plastic treated by alkali solution.

[0032] Figure 4 The distribution of liquid products after the degradation of polystyrene plastic.

[0033] Figure 5 The SEM image of the solid residue after the degradation of polystyrene plastic. DETAILED DESCRIPTION

[0034] Example 1

[0035] The present embodiment provides a method for degrading plastics, comprising:

[0036] Step one, preparing an acid solution, specifically comprising: diluting a 50wt% hydrochloric acid solution to a concentration of 5wt% to obtain an acid solution;

[0037] Step two, degrading, specifically comprising:

[0038] Step 201, taking 0.15g of polystyrene plastic and placing it in a reaction kettle, adding 1mL of the acid solution; the reaction kettle has an inner diameter of 1cm and a length of 15cm;

[0039] Step 202, tightening the reaction kettle and purging the reaction kettle with CO2 to remove all air in the reaction kettle;

[0040] Step 203, continue to introduce CO2 until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and the introduction of CO2 is stopped when the pressure in the kettle reaches 6MPa;

[0041] Step 204, start the heating furnace to a temperature of 400°C, place the reaction kettle in the heating furnace, as the temperature rises, the pressure in the reaction kettle rises, when the pressure in the reaction kettle rises to the critical pressure of CO2, start timing, to the preset reaction time, complete the degradation of the plastic; the preset reaction time is 120min; the critical pressure of CO2 is 7.29MPa; marked as Sc-CO2 / HCl.

[0042] After the reaction kettle cools down, first collect the gas produced after the degradation of polystyrene with a gas bag, then open the reaction kettle to collect the remaining products (solid residues and liquid oil). In this embodiment, the degradation efficiency of polystyrene is 90.34%, the volume of CO2 consumed is 71.5mL, the volume of gas produced is 126.88mL, of which the volume of H2 is 62.78mL, the volume of CO is 13.22mL, the volume of CH4 is 45.29mL, and the volume of C2H x (x=4,6) is 5.59mL.

[0043] Example 2

[0044] The present embodiment provides a method for degrading plastics, comprising:

[0045] Step one, preparing an acid solution, specifically comprising: diluting a 50wt% hydrochloric acid solution to a concentration of 5wt% to obtain an acid solution;

[0046] Step two, degrading, specifically comprising:

[0047] Step 201, take 0.15g polystyrene plastic and place it in a reaction kettle, add 1 mL of the base solution;

[0048] Step 202, tighten the reaction kettle, and use CO2 to purge the reaction kettle to remove all air in the reaction kettle;

[0049] Step 203, continue to pass CO2 until the initial pressure in the reaction kettle is 6 MPa; the reaction kettle is a closed reaction kettle, and the CO2 is stopped after the pressure in the kettle reaches 6 MPa;

[0050] Step 204, start the heating furnace to a temperature of 400°C, place the reaction kettle in the heating furnace, and as the temperature rises, the pressure in the reaction kettle rises, when the pressure in the reaction kettle rises to the critical pressure of CO2, start timing, to the preset reaction time, complete the degradation of the plastic; the preset reaction time is 120 min; the critical pressure of CO2 is 7.29 MPa; marked as Sc-CO2 / NaOH.

[0051] After the reaction kettle is cooled, first collect the gas produced after the degradation of polystyrene with a gas bag, then open the reaction kettle to collect the remaining products (solid residues and liquid oil). In this example, the degradation efficiency of polystyrene is 84.96%, the volume of CO2 consumed is 81 mL, the volume of gas produced is 119.99 mL, of which the volume of H2 is 74.18 mL, the volume of CO is 7.33 mL, the volume of CH4 is 34.68 mL, and the volume of C2H x (x = 4, 6) is 3.8 mL.

[0052] Example 3

[0053] This example provides a method for degrading plastic, comprising:

[0054] Step one, prepare an acid solution, specifically including: dilute a 50wt% hydrochloric acid solution to a concentration of 5wt% to obtain an acid solution;

[0055] Step two, degradation, specifically including:

[0056] Step 201, take 0.15g polystyrene plastic and place it in a reaction kettle, add 1 mL of the acid solution;

[0057] Step 202, tighten the reaction kettle, and use CO2 to purge the reaction kettle to remove all air in the reaction kettle;

[0058] Step 203, continue to pass CO2 until the initial pressure in the reaction kettle is 6 MPa; the reaction kettle is a closed reaction kettle, and the CO2 is stopped after the pressure in the kettle reaches 6 MPa;

[0059] Step 204, start the heating furnace to a temperature of 500℃, place the reaction kettle in the heating furnace, as the temperature rises, the pressure in the reaction kettle rises, when the pressure in the reaction kettle rises to the critical pressure of CO2, start timing, to the preset reaction time, complete the degradation of the plastic; the preset reaction time is 120 min; the critical pressure of CO2 is 7.29 MPa; marked as Sc-CO2 / HCl.

[0060] After the reaction kettle is cooled, first collect the gas generated after the degradation of polystyrene using a gas bag, and then open the reaction kettle to collect the remaining products (solid residues and liquid oil). In this embodiment, the degradation efficiency of polystyrene is as shown in Figure 1 .

[0061] Example 4

[0062] This embodiment provides a method for degrading plastic, comprising:

[0063] Step one, prepare an acid solution, specifically including: dilute a 50wt% hydrochloric acid solution to a concentration of 5wt% to obtain an acid solution;

[0064] Step two, degradation, specifically including:

[0065] Step 201, take 0.15g of polystyrene plastic and place it in a reaction kettle, and add 1mL of the acid solution;

[0066] Step 202, tighten the reaction kettle, and use CO2 to purge the reaction kettle to remove all air in the reaction kettle;

[0067] Step 203, continue to introduce CO2 until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a sealed reaction kettle, and the introduction of CO2 is stopped after the pressure in the kettle is 6MPa;

[0068] Step 204, start the heating furnace to a temperature of 300℃, place the reaction kettle in the heating furnace, as the temperature rises, the pressure in the reaction kettle rises, when the pressure in the reaction kettle rises to the critical pressure of CO2, start timing, to the preset reaction time, complete the degradation of the plastic; the preset reaction time is 120 min; the critical pressure of CO2 is 7.29 MPa; marked as Sc-CO2 / HCl.

[0069] After the reaction kettle is cooled, first collect the gas generated after the degradation of polystyrene using a gas bag, and then open the reaction kettle to collect the remaining products (solid residues and liquid oil). In this embodiment, the degradation efficiency of polystyrene is as shown in Figure 1 .

[0070] Example 5

[0071] This embodiment provides a method for degrading plastic, comprising:

[0072] Step one, preparing the base solution, specifically including: dissolving sodium hydroxide in water to obtain a concentration of 5wt%, obtaining a base solution;

[0073] Step two, degradation, specifically including:

[0074] Step 201, take 0.15g of polystyrene plastic and place it in a reaction kettle, add 1mL of the base solution;

[0075] Step 202, tighten the reaction kettle, and use CO2 to purge the reaction kettle to remove all air in the reaction kettle;

[0076] Step 203, continue to introduce CO2 until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and the introduction of CO2 is stopped when the pressure in the kettle is 6MPa;

[0077] Step 204, start the heating furnace to a temperature of 300°C, place the reaction kettle in the heating furnace, and as the temperature rises, the pressure in the reaction kettle rises, when the pressure in the reaction kettle rises to the critical pressure of CO2, start timing, to the preset reaction time, complete the degradation of the plastic; the preset reaction time is 120min; the critical pressure of CO2 is 7.29MPa; marked as Sc-CO2 / NaOH.

[0078] After the reaction kettle is cooled, first collect the gas produced after the degradation of polystyrene with a gas bag, then open the reaction kettle to collect the remaining products (solid residues and liquid oil). In this example, the degradation efficiency of polystyrene is shown in Table 1. Figure 1

[0079] Example 6

[0080] This example provides a method for degrading plastic, comprising:

[0081] Step one, preparing the base solution, specifically including: dissolving sodium hydroxide in water to obtain a concentration of 5wt%, obtaining a base solution;

[0082] Step two, degradation, specifically including:

[0083] Step 201, take 0.15g of polystyrene plastic and place it in a reaction kettle, add 1mL of the base solution;

[0084] Step 202, tighten the reaction kettle, and use CO2 to purge the reaction kettle to remove all air in the reaction kettle;

[0085] Step 203, continue to introduce CO2 until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and the introduction of CO2 is stopped when the pressure in the kettle is 6MPa;

[0086] ​Step 204, start the heating furnace to a temperature of 500℃, place the reaction kettle in the heating furnace, as the temperature rises, the pressure in the reaction kettle rises, when the pressure in the reaction kettle rises to the critical pressure of CO2, start timing, to the preset reaction time, complete the degradation of the plastic; the preset reaction time is 120 min; the critical pressure of CO2 is 7.29 MPa; marked as Sc-CO2 / NaOH.

[0087] After the reaction kettle is cooled, first collect the gas generated after the degradation of polystyrene using a gas bag, and then open the reaction kettle to collect the remaining products (solid residues and liquid oil). In this embodiment, the degradation efficiency of polystyrene is 99.25%.

[0088] Example 7

[0089] This embodiment provides a method for degrading plastic, comprising:

[0090] Step one, prepare an acid solution, specifically including: dilute a 50wt% hydrochloric acid solution to a concentration of 1wt% to obtain an acid solution;

[0091] Step two, degradation, specifically including:

[0092] Step 201, take 0.15g of polystyrene plastic and place it in a reaction kettle, add 1mL of the acid solution;

[0093] Step 202, tighten the reaction kettle, and use CO2 to purge the reaction kettle to remove all air in the reaction kettle;

[0094] Step 203, continue to introduce CO2 until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a sealed reaction kettle, and the introduction of CO2 is stopped after the pressure in the kettle reaches 6MPa;

[0095] Step 204, start the heating furnace to a temperature of 400℃, place the reaction kettle in the heating furnace, as the temperature rises, the pressure in the reaction kettle rises, when the pressure in the reaction kettle rises to the critical pressure of CO2, start timing, to the preset reaction time, complete the degradation of the plastic; the preset reaction time is 30 min; the critical pressure of CO2 is 7.29 MPa; marked as Sc-CO2 / HCl.

[0096] After the reaction kettle is cooled, first collect the gas generated after the degradation of polystyrene using a gas bag, and then open the reaction kettle to collect the remaining products (solid residues and liquid oil). In this embodiment, the degradation efficiency of polystyrene is 99.88%.

[0097] Example 8

[0098] This embodiment provides a method for degrading plastic, comprising:

[0099] Step one, preparing an acid solution, specifically including: diluting a 50wt% hydrochloric acid solution to a concentration of 3wt% to obtain an acid solution;

[0100] Step two, degradation, specifically including:

[0101] Step 201, taking 0.15g of polystyrene plastic and placing it in a reaction kettle, and adding 1mL of the acid solution;

[0102] Step 202, tightening the reaction kettle, and purging the reaction kettle with CO2 to remove all air in the reaction kettle;

[0103] Step 203, continuing to introduce CO2 until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and the introduction of CO2 is stopped when the pressure in the kettle is 6MPa;

[0104] Step 204, starting the heating furnace to a temperature of 400°C, placing the reaction kettle in the heating furnace, and as the temperature rises, the pressure in the reaction kettle rises, and when the pressure in the reaction kettle rises to the critical pressure of CO2, the timing starts, and the preset reaction time is 90min; the critical pressure of CO2 is 7.29MPa; marked as Sc-CO2 / HCl.

[0105] After the reaction kettle is cooled, the gas produced after the degradation of polystyrene is first collected with a gas bag, and then the remaining products (solid residues and liquid oil) are collected by opening the reaction kettle. In this example, the degradation efficiency of polystyrene is 89.41%.

[0106] Example 9

[0107] This example provides a method for degrading plastics, comprising:

[0108] Step one, preparing an acid solution, specifically including: dissolving sodium hydroxide in water to obtain a concentration of 1wt% to obtain an alkali solution;

[0109] Step two, degradation, specifically including:

[0110] Step 201, taking 0.15g of polystyrene plastic and placing it in a reaction kettle, and adding 1mL of the acid solution;

[0111] Step 202, tightening the reaction kettle, and purging the reaction kettle with CO2 to remove all air in the reaction kettle;

[0112] Step 203, continuing to introduce CO2 until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and the introduction of CO2 is stopped when the pressure in the kettle is 6MPa;

[0113] Step 204, start the heating furnace to a temperature of 400℃, place the reaction kettle in the heating furnace, as the temperature rises, the pressure in the reaction kettle rises, when the pressure in the reaction kettle rises to the critical pressure of CO2, start timing, to the preset reaction time, complete plastic degradation; the preset reaction time is 30 min; the critical pressure of CO2 is 7.29 MPa; marked as Sc-CO2 / NaOH.

[0114] After the reaction kettle is cooled, first collect the gas generated after the polystyrene is degraded by using a gas bag, and then open the reaction kettle to collect the remaining products (solid residues and liquid oil). In this embodiment, the degradation efficiency of the polystyrene is 75.98%.

[0115] Example 10

[0116] The embodiment provides a method for degrading plastic, comprising:

[0117] Step one, preparing an alkali solution, specifically comprising: dissolving sodium hydroxide in water to obtain an alkali solution with a concentration of 3 wt%;

[0118] Step two, degrading, specifically comprising:

[0119] Step 201, taking 0.15 g of polystyrene plastic and placing it in a reaction kettle, and adding 1 mL of the alkali solution;

[0120] Step 202, tighten the reaction kettle, and use CO2 to purge the reaction kettle to remove air in the reaction kettle;

[0121] Step 203, continue to introduce CO2 until the initial pressure in the reaction kettle is 6 MPa; the reaction kettle is a closed reaction kettle, and the introduction of CO2 is stopped after the pressure in the kettle is 6 MPa;

[0122] Step 204, start the heating furnace to a temperature of 400℃, place the reaction kettle in the heating furnace, as the temperature rises, the pressure in the reaction kettle rises, when the pressure in the reaction kettle rises to the critical pressure of CO2, start timing, to the preset reaction time, complete plastic degradation; the preset reaction time is 90 min; the critical pressure of CO2 is 7.29 MPa; marked as Sc-CO2 / NaOH.

[0123] After the reaction kettle is cooled, first collect the gas generated after the polystyrene is degraded by using a gas bag, and then open the reaction kettle to collect the remaining products (solid residues and liquid oil). In this embodiment, the degradation efficiency of the polystyrene is 82.95%.

[0124] In the above embodiments, the polystyrene plastic is commercially available, preferably, the polystyrene plastic of the present application is purchased from Hengfa Plastic, and the molecular formula is The elemental analysis results are shown in Table 1.

[0125] Table 1. Elemental analysis results of polystyrene plastics

[0126]

[0127] Comparative Example 1

[0128] This comparative example provides a method for degrading polystyrene plastic in the environment, comprising: placing 0.15g of polystyrene plastic in a reaction vessel, starting a heating furnace to a temperature of 400°C, placing the reaction vessel in the heating furnace, starting a timer, and reacting for 120 minutes; marked as a blank.

[0129] After the reactor cools down, the gas produced by the degradation of polystyrene is first collected using a gas bag, and then the reactor is opened to collect the remaining products (solid residues and liquid oil). In this embodiment, the degradation efficiency of polystyrene is 75.38%.

[0130] Comparative Example 2

[0131] This comparative example is the same as Comparative Example 1, except that the temperature is 300℃.

[0132] Comparative Example 3

[0133] This comparative example is the same as Comparative Example 1, except that the temperature is 500℃.

[0134] Comparative Example 4

[0135] This comparative example provides a method for degrading polystyrene plastic in the environment, comprising:

[0136] Step 1: Weigh 0.15g of polystyrene plastic and place it in the reaction vessel. Tighten the reaction vessel and purge it with CO2 to remove all air from the reaction vessel.

[0137] Step 2: Continue to introduce CO2 until the initial pressure inside the reactor reaches 6 MPa; the reactor is a closed reactor, and the introduction of CO2 is stopped after the pressure inside the reactor reaches 6 MPa;

[0138] Step 3: Start the heating furnace to a temperature of 400℃, place the reactor in the heating furnace, and as the temperature rises, the pressure inside the reactor will rise. When the pressure inside the reactor rises to the critical pressure of CO2, start timing and continue until the preset reaction time is reached to complete the degradation of the plastic; the preset reaction time is 120 min; the critical pressure of CO2 is 7.29 MPa; it is labeled as Sc-CO2.

[0139] After the reactor was cooled, the gas produced after the degradation of polystyrene was first collected with a gas bag, and then the remaining products (solid residues and liquid oil) were collected by opening the reactor. In this example, the degradation efficiency of polystyrene was 79.86%.

[0140] Comparative Example 5

[0141] This comparative example is the same as Comparative Example 4, except that the temperature is 300°C.

[0142] Comparative Example 6

[0143] This comparative example is the same as Comparative Example 4, except that the temperature is 500°C.

[0144] Comparative Example 7

[0145] This comparative example provides a method for degrading plastics, specifically comprising:

[0146] Step one, weigh 0.15 g of polystyrene plastic and place it in a reactor, add 1 mL of water;

[0147] Step two, tighten the reactor, and use CO2 to purge the reactor to remove all air in the reactor;

[0148] Step three, continue to introduce CO2 until the initial pressure in the reactor is 6 MPa; the reactor is a closed reactor, and the introduction of CO2 is stopped when the pressure in the reactor reaches 6 MPa;

[0149] Step four, start the heating furnace to a temperature of 400°C, place the reactor in the heating furnace, and as the temperature rises, the pressure in the reactor rises, when the pressure in the reactor rises to the critical pressure of CO2, start timing, to the preset reaction time, complete the degradation of plastics; the preset reaction time is 120 min; the critical pressure of CO2 is 7.29 MPa; marked as Sc-CO2 / H2O.

[0150] After the reactor was cooled, the gas produced after the degradation of polystyrene was first collected with a gas bag, and then the remaining products (solid residues and liquid oil) were collected by opening the reactor. In this example, the degradation efficiency of polystyrene was 79.86%. Figure 1

[0151] Comparative Example 8

[0152] This comparative example is the same as Comparative Example 7, except that the temperature is 500°C.

[0153] Comparative Example 9

[0154] This comparative example is the same as Comparative Example 7, except that the temperature is 300°C.

[0155] Performance Evaluation​

[0156] Degradation efficiency

[0157] The degradation efficiency of polystyrene in Examples 1-6 and Comparative Examples 1-9 is as follows: Figure 1 As shown. According to Figure 1 It is evident that the degradation efficiency of polystyrene increases with temperature from 300℃ to 500℃, and at 500℃, polystyrene is almost completely degraded. When the reaction conditions are changed from environmental conditions to Sc-CO2 conditions, the degradation efficiency of polystyrene significantly increases from 52.84%, 75.38%, and 97.81% at 300℃, 400℃, and 500℃ to 58.35%, 79.86%, and 98.63%, respectively. This may be because the introduction of Sc-CO2 creates a homogeneous environment for polystyrene.

[0158] When the auxiliary solution is added to the Sc-CO2 system, the degradation efficiency of polystyrene shows a further significant improvement, reaching 82.53%–85.42%, 84.96%–90.34%, and 99.25%–99.88% at 300℃, 400℃, and 500℃, respectively. This may be due to the auxiliary solution increasing the solubility of polystyrene in Sc-CO2, causing the plastic polymer to swell, or the OH- / H+ provided by NaOH / HCl. + An alkaline / acidic environment was created, which lowered the activation energy of the reaction, thereby accelerating the depolymerization of polystyrene. The formula for calculating the degradation efficiency is as follows:

[0159]

[0160] Where m is the initial mass of polystyrene in g; m0 is the mass of the solid residue after degradation in g.

[0161] Gas product distribution

[0162] The distribution of gaseous products after polystyrene degradation at different reaction times is as follows: Figure 2 and Figure 3 As shown, where, Figure 2 The data corresponding to the horizontal axis 120 represents the distribution of gaseous products after degradation in Example 1. Figure 2 The data corresponding to the remaining processing times are the distribution of gaseous products after degradation after adjusting only the reaction time in Example 1; Figure 3 The data corresponding to the horizontal axis 120 in Example 2 represents the distribution of gaseous products after degradation. Figure 3 The data corresponding to the remaining processing times are the distribution of gaseous products after degradation after adjusting only the reaction time in Example 2. Figure 2 and 3It can be seen that the gaseous products of polystyrene degradation in Sc-CO2 include H2, CO, CH4 and C2H x (x = 4, 6).

[0163] As can be seen from the figure, with the extension of reaction time, polystyrene is converted into more gas, when the reaction time is 120 min, the total amount of gas produced by polystyrene degradation is 126.88 (alkali solution) / 116.99 mL (acid solution), in which the amount of H2 and CH4 is 74.18 (alkali solution) / 62.78 mL (acid solution) and 31.68 (alkali solution) / 45.29 mL (acid solution) respectively.

[0164] In addition, it can be seen that the consumption of CO2 increases with the extension of reaction time, when the reaction time is 120 min, the consumption of CO2 is 81.2 mL (alkali solution) / 71.5 mL (acid solution), indicating that compared with the acid solution, the polystyrene degradation process consumes more CO2 when the alkali solution is used as the auxiliary solution, which may be due to a small amount of CO2 reacts with NaOH to form Na2CO3.

[0165] Liquid products

[0166] The distribution of liquid products after plastic degradation in examples 1-6 is shown in Figure 4 , in which figure a is examples 1, 3 and 4, and figure b is examples 2, 5 and 6. The components of liquid products after polystyrene degradation mainly include phenanthrene (C 14 H 10 ), anthracene (C 14 H 10 ), 1-phenyl naphthalene (C 16 H 12 ), 2-phenyl naphthalene (C 16 H 12 ), fluoranthene (C 16 H 10 ), triphenylene (C 18 H 12 ) and 1,3,5-triphenyl benzene (C 24 H 18 ). Figure 4 It can be seen that when the temperature is 300℃, there are more biphenyl, fluorene and benzene in the liquid products, and there are no above liquid products at 400℃ and 500℃. This indicates that the polystyrene degradation is more complete at 400℃ and 500℃ compared with 300℃. This may be due to the condensation of the carbon chain structure of polystyrene at higher reaction temperature, resulting in more phenanthrene, 1-phenyl naphthalene, m-triphenyl, triphenyl and other condensed ring aromatic hydrocarbon substances.

[0167] Structure

[0168] Figure 5The structure of the solid residue after polystyrene degradation under scanning electron microscope is scanned for examples 1 and 2. According to Figure 5 It can be seen that the alkali solution corresponds to the solid residue after polystyrene degradation, mainly in the form of microspheres and scattered flocculation, while the acid solution corresponds to the solid residue after polystyrene degradation, mainly in the form of irregular strips and a small amount of microspheres, which shows that the acid solution and the alkali solution have different treatment effects on the plastic.

[0169] The above is only a preferred embodiment of the present application, not any limitation on the present application, any simple modification, change and equivalent structure change according to the essence of the application to the above embodiment, still belongs to the protection scope of the technical scheme of the present application.

Claims

1. A method of degrading plastic, characterized by, The application relates to a method for degrading plastic in a supercritical CO2 environment. The auxiliary solution is an acid solution or a base solution; the acid solution is a hydrochloric acid solution, the base solution is a sodium hydroxide solution, the concentration of the hydrochloric acid solution is 1wt%-5wt%, the solubility of the base solution is 1wt%-5wt%, the mass of the plastic is 0.15 times the volume of the auxiliary solution, the mass of the plastic is g, and the volume of the auxiliary solution is mL; the plastic is polystyrene plastic; the supercritical CO2 environment comprises 7.29MPa of CO2 pressure; and the treatment temperature is 300 DEG C-500 DEG C. The treatment time is 30min-120min.

2. A method of degrading plastic according to claim 1, wherein, The application further provides a method for degrading plastic in a supercritical CO2 environment.

3. A method of degrading plastic according to any one of claims 1 to 2, wherein, Step one: preparing an auxiliary solution, the auxiliary solution being an acid solution or a base solution; when the auxiliary solution is an acid solution, the method for preparing the auxiliary solution comprises the following steps: diluting 50wt% hydrochloric acid to 1wt%-5wt% to obtain an acid solution; when the auxiliary solution is a base solution, the method for preparing the auxiliary solution comprises the following steps: dissolving sodium hydroxide in water to obtain a base solution with a concentration of 1wt%-5wt%; Step two: degrading, specifically comprising the following steps: Step 201: placing plastic in a reaction kettle and adding the auxiliary solution; Step 202: tightening the reaction kettle and purging the reaction kettle with CO2 to remove air in the reaction kettle; Step 203: continuously introducing CO2 to the initial pressure in the reaction kettle and keeping the pressure; Step 204: starting a heating furnace to a temperature of 300 DEG C-500 DEG C, placing the reaction kettle in the heating furnace, increasing the pressure in the reaction kettle with the temperature, starting timing when the pressure in the reaction kettle rises to the critical pressure of CO2, and completing plastic degradation after a preset reaction time; the preset reaction time is 30min-120min. In step 201, the mass of the plastic is 0.15 times the volume of the auxiliary solution, the mass of the plastic is g, and the volume of the auxiliary solution is mL; and in step 203, the initial pressure is 6MPa.

4. A method of degrading plastic according to claim 3, wherein, In step 204, the critical pressure of CO2 is 7.29MPa.

5. A method of degrading plastic according to claim 3, wherein, ​

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