Application of a metal-solid acid bifunctional catalyst in the hydrocracking of polystyrene plastics

Abstract

A metal-acid bifunctional catalyst is used in hydrocracking, and the invention relates to the field of hydrocracking of polystyrene. The preparation method of the catalyst is to directly prepare the metal-acid supported catalyst by a one-step hydrothermal method. The catalyst of the present invention is a bifunctional catalyst including a metal and an acidic site. The metal site is mainly on the surface of the support, can be fully in contact with the substrate, has a strong ability to activate hydrogen, and has many acidic sites, which is conducive to the breaking of carbon-carbon bonds during the hydrocracking process. The present invention provides a catalyst that can react in one step under mild reaction conditions and is applied in a kettle reactor or a fixed-bed reactor, efficiently hydrocracking polystyrene, with high catalytic activity and selectivity of the target product. At the same time, the method is simple during the synthesis of the catalyst, and it is easy to prepare and suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of waste plastic hydrogenation degradation and relates to the application of a metal-solid acid bifunctional catalyst in the cracking of polystyrene plastic. Background Art

[0002] Polystyrene (PS) is the fourth most produced polymer globally, dominating the market thanks to its cost-effectiveness, excellent processing properties, low density, clear appearance, dimensional stability, and ease of radiation sterilization. Polystyrene has diverse applications, ranging from low-end uses (such as standard packaging and transparent storage containers) to high-end applications (such as electronics and automotive materials). However, the vast majority of polystyrene is not recycled and becomes waste plastic after a single use. Due to its high stability, low density, and hydrophobicity, polystyrene degrades extremely slowly. The large production volumes, slow degradation rate, and complex recycling of polystyrene result in its high concentration in landfills and the environment, even entering the oceans, with serious ecological impacts. Common chemical recycling methods for polystyrene include pyrolysis, microwave-assisted pyrolysis, hydrogenolysis, catalytic cracking, and hydrocracking. The depolymerization of polystyrene involves initiation, depolymerization propagation, and free radical coupling, transforming polymer chains into free radical, cationic, or anionic transition states. During the degradation process, at lower temperatures, no volatile products are produced. However, above 300°C, volatile products and oligomers such as dimers and trimers are produced. Above 350°C, further volatile products such as toluene, ethylbenzene, cumene, styrene, naphthalene, and indane are produced. Conventional processes require excessively high reaction temperatures and long reaction times.

[0003] Bifunctional metal-solid acid catalytic systems have been extensively studied for the conversion of plastics. Metal nanoparticles possess excellent hydrogenation and dehydrogenation capabilities, while solid acid supports possess good acidity and strong benzene ring binding. The interaction between these two can promote the degradation of polystyrene. Currently, no catalysts have been combined to hydrocracking polystyrene to produce a variety of monomer molecules. Summary of the Invention

[0004] Aiming at the problems existing in the traditional polystyrene degradation process, the present invention proposes a novel polystyrene hydrocracking catalyst and application thereof.

[0005] In order to achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] The invention discloses an application of a metal-acid catalyst in a hydrocracking process, wherein the hydrocracking process is the hydrocracking of waste aromatic hydrocarbon plastics.

[0007] The metal-acid bifunctional catalyst is prepared as follows: a metal salt, a niobium source, an ammonium source, and an additive are added to ultrapure water, stirred for a predetermined period of time, and then subjected to a hydrothermal treatment. After the hydrothermal reaction, the solution is filtered and dried, then calcined and reduced in a hydrogen atmosphere to obtain a solid catalyst.

[0008] Preferably, the metal salt can be nitrate, hydrochloride, sulfate, organic salt of platinum, nickel, copper, or any one or more mixtures thereof.

[0009] Preferably, the niobium source is any one or more of niobium pentachloride, niobium oxide, ammonium niobium oxalate, niobium oxalate, and niobium tartrate.

[0010] Preferably, the ammonium source is ammonia water or any one or more of ammonium nitrate, hydrochloride, sulfate, organic salt, etc., the auxiliary agent is any one or more of metal nitrate, metal hydrochloride or metal organic salt of zirconium, titanium, and cerium, and the mass ratio of niobium source: ammonium: metal: auxiliary agent is (50-78): (0.5-6): (0.5-8): (0.1-8).

[0011] Preferably, the hydrothermal temperature is 120-220°C, the time is 12-72 hours, the calcination temperature is 400-600°C, the calcination time is 3-5 hours, and the reduction reaction temperature is 200-500°C.

[0012] Preferably, the hydrocracking process is the hydrocracking of polystyrene.

[0013] Preferably, the reactor is a kettle reactor, the raw material is polystyrene, the reaction temperature is 200-300° C., the reaction atmosphere is hydrogen, the pressure is 1-3 MPa, and the reaction is a one-step reaction.

[0014] Preferably, the reactor is a fixed bed reactor, the raw material is polystyrene, the reaction temperature is 200-260°C, the reaction atmosphere is hydrogen, the pressure is 1-3 MPa, and the mass space velocity of the raw material is 1-10 h -1 .

[0015] The catalyst of the present invention is prepared using a one-step hydrothermal method. Metal particles are uniformly dispersed on the surface of a carrier, and the catalyst is obtained after drying, calcination, and reduction. The prepared catalyst is then applied to the hydrogenation degradation of polystyrene plastics. The catalytic products are primarily benzene, ethylbenzene, cumene, indane, and 1-methylindane, with superior catalytic performance compared to similar catalysts. This provides a new approach for the degradation of polystyrene plastics and the production of aromatic compounds.

[0016] Compared with the prior art, the advantages and positive effects of the present invention are:

[0017] 1. The metal-acid catalyst prepared in the present invention has high catalytic activity under mild conditions, and the reaction is a one-step reaction.

[0018] 2. In the hydrocracking reaction of polystyrene plastics, the catalyst of the present invention achieves the best conversion effect on polystyrene, and the selectivity for the main aromatic products is greater than 75%.

[0019] 3. The catalyst prepared by the present invention has a strong metal-support interaction, so the active components are stable and not easily lost during the reaction. After multiple reactions and regeneration, the catalyst performance can still maintain about 90% of the initial performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the TEM characterization image of the catalyst prepared in Example 1.

[0021] Figure 2 These are XRD characterization patterns of the catalysts prepared in Examples 1, 3, and 5.

[0022] Figure 3 This is the product selectivity distribution diagram of the catalytic conversion of polystyrene using the bifunctional catalyst in Example 1.

[0023] Figure 4 This is the distribution diagram of the degradation products of polystyrene hydrogenation by the dual-functional catalyst in Example 2.

[0024] Figure 5 The figure shows the comparison of ammonia adsorption and desorption between Example 1 and Comparative Examples 1, 2 and 3. DETAILED DESCRIPTION

[0025] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described below in conjunction with specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0026] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0027] In the following embodiments or comparative examples, the operation process of the kettle reactor is as follows:

[0028] The catalyst was mixed with polystyrene (polystyrene / catalyst mass ratio was 20:1) and placed in a reactor. After hydrogen replacement for 3-5 times, hydrogen was charged into the reactor. The hydrogen charging amount was adjusted to the reaction pressure. The temperature heater was turned on and the reactor temperature was gradually increased to the reaction temperature. The reaction time was controlled to test the catalyst performance. After the reaction was completed, condensed water was passed through the outside of the reactor to cool it to room temperature. The gas and liquid products were collected and the corresponding chromatograms were used for data analysis.

[0029] The fixed bed reactor operation process is as follows:

[0030] 2 grams of polystyrene and 0.1 grams of catalyst were mixed and ground into a uniform mixture, then pelletized. The pellets were then placed in a quartz tube. The pressure, mass space velocity, and hydrogen to feedstock ratio within the tube were adjusted to the desired values. The reaction temperature was gradually raised to the desired reaction temperature to initiate the reaction. The temperature in the reactor was gradually increased, and after 1.5 hours of equilibrium, the product was sampled and analyzed by chromatography.

[0031] The product conversion and selectivity were calculated according to the following formula:

[0032] Polystyrene conversion rate = (mass before reaction - mass of residual solid after reaction) / mass before reaction * 100%.

[0033] Main product selectivity = main product mass / (mass before reaction - mass of residual solid after reaction)*100%.

[0034] In each embodiment of the present invention, products with higher economic value are selected as the main products to calculate the reaction selectivity. The selected main products include: benzene, ethylbenzene, isopropylbenzene, indane and 1-methylindane.

[0035] Example 1

[0036] 20g of niobium pentachloride, 3g of zirconium sulfate, and 1.0g of platinum nitrate were weighed and added sequentially to a beaker containing 50ml of ultrapure water. While stirring, 20ml of 1mol / L ammonia aqueous solution was slowly added dropwise at 600 rpm. The total addition time was controlled to be approximately 3 minutes. After the addition was completed, stirring was continued for 1 hour. The solution was then transferred to the polytetrafluoroethylene liner of a hydrothermal autoclave, sealed, and placed in a 200°C oven for a hydrothermal reaction for 24 hours. After the reaction was completed, the autoclave was cooled to room temperature, the liner was removed, the solution was filtered, and the filter cake was washed several times with 1L of ultrapure water. The washed solid was then dried in a 100°C oven for 12 hours. It was then calcined in a muffle furnace under static air at 400°C for 4 hours. The catalyst was then reduced in a tube furnace under a hydrogen atmosphere at a rate of 2°C / min to 300°C for 3 hours. After the reduction was complete, the catalyst was naturally cooled to room temperature to obtain the Pt / Nb-Zr-O catalyst.

[0037] The catalyst prepared in this example was dispersed in an ethanol solution and characterized by TEM. The results are as follows: Figure 1 ,from Figure 1 It can be seen from the figure that the platinum nanoparticles prepared in this example are uniformly loaded on the surface of the catalyst.

[0038] The catalyst prepared in this example was characterized by XRD. Figure 2 ,from Figure 2 It can be seen from the figure that the metal nanoparticles are small in size and evenly dispersed during the preparation process of the catalyst.

[0039] Polystyrene (molecular weight 4 kDa) was added to the autoclave reactor and heated at 260 o C, hydrogen pressure is 3MPa, reaction time is 5 hours; the product selectivity distribution is as follows Figure 3 ,from Figure 3 It can be seen that the products after polystyrene hydrocracking are mainly aromatic compounds. The five main products, benzene, ethylbenzene, isopropylbenzene, indane and 1-methylindane, have high selectivity and high economic value.

[0040] Example 2

[0041] The catalyst preparation method and application were the same as in Example 1. Reaction conditions: hydrogen was introduced into the fixed bed reactor, the reaction temperature was 200 degrees Celsius, the sampling time was 8 hours, the reaction hydrogen pressure was 2 MPa, and the mass space velocity (WHSV) of the feedstock was 8.

[0042] The product obtained by the reaction of this embodiment was analyzed, and its selectivity distribution diagram is shown in FIG. Figure 4 ,from Figure 4 It can be seen that the products after hydrocracking of polystyrene are mainly compounds such as benzene, ethylbenzene, isopropylbenzene, indane and 1-methylindane, which proves that the catalyst has good hydrodegradation ability.

[0043] Example 3

[0044] This embodiment is consistent with the embodiment 1 except for special explanation.

[0045] 20g of niobium oxide, 3g of titanium sulfate, and 1.0g of nickel nitrate were weighed and added to a beaker containing 50ml of ultrapure water. While stirring, 20ml of 1mol / L ammonium nitrate was slowly added dropwise at a stirring rate of 600 rpm. The addition time was controlled to be approximately 10 minutes. After the addition was completed, stirring was continued for 1 hour. The solution was then transferred to the polytetrafluoroethylene liner of a hydrothermal autoclave, sealed, and then hydrothermally reacted in an oven at 200°C for 24 hours. After the hydrothermal reaction, it was cooled to room temperature. The liner of the hydrothermal autoclave was removed, the solution was filtered, and the filter cake was washed with 1L of ultrapure water. It was then dried in a 100°C oven for 12 hours and subsequently calcined at 400°C in a muffle furnace under static air for 4 hours. The catalyst No. 2, Ni / Nb-Ti-O, was then reduced in a tube furnace under a hydrogen atmosphere at a rate of 2°C / min to 300°C for 3 hours. The catalyst was then naturally cooled to room temperature to obtain. Reaction conditions: polystyrene was added to a kettle reactor, the reaction temperature was 260 degrees Celsius, the reaction time was 5 hours, and the reaction hydrogen pressure was 3 MPa.

[0046] Example 4

[0047] The catalyst preparation method and application were the same as those in Example 3. Reaction conditions: hydrogen was introduced into the fixed bed reactor, the reaction temperature was 200 degrees Celsius, the sampling time was 8 hours, the reaction hydrogen pressure was 2 MPa, and the mass space velocity (WHSV) of the feedstock was 8.

[0048] The product obtained by hydrocracking polystyrene in this embodiment was analyzed, and its selectivity distribution diagram is shown as follows: Figure 4 As can be seen from the figure, the products after polystyrene hydrocracking are mainly benzene, ethylbenzene, isopropylbenzene, indane and 1-methylindane, which proves that the catalyst has good hydrogenation degradation ability.

[0049] Example 5

[0050] 20g of ammonium niobium oxalate, 3g of cerium sulfate, and 1.0g of copper nitrate were weighed and added to a beaker containing 50ml of ultrapure water. While the mixture was stirring, 20ml of 1mol / L ammonium nitrate was slowly added dropwise at a stirring rate of 500 rpm. The addition time was controlled within 2 minutes. Stirring was continued for 1 hour after the addition was completed. The solution was then transferred to the polytetrafluoroethylene-lined liner of a hydrothermal autoclave, sealed, and then hydrothermally reacted in an oven at 200°C for 24 hours. After the reaction, the mixture was cooled to room temperature, the liner of the hydrothermal autoclave was removed, the solution was filtered, and the filter cake was washed with 1L of ultrapure water. The mixture was then dried in a 100°C oven for 12 hours. Subsequently, the mixture was calcined in a muffle furnace under static air at 400°C for 4 hours. The mixture was then placed in a tube furnace under a hydrogen atmosphere and heated at 2°C / min to 300°C for 3 hours. After the reduction, the mixture was naturally cooled to room temperature to obtain catalyst No. 3, Cu / Nb-Ce-O. Reaction conditions: polystyrene was added to a kettle reactor, the reaction temperature was 260 degrees Celsius, the reaction time was 5 hours, and the reaction hydrogen pressure was 3 MPa.

[0051] Example 6

[0052] The catalyst preparation method and application were the same as in Example 5. Reaction conditions: a mixture of hydrogen and argon was introduced into a fixed bed reactor, the reaction temperature was 200°C, the sampling time was 12 hours, the reaction hydrogen pressure was 2 MPa, and the mass space velocity (WHSV) of the feedstock was 8.

[0053] Catalyst Performance Testing: The catalyst obtained in Examples 1 and 2 is designated as Catalyst No. 1, the catalyst obtained in Examples 3 and 4 is designated as Catalyst No. 2, and the catalyst obtained in Examples 5 and 6 is designated as Catalyst No. 3. Catalyst No. 1 was tested for its performance in hydrocracking of polystyrene (molecular weight, 4 kDa) in a kettle reactor; Catalyst No. 2 was tested for its performance in hydrocracking of polystyrene (molecular weight, 4 kDa) in a fixed-bed reactor; and Catalyst No. 3 was tested for its performance in hydrocracking of polystyrene (molecular weight, 4 kDa) in a fixed-bed reactor.

[0054] The above method was followed and the catalyst performance was shown in Table 1.

[0055] Table 1 Conversion comparison of catalysts in various examples

[0056]

[0057] As can be seen from Table 1, the catalyst prepared by the present invention can efficiently achieve the hydrocracking technical effect of polystyrene at low temperature and low pressure. Taking Example 1 as an example, the polystyrene conversion rate is 97.8%, and the main product selectivity is as high as 75%. In addition, from the test results of each embodiment, when different metal-acid catalysts adopt a fixed bed reactor, the catalytic degradation trend is the same as that of the kettle reactor, indicating that the difference in the reactor does not significantly change the performance of the catalyst. In the bifunctional catalyst, the metal component of the catalyst has the ability to add dehydrogenation, which can strengthen the activation of hydrogen and form active Nb-H and Nb-OH species through hydrogen overflow, thereby significantly promoting the rupture of the C-C bond and then promoting depolymerization. The solid acid carrier can provide strong acidity and has a strong benzene ring binding ability, so that the intermediate product (polymer / dimer) is converted into a volatile target product (benzene, ethylbenzene, etc.). Both are particularly important in the catalytic reaction and can significantly affect the activity of the catalyst, thereby affecting the production rate and selectivity of the product. Therefore, the combination of the two can achieve good degradation effect with low energy consumption, environmental protection, and high efficiency under mild conditions. Within the scope of the examples, the stronger the acidity of the catalyst, the better the catalytic effect. The preparation conditions of the catalyst have a significant impact on the performance of the catalyst. First, the ratio of niobium source, ammonium source, additive, and metal. Too high or too low a ratio will cause changes in the acidity of the catalyst. Second, the influence of synthesis conditions. The time and temperature of catalyst synthesis can also lead to performance differences. The longer the hydrothermal synthesis time and the higher the temperature, the weaker the acidity and the correspondingly weakened catalytic effect of the catalyst.

[0058] Comparative Example 1

[0059] The catalyst was prepared by weighing 20g of niobium pentachloride and 4g of zirconium sulfate (the mass fraction of the additive and niobium source was 10%). The remaining preparation process was the same as in Example 1. Reaction conditions: polystyrene was added to a kettle reactor, the reaction temperature was 260°C, the reaction time was 5 hours, and the reaction hydrogen pressure was 3 MPa. Testing showed a conversion rate of 78% and a selectivity of 58.5%. Therefore, when the amount of the zirconium sulfate additive added was too high, the catalytic performance was significantly reduced.

[0060] Comparative Example 2

[0061] During the catalyst preparation process, the hydrothermal conditions were changed to an oven at 220°C for 72 hours. The remaining preparation process was the same as in Example 1. Reaction conditions: polystyrene was added to the autoclave reactor, the reaction temperature was 260°C, the reaction time was 5 hours, and the reaction hydrogen pressure was 3 MPa. Testing showed a conversion rate of 66.5% and a selectivity of 49.2%. This comparative example shows that the catalytic conversion rate of polystyrene decreased significantly with increasing hydrothermal synthesis temperature and time.

[0062] Comparative Example 3

[0063] The catalyst was prepared using a one-step hydrothermal method with the addition of 1.5 g of platinum nitrate, resulting in a 20% metal to support ratio by mass in this comparative example. The remaining preparation process was the same as in Example 1. Reaction conditions: polystyrene was added to a kettle reactor, the reaction temperature was 260°C, the reaction time was 5 hours, and the hydrogen pressure was 3 MPa. Testing revealed a conversion of 62.5% and a selectivity of 42.5%. This comparative example demonstrates that excessive addition of platinum significantly reduces catalytic performance.

[0064] Comparative Example 4

[0065] Weigh 0.5 g of platinum nitrate and 2.0 g of ultrapure water, dissolve the platinum nitrate in water, ultrasonically dissolve it, and slowly drop it into 4.0 g of alumina support while stirring until it is evenly mixed. Let it stand in static air for 2 h, then put the beaker into an oven at 100 o C overnight, grind the catalyst evenly, and place it in a muffle furnace at 400 o C was calcined for 3 h and then heated in a tube furnace under a hydrogen atmosphere at 300 o C reduction for 3 hours. After the tube furnace cooled to room temperature, the resulting powder was platinum / alumina. Reaction conditions: Polystyrene was added to a kettle reactor, the reaction temperature was 260 degrees Celsius, the reaction time was 5 hours, and the reaction hydrogen pressure was 3 MPa. Testing showed a reaction conversion rate of 6.0% and a selectivity of 3.0%. This comparative example shows that when only the metal component is involved in the reaction, the catalyst has little degradation of polystyrene.

[0066] Comparative Example 5

[0067] The catalyst was prepared without adding metal nitrate. The remaining preparation process was identical to Example 1. Reaction conditions: polystyrene was added to a kettle reactor, the reaction temperature was 260°C, the reaction time was 5 hours, and the hydrogen pressure was 3 MPa. Testing showed a conversion rate of 8.0% and a selectivity of 4.0%. This comparative example demonstrates that a catalyst containing only the acidic component and no metal component exhibits virtually no performance.

[0068] The results of the comparative examples show that when either the metal compound or the acidic carrier participates in the reaction alone, the degradation of polystyrene is poor, with conversion rates below 10%. However, when both the metal component and the acidic carrier participate in the reaction, the conversion rate reaches 97.8% and the selectivity reaches 75.0%, significantly improving the catalytic effects of both. Therefore, neither active component (the metal component that activates hydrogen or the acid component that breaks the intermediate) acting alone can degrade polystyrene. Only the tandem action of the two components can maximize the catalyst's degradation capacity. If the metal-acid balance of the bifunctional catalyst is imbalanced, with too little metal, the tandem reaction will not fully activate hydrogen, affecting the acid component's ability to break CC. If the acidic carrier is present in a low proportion or the acidity is weakened, even if hydrogen activation reaches a certain level, it will not promote further cracking and depolymerization, but will instead reduce the catalyst's performance.

[0069] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any person skilled in the art may utilize the technical contents disclosed above to change or modify them into equivalent embodiments with equivalent changes for application in other fields. However, any simple modification, equivalent change, and modification of the above embodiments made in accordance with the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. Application of a metal-solid acid bifunctional catalyst in the hydrocracking of polystyrene plastics, characterized in that: The plastic is a waste aromatic hydrocarbon plastic. The catalyst preparation process comprises: adding a metal salt, a niobium source, an ammonium source, and an additive into ultrapure water, mixing them evenly, and then performing a hydrothermal reaction; after the hydrothermal reaction, filtering, drying, calcining, and then performing a reduction treatment on the reaction liquid to obtain the catalyst; The metal salt is any one or more mixtures of nitrates, hydrochlorides, sulfates, and organic salts of platinum, nickel, and copper ions; The additive is any one or more of metal nitrates, metal hydrochlorides or metal organic salts of zirconium, titanium or cerium, and the mass ratio of niobium source: ammonium source: metal salt: additive is (50-78): (0.5-6): (0.5-8): (0.1-8); The hydrothermal reaction temperature is 120-220° C., the hydrothermal reaction time is 12-72 hours; the calcination temperature is 400-600° C., the calcination time is 3-5 hours, the reducing atmosphere is hydrogen, and the temperature is 200-500° C.

2. The application according to claim 1, characterized in that The niobium source is any one or more of niobium pentachloride, niobium oxide, ammonium niobium oxalate, niobium oxalate, and niobium tartrate.

3. The application according to claim 1, characterized in that The ammonium source is any one or more of ammonia water or ammonium nitrate, hydrochloride, sulfate, and organic salt.

4. The application according to claim 1, characterized in that The waste aromatic hydrocarbon plastic is polystyrene, the reactor is a kettle reactor, the temperature of the catalytic hydrocracking reaction is 200-300° C., the reaction atmosphere is hydrogen, and the pressure is 1-3 MPa.

5. The application according to claim 1, characterized in that: The waste aromatic hydrocarbon plastic is polystyrene, the reactor is a fixed bed reactor, the reaction temperature is 200-260°C, the reaction atmosphere is hydrogen, the pressure is 1-3MPa, and the mass space velocity of the raw material is 1-10h -1 .

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