Method for preparing liquid fuel by catalytic cracking of waste plastics

Abstract

The application discloses a method for preparing liquid fuel by catalytic cracking of waste plastics. The method comprises the following steps: uniformly mixing a nano-Beta molecular sieve catalyst and waste plastics, adding the mixture into a reactor, introducing nitrogen, reacting under certain temperature conditions for a certain time, taking out the obtained product by nitrogen, condensing, collecting liquid product, and obtaining liquid fuel. The method has the advantages of high efficiency, high selectivity of liquid fuel components, stable catalyst, and simple and environment-friendly reaction process.

Description

Technical Field

[0001] This invention relates to the field of waste plastic pyrolysis and conversion, and in particular to a method for preparing liquid fuels by catalytic pyrolysis of waste plastics using solid acidic molecular sieves. Background Technology

[0002] Plastic products have brought immense convenience to our modern lives, but they have also generated a large amount of non-biodegradable plastic waste, causing significant harm to the ecological environment and human health, drawing worldwide attention. The United Nations Environment Programme designated the theme of World Environment Day 2018 as "Beat Plastic Quickly." my country currently has approximately 1 billion tons of waste plastic, and generates about 40 million tons annually, highlighting the serious pollution and resource waste caused by waste plastics.

[0003] Waste plastic treatment mainly includes landfill, incineration, and recycling. Landfill and incineration waste resources and cause environmental pollution. Physical recycling (granulation) recycles some high-quality plastic waste into granules to produce recycled plastic products, extending the lifespan of plastics. However, physical recycling cannot continue indefinitely, and ultimately, the plastic remains waste. Chemical recycling refers to converting waste plastics into valuable petrochemical products such as chemicals (ethylene, propylene, aromatics, etc.) or fuel oils (gasoline, kerosene, diesel, etc.) through pyrolysis (thermal pyrolysis or catalytic pyrolysis). Chemical recycling is the ultimate solution to the problems of waste plastic pollution and resource waste, and it is of great significance. Patent WO2021257783A1 reports the use of a physical mixture of Pt / WO3 / ZrO2 and HY molecular sieve as a catalyst to convert waste plastics into gasoline and diesel under hydrogen conditions of 200-250℃ and 30 bar. However, the use of precious metals and high-pressure hydrogen increases production costs and reduces operational safety. Patent CN1141359C reports a method for converting waste plastics into gasoline and diesel at 320℃. However, its process is complex, requiring plastic thermal cracking, aluminosilicate catalytic thermal cracking, distillation, and rare earth / ferric oxide catalytic cracking to produce gasoline and diesel. Patent CN1084546A uses aluminosilicate as a catalyst to catalytically crack waste plastics to produce liquid fuels at multiple temperature gradients (160-200℃, 200-300℃, 300-350℃, 400-500℃). However, these multiple temperature gradients increase the difficulty of process control, raise production costs, and temperature control deviations can easily lead to reduced product quality. Patent CN1077479A uses a Y-type molecular sieve and an Al(OH)3 composite catalyst to catalytically crack waste plastics to prepare liquid fuels. Y-type molecular sieves are commonly used catalysts in petroleum catalytic cracking (FCC) units. Because Y-type molecular sieves are prone to carbon deposition and deactivation, an FCC unit is required, operating under fluidized conditions to achieve a rapid deactivation-activation process. However, the catalytic cracking of waste plastics is difficult to carry out in FCC units like petroleum cracking, so the deactivation problem of Y-type molecular sieve catalysts limits their application in plastic cracking.

[0004] In summary, existing technologies for preparing liquid fuels from waste plastics still have drawbacks such as complex processes, high costs, and easy deactivation of catalysts. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for preparing liquid fuels from waste plastics through catalytic cracking using nano-Beta molecular sieves, thereby achieving the goal of efficient and highly selective production of liquid fuels.

[0006] To achieve the above objectives, the technical solution adopted in this invention is as follows: nano-Beta molecular sieve catalyst and waste plastic are mixed evenly and added to a reactor, nitrogen gas is introduced, and the reaction is carried out for a certain time under certain temperature conditions. The resulting product is carried out by nitrogen gas, condensed, and the liquid product is collected to obtain liquid fuel.

[0007] The method for preparing liquid fuel from waste plastics provided by this invention includes the following steps:

[0008] 1) Mix waste plastics with the catalyst, add to the reactor, and form a reaction system.

[0009] 2) The reaction system is made to react, and the products are carried out by the flowing nitrogen gas and condensed to obtain liquid fuel;

[0010] In step 1) of the above method, the waste plastic is a polymer whose backbone is composed of carbon-carbon saturated bonds, including but not limited to polyethylene, polypropylene, polystyrene, and polyvinyl chloride;

[0011] The catalyst is a nano-Beta molecular sieve with acidic sites on its outer surface and a crystal size of less than 100 nm.

[0012] Nanoscale molecular sieves have small crystal size, large external specific surface area, and abundant acidic sites on their outer surface, which can effectively contact plastic macromolecules. The resulting primary fracture products can enter the micropores of Beta molecular sieves for further shape-selective reactions. The channels of Beta molecular sieves are suitable for producing C5-C12 hydrocarbon products, and can be used to prepare liquid fuels with high selectivity.

[0013] The nano-Beta molecular sieve was prepared by the following method: Sodium hydroxide and tetraethylammonium hydroxide (TEAOH) aqueous solution were mixed, and then silica sol was added while stirring until a transparent gel was formed. Aluminum sulfate was then added, and the mixture was stirred for 24 hours, while allowing the ethanol formed by hydrolysis to evaporate. The resulting mixture had the following composition: 1SiO2:0.025Al2O3:0.6TEAOH:0.3NaOH:14H2O. The mixture was sealed in a high-pressure hydrothermal reactor and heated at 140°C for 48 hours. The product was centrifuged and washed several times with distilled water until the pH value was below 9. The product was then dried at 70°C for 12 hours and calcined at 550°C for 16 hours. Ion exchange was then performed using a 1 mol / L ammonium chloride aqueous solution at 80°C, repeated three times. The solid was washed, dried at 70°C, and calcined at 550°C for 4 hours to convert the sodium-type molecular sieve into a hydrogen-type molecular sieve.

[0014] The Si:Al molar ratio of the nano-Beta molecular sieve is 5 to 200, specifically 20.

[0015] The weight ratio of waste plastic to catalyst can be 200:1 to 0.1:1, specifically 50:1;

[0016] Before mixing, the process also includes crushing, rinsing, and drying the waste plastics.

[0017] In step 2) of the above method, the reaction temperature can be 300-500℃, specifically 350-400℃, and more specifically 380℃; the reaction time can be 0.1-5 hours, specifically 0.5-2 hours, and more specifically 1 hour.

[0018] The reaction process is carried out under normal pressure, and the product is condensed to obtain liquid fuel.

[0019] The liquid fuel is a liquid fuel mainly composed of C5-C12 alkanes.

[0020] Compared with the prior art, the present invention has the following significant advantages:

[0021] (1) Nano Beta molecular sieves catalyze the cracking of waste plastics with high efficiency and high selectivity for C5-C12 liquid fuel components;

[0022] (2) The catalyst is stable and not easily deactivated;

[0023] (3) The reaction process is simple and environmentally friendly. Attached Figure Description

[0024] Figure 1 The conversion rate of HDPE after 4 cycles of nano-Beta molecular sieve in Example 4 of this invention is shown.

[0025] Figure 2 The C5-C12 hydrocarbon selectivity of the nano-Beta molecular sieve used four times in Example 4 of this invention is demonstrated. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0027] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0028] This invention provides a method for preparing liquid fuel from waste plastics. Specifically, a nano-Beta molecular sieve catalyst and waste plastics are mixed evenly and added to a reactor. Nitrogen gas is introduced, and the reaction is carried out for a certain time under certain temperature conditions. The resulting product is carried out by nitrogen gas, condensed, and the liquid product is collected to obtain liquid fuel.

[0029] The liquid fuel is mainly composed of C5-C12 hydrocarbons.

[0030] The nano-Beta molecular sieves used in the following examples were prepared by the following method: 0.8 g of sodium hydroxide and 16.5 g of a 35% tetraethylammonium hydroxide (TEAOH) aqueous solution were mixed, and then 9.8 g of a 40% silica sol was added while stirring until a transparent gel was formed; then 0.56 g of aluminum sulfate was added and stirred for 24 hours, while allowing the ethanol formed by hydrolysis to evaporate; the composition of the resulting mixture was 1SiO2:0.025Al2O3:0.6TEAOH:0.3NaOH:14H2O; the mixture was then densely packed... The product was sealed in a high-pressure hydrothermal reactor and heated at 140°C for 48 hours. The product was then centrifuged and washed several times with distilled water until the pH value was below 9. The product was then dried at 70°C for 12 hours and calcined at 550°C for 16 hours. Then, ion exchange was performed using a 1 mol / L ammonium chloride aqueous solution at 80°C, repeated three times. The solid was washed, dried at 70°C, and calcined at 550°C for 4 hours to convert the sodium-type molecular sieve into a hydrogen-type molecular sieve. The resulting nano-Beta molecular sieve had a Si / Al molar ratio of 20 and a particle size of 50-100 nm.

[0031] Example 1

[0032] The first step is to mix the waste plastic with the catalyst (by grinding and mixing), then add the mixture to the reactor to form a reaction system.

[0033] The catalyst is a nano-Beta molecular sieve (Si / Al = 20), and the waste plastic is high-density polyethylene (HDPE). The two are mixed evenly, and the weight ratio of waste plastic to catalyst is 50:1.

[0034] In the second step, the reaction system from the first step is reacted at 380°C for 1 hour. The resulting product is carried out by nitrogen gas, condensed, and the liquid product is collected.

[0035] The analysis results showed that the HDPE conversion rate was 91% and the C5-C12 hydrocarbon selectivity was 76% (Table 1).

[0036] Example 2

[0037] Except for the following differences, everything else is the same as in Example 1:

[0038] In the first step, the waste plastic (reactant) is low-density polyethylene.

[0039] The analysis results showed that the LDPE conversion rate was 95% and the C5-C12 hydrocarbon selectivity was 70% (Table 1).

[0040] Example 3

[0041] Except for the following differences, everything else is the same as in Example 1:

[0042] In the first step, the waste plastic (reactant) is polypropylene (PP).

[0043] The analysis results showed that the PP conversion rate was 94% and the C5-C12 hydrocarbon selectivity was 73% (Table 1).

[0044] Table 1. Preparation of liquid fuels from waste plastics via catalytic cracking using nano-Beta molecular sieves.

[0045]

[0046] As can be seen from the results of the above embodiments, nano-Beta molecular sieves can efficiently catalyze the degradation of waste plastics through cracking and produce liquid fuels with high selectivity, mainly composed of C5-C12 hydrocarbons.

[0047] Example 4

[0048] Except for the following differences, everything else is the same as in Example 1:

[0049] After the reaction, the catalyst was collected, and Example 1 was repeated three more times to test the catalyst stability.

[0050] The analysis results show that the HDPE conversion rate remained between 87% and 90% in the three tests. Figure 1 The selectivity for C5-C12 hydrocarbons remained between 73-75%. Figure 2 This indicates that the catalyst has good stability.

[0051] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope, and without requiring unnecessary experiments. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A method for preparing liquid fuel from waste plastics by catalytic cracking, comprising the following steps: 1) Mix waste plastics with the catalyst, add to the reactor, and form a reaction system. 2) The reaction system is made to react, nitrogen gas is introduced to carry out the products, and the products are condensed to obtain liquid fuel; The catalyst is a nano-Beta molecular sieve; The nano-Beta molecular sieve was prepared by the following method: 0.8 g of sodium hydroxide and 16.5 g of a 35% tetraethylammonium hydroxide (TEAOH) aqueous solution were mixed, and then 9.8 g of a 40% silica sol was added while stirring until a transparent gel was formed; then 0.56 g of aluminum sulfate was added and stirred for 24 hours, while allowing the ethanol formed by hydrolysis to evaporate; the composition of the resulting mixture was 1 SiO2: 0.025 Al2O3: 0.6 TEAOH: 0.3 NaOH: 14 H2O; the mixture was sealed in a high-pressure hydrothermal reactor and heated at 140 °C for 48 hours. The product was centrifuged and washed several times with distilled water until the pH value was below 9; then the product was dried at 70 °C for 12 hours and calcined at 550 °C for 16 hours; then, ion exchange was performed using a 1 mol / L ammonium chloride aqueous solution at 80 °C, repeated three times, and the solid was washed, dried at 70 °C, and calcined at 550 °C. Calcination at ℃ for 4 hours converts sodium-type molecular sieves into hydrogen-type molecular sieves; The Si:Al molar ratio of the nano-Beta molecular sieve is 20; The nano-Beta molecular sieve has acidic sites on its outer surface and a particle size of 50-100 nm. The weight ratio of waste plastic to catalyst is 50:1; The reaction is carried out at a temperature of 350-400℃ for a time of 0.5-2 hours. The resulting liquid fuel is mainly composed of C5-C12 alkanes.

2. The method according to claim 1, characterized in that: In step 1), the waste plastic is a polymer with a carbon-carbon saturated bond skeleton, and is one or a mixture of several of polyethylene, polypropylene, polystyrene, and polyvinyl chloride.

3. The method according to claim 1 or 2, characterized in that: The reaction was carried out under normal pressure conditions.

Images