Method for preparing naphtha by catalytic pyrolysis of waste mulch film

Abstract

The application provides a method for preparing naphtha by catalytic pyrolysis of waste mulch film, and a porous amorphous silicon aluminum catalyst with controllable acid strength, distribution and pore structure is developed according to the structural composition characteristics of the waste mulch film, so that the granulated polymer is contacted with the catalyst in a fluidized state in a microwave heating fluidized bed reactor to perform a catalytic cracking reaction, the liquid after cracking is mixed with hydrogen to enter a hydrogenation refining tower provided with a hydrogenation refining catalyst to perform olefin saturation and hydrogenation refining to produce naphtha, and the problems of wide carbon number distribution of the traditional polymer pyrolysis product, uneven heating of the melt in the cracking process, slow cracking reaction rate, much gas and solid residue and low liquid yield are solved. The pyrolysis oil hydrogenation refining catalyst and hydrogenation process are developed to solve the problems of much cracking reaction in the pyrolysis oil hydrogenation process, low hydrogenation saturation degree and high product bromine value.

Description

Technical Field

[0001] This invention belongs to the field of waste resource recycling technology and relates to a method for producing naphtha from waste plastic film through catalytic pyrolysis. Background Technology

[0002] Currently, methods for treating waste plastics include open-air stockpiling, landfilling, incineration as fuel, melt recycling, and chemical recycling. Among these, stockpiling and landfilling are the most passive methods, occupying large amounts of land over a long period. Improper disposal can lead to leachate leakage and pollution of surrounding soil and water bodies. These methods are mainly suitable for waste plastics with many impurities, difficult classification, high pretreatment costs, and low reuse value. Using waste plastics as fuel and melt recycling are technologies that treat waste plastics as resource raw materials for resource reuse, but they still suffer from secondary pollution, low strength of recycled products, and high energy consumption. Chemical recycling typically involves placing waste plastics in an oxygen-free, closed environment and converting them into small-molecule products such as fuel oil and chemical raw materials through methods like thermal pyrolysis, catalytic pyrolysis, and hydrocracking, thus achieving resource reuse. This is a very promising recycling method. Recovering fuel oil and gas through pyrolysis of PE can, on the one hand, reduce the environmental harm caused by waste polymers to a certain extent, and on the other hand, alleviate the global energy crisis.

[0003] Waste plastic film is a high-molecular polymer. It is treated through catalytic cracking, placing it in an oxygen-free or low-oxygen, slightly negative pressure environment. In this environment, the polymer macromolecules of the waste plastic film open, reducing it to a low-molecular-weight state or monomeric state, while other combinations become basic organic raw materials. Simple thermal cracking suffers from drawbacks such as high cracking temperature, high energy consumption, and uncontrollable products. The use of catalysts, however, can lower the cracking temperature while regulating the product yield and composition to some extent, becoming a major approach for the chemical recycling and reuse of waste plastic film. Commonly used catalysts include catalytic cracking catalysts, natural zeolites, mesoporous molecular sieves, and aluminosilicates. Solid acid catalysts rely on acidic sites on the catalyst to provide catalytic activity. These catalysts depend on their abundant pore structure and large specific surface area to increase the contact area between the catalyst and the waste plastic melt. However, in the thermal cracking of waste plastic film, a high-molecular polymer, the use of traditional molecular sieve-based solid acid catalysts suffers from problems such as large catalyst dosage, poor polymer melt diffusion, uneven reaction temperature, catalyst deactivation due to coking, and inability to be reused. The specific reasons are as follows: On the one hand, polyolefins undergo pyrolysis at the acidic centers within the pores of the pyrolysis catalyst. Due to the uneven acid strength and irregular pores, the pyrolysis reaction is irregular, resulting in a wide carbon number distribution in the pyrolysis products. The olefins often accumulate and coke during their residence time within the pores. As coking occurs, the coke products can block the internal pores of the catalyst, preventing polymer molecules from entering and contacting the active centers, directly leading to a significant decrease in catalyst activity. Furthermore, after the reaction, the coke products adhering to the catalyst pores are difficult to remove, rendering the catalyst unusable. On the other hand, the catalytic pyrolysis reaction is slow, the polymer molecular chains are long and intertwined, and the viscosity after melting is high. During the reaction, the flow of the catalyst and polymer melt is restricted, preventing rapid and uniform diffusion. This limits the contact area between the catalyst and the polymer, ultimately resulting in a wide carbon number distribution in the polymer pyrolysis products, uneven heating of the melt during pyrolysis, a slow pyrolysis reaction rate, more gas and solid residues, and a low liquid yield. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a method for producing naphtha from waste plastic film through catalytic pyrolysis. It provides a catalytic cracking catalyst and a matching pyrolysis process, solving the problems of wide carbon number distribution in traditional polymer pyrolysis products, uneven melting during cracking, slow cracking reaction rate, high levels of gas and solid residues, and low liquid yield.

[0005] To achieve the above objectives, the following technical solution is adopted: a method for producing naphtha from waste plastic film through catalytic pyrolysis, the method comprising,

[0006] a. The collected waste plastic film is washed, floated and granulated, and the washed ash is dried and used as soil fertilizer;

[0007] b. The microwave-heated fluidized bed reactor is filled with thermal fluidizing medium porous amorphous silica-alumina. The granulated polymer raw material enters the microwave-heated fluidized bed reactor and comes into contact with the porous amorphous silica-alumina catalyst in a fluidized state to carry out a rapid catalytic cracking reaction.

[0008] c. The pyrolysis products enter the cyclone separator to separate solid products and catalyst particles, while the remaining substances enter the condenser to condense and separate liquid and gaseous products.

[0009] d. The catalyst particles enter the catalyst regeneration tower, where, under oxygen-rich conditions, the coke on the porous amorphous silica-alumina surface is removed, and the particles re-enter the microwave-heated fluidized bed reactor to participate in the reaction.

[0010] e. The liquid product is mixed with hydrogen and fed into a hydrorefining tower containing a hydrorefining catalyst to produce naphtha through olefin saturation and hydrorefining.

[0011] Preferably, the reaction temperature of the microwave-heated fluidized bed reactor is 380-450℃.

[0012] Preferably, the reaction temperature of the catalyst regeneration tower is 500°C.

[0013] Preferably, the porous amorphous silica-alumina catalyst has a particle size of 0.2-0.4 mm.

[0014] Preferred methods for synthesizing porous amorphous silica-alumina catalysts include:

[0015] s1, prepared with sodium metasilicate at a concentration of 0.30 mol / L -1 An aqueous solution of SiO2 was prepared, and a 0.21 mol L solution was prepared. -1 An aqueous solution of octadecyltrimethylammonium chloride (OTAC);

[0016] s2, After preheating the two solutions to 40℃, they were mixed evenly and the pH of the sol was adjusted to 6.7. The sol ratio was kept at OTAC:SiO2:Al2O3:H2O=0.08:1:240. Precursor sols with different SiO2 / Al2O3 ratios of 20, 40, and 160 were prepared by adding different proportions of sodium aluminate. s3, After static aging at 60℃ for 1 h, the solid was filtered, washed, and dried. The obtained solid was then calcined in air at 550℃ for 2 h to obtain a porous amorphous silica-alumina catalyst.

[0017] Preferably, the hydrorefining catalyst is NiMoS / SiO2-Al2O3, with a Ni content of 4% and a Mo content of 16%.

[0018] Preferably, the hydrorefining reaction conditions in the hydrorefining tower are: reaction temperature 220-280℃, reaction pressure 3-5MPa, and volume hourly space velocity 1.0-4.0h⁻¹. -1 The hydrogen-to-oil volume ratio is 200-600.

[0019] The above technical solution, based on the structural composition characteristics of waste plastic film, develops a catalytic cracking catalyst with controllable acid strength, distribution and pore structure, which solves the problems of wide carbon number distribution of cracking products, coking phenomenon, and coking causing the catalyst to lose its value for reuse. Furthermore, the catalyst SiO2 reduces the viscosity of polymer melt in the catalytic cracking reaction, increases the contact area between polymer melt and catalyst, and improves catalytic activity.

[0020] Microwave heating is used to control the internal temperature, ensuring a constant temperature and heating rate, thus solving the problems of the polymer's low thermal conductivity, uneven melting during pyrolysis, and difficulty in precise temperature control.

[0021] By using a pyrolysis oil hydrorefining catalyst and hydrorefining process, the problems of excessive cracking reactions, low hydrogenation saturation, and high bromine value in the pyrolysis oil hydrorefining process can be solved.

[0022] This method ultimately realizes the technology of catalytic cracking and hydrorefining of waste plastic film to produce naphtha, a feedstock for olefin cracking, thus ensuring that waste plastic film "goes back to where it came from" and solving the problem of soil pollution. Detailed Implementation

[0023] A method for producing naphtha from waste plastic film through catalytic pyrolysis includes,

[0024] a. The collected waste plastic film is washed, floated and granulated, and the washed ash is dried and used as soil fertilizer;

[0025] b. The microwave-heated fluidized bed reactor is filled with thermal fluidizing medium porous amorphous silica-alumina. The granulated polymer raw material enters the microwave-heated fluidized bed reactor and comes into contact with the porous amorphous silica-alumina catalyst in a fluidized state to carry out a rapid catalytic cracking reaction.

[0026] c. The pyrolysis products enter the cyclone separator to separate solid products and catalyst particles, while the remaining substances enter the condenser to condense and separate liquid and gaseous products.

[0027] d. The catalyst particles enter the catalyst regeneration tower, where, under oxygen-rich conditions, the coke on the porous amorphous silica-alumina surface is removed, and the particles re-enter the microwave-heated fluidized bed reactor to participate in the reaction.

[0028] e. The liquid product is mixed with hydrogen and fed into a hydrorefining tower containing a hydrorefining catalyst to produce naphtha through olefin saturation and hydrorefining.

[0029] Among them, the synthesis methods of porous amorphous silica-alumina catalysts include:

[0030] s1, prepared with sodium metasilicate at a concentration of 0.30 mol / L -1 An aqueous solution of SiO2 was prepared, and a 0.21 mol L solution was prepared. -1 An aqueous solution of octadecyltrimethylammonium chloride (OTAC);

[0031] s2, After preheating the two solutions to 40℃, they were mixed evenly and the pH of the sol was adjusted to 6.7. The sol ratio was kept at OTAC:SiO2:Al2O3:H2O=0.08:1:240. Precursor sols with different SiO2 / Al2O3 ratios of 20, 40, and 160 were prepared by adding different proportions of sodium aluminate. s3, After static aging at 60℃ for 1 h, the solid was filtered, washed, and dried. The obtained solid was then calcined in air at 550℃ for 2 h to obtain a porous amorphous silica-alumina catalyst.

[0032] The present invention will be described in detail below through embodiments, but the present invention is not limited to these embodiments.

[0033] Example 1

[0034] Waste agricultural film is washed, floated, and granulated. After screening, material smaller than 30 mesh is used as feed to the fluidized bed, while material larger than 30 mesh is re-granulated, and the above process is repeated. Porous amorphous aluminum silicate (ASA) is used. 20 The catalyst particles (SiO2 / Al2O3 = 20) were used as the fluidizing medium, with a particle size of 0.2 mm. The fluidized bed reaction temperature was 380-450℃. The residence time of the granulated polymer raw material in the microwave-heated fluidized bed was 120 s. Table 1 below shows the reaction process conditions and product properties.

[0035]

[0036]

[0037] Table 1

[0038] Table 1 shows that porous amorphous aluminum silicate (ASA) 20 When SiO2 / Al2O3 = 20) catalyst particles are used as the fluidizing medium, the highest liquid yield is achieved at a reaction temperature of 450℃.

[0039] Example 2

[0040] Porous amorphous aluminum silica (ASA) 20The catalyst particles (SiO2 / Al2O3 = 20) were used as the fluidizing medium, with a particle size of 0.2 mm. The fluidized bed reaction temperature was 450 °C and the fluidized bed residence time was 120 s. The effect of whether the fluidized bed was equipped with a microwave heating system on the reaction was investigated. Table 2 below shows the effect of reactor type on the properties of pyrolysis products.

[0041]

[0042] Table 2

[0043] As shown in Table 2, the polymer has a very low thermal conductivity, leading to uneven melting and difficulty in precise temperature control during pyrolysis. The part in direct contact with the reactor heats up rapidly and easily reaches the experimental set temperature, while the internal material heats up more slowly. Microwave heating is used to control the internal temperature, ensuring a constant temperature and heating rate, thus significantly improving the liquid yield.

[0044] Example 3

[0045] Porous amorphous aluminum silica (ASA) 20 The catalyst particles (SiO2 / Al2O3 = 20) were used as the fluidizing medium, with a particle size of 0.2 mm. The fluidized bed reaction temperature was 450℃. The residence time of the granulated polymer raw material in different fluidized beds is shown in Table 3 below.

[0046]

[0047] Table 3

[0048] Table 3 shows that porous amorphous aluminum silicate (ASA) 20 When SiO2 / Al2O3 = 20) catalyst particles are used as the fluidizing medium, the liquid yield is the highest when the reaction temperature is 450℃ and the residence time is 240s, and the solid yield is the carrier.

[0049] Example 4

[0050] Porous amorphous aluminum silica (ASA) 20 ASA 40 ASA 160 The catalyst particles, with a particle size of 0.2 mm, were used as the fluidizing medium. The fluidized bed reaction temperature was 450℃, and the residence time of the granulated polymer raw material in the fluidized bed was 240 s. Table 4 below shows the effect of different catalysts on product properties.

[0051]

[0052] Table 4

[0053] Table 4 shows that the catalytic cracking activity of porous amorphous silica-alumina film varies significantly with different SiO2 / Al2O3 ratios. 40 The catalyst has a suitable amount of acid and pores to maximize the liquid yield.

[0054] Example 5

[0055] Based on Example 4, using ASA 40 The liquid product produced by the catalyst (bromine value 78.2 gBr. (100 g)) -1 Hydrogenation purification experiments were conducted using a raw material (chlorine content of 260 ppm) as feedstock. The catalyst used was NiMo / SiO2-Al2O3, with NiO content of 4% and MoO3 content of 16%. Before use, the catalyst needed to be prepared by in-situ sulfidation to obtain NiMoS / SiO2-Al2O3 catalyst. Hydrogenation purification reaction conditions: reaction temperature 220-280℃, reaction pressure 3-5 MPa, volume hourly space velocity 1.0-4.0 h⁻¹. -1 The hydrogen-to-oil volume ratio is 200-600. Table 5 below shows the properties of the products obtained under different hydrorefining reaction conditions.

[0056]

[0057] Table 5

[0058] Table 5 shows that when the temperature is below 240℃ and the liquid hourly space velocity is greater than 2.0 h⁻¹, the effects of hydrogenation on olefin saturation and hydrodechlorination deteriorate. The reaction pressure and hydrogen-to-oil volume ratio have relatively little impact on olefin saturation and the effects of hydrogenation on hydrodechlorination. The hydrorefined product basically meets the national standards for naphtha.

Claims

1. A method for producing naphtha from waste plastic film through catalytic pyrolysis, characterized in that, The method includes, a. Collected waste plastic film is washed, floated, and granulated. The ash removed from the washing process is dried and used as soil fertilizer. b. The microwave-heated fluidized bed reactor is filled with a porous amorphous silica-alumina thermal fluidizing medium. The granulated polymer raw material enters the microwave-heated fluidized bed reactor and contacts the porous amorphous silica-alumina catalyst in a fluidized state, undergoing a rapid catalytic cracking reaction. The synthesis methods for porous amorphous silica-alumina catalysts include: s1, prepare a solution with a concentration of 0.30 mol / L using sodium metasilicate. -1 Prepare an aqueous solution of SiO2 and a 0.21 mol / L solution. -1 An aqueous solution of octadecyltrimethylammonium chloride (OTAC); s2, after preheating the above solution to 40℃, mix it evenly and adjust the pH of the sol to 6.7, keeping the sol ratio at OTAC:SiO2:H2O=0.08:1:240, and prepare the precursor sol by adding sodium aluminate; The SiO2 / Al2O3 ratio of the precursor sol prepared by the sodium aluminate is 20, 40 or 160; S3 was statically aged at 60℃ for 1 hour, filtered, washed and dried, and the resulting solid was calcined in air at 550℃ for 2 hours to obtain a porous amorphous silica-alumina catalyst with a particle size of 0.2-0.4 mm. c. The pyrolysis products enter the cyclone separator to separate solid products and catalyst particles, while the remaining substances enter the condenser to condense and separate liquid and gaseous products. d. The catalyst particles enter the catalyst regeneration tower at a reaction temperature of 500℃. Under oxygen-rich conditions, the coke on the surface of the porous amorphous silica-alumina is removed, and the particles re-enter the microwave-heated fluidized bed reactor at a reaction temperature of 380-450℃ to participate in the reaction. e. The liquid product is mixed with hydrogen and fed into a hydrorefining tower containing a hydrorefining catalyst to produce naphtha through olefin saturation and hydrorefining. The hydrorefining catalyst is NiMoS / SiO2-Al2O3 with a Ni content of 4% and a Mo content of 16%.

2. The method for producing naphtha from waste plastic film through catalytic pyrolysis according to claim 1, characterized in that, The hydrorefining reaction conditions in the aforementioned hydrorefining tower are: reaction temperature 220-280℃, reaction pressure 3-5MPa, and volume hourly space velocity 1.0-4.0 h⁻¹. -1 The hydrogen-to-oil volume ratio is 200-600.

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