Method for degrading waste polypropylene through photo-thermal catalysis

Abstract

The invention discloses a method for degrading waste polypropylene through photo-thermal catalysis, which comprises the following steps: mixing waste polypropylene and a catalyst, putting into a photo-thermal reaction environment, and realizing directional decomposition of polypropylene into propylene and propane through photo-thermal catalysis under the protection of inert gas, the catalyst is SrTiO3 / LaFeO3, and the molar ratio of SrTiO3 The photo-thermal reaction environment is as follows: the light intensity in the reactor is 10-400 sunlight, the temperature is 100-500 DEG C, and the pressure is 0.1-1 MPa; according to the method, the waste polypropylene can be completely decomposed, the selectivity of propane and propylene in decomposition products can reach 60% or above, a photo-thermal catalytic reaction environment required by the reaction can be provided by a condensation technology or a high-power light source, and the catalyst is a composite metal oxide semiconductor catalyst with a special out-phase junction structure; sunlight is used as driving force, energy conservation and environmental protection are achieved, and the obtained product has high economic value and good practical application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of plastic recycling, and specifically relates to a method for realizing photothermal catalytic degradation of waste polypropylene by utilizing a semiconductor catalyst. Background Art

[0002] As the world population grows, the demand and consumption of plastic products is also increasing. Various industrial sectors such as automobiles, food, packaging and construction require different types of plastics every day, and the demand for these materials is increasing. According to statistics, the total global plastic production between 2016 and 2021 exceeded 330 million tons, and there is no downward trend yet.

[0003] Plastics are characterized by a very short lifespan and are quickly converted into solid waste after a short period of use. The amount of plastic waste generated each year is huge and is increasing. Plastics are mainly composed of hydrocarbons and different chemicals such as flame retardants, stabilizers and oxidants. They are very difficult to degrade naturally, resulting in "white pollution". Although plastics can be recycled in a variety of ways, the most common way to manage plastic waste is to dump them in the open air or in landfills. This pollution has a significant impact on the environment and public health, including marine ecology, water and soil quality, and biological health. In 2015, nearly 6.3 billion tons of waste plastics accumulated worldwide. If effective management measures are not taken, it is estimated that about 12 billion tons of plastic will enter the landfill by 2050.

[0004] This situation has attracted the attention of researchers, and many different plastic degradation methods have been developed, including physical and chemical methods and means such as light, heat and biodegradation. Traditional methods include mechanical recycling, incineration and landfill, but these methods often face inevitable challenges such as low recovery rate, poor quality of recycled resources / energy and secondary pollution, and may be gradually eliminated. Thermochemical conversion technology, including new technologies such as pyrolysis, thermal liquefaction and gasification, is expected to solve the problem of solid waste management. On the other hand, although thermochemical conversion has the advantages of being able to produce valuable commodities, sustainability and circular economy principles, the disadvantages of thermochemistry are complex processes and high energy consumption. This transforms the problem of plastic disposal from an environmental problem to an energy problem, leading to the emergence of research on the use of renewable energy to convert waste plastics.

[0005] Photocatalysis is a very promising and sustainable method for the treatment of waste plastics because it uses renewable energy. In addition, the reaction apparatus requirements are very low, which makes photocatalysis a very economical strategy. Photocatalysis is often used in various environmental remediation and sustainable development applications such as nitrogen fixation, pollutant degradation, and drug degradation. It would be even more beneficial to use photocatalytic methods to treat plastic waste. Unlike thermochemical conversions, sunlight is usually the only energy required for photocatalytic reactions. Depending on the energy requirements of the reaction, sunlight can also provide some additional energy in the form of heat.

[0006] The disadvantage of photocatalysis is that it has low efficiency and can usually only process waste at lower concentrations. In order to solve this shortcoming, the concept of photothermal catalysis was created. For example, the research group of Professor Martin of Peking University uses a thermal catalytic method that uses sunlight as the only energy source. This method uses a nickel-based catalyst with abundant reserves on the earth to convert a mixture of plastic waste collected from daily use into methane and hydrogen chloride. The process successfully converted 1.03g of a mixture of plastic waste containing five polyolefins, polyesters and polyvinyl chloride into 1.08g of methane (C yield 98%) and 0.045g of HCl (Cl yield 91%). The temperature increase process driven by the day and night photoperiod prevents the deactivation of the catalyst caused by chlorine poisoning, thereby ensuring catalytic activity that lasts for 10 days. Of course, the characteristic of this method is that it first converts sunlight into heat and then catalyzes the degradation of plastics. It is essentially a thermal catalysis.

[0007] Patent document CN117304015A discloses a method for solar thermal catalytic oxidative depolymerization of polyolefins into short-chain aliphatic dicarboxylic acids. The method is characterized in that polyolefin waste plastic particles, photothermal catalyst, and reaction solution are added to a photothermal catalytic reactor, filled with oxygen, heated to a specified temperature, irradiated with sunlight, and stirred for oxidative depolymerization to oxidize polyolefins into short-chain (C3-C16) aliphatic dicarboxylic acids.

[0008] Compared with these methods of converting plastics into indefinite compounds, if the products can be converted into specific monomers, the value of plastic recycling will obviously be greatly increased. Therefore, we hope to provide a low-cost, high-efficiency, and good selectivity method to increase the recycling value of waste plastics. Summary of the invention

[0009] Aiming at waste polypropylene in waste plastics, the present invention provides a method for photothermal catalytic selective decomposition of polypropylene into propylene and propane, and relates to a catalyst used in the method. The present invention has simple process, environmental protection, low cost, and the obtained product has high recycling value.

[0010] The technical solution of the present invention is as follows:

[0011] A method for photothermal catalytic degradation of waste polypropylene, comprising:

[0012] Mix the waste polypropylene and the catalyst, put them into a photothermal reaction environment, and achieve the directional decomposition of polypropylene into propylene and propane through photothermal catalysis under the protection of inert gas;

[0013] The photothermal reaction environment refers to: the light intensity in the reactor is 10 to 400 suns (the light intensity of one sun = natural light intensity ≈ 1000W / m 2 ), temperature 100-500°C, pressure 0.1-1MPa; wherein the light intensity can be provided by focusing technology or a high-power light source, and the corresponding temperature can be provided at the same time. The focusing technology is to use a focusing mirror to concentrate sunlight in a large range into a small range of the reactor; the pressure in the reactor is provided by an inert gas, and the inert gas is selected from N2 or CO2, etc.;

[0014] The mass ratio of catalyst to polypropylene is between 9:1 and 7:3;

[0015] The specific operation method is as follows: waste polypropylene and catalyst (granular) are mixed in solid form, pressed into tablets and placed in a reactor, and then the reactor is fixed to the attached Figure 1 (but not limited to the attached Figure 1 ) is introduced into the light-collecting reaction system shown in FIG. 1 , and the impurity gas such as air is purged for 10 minutes, and the pressure in the reactor is raised to the required pressure, and then the light is focused into the reactor to provide the light intensity and the required reaction temperature, and the reaction is started until the waste polypropylene is completely decomposed (i.e., no product escapes), and the product is led out through the pipeline and detected by chromatography;

[0016] After complete decomposition of polypropylene, small molecular compounds and monomers can be obtained with high selectivity, mainly methane, ethane, ethylene, propane and propylene, among which the selectivity of propane and propylene can reach more than 60%.

[0017] In the method for photothermal catalytic degradation of waste polypropylene described in the present invention, the catalyst used is composed of the elements La, Fe, Sr, Ti and O, and its main structure has the characteristics of LaFeO3 / SrTiO3, that is, a heterojunction structure composed of LaFeO3 and SrTiO3, and the molar ratio of LaFeO3 to SrTiO3 is between 9:1 and 1:9.

[0018] The catalyst can be prepared by a secondary hydrothermal method, and the specific preparation process is as follows:

[0019] (1) K3[Fe(CN)6] and La(NO3)3·6H2O were dissolved in deionized water, anhydrous citric acid was added, and the mixture was stirred and mixed. The mixture was transferred to a hydrothermal reactor, sealed, reacted at 180°C for 12 hours, naturally cooled to room temperature, washed, dried, ground evenly, and placed in a muffle furnace, heated to 800°C at a rate of 5°C / min, and calcined for 2 hours to obtain LaFeO3;

[0020] (2) LaFeO3, Sr(NO3)2·6H2O and NaOH solution are mixed and dispersed uniformly, and TiO2 is added and stirred to mix uniformly. The mixed solution is transferred to a hydrothermal reactor, sealed, reacted at 130°C for 48 hours, naturally cooled to room temperature, washed, dried, and ground uniformly to obtain SrTiO3 / LaFeO3 (abbreviated as: STO / LFO).

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention uses semiconductor catalysts to efficiently and selectively decompose waste polypropylene into propylene and propane, as well as a small amount of methane, ethane, ethylene and other small molecules. Compared with traditional thermal catalysis and existing photocatalytic technology, the present invention has higher decomposition efficiency and is more environmentally friendly. At the same time, it has good selectivity for small molecules and monomers and has industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 :Actual picture of the focusing reaction system.

[0024] Figure 2 : Schematic diagram of the reactor used in the examples and its dimensions. DETAILED DESCRIPTION

[0025] The present invention is further described below by means of specific embodiments, but the protection scope of the present invention is not limited thereto.

[0026] In the following examples, commercial polypropylene powder (a product of Merrill, molecular weight 6000±500) was used as polypropylene.

[0027] Example 1

[0028] Dissolve K3[Fe(CN)6](4.879g, 0.015mol) and La(NO3)3·6H2O(6.495g, 0.015mol) in 60ml deionized water, stir for 10min, add anhydrous citric acid (5.76g, 0.03mol), stir for another 10min, then transfer the mixed solution to a 100mL polytetrafluoroethylene hydrothermal autoclave, seal it and place it in a 180℃ oven for 12h. After natural cooling, wash it with ethanol and deionized water 4 times, dry it at 100℃ overnight, grind it evenly, put it in a muffle furnace, heat it to 800℃ at a heating rate of 5℃ per minute, and calcine it for 2h to obtain LaFeO3.

[0029] Weigh LaFeO3 (3.644g, 0.015mol), Sr(NO3)2·6H2O (3.175g, 0.015mol) and 40ml 3mol / L NaOH solution, mix and stir for 1h to make them dispersed evenly, then add TiO2 (1.198g, 0.015mol), stir for another 1h, and then transfer the mixed solution to a 150mL polytetrafluoroethylene hydrothermal autoclave, seal it and place it in a 130 degrees Celsius oven for 48h. After natural cooling, wash it with ethanol and deionized water 4 times, dry it at 80 degrees Celsius overnight, and grind it evenly to obtain 6.395g of SrTiO3 / LaFeO3 (abbreviated as: STO / LFO) with a molar ratio of SrTiO3 to LaFeO3 of 1:1.

[0030] Embodiment 2:

[0031] a. Weigh STO / LFO and polypropylene in a 9:1 (mass ratio), mix them evenly in a mortar, pour them into a tableting mold and press them into tablets with a diameter of 2 cm and a thickness of 0.1 cm for subsequent use.

[0032] b. Load the compressed tablets into the reactor (specific size as Figure 2 As shown in the figure, the device is sealed, CO2 (10mL / min) is introduced and leaks are checked, and the pressure of the reaction system is controlled at 0.70Mpa through the back pressure valve. After everything is completed, the light is turned on, the spot diameter is adjusted to 2cm, and the reaction is started. The light source for the reaction is a 1000W xenon lamp. Under the action of the lens, the light is concentrated in the reactor as much as possible, and the temperature in the reactor is 230-250℃.

[0033] c. After 6 hours of reaction, the slices were taken out, weighed and the products were calculated according to the gas chromatography results. It was finally determined that the polypropylene was completely decomposed, and the selectivities of methane, ethane, ethylene, propane, propylene and CO in the products were 19.08%, 4.18%, 3.80%, 0.22%, 11.91% and 60.82%, respectively.

[0034] Embodiment 3:

[0035] a. Weigh STO / LFO and polypropylene in a ratio of 9:1, mix them evenly in a mortar, pour them into a tableting mold and press them into tablets with a diameter of 3 cm and a thickness of 0.1 cm for subsequent use.

[0036] b. Load the pressed tablets into the reactor, seal the device, introduce N2 (10 mL / min) and check for leaks. Control the pressure of the reaction system at 0.70 MPa through the back pressure valve. Turn on the light after everything is completed, adjust the spot diameter to 3 cm, and start the reaction. The light source for the reaction is a 1000W xenon lamp. Under the action of the lens, the light is concentrated in the reactor as much as possible. The temperature in the reactor is 200-220°C.

[0037] c. After 6 hours of reaction, the slices were taken out, weighed and the products were calculated according to the gas chromatography results. It was finally determined that the polypropylene was completely decomposed, and the selectivities of methane, ethane, ethylene, propane, propylene and CO in the products were 16.54%, 15.80%, 2.23%, 12.13%, 53.31% and 0.00%, respectively.

[0038] Embodiment 4:

[0039] a. Weigh STO / LFO and polypropylene in a ratio of 9:1, mix them evenly in a mortar, pour them into a tableting mold and press them into tablets with a diameter of 3 cm and a thickness of 0.1 cm for subsequent use.

[0040] b. Load the pressed tablets into the reactor, seal the device, introduce CO2 (10mL / min) and check for leaks, and control the pressure of the reaction system at 0.10Mpa through the back pressure valve. After everything is completed, turn on the light, adjust the spot diameter to 3cm, and start the reaction. The light source used for the reaction is a 1000W xenon lamp. Under the action of the lens, the light is concentrated in the reactor as much as possible, and the temperature in the reactor is 200-220℃.

[0041] c. After 6 hours of reaction, the slices were taken out, weighed and the products were calculated according to the gas chromatography results. It was finally determined that the polypropylene was completely decomposed, and the selectivities of methane, ethane, ethylene, propane, propylene and CO in the products were 3.40%, 1.12%, 2.52%, 0.83%, 18.18% and 73.93%, respectively.

[0042] Embodiment 5:

[0043] a. Weigh STO / LFO and polypropylene in a ratio of 9:1, mix them evenly in a mortar, pour them into a tableting mold and press them into tablets with a diameter of 3 cm and a thickness of 0.1 cm for subsequent use.

[0044] b. Load the pressed tablets into the reactor, seal the device, introduce CO2 (10mL / min) and check for leaks, and control the pressure of the reaction system at 0.70Mpa through the back pressure valve. After everything is completed, turn on the light, adjust the spot diameter to 3cm, and start the reaction. The light source used for the reaction is a 1000W xenon lamp. Under the action of the lens, the light is concentrated in the reactor as much as possible, and the temperature in the reactor is 200-220℃.

[0045] c. After 6 hours of reaction, the slices were taken out, weighed and the products were calculated according to the gas chromatography results. It was finally determined that the polypropylene was completely decomposed, and the selectivities of methane, ethane, ethylene, propane, propylene and CO in the products were 12.92%, 7.16%, 3.08%, 6.20%, 42.89% and 27.76%, respectively.

[0046] Embodiment 6:

[0047] a. Weigh STO / LFO and polypropylene in a ratio of 9:1, mix them evenly in a mortar, pour them into a tableting mold and press them into tablets with a diameter of 3 cm and a thickness of 0.1 cm for subsequent use.

[0048] b. Load the pressed tablets into the reactor, seal the device, introduce CO2 (10mL / min) and check for leaks, and control the pressure of the reaction system at 0.70Mpa through the back pressure valve. After everything is completed, turn on the light, adjust the spot diameter to 4cm, and start the reaction. The light source used for the reaction is a 1000W xenon lamp. Under the action of the lens, the light is concentrated in the reactor as much as possible, and the temperature in the reactor is 180-200℃.

[0049] c. After 6 hours of reaction, the slices were taken out, weighed and the products were calculated according to the gas chromatography results. It was finally determined that the polypropylene was completely decomposed, and the selectivities of methane, ethane, ethylene, propane, propylene and CO in the products were 12.00%, 3.45%, 2.98%, 2.74%, 18.40% and 60.43%, respectively.

[0050] Embodiment 7:

[0051] a. Weigh STO / LFO and polypropylene in a ratio of 9:1, mix them evenly in a mortar, pour them into a tableting mold and press them into tablets with a diameter of 3 cm and a thickness of 0.1 cm for subsequent use.

[0052] b. Load the pressed tablets into the reactor, seal the device, introduce CO2 (10mL / min) and check for leaks, and control the pressure of the reaction system at 0.70Mpa through the back pressure valve. After everything is completed, turn on the light, adjust the spot diameter to 5cm, and start the reaction. The light source used for the reaction is a 1000W xenon lamp. Under the action of the lens, the light is concentrated in the reactor as much as possible, and the temperature in the reactor is 155-175℃.

[0053] c. After 6 hours of reaction, the slices were taken out, weighed and the products were calculated according to the gas chromatography results. It was finally determined that the polypropylene was completely decomposed, and the selectivities of methane, ethane, ethylene, propane, propylene and CO in the products were 17.63%, 6.75%, 2.50%, 5.22%, 21.85% and 46.04%, respectively.

[0054] Embodiment 8:

[0055] a. Weigh STO / LFO and polypropylene in a ratio of 8:2, mix them evenly in a mortar, pour them into a tableting mold and press them into tablets with a diameter of 3 cm and a thickness of 0.1 cm for subsequent use.

[0056] b. Load the pressed tablets into the reactor, seal the device, introduce CO2 (10mL / min) and check for leaks, and control the pressure of the reaction system at 0.70Mpa through the back pressure valve. After everything is completed, turn on the light, adjust the spot diameter to 3cm, and start the reaction. The light source used for the reaction is a 1000W xenon lamp. Under the action of the lens, the light is concentrated in the reactor as much as possible, and the temperature in the reactor is 200-220℃.

[0057] c. After 6 hours of reaction, the slices were taken out, weighed and the products were calculated according to the gas chromatography results. It was finally determined that the polypropylene was completely decomposed, and the selectivities of methane, ethane, ethylene, propane, propylene and CO in the products were 13.90%, 5.91%, 9.99%, 2.29%, 32.20% and 35.71%, respectively.

[0058] Embodiment 9:

[0059] a. Weigh STO / LFO and polypropylene in a ratio of 7:3, mix them evenly in a mortar, pour them into a tableting mold and press them into tablets with a diameter of 3 cm and a thickness of 0.1 cm for subsequent use.

[0060] b. Load the pressed tablets into the reactor, seal the device, introduce CO2 (10mL / min) and check for leaks, and control the pressure of the reaction system at 0.70Mpa through the back pressure valve. After everything is completed, turn on the light, adjust the spot diameter to 3cm, and start the reaction. The light source used for the reaction is a 1000W xenon lamp. Under the action of the lens, the light is concentrated in the reactor as much as possible, and the temperature in the reactor is 200-220℃.

[0061] c. After 6 hours of reaction, the slices were taken out, weighed and the products were calculated according to the gas chromatography results. It was finally determined that the polypropylene was completely decomposed, and the selectivities of methane, ethane, ethylene, propane, propylene and CO in the products were 11.64%, 9.23%, 2.17%, 4.94%, 39.86% and 32.16%, respectively.

[0062] Embodiment 10:

[0063] a. Weigh STO / LFO and polyethylene in a ratio of 9:1, mix them evenly in a mortar, pour them into a tableting mold and press them into tablets with a diameter of 3 cm and a thickness of 0.1 cm for subsequent use.

[0064] b. Load the pressed tablets into the reactor, seal the device, introduce CO2 (10mL / min) and check for leaks, and control the pressure of the reaction system at 0.70Mpa through the back pressure valve. After everything is completed, turn on the light, adjust the spot diameter to 3cm, and start the reaction. The light source used for the reaction is a 1000W xenon lamp. Under the action of the lens, the light is concentrated in the reactor as much as possible, and the temperature in the reactor is 200-220℃.

[0065] c. After 6 hours of reaction, the sheets were taken out, weighed and the products were calculated according to the gas chromatography results. It was finally determined that the polyethylene was completely decomposed, and the selectivities of methane, ethane, ethylene, propane, propylene and CO in the products were 5.65%, 2.17%, 5.58%, 1.68%, 5.18% and 79.73%, respectively.

[0066] The results of the above examples are summarized in Table 1.

[0067] Table 1 Summary of selectivity of STO / LFO photothermolysis polypropylene products in Example 2-10

[0068]

[0069] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. The present invention can be improved in many aspects without violating the overall concept, and those familiar with the technology can modify or change the above embodiments without violating the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the art without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for photothermal catalytic degradation of waste polypropylene, characterized in that: The method comprises: Mix the waste polypropylene and the catalyst, put them into a photothermal reaction environment, and achieve the directional decomposition of polypropylene into propylene and propane through photothermal catalysis under the protection of inert gas; The catalyst is SrTiO3 / LaFeO3; The photothermal reaction environment refers to: the light intensity in the reactor is 10 to 400 suns, the temperature is 100 to 500° C., and the pressure is 0.1 to 1 MPa.

2. The method for photothermal catalytic degradation of waste polypropylene according to claim 1, characterized in that: The catalyst is a heterojunction structure composed of LaFeO3 and SrTiO3, and the molar ratio of LaFeO3 to SrTiO3 is between 9:1 and 1:

9.

3. The method for photothermal catalytic degradation of waste polypropylene according to claim 2, characterized in that: The preparation method of the catalyst is as follows: (1) K3[Fe(CN)6] and La(NO3)3·6H2O were dissolved in deionized water, anhydrous citric acid was added, and the mixture was stirred and mixed. The mixture was transferred to a hydrothermal reactor, sealed, reacted at 180°C for 12 hours, naturally cooled to room temperature, washed, dried, ground evenly, and placed in a muffle furnace, heated to 800°C at a rate of 5°C / min, and calcined for 2 hours to obtain LaFeO3; (2) LaFeO3, Sr(NO3)2·6H2O and NaOH solution are mixed and dispersed uniformly, and TiO2 is added and stirred to mix uniformly. The mixed solution is transferred to a hydrothermal reactor, sealed, reacted at 130°C for 48 hours, naturally cooled to room temperature, washed, dried, and ground uniformly to obtain SrTiO3 / LaFeO3.

4. The method for photothermal catalytic degradation of waste polypropylene according to claim 1, characterized in that: The mass ratio of the catalyst to the polypropylene is between 9:1 and 7:

3.

5. The method for photothermal catalytic degradation of waste polypropylene according to claim 1, characterized in that: The inert gas is selected from N2 or CO2.

6. The method for photothermal catalytic degradation of waste polypropylene according to claim 1, characterized in that: The operation is as follows: Waste polypropylene and catalyst are mixed in solid form, compressed into tablets and placed in a reactor. The reactor is then fixed to a light-focusing reaction system and purged with inert gas for 10 minutes. The pressure in the reactor is raised to the required pressure, and light is focused into the reactor to provide the light intensity and the required reaction temperature. The reaction is started until the waste polypropylene is completely decomposed, and the product is discharged through a pipeline and detected by chromatography.

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