Process for preparing wax-based chemicals and alpha-olefin from waste plastics based on self-hot melting dechlorination

Abstract

The invention relates to a process for preparing wax-based chemicals and alpha-olefin from waste plastics based on self-hot-melting dechlorination, which comprises the following steps: adding clean fragments of the waste plastics into a water-cooling feed pipe through a controllable feeder, and then falling into a hot-melting dechlorination reactor; one path of molten plastic liquid extracted from the bottom of the hot-melting dechlorination reactor is returned to the upper part of the hot-melting dechlorination reactor, the other path of molten plastic liquid is sent to the middle upper part of the downer catalytic pyrolysis reactor as a raw material, and fuel gas extracted from the top of the hot-melting dechlorination reactor enters a riser regenerator; carrying out gas-solid separation at the bottom of the downer catalytic pyrolysis reactor; the separated spent catalyst flows into the bottom of the riser regenerator, a coarse particle catalyst is separated by the first-stage gas-solid separator at the top of the riser regenerator, fine ash is separated by the second-stage gas-solid separator, and the coarse particle catalyst and the fine ash are circulated back to the bottom of the riser regenerator; the pyrolysis oil gas flows into a fractionating tower and then is separated into alpha-olefin fraction wax oil, high-temperature oil slurry and pyrolysis dry gas, part of the pyrolysis dry gas is circulated and returned to the water-cooling feeding pipe, and the high-temperature oil slurry is directly circulated and returned to the upper part of the hot-melting dechlorination reactor.

Description

1. Technical Field

[0001] The invention provides a process for preparing wax-based chemicals and alpha-olefins from waste plastics based on self-thermal melting dechlorination, and belongs to the field of environmental engineering. 2. Background technology

[0002] While the widespread use of plastics has brought great convenience to people's lives, it has also brought a lot of white pollution. The use cycle of plastics is very short. A large number of plastic products, especially packaging materials, are discarded after about 6-12 months. 40% of plastics are discarded after 1-2 years. The total annual output of plastic waste in the world has reached 50 million tons. In the past few decades, waste plastics have been regarded as part of municipal solid waste (MSW). According to surveys, waste plastics account for 4%-10% (wt) or 10%-20% (v%) in MSW in industrially developed countries, mainly from packaging waste, automobile garbage and processing waste. The percentages of various types of waste plastics are: low-density polyethylene (LDPE) 27%; high-density polyethylene (HDPE) 21%; polypropylene (PP) 18%; polystyrene (PS) 16%; polyvinyl chloride (PVC) 7%. Due to the lack of efficient, clean and large-scale technology, waste plastics have become an environmental problem that needs to be solved in the world.

[0003] In the treatment of urban plastic solid waste, landfill, incineration and recycling are the three main methods. Due to different national conditions, the methods vary from country to country. The United States mainly uses landfill, while Europe and Japan mainly use incineration. At present, rapid pyrolysis / catalytic pyrolysis liquefaction or chemical production of waste plastics has become a hot topic at home and abroad, and is also the waste plastic treatment technology with the most promising industrialization prospects.

[0004] Rapid pyrolysis / catalytic pyrolysis of waste plastics is an effective recycling method that heats waste plastics at high temperatures under oxygen-free or low-oxygen conditions to decompose them and produce valuable products, such as the pyrolysis and liquefaction of waste plastics to produce gasoline, diesel, petroleum wax and other chemical raw materials. However, due to the characteristics of waste plastics such as large size and light weight, difficulty in compression, airtightness, easy expansion, easy melting and bonding, and poor thermal conductivity, it is difficult to solve the problem of continuous feeding and rapid heating. At present, most of the pyrolysis and liquefaction of waste plastics adopt reactor-type intermittent reactions and horizontal rotary kiln reactions, with slow heating rates, severe feed adhesion and coking, low liquid product yield and added value, and difficult to improve processing capacity. It is difficult to scale up the pyrolysis device, and the subsequent processing of the liquid product containing chlorine is difficult, which restricts the efficient and clean large-scale utilization of waste plastics. At present, there is no large-scale waste plastic pyrolysis device in commercial operation. It is urgent to develop waste plastic wax-based chemicals and α-olefin processes and equipment technologies based on self-thermal melting and dechlorination. 3. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing waste plastic pyrolysis liquefaction technology and provide a process for preparing wax-based chemicals and α-olefins from waste plastics based on self-thermal melting dechlorination. The process solves the difficulties in pyrolysis feeding and the removal of chlorine and sulfur heteroatoms through the pyrolysis dry gas of the waste plastic and the circulation of high-temperature oil slurry for hot melting dechlorination pretreatment and atomization feeding; catalytic pyrolysis regulates the breakage of CC bonds, inhibits condensation and coking, and realizes controllable cracking of waste plastics; adopts a down-going bed reactor to inhibit secondary cracking, eliminate the amplification effect, maximize the production of wax-based chemicals and α-olefins, and improve the catalytic pyrolysis heating rate. The process solves the five common problems in the industry, namely, adhesion and coking of waste plastic feed, difficulty in mixing with heat carriers, low yield and added value of liquid products, difficulty in removing chlorine and sulfur heteroatoms of liquid products, thereby affecting subsequent processing, and difficulty in scaling up pyrolysis equipment, so as to realize efficient, clean and high-value large-scale utilization of waste plastics.

[0006] The technical solution of the present invention:

[0007] The process for preparing wax-based chemicals and α-olefins from waste plastics based on self-thermal melting dechlorination provided by the present invention comprises the following steps: the clean fragments of sorted PE and PP waste plastics are added into a water-cooled feed pipe at 20-95°C through a controllable feeder, and fall into a 240-320°C slurry melt in a hot melt dechlorination reactor under the influence of pyrolysis dry gas, and are subjected to melt dechlorination and desulfurization pretreatment by stirring and mixing; a portion of the molten plastic liquid drawn from the bottom of the hot melt dechlorination reactor is heated to a temperature 20-60°C higher than that of the slurry melt through a high-speed circulation pipe with external heating, and then returned to the hot melt dechlorination reactor; The fuel gas is returned to the upper part of the hot melt dechlorination reactor, and the other part is sent to the upper part of the descending bed catalytic pyrolysis reactor as raw material through the atomizing feed nozzle. The fuel gas extracted from the top of the hot melt dechlorination reactor is used as the fuel gas of the riser regenerator after desulfurization and dechlorination. The flow rate of the high-speed circulation pipe is 2-30 m / s, the circulation ratio of the molten plastic liquid to the raw material is 1-10:1, and the steam consumption of the atomizing feed nozzle is 4%-12% of the raw material amount; the atomized particle feed of the molten plastic liquid is mixed with the 600- The 800℃ regenerated catalyst undergoes rapid mixing, vaporization and controllable cracking reactions, with a reaction temperature of 410-550℃, a slightly negative pressure, and a reaction time of 200 milliseconds to 2 seconds, maximizing the production of wax-based chemicals and α-olefins, and undergoing gas-solid separation at the bottom of the descending bed catalytic pyrolysis reactor; the separated catalyst to be regenerated flows through a return feeder into the bottom of the riser regenerator for air fluidization coking regeneration at 500-750℃ and fuel gas combustion-assisted heating, and is separated into coarse particles of regenerated catalyst by the first-stage gas-solid separator at the top of the riser regenerator The waste plastics are circulated back to the top of the descending bed catalytic pyrolysis reactor to catalytically pyrolyze, and the fine ash separated by the second-stage gas-solid separator is circulated back to the bottom of the riser regenerator for fluidized coking regeneration. The flue gas is discharged after recovering the waste heat through the waste heat boiler; the 410-550°C pyrolysis oil and gas flows into the distillation tower and is separated into α-olefin fraction, light wax oil, heavy wax oil, high-temperature slurry oil and pyrolysis dry gas, 3%-20% of the pyrolysis dry gas is circulated back to the water-cooled feed pipe as a carrying gas, and the high-temperature slurry oil of ≥350°C is directly circulated back to the upper part of the hot melt dechlorination reactor as a melting heat source.

[0008] The outer wall of the water-cooled feed pipe is provided with a water-cooling jacket, which is in the shape of a positive cone, a straight tube or an inverted cone, preferably a positive cone.

[0009] The controllable feeder is a rotary feeder, a double-shaft screw feeder or a single-shaft screw feeder.

[0010] The high-speed circulation tube is heated by electromagnetic induction heating, thermal oil heating, steam heating or resistance heating, preferably electromagnetic induction heating.

[0011] The riser regenerator is composed of a turbulent fluidized bed at the bottom and a carrying reactor at the top. The turbulent fluidized bed has a larger equivalent diameter, while the carrying reactor has a smaller equivalent diameter, with a diameter ratio of 2 to 3:1. The carrying reactor can be a straight tube reactor with a uniform equivalent diameter, or can be composed of large and small straight tubes with diameters of different multiples of the equivalent diameter connected by large and small head pipe fittings, with a diameter ratio of 1.2 to 2:1. The equivalent diameter of the fluidized bed is only 10%-50% of the equivalent diameter of the turbulent fluidized bed.

[0012] The present invention will be described in detail with reference to embodiments. 4. Description of the drawings

[0013] Attached Figure 1 The present invention is a schematic diagram of the process of preparing wax-based chemicals and α-olefins from waste plastics based on self-thermal melting dechlorination.

[0014] Attached Figure 1 The drawing settings are as follows:

[0015] 1. Waste plastic crusher 2. Controllable feeder 3. Water-cooled feed pipe 4. Hot melt dechlorination reactor 5. Delivery pump 6. High-speed circulation pipe 7. Oil-gas solid separator 8. Desulfurization and dechlorination reactor 9. Fractionation tower 10. Heavy wax oil outlet 11. Light wax oil outlet 12. α-olefin fraction outlet 13. Pyrolysis dry gas outlet 14. Induced draft fan 15. Waste heat boiler 16. Flue gas outlet 17. Regenerated catalyst return device 18. Riser regenerator 19. Gas distributor 20. Inlet pipe 21. Ash discharge port 22. First-stage gas-solid separator 23. First-stage coarse catalyst return device 24. Second-stage gas-solid separator 25. Second-stage fine catalyst return device

[0016] The process characteristics of the present invention are described in detail below in conjunction with the accompanying drawings and embodiments. 5. Specific implementation methods

[0017] In the process of preparing wax-based chemicals and α-olefins from waste plastics based on self-thermal melt dechlorination, the clean PE and PP waste plastics are sorted through a waste plastic crusher (1), and the waste plastic fragments are added to a 20-95°C water-cooled feed pipe (3) through a controllable feeder (2), and fall into a 240-320°C slurry melt in a hot melt dechlorination reactor (4) with stirring under the influence of pyrolysis dry gas, and are melt-dechlorinated and desulfurized by stirring and mixing. The molten plastic liquid drawn from the bottom of the hot melt dechlorination reactor (4) is conveyed under pressure by a conveying pump (5), and a part of it is heated to a temperature 20-60°C higher than that of the slurry melt by a high-speed circulation pipe (6) with external heating, and then returned to the hot melt dechlorination reactor (4). The upper part of the hot melt dechlorination reactor (4) and the other part are sent as raw materials to the upper middle part of the descending bed catalytic pyrolysis reactor (9) through an atomizing feed nozzle for feeding. The fuel gas extracted from the top of the hot melt dechlorination reactor (4) is treated by the desulfurization and dechlorination reactor (8) and used as the fuel gas of the riser regenerator (18). The flow rate of the high-speed circulation pipe (6) is 2-30 m / s, the circulation ratio of the molten plastic liquid to the raw material is 1-10:1, and the steam consumption of the atomizing feed nozzle is 4%-12% of the raw material amount. The atomized particle feed of the molten plastic liquid and the 600-800°C regenerated catalyst falling from the top of the descending bed catalytic pyrolysis reactor are rapidly mixed, vaporized and controllably cracked. The reaction temperature is 410-550°C, the pressure is slightly negative pressure, and the reaction time is 200 milliseconds-2 seconds, so as to maximize the production of wax-based chemicals and α-olefins, and perform gas-solid separation at the bottom of the descending bed catalytic pyrolysis reactor; the separated catalyst to be regenerated flows into the bottom of the riser regenerator (18) through the catalyst to be regenerated return device (17) and is regenerated by air fluidization at 500-750°C and fuel gas is used for combustion and heating, and the coarse particles are separated by the first-stage gas-solid separator (22) at the top of the riser regenerator (18); the regenerated catalyst is circulated back to the top of the descending bed catalytic pyrolysis reactor through the first-stage solid heat carrier return device (23) to catalytically pyrolyze the waste plastics, and is separated by the second-stage gas-solid separator. (24) The separated fine ash is circulated back to the bottom of the riser regenerator (18) through the hot ash circulation return device (25) to continue fluidized coke regeneration, and the flue gas is discharged after recovering the waste heat through the waste heat boiler (15); the 410-550°C pyrolysis oil gas flows into the distillation tower (9) and is separated into α-olefin fraction, light wax oil, heavy wax oil, pyrolysis dry gas and high-temperature oil slurry through the heavy wax oil outlet (10), the light wax oil outlet (11), the α-olefin fraction outlet (12) and the pyrolysis dry gas outlet (13); 3%-20% of the pyrolysis dry gas is circulated back to the water-cooled feed pipe (3) as a carrying gas, and the high-temperature oil slurry of ≥350°C is directly circulated back to the upper part of the hot melt dechlorination reactor (4) as a melting heat source.

[0018] The outer wall of the water-cooled feed pipe (3) is provided with a water-cooled jacket, which has a shape of a positive cone, a straight tube or an inverted cone, preferably a positive cone.

[0019] The controllable feeder (2) is a rotary feeder, a double-shaft screw feeder or a single-shaft screw feeder.

[0020] The high-speed circulation pipe (6) is heated by electromagnetic induction heating, heat-conducting oil heating, steam heating or resistance heating, preferably electromagnetic induction heating.

[0021] The riser regenerator (18) is composed of a turbulent fluidized bed at the bottom and a carrying reactor at the top. The turbulent fluidized bed has a larger equivalent diameter, while the carrying reactor has a smaller equivalent diameter, and the diameter ratio is 2 to 3:1. The carrying reactor can be a straight tube reactor with a uniform equivalent diameter, or can be composed of large and small straight tubes with diameters of different multiples of the equivalent diameter connected by large and small head pipe fittings, and the diameter ratio of the large and small straight tubes is 1.2 to 2:1. The equivalent diameter of the fluidized bed is only 10% to 50% of the equivalent diameter of the turbulent fluidized bed.

[0022] The process for producing wax-based chemicals and α-olefins from waste plastics based on self-thermal melting and dechlorination can continuously, on a large scale, efficiently, cleanly and in a high-value manner by pyrolysis. It has solved five common industry problems: adhesion and coking of waste plastic feed, difficulty in mixing with high-temperature catalysts, low yield and added value of liquid products, difficulty in scaling up pyrolysis equipment, and difficulty in subsequent processing of liquid products containing chlorine. The yield of liquefied gas is ≥10%, the yield of α-olefin fraction is ≥20%, the light wax oil fraction is 40%, the heavy wax oil fraction is 25%, and the total yield of liquid products is more than 95%, which is more than 25 percentage points higher than that of traditional waste plastic pyrolysis technology. It has high pyrolysis intensity, small equipment size, low steel consumption, greatly reduced fixed investment, and a simple ash removal process, thus achieving stable, long-term, full and optimal operation of the device.

Claims

1. A process for preparing wax-based chemicals and α-olefins from waste plastics based on self-thermal melt dechlorination, wherein the clean fragments of sorted PE and PP waste plastics are added into a water-cooled feed pipe at 20-95°C through a controllable feeder, and fall into the 240-320°C slurry melt of the hot melt dechlorination reactor under the influence of pyrolysis dry gas, and are subjected to melt dechlorination and desulfurization pretreatment by stirring and mixing, and a portion of the molten plastic liquid drawn from the bottom of the hot melt dechlorination reactor is heated to a temperature 20-60°C higher than that of the slurry melt through a high-speed circulation pipe with external heating. ℃ and then returned to the upper part of the hot melt dechlorination reactor, and the other part is sent to the upper part of the descending bed catalytic pyrolysis reactor as a raw material through an atomizing feed nozzle. The fuel gas extracted from the top of the hot melt dechlorination reactor is used as the fuel gas of the riser regenerator after desulfurization and dechlorination treatment. The flow rate of the high-speed circulation pipe is 2-30m / s, the circulation ratio of the molten plastic liquid to the raw material is 1-10:1, and the steam consumption of the atomizing feed nozzle is 4wt%-12wt% of the raw material amount; the atomized particle feed of the molten plastic liquid is the same as the feed from the top of the descending bed catalytic pyrolysis reactor. The falling 600-800℃ regenerated catalyst undergoes rapid mixing, vaporization and controllable cracking reaction, the reaction temperature is 410-550℃, the pressure is 80-100KPa (absolute pressure), the reaction time is 200 milliseconds to 2 seconds, and gas-solid separation is carried out at the bottom of the descending bed catalytic pyrolysis reactor; the separated catalyst to be regenerated flows into the bottom of the riser regenerator through the return feeder, and is regenerated by air fluidization at 500-750℃ and fuel gas is used for combustion and heating, and the coarse particles of regenerated catalyst are separated by the first-stage gas-solid separator at the top of the riser regenerator. The top of the loop-down bed catalytic pyrolysis reactor is used to catalytically pyrolyze waste plastics, and the fine ash separated by the second-stage gas-solid separator is recycled to the bottom of the riser regenerator for fluidized coking regeneration. The flue gas is discharged after recovering the waste heat through the waste heat boiler; the 410-550°C pyrolysis oil and gas flow into the distillation tower and are separated into α-olefin fractions, light wax oil, heavy wax oil, high-temperature slurry oil and pyrolysis dry gas. 3v%-20v% of the pyrolysis dry gas is recycled back to the water-cooled feed pipe as a carrying gas, and the high-temperature slurry oil of ≥350°C is directly circulated back to the upper part of the hot melt dechlorination reactor as a melting heat source.

2. The process for preparing wax-based chemicals and α-olefins from waste plastics based on self-thermal melting dechlorination according to claim 1, characterized in that The outer wall of the water-cooled feed pipe is provided with a water-cooling jacket, which is in the shape of a positive cone, a straight tube or an inverted cone, preferably a positive cone.

3. The process for preparing wax-based chemicals and α-olefins from waste plastics based on self-thermal melting dechlorination according to claim 1, characterized in that The controllable feeder is a rotary feeder, a double-shaft screw feeder or a single-shaft screw feeder.

4. The process for preparing wax-based chemicals and α-olefins from waste plastics based on self-thermal melting dechlorination according to claim 1, characterized in that The high-speed circulation tube is heated by electromagnetic induction heating, thermal oil heating, steam heating or resistance heating, preferably electromagnetic induction heating.

5. The process for preparing wax-based chemicals and α-olefins from waste plastics based on self-thermal melting dechlorination according to claim 1, characterized in that The riser regenerator is composed of a turbulent fluidized bed at the bottom and an entrained reactor at the top, the ratio of the equivalent diameter of the turbulent fluidized bed to the equivalent diameter of the entrained reactor is 2 to 3:1; the entrained reactor is a straight tube reactor with a uniform equivalent diameter, or is composed of large and small straight tubes with diameters of different multiples of the equivalent diameter connected by large and small head pipe fittings, the diameter ratio of the large and small straight tubes is 1.2 to 2:1; the equivalent diameter of the fluidized bed is 10%-50% of the equivalent diameter of the turbulent fluidized bed.

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