A method for preparing light oil by catalytic cracking of polyethylene

Abstract

The present invention discloses a method for preparing light oil by catalytic cracking of polyethylene, comprising the following steps: 1) continuously conveying polyethylene solid powder to a thermal cracking reaction unit, performing a thermal cracking reaction at a temperature of 450-550°C to generate vaporized polyethylene wax; 2) continuously feeding the vaporized polyethylene wax to a catalytic cracking reaction unit filled with a catalyst, and simultaneously continuously feeding an organic peroxide to the catalytic cracking reaction unit, performing a catalytic cracking reaction at a temperature of 350-450°C; 3) conveying the cracking product obtained in step 2) to a condensing unit for condensation treatment, wherein the bottom is collected to obtain C3-C 12 The light oil is produced, and part of the non-condensable gas at the top is returned to the catalytic cracking reaction unit, and the other part is sent to the incinerator for treatment. This method can achieve the purpose of producing light oil based on a process combining thermal cracking and catalytic cracking.

Description

Technical Field

[0001] The present invention relates to a method, in particular to a method for preparing light oil through catalytic cracking of polyethylene. Background Art

[0002] The rapid development of the synthetic resin industry has resulted in a large number of plastic products. These products have short lifespans and poor biodegradability, causing significant environmental damage if not promptly disposed of. Plastic products primarily include polyethylene, polypropylene, polystyrene, and polyvinyl chloride. Polyethylene, however, has a wider range of applications and, due to its linear structure, is more susceptible to decomposition.

[0003] Currently, the main methods for cracking waste polyethylene are thermal cracking and catalytic cracking. For example, patent publication CN107286277B mixes fine particles of fluoroethylene polymer and magnesium oxide particles with recycled polyethylene plastic and cracks them at low temperatures to produce a polyethylene wax product. However, this method produces high-molecular-weight polyethylene wax, which has insufficient cracking depth and requires further processing before use. Patent publication CN109370632A uses co-pyrolysis of lignin and low-density polyethylene to produce aromatic-rich fuel oil. The optimal catalytic reaction temperature is 650°C, which is relatively harsh. Due to the production of a large amount of benzene series, the catalyst cokes relatively severely. Therefore, developing a polyethylene cracking process with relatively mild conditions and a high cracking depth has become an urgent problem in this field. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention proposes a method for preparing light oil by catalytic cracking of polyethylene. The method can achieve the purpose of preparing light oil by combining thermal cracking and catalytic cracking.

[0005] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0006] A method for preparing light oil by catalytic cracking of polyethylene comprises the following steps:

[0007] 1) Continuously conveying polyethylene solid powder to a thermal cracking reaction unit, performing a thermal cracking reaction at a temperature of 450-550°C to generate vaporized polyethylene wax;

[0008] 2) continuously feeding the vaporized polyethylene wax into a catalytic cracking reaction unit filled with a catalyst, and simultaneously continuously feeding the organic peroxide into the catalytic cracking reaction unit to carry out a catalytic cracking reaction at 350-450° C.;

[0009] 3) The cracking product obtained in step 2) is sent to a condensation unit for condensation treatment, wherein the bottom is collected to obtain C3-C 12The light oil, the non-condensable gas at the top is optionally refluxed or not refluxed to the catalytic cracking reaction unit.

[0010] In one aspect of the present invention, a light oil is produced using a combined thermal and catalytic cracking process. During the thermal cracking stage, polyethylene undergoes random C-C bond cleavage at high temperatures, generating two free radicals. These free radicals then extract hydrogen from other carbon atoms in the chain, transforming into short-chain alkanes or alkenes. Simultaneously, the carbon chain is induced to transform into new free radicals, undergoing chain transfer, ultimately forming a relatively low-molecular-weight polyethylene wax. Under high-temperature reaction conditions, the polyethylene wax vaporizes, remains in gaseous form, and is fed to the next unit.

[0011] After polyethylene wax and organic peroxide enter the catalytic cracking unit, catalytic cracking reaction occurs. a H b O2) decomposes under the action of a catalyst to produce hydroxyl radicals and small molecular carbon cations. The reaction expression is as follows:

[0012] C a H b O2——C a H b-1 O + +.OH

[0013] Hydroxyl radicals ( . OH) is the most active free radical, which can react with small molecular hydrocarbons (using C n H 2n+2 Represents) reaction, breaking it down into smaller molecules. The reaction expression is as follows:

[0014] . OH+C n H 2n+2 ——C x H 2x + . C y H 2y+1 +H2O

[0015] n=x+y

[0016] Produced . C y H 2y+1 Can be further chain-transferred to produce smaller molecular alkanes (C1-C 12 ); The catalytic cracking reaction of polyolefins belongs to the carbon cation mechanism. The small molecular carbon cations produced by the decomposition of organic peroxides can further attack polyethylene molecules and crack them into smaller molecules.

[0017] The small molecule alkanes (C1-C 12) After condensation, C3-C 12 The light oil is converted into a part of C1-C6 small molecule alkanes and unreacted organic peroxides to form non-condensable gas, part of which is refluxed to the catalytic cracking reaction unit to provide gas flow and highly active free radicals, and the rest can be used for waste treatment, such as being sent to an incinerator for direct incineration.

[0018] In some examples, in step 1), the feed rate of the polyethylene solid powder is 10-60 g / h;

[0019] Preferably, the diameter of the polyethylene solid powder is less than 0.5 cm;

[0020] Preferably, the polyethylene solid powder is one or more of high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE).

[0021] In some examples, the catalyst is a mixture of corroded bricks of an incinerator and solids collected by a slag remover of the incinerator in a mass ratio of (1-10):1, such as 1:1, 2:1, 4:1, 6:1, 10:1, etc.;

[0022] Preferably, the incinerator corrosion furnace bricks contain 40-60wt% Al2O3, 10-25wt% alkali metal oxides, and the rest are other components, with a bulk density of 3-4g / cm 3 ; Alkali metal oxides include oxides of Li, Na, and K.

[0023] Preferably, the solid collected by the incinerator slag remover contains 30-50 wt% of iron oxide, 5-10 wt% of nickel oxide, 3-6 wt% of chromium oxide, and the balance is other components.

[0024] Preferably, the particle size of the catalyst particles is 0.4-1 mm. The solids collected from the corroded bricks of the incinerator and the slag remover of the incinerator are crushed, tableted, sieved and then mixed in proportion to obtain the catalyst.

[0025] The waste liquid treated by incinerators usually contains alkali metal salts such as NaCl. After the incinerator bricks fall off due to the corrosion of alkaline metals over time, they are generally disposed of as waste. However, they still contain a large amount of Al2O3 and alkali metal oxides, which are directly discarded and waste resources are wasted. The solids collected by the incinerator slag remover are black particles precipitated after the waste materials and waste liquids are incinerated and condensed. Their main components are iron oxides, and also include heavy metals such as nickel and chromium oxides. The inventors have found in the process of continuous research that the catalyst composed of the corroded incinerator bricks and the solids collected by the incinerator slag remover has a good catalytic cracking effect on polyethylene wax in the presence of organic peroxides, and can be used to prepare C3-C12 The light oil is conducive to the resource reuse of waste materials.

[0026] In some examples, in step 2), the feed amount of the organic peroxide is 0.02-1 wt % of the polyethylene solid powder.

[0027] In some examples, in step 2), the organic peroxide is selected from one or more of methyl hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl hydroperoxide, and ethylbenzene hydroperoxide.

[0028] In some examples, in step 3), the processing temperature of the condensation unit is -10°C to 0°C.

[0029] In some examples, the amount of the non-condensable gas produced in step 3) that is refluxed to the catalytic cracking reaction unit is 0-15% of its total flow rate, and the remainder is discharged for treatment.

[0030] In some examples, the vaporized polyethylene wax produced in the thermal cracking reaction unit and the cracking products produced in the catalytic cracking reaction unit are both transported to the next unit under the action of nitrogen carrier gas;

[0031] Preferably, the residence time of the polyethylene solid powder in the thermal cracking reaction unit is 0.5-2h;

[0032] Preferably, in the catalytic cracking reaction unit, the residence time of the vaporized polyethylene wax on the catalyst is 0.5-5s;

[0033] Preferably, in the condensation unit, the residence time of the cracking product obtained in step 2) is 0.5-2 min.

[0034] In some examples, the reaction system including the thermal cracking reaction unit, the catalytic cracking reaction unit, and the condensation unit is first replaced with nitrogen to obtain an oxygen-free environment before the polyethylene solid powder is fed.

[0035] In some examples, during nitrogen replacement, the residence time of nitrogen in the thermal cracking reaction unit is 1-2 seconds, and the total replacement time is 1-2 hours.

[0036] The thermal cracking reaction unit described in the present invention is, for example, a tubular resistance furnace, wherein nitrogen-loaded polyethylene solid powder is fed into one end of the tubular resistance furnace and discharged from the other end, and a thermal cracking reaction is carried out in the furnace to generate vaporized polyethylene wax.

[0037] The catalytic cracking reaction unit of the present invention is, for example, a tubular resistance furnace. The organic peroxide discharged from the thermal cracking reaction is fed into one end of the tubular resistance furnace filled with catalyst and discharged from the other end. Under the action of the catalyst, the organic peroxide is cracked to generate C3-C 12 The catalyst loading amount is preferably 40-60% of the volume of the tubular resistance furnace.

[0038] The condensing unit described in the present invention can be a condensing tower, a condensing coil or other equipment, the catalytic cracking product is fed in a bottom-in and top-out manner, and the cooling medium is, for example, an ethylene glycol aqueous solution with a mass concentration of 50%.

[0039] The beneficial effects of the present invention are:

[0040] 1) Polyethylene is processed by thermal cracking and catalytic cracking to deeply crack it into C3-C 12 Light oil to improve product quality and application;

[0041] 2) The catalyst is prepared using the solids collected from the incinerator's corroded bricks and the incinerator's slag remover. In the presence of organic peroxides, it has a good deep catalytic cracking effect on polyethylene wax, which can improve the oil yield;

[0042] 3) The preparation and use of the above catalyst is conducive to the resource reuse of waste materials and reduces environmental damage. DETAILED DESCRIPTION

[0043] The present invention will be further described below through specific examples. The examples of the present invention are only for illustration of the present invention and do not limit the scope of the present invention.

[0044] The following is the main raw material information involved in the embodiment:

[0045] High-density polyethylene (HDPE): Dow DGDC-2480NT, density 0.949 g / cm 3 , melt temperature 193-227℃.

[0046] Low-density polyethylene (LDPE): ExxonMobil LD 136, density 0.921 g / cm 3 , melting peak temperature is 109℃.

[0047] Linear low-density polyethylene (LLDPE): ExxonMobil LL 1001AV, density 0.918 g / cm 3 , melt index 1.0g / 10min.

[0048] In addition, the corroded furnace bricks of the incinerator and the solids collected by the incinerator slag remover in the embodiment of the present invention are all collected from the incinerator supporting the Wanhua Chemical POSM device.

[0049] The following are the main test methods involved in the embodiment:

[0050] <1> Metal content test

[0051] 0.1 g of incinerator corroded bricks or solids collected from the incinerator's slag remover were ground into a powder, added with 1.4 g of lithium hydroxide and 0.1 g of boric acid, and melted in a muffle furnace at 730°C for 60 min. The powder was then ultrasonically treated in an 8 wt% aqueous HCl solution at a frequency of 20 kHz for 30 min. The metal content was analyzed by ICP. The analysis conditions are shown in Table 1.

[0052] Table 1. ICP analysis conditions for metal content

[0053]

[0054] <2> Light oil analysis

[0055] The composition of light oil was analyzed by gas chromatography. The analysis conditions are shown in Table 2:

[0056] Table 2. Gas chromatography analysis conditions for light oil

[0057]

[0058] <3> Oil recovery rate

[0059] Oil recovery rate = light oil mass / polyethylene mass * 100%

[0060] Before the formal operation, the reaction systems in the following embodiments and comparative examples were all introduced with nitrogen for nitrogen replacement, wherein the residence time of nitrogen in the thermal cracking reaction unit was 1 s and the total replacement time was 1 h; and nitrogen was continuously introduced as a carrier gas during the reaction process.

[0061] In addition, the thermal cracking reaction units in the following embodiments and comparative examples all used a tubular resistance furnace with an internal volume of 200 ml. A solid feed port was provided on a nitrogen pipeline connected to the tubular resistance furnace so that nitrogen-loaded polyethylene solid powder could enter the thermal cracking reaction unit. The discharge end of the thermal cracking reaction unit was connected to the feed end of the catalytic cracking reaction unit. The catalytic cracking reaction units all used a tubular resistance furnace with an internal volume of 10 ml. A feed port for organic peroxide was provided on the feed pipeline connected to the tubular resistance furnace. The condensing unit was a condensing coil with a gas phase condensing space of 200 ml. The reaction discharge of the catalytic cracking reaction unit was fed into the condensing coil in a bottom-in, top-out manner. The cooling medium was an ethylene glycol aqueous solution with a mass concentration of 50%.

[0062] [Example 1]

[0063] A method for preparing light oil by catalytic cracking of polyethylene comprises the following steps:

[0064] 1) HDPE+LDPE mixture powder (mass ratio 1:1) with a powder diameter of less than 0.5 cm was continuously fed to a thermal cracking reaction unit at a feed rate of 100 g / h, and thermal cracking reaction was carried out at a temperature of 550° C. to generate vaporized polyethylene wax. The residence time of the mixture powder in the thermal cracking reaction unit was 2 h. After nitrogen was preheated to 550° C., the thermal cracking reaction unit was continuously purged at a nitrogen flow rate of 0.3 L / h.

[0065] 2) continuously feeding the vaporized polyethylene wax into a catalytic cracking reaction unit loaded with a catalyst. Simultaneously, continuously feeding tert-butyl hydroperoxide into the catalytic cracking reaction unit at a feed rate of 1 g / h, with a catalyst loading of 60%. The catalytic cracking reaction was carried out at 450° C., with the residence time of the polyethylene wax on the catalyst being 3.2 s.

[0066] 3) The cracking product obtained in step 2) was sent to a condensation unit for condensation at -10°C. The residence time of the cracking product was 1.8 min, and C3-C 12 The light oil and the non-condensable gas at the top are not refluxed and are all discharged externally for treatment.

[0067] The catalyst in this embodiment is composed of a mixture of incinerator corroded furnace bricks and solids collected by the incinerator slag remover in a mass ratio of 10:1. The incinerator corroded furnace bricks contain 40wt% Al2O3, 22.8wt% Na2O, and 2.2wt% K2O, with a bulk density of 3g / cm 3 The solid collected from the incinerator slag remover contains 50wt% of iron oxide, 9wt% of NiO, and 6wt% of Cr2O3.

[0068] In this embodiment, the oil recovery rate is 90%. The light oil is subjected to gas chromatography carbon number analysis, and the analysis results are as follows:

[0069] Table 3 Carbon number composition analysis of light oil prepared in Example 1

[0070]

[0071] [Example 2]

[0072] A method for preparing light oil by catalytic cracking of polyethylene comprises the following steps:

[0073] 1) HDPE powder with a diameter of less than 0.5 cm was continuously fed to a thermal cracking reaction unit at a feed rate of 150 g / h, and thermally cracked at 550° C. to generate vaporized polyethylene wax. The mixture powder was retained in the thermal cracking reaction unit for 1.3 h. Nitrogen was preheated to 550° C. and then continuously purged through the thermal cracking reaction unit at a nitrogen flow rate of 0.6 L / h.

[0074] 2) continuously feeding the vaporized polyethylene wax into a catalytic cracking reaction unit loaded with a catalyst. Simultaneously, continuously feeding methyl hydroperoxide into the catalytic cracking reaction unit at a feed rate of 1.2 g / h, with a catalyst loading of 60%. The catalytic cracking reaction was carried out at 450° C., with the residence time of the polyethylene wax on the catalyst being 2 s.

[0075] 3) The cracking product obtained in step 2) was sent to a condensation unit for condensation at -10°C. The residence time of the cracking product was 1.1 min, and C3-C 12 The light oil and the non-condensable gas at the top are not refluxed and are all discharged externally for treatment.

[0076] The catalyst in this embodiment is composed of a mixture of incinerator corroded furnace bricks and solids collected by the incinerator slag remover in a mass ratio of 6:1. The incinerator corroded furnace bricks contain 45wt% Al2O3, 20wt% Na2O, and 2.7wt% K2O, with a bulk density of 3.1g / cm 3 The solid collected by the incinerator slag remover contains 40wt% of iron oxide, 8wt% of NiO, and 5wt% of Cr2O3.

[0077] In this embodiment, the oil recovery rate is 88%. The light oil is subjected to gas chromatography carbon number analysis, and the analysis results are as follows:

[0078] Table 4 Carbon number composition analysis of light oil prepared in Example 2

[0079]

[0080] [Example 3]

[0081] A method for preparing light oil by catalytic cracking of polyethylene comprises the following steps:

[0082] 1) LDPE powder with a diameter of less than 0.5 cm was continuously fed to a thermal cracking reaction unit at a feed rate of 200 g / h, and thermally cracked at 500° C. to generate vaporized polyethylene wax. The mixture powder was retained in the thermal cracking reaction unit for 1 hour. Nitrogen was preheated to 550° C. and then continuously purged through the thermal cracking reaction unit at a nitrogen flow rate of 0.6 L / h.

[0083] 2) continuously feeding the vaporized polyethylene wax into a catalytic cracking reaction unit loaded with a catalyst. Simultaneously, continuously feeding tert-butyl hydroperoxide into the catalytic cracking reaction unit at a feed rate of 0.8 g / h, with a catalyst loading of 50%. The catalytic cracking reaction was carried out at 400° C., with a residence time of the polyethylene wax on the catalyst of 1.4 s.

[0084] 3) The cracking product obtained in step 2) was sent to a condensation unit for condensation at -5°C. The residence time of the cracking product was 0.9 min, and C3-C 12 The light oil, a part of the non-condensable gas at the top is refluxed to the catalytic cracking reaction unit, and the other part is discharged for treatment, wherein the flow rate of the reflux non-condensable gas is 5% of its total flow rate.

[0085] The catalyst in this embodiment is composed of a mixture of incinerator corroded furnace bricks and solids collected by the incinerator slag remover in a mass ratio of 4:1. The incinerator corroded furnace bricks contain 52wt% Al2O3, 14wt% Na2O, and 4wt% K2O, with a bulk density of 3.5g / cm 3 The solids collected from the incinerator slag remover contain 34 wt% of iron oxides, 6 wt% of NiO, and 4 wt% of Cr2O3.

[0086] In this embodiment, the oil recovery rate was 86%. The light oil was subjected to gas chromatography carbon number analysis, and the analysis results were as follows:

[0087] Table 5 Carbon number composition analysis of light oil prepared in Example 3

[0088]

[0089] [Example 4]

[0090] A method for preparing light oil by catalytic cracking of polyethylene comprises the following steps:

[0091] 1) LLDPE powder with a diameter of less than 0.5 cm was continuously fed to a thermal cracking reaction unit at a feed rate of 300 g / h, and thermal cracking reaction was carried out at a temperature of 450° C. to generate vaporized polyethylene wax. The residence time of the mixture powder in the thermal cracking reaction unit was 0.7 h. After nitrogen was preheated to 550° C., the thermal cracking reaction unit was continuously purged at a nitrogen flow rate of 0.9 L / h.

[0092] 2) continuously feeding the vaporized polyethylene wax into a catalytic cracking reaction unit loaded with a catalyst. Simultaneously, continuously feeding di-tert-butyl hydroperoxide into the catalytic cracking reaction unit at a feed rate of 0.6 g / h, with a catalyst loading of 40%. The catalytic cracking reaction was carried out at 350° C., with the residence time of the polyethylene wax on the catalyst being 0.8 s.

[0093] 3) The cracking product obtained in step 2) was sent to a condensation unit for condensation at 0°C. The residence time of the cracking product was 0.7 min, and C3-C 12The light oil, a part of the non-condensable gas at the top is refluxed to the catalytic cracking reaction unit, and the other part is discharged for treatment, wherein the flow rate of the reflux non-condensable gas is 10% of its total flow rate.

[0094] The catalyst in this embodiment is composed of a mixture of incinerator corroded furnace bricks and solids collected by the incinerator slag remover in a mass ratio of 2:1. The incinerator corroded furnace bricks contain 58wt% Al2O3, 10wt% Na2O, and 5.8wt% K2O, with a bulk density of 3.7g / cm 3 The solids collected from the incinerator slag remover contain 37 wt% of iron oxides, 8 wt% of NiO, and 4 wt% of Cr2O3.

[0095] In this embodiment, the oil recovery rate is 85%. The light oil is subjected to gas chromatography carbon number analysis, and the analysis results are as follows:

[0096] Table 6 Carbon number composition analysis of light oil prepared in Example 4

[0097]

[0098]

[0099] [Example 5]

[0100] A method for preparing light oil by catalytic cracking of polyethylene comprises the following steps:

[0101] 1) continuously feeding a mixture of HDPE, LDPE, and LLDPE powder (mass ratio 1:1:1) with a powder diameter of less than 0.5 cm into a thermal cracking reaction unit at a feed rate of 400 g / h, performing a thermal cracking reaction at a temperature of 450° C. to generate vaporized polyethylene wax. The mixture powder resides in the thermal cracking reaction unit for 0.5 h. After nitrogen is preheated to 450° C., the thermal cracking reaction unit is continuously purged at a nitrogen flow rate of 1.2 L / h.

[0102] 2) continuously feeding the vaporized polyethylene wax into a catalytic cracking reaction unit loaded with a catalyst, and simultaneously continuously feeding a mixture of methyl hydroperoxide and tert-butyl hydroperoxide (molar ratio of 1:1) into the catalytic cracking reaction unit at a feed rate of 0.2 g / h, with a catalyst loading of 40%, and conducting a catalytic cracking reaction at 350° C. with a residence time of the polyethylene wax on the catalyst of 0.6 s;

[0103] 3) The cracking product obtained in step 2) is sent to a condensation unit for condensation at 0°C. The residence time of the cracking product is 0.5 min, and C3-C 12The light oil, a part of the non-condensable gas at the top is refluxed to the catalytic cracking reaction unit, and the other part is discharged for treatment, wherein the reflux non-condensable gas flow rate is 15% of its total flow rate.

[0104] The catalyst in this embodiment is composed of a mixture of incinerator corroded furnace bricks and solids collected by the incinerator slag remover in a mass ratio of 1:1. The incinerator corroded furnace bricks contain 60wt% Al2O3, 9.5wt% Na2O, and 0.5wt% K2O, with a bulk density of 4g / cm 3 The solids collected from the incinerator slag remover contain 32 wt% of iron oxide, 5 wt% of NiO, and 3 wt% of Cr2O3.

[0105] In this embodiment, the oil recovery rate is 82%. The light oil is subjected to gas chromatography carbon number analysis, and the analysis results are as follows:

[0106] Table 7 Carbon number composition analysis of light oil prepared in Example 5

[0107]

[0108]

[0109] [Comparative Example 1]

[0110] Light oil was prepared by catalytic cracking of polyethylene using a method substantially the same as that in Example 5, with the only difference being that the catalyst was replaced by incinerator corroded furnace bricks having the same composition as that in Example 5.

[0111] The oil recovery rate in this comparative example is 76%. The light oil is subjected to gas chromatography carbon number analysis, and the analysis results are as follows:

[0112] Table 8 Carbon number composition analysis of light oil prepared in Comparative Example 1

[0113]

[0114] [Comparative Example 2]

[0115] Light oil was prepared by catalytic cracking of polyethylene using a method substantially the same as that of Example 5, except that the catalyst was replaced with solids collected from an incinerator slag remover having the same composition as that of Example 5.

[0116] The oil recovery rate in this comparative example is 72%. The light oil is subjected to gas chromatography carbon number analysis, and the analysis results are as follows:

[0117] Table 9 Carbon number composition analysis of light oil prepared in Comparative Example 2

[0118]

[0119] [Comparative Example 3]

[0120] Polyethylene was subjected to thermal cracking and catalytic cracking according to the method in Example 5, wherein no catalyst was placed in the catalytic cracking reaction unit.

[0121] The oil recovery rate in this comparative example is 46%. The light oil was subjected to gas chromatography carbon number analysis, and the analysis results are as follows:

[0122] Table 10 Carbon number composition analysis of light oil prepared in Comparative Example 3

[0123]

[0124]

[0125] [Comparative Example 4]

[0126] Polyethylene was thermally cracked and catalytically cracked according to the method in Example 5, except that the catalyst was replaced by a mixed catalyst of Al2O3 and Fe3O4 in a mass ratio of 1:1.

[0127] The oil recovery rate in this comparative example is 56%. The light oil was subjected to gas chromatography carbon number analysis, and the analysis results are as follows:

[0128] Table 11 Carbon number composition analysis of light oil prepared in Comparative Example 4

[0129]

[0130] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing light oil by catalytic cracking of polyethylene, characterized in that: The following steps are involved: 1) Continuously conveying polyethylene solid powder to a thermal cracking reaction unit, performing a thermal cracking reaction at a temperature of 450-550°C to generate vaporized polyethylene wax; 2) Vaporized polyethylene wax is continuously fed into a catalytic cracking reaction unit filled with a catalyst, and at the same time, an organic peroxide is continuously fed into the catalytic cracking reaction unit to perform a catalytic cracking reaction at 350-450° C. The catalyst is a mixture of corroded furnace bricks of an incinerator and solids collected by a slag remover of the incinerator in a mass ratio of (1-10):1; the corroded furnace bricks of the incinerator contain 40-60 wt% of Al2O3 and 10-25 wt% of an alkali metal oxide, and have a bulk density of 3-4 g / cm3. 3 The solids collected by the incinerator slag remover contain 30-50wt% iron oxide, 5-10wt% nickel oxide, 3-6wt% chromium oxide, and the remainder other components; 3) The cracking product obtained in step 2) is sent to a condensation unit for condensation treatment, wherein the bottom is collected to obtain C3-C 12 The light oil, the non-condensable gas at the top is refluxed or not refluxed to the catalytic cracking reaction unit.

2. The method for preparing light oil by catalytic cracking of polyethylene according to claim 1, characterized in that: In step 1), the feed rate of the polyethylene solid powder is 10-60 g / h.

3. The method for preparing light oil by catalytic cracking of polyethylene according to claim 2, characterized in that: The diameter of the polyethylene solid powder is less than 0.5 cm.

4. The method for preparing light oil by catalytic cracking of polyethylene according to claim 2, characterized in that: The polyethylene solid powder is one or more of high-density polyethylene, low-density polyethylene, and linear low-density polyethylene.

5. The method for preparing light oil by catalytic cracking of polyethylene according to any one of claims 1 to 4, characterized in that: In step 2), the feed amount of the organic peroxide is 0.02-1 wt% of the polyethylene solid powder.

6. The method for preparing light oil by catalytic cracking of polyethylene according to claim 5, characterized in that: In step 2), the organic peroxide is selected from one or more of methyl hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl hydroperoxide, and ethylbenzene hydroperoxide.

7. The method for preparing light oil by catalytic cracking of polyethylene according to any one of claims 1 to 4, characterized in that: In step 3), the processing temperature of the condensation unit is -10°C to 0°C.

8. The method for preparing light oil by catalytic cracking of polyethylene according to claim 7, characterized in that: The amount of the non-condensable gas generated in step 3) that is refluxed to the catalytic cracking reaction unit is 0-15% of its total flow rate, and the remaining portion is discharged for treatment.

9. The method for preparing light oil by catalytic cracking of polyethylene according to any one of claims 1 to 4, characterized in that: The vaporized polyethylene wax produced in the thermal cracking reaction unit and the cracking products produced in the catalytic cracking reaction unit are both transported to the next unit under the action of nitrogen carrier gas.

10. The method for preparing light oil by catalytic cracking of polyethylene according to claim 9, characterized in that: The residence time of the polyethylene solid powder in the thermal cracking reaction unit is 0.5-2h.

11. The method for preparing light oil by catalytic cracking of polyethylene according to claim 9, characterized in that: In the catalytic cracking reaction unit, the residence time of the vaporized polyethylene wax on the catalyst is 0.5-5s.

12. The method for preparing light oil by catalytic cracking of polyethylene according to claim 9, characterized in that: In the condensation unit, the residence time of the cracking product obtained in step 2) is 0.5-2 min.

13. The method for preparing light oil by catalytic cracking of polyethylene according to any one of claims 1 to 4, characterized in that: The reaction system including a thermal cracking reaction unit, a catalytic cracking reaction unit and a condensing unit is firstly replaced with nitrogen to obtain an oxygen-free environment before the polyethylene solid powder is fed.

14. The method for preparing light oil by catalytic cracking of polyethylene according to claim 13, characterized in that: During nitrogen replacement, the residence time of nitrogen in the thermal cracking reaction unit is 1-2s, and the total replacement time is 1-2h.

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