PET steam pyrolysis method and device

Abstract

The invention relates to a pyrolytic reaction device technology and the field of plastic pyrolysis, in particular to a PET (polyethylene glycol terephthalate) steam pyrolysis method and device, and the device comprises a mixed gas inlet system, a PET powder feeding system, a pyrolytic reaction system, a high and low temperature partition separation system and the like. Water vapor, nitrogen and auxiliary agent gas are mixed through a three-way gas inlet system and enter the pyrolytic reaction system from the bottom end of the pyrolytic device; pET raw material powder is arranged at the upper part of the mixed gas inlet system, is continuously fed through conveying of nitrogen with the temperature lower than 100 DEG C, and enters the pyrolytic reaction system; under the action of the mixed gas, fluidizing the PET at the temperature of 400-600 DEG C, carrying the PET by airflow and lifting the PET upwards; in the lifting process, the pyrolytic reaction starts to be carried out and is gradually and completely converted into high-temperature pyrolytic steam; high-temperature pyrolysis steam enters a high-low temperature partition separation system from the tail of a pyrolysis reaction system, the temperature of the high-temperature pyrolysis steam is reduced, the steam enters a high-temperature cyclone separator with the temperature of 300-200 DEG C, deposition and collection of a product TPA (terephthalic acid) are achieved, then the temperature of the pyrolysis steam is reduced to the room temperature, and pyrolysis liquid and pyrolysis non-condensable gas are collected. The method and the device can effectively overcome the defects of high coking amount, complex product, difficult reaction control and the like in the conventional PET pyrolysis process, and can directionally prepare high-yield and high-purity TPA.

Description

Technical Field

[0001] The present invention relates to the technology of pyrolysis reaction devices and the field of plastic pyrolysis, and particularly relates to a method and device for the steam pyrolysis of PET. Background Art

[0002] In the past decade, the global production and production capacity of PET have been increasing year by year, and only bottle-grade PET has reached tens of millions of tons. At present, although there are various recycling methods, the overall recycling rate is low, and most of them are physical recycling. Therefore, developing an efficient chemical recycling method has become a very urgent task.

[0003] Currently, most of the chemical recycling of PET is alcoholysis. CN 115945222 A discloses a preparation method of an ionic catalyst material for PET chemical recycling, and adds it to PET waste and ethylene glycol for alcoholysis to obtain BHET monomers; CN118543369 A applies a prepared "Y"-shaped zinc carboxylate catalyst to the glycolysis of PET; CN114773197 B discloses a method for recycling PET mixed plastics by one-pot methanol under relatively mild conditions and catalyzed by a zinc catalyst.

[0004] Pyrolysis, as a chemical recycling method, has the characteristics of mature technology, short cycle, simple process, etc. At present, there are still few studies on recycling PET by pyrolysis. Moreover, in the conventional pyrolysis process of PET, due to dehydration and decarboxylation and the secondary cracking of TPA molecules, problems such as uncontrollable product recovery, excessive gas products, and inevitable coke generation will occur.

[0005] The inventor has disclosed a patent (CN 112920040 B) to develop a method for the steam pyrolysis of PET to prepare TPA and eliminate carbon black. This method introduces steam to adjust the pyrolysis atmosphere on the basis of conventional pyrolysis, can prepare TPA directionally, and the yield of the obtained TPA can reach more than 60%. Compared with conventional pyrolysis, the yield and purity of TPA prepared by the steam pyrolysis of PET are greatly improved.

[0006] On the basis of the steam pyrolysis of PET, the inventor further developed a reactor type specifically, that is, a steam pyrolysis device for PET, which can realize the fluidization of PET powder in a pyrolysis reaction device at 400-600°C; and introduce an auxiliary gas for the steam pyrolysis of PET to develop a new method for the steam pyrolysis of PET. Summary of the Invention

[0007] The object of the present invention is to provide a method and device for pyrolyzing PET with water vapor, to clarify the adaptability of the fluidized reaction to the PET pyrolysis system through the pyrolysis reaction device, and to master the law of fluidized pyrolysis of PET; the PET pyrolysis method provided by this application adopts a pyrolysis mode of fluidized lifting, and introduces an auxiliary gas to adjust the pyrolysis atmosphere, further improving the yield and purity of TPA.

[0008] To achieve the object of this invention, in the first aspect of this invention, a device for pyrolyzing PET with water vapor is provided, which includes a mixed gas inlet system, a PET powder feeding system, a pyrolysis reaction system, and a high and low temperature zone separation system.

[0009] The mixed gas inlet system is a water vapor inlet system, a nitrogen inlet system, and an auxiliary gas inlet system; the water vapor inlet system is provided with a water flow meter and a vaporization furnace, and both the nitrogen inlet system and the auxiliary gas inlet system are provided with solenoid valves and mass flow controllers.

[0010] The mixed gas inlet system is connected to the gas inlet at the bottom end of the pyrolysis reaction system, where the mixed gas inlet system can mix and inlet gas, or a single gas inlet system can inlet gas alone here.

[0011] The continuous feeding port is provided with a sleeve and a cooling water circulation pipe, and this feeding port can feed materials in a spiral manner or by gas transportation with a temperature lower than 100°C.

[0012] The pyrolysis reaction system includes a heating furnace and a metal reaction tube. The temperature of the heating furnace can be adjusted to 600°C, and the metal reaction tube is the place for fluidized pyrolysis of PET raw material powder and mixed gas.

[0013] The high and low temperature zone separation system is divided into a high temperature zone and a low temperature zone. The high temperature zone consists of a heating furnace, a separator, and a solid collection tank. The separator includes, but is not limited to, a cyclone separator, an electrostatic precipitator, etc. The separation and collection of TPA in the pyrolysis steam can be achieved at a temperature of 300 - 200°C in the high temperature zone.

[0014] The low temperature zone in the high and low temperature zone separation system includes a cooling water circulation pipe, a condensate tank, and a non-condensable gas exhaust pipe, to achieve the collection of condensate and the separation of non-condensable gas.

[0015] Preferably, the PET powder is fed into the pyrolysis reaction system by gas transportation with a temperature lower than 100°C at the continuous feeding port, and at the same time, the circulating cooling water is turned on to avoid the problems of melting and blockage of the PET powder at the continuous feeding port.

[0016] Preferably, the separator in the high-temperature zone adopts a cyclone separator, which can effectively separate the TPA sublimated in the high-temperature zone from the mixed gas, so that the solid product enters the solid collection tank for collection, and the mixed gas such as water vapor enters the low-temperature zone for cold separation and collection.

[0017] The second aspect of the present invention provides a PET pyrolysis method, which is implemented by the PET steam pyrolysis reaction device described in the first aspect. The specific steps of the PET steam pyrolysis method are as follows:

[0018] S1. Select dry PET powder as the pyrolysis raw material and transport it into the pyrolysis reaction system through the feed port with a gas at a temperature lower than 100°C.

[0019] S2. Select the auxiliary gas, determine the inlet gas modes of water vapor, nitrogen and the auxiliary gas, and precisely control the flow rate through the water flow meter and mass flow controller to adjust the pyrolysis atmosphere.

[0020] S3. Control the volume content of the auxiliary gas in the mixed gas to be 1 / 1000 - 10 / 1000 through the mass flow controller.

[0021] S4. Set the final pyrolysis temperature through the heating furnace in the pyrolysis reaction system, and realize the fluidized pyrolysis of PET powder under different pyrolysis atmospheres to obtain the pyrolysis products.

[0022] In the present invention, in step S1, optionally, the mesh number of the PET powder is 40 - 800 mesh, and 100 mesh is preferred.

[0023] In the present invention, in step S1, the PET powder is dried in a 65°C blast drying oven for more than 24 hours to fully remove the moisture in the PET; the low-temperature gas is nitrogen, and the PET powder is sent into the pyrolysis reaction system through low-temperature nitrogen transportation to avoid melting of the PET raw material at the feed port, thus causing blockage problems.

[0024] In the present invention, in step S2, optionally, the auxiliary gas includes one or several mixed gases such as CH4, C2H6, C2H4, C3H8, C3H6, etc., and C3H8 is preferred.

[0025] In the present invention, in step S2, the inlet gas modes include the mixed inlet of nitrogen and water vapor, and the mixed inlet of nitrogen, water vapor and the auxiliary gas.

[0026] In the present invention, in step S3, the volume content of the auxiliary gas is 1 / 1000 - 10 / 1000 of the mixed gas, and 6 / 1000 is preferred.

[0027] In the present invention, optionally in step S4, the final pyrolysis temperature is controlled at a certain temperature within the range of 400 - 600 °C, preferably 450 °C.

[0028] In the present invention, the solid product obtained by pyrolysis in step S4 is TPA, and the yield is 74% - 81%.

[0029] In the present invention, the purity of the TPA product obtained in step S4 is significantly affected by parameters such as the pyrolysis atmosphere, and its purity is 75% - 91%.

[0030] Beneficial effects

[0031] The PET steam pyrolysis method provided by the present invention adjusts the PET pyrolysis atmosphere through H2O and auxiliary gas, provides H and O for PET pyrolysis, overcomes problems such as complex and uncontrollable products and inevitable coke generation in the conventional PET pyrolysis process, and improves the yield and purity of TPA.

[0032] The PET steam pyrolysis device designed by the present invention adopts a fluidized lifting technology, and through low-temperature gas feeding, continuous feeding and continuous pyrolysis of PET can be achieved; at the same time, the temperature of the feeding port can be reduced by circulating cooling water, which can overcome the problem of melting of the PET powder raw material at the feeding port, thus avoiding blockage of the feeding port. Brief description of the drawings

[0033] In order to clearly illustrate the PET steam pyrolysis method and device of the present invention, the specific implementation manners are briefly introduced through the drawings.

[0034] Figure 1 is the overall schematic diagram of the PET steam pyrolysis device of the present invention

[0035] Figure 2 is the HPLC chromatogram corresponding to Example 1

[0036] Figure 3 is the HPLC chromatogram corresponding to Example 2

[0037] Figure 4 is the HPLC chromatogram corresponding to Example 3

[0038] Figure 5 is the HPLC chromatogram corresponding to Example 4

[0039] Figure 6 is the HPLC chromatogram corresponding to Example 5

[0040] Figure 7 is the HPLC chromatogram corresponding to Example 6 Detailed description of the invention

[0041] The technical solution of the present invention will be further described below through specific embodiments and drawings. The embodiments are for helping to understand the present invention and shall not be construed as a limitation to the present invention.

[0042] Example 1

[0043] Take dry PET powder of 100 mesh and feed the PET powder into the pyrolysis reaction system with low-temperature nitrogen.

[0044] Set the mixed inlet of N2 and water vapor, without a promoter gas, and carry out the steam pyrolysis of PET. The water vapor is obtained by vaporizing liquid water in the vaporization furnace of the water vapor inlet system.

[0045] Set the final pyrolysis temperature at 450 °C through a heating furnace to fluidize the PET powder in the pyrolysis reaction system.

[0046] Measure the yield and purity of the solid product TPA. The yield is 74.62%, and the purity measured by HPLC is 75.91%. The HPLC spectrum is as Figure 2 .

[0047] Example 2

[0048] Take dry PET powder of 100 mesh and feed the PET powder into the pyrolysis reaction system with low-temperature nitrogen.

[0049] Set the mixed inlet of N2, water vapor and propane, and carry out the steam pyrolysis of PET. The water vapor is obtained by vaporizing liquid water in the vaporization furnace of the water vapor inlet system, and the volume content of propane is 6 / 1000 of the mixed gas.

[0050] Set the final pyrolysis temperature at 450 °C through a heating furnace to fluidize the PET powder in the pyrolysis reaction system.

[0051] Measure the yield and purity of the solid product TPA. The yield is 81.40%, and the purity measured by HPLC is 91.63%. The HPLC spectrum is as Figure 3 .

[0052] Example 3

[0053] Take dry PET powder of 100 mesh and feed the PET powder into the pyrolysis reaction system with low-temperature nitrogen.

[0054] Set the mixed inlet of N2, water vapor and propane, and carry out the steam pyrolysis of PET. The water vapor is obtained by vaporizing liquid water in the vaporization furnace of the water vapor inlet system, and the volume content of propane is 6 / 1000 of the mixed gas.

[0055] Set the final pyrolysis temperature at 500 °C through a heating furnace to fluidize the PET powder in the pyrolysis reaction system.

[0056] The yield and purity of the solid product TPA were determined. The yield was 75.98%, and the purity measured by HPLC was 91.17%. The HPLC chromatogram is as shown in Figure 4 .

[0057] Example 4

[0058] Take dry PET powder of 100 mesh and feed the PET powder into the pyrolysis reaction system with low-temperature nitrogen.

[0059] Set the mixed intake of N2, water vapor and propylene, and carry out the steam pyrolysis of PET. The water vapor is obtained by vaporizing liquid water in the vaporization furnace of the water vapor intake system, and the volume content of propylene is 6 / 1000 of the mixed gas.

[0060] Set the final pyrolysis temperature to 450 °C through the heating furnace to fluidize the PET powder in the pyrolysis reaction system.

[0061] The yield and purity of the solid product TPA were determined. The yield was 79.70%, and the purity measured by HPLC was 84.49%. The HPLC chromatogram is as shown in Figure 5 .

[0062] Example 5

[0063] Take dry PET powder of 100 mesh and feed the PET powder into the pyrolysis reaction system with low-temperature nitrogen.

[0064] Set the mixed intake of N2, water vapor and methane, and carry out the steam pyrolysis of PET. The water vapor is obtained by vaporizing liquid water in the vaporization furnace of the water vapor intake system, and the volume content of methane is 6 / 1000 of the mixed gas.

[0065] Set the final pyrolysis temperature to 450 °C through the heating furnace to fluidize the PET powder in the pyrolysis reaction system.

[0066] The yield and purity of the solid product TPA were determined. The yield was 74.30%, and the purity measured by HPLC was 76.40%. The HPLC chromatogram is as shown in Figure 6 .

[0067] Example 6

[0068] Take dry PET powder of 80 mesh and feed the PET powder into the pyrolysis reaction system with low-temperature nitrogen.

[0069] Set the mixed intake of N2, water vapor and propane, and carry out the steam pyrolysis of PET. The water vapor is obtained by vaporizing liquid water in the vaporization furnace of the water vapor intake system, and the volume content of propane is 6 / 1000 of the mixed gas.

[0070] Set the final pyrolysis temperature to 450 °C through the heating furnace to fluidize the PET powder in the pyrolysis reaction system.

[0071] The yield and purity of the solid product TPA were determined. The yield was 80.86%, and the purity measured by HPLC was 88.50%. The HPLC chromatogram is as follows Figure 7 .

[0072] The above are only embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Any changes made by other technicians without changing the essence of the present invention shall fall within the scope of the present invention.

Claims

1. A PET steam pyrolysis method and device, characterized in that: The device comprises a mixed air intake system I, a PET powder feeding system II, a pyrolysis reaction system III, and a high and low temperature partition separation system IV. The mixed air intake system I is divided into a water vapor intake system 1, a nitrogen intake system 2, and an auxiliary gas intake system 3. The water vapor intake system 1 is provided with a water flow meter 4 and a vaporization furnace 5, the nitrogen intake system 2 is provided with a solenoid valve 6 and a mass flow controller 7, and the auxiliary gas intake system 3 is provided with a solenoid valve 6 and a mass flow controller 7; the mixed air intake system I is connected to the air inlet 8 at the bottom end of the pyrolysis reaction system III; the PET powder feeding system II is arranged at the upper part of the mixed air intake system I, and is composed of a continuous feed port 9, a sleeve 10 and a cooling water circulation pipe 11; the pyrolysis reaction system III includes an air inlet 8, a heating furnace and a metal reaction tube; the high and low temperature partition separation system IV is divided into a high temperature zone and a low temperature zone, the high temperature zone includes a temperature-controllable cyclone separator 12 and a solid collection tank 13, and the low temperature zone includes a cooling water circulation pipe 14, a condensation tank 15 and a non-condensable gas exhaust pipe 16.

2. A PET steam pyrolysis method and device according to claim 1, characterized in that: The temperature of the vaporization furnace 5 is adjustable and can be heated to 140-200° C. to vaporize liquid water into water vapor, and the water vapor enters the pyrolysis reaction system II through the air inlet 8.

3. A PET steam pyrolysis method and device according to claim 2, characterized in that: The air inlet 8 can realize mixed air intake of the mixed air intake system I, and can also realize separate air intake of each air intake system.

4. A PET steam pyrolysis method and device according to claim 3, characterized in that: The continuous feed port 9 can be fed by gas with a temperature lower than 100° C., and circulating cooling water can be turned on to prevent the PET powder from melting in the continuous feed port 9 and causing blockage.

5. A PET steam pyrolysis method and device according to claim 4, characterized in that: The temperature of the heating furnace included in the pyrolysis reaction system III is adjustable and can be heated to 600° C. The metal reaction tube included is the reaction place where the PET powder and the mixed gas undergo fluidized pyrolysis.

6. A PET steam pyrolysis method and device according to claim 5, characterized in that: The high-low temperature partition separation system IV integrates a heating furnace and a separator 12 and a solid collection tank 13 in the high temperature zone, and integrates a cooling water circulation pipe 14, a condenser 15 and a non-condensable gas exhaust pipe 16 in the low temperature zone. The high-temperature pyrolysis steam enters the high-low temperature partition separation system IV from the tail of the pyrolysis reaction system III, and the pyrolysis product TPA is deposited and collected in the high temperature zone of 300-200°C, and the pyrolysis liquid and non-condensable gas are collected in the low temperature zone that drops to room temperature.

7. A PET steam pyrolysis method and device according to claim 6, characterized in that: The PET steam pyrolysis method is: S1. The dried PET powder raw material enters the pyrolysis reaction system III through a continuous feed port 9 in a gas delivery manner; S2. The raw water of the water vapor inlet system 1 is liquid water, the water flow rate is controlled by the water flow meter 4, and the vaporizer 5 is heated to 140-200°C to vaporize the liquid water into water vapor; S3. The nitrogen intake system 2 adjusts the nitrogen flow rate through the solenoid valve 6 and the mass flow controller 7; S4. The auxiliary gas of the auxiliary gas intake system 3 includes CH4, C2H6, C2H4, C3H8, C3H6, etc. The auxiliary flow rate is adjusted by the solenoid valve 6 and the mass flow controller 7. The volume content of the auxiliary gas is 1 / 1000 to 10 / 1000 of the mixed gas, wherein 6 / 1000 is preferred; S5. Setting the final pyrolysis temperature by the heating furnace in the pyrolysis reaction system III; S6.PET powder and gas are fluidized and pyrolyzed in the metal reaction tube of pyrolysis reaction system III, and the products enter the high and low temperature partition separation system IV for separation and collection; S7. Collect the solid product in the solid collection tank 13, which is the TPA product.

Images