CN115947977A - Method for degrading plastics - Google Patents
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Abstract
The invention discloses a method for degrading plastics, which comprises the following steps: preparing an auxiliary solution, wherein the auxiliary solution is an acid solution or an alkali solution; step two, degradation is carried out, and the method specifically comprises the following steps: step 201, placing plastics into a reaction kettle, and adding the auxiliary solution; step 202, using CO 2 Purging the reaction kettle; step 203, continuously introducing CO 2 The initial pressure in the reaction kettle is reached and maintained; step 204, starting the heating furnace, placing the reaction kettle in the heating furnace, increasing the pressure in the reaction kettle along with the increase of the temperature, and increasing the pressure in the reaction kettle to CO when the pressure in the reaction kettle rises 2 Starting timing at the critical pressure till the preset reaction time, and finishing the degradation of the plastic. The auxiliary solution is mixed with the plastic and then subjected to supercritical CO 2 The method for treating the polystyrene plastic in the medium and high temperature environment has the advantages that the degradation efficiency of the polystyrene plastic is up to 90 percent, and the method has the characteristics of high plastic degradation efficiency and good degradation effect.
Description
Technical Field
The invention belongs to the technical field of degradation, and particularly relates to a method for degrading plastics.
Background
Plastics are widely used for their outstanding advantages, such as light weight, good ductility, durability, low cost, ease of processing, etc. Plastic products play an important role in protecting people, and the wide application of plastic products also brings new challenges, such as statistics showing that up to 160 ten thousand tons of plastic waste can be generated every day. Only about 2% of these plastics are recycled and the majority (about 92%) are discarded in landfills or in the natural environment.
Plastics are highly inert and take approximately 200-400 years to completely degrade in the natural environment. The waste plastics in the environment not only cause visual 'white pollution', but also destroy the ecological environment, thereby threatening the survival of animals, plants, microorganisms and even human beings.
Among the methods for processing waste plastics, the most widely used is landfill processing together with other wastes. Although the method is simple to operate and low in investment cost, secondary pollution is caused to soil, and land resources are wasted. Incineration is also a common method of processing waste plastics. Compared with the landfill method, the incineration method has the advantages of short treatment period, high efficiency and small occupied area. In addition, a large amount of heat energy released by incineration can be reused for power generation and heating. However, burning plastics can produce smoke, solid particulates, and other substances that are harmful to the environment and humans. Therefore, new methods for degrading plastics and recovering the degradation products are needed to improve the resource utilization.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a method for degrading plastics by mixing an auxiliary solution with plastics and then subjecting the mixture to supercritical CO 2 After the treatment is carried out in medium and high temperature environment, the degradation efficiency of the polystyrene plastic reaches up to 90 percent, and the polystyrene plastic has the characteristics of high degradation efficiency and good degradation effect.
In order to solve the technical problems, the invention adopts the technical scheme that: a method of degrading a plastic, comprising: mixing the plastic with an auxiliary solutionMixing and then supercritical CO 2 And (4) processing in the environment.
The method for degrading the plastic is characterized in that the auxiliary solution is an acid solution or an alkali solution.
The method for degrading the plastic is characterized in that the acid solution is a hydrochloric acid solution, the alkali solution is a sodium hydroxide solution, the concentration of the hydrochloric acid solution is 1wt% -5 wt%, and the solubility of the alkali solution is 1wt% -5 wt%; the mass of the plastic is 0.15 times of the volume of the auxiliary solution, the mass unit of the plastic is g, and the volume unit of the auxiliary solution is mL.
The method for degrading the plastic is characterized in that the plastic is polystyrene plastic.
The method for degrading plastics is characterized in that the supercritical CO is 2 The environment comprises CO in the environment 2 The pressure was 7.29MPa.
The method for degrading the plastic is characterized in that the treatment temperature is 300-500 ℃.
The method for degrading the plastic is characterized in that the treatment time is 30-120 min.
The method for degrading the plastic is characterized by comprising the following steps:
step one, preparing an auxiliary solution, wherein the auxiliary solution is an acid solution or an alkali solution, and when the auxiliary solution is the acid solution, the method for preparing the auxiliary solution comprises the following steps: diluting hydrochloric acid with the concentration of 50wt% to the concentration of 1wt% -5 wt% to obtain an acid solution; when the auxiliary solution is an alkali solution, the method for preparing the auxiliary solution comprises the steps of dissolving sodium hydroxide in water to obtain an alkali solution with the concentration of 1-5 wt%;
step two, degradation is carried out, and the method specifically comprises the following steps:
step 201, placing plastics into a reaction kettle, and adding the auxiliary solution;
202, screwing down the reaction kettle by using CO 2 Purging the reaction kettle to remove air in the reaction kettle;
step 203, a,Continuously introducing CO 2 The initial pressure in the reaction kettle is reached and maintained;
step 204, starting the heating furnace to the temperature of 300-500 ℃, placing the reaction kettle in the heating furnace, and increasing the pressure in the reaction kettle along with the increase of the temperature until the pressure in the reaction kettle rises to CO 2 Starting timing at the critical pressure until the preset reaction time, and finishing the degradation of the plastic; the preset reaction time is 30 min-120 min.
The method for degrading the plastic is characterized in that, in step 201, the mass of the plastic is 0.15 times of the volume of the auxiliary solution, the mass unit of the plastic is g, and the volume unit of the auxiliary solution is mL; step 203 the initial pressure is 6MPa.
The method for degrading plastics, wherein the CO in step 204 2 The critical pressure of (A) is 7.29MPa.
Compared with the prior art, the invention has the following advantages:
1. the method for degrading the plastic comprises the steps of mixing the auxiliary solution with the plastic and then performing supercritical CO 2 After the treatment is carried out in medium and high temperature environment, the degradation efficiency of the polystyrene plastic reaches up to 90 percent, and the polystyrene plastic has the characteristics of high degradation efficiency and good degradation effect.
2. In the process of the invention, supercritical CO is utilized 2 Provides homogeneous environment and solvent for plastic degradation, and can effectively reduce the mass transfer resistance between material interfaces.
3. In the method, the acid solution and the alkali solution are used as auxiliary solutions to strengthen the plastic in the supercritical CO 2 Solubility, reduction of activation energy of reaction, and promotion of degradation of plastics.
4. After the method is adopted to degrade the plastic, when the reaction temperature is 400 ℃, the reaction time is 120min and the concentration of the auxiliary solution is 5wt%, the degradation efficiency of the polystyrene plastic is 84.96-90.34%, and the total volume of generated gas is 116.99-126.88 mL.
The technical solution of the present invention is further described in detail with reference to the accompanying drawings and embodiments.
Drawings
FIG. 1 shows the degradation efficiency of polystyrene plastics in examples 1 to 6 and comparative examples 1 to 9.
FIG. 2 shows the gas products after degradation of the polystyrene plastic after treatment with an acid solution.
FIG. 3 shows the gaseous products of the degradation of polystyrene plastics after the treatment with alkali solution.
FIG. 4 shows the distribution of the liquid products after degradation of the polystyrene plastic.
FIG. 5 is an SEM image of the solid residue after degradation of polystyrene plastic.
Detailed Description
Example 1
The present embodiment provides a method of degrading plastic, comprising:
step one, preparing an acid solution, which specifically comprises the following steps: diluting a hydrochloric acid solution with the concentration of 50wt% to the concentration of 5wt% to obtain an acid solution;
step two, degradation is carried out, and the method specifically comprises the following steps:
step 201, placing 0.15g of polystyrene plastic in a reaction kettle, and adding 1mL of the acid solution; the inner diameter of the reaction kettle is 1cm, and the length of the reaction kettle is 15cm;
202, screwing down the reaction kettle by using CO 2 Purging the reaction kettle to remove air in the reaction kettle;
step 203, continuously introducing CO 2 Until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and CO is stopped to be introduced after the pressure in the reaction kettle is 6MPa 2 ；
Step 204, starting the heating furnace to the temperature of 400 ℃, placing the reaction kettle in the heating furnace, and increasing the pressure in the reaction kettle along with the increase of the temperature until the pressure in the reaction kettle rises to CO 2 Starting timing at the critical pressure until the preset reaction time, and finishing the degradation of the plastic; the preset reaction time is 120min; the CO is 2 The critical pressure of (A) is 7.29MPa; marked as Sc-CO 2 /HCl。
After the reaction kettle is cooled, a gas bag is used for collecting gas generated after the polystyrene is degraded, and then the reaction kettle is opened to collect residual products (solid residues and liquid oil). In this example, degradation of polystyreneThe efficiency is 90.34%, and CO is consumed 2 Has a volume of 71.5mL, generates a gas volume of 126.88mL, wherein H 2 Has a volume of 62.78mL, a volume of CO of 13.22mL, and CH 4 Has a volume of 45.29mL 2 H x Volume of (x =4,6) was 5.59mL.
Example 2
The present embodiment provides a method of degrading plastic, comprising:
step one, preparing an alkali solution, which specifically comprises the following steps: dissolving sodium hydroxide in water to obtain an alkali solution with the concentration of 5wt%;
step two, degradation is carried out, and the method specifically comprises the following steps:
step 201, taking 0.15g of polystyrene plastic, placing the polystyrene plastic in a reaction kettle, and adding 1mL of the alkali solution;
202, screwing down the reaction kettle by using CO 2 Purging the reaction kettle to remove air in the reaction kettle;
step 203, continuously introducing CO 2 Until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and CO is stopped to be introduced after the pressure in the reaction kettle is 6MPa 2 ；
Step 204, starting the heating furnace to the temperature of 400 ℃, placing the reaction kettle in the heating furnace, and increasing the pressure in the reaction kettle along with the increase of the temperature until the pressure in the reaction kettle rises to CO 2 Starting timing at the critical pressure until the preset reaction time, and finishing the degradation of the plastic; the preset reaction time is 120min; said CO 2 The critical pressure of (A) is 7.29MPa; marked as Sc-CO 2 /NaOH。
After the reaction kettle is cooled, a gas bag is used for collecting gas generated after the polystyrene is degraded, and then the reaction kettle is opened to collect residual products (solid residues and liquid oil). In this example, the degradation efficiency of polystyrene was 84.96%, consuming CO 2 Has a volume of 81mL, generates a gas volume of 119.99mL, wherein H 2 Has a volume of 74.18mL, a volume of CO of 7.33mL, CH 4 Has a volume of 34.68mL 2 H x Volume of (x =4,6) was 3.8mL.
Example 3
The present embodiment provides a method of degrading plastic, comprising:
step one, preparing an acid solution, which specifically comprises the following steps: diluting a hydrochloric acid solution with the concentration of 50wt% to the concentration of 5wt% to obtain an acid solution;
step two, degradation is carried out, and the method specifically comprises the following steps:
step 201, placing 0.15g of polystyrene plastic in a reaction kettle, and adding 1mL of the acid solution;
202, screwing down the reaction kettle by using CO 2 Purging the reaction kettle to remove air in the reaction kettle;
step 203, continuously introducing CO 2 Until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and CO is stopped to be introduced after the pressure in the reaction kettle is 6MPa 2 ；
Step 204, starting the heating furnace to the temperature of 500 ℃, placing the reaction kettle in the heating furnace, increasing the pressure in the reaction kettle along with the increase of the temperature, and increasing the pressure in the reaction kettle to CO when the pressure in the reaction kettle increases 2 Starting timing at the critical pressure until the preset reaction time, and finishing the degradation of the plastic; the preset reaction time is 120min; the CO is 2 The critical pressure of (A) is 7.29MPa; marked as Sc-CO 2 /HCl。
After the reaction kettle is cooled, gas generated after the polystyrene is degraded is collected by a gas bag, and then the reaction kettle is opened to collect the residual products (solid residues and liquid oil). In this example, the degradation efficiency of polystyrene is shown in FIG. 1.
Example 4
The present embodiment provides a method of degrading plastic, comprising:
step one, preparing an acid solution, which specifically comprises the following steps: diluting a hydrochloric acid solution with the concentration of 50wt% to the concentration of 5wt% to obtain an acid solution;
step two, degradation is carried out, and the method specifically comprises the following steps:
step 201, placing 0.15g of polystyrene plastic in a reaction kettle, and adding 1mL of the acid solution;
202, screwing down the reaction kettle by using CO 2 Purging the reaction kettle to remove the inside of the reaction kettleAir;
step 203, continuously introducing CO 2 Until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and CO is stopped to be introduced after the pressure in the reaction kettle is 6MPa 2 ；
Step 204, starting the heating furnace to the temperature of 300 ℃, placing the reaction kettle in the heating furnace, increasing the pressure in the reaction kettle along with the increase of the temperature, and increasing the pressure in the reaction kettle to CO when the pressure in the reaction kettle increases 2 Starting timing at the critical pressure until the preset reaction time, and finishing the degradation of the plastic; the preset reaction time is 120min; the CO is 2 The critical pressure of (A) is 7.29MPa; marked as Sc-CO 2 /HCl。
After the reaction kettle is cooled, gas generated after the polystyrene is degraded is collected by a gas bag, and then the reaction kettle is opened to collect the residual products (solid residues and liquid oil). In this example, the degradation efficiency of polystyrene is shown in FIG. 1.
Example 5
The present embodiment provides a method of degrading plastic, comprising:
step one, preparing an alkali solution, which specifically comprises the following steps: dissolving sodium hydroxide in water to obtain an alkali solution with the concentration of 5wt%;
step two, degradation is carried out, and the method specifically comprises the following steps:
step 201, taking 0.15g of polystyrene plastic, placing the polystyrene plastic in a reaction kettle, and adding 1mL of the alkali solution;
step 202, screwing down the reaction kettle by using CO 2 Purging the reaction kettle to remove air in the reaction kettle;
step 203, continuously introducing CO 2 Until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and CO is stopped to be introduced after the pressure in the reaction kettle is 6MPa 2 ；
Step 204, starting the heating furnace to the temperature of 300 ℃, placing the reaction kettle in the heating furnace, increasing the pressure in the reaction kettle along with the increase of the temperature, and increasing the pressure in the reaction kettle to CO when the pressure in the reaction kettle increases 2 Starting timing at the critical pressure until the preset reaction time, and finishing the degradation of the plastic; the preset reaction time is 120min; the CO is 2 Critical pressure ofIs 7.29MPa; marked as Sc-CO 2 /NaOH。
After the reaction kettle is cooled, gas generated after the polystyrene is degraded is collected by a gas bag, and then the reaction kettle is opened to collect the residual products (solid residues and liquid oil). In this example, the degradation efficiency of polystyrene is shown in FIG. 1.
Example 6
The present embodiment provides a method of degrading plastic, comprising:
step one, preparing an alkali solution, which specifically comprises the following steps: dissolving sodium hydroxide in water to obtain an alkali solution with the concentration of 5wt%;
step two, degradation is carried out, and the method specifically comprises the following steps:
step 201, placing 0.15g of polystyrene plastic in a reaction kettle, and adding 1mL of the alkali solution;
202, screwing down the reaction kettle by using CO 2 Purging the reaction kettle to remove air in the reaction kettle;
step 203, continuously introducing CO 2 Until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and CO is stopped to be introduced after the pressure in the reaction kettle is 6MPa 2 ；
Step 204, starting the heating furnace to the temperature of 500 ℃, placing the reaction kettle in the heating furnace, increasing the pressure in the reaction kettle along with the increase of the temperature, and increasing the pressure in the reaction kettle to CO when the pressure in the reaction kettle increases 2 Starting timing at the critical pressure until the preset reaction time, and finishing the degradation of the plastic; the preset reaction time is 120min; the CO is 2 The critical pressure of (A) is 7.29MPa; marked as Sc-CO 2 /NaOH。
After the reaction kettle is cooled, a gas bag is used for collecting gas generated after the polystyrene is degraded, and then the reaction kettle is opened to collect residual products (solid residues and liquid oil). In this example, the degradation efficiency of polystyrene is 99.25% in this example.
Example 7
The present embodiment provides a method of degrading plastic, comprising:
step one, preparing an acid solution, which specifically comprises the following steps: diluting a hydrochloric acid solution with the concentration of 50wt% to the concentration of 1wt% to obtain an acid solution;
step two, degradation is carried out, and the method specifically comprises the following steps:
step 201, placing 0.15g of polystyrene plastic in a reaction kettle, and adding 1mL of the acid solution;
202, screwing down the reaction kettle by using CO 2 Purging the reaction kettle to remove air in the reaction kettle;
step 203, continuously introducing CO 2 Until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and CO is stopped to be introduced after the pressure in the reaction kettle is 6MPa 2 ；
Step 204, starting the heating furnace to the temperature of 400 ℃, placing the reaction kettle in the heating furnace, increasing the pressure in the reaction kettle along with the increase of the temperature, and increasing the pressure in the reaction kettle to CO when the pressure in the reaction kettle increases 2 Starting timing at the critical pressure until the preset reaction time, and finishing the degradation of the plastic; the preset reaction time is 30min; the CO is 2 The critical pressure of (A) is 7.29MPa; marked as Sc-CO 2 /HCl。
After the reaction kettle is cooled, gas generated after the polystyrene is degraded is collected by a gas bag, and then the reaction kettle is opened to collect the residual products (solid residues and liquid oil). In this example, the degradation efficiency of polystyrene was 99.88%.
Example 8
The present embodiment provides a method of degrading plastic, comprising:
step one, preparing an acid solution, which specifically comprises the following steps: diluting a hydrochloric acid solution with the concentration of 50wt% to the concentration of 3wt% to obtain an acid solution;
step two, degradation is carried out, and the method specifically comprises the following steps:
step 201, placing 0.15g of polystyrene plastic in a reaction kettle, and adding 1mL of the acid solution;
step 202, screwing down the reaction kettle by using CO 2 Purging the reaction kettle to remove air in the reaction kettle;
step 203, continuously introducing CO 2 Until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reactionThe pressure in the kettle is 6MPa, and then the introduction of CO is stopped 2 ；
Step 204, starting the heating furnace to the temperature of 400 ℃, placing the reaction kettle in the heating furnace, and increasing the pressure in the reaction kettle along with the increase of the temperature until the pressure in the reaction kettle rises to CO 2 Starting timing at the critical pressure until the preset reaction time, and finishing the degradation of the plastic; the preset reaction time is 90min; said CO 2 The critical pressure of (A) is 7.29MPa; marked as Sc-CO 2 /HCl。
After the reaction kettle is cooled, gas generated after the polystyrene is degraded is collected by a gas bag, and then the reaction kettle is opened to collect the residual products (solid residues and liquid oil). In this example, the degradation efficiency of polystyrene was 89.41%.
Example 9
The present embodiment provides a method of degrading plastic, comprising:
step one, preparing an alkali solution, which specifically comprises the following steps: dissolving sodium hydroxide in water to obtain an alkali solution with the concentration of 1 wt%;
step two, degradation is carried out, and the method specifically comprises the following steps:
step 201, taking 0.15g of polystyrene plastic, placing the polystyrene plastic in a reaction kettle, and adding 1mL of the alkali solution;
202, screwing down the reaction kettle by using CO 2 Purging the reaction kettle to remove air in the reaction kettle;
step 203, continuously introducing CO 2 Until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and CO is stopped to be introduced after the pressure in the reaction kettle is 6MPa 2 ；
Step 204, starting the heating furnace to the temperature of 400 ℃, placing the reaction kettle in the heating furnace, increasing the pressure in the reaction kettle along with the increase of the temperature, and increasing the pressure in the reaction kettle to CO when the pressure in the reaction kettle increases 2 Starting timing at the critical pressure until the preset reaction time, and finishing the degradation of the plastic; the preset reaction time is 30min; the CO is 2 The critical pressure of (A) is 7.29MPa; marked as Sc-CO 2 /NaOH。
After the reaction kettle is cooled, a gas bag is used for collecting gas generated after the polystyrene is degraded, and then the reaction kettle is opened to collect residual products (solid residues and liquid oil). In this example, the degradation efficiency of polystyrene was 75.98%.
Example 10
The present embodiment provides a method of degrading plastic, comprising:
step one, preparing an alkali solution, which specifically comprises the following steps: dissolving sodium hydroxide in water to obtain an alkali solution with the concentration of 3 wt%;
step two, degradation is carried out, and the method specifically comprises the following steps:
step 201, placing 0.15g of polystyrene plastic in a reaction kettle, and adding 1mL of the alkali solution;
202, screwing down the reaction kettle by using CO 2 Purging the reaction kettle to remove air in the reaction kettle;
step 203, continuously introducing CO 2 Until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and CO is stopped to be introduced after the pressure in the reaction kettle is 6MPa 2 ；
Step 204, starting the heating furnace to the temperature of 400 ℃, placing the reaction kettle in the heating furnace, and increasing the pressure in the reaction kettle along with the increase of the temperature until the pressure in the reaction kettle rises to CO 2 Starting timing at the critical pressure until the preset reaction time, and finishing the degradation of the plastic; the preset reaction time is 90min; the CO is 2 The critical pressure of (A) is 7.29MPa; marked as Sc-CO 2 /NaOH。
After the reaction kettle is cooled, gas generated after the polystyrene is degraded is collected by a gas bag, and then the reaction kettle is opened to collect the residual products (solid residues and liquid oil). In this example, the degradation efficiency of polystyrene was 82.95%.
In the above examples, the polystyrene plastic is commercially available, and preferably, the polystyrene plastic of the present invention is a self-sustained-release plasticized polystyrene plastic having a molecular formula of
The results of elemental analysis are shown in Table 1.
TABLE 1 elemental analysis results of polystyrene plastics
Comparative example 1
This comparative example provides a method of degrading polystyrene plastic in an environment comprising: placing 0.15g of polystyrene plastic in a reaction kettle, starting a heating furnace to the temperature of 400 ℃, placing the reaction kettle in the heating furnace, starting timing, and reacting for 120min; the mark is blank.
After the reaction kettle is cooled, gas generated after the polystyrene is degraded is collected by a gas bag, and then the reaction kettle is opened to collect the residual products (solid residues and liquid oil). In this example, the degradation efficiency of polystyrene was 75.38%.
Comparative example 2
This comparative example is the same as comparative example 1 except that the temperature is 300 ℃.
Comparative example 3
This comparative example is the same as comparative example 1 except that the temperature is 500 ℃.
Comparative example 4
This comparative example provides a method of degrading polystyrene plastic in an environment comprising:
step one, weighing 0.15g of polystyrene plastic, placing the polystyrene plastic in a reaction kettle, screwing the reaction kettle tightly, and using CO 2 Purging the reaction kettle to remove air in the reaction kettle;
step two, continuously introducing CO 2 Until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and CO is stopped to be introduced after the pressure in the reaction kettle is 6MPa 2 ；
Step three, starting the heating furnace to the temperature of 400 ℃, placing the reaction kettle in the heating furnace, increasing the pressure in the reaction kettle along with the increase of the temperature, and increasing the pressure in the reaction kettle to CO when the pressure in the reaction kettle increases 2 Starting timing at the critical pressure until the preset reaction time, and finishing the degradation of the plastic; the preset reaction time is 120min; said CO 2 The critical pressure of (A) is 7.29MPa; marked as Sc-CO 2 。
After the reaction kettle is cooled, gas generated after the polystyrene is degraded is collected by a gas bag, and then the reaction kettle is opened to collect the residual products (solid residues and liquid oil). In this example, the degradation efficiency of polystyrene was 79.86%.
Comparative example 5
This comparative example is the same as comparative example 4 except that the temperature is 300 ℃.
Comparative example 6
This comparative example is the same as comparative example 4 except that the temperature is 500 ℃.
Comparative example 7
The comparative example provides a method of degrading a plastic, comprising:
step one, weighing 0.15g of polystyrene plastic, placing the polystyrene plastic in a reaction kettle, and adding 1mL of water;
step two, screwing down the reaction kettle and using CO 2 Purging the reaction kettle to remove air in the reaction kettle;
step three, continuously introducing CO 2 Until the initial pressure in the reaction kettle is 6MPa; the reaction kettle is a closed reaction kettle, and CO is stopped to be introduced after the pressure in the reaction kettle is 6MPa 2 ；
Step four, starting the heating furnace to the temperature of 400 ℃, placing the reaction kettle in the heating furnace, and increasing the pressure in the reaction kettle along with the increase of the temperature until the pressure in the reaction kettle rises to CO 2 Starting timing at the critical pressure until the preset reaction time, and finishing the degradation of the plastic; the preset reaction time is 120min; the CO is 2 The critical pressure of (A) is 7.29MPa; marked as Sc-CO 2 /H 2 O。
After the reaction kettle is cooled, gas generated after the polystyrene is degraded is collected by a gas bag, and then the reaction kettle is opened to collect the residual products (solid residues and liquid oil). In this example, the degradation efficiency of polystyrene is shown in fig. 1.
Comparative example 8
This comparative example is the same as comparative example 7 except that the temperature is 500 ℃.
Comparative example 9
This comparative example is the same as comparative example 7 except that the temperature is 300 ℃.
Evaluation of Performance
Efficiency of degradation
The degradation efficiency of polystyrene of examples 1 to 6 and comparative examples 1 to 9 is shown in FIG. 1. As can be seen from fig. 1, the degradation efficiency of polystyrene increases as the temperature increases from 300 ℃ to 500 ℃, and polystyrene is almost completely degraded when the temperature is 500 ℃; when only the reaction conditions are set from ambient conditions to Sc-CO 2 Under the conditions, the degradation efficiency of polystyrene is remarkably improved from 52.84%, 75.38% and 97.81% at 300 ℃, 400 ℃ and 500 ℃ to 58.35%, 79.86% and 98.63%, which is probably due to Sc-CO 2 The introduction of (2) creates a homogeneous environment for the polystyrene.
When the auxiliary solution is added to Sc-CO 2 When in a system, the degradation efficiency of the polystyrene shows a trend of further obviously improving, which is reflected in that the degradation efficiency of the polystyrene respectively reaches 82.53-85.42 percent, 84.96-90.34 percent and 99.25-99.88 percent at 300 ℃, 400 ℃ and 500 ℃, which is probably because the auxiliary solution improves the Sc-CO of the polystyrene 2 Medium solubility, swelling of the plastic polymer, or OH-/H-provided by NaOH/HCl + An alkali/acid environment is created, so that the activation energy of the reaction is reduced, thereby accelerating the depolymerization of the polystyrene, wherein the degradation efficiency is calculated by the formula:
wherein m is the mass of the initial polystyrene in g; m is 0 Is the mass of the solid residue after degradation in g.
Gas product distribution
The distribution of the gas products after degradation of polystyrene at different reaction times is shown in FIGS. 2 and 3, wherein the data corresponding to the abscissa 120 in FIG. 2 is the distribution of the gas products after degradation in example 1, and the data corresponding to the remaining processing times in FIG. 2 are the data corresponding to example 1 after only the reaction time is adjustedThe distribution of degraded gas products; the data corresponding to the abscissa 120 in fig. 3 is the distribution of the degraded gas product in example 2, and the data corresponding to the rest of the processing time in fig. 3 is the distribution of the degraded gas product after only the reaction time is adjusted in example 2. As can be seen from FIGS. 2 and 3, in Sc-CO 2 The gaseous products of polystyrene degradation include H 2 、CO、CH 4 And C 2 H x (x＝4，6)。
As can be seen from the figure, polystyrene is converted into more gas with the extension of the reaction time, and the total gas amount generated by the degradation of polystyrene is 126.88 (alkali solution)/116.99 mL (acid solution) when the reaction time is 120min, wherein H is 2 And CH 4 The amounts were 74.18 (base solution)/62.78 mL (acid solution) and 31.68 (base solution)/45.29 mL (acid solution), respectively.
In addition, it can be seen that CO 2 The consumption of (A) increases with the reaction time, and when the reaction time is 120min, CO is added 2 The consumption amounts of (A) were 81.2mL (alkali solution)/71.5 mL (acid solution), respectively, indicating that the polystyrene degradation process consumes more CO when the alkali solution is used as an auxiliary solution than the acid solution 2 This may be due to small amounts of CO 2 Will react with NaOH to form Na 2 CO 3 。
Liquid product
Examples 1-6 the distribution of liquid product after degradation of the plastic is shown in fig. 4, where fig. a is examples 1,3 and 4 and fig. b is examples 2, 5 and 6. The liquid product after the degradation of the polystyrene mainly comprises phenanthrene (C) 14 H 10 ) Anthracene (C) 14 H 10 ) 1-phenylnaphthalene (C) 16 H 12 ) 2-phenylnaphthalene (C) 16 H 12 ) Fluoranthene (C) 16 H 10 ) Triphenylene (C) 18 H 12 ) And 1,3, 5-triphenylbenzene (C) 24 H 18 ). As can be seen from fig. 4, the liquid product contained more biphenyl, fluorene and benzene at a temperature of 300 c, whereas it was not at 400 c and 500 c. This indicates that the polystyrene degradation is more complete at 400 ℃ and 500 ℃ compared to 300 ℃. This is probably due to the fact that at higher reaction temperatures, polystyrene is usedThe carbon chain structure can be condensed to generate more phenanthrene, 1-phenylnaphthalene, m-terphenyl, terphenyl and other condensed ring aromatic hydrocarbon substances.
Structure of the product
FIG. 5 is a photograph of the structure of the solid residue after degradation of polystyrene under a scanning electron microscope according to examples 1 and 2. As can be seen from fig. 5, the solid residue after the degradation of polystyrene in the alkaline solution mainly presents microspheres and loose flocs, while the solid residue after the degradation of polystyrene in the acidic solution mainly presents irregular stripes and trace microspheres, which indicates that the plastic treated by the acidic solution and the alkaline solution has different treatment effects.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, changes and equivalent structural changes made to the above embodiment according to the technical spirit of the present invention still fall within the protection scope of the technical solution of the present invention.
Claims (10)
1. A method of degrading a plastic, comprising: mixing the plastic with the auxiliary solution and then subjecting the mixture to supercritical CO 2 The treatment is carried out in the environment.
2. A method for degrading plastics according to claim 1, wherein said auxiliary solution is an acid or base solution.
3. The method for degrading plastic according to claim 1, wherein the acid solution is hydrochloric acid solution, the alkali solution is sodium hydroxide solution, the concentration of the hydrochloric acid solution is 1-5 wt%, and the solubility of the alkali solution is 1-5 wt%; the mass of the plastic is 0.15 times of the volume of the auxiliary solution, the mass unit of the plastic is g, and the volume unit of the auxiliary solution is mL.
4. A method of degrading a plastic according to claim 1, wherein said plastic is a polystyrene plastic.
5. The method for degrading plastic according to claim 1, wherein the supercritical CO is 2 The environment comprises CO in the environment 2 The pressure was 7.29MPa.
6. The method for degrading plastic according to claim 1, wherein the temperature of the treatment is 300-500 ℃.
7. The method for degrading plastic according to claim 1, wherein the treatment time is 30min to 120min.
8. A method for degrading plastics according to any one of claims 1 to 7, specifically comprising:
step one, preparing an auxiliary solution, wherein the auxiliary solution is an acid solution or an alkali solution, and when the auxiliary solution is the acid solution, the method for preparing the auxiliary solution comprises the following steps: diluting hydrochloric acid with the concentration of 50wt% to the concentration of 1wt% -5 wt% to obtain an acid solution; when the auxiliary solution is an alkali solution, the method for preparing the auxiliary solution comprises the steps of dissolving sodium hydroxide in water to obtain an alkali solution with the concentration of 1-5 wt%;
step two, degradation is carried out, and the method specifically comprises the following steps:
step 201, placing plastics into a reaction kettle, and adding the auxiliary solution;
202, screwing down the reaction kettle by using CO 2 Purging the reaction kettle to remove air in the reaction kettle;
step 203, continuously introducing CO 2 The initial pressure in the reaction kettle is reached and maintained;
step 204, starting the heating furnace to the temperature of 300-500 ℃, placing the reaction kettle in the heating furnace, and increasing the pressure in the reaction kettle along with the increase of the temperature until the pressure in the reaction kettle rises to CO 2 Starting timing at the critical pressure until the preset reaction time, and finishing the degradation of the plastic; the preset reaction time is 30-120 min.
9. The method of claim 8, wherein 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; step 203 the initial pressure is 6MPa.
10. A method for degrading plastics according to claim 8, wherein said CO of step 204 is 2 The critical pressure of (A) is 7.29MPa.
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| CN116986579A (en) * | 2023-08-31 | 2023-11-03 | 西安交通大学 | Byproduct CO based on supercritical water gasification 2 System for preparing carbon microsphere with waste plastic |
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| CN116986579A (en) * | 2023-08-31 | 2023-11-03 | 西安交通大学 | Byproduct CO based on supercritical water gasification 2 System for preparing carbon microsphere with waste plastic |
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