Tandem catalyst system and application thereof in hydrogen production from waste plastics

Abstract

The invention provides a series catalyst system and application thereof in hydrogen production from waste plastics, and belongs to the technical field of solid waste resource utilization. The tandem catalytic system comprises an in-situ catalyst and an ectopic catalyst, the in-situ catalyst and the heterotopic catalyst are respectively selected from one of metal oxides and metal modified molecular sieves. The series catalyst system can effectively inhibit generation of tar, sintering of the catalyst and deactivation caused by carbon deposition, so that the recovery rate of H in the waste plastics is increased.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, and in particular to a tandem catalyst system and its application in hydrogen production from waste plastics. Background Technology

[0002] With the rapid growth in demand for plastics, the environmental and climate change problems caused by large amounts of plastic waste urgently need to be addressed. Currently, pyrolysis technology is gradually becoming the most promising chemical recycling technology for waste plastics, but the quality and selectivity of the products are difficult to meet the demands. Catalytic pyrolysis technology can effectively improve the selectivity and yield of target products, the key being the structural control of in-situ or ex-situ catalysts. For example, patent CN 117551469 A provides an in-situ catalytic pyrolysis technology, which involves mixing waste plastics with a catalyst for catalytic pyrolysis to obtain a high yield of pyrolysis oil; the in-situ catalyst is a metal-supported catalyst. Patent CN 120924302 A provides a method of first pyrolyzing and then catalytically upgrading to prepare high-quality oil from plastics; the ex-situ catalyst is a zeolite molecular sieve or an alkali metal oxide. To further improve reaction efficiency and energy utilization efficiency, it is necessary to explore new catalyst action modes to meet the significant demand for synergistic efficiency improvement in waste plastic pollution reduction and carbon reduction. Summary of the Invention

[0003] The purpose of this invention is to provide a tandem catalyst system and its application in hydrogen production from waste plastics, in order to solve the above-mentioned technical problems.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a tandem catalyst system comprising an in-situ catalyst and an ex-situ catalyst; The in-situ catalyst and the ex-situ catalyst are respectively selected from metal oxides and metal-modified molecular sieves; The metal oxide has the structural formula M1O x The structure of the metal-modified molecular sieve is Ni-molecular sieve; M1 is one or more of Ni, Fe, Al, Mg, La, Y, Zr, Ce and Ca.

[0005] Furthermore, the molecular sieve is one or two of the structures MFI, MOR, BEA, FAU, and MCM-41.

[0006] Furthermore, the metal oxide is prepared by impregnation, sol-gel method, co-precipitation method or hydrothermal method; the metal-modified molecular sieve is prepared by ion exchange method, impregnation method or hydrothermal method.

[0007] This invention also provides the application of the above-mentioned tandem catalyst system in hydrogen production from waste plastics, including the following steps: 1) The in-situ catalyst is mixed with waste plastic and placed in the first-stage reactor or the first section of the reactor to carry out catalytic pyrolysis reaction to obtain pyrolysis products; 2) The pyrolysis products simultaneously enter the second-stage reactor or the second section of the reactor, where they undergo catalytic upgrading reactions on the surface of the anatopic catalyst and are converted into hydrogen.

[0008] Furthermore, the waste plastics include one or more of polyethylene, polypropylene, polystyrene, and polyethylene terephthalate; the particle size of the waste plastics is ≤5mm.

[0009] Furthermore, the mass ratio of the waste plastic to the in-situ catalyst is 1:1~4; the mass ratio of the waste plastic to the ex-situ catalyst is 1:0.2~1.

[0010] Furthermore, the catalytic pyrolysis reaction and the catalytic upgrading reaction are carried out in a protective gas atmosphere, wherein the protective gas is one or more of nitrogen, argon and helium.

[0011] Furthermore, the temperature of the catalytic pyrolysis reaction is 500~700℃, and the reaction time is 30~70min; the pyrolysis products are CO, CO2, C1~C6, H2, and pyrolysis oil.

[0012] Furthermore, the temperature of the catalytic upgrading reaction is 600~850℃, and the time of the catalytic upgrading reaction is 30~70min.

[0013] Furthermore, the physical distance between the first stage reactor or the first section of the reactor and the second stage reactor or the second section of the reactor is not less than 20 cm.

[0014] The beneficial effects of this invention are: 1) This invention provides a series catalyst system, which significantly improves the hydrogen yield when applied to the hydrogen production process from waste plastics compared to the single-catalyst mode.

[0015] 2) The tandem catalyst system of the present invention can effectively suppress the formation of tar, catalyst sintering and deactivation caused by carbon deposition, thereby improving the recovery rate of H in waste plastics. Detailed Implementation

[0016] This invention provides a tandem catalyst system comprising an in-situ catalyst and an ex-situ catalyst; The in-situ catalyst and the ex-situ catalyst are respectively selected from metal oxides and metal-modified molecular sieves; The metal oxide has the structural formula M1O xThe structure of the metal-modified molecular sieve is Ni-molecular sieve; M1 is one or more of Ni, Fe, Al, Mg, La, Y, Zr, Ce and Ca.

[0017] In this invention, M1 is preferably one or more of Ni, Y, Zr and Ce.

[0018] In this invention, the molecular sieve is one or two of the structures MFI, MOR, BEA, FAU, and MCM-41, preferably MFI or MOR.

[0019] In this invention, the metal oxide is prepared by impregnation, sol-gel method, co-precipitation method or hydrothermal method; the metal-modified molecular sieve is prepared by ion exchange method, impregnation method or hydrothermal method; the preparation process of the metal oxide and the metal-modified molecular sieve includes a calcination process, which is carried out by muffle furnace heating, microwave heating or plasma heating.

[0020] This invention also provides the application of the above-mentioned tandem catalyst system in hydrogen production from waste plastics, including the following steps: 1) The in-situ catalyst is mixed with waste plastic and placed in the first-stage reactor or the first section of the reactor to carry out catalytic pyrolysis reaction to obtain pyrolysis products; 2) The pyrolysis products simultaneously enter the second-stage reactor or the second section of the reactor, where they undergo catalytic upgrading reactions on the surface of the anatopic catalyst and are converted into hydrogen.

[0021] In this invention, the waste plastic comprises one or more of polyethylene, polypropylene, polystyrene and polyethylene terephthalate, preferably polyethylene, polypropylene or polystyrene; the particle size of the waste plastic is ≤5mm.

[0022] In this invention, the mass ratio of the waste plastic to the in-situ catalyst is 1:1 to 4, preferably 1:1, 1:2, 1:3, or 1:4; the mass ratio of the waste plastic to the ex-situ catalyst is 1:0.2 to 1, preferably 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, or 1:1.

[0023] In this invention, the catalytic pyrolysis reaction and the catalytic upgrading reaction are carried out in a protective gas atmosphere, wherein the protective gas is one or more of nitrogen, argon and helium, preferably nitrogen.

[0024] In this invention, the temperature of the catalytic pyrolysis reaction is 500~700℃, preferably 550~650℃, and more preferably 600℃; the time of the catalytic pyrolysis reaction is 30~70 min, preferably 40~60 min, and more preferably 50~60 min; the pyrolysis products are CO, CO2, C1~C6, H2 and pyrolysis oil.

[0025] In this invention, the temperature of the catalytic upgrading reaction is 600~850℃, preferably 650~800℃, and more preferably 700~750℃; the time of the catalytic upgrading reaction is 30~70 min, preferably 40~60 min, and more preferably 50~60 min.

[0026] In this invention, the physical distance between the first stage reactor or the first section of the reactor and the second stage reactor or the second section of the reactor is not less than 20 cm.

[0027] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0028] Example 1

[0029] Ni prepared by sol-gel method 1.8 YO x Catalyst, 0.5g Ni 1.8 YO x The catalyst was placed in the second section of the reactor. 1g of PE, PP and 2g of commercial NiO were mixed evenly and placed in the first section of the reactor. Nitrogen gas was introduced to purge the mixture. The second section was heated to 800°C and maintained for 70 minutes. Then the first section was heated and the temperature was increased to 700°C at a rate of 10°C / min. At the same time, the generated pyrolysis products were introduced into the second section, and the gas was collected at the reactor outlet.

[0030] Example 2

[0031] Ni prepared by sol-gel method 1.8 Zr 0.1 Y 0.9 O x Catalyst, 0.4g Ni 1.8 Zr 0.1 Y 0.9 O xThe catalyst was placed in the second section of the reactor. 1g of PE, PP and 1.5g of commercial NiO were mixed evenly and placed in the first section of the reactor. Nitrogen gas was introduced to purge the mixture. The second section was heated to 850°C and maintained for 60 minutes. Then the first section was heated and the temperature was increased to 600°C at a rate of 10°C / min. At the same time, the generated pyrolysis products were introduced into the second section, and the gas was collected at the reactor outlet.

[0032] Example 3

[0033] Ni-ZSM-5 catalyst was prepared by ion exchange method. 0.8g of Ni-ZSM-5 catalyst was placed in the second section of the reactor. 1g of PE, PP and 2g of commercial NiO were mixed evenly and placed in the first section of the reactor. Nitrogen gas was purged and the second section was heated to 750℃ and maintained for 60 minutes. Then the first section was heated and the temperature was increased to 600℃ at a rate of 10℃ / min. At the same time, the generated pyrolysis products were introduced into the second section and the gas was collected at the reactor outlet.

[0034] Example 4

[0035] Ni-ZSM-5 and Ni-MOR catalysts were prepared by ion exchange. 0.6 g of Ni-ZSM-5 catalyst was placed in the second section of the reactor. 1 g of PE, PP, PS and 1.5 g of Ni-MOR+NiO were mixed evenly and placed in the first section of the reactor. Nitrogen gas was purged and the second section was heated to 800 °C and held for 65 minutes. Then the first section was heated and the temperature was increased to 650 °C at a rate of 10 °C / min. At the same time, the generated pyrolysis products were introduced into the second section and the gas was collected at the reactor outlet.

[0036] Example 5

[0037] Ni prepared by sol-gel method 1.8 YO x Catalyst, 0.5g Ni 1.8 YO x The catalyst was placed in the second section of the reactor. 1g of PET and 4g of CaO+NiO were mixed evenly and placed in the first section of the reactor. Nitrogen gas was introduced to purge the second section, which was then heated to 800°C and maintained for 65 minutes. The first section was then heated to 600°C at a rate of 10°C / min, while the generated pyrolysis products were introduced into the second section. The gas was collected at the reactor outlet.

[0038] Example 6

[0039] Ni-ZSM-5 catalyst was prepared by ion exchange method, and FeAlO was prepared by impregnation method. x Catalyst, 0.5g FeAlO xThe catalyst was placed in the second section of the reactor. 1g of PE, PP, PS and 0.8g of Ni-ZSM-5 in a mass ratio of 2:2:1 were mixed evenly and placed in the first section of the reactor. Nitrogen gas was introduced to purge the reactor. The second section was heated to 800°C and held for 65 minutes. Then the first section was heated and the temperature was increased to 650°C at a rate of 10°C / min. At the same time, the generated pyrolysis products were introduced into the second section, and the gas was collected at the reactor outlet.

[0040] Comparative Example 1

[0041] Mix 1g of PE, PP and 2g of NiO in a 1:1 mass ratio and place the mixture in the first section of the reactor. Heat the mixture to 700℃ in a nitrogen atmosphere at a rate of 10℃ / min and react for 60min. Collect the gas at the reactor outlet.

[0042] Comparative Example 2

[0043] Mix 1g of PE, PP and 2g of Ni-ZSM-5 in a 1:1 mass ratio and place them in the first section of the reactor. Heat the mixture to 700℃ in a nitrogen atmosphere at a rate of 10℃ / min and react for 60min. Collect the gas at the outlet of the pyrolysis reactor.

[0044] Comparative Example 3

[0045] 0.5g of Ni-ZSM-5 catalyst was placed in the second section of the reactor. 1g of PE and PP mixed in a 1:1 mass ratio was placed in the first section. Nitrogen gas was introduced to purge the mixture. The second section was heated to 800°C and maintained for 70 minutes. Then the first section was heated to 700°C at a rate of 10°C / min. At the same time, the generated pyrolysis products were introduced into the second section. The gas was collected at the reactor outlet.

[0046] The experimental results of the above embodiments and comparative examples were analyzed, and the syngas yield, CO selectivity, and waste plastic carbon conversion rate were summarized in Table 1.

[0047] Table 1

[0048] As can be seen from the above embodiments, the present invention provides a tandem catalyst system and its application in hydrogen production from waste plastics. The data in the table above shows that, compared to single in-situ or ex-situ catalysts, using a tandem catalyst system can significantly improve the hydrogen yield and H recovery rate in hydrogen production from waste plastics.

[0049] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A tandem catalyst system, characterized in that, Includes in-situ catalysts and ex-situ catalysts; The in-situ catalyst and the ex-situ catalyst are respectively selected from metal oxides and metal-modified molecular sieves; The metal oxide has the structural formula M1O x The structure of the metal-modified molecular sieve is Ni-molecular sieve; M1 is one or more of Ni, Fe, Al, Mg, La, Y, Zr, Ce and Ca.

2. The tandem catalyst system according to claim 1, characterized in that, The molecular sieve is one or two of the structures MFI, MOR, BEA, FAU, and MCM-41.

3. The tandem catalyst system according to claim 1 or 2, characterized in that, The metal oxide is prepared by impregnation, sol-gel method, co-precipitation method or hydrothermal method; the metal-modified molecular sieve is prepared by ion exchange method, impregnation or hydrothermal method.

4. The application of the tandem catalyst system according to any one of claims 1 to 3 in hydrogen production from waste plastics, characterized in that, Includes the following steps: 1) The in-situ catalyst is mixed with waste plastic and placed in the first-stage reactor or the first section of the reactor to carry out catalytic pyrolysis reaction to obtain pyrolysis products; 2) The pyrolysis products simultaneously enter the second-stage reactor or the second section of the reactor, where they undergo catalytic upgrading reactions on the surface of the anatopic catalyst and are converted into hydrogen.

5. The application of the tandem catalyst system according to claim 4 in hydrogen production from waste plastics, characterized in that, The waste plastics contain one or more of polyethylene, polypropylene, polystyrene, and polyethylene terephthalate; the particle size of the waste plastics is ≤5mm.

6. The application of the tandem catalyst system according to claim 5 in hydrogen production from waste plastics, characterized in that, The mass ratio of the waste plastic to the in-situ catalyst is 1:1~4; the mass ratio of the waste plastic to the ex-situ catalyst is 1:0.2~1.

7. The application of the tandem catalyst system according to claim 5 or 6 in hydrogen production from waste plastics, characterized in that, The catalytic pyrolysis reaction and the catalytic upgrading reaction are carried out in a protective gas atmosphere, wherein the protective gas is one or more of nitrogen, argon and helium.

8. The application of the tandem catalyst system according to claim 7 in hydrogen production from waste plastics, characterized in that, The temperature of the catalytic pyrolysis reaction is 500~700℃, and the reaction time is 30~70 min; the pyrolysis products are CO, CO2, C1~C6, H2 and pyrolysis oil.

9. The application of the tandem catalyst system according to claim 8 in hydrogen production from waste plastics, characterized in that, The temperature of the catalytic upgrading reaction is 600~850℃, and the time of the catalytic upgrading reaction is 30~70 min.

10. The application of the tandem catalyst system according to claim 9 in hydrogen production from waste plastics, characterized in that, The physical distance between the first stage reactor or the first section of the reactor and the second stage reactor or the second section of the reactor is not less than 20 cm.

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