A sulfated iron-doped zirconia catalyst, its preparation method and application

Abstract

The present invention relates to a sulfated iron-doped zirconia catalyst, a preparation method thereof and an application thereof, belonging to the technical fields of catalyst synthesis and plastic degradation. The method includes: in the presence of water, zirconium oxychloride and an iron salt are subjected to a first stirring to obtain an intermediate I; after adjusting the pH value of the intermediate I to 9-10, a second stirring is carried out to obtain an intermediate II; after aging the intermediate II, solid-liquid separation is carried out, and the solid matter is taken for a first drying treatment to obtain an Fe / Zr composite; the Fe / Zr composite and a sulfuric acid solution are subjected to a third stirring to obtain an intermediate III; the concentration of the sulfuric acid solution is 0.5-1.2 mol / L; the intermediate III is successively subjected to a second drying treatment and calcination to obtain the sulfated iron-doped zirconia catalyst. The sulfated iron-doped zirconia catalyst provided by the present invention has a large specific surface area and a large number of acidic sites, can degrade plastics, and has a high degradation rate.

Description

Technical Field

[0001] The present invention relates to a sulfated iron-doped zirconia catalyst, a preparation method thereof, and an application thereof, belonging to the technical fields of catalyst synthesis and plastic degradation. Background Art

[0002] Currently, the annual global plastic production has exceeded 4 billion tons. They are difficult to degrade naturally in the environment and exist for a long time. Microplastics generated will enter the human body through food chains and other channels, endangering health. According to data released by the Organization for Economic Co-operation and Development (OECD) in 2019, the current situation of global waste plastic treatment is worrying: as high as 68% is treated by landfill or incineration, and another 22% flows directly into the natural environment without treatment due to lack of supervision. Only less than 9% is effectively recycled. Therefore, developing efficient and green plastic degradation and recycling technologies has become a major problem that urgently needs to be solved.

[0003] It is worth noting that polyethylene (PE), as a major plastic variety with a production proportion as high as 25%, has a very unsatisfactory recycling rate. Among the existing traditional treatment technologies, mechanical recycling or high-temperature incineration (>850°C) energy recovery methods have the disadvantages of long processes, high energy consumption, and volatile harmful gases (such as dioxins). In view of the limitations of traditional methods, more and more scientific researchers have begun to pay attention to and explore more green and efficient chemical recycling means. However, existing degradation methods usually select high-temperature conditions (>400°C), rely on noble metal catalysts (including iridium, platinum, etc.) or hydrogen assistance to promote the degradation of polyethylene and convert it into valuable chemicals. The above factors seriously restrict the large-scale application of degradation technologies.

[0004] Therefore, developing an efficient, durable and relatively inexpensive new catalyst system to promote plastic degradation and the directional conversion to high-value-added chemicals has become an important research direction in the current plastic recycling field. Summary of the Invention

[0005] Aiming at the problems existing in the above-mentioned prior art, one of the purposes of the present invention is to provide a preparation method of a sulfated iron-doped zirconia catalyst. This method regulates the raw material composition and properties of the catalyst, and introduces sulfate groups through the sulfonation reaction of iron-doped zirconia with a low-concentration sulfuric acid solution, synthesizing a sulfated iron-doped zirconia catalyst with a larger specific surface area and more acidic sites. The preparation method provided by the present invention is simple and convenient for industrial production.

[0006] The second object of the present invention is to provide a sulfonated iron-doped zirconia catalyst, which contains more acidic sites and a larger specific surface area compared with the unsulfonated iron-doped zirconia catalyst, can effectively activate the inert C-H bonds on the plastic to form carbocations, is conducive to the isomerization of C-H bonds in polyethylene and the occurrence of chain breakage, generates branched-chain products with lower molecular weights, and improves the degradation rate of plastics.

[0007] The third object of the present invention is to provide the application of the sulfonated iron-doped zirconia catalyst in degrading plastics. Degrading plastics with the catalyst provided by the present invention, compared with high-temperature incineration, the degradation temperature of the present invention is lower, and no additional hydrogen and noble metal catalysts are required to achieve a higher polyethylene degradation conversion rate. Further, the method provided by the present invention does not generate toxic waste gases, waste liquids and solid wastes.

[0008] In order to achieve the above object, the first aspect of the present invention is to provide a preparation method of a sulfonated iron-doped zirconia catalyst, which method includes:

[0009] (1) In the presence of water, zirconium oxychloride and an iron salt are subjected to a first stirring to obtain Intermediate I;

[0010] (2) After adjusting the pH value of the Intermediate I to 9-10, a second stirring is carried out to obtain Intermediate II;

[0011] (3) After aging the Intermediate II, solid-liquid separation is carried out, and the solid matter is taken for a first drying treatment to obtain an Fe / Zr composite;

[0012] (4) The Fe / Zr composite and a sulfuric acid solution are subjected to a third stirring to obtain Intermediate III; the concentration of the sulfuric acid solution is 0.5-1.2 mol / L;

[0013] (5) The Intermediate III is successively subjected to a second drying treatment and calcination to obtain the sulfonated iron-doped zirconia catalyst.

[0014] The present invention introduces sulfate groups in a low-concentration sulfuric acid solution (0.5-1.2 mol / L) into iron-doped zirconia by regulating the composition and properties of the catalyst. The sulfate groups have a strong interaction with Fe and Zr in the catalyst, change the chemical environment of the metal species, and thereby increase the acidic sites and specific surface area of the catalyst. This catalyst can effectively activate the inert C-H bonds in plastics to form carbocations, is conducive to the isomerization of C-H polymer chains in polyethylene and the occurrence of chain breakage, generates branched-chain products with lower molecular weights, and thus effectively promotes the chain-breaking degradation of polyethylene.

[0015] Further, Fe in the catalyst can promote redox, and the ionic radius of Fe 3+ is smaller than that of Zr 4+, iron can be incorporated into the lattice of ZrO2 to form a solid solution, further enhancing the catalytic performance without changing the structural stability of zirconia.

[0016] It should be noted that in step (1), the present invention has no special requirements for the amount of water used, and those known in the art can be adopted.

[0017] It should be noted that the present invention has no special requirements for the amount of the sulfuric acid solution, and it is only necessary to completely immerse the Fe / Zr composite.

[0018] As a preferred embodiment, the conditions of the first stirring include: the time is 1 - 1.5 h, and the stirring rate is 300 - 500 rpm.

[0019] As a preferred embodiment, the conditions of the first stirring include: the temperature is 10 - 35 °C.

[0020] As a preferred embodiment, the molar ratio of iron in the iron salt to zirconium in the zirconyl dichloride is 1:1.25 - 10.

[0021] As a preferred embodiment, the iron salt is selected from ferric nitrate and / or ferric chloride.

[0022] As a preferred embodiment, the conditions of the second stirring include: the time is 30 - 60 min, and the stirring rate is 300 - 500 rpm. Under this preferred condition, a homogenized colloid can be formed. If the stirring speed is too low, the pH regulator cannot be evenly stirred, making it difficult to form more colloids, which will lead to a decrease in the yield of the catalyst.

[0023] As a preferred embodiment, when adjusting the pH value, it is carried out under stirring conditions, and the stirring rate is 300 - 500 rpm.

[0024] It should be noted that the present invention has no special requirements for the reagent for adjusting the pH value, and those known in the art can be adopted. Exemplarily, ammonia water with a concentration of 1 - 10 wt% is used for adjustment.

[0025] As a preferred embodiment, the conditions of the first drying treatment include: the temperature is 100 - 120 °C, and the time is 24 - 30 h.

[0026] As a more preferred embodiment, the conditions of the first drying treatment include: the temperature is 100 - 110 °C.

[0027] As a preferred embodiment, the aging time is 12 - 14 h.

[0028] As a preferred embodiment, the concentration of the sulfuric acid solution is 0.5 - 1 mol / L. The catalyst prepared under this preferred condition has higher catalytic activity. If the concentration of the sulfuric acid solution is too high, the original composition and crystal lattice of the catalyst will be damaged; if the concentration is too low, the sulfonation efficiency will decrease. Both of the above situations will reduce the catalytic performance of the catalyst for plastics.

[0029] As a preferred embodiment, the conditions for the third stirring include: the time is at least 1 h, and the stirring rate is 200 - 300 rpm.

[0030] As a preferred embodiment, first perform solid-liquid separation on the intermediate III without washing, and perform a second drying treatment and calcination on the obtained solid.

[0031] As a preferred embodiment, the conditions for the calcination include: heating at a heating rate of 3 - 5 °C / min to 600 - 700 °C and holding for 3 - 4 h.

[0032] As a preferred embodiment, the conditions for the second drying treatment include: the temperature is 100 - 120 °C, and the time is 12 - 20 h.

[0033] As a preferred embodiment, the calcination is carried out in a tubular furnace, and the calcination atmosphere is an air atmosphere.

[0034] The second aspect of the present invention provides a sulfated iron-doped zirconia catalyst prepared by the preparation method of a sulfated iron-doped zirconia catalyst described in the foregoing first aspect.

[0035] As a preferred embodiment, in the sulfated iron-doped zirconia catalyst, the molar content of Fe element is 3.53% - 14.12%, the molar content of Zr element is 27.95% - 29.00%, the molar content of O element is 55.93% - 65.92%, and the molar content of S element is 1.55% - 2.00%.

[0036] The third aspect of the present invention provides the application of a sulfated iron-doped zirconia catalyst in degrading plastics.

[0037] As a preferred embodiment, the application method includes: in an inert atmosphere, in a reaction kettle, mixing and reacting a sulfated iron-doped zirconia catalyst with plastics.

[0038] As a preferred embodiment, first mix the sulfated iron-doped zirconia catalyst with plastics and grind them to an average particle size of 50 - 150 µm, and then carry out the mixing reaction.

[0039] As a preferred embodiment, the inert atmosphere is a nitrogen atmosphere and / or an argon atmosphere.

[0040] As a preferred embodiment, the conditions for the mixing reaction include: a pressure of 0.2 - 0.6 MPa, a temperature of 260 - 280 °C, and a time of 2 - 24 h.

[0041] As a more preferred embodiment, the time for the mixing reaction is 12 - 24 h. Further preferably, it is 16 - 22 h. Under the conditions of 16 - 22 h, the conversion rate of the plastic is higher.

[0042] As a preferred embodiment, the conditions for the mixing reaction further include: a stirring rate of 150 - 200 rpm.

[0043] As a preferred embodiment, the mass ratio of the iron sulfide-doped zirconia catalyst to the plastic is 1:1.5 - 2.5.

[0044] As a preferred embodiment, the plastic is selected from at least one of polyethylene plastic, polypropylene plastic, and polyvinyl chloride plastic, and more preferably polyethylene plastic.

[0045] Compared with the prior art, the present invention has at least the following advantages:

[0046] (1) The iron sulfide-doped zirconia catalyst provided by the present invention has a large number of acidic sites and a larger specific surface area, can efficiently degrade plastics, and the degradation reaction is more green chemistry and has strong applicability.

[0047] (2) When the catalyst provided by the present invention is used to degrade plastics, compared with high-temperature incineration, the degradation temperature of the present invention is lower, and without the need to additionally provide hydrogen and noble metal catalysts, a high polyethylene degradation conversion rate can be achieved. Further, the method provided by the present invention does not produce toxic waste gases, waste liquids, and solid wastes. Description of the Drawings

[0048] Figure 1 is the X-ray diffraction pattern of Catalyst 1 and Catalyst D-1;

[0049] Figure 2 is the SEM and EDS diagrams of Catalyst 1; Figure 2 A in is the SEM diagram of Catalyst 1; Figure 2 B, C, and D in are the EDS diagrams of the Fe element, S element, and Zr element of Catalyst 1, respectively;

[0050] Figure 3 is the SEM and EDS diagrams of Catalyst D-1; Figure 3 A in is the SEM diagram of Catalyst D-1; Figure 3 B, C, and D in are the EDS diagrams of the Fe element, Zr element, and O element of Catalyst D-1, respectively;

[0051] Figure 4is the infrared spectrum of Catalyst 1 and Catalyst D-1;

[0052] Figure 5 is the X-ray photoelectron spectrum of Catalyst 1 and Catalyst D-1; Figure 5 the left in is the Zr 3d spectrum, Figure 5 the right in is the Fe 2p spectrum;

[0053] Figure 6 is the nitrogen adsorption-desorption isotherm of Catalyst D and Catalyst D-1;

[0054] Figure 7 is the gel permeation chromatography of low-density polyethylene in the application example and the products obtained after plastic degradation in Application Examples 1-5. Detailed implementation manners

[0055] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0056] In the present invention, room temperature refers to 25±2°C.

[0057] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by those skilled in the art without creative efforts still fall within the protection scope of the present invention.

[0058] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or can be prepared by existing methods.

[0059] Example 1

[0060] (1) Respectively take 16.11 g of zirconium oxychloride octahydrate and 2.02 g of iron nitrate and dissolve them in 100 mL of deionized water, stir at room temperature for 1 h, and the stirring rate is 400 rpm;

[0061] (2) Add ammonia water with a concentration of 10 wt% to the solution obtained in step (1), stir while dropping (the stirring rate is 400 rpm), adjust the pH value of the solution to 9, and then continue to stir for 30 min under the condition of 400 rpm;

[0062] (3) Stop stirring. Cover the solution obtained in step (2) with plastic wrap at room temperature to prevent contamination, and then place it in a fume hood for further aging for 12 h;

[0063] (4) After aging, filter and wash the yellow colloid obtained after filtration with deionized water. Place the colloid in an oven at 110 °C and dry it for 24 h;

[0064] (5) Take the powder obtained in step (4), disperse it in 1 mol / L H2SO4 solution, and continue stirring at room temperature for 1 h (stirring rate is 250 rpm), then perform solid-liquid separation without washing. Take the solid and dry it in a drying oven at 100 °C for 12 h.

[0065] (6) After drying, take the powder to make tablets, put them into a tubular furnace, and heat them to 650 °C at a heating rate of 5 °C / min in a dry air atmosphere and calcine for 3 h. The calcined sample is the sulfated iron-doped zirconia catalyst, named Catalyst 1.

[0066] Example 2

[0067] This example is carried out by referring to a method similar to that of Example 1. The difference is that the concentration of the sulfuric acid solution in step (5) is adjusted to 0.5 mol / L, and the volume dosage remains unchanged, to obtain Catalyst 2.

[0068] Comparative Example 1

[0069] (1) Respectively take 16.11 g of zirconium oxychloride octahydrate and 2.02 g of iron nitrate and dissolve them in 100 mL of deionized water, stir at room temperature for 1 h, and the stirring rate is 400 rpm;

[0070] (2) Add ammonia water with a concentration of 10 wt% to the solution obtained in step (1), stir while dropping (stirring rate is 400 rpm), adjust the pH value of the solution to 9, and then continue to stir for 30 min under the condition of 400 rpm;

[0071] (3) Stop stirring. Cover the solution obtained in step (2) with plastic wrap at room temperature to prevent contamination, and then place it in a fume hood for further aging for 12 h;

[0072] (4) After aging, filter and wash the yellow colloid obtained after filtration with deionized water. Place the colloid in an oven at 110 °C and dry it for 24 h;

[0073] (5) After drying, take the powder to make tablets, put them into a tubular furnace, and heat them to 650 °C at a heating rate of 5 °C / min in a dry air atmosphere and calcine for 3 h. The calcined sample is the iron-doped zirconia catalyst, named Catalyst D-1.

[0074] Application Example

[0075] The catalyst prepared in the above example was used for the degradation experiment of polyethylene plastics. The specific steps were as follows: 500 mg of low-density polyethylene (LDPE, with a molecular weight of 150,000 kDa) and 250 mg of the catalyst were pre-ground and stirred in a mortar for 5 min until the average particle size was 100 μm. Subsequently, the uniformly mixed polyethylene and the catalyst were transferred to the inner lining of a high-pressure reactor, and the polyethylene plastic was degraded under a nitrogen atmosphere at a temperature of 280 °C and a stirring paddle speed of 150 rpm to obtain a depolymerized oily product. The specific types of substances, reaction time, and test results are shown in Table 1.

[0076] Calculation method for polyethylene conversion rate: The mass conversion rate was measured by weighing the change in the mass of polyethylene plastic before and after the reaction. Conversion rate = (initial plastic mass - plastic mass after reaction) / initial plastic mass × 100%.

[0077]

[0078] Test Example

[0079] Catalyst 1 and catalyst D-1 were subjected to X-ray diffraction (XRD) tests, and the obtained spectra are as Figure 1 shown. It can be seen from Figure 1 that the sulfated iron-doped zirconia catalyst (catalyst 1) and the iron-doped zirconia catalyst (catalyst D-1) have been successfully synthesized. The positions of the main diffraction peaks of the two catalysts are basically the same as those of tetragonal zirconia, indicating that the main crystal phase is tetragonal zirconia. Moreover, it can be seen from the X-ray diffraction pattern of catalyst 1 that the introduction of SO4 2- has reduced the crystallinity of the catalyst.

[0080] Catalyst 1 was observed by scanning electron microscopy (SEM) to obtain the SEM and EDS diagrams of catalyst 1, as shown in Figure 2 . It can be seen from Figure 2 that the sulfated iron-doped zirconia catalyst has an irregular shape, and the iron, sulfur, and zirconium elements are evenly distributed, which can prove that the catalyst has been successfully synthesized and sulfated by SO4 2- .

[0081] Catalyst D-1 was observed by scanning electron microscopy (SEM) to obtain the SEM and EDS diagrams of catalyst D-1, as shown in Figure 3 . It can be seen from Figure 3 that the iron-doped zirconia catalyst has an irregular shape, and the iron and zirconium elements are evenly distributed.

[0082] The elemental content analysis of the catalysts was carried out through the SEM and EDS diagrams of catalyst 1 and catalyst D-1, and the specific results are shown in Table 2.

[0083]

[0084] The Fourier transform infrared spectroscopy (FT-IR) characterization was carried out on catalyst 1 and catalyst D-1, and the specific results are shown in Figure 4 . From Figure 4 , it can be seen that for catalyst 1, stretching vibration peaks representing S-O and S=O bonds appear in the wavelength range of 1000 cm -1 to 1400 cm -1 , which proves that sulfated iron-doped zirconia (catalyst 1) contains sulfate groups, while iron-doped zirconia (catalyst D-1) does not contain sulfate groups.

[0085] The X-ray photoelectron spectroscopy (XPS) test was carried out on catalyst 1 and catalyst D-1, and the specific results are shown in Figure 5 . It can be known from Figure 5 that in the Zr 3d spectrum, both Zr 3d 5 / 2 (181.7 eV) and Zr 3d 3 / 2 (184.1 eV) belong to Zr 4+ . After sulfonation, the Zr 3d spectrum shifted to the left by 0.41 eV, which is attributed to the combination of sulfate SO4 with Zr species, resulting in a decrease in the electron density around Zr, so it shifts to the high-energy direction. In the Fe 2p spectrum, both Fe 2p 3 / 2 (711.30 eV) and Fe 2p 1 / 2 (724.67 eV) belong to Fe 3+ . After sulfonation, the Fe 2p spectrum shifted to the left by 0.23 eV. However, the shifting trend of Zr 3d (+0.42 eV) is larger than that of Fe 2p (+0.23 eV), indicating that the interaction between Zr species and SO4 is stronger than that between Fe species and SO4.

[0086] The nitrogen adsorption-desorption specific surface area measurement (BET) was carried out on catalyst 1 and catalyst D-1, and the specific results are shown in Table 3 and Figure 6 . It can be seen from Table 3 and Figure 6 that the specific surface area of catalyst 1 is 97.0335 m 2 / g, and the specific surface area of catalyst D-1 is 37.2469 m 2 / g. The specific surface area of catalyst 1 is more than twice that of catalyst D-1, which can contact more reactants and adsorb more molecules in the reaction, contributing to the forward progress of the degradation reaction.

[0087]

[0088] The low-density polyethylene used in the application example and the products obtained after the degradation of the polyethylene plastics in Application Examples 1-5 were characterized by gel permeation chromatography (GPC) to determine the polymer molecular weight and its distribution. The specific results are shown in Figure 7 . It can be seen from Figure 7 that the peak of the logarithmic molecular weight of the low-density polyethylene appears at about 5.0, indicating a larger molecular weight. While the peak of the logarithmic molecular weight of the oily product obtained by using Catalyst 1 as the degradation catalyst and keeping it warm for 18 h appears at about 3.0, indicating a smaller molecular weight. This shows that the polyethylene plastics have been successfully degraded by using the catalyst provided by the present invention.

[0089] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. Application of sulfated iron-doped zirconia catalyst in degrading plastics, characterized in that: In an inert atmosphere, in a reaction kettle, the sulfated iron-doped zirconia catalyst and plastics are mixed and reacted; The preparation method of the sulfated iron-doped zirconia catalyst comprises the following steps: (1) In the presence of water, zirconium oxychloride and an iron salt are subjected to a first stirring to obtain intermediate I; (2) After adjusting the pH value of the intermediate I to 9-10, a second stirring is carried out to obtain intermediate II; (3) After aging the intermediate II, solid-liquid separation is carried out, and the solid matter is taken for a first drying treatment to obtain an Fe / Zr composite; (4) The Fe / Zr composite and a sulfuric acid solution are subjected to a third stirring to obtain intermediate III; the concentration of the sulfuric acid solution is 0.5-1.2 mol / L; (5) The intermediate III is successively subjected to a second drying treatment and calcination to obtain the sulfated iron-doped zirconia catalyst.

2. Use of a sulfated iron-doped zirconia catalyst according to claim 1 in the degradation of plastics, characterized in that: The conditions of the first stirring include: the time is 1-1.5 h, and the stirring rate is 300-500 rpm; And / or, the molar dosage ratio of iron in the iron salt to zirconium in the zirconium oxychloride is 1:1.25-10.

3. Use of a sulfated iron-doped zirconia catalyst according to claim 1 or 2 in the degradation of plastics, characterized in that: The conditions of the second stirring include: the time is 30-60 min, and the stirring rate is 300-500 rpm; And / or, when adjusting the pH value, it is carried out under the condition of stirring, and the stirring rate is 300-500 rpm.

4. Use of a sulfated iron-doped zirconia catalyst according to claim 1 or 2 in the degradation of plastics, characterized in that: The conditions of the first drying treatment include: the temperature is 100-120 °C, and the time is 24-30 h; And / or, the aging time is 12-14 h.

5. Use of a sulfated iron-doped zirconia catalyst according to claim 1 or 2 in the degradation of plastics, characterized in that: The concentration of the sulfuric acid solution is 0.5-1 mol / L; And / or, the conditions of the third stirring include: the time is at least 1 h, and the stirring rate is 200-300 rpm.

6. Use of a sulfated iron-doped zirconia catalyst according to claim 1 or 2 in the degradation of plastics, characterized in that: The conditions of the calcination include: heating up to 600-700 °C at a heating rate of 3-5 °C / min and holding for 3-4 h.

7. Use of a sulfated iron-doped zirconia catalyst according to claim 1 or 2 in the degradation of plastics, characterized in that: In the sulfated iron-doped zirconia catalyst, the molar content of Fe element is 3.53%-14.12%, the molar content of Zr element is 27.95%-29.00%, the molar content of O element is 55.93%-65.92%, and the molar content of S element is 1.55%-2.00%.

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