Method for preparing nanographene by high-temperature flash pyrolysis of PET waste plastic powder

Abstract

The invention discloses a method for preparing nano-graphene by high-temperature flash pyrolysis of PET waste plastic powder, comprising: tearing and crushing, washing and impurity removal, deep cold crushing, warehouse pump gas delivery, flash carbonization, chemical activation, pyrolysis activation, neutralization washing, air flow drying, and product collection. The invention proposes a method for preparing nano-graphene by high-temperature flash pyrolysis of PET waste plastic powder in an oxygen-free environment using recycled waste PET plastic as a precursor carbon source and solid waste treatment. The method has the advantages of abundant raw material sources, easy solid waste recycling, high plastic carbon content, simple preparation process, green, low-carbon and environmentally friendly, low production cost, high product added value and high comprehensive utilization efficiency, and suitability for industrial-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling and comprehensive utilization of PET waste plastics and preparing nanographene by high-temperature thermal cracking of hydrocarbon macromolecular thermoplastic polymer materials. Background Art

[0002] PET or PETP plastic (or polyester chips, polyester resin), Chinese means polyethylene terephthalate plastics, chemical formula (C10H8O4)n, temperature resistance of about 120 ℃, belongs to hydrocarbon polymer thermoplastic polymer materials, PET plastics have good optical properties and weather resistance, amorphous PET plastics have good optical transparency. In addition, PET plastics have excellent wear resistance, friction, stability, insulation. Bottles made of PET have high strength, good transparency, non-toxic and harmless, anti-permeability, light weight, high production efficiency, etc., so they are widely used. For example, plastic packaging bottles are used in mineral water bottles, edible oil bottles, condiment bottles, medicine bottles, cosmetic bottles, etc.; plastic film sheets are used in various types of food, medicine, non-toxic and sterile packaging materials, etc. Due to the wide application of plastics, the production and consumption demand has increased sharply, resulting in a large amount of waste PET plastics worldwide. At present, the problem of plastic pollution has gradually become the second largest global environmental issue after climate change. Statistics show that from 1950 to 2017, the world produced a total of about 9.2 billion tons of plastics. It is estimated that by 2050, the global cumulative plastic production will reach 34 billion tons, and the annual generation of plastic waste will be about 300 million tons. As a major plastic producer and consumer, my country generates 60 million tons of plastic waste annually.

[0003] At present, there are three common methods for recycling waste plastics: granulation, landfill and incineration. However, granulation has the disadvantage of low utilization rate, landfill has the disadvantage of difficult degradation, and incineration has the disadvantage of air pollution, and none of them can meet the demand.

[0004] In order to solve the problem of plastic pollution, accelerate the technological innovation achievements of recycling and comprehensive utilization of waste plastics, and develop plastic recycling economy and comprehensive utilization, it is necessary to guide the society to participate widely, among which the role of enterprises is crucial. Therefore, in order to solve the pain points of waste plastics such as difficult treatment, heavy pollution, and low added value. The invention of "the method of preparing nanographene by high-temperature flash pyrolysis of PET waste plastic powder" is an innovative industrial large-scale waste plastic solid waste treatment production and preparation technology, which can pyrolyze and carbonize PET waste plastics in an oxygen-free environment to prepare high-value-added nanographene, fuel oil, gas and other terminal products, with solid waste regeneration, harmless treatment of reduction, turning waste into treasure, recycling resources, low cost and high added value, green and low-carbon environmental protection. The innovative method takes PET plastic as the precursor carbon source of the invention, and the carbon content of PET plastic is 45%. The system carbonization rate can reach 18-25%, and the recycling rate of combustibles is about 65%. The promotion significance of the invention lies in solving the two major problems of "difficult recycling of waste plastics" and "high cost of graphene preparation" at the same time. This nanographene product has the characteristics of small particle size, thin thickness, large specific surface area, developed pores, strong adsorption and high electrical conductivity. Summary of the invention

[0005] The present invention provides a method for preparing nano-graphene by utilizing high-temperature flash pyrolysis of PET waste plastic powder, in order to address the problems of difficulty in recycling and processing of existing waste plastics, backward and low-end technology, and serious environmental pollution. In order to solve the pain points of plastic pollution, difficulty in processing, and low added value, the innovative technology of the present invention has rich sources of raw materials, high content of precursor carbon sources, simple pyrolysis technology, low preparation and production costs, and can recycle and reuse waste plastics, thereby realizing resource utilization, reduction, and harmless treatment of PET waste plastic recycling, and the system is suitable for industrial large-scale production of nano-graphene methods.

[0006] In order to achieve the purpose of the present invention, the present invention adopts the following production and preparation technical scheme: a method for preparing nano-graphene by high-temperature flash pyrolysis of PET waste plastic powder, and innovative technical results processing of PET waste plastic includes: tearing and crushing, cleaning and impurity removal, deep cold crushing, warehouse pump air delivery, flash carbonization, chemical activation, pyrolysis activation, neutralization washing, air flow drying, product collection and other ten production technology preparation steps and links, by crushing the PET plastic into fine powder, and then, in an oxygen-free environment, under the power of superheated steam, the small molecules of the plastic powder particles atomized by the air flow are heated (carbonized / activated) in a high-temperature tubular pyrolysis furnace for reaction, and the flash evaporation is instantly heated and expanded, and the powder is flashed and pyrolyzed in dynamic motion and then collected and cooled to produce nano-graphene and combustible products.

[0007] The specific steps include:

[0008] (1) Tearing and crushing: The recycled PET waste plastic is first shredded into 5-20 mm fragments through a tearing machine;

[0009] (2) Cleaning and removing impurities: The contaminated plastic fragments torn into 5-20 mm pieces in step (1) are cleaned and label impurities are removed in a drum cleaning machine with water, and then dehydrated and air-dried;

[0010] (3) Cryogenic pulverization: the plastic fragments that have been dehydrated and air-dried in step (2) are pulverized into plastic powder with a particle size of 80-300 meshes by a low-temperature liquid nitrogen refrigerant plastic pulverizer;

[0011] (4) pneumatic conveying by a silo pump; the plastic powder and potassium hydroxide powder crushed into a particle size of 80-300 mesh in step (3) are stirred and mixed, and the mixed powder is pneumatically conveyed to a silo pump for storage so as to be conveyed to the next production step;

[0012] (5) Flash carbonization: The mixed powder stored in the warehouse pump in step (4) is transported to a Laval collision mixer and a heat pipe thermal cracking reactor for high-temperature flash carbonization in an oxygen-free environment; the plastic powder is carbonized and stored at a constant temperature in a cyclone separator; the combustible fuel recovery product generated by the thermal cracking volatile matter is condensed and recovered in a condensation tower;

[0013] (6) Chemical activation: mixing the carbon powder of the plastic carbonization intermediate product obtained by flash carbonization in step (5) with 5% conductive carbon black and 30% hydrogen peroxide in a homogenizer for chemical activation;

[0014] (7) Pyrolysis activation: The mixed slurry chemically activated in step (6) is pumped into a Laval collision mixer and a heat pipe thermal cracking reactor by a single screw pump for high temperature activation reaction; after pyrolysis activation, it is stored at a constant temperature in a cyclone separator;

[0015] (8) Neutralization and washing: adding deionized water to the nanographene activated carbon intermediate product obtained by pyrolysis and activation in step (7), mixing, stirring, washing, neutralizing and filtering; the slurry is neutralized to a pH value of 7, and the neutralized and washed powder slurry is placed in a storage tank;

[0016] (9) airflow drying; conveying the slurry after neutralization and washing in step (8) to a Laval collision mixer and a heat pipe thermal cracking reactor through a single screw pump for airflow drying; and storing the slurry at a constant temperature in a cyclone separator and a dust collector after drying;

[0017] (10) Product collection: The nanographene product dried by airflow in step (9) is sorted by a secondary cyclone separator and collected by a dust collector, and then transported by airflow to a product storage bin, cooled to below 45° C., and then packaged and stored.

[0018] The advantages of the present invention compared with the prior art are:

[0019] 1. The present invention proposes a method for preparing nanographene by recycling waste PET plastic as a precursor carbon source, treating solid waste, and utilizing PET waste plastic powder for high-temperature flash pyrolysis in an oxygen-free environment. The method has the advantages of abundant raw material sources, easy solid waste recycling, high plastic carbon content, simple preparation process, green and low-carbon environmental protection, low production cost, high product added value and high comprehensive utilization efficiency, and is suitable for industrial-scale production.

[0020] 2. Regardless of the carbonization or activation process, the plastic powder is flash-pyrolyzed and carbonized in the tubular furnace of the thermal cracking reactor under an oxygen-free environment. The pressure and temperature of the steam can be adjusted arbitrarily; superheated steam and carbon dioxide are used as physical activators; potassium hydroxide and hydrogen peroxide (hydrogen peroxide) are used as chemical activators; the chemical activation method and the physical activation method are used in combination at the same time, the activation effect is better, the product quality is better, and the product has the characteristics of small particle size, thin thickness, large specific surface area, developed pores, strong adsorption, and high conductivity.

[0021] 3. The present invention utilizes plastic to prepare nano-graphene materials, which have the common advantages of nano-porous hard carbon materials and nano-graphene material products, and are widely used. The main application fields include: graphene composite material additives, cement concrete reinforcers, new energy battery materials, supercapacitor materials, graphene coatings, semiconductor materials, electronic and electrical materials, graphene conductive and thermal conductive materials, graphene plastic composite materials, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Process flow chart for preparing nanographene by flash pyrolysis of waste plastic powder according to the embodiment of the present invention

[0023] Figure 2 The particle size distribution of the nanographene material prepared from the waste plastic powder in the embodiment of the present invention.

[0024] Figure 3 This is a scanning electron microscope photo of the nanographene material prepared from waste plastic powder in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0026] Example:

[0027] Reference Figure 1 The present invention is a process flow chart of preparing nanographene by flash pyrolysis of PET waste plastic powder in accordance with an embodiment of the present invention. In combination with the accompanying drawings and specific embodiments, the detection equipment of the powder in the embodiment mainly includes: laser particle size analyzer, specific surface area detector, scanning electron microscope, powder resistivity tester and other related detection equipment. In order to further elaborate on the technical scheme of the present invention, the production process of industrially producing nanographene by flash pyrolysis of PET waste plastic powder includes the following ten preparation steps:

[0028] (1) Tearing and crushing: my country has abundant PET waste plastic resources, with an annual output of 50 to 60 million tons of waste plastics. Plastic resources can be recycled and comprehensively utilized. In particular, PET waste plastics have the advantages of being cheap, easy to obtain, with few impurities, low ash content, and high carbon content. Specifically, tearing and crushing is to tear the recycled PET waste plastics into 5 to 20 mm fragments through a multi-tooth tearing machine.

[0029] (2) Cleaning and removing impurities: The 5-20 mm plastic fragments in the above tearing and crushing are transported to a drum machine to be cleaned with water to remove sludge and impurities from bottle labels, and then dehydrated by a centrifuge and dried by heat in a drying drum.

[0030] (3) Cryogenic pulverization: The 5-20 mm plastic fragments that have been cleaned, decontaminated, dehydrated and air-dried are pulverized into plastic powder with a particle size of 80-300 meshes by a liquid nitrogen refrigerant plastic pulverizer at -196°C.

[0031] (4) Silo pump pneumatic delivery: The above-mentioned deep-cold crushed 80-300 mesh powder is stirred and mixed with potassium hydroxide powder, and the mixing ratio of carbon alkali powder is 3:1. Then, the carbon alkali mixed powder is pneumatically transported to a silo pump for storage by compressed air so as to be transported to the next thermal cracking carbonization production stage.

[0032] (5) Flash carbonization: The carbon alkali mixed powder (plastic powder + potassium hydroxide powder) delivered by the above-mentioned silo pump is transported to the Laval collision mixer and the heat pipe thermal cracking reactor for high-temperature flash carbonization reaction in an oxygen-free environment. The thermal cracking power gas source is superheated steam, the superheated steam temperature is 500°C, and the pressure is 0.5-1.6MPa; the flash carbonization temperature of the plastic powder is 800-1100°C; the carbonization time is 5-10 seconds; after carbonization, the plastic powder needs to be stored at a constant temperature in a cyclone separator for 30 minutes; the combustible fuel (gasoline, diesel, combustible gas) produced by the thermal cracking volatiles produced by the flash carbonization of the plastic must be condensed and recycled in a condensation tower.

[0033] (6) Chemical activation: The carbon powder of the plastic carbonization intermediate product obtained by flash carbonization is chemically activated, mixed, stirred, homogenized, and oxidized in a homogenizer; the chemical activation temperature is 60° C., and the chemical activation time is 1 hour.

[0034] (7) Pyrolysis activation: The chemically activated mixed slurry is pumped into a Laval collision mixer and a heat pipe thermal cracking reactor through a single screw pump for high-temperature activation reaction; the physical activators are superheated steam and carbon dioxide gas; the superheated steam temperature is 500°C and the pressure is 0.5-1.6 MPa; the pyrolysis activation temperature is 600-900°C; the pyrolysis activation time is 5-10 seconds, and after pyrolysis activation, it is stored at a constant temperature in a cyclone separator for 30 minutes.

[0035] (8) Neutralization and washing: The nanographene activated carbon intermediate product obtained by pyrolysis and activation is added with deionized water for mixing, stirring, washing, neutralization and filtering; the slurry is neutralized to a pH value of 7, and the neutralized and washed powder slurry is placed in a storage tank.

[0036] (9) Airflow drying: The neutralized and washed slurry is transported to a Laval collision mixer and a heat pipe thermal cracking reactor through a single screw pump for airflow drying; the required power source is superheated steam with a temperature of 500°C and a pressure of 0.5 to 1.6 MPa; the required airflow drying temperature is 300 to 500°C; the required drying time is 5 to 10 seconds, and after drying, it is stored at a constant temperature in a cyclone separator and a dust collector for 30 minutes.

[0037] (10) Product collection: The above-mentioned nanographene products dried by air flow are graded and sorted by a secondary cyclone separator and collected by a dust collector. They are then transported by air flow to a product storage bin, cooled to below 45° C., and then packaged and stored.

[0038] In the implementation of preparing nanographene using waste plastics, the nanographene product testing parameters of the example are shown in the following table:

[0039]

[0040] In summary, the particle size of nanographene is 200-800nm, the thickness is less than 10 layers, and the BET surface area is 500-1500m 2 / g, and the electrical conductivity is 0.35-0.45s / cm.

[0041] The invention adopts PET waste plastic as raw material, the precursor carbon source has a high carbon content, adopts the popcorn carbonization principle to perform high-temperature, high-pressure, high-speed and high-efficiency fluid collision mixing, flash carbonization in an oxygen-free environment, pyrolysis activation, and the atomized plastic powder small molecules are instantly flash-evaporated and heated to expand, and are instantly carbonized into porous graphene materials by thermal cracking during dynamic movement. The carbonization / activation process is short in time, high in efficiency and fast in speed. The entire carbonization / activation time is only about 5 to 10 seconds, which is energy-saving, efficient, green and environmentally friendly, and can produce nano-graphene with developed pores, large specific surface area, high efficiency and high quality, and condensed and recovered combustibles (gasoline, diesel) Oil, combustible gas); the present invention has the advantages of plastic solid waste regeneration, harmless treatment, resource recycling, low cost and high added value, green, low-carbon and environmentally friendly high added value innovative preparation method of nano graphene, according to the carbon content of PET plastic is 45% calculated system carbonization rate can reach 18-25%, combustible recycling rate is about 65%, at the same time solves the two major problems of "waste plastic recycling is difficult" and "graphene preparation cost is high"; this invention creates a new method for preparing nano graphene with high molecular polymer materials such as plastics, resins, phenolic resins, fiber materials, rubber, viscose materials, etc.

[0042] From the above content, it can be seen that the nanographene product prepared by the present invention has the characteristics of small particle size, thin thickness, large specific surface area, developed pores, strong adsorption, high conductivity, etc.

[0043] Obviously, the above embodiments of the present invention are merely examples to more clearly illustrate the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing nanographene by high-temperature flash pyrolysis of PET waste plastic powder, characterized in that: The following steps are involved: (1) Tearing and crushing: The recycled PET waste plastic is first shredded into 5-20 mm fragments through a tearing machine; (2) Cleaning and removing impurities: The contaminated plastic fragments torn into 5-20 mm pieces in step (1) are cleaned and label impurities are removed in a drum cleaning machine with water, and then dehydrated and air-dried; (3) Cryogenic pulverization: the plastic fragments that have been dehydrated and air-dried in step (2) are pulverized into plastic powder with a particle size of 80-300 meshes by a low-temperature liquid nitrogen refrigerant plastic pulverizer; (4) Gas delivery by warehouse pump; The plastic powder and potassium hydroxide powder crushed into 80-300 mesh size in step (3) are stirred and mixed, and the mixed powder is pneumatically conveyed to a silo pump for storage so as to be conveyed to the next production step; (5) Flash carbonization: The mixed powder stored in the warehouse pump in step (4) is transported to a Laval collision mixer and a heat pipe thermal cracking reactor for high-temperature flash carbonization in an oxygen-free environment; after the plastic powder is carbonized, it is stored at a constant temperature in a cyclone separator; The combustible fuel recovery produced by the thermal cracking volatile matter is condensed and recovered in a condensation tower; (6) Chemical activation: mixing the carbon powder of the plastic carbonization intermediate product obtained by flash carbonization in step (5) with 5% conductive carbon black and 30% hydrogen peroxide in a homogenizer for chemical activation; (7) Pyrolysis activation: The mixed slurry chemically activated in step (6) is pumped into a Laval collision mixer and a heat pipe thermal cracking reactor by a single screw pump for high temperature activation reaction; after pyrolysis activation, it is stored at a constant temperature in a cyclone separator; (8) Neutralization and washing: adding deionized water to the nanographene activated carbon intermediate product obtained by pyrolysis and activation in step (7), mixing, stirring, washing, neutralizing and filtering; the slurry is neutralized to a pH value of 7, and the neutralized and washed powder slurry is placed in a storage tank; (9) airflow drying; conveying the slurry after neutralization and washing in step (8) to a Laval collision mixer and a heat pipe thermal cracking reactor through a single screw pump for airflow drying; and storing the slurry at a constant temperature in a cyclone separator and a dust collector after drying; (10) Product collection: The nanographene product dried by airflow in step (9) is sorted by a secondary cyclone separator and collected by a dust collector, and then transported by airflow to a product storage bin, cooled to below 45° C., and then packaged and stored.

2. The method for preparing nano-graphene by high-temperature flash pyrolysis of PET waste plastic powder according to claim 1, characterized in that: In step (3), the temperature of the low-temperature deep-cold crushing liquid nitrogen refrigerant is minus 196°C.

3. The method for preparing nano-graphene by high-temperature flash pyrolysis of PET waste plastic powder according to claim 1, characterized in that: In step (4), the ratio of carbon alkali mixed powder is 3:1, and the gas source of the silo pump air delivery power is compressed air or carbon dioxide gas.

4. The method for preparing nano-graphene by high-temperature flash pyrolysis of PET waste plastic powder according to claim 1, characterized in that: In step (5), the thermal cracking power gas source is superheated steam, the temperature is 500°C, and the pressure is 0.5-1.6 MPa; the carbonization temperature is 800-1100°C; the carbonization time is 5-10 seconds, and the plastic powder is stored at a constant temperature in a cyclone separator for 30 minutes after carbonization.

5. The method for preparing nano-graphene by high-temperature flash pyrolysis of PET waste plastic powder according to claim 1, characterized in that: In step (5), the combustible fuel includes gasoline, diesel, and combustible gas.

6. The method for preparing nano-graphene by high-temperature flash pyrolysis of PET waste plastic powder according to claim 1, characterized in that: In step (6), the chemical activation temperature is 60° C. and the chemical activation time is 1 hour.

7. The method for preparing nano-graphene by high-temperature flash pyrolysis of PET waste plastic powder according to claim 1, characterized in that: In step (7), a physical activator is used in the high-temperature activation reaction, and the physical activator is superheated steam and carbon dioxide gas; the superheated steam temperature is 500°C and the pressure is 0.5-1.6MPa; the pyrolysis activation temperature is 600-900°C; the pyrolysis activation time is 5-10 seconds, and after pyrolysis activation, it is stored at a constant temperature in a cyclone separator for 30 minutes.

8. The method for preparing nano-graphene by high-temperature flash pyrolysis of PET waste plastic powder according to claim 1, characterized in that: In step (9), the power source of the air flow drying is superheated steam, the temperature is 500°C, and the pressure is 0.5-1.6MPa; the air flow drying temperature is 300-500°C; the drying time is 5-10 seconds, and after drying, it is stored at a constant temperature in a cyclone separator and a dust collector for 30 minutes.

9. The method for preparing nano-graphene by high-temperature flash pyrolysis of PET waste plastic powder according to claim 1, characterized in that: In step (10), the nanographene has a particle size of 200 to 800 nm, a thickness of less than 10 layers, and a BET surface area of ​​500 to 1500 m 2 / g, and the electrical conductivity is 0.35-0.45S / cm.

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