Method and system for improving quality of hydrocarbon stream

Abstract

The invention relates to a method and system for improving the quality of a hydrocarbon stream. The method for improving the quality of the hydrocarbon material flow comprises the following steps: 1) providing a hydrocarbon material flow containing C5-C6 isoalkanes, the content of the C5-C6 isoalkanes in the hydrocarbon material flow is 60-90 wt%, and the total weight of the hydrocarbon material flow is 100 wt%; and 2) carrying out a conversion reaction on at least a part of the C5-C6 isoparaffin in the presence of hydrogen to convert the C5-C6 isoparaffin into C2-C6 n-alkanes, so as to obtain a conversion product. According to the present invention, the low-quality ethylene raw material can be effectively converted into the high-quality ethylene raw material, the hydrocarbon material flow subjected to the hydrogenation conversion can substantially improve the normal hydrocarbon content in the hydrogenation product so as to improve the ethylene and triene yield of the ethylene device, and the process has characteristics of simple process, low operation difficulty and good economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of petrochemical engineering, and in particular to a method and system for improving the quality of hydrocarbon streams. Background Art

[0002] In the process of oil processing, C5 and C6 isoparaffins can generally be obtained through reaction processes with cracking properties such as crude oil separation or hydrocracking. Due to their small molecular weight, high bond energy between atoms and weak molecular polarity, it is difficult for them to undergo further chemical reactions in conventional cracking processes such as hydrocracking or catalytic cracking. There are currently two main ways to utilize C5 and C6 isoparaffins: one is to use them directly as gasoline blending components, but due to the influence of saturated vapor pressure, the amount of them added as gasoline blending components is relatively low; the other is to use them as steam cracking ethylene raw materials, but the inventors of the present invention found that the yields of ethylene and triene in the thermal cracking process of isoparaffins are relatively low, so they are not high-quality ethylene raw materials.

[0003] With the rapid development of my country's chemical industry, the production capacity of ethylene has increased year by year. Therefore, the demand for ethylene raw materials has also continued to increase. How to broaden the selection range of ethylene raw materials and how to obtain high-quality ethylene raw materials have become urgent issues that need to be solved in the development of the ethylene industry. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for the hydrogenation conversion of C5 and C6 isoparaffins, which can effectively convert isoparaffins with poor cracking performance into C2-C6 normal alkanes with better cracking performance, thereby greatly improving the ethylene and triene yields of the ethylene plant, wherein 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 stream, comprising the following steps: 1) providing a hydrocarbon stream containing C5-C6 isoparaffins, wherein the content of the C5-C6 isoparaffins in the hydrocarbon stream is 60-90 wt% (preferably 70-80 wt%), based on the total weight of the hydrocarbon stream being 100 wt%, and 2) converting 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 into C2-C6 normal alkanes in the presence of hydrogen to obtain conversion products.

[0007] 2. The method according to any one of the preceding or following aspects, wherein the hydrocarbon stream has an initial boiling point of 10-30°C (preferably 15-25°C) and a final boiling point of 50-100°C (preferably 55-70°C).

[0008] 3. The method according to any one of the preceding or following aspects, wherein the hydrocarbon stream contains C 7+ The content of C7+ hydrocarbons in the conversion product is not higher than 5wt% (preferably not higher than 1wt%), the content of C5-C6 isoparaffins is 0-50wt% (preferably 10-40wt%), the content of C2-C6 normal alkanes is 40-90wt% (preferably 50-80wt%), and the content of cyclic hydrocarbons is not higher than 3wt% (preferably not higher than 1wt%), based on the total weight of the conversion product being 100wt%.

[0009] 4. The method according to any one of the preceding or following aspects, wherein the hydrocarbon stream is a light naphtha component obtained by cracking a hydrocarbon oil feedstock, such as hydrocracking or catalytic cracking.

[0010] 5. The method according to any one of the preceding or following aspects, 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.

[0011] 6. The method according to any one of the preceding or following aspects, wherein the molecular sieve is a molecular sieve having 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, in particular selected from one or more of mordenite and ZSM-5 molecular sieve.

[0012] 7. The method according to any one of the preceding or following aspects, wherein the catalyst further comprises a binder (preferably alumina), and the content of the binder is 5-65wt% (preferably 10-35wt%) based on the weight of the catalyst.

[0013] 8. The method according to any of the preceding or following aspects, wherein the active metal component is selected from one or more of the metals of Group VIB and the non-precious metals of Group VIII of the Periodic Table, the metal of Group VIB is preferably selected from one or more of molybdenum and tungsten (particularly preferably molybdenum), and the non-precious metal of Group VIII is preferably selected from one or more of cobalt and nickel (particularly preferably nickel).

[0014] 9. The method according to any one of the preceding or following aspects, wherein the content of the VIB group metal (calculated as oxide) is 5.0-30.0 wt% (preferably 10-20 wt%), and the content of the VIII group non-noble metal (calculated as oxide) is 0.5-15.0 wt% (preferably 3-10 wt%), based on the weight of the catalyst.

[0015] 10. The method according to any one of the preceding or following aspects, wherein the content of the molecular sieve is 30-80 wt% (preferably 40-70 wt%) based on the weight of the catalyst.

[0016] 11. The method according to any one of the preceding or following aspects, wherein the specific surface area of ​​the catalyst is 200-400 m 2 / g, and the pore volume is 0.25-0.45mL / g.

[0017] 12. The method according to any of the preceding or following aspects, 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), a liquid hourly volume space velocity of 0.1-15.0 h -1 (Preferably 0.5-5.0h -1 ), the volume ratio of hydrogen to oil is 10:1-2500:1 (preferably 100:1-2000:1 or 100:1-1000:1).

[0018] 13. The method according to any of the preceding or following aspects, wherein the operating conditions of the steam cracking include: reaction temperature 750-900°C, reaction pressure 0.1-0.5MPaG, water-oil mass ratio 0.2-0.6.

[0019] 14. The method according to any of the preceding or following aspects further comprises the following steps: Separating the conversion product to obtain a separation stream mainly composed of the C2-C6 normal alkanes (e.g., accounting for more than 80 wt%, more than 90 wt%, or more than 95 wt% of the total amount), and The separated stream is steam cracked to obtain a cracking product comprising ethylene.

[0020] 15. The method according to any one of the preceding or following aspects, wherein the weight ratio of the separation stream to the hydrocarbon stream is 0.4-0.9:1 (preferably 0.5-0.8:1).

[0021] 16. The method according to any of the preceding or following aspects further comprises the following steps: Separating the conversion products to obtain a normal stream mainly composed of C4-C6 normal alkanes (e.g., accounting for more than 80 wt%, more than 90 wt%, or more than 95 wt% of the total amount) and / or a low-carbon stream mainly composed of C2-C3 hydrocarbons (e.g., accounting for more than 90 wt% or more than 95 wt% of the total amount), and The normal stream and / or the low carbon stream are steam cracked to obtain a cracking product comprising ethylene.

[0022] 17. A system for improving the quality of a hydrocarbon stream, comprising the following units: 1) a hydrocarbon stream providing unit, which is configured to provide a hydrocarbon stream containing C5-C6 isoparaffins, wherein the content of the C5-C6 isoparaffins in the hydrocarbon stream is 60-90 wt% (preferably 70-80 wt%), based on the total weight of the hydrocarbon stream being 100 wt%, and 2) A hydrocarbon stream conversion unit, which is configured to convert 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 total amount) of the C5-C6 isoalkanes into C2-C6 normal alkanes by a conversion reaction in the presence of hydrogen to obtain conversion products.

[0023] Technical Effects Compared with the prior art, the method and system provided by the present invention can achieve one of the following technical effects or a combination of all or part of them: 1. For hydrocracking reactions, the smaller the molecules, the more difficult it is to undergo cracking reactions, especially for small molecular hydrocarbons such as C5 and C6. It is necessary to ensure that the reactants have a certain residence time in the catalyst pores. At the same time, when producing normal alkanes as the target product, the molecular sieve of the catalyst needs to have a straight pore structure, which is also more conducive to the generation of normal alkanes. Therefore, when processing raw materials rich in C5 and C6 isoalkanes, it is necessary to select a catalyst with a special pore structure. The inventor has found through research that a molecular sieve with shape-selective performance has very good reaction performance for the reaction of molecules with smaller molecular weights (including normal alkanes and short-chain isoalkanes), and can effectively convert C5 and C6 isoalkanes. After hydroconversion, the hydrocarbon stream containing C5 and C6 isoalkanes can significantly improve the triolefin yield of the steam cracking ethylene unit and improve the economic benefits of the ethylene unit.

[0024] 2. The processing capacity of an ethylene plant is based on the yield of ethylene, that is, the higher the yield of ethylene, the less raw materials the ethylene plant consumes. The raw material cost accounts for more than 60% of the processing cost of an ethylene plant. Therefore, increasing the yield of ethylene can significantly reduce the processing cost of an ethylene plant.

[0025] 3. The content of C5 and C6 isoparaffins in the hydrocarbon stream is controlled at 60-90%. Since the hydroconversion process mainly includes two reactions, normalization and cracking, and the normalization reaction does not consume hydrogen, it is a more ideal reaction path. The inventors have found through research that the normalization reaction of isoparaffins is affected by chemical equilibrium. A high content of normal paraffins in the reactants will inhibit the normalization reaction. At the same time, too low an isoparaffin content will cause the loss of normal paraffins in the raw materials, converting C5 and C6 normal paraffins in the raw materials into isoparaffins or small molecular normal paraffins, which will deteriorate the product quality or cause unnecessary hydrogen consumption. In the current petroleum processing process, hydrocracking and catalytic cracking and other reaction processes that follow the positive carbon ion reaction mechanism will have a large amount of isoparaffins in their C5 and C6 products, but the isoparaffins do not exceed 90%. If you want to obtain a raw material containing higher isoparaffins, you need special separation methods, including adsorption separation and distillation, etc., and these separation methods all require high energy consumption, which greatly increases the processing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a process flow diagram of the process method of the present invention.

[0027] exist Figure 1 In the figure, 1-hydrocarbon stream, 2-hydrogen, 3-hydrogenation reaction zone, 4-hydrogenation reaction zone effluent, 5-high-pressure separator, 6-gas phase stream hydrogen-rich gas, 7-liquid phase stream.

[0028] Figure 2 It is a process flow diagram of the process method of the present invention.

[0029] exist Figure 2 In the figure, 1-hydrocarbon stream, 2-hydrogen, 3-hydrogenation reaction zone, 4-hydrogenation reaction zone effluent, 5-high-pressure separator, 6-gas stream hydrogen-rich gas, 7-liquid stream, 8-fractionation tower, 9-gas product, 10-liquid product. DETAILED DESCRIPTION

[0030] The specific embodiments of the present invention are described in detail below, but it should be pointed out that the protection scope of the present invention is not limited by these specific embodiments, but is determined by the claims in the appendix.

[0031] 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 conventionally understood by those skilled in the art. In the event of a conflict, the definitions in this specification shall prevail.

[0032] When this specification uses the prefix "well-known to those skilled in the art", "prior art" or similar terms to introduce materials, substances, methods, steps, devices or components, etc., the objects introduced by the prefix cover those commonly used in the art when this application is filed, but also include those that are not commonly used at present but will become recognized in the art as being suitable for similar purposes.

[0033] In the context of the present invention, all numerical values ​​of parameters (eg amounts or conditions) are to be understood as being modified in all instances by the term "about", regardless of whether "about" actually appears before the numerical value.

[0034] In the context of the present invention, unless otherwise specified, each device used in the present invention may use a structure conventionally selected in the art without any particular limitation.

[0035] In the context of the present invention, the measurement method of the initial boiling point and the final boiling point is in accordance with the ASTM D86 measurement method.

[0036] In the context of the present invention, the term "C2-C6 normal alkane" refers to a normal alkane having a carbon number of from 2 to 6. It should be particularly clarified that, although there is no distinction between normal alkanes and isoalkanes for alkanes having a carbon number of from 2 to 3, for the sake of convenience of description, alkanes having a carbon number of from 2 to 3 are also regarded as normal alkanes. In addition, unless otherwise specified, the present invention may refer to any one or more of the normal alkanes having a carbon number of from 2 to 6, or may refer to all normal alkanes having a carbon number of from 2 to 6.

[0037] In the context of the present invention, cyclic hydrocarbons refer to hydrocarbons having a ring structure in their molecular structure, such as cycloalkanes and aromatic hydrocarbons.

[0038] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this specification are based on weight and pressure is gauge pressure.

[0039] In the context of the present invention, any two or more embodiments or aspects of the present invention may be arbitrarily combined, and the technical solutions thus formed belong to part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0040] According to one embodiment of the present invention, a method for improving the quality of a hydrocarbon stream is provided. Here, "improving the quality" means changing the chemical composition of the hydrocarbon stream by chemical conversion, so that it is easier to be converted into high value-added products such as ethylene by subsequent chemical treatment (such as steam cracking).

[0041] According to one embodiment of the present invention, the method includes the step of providing a hydrocarbon stream containing C5-C6 isoparaffins. According to the present invention, the hydrocarbon stream can be manufactured by any method known in the art, as long as it meets the requirements of the present invention for the hydrocarbon stream. As the manufacturing method of the hydrocarbon stream, for example, hydrocracking, catalytic cracking or atmospheric and vacuum distillation can be cited. Preferably, the initial distillation point of the hydrocarbon stream is 10-30°C (preferably 15-25°C), and the final distillation point is 50-100°C (preferably 55-70°C), and more preferably, the hydrocarbon stream is a light naphtha component obtained by hydrocracking a hydrocarbon oil feedstock.

[0042] According to one embodiment of the present invention, in order to achieve the technical effect of the present invention, the content of the C5-C6 isoparaffins in the hydrocarbon stream is generally 60-90wt%, preferably 70-80wt%, based on the total weight of the hydrocarbon stream as 100wt%. According to the present invention, the isoparaffin content in the hydrocarbon stream must have a certain proportion. If the isoparaffin content is too low, the proportion of normal paraffins in the product will be limited, and at the same time, some normal paraffins will be cracked, resulting in hydrogen loss; if the isoparaffin content is too high, conventional separation means cannot be obtained, and adsorption separation or distillation is required, which consumes a high amount of energy.

[0043] According to one embodiment of the present invention, C 7+ There is no particular restriction on the content of hydrocarbons, but in order to make the technical effect of the present invention more excellent, the C 7+ The content of hydrocarbon is generally 0-10 wt% (preferably 0.5-5 wt%), based on the total weight of the hydrocarbon stream being 100 wt%. 7+ If the content of hydrocarbons is too high, a certain amount of aromatic hydrocarbons will be entrained. However, aromatic hydrocarbons are difficult to be effectively converted under the conversion reaction conditions of the present invention (for example, the conversion rate is generally less than 10%) and behave as reaction inert components. 7+ Too high a hydrocarbon content will significantly inhibit the conversion activity of the hydrocarbon stream of the present invention, which is disadvantageous to the present invention.

[0044] According to one embodiment of the present invention, there is no particular restriction on the content of C5-C6 normal alkanes in the hydrocarbon stream, but in order to make the technical effect of the present invention more excellent, the content of C5-C6 normal alkanes in the hydrocarbon stream is generally 10-30wt% (preferably 15-25wt%), based on the total weight of the hydrocarbon stream as 100wt%. The inventors of the present invention have found that a high content of normal alkanes in the hydrocarbon stream will inhibit the conversion reaction of isoparaffins, and at the same time, the increase in normal alkanes after conversion is limited, which has little effect on the ethylene yield.

[0045] According to one embodiment of the present invention, there is no particular restriction on the content of C4-hydrocarbons in the hydrocarbon stream, but in order to make the technical effect of the present invention more excellent, the content of C4-hydrocarbons in the hydrocarbon stream is generally 0-10wt% (preferably 2-5wt%), based on the total weight of the hydrocarbon stream as 100wt%. The inventors of the present invention have found that C4-hydrocarbons are gaseous at normal temperature and pressure, and have limited solubility in C5-C6 hydrocarbons. Therefore, in order to obtain a hydrocarbon stream with a high C4-hydrocarbon content, a special manufacturing method is required, which will significantly increase the manufacturing cost of the hydrocarbon stream of the present invention. In addition, the inventors of the present invention have found that compared with C5-C6 isoparaffins, C4 hydrocarbons are more difficult to be effectively converted under the conversion reaction conditions of the present invention (for example, the conversion rate is generally less than 20%), so the excessive content of C4 hydrocarbons will significantly inhibit the conversion activity of the hydrocarbon stream of the present invention, which is not conducive to the present invention.

[0046] According to one embodiment of the present invention, there is no particular restriction on the content of cyclic hydrocarbons in the hydrocarbon stream, but in order to make the technical effect of the present invention more excellent, the content of cyclic hydrocarbons in the hydrocarbon stream is generally 1-10wt% (preferably 2-5wt%), based on the total weight of the hydrocarbon stream as 100wt%. The inventors of the present invention have found that cycloalkanes with a relatively small carbon number can be converted, while cycloalkanes and aromatics with a relatively large carbon number are difficult to be effectively converted under the process conditions of the present invention. These components entering the ethylene unit will affect the ethylene yield of the ethylene unit, which is not conducive to the present invention.

[0047] According to one embodiment of the present invention, the method includes converting at least a portion of the C5-C6 isoparaffins into C2-C6 normal alkanes by a conversion reaction in the presence of hydrogen to obtain a conversion product. Here, the so-called at least a portion, for example, accounts for more than 30wt%, more than 40wt%, more than 50wt%, more than 60wt%, more than 70wt%, more than 80wt% or more than 90wt% of the total amount. According to the present invention, there is no particular limitation on the conversion rate of C5-C6 isoparaffins. Therefore, C5-C6 isoparaffins can achieve the conversion rate (single-pass conversion rate) after a single conversion reaction, or can achieve the conversion rate after multiple recycling (such as the conversion reaction after the unreacted C5-C6 isoparaffins are separated from the conversion product).

[0048] According to one embodiment of the present invention, the conversion reaction may be a hydrogenation normalization reaction to obtain a conversion product with C4-C6 normal 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 found through research that C5 and C6 isoalkanes can undergo unimolecular reactions and bimolecular reactions during the conversion reaction of the present invention, wherein unimolecular reactions can convert isoalkanes into normal alkanes, and only a small amount of isoalkanes can directly undergo cracking reactions, while bimolecular reactions refer to two small molecular isoalkanes being spliced ​​into a long-chain isoalkanes and then undergoing cracking reactions. As described below in this specification, the inventors of the present invention have found that by selecting a molecular sieve with shape-selective catalytic performance, especially a molecular sieve with a special straight pore structure and containing more medium-strong acid or strong acid, and then loading a suitable hydrogenation metal, it is possible to achieve flexible regulation of the occurrence of unimolecular reactions and bimolecular reactions. Moreover, since the normalization reaction is affected by the concentrations of n-alkanes and isoalkanes in the reactants, that is, when the concentration of n-alkanes in the reactants is high, the normalization reaction will be inhibited, so that the increase in the proportion of n-alkanes in the conversion products is subject to certain restrictions. Therefore, in order to obtain conversion products with higher n-alkanes content, it is necessary to ensure that a certain cracking reaction occurs.

[0049] According to one embodiment of the present invention, 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), a liquid hourly volume space velocity of 0.1-15.0 h -1 (Preferably 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). The inventors of the present invention have found that, compared with the hydrocarbon stream conversion reaction of the prior art (such as the conversion reaction of C4 hydrocarbon stream), the reaction conditions of the conversion reaction of the present invention are milder, especially the reaction temperature is lower, such as generally 10-50°C lower. The inventors of the present invention have also found that at this lower reaction temperature, C5-C6 isoparaffins still show a higher conversion rate, such as C5-C6 isoparaffins can show a single-pass conversion rate of more than 40wt%, more than 50wt%, more than 60wt%, more than 70wt%, more than 80wt% or more than 90wt% under the reaction conditions of the present invention. In contrast, due to its molecular structure, C4 hydrocarbon molecules are smaller and have a short residence time in the pores of the catalyst molecular sieve of the present invention, making it impossible to achieve effective reaction. At the same time, the conversion of C4 hydrocarbons requires a catalyst with stronger dehydrogenation ability, and requires a much higher reaction temperature (e.g., 20-30°C higher) than that of the present invention to achieve this process. 7+ In the conversion of components, it is difficult for large molecular cycloalkanes with a higher carbon number to enter the catalyst pores for ring-opening reaction, and the cracking reaction of aromatics must first be hydrogenated and saturated. The hydrogenation and saturation of aromatics are directly affected by the reaction pressure. In order to obtain a better conversion effect of isoparaffins, the reaction pressure of the present invention is low, which is not conducive to the hydrogenation and saturation of aromatics, and thus the conversion effect of aromatics is poor.

[0050] According to one embodiment of the present 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.

[0051] According to one embodiment of the present invention, the molecular sieve is a molecular sieve with shape-selective catalytic performance, 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 30-80wt% (preferably 40-70wt%). The inventors of the present invention have found that the acid strength of the molecular sieve directly affects the reaction characteristics of isoparaffins. The molecular sieve has more strong acid centers and is more prone to cracking reactions, such as ZSM-5 molecular sieves; while the medium-strong acid centers are more, and it is easier to undergo 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.

[0052] According to one embodiment of the present invention, the active metal component is an active non-noble metal component, preferably selected from one or more of the metals of Group VIB and Group VIII of the periodic table, the metals of Group VIB are preferably selected from one or more of molybdenum and tungsten (particularly preferably molybdenum), and the non-noble metals of Group VIII are preferably selected from one or more of cobalt and nickel (particularly preferably nickel). Here, based on the weight of the catalyst, the content of the metal of Group VIB (calculated as oxide) is 5.0-30.0wt% (10.0-20.0wt%), and the content of the non-noble metal of Group VIII (calculated as oxide) is 0.5-15.0wt% (preferably 3.0-10.0wt%).

[0053] According to one embodiment of the present invention, the catalyst further comprises a binder. The type of the binder can be a conventional choice in the art, including but not limited to aluminum oxide and silicon oxide, wherein aluminum oxide is preferred. Here, based on the weight of the catalyst, the content of the binder is 5-65wt% (preferably 10-35wt%).

[0054] According to one embodiment of the present invention, the specific surface area of ​​the catalyst is 200-400m 2 / g, and the pore volume is 0.25-0.45mL / g.

[0055] According to one embodiment of the present invention, the preparation method of the catalyst can be prepared according to conventional methods in the art. The preparation method includes the preparation of a carrier and the loading of an active metal component, wherein the preparation process of the carrier is as follows: the molecular sieve and the binder are mechanically mixed, molded, and then dried and calcined to prepare a catalyst carrier. Conventional conditions can be used for drying and calcining the carrier. The drying condition is: drying at 100°C-150°C for 1-12 hours. The calcination condition is: calcining at 450°C-550°C for 2.5-6.0 hours.

[0056] According to one embodiment of the present invention, in the preparation method of the catalyst, the method for loading the active metal component is a conventional method, such as a kneading method, an impregnation method, etc., preferably an impregnation method. The impregnation method can be a saturated impregnation method, an excess impregnation method or a complex impregnation method, that is, the catalyst carrier is impregnated with a solution containing the required active metal component, and then dried and calcined to obtain the first catalyst. The drying conditions are: drying at 100°C-150°C for 1-12 hours. The calcination conditions are: calcining at 450°C-550°C for 2.5-6.0 hours.

[0057] According to one embodiment of the present invention, from the perspective of the balance between quality improvement effect and energy consumption, the content of C7+ hydrocarbons in the conversion product is not higher than 5wt% (preferably not higher than 1wt%), the content of C5-C6 isoparaffins is 0-50wt% (preferably 10-40wt%), the content of C2-C6 normal paraffins is 40-90wt% (preferably 50-80wt%), and the content of cyclic hydrocarbons is not higher than 3wt% (preferably not higher than 1wt%), based on the total weight of the conversion product as 100wt%.

[0058] According to one embodiment of the present invention, the method further comprises the following steps: separating the conversion product to obtain a separation stream mainly composed of the C2-C6 normal alkanes (e.g., accounting for more than 80wt%, more than 90wt% or more than 95wt% of the total amount). According to the specific situation of the conversion rate, unreacted C5-C6 isoparaffins may also be obtained through the separation. The unreacted C5-C6 isoparaffins may be used as a circulating material to continue the conversion reaction together with the raw hydrocarbon stream, thereby converting a higher proportion of C5-C6 isoparaffins into C2-C6 normal alkanes.

[0059] According to one embodiment of the present invention, the weight ratio of the separation stream to the hydrocarbon stream is 0.4-0.9:1 (preferably 0.5-0.8:1).

[0060] According to this embodiment of the present invention, the method further comprises the following steps: separating the conversion product to obtain a normal stream mainly composed of C4-C6 normal alkanes (e.g., accounting for more than 80wt%, more than 90wt% or more than 95wt% of the total amount) and / or a low-carbon stream mainly composed of C2-C3 hydrocarbons (e.g., accounting for more than 90wt% or more than 95wt% of the total amount). According to the specific circumstances of the conversion rate, unreacted C5-C6 isoparaffins may also be obtained through this separation. The unreacted C5-C6 isoparaffins may be used as a circulating material to continue the conversion reaction with the raw hydrocarbon stream, thereby converting a higher proportion of C5-C6 isoparaffins into C2-C6 normal alkanes.

[0061] According to one embodiment of the present invention, the conversion product, the separation stream, the normal stream or the low-carbon stream shows high chemical activity compared with the hydrocarbon stream, and can therefore be advantageously used in chemical treatments such as steam cracking, alkane degassing, hydrocracking, etc. to obtain high value-added chemicals, preferably used in steam cracking to produce ethylene.

[0062] According to one embodiment of the present invention, the conversion product, the separation stream, the normal stream or the low-carbon stream are steam cracked to obtain a cracking product containing ethylene. According to the present invention, the conversion product, the separation stream, the normal stream or the low-carbon stream is an ideal ethylene cracking feedstock, and the ethylene yield when using these streams is generally above 30wt%, thereby finding a high-value utilization method for the low-value-added hydrocarbon stream in the prior art.

[0063] According to one embodiment of the present invention, the operating conditions of the steam cracking include: reaction temperature 750-900° C., reaction pressure 0.1-0.5 MPaG, and water-to-oil mass ratio 0.2-0.6.

[0064] According to one embodiment of the present invention, a system for improving the quality of a hydrocarbon stream is also provided, which comprises a hydrocarbon stream providing unit and a hydrocarbon stream conversion unit. According to the present invention, the system is specifically configured to implement the method described in the foregoing text of this specification, so except for the contents clearly defined in this paragraph, any other contents or matters not clearly defined can be directly referred to the contents or matters correspondingly described in the foregoing text of this specification for the method, and there is no special limitation.

[0065] The present invention is further described below in conjunction with the accompanying drawings, but the present invention is not limited thereto.

[0066] according to Figure 1 The hydrocarbon stream 1 is mixed with hydrogen 2 and enters the hydroconversion reaction zone 3. The effluent 4 of the hydroconversion reaction zone enters the high-pressure separator 5. The separated gaseous stream hydrogen-rich gas 6 is recycled, and the liquid stream is used as an ethylene feedstock.

[0067] according to Figure 2 The hydrocarbon stream 1 is mixed with hydrogen 2 and enters the hydroconversion reaction zone 3. The effluent 4 of the hydroconversion reaction zone enters the high-pressure separator 5. The separated gaseous stream hydrogen-rich gas 6 is recycled. The liquid stream 7 enters the distillation tower for separation to obtain a gaseous product 9 as an ethylene feedstock. The liquid product 10 is circulated to the inlet of the hydroconversion reaction zone 3.

[0068] Example The present invention is further described in detail below using examples and comparative examples, but the present invention is not limited to these examples.

[0069] In the following examples and comparative examples, the calculation method of ethylene yield is the mass percentage of ethylene output to the feed amount of ethylene unit, and the ton-oil processing benefit refers to the income obtained from processing 1 ton of raw materials, and the calculation method is (ethylene product price - raw material and hydrogen price - processing energy consumption) / processing amount, and the ton-oil processing benefit is based on the raw material being directly used as ethylene raw material without hydrogenation conversion.

[0070] In the following examples and comparative examples, each hydroconversion catalyst is represented by Cat-A plus a number, such as Cat-A1, Cat-A2, Cat-A3, etc. The hydroconversion catalyst is prepared by a conventional active metal saturation impregnation method, and the physicochemical properties of the obtained catalyst are shown in Table 1.

[0071] The preparation method of Cat-A1 to Cat-A3 catalysts is: (1) Mordenite with a SiO2 / Al2O3 molar ratio of 15 was selected and mechanically mixed with a binder, molded, dried at 120°C for 10 hours, and calcined at 500°C for 4 hours to prepare a catalyst carrier.

[0072] (2) The catalyst carrier obtained in step (1) was impregnated with the active component, dried at 120°C for 10 hours, and calcined at 500°C for 4 hours to prepare a hydroconversion catalyst.

[0073] The preparation method of Cat-A4 to Cat-A7 catalysts is: (1) ZSM-5 with a SiO2 / Al2O3 molar ratio of 10 was selected and mechanically mixed with a binder, molded, dried at 120°C for 10 hours, and calcined at 500°C for 4 hours to prepare a catalyst carrier.

[0074] (2) The catalyst carrier obtained in step (1) was impregnated with the active component, dried at 120°C for 10 hours, and calcined at 500°C for 4 hours to prepare a hydroconversion catalyst.

[0075] The properties of the raw materials are shown in Table 2. Among them, the raw material 5 needs to be obtained by adsorption separation or distillation of an isoparaffin-containing raw material.

[0076] Table 1

[0077] Table 2

[0078] Example 1 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) Raw material 1 and hydrogen are mixed and sequentially enter the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with hydroconversion catalyst Cat-A1; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0079] In this example, about 49 wt% of the total C5-C6 isoparaffins are converted into C2-C6 normal paraffins. The weight ratio of the liquid phase stream to the feedstock 1 is 0.30:1.

[0080] Example 2 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) Raw material 1 and hydrogen are mixed and sequentially enter the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with hydroconversion catalyst Cat-A2; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0081] In this example, about 45 wt% of the total C5-C6 isoparaffins are converted into C2-C6 normal paraffins. The weight ratio of the liquid phase stream to the feedstock 1 is 0.37:1.

[0082] Example 3 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) Raw material 1 and hydrogen are mixed and sequentially enter the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with hydroconversion catalyst Cat-A3; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0083] In this example, about 34 wt% of the total C5-C6 isoparaffins are converted into C2-C6 normal paraffins. The weight ratio of the liquid phase stream to the feedstock 1 is 0.62:1.

[0084] Example 4 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) Raw material 1 and hydrogen are mixed and sequentially enter the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with hydroconversion catalyst Cat-A4; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0085] In this example, about 64 wt% of the total C5-C6 isoparaffins are converted into C2-C6 normal paraffins. The weight ratio of the liquid phase stream to the feedstock 1 is 0.06:1.

[0086] Example 5 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) Raw material 1 and hydrogen are mixed and sequentially enter the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with hydroconversion catalyst Cat-A5; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0087] In this example, about 60 wt% of the total C5-C6 isoparaffins are converted into C2-C6 normal paraffins. The weight ratio of the liquid phase stream to the feedstock 1 is 0.15:1.

[0088] Example 6 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) Raw material 1 and hydrogen are mixed and sequentially enter the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with hydroconversion catalyst Cat-A6; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0089] In this example, about 52 wt% of the total C5-C6 isoparaffins are converted into C2-C6 normal paraffins. The weight ratio of the liquid phase stream to the feedstock 1 is 0.24:1.

[0090] Example 7 Methods for improving the quality of hydrocarbon streams include: Figure 2 Process, including: (1) Raw material 1 and hydrogen are mixed and sequentially enter the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with hydroconversion catalyst Cat-A4; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is carried out into hydrogen-rich gas and liquid phase stream. The hydrogen-rich gas is recycled, and the C2 and C3 obtained by separation of the liquid phase stream are used as ethylene feedstocks. The remaining stream (called C4-C6 circulating stream) is cracked. The process conditions and quality improvement results in this example are shown in Table 3.

[0091] In this example, about 78 wt% of the total C5-C6 isoparaffins are converted into C2-C3 normal paraffins. The weight ratio of the C4-C6 recycle stream to the feedstock 1 is 0.3:1.

[0092] Example 8 Methods for improving the quality of hydrocarbon streams include: Figure 2 Process, including: (1) Raw material 1 and hydrogen are mixed and sequentially enter the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with hydroconversion catalyst Cat-A5; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is carried out into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, the C2 and C3 obtained by separation of the liquid phase stream are used as ethylene feedstock, and C4-C6 are cyclically cracked. The process conditions and quality improvement results in this example are shown in Table 3.

[0093] In this example, about 78 wt% of the total C5-C6 isoparaffins are converted into C2-C3 normal paraffins. The weight ratio of the C4-C6 recycle stream to the feedstock 1 is 0.4:1.

[0094] Example 9 Methods for improving the quality of hydrocarbon streams include: Figure 2 Process, including: (1) Raw material 1 and hydrogen are mixed and sequentially enter the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with hydroconversion catalyst Cat-A5; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is carried out into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, the C2 and C3 obtained by separation of the liquid phase stream are used as ethylene feedstock, and C4-C6 are cyclically cracked. The process conditions and quality improvement results in this example are shown in Table 3.

[0095] In this example, about 78 wt% of the total C5-C6 isoparaffins are converted into C2-C3 normal paraffins. The weight ratio of the C4-C6 recycle stream to the feedstock 1 is 0.3:1.

[0096] Example 10 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) Raw material 2 is mixed with hydrogen and sequentially enters the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with hydroconversion catalyst Cat-A1; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0097] In this example, about 34 wt% of the total C5-C6 isoparaffins are converted into C2-C6 normal paraffins. The weight ratio of the liquid phase stream to the feedstock 1 is 0.28:1.

[0098] Embodiment 11 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) The raw material 3 is mixed with hydrogen and sequentially enters the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with the hydroconversion catalyst Cat-A4; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0099] In this example, about 65 wt% of the total C5-C6 isoparaffins are converted into C2-C6 normal paraffins. The weight ratio of the liquid phase stream to the feedstock 1 is 0.17:1.

[0100] Example 12 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) Raw material 1 and hydrogen are mixed and sequentially enter the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with hydroconversion catalyst Cat-A1; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0101] In this example, about 27 wt% of the total C5-C6 isoparaffins are converted into C2-C6 normal paraffins. The weight ratio of the liquid phase stream to the feedstock 1 is 0.72:1.

[0102] Comparative Example 1 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) The raw material 4 is mixed with hydrogen and sequentially enters the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with the hydroconversion catalyst Cat-A1; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0103] Comparative Example 2 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) The raw material 4 is mixed with hydrogen and sequentially enters the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with the hydroconversion catalyst Cat-A4; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0104] Comparative Example 3 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) The raw material 5 is mixed with hydrogen and sequentially enters the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with the hydroconversion catalyst Cat-A1; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0105] Comparative Example 4 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) The raw material 5 is mixed with hydrogen and sequentially enters the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with the hydroconversion catalyst Cat-A4; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0106] Comparative Example 5 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) Raw material 1 and hydrogen are mixed and sequentially enter the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with hydroconversion catalyst Cat-A7; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0107] Comparative Example 6 Methods for improving the quality of hydrocarbon streams include: Figure 1 Process, including: (1) The raw material 6 is mixed with hydrogen and sequentially enters the hydroconversion reaction zone; the hydroconversion reaction zone is loaded with the hydroconversion catalyst Cat-A1; (2) Step (1) The gas-liquid separation of the reaction effluent from the hydroconversion reaction zone is into hydrogen-rich gas and liquid phase stream, the hydrogen-rich gas is recycled, and the liquid phase stream is directly used as ethylene feedstock. The process conditions and quality improvement results in this example are shown in Table 3.

[0108] Table 3 Quality improvement results

[0109] Table 3 Quality improvement results

[0110] Table 3 Quality improvement results

[0111] By comparison, it can be seen that the method of the present invention can effectively convert low-quality ethylene raw materials into high-quality ethylene raw materials. The hydrocarbon stream after hydrogenation conversion can greatly increase the content of normal hydrocarbons in its hydrogenation product, thereby increasing the ethylene and triene yields of the ethylene device. In addition, the process is simple, the operation difficulty is low, and it has very good economic benefits.

Claims

1. A method for improving the quality of a hydrocarbon stream, comprising the following steps: 1) providing a hydrocarbon stream containing C5-C6 isoparaffins, wherein the content of the C5-C6 isoparaffins in the hydrocarbon stream is 60-90 wt% (preferably 70-80 wt%), based on the total weight of the hydrocarbon stream being 100 wt%, and 2) converting 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 into C2-C6 normal alkanes in the presence of hydrogen to obtain conversion products.

2. The method according to claim 1, wherein the initial distillation point of the hydrocarbon stream is 10-30°C (preferably 15-25°C) and the final distillation point is 50-100°C (preferably 55-70°C).

3. The method according to claim 1, wherein the content of C7+ hydrocarbons in the hydrocarbon stream is 0-10wt% (preferably 0.5-5wt%), the content of C5-C6 normal alkanes is 10-30wt% (preferably 15-25wt%), the content of C4- hydrocarbons is 0-10wt% (preferably 2-5wt%), and the content of cyclic hydrocarbons is 1-10wt% (preferably 2-5wt%), based on the total weight of the hydrocarbon stream as 100wt%, and / or the content of C7+ hydrocarbons in the conversion product is not higher than 5wt% (preferably not higher than 1wt%), the content of C5-C6 isoparaffins is 0-50wt% (preferably 10-40wt%), the content of C2-C6 normal alkanes is 40-90wt% (preferably 50-80wt%), and the content of cyclic hydrocarbons is not higher than 3wt% (preferably not higher than 1wt%), based on the total weight of the conversion product as 100wt%.

4. The method of claim 1, wherein the hydrocarbon stream is a light naphtha component obtained by cracking a hydrocarbon oil feedstock, such as hydrocracking or catalytic cracking.

5. The method of claim 1, 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.

6. The method according to claim 5, wherein the molecular sieve is a molecular sieve having shape-selective catalytic performance, 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, in particular selected from one or more of mordenite and ZSM-5 molecular sieve.

7. The method according to claim 5, wherein the catalyst further comprises a binder (preferably alumina), and the content of the binder is 5-65wt% (preferably 10-35wt%) based on the weight of the catalyst.

8. The method of claim 5, wherein the active metal component is selected from one or more of Group VIB metals and Group VIII non-noble metals of the periodic table, the Group VIB metal is preferably selected from one or more of molybdenum and tungsten (particularly preferably molybdenum), and the Group VIII non-noble metal is preferably selected from one or more of cobalt and nickel (particularly preferably nickel).

9. The method of claim 8, wherein the content of the Group VIB metal (calculated as oxide) is 5.0-30.0 wt% (preferably 10-20 wt%), and the content of the Group VIII non-noble metal (calculated as oxide) is 0.5-15.0 wt% (preferably 3-10 wt%), based on the weight of the catalyst.

10. The method according to claim 5, wherein the content of the molecular sieve is 30-80 wt% (preferably 40-70 wt%) based on the weight of the catalyst.

11. The method of claim 1, wherein the reaction conditions of the conversion reaction include: The reaction pressure is 0.5-10.0MPaG (preferably 2.0-8.0MPaG or 2.0-5.0MPaG), the reaction temperature is 250-500℃ (preferably 350-450℃), and the liquid hourly volume space velocity is 0.1-15.0h -1 (Preferably 0.5-5.0h -1 ), the volume ratio of hydrogen to oil is 10:1-2500:1 (preferably 100:1-2000:1 or 100:1-1000:1).

12. The method of claim 1, further comprising the steps of: Optionally separating the conversion product to obtain a separated stream mainly composed of the C2-C6 normal alkanes (e.g., accounting for more than 80 wt%, more than 90 wt%, or more than 95 wt% of the total amount), or separating the conversion product to obtain a normal stream mainly composed of C4-C6 normal alkanes (e.g., accounting for more than 80 wt%, more than 90 wt%, or more than 95 wt% of the total amount) and / or a low-carbon stream mainly composed of C2-C3 hydrocarbons (e.g., accounting for more than 90 wt% or more than 95 wt% of the total amount), and The conversion product, the separation stream, the normal stream or the low-carbon stream is steam cracked to obtain a cracking product comprising ethylene.

13. The process of claim 12, wherein the weight ratio of the separation stream to the hydrocarbon stream is 0.4-0.9:1 (preferably 0.5-0.8:1).

14. The method of claim 12, wherein the operating conditions of the steam cracking include: The reaction temperature is 750-900°C, the reaction pressure is 0.1-0.5MPaG, and the water-oil mass ratio is 0.2-0.

6.

15. A system for improving the quality of a hydrocarbon stream, comprising the following units: 1) a hydrocarbon stream providing unit, which is configured to provide a hydrocarbon stream containing C5-C6 isoparaffins, wherein the content of the C5-C6 isoparaffins in the hydrocarbon stream is 60-90 wt% (preferably 70-80 wt%), based on the total weight of the hydrocarbon stream being 100 wt%, and 2) A hydrocarbon stream conversion unit, which is configured to convert 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 total amount) of the C5-C6 isoalkanes into C2-C6 normal alkanes by a conversion reaction in the presence of hydrogen to obtain conversion products.

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