A dynamic solid-phase dechlorination system and method for pyrolysis or catalytic cracking of chlorinated waste plastics

Abstract

The application discloses a dynamic solid-phase dechlorination system and method for pyrolysis or catalytic cracking of chlorinated waste plastics. The system comprises a pyrolysis or catalytic cracking reaction unit, a solid-phase chlorine capture unit, a switching unit, a regeneration unit and a control unit, wherein the solid-phase chlorine capture unit comprises at least two switchable solid-phase chlorine capture beds. Chlorine-containing pyrolysis gas generated during the pyrolysis or catalytic cracking of chlorinated waste plastics is removed by chemical adsorption and / or chemical reaction in the chlorine capture bed. When the chlorine capture capacity of the chlorine capture bed decreases, the gas flow is switched to another chlorine capture bed through the switching unit, and the chlorine capture bed that is out of operation is regenerated in situ. Through the alternate operation and regeneration of the chlorine capture bed, continuous dechlorination operation of the pyrolysis or catalytic cracking process of chlorinated waste plastics is realized. The application does not require liquid-phase alkaline washing, does not produce salt wastewater or salt solution, reduces the generation of solid waste, and improves the stability of the dechlorination process and the continuity of the system operation.

Description

Technical Field

[0001] This application relates to the field of waste plastic resource utilization and pollution control technology, specifically to a system and method for dynamic dechlorination and in-situ regeneration of chlorine-containing waste plastics using solid-phase chlorine-capturing materials during pyrolysis or catalytic cracking, and particularly to a technical solution for continuous dechlorination operation through a switchable solid-phase chlorine-capturing bed. Background Technology

[0002] Pyrolysis and catalytic cracking technologies are important ways to realize the resource utilization of waste plastics. However, in actual processing, polyvinyl chloride (PVC) or chlorine-containing additives are often inevitably mixed in with the waste plastic raw materials, resulting in the generation of a large amount of hydrogen chloride (HCl) and other chlorine-containing components during pyrolysis or catalytic cracking.

[0003] The aforementioned chlorine-containing components can lead to corrosion of the reaction system, increased chlorine content in pyrolysis oil or cracking products, and may cause catalyst deactivation, thereby affecting the safety of the unit and product quality. To reduce the impact of chlorine, existing technologies typically employ one of the following dechlorination methods: One method is wet alkaline washing, which uses liquid-phase alkaline washing or absorption to neutralize and absorb hydrogen chloride in pyrolysis gas. However, this method generates a large amount of salt wastewater or salt solution, has high alkali consumption, high operating costs, and increases the burden of subsequent environmental treatment.

[0004] Another method is solid-phase adsorption dechlorination, which uses solid dechlorination agents to capture hydrogen chloride. Although this can avoid liquid waste, traditional methods are mostly single-bed single-use or intermittent operation. Once the adsorbent is saturated, the machine needs to be shut down and replaced, which is difficult to meet the needs of continuous industrial production.

[0005] In addition, some technologies attempt to pre-dechlorinate waste plastics before pyrolysis (such as steam stripping, solvent extraction, etc.), but due to the complexity of raw materials and the diversity of chlorine forms, it is difficult to completely remove organic chlorine and still cannot avoid the generation of HCl during the pyrolysis stage.

[0006] Although existing patents have proposed integrating dechlorination units into pyrolysis systems, these either rely on liquid alkali washing or lack bed regeneration and switching mechanisms, making it impossible to achieve efficient, continuous, and wastewater-free dechlorination operation.

[0007] Therefore, there is an urgent need for a dechlorination system and method that can effectively remove HCl from pyrolysis gas without the need for liquid alkali, without generating chlorine-containing wastewater, and support continuous and stable operation, so as to promote the greening and large-scale application of thermochemical recycling technology for chlorine-containing waste plastics. Summary of the Invention

[0008] According to one aspect of this application, a dynamic solid-phase dechlorination system and method are provided, capable of simultaneously and continuously operating the pyrolysis / catalytic cracking process and the dechlorination process. By setting up at least two parallel solid-phase dechlorination beds, and coordinating a rapid airflow switching unit and an in-situ regeneration unit, a closed-loop operating system is constructed: when one dechlorination bed becomes saturated, the system automatically switches it out of the main airflow path and initiates the in-situ regeneration program, while the other regenerated or fresh dechlorination bed is immediately connected to the airflow to perform the dechlorination function. This design eliminates the need to interrupt the pyrolysis reaction feed or stop the system to replace the adsorbent, fundamentally solving the technical bottleneck of traditional solid-phase dechlorination technology's inability to operate continuously, and combining high dechlorination efficiency, low operating costs, and environmental friendliness.

[0009] A dynamic solid-phase dechlorination system for pyrolysis or catalytic cracking of chlorine-containing waste plastics, characterized in that it comprises: A pyrolysis or catalytic cracking reaction unit is used to pyrolyze or catalytically crack chlorine-containing waste plastics to generate chlorine-containing pyrolysis gas. A solid-phase chlorine-catching unit, comprising at least two solid-phase chlorine-catching beds arranged in parallel, wherein the solid-phase chlorine-catching beds are filled with solid-phase chlorine-catching material; A switching unit is connected between the pyrolysis or catalytic cracking reaction unit and each of the solid phase chlorine-collecting beds, and is used to switch the direction of pyrolysis gas flow between different solid phase chlorine-collecting beds; The regeneration unit achieves in-situ regeneration by raising the temperature to release chlorides from the solid-phase chloride-collecting bed. The control unit is used to control the solid phase chlorine-collecting bed to alternate between chlorine-collecting state and regeneration state in order to achieve continuous operation of the dechlorination process.

[0010] Optionally, the solid-phase chlorine-capturing bed is disposed in the downstream gas phase channel of the pyrolysis or catalytic cracking reaction unit; Preferably, the solid-phase chlorine-capturing bed achieves dechlorination by capturing hydrogen chloride and / or chlorine-containing components in the pyrolysis gas.

[0011] The solid-phase chlorine-capturing material includes at least one of alkaline earth metal oxides, alkaline earth metal hydroxides, and supported alkaline materials.

[0012] Optionally, the switching unit includes a multi-way switching valve or a valve group composed of multiple switching valves, which can switch between the working bed and the regeneration bed without interrupting the pyrolysis gas flow.

[0013] Optionally, the regeneration unit utilizes waste heat from the pyrolysis system, inert gas, or reducing gas for regeneration; Preferably, the chlorine-containing gas released during the regeneration process is discharged to a chlorine resource recovery device or a safe disposal system for centralized treatment.

[0014] Optionally, it also includes an online hydrogen chloride monitoring device, which is installed at the outlet end of any of the solid phase chlorine-collecting beds, for real-time detection of hydrogen chloride concentration and feedback of the signal to the control unit; Preferably, the control unit controls the bed switching based on the hydrogen chloride concentration at the outlet of the solid-phase chlorine-collecting bed.

[0015] A dynamic solid-phase dechlorination method for pyrolysis or catalytic cracking of chlorine-containing waste plastics, characterized by comprising the following steps: S1: Chlorine-containing waste plastics are fed into a pyrolysis or catalytic cracking reaction unit to generate chlorine-containing pyrolysis gas; S2: The chlorine-containing pyrolysis gas is introduced into one of the solid phase chlorine-capturing beds in the adsorption state for dechlorination; S3: When the solid phase chlorine-capturing bed is close to saturation, the pyrolysis gas is switched to another solid phase chlorine-capturing bed that is in standby state through the switching unit; S4: In-situ thermal regeneration of the saturated solid-phase chlorine-capturing bed to restore its adsorption capacity; S5: After regeneration is complete, the bed is switched to standby mode, and steps S2-S4 are repeated to achieve continuous dechlorination.

[0016] Optionally, in step S3, the basis for determining that the solid phase chlorine-capturing bed is close to saturation is: the outlet hydrogen chloride concentration exceeds a preset threshold, or the cumulative operating time reaches a set cycle.

[0017] Optionally, in step S4, the saturated bed is heated to decompose or desorb the metal chloride and release chlorine-containing gas, thereby achieving in-situ thermal regeneration. Preferably, the heating temperature is 400-800℃; Preferably, the chlorine-containing gas released during the regeneration process is discharged from the system for treatment.

[0018] Optionally, steps S3 and S4 can be performed simultaneously without interrupting the pyrolysis or catalytic cracking reaction process, ensuring continuous and stable operation of the system.

[0019] The beneficial effects that this application can produce include: 1) No wastewater discharge: The entire process adopts solid-phase chlorine removal, avoiding the use of alkaline solutions, completely eliminating the generation of saline wastewater, and meeting the requirements of clean production; 2) Continuous and stable operation: Through dynamic switching of multiple beds, the dechlorination process is ensured to be uninterrupted, which is suitable for industrial continuous pyrolysis production lines; 3) In-situ regeneration: No need to stop the machine to replace the adsorbent; the regeneration process is completed inside the system, reducing manual intervention and material consumption. 4) Strong resistance to chlorine load fluctuations: The system always retains a spare bed layer, which can be quickly switched when the chlorine content of the feed suddenly increases, effectively buffering the instantaneous HCl impact and preventing penetration; 5) Low operating cost and environmentally friendly: Solid phase chlorine capture materials can be recycled multiple times, reducing the generation of hazardous waste. Their overall economic and environmental benefits are significantly better than traditional solutions. Detailed Implementation

[0020] In this application, "continuous operation" means that the pyrolysis reaction unit does not need to be shut down, the dechlorination process is seamlessly connected through bed switching, and the airflow interruption time is ≤10 seconds; The so-called "in-situ regeneration" does not refer to the complete reversal of metal chlorides (such as CaCl2) into the original oxides (such as CaO). Instead, it involves heat treatment at 400-800℃ in an inert atmosphere to induce structural relaxation, micropore re-opening, or exposure of unreacted active components in the chlorine-collecting products, thereby restoring their dechlorination activity to a level that meets industrial emission standards. All gas concentration units “ppm” refer to volume fraction. Under standard conditions (0℃, 101.325 kPa), 1 ppmHCl ≈ 1.63 mg / Nm³.

[0021] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0022] The specific embodiments of this application are described in detail below. The specific embodiments described herein are for illustration and explanation only, and are not intended to limit this application.

[0023] Example 1 Construct an integrated pyrolysis-dechlorination pilot plant, including: Pyrolysis reaction unit: An externally heated rotary kiln pyrolysis furnace (Φ1.2 m × 8 m) is used, heated by natural gas combustion; pyrolysis temperature 500℃, residence time 45 min; chlorine-containing pyrolysis gas production flow rate approximately 120 Nm³. 3 / h, temperature 480℃, HCl concentration 5000-8000 mg / Nm 3 .

[0024] Solid-phase chlorine capture unit: Two parallel vertical fixed-bed reactors with dimensions of Φ500 mm × 2000 mm are set up (labeled as beds A and B); each bed is filled with granular calcium oxide (CaO) (particle size 3-5 mm, specific surface area 25 m²). 2 / g, filling amount 200 kg); the bed is placed in the high-temperature gas phase channel after the outlet of the pyrolysis furnace (the gas enters directly without cooling).

[0025] Switching unit: A valve group consisting of 6 pneumatic switching valves is installed between the pyrolysis gas main pipeline and the inlet of bed A and B; the valve action is controlled by PLC, the switching time is ≤5 seconds, and the system pressure fluctuation during the switching process is <±3 kPa.

[0026] Regeneration unit: Each bed is wrapped with an electric heating belt (total power 15 kW / bed); equipped with a high-purity nitrogen (99.999%) supply system with a flow rate of 0-10 Nm³. 3 / h adjustable; the regenerated tail gas outlet is connected to the chlorine resource recovery unit (including quench tower + NaOH absorption tower + evaporator crystallizer) through a corrosion-resistant pipeline.

[0027] Control unit: Adopts industrial PLC control system (Siemens S7-1500); integrates sensor signals such as temperature, pressure, flow rate, and HCl concentration to achieve fully automatic logic control.

[0028] Online monitoring device: TDLAS (tunable diode laser absorption spectroscopy) HCl online analyzers (range 0-10,000 ppm, accuracy ±1%, response time <5 s) are installed at the A and B outlets of the bed respectively; real-time data is transmitted to the PLC for determining the saturation state.

[0029] Example 2 Both solid-phase chlorine-capturing beds A and B are arranged in the high-temperature gas phase channel (gas temperature about 450°C) after the outlet of the pyrolysis reaction unit. The pyrolysis gas enters the chlorine-capturing bed directly without cooling, achieving efficient chemical capture of hydrogen chloride in the pyrolysis gas with a dechlorination rate of >95%.

[0030] Under the condition that the dual-bed switching structure remains unchanged, alkaline earth metal oxides, supported alkaline materials, and combinations of the two were selected and packed into the chlorine-capturing bed. Comparative operation showed that different solid-phase chlorine-capturing materials could effectively capture hydrogen chloride in the pyrolysis gas and continue to be put into chlorine-capturing operation after in-situ regeneration.

[0031] Example 3 Infrared HCl online analyzers (range 0-10,000 ppm, accuracy ±2%) are installed at outlets A and B of bed respectively. When the HCl concentration in the gas at the outlet of either bed exceeds 50 ppm (preset threshold), the PLC immediately triggers a switching command, directing the gas flow to another standby bed and initiating the regeneration program of the saturated bed. High-purity nitrogen gas (5 Nm) is introduced. 3 The bed temperature is raised to 650℃ using an electric heating mantle and maintained for 60 minutes. The regeneration tail gas (containing a high concentration of HCl, approximately 20-50 g / Nm³) 3 The solution is piped to an alkali absorption tower and a NaCl crystallization recovery unit for centralized processing, thereby realizing the resource utilization of chlorine.

[0032] Example 4 Chlorine-containing waste plastic (15% PVC content) is continuously fed into a pyrolysis furnace via a conveyor and pyrolyzed at 500℃ to generate chlorine-containing pyrolysis gas. The pyrolysis gas is introduced into bed A (in chlorine-capturing state), with an outlet HCl concentration of <30 ppm. After 90 minutes of operation, the HCl concentration at the outlet of bed A rises to 60 ppm (>50 ppm threshold), and the PLC determines that it is close to saturation. The six-way valve switches the gas flow to bed B, while N2 is introduced into bed A and the temperature is raised to 650℃ for 60 minutes for in-situ thermal regeneration. After regeneration, bed A regains its adsorption capacity and is switched to standby mode. Subsequently, when bed B becomes saturated, the flow is switched back to A, and the cycle continues. The pyrolysis reaction runs continuously throughout the entire process (24 h / d) without shutdown, and the dechlorination efficiency remains consistently >95%. The regeneration temperature is strictly controlled at 650℃. All chlorine-containing gases released during regeneration are discharged from the system for centralized treatment. No liquid alkali washing is used throughout the process, and no chlorine-containing wastewater is generated.

[0033] Example 5 The pyrolysis system was started, with waste plastics continuously fed in, and pyrolysis gas introduced into bed A; after 118 minutes of operation in bed A, the outlet HCl level rose to 52 mg / Nm³. 3 Trigger the switching; switch the pyrolysis gas to bed B; introduce N2 and heat to 400℃ at 8℃ / min, maintain the temperature for 90 minutes to regenerate bed A; introduce the regeneration tail gas into the chlorine recovery device; after regeneration, cool bed A to 480℃ and switch to standby; run the cycle for 5 cycles (about 10 hours in total) and record the data.

[0034] Example 6 The pyrolysis system is started, waste plastics are continuously fed in, and pyrolysis gas is introduced into bed A; after bed A has been running for 115 minutes, HCl = 55 mg / Nm³. 3 Switch to bed B; heat to 600℃ (rate 10℃ / min), maintain temperature for 90 minutes to regenerate bed A; introduce regeneration tail gas into chlorine recovery device; after regeneration, cool bed A to 480℃ and switch to standby; run for 10 cycles (approximately 20 hours in total) and record data.

[0035] Example 7 The pyrolysis system is started, waste plastics are continuously fed in, and pyrolysis gas is introduced into bed A; after bed A has been running for 112 minutes, HCl = 58 mg / Nm³. 3 Switch to bed B; heat to 800℃ (rate 12℃ / min), maintain temperature for 90 minutes to regenerate bed A; introduce regeneration tail gas into chlorine recovery device; after regeneration, cool bed A to 480℃ and switch to standby; run for 8 cycles (approximately 20 hours in total) and record data.

[0036] Table 1

[0037] As shown in Table 1, under regeneration conditions at 600℃, the dechlorination efficiency of CaO-based materials can be restored to more than 92% of the initial value, with a single cycle activity loss rate of less than 5%, supporting continuous operation for more than 10 cycles, which is sufficient to ensure the long-term stable dechlorination operation of the pyrolysis system without shutting down.

[0038] Comparative Example 1 A pyrolysis system consisting of a single solid-phase chlorine-removing bed (filled with 150 kg CaO) was constructed, located downstream of the pyrolysis gas outlet. Waste plastics were continuously fed into the bed, and pyrolysis gas was introduced for dechlorination. No switching unit, regeneration unit, or control logic was installed; the bed was continuously used once filled. The outlet HCl concentration was monitored in real time. When the outlet HCl > 100 mg / Nm³, the system was activated. 3 When the process is considered to be in failure, stop the machine and replace all the CaO, and record the running time; repeat the "run-stop-replace" cycle 3 times, and calculate the total processing volume and downtime.

[0039] Comparative Example 2 The pyrolysis system is followed by a packed alkaline scrubbing tower (Φ600 mm × 3000 mm); a 10 wt% NaOH solution is prepared and sprayed from the top of the tower at a flow rate of 5 L / min; the pyrolysis gas enters from the bottom of the tower and comes into countercurrent contact with the alkaline solution; the outlet gas is discharged after passing through a demister. The alkali solution is recycled; when pH < 9 or Cl... - When the concentration is >15 wt%, drain the waste liquid and replenish with fresh alkali solution; run continuously for 24 hours and record alkali consumption, wastewater generation and dechlorination efficiency.

[0040] Comparative Example 3 Waste plastics are first fed into a pre-dechlorination reactor (300℃, atmospheric pressure) and saturated steam (200 kg / h) is introduced. During this stage, PVC releases HCl, which is carried out by the steam. The HCl-containing steam is introduced into a lime water scrubbing tower (Ca(OH)2 slurry, 10 wt%), where it is absorbed to form CaCl2 precipitate. The dechlorinated plastics are then sent to a pyrolysis furnace (500℃) for pyrolysis. The pyrolysis gas undergoes no further dechlorination treatment, and its residual HCl is directly analyzed. The system is run continuously for 12 hours, and the pre-dechlorination efficiency, waste residue (CaCl2 sludge) yield, and final HCl concentration of the pyrolysis gas are recorded.

[0041] Table 2

[0042] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A dynamic solid-phase dechlorination system for pyrolysis or catalytic cracking of chlorine-containing waste plastics, characterized in that, include: A pyrolysis or catalytic cracking reaction unit is used to pyrolyze or catalytically crack chlorine-containing waste plastics to generate chlorine-containing pyrolysis gas. A solid-phase chlorine-catching unit, comprising at least two solid-phase chlorine-catching beds arranged in parallel, wherein the solid-phase chlorine-catching beds are filled with solid-phase chlorine-catching material; The solid-phase chlorine-capturing bed achieves dechlorination by capturing hydrogen chloride and / or chlorine-containing components in the pyrolysis gas; A switching unit is connected between the pyrolysis or catalytic cracking reaction unit and each of the solid phase chlorine-collecting beds, and is used to switch the direction of pyrolysis gas flow between different solid phase chlorine-collecting beds; The regeneration unit achieves in-situ regeneration by raising the temperature to release chlorides from the solid-phase chloride-collecting bed. The control unit is used to control the solid phase chlorine-collecting bed to alternate between chlorine-collecting state and regeneration state in order to achieve continuous operation of the dechlorination process.

2. The dynamic solid-phase dechlorination system according to claim 1, characterized in that, The solid-phase chlorine-capturing bed is located in the downstream gas phase channel of the pyrolysis or catalytic cracking reaction unit.

3. The dynamic solid-phase dechlorination system according to claim 1, characterized in that, The solid-phase chlorine-capturing material is selected from at least one of alkaline earth metal oxides, alkaline earth metal hydroxides, and supported alkaline materials.

4. The dynamic solid-phase dechlorination system according to claim 1, characterized in that, The switching unit includes a multi-way switching valve or a valve group composed of multiple switching valves, which can switch between the working bed and the regeneration bed without interrupting the pyrolysis gas flow.

5. The dynamic solid-phase dechlorination system according to claim 1, characterized in that, The regeneration unit utilizes waste heat from the pyrolysis system, inert gas, or reducing gas for regeneration; Preferably, the chlorine-containing gas released during the regeneration process is discharged to a chlorine resource recovery device or a safe disposal system for centralized treatment.

6. The dynamic solid-phase dechlorination system according to claim 1, characterized in that, It also includes an online hydrogen chloride monitoring device, which is installed at the outlet end of any of the solid phase chlorine-collecting beds, for real-time detection of hydrogen chloride concentration and feedback of the signal to the control unit; Preferably, the control unit controls the bed switching based on the hydrogen chloride concentration at the outlet of the solid-phase chlorine-collecting bed.

7. A dynamic solid-phase dechlorination method for pyrolysis or catalytic cracking of chlorine-containing waste plastics, characterized in that, Includes the following steps: S1: Chlorine-containing waste plastics are fed into a pyrolysis or catalytic cracking reaction unit to generate chlorine-containing pyrolysis gas; S2: The chlorine-containing pyrolysis gas is introduced into one of the solid phase chlorine-capturing beds in an adsorption state under anhydrous conditions to directly capture the hydrogen chloride therein; S3: When the solid phase chlorine-capturing bed is close to saturation, the pyrolysis gas is switched to another solid phase chlorine-capturing bed that is in standby state through the switching unit; S4: In-situ thermal regeneration of saturated solid-phase chlorine-capturing beds under an oxygen-free or reducing atmosphere to restore their adsorption capacity. S5: After regeneration is complete, the bed is switched to standby mode, and steps S2-S4 are repeated to achieve continuous dechlorination.

8. The method according to claim 7, characterized in that, In step S3, the criteria for determining that the solid phase chlorine-capturing bed is close to saturation are: the outlet hydrogen chloride concentration exceeds the preset threshold, or the cumulative operating time reaches the set cycle.

9. The method according to claim 7, characterized in that, In step S4, the saturated bed is heated to decompose or desorb the metal chloride, releasing chlorine-containing gas and achieving in-situ thermal regeneration. Preferably, the heating temperature is 400-800℃; Preferably, the heating temperature is 550-700℃; Preferably, the chlorine-containing gas released during the regeneration process is discharged from the system for treatment.

10. The method according to claim 7, characterized in that, Steps S3 and S4 are carried out simultaneously without interrupting the pyrolysis or catalytic cracking reaction process, ensuring continuous and stable operation of the system.

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