Method for preparing ethylene and propylene through catalytic cracking of light hydrocarbon by adopting tubular fixed bed reactor

Abstract

The invention relates to a method for preparing ethylene and propylene by catalytic cracking of light hydrocarbon with a tubular fixed bed reactor, the tubular fixed bed reactor comprises a shell, a plurality of longitudinally arranged tube bundles are arranged in the shell, and the tube bundles are filled with a catalyst special for catalytic cracking. A gaseous light hydrocarbon raw material mixed with diluent gas is preheated and then enters a tube bundle from a reactor tube pass inlet for a catalytic cracking reaction, compressed high-temperature gas is adopted as a heat source to provide heat for the catalytic cracking reaction, and the compressed high-temperature gas enters the reactor from a reactor shell pass inlet for convective heat transfer; the tube bundle and the internal temperature of the tube bundle are maintained at the reaction temperature of catalytic cracking, and the tube bundle is discharged from a shell pass outlet of the reactor for cyclic utilization after heat exchange. The process method provided by the invention has the advantages of high heat supply efficiency, high ethylene and propylene selectivity, long catalyst service life, simple process flow, easy operation, low equipment cost and the like.

Description

Technical Field

[0001] The invention relates to the technical field of petrochemical industry, and in particular to a method for preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor. Background Art

[0002] Ethylene and propylene are the most important components of the global petrochemical industry. Most light olefins at home and abroad are produced by thermal cracking of hydrocarbons, also known as steam cracking. This process has been used in production for more than half a century. The typical disadvantages of the steam cracking process include high reaction temperature (greater than 800°C), limited P / E ratio (propylene / ethylene), high energy consumption, and difficulty in adjusting the distribution of light olefins. In contrast, the technology of catalytic cracking of light hydrocarbons to produce ethylene and propylene has a lower reaction temperature, better economy, practicality and high light olefin selectivity. Catalytic cracking reduces energy consumption and carbon dioxide emissions, increases the yield of low-carbon olefins, and adjusts the distribution of products. Therefore, the catalytic cracking process is more attractive and has more in-depth research value than steam cracking, and has received extensive attention from the petrochemical industry.

[0003] At present, fluidized bed reactors are widely used for catalytic cracking of light hydrocarbons to produce ethylene and propylene. The reaction-regeneration system includes a riser reactor, a regenerator, and a settler. The regenerator and the riser reactor are independent of each other. The raw materials enter the riser reactor and react with the regenerated catalyst to generate various products, and at the same time form a catalyst to be regenerated. The catalyst to be regenerated enters the regenerator and returns to the riser reactor to participate in the reaction after regeneration. However, light hydrocarbons have a high hydrogen content, and even at high temperature, the amount of coke produced is still very small. At present, the heat required for the reaction in the circulating fluidized bed process is supplied by the heat generated by the regeneration of the regenerator, which has problems such as insufficient heat supply, high energy consumption, and serious backmixing.

[0004] To solve this problem, patent CN101522866A discloses a dual riser fluidized catalytic cracking reactor method using light and mixed light / heavy feeds, adding a small amount of coke precursor to the light hydrocarbon feed to increase the light hydrocarbon cracking temperature, but the introduced coke precursor will affect the reaction process, and the diene yield and selectivity are low. Patent CN1912065A discloses a catalytic conversion method for increasing propylene production, using main and auxiliary dual risers to combine light hydrocarbon catalytic cracking with heavy oil catalytic cracking. Although this method can meet the high temperature required for light hydrocarbon cracking and improve the light hydrocarbon yield to a certain extent compared with heavy oil catalytic cracking, the light hydrocarbon catalytic cracking is subject to the heavy oil catalytic cracking and cannot be catalytically cracked into ethylene and propylene to the maximum extent, and the ethylene and propylene yields are low. Patent CN1962576A discloses a method for preparing propylene and ethylene by catalytic cracking of carbon-containing olefins. The liquid raw material is vaporized by heat exchange with the cracking product and then heated by a heating furnace to reach the reaction temperature. The liquid raw material then enters a fixed bed reactor for catalytic cracking reaction. This method overcomes the serious back-mixing phenomenon of the fluidized bed and reduces the equipment cost. It also improves the service life of the catalyst and the selectivity of ethylene and propylene to a certain extent. However, from the perspective of practical application, it needs to be heated by a heating furnace to the reaction temperature before entering the fixed bed reactor. The reaction process is complicated and the heat utilization efficiency is low. The yield and selectivity of ethylene and propylene are still limited. Patent CN118271148A discloses a method for preparing chemical raw materials by catalytic cracking of light hydrocarbons. The method adopts an integrated device of a heating furnace and a catalytic cracking reactor, and utilizes the convection section and the radiation section of the heating furnace to preheat the raw materials and provide heat for the reaction. The shell-and-tube fixed bed reactor is placed in the radiation section of the heating furnace and is directly heated by the heating furnace, which simplifies the process flow, improves the heat utilization rate, and improves the selectivity of ethylene and propylene to a certain extent. However, the heat source used in the method is electric heating alone or various combustible media such as gas fuel, liquid fuel, and solid fuel, which consumes a lot of energy and has a certain risk of explosion of the fuel.

[0005] From the above analysis, it can be seen that the prior art discloses some methods for preparing ethylene and propylene by catalytic cracking of light hydrocarbons, but there are still some shortcomings to varying degrees, such as: high reaction temperature during use, low olefin selectivity, low P / E ratio (propylene / ethylene), insufficient heat supply, high energy consumption, low heat utilization efficiency and other problems. Summary of the invention

[0006] In order to overcome the problems of high reaction temperature, insufficient heat supply, large energy consumption, low heat utilization efficiency, complex reaction form, low diene selectivity, low P / E (propylene / ethylene) ratio, poor catalyst activity stability, short catalyst service life, etc. in the prior art of catalytic cracking of light hydrocarbons to prepare ethylene and propylene, the present invention provides a method for catalytic cracking of light hydrocarbons to prepare ethylene and propylene by using a tubular fixed bed reactor. The process method has the advantages of high heating efficiency, high heat utilization efficiency, low energy consumption, high ethylene and propylene selectivity, long catalyst service life, simple process flow, easy operation, low equipment cost, etc.

[0007] The present invention is specifically implemented by the following technical scheme. According to a method for preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor proposed by the present invention, the tubular fixed bed reactor comprises a shell, a plurality of longitudinally arranged tube bundles are arranged in the shell, and a special catalyst for catalytic cracking is filled in the tube bundle. The upper end of the shell is connected to a bed feed side tube box, and the lower end is connected to a bed discharge side tube box. The top of the bed feed side tube box and the bottom of the bed discharge side tube box are respectively provided with a reactor tube side inlet and a reactor tube side outlet. The shell side wall is provided with a reactor shell side inlet and a reactor shell side outlet, and the central axis of the reactor shell side inlet and the central axis of the reactor shell side outlet are located in the same vertical plane; any one of the reactor shell side inlet and the reactor shell side outlet is arranged at the upper part of the shell side wall, and the other is arranged at the lower part of the shell side wall;

[0008] The steps of using the tubular fixed bed reactor to catalytically crack light hydrocarbons to prepare ethylene and propylene include: using gaseous light hydrocarbons as reaction raw materials, preheating the gaseous light hydrocarbon raw materials mixed with diluent gas, entering the bed feed side pipe box from the reactor tube side inlet, and then entering the tube bundle for catalytic cracking reaction, and the product enters the bed discharge side pipe box from the lower end of the tube bundle, and then is discharged through the reactor tube side outlet; compressed high-temperature gas is used as a heat source to enter the tubular fixed bed reactor from the reactor shell side inlet for convective heat transfer, providing heat for the catalytic cracking reaction, so that the tube bundle and its internal temperature are maintained at the reaction temperature of catalytic cracking, and the compressed high-temperature gas enters the tubular fixed bed reactor for heat exchange and is discharged from the reactor shell side outlet for recycling.

[0009] In the aforementioned method of preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor, the top and bottom of the shell are respectively provided with a bed feed side tube sheet and a bed discharge side tube sheet, the bed feed side tube sheet and the bed discharge side tube sheet are both tightly connected to the inner wall of the shell, and the bed feed side tube sheet and the bed discharge side tube sheet are respectively provided with a feed hole and a discharge hole, the upper end of the tube bundle is connected to the feed hole, and the lower end is connected to the discharge hole.

[0010] In the aforementioned method of preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor, a baffle is also provided in the shell.

[0011] In the above-mentioned method of preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor, during the catalytic cracking reaction, the feed temperature at the reactor tube inlet is 600-630°C, the discharge temperature at the reactor tube outlet is 550-570°C, the average reaction temperature in the tube bundle is 550-630°C, the reaction pressure is -0.1-0.5 MPa(a), and the weight hourly space velocity is 0.5-15h -1 .

[0012] Preferably, the catalyst density in the tube bundle is 600-800 kg / m 3 The linear velocity of the gaseous light raw material mixed with diluent gas entering the reactor is 0.8 to 8 m / s.

[0013] Preferably, the light hydrocarbon feedstock is selected from one or more of isobutane, n-butane, butenes, n-pentane, isopentane, neopentane, cyclopentane, C5 olefins, pentane oil, topped oil, raffinate, light naphtha, catalytic cracking gasoline, catalytic pyrolysis gasoline, coker gasoline, thermal pyrolysis gasoline, coal-based naphtha and hydrocracking naphtha.

[0014] Preferably, the diluent gas is selected from one of nitrogen, hydrogen, methane, ethane, propane, butane, refinery dry gas, liquefied gas, CO2, preferably ethane and propane, and the molar ratio of the diluent gas to the light hydrocarbon feedstock (dilution ratio) is 1:10 to 30, preferably 1:15.

[0015] Preferably, the heat carrier is nitrogen or air, which is heated to 400-500°C and then heated and pressurized by a heat pump to a temperature of 600-650°C to become compressed high-temperature gas. The compressed high-temperature gas is used as a heat source to heat the catalytic cracking reaction in the tube bundle.

[0016] Preferably, the shape of the catalyst for catalytic cracking is cylindrical, hollow cylindrical, spherical, hollow spherical, butterfly-shaped, etc., and its active components include one or more of ZSM-5, ZSM-23, ZSM-11, β, SAPO-34, or the catalyst described in patent CN115888797A.

[0017] Furthermore, the volume equivalent diameter of the special catalyst for catalytic cracking is 1 to 8 mm, and the length of the hollow cylindrical catalyst is 1 to 8 mm.

[0018] Compared with the prior art, the present invention has obvious advantages and beneficial effects. By means of the above technical solution, the present invention can achieve considerable technical progress and practicality, and has a wide range of utilization value, and has at least the following advantages:

[0019] (1) The present invention adopts a tube-in-tube fixed bed reactor to carry out catalytic cracking reaction of light hydrocarbons to produce ethylene and propylene. The gaseous light hydrocarbon feedstock mixed with diluent gas is preliminarily preheated and then introduced into the tube bundle filled with catalyst of the tube-in-tube fixed bed reactor for catalytic cracking reaction. By adding diluent gas, the reaction rate limit is increased, the reaction residence time is shortened, the dry gas yield is reduced, and the selectivity of ethylene and propylene is improved.

[0020] (2) The present invention uses compressed high-temperature air or compressed high-temperature nitrogen as a heat source to provide heat for the catalytic cracking reaction. The heat carrier nitrogen or air is heated and heated and pressurized by a heat pump to form a compressed high-temperature gas, which then enters the shell side to provide heat for the tube side catalytic cracking reaction through convection heat transfer, so that the tube bundle and its internal temperature are maintained at the reaction temperature of 550-630°C for catalytic cracking. The compressed high-temperature gas enters the reactor for heat exchange and is discharged from the reactor shell side outlet and recycled. Compared with the traditional method of directly heating the heat carrier to the heating temperature to provide heat for the catalytic cracking reaction and the fuel furnace burning fuel heat radiation to provide heat, the heating method of the present invention (the heat carrier heating method is obtained by heating and heat pump pressure increase (heat pump pressure increase causes secondary heating) to obtain compressed high-temperature gas, and the compressed high-temperature gas is passed into the shell side of the tube-in-tube fixed bed reactor through tube-shell convection heat transfer to provide heat for the catalytic cracking reaction) is more energy-saving and environmentally friendly, safer, and the raw materials are heated more evenly. The heating method of the present invention has the advantages of a shell and tube heat exchanger, and baffles are arranged on the shell side to increase the turbulent velocity of the heating gas, continuously providing heat for the tube side reaction through convective heat exchange, greatly improving the heat transfer efficiency, providing sufficient heat for the catalytic cracking reaction, allowing the reaction to proceed smoothly, and solving the problems of insufficient heat supply, low heating efficiency, and high energy consumption in the production of ethylene and propylene by catalytic cracking reaction.

[0021] (3) The catalyst for catalytic cracking is in the shape of cylinder, sphere, hollow cylinder, hollow sphere, butterfly, etc., which can reduce the bulk density, reduce the bed pressure drop, reduce the flow resistance of raw materials, improve the heat transfer efficiency and the yield and selectivity of propylene and ethylene. At the same time, the catalyst for catalytic cracking is fixed in the bed tube bundle, which is not easy to wear, helps to maintain the activity of the catalyst, prolong the service life of the catalyst, and achieve a larger production capacity with less catalyst and smaller reactor volume. The design and operation are simpler than the fluidized bed, and the production cost is lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic structural diagram of a tubular fixed bed reactor used in Example 1;

[0023] Figure 2 Schematic diagram of the structure of the tube-in-tube fixed bed reactor used in Example 2.

[0024] The following are the descriptions of the reference numerals:

[0025] 1-shell, 2-tube bundle, 3-bed feed side tube box, 4-bed discharge side tube box, 5-bed feed side tube sheet, 6-bed discharge side tube sheet, 7-reactor shell side inlet, 8-reactor shell side outlet, 9-reactor tube side inlet, 10-reactor tube side outlet, 11-catalyst dedicated for catalytic cracking, 12-gaseous light hydrocarbon feed mixed with diluent gas, 13-reaction product, 14-compressed high-temperature gas, 15-baffle. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The present invention provides a method for preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor. The tubular fixed bed reactor is used for reaction. The tubular fixed bed reactor can be a commercially available reactor or customized. The structure of a tubular fixed bed reactor is as follows: Figure 1 As shown, it comprises a cylindrical shell 1, in which a plurality of longitudinally arranged tube bundles 2 are arranged, in which a catalyst 11 dedicated for catalytic cracking is filled, the upper end of the shell 1 is connected to a bed feed side tube box 3, and the lower end is connected to a bed discharge side tube box 4; the top of the bed feed side tube box 3 is provided with a reactor tube side inlet 9, and the bottom of the bed discharge side tube box 4 is provided with a reactor tube side outlet 10. The top and bottom of the shell 1 are respectively provided with a bed feed side tube sheet 5 and a bed discharge side tube sheet 6, and the diameters of the bed feed side tube sheet 5 and the bed discharge side tube sheet 6 are equal to the inner diameter of the shell 1, that is, the bed feed side tube sheet 5 and the bed discharge side tube sheet 6 are both tightly connected to the inner wall of the shell 1. Feed holes and discharge holes are respectively provided on the bed feed side tube sheet and the bed discharge side tube sheet. The positions of the feed holes and the discharge holes correspond to the positions of the tube bundle. The upper end of the tube bundle 2 is connected to the feed hole on the bed feed side tube sheet 5, and the lower end is connected to the discharge hole on the bed discharge side tube sheet 6. A single arched baffle 15 perpendicular to the axial direction of the tube bundle is also provided in the shell 1. A reactor shell side inlet 7 and a reactor shell side outlet 8 are provided on the side wall of the shell 1. The reactor shell side inlet and the reactor shell side outlet are respectively located on both sides of the shell, and the central axis of the reactor shell side inlet 7 and the central axis of the reactor shell side outlet 8 are located in the same vertical plane. Any one of the reactor shell side inlet 7 and the reactor shell side outlet 8 is provided at the upper part of the side wall of the shell 1, and the other is provided at the lower part of the side wall of the shell 1. In one embodiment, the reactor shell side inlet 7 is located at the upper part of the side wall of the shell, and the reactor shell side outlet 8 is located at the lower part of the side wall of the shell, such as Figure 1In another embodiment, the reactor shell side inlet 7 is located at the lower part of the shell side wall, and the reactor shell side outlet 8 is located at the upper part of the shell side wall, as shown in FIG. Figure 2 shown.

[0028] When the above tubular fixed bed reactor is used to catalytically crack light hydrocarbons to produce ethylene and propylene, the reaction raw material is a gaseous light hydrocarbon raw material. The gaseous light hydrocarbon raw material mixed with diluent gas is preheated and enters the bed feed side pipe box 3 through the reactor tube side inlet 9, and enters the corresponding tube bundle 2 through the feed hole on the bed feed side tube sheet 5 for catalytic cracking reaction. The tube bundle is filled with a special catalyst for catalytic cracking. The gaseous light hydrocarbon raw material mixed with diluent gas is catalytically cracked in the tube bundle under certain reaction conditions to produce ethylene, propylene, by-products, etc. The product enters the bed discharge side pipe box 4 from the lower end of the tube bundle through the discharge hole on the bed discharge side tube sheet 6, and then is discharged through the reactor tube side outlet 10.

[0029] The catalytic cracking reaction of the gaseous light hydrocarbon raw material mixed with diluent gas in the tube bundle is an endothermic reaction. The feed temperature at the reactor tube inlet is 600-630°C, the discharge temperature at the reactor tube outlet is 550-570°C, the average reaction temperature in the tube bundle is 550-630°C, the reaction pressure is -0.1-0.5MPa(a) (absolute pressure), and the weight hourly space velocity is 0.5-15h -1 . Catalyst density in tube bundle 600~800kg / m 3 The linear velocity of the raw gas (gaseous light raw material mixed with diluent gas) entering the reactor is 0.8 to 8 m / s.

[0030] In the above catalytic cracking reaction, the compressed high-temperature gas is used as a heat source to enter the tube-in-tube fixed bed reactor from the reactor shell inlet for convective heat transfer, providing heat for the catalytic cracking reaction, so that the temperature of the tube bundle and its interior is maintained at the reaction temperature of catalytic cracking of 550-630°C. The compressed high-temperature gas enters the reactor for heat exchange and is discharged from the reactor shell outlet for recycling. The compressed high-temperature gas is formed by heating the heat carrier nitrogen or air and increasing the temperature and pressure by a heat pump, and then enters the shell to provide heat for the tube catalytic cracking reaction through convective heat transfer.

[0031] In the above catalytic cracking reaction, the light hydrocarbon raw material is selected from one or more of isobutane, normal butane, butene, normal pentane, isopentane, neopentane, cyclopentane, C5 olefins, pentane oil, topped oil, raffinate, light naphtha, catalytic cracking gasoline, catalytic pyrolysis gasoline, coker gasoline, thermal cracking gasoline, coal-based naphtha and hydrocracking naphtha. The diluent gas can be selected from one of nitrogen, hydrogen, methane, ethane, propane, butane, refinery dry gas, liquefied gas, CO2, etc., preferably ethane and propane; the molar ratio of the diluent gas to the light hydrocarbon (hereinafter referred to as "dilution ratio") is 1:10 to 30, preferably 1:15.

[0032] In the above-mentioned catalytic cracking reaction, the special catalyst for catalytic cracking is in the shape of a cylinder, a hollow cylinder, a sphere, a hollow sphere, a butterfly, etc. The active components of the special catalyst for catalytic cracking include one or more of ZSM-5, ZSM-23, ZSM-11, β, and SAPO-34. In one embodiment, the special catalyst for catalytic cracking is selected from the catalyst disclosed in patent CN115888797A.

[0033] Further preferably, the volume equivalent diameter of the catalyst dedicated to catalytic cracking is 1 to 8 mm, preferably 2 to 5 mm, the length of the hollow cylindrical catalyst is 1 to 8 mm, preferably 2 to 5 mm, and the shape of the special-shaped structure catalyst is beneficial to reducing the bulk density, and its structural size is equivalent to that of the hollow cylindrical catalyst.

[0034] The present invention is described in detail with specific examples below. If no specific conditions are specified in the following examples, they are all carried out according to conventional conditions or conditions recommended by the manufacturer. The raw materials and reagents used without specifying the manufacturer are all conventional products that can be purchased commercially.

[0035] Example 1

[0036] refer to Figure 1 The present embodiment provides a method for preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor. In the present embodiment, the gaseous light hydrocarbon feedstock uses light naphtha, and the feedstock composition is shown in Table 1. The dilution gas is propane, and the dilution ratio is 1:15. The heat source uses compressed high-temperature air. The gaseous light hydrocarbon feedstock mixed with the dilution gas has the same flow direction as the compressed high-temperature hot air medium, that is, the reactor shell side inlet is arranged at the upper part of the shell side wall, and the reactor shell side outlet is arranged at the lower part of the shell side wall. The tube bundle diameter of the tubular fixed bed reactor is DN40, the tube length is 5m, and the reactor space velocity is 5h -1 The catalyst for catalytic cracking is a hollow cylindrical catalyst, whose active ingredient is ZSM-5, the catalyst diameter is 3mm, the catalyst height is 3mm, the reactor tube inlet temperature (i.e., feed temperature) is 600°C, the reactor tube outlet temperature (i.e., discharge temperature) is 570°C, the gaseous light hydrocarbon feed mixed with diluent gas is heated to 600°C after heat exchange with the product in the early stage and heating; the reactor shell inlet temperature (i.e., compressed high-temperature hot air temperature) is 600-650°C. The catalytic cracking reaction results of this embodiment are shown in Table 2.

[0037] Example 2

[0038] refer to Figure 2 The gaseous light hydrocarbon feedstock mixed with the dilution gas flows in the opposite direction to the compressed high-temperature hot air medium, that is, the reactor shell side inlet is arranged at the lower part of the shell side wall, and the reactor shell side outlet is arranged at the upper part of the shell side wall. The rest is the same as Example 1. The catalytic cracking reaction results are shown in Table 2.

[0039] Example 3

[0040] The catalyst for catalytic cracking is a spherical catalyst with a diameter of 3 mm. The rest is the same as in Example 1. The catalytic cracking reaction results are shown in Table 2.

[0041] Example 4

[0042] The reactor space velocity is 3h -1 , the rest is the same as Example 1, and the catalytic cracking reaction results are shown in Table 2.

[0043] Example 5

[0044] No diluent gas was added to the gaseous light hydrocarbon feedstock, and the rest was the same as in Example 1. The catalytic cracking reaction results are shown in Table 2.

[0045] Comparative Example 1

[0046] Compared with Example 1, an existing fixed bed reactor (non-tube fixed bed reactor) is used, and the product and raw gas (raw gas is the same as Example 1) are used for heat exchange to preheat the raw gas to a certain temperature, and then the raw gas is heated to a reaction temperature of 550-630°C by a heating furnace, and then enters the existing fixed bed reactor to contact and react with a special catalyst for catalytic cracking. The diluent gas is propane, the dilution ratio is 1:15, the special catalyst for catalytic cracking is the same as Example 1, and the catalytic cracking reaction results are shown in Table 2.

[0047] Comparative Example 2

[0048] Compared with Example 1, the existing double riser reactor is used, and the product and raw gas (raw gas is the same as Example 1) are used for heat exchange to preheat the raw gas to a certain temperature, and then the raw gas is heated to a reaction temperature of 550-630°C by a heating furnace, and then enters the existing double riser reactor to contact and react with a special catalyst for catalytic cracking. The diluent gas is propane, and the dilution ratio is 1:15. The special catalyst for catalytic cracking is a hollow cylindrical catalyst, the volume equivalent diameter of the catalyst is 50-90μm, and the oil and gas residence time is 1-4s; the reaction pressure is 0.2-0.6MPa(a); the weight ratio of the catalyst to the raw light naphtha is 4-50, preferably 8-40, and the weight ratio of the catalyst to the raw light naphtha in this comparative example is selected as 20; the results of the catalytic cracking reaction are shown in Table 2.

[0049] Table 1. Composition of light naphtha feedstock of Example 1

[0050] Components Weight percentage (wt%) C4 normal alkanes 0.44 C4 isoalkanes 0.03 C5 normal alkanes 12.58 C5 isoalkanes 48.80 C5 olefins 0.03 C5 Cycloalkanes 0.53 C6 normal alkanes 3.07 C6 isoalkanes 29.79 C6 Cycloalkanes 3.63 C6 Aromatics 0.47 C7 isoalkanes 0.44 C7 olefins 0.08 C7 Cycloalkanes 0.11 total 100

[0051] Table 2. Catalytic cracking reaction results of examples and comparative examples

[0052]

[0053]

[0054] Through the above comparison, it can be seen that compared with the comparative example, the process method of Example 1 of the present invention significantly improves the selectivity of ethylene and propylene, and the service life of the catalyst is longer. In addition, the present invention uses compressed high-temperature gas as a heat source for heating. The compressed high-temperature gas is formed by heating nitrogen or air and then heating and pressurizing the heat pump, and then enters the shell side to heat the tube side catalytic cracking reaction through convection heat transfer, so that the tube bundle and its internal temperature are maintained at the reaction temperature of catalytic cracking 550-630°C. Compared with the existing direct heating of the heat carrier to the heating temperature for the catalytic cracking reaction and the traditional fuel furnace burning fuel heat radiation heating method, the heating method of the present invention is more energy-saving, environmentally friendly and safer. The present invention uses the shell and tube convection heat transfer of the tube and tube fixed bed reactor to continuously heat the reaction. Compared with the existing fluidized bed reactor and the non-tube fixed bed reactor, the process flow of the present invention is simple and easy to operate, the equipment cost is low, the raw materials are heated more evenly, the heating efficiency is good, and the energy utilization rate is high.

[0055] The above is only an embodiment of the present invention, and does not limit the present invention in any form. The present invention can also have other forms of embodiments according to the above structures and functions, which are not listed one by one. Therefore, any simple modification, equivalent change and modification made by any technician familiar with the profession to the above embodiment according to the technical essence of the present invention without departing from the scope of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor, characterized in that The tubular fixed bed reactor comprises a shell (1), a plurality of longitudinally arranged tube bundles (2) are arranged in the shell (1), a catalyst (11) dedicated for catalytic cracking is filled in the tube bundles (2), the upper end of the shell (1) is connected to a bed feed side tube box (3), and the lower end is connected to a bed discharge side tube box (4), a reactor tube side inlet (9) and a reactor tube side outlet (10) are respectively arranged at the top of the bed feed side tube box (3) and the bottom of the bed discharge side tube box (4), a reactor shell side inlet (7) and a reactor shell side outlet (8) are arranged on the side wall of the shell (1), and the central axis of the reactor shell side inlet (7) and the central axis of the reactor shell side outlet (8) are located in the same vertical plane; any one of the reactor shell side inlet (7) and the reactor shell side outlet (8) is arranged at the upper part of the side wall of the shell (1), and the other is arranged at the lower part of the side wall of the shell (1); The steps of using the tubular fixed bed reactor to catalytically crack light hydrocarbons to prepare ethylene and propylene include: using gaseous light hydrocarbons as reaction raw materials, preheating the gaseous light hydrocarbon raw materials mixed with diluent gas, entering the bed feed side pipe box (3) from the reactor tube side inlet (9), and then entering the tube bundle (2) for catalytic cracking reaction, and the product enters the bed discharge side pipe box (4) from the lower end of the tube bundle (2), and then is discharged through the reactor tube side outlet (10); compressed high-temperature gas as a heat source enters the tubular fixed bed reactor from the reactor shell side inlet (7) for convective heat transfer, provides heat for the catalytic cracking reaction, maintains the tube bundle and its internal temperature at the reaction temperature of catalytic cracking, and the compressed high-temperature gas enters the tubular fixed bed reactor for heat exchange and is discharged from the reactor shell side outlet (8) for recycling.

2. The method for preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor as claimed in claim 1, characterized in that The top and bottom of the shell (1) are respectively provided with a bed feed side tube sheet (5) and a bed discharge side tube sheet (6); the bed feed side tube sheet (5) and the bed discharge side tube sheet (6) are both tightly connected to the inner wall of the shell (1); a feed hole and a discharge hole are respectively provided on the bed feed side tube sheet (5) and the bed discharge side tube sheet (6); the upper end of the tube bundle (2) is connected to the feed hole, and the lower end is connected to the discharge hole.

3. The method for preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor as claimed in claim 1, characterized in that A baffle is also provided inside the shell (1).

4. The method for preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor as claimed in claim 1, characterized in that The feed temperature at the reactor tube inlet is 600-630°C, the discharge temperature at the reactor tube outlet is 550-570°C, the average reaction temperature in the tube bundle is 550-630°C, the reaction pressure is -0.1-0.5MPa(a), and the weight hourly space velocity is 0.5-15h -1 .

5. The method for preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor as claimed in claim 1, characterized in that The catalyst density in the tube bundle is 600-800 kg / m 3 The linear velocity of the gaseous light raw material mixed with diluent gas entering the reactor is 0.8 to 8 m / s.

6. The method for preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor as claimed in claim 1, characterized in that The light hydrocarbon feedstock is selected from one or more of isobutane, normal butane, butene, normal pentane, isopentane, neopentane, cyclopentane, C5 olefins, pentane oil, topped oil, raffinate, light naphtha, catalytic cracking gasoline, catalytic pyrolysis gasoline, coker gasoline, thermal pyrolysis gasoline, coal-based naphtha and hydrocracking naphtha.

7. The method for preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor as claimed in claim 1 or 6, characterized in that The diluent gas is selected from one of nitrogen, hydrogen, methane, ethane, propane, butane, refinery dry gas, liquefied gas, and CO2; the molar ratio of the diluent gas to the light hydrocarbon is 1:10-30.

8. The method for preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor as claimed in claim 1, characterized in that The heat carrier is nitrogen or air, which is heated to 400-500°C and then heated and pressurized to 600-650°C by a heat pump to become a compressed high-temperature gas to provide heat for the catalytic cracking reaction in the tube bundle.

9. The method for preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor as claimed in claim 1, characterized in that The shape of the catalyst for catalytic cracking is at least cylindrical, hollow cylindrical, spherical, hollow spherical, or butterfly-shaped, and its active components include one or more of ZSM-5, ZSM-23, ZSM-11, β, and SAPO-34, or the catalyst described in patent CN115888797A.

10. The method for preparing ethylene and propylene by catalytic cracking of light hydrocarbons using a tubular fixed bed reactor as claimed in claim 9, characterized in that The volume equivalent diameter of the special catalyst for catalytic cracking is 1 to 8 mm, and the length of the hollow cylindrical catalyst is 1 to 8 mm.

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