A dechlorination adsorbent, a preparation method thereof and application of the dechlorination adsorbent in dechlorination of pyrolysis gas of waste plastics containing chlorine

Abstract

The application discloses a kind of dechlorination adsorbents and preparation method and application in chlorine-containing waste plastic pyrolysis gas dechlorination, and preparation method steps are as follows: after plasma etching ZIF-8 is mixed with GO and ultrasonic dispersion, after freeze drying, calcination, impregnation in Mg / Al-LDH sol solution, after drying, activation, obtain molecular trap carrier;La, Nd, Zn containing solution is mixed with precipitant after stirring, then centrifugation, washing, drying, obtain precursor and calcination, grinding, obtain active powder;Molecular trap carrier is coated with mesoporous ZrO2 layer after impregnation in active powder glue liquid and calcination under protective gas after grinding, obtain composite powder after spray drying granulation, drying, calcination, obtain the dechlorination adsorbent with high chlorine capacity, and excellent adsorption performance to HCl.

Description

Technical Field

[0001] This invention relates to a dechlorination adsorbent, its preparation method, and its application in the dechlorination of chlorine-containing waste plastic pyrolysis gas, belonging to the field of environmental protection technology. Background Technology

[0002] With the massive production and use of plastics globally, the recycling and reuse of waste plastics is urgently needed to achieve sustainable development.

[0003] The catalytic cracking of waste plastics after pyrolysis to produce oil and gas fuels has become a new approach to controlling plastic pollution. However, chlorine-containing waste plastics exist in the form of HCl after pyrolysis. Industrially, dechlorination adsorbents are loaded into a fixed bed and brought into contact with the chlorine-containing pyrolysis gas to achieve adsorption dechlorination. However, the breakthrough chlorine capacity of dechlorination adsorbents used in industrial applications is usually between 30-40%, resulting in unsatisfactory dechlorination effects. Summary of the Invention

[0004] The purpose of this invention is to provide a dechlorination adsorbent, its preparation method, and its application in the dechlorination of chlorine-containing waste plastic pyrolysis gas. The prepared dechlorination adsorbent has high chlorine penetration capacity and excellent adsorption performance for HCl.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a dechlorination adsorbent includes the following steps:

[0007] S1. The plasma-etched ZIF-8 was mixed with GO and ultrasonically dispersed. After freeze-drying, it was calcined under a protective gas and then impregnated in Mg / Al-LDH sol. After drying and activation, the molecular trap carrier was obtained.

[0008] S2. The solution containing La salt, Nd salt and Zn salt is mixed with a precipitant and stirred. Then, it is centrifuged, washed and dried to obtain a precursor. The precursor is calcined and then ground to obtain an active powder.

[0009] S3. After immersing the molecular trap carrier in ZrOCl2 solution and drying it, place it in a fluidized bed and pass zirconium n-butoxide vapor and water vapor through it successively to obtain a mesoporous ZrO2 layer coated molecular trap carrier.

[0010] S4. The active powder is made into a slurry, and then the mesoporous ZrO2 layer coated molecular trap carrier is immersed in the active powder slurry, calcined under a protective gas and then ground to obtain a composite powder.

[0011] S5. The composite powder, binder, pore-forming agent and water are mixed and spray-dried into granules, and then dried and calcined to obtain the dechlorination adsorbent.

[0012] Preferably, the method for plasma etching ZIF-8 is to place ZIF-8 in a plasma reactor, and at room temperature, introduce a gas mixture of Ar and H2 in a volume ratio of (5-10):1 at a flow rate of 30-100 mL / min, and treat it at a power of 200-500 W for 25-45 min; after removal, wash it, and then vacuum dry it at 70-90℃ for 12 h.

[0013] Preferably, in step S1, the content of Mg / Al-LDH sol in the Mg / Al-LDH sol solution is 5-15 wt%, and the molar ratio of Mg to Al in the Mg / Al-LDH sol solution is (1-3):1;

[0014] The mass ratio of ZIF-8 after plasma etching to the sol in GO and Mg / Al-LDH sol solution is 1:(1-5):(0.2-0.5);

[0015] The conditions for ultrasonic dispersion are: 300-500w, 20-40min;

[0016] The freeze-drying conditions are: -50~-20℃, 15-30h;

[0017] The calcination conditions are: under a nitrogen atmosphere, a heating rate of 1-5℃ / min, and calcination at 250-300℃ for 1.5-3h;

[0018] The activation conditions are: 300-350℃, 0.5-1.5h.

[0019] Preferably, in step S2, the La salt, Nd salt, and Zn salt are La(NO3)3·6H2O, Nd(NO3)3·6H2O, and ZnCl2, respectively, with concentrations of 0.2-0.5 mol / L, 0.1-0.3 mol / L, and 0.05-0.2 mol / L, respectively.

[0020] The precipitant is an NH4HCO3 solution with a concentration of 0.5-2 mol / L;

[0021] The volume ratio of the solution containing La salt, Nd salt, and Zn salt to the precipitant is 1:(1-1.3);

[0022] The calcination conditions are: in an air atmosphere, heating rate of 3-5℃ / min, calcination at 550-750℃ for 3-5 hours.

[0023] Preferably, in step S3, the concentration of the ZrOCl2 solution is 0.3-1 mol / L, the impregnation time is 1-2 h, and the drying temperature is 100-150℃ for 1-2 h.

[0024] The ratio of molecular trap carrier to zirconium n-butoxide is (30-80) g: (40-100) mL; the carrier gas for zirconium n-butoxide vapor is N2, the temperature is 300-350℃, and the ventilation time is 15-45 min.

[0025] The water vapor should be ventilated for 20-30 minutes.

[0026] Preferably, in step S4, the preparation method of the active powder solution is as follows: the active powder is mixed with citric acid and ethanol in a ratio of (10-30)g:(1-2)g:(100-300)mL, stirred at 50-65℃ for 1-2h, and centrifuged to obtain modified powder; the modified powder is then mixed with tetramethylammonium hydroxide and alcohol in a ratio of (10-30)g:(1-2)g:(100-300)mL, ultrasonically treated at 300-600W power for 15-45min, aged at 40-50℃ for 10-15h, and the pH is adjusted to 7.5-8.5. Then, ethanol is added until the solid content is 15-25wt%.

[0027] Preferably, in step S4, the mass ratio of the mesoporous ZrO2 layer-coated molecular trap carrier to the active powder adhesive is (3-8):(1-3);

[0028] The calcination conditions are: under a N2 atmosphere, 350-450℃, for 1-3 hours.

[0029] Preferably, in step S5, the binder is a silica sol with a SiO2 solid content of 25-35 wt%; the pore-forming agent is PEG-1000.

[0030] The mass ratio of composite powder, binder, pore-forming agent and water is (80-120):(5-15):(2-5):(30-60);

[0031] The conditions for spray drying granulation are: inlet air temperature 130-180℃, outlet air temperature 70-90℃, feeding rate 10-30mL / min, and spray pressure 0.2-0.8MPa.

[0032] The drying conditions are: 120-150℃, 1.5-3h;

[0033] The calcination conditions are: under N2 atmosphere, 350-450℃, for 3-5 hours.

[0034] A dechlorination adsorbent prepared by any of the methods described above.

[0035] Application of dechlorination adsorbents prepared by any of the above methods in the dechlorination of chlorine-containing waste plastic pyrolysis gas.

[0036] The beneficial effects of this invention are as follows:

[0037] Plasma etching of ZIF-8, using H + Bombardment selectively removes some Zn nodes, and the resulting local defects / vacancies (holes in the framework) after node removal can easily lead to structural collapse in subsequent processing. The confinement effect of GO prevents the collapse of ZIF-8 pores, maintaining the porous structure and allowing it to better match the HCl kinetic diameter. Simultaneously, GO's large specific surface area provides a basis for loading the Mg / Al-LDH positively charged layer, utilizing the electrostatic adsorption of Cl by the Mg / Al-LDH positively charged layer. - It repels electrically neutral organochlorine molecules, achieving selective dechlorination and improving the dechlorination effect. The mesoporous ZrO2 layer coating provides thermal shielding for the porous structure, which helps maintain structural stability.

[0038] Furthermore, the La3Nd2ZnO7 fluorite structure formed from the active powder exhibits high entropy stability, which can suppress Zn 0 High-temperature agglomeration. The introduction of citric acid molecules on the surface of the active powder can improve the dispersion of the active powder through electrostatic repulsion, prevent agglomeration, and ensure stable dispersion in the colloid, which is conducive to uniform loading on the composite powder and improves the dechlorination adsorption effect. Detailed Implementation

[0039] Example 1: This example provides a method for preparing a dechlorination adsorbent, including the following steps: 1) Dissolve 5.6g of 2-methylimidazole in 50mL of methanol, and simultaneously dissolve 2.5g of zinc nitrate hexahydrate Zn(NO3)2·6H2O in 50mL of methanol. Mix the two solutions evenly, stir magnetically for 1h, and let stand for 24h. Centrifuge the product, wash it three times with methanol, and dry it to obtain ZIF-8.

[0040] 2) The ZIF-8 prepared according to the above method was placed in a plasma reactor and Ar / H2 mixed gas (volume ratio 9:1) was introduced at a flow rate of 50 mL / min at room temperature and treated at 300 W power for 30 min. After removal, it was washed with ethanol 3 times and then vacuum dried at 80 °C for 12 h.

[0041] 3) Add 4.04 g of magnesium chloride hexahydrate and 2.4 g of aluminum chloride hexahydrate to 50 mL of deionized water, stir and dissolve to obtain a salt solution; add 6 mL of ammonia water to 94 mL of deionized water to obtain an ammonia solution with a volume concentration of 6%, add it to the salt solution, a precipitate is formed, then add sodium hydroxide solution to adjust the pH to 10±0.2 to obtain a precipitate; let the precipitate stand in the mother liquor for 45 min, centrifuge at 3000 rpm for 5 min, wash with deionized water, store the precipitate in an 80℃ oven to dry for 24 h, and then grind to obtain Mg / Al-LDH powder; mix Mg / Al-LDH powder with ethanol and water (volume ratio of ethanol to water is 7:3) to prepare a 10 wt% Mg / Al-LDH sol solution.

[0042] 4) The plasma-etched ZIF-8 and GO (graphene oxide) were mixed at a mass ratio of 1:2 and ultrasonically dispersed at 500 W (20 kHz) for 30 min. After being freeze-dried in vacuum at -30 °C for 24 h, the mixture was calcined at 300 °C for 2 h under N2 protection with a heating rate of 2 °C / min. The calcined product was then immersed in Mg / Al-LDH sol (the mass ratio of plasma-etched ZIF-8 to Mg / Al-LDH sol was 1:0.3) for 2 h, dried at 120 °C for 1 h, and activated at 320 °C for 1 h to obtain the molecular trap carrier.

[0043] 5) La(NO3)3·6H2O, Nd(NO3)3·6H2O, and ZnCl2 were co-dissolved in water at target concentrations of 0.3 mol / L, 0.2 mol / L, and 0.1 mol / L, respectively. These solutions were then added dropwise in a 1 mol / L NH4HCO3 solution (the solvent being a mixture of ethanol and water in a 7:3 volume ratio) at a 1:1 volume ratio. After the addition was complete, the mixture was stirred at 500 rpm for 2 hours at room temperature, then centrifuged. The mixture was washed three times with an ethanol-water mixture (7:3 volume ratio) and then vacuum-dried at 60°C for 12 hours. The resulting precursor was calcined at 600°C for 4 hours in air at a heating rate of 3°C / min, then naturally cooled to room temperature under a N2 atmosphere and ground to obtain the active powder.

[0044] 6) Mix the active powder with citric acid and ethanol at a ratio of 10g:1.5g:150mL, stir at 60℃ for 2h, and centrifuge to obtain modified powder; then mix the modified powder with tetramethylammonium hydroxide and alcohol solution (ethanol-water mixture, volume ratio 7:3) at a ratio of 20g:1g:200mL, sonicate at 500W (20KHz) for 30min, age at 45℃ for 12h, adjust the pH to 8, and then add ethanol to the solid content to 20wt% to obtain active powder colloid.

[0045] 7) Immerse 60g of molecular trap carrier in 200mL of 0.5 mol / L ZrOCl2 solution for 1h, then remove and dry at 120℃ for 1h. Place it in a fluidized bed and pass zirconium n-butoxide vapor (300℃, N2 as carrier gas, 50mL of zirconium n-butoxide) for 30min. After the process is completed, pass water vapor for 10min to obtain a mesoporous ZrO2 layer coated molecular trap carrier.

[0046] 8) The mesoporous ZrO2 layer coated molecular trap carrier was impregnated in an active powder syrup at a mass ratio of 5:2, calcined at 400℃ for 2 hours under N2 atmosphere, and then ground to obtain composite powder.

[0047] 9) The composite powder, silica sol binder (SiO2 solid content of 30wt%), pore-forming agent (PEG-1000) and water are mixed in a mass ratio of 100:10:5:50 to prepare a slurry. The slurry is then spray-dried and granulated (inlet air temperature 180℃, outlet air temperature 80℃, feeding rate 10mL / min, spray pressure 0.3MPa). After drying at 120℃ for 2h, the slurry is calcined at 400℃ for 3.5h under N2 atmosphere to obtain the dechlorination adsorbent.

[0048] Comparative Example 1: It is basically the same as Example 1, except that when preparing the molecular trap carrier, the plasma-etched ZIF-8 was directly immersed in Mg / Al-LDH sol (the mass ratio of plasma-etched ZIF-8 to Mg / Al-LDH sol was 1:0.3) for 2 hours, then dried at 120°C for 1 hour, and activated at 320°C for 1 hour.

[0049] Comparative Example 2: Essentially the same as Example 1, except that in preparing the molecular trap support, the plasma-etched ZIF-8 and GO (graphene oxide) were directly mixed at a mass ratio of 1:2, ultrasonically dispersed at 500 W (20 kHz) for 30 min, freeze-dried under vacuum at -30°C for 24 h, and then calcined at 300°C for 2 h under N2 protection at a heating rate of 2°C / min. The calcined product was not impregnated in Mg / Al-LDH sol.

[0050] Comparative Example 3: It is basically the same as Example 1, except that the active powder is directly mixed with ethanol to obtain an active powder slurry with a solid content of 20wt%, and then the mesoporous ZrO2 layer coated molecular trap carrier is impregnated in the active powder slurry at a mass ratio of 5:2. Under N2 atmosphere, it is calcined at 400°C for 2 hours and then ground to obtain composite powder.

[0051] The breakthrough chlorine capacity of the dechlorination adsorbents prepared in Example 1 and Comparative Examples 1-3 was tested. The test method was as follows: 50g of dechlorination adsorbent was measured and filled into a quartz glass tube with an inner diameter of 40mm and a length of 400mm. The stainless steel tube was kept at 500℃ in a heating furnace. Nitrogen gas was passed into 250 mL of concentrated hydrochloric acid with a mass concentration of 37.5%. After bubbling, the gas was passed into the quartz glass tube, and AgNO3 solution was passed into the outlet. When the AgNO3 solution became turbid, it was determined that the dechlorination adsorbent had broken through, and the experiment was stopped immediately. The breakthrough chlorine capacity of the dechlorination adsorbent was obtained according to the formula: Breakthrough chlorine capacity = (mass content of chlorine in the dechlorination adsorbent after breakthrough) / (total mass of the dechlorination adsorbent after breakthrough) × 100%. The test results are shown in Table 1.

[0052] Table 1. Transmission chlorine capacity of the dechlorination adsorbents prepared in Example 1 and Comparative Examples 1-2

[0053]

[0054] As can be seen from Table 1, the dechlorination adsorbent prepared in Example 1 has excellent chlorine penetration capacity, while the dechlorination adsorbents without GO confinement (Comparative Example 1), without electrostatic adsorption (Comparative Example 2), and with relatively poor active powder dispersion (Comparative Example 3) have relatively low chlorine penetration capacity.

[0055] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a dechlorination adsorbent, characterized in that, Includes the following steps: S1. The plasma-etched ZIF-8 was mixed with GO and ultrasonically dispersed. After freeze-drying, it was calcined under a protective gas and then impregnated in Mg / Al-LDH sol. After drying and activation at 300-350℃ for 0.5-1.5h, a molecular trap carrier was obtained. S2. The solution containing La salt, Nd salt and Zn salt is mixed with a precipitant and stirred. Then, it is centrifuged, washed and dried to obtain a precursor. The precursor is calcined at 550-750℃ for 3-5 hours and then ground to obtain an active powder. S3. After immersing the molecular trap carrier in ZrOCl2 solution and drying it, place it in a fluidized bed and successively introduce zirconium butoxide vapor and water vapor to obtain a mesoporous ZrO2 layer coated molecular trap carrier; the carrier gas of zirconium butoxide vapor is N2, the temperature is 300-350℃, and the aeration time is 15-45min. S4. The active powder is made into a slurry, and then the mesoporous ZrO2 layer coated molecular trap carrier is immersed in the active powder slurry and calcined at 350-450℃ for 1-3 hours under protective gas and then ground to obtain the composite powder. S5. After mixing the composite powder, binder, pore-forming agent and water, spray dry and granulate, then dry and calcine at 350-450℃ for 3-5 hours under N2 atmosphere to obtain the dechlorination adsorbent.

2. The method for preparing the dechlorination adsorbent according to claim 1, characterized in that, The method for plasma etching ZIF-8 is to place ZIF-8 in a plasma reactor, and at room temperature, introduce a gas mixture of Ar and H2 in a volume ratio of (5-10):1 at a flow rate of 30-100 mL / min, and treat it at a power of 200-500 W for 25-45 min; after removal, wash it, and then vacuum dry it at 70-90℃ for 12 h.

3. The method for preparing the dechlorination adsorbent according to claim 1, characterized in that, In step S1, the content of Mg / Al-LDH sol in the Mg / Al-LDH sol solution is 5-15 wt%, and the molar ratio of Mg to Al in the Mg / Al-LDH sol solution is (1-3):1; The mass ratio of ZIF-8 after plasma etching to the sol in GO, Mg / Al-LDH sol solution is 1:(1-5):(0.2-0.5); The conditions for ultrasonic dispersion are: 300-500w, 20-40min; The freeze-drying conditions are: -50~-20℃, 15-30h; The calcination conditions are as follows: under a nitrogen atmosphere, the heating rate is 1-5℃ / min, and calcination is carried out at 250-300℃ for 1.5-3h.

4. The method for preparing the dechlorination adsorbent according to claim 1, characterized in that, In step S2, the La salt, Nd salt, and Zn salt are La(NO3)3·6H2O, Nd(NO3)3·6H2O, and ZnCl2, respectively, with concentrations of 0.2-0.5 mol / L, 0.1-0.3 mol / L, and 0.05-0.2 mol / L, respectively. The precipitant is an NH4HCO3 solution with a concentration of 0.5-2 mol / L; The volume ratio of the solution containing La salt, Nd salt, and Zn salt to the precipitant is 1:(1-1.3); The calcination conditions are: in an air atmosphere, the heating rate is 3-5℃ / min.

5. The method for preparing the dechlorination adsorbent according to claim 1, characterized in that, In step S3, the concentration of the ZrOCl2 solution is 0.3-1 mol / L, the impregnation time is 1-2 h, and the drying temperature is 100-150℃ for 1-2 h. The ratio of molecular trap carrier to zirconium n-butoxide is (30-80) g: (40-100) mL; The water vapor should be ventilated for 20-30 minutes.

6. The method for preparing the dechlorination adsorbent according to claim 1, characterized in that, In step S4, the preparation method of the active powder solution is as follows: the active powder is mixed with citric acid and ethanol in a ratio of (10-30)g:(1-2)g:(100-300)mL, stirred at 50-65℃ for 1-2h, and centrifuged to obtain modified powder; the modified powder is then mixed with tetramethylammonium hydroxide and alcohol in a ratio of (10-30)g:(1-2)g:(100-300)mL, ultrasonically treated at 300-600W power for 15-45min, aged at 40-50℃ for 10-15h, and the pH is adjusted to 7.5-8.

5. Then, ethanol is added until the solid content is 15-25wt%.

7. The method for preparing the dechlorination adsorbent according to claim 1, characterized in that, In step S4, the mass ratio of the mesoporous ZrO2 layer-coated molecular trap carrier to the active powder adhesive is (3-8):(1-3); The calcination conditions are: under a nitrogen atmosphere.

8. The method for preparing the dechlorination adsorbent according to claim 1, characterized in that, In step S5, the binder is a silica sol with a SiO2 solid content of 25-35 wt%; the pore-forming agent is PEG-1000. The mass ratio of composite powder, binder, pore-forming agent and water is (80-120):(5-15):(2-5):(30-60); The conditions for spray drying granulation are: inlet air temperature 130-180℃, outlet air temperature 70-90℃, feeding rate 10-30mL / min, and spray pressure 0.2-0.8MPa. The drying conditions are: 120-150℃, 1.5-3h.

9. A dechlorination adsorbent, characterized in that, Prepared by the method described in any one of claims 1-8.

10. The application of the dechlorination adsorbent prepared by the method according to any one of claims 1-8 in the dechlorination of chlorine-containing waste plastic pyrolysis gas.

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