Method for preparing aromatic hydrocarbon through graded catalytic co-pyrolysis

Abstract

The invention provides a method for preparing aromatic hydrocarbon through graded catalytic co-pyrolysis, and belongs to the technical field of pyrolysis. According to the method provided by the invention, synergistic utilization of the marine waste plastics and the algal biomass is realized, the marine waste plastics as a'hydrogen donor 'and the algal biomass are subjected to synergistic co-pyrolysis, the yield of an oil-phase product is improved, the advantages of two-stage pyrolysis and catalysis are integrated, oxygen-containing and nitrogen-containing functional group products are removed in first-stage low-temperature catalytic pyrolysis, and the yield of the oil-phase product is improved. In the second-stage high-temperature catalytic pyrolysis, a deoxidation reaction and a cyclization reaction are promoted, the complexity of product components is reduced, the generation of aromatic hydrocarbon is greatly promoted, the content of aromatic hydrocarbon substances in the pyrolysis oil is increased, particularly, the content of heavy components is low, the carbon number is mainly distributed between C5-C11, the selectivity of products such as benzene, methylbenzene and xylene in the aromatic hydrocarbon components is improved, and the yield of the pyrolysis oil is increased. The contents of oxygen-containing compounds and nitrogen-containing compounds are obviously reduced, and the quality of the pyrolytic oil is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of pyrolysis technology, and in particular to a method for preparing aromatics by staged catalytic co-pyrolysis. Background Technology

[0002] Marine plastic pollution seriously threatens the marine ecological environment. With increasing awareness of protecting marine ecological civilization, marine environmental pollution prevention and control has become an inevitable requirement. Currently, the main methods for treating marine waste plastics include landfill, pyrolysis, and incineration. While pyrolysis of plastics alone can achieve resource utilization and reduce environmental pollution, plastics are prone to sticking when heated, affecting continuous feeding. Furthermore, pyrolysis alone results in high pyrolysis temperatures, poor product quality, and low yield of pyrolysis oil. Moreover, marine waste plastics are often mixed with algae and other marine biomass during the salvage process, and removing them increases processing costs. Co-pyrolysis of marine waste plastics with marine biomass can improve the yield of liquid and gaseous products, enhance the quality of pyrolysis oil, and promote resource utilization. However, the composition of the pyrolysis oil products is more complex, containing more oxygen-containing substances. Additionally, algae biomass is rich in protein, and single-stage co-pyrolysis results in a higher content of nitrogen-containing substances in the pyrolysis products, making the pyrolysis oil difficult to use. Therefore, how to realize the resource utilization of marine waste plastics and marine biomass has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing aromatics by staged catalytic co-pyrolysis. The pyrolysis oil obtained by the method of this invention has a high content of aromatics and a high selectivity for monocyclic aromatics, realizing the resource utilization of marine waste plastics and marine biomass.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing aromatics by staged catalytic co-pyrolysis, comprising the following steps: (1) Mix marine waste plastics and algal biomass to obtain a mixture; (2) The mixture obtained in step (1) and the catalyst are subjected to first-stage catalytic pyrolysis and second-stage catalytic pyrolysis in a catalytic manner in situ to obtain pyrolysis oil with high aromatic content; The catalyst in step (2) is a transition metal modified HZSM-5 zeolite molecular sieve catalyst; the holding temperature of the first-stage catalytic pyrolysis is 450~550℃; the holding temperature of the second-stage catalytic pyrolysis is 700~800℃.

[0005] Preferably, in step (1), the marine waste plastics include any one or more of waste polypropylene, polystyrene and polyethylene in the ocean, and the algal biomass includes any one or more of Ulva prolifera, Chlorella vulgaris and cyanobacteria, and the mass ratio of marine waste plastics to algal biomass is (1~10):(1~10).

[0006] Preferably, the particle size of the catalyst in step (2) is 50~200 mesh.

[0007] Preferably, the transition metal in the transition metal modified HZSM-5 zeolite molecular sieve catalyst includes any one or more of Fe, Cu and Co; the loading of the transition metal is 5~20wt%.

[0008] Preferably, the preparation method of the transition metal modified HZSM-5 zeolite molecular sieve catalyst includes: firstly, subjecting the HZSM-5 zeolite molecular sieve to a first calcination and grinding sieving to obtain the calcined HZSM-5 zeolite molecular sieve; then, mixing and adsorbing the calcined HZSM-5 zeolite molecular sieve with a transition metal compound solution; and finally, subjecting it to drying and a second calcination to obtain the transition metal modified HZSM-5 zeolite molecular sieve catalyst.

[0009] Preferably, the ex-situ catalysis in step (2) is performed by placing the mixture in the middle, then placing the catalyst on both sides of the mixture, and then separating them with quartz wool.

[0010] Preferably, in step (2), the mass ratio of catalyst to mixture is (1~10):5.

[0011] Preferably, the holding time for the first-stage catalytic pyrolysis in step (2) is 3-5 minutes, and the atmosphere for the first-stage catalytic pyrolysis is an oxygen-free atmosphere.

[0012] Preferably, the holding time for the second-stage catalytic pyrolysis in step (2) is 10~40 min, and the atmosphere for the second-stage catalytic pyrolysis is an oxygen-free atmosphere.

[0013] Preferably, the oxygen-free atmosphere is independently a nitrogen atmosphere or a helium atmosphere.

[0014] This invention provides a method for preparing aromatics by staged catalytic co-pyrolysis, comprising the following steps: (1) mixing marine waste plastics and algal biomass to obtain a mixture; (2) sequentially subjecting the mixture obtained in step (1) and the catalyst to first-stage catalytic pyrolysis and second-stage catalytic pyrolysis via ex-situ catalysis to obtain pyrolysis oil with high aromatic content; the catalyst in step (2) is a transition metal modified HZSM-5 zeolite molecular sieve catalyst; the holding temperature of the first-stage catalytic pyrolysis is 450~550℃; the holding temperature of the second-stage catalytic pyrolysis is 700~800℃. The method provided by this invention achieves the synergistic utilization of marine waste plastics and algal biomass. Marine waste plastics act as a "hydrogen donor" in synergistic co-pyrolysis with algal biomass, increasing the yield of oil-phase products. It integrates the advantages of two-stage pyrolysis and catalysis. In the first-stage low-temperature catalytic pyrolysis, oxygen- and nitrogen-containing functional group products are removed. In the second-stage high-temperature catalytic pyrolysis, deoxygenation and cyclization reactions are promoted, reducing the complexity of product components and significantly promoting the formation of aromatics. This increases the content of aromatics in the pyrolysis oil, especially reducing the content of heavy components, with the carbon number mainly distributed between C5 and C6. 11 This method improves the selectivity of products such as benzene, toluene, and xylene in aromatic hydrocarbon components, significantly reduces the content of oxygen-containing and nitrogen-containing compounds, and effectively improves the quality of pyrolysis oil. The results of the examples show that the pyrolysis oil obtained by the method provided by this invention has an aromatic hydrocarbon content >75%, with a monocyclic aromatic hydrocarbon selectivity greater than 70%. Detailed Implementation

[0015] This invention provides a method for preparing aromatics by staged catalytic co-pyrolysis, comprising the following steps: (1) Mix marine waste plastics and algal biomass to obtain a mixture; (2) The mixture obtained in step (1) and the catalyst are subjected to first-stage catalytic pyrolysis and second-stage catalytic pyrolysis in a catalytic manner in situ to obtain pyrolysis oil with high aromatic content; The catalyst in step (2) is a transition metal modified HZSM-5 zeolite molecular sieve catalyst; the holding temperature of the first-stage catalytic pyrolysis is 450~550℃; the holding temperature of the second-stage catalytic pyrolysis is 700~800℃.

[0016] Unless otherwise specified, all raw materials used in this invention are commercially available products well known to those skilled in the art.

[0017] This invention mixes marine waste plastics and algal biomass to obtain a mixture.

[0018] In this invention, the marine waste plastics preferably include any one or more of waste polypropylene, polystyrene, and polyethylene from the ocean; the algal biomass preferably includes any one or more of *Ulva prolifera*, *Chlorella vulgaris*, and cyanobacteria; the preferred mass ratio of the marine waste plastics to the algal biomass is (1~10):(1~10). As one embodiment of this invention, the mass ratio of the marine waste plastics to the algal biomass can be (2~9):(2~9). This invention uses marine waste plastics and algal biomass as raw materials to achieve the synergistic utilization of marine waste plastics and algal biomass. Marine waste plastics act as a "hydrogen donor" in synergistic co-pyrolysis with biomass, increasing the yield of oil-phase products. This realizes the utilization of marine biomass energy and the reduction and resource utilization of marine plastic solid waste, generating significant environmental and economic benefits.

[0019] The present invention does not have any particular limitation on the specific method of mixing the marine waste plastics and algal biomass. Any method known to those skilled in the art can be used to mix them evenly.

[0020] After obtaining the mixture, the present invention sequentially performs first-stage catalytic pyrolysis and second-stage catalytic pyrolysis on the mixture and catalyst through ex-situ catalysis to obtain pyrolysis oil with high aromatic content.

[0021] In this invention, the catalyst is a transition metal-modified HZSM-5 zeolite molecular sieve catalyst; the particle size of the catalyst is preferably 50-200 mesh; the transition metal in the transition metal-modified HZSM-5 zeolite molecular sieve catalyst preferably includes any one or more of Fe, Cu, and Co; the loading of the transition metal is preferably 5-20 wt%. As one embodiment of this invention, the particle size of the catalyst can be 50 mesh, 80 mesh, 100 mesh, 120 mesh, 150 mesh, 180 mesh, or 200 mesh; the loading of the transition metal can be 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, or 20 wt%. This invention, by modifying HZSM-5 zeolite molecular sieve with transition metals, can significantly improve its catalytic efficiency and increase the yield of oil-phase products.

[0022] In this invention, the preferred method for preparing the transition metal modified HZSM-5 zeolite molecular sieve catalyst includes: firstly, subjecting the HZSM-5 zeolite molecular sieve to a first calcination and grinding sieving to obtain the calcined HZSM-5 zeolite molecular sieve; then, mixing and adsorbing the calcined HZSM-5 zeolite molecular sieve with a transition metal compound solution; and finally, subjecting it to drying and a second calcination to obtain the transition metal modified HZSM-5 zeolite molecular sieve catalyst.

[0023] In this invention, the preferred temperature for the first calcination is 500-600℃; the preferred calcination time is 3-5 hours. As one embodiment of this invention, the temperature for the first calcination can be 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, or 600℃; the calcination time can be 3 hours, 4 hours, or 5 hours. This invention, through the first calcination, can remove the template agent from the HZSM-5 zeolite molecular sieve, reducing impurities.

[0024] This invention does not impose any special limitations on the specific operation of the grinding and sieving process. Conventional grinding and sieving methods can be used to ensure that the particle size of the transition metal-modified HZSM-5 zeolite molecular sieve catalyst meets the requirements. In one embodiment of this invention, the grinding and sieving process involves first cooling to room temperature before proceeding with the grinding and sieving.

[0025] In this invention, the preferred method for preparing the transition metal compound solution is to mix the transition metal compound with water to obtain the solution. In this invention, the transition metal compound is preferably a soluble transition metal compound, more preferably copper nitrate, cobalt nitrate, ferric nitrate, copper chloride, ferric chloride, or cobalt chloride. This invention does not impose any particular limitations on the amount of transition metal compound and water used, or on the mixing method, as long as the transition metal compound is completely dissolved in water. This invention, by preparing the transition metal compound solution, facilitates the subsequent adsorption of HZSM-5 zeolite molecular sieves.

[0026] In this invention, the preferred method for mixing and adsorbing the HZSM-5 zeolite molecular sieve and the transition metal compound solution is magnetic stirring; the preferred temperature for magnetic stirring is 40~80℃, more preferably 50~70℃, and even more preferably 60℃; the preferred time for magnetic stirring is 2~6h, more preferably 3~5h, and even more preferably 4h.

[0027] This invention does not impose any special restrictions on the ratio of the transition metal compound to the HZSM-5 zeolite molecular sieve, as long as the loading of the transition metal in the transition metal-modified HZSM-5 zeolite molecular sieve catalyst meets the requirements.

[0028] In this invention, the drying temperature is preferably 100-110℃; the drying time is preferably 8-16h; the second firing temperature is preferably 500-600℃; and the second firing time is preferably 3-5h. As one embodiment of this invention, the drying temperature can be 100℃, 102℃, 104℃, 105℃, 106℃, 108℃, or 110℃; the drying time can be 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, or 16h; the second firing temperature can be 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, or 600℃; and the second firing time can be 3h, 4h, or 5h. The present invention removes residual moisture by drying, and then reduces the metal components by a second calcination to obtain a transition metal modified HZSM-5 zeolite molecular sieve catalyst with a particle size that meets the requirements.

[0029] In this invention, the preferred method of ex-situ catalysis is to place the mixture in the middle, then place the catalyst on both sides of the mixture, and then separate them using quartz wool. In this invention, when placing the catalyst on both sides of the mixture, the catalyst is preferably placed uniformly. This invention, through ex-situ catalysis, achieves excellent catalytic effects while also facilitating the recovery and reuse of the catalyst.

[0030] In this invention, the preferred mass ratio of the catalyst to the mixture is (1~10):5. As one embodiment of this invention, the mass ratio of the catalyst to the mixture can be 1:5, 2:5, 3:5, 4:5, 5:5, 6:5, 7:5, 8:5, 9:5, or 10:5.

[0031] In this invention, the holding temperature for the first-stage catalytic pyrolysis is 450~550℃; the holding time for the first-stage catalytic pyrolysis is preferably 3~5 min; the atmosphere for the first-stage catalytic pyrolysis is preferably an oxygen-free atmosphere, more preferably a nitrogen atmosphere or a helium atmosphere. As one embodiment of this invention, the holding temperature for the first-stage catalytic pyrolysis can be 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, or 550℃; the holding time for the first-stage catalytic pyrolysis can be 3 min, 3.5 min, 4 min, 4.5 min, or 5 min. This invention utilizes a relatively low catalytic pyrolysis temperature in the first-stage catalytic pyrolysis to remove oxygen- and nitrogen-containing functional group products.

[0032] After the first-stage catalytic pyrolysis is completed, the present invention preferably further includes collecting the liquid products of the first-stage catalytic pyrolysis. The present invention does not specifically limit the method of collection; any method well-known to those skilled in the art can be used. The present invention avoids environmental pollution through the above operations.

[0033] In this invention, the holding temperature for the second-stage catalytic pyrolysis is 700-800℃; the holding time for the second-stage catalytic pyrolysis is preferably 10-40 min; the atmosphere for the second-stage catalytic pyrolysis is preferably an oxygen-free atmosphere, more preferably a nitrogen atmosphere or a helium atmosphere. As one embodiment of this invention, the holding temperature for the second-stage catalytic pyrolysis can be 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, or 800℃; the holding time for the second-stage catalytic pyrolysis can be 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, or 40 min. This invention utilizes a higher catalytic pyrolysis temperature in the second-stage high-temperature catalytic pyrolysis to promote deoxygenation and cyclization reactions, reducing the complexity of the product components and significantly promoting the formation of aromatics.

[0034] The method provided by this invention achieves the synergistic utilization of marine waste plastics and algal biomass. Marine waste plastics act as a "hydrogen donor" in synergistic co-pyrolysis with algal biomass, increasing the yield of oil-phase products. It integrates the advantages of two-stage pyrolysis and catalysis. In the first-stage low-temperature catalytic pyrolysis, oxygen- and nitrogen-containing functional group products are removed. In the second-stage high-temperature catalytic pyrolysis, deoxygenation and cyclization reactions are promoted, reducing the complexity of product components and significantly promoting the formation of aromatics. This increases the content of aromatics in the pyrolysis oil, especially reducing the content of heavy components, with the carbon number mainly distributed between C5 and C6. 11 This process improves the selectivity of products such as benzene, toluene, and xylene in aromatic hydrocarbon components, significantly reduces the content of oxygen-containing and nitrogen-containing compounds, and effectively improves the quality of pyrolysis oil.

[0035] The method provided by this invention enables the utilization of marine biomass energy and the reduction and resource utilization of marine plastic solid waste, which can generate good environmental and economic benefits.

[0036] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0037] Example 1 A method for preparing aromatics by staged catalytic co-pyrolysis includes the following steps: (1) Mix marine waste plastics and algal biomass to obtain a mixture; the marine waste plastics are waste polypropylene in the ocean, the algal biomass is seaweed, and the mass ratio of marine waste plastics to algal biomass is 1:1; (2) The mixture obtained in step (1) is placed in the middle of the crucible of the fixed bed pyrolysis reactor, and then the catalyst is evenly placed on both sides of the mixture. Then, quartz wool is used to separate the mixture. The first-stage catalytic pyrolysis is carried out by ex-situ catalysis. The first-stage product is collected, and then the second-stage catalytic pyrolysis is carried out to obtain pyrolysis oil with high aromatic content. The mass ratio of the catalyst to the mixture is 1:1. In step (2), the catalyst is a transition metal modified HZSM-5 zeolite molecular sieve catalyst, the transition metal is Cu, and the loading of the transition metal is 5wt%. The preparation method of the transition metal modified HZSM-5 zeolite molecular sieve catalyst is as follows: first, the HZSM-5 zeolite molecular sieve is calcined at 550℃ for 4h to remove the template agent, cooled to room temperature and then ground and sieved to obtain calcined HZSM-5 zeolite molecular sieve with a particle size of 100 mesh. Then, 3.78g of Cu(NO3)2·3H2O crystals are mixed with deionized water to obtain a transition metal compound solution. Then, 20g of calcined HZSM-5 zeolite molecular sieve and the transition metal compound solution are mixed and magnetically stirred at 60℃ for 4h. Finally, the mixture is dried at 105℃ for 12h and calcined at 550℃ for 4h to obtain a transition metal modified HZSM-5 zeolite molecular sieve catalyst with a particle size of 100 mesh. In step (2), the holding temperature of the first-stage catalytic pyrolysis is 550℃, the holding time of the first-stage catalytic pyrolysis is 5min, and the atmosphere of the first-stage catalytic pyrolysis is nitrogen atmosphere; the holding temperature of the second-stage catalytic pyrolysis is 700℃, the holding time of the second-stage catalytic pyrolysis is 20min, and the atmosphere of the second-stage catalytic pyrolysis is nitrogen atmosphere.

[0038] The pyrolysis oil with high aromatic content obtained in Example 1 was tested using gas chromatography-mass spectrometry. The results showed that the aromatic content in the pyrolysis oil was 89.4%, of which the selectivity of monocyclic aromatic hydrocarbons reached 78.6%.

[0039] Example 2 A method for preparing aromatics by staged catalytic co-pyrolysis, wherein the mass ratio of catalyst to mixture in step (2) is 6:5, and other conditions are the same as in Example 1.

[0040] The pyrolysis oil with high aromatic content obtained in Example 2 was tested using gas chromatography-mass spectrometry. The results showed that the aromatic content in the pyrolysis oil was 90.2%, of which the selectivity of monocyclic aromatic hydrocarbons reached 87.5%.

[0041] Example 3 A method for preparing aromatic hydrocarbons by graded catalytic co-pyrolysis, wherein the preparation method of the transition metal modified HZSM-5 zeolite molecular sieve catalyst in step (2) is as follows: first, the HZSM-5 zeolite molecular sieve is calcined at 550℃ for 4h to remove the template agent, cooled to room temperature and then ground and sieved to obtain calcined HZSM-5 zeolite molecular sieve with a particle size of 100 mesh; then, 4.93g of Co(NO3)2·6H2O crystals are mixed with deionized water to obtain a transition metal compound solution; then, 20g of calcined HZSM-5 zeolite molecular sieve and the transition metal compound solution are mixed and magnetically stirred at 60℃ for 4h; finally, the mixture is dried at 105℃ for 12h and calcined at 550℃ for 4h to obtain the transition metal modified HZSM-5 zeolite molecular sieve catalyst with a particle size of 100 mesh. Other conditions are the same as in Example 1.

[0042] The pyrolysis oil with high aromatic content obtained in Example 3 was tested using gas chromatography-mass spectrometry. The results showed that the aromatic content in the pyrolysis oil was 79.0%, of which the selectivity of monocyclic aromatic hydrocarbons reached 73.2%.

[0043] Example 4 A method for preparing aromatics by graded catalytic co-pyrolysis, wherein the preparation method of the transition metal modified HZSM-5 zeolite molecular sieve catalyst in step (2) is as follows: first, the HZSM-5 zeolite molecular sieve is calcined at 550℃ for 4h to remove the template agent, cooled to room temperature and then ground and sieved to obtain calcined HZSM-5 zeolite molecular sieve with a particle size of 100 mesh; then, 7.21g of Fe(NO3)3·9H2O crystals are mixed with deionized water to obtain a transition metal compound solution; then, 20g of calcined HZSM-5 zeolite molecular sieve and the transition metal compound solution are mixed and magnetically stirred at 60℃ for 4h; finally, it is dried at 105℃ for 12h and calcined at 550℃ for 4h to obtain the transition metal modified HZSM-5 zeolite molecular sieve catalyst with a particle size of 100 mesh; Other conditions are the same as in Example 1.

[0044] The pyrolysis oil with high aromatic content obtained in Example 4 was tested using gas chromatography-mass spectrometry. The results showed that the aromatic content in the pyrolysis oil was 83.1%, of which the selectivity of monocyclic aromatic hydrocarbons reached 76.2%.

[0045] Comparative Example 1 A method for preparing aromatics by staged catalytic co-pyrolysis includes the following steps: (1) Mix marine waste plastics and algal biomass to obtain a mixture; the marine waste plastics are waste polypropylene in the ocean, the algal biomass is seaweed, and the mass ratio of marine waste plastics to algal biomass is 1:1; (2) The mixture obtained in step (1) is placed in the middle of the crucible of the fixed bed pyrolysis reactor, and then HZSM-5 zeolite molecular sieves with a particle size of 100 mesh are evenly placed on both sides of the mixture. Then, quartz wool is used for separation, and the first-stage catalytic pyrolysis is carried out by ex-situ catalysis. The first-stage product is collected, and then the second-stage catalytic pyrolysis is carried out to obtain pyrolysis oil with high aromatic content. The mass ratio of the catalyst to the mixture is 1:1. In step (2), the holding temperature of the first-stage catalytic pyrolysis is 550℃, the holding time of the first-stage catalytic pyrolysis is 5min, and the atmosphere of the first-stage catalytic pyrolysis is nitrogen atmosphere; the holding temperature of the second-stage catalytic pyrolysis is 700℃, the holding time of the second-stage catalytic pyrolysis is 20min, and the atmosphere of the second-stage catalytic pyrolysis is nitrogen atmosphere.

[0046] The pyrolysis oil with high aromatic content obtained in Comparative Example 1 was tested using gas chromatography-mass spectrometry. The results showed that the aromatic content in the pyrolysis oil was 66.3%, of which the selectivity of monocyclic aromatic hydrocarbons reached 68.4%.

[0047] A comparison of Examples 1-4 and Comparative Example 1 shows that the present invention, by loading transition metals onto HZSM-5 zeolite molecular sieves, can significantly increase the aromatic content in pyrolysis oil, while also significantly improving the selectivity for monocyclic aromatic hydrocarbons. Loading different types of transition metals onto HZSM-5 zeolite molecular sieves can improve the selectivity for monocyclic aromatic hydrocarbons to varying degrees. Furthermore, when using transition metal-modified HZSM-5 zeolite molecular sieve catalysts for the catalytic pyrolysis of mixtures of marine waste plastics and algal biomass, increasing the amount of catalyst significantly improves the catalytic pyrolysis effect.

[0048] 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 method for preparing aromatics by staged catalytic co-pyrolysis, comprising the following steps: (1) Mix marine waste plastics and algal biomass to obtain a mixture; (2) The mixture obtained in step (1) and the catalyst are subjected to first-stage catalytic pyrolysis and second-stage catalytic pyrolysis in a catalytic manner in situ to obtain pyrolysis oil with high aromatic content; The catalyst in step (2) is a transition metal modified HZSM-5 zeolite molecular sieve catalyst; the holding temperature of the first-stage catalytic pyrolysis is 450~550℃; the holding temperature of the second-stage catalytic pyrolysis is 700~800℃.

2. The method according to claim 1, characterized in that, In step (1), marine waste plastics include any one or more of waste polypropylene, polystyrene and polyethylene in the ocean, and algal biomass includes any one or more of seaweed, green algae and blue algae. The mass ratio of marine waste plastics to algal biomass is (1~10):(1~10).

3. The method according to claim 1, characterized in that, The particle size of the catalyst in step (2) is 50~200 mesh.

4. The method according to claim 1, characterized in that, The transition metal in the HZSM-5 zeolite molecular sieve catalyst modified with transition metals includes any one or more of Fe, Cu, and Co; the loading of the transition metal is 5~20 wt%.

5. The method according to claim 1, characterized in that, The preparation method of the transition metal modified HZSM-5 zeolite molecular sieve catalyst includes: firstly, subjecting the HZSM-5 zeolite molecular sieve to a first calcination and grinding sieve in sequence to obtain the calcined HZSM-5 zeolite molecular sieve; then, mixing and adsorbing the calcined HZSM-5 zeolite molecular sieve with a transition metal compound solution; and finally, subjecting it to drying and a second calcination in sequence to obtain the transition metal modified HZSM-5 zeolite molecular sieve catalyst.

6. The method according to claim 1, characterized in that, The ex-situ catalysis method in step (2) is as follows: the mixture is placed in the middle, and then the catalyst is placed on both sides of the mixture, and then separated by quartz wool.

7. The method according to claim 1, characterized in that, In step (2), the mass ratio of catalyst to mixture is (1~10):

5.

8. The method according to claim 1, characterized in that, In step (2), the holding time for the first-stage catalytic pyrolysis is 3-5 minutes, and the atmosphere for the first-stage catalytic pyrolysis is an oxygen-free atmosphere.

9. The method according to claim 1, characterized in that, The holding time for the second-stage catalytic pyrolysis in step (2) is 10~40 min, and the atmosphere for the second-stage catalytic pyrolysis is an oxygen-free atmosphere.

10. The method according to claim 8 or 9, characterized in that, The oxygen-free atmosphere is either a nitrogen atmosphere or a helium atmosphere.