PVC (polyvinyl chloride) cracking dechlorination method and catalyst used in PVC cracking dechlorination method

Abstract

The invention belongs to the technical field of waste plastic cracking, and particularly relates to a PVC cracking dechlorination method and a catalyst used in the method. The used catalyst is X / ZSM-5; and the mass of the active component X is 8-16 wt% of the ZSM-5 molecular sieve. And adding a ZSM-5 molecular sieve into the precursor X salt solution, heating in a water bath, stirring, carrying out rotary evaporation, drying and roasting to obtain the catalyst. In the PVC cracking dechlorination method, PVC is pretreated and then crushed into solid particles, the solid particles are put into a high-pressure feeding pipe, and a catalyst X / ZSM-5 is put into a fluidized bed; and after fluidizing the catalyst, blowing PVC into the reactor, and reacting in an inert gas atmosphere to obtain an oil product and olefin. According to the catalyst disclosed by the invention, the active components are in the pore channels and the outer surfaces of the molecular sieves, so that the preparation method is simple, HCl in high-temperature cracked oil gas can be fixed, the chlorine content in a gas-phase product and a liquid oil product can be reduced, the reaction time is short, the cost is low, the dechlorination process is strong, and the added value of the product is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste plastic pyrolysis, and particularly relates to a method for PVC pyrolysis dechlorination and a catalyst used therefor. Background Art

[0002] With the increase in plastic consumption, the quantity of waste plastics is also continuously increasing, and its recycling method has become an urgent task. At present, most waste plastics in China are treated by landfilling and incineration methods. The waste plastics are buried underground together with other garbage and decomposed by the natural environment over a long period; or they are put into an incinerator to replace fuel oil as solid fuel. However, the landfilling method occupies a large amount of land and pollutes the environment, and the incineration method generates high carbon emissions and toxic organic gases such as polycyclic aromatic hydrocarbons, dioxins, and furans. These two types of treatment methods no longer meet the requirements of China for the "same-level treatment" and "high-value utilization" of plastic waste.

[0003] Among various methods for recycling waste plastics currently, methods such as thermal cracking, catalytic cracking, and hydrocracking have been studied more. That is, in an inert or hydrogen atmosphere, waste plastics are subjected to a cracking reaction to generate pyrolysis oil, combustible gas, and a small amount of solid coke. By adding a catalyst, the composition and distribution of the products are regulated, and high-value products such as natural gas, gasoline, diesel, and kerosene are obtained through separation and purification. This treatment method effectively converts waste plastics into recycled chemical resources, achieving the same-level or even upgraded conversion.

[0004] In the pyrolysis process of waste plastics, the treatment of chlorine-containing waste plastics such as polyvinyl chloride (PVC) faces great challenges. The chlorine released during the depolymerization of PVC will not only affect the catalyst activity and product value, but also pose certain risks to equipment and operators. Fixing, converting, and removing chlorine in waste plastics in various ways is the key research direction for treating chlorine-containing waste plastics.

[0005] The current main dechlorination method is aimed at liquid oil products, that is, a dechlorinating agent is added to the product oil after cracking for removal; in a small number of methods, the dechlorinating agent is directly added to the reactor, and the mixed oil and gas generated by cracking are adsorbed and removed by the dechlorinating agent and then condensed. Chinese Patent Application Publication CN118909657A discloses a method for dechlorination and quality improvement of pyrolysis oil and gas from medium- and high-chlorine coal; the oil and gas generated by the pyrolysis reaction enter the dechlorination unit, and HCl in it is absorbed by two-stage alkaline metal oxide ceramics to achieve the dechlorination effect. However, its product added value is low and the process is complex, requiring three reaction units in series, with high cost and energy consumption. Chinese Patent Application CN118949924A discloses a high-chlorine-capacity and high-strength molecular sieve dechlorinating agent for removing HCl from reformed product oil. The mass transfer rate in the liquid phase is lower than that in the gas phase, and the diffusion resistance is significantly higher than that in the gas phase, with poor basic and application effects. At the same time, the solid-phase catalyst is prone to wear and powdering during the dechlorination process, which easily contaminates the materials in the device, and the catalyst needs to be replaced and separated, increasing the operating cost of dechlorination. Chinese Patent Application CN119158532A discloses a preparation and dechlorination method of a red mud-based composite dechlorinating agent for cracking of chlorine-containing mixed plastics. This method is used for dechlorination in the pyrolysis process of a fixed-bed reactor, with a long reaction time. The obtained product is mainly pyrolysis oil, with low added value. Although it can reduce the chlorine content in the oil from the source, the process still needs to be optimized to obtain higher-value products. Chinese Patent Application CN102268275A discloses a method and device for the efficient resource utilization of all components of chlorine-containing plastic waste. Its treatment process is complex. After PVC is pyrolyzed in a fluidized bed, it needs to enter a catalytic tower for catalytic upgrading, and the main product is fuel oil, with low added value. The process can be optimized to integrate pyrolysis and catalytic cracking together and obtain high-added-value products such as low-carbon olefins.

[0006] Therefore, there is an urgent need for a PVC cracking and dechlorination process with low cost, strong dechlorination process, high product added value and high speed. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for PVC cracking and dechlorination, and to provide a catalyst used in the method for PVC cracking and dechlorination. The adopted technical solution is as follows:

[0008] A catalyst for a method of PVC cracking and dechlorination is prepared by loading active metals in the pore channels of ZSM-5 molecular sieve through an ion exchange method, and covering the surface of ZSM-5 molecular sieve with active metals through an impregnation method in excess, to form a catalyst with the structural formula X / ZSM-5; wherein, X is any one of the elements Ca, Cu, Fe, Zn, Co, Mg, Al, and the mass of X element is 1-20 wt% of the mass of ZSM-5 molecular sieve. One or more catalysts can be used simultaneously during use.

[0009] As a further preference, the mass of element X is 8-16 wt% of the mass of the ZSM-5 molecular sieve.

[0010] Preferably, the preparation method of the catalyst comprises the following steps:

[0011] (1) Add ZSM-5 molecular sieve to an excessive precursor X salt solution, heat and stir in a water bath for ion exchange.

[0012] (2) The stirred solution enters a rotary evaporator for drying, and the excessive unexchanged ions are loaded on the surface of the carrier in the form of impregnation.

[0013] (3) Calcinate the dried ZSM-5 molecular sieve impregnated with X salt solution to obtain the catalyst X / ZSM-5.

[0014] Preferably, the temperature of the water bath heating is 80 °C, the stirring time is 18-30 h, and the rotary evaporation drying is carried out at 75 °C for 1 h.

[0015] Preferably, the calcination is carried out at 450-600 °C in an air atmosphere for 4-6 h.

[0016] A method for dechlorination of PVC cracking uses the catalyst of the method for dechlorination of PVC cracking prepared by the present invention. The PVC dechlorination equipment used includes a fluidized bed reactor, a high-pressure feeding pipe, a condensation device, and a gas absorption bottle. Above the fluidized bed reactor is a variable-diameter reaction tube. The high-pressure feeding pipe is obliquely connected to the lower side of the variable-diameter reaction tube. The outlet at the top of the variable-diameter reaction tube is connected to the inlet at the top of the condensation device through a gas pipe, and the outlet at the lower side of the condensation device is connected to the gas absorption bottle.

[0017] The technological steps include:

[0018] S1. Pretreat the PVC and then crush it into solid particles smaller than 50 mesh.

[0019] S2. Load the PVC solid particles into a high-pressure feeding pipe, and load the catalyst X / ZSM-5 into the fluidized bed.

[0020] S3. Heat, and preheat the catalyst in the range of 350-600 °C; as a further preferred temperature, preheat the catalyst in the range of 450-550 °C.

[0021] S4. After the catalyst is fluidized, blow the PVC into the reactor, and react in an inert gas atmosphere to obtain low-chlorine-content oil products and low-carbon olefins.

[0022] Preferably, the variable-diameter reaction tube includes a sedimentation section at the top and a fluidization section at the bottom. The diameter of the sedimentation section is larger than that of the fluidization section, and the diameter of the sedimentation section is 2-5 times that of the fluidization section. The high-pressure feeding tube is obliquely connected to the fluidization section; the gas absorption bottle is filled with NaOH solution.

[0023] As a further preference, a condenser is wound around the outside of the high-pressure feeding tube to assist in feeding. After the cracking reaction is completed, the connected condensation device may have 1-6 product condenser tubes. Preferably, 3-5 condenser tubes are used.

[0024] Preferably, in the step (1), the pretreatment includes cleaning and drying. It is cleaned 2-3 times with water and / or ethanol solution, and dried at 40-60 °C.

[0025] Preferably, in the step (2), the mass ratio of PVC to the catalyst is 1:3-8; as a further preference, the mass ratio is 1:5-7.

[0026] Preferably, in the step (4), the concentration of the NaOH solution is 1-15 wt%, and as a further preference, the concentration is 4-9 wt%.

[0027] Preferably, in the step (4), the inert gas is nitrogen or argon, the reaction temperature is 480-640 °C, and the reaction time is controlled within 5 min-30 min.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] The catalyst for PVC cracking and dechlorination provided by the present invention has a simple preparation method. By combining the ion exchange method and the impregnation method in excess, the active components are uniformly loaded inside and on the outer surface of the catalyst pores. The catalyst obtained by the present invention, because the active components are inside and on the outer surface of the molecular sieve pores and no core-shell structure is formed, has a simple preparation method, fewer process steps, and faster reaction. This catalyst can fix HCl in the high-temperature cracked oil and gas, reduce the chlorine content in the gas-phase products and liquid oil products, and at the same time catalyze the cracking of PVC to obtain high-value-added products such as ethylene, propylene, and liquid oil products.

[0030] The raw materials of the present invention, PVC and the catalyst, are mixed and then subjected to catalytic cracking reaction. The reaction time is short, the cost is low, the dechlorination process is strong, the product added value is high, the yield of light olefins in the obtained products exceeds 40%, and the application range is wide. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic structural diagram of a catalyst for PVC cracking and dechlorination of the present invention.

[0032] Figure 2 It is a schematic process diagram of a method for PVC cracking and dechlorination of the present invention.

[0033] In the figure, 1 is a high-pressure feeding pipe; 2 is a variable-diameter reaction pipe, 2-1: fluidization section, 2-2: sedimentation section; 3 is a condensation device; 4 is a gas absorption bottle; 5 is a molecular sieve framework; 6 is a molecular sieve pore; 7 is an active component. Specific implementation mode

[0034] The attached drawings are only for illustrative purposes; the technical solutions of the present invention will be further described in detail below. It does not limit the protection scope of this application. It should be understood that certain disclosed specific details provide a comprehensive understanding of each disclosed implementation. Some common knowledge or omissions may be omitted. If there is no special description, they can all be achieved by conventional means or methods.

[0035] "And / or" means that it can be either one or a selected case, or both can be included at the same time.

[0036] A catalyst for a method of PVC cracking and dechlorination, with the structural formula X / ZSM-5.

[0037] When X = Cu, the synthesis method of the Cu / ZSM-5 catalyst is as follows:

[0038] Dissolve 5.89 g of copper nitrate (trihydrate) in 100 ml of deionized water, stir evenly and set aside. Add 10 g of commercial ZSM-5 molecular sieve while stirring at 80 °C, and stir for 18 - 30 hours. Then keep it under rotary evaporation and drying at 75 °C for 1 hour. After drying, calcine the obtained catalyst at 450 - 600 °C for 4 - 6 hours, with a heating rate of 2.5 °C / min to obtain Cu / ZSM-5.

[0039] As Figure 1 shown, for the catalyst prepared by the present invention, the main structure is the ZSM-5 molecular sieve framework 5, in which the active component 7 is mainly loaded by the ion exchange method in the molecular sieve pores, and the active component covering the surface is mainly by the impregnation method in excess, that is, metallic Cu.

[0040] When X = Ca, the synthesis method of the Ca / ZSM-5 catalyst is as follows:

[0041] First, dissolve 5.05 g of calcium nitrate (tetrahydrate) in 100 ml of deionized water, stir evenly and set aside. Add 10 g of commercial ZSM-5 molecular sieve while stirring at 80 °C, and stir for 18 - 30 hours. Then keep it under rotary evaporation and drying at 75 °C for 1 hour. After drying, calcine the obtained catalyst at 450 - 600 °C for 4 - 6 hours, with a heating rate of 2.5 °C / min to obtain Ca / ZSM-5.

[0042] When X = Fe, the synthesis method of the Fe / ZSM-5 catalyst is as follows:

[0043] First, dissolve 4.79 g of iron(III) nitrate nonahydrate in 100 ml of deionized water, stir well and set aside. Add 10 g of commercial ZSM-5 zeolite under stirring at 80 °C and stir for 18 - 30 hours. Then keep it under rotary evaporation and drying at 75 °C for 1 hour. After drying, calcine the obtained catalyst at 450 - 600 °C for 4 - 6 hours with a heating rate of 2.5 °C / min to obtain Fe / ZSM-5.

[0044] When X = Zn, the synthesis method of the Zn / ZSM-5 catalyst is as follows:

[0045] First, dissolve 6.36 g of zinc nitrate hexahydrate in 100 ml of deionized water, stir well and set aside. Add 10 g of commercial ZSM-5 zeolite under stirring at 80 °C and stir for 18 - 30 hours. Then keep it under rotary evaporation and drying at 75 °C for 1 hour. After drying, calcine the obtained catalyst at 450 - 600 °C for 4 - 6 hours with a heating rate of 2.5 °C / min to obtain Zn / ZSM-5.

[0046] When X = Co, the synthesis method of the Co / ZSM-5 catalyst is as follows:

[0047] First, dissolve 5.28 g of cobalt(II) nitrate hexahydrate in 100 ml of deionized water, stir well and set aside. Add 10 g of commercial ZSM-5 zeolite under stirring at 80 °C and stir for 18 - 30 hours. Then keep it under rotary evaporation and drying at 75 °C for 1 hour. After drying, calcine the obtained catalyst at 450 - 600 °C for 4 - 6 hours with a heating rate of 2.5 °C / min to obtain Co / ZSM-5.

[0048] When X = Mg, the synthesis method of the Mg / ZSM-5 catalyst is as follows:

[0049] First, dissolve 6.25 g of magnesium nitrate hexahydrate in 100 ml of deionized water, stir well and set aside. Add 10 g of commercial ZSM-5 zeolite under stirring at 80 °C and stir for 18 - 30 hours. Then keep it under rotary evaporation and drying at 75 °C for 1 hour. After drying, calcine the obtained catalyst at 450 - 600 °C for 4 - 6 hours with a heating rate of 2.5 °C / min to obtain Mg / ZSM-5.

[0050] When X = Al, the synthesis method of the Al / ZSM-5 catalyst is as follows:

[0051] First, dissolve 5.39 g of aluminum nitrate nonahydrate in 100 ml of deionized water, stir well and set aside. Add 10 g of commercial ZSM-5 zeolite under stirring at 80 °C and stir for 18 - 30 hours. Then keep it under rotary evaporation and drying at 75 °C for 1 hour. After drying, calcine the obtained catalyst at 450 - 600 °C for 4 - 6 hours with a heating rate of 2.5 °C / min to obtain Al / ZSM-5.

[0052] The performance of the various catalysts prepared above was compared with that of the unmodified commercial ZSM-5 molecular sieve. PVC was reacted with different catalysts respectively, and the mass ratio of PVC to the catalyst was 1:4. Under the conditions of 560 °C and 0.3 MPa nitrogen, a cracking reaction was carried out for 10 min. The results are shown in Table 1 below.

[0053] Table 1 Comparison results of the catalytic performance of Cu / ZSM-5 catalyst and ZSM-5 molecular sieve

[0054]

[0055] It can be seen from Table 1 that the catalyst prepared by the present invention has a higher diolefin yield than the unmodified catalyst, the residual chlorine content in the gas phase is reduced, and the chlorine content in the oil phase is also lower.

[0056] According to the catalytic reaction results in Table 1, it can be seen that the X / ZSM-5 catalyst synthesized by this process has significantly better dechlorination performance than the commercial ZSM-5 molecular sieve, and can greatly reduce the chlorine content in the subsequent products.

[0057] Examples 1 - 6

[0058] As Figure 2 shown, a method for cracking and dechlorinating PVC catalytically cracks and dechlorinates PVC in a fluidized bed reactor. The catalyst Cu / ZSM-5 for the method for cracking and dechlorinating PVC prepared by the present invention is used. The equipment for cracking and dechlorinating PVC includes a fluidized bed reactor, a high-pressure feeding pipe 1, a condensation device 3, and a gas absorption bottle 4. Above the fluidized bed reactor is a variable-diameter reaction tube 2. The high-pressure feeding pipe 1 is obliquely connected to the lower side of the variable-diameter reaction tube 2. The outlet at the top of the variable-diameter reaction tube 2 is connected to the inlet at the top of the condensation device 3 through a gas pipe, and the outlet at the lower side of the condensation device 3 is connected to the gas absorption bottle 4.

[0059] The process steps include:

[0060] S1. Pretreat PVC and then crush it into solid particles smaller than 50 mesh.

[0061] S2. Load the PVC solid particles into a high-pressure feeding pipe 1, and load the catalyst Cu / ZSM-5 into the fluidized bed.

[0062] S3. Heat, and preheat the catalyst at a temperature of about 460 °C.

[0063] After the catalyst is fluidized, PVC is blown into the fluidized section 2-2 of the variable-diameter reaction tube 2 to be mixed with the catalyst. The reaction temperature is 560 °C, the mass ratio of the catalyst to PVC is 1:4, and the reaction times are 5 (Example 1), 6 (Example 2), 9 (Example 3), 11 (Example 4), 13 (Example 5), and 15 min (Example 6), respectively. After the reaction, it enters the condensation device 3 through the gas pipe and then enters the gas absorption bottle 4. The total chlorine in the liquid in the condensation device 3 and the NaOH solution is measured, and the gas product is collected by a gas bag and analyzed by gas chromatography. The results are shown in Table 2 below.

[0064] Table 2 Reaction results of catalytic dechlorination of PVC in Examples 1-6

[0065]

[0066] As can be seen from Table 2, when the reaction time is 13-15 min, the yield of dienes in the PVC pyrolysis product is relatively high, reaching 41.6%; at the same time, 75% of the chlorine in the fixed gas phase is fixed, and the chlorine content in the oil product is also significantly reduced. At this time, both the dechlorination ability and the pyrolysis ability of the catalyst are well demonstrated.

[0067] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A catalyst for PVC cracking and dechlorination, characterized in that, The active metal is loaded into the pores of ZSM-5 molecular sieve by the ion exchange method, and the active metal is covered on the surface of ZSM-5 molecular sieve by the impregnation method in excess to form the catalyst X / ZSM-5; wherein, X is any one of the elements Ca, Cu, Fe, Zn, Co, Mg, and Al, and the mass of element X is 8-16 wt% of the mass of ZSM-5 molecular sieve.

2. The catalyst for PVC cracking and dechlorination according to claim 1, characterized in that, The preparation method of the catalyst comprises the following steps: (1) Add ZSM-5 molecular sieve to the precursor X salt solution, heat and stir in a water bath for ion exchange; (2) The stirred solution enters a rotary evaporator for drying, and the excessive unexchanged ions are loaded on the surface of the carrier in the form of impregnation; (3) Roast the dried ZSM-5 molecular sieve impregnated with X salt solution to obtain the catalyst X / ZSM-5.

3. The catalyst for the method of PVC cracking and dechlorination according to claim 2, characterized in that, The temperature of the water bath heating is 80 °C, the stirring time is 18-30 h, and the rotary evaporation drying is carried out at 75 °C for 1 h.

4. The catalyst for a method of PVC cracking and dechlorination according to claim 2, characterized in that, The roasting is carried out at 450-600 °C in an air atmosphere for 4-6 h.

5. A method for dechlorination of PVC cracking, using the catalyst of the method for dechlorination of PVC cracking according to any one of claims 1-4, characterized in that, The PVC cracking and dechlorination equipment adopted includes a fluidized bed reactor, a high-pressure feeding pipe, a condensation device, and a gas absorption bottle. Above the fluidized bed reactor is a variable-diameter reaction tube. The high-pressure feeding pipe is obliquely connected to the lower side of the variable-diameter reaction tube. The outlet at the top of the variable-diameter reaction tube is connected to the inlet at the top of the condensation device through a gas pipe, and the outlet at the lower side of the condensation device is connected to the gas absorption bottle; The technological steps include: S1. Pretreat PVC and then crush it into solid particles with a particle size less than 50 mesh; S2. Load the PVC solid particles into a high-pressure feeding pipe, and load the catalyst X / ZSM-5 into the fluidized bed; S3. Heat, and preheat the catalyst in the range of 350-600 °C; S4. After the catalyst is fluidized, blow PVC into the reactor, and react in an inert gas atmosphere to obtain oil products and olefins.

6. The method for PVC cracking and dechlorination according to claim 5, characterized in that, The variable-diameter reaction tube includes a settling section and a fluidization section. The diameter of the settling section is larger than that of the fluidization section. The diameter of the settling section is 2-5 times that of the fluidization section. The high-pressure feeding pipe is obliquely connected to the fluidization section; the gas absorption bottle is filled with NaOH solution.

7. A method for PVC cracking and dechlorination according to claim 6, characterized in that, In the step (1), the pretreatment includes cleaning and drying. Clean with water and / or ethanol solution for 2-3 times, and dry at 40-60 °C.

8. A method for PVC cracking and dechlorination according to claim 6, characterized in that, In the step (2), the mass ratio of PVC to the catalyst is 1:3-8.

9. A method for PVC cracking and dechlorination according to claim 6, characterized in that, In the step (4), the concentration of the NaOH solution is 1-15 wt%.

10. A method for PVC cracking and dechlorination according to claim 6, characterized in that, In the step (4), the inert gas is nitrogen or argon, the reaction temperature is 480-640 °C, and the reaction time is controlled within 5 min-30 min.

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