Method for plastic dechlorination by microwave-assisted magnetic catalyst

Abstract

The invention provides a microwave-assisted magnetic catalyst plastic dechlorination method, which comprises: placing plastic in a reactor containing a magnetic nano composite catalyst, carrying out an irradiation reaction by using microwaves, continuously adsorbing a plastic melt generated after the irradiation by using a composite adsorption bed, recycling hydrogen chloride gas generated by the irradiation reaction; according to the method provided by the invention, the dechlorination efficiency is 85%-90% of that of a traditional method, the dechlorination efficiency can reach 98% or above, and the treatment time is shortened to 15-30 min; the comprehensive energy consumption is not higher than 0.8 kWh / kg of waste plastics, 0.2-0.5 ton of hydrochloric acid (with the concentration of 30%-35%) is co-produced by per ton of waste plastics, the economic benefit is increased by 200-500 yuan / ton, solid waste is reduced by 90% by recycling the catalyst, and the method has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of plastics processing technology, and more particularly to a method for dechlorination of plastics using a microwave-assisted magnetic catalyst. Background Technology

[0002] With the surge in plastic consumption, the treatment of chlorinated waste plastics (such as PVC) has become a global environmental challenge. Traditional dechlorination technologies suffer from the following problems: 1. High energy consumption: Pyrolysis or steam stripping requires high temperatures (300-500℃), with energy consumption accounting for over 60% of the treatment cost. 2. Non-recyclable catalysts: Conventional catalysts (such as metal oxides) are easily deactivated and difficult to separate, resulting in low reuse rates. 3. Waste of chlorine resources: The released HCl gas is mostly directly neutralized and emitted, without being converted into high-value chemicals. 4. Risk of secondary pollution: Residual chlorine (>100ppm) affects the quality of recycled plastics, and exhaust gas treatment is incomplete.

[0003] CNl04530473B discloses a method and system for dechlorination of waste plastics based on steam flow dispersion stripping. The principle is that when polyvinyl chloride (PVC) plastic melts, HCl is released. Steam is used to carry away the HCl released by the waste plastic. At the same time, the steam can also convert the inorganic chloride salts mixed in the waste plastic into HCl and precipitate them out. In this way, the Cl in the waste plastic is separated.

[0004] CN116064066A discloses a method and system for liquefying, reducing viscosity, and dechlorinating chlorinated waste plastics, comprising the following steps: feeding chlorinated waste plastic particles into a first screw pump for dehydration, degassing, and volume reduction treatment to obtain pretreated chlorinated waste plastic material; feeding the pretreated material and high-temperature solvent oil into a second screw pump for hot-melt dechlorination treatment to obtain hydrogen chloride-containing gaseous material and dechlorinated waste plastic oil; and introducing stripping gas into the second screw pump to discharge the hydrogen chloride-containing gaseous material from the second screw pump under the action of the stripping gas. This method can achieve dechlorination treatment of PVC-containing waste plastics simultaneously with liquefaction and viscosity reduction, resulting in dechlorinated waste plastic liquefied oil that is easy to transport, has uniform thermal conductivity, and low melt viscosity.

[0005] While the aforementioned methods include steam stripping and solvent dechlorination, they still fail to solve the problems of high energy consumption and chlorine resource recovery. Therefore, developing a low-energy-consumption chlorine resource recovery method is of great significance for practical applications. Summary of the Invention

[0006] The technical problem that this invention aims to solve is that existing dechlorination methods have high energy consumption and low chlorine resource recovery efficiency.

[0007] To address the aforementioned technical problems, this invention provides a method for dechlorination of plastics using a microwave-assisted magnetic catalyst. The method includes: placing the plastic in a reactor containing a magnetic nanocomposite catalyst; irradiating the plastic with microwaves; allowing the resulting plastic melt to be adsorbed through a composite adsorption bed; and recovering the hydrogen chloride gas generated during the irradiation reaction.

[0008] The method provided by this invention replaces traditional heat conduction with microwave directional heating and employs magnetic nanocatalysts. Compared with other existing technologies, it reduces energy consumption by 40% to 60% by lowering the reaction temperature to 150–250°C; it enables catalyst recycling by rapidly recovering and regenerating the catalyst through magnetic separation technology, with a recycling rate of no less than 10 times; it facilitates HCl resource utilization by efficiently converting HCl gas generated during dechlorination into industrial hydrochloric acid (concentration ≥30%), increasing added value by more than 20%; and it achieves deep purification by using an activated carbon-molecular sieve composite adsorption bed to ensure that the chlorine content of recycled plastics does not exceed 50 ppm, meeting the standards for pyrolysis feedstocks.

[0009] In this invention, the reactor is lined with corrosion-resistant ceramic and has a built-in temperature sensor and infrared monitoring module to regulate the reaction temperature in real time (accuracy ±5℃).

[0010] In this invention, before the plastic is placed into the reactor, the raw material can be pretreated: waste plastic containing polyvinyl chloride (mass content ≤15%), polyethylene and polypropylene (mass content ≥80%) is crushed to a particle size of no more than 3cm using a twin-shaft shear crusher.

[0011] Preferably, the magnetic nanocomposite material is a Fe3O4@SiO2 core-shell supported Ni-Mo bimetal, and the molar ratio of Ni to Mo is 1:(1 to 3), for example, it can be 1:1, 1:2 or 1:3, etc.

[0012] Fe3O4@SiO2 is a mesoporous silica-encapsulated magnetite. This magnetic nanocomposite material can catalyze the release of HCl, and its activity retention rate after regeneration is no less than 90%.

[0013] Preferably, the specific surface area of ​​the magnetic nanocomposite material is 200–600 m². 2 / g, for example, could be 200m 2 / g、400m 2 / g、500m 2 / g、600m 2 / g etc.

[0014] Preferably, the addition mass of the magnetic nanocomposite material is 3% to 10% of the mass of the plastic, for example, it can be 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.

[0015] Preferably, the power of the microwave is 50 to 1000 kW, for example, it can be 50 kW, 100 kW, 300 kW, 700 kW, 900 kW or 1000 kW, and the frequency is 2.4 to 2.5 GHz.

[0016] Preferably, the irradiation reaction time is 10 to 30 minutes, for example, 10 minutes, 12 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes.

[0017] In this invention, microwaves can precisely heat the molecular chains of chlorine-containing plastics, promoting the breaking of Cl-Cl bonds.

[0018] Preferably, the composite adsorption bed comprises activated carbon and molecular sieve, wherein the mass ratio of activated carbon to molecular sieve is 4:1. In this invention, the composite adsorption bed is capable of adsorbing residual chlorine and volatile organic compounds.

[0019] Preferably, the recovery process is as follows: after condensation, hydrogen chloride gas enters a countercurrent absorption tower and comes into contact with water to produce hydrochloric acid; the remaining hydrogen chloride gas that does not produce hydrochloric acid is washed with alkaline solution.

[0020] In this invention, a combination of multi-stage condensation and countercurrent absorption towers is used to generate hydrochloric acid by countercurrent contact between condensed HCl gas and water, with an absorption efficiency of not less than 99%, ensuring that the HCl content in the tail gas is less than 10 ppm.

[0021] Preferably, the spray flow rate in the countercurrent absorption tower is 1 to 3 L / min, for example, it can be 1 L / min, 2 L / min or 3 L / min, etc.

[0022] Implementing this invention has the following beneficial effects:

[0023] The method provided by this invention achieves a dechlorination efficiency of over 98% compared to the traditional method's 85%–90%, and reduces the processing time to 15–30 minutes. The overall energy consumption is no higher than 0.8 kWh / kg of waste plastic, and each ton of waste plastic co-produces 0.2–0.5 tons of hydrochloric acid (concentration 30%–35%), increasing economic benefits by 200–500 yuan / ton. The catalyst is recycled, reducing solid waste by 90%, and the exhaust emissions meet the GB 16297-1996 standard.

[0024] In the waste plastic recycling industry: it is suitable for the resource recovery of chlorinated plastics in municipal waste treatment plants and electronic waste dismantling centers. In the chemical industry chain extension: co-producing hydrochloric acid can supply industries such as metallurgy and pharmaceuticals, forming a closed loop of "waste plastics - hydrochloric acid - industrial raw materials". Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] The specific equipment used in this invention is as follows:

[0027] Microwave reactor: 50L volume, material: SiC ceramic; magnetic separator: magnetic field strength 0.5T; hydrochloric acid storage tank: acid-resistant PP material, with online pH monitoring.

[0028] Pre-treat the plastic raw materials before the dechlorination process:

[0029] Waste plastics containing polyvinyl chloride (mass content ≤15%) and polyethylene + polypropylene (mass content ≥80%) are crushed to a particle size of no more than 3cm using a twin-shaft shear crusher.

[0030] Example 1

[0031] This embodiment provides a method for dechlorination of plastics using a microwave-assisted magnetic catalyst.

[0032] (1) Place the treated plastic in the reactor and set the microwave frequency to 2.45 GHz and the power to 800 kW. The reactor has a volume of 50 L, is lined with corrosion-resistant (SiC) ceramic, and has a built-in temperature sensor and infrared temperature measurement module to control the reaction temperature in real time at 200 ℃ (±5 ℃ accuracy).

[0033] The catalyst is a Fe3O4@SiO2 core-shell supported Ni-Mo bimetallic catalyst (Ni:Mo molar ratio 1:2) with a specific surface area of ​​not less than 200 m². 2 / g, the addition amount is 5% of the mass of waste plastic, and the reaction time is 20 minutes.

[0034] (2) The HCl gas produced in the reaction is initially condensed to remove water vapor and volatile organic compounds (VOCs), resulting in HCl gas with high purity. After condensation, the gas enters a countercurrent absorption tower and comes into contact with deionized water (spray flow rate 2 L / min) to produce a 32% hydrochloric acid solution with an absorption efficiency greater than 99%. The tail gas is then washed in an alkaline spray tower (NaOH solution) to ensure that the HCl content in the tail gas is less than 10 ppm.

[0035] (3) The dechlorinated plastic melt passes through a composite adsorption bed (activated carbon: molecular sieve = 4:1) to adsorb residual chlorine and volatile organic compounds (VOCs).

[0036] Using a microcoulometric chlorine analyzer and the principle of microcoulometric titration, the residual chlorine content was reduced to 42 ppm. The catalyst was recovered by magnetic separation, regenerated by calcination at 550℃ for 2 hours, and retained 88% of its activity after 12 cycles.

[0037] Example 2

[0038] This embodiment provides a method for dechlorination of plastics using a microwave-assisted magnetic catalyst.

[0039] (1) Place the treated plastic in the reactor and set the microwave frequency to 2.45 GHz and the power to 300 kW. The reactor has a volume of 50 L, is lined with corrosion-resistant (SiC) ceramic, and has a built-in temperature sensor and infrared temperature measurement module to control the reaction temperature in real time at 200 ℃ (±5 ℃ accuracy).

[0040] The catalyst is a Fe3O4@SiO2 core-shell supported Ni-Mo bimetallic catalyst (Ni:Mo molar ratio 1:2) with a specific surface area of ​​not less than 200 m². 2 / g, the addition amount is 3% of the mass of waste plastic, and the reaction time is 30 minutes.

[0041] (2) The HCl gas produced by the reaction is initially condensed to remove water vapor and volatile organic compounds (VOCs), resulting in HCl gas with high purity. After condensation, the gas enters a countercurrent absorption tower and comes into contact with deionized water (spray flow rate 2 L / min) to produce a 30% hydrochloric acid solution with an absorption efficiency greater than 99%. The tail gas is then washed by an alkaline spray tower (NaOH solution) to ensure that the HCl content in the tail gas is less than 10 ppm.

[0042] (3) The dechlorinated plastic melt passes through a composite adsorption bed (activated carbon: molecular sieve = 4:1) to adsorb residual chlorine and volatile organic compounds (VOCs).

[0043] Using a microcoulometric chlorine analyzer and the principle of microcoulometric titration, the residual chlorine content was reduced to 45 ppm. The catalyst was recovered by magnetic separation, regenerated by calcination at 550℃ for 2 hours, and retained 85% of its activity after 12 cycles.

[0044] Example 3

[0045] This embodiment provides a method for dechlorination of plastics using a microwave-assisted magnetic catalyst.

[0046] (1) Place the treated plastic in the reactor and set the microwave frequency to 2.45 GHz and the power to 1000 kW. The reactor has a volume of 50 L, is lined with corrosion-resistant (SiC) ceramic, and has a built-in temperature sensor and infrared temperature measurement module to control the reaction temperature in real time at 200 ℃ (±5 ℃ accuracy).

[0047] The catalyst is a Fe3O4@SiO2 core-shell supported Ni-Mo bimetallic catalyst (Ni:Mo molar ratio 1:2) with a specific surface area of ​​not less than 200 m². 2 / g, the addition amount is 7% of the mass of waste plastic, and the reaction time is 10 minutes.

[0048] (2) The HCl gas produced in the reaction is initially condensed to remove water vapor and volatile organic compounds (VOCs), resulting in HCl gas with high purity. After condensation, the gas enters a countercurrent absorption tower and comes into contact with deionized water (spray flow rate 2 L / min) to produce a 31% hydrochloric acid solution with an absorption efficiency greater than 99%. The tail gas is then washed in an alkaline spray tower (NaOH solution) to ensure that the HCl content in the tail gas is less than 10 ppm.

[0049] (3) The dechlorinated plastic melt passes through a composite adsorption bed (activated carbon: molecular sieve = 4:1) to adsorb residual chlorine and volatile organic compounds (VOCs).

[0050] Using a microcoulometric chlorine analyzer and the principle of microcoulometric titration, the residual chlorine content was reduced to 43 ppm. The catalyst was recovered by magnetic separation, regenerated by calcination at 550℃ for 2 hours, and retained 86% of its activity after 12 cycles.

[0051] Comparative Example 1

[0052] This comparative example is basically the same as Example 1, except that microwave radiation is not used in this comparative example, but ordinary heating reaction is used instead.

[0053] After dechlorination using this method, the residual chlorine was analyzed by microcoulometric titration using a microcoulometric chlorine analyzer, and the chlorine residue was reduced to 85 wppm. The catalyst was recovered by magnetic separation, regenerated by calcination at 550℃ for 2 hours, and retained 80% of its activity after 12 cycles.

[0054] Comparative Example 2

[0055] This comparative example is basically the same as Example 1, except that no magnetic nanocomposite catalyst Fe3O4@SiO2 core-shell supported Ni-Mo bimetal is added in this comparative example.

[0056] Following dechlorination in this case, a microcoulometric chlorine analyzer was used to analyze the sample, and the residual chlorine level was reduced to 128 ppm. The catalyst was recovered by magnetic separation, regenerated by calcination at 550°C for 2 hours, and retained 73% of its activity after 12 cycles.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for dechlorination of plastics using a microwave-assisted magnetic catalyst, characterized in that, The method includes: placing plastic in a reactor containing a magnetic nanocomposite catalyst, irradiating the reaction with microwaves, and then adsorbing the resulting plastic melt through a composite adsorption bed. The hydrogen chloride gas generated during the irradiation reaction is then recovered.

2. The method according to claim 1, characterized in that, The magnetic nanocomposite material is a Fe3O4@SiO2 core-shell supported Ni-Mo bimetal, with a molar ratio of Ni to Mo of 1:(1-3).

3. The method according to claim 2, characterized in that, The specific surface area of ​​the magnetic nanocomposite material is 200–600 m². 2 / g.

4. The method according to claim 2, characterized in that, The magnetic nanocomposite material is added at a mass of 3% to 10% of the plastic mass.

5. The method according to claim 1, characterized in that, The microwave has a power of 50–1000 kW and a frequency of 2.4–2.5 GHz.

6. The method according to claim 1, characterized in that, The irradiation reaction time is 10 to 30 minutes.

7. The method according to claim 1, characterized in that, The composite adsorption bed comprises activated carbon and molecular sieve, wherein the mass ratio of activated carbon to molecular sieve is 4:

1.

8. The method according to claim 1, characterized in that, The recovery process is as follows: after condensation, hydrogen chloride gas enters a countercurrent absorption tower and comes into contact with water to produce hydrochloric acid. The remaining hydrogen chloride gas that does not produce hydrochloric acid is washed with alkaline solution.

9. The method according to claim 8, characterized in that, The spray flow rate in the countercurrent absorption tower is 1-3 L / min.