A method and system for improving the quality of a hydrocarbon stream

Abstract

The present application relates to a method and system for improving the quality of a hydrocarbon stream. The method for improving the quality of a hydrocarbon stream of the present application comprises the following steps: 1) providing a hydrocarbon stream containing C5-C6 isomeric alkanes, wherein the content of the C5-C6 isomeric alkanes in the hydrocarbon stream is 60-90 wt%, based on the total weight of the hydrocarbon stream being 100 wt%, and 2) converting at least a portion of the C5-C6 isomeric alkanes into C2-C6 n-alkanes in the presence of hydrogen to obtain a conversion product. According to the present application, low-quality ethylene raw materials can be effectively converted into high-quality ethylene raw materials. The hydrocarbon stream after hydroconversion can significantly increase the content of n-alkanes in the hydrogenation product, thereby improving the ethylene and triene yield of the ethylene device. The process is simple, the operation difficulty is low, and it has very good economic benefits.

Description

Technical Field

[0001] This invention relates to the field of petrochemical technology, and more specifically, to a method and system for improving the quality of hydrocarbon feedstocks. Background Technology

[0002] In petroleum processing, C5 and C6 isoalkanes are generally obtained through cracking processes such as crude oil separation or hydrocracking. Due to their small molecular weight, high bond energy between atoms, and weak molecular polarity, they are difficult to undergo further chemical reactions in conventional cracking processes such as hydrocracking or catalytic cracking. Currently, there are two main ways to utilize C5 and C6 isoalkanes: one is to use them directly as gasoline blending components, but due to the influence of saturated vapor pressure, the amount added when used as a gasoline blending component is relatively low; the other is to use them as feedstock for steam cracking to produce ethylene, but the inventors of this invention have found that isoalkanes have relatively low yields of both ethylene and trienes during thermal cracking, and therefore are not high-quality ethylene feedstocks.

[0003] With the rapid development of my country's chemical industry, ethylene production capacity has increased year by year. As a result, the demand for ethylene feedstock has also been increasing. How to broaden the selection range of ethylene feedstock and how to obtain high-quality ethylene feedstock have become urgent problems to be solved in the development of the ethylene industry. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a hydrogenation conversion method for C5 and C6 isoalkanes, which can effectively convert isoalkanes with poor cracking performance into C2-C6 n-alkanes with better cracking performance, thereby significantly improving the yield of ethylene and trienes in ethylene plants. The triene yield refers to the mass yield of ethylene, propylene, and butadiene.

[0005] Specifically, the present invention relates to the following aspects.

[0006] 1. A method for improving the quality of a hydrocarbon feed stream, comprising the following steps:

[0007] 1) Providing a hydrocarbon stream containing C5-C6 isoalkanes, wherein the content of the C5-C6 isoalkanes in the hydrocarbon stream is 60-90 wt% (preferably 70-80 wt%), and based on a total weight of 100 wt% of the hydrocarbon stream, and

[0008] 2) At least a portion (e.g., more than 30 wt%, more than 40 wt%, more than 50 wt%, more than 60 wt%, more than 70 wt%, more than 80 wt%, or more than 90 wt%) of the C5-C6 isoalkanes are converted into C2-C6 n-alkanes in the presence of hydrogen to obtain the conversion product.

[0009] 2. The method according to any of the foregoing or the following, wherein the initial boiling point of the hydrocarbon stream is 10-30°C (preferably 15-25°C) and the final boiling point is 50-100°C (preferably 55-70°C).

[0010] 3. The method according to any of the foregoing or hereinafter described, wherein the hydrocarbon stream contains C 7+ The hydrocarbon content is 0-10 wt% (preferably 0.5-5 wt%), the C5-C6 n-alkanes content is 10-30 wt% (preferably 15-25 wt%), the C4-hydrocarbon content is 0-10 wt% (preferably 2-5 wt%), and the cyclic hydrocarbon content is 1-10 wt% (preferably 2-5 wt%), based on a total weight of 100 wt% of the hydrocarbon stream, and / or, the conversion product has a C7+ hydrocarbon content of not more than 5 wt% (preferably not more than 1 wt%), a C5-C6 isoalkanes content of 0-50 wt% (preferably 10-40 wt%), a C2-C6 n-alkanes content of 40-90 wt% (preferably 50-80 wt%), and a cyclic hydrocarbon content of not more than 3 wt% (preferably not more than 1 wt%), based on a total weight of 100 wt% of the conversion product.

[0011] 4. The method according to any of the foregoing or the following, wherein the hydrocarbon feed stream is a light naphtha component obtained by cracking (e.g., hydrocracking or catalytic cracking) a hydrocarbon feedstock.

[0012] 5. The method according to any of the foregoing or hereinafter, wherein the conversion reaction is carried out in the presence of a catalyst, and the catalyst comprises a molecular sieve and an active metal component.

[0013] 6. The method according to any of the foregoing or hereinafter, wherein the molecular sieve is a molecular sieve with shape-selective catalytic properties, preferably selected from one or more of mordenite, ZSM molecular sieve, SAPO molecular sieve and EU-1 molecular sieve, more preferably selected from one or more of mordenite and ZSM molecular sieve, particularly preferably selected from one or more of mordenite, ZSM-5 molecular sieve, ZSM-11 molecular sieve, ZSM-12 molecular sieve, ZSM-22 molecular sieve, ZSM-23 molecular sieve, ZSM-35 molecular sieve, Beta molecular sieve and ZSM-38 molecular sieve, especially selected from one or more of mordenite and ZSM-5 molecular sieve.

[0014] 7. The method according to any of the foregoing or the following aspects, wherein the catalyst further comprises a binder (preferably alumina), and the binder content is 5-65 wt% (preferably 10-35 wt%) based on the weight of the catalyst.

[0015] 8. The method according to any of the foregoing or the following aspects, wherein the active metal component is selected from one or more of Group VIB metals and Group VIII non-precious metals of the periodic table, wherein the Group VIB metal is preferably selected from one or more of molybdenum and tungsten (particularly preferred), and wherein the Group VIII non-precious metal is preferably selected from one or more of cobalt and nickel (particularly preferred).

[0016] 9. The method according to any of the foregoing or the following, wherein the content of the Group VIB metal (based on oxides) is 5.0-30.0 wt% (preferably 10-20 wt%) based on the weight of the catalyst, and the content of the Group VIII non-precious metal (based on oxides) is 0.5-15.0 wt% (preferably 3-10 wt%).

[0017] 10. The method according to any of the foregoing or the following, wherein the content of the molecular sieve is 30-80 wt% (preferably 40-70 wt%) based on the weight of the catalyst.

[0018] 11. The method according to any one of the foregoing or the following aspects, wherein the specific surface area of ​​the catalyst is 200-400 m². 2 / g, with a pore volume of 0.25-0.45mL / g.

[0019] 12. The method according to any one of the foregoing or the following, wherein the reaction conditions of the conversion reaction include: a reaction pressure of 0.5-10.0 MPaG (preferably 2.0-8.0 MPaG or 2.0-5.0 MPaG), a reaction temperature of 250-500°C (preferably 350-450°C), and a liquid hourly space velocity of 0.1-15.0 h⁻¹. -1 (Preferred 0.5-5.0h) -1 The hydrogen-to-oil volume ratio is 10:1-2500:1 (preferably 100:1-2000:1 or 100:1-1000:1).

[0020] 13. The method according to any of the foregoing or hereinafter, wherein the operating conditions for the steam cracking include: a reaction temperature of 750-900°C, a reaction pressure of 0.1-0.5 MPaG, and a water-to-oil mass ratio of 0.2-0.6.

[0021] 14. The method according to any of the foregoing or hereinafter described further comprises the following step:

[0022] The conversion products are separated to obtain a separate stream mainly composed of C2-C6 n-alkanes (e.g., accounting for more than 80 wt%, 90 wt%, or 95 wt% of the total amount), and

[0023] Steam cracking of the separated feed stream yields cracking products containing ethylene.

[0024] 15. The method according to any of the foregoing or hereinafter, wherein the weight ratio of the separated feed stream to the hydrocarbon feed stream is 0.4-0.9:1 (preferably 0.5-0.8:1).

[0025] 16. The method according to any of the foregoing or hereinafter described further comprises the following step:

[0026] The conversion products are separated to obtain a n-alkanes stream dominated by C4-C6 (e.g., accounting for more than 80 wt%, 90 wt%, or 95 wt% of the total) and / or a low-carbon stream dominated by C2-C3 hydrocarbons (e.g., accounting for more than 90 wt% or 95 wt% of the total).

[0027] Steam cracking of the orthocarbon feed stream and / or the low-carbon feed stream yields cracking products containing ethylene.

[0028] 17. A system for improving the quality of a hydrocarbon feed stream, comprising the following units:

[0029] 1) A hydrocarbon feed stream providing unit configured to provide a hydrocarbon feed stream containing C5-C6 isoalkanes, wherein the content of the C5-C6 isoalkanes in the hydrocarbon feed stream is 60-90 wt% (preferably 70-80 wt%), and based on a total weight of 100 wt% of the hydrocarbon feed stream, and

[0030] 2) A hydrocarbon feed conversion unit, configured to convert at least a portion (e.g., more than 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, or 90 wt%) of the C5-C6 isoalkanes into C2-C6 n-alkanes in the presence of hydrogen, thereby obtaining the conversion product.

[0031] Technical effect

[0032] Compared with the prior art, the method and system provided by the present invention can achieve one or more or a combination of the following technical effects:

[0033] 1. For hydrocracking reactions, smaller molecules are more difficult to crack, especially small-molecule hydrocarbons such as C5 and C6. It is necessary to ensure that reactants have a certain residence time in the catalyst channels. Furthermore, when the goal is to produce n-alkanes, the molecular sieve of the catalyst needs to have a straight-channel structure, which is more conducive to the formation of n-alkanes. Therefore, when processing feedstocks rich in C5 and C6 isoalkanes, catalysts with special channel structures need to be selected. The inventors have discovered that shape-selective molecular sieves exhibit excellent reaction performance for directly smaller molecules (including n-alkanes and short-branched isoalkanes), and can effectively convert C5 and C6 isoalkanes. Hydroconversion of hydrocarbon streams containing C5 and C6 isoalkanes can significantly improve the yield of terenes in steam cracking ethylene plants, thereby improving the economic efficiency of the ethylene plant.

[0034] 2. The processing capacity of an ethylene plant is based on the ethylene yield. The higher the ethylene yield, the less raw material the ethylene plant consumes. Since raw material costs account for more than 60% of the processing cost of an ethylene plant, increasing the ethylene yield can significantly reduce the processing cost of the ethylene plant.

[0035] 3. The C5 and C6 isoalkanes content in the hydrocarbon feed stream is controlled at 60-90%. Since hydroconversion mainly involves two reactions—ortho-alkanes and cracking—ortho-alkanes are the more ideal reaction pathway because they do not consume hydrogen. The inventors discovered that the ortho-alkanes reaction of isoalkanes is affected by chemical equilibrium. A high content of n-alkanes in the reactants inhibits the ortho-alkanes reaction, while an excessively low content of isoalkanes leads to the loss of n-alkanes in the feedstock, causing C5 and C6 n-alkanes to be converted into isoalkanes or small-molecule n-alkanes, resulting in poor product quality or unnecessary hydrogen consumption. In current petroleum processing, hydrocracking and catalytic cracking, which follow the carbocation reaction mechanism, produce C5 and C6 products rich in isoalkanes, but these isoalkanes do not exceed 90%. Obtaining feedstocks with higher isoalkane content requires special separation methods, including adsorption separation and distillation, which consume significant amounts of energy, greatly increasing processing costs. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a process flow of the present invention.

[0037] exist Figure 1 In the diagram, 1-hydrocarbon feed, 2-hydrogen, 3-hydrogenation conversion reaction zone, 4-hydrogenation conversion reaction zone effluent, 5-high pressure separator, 6-hydrogen-rich gas phase stream, 7-liquid phase stream.

[0038] Figure 2 This is a schematic diagram of a process flow of the present invention.

[0039] exist Figure 2 In the diagram, 1-hydrocarbon feed, 2-hydrogen, 3-hydrogenation conversion reaction zone, 4-hydrogenation conversion reaction zone effluent, 5-high pressure separator, 6-hydrogen-rich gas phase stream, 7-liquid phase stream, 8-fractionation tower, 9-gas phase product, 10-liquid phase product. Detailed Implementation

[0040] The specific embodiments of the present invention will be described in detail below. However, it should be noted that the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the claims in the appendix.

[0041] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0042] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0043] In the context of this invention, all numerical values ​​of parameters (e.g., quantity or condition) should be understood to be modified by the term “about” in all cases, regardless of whether “about” actually appears before the numerical value.

[0044] In the context of this invention, unless otherwise specified, the various devices used in this invention may use structures conventionally chosen in the art, and there are no particular limitations.

[0045] In the context of this invention, the initial boiling point and final boiling point are measured in accordance with ASTM D86 measurement method.

[0046] In the context of this invention, the term "C2-C6 n-alkanes" refers to n-alkanes with 2 to 6 carbon atoms. It should be particularly clarified that although there is no distinction between n-alkanes and isoalkanes among alkanes with 2 to 3 carbon atoms, for ease of description, this invention also considers alkanes with 2 to 3 carbon atoms as n-alkanes. Furthermore, unless otherwise specified, this invention may use the term to refer to any one or more of n-alkanes with 2 to 6 carbon atoms, or it may refer to all n-alkanes with 2 to 6 carbon atoms.

[0047] In the context of this invention, cyclic hydrocarbons refer to hydrocarbons such as cycloalkanes and aromatics that have a cyclic structure in their molecular structure.

[0048] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this instruction manual are based on weight, and the pressure is gauge pressure.

[0049] In the context of this invention, any two or more embodiments or aspects of this invention can be arbitrarily combined, and the resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of this invention.

[0050] According to one embodiment of the present invention, a method for improving the quality of a hydrocarbon feed stream is provided. Here, "improving quality" refers to altering the chemical composition of the hydrocarbon feed stream through chemical conversion, making it easier to convert into high-value-added products such as ethylene through subsequent chemical treatment (such as steam cracking).

[0051] According to one embodiment of the present invention, the method includes the step of providing a hydrocarbon feed stream containing C5-C6 isoalkanes. According to the present invention, the hydrocarbon feed stream can be produced by any method known in the art, as long as it meets the requirements of the present invention for the hydrocarbon feed stream. Examples of methods for producing the hydrocarbon feed stream include hydrocracking, catalytic cracking, or atmospheric and vacuum distillation. Preferably, the initial boiling point of the hydrocarbon feed stream is 10-30°C (preferably 15-25°C), and the final boiling point is 50-100°C (preferably 55-70°C). More preferably, the hydrocarbon feed stream is a light naphtha component obtained by hydrocracking a hydrocarbon feedstock.

[0052] According to one embodiment of the present invention, in order to achieve the technical effects of the present invention, the content of C5-C6 isoalkanes in the hydrocarbon stream is generally 60-90 wt%, preferably 70-80 wt%, based on a total weight of 100 wt% of the hydrocarbon stream. According to the present invention, the isoalkanes in the hydrocarbon stream must have a certain proportion. If the isoalkanes content is too low, the increase in the proportion of n-alkanes in the product is limited, and some n-alkanes will be cracked, resulting in hydrogen loss. If the isoalkanes content is too high, conventional separation methods cannot obtain them, requiring adsorption separation or distillation, which consumes a lot of energy.

[0053] According to one embodiment of the present invention, C in the hydrocarbon stream 7+ There is no particular limitation on the hydrocarbon content, but in order to make the technical effect of the present invention more excellent, the C content in the hydrocarbon stream is... 7+ The hydrocarbon content is generally 0-10 wt% (preferably 0.5-5 wt%), based on a total hydrocarbon stream weight of 100 wt%. The inventors of this invention have discovered that C in the hydrocarbon stream... 7+Excessive hydrocarbon content will result in the inclusion of a certain amount of aromatic hydrocarbons. However, aromatic hydrocarbons are difficult to convert effectively under the conversion reaction conditions of this invention (e.g., the conversion rate is generally less than 10%) and thus exhibit inert reaction properties. Therefore, C 7+ Excessive hydrocarbon content will significantly inhibit the conversion activity of the hydrocarbon feed stream in this invention, which is detrimental to this invention.

[0054] According to one embodiment of the present invention, there is no particular limitation on the content of C5-C6 n-alkanes in the hydrocarbon feed stream. However, in order to improve the technical effect of the present invention, the content of C5-C6 n-alkanes in the hydrocarbon feed stream is generally 10-30 wt% (preferably 15-25 wt%), based on a total weight of 100 wt% of the hydrocarbon feed stream. The inventors of the present invention have found that a high content of n-alkanes in the hydrocarbon feed stream will inhibit the conversion reaction of isoalkanes, and the increase in n-alkanes after conversion is limited, resulting in a small impact on the ethylene yield.

[0055] According to one embodiment of the present invention, there is no particular limitation on the content of C4-hydrogen in the hydrocarbon stream. However, in order to improve the technical effect of the present invention, the content of C4-hydrogen in the hydrocarbon stream is generally 0-10 wt% (preferably 2-5 wt%), based on a total weight of 100 wt% of the hydrocarbon stream. The inventors of the present invention have discovered that C4-hydrogen is gaseous at room temperature and pressure and has limited solubility in C5-C6 hydrocarbons. Therefore, to obtain a hydrocarbon stream with a high C4-hydrogen content, a special manufacturing method is required, which will significantly increase the manufacturing cost of the hydrocarbon stream of the present invention. Furthermore, the inventors of the present invention have discovered that, compared with C5-C6 isoalkanes, C4 hydrocarbons are more difficult to effectively convert under the conversion reaction conditions of the present invention (e.g., the conversion rate is generally less than 20%). Therefore, an excessively high content of C4 hydrocarbons will significantly inhibit the conversion activity of the hydrocarbon stream of the present invention, which is detrimental to the present invention.

[0056] According to one embodiment of the present invention, there is no particular limitation on the content of cyclic hydrocarbons in the hydrocarbon feed stream. However, in order to improve the technical effect of the present invention, the content of cyclic hydrocarbons in the hydrocarbon feed stream is generally 1-10 wt% (preferably 2-5 wt%), based on a total weight of 100 wt% of the hydrocarbon feed stream. The inventors of the present invention have discovered that cycloalkanes with fewer carbon atoms can be converted, while cycloalkanes and aromatics with higher carbon atoms are difficult to convert effectively under the process conditions of the present invention. These components entering the ethylene plant will affect the ethylene yield of the ethylene plant, which is detrimental to the present invention.

[0057] According to one embodiment of the present invention, the method includes converting at least a portion of the C5-C6 isoalkanes into C2-C6 n-alkanes in the presence of hydrogen, thereby obtaining a conversion product. Here, "at least a portion" refers to, for example, 30 wt% or more, 40 wt% or more, 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more of the total amount. According to the present invention, the conversion rate of the C5-C6 isoalkanes is not particularly limited; therefore, the conversion rate can be achieved in a single conversion reaction (single-pass conversion rate), or it can be achieved after multiple recycling processes (e.g., separating unreacted C5-C6 isoalkanes from the conversion product before performing the conversion reaction).

[0058] According to one embodiment of the present invention, the conversion reaction can be a hydronormative reaction to obtain a conversion product with C4-C6 n-alkanes as the main product, or a hydrocracking reaction to obtain a conversion product with C2-C3 hydrocarbons as the main product. The inventors of the present invention have discovered that C5 and C6 isoalkanes can undergo unimolecular and bimolecular reactions during the conversion reaction process of the present invention. Unimolecular reactions can convert isoalkanes into n-alkanes, with only a small amount of isoalkanes undergoing direct cracking reactions. Bimolecular reactions refer to the combination of two small isoalkanes into a long-chain isoalkane, followed by cracking. As described below, the inventors of the present invention have discovered that by selecting molecular sieves with shape-selective catalytic properties, especially molecular sieves with special straight-channel structures and containing a large amount of medium-strong or strong acids, and loading them with suitable hydrogenation metals, the occurrence of unimolecular and bimolecular reactions can be flexibly controlled. Moreover, since the normalization reaction is affected by the concentration of n-alkanes and isoalkanes in the reactants, a higher concentration of n-alkanes in the reactants will inhibit the normalization reaction, thus limiting the increase of the proportion of n-alkanes in the conversion product. Therefore, in order to obtain a conversion product with a higher n-alkane content, it is necessary to ensure that a certain amount of cracking reaction occurs.

[0059] According to one embodiment of the present invention, the reaction conditions for the conversion reaction include: a reaction pressure of 0.5-10.0 MPaG (preferably 2.0-8.0 MPaG or 2.0-5.0 MPaG), a reaction temperature of 250-500°C (preferably 350-450°C), and a liquid hourly space velocity of 0.1-15.0 h⁻¹. -1 (Preferred 0.5-5.0h) -1The hydrogen-to-oil volume ratio is 10:1-2500:1 (preferably 100:1-2000:1 or 100:1-1000:1). The inventors of this invention have discovered that, compared to prior art hydrocarbon feedstock conversion reactions (such as C4 hydrocarbon feedstock conversion reactions), the reaction conditions of the present invention are milder, particularly the reaction temperature is lower, typically 10-50°C lower. The inventors of this invention have also discovered that, at this lower reaction temperature, C5-C6 isoalkanes still exhibit high conversion rates; for example, C5-C6 isoalkanes can exhibit single-pass conversion rates of 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, or 90 wt% or higher under the reaction conditions of this invention. In contrast, due to their smaller molecular structure, C4 hydrocarbon molecules have a shorter residence time in the molecular sieve channels of the catalyst of this invention, making effective reactions impossible. Furthermore, the conversion of C4 hydrocarbons requires catalysts with stronger dehydrogenation capabilities, necessitating reaction temperatures much higher than those of this invention (e.g., 20-30°C higher) to achieve this process. Additionally, for C... 7+ In the conversion of components, large cycloalkanes with high carbon number have difficulty entering the catalyst channels to carry out ring-opening reactions. The cracking reaction of aromatics first requires the hydrogenation saturation of aromatics, which is directly affected by the reaction pressure. In order to achieve better conversion of isoalkanes, the reaction pressure of this invention is low, which is not conducive to the hydrogenation saturation of aromatics. Therefore, the conversion effect of aromatics is poor.

[0060] According to one embodiment of the invention, the conversion reaction is carried out in the presence of a catalyst, and the catalyst comprises a molecular sieve and an active metal component.

[0061] According to one embodiment of the present invention, the molecular sieve is a molecular sieve with shape-selective catalytic properties, preferably selected from one or more of mordenite, ZSM molecular sieve, SAPO molecular sieve, and EU-1 molecular sieve, more preferably selected from one or more of mordenite and ZSM molecular sieve, particularly preferably selected from one or more of mordenite, ZSM-5 molecular sieve, ZSM-11 molecular sieve, ZSM-12 molecular sieve, ZSM-22 molecular sieve, ZSM-23 molecular sieve, ZSM-35 molecular sieve, Beta molecular sieve, and ZSM-38 molecular sieve, especially selected from one or more of mordenite and ZSM-5 molecular sieve. Here, based on the weight of the catalyst, the content of the molecular sieve is 30-80 wt% (preferably 40-70 wt%). The inventors of the present invention have discovered that the acid strength of the molecular sieve directly affects the reaction characteristics of isoalkanes. Molecular sieves with more strong acid centers are more prone to cracking reactions, such as ZSM-5 molecular sieve; while those with more moderately strong acid centers are more prone to normalization reactions, such as mordenite. Therefore, according to the present invention, different reaction pathways can be achieved by selecting the acid strength of the molecular sieve.

[0062] According to one embodiment of the present invention, the active metal component is an active non-precious metal component, preferably selected from one or more of Group VIB metals and Group VIII non-precious metals of the periodic table. The Group VIB metals are preferably selected from one or more of molybdenum and tungsten (particularly preferred), and the Group VIII non-precious metals are preferably selected from one or more of cobalt and nickel (particularly preferred). Here, based on the weight of the catalyst, the content of the Group VIB metals (calculated as oxides) is 5.0-30.0 wt% (10.0-20.0 wt%), and the content of the Group VIII non-precious metals (calculated as oxides) is 0.5-15.0 wt% (preferably 3.0-10.0 wt%).

[0063] According to one embodiment of the invention, the catalyst further includes a binder. The type of binder can be conventionally chosen in the art, including but not limited to alumina and silicon dioxide, with alumina being preferred. Here, the binder content is 5-65 wt% (preferably 10-35 wt%) based on the weight of the catalyst.

[0064] According to one embodiment of the present invention, the catalyst has a specific surface area of ​​200-400 m². 2 / g, with a pore volume of 0.25-0.45mL / g.

[0065] According to one embodiment of the present invention, the catalyst can be prepared according to conventional methods in the art. The preparation method includes the preparation of a support and the loading of an active metal component, wherein the support preparation process is as follows: the molecular sieve and the binder are mechanically mixed, shaped, and then dried and calcined to form a catalyst support. The drying and calcination of the support can be performed under conventional conditions. The drying conditions are: drying at 100℃-150℃ for 1-12 hours. The calcination conditions are: calcination at 450℃-550℃ for 2.5-6.0 hours.

[0066] According to one embodiment of the present invention, in the method for preparing the catalyst, the method for loading the active metal component is a conventional method, such as kneading, impregnation, etc., with impregnation being preferred. The impregnation method can be a saturated impregnation method, an excess impregnation method, or a complex impregnation method, that is, impregnating the catalyst support with a solution containing the desired active metal component, followed by drying and calcination to obtain the first catalyst. The drying conditions are: drying at 100℃-150℃ for 1-12 hours. The calcination conditions are: calcination at 450℃-550℃ for 2.5-6.0 hours.

[0067] According to one embodiment of the present invention, from the perspective of balancing the quality improvement effect and energy consumption, the content of C7+ hydrocarbons in the conversion product is not higher than 5 wt% (preferably not higher than 1 wt%), the content of C5-C6 isoalkanes is 0-50 wt% (preferably 10-40 wt%), the content of C2-C6 n-alkanes is 40-90 wt% (preferably 50-80 wt%), and the content of cyclic hydrocarbons is not higher than 3 wt% (preferably not higher than 1 wt%), based on a total weight of 100 wt% of the conversion product.

[0068] According to one embodiment of the present invention, the method further includes the following step: separating the conversion product to obtain a separated stream mainly composed of the C2-C6 n-alkanes (e.g., accounting for more than 80 wt%, 90 wt%, or 95 wt% of the total). Depending on the specific conversion rate, unreacted C5-C6 isoalkanes may also be obtained through this separation. The unreacted C5-C6 isoalkanes can be recycled and continued to undergo conversion reactions together with the feedstock hydrocarbon stream, thereby converting a higher proportion of C5-C6 isoalkanes into C2-C6 n-alkanes.

[0069] According to one embodiment of the present invention, the weight ratio of the separated feed stream to the hydrocarbon feed stream is 0.4-0.9:1 (preferably 0.5-0.8:1).

[0070] According to this embodiment of the invention, the method further includes the following steps: separating the conversion products to obtain a normal-carbon feed stream mainly composed of C4-C6 n-alkanes (e.g., accounting for more than 80 wt%, 90 wt%, or 95 wt% of the total) and / or a low-carbon feed stream mainly composed of C2-C3 hydrocarbons (e.g., accounting for more than 90 wt% or 95 wt% of the total). Depending on the specific conversion rate, unreacted C5-C6 isoalkanes may also be obtained through this separation. The unreacted C5-C6 isoalkanes can be recycled and continued to undergo conversion reactions together with the feed hydrocarbon stream, thereby converting a higher proportion of C5-C6 isoalkanes into C2-C6 n-alkanes.

[0071] According to one embodiment of the invention, the conversion product, the separated feed stream, the ortho-form feed stream, or the low-carbon feed stream exhibits high chemical activity compared to the hydrocarbon feed stream, and therefore can be advantageously used in chemical processes such as steam cracking, alkane degassing, and hydrocracking to obtain high-value-added chemicals, preferably for steam cracking to produce ethylene.

[0072] According to one embodiment of the present invention, the conversion product, the separated feed stream, the ortho-form feed stream, or the low-carbon feed stream are steam-cracked to obtain a cracking product containing ethylene. According to the present invention, the conversion product, the separated feed stream, the ortho-form feed stream, or the low-carbon feed stream are ideal ethylene cracking feedstocks, and the ethylene yield using these feed streams is generally above 30 wt%, thereby providing a high-value utilization pathway for low-value hydrocarbon feed streams in the prior art.

[0073] According to one embodiment of the present invention, the operating conditions for the steam cracking include: a reaction temperature of 750-900°C, a reaction pressure of 0.1-0.5 MPaG, and a water-to-oil mass ratio of 0.2-0.6.

[0074] According to one embodiment of the present invention, a system for improving the quality of a hydrocarbon stream also relates to, comprising a hydrocarbon stream supply unit and a hydrocarbon stream conversion unit. According to the present invention, the system is specifically designed for implementing the methods described above in this specification; therefore, apart from the content explicitly stated in this paragraph, any content or matter not explicitly stated can be directly referred to the corresponding content or matter described above in relation to the methods, without any particular limitation.

[0075] The present invention will be further described below with reference to the accompanying drawings, but the present invention is not limited thereto.

[0076] according to Figure 1 The hydrocarbon feed stream 1 is mixed with hydrogen gas 2 and enters the hydroconversion reaction zone 3. The effluent 4 from the hydroconversion reaction zone enters the high-pressure separator 5. The separated gaseous stream 6, rich in hydrogen, is recycled, while the liquid stream is used as ethylene feedstock.

[0077] according to Figure 2 The hydrocarbon feed stream 1 is mixed with hydrogen gas 2 and enters the hydroconversion reaction zone 3. The effluent 4 from the hydroconversion reaction zone enters the high-pressure separator 5. The separated gaseous stream 6, rich in hydrogen, is recycled. The liquid stream 7 enters the fractionation tower to separate the gaseous product 9, which is used as ethylene feedstock. The liquid product 10 is recycled back to the inlet of the hydroconversion reaction zone 3.

[0078] Example

[0079] The present invention will be further described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0080] In the following examples and comparative examples, the ethylene yield is calculated as a percentage of the ethylene production to the feed amount of the ethylene plant. The processing benefit per ton of oil refers to the revenue obtained from processing 1 ton of raw material, and is calculated as (ethylene product price - raw material and hydrogen price - processing energy consumption) / processing volume. The benchmark for the processing benefit per ton of oil is that the raw material is used directly as ethylene feedstock without undergoing hydrogenation conversion.

[0081] In the following examples and comparative examples, each hydroconversion catalyst is designated as Cat-A followed by a number, such as Cat-A1, Cat-A2, Cat-A3, etc. The hydroconversion catalysts were prepared using a conventional active metal saturation impregnation method, and the physicochemical properties of the obtained catalysts are shown in Table 1.

[0082] The preparation methods for Cat-A1 to Cat-A3 catalysts are as follows:

[0083] (1) Select mordenite with a SiO2 / Al2O3 molar ratio of 15 and mechanically mix it with a binder, shape it, dry it at 120°C for 10 hours, and calcine it at 500°C for 4 hours to prepare a catalyst support.

[0084] (2) The catalyst support obtained in step (1) containing active components is dried at 120°C for 10 hours and calcined at 500°C for 4 hours to prepare a hydrogenation conversion catalyst.

[0085] The preparation methods for Cat-A4 to Cat-A7 catalysts are as follows:

[0086] (1) Select ZSM-5 with a SiO2 / Al2O3 molar ratio of 10 and mechanically mix it with the binder, shape it, dry it at 120℃ for 10 hours, and calcine it at 500℃ for 4 hours to prepare a catalyst support.

[0087] (2) The catalyst support obtained in step (1) containing active components is dried at 120°C for 10 hours and calcined at 500°C for 4 hours to prepare a hydrogenation conversion catalyst.

[0088] The properties of the raw materials are shown in Table 2. Among them, raw material 5 requires isoparaffinic raw materials to be obtained through adsorption separation or distillation.

[0089] Table 1

[0090]

[0091] Table 2

[0092]

[0093] Example 1

[0094] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0095] (1) Raw material 1 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A1;

[0096] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0097] In this example, approximately 49 wt% of the total C5-C6 isoalkanes were converted to C2-C6 n-alkanes. The weight ratio of the liquid stream to feedstock 1 was 0.30:1.

[0098] Example 2

[0099] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0100] (1) Raw material 1 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A2;

[0101] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0102] In this example, approximately 45 wt% of the total C5-C6 isoalkanes were converted to C2-C6 n-alkanes. The weight ratio of the liquid stream to feedstock 1 was 0.37:1.

[0103] Example 3

[0104] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0105] (1) Raw material 1 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A3;

[0106] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0107] In this example, approximately 34 wt% of the total C5-C6 isoalkanes were converted to C2-C6 n-alkanes. The weight ratio of the liquid stream to feedstock 1 was 0.62:1.

[0108] Example 4

[0109] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0110] (1) Raw material 1 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A4;

[0111] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0112] In this example, approximately 64 wt% of the total C5-C6 isoalkanes were converted to C2-C6 n-alkanes. The weight ratio of the liquid stream to feedstock 1 was 0.06:1.

[0113] Example 5

[0114] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0115] (1) Raw material 1 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A5;

[0116] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0117] In this example, approximately 60 wt% of the total C5-C6 isoalkanes were converted to C2-C6 n-alkanes. The weight ratio of the liquid stream to feedstock 1 was 0.15:1.

[0118] Example 6

[0119] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0120] (1) Raw material 1 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A6;

[0121] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0122] In this example, approximately 52 wt% of the total C5-C6 isoalkanes were converted to C2-C6 n-alkanes. The weight ratio of the liquid stream to feedstock 1 was 0.24:1.

[0123] Example 7

[0124] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 2 The process includes:

[0125] (1) Raw material 1 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A4;

[0126] (2) In step (1), the effluent from the hydroconversion reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the C2 and C3 obtained from the liquid stream are used as ethylene feedstock. The remaining stream (referred to as the C4-C6 recycled stream) is cracked. The process conditions and quality improvement results in this example are shown in Table 3.

[0127] In this example, approximately 78 wt% of the total C5-C6 isoalkanes were converted to C2-C3 n-alkanes. The weight ratio of the C4-C6 recycled stream to feedstock 1 was 0.3:1.

[0128] Example 8

[0129] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 2 The process includes:

[0130] (1) Raw material 1 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A5;

[0131] (2) In step (1), the effluent from the hydroconversion reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the C2 and C3 obtained from the liquid stream are used as ethylene feedstock. C4-C6 are then recycled for cracking. The process conditions and quality improvement results in this example are shown in Table 3.

[0132] In this example, approximately 78 wt% of the total C5-C6 isoalkanes were converted to C2-C3 n-alkanes. The weight ratio of the C4-C6 recycled stream to feedstock 1 was 0.4:1.

[0133] Example 9

[0134] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 2 The process includes:

[0135] (1) Raw material 1 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A5;

[0136] (2) In step (1), the effluent from the hydroconversion reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the C2 and C3 obtained from the liquid stream are used as ethylene feedstock. C4-C6 are then recycled for cracking. The process conditions and quality improvement results in this example are shown in Table 3.

[0137] In this example, approximately 78 wt% of the total C5-C6 isoalkanes were converted to C2-C3 n-alkanes. The weight ratio of the C4-C6 recycled stream to feedstock 1 was 0.3:1.

[0138] Example 10

[0139] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0140] (1) Raw material 2 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A1;

[0141] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0142] In this example, approximately 34 wt% of the total C5-C6 isoalkanes were converted to C2-C6 n-alkanes. The weight ratio of the liquid stream to feedstock 1 was 0.28:1.

[0143] Example 11

[0144] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0145] (1) Raw material 3 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A4;

[0146] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0147] In this example, approximately 65 wt% of the total C5-C6 isoalkanes were converted to C2-C6 n-alkanes. The weight ratio of the liquid stream to feedstock 1 was 0.17:1.

[0148] Example 12

[0149] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0150] (1) Raw material 1 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A1;

[0151] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0152] In this example, approximately 27 wt% of the total C5-C6 isoalkanes were converted to C2-C6 n-alkanes. The weight ratio of the liquid stream to feedstock 1 was 0.72:1.

[0153] Comparative Example 1

[0154] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0155] (1) Raw material 4 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A1;

[0156] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0157] Comparative Example 2

[0158] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0159] (1) Raw material 4 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A4;

[0160] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0161] Comparative Example 3

[0162] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0163] (1) Raw material 5 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A1;

[0164] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0165] Comparative Example 4

[0166] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0167] (1) Raw material 5 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A4;

[0168] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0169] Comparative Example 5

[0170] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0171] (1) Raw material 1 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A7;

[0172] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0173] Comparative Example 6

[0174] Methods to improve the quality of hydrocarbon feedstock include, for example Figure 1 The process includes:

[0175] (1) Raw material 6 is mixed with hydrogen and enters the hydroconversion reaction zone in sequence; the hydroconversion reaction zone is filled with hydroconversion catalyst Cat-A1;

[0176] (2) In step (1), the effluent from the hydrogenation reaction zone is separated into hydrogen-rich gas and liquid stream. The hydrogen-rich gas is recycled, and the liquid stream is used directly as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0177] Table 3 Results of Quality Improvement

[0178]

[0179] Table 3 (Continued) Results of Quality Improvement

[0180]

[0181] Table 3 (Continued) Results of Quality Improvement

[0182]

[0183] The comparison shows that the method of the present invention can effectively convert low-quality ethylene feedstock into high-quality ethylene feedstock. The hydrocarbon stream after hydrogenation conversion can significantly increase the content of n-hydrocarbons in its hydrogenation products, thereby increasing the yield of ethylene and trienes in the ethylene plant. Moreover, the process is simple, easy to operate, and has very good economic benefits.

Claims

1. A method for improving the quality of a hydrocarbon feed stream, comprising the following steps: 1) Providing a hydrocarbon stream containing C5-C6 isoalkanes, wherein the content of the C5-C6 isoalkanes in the hydrocarbon stream is 60-80 wt%, and based on a total weight of 100 wt% of the hydrocarbon stream, and 2) The C5-C6 isoalkanes, comprising more than 50 wt% of the total amount, undergo a conversion reaction in the presence of hydrogen to convert them into C2-C6 n-alkanes, obtaining the conversion product. The conversion reaction is carried out in the presence of a catalyst. The catalyst comprises a molecular sieve and an active metal component, wherein the active metal component is selected from one or more metals of Group VIB and one or more non-noble metals of Group VIII of the periodic table, and the molecular sieve is a molecular sieve with shape-selective catalytic properties. Based on the weight of the catalyst, the content of the Group VIB metal, calculated as oxide, is 5.0-30.0 wt%, and the content of the Group VIII non-precious metal, calculated as oxide, is 0.5-15.0 wt%. The method further includes the following steps: Optionally, the conversion products can be separated to obtain a separated stream containing more than 80 wt% C2-C6 n-alkanes, or optionally, the conversion products can be separated to obtain a n-alkane stream containing more than 80 wt% C4-C6 n-alkanes or a low-carbon stream containing more than 90 wt% C2-C3 hydrocarbons. Steam cracking of the conversion products, the separated feed stream, the ortho-form feed stream, or the low-carbon feed stream yields cracking products containing ethylene.

2. The method according to claim 1, wherein the content of the C5-C6 isoalkanes in the hydrocarbon stream is 70-80 wt%, based on a total weight of 100 wt% of the hydrocarbon stream.

3. The method according to claim 1, wherein more than 90 wt% of the C5-C6 isoalkanes are converted into C2-C6 n-alkanes in the presence of hydrogen to obtain the conversion product.

4. The method according to claim 1, wherein the initial boiling point of the hydrocarbon stream is 10-30°C and the final boiling point is 50-100°C.

5. The method according to claim 1, wherein the initial boiling point of the hydrocarbon stream is 15-25°C and the final boiling point is 55-70°C.

6. The method according to claim 1, wherein the content of C7+ hydrocarbons in the hydrocarbon stream is 0-10 wt%, the content of C5-C6 n-alkanes is 10-30 wt%, the content of C4- hydrocarbons is 0-10 wt%, and the content of cyclic hydrocarbons is 1-10 wt%, based on a total weight of 100 wt% of the hydrocarbon stream.

7. The method according to claim 1, wherein the content of C7+ hydrocarbons in the conversion product is not higher than 5 wt%, the content of C5-C6 isoalkanes is 0-50 wt%, the content of C2-C6 n-alkanes is 40-90 wt%, and the content of cyclic hydrocarbons is not higher than 3 wt%, based on a total weight of 100 wt% of the conversion product.

8. The method according to claim 1, wherein the content of C7+ hydrocarbons in the hydrocarbon stream is 0.5-5 wt%, the content of C5-C6 n-alkanes is 15-25 wt%, the content of C4- hydrocarbons is 2-5 wt%, and the content of cyclic hydrocarbons is 2-5 wt%, based on a total weight of 100 wt% of the hydrocarbon stream.

9. The method according to claim 1, wherein the content of C7+ hydrocarbons in the conversion product is not higher than 1 wt%, the content of C5-C6 isoalkanes is 10-40 wt%, the content of C2-C6 n-alkanes is 50-80 wt%, and the content of cyclic hydrocarbons is not higher than 1 wt%, based on a total weight of 100 wt% of the conversion product.

10. The method according to claim 1, wherein the hydrocarbon feed stream is a light naphtha component obtained by cracking a hydrocarbon feedstock.

11. The method according to claim 1, wherein the molecular sieve is selected from one or more of mordenite, ZSM molecular sieve, SAPO molecular sieve and EU-1 molecular sieve.

12. The method of claim 11, wherein the molecular sieve is selected from one or more of mordenite and ZSM molecular sieve.

13. The method according to claim 1, wherein the molecular sieve is selected from one or more of mordenite, ZSM-5 molecular sieve, ZSM-11 molecular sieve, ZSM-12 molecular sieve, ZSM-22 molecular sieve, ZSM-23 molecular sieve, ZSM-35 molecular sieve, Beta molecular sieve and ZSM-38 molecular sieve.

14. The method of claim 1, wherein the catalyst further comprises a binder, and the binder content is 5-65 wt% based on the weight of the catalyst.

15. The method of claim 1, wherein the Group VIB metal is selected from one or more of molybdenum and tungsten, and the Group VIII non-precious metal is selected from one or more of cobalt and nickel.

16. The method of claim 15, wherein the Group VIB metal is molybdenum and the Group VIII non-noble metal is nickel.

17. The method according to claim 1, wherein, based on the weight of the catalyst, the content of the Group VIB metal as oxide is 10-20 wt%, and the content of the Group VIII non-precious metal as oxide is 3-10 wt%.

18. The method according to claim 1, wherein the content of the molecular sieve is 30-80 wt% based on the weight of the catalyst.

19. The method according to claim 1, wherein the content of the molecular sieve is 40-70 wt% based on the weight of the catalyst.

20. The method according to claim 1, wherein the reaction conditions for the conversion reaction include: The reaction pressure was 0.5-10.0 MPaG, the reaction temperature was 250-500℃, and the liquid hourly space velocity was 0.1-15.0 h⁻¹. -1 The hydrogen-to-oil volume ratio is 10:1-2500:

1.

21. The method according to claim 1, wherein the reaction conditions for the conversion reaction include: The reaction pressure was 2.0-5.0 MPaG, the reaction temperature was 350-450℃, and the liquid hourly space velocity was 0.5-5.0 h⁻¹. -1 The hydrogen-to-oil volume ratio is 100:1-1000:

1.

22. The method according to claim 1, wherein the content of C2-C6 n-alkanes in the separated feed stream accounts for more than 95 wt% of the total amount.

23. The method according to claim 1, wherein the content of C4-C6 n-alkanes in the n-alkane stream is more than 95 wt% of the total amount.

24. The method according to claim 1, wherein the content of C2-C3 hydrocarbons in the low-carbon feed stream is more than 95 wt% of the total amount.

25. The method according to claim 1, wherein the weight ratio of the separated feed stream to the hydrocarbon feed stream is 0.4-0.9:

1.

26. The method according to claim 1, wherein the weight ratio of the separated feed stream to the hydrocarbon feed stream is 0.5-0.8:

1.

27. The method according to claim 1, wherein the operating conditions for steam cracking include: The reaction temperature is 750-900℃, the reaction pressure is 0.1-0.5MPaG, and the water-oil mass ratio is 0.2-0.6.

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