CN116064063A - Method for treating waste plastics - Google Patents

Abstract

The present disclosure relates to a method of treating waste plastics, the method comprising the steps of: s1, mixing the waste plastics with a high-temperature heat carrier in a thermal melting kettle to obtain a mixed material containing molten waste plastics and a first gaseous hydrocarbon mixture; s2, separating the mixed material obtained in the step S1 in a first separator to obtain a molten material from which solid impurities are removed; s3, enabling the melted material to contact with a catalyst in a catalytic cracking reactor for catalytic cracking to obtain a second gaseous hydrocarbon mixture, heavy oil and a bottom product; wherein the high-temperature heat carrier comprises molten inorganic alkali and/or high-temperature inorganic alkaline water solution, and the temperature of the high-temperature heat carrier is 150-550 ℃. The method disclosed by the invention is suitable for waste plastics with various shapes, solves the problem of difficult waste plastic conveying, reduces the problems of corrosion of HCl to equipment and pipelines and tail gas pollution, and improves the reaction rate and the product selectivity.

Description

Method for treating waste plastics

Technical Field

The present disclosure relates to the field of waste plastic treatment, and in particular, to a method of treating waste plastic.

Background

Plastics have become the main materials in many fields, such as daily life, construction, packaging and electronic products of people, because the plastics have the characteristics of light weight, low price and the like, great convenience is brought to life and production of people, the world plastic yield breaks through 1 hundred million for the first time in 1991, the world plastic yield is 3.45 hundred million by 2017, the global plastic yield reaches 78 hundred million tons from 1950 to 2015, meanwhile, the industrialization is difficult to realize due to higher cost of recovery, cleaning, sorting and the like in use, the total recovery rate is about 14 percent, the degradation speed is slow, and the people have to live together with a large amount of waste plastics, the living environment of people is greatly influenced, and the situation of white pollutants of the waste plastics appears in the rare south poles of the life of people.

Waste plastics produced in daily life mainly comprise PP (polyethylene), PE (polypropylene), PVC (polyvinyl chloride) and PS (polystyrene) polymer films, mainly comprise C, H, cl and metal elements, have large daily amount and large volume, are slow in degradation speed, and are one of main pollutants causing the environment. If the waste plastics can be recycled, the waste plastics has higher economic value, for example, waste plastics are combusted to generate heat, and the heat value generated by polypropylene incineration of the waste plastics is 43MJ/kg, which is equivalent to fossil energy (gasoline 42.30 MJ/kg; kerosene, 46.50MJ/kg, diesel oil, 45.20 MJ/kg); the waste plastics are cleaned and sorted, granulated into regenerated plastics with the price of 2500-5000 yuan/ton, if the waste plastics can be accurately classified according to the same color and purity grade, the waste plastics can be prepared into high-grade regenerated plastics, and when the quality of the waste plastics reaches the quality of raw materials, the price of the waste plastics is close to that of the raw materials, so that the waste plastics have higher economic value.

In the prior art: patent ZL201811062180.0 discloses a method for separating and collecting waste plastics in a household garbage power station and a production line. The waste plastic in the garbage power station is classified through crushing, screening and winnowing, and a great amount of heat energy contained in the tail gas generated in dust removal of the power station is utilized to deodorize and sterilize the garbage through circulating hot air, so that dust and peculiar smell in the garbage are greatly reduced. The water content in the garbage is reduced by cyclic heat treatment, the heat loss of garbage incineration is reduced, and the incineration power generation efficiency is improved. In addition, through the secondary circulation of the tail gas, the emission of incompletely toxic gases generated by incineration can be reduced. The technology is a low-additional utilization process only by the heat value recycling process of waste plastics through combustion, dioxin is easy to generate in the combustion process, and pollution is generated to the atmospheric environment.

Patent ZL03813514.0 describes a multi-step recycling process for preparing recycled plastics, characterized by an operating sequence selected from the group consisting of a pre-processing operation, a crushing operation, a gravity concentration sorting operation, a sorting by color, a sorting by thickness, friction or differential terminal velocity or resistance in air, a surface area to mass ratio control operation, a separation process enhanced by a narrow surface area to mass ratio distribution, a blending operation, and an extrusion and compounding operation. The plastic-rich mixture is subjected to the process, and one or more recycled plastics are collected as an output of the sequential process. The technology can effectively separate blocky materials, the resistance of the filmy and flaky materials in the air is mainly related to the appearance and the area, and when the density influence is not a main factor, the separation effect is greatly reduced, so that the technology is not suitable for separating the filmy and flaky materials waste plastics generated in life.

Patent ZL201910752724.4 describes a waste plastic treatment recovery system, including first recovery pond, the second recovery pond, multistage separation breaker, wash separator, packing apparatus and air supporting device, separation breaker includes fly cutter round pond and first high-speed separating centrifuge, fly cutter round pond and first high-speed separating centrifuge pass through the pipeline and are connected with first recovery pond, first recovery pond passes through the pipeline and is connected with air supporting device, air supporting device passes through the pipeline and is connected with the second recovery pond, wash separator passes through the pipeline and is connected with the second recovery pond, the second recovery pond passes through the pipeline and is connected with packing apparatus, the second recovery pond passes through the pipeline and is connected with fly cutter round pond, wash separator and separation breaker's end links to each other, packing apparatus links to each other with washing separator's end. The invention treats the waste water by the air floatation device, the treated water is reused for treating and recycling the waste plastic, the waste water is not required to be discharged, and the environmental pollution is reduced. The technology also has no problem related to how to sort waste plastics of different materials.

Because of the hydrophobicity of the surface of the membranous and lamellar waste plastics, bubbles are easily wrapped in water, the densities of PP, PE and PS are close to those of water, and the separation from the density of liquid is difficult to use.

In view of the above, the prior art has not been directed to a method for treating waste plastics without screening.

Disclosure of Invention

The object of the present disclosure is to provide a method for treating waste plastics, which is suitable for waste plastics of various shapes, and solves the problem of difficult waste plastic transportation, reduces corrosion of HCl to equipment and pipelines and problems of tail gas pollution, and improves reaction rate and product selectivity.

In order to achieve the above object, the present disclosure provides a method of treating waste plastics, the method comprising the steps of:

s1, mixing the waste plastics with a high-temperature heat carrier in a thermal melting kettle to obtain a mixed material containing molten waste plastics and a first gaseous hydrocarbon mixture;

s2, separating the mixed material obtained in the step S1 in a first separator to obtain a molten material from which solid impurities are removed;

s3, enabling the melted material to contact with a catalyst in a catalytic cracking reactor for catalytic cracking to obtain a second gaseous hydrocarbon mixture, heavy oil and a bottom product;

wherein the high-temperature heat carrier comprises molten inorganic alkali and/or high-temperature inorganic alkaline water solution, and the temperature of the high-temperature heat carrier is 150-550 ℃.

Optionally, the temperature of the high temperature heat carrier is 300-500 ℃.

Optionally, the inorganic base comprises one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, barium hydroxide and strontium hydroxide;

the mass fraction of inorganic alkali in the high-temperature inorganic alkali aqueous solution is more than 20%.

Optionally, in step S1, a mass ratio of the waste plastic to the inorganic base is 1: (3-10);

the mixing is carried out under the stirring condition, the stirring speed is 40-160r/min, and the time is 0.5-1h.

Optionally, the method further comprises: and enabling the first gaseous hydrocarbon mixture and the second gaseous hydrocarbon mixture to enter a fractionating tower for fractionating to obtain a dry gas fraction, a fuel oil fraction and a heavy oil fraction.

Optionally, the method further comprises: condensing a portion of the dry gas fraction by an overhead condenser and refluxing the condensed dry gas fraction to the fractionation column; enabling the other part of dry gas fraction to enter an alkali liquor washing tower to be contacted with alkali liquor for washing, so as to obtain washed dry gas;

the washing temperature is 20-90 ℃, the mass fraction of the alkali solution is 10-35%, and the mass ratio of the dry gas fraction of the other part to the alkali solution is 1: (2.5-10);

the alkali in the alkali solution is selected from NaOH, KOH and Ca (OH) ₂ One or more of them.

Optionally, the method further comprises: feeding the bottom product obtained in the step S3 into a second separator to separate out a heat carrier after reaction; heating the reacted heat carrier in a heater to obtain the high-temperature heat carrier;

optionally, a heat carrier is supplemented into the heater.

Optionally, in step S3, the catalyst includes a carrier, a binder, and an active component, where a mass ratio of the carrier, the binder, and the active component is (1.5-6): (0.6-1): 1, a step of;

the carrier comprises kaolin;

the binder comprises one or more of pseudo-boehmite, alumina sol and silica sol;

the active component comprises one or more of metal oxide, HUSY molecular sieve, ZSM-5 molecular sieve and aluminum phosphate molecular sieve;

the metal oxide comprises one or more of platinum oxide, palladium oxide, rhodium oxide, nickel oxide, zirconium oxide, zinc oxide and ferric oxide.

Optionally, in step S3, the catalytic cracking temperature is 400-550 ℃ and the catalytic cracking time is 5-30S; the mass ratio of the catalyst to the waste plastic is (5-12): 1, a step of;

optionally, the molten waste plastic and the high temperature heat carrier are fluidly fed into the catalytic cracking reactor;

optionally, the catalytic cracking reactor is a fixed bed reactor and/or a fluidized bed reactor.

Optionally, the chlorine content of the waste plastic is 0.5-6%;

the waste plastic comprises one or more of polyethylene, polypropylene, polyvinyl chloride and polystyrene.

By the technical scheme, the method rapidly melts the waste plastics into the flowable fluid by using the high-temperature heat carrier, and solves the problems of low density, large volume and difficult conveying and flowing of the film-shaped and sheet-shaped waste plastics; the alkaline high-temperature heat carrier can react with HCl gas generated in the process of decomposing waste plastics to generate chloride salt, so that the problems of corrosion of HCl to equipment and pipelines and tail gas pollution are reduced; and the process of the present application can increase the reaction rate and product selectivity.

Additional features and advantages of the present disclosure will be set forth in the detailed description which follows.

Drawings

The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification, illustrate the disclosure and together with the description serve to explain, but do not limit the disclosure. In the drawings:

fig. 1 is a diagram of a waste plastic treatment apparatus in one embodiment of the present application.

Description of the reference numerals

1. Feeding hopper valve of waste plastic feeding hopper 3 for waste plastic particles 2

4. Thermal melting kettle with waste plastic storage tank 5 and storage tank valve 6

7. First gaseous hydrocarbon mixture 8 heat carrier feed 9 hot melt pot valve

10. Catalytic cracking reactor for solid impurities 12 of first separator 11

13. Catalyst regenerator 14 heat carrier surge tank 15 for catalyst and coke

16. Heat carrier heating supplementary tank 17 heating part 18 heat carrier supplementary

19. Heat carrier circulation pump 20 heat carrier circulation control valve 21 fractionating tower

22. Heavy oil fraction 23 dry gas fraction 24 condenser

25. Temporary storage tank for cooling liquid reflux 26 alkali liquor washing tower 27 alkali liquor

28. Alkaline washing tail liquid 29 alkaline solution supplementing port 30 alkaline solution circulating pump

31. Dry gas after washing

Detailed Description

Specific embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating and illustrating the disclosure, are not intended to limit the disclosure.

The present disclosure provides a method of treating waste plastics, the method comprising the steps of:

s1, mixing the waste plastics with a high-temperature heat carrier in a thermal melting kettle 6 to obtain a mixed material containing molten waste plastics and a first gaseous hydrocarbon mixture 7;

s2, separating the mixed material obtained in the step S1 in a first separator 10 to obtain a molten material from which solid impurities 11 are removed;

s3, enabling the melted material to contact with a catalyst in a catalytic cracking reactor 12 for catalytic cracking to obtain a second gaseous hydrocarbon mixture, heavy oil and a bottom product;

wherein the high-temperature heat carrier comprises molten inorganic alkali and/or high-temperature inorganic alkaline water solution, and the temperature of the high-temperature heat carrier is 150-550 ℃.

In the present disclosure, step S1 also yields HCl gas and coke, wherein the HCl gas reacts with the high temperature hot carrier to form chloride salt, and the mixed material comprises molten waste plastic, chloride salt and coke.

In the present disclosure, the bottom product in step S3 includes: coke, chloride salt, high temperature heat carrier and a small portion of the fine powder catalyst.

In one embodiment of the present disclosure, the method further comprises: feeding the bottom product in the step S3 into a second separator to separate out a heat carrier after reaction; and heating the reacted heat carrier in a heater to obtain the high-temperature heat carrier. The operation is used for removing solid impurities such as chloride, coke, catalyst and the like in the bottom product, so that the heat carrier after the reaction is heated and then conveyed back to the melting kettle for carrying out the step S1, and the recycling of the heat carrier is realized.

In one embodiment of the present disclosure, the temperature of the high temperature heat carrier is 300-500 ℃. The high-temperature heat carrier meeting the temperature range is in quick and full contact with the waste plastic, so that the waste plastic can be quickly heated and instantly melted into molten fluid, and convenience is provided for subsequent conveying.

In the present disclosure, the inorganic base does not decompose within the temperature interval of the present disclosure, can form a stable molten state or dissolve in water to form a high temperature inorganic alkaline aqueous solution; further, the inorganic base includes one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, barium hydroxide and strontium hydroxide; the mass fraction of the inorganic base in the high-temperature inorganic base aqueous solution is 20% or more, preferably 25% or more.

In one embodiment of the present disclosure, in step S1, the mass ratio of waste plastics to inorganic base is 1: (3-10), preferably 1: (4-8). Wherein, the mass ratio of the waste plastic to the inorganic base refers to the mass ratio of the waste plastic to the initial charge of the molten inorganic base or the mass ratio of the waste plastic to the initial charge of the inorganic base in the high-temperature inorganic alkaline aqueous solution.

In one embodiment of the present disclosure, the mixing in step S1 is performed under stirring conditions at a rotational speed of 40-160r/min, preferably 50-140r/min; the time is 0.5-1h, preferably 0.5-0.8h.

In one embodiment of the present disclosure, the method further comprises, before step S1, pulverizing the waste plastics into waste plastics particles having a size of 2 to 20mm, preferably 5 to 20mm, for example, the waste plastics particles are film-like and have a size of (2×2) - (20×20) mm, preferably (5×5) - (20×20) mm. The manner of comminution is conventional in the art and may be, for example, a rotary chopper.

In the present disclosure, solid impurities include silt, stone, metal, and the like.

In one embodiment of the present disclosure, the method further comprises: the first gaseous hydrocarbon mixture 7 and the second gaseous hydrocarbon mixture are fed to a fractionation column 21 for fractionation to obtain a dry gas fraction 23, a fuel oil fraction and a heavy oil fraction 22.

In a further embodiment, the method further comprises: a part of the dry gas fraction is condensed 24 by an overhead condenser and then returned to the fractionating tower 21; and (3) enabling the other part of the dry gas fraction to enter an alkali liquor washing tower 26 to be contacted with alkali liquor for washing, so as to obtain washed dry gas 31. The dry gas after washing can be recovered or burnt in a torch, thereby meeting the requirements of tail gas environmental protection and emission. The alkali solution in the alkali liquor washing tower is continuously consumed in the circulating process, and needs to be continuously supplemented to ensure the smooth washing. In addition, a small amount of HCl gas enters the alkali liquor washing tower together with the other part of dry gas fraction, and can be trapped by alkali liquor washing, so that the problem of tail gas pollution is avoided.

In one embodiment of the present disclosure, the temperature of the wash is 20-90 ℃, preferably 20-80 ℃; the mass fraction of the alkali solution is 10-35%, preferably 10-30%; the mass ratio of the dry gas fraction to the alkaline solution of the other part is 1: (2.5-10), preferably 1: (3.5-10). Wherein the alkali in the alkali solution is selected from NaOH, KOH and Ca (OH) ₂ One or more of them.

In one embodiment of the present disclosure, the bottom product of step S3 is fed to a second separator to separate out the post-reaction heat carrier; and (3) enabling the heat carrier after the reaction to enter a heater for heating to obtain a high-temperature heat carrier, and returning the high-temperature heat carrier to a hot melting kettle for continuous use.

In one embodiment of the present disclosure, a heat carrier is supplemented into the heater. Since the reaction of the heat carrier with HCl generated by the reaction is consumed, it is required to be continuously supplemented to ensure the smooth progress of step S1.

In one embodiment of the present disclosure, in step S3, the catalyst includes a support, an active component, and a binder. The carrier comprises kaolin, the binder comprises one or more of pseudo-boehmite, alumina sol and silica sol, and the active component comprises one or more of metal oxide, HUSY molecular sieve, ZSM-5 molecular sieve and aluminum phosphate molecular sieve; wherein, the modification mode of the HUSY molecular sieve is high-temperature hydrothermal modification; the metal oxide includes one or more of platinum oxide, palladium oxide, rhodium oxide, nickel oxide, zirconium oxide, zinc oxide and iron oxide. Specifically, the active components can be HUSY molecular sieve and ZSM-5 molecular sieve, and the mass ratio of the HUSY molecular sieve to the ZSM-5 molecular sieve is (10-20): 1. further, the mass ratio of the carrier, the binder and the active component is (1.5-6): (0.6-1): 1, preferably (3-6): (0.6-0.8): 1.

in the present disclosure, the catalyst is subjected to a regeneration treatment after a period of reaction, and the regenerated catalyst is continuously returned to the reactor. The above regeneration treatment is performed in a regenerator.

In one embodiment of the present disclosure, in step S3, the catalytic cracking temperature is 400-550 ℃ for 5-30S; preferably, the temperature is 450-530 ℃ and the time is 6-20s; the mass ratio of the catalyst to the waste plastic is (5-12): 1, a step of; preferably (5.5-8.5): 1.

in one embodiment of the present disclosure, the molten waste plastic and the high temperature heat carrier are fluidly fed into the catalytic cracking reactor 12, and further, the catalytic cracking reactor 12 is a fixed bed reactor and/or a fluidized bed reactor.

In one embodiment of the present disclosure, the waste plastic has a chlorine content of 0.5-6%; preferably 0.5-5.5%.

In the present disclosure, the waste plastics include one or more of polyethylene (PP), polypropylene (PE), polyvinyl chloride (PVC), and Polystyrene (PS). The shape of the waste plastic may be a block, a film, a sheet, etc., and is not particularly limited herein.

In the present disclosure, step S1 is performed in a thermal dissolution kettle, and the waste plastic is added by a hopper and a valve is sealed. The bottom of the thermal melting kettle is provided with a sealing valve, the top of the thermal melting kettle is provided with a waste plastic adding port, a heat carrier circulating port, a heat carrier supplementing port and a first gaseous hydrocarbon mixture outlet, wherein the waste plastic adding port is used for adding waste plastic raw materials, the heat carrier circulating port is used for adding heat carriers after the reaction heated by a heater, the heat carrier supplementing port is used for supplementing the heat carriers to the thermal melting kettle, and the first gaseous hydrocarbon mixture outlet is used for discharging the first gaseous hydrocarbon mixture generated by pyrolysis.

In one embodiment of the disclosure, the catalytic cracking reactors are 2 reactors which are operated in parallel, and when the catalyst of one reactor is deactivated, the operation is switched to the other reactor to ensure that the deactivated catalyst is regenerated in time; in another embodiment, a catalyst regenerator is positioned adjacent to the reactor, and the deactivated catalyst is transported to the regenerator for regeneration in time and then returned to the reactor for continued catalytic reaction, with such cyclic regeneration being performed continuously.

In the present disclosure, a small portion of the catalyst enters the fractionation column with the second gaseous hydrocarbon mixture and is withdrawn from the bottom of the fractionation column along with the heavy oil produced by the fractionation.

In the present disclosure, the fuel oil fraction is further separated to obtain substances with different components, and the apparatus used for the separation is a conventional rectifying device, which is not specifically required herein.

In one embodiment of the present disclosure, as shown in fig. 1, waste plastics are crushed to obtain waste plastics particles 1, the waste plastics particles are added into a waste plastics hopper 2, a hopper valve 3 is opened, a storage tank valve 5 is closed, the waste plastics particles 1 to be treated are added into a waste plastics storage tank 4 from the hopper 2, after the waste plastics are added to a set amount, the hopper valve 3 is closed, the storage tank valve 5 is opened, an evacuation pipe of a first gaseous hydrocarbon mixture 7 is emptied, the waste plastics particles 1 in the storage tank are discharged into a thermal melting kettle 6, a high-temperature heat carrier is added into the thermal melting kettle 6, a stirring paddle of the thermal melting kettle 6 is opened, the waste plastics particles 1 are fully contacted with the high-temperature heat carrier, and the waste plastics particles 1 are rapidly melted into a molten state to obtain a mixed material containing molten waste plastics, the first gaseous hydrocarbon mixture 7 and HCl gas. The hot melting kettle valve 9 is opened, the mixed material is discharged into the first separator 10, the solid impurities 11 such as sand, soil, metal and the like in the mixed material are removed, and the mixed material is conveyed into the catalytic cracking reactor 12 for catalytic cracking reaction, so that heavy oil, coke, HCl gas and a second gaseous hydrocarbon mixture are generated. The second gaseous hydrocarbon mixture is discharged from an outlet at the top of the catalytic cracking reactor 12, mixed with the first gaseous hydrocarbon mixture 7 and HCl gas, and then introduced into a fractionating tower, and separated to obtain a dry gas fraction 23, a fuel oil fraction and a heavy oil fraction 22. Part of the overhead gas is condensed into liquid by a condenser 24 and flows back to the fractionating tower 21, and the other part of the overhead gas enters an alkali liquor washing tower 26 to be contacted with alkali liquor for washing, and the washed dry gas is recovered or burnt by a torch. The heat carrier of the catalytic cracking reactor 12, the coke, chloride and catalyst produced by the reaction are discharged from the bottom of the catalytic cracking reactor 12 in a liquid state, the solid impurities such as chloride, catalyst and coke 15 in the heat carrier are removed by the heat carrier temporary storage tank 14 and then discharged into the heat carrier heating supplementing tank 16, and the heat carrier is conveyed back to the thermal melting kettle 6 by the heating of the heating component 17, the heat carrier supplementing 18 and the heat carrier circulating pump 19 for melting the waste plastic particles 1. The catalyst carried along with the second gaseous hydrocarbon mixture is separated by fractionation column 21 and discharged from the bottom of the fractionation column together with the heavy oil.

In the examples and comparative examples of the present application, the reagents used were all commercially available unless otherwise specified.

Example 1

With the waste plastic treatment apparatus shown in fig. 1, the waste plastic sample A1 is a mixture of PP film (polypropylene), PE film (polyethylene) and PVC film (polyvinyl chloride), wherein PP: PE: pvc=4.58:7.42:1 (mass ratio), chopped into waste plastic particles of about 10×10mm size, and dried at 105 ℃ for 24 hours to obtain 16kg of moisture in the plastic.

(1) Putting waste plastic particles into a thermal melting kettle, heating 90kg of sodium hydroxide with the mass fraction of 100% to 550 ℃, putting into the thermal melting kettle, starting a stirring motor, converting the waste plastic particles into a molten state after 10min at the speed of 85r/min, stirring for 0.5h, and obtaining a mixed material containing molten waste plastic, chloride and coke and a first gaseous hydrocarbon mixture at the temperature of 490 ℃ in the thermal melting kettle after thermal equilibrium.

(2) And (3) passing the mixed material obtained in the step (1) through a first separator to remove stone and other solid impurities with diameters larger than 2mm, so as to obtain a molten material, wherein the total weight of the solid impurities is 0.25kg.

(3) The melted material is introduced into a catalytic cracking reactor and reacted for 20s at 520 ℃.

(4) And (3) introducing the first gaseous hydrocarbon mixture obtained in the step (1) and the second gaseous hydrocarbon mixture obtained in the step (4) into a fractionating tower for fractionating to obtain a dry gas fraction, a fuel oil fraction and a heavy oil fraction.

(5) A part of dry gas fraction is condensed by a tower top condenser and then flows back to the fractionating tower, and the condensing temperature is 35 ℃; and (3) the other part of the dry gas fraction and HCl which does not react with the heat carrier enter an alkali liquor washing tower to be contacted with alkali liquor for washing, so that the washed dry gas is obtained.

(6) And (3) sending the bottom product obtained in the step (3) into a second separator to separate out the heat carrier after the reaction, and sending the heat carrier into a heater for heating and recycling to obtain the high-temperature heat carrier.

Wherein the washing temperature is 25 ℃, the alkali solution is a NaOH solution with the mass fraction of 30%, and the mass ratio of the other part of overhead gas to the alkali solution is 1:6.7. The mass ratio of the waste plastics to the inorganic base is 1:6, and the mass ratio of the waste plastics to the catalyst is 1:6. the catalyst is prepared by a conventional method, wherein the active components are ZSM-5 molecular sieve and HUSY molecular sieve, the carrier of the catalyst is kaolin, the binder is pseudo-boehmite, and the mass ratio of the carrier, the binder and the active components is 3: the mass ratio of the ZSM-5 molecular sieve to the HUSY molecular sieve is 1:10 and is 0.8:1. The chlorine content of the waste plastic was 3.4%. The feed temperature of the cooling medium in the condenser was 25℃and the discharge temperature was 42 ℃.

Each isolated product was analyzed and the results are shown in Table 1.

Reaction conversion rate:

example 2

Using the flow chart shown in fig. 1, the waste plastic sample A2 is a mixture of PP film (polypropylene), PE film (polyethylene) and PVC film (polyvinyl chloride), wherein PP: PE: pvc=5.77:1.93:1 (mass ratio), chopped into waste plastic particles of about 10×10mm size, weighing 20kg.

(1) Putting waste plastic particles into a thermal melting kettle, heating 160kg of sodium hydroxide with the mass fraction of 100% to 550 ℃, putting into the thermal melting kettle, starting a stirring motor, converting the waste plastic particles into a molten state after 10min at the speed of 85r/min, stirring for 0.5h, and obtaining a mixed material containing molten waste plastic, chloride and coke and a first gaseous hydrocarbon mixture at the temperature of 460 ℃ in the thermal melting kettle after thermal equilibrium.

(2) And (3) passing the mixed material obtained in the step (1) through a first separator to remove stone and other solid impurities with diameters larger than 2mm, so as to obtain a molten material, wherein the total weight of the solid impurities is 0.27kg.

(3) The melted material is introduced into a catalytic cracking reactor to react for 20s at 500 ℃.

(4) And (3) introducing the first gaseous hydrocarbon mixture obtained in the step (1) and the second gaseous hydrocarbon mixture obtained in the step (4) into a fractionating tower for fractionating to obtain a dry gas fraction, a fuel oil fraction and a heavy oil fraction.

(5) A part of dry gas fraction is condensed by a tower top condenser and then flows back to the fractionating tower, and the condensing temperature is 35 ℃; and (3) the other part of the dry gas fraction and HCl which does not react with the heat carrier enter an alkali liquor washing tower to be contacted with alkali liquor for washing, so that the washed dry gas is obtained.

(6) And (3) sending the bottom product obtained in the step (3) into a second separator to separate out the heat carrier after the reaction, and sending the heat carrier into a heater for recycling to obtain the high-temperature heat carrier.

Wherein the washing temperature is 25 ℃, the alkali solution carrier is NaOH solution with the mass fraction of 30%, and the mass ratio of the other part of overhead gas to the alkali solution is 2.42:15. The mass ratio of the waste plastics to the inorganic base is 1:8, and the mass ratio of the waste plastics to the catalyst is 1:6. The active components of the catalyst are ZSM-5 molecular sieve and HUSY molecular sieve, the carrier of the catalyst is kaolin, the binder is pseudo-boehmite, and the mass ratio of the carrier, the binder and the active components is 3: the mass ratio of the ZSM-5 molecular sieve to the HUSY molecular sieve is 1:10. the chlorine content of the waste plastic was 4.82%. The feed temperature of the cooling medium in the condenser was 25℃and the discharge temperature was 42 ℃.

Each isolated product was analyzed and the results are shown in Table 1.

Comparative example 1

A16 kg sample A1 of waste plastic was treated by the method of example 1, except that the waste plastic sample A1 was directly added to a volume of 1m without going through steps (1) and (2) ³ The high-temperature pyrolysis reaction kettle is used for carrying out thermal cracking reaction, the temperature is 520 ℃, and the time is 2.5h. Each isolated product was analyzed and the results are shown in Table 1.

Comparative example 2

20kg of waste plastic sample A2 was treated by the method of comparative example 1 at 500℃for 2.5 hours, and each of the separated products was analyzed, and the results are shown in Table 1.

TABLE 1

Examples/comparative example numbering	Example 1	Example 2	Comparative example 1	Comparative example 2
					Waste plastic sample numbering	A1	A2	A1	A2
Total mass/kg of liquid oil	10.53	13.92	7.89	10.72
					Total amount of coke/kg	1.11	1.03	1.75	1.89
Chlorine total/kg	0.53	0.95	0.653	0.88
					Total mass/kg of hydrocarbon gas	2.17	2.30	3.21	3.05
Total mass/kg of unreacted plastics	0.59	1.03	1.83	2.72
					Reaction conversion/%	96.2	94.8	88.56	86.4
Chlorine content/ppm in liquid oil	146	152	2351	2546
					Yield of liquid oil/%	68.1	71.5	51.5	55.6
Coke rate/%	7.2	5.3	11.3	9.8
					Total mass/kg of dry gas fraction	2.23	2.42	3.21	3.05
Total mass/kg of dry gas after washing	2.2	2.36	-	-
					Carbon content in wt% in the catalyst	0.53	0.58	-	-
Chlorine content in wt% in the heat carrier	0.56	0.57	-	-
					Chlorine content in alkaline solution/ppm	1770	2206	-	-
Steam content in dry gas after washing	1.3	2.5	-	-
					Hydrocarbon gas content in wt% in the dry gas after washing	98.7	97.5	-	-

The liquid oil in Table 1 refers to the liquid recovered by condensing pyrolysis gas in a cooling tower, the total coke refers to the sum of the coke amount in the catalyst and the coke amount in the heat carrier temporary storage tank residue, the total chlorine amount refers to the chlorine content in waste plastics, the coke yield refers to the coke formation amount divided by the waste plastics amount in the reaction, the liquid oil recovery refers to the liquid oil yield divided by the waste plastics addition amount, the chlorine content in the liquid oil is tested by the chlorine content measurement method (flask combustion method) standard in SHT 0161-1992 petroleum products, the chlorine content in the heat carrier is tested by silver nitrate titration (taking a certain sample, hydrolyzing the dissolved sample first, neutralizing pH 7 with nitric acid, titrating with silver nitrate, and after all chlorine ions in the water sample react with silver nitrate, the excessive silver nitrate reacts with a potassium chromate indicator to generate a brick red silver chromate precipitate, and the chlorine ion is reversely calculated), and the chlorine content in the alkali solution is tested by silver nitrate titration.

From the data in Table 1, it can be seen that the recovery of liquid oil is higher and the chlorine content therein is lower, as are the gaseous hydrocarbon and coke yields, when the process of the present application is used to treat waste plastics; and the catalytic cracking time of the method is greatly shortened compared with the prior art. The method can obtain higher reaction efficiency and product selectivity, and the chlorine content in the product is lower.

The preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, but the present disclosure is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solutions of the present disclosure within the scope of the technical concept of the present disclosure, and all the simple modifications belong to the protection scope of the present disclosure.

In addition, the specific features described in the above embodiments may be combined in any suitable manner without contradiction. The various possible combinations are not described further in this disclosure in order to avoid unnecessary repetition.

Moreover, any combination between the various embodiments of the present disclosure is possible as long as it does not depart from the spirit of the present disclosure, which should also be construed as the disclosure of the present disclosure.

Claims (10)

1. A method of treating waste plastics, the method comprising the steps of:

s1, mixing the waste plastics with a high-temperature heat carrier in a thermal melting kettle (6) to obtain a mixed material containing molten waste plastics and a first gaseous hydrocarbon mixture (7);

s2, separating the mixed material obtained in the step S1 in a first separator (10) to obtain a molten material from which solid impurities (11) are removed;

s3, enabling the molten material to contact with a catalyst in a catalytic cracking reactor (12) for catalytic cracking to obtain a second gaseous hydrocarbon mixture, heavy oil and a bottom product;

wherein the high-temperature heat carrier comprises molten inorganic alkali and/or high-temperature inorganic alkaline water solution, and the temperature of the high-temperature heat carrier is 150-550 ℃.

2. The method of claim 1, wherein the high temperature heat carrier has a temperature of 300-500 ℃.

3. The method of claim 1, wherein the inorganic base comprises one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, barium hydroxide, and strontium hydroxide;

the mass fraction of inorganic alkali in the high-temperature inorganic alkali aqueous solution is more than 20%.

4. The method according to claim 1, wherein in step S1, a mass ratio of the waste plastic to the inorganic base is 1: (3-10);

the mixing is carried out under the stirring condition, the stirring speed is 40-160r/min, and the time is 0.5-1h.

5. The method of claim 1, wherein the method further comprises: the first gaseous hydrocarbon mixture (7) and the second gaseous hydrocarbon mixture are led to a fractionating tower (21) for fractionation, and a dry gas fraction (23), a fuel oil fraction and a heavy oil fraction (22) are obtained.

6. The method of claim 5, wherein the method further comprises: condensing a portion of the dry gas fraction by an overhead condenser (24) and refluxing the condensed portion to the fractionation column (21); enabling the other part of dry gas fraction to enter an alkali liquor washing tower (26) to be contacted with alkali liquor for washing, so as to obtain washed dry gas (31);

the washing temperature is 20-90 ℃, the mass fraction of the alkali solution is 10-35%, and the mass ratio of the dry gas fraction of the other part to the alkali solution is 1: (2.5-10);

the alkali in the alkali solution is selected from NaOH, KOH and Ca (OH) ₂ One or more of them.

7. The method of claim 1, wherein the method further comprises: feeding the bottom product obtained in the step S3 into a second separator to separate out a heat carrier after reaction; heating the reacted heat carrier in a heater to obtain the high-temperature heat carrier;

optionally, a heat carrier is supplemented into the heater.

8. The method according to claim 1, wherein in step S3, the catalyst comprises a carrier, a binder and an active component, and the mass ratio of the carrier, the binder and the active component is (1.5-6): (0.6-1): 1, a step of;

the carrier comprises kaolin;

the binder comprises one or more of pseudo-boehmite, alumina sol and silica sol;

the active component comprises one or more of metal oxide, HUSY molecular sieve, ZSM-5 molecular sieve and aluminum phosphate molecular sieve;

the metal oxide comprises one or more of platinum oxide, palladium oxide, rhodium oxide, nickel oxide, zirconium oxide, zinc oxide and ferric oxide.

9. The method according to claim 1, wherein in step S3, the catalytic cracking is performed at a temperature of 400-550 ℃ for a time of 5-30S; the mass ratio of the catalyst to the waste plastic is (5-12): 1, a step of;

optionally, the molten waste plastic and the high temperature heat carrier are fluidly fed into the catalytic cracking reactor (12);

optionally, the catalytic cracking reactor (12) is a fixed bed reactor and/or a fluidized bed reactor.

10. The method of claim 1, wherein the waste plastic has a chlorine content of 0.5-6%;

the waste plastic comprises one or more of polyethylene, polypropylene, polyvinyl chloride and polystyrene.

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