A waste plastic recycling catalyst, its preparation method and application

Abstract

The present invention relates to a catalyst with high activity and stability for waste plastic recycling, a preparation method thereof, and a method for using the same in waste plastic recycling. The catalyst comprises lactide-modified NaY zeolite, ZnO and CuO supported on the zeolite; wherein, based on the mass percentage content of NaY zeolite being 100 wt%, the loading amounts of ZnO and CuO are 1-9 wt% and 0.1-1 wt% respectively. This catalyst has the following advantages: it enhances the activation of macromolecular alkanes and shape selectivity, has high stability, and realizes the resource utilization of waste plastics such as PP and PE.

Description

Technical Field

[0001] The present invention relates to the field of waste plastic recycling. Specifically, it relates to a catalyst with high activity and stability for waste plastic recycling, a preparation method thereof, and a method for using the same in waste plastic recycling. Background Art

[0002] In the past 70 years, the global production of synthetic petroleum-based plastics has increased sharply, and it is expected to double again within the next 20 years. Among them, 40% of waste plastics are used as disposable items, but less than 10% of waste plastics are recycled. The recycling cost of the vast majority of plastics is high and it is difficult to degrade in a short time, bringing great pressure to the environmental ecology.

[0003] Methods for treating waste plastics include landfill, incineration, and resource utilization. Landfill and incineration will cause environmental pollution. Resource utilization is the future trend of waste plastic treatment. Currently, resource utilization is mainly divided into two types of technologies: physical method and chemical method. Physical regeneration and recycling have high requirements for the quality of plastics. The quality stability of most recycled plastics is low, and their performance is poor, making them unsuitable for making high-grade plastic products. The chemical method decomposes plastics that are difficult to recycle by physical methods into initial monomers or light oil products through catalytic cracking and other means, and then produces chemical raw materials (such as ethylene, styrene, tar, etc.) and liquid fuels (such as naphtha, diesel), while also reducing pollution and carbon emissions. Currently, plastic cracking catalysts mainly include three categories: molecular sieves, metal oxides, and supported catalysts.

[0004] Patent CN201410240216.5 discloses a catalyst for the production of vehicle fuel by catalytic cracking of waste plastics and a preparation method thereof, which is prepared by kneading and molding a mesoporous and microporous composite MCM-41 molecular sieve and a binder and then further modifying it;

[0005] Patent CN201010292245.8 discloses a catalytic reforming catalyst for the catalytic cracking of waste plastics to produce fuel oil and a preparation method thereof. The catalyst is composed of oxides such as molybdenum oxide, cerium oxide, bismuth oxide, zirconium oxide, tin oxide or lead oxide and molecular sieves such as MCM-22, ZSM-35, Beta or MOR;

[0006] Patent CN202010922408.X discloses a catalyst for catalytic cracking of waste plastics and a preparation method of fuel oil. The catalyst is composed of quartz sand, clay and zeolite powder;

[0007] However, existing chemical recycling processes for waste plastics have problems such as poor catalyst activity, low oil yield, high content of heavy components, and easy carbon deposition and deactivation of the catalyst. High acidity of the catalyst easily leads to carbon deposition and deactivation, affecting its stability and causing the cracking oil to gradually deteriorate. However, reducing the acidity of the catalyst will also affect its cracking activity. Therefore, finding a catalyst with both high activity and stability is one of the keys to realizing the resource utilization of waste plastics. Summary of the Invention

[0008] The object of the present invention is to provide a cracking catalyst with both high activity and stability and a preparation method thereof. The catalyst is used in the field of waste plastic recycling, can be recycled, strengthens the activation ability of plastic macromolecules and the shape selectivity of products, and has high stability.

[0009] To solve the above technical problems, the present invention provides the following technical solutions:

[0010] A waste plastic recycling catalyst, characterized in that it contains lactide-modified NaY zeolite, ZnO and CuO supported on the zeolite; wherein, based on the mass percentage content of NaY zeolite being 100 wt%, the loading amounts of ZnO and CuO are 1-9 wt% and 0.1-1 wt% respectively.

[0011] The waste plastic cracking catalyst with high activity and stability and its preparation method of the present invention include the following steps:

[0012] Step 1: Dissolve NaY zeolite in lactide to obtain a carrier suspension; Step 2: Add a mixed solution of soluble zinc salt and copper salt to the carrier suspension, and perform pickling treatment using the hydrolysis of lactide to obtain a NaY zeolite carrier with a hierarchical pore structure and surface hydroxylation modification; Step 3: Adjust the pH of the catalyst suspension in Step 2 with an alkali solution, perform drying treatment and calcination to obtain a hierarchical pore NaY catalyst loaded with CuO and ZnO.

[0013] The mass ratio of the NaY zeolite carrier to lactide is 1:2-5.

[0014] Preferably, the lactide is pure lactide or a by-product from a lactic acid plant, and the main components of the by-product are lactide and primary lactide polymer; the NaY zeolite carrier is a commercial zeolite with SiO2 / Al2O3 = 4.8-5.4.

[0015] Preferably, the mass ratio of the NaY carrier to lactide is 1:2-5, preferably 1:2-3; the hydrolysis temperature of lactide is 80-120 °C, preferably 90-100 °C;

[0016] Preferably, a mixed solution of ZnCl2 and CuCl2 is prepared. The soluble zinc salt and copper salt in the mixed solution of ZnCl2 and CuCl2 are water as the solvent. The concentration of ZnCl2 is 10 - 50 g / L, and the concentration of CuCl2 is 1 - 5 g / L, ensuring that the theoretical loading of ZnCl2 on the NaY support is 1 - 9 w%, preferably 3 - 5 w%, and the theoretical loading of CuCl2 is 0.1 - 1 w%, preferably 0.2 - 0.5 w%.

[0017] Preferably, the mixed solution of ZnCl2 and CuCl2 is added to the suspension of the support and lactide at 90 - 100 °C. In this process, lactic acid generated by the hydrolysis of lactide has a pickling effect on the NaY support, introducing a mesoporous structure and increasing the surface hydroxyl functional groups, which is beneficial to the introduction of Cu and Zn elements. The mass ratio of the mixed solution of ZnCl2 and CuCl2 to lactide is 1:1 - 5, preferably 1:1 - 2.

[0018] Preferably, after the addition of the mixed solution of ZnCl2 and CuCl2, the reaction is carried out at 90 - 100 °C for 0.5 - 5 h, preferably 0.5 - 2 h. 10% sodium hydroxide solution is added to the system to adjust the pH to 4.0 - 7.0, preferably 5.5 - 6.0. After the pH adjustment is completed, stirring is carried out for 0.5 - 2 h.

[0019] The catalyst is dried and calcined. The drying temperature of the catalyst suspension is 120 - 170 °C, the drying time is 1 - 3 h, the calcination temperature is 500 - 650 °C, and the calcination time is 4 - 8 h. Preferably, the drying temperature is 140 - 160 °C, the drying time is 1 - 2 h, the calcination temperature is 550 - 600 °C, and the calcination time is 5 - 7 h, thus obtaining the final catalyst.

[0020] The performance evaluation of the catalyst is carried out on a small-scale reaction device, using PP and PE plastics as raw materials. The mass ratio of the catalyst to the plastic is 1:20 - 50, and the reaction temperature is 250 - 350 °C.

[0021] The beneficial effects of the present invention are as follows:

[0022] (1) Through the hydrolysis modification of lactide, the NaY support has a hierarchical pore structure with mesoporous and microporous composites, strengthening the reaction mass transfer process.

[0023] (2) The lactide described in the present invention can be by-produced from waste liquid in the device separation process, which is simple to obtain, low in cost, and realizes the recycling of waste.

[0024] (3) Through the hydrolysis modification of lactide, the specific surface area of the catalyst support was increased, and at the same time, more surface hydroxyl groups were introduced, enhancing the interaction between the support surface and the active components. By regulating the pH with NaOH, zinc lactate and copper lactate clusters were in-situ generated, promoting the dispersion of ZnO active components and CuO promoters, and improving the atomic utilization efficiency.

[0025] (4) Combining the dehydrogenation activation effect of the active components on plastic macromolecules with the low-acidity support enables the catalyst to have both high hydrocarbon activation ability and low surface carbon deposition rate, which is beneficial to slowing down carbon deposition during the plastic cracking reaction and improving the stability. Specific implementation manners

[0026] The technical solutions and their effects of the present invention are further described below through specific examples. The following examples are only used to illustrate the content of the present invention and do not limit the protection scope of the present invention. Simple changes made to the present invention using the concept of the present invention are within the scope of protection required by the present invention.

[0027] Unless otherwise specified, the raw materials used in the examples or comparative examples can be obtained from commercial channels.

[0028] The related methods used or possibly used in the examples or comparative examples of the present invention are introduced below:

[0029] Example 1:

[0030] Preparation of catalyst A:

[0031] Take 150 g of lactide in a beaker, melt it into a homogeneous state in an oil bath at 90 °C and stir. Put 30 g of NaY molecular sieve support (SiO2 / Al2O3 = 5.0) into the lactide liquid and stir for 1 h. Slowly add 30.0 g of the prepared mixed solution of ZnCl2 and CuCl2 (Zn element content 0.51 g, Cu element content 0.05 g), and continue to stir at 90 °C for 0.5 h to carry out hydrolysis and pickling modification of the NaY molecular sieve support. Then, slowly add 10% NaOH solution dropwise until the system pH = about 6, and continue to stir for 1 h to uniformly deposit the active components on the support surface. Heat the system to 100 °C to evaporate most of the water, then dry it in an oven at 150 °C for 1 h, and calcine it in an air atmosphere at 550 °C for 6 h to obtain a CuO / ZnO-loaded CuO / ZnO / mesoporous NaY catalyst, marked as catalyst A.

[0032] Example 2:

[0033] Preparation of catalyst B:

[0034] Take 60 g of lactide in a beaker, melt it into a homogeneous state in an oil bath at 90 °C and stir. Put 30 g of NaY molecular sieve support (SiO2 / Al2O3 = 5.0) into the lactide liquid and stir for 1 h. Slowly add 14.4 g of the prepared mixed solution of ZnCl2 and CuCl2 (Zn element content 0.25 g, Cu element content 0.025 g), and continue to stir at 80 °C for 1.5 h to carry out hydrolysis and pickling modification on the NaY molecular sieve support. Then, slowly add a 10% NaOH solution dropwise until the system pH is about 6, and continue to stir for 1 h to uniformly deposit the active components on the surface of the support. Heat the system to 100 °C to evaporate most of the water, then dry it in an oven at 150 °C, and calcine it in an air atmosphere at 550 °C for 6 h to obtain the CuO / ZnO-loaded CuO / ZnO / mesoporous NaY catalyst, marked as catalyst B.

[0035] Example 3:

[0036] Preparation of catalyst C:

[0037] Take 100 g of waste lactide in a beaker, melt it into a homogeneous state in an oil bath at 90 °C and stir. Put 30 g of NaY molecular sieve support (SiO2 / Al2O3 = 5.0) into the lactide liquid and stir for 1 h. Slowly add 123.5 g of the prepared mixed solution of ZnCl2 and CuCl2 (Zn element content 2.1 g, Cu element content 0.21 g), and continue to stir at 100 °C for 1 h to carry out hydrolysis and pickling modification on the NaY molecular sieve support. Then, slowly add a 10% NaOH solution dropwise until the system pH is about 4, and continue to stir for 1 h. Heat the system to 100 °C to evaporate most of the water, then dry it in an oven at 150 °C, and calcine it in an air atmosphere at 550 °C for 6 h to obtain the CuO / ZnO-loaded CuO / ZnO / mesoporous NaY catalyst, marked as catalyst C.

[0038] Example 4:

[0039] Plastic pyrolysis performance of CuZn / mesoporous NaY catalyst:

[0040] The catalyst evaluation was carried out on a self-built small-scale plastic pyrolysis device. The catalyst was pressed into tablets and sieved into 20-40 mesh particles. Take 50 g of waste plastic (PP:PE = 3:1) and 2 g of the pressed catalyst. The mass ratio of waste plastic to catalyst is 20:1. The evaluation was carried out by thermal pyrolysis + catalytic pyrolysis. The experiment was carried out in a nitrogen atmosphere with a nitrogen flow rate of 100 mL / min, a pyrolysis temperature of 450 °C, a catalytic pyrolysis section temperature of 400 °C, and a reaction time of 4 h. After the experiment, the oil product was collected and weighed, and the oil product yield was calculated by chromatographic analysis and testing.

[0041] Among them, the waste plastics are mixed with commercially available PP particles and PE particles. The carbon number distribution of the products is measured by gas chromatography, and the instrument is GC7890 from Agilent Technologies, USA. The test conditions are as follows:

[0042] The chromatographic column type is ZB-5HT; carrier gas: N2 (30 mL / min), H2 (30 mL / min), air (300 mL / min); detector FID (300 °C), injector (300 °C), injection volume 3.5 μL; The programmed temperature rise mode is adopted, maintained at 50 °C for 10 min, then heated to 200 °C at a rate of 2 °C / min and maintained for 1 min, and then heated to 350 °C at a rate of 5 °C / min and maintained for 5 min.

[0043] Table 1: Yields of pyrolysis oils of different catalysts

[0044] Catalyst Yield (%) Catalyst A 85.5 Catalyst B 80.3 Catalyst C 73.6

[0045] From the above data, it can be seen that Catalyst A, Catalyst B and Catalyst C have good oil yields.

[0046] Example 5:

[0047] Evaluation of the pyrolysis performance of different mixed plastics:

[0048] The catalyst evaluation is carried out on a self-built small-scale plastic pyrolysis equipment. Catalyst A is pressed and sieved into particles with a mesh size of 20-40. Take 50 g of waste plastics (PP:PE = 1-3:1) and 2 g of the pressed Catalyst A. The mass ratio of waste plastics to Catalyst A is 20:1. The evaluation is carried out by the method of thermal pyrolysis + catalytic pyrolysis. The experiment is carried out in a nitrogen atmosphere with a nitrogen flow rate of 100 mL / min, a thermal decomposition temperature of 450 °C, a catalytic pyrolysis section temperature of 400 °C, and a reaction time of 4 h. After the experiment, the oil products are collected and weighed, and the oil yield is calculated by chromatographic analysis and testing.

[0049] Among them, the waste plastics are mixed with commercially available PP particles and PE particles. The carbon number distribution of the products is measured by gas chromatography, and the instrument is GC7890 from Agilent Technologies, USA. The test conditions are as follows:

[0050] The chromatographic column type is ZB-5HT; carrier gas: N2 (30 mL / min), H2 (30 mL / min), air (300 mL / min); detector FID (300 °C), injector (300 °C), injection volume 3.5 μL; The programmed temperature rise mode is adopted, maintained at 50 °C for 10 min, then heated to 200 °C at a rate of 2 °C / min and maintained for 1 min, and then heated to 350 °C at a rate of 5 °C / min and maintained for 5 min.

[0051] The cracking results of the catalyst for different waste plastics are shown in Table 2. The cracking yield of the catalyst for waste plastics with different PP / PE ratios is >70%, and the cracking oil yield of waste plastics with a higher PP content is higher.

[0052] Table 2: Light oil yield in the cracked oil products of different waste plastics

[0053] Waste plastic Yield (%) Waste plastic 1 (PP:PE = 1:1) 71.5 Waste plastic 2 (PP:PE = 2:1) 80.8 Waste plastic 3 (PP:PE = 3:1) 85.5

[0054] Example 6:

[0055] Catalyst stability evaluation:

[0056] Take 50 g of waste plastics (PP:PE = 3:1) and 2 g of the tableted CuZn / mesoporous NaY catalyst A. The mass ratio of waste plastics to catalyst A is 20:1. It is evaluated by the method of thermal cracking + catalytic cracking. The experiment is carried out in a nitrogen atmosphere with a nitrogen flow rate of 100 mL / min, a pyrolysis temperature of 450 °C, a catalytic cracking section temperature of 400 °C, and a single reaction time of 4 h. Continuous cracking small-scale evaluation is carried out, and the results are shown in Table 3:

[0057] Table 3 Catalyst continuous cracking small-scale evaluation:

[0058]

[0059]

[0060] Under the test conditions, the CuZn / mesoporous NaY catalyst A was continuously cracked for 28 h, and the cracking oil yield of waste plastics was still above 85.0%, showing high cracking stability.

[0061] Comparative Example 1:

[0062] Preparation of catalyst D: (without adding ZnCl2 and CuCl2)

[0063] Take 100 g of lactide waste in a beaker, melt it into a homogeneous state in a 90 °C oil bath and stir. Put 30 g of NaY molecular sieve support into the lactide liquid and stir for 1 h. Slowly add 40 g of water and continue to stir at 90 °C for 1 h to carry out hydrolysis and pickling modification of the NaY molecular sieve support. Then dropwise add 10% NaOH solution by mass to the system until the pH of the system is about 6, and continue to stir for 1 h. Heat the system to 100 °C to evaporate most of the water, then dry it in an oven at 150 °C, and calcine it in an air atmosphere at 550 °C for 6 h to obtain a mesoporous NaY catalyst, marked as catalyst D.

[0064] Comparative Example 2:

[0065] Preparation of catalyst E: (not treated with lactide)

[0066] Put 30 g of NaY molecular sieve support into 30 g of the prepared mixed solution of ZnCl2 and CuCl2 (Zn element content is 0.72 g, Cu element content is 0.09 g), add water until the powder is submerged, continue stirring at 90 °C for 1 h, slowly add 10% NaOH solution dropwise until the system pH is about 6, and continue stirring for 1 h. Heat the system to 100 °C to evaporate most of the water, then dry it in an oven at 150 °C, and calcine it in an air atmosphere at 550 °C for 6 h to obtain the catalyst CuZn / NaY prepared by the conventional impregnation method, marked as Catalyst E.

[0067] Comparative Example 3:

[0068] Preparation of Catalyst F: (Different element contents)

[0069] Take 100 g of lactide waste in a beaker, melt it into a homogeneous state and stir in a 90 °C oil bath. Put 30 g of NaY molecular sieve support into the lactide liquid and stir for 1 h. Slowly add 164.7 g of the prepared mixed solution of ZnCl2 and CuCl2 (Zn element content is 2.8 g, Cu element content is 0.28 g), and continue stirring at 90 °C for 1 h to carry out hydrolysis and pickling modification on the NaY molecular sieve support. Then slowly add 10% NaOH solution dropwise until the system pH is about 6, and continue stirring for 1 h to uniformly deposit the active components on the surface of the support. Heat the system to 100 °C to evaporate most of the water, then dry it in an oven at 150 °C, and calcine it in an air atmosphere at 550 °C for 6 h to obtain a hierarchical pore NaY catalyst with a high Zn / Cu loading, marked as F.

[0070] Comparative Example 4:

[0071] Evaluation of catalyst performance:

[0072] Take 50 g of waste plastics (PP:PE = 3:1) and 2 g of the pressed catalyst. The mass ratio of waste plastics to the catalyst is 20:1. Use the method of thermal cracking + catalytic cracking for evaluation. The experiment is carried out in a nitrogen atmosphere with a nitrogen flow rate of 100 mL / min, a pyrolysis temperature of 450 °C, and a catalytic cracking section temperature of 400 °C. Test the cracking oil yield and stability of the catalyst. The results are shown in Table 4:

[0073] Table 4: Pyrolysis results of waste plastics with different catalysts

[0074] Catalyst Initial oil yield (%) Stable duration (h) Catalyst A 85.5 ＞28 Catalyst D 70.6. ＞28 Catalyst E 74.3 12 Catalyst F 76.5 20

[0075] Comparing with catalyst A (CuZn / mesoporous NaY catalyst) and catalyst D (mesoporous NaY), it can be seen that introducing Cu / Zn active components helps to improve the activation ability of the catalyst for macromolecules in waste plastics and further increase the oil yield. Comparing with catalyst A and catalyst E, it can be seen that lactide treatment helps to form the mesoporous structure of NaY zeolite, and at the same time, surface hydroxyl modification of the zeolite is carried out to strengthen macromolecular mass transfer, promote the high dispersion of active components, and improve the cracking activity and stability of the catalyst. Comparing with catalyst A and catalyst F, it can be seen that too high a loading of active components will cause a decrease in activity and stability.

[0076] Comparative Example 5:

[0077] Comparison with other types of zeolite catalysts:

[0078] According to the preparation method in Example 1, replace NaY zeolite with other types of zeolites such as ZSM-5, SAPO-34, USY, HY, MCM-41 for catalyst preparation and cracking performance evaluation. The obtained catalysts are respectively labeled as catalysts G, H, I, J, and K. The results are shown in Table 5.

[0079] Table 5: Cracking activities of different zeolites:

[0080] Catalyst Initial oil yield (%) Stable duration (h) Catalyst G 83.2 2 Catalyst H 75.4 4 Catalyst I 87.6 1 Catalyst J 86.9 2 Catalyst K 78.3 6 Catalyst A 85.5 >28

[0081] Among them, the catalysts with ZSM-5, USY, and HY as carriers have relatively high initial oil yields, but due to their strong surface acidity, they quickly deactivate due to carbon deposition and have low stability. Due to its low surface acidity and high anti-carbon deposition performance, and the synergistic effect of highly dispersed active components and zeolite, NaY zeolite shows relatively high activity and stability in the reaction.

[0082] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A waste plastic recycling catalyst, characterized in that, It contains lactide-modified NaY molecular sieve, ZnO and CuO supported on the molecular sieve; wherein, based on the mass percentage of NaY molecular sieve being 100 wt%, the loading amounts of ZnO and CuO are 1-9 wt% and 0.1-1 wt% respectively.

2. The preparation method of the catalyst according to claim 1, characterized in that, It includes the following steps: Step 1: Dissolve NaY molecular sieve in lactide to obtain a carrier suspension; Step 2: Add a mixed solution of soluble zinc salt and copper salt to the carrier suspension, and adjust the temperature to hydrolyze lactide; Step 3: Adjust the pH of the catalyst suspension in Step 2 with an alkali solution, dry and calcine to obtain a hierarchically porous NaY catalyst loaded with CuO and ZnO.

3. The preparation method according to claim 2, characterized in that, In Step 1, the mass ratio of NaY molecular sieve to lactide solution is 1:2-5.

4. The preparation method according to claim 3, characterized in that, In Step 1, the mass ratio of NaY molecular sieve to lactide solution is 1:2-3.

5. The preparation method according to any one of claims 2-4, characterized in that, In Step 1, the NaY molecular sieve carrier is a molecular sieve with SiO2 / Al2O3 = 4.8-5.

4.

6. The preparation method according to any one of claims 2-4, characterized in that, In Step 2, the soluble zinc salt and copper salt are a mixed solution of ZnCl2 and CuCl2, the solvent is water, the concentration of ZnCl2 is 10-50 g / L, the concentration of CuCl2 is 1-5 g / L, and the mass ratio of the mixed solution to lactide is 1:1-5; and / or, the temperature for lactide hydrolysis is 80-120 °C, and the hydrolysis time is 0.5-1.5 h.

7. The preparation method according to claim 6, characterized in that, The mass ratio of the mixed solution to lactide is 1:1-2; and / or, the temperature for lactide hydrolysis is 90-100 °C, and the hydrolysis time is 0.8-1.2 h.

8. The preparation method according to any one of claims 2-4, characterized in that, The alkali solution is an aqueous solution of sodium hydroxide. Step 3 specifically is: Add an aqueous solution of sodium hydroxide to the system, adjust the pH to 4.0-7.0, and stir for 0.5-2 h after the pH adjustment is completed.

9. The preparation method according to any one of claims 2 to 4, characterized in that, In Step 3, the drying temperature of the catalyst suspension is 120-170 °C, the drying time is 1-3 h, the calcination temperature is 500-650 °C, and the calcination time is 4-8 h.

10. The use of the catalyst obtained by the preparation method according to any one of claims 2-9 or the catalyst according to claim 1 in the recycling of waste plastics.

11. A method for recycling waste plastics, characterized in that, Add the catalyst obtained by the preparation method according to any one of claims 2-9 or the catalyst according to claim 1 to waste plastics, and perform thermal cracking and catalytic cracking on the waste plastics.

12. The method according to claim 11, characterized in that: The waste plastics contain one or both of PP and PE, the mass ratio of the catalyst to the plastics is 1:20-50, and the reaction temperature for thermal cracking and catalytic cracking is 250-350 °C.

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