A closed-loop chlorine capture and regeneration system for pyrolysis / catalytic dechlorination of chlorine-containing waste plastics

Abstract

This application discloses a closed-loop chlorine capture and regeneration system and method for pyrolysis / catalytic dechlorination of chlorine-containing waste plastics. The system includes a pyrolysis / catalytic dechlorination reaction unit, a gas-solid separation unit, a condensation separation unit, an acidic gas absorption unit, and a bipolar membrane electrodialysis (BMED) regeneration unit. Hydrogen chloride generated during the pyrolysis or catalytic cracking of chlorine-containing waste plastics is absorbed by an alkaline absorbent to form a chloride-containing salt solution. This chloride-containing salt solution is regenerated through bipolar membrane electrodialysis to obtain a hydrochloric acid solution and an alkaline solution. The alkaline solution is recycled back to the absorption unit, while the hydrochloric acid solution is output as a byproduct or reused. This application achieves closed-loop recycling and resource utilization of chlorine during the pyrolysis / catalytic dechlorination process, reduces alkali consumption and salt wastewater discharge, and improves the stability of the dechlorination process and the economic efficiency of system operation.

Description

Technical Field

[0001] This application relates to the field of waste plastic resource utilization technology, specifically to a system and method for capturing, regenerating and recycling hydrogen chloride gas generated during the pyrolysis / catalytic dechlorination process of chlorine-containing waste plastics, and in particular a system and method capable of realizing closed-loop internal circulation and resource utilization of chlorine. Background Technology

[0002] With the continuous expansion of the scale of waste plastic resource utilization, pyrolysis and catalytic cracking technologies are widely used to convert waste plastics into fuel oil, chemical raw materials, or combustible gases. However, in actual industrial raw materials, polyvinyl chloride (PVC) or plastics containing chlorine additives are often inevitably mixed in, resulting in the generation of large amounts of hydrogen chloride (HCl) and other chlorine-containing components during pyrolysis or catalytic cracking.

[0003] Chlorine-containing components can cause several problems during pyrolysis / catalytic cracking: First, hydrogen chloride is highly corrosive and can corrode reactors, pipelines and downstream equipment; second, chlorine can easily enter pyrolysis oil or cracking products, resulting in excessive chlorine content in the oil and affecting its further utilization as fuel or chemical feedstock; in addition, chlorides can also cause catalyst poisoning and deactivation, shortening the operating cycle of the unit.

[0004] In existing technologies, the treatment of chlorine-containing waste plastics typically employs one of the following technical approaches: (1) Set up a dechlorination reaction zone in the reactor or add a dechlorination catalyst to remove chlorine from the chlorine-containing polymer before or during pyrolysis; (2) Hydrogen chloride in the tail gas is absorbed at the rear end of the reactor by means of alkaline washing, absorption tower, etc.; (3) Post-treatment of pyrolysis oil, such as hydrodechlorination, extraction dechlorination, etc.

[0005] However, existing alkaline washing or absorption methods generally have the following shortcomings: after absorbing hydrogen chloride, a large amount of chloride wastewater or solid salt is formed, resulting in high alkali consumption and high operating costs; the salt wastewater or waste salt needs to be further treated or discharged, increasing the environmental burden; at the same time, when the chlorine content of the raw material fluctuates, it is difficult to maintain long-term stable control over the dechlorination effect and the compliance of the exhaust gas.

[0006] Therefore, there is an urgent need to develop a closed-loop system that integrates pyrolysis dechlorination, high-efficiency absorption, and salt solution regeneration. This system can ensure the cleanliness and efficiency of the pyrolysis process and achieve closed-loop resource utilization of chlorine, thereby promoting the development of waste plastic chemical recycling towards a green, low-carbon, and high-value direction. Summary of the Invention

[0007] According to one aspect of this application, a closed-loop chlorine capture and regeneration system for pyrolysis / catalytic dechlorination of chlorine-containing waste plastics is provided, characterized in that it comprises, in sequence, the following: The pyrolysis / catalytic dechlorination reaction unit is used to pyrolyze or catalytically crack chlorine-containing waste plastics to produce pyrolysis gas containing hydrogen chloride. A gas-solid separation unit is used to separate solid particles entrained in the pyrolysis gas; A condensation separation unit is used to condense the pyrolysis gas to separate pyrolysis oil and non-condensable gas. An acidic gas absorption unit is used to absorb hydrogen chloride in the non-condensable gas with an alkaline absorption liquid to generate a chloride-containing salt solution. A bipolar membrane electrodialysis regeneration unit is used to electrolytically regenerate the chloride-containing salt solution into hydrochloric acid solution and alkaline solution; The alkaline solution is returned to the acidic gas absorption unit as an alkaline absorbent for recycling, while the hydrochloric acid solution is output as a product or recycled for internal processes, thereby achieving a closed-loop cycle of chlorine.

[0008] Optionally, the pyrolysis / catalytic dechlorination reaction unit includes a dechlorination zone and a pyrolysis zone arranged sequentially along the material flow direction, wherein the operating temperature of the dechlorination zone is lower than the operating temperature of the pyrolysis zone; Preferably, the operating temperature of the dechlorination zone is 250–350°C, and the operating temperature of the pyrolysis zone is 400–550°C. Preferably, the dechlorination zone is filled with a dechlorination catalyst containing alkaline components.

[0009] Optionally, the pyrolysis / catalytic dechlorination reaction unit is provided with a catalyst containing alkaline components to promote the removal of hydrogen chloride; Preferably, the alkaline component is selected from at least one of alkaline earth metal oxides, alkaline earth metal hydroxides, and supported alkaline materials.

[0010] Optionally, the alkaline absorbent is selected from at least one of sodium hydroxide solution, sodium carbonate solution, and potassium hydroxide solution; Preferably, the acidic gas absorption unit is equipped with an online detection device for detecting the pH value of the absorption liquid, so as to control the pH of the absorption liquid to be ≥ 9.

[0011] Optionally, the bipolar membrane electrodialysis regeneration unit includes a membrane stack formed by alternating stacks of bipolar membranes, cation exchange membranes, and anion exchange membranes. The membrane stack is configured with alternating salt chambers, acid chambers, and alkali chambers, wherein the salt chamber is fed with the chloride-containing salt solution, the acid chamber produces hydrochloric acid solution, and the alkali chamber produces an alkaline solution.

[0012] Optionally, the bipolar membrane electrodialysis regeneration unit is provided with a salt solution pretreatment unit on the inlet side. The salt solution pretreatment unit is selected from at least one of an oil removal device, a filtration device, and an adsorption purification device, and is used to remove organic matter, suspended solids, and impurity ions from the chloride-containing salt solution.

[0013] Optionally, the system also includes a control unit, which is used to adjust the amount of alkaline absorbent added according to the concentration of hydrogen chloride in the exhaust gas or the pH value of the absorbent, so as to maintain the pH value of the absorbent within a preset range; and to adjust the current density or flow rate of the bipolar membrane electrodialysis regeneration unit according to the conductivity or chloride ion concentration of the chloride-containing salt solution, so as to maintain stable operation and high regeneration efficiency of the system.

[0014] A closed-loop chlorine capture and regeneration method for chlorine-containing waste plastics via pyrolysis / catalytic dechlorination, characterized by comprising the following steps: (1) Chlorine-containing waste plastics are fed into a pyrolysis / catalytic dechlorination reaction unit for pyrolysis or catalytic cracking to generate pyrolysis gas containing hydrogen chloride; (2) The pyrolysis gas is subjected to gas-solid separation and condensation separation in sequence to obtain pyrolysis oil and non-condensed gas; (3) The non-condensable gas is introduced into the acidic gas absorption unit, and the hydrogen chloride is absorbed by the alkaline absorption liquid to form a chloride-containing salt solution; (4) The chloride-containing salt solution is introduced into the bipolar membrane electrodialysis regeneration unit and electrolyzed to regenerate into hydrochloric acid solution and alkaline solution; (5) The alkaline solution is returned to step (3) as an absorbent for recycling, and the hydrochloric acid solution is output as a by-product or recycled for internal processes of the system to realize closed-loop resource utilization of chlorine.

[0015] Optionally, a segmented temperature control strategy is adopted in step (1): first, dechlorination is carried out at a lower temperature, and then pyrolysis is carried out at a higher temperature.

[0016] Optionally, before step (4), the chloride-containing salt solution is pretreated, including oil removal, filtration and adsorption purification, to ensure the long-term stable operation of the bipolar membrane electrodialysis regeneration unit.

[0017] The beneficial effects that this application can produce include: 1) Achieve closed-loop recycling of chlorine: After HCl is captured, it is regenerated into alkali and acid through BMED, realizing internal recycling of chlorine resources and eliminating waste brine discharge; 2) Reduce alkali consumption and operating costs: By regenerating alkali solution through bipolar membrane electrodialysis and recycling it, the alkali solution regeneration rate is ≥90%, reducing annual alkali consumption by more than 70% and reducing the need for continuous alkali replenishment. 3) Stable and controllable dechlorination process: Through online monitoring and linkage control, inorganic chlorine is preferentially released in the low-temperature dechlorination zone, reducing the formation of organic chlorides in the high-temperature zone, and the dechlorination efficiency can remain stable even under fluctuating raw material chlorine content. 4) By-product resource utilization: The hydrochloric acid produced can be used as a chemical raw material or reused within the plant, improving overall economic efficiency; 5) High adaptability: Each unit is a mature or quasi-industrialized technology. The system can be coupled with various pyrolysis or catalytic cracking processes as a modular unit, which is convenient for industrial promotion and application. Detailed Implementation

[0018] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0019] 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.

[0020] Example 1 Mixed waste plastics containing a small amount of PVC at a rate of 5 kg / h are crushed, dried, and then fed into a single-stage pyrolysis reaction unit.

[0021] (1) Pyrolysis is carried out at 500℃ (without catalyst) to generate pyrolysis gas containing HCl; (2) The pyrolysis gas is separated from solid particles such as coke powder by the gas-solid separation unit, and then enters the condensation separation unit to separate pyrolysis oil and non-condensed gas (mainly containing H2, CH4, CO and HCl). (3) Then, non-condensable gas is introduced into the bottom of the packed absorption tower, and 5 wt% NaOH solution is sprayed from the top of the tower as alkaline absorbent to absorb HCl in a countercurrent manner; the acidic gas absorption unit is equipped with an online detection device for detecting the pH value of the absorbent, and a small amount of fresh NaOH is manually added when pH < 9; the HCl concentration in the tail gas after absorption is < 5 mg / m³. 3 The absorption solution was a NaCl solution (concentration approximately 8 wt%). (4) NaCl solution is pumped through a pipeline into a membrane stack formed by alternating layers of bipolar membranes, cation exchange membranes, and anion exchange membranes. The membrane stack is configured with alternating salt chambers, acid chambers, and base chambers. The salt chambers are fed with the chloride-containing salt solution, while the acid and base chambers produce 1.0 mol / L HCl solution and 1.0 mol / L NaOH solution, respectively. The operating current density is 40 mA / cm². 2 ; (5) All the regenerated NaOH solution is returned to the absorption tower and recycled as absorbent; the HCl solution is collected in the storage tank and output as a by-product.

[0022] The system can run continuously for 72 hours with a chlorine recovery rate of >95% and no chlorine-containing wastewater discharge, achieving closed-loop circulation.

[0023] Example 2 The pyrolysis / catalytic dechlorination reaction unit consists of a dechlorination zone and a pyrolysis zone arranged sequentially along the material flow direction. The operating temperature of the dechlorination zone is lower than that of the pyrolysis zone. The dechlorination zone is filled with a CaO-MgO composite catalyst (alkaline earth metal oxides, CaO:MgO = 3:1, specific surface area 120 m²). 2 / g).

[0024] Mixed waste plastics containing a small amount of PVC at a rate of 5 kg / h are crushed, dried, and then fed into a dual-zone fixed-bed reactor.

[0025] (1) First, keep the PVC at a temperature of 300℃ for 15 minutes in the dechlorination zone for selective dechlorination; (2) The material enters the pyrolysis zone and is pyrolyzed at 500°C to generate pyrolysis gas; (3) After the pyrolysis gas is separated into gas and solid and condensed, the non-condensed gas is passed into the absorption tower, and the NaOH solution absorbs HCl to generate NaCl solution; (4) After being pretreated by oil removal, filtration and adsorption purification, the NaCl solution enters the bipolar membrane electrodialysis regeneration unit to be regenerated into HCl and NaOH, and the alkali solution is reused. (5) The system runs continuously for 72 hours.

[0026] The HCl concentration at the exhaust gas outlet remained stable at 3-4 mg / m³. 3 The total removal rate reached 96.8%; there was no equipment corrosion or blockage, and the system operated stably.

[0027] Example 3 Mixed waste plastics containing a small amount of PVC at a rate of 5 kg / h are crushed, dried, and then fed into a dual-zone fixed-bed reactor.

[0028] (1) First, the PVC is selectively dechlorinated at 250°C for 20 minutes in the dechlorination zone; then it is deeply decomposed at 400°C in the pyrolysis zone to generate pyrolysis gas. The subsequent gas purification and chlorine regeneration process is the same as steps (3)-(5) in Example 2.

[0029] The HCl removal rate in the exhaust gas is 93.5%, and the system is operating stably.

[0030] Example 4 The pyrolysis / catalytic dechlorination reaction unit is a dual-zone fixed-bed reactor, with the dechlorination zone filled with a supported K2CO3 / Al2O3 catalyst. Mixed waste plastics containing a small amount of PVC (5 kg / h) are crushed, dried, and fed into the reactor.

[0031] (1) Waste plastics are first placed in the dechlorination zone at 350℃ for 10 minutes for rapid dechlorination; (2) The high-temperature 550℃ pyrolysis zone promotes the pyrolysis of heavy components; The subsequent gas purification and chlorine regeneration process is the same as steps (3)-(5) in Example 2.

[0032] The overall HCl removal rate was 95.2%; the system operated without failure for 72 hours, with only slight carbon buildup in the pyrolysis zone requiring periodic descaling, but this did not affect continuous operation.

[0033] Table 1

[0034] Example 5 Feed NaCl solution: 8 wt%, pretreated by degreasing, filtration, and adsorption; BMED current density: 20 mA / cm² 2 The rest is the same as in Example 2.

[0035] (1) The absorption unit produces NaCl solution; (2) After solution pretreatment, BMED is pumped in at 20 mA / cm 2 Electrolysis; (3) The control unit monitors the conductivity and maintains the salt chamber concentration.

[0036] The acid chamber and alkali chamber produce 0.95 mol / L HCl and 0.95 mol / L NaOH, respectively; the current efficiency is 78%, and the energy consumption is 3.8 kWh / kg HCl; the membrane stack pressure difference increases slowly (0.1 kPa / h), and there is no pollution during continuous operation for more than 500 hours.

[0037] Example 6 Feed NaCl solution: 8 wt%, pretreated by degreasing, filtration, and adsorption; BMED current density: 20 mA / cm² 2 The rest is the same as in Example 2.

[0038] (1) The absorption unit produces NaCl solution; (2) After solution pretreatment, BMED is pumped in at 40 mA / cm 2 Electrolysis; (3) The control unit monitors the conductivity and maintains the salt chamber concentration.

[0039] The acid chamber and alkali chamber produce 1.00 mol / L HCl and 1.00 mol / L NaOH, respectively; the current efficiency is 89%, and the energy consumption is 2.9 kWh / kg HCl; the membrane stack pressure difference increases slowly (0.2 kPa / h), and there is no pollution during continuous operation for more than 500 hours.

[0040] Example 7 Feed NaCl solution: 8 wt%, pretreated by degreasing, filtration, and adsorption; BMED current density: 20 mA / cm² 2 The rest is the same as in Example 2.

[0041] (1) The absorption unit produces NaCl solution; (2) After solution pretreatment, BMED is pumped in at 60 mA / cm 2 Electrolysis; (3) The control unit monitors the conductivity and maintains the salt chamber concentration.

[0042] The acid and alkali chambers produce 1.02 mol / L HCl and 1.02 mol / L NaOH, respectively; the current efficiency is 89%, and the energy consumption is 4.5 kWh / kg HCl; the membrane stack pressure difference increases rapidly (1.6 kPa / h), and the machine needs to be shut down for cleaning after 96 hours of operation.

[0043] Table 2

[0044] Example 8 This embodiment, based on Embodiment 1, adds a brine pretreatment unit and a control unit before the bipolar membrane electrodialysis regeneration unit. The pretreatment unit sequentially includes gravity oil removal, filtration, and adsorption purification steps to remove oil and organic impurities from the brine solution.

[0045] 5 kg / h of mixed waste plastic containing a small amount of PVC was crushed, dried, and then fed into the pyrolysis reaction unit. (1)-(3) Same as in Example 1, to obtain NaCl solution; (4) The NaCl solution is first pretreated by three steps: oil removal, filtration and adsorption, before entering BMED; (5) The control unit executes the following logic in real time: if the exhaust gas HCl > 10 mg / m³ 3 If the pH of the absorption solution is <9, the fresh NaOH replenishment valve will automatically open; if the conductivity of the salt solution is >90 mS / cm, the BMED current density will automatically be reduced from 40 mA / cm. 2 Increased to 50 mA / cm 2 If the conductivity is <80 mS / cm, the BMED current density will be automatically adjusted from 40 mA / cm. 2 Reduced to 30 mA / cm²; (6) The regenerated alkali solution is reused and the acid solution is output. The system runs continuously for 500 hours.

[0046] The BMED membrane stack differential pressure growth rate is <0.2 kPa / h, with no fouling or clogging; the exhaust gas HCl concentration remains <5 mg / m³. 3 The NaOH recycling rate is >98%.

[0047] Example 9 High-chlorine waste plastics: Artificially prepared mixture (PVC 50 wt% + PE 30 wt% + PP 20 wt%) Low-chlorine waste plastics: Artificially prepared mixture (PVC 10 wt% + PE 50 wt% + PP 40 wt%) Feeding mode (continuous operation for 96 hours): 0-24 h: high chlorine content feed (5 kg / h); 24-48 h: low chlorine content feed (5 kg / h); 48-72 h: high chlorine content feed (5 kg / h); 72-96 h: low chlorine content feed (5 kg / h).

[0048] (a) 0-24 h (high chlorine content stage): (1) High-chlorine waste plastics are fed into a pyrolysis reactor (300°C dechlorination + 500°C pyrolysis) to generate high-concentration HCl pyrolysis gas (~9.2 g / Nm³). (2) After gas-solid separation and condensation, the non-condensed gas enters the absorption tower; (3) The initial absorbent is regenerated NaOH (1.0 mol / L), and HCl is absorbed by circulation; (4) The conductivity sensor detected that the conductivity of the absorbent liquid increased from 85 mS / cm to 92 mS / cm (12 h). (5) The control unit automatically adjusts the BMED current density from 40 mA / cm². 2 Increased to 50 mA / cm 2 This accelerates the consumption of NaCl; (6) By the 24th hour, the NaCl concentration in the absorbent was stable at 8.2 wt%, and the HCl concentration in the tail gas was maintained at 3-4 mg / m³. 3 .

[0049] (ii) 24-48 h (low chlorine content stage): (1) Switching to low-chlorine feedstock, the HCl concentration in the pyrolysis gas is reduced to ~3.5 g / Nm³. 3 ; (2) The absorption load decreased, and the conductivity gradually decreased to 78 mS / cm (36 h); (3) The control unit automatically reduces the BMED current density to 30 mA / cm². 2 To avoid over-electrolysis; (4) The NaCl concentration in the absorbent was stable at 7.9-8.1 wt%, and the HCl concentration in the tail gas was 2-3 mg / m³. 3 .

[0050] (III) 48-96 h: Repeating the above control logic, the system consistently maintains the NaCl concentration in the absorbent within the range of 7.9–8.3 wt%, with minimal fluctuations in the HCl content of the tail gas.

[0051] Comparative Example 1 Mixed waste plastics containing a small amount of PVC at a rate of 5 kg / h are crushed, dried, and then fed into a single-stage pyrolysis reaction unit.

[0052] (1) The waste plastic is fed into a single-stage pyrolysis furnace and pyrolyzed at 600°C in one go (without a low-temperature dechlorination stage); (2) After the pyrolysis gas undergoes gas-solid separation and condensation, the non-condensed gas is introduced into the NaOH absorption tower; (3) The absorbent is for single use only. After 24 hours of operation, the entire tower is discharged because the pH drops to 7.5. (4) Collect the pyrolysis oil and test its chlorine content, and monitor the HCl concentration in the tail gas.

[0053] During pyrolysis, HCl reacts with heavy hydrocarbons at high temperatures to form organochlorides that are difficult to remove. The initial HCl removal rate in the tail gas is about 90%, but it rapidly decreases to 75% over time.

[0054] This indicates that the lack of a low-temperature dechlorination step leads to the generation of organic chlorine, reducing the system's dechlorination efficiency and stability.

[0055] Comparative Example 2 The pyrolysis / separation / absorption unit is the same as in Example 1; there is no BMED device or salt solution pretreatment; the absorbent is a disposable NaOH solution, which is discharged periodically.

[0056] Mixed waste plastics containing a small amount of PVC at a rate of 5 kg / h are crushed, dried, and then fed into a single-stage pyrolysis reaction unit.

[0057] (1) Waste plastics are pyrolyzed at 600℃ to generate pyrolysis gas containing HCl; (2) After purification, the gas enters the absorption tower and is absorbed by spraying with 5 wt% NaOH; (3) Check the pH of the absorption liquid every 24 hours. When the pH is <8, discharge all waste liquid (about 120 L) and replace with new alkali solution; (4) Record the changes in NaOH consumption, waste liquid volume, and HCl concentration in the tail gas.

[0058] A total of 240 L of high-salinity wastewater (containing approximately 10 wt% NaCl) was discharged; 28.5 kg of fresh NaOH was consumed; the HCl concentration in the tail gas increased from 5 mg / m³ on day 1. 3 Rising to 38 mg / m³ on day 3 3； There is no chlorine resource recovery; all HCl is converted into waste salt.

[0059] This indicates that failure to use BMED regeneration will result in high alkali consumption and high-salt wastewater discharge, making it impossible to achieve closed-loop circulation.

[0060] Comparative Example 3 High-chlorine waste plastics: Artificially prepared mixture (PVC 50 wt% + PE 30 wt% + PP 20 wt%) Low-chlorine waste plastics: Artificially prepared mixture (PVC 10 wt% + PE 50 wt% + PP 40 wt%) Feeding mode (continuous operation for 96 hours): 0-24 h: high chlorine content feed (5 kg / h); 24-48 h: low chlorine content feed (5 kg / h); 48-72 h: high chlorine content feed (5 kg / h); 72-96 h: low chlorine content feed (5 kg / h).

[0061] The process is carried out using the above-mentioned raw material switching strategy through the traditional alkaline washing step: (1) From 0 to 24 h: the NaCl concentration in the absorbent rapidly increased from 0 to 12.5 wt%, the pH dropped to 7.8, and 120 L of high-salt waste liquid was discharged from the entire tower on the 24th h, and the alkali solution was replaced; (2) 24-48 h: Due to high residual salt and low load, the absorption efficiency is unstable, and the HCl in the tail gas gradually decreases from 45 mg / m³ to 10 mg / m³; (3) Salt accumulation occurred again at 48 h due to high chlorine feed, and waste liquid was discharged for the second time at 72 h; The HCl concentration in the exhaust gas throughout the entire process is 8-50 mg / m³. 3 Significant fluctuations.

[0062] 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 closed-loop chlorine capture and regeneration system for pyrolysis / catalytic dechlorination of chlorine-containing waste plastics, characterized in that, Including those connected in sequence: The pyrolysis / catalytic dechlorination reaction unit is used to pyrolyze or catalytically crack chlorine-containing waste plastics to produce pyrolysis gas containing hydrogen chloride. The pyrolysis / catalytic dechlorination reaction unit includes a dechlorination zone and a pyrolysis zone arranged sequentially along the material flow direction, wherein the operating temperature of the dechlorination zone is lower than the operating temperature of the pyrolysis zone; A gas-solid separation unit is used to separate solid particles entrained in the pyrolysis gas; A condensation separation unit is used to condense the pyrolysis gas to separate pyrolysis oil and non-condensable gas. An acidic gas absorption unit is used to absorb hydrogen chloride in the non-condensable gas with an alkaline absorption liquid to generate a chloride-containing salt solution. A bipolar membrane electrodialysis regeneration unit is used to electrolytically regenerate the chloride-containing salt solution into hydrochloric acid solution and alkaline solution; The alkaline solution is returned to the acidic gas absorption unit as an alkaline absorbent for recycling, while the hydrochloric acid solution is output as a product or recycled for internal processes, thereby achieving a closed-loop cycle of chlorine.

2. The system according to claim 1, characterized in that, The operating temperature of the dechlorination zone is 250–350°C, and the operating temperature of the pyrolysis zone is 400–550°C. Preferably, the dechlorination zone is filled with a dechlorination catalyst containing alkaline components.

3. The system according to claims 1 and 2, characterized in that, The pyrolysis / catalytic dechlorination reaction unit is equipped with a catalyst containing alkaline components to promote the removal of hydrogen chloride; Preferably, the alkaline component is selected from at least one of alkaline earth metal oxides, alkaline earth metal hydroxides, and supported alkaline materials.

4. The system according to claim 1, characterized in that, The alkaline absorbent is selected from at least one of sodium hydroxide solution, sodium carbonate solution, and potassium hydroxide solution; Preferably, the acidic gas absorption unit is equipped with an online detection device for detecting the pH value of the absorption liquid.

5. The system according to claim 1, characterized in that, The bipolar membrane electrodialysis regeneration unit includes a membrane stack formed by alternating layers of bipolar membranes, cation exchange membranes, and anion exchange membranes. The membrane stack is configured with alternating salt chambers, acid chambers, and alkali chambers, wherein the salt chamber is fed with the chloride-containing salt solution, the acid chamber produces hydrochloric acid solution, and the alkali chamber produces alkaline solution.

6. The system according to claim 1, characterized in that, The bipolar membrane electrodialysis regeneration unit is provided with a salt solution pretreatment unit on the inlet side. The salt solution pretreatment unit is selected from at least one of an oil removal device, a filtration device, and an adsorption purification device, and is used to remove organic matter, suspended solids, and impurity ions from the chloride-containing salt solution.

7. The system according to claim 1, characterized in that, It also includes a control unit, which is used to adjust the amount of alkaline absorbent added according to the concentration of hydrogen chloride in the exhaust gas or the pH value of the absorbent, so that the pH value of the absorbent is maintained within a preset range; and to adjust the current density or flow rate of the bipolar membrane electrodialysis regeneration unit according to the conductivity or chloride ion concentration of the chloride-containing salt solution, so as to maintain stable operation and high regeneration efficiency of the system.

8. A closed-loop chlorine capture and regeneration method for chlorine-containing waste plastics via pyrolysis / catalytic dechlorination, characterized in that, Includes the following steps: (1) Chlorine-containing waste plastics are fed into a pyrolysis / catalytic dechlorination reaction unit for pyrolysis or catalytic cracking to generate pyrolysis gas containing hydrogen chloride; (2) The pyrolysis gas is subjected to gas-solid separation and condensation separation in sequence to obtain pyrolysis oil and non-condensed gas; (3) The non-condensable gas is introduced into the acidic gas absorption unit, and the hydrogen chloride is absorbed by the alkaline absorption liquid to form a chloride-containing salt solution; (4) The chloride-containing salt solution is introduced into the bipolar membrane electrodialysis regeneration unit and electrolyzed to regenerate into hydrochloric acid solution and alkaline solution; (5) The alkaline solution is returned to step (3) as an absorbent for recycling, and the hydrochloric acid solution is output as a by-product or recycled for internal processes of the system to realize closed-loop resource utilization of chlorine.

9. The method according to claim 8, characterized in that, In step (1), a segmented temperature control strategy is adopted: first, dechlorination is carried out at a lower temperature, and then pyrolysis is carried out at a higher temperature.

10. The method according to claim 8, characterized in that, Before step (4), the chloride-containing salt solution is pretreated, including oil removal, filtration and adsorption purification, to ensure the long-term stable operation of the bipolar membrane electrodialysis regeneration unit.

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