EP4775652A1

EP4775652A1 - Method for improving quality of hydrocarbon stream

Info

Publication number: EP4775652A1
Application number: EP24861761.5A
Authority: EP
Inventors: Zhe CUI; Yanze Du; Ronghui Zeng; Shaozhong Peng; Chang Liu; Ziming Wu; Wenyue HAO
Original assignee: China Petroleum and Chemical Corp; Sinopec Dalian Research Institute of Petroleum and Petrochemicals
Current assignee: China Petroleum and Chemical Corp; Sinopec Dalian Research Institute of Petroleum and Petrochemicals
Priority date: 2023-09-04
Filing date: 2024-08-08
Publication date: 2026-07-15
Also published as: KR20260065851A; WO2025050916A1; TW202528525A

Abstract

The present invention relates to a process for improving the quality of a hydrocarbon stream. The process for improving the quality of a hydrocarbon stream according to the present invention comprises the steps of: providing a hydrocarbon stream containing C₅-C₆ iso-alkanes, wherein the content of the C₅-C₆ iso-alkanes in the hydrocarbon stream is 60-90 wt%, based on the total weight of the hydrocarbon stream being 100 wt%; converting at least a part of the C₅-C₆ iso-alkanes in the presence of a catalyst and hydrogen by a conversion reaction into C₂-C₆ n-alkanes, to obtain a conversion product, wherein the catalyst comprises a molecular sieve and a non-noble metal hydrogenation-active metal component; steam cracking the conversion product to obtain a cracking product comprising ethylene. According to the present invention, low-quality ethylene raw material can be effectively converted into high-quality ethylene raw material. The hydrocarbon stream after the hydro-conversion can greatly improve the yield of ethylene and the yield of triene of the ethylene device. Moreover, the process procedures according to the present invention was simple with low difficulty of operation, thus had very good economic benefit.

Description

TECHNICAL FIELD

The present invention relates to the technical field of petrochemicals, more specifically, to a process for improving the quality of a hydrocarbon stream.

BACKGROUND

In petroleum processing, C₅ and C₆ iso-alkanes are generally obtained through processes such as crude oil separation or hydrocracking, which show cracking performances. Due to small molecular weight, the bond energy between atoms of C₅ and C₆ iso-alkanes is relatively high, and the molecular polarity is weak, making it difficult for them 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 iso-alkanes: one is to directly use them as gasoline blending components, but the blending amount is low due to the influence of saturated vapor pressure; the other is to use them as feedstock for steam cracking to produce ethylene. However, the inventors of the present invention have found that the yields of ethylene and trienes are both relatively low when iso-alkanes are used in thermal cracking processes, so they are not high-quality ethylene raw material either.
During the production process in an ethylene device, a series of complex chemical reactions occur after the feedstock undergoes high-temperature cracking, leading to varying degrees of coking on the inner walls of the radiant section tubes of the cracking furnace and the inner walls of the jacket of the quenching boiler. As the coke layer thickens continuously, the heat transfer resistance of the tubes increases, and the heat from outside the tubes cannot be transferred to the cracking feedstock inside the tubes in a timely manner, seriously affecting the cracking depth of the feedstock. Furthermore, the outer surface temperature of the tubes rises continuously, which may lead to localized overheating, shortening the service life of the tubes. When the temperature exceeds the maximum design temperature of the tube material, the furnace must be shut down for decoking. Therefore, if the ethylene raw material contains little or no sulfides, sulfur must be injected during the reaction process to prevent tube coking; if the ethylene raw material contains a certain amount of sulfides, sulfur injection during the reaction process can lower the operating cost of the plant.
When iso-alkanes are used as ethylene raw material, both ethylene yield and triene yield are relatively low. Therefore, effectively converting iso-alkanes to n-alkanes can significantly increase the yield of high-value products in an ethylene device. Among n-alkanes, low-carbon alkanes (including ethane and propane) are better cracking feedstocks, as they are easier to separate and provide high ethylene product yield. However, the process of obtaining ethane and propane through hydrogenation consumes more hydrogen. On the other hand, C₄ and C₄₊ n-alkanes, which have isomers, can also achieve relatively high ethylene yields, while the hydrogen consumption during hydrogenation is lower; however, separating isomers with the same carbon number is difficult, and the hydrogenation products usually contain iso-alkanes, resulting in lower ethylene yields compared to using low-carbon alkanes as feedstock. If hydrogenation the proportion of low-carbon alkanes and n-alkanes in the hydrogenation products can be flexibly adjusted through a hydrogenation process, operational flexibility can be greatly enhanced.
With the rapid development of chemical industry, ethylene production capacity has increased year by year. Consequently, the demand for ethylene raw material is also continuously rising. How to broaden the selection range of ethylene raw materials and how to obtain high-quality ethylene raw materials have become urgent problems to be solved in the development of the ethylene industry.

SUMMARY OF THE INVENTION

To address the deficiencies of the prior art, the present invention provides a hydrogenation process for C₅ and C₆ iso-alkanes, which can effectively convert iso-alkanes with poor cracking performance into C₂-C₆ n-alkanes with better cracking performance, thereby significantly improving the ethylene and triene yields of an ethylene device, where the triene yield refers to the yield by weight of ethylene, propylene, and butadiene.
The inventors of the present invention have also found that the ethylene raw material obtained through the hydroprocess allows desulfurization of organic sulfur in the feedstock during the hydrogenation reaction to be converted into hydrogen sulfide, and the hydrogen sulfide is removed during product separation. Therefore, the sulfur content in the ethylene raw material is usually low, and sulfur injection is required before entering the ethylene cracking furnace to prevent tube coking. If a part of the hydrogen sulfide is retained in the hydrogenation products during the separation process, the need for sulfur injection before the hydrogenation products, when used as an ethylene raw material, are fed into the ethylene cracking furnace can be reduced or even eliminated, enabling high-value utilization of waste gas.
The inventors of the present invention have further found that small molecular iso-alkanes mainly undergoes two types of reaction processes of cracking and normalization in the hydroconversion process, wherein the conversion by the cracking reaction results in more low-carbon alkanes, while the conversion of iso-alkanes by the normalization reaction results in iso-alkanes with the same carbon number. By adjusting the catalyst and the process conditions, the molecular composition of the hydrogenation product can be flexibly adjusted, and the production flexibility is improved.
The present invention aims to produce C₂-C₆ n-alkanes in a maximized amount. In the prior art, C₅-C₆ iso-alkanes are usually converted into n-alkanes where only normalization reaction occurs, while cracking reaction is inhibited, wherein the whole normalization reaction process needs reduced reaction temperature and reduced hydrogen-to-oil volume ratio. However, the normalization reaction is influenced by chemical equilibrium, such that when the concentration of n-alkanes in the product reaches a certain proportion (about 30%), the normalization reaction is inhibited, and it is difficult to improve the yield of normal hydrocarbons in the product by adjusting the reaction process. Hence, the reaction route needs to be combined with separation of normal hydrocarbons and isomerized hydrocarbons, so as to separate out n-alkanes followed by further conversion of the unconverted iso-alkanes. However, C₂-C₆ n-alkanes are all ideal raw materials for preparing ethylene by steam cracking, for which the invention uses a special catalyst and controls the reaction conditions, so as to strengthen the both occurrences of normalization and cracking reaction at the same time, which breaks the influence of chemical equilibrium on the normalization reaction, wherein the yield of n-alkanes in the conversion product are further improved by cracking reaction, which is particularly suitable for being directly used as a raw material for steam cracking to prepare ethylene. The present invention has been developed based on this object.
Specifically, the present invention relates to the following aspects.

1. A process for improving the quality of a hydrocarbon stream, comprising the steps of:
1. 1) providing a hydrocarbon stream containing C₅-C₆ iso-alkanes, wherein the content of the C₅-C₆ iso-alkanes in the hydrocarbon stream is 60-90 wt% (preferably 70-80 wt%), based on the total weight of the hydrocarbon stream being 100 wt%,
2. 2) converting at least a part (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) of the C₅-C₆ iso-alkanes in the presence of a catalyst and hydrogen by a conversion reaction to C₂-C₆ n-alkanes, so as to obtain a conversion product, wherein the catalyst comprises a molecular sieve and a non-noble metal hydrogenation-active metal component,
3. 3) steam cracking the conversion product to obtain a cracking product comprising ethylene.
2. The process according to any one of the preceding or subsequent aspects, wherein the hydrocarbon stream has an initial boiling point of 10-30°C (preferably 15-25°C) and an end boiling point of 50-100°C (preferably 55-70°C).
3. The process according to any one of the preceding or subsequent aspects, wherein the hydrocarbon stream has a sulfur content of 50-5000 mg/kg (preferably 200-1000 mg/kg), based on the total weight of the hydrocarbon stream.
4. The process according to any one of the preceding or subsequent aspects, wherein the hydrocarbon stream comprises C₇₊ hydrocarbons in an amount of 0-10 wt% (preferably 0.5-5 wt%), C₅-C₆ n-alkanes in an amount of 10-30 wt% (preferably 15-25 wt%), C_4- hydrocarbons in an amount of 0-10 wt% (preferably 2-5 wt%), and cyclic hydrocarbons in an amount of 1-10 wt% (preferably 2-5 wt%), based on the total weight of the hydrocarbon stream being 100 wt%.
5. The process according to any one of the preceding or subsequent aspects, wherein the conversion product comprises C₂-C₃ alkanes and C₄-C₆ n-alkanes (preferably C₅-C₆ n-alkanes), and the weight ratio of the C₂-C₃ alkanes to the C₄-C₆ n-alkanes (preferably C₅-C₆ n-alkanes) is 0.5:1 to 8:1 (preferably 0.9:1 to 5:1).
6. The process according to any one of the preceding or subsequent aspects, wherein the conversion product comprises C₇₊ hydrocarbons in an amount of not more than 5 wt% (preferably not more than 1 wt%), C₅-C₆ iso-alkanes in an amount of 0-50 wt% (preferably 10-40 wt%), C₂-C₆ n-alkanes in an amount of 40-90 wt% (preferably 50-80 wt%), and cyclic hydrocarbons in an amount of not more than 3 wt% (preferably not more than 1 wt%), based on the total weight of the conversion product being 100 wt%.
7. The process according to any one of the preceding or subsequent aspects, wherein the hydrocarbon stream is a light naphtha component obtained by cracking (such as hydrocracking or catalytic cracking) a hydrocarbon oil feedstock.
8. The process according to any one of the preceding or subsequent aspects, wherein the molecular sieve is one or more selected from the group consisting of mordenite, ZSM molecular sieves, SAPO molecular sieves, and EU-1 molecular sieves, more preferably one or more selected from the group consisting of mordenite and ZSM molecular sieves, particularly preferably one or more selected from the group consisting 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 one or more selected from the group consisting of mordenite and ZSM-5 molecular sieve (particularly preferably, the weight ratio of mordenite to ZSM-5 molecular sieve is 0-100:100-0, preferably 10-50:50-10).
9. The process according to any one of the preceding or subsequent aspects, wherein the catalyst further comprises a binder (preferably alumina), and based on the weight of the catalyst, the binder is present in an amount of 5-65 wt% (preferably 10-35 wt%).
10. The process according to any one of the preceding or subsequent aspects, wherein the non-noble metal hydrogenation-active metal component is one or more selected from the group consisting of non-noble metals of Group VIB of the Periodic Table and non-noble metals of Group VIII of the Periodic Table.
11. The process according to any one of the preceding or subsequent aspects, wherein the non-noble metals of Group VIB is one or more selected from the group consisting of molybdenum and tungsten (particularly preferably molybdenum), and the non-noble metals of Group VIII is one or more selected from the group consisting of cobalt and nickel (particularly preferably nickel).
12. The process according to any one of the preceding or subsequent aspects, wherein based on the weight of the catalyst, the non-noble metal of Group VIB (calculated as oxide) is present in an amount of 5.0-30.0 wt% (preferably 10-20 wt%), and the non-noble metal of Group VIII (calculated as oxide) is present in an amount of 0.5-15.0 wt% (preferably 3-10 wt%).
13. The process according to any one of the preceding or subsequent aspects, wherein based on the weight of the catalyst, the molecular sieve is present in an amount of 30-80 wt% (preferably 40-70 wt%).
14. The process according to any one of the preceding or subsequent aspects, wherein the catalyst has a specific surface area of 200-400 m²/g and a pore volume of 0.25-0.45 mL/g.
15. The process according to any one of the preceding or subsequent aspects, wherein the conversion reaction is carried out under the reaction conditions of: 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 300-500°C (preferably 350-450°C), a liquid hourly volume space velocity of 0.1-15.0 h^-1 (preferably 0.5-5.0 h^-1), and a hydrogen-to-oil volume ratio of 50:1-2500:1 (preferably 100:1-2000:1 or 100:1-1000:1).
16. The process according to any one of the preceding or subsequent aspects, wherein the step 3) comprises the steps of:
- 3-A-1) separating the conversion product (called as a first separation) to obtain a separated stream with C₂+ hydrocarbons as the main part (such as representing 95 wt% or more, 98 wt% or more, 99 wt% or more, or essentially 100 wt% of the total amount),
- 3-A-2) steam cracking the separated stream to obtain a cracked product comprising ethylene.
17. The process according to any one of the preceding or subsequent aspects, wherein the first separation is operated under conditions comprising a pressure of 0.5-10.0 MPaG (preferably 2.0-8.0 MPaG or 2.0-5.0 MPaG) and a temperature of 40-70 °C.
18. The process according to any one of the preceding or subsequent aspects, wherein the step 3) comprises the steps of:
- 3-B-1) separating the conversion product (called as a first separation) to obtain a separated stream with C₂+ hydrocarbons as the main part (such as representing 95 wt% or more, 98 wt% or more, 99 wt% or more, or essentially 100 wt% of the total amount),
- 3-B-2) separating the separated stream (called as a second separation) to obtain a higher-carbon stream comprising C₄+ hydrocarbons as the main part (such as 90 wt% or more, 95 wt% or more, 98 wt% or more, 99 wt% or more, or substantially 100 wt% of the total amount) and a lower-carbon stream comprising C₂-C₃ hydrocarbons as the main part (such as 90 wt% or more, 95 wt% or more, 98 wt% or more, 99 wt% or more, or substantially 100 wt% of the total amount),
- 3-B-3) optionally recycling the higher-carbon stream as a hydrocarbon stream back to step 2) for the conversion reaction,
- 3-B-4) steam cracking the lower-carbon stream to obtain a cracked product comprising ethylene.
19. The process according to any one of the preceding or subsequent aspects, wherein the first separation is operated under conditions comprising a pressure of 0.5-10.0 MPaG (preferably 2.0-8.0 MPaG or 2.0-5.0 MPaG) and a temperature of 40-70 °C, and the second separation is operated under conditions comprising a pressure of 0.5-1.5 MPaG and a temperature of 30-60 °C.
20. The process according to any one of the preceding or subsequent aspects, wherein the operating conditions for the steam cracking comprise: a reaction temperature of 750-900°C, a reaction pressure of 0.1-0.5 MPaG, a water-to-oil ratio by weight of 0.2-0.6, and a system sulfur content of 100-200 mg/kg.
21. A system for improving the quality of a hydrocarbon stream, comprising the units of:
1. 1) a hydrocarbon stream providing unit, configured to be capable of providing a hydrocarbon stream containing C₅-C₆ iso-alkanes, wherein the content of the C₅-C₆ iso-alkanes 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. 2) a hydrocarbon stream conversion unit, configured to be capable of converting at least a part (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) of the C₅-C₆ iso-alkanes in the presence of a catalyst and hydrogen by a conversion reaction to C₂-C₆ n-alkanes, so as to obtain a conversion product, wherein the catalyst comprises a molecular sieve and a non-noble metal hydrogenation-active metal component,
3. 3) a steam cracking unit, configured to be capable of steam cracking the conversion product to obtain a cracking product comprising ethylene.

TECHNICAL EFFECTS

Compared with the prior art, the process and system provided by the present invention can achieve one or all or a part of the following technical effects:

1. For hydrocracking reactions, the smaller the molecule, the more difficult it is to undergo cracking, 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. Meanwhile, when the target product is n-alkanes, the molecular sieve of the catalyst needs to have a straight pore structure, which is also more beneficial for the formation of n-alkanes. Therefore, when processing feedstocks rich in C₅ and C₆ iso-alkanes, a catalyst with a special pore structure needs to be selected. The inventors have found through research that molecular sieves with shape-selective properties have very good reaction performance for reactions involving molecules with small molecular diameters (including n-alkanes and short-chain iso-alkanes), and can effectively convert C₅ and C₆ iso-alkanes. The hydrocarbon stream containing C₅ and C₆ iso-alkanes, after hydroconversion, can significantly improve the triene yield of a steam cracking plant for ethylene production, improving the economic benefits of the ethylene device.
2. The processing capacity of an ethylene device is based on ethylene yield. That is, the higher the ethylene yield, the less feedstock is consumed by the ethylene device. Since feedstock cost accounts for more than 60% of the processing cost of an ethylene device, improving ethylene yield can significantly reduce the processing cost of the ethylene device.
3. The content of C₅ and C₆ iso-alkanes in the hydrocarbon stream is controlled to be 60-90%. Since the hydroconversion process mainly includes two reactions: normalization and cracking, and the normalization reaction is more ideal because it does not consume hydrogen. The inventors have found through research that the normalization reaction of iso-alkanes is affected by chemical equilibrium, where a high content of n-alkanes in the reactants inhibits the normalization reaction; meanwhile, an excessively low iso-alkane content causes loss of n-alkanes in the feedstock, converting C₅ and C₆ n-alkanes in the feedstock into iso-alkanes or small-molecule n-alkanes, deteriorating product quality or causing unnecessary hydrogen consumption. In current petroleum processing, reaction processes following the carbocation reaction mechanism, such as hydrocracking and catalytic cracking, produce C₅ and C₆ products rich in iso-alkanes, but the iso-alkane content does not exceed 90%. To obtain a raw material with higher iso-alkane content, special separation methods are required, including adsorption separation and distillation, which consume high energy and significantly increase processing costs.
4. During the steam cracking process for ethylene production, the feedstock needs to have a controlled sulfur content. If the sulfur content is too low, sulfur injection is required before the cracking furnace; otherwise, coking in the ethylene cracking furnace is accelerated, affecting the operating cycle and cracking performance. If the sulfur content in the feedstock is too high, the operating cost of subsequent desulfurization increases. When producing ethylene raw material through a hydrogenation reaction, by processing a sulfur-containing feedstock and controlling an appropriate sulfur content in the hydrogenation products, the sulfur content in the ethylene device feedstock can be effectively controlled, reducing or even eliminating the sulfur injection requirement for the ethylene cracking furnace.
5. During the hydrogenation of a sulfur-containing hydrocarbon stream, organic sulfides are converted into hydrogen sulfide, which part of hydrogen sulfide is a worthless product for the hydrogenation device and even needs to be removed by separation means such as stripping. The removed hydrogen sulfide then requires subsequent harmless treatment. When the hydrogenation product containing a certain amount of hydrogen sulfide is used as ethylene raw material, it can solve the problem of sulfur injection for ethylene production, achieving high-value utilization of a non-beneficial component.
6. When C₅-C₆ iso-alkanes are directly used as raw material for ethylene, the yield of either ethylene or triene is lower, while the ratio of C₂-C₃ low-carbon alkanes to C₄-C₆ n-alkanes in the hydrogenation product can be flexibly adjusted through hydrogenation conversion. Depending on the two different reaction routes of C₅-C₆ iso-alkanes, the two different reaction routes of cracking and normalization can be flexibly adjusted by adjusting the acid strength of the acid center of the catalyst. If the hydrogen is of lower cost or the hydrogen is of higher surplus, then more C₂-C₃ low-carbon alkanes can be produced, so that the yield of the target product of ethylene is improved greatly; whilst if the hydrogen is of higher cost or the hydrogen is of lower surplus, more C₄-C₆ n-alkanes can be produced, and the improvement of the ethylene raw material quality is realized with lower hydrogen consumption.
7. The hydrocarbon structure composition of the ethylene hydrocarbon streams is flexibly adjusted, and the operation flexibility of the ethylene device can be realized to the maximum extent, including flexibly adjusting the yield of main target products of ethylene, propylene, butadiene and aromatic hydrocarbons of the ethylene device, such that the product structure can be adjusted according to the change of market demands, and the market competitiveness of the ethylene device is improved.
8. The hydro-conversion product has high content of C₂-C₆ n-alkanes, especially C₂-C₃ small molecular n-alkanes, such that better ethylene yield can be obtained in the steam cracking process, and meanwhile, C₄-C₆ n-alkanes in the hydro-conversion product is greatly improved compared with the raw material, which thus can be directly used as an ethylene raw material.
9. The present invention aims at maximizing the production of C₂-C₆ n-paraffinic alkanes, while the prior art usually converts C₅-C₆ iso-alkanes into n-alkanes, i.e., only normalization reaction occurring while inhibiting cracking reactions, where the whole normalization reaction process needs to be carried out at a reduced reaction temperature and a reduced hydrogen-to-oil volume ratio. However, the normalization reaction is influenced by chemical equilibrium, and the normalization reaction is inhibited after the n-alkane concentration in the product reaches a certain ratio (about 30%), such that the yield of n-alkanes in the product is difficult to be improved by adjusting the reaction process, and the process needs to be combined with separation of n- and iso-alkanes to separate out n-alkanes and then to convert the unconverted iso-alkanes. However, C₂-C₆ n-alkanes are all ideal raw materials for preparing ethylene by steam cracking, and the invention uses a special catalyst and controls the reaction conditions, strengthens the occurrences of both normalization and cracking reaction at the same time, breaks the influence of chemical equilibrium on the normalization reaction, and further improves the yield of n-alkanes in the conversion product by the cracking reaction, where the latter is particularly suitable for being directly used as a steam cracking raw material to prepare ethylene. The present invention has been developed based on this object.

Description of Drawings

Fig.1 is a schematic figure of the process according to the present invention. In Fig.1, 1-hydrocarbon stream, 2-hydrogen, 3-hydroconversion reaction zone, 4-hydroconversion reaction zone effluent, 5-high pressure separator, 6-hydrogen-enriched gas-phase stream, 7-liquid-phase stream.
Fig.2 is a schematic figure of the process according to the present invention. In Fig.2, 1-hydrocarbon stream, 2-hydrogen, 3-hydroconversion reaction zone, 4-hydroconversion reaction zone effluent, 5-high pressure separator, 6-hydrogen-enriched gas-phase stream, 7-liquid-phase stream, 8-fractionation column, 9-gas-phase product, 10-liquid-phase product.

Embodiments of the Invention

The embodiments of the present invention will be illustrated in more detail below, but it should be understood that the scope of the invention is not limited by the embodiments, but is defined by the claims appended.
All publications, patent applications, patents, and other references mentioned in this specification are herein incorporated by reference in their entirety. Unless defined otherwise, all technical and scientific terms used herein are understood same as the meanings commonly known to those skilled in the art. In case of conflict, definitions according to the present specification will control.
When the specification introduces materials, substances, processes, steps, devices, components, or the like initiated with "known to those ordinary skill in the art", "prior art", or the like, it is intended that the subject matter so initiated encompass not only those conventionally used in the art at the time of filing this application, but also those may not be so commonly used at the present time, but will become known in the art as being suitable for a similar purpose.
In the context of the present invention, all numerical values of a parameter (e.g., quantity or condition) are to be understood as being modified in all instances by the term "about", whether or not "about" actually appears before the numerical value.
In the context of the present invention, each device used in the present invention may adopt a structure conventionally selected in the art without being particularly limited thereto.
In the context of present invention, the term "substantially" means a deviation acceptable or considered as reasonable by a person skilled in the art, such as within ± 5%, within ± 1%, within ± 0.5% or within ± 0.1%.
In the context of the present invention, the initial boiling point and the end boiling point are measured according to the method of ASTM D86
In the context of the present invention, the sulfur content is measured according to the method of GB/T 380.
In the context of the present invention, the term " C₂-C₆ n-alkanes" refers to n-alkanes having from 2 to 6 carbon atoms. It is to be specifically understood that although the alkanes having from 2 to 3 carbon atoms cannot be classified into n-alkane and iso-alkane, the alkanes having from 2 to 3 carbon atoms are also called as n-alkanes in the present invention for convenience of description. In addition, when the term is used in the present invention, the term may refer to any one or more of n-alkanes having from 2 to 6 carbon atoms, or all of n-alkanes having from 2 to 6 carbon atoms, unless otherwise specified.
In the context of the present invention, a cyclic hydrocarbon refers to a hydrocarbon having a cyclic structure in the molecular structure, such as cycloalkanes and aromatics.
All percentages, parts, ratios, and the like referred to in the specification are based on weight, and pressures denote gauge pressures unless explicitly indicated.
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 resulted are part of the original disclosure of the present specification, and also fall within the scope of the present invention.
According to one embodiment of the present invention, a process for improving the quality of a hydrocarbon stream is involved. Herein, "improving the quality" refers to changing the chemical composition of a hydrocarbon stream through chemical conversion to make it more easily convertible into high-value-added products such as ethylene via steam cracking.
According to one embodiment of the present invention, the process comprises the step of providing a hydrocarbon stream containing C₅-C₆ iso-alkanes. According to the present invention, the hydrocarbon stream may be produced by any known method in the art, as long as it meets the requirements of the present invention for the hydrocarbon stream. As a method for producing the hydrocarbon stream, for example, hydrocracking, catalytic cracking, or atmospheric and vacuum distillation may be mentioned. Preferably, the hydrocarbon stream has an initial boiling point of 10-30°C (preferably 15-25°C) and an end boiling point of 50-100°C (preferably 55-70°C), and more preferably the hydrocarbon stream is a light naphtha fraction obtained by hydrocracking a hydrocarbon oil feedstock.
According to one embodiment of the present invention, to achieve the technical effects of the present invention, the content of the C₅-C₆ iso-alkanes in the hydrocarbon stream is generally 60-90 wt%, preferably 70-80 wt%, based on the total weight of the hydrocarbon stream being 100 wt%. The inventors of the present invention have found that the iso-alkane content in the hydrocarbon stream must be within a certain proportion. If the iso-alkane content is too low, the increase of n-alkane proportion in the product is limited, and at the same time, some n-alkanes may be cracked, causing loss of hydrogen. If the iso-alkane content is too high, conventional separation methods cannot achieve it; while adsorption separation or distillation is required, consuming higher energy.
According to one embodiment of the present invention, the C₇₊ hydrocarbon content in the hydrocarbon stream is not particularly limited, but to make the technical effects of the present invention more excellent, the C₇₊ hydrocarbon content in the hydrocarbon stream is generally 0-10 wt% (preferably 0.5-5 wt%), based on the total weight of the hydrocarbon stream being 100 wt%. The inventors of the present invention have found that a too high C₇₊ hydrocarbon content in the hydrocarbon stream will entrain a certain amount of aromatic hydrocarbons. However, aromatic hydrocarbons are difficult to be converted effectively under the conversion reaction conditions of the present invention (e.g., conversion is generally less than 10%) and behave as inert components. Therefore, a too high C₇₊ hydrocarbon content will significantly inhibit the conversion activity of the hydrocarbon stream of the present invention, which is disadvantageous for the present invention.
According to one embodiment of the present invention, the C₅-C₆ n-alkane content in the hydrocarbon stream is not particularly limited, but to make the technical effects of the present invention more excellent, the C₅-C₆ n-alkane content in the hydrocarbon stream is generally 10-30 wt% (preferably 15-25 wt%), based on the total weight of the hydrocarbon stream being 100 wt%. The inventors of the present invention have found that a high n-alkane content in the hydrocarbon stream will inhibit the conversion reaction of iso-alkanes, and simultaneously, the increase of n-alkanes after conversion is limited, having little effect on ethylene yield.
According to one embodiment of the present invention, the C_4- hydrocarbon content in the hydrocarbon stream is not particularly limited, but to make the technical effects of the present invention more excellent, the C_4- hydrocarbon content in the hydrocarbon stream is generally 0-10 wt% (preferably 2-5 wt%), based on the total weight of the hydrocarbon stream being 100 wt%. The inventors of the present invention have found that C_4- hydrocarbons are gaseous at room temperature under normal pressure, and their solubilities in C₅-C₆ hydrocarbons are limited. Therefore, to obtain a hydrocarbon stream with high C_4- hydrocarbon content, special producing methods are required, which will significantly increase the production cost of the hydrocarbon stream of the present invention. Furthermore, the inventors of the present invention have found that compared to C₅-C₆ iso-alkanes, C₄ hydrocarbons are more difficult to be converted effectively under the conversion reaction conditions of the present invention (e.g., conversion rate is generally less than 20%). Therefore, a too high C₄ hydrocarbon content will significantly inhibit the conversion activity of the hydrocarbon stream of the present invention, which is disadvantageous for the present invention.
According to one embodiment of the present invention, the cyclic hydrocarbon content in the hydrocarbon stream is not particularly limited, but to make the technical effects of the present invention more excellent, the cyclic hydrocarbon content in the hydrocarbon stream is generally 1-10 wt% (preferably 2-5 wt%), based on the total weight of the hydrocarbon stream being 100 wt%. The inventors of the present invention have found that cycloalkanes with fewer carbon numbers can be converted, while cycloalkanes with higher carbon numbers and aromatics are difficult to be converted effectively under the processing conditions of the present invention, which components entering the ethylene device will affect the ethylene yield of the ethylene device, which is disadvantageous for the present invention.
According to one embodiment of the present invention, the process comprises converting at least a part of the C₅-C₆ iso-alkanes in the presence of a catalyst and hydrogen by a conversion reaction into C₂-C₆ n-alkanes to obtain a conversion product. Herein, "at least a part" means, 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 for C₅-C₆ iso-alkanes is not particularly limited. Therefore, the C₅-C₆ iso-alkanes may achieve this conversion rate after one conversion reaction (single-pass conversion) or after multiple cycles of recycling (e.g., unconverted C₅-C₆ iso-alkanes are separated from the conversion product and then subjected to the conversion reaction again).
According to a preferred embodiment of the present invention, the hydrocarbon stream is a sulfur-containing hydrocarbon stream. According to the present invention, by converting the sulfur-containing hydrocarbon stream, a sulfur-containing conversion product is obtained. The inventors of the present invention have found that by retaining a part of the generated hydrogen sulfide in the conversion product during separation, when the conversion product is used as an ethylene cracking feedstock, for example, when steam cracking the sulfur-containing conversion product, the need for sulfur injection before entering the ethylene cracking furnace can be reduced or even eliminated, enabling high-value utilization of waste gas.
According to the present invention, the hydrocarbon stream has a sulfur content of 50-5000 mg/kg (preferably 200-1000 mg/kg), based on the total weight of the hydrocarbon stream. The inventors of the present invention have found that a too low sulfur content in the hydrocarbon stream can easily cause continuous sulfur loss of the hydrogenation catalyst during the reaction, changing the valence state of the hydrogenation components and thereby deactivating the catalyst. Simultaneously, a too low sulfur content prevents the transfer of sulfur from the hydrocarbon stream to the hydrogenation product, failing to solve the sulfur injection issue in ethylene devices. A too high sulfur content in the hydrocarbon stream increases the difficulty of its removal by the hydrogenation reaction, especially for a low-pressure reaction process where hydrodesulfurization becomes much more difficult, while excessive sulfide residues in the hydrogenation product entering the ethylene device also increase the sulfur content of the ethylene product, increasing subsequent removal difficulty.
According to one embodiment of the present invention, the conversion reaction may be a hydro-normalization reaction to obtain a conversion product mainly comprising C₄-C₆ n-alkanes, or a hydrocracking reaction to obtain a conversion product mainly comprising C₂-C₃ alkanes. The inventors of the present invention have found through research that C₅ and C₆ iso-alkanes can undergo monomolecular and bimolecular reactions during the conversion reaction of the present invention, wherein the monomolecular reaction may convert iso-alkanes into n-alkanes, with only a small amount of iso-alkanes directly undergoing cracking reactions, while the bimolecular reaction refers to two small molecular iso-alkanes combining into a long-chain iso-alkane which then undergoes a cracking reaction. As described later 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 or strong acid, and then being loaded with a suitable hydrogenation metal, the occurrence of monomolecular and bimolecular reactions can be flexibly regulated. Moreover, as the normalization reaction is influenced by the concentration of n-alkanes and iso-alkanes in the reactants, that is, a high n-alkane concentration in the reactants inhibits the normalization reaction, such that the increase in n-alkane proportion in the conversion product is limited to some extent. Therefore, to obtain a conversion product with higher n-alkane content, the occurrence of some cracking reaction must be ensured. The inventors of the present invention also have found that cracking and normalization reactions generally occur simultaneously. However, by adjusting the molecular sieve and the acid strength of acid centers, enhancement of different reaction processes can be achieved, where strong acid centers are favorable for cracking reactions, while medium-strong acid centers are favorable for normalization reactions. Based on such reaction mechanism, the generation ratio of C₂-C₃ alkanes to C₄-C₆ n-alkanes in the conversion product can be flexibly adjusted. The inventors of the present invention have further found through research that the iso-alkane content in the feedstock also has a direct impact on the conversion process. For a cracking reaction, although the reactant is not limited to be n-alkanes or iso-alkanes, the higher the content of iso-alkanes in the raw material is, the higher the probability of cracking reaction is, and the quality of the conversion product can be improved more. For a normalization reaction, the reactant only involves iso-alkanes, and the normalization reaction is influenced by chemical equilibrium, where a higher content of iso-alkanes is more beneficial to the conversion reaction towards normalization.
According to an embodiment of the invention, the reaction conditions for the conversion reaction include: a reaction pressure of 0.5-10.0MPaG (preferably 2.0-8.0MPaG or 2.0-5.0 MPaG), a reaction temperature of 250-500 °C, preferably 300-500 °C or 350-450 °C, a liquid hourly space velocity of 0.1-15.0 h^-1 (preferably 0.5-5.0 h^-1), and a hydrogen-oil volume ratio of 10:1-2500:1, preferably 50:1-2500:1, 100:1-2000:1 or 100:1-1000:1. The inventors of the present invention have found that during the process of hydroconversion of C₅-C₆ iso-alkanes, both normalization reaction and cracking reaction are typically endothermic reactions, where the higher the reaction temperature is, the more favorable the chemical reaction is to proceed towards the positive reaction direction. A too low reaction temperature can inhibit both the normalization reaction and the cracking reaction, thus seriously affecting the iso-alkane conversion. C₅-C₆ iso-alkanes are in gas form at a high temperature, such that during the gas-phase reaction, the hydrogen-oil ratio is represented as the hydrogen concentration per unit volume, and a higher hydrogen concentration is beneficial for hydrogen to be bound with reactants, so as to promote the normalization and hydrogenolysis reaction.
The inventors of the present invention have found that the paraffinic alkanes or the C₅-C₆ iso-alkanes may exhibit a one-pass conversion rate of 40wt% or more, 50wt% or more, 60wt% or more, 70wt% or more, 80wt% or more, or 90wt% or more under the reaction conditions of the present invention. Furthermore, regarding the conversion of C₇₊ components, larger molecule cycloalkanes with higher carbon numbers are difficult to enter the catalyst pores for ring-opening reactions, while the cracking reaction of aromatics first requires hydrogenation saturation of the aromatics. The hydrogenation saturation of aromatics is directly affected by reaction pressure. However, to achieve better conversion effects for iso-alkanes, the present invention uses lower reaction pressure, which is not favorable for the hydrogenation saturation of aromatics, resulting in poor conversion effects for aromatics. The inventors of the invention have found that in the process of the hydroconversion of low-carbon hydrocarbons, the reactant is firstly subjected to a dehydrogenation reaction to generate carbonium ions, and the bond energy between C-C bonds is gradually increased along with the reduction of the molecular weight of the hydrocarbon, namely, the smaller the molecular weight is, the more difficult the dehydrogenation reaction occurs, so that C₄ is difficult to be reacted under conversion conditions appropriate for C₅-C₆ iso-alkanes, and harsher reaction conditions are required for sufficient reaction of a C₄ component, which causes excessive cracking of C₅-C₆ iso-alkanes, resulting in great increase of hydrogen consumption of the reaction, which reduces the economic benefit.
According to one embodiment of the present invention, the conversion reaction is carried out in the presence of a catalyst, the catalyst comprises a molecular sieve and a non-noble metal hydrogenation active metal component. According to the invention, the molecular sieve is one or more selected from the group consisting of mordenite, ZSM molecular sieve, SAPO molecular sieve and EU-1 molecular sieve, more preferably one or more selected from the group consisting of mordenite and ZSM molecular sieve, particularly preferably one or more selected from the group consisting 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, and especially one or more selected from the group consisting of mordenite and ZSM-5 molecular sieve. Here, the molecular sieve is present in an amount of 30-80wt% (preferably 40-70 wt%), based on the weight of the catalyst. The inventors of the invention have found that the acid strength of the molecular sieve directly influences the reaction behaviors of iso-alkane, where the molecular sieves having more strong acid centers are more likely to cause a cracking reaction, such as ZSM-5 molecular sieve; while the molecular sieves having more medium-strong acid centers are more likely to cause a normalization reaction, such as mordenite. Thus, according to the present invention, different reaction routes can be achieved by selection of molecular sieve acid strength. The inventors of the invention have found that in the conversion process of C₅-C₆ iso-alkanes, the pore structure of the molecular sieve directly affects the reaction effect. For example, a molecular sieve such as Y molecular sieve having a super cage structure has large pore channels, such that the retention time of small molecular iso-alkanes in the pore channels of the catalyst is short, resulting in the reaction difficult to be effectively carried out. Meanwhile, when a cracking reaction occurs, the large pore structure can cause excessive amount of isobutane generated, which is not beneficial to improve the yield of n-alkanes in the conversion product.
The inventors of the invention have found that two types of reaction routes are mainly available in the hydroconversion process, one being a cracking reaction for converting to C₂-C₃ hydrocarbons, and the other being a normalization reaction for generating C₄-C₆ n-alkanes. Generally, the two types of reactions occur simultaneously, but different reaction processes can be respectively enhanced by adjusting the molecular sieve and the acid strength of the acid center. A strong acid center is favorable for the cracking reaction, while a medium-strong acid center is favorable for the normalization reaction. For example, a mordenite containing more medium-strong acid results in more normalization reactions; while a ZSM-5 molecular sieve containing more strong acid results in more cracking reactions. According to the invention, the weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the conversion product can be flexibly adjusted by adjusting the weight ratio of mordenite to ZSM-5 molecular sieve in the range of 0-100:100-0 (preferably 10-50:50-10). Therefore, according to the present invention, the molecular sieve type and the acid center strength of the catalyst, and the process parameters can be adjusted to provide a conversion product having a weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes flexibly adjusted within the range of 0.5:1-8:1 (preferably 0.9:1-5:1), so that different hydrocarbon components can be obtained useful for ethylene raw materials. A conversion product with higher content of C₂-C₃ hydrocarbons has higher content of normal hydrocarbons, but the conversion process thereof consumes more hydrogen; while a conversion product with higher content of C₄-C₆ n-alkanes content consumes less hydrogen during the reaction process, which also improves the quality of the ethylene raw material. Here, the C₄-C₆ n-alkanes are more preferably C₅-C₆ n-alkanes in view of more excellent achievement of the technical effect of the present invention.
According to one embodiment of the present invention, the non-noble metal hydrogenation-active metal component is one or more selected from the group consisting of non-noble metals of Group VIB and non-noble metals of Group VIII of the periodic table. Preferably, the non-noble metal of Group VIB is one or more selected from the group consisting of molybdenum and tungsten (particularly preferably molybdenum), and the non-noble metal of Group VIII is one or more selected from the group consisting of cobalt and nickel (particularly preferably nickel). Here, the non-noble metal of Group VIB (as oxide) is present in an amount of 5.0-30.0 wt% (10.0-20.0 wt%), and the non-noble metal of Group VIII (as oxide) is present in an amount of 0.5-15.0 wt% (preferably 3.0-10.0 wt%), based on the weight of the catalyst. Preferably, the non-noble metal hydrogenation-active metal component of the present invention does not contain a noble metal such as Pt or the like. The inventors of the present invention have found that a noble metal component has a stronger hydrogenation/dehydrogenation performance than a non-noble metal component, and can cause a dehydrogenation reaction at a lower reaction temperature to convert C₅-C₆ iso-alkanes into C₅-C₆ n-alkanes, while it is known that a cracking reaction is mainly affected by the reaction temperature, and the lower reaction temperature and the stronger hydrogenation performance suppress the cracking reaction. Therefore, use of a noble metal catalyst, result in difficult to produce more C₂-C₃ alkanes in an operation aiming at normalization. As compared, the non-noble metal catalyst has relatively weak dehydrogenation performance, so that the reaction needs a higher reaction temperature, and a large scale of cracking reaction is accompanied with the normalization reaction, so that more C₂-C₃ alkanes are generated.
According to an embodiment of the invention, the catalyst further comprises a binder. The binder may be of any conventional type in the art and comprises, but not limited to, alumina and silica, preferably alumina. Here, the binder is present in an amount of 5-65 wt% (preferably 10-35 wt%), based on the weight of the catalyst.
According to an embodiment of the invention, the catalyst has a specific surface area of 200-400 m²/g, and a pore volume of 0.25-0.45 mL/g.
According to an embodiment of the present invention, the catalyst may be prepared according to a conventional process in the art. The preparation process comprises the steps of preparing the support and loading the non-noble metal hydrogenation-active metal component, wherein the support is prepared by: mechanically mixing the molecular sieve and the binder, molding, drying and calcinating, to prepare the catalyst support. The drying and calcination of the support may be carried out under conventional conditions. Conditions for drying may comprise: drying for 1-12 hours at 100-150 °C. Conditions for calcination may comprise: calcinating at 450-550 °C for 2.5-6.0 hr.
According to an embodiment of the present invention, for the preparation process of the catalyst, the non-noble metal hydrogenation-active metal component is loaded by a conventional process such as a kneading process, an impregnation process, and the like, preferably an impregnation process. The impregnation process can be a saturated impregnation process, an excess impregnation process or a complexing impregnation process, where the catalyst support is impregnated by a solution containing the non-noble metal hydrogenation-active metal component, followed by drying and calcinating, to obtain a first catalyst. Conditions for drying may comprise: drying at 100-150 °C for 1-12 hr. Conditions for calcination may comprise: calcinating at 450-550 °C for 2.5-6.0 hr.
According to one embodiment of the present invention, from the perspective of balancing quality improvement effect and energy consumption, the conversion product has a C₇₊ hydrocarbon content of not more than 5 wt% (preferably not more than 1 wt%), a C₅-C₆ iso-alkane content of 0-50 wt% (preferably 10-40 wt%), a C₂-C₆ n-alkane 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 100 wt% of the total weight of the conversion product.
According to a preferred embodiment of the present invention, if the hydrocarbon stream comprises sulfur, then the conversion product also comprises sulfur. Preferably, substantially all of the sulfur contained in the hydrocarbon stream is retained in the conversion product. For this purpose, the sulfur content of the conversion product is generally 50-1000 mg/kg (preferably 100-200 mg/kg), based on the total weight of the conversion product.
According to an embodiment of the present invention, the step 3) may comprise the steps of: separating the conversion product (called as a first separation) to obtain a separated stream having C₂+ hydrocarbons as the main part (e.g., 95 wt% or more, 98 wt% or more, 99 wt% or more, or substantially 100 wt% of the total amount). Here, the C₂+ hydrocarbon means a hydrocarbon having 2 or more carbon atoms. To this end, according to the invention, the first separation is aimed at removing, by separation, hydrogen from the conversion product, which hydrogen possibly is formed during the conversion reaction or possibly unreacted hydrogen, in order to avoid hydrogen adversely affecting the subsequent steam cracking step. According to the present invention, the first separation is not particularly limited, as long as it can effectively separate hydrogen from the conversion product, and the first separation may be performed in any gas-liquid separation device conventionally known in the art, such as a flash drum, without being particularly limited. According to the invention, the first separation is generally operated under conditions comprising a pressure of 0.5-10.0MPaG (preferably 2.0-8.0MPaG or 2.0-5.0MPaG) and a temperature of 40-70 °C. Further according to the invention, the separated hydrogen can be recycled as a recycled stream to the step 2) for the conversion reaction.
According to an embodiment of the present invention, the step 3) may further comprise the steps of: separating the separated stream (called as a second separation) to obtain a higher-carbon stream having C₄+ hydrocarbons as the main part (such as 90 wt% or more, 95 wt% or more, 98 wt% or more, 99 wt% or more, or substantially 100 wt% of the total amount) and a lower-carbon stream having C₂-C₃ hydrocarbons as the main part (such as 90 wt% or more, 95 wt% or more, 98 wt% or more, 99 wt% or more, or substantially 100 wt% of the total amount). Here, the C₄+ hydrocarbon refers to a hydrocarbon having 4 or more carbon atoms, and encompasses C₄-C₆ iso-alkane and C₄-C₆ n-alkanes, while the C₂-C₃ hydrocarbon encompasses ethane and propane. To this end, according to the invention, the second separation is aimed at an efficient separation of hydrocarbons having 4 or more carbon atoms from hydrocarbons having 2 and 3 carbon atoms in the separated stream. However, the second separation is not intended to separate any isomers, e.g., the second separation being not intended to separate C₄-C₆ iso-alkanes from C₄-C₆ n-alkanes in the separated stream, which is a characteristic of the present invention. The invention aims to produce C₂-C₆ n-alkanes in maximum quantity. In the prior art, C₅-C₆ iso-alkanes are generally converted into n-alkanes, namely only normalization reaction occurs, while cracking reaction is inhibited, where the whole normalization reaction process prefers reduced reaction temperature and reduced hydrogen-oil volume ratio. However, the normalization reaction is influenced by chemical equilibrium, such that when the n-alkanes concentration in the product reaches a certain proportion (about 30%), the normalization reaction is inhibited, resulting in the yield of n-alkanes in the product difficult to be improved by adjusting the reaction process, which means this reaction route needs to be combined with a separation of n- and iso-alkanes, wherein after the n-alkanes are separated, the unconverted iso-alkanes are continuously converted. However, C₂-C₆ n-alkanes are ideal raw materials for preparing ethylene by steam cracking. The invention uses a special catalyst and controls reaction conditions, which strengthens the occurrence of both normalization and cracking reaction at the same time, breaking the influence of chemical equilibrium on the normalization reaction, so as to further improve the yield of n-alkanes in the conversion product by conducting the cracking reaction, and thus is particularly suitable for being directly used as a steam cracking raw material to prepare ethylene. The inventors of the present invention have found that generally, a steam cracking device comprises a plurality of reactors depending on different feeds, mainly because a reaction feed with lower molecular weight needs higher cracking temperature, such as a gas reactor and a liquid reactor. In the process of converting iso-alkanes, the distribution of the conversion product can be flexibly adjusted according to different requirements. If the content of C₂-C₃ in the conversion product is lower, a second part of separation is not needed, and the conversion product is fed directly into a liquid reactor for conversion; while if the content of C₂-C₃ is higher, a second part of separation needs to be carried out, and the separated products are fed respectively into a gas reactor and a liquid reactor. The invention does not provide a traditional normalization reaction, namely, iso-alkanes being converted into n-alkanes with the same molecular weight, in which conversion process, in order to obtain higher yield of n-alkanes, a certain amount of cracking reaction is accompanied, where the generated C₂-C₃ alkanes are very easy to be separated from the liquid-phase product, and the liquid-phase product obtained after conversion is greatly reduced compared with the fresh feed, meanwhile, the proportion of n-alkanes is greatly improved, such that the separation of n- and iso-alkanes carried out subsequently will result in greatly increased energy consumption and reduced overall economic benefit.
According to the present invention, the second separation is not particularly limited, as long as it can effectively separate the C₄+ hydrocarbons from the C₂-C₃ hydrocarbons, and the second separation can be performed in any gas-liquid separation device conventionally known in the art, such as a rectifying column, without being particularly limited. According to the invention, the operating conditions of the second separation comprise a pressure of 0.5-1.5MPaG and a temperature of 30-60 °C. In the process of converting iso-alkanes, the distribution of the conversion products can be flexibly adjusted according to different requirements, where if the content of C₂-C₃ in the conversion product is low, the conversion product does not need a second separation and can be directly fed into a liquid reactor for conversion, while if the content of C₂-C₃ is high, the conversion product needs a second separation and the separated products are fed respectively into a gas reactor and a liquid reactor.
According to an embodiment of the present invention, the step 3) may further comprise the step of: recycling the higher-carbon stream as a hydrocarbon stream back to the step 2) for the conversion reaction. The inventors of the present invention have found that the higher-carbon stream contains unreacted C₅-C₆ iso-alkanes and is therefore suitable for continuing the conversion reaction as a hydrocarbon stream. This recycling step is an optional step, but is preferably an essential step.
According to an embodiment of the present invention, the step 3) may further comprise the step of: steam cracking the separated stream or the lower-carbon stream, to obtain a cracked product comprising ethylene. The inventors of the present invention have found that the lower-carbon stream or the separated stream can be directly used as a feedstock for steam cracking without any additional treatment, such as separation to enrich the n-alkanes or separation to remove any light or heavy components. Here, the steam cracking may be performed in any manner conventionally known in the art, without being particularly limited. Generally, the operating conditions for the steam cracking comprise: a reaction temperature of 750-900 °C, a reaction pressure of 0.1-0.5MPaG, and a water-to-oil ratio by weight of 0.2-0.6. According to a preferred embodiment of the present invention, in the steam cracking, the amount of sulfur injected is controlled so that the sulfur content in the feedstock is 100-200 mg/kg. According to this preferred embodiment of the present invention, as the conversion product, the separation stream, or the lower-carbon stream substantially retains all of the sulfur contained in the sulfur-containing feedstock hydrocarbon, the sulfur injection requirement for the steam cracking can be reduced by at least 50%. In the most preferred case, the steam cracking may completely eliminate the need for additional sulfur injection, as the sulfur contained in the conversion product, the separation stream, or the lower-carbon stream alone can meet the steam cracking requirement.
According to one embodiment of the present invention, a system for improving the quality of a hydrocarbon stream is also involved, comprising a hydrocarbon stream providing unit and a hydrocarbon stream conversion unit. According to the invention, the system is provided to conduct the process described above, such that in addition to the contents explicitly stated in this paragraph, any other contents or items not explicitly stated may be directly referred to the contents or items correspondingly stated in the process, without being particularly limited.
The present invention will be further described with reference to the drawings, but the present invention is not limited thereto.
Referring to Fig.1, a hydrocarbon stream 1 and hydrogen 2 are mixed and fed into a hydroconversion reaction zone 3, the hydroconversion reaction zone effluent 4 is fed into a high-pressure separator 5, hydrogen-enriched gas-phase stream 6 obtained by separation is recycled, and the liquid-phase stream is used as an ethylene raw material.
Referring to Fig.2, a hydrocarbon stream 1 and hydrogen 2 are mixed and fed into a hydro-conversion reaction zone 3, the hydro-conversion reaction zone effluent 4 is fed into a high-pressure separator 5, hydrogen-enriched gas-phase stream 6 obtained by separation is recycled, a liquid phase stream 7 is fed into a fractionating column for separation to obtain a gas-phase product 9 serving as an ethylene raw material, and a liquid-phase product 10 is recycled to an inlet of the hydro-conversion reaction zone 3.

Examples

The present invention will be further described in detail below referring to Examples and Comparative Examples, but the present invention is not limited to these Examples.
In the following Examples and Comparative Examples, the high-pressure separator 5 was operated at a pressure of 2.5 MPaG and a temperature of 50 °C and the fractionation column was operated at a pressure of 1.0 MPaG and a temperature of 40 °C.

First Series of Examples

In the following Examples and Comparative Examples, the yield was calculated as the mass percent of the output compared to the feed amount. The processing benefit per ton oil denoted the gain per 1 ton of feedstock processed, calculated as (price of ethylene product-price of feedstock and hydrogen-energy consumption of processing)/processing capacity, taking the benefit obtained by using the feedstock without hydroconversion directly as the ethylene raw material as the reference of the processing benefit per ton oil.
In the following Examples and Comparative Examples, each hydroconversion catalyst was represented by Cat-A with a number, such as Cat- A1, Cat-A2, Cat-A3, and the like. The hydroconversion catalyst was prepared by a conventional saturation impregnation process for active metal, and the physicochemical properties of the obtained catalyst were shown in Table 1.
The catalyst of Cat-A was prepared by the process comprising:

(1) selecting mordenite with a SiO₂/Al₂O₃ molar ratio of 15, mechanically mixing the mordenite with a binder, molding, drying at 120°C for 10 hours, and calcinating at 500°C for 4 hours, to prepare a catalyst support.
(2) impregnating the catalyst support obtained in step (1) with a solution containing active components, drying at 120°C for 10 hours, and calcinating at 500°C for 4 hours, to prepare the hydroconversion catalyst.

The catalysts of Cat-A4 to Cat-A7 were prepared by the process comprising:

(1) selecting ZSM-5 molecular sieve with a SiO₂/Al₂O₃ molar ratio of 10, mechanically mixing the ZSM-5 with a binder, molding, drying at 120°C for 10 hours, and calcinating at 500°C for 4 hours, to prepare a catalyst support.
(2) impregnating the catalyst support obtained in step (1) with a solution containing active components, drying at 120°C for 10 hours, and calcinating at 500°C for 4 hours, to prepare the hydroconversion catalyst.

The properties of raw materials were shown in Table 2, wherein, the raw material 5 needed to be obtained by adsorption separation or rectification for a raw material containing iso-alkanes.

Table 1

Catalyst	Cat-A1	Cat-A2	Cat-A3	Cat-A4	Cat-A5	Cat-A6	Cat-A7
Pore Volume, cm³/g	0.35	0.45	0.25	0.35	0.45	0.25	0.35
Specific Surface Area, m²/g	300	200	400	300	200	400	300

Content, wt%, based on carrier weight
Mordenite	55	40	70
ZSM-5				55	40	70	55
Alumina	19	25	17	19	25	17	44

Active Metal Content in Catalyst, wt%
MoO₃	20	25	10	20	25	10
NiO	6	10	3	6	10	3
Pt							1

Table 2

Raw material	Raw material 1	Raw material 2	Raw material 3	Raw material 4	Raw material 5	Raw material 6	Raw material 7
C₄ iso-alkane content, wt%	1	2	0.5	1	0.4	80	100
C₄ n-alkane content, wt%	2	3	1.5	2	0.6	11	0
C₅-C₆ n-alkanes content, wt%	16	28	10	42	3	2	0
C₅-C₆ iso-alkanes content, wt%	78	65	85	50	95	7	0
C₇₊ Hydrocarbons and Cyclic Hydrocarbon content, wt%	3	2	3	5	1	0	0
Initial boiling point, °C	24	25	22	25	23	16
End boiling point, °C	64	66	63	67	62	45

Example 1

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

In this Example, about 49 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 2

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A2;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

In this Example, about 45 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 3

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A3;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

In this Example, about 34 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 4

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A4;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

In this Example, about 64 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 5

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A5;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

In this Example, about 60 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 6

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A6;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

In this Example, about 52 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 7

The process shown in Fig.2 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A4;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was separated by the fractionation column to provide C₂ and C₃ hydrocarbons to be used as ethylene raw material, while the remaining stream was cracked. The process conditions and quality improvement results in this Example are shown in Table 3.

In this Example, about 78 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₃ n-alkanes.

Example 8

The process shown in Fig.2 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A5;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was separated by the fractionation column to provide C₂ and C₃ hydrocarbons to be used as ethylene raw material, and the C₄-C₆ hydrocarbons were recycled for cracking. The process conditions and quality improvement results in this Example are shown in Table 3.

Example 9

The process shown in Fig.2 was used, comprising:

Example 10

The process shown in Fig.1 was used, comprising:

(1) the raw material 2 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

Example 11

The process shown in Fig.1 was used, comprising:

(1) the raw material 3 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A4;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

In this Example, about 65 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 12

The process shown in Fig.1 was used, comprising:

In this Example, about 27 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 13

The process shown in Fig.2 was used for improving hydrocarbon stream quality, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A4;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was separated to provide C₂ and C₃ hydrocarbons to be used as ethylene raw material, while the remaining stream (called as the C₄-C₆ recycling stream) was cracked. The process conditions and quality improvement results in this Example are shown in Table 3.

In this Example, about 78 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₃ n-alkanes. The weight ratio of the C₄-C₆ recycling stream to the raw material 1 was 0.3:1.

Example 14

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A5;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was separated to provide C₂ and C₃ hydrocarbons to be used as ethylene raw material, and the C₄-C₆ hydrocarbons were recycled for cracking. The process conditions and quality improvement results in this Example are shown in Table 3.

In this Example, about 78 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₃ n-alkanes. The weight ratio of the C₄-C₆ recycling stream to the raw material 1 was 0.4:1.

Example 15

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A6;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was separated to provide C₂ and C₃ hydrocarbons to be used as ethylene raw material, and the C₄-C₆ hydrocarbons were recycled for cracking. The process conditions and quality improvement results in this Example are shown in Table 3.

Comparative Example 1

The process shown in Fig.1 was used, comprising:

(1) the raw material 4 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

Comparative Example 2

The process shown in Fig.1 was used, comprising:

(1) the raw material 4 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A4;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

Comparative Example 3

The process shown in Fig.1 was used, comprising:

(1) the raw material 5 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

Comparative Example 4

The process shown in Fig.1 was used, comprising:

(1) the raw material 5 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A4;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

Comparative Example 5

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A7;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

Comparative Example 6

The process shown in Fig.1 was used, comprising:

(1) the raw material 6 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

Comparative Example 7

The process shown in Fig.1 was used, comprising:

(1) the raw material 7 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

Comparative Example 8

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone, with a reaction temperature of 250°C; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

Comparative Example 9

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone, with a reaction temperature of 200°C; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

Comparative Example 10

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone, with a hydrogen-to-oil volume ratio of 20:1; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

Comparative Example 11

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone, with a hydrogen-to-oil volume ratio of 5:1; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

Comparative Example 12

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with a commercially available solid acid catalyst;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and quality improvement results in this Example are shown in Table 3.

Table 3 Quality Improvement Results

No.	Example 1	Example 2	Example 3
Hydroconversion
Raw material	Raw material1	Raw material1	Raw material1
Catalyst	Cat-A1	Cat-A2	Cat-A3
Reaction temperature/°C	400	400	380
Reaction pressure/MPa	3.0	3.0	3.0
Volume ratio of hydrogen-to-oil	400	400	400
Volume space velocity/h^-1	0.8	0.8	0.8
Content of C₂-C₆ n-alkanes in the product, wt%	65	61	50

Preparation of ethylene by steam cracking
Reaction temperature/°C	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3
Water-to-oil ratio by weight	0.4	0.4	0.4
Yield of ethylene, wt%	37.5	35.1	33.2
Yield of propylene, wt%	15.8	16.3	17.7
Yield of butadiene, wt%	3.5	3.7	3.8
Processing benefit per ton oil, CNY/ton	Reference+200	Reference+180	Reference+130

No.	Example 4	Example 5	Example 6
Hydroconversion
Raw material	Raw material 1	Raw material 1	Raw material 1
Catalyst	Cat-A4	Cat-A5	Cat-A6
Reaction temperature/°C	410	415	405
Reaction pressure/MPa	3.0	3.0	3.0
Volume ratio of hydrogen to oil	400	400	400
Volume space velocity/h^-1	0.6	0.6	0.6
Content of product C2-C6 n-alkanes, wt%	80	76	68

Preparation of ethylene by steam cracking
Reaction temperature/°C	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3
Water-to-oil ratio by weight	0.4	0.4	0.4
Yield of ethylene, wt%	40.6	39.5	38.1
Yield of propylene, wt%	13.3	13.8	14.5
Yield of butadiene, wt%	3.3	3.4	3.6
Processing benefit per ton oil, CNY/ton	Reference+190	Reference+180	Reference+140

Continued Table 3 Quality Improvement Results

No.	Example 7	Example 8	Example 9
Hydroconversion
Raw material	Raw material 1	Raw material 1	Raw material 1
Catalyst	Cat-A4	Cat-A5	Cat-A6
Reaction temperature/°C	395	393	398
Reaction pressure/MPa	3.0	3.0	3.0
Volume ratio of hydrogen-to-oil	400	400	400
Volume space velocity/h^-1	1.0	1.0	1.0
Content of C₂-C₆ n-alkanes in the product, wt%	92	90	89

Preparation of ethylene by steam cracking
Reaction temperature/°C	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3
Water-to-oil ratio by weight	0.4	0.4	0.4
Yield of ethylene, wt%	47.0	45.8	45.3
Yield of propylene, wt%	9.8	10.2	10.5
Yield of butadiene, wt%	4.0	4.1	4.1
Processing benefit per ton oil, CNY/ton	Reference+160	Reference+60	Reference+80

No.	Example 10	Example 11	Example 12
Hydroconversion
Raw material	Raw material 2	Raw material 3	Raw material 1
Catalyst	Cat-A1	Cat-A4	Cat-A1
Reaction temperature/°C	420	415	370
Reaction pressure/MPa	3.0	3.0	3.0
Volume ratio of hydrogen-to-oil	400	400	400
Volume space velocity/h^-1	0.8	0.6	0.8
Content of C₂-C₆ n-alkanes in the product, wt%	67	75	43

Preparation of ethylene by steam cracking
Reaction temperature/°C	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3
Water-to-oil ratio by weight	0.4	0.4	0.4
Yield of ethylene, wt%	37.8	39.2	30.8
Yield of propylene, wt%	14.6	13.9	18.9
Yield of butadiene, wt%	2.8	3.6	3.9
Processing benefit per ton oil, CNY/ton	Reference+60	Reference+80	Reference+50

Continued Table 3 Quality Improvement Results

No.	Example 13	Example 14	Example 15
Hydroconversion
Raw material	Raw material 1	Raw material 1	Raw material 1
Catalyst	Cat-A4	Cat-A5	Cat-A6
Reaction temperature/°C	395	393	398
Reaction pressure/MPa	3.0	3.0	3.0
Volume ratio of hydrogen to oil	400	400	400
Volume space velocity/h^-1	1.0	1.0	1.0
Content of C₂-C₆ n-alkanes in the product, wt%	92	90	89

Continued Table 3 Quality Improvement Results

No.	Comparative Example 1	Comparative Example 2	Comparative Example 3	Comparative Example 4
Hydroconversion
Raw material	Raw material4	Raw material4	Raw material5	Raw material5
Catalyst	Cat-A1	Cat-A4	Cat-A1	Cat-A4
Reaction temperature/°C	400	400	400	400
Reaction pressure/MPa	3.0	3.0	3.0	3.0
Volume ratio of hydrogen to oil	400	400	400	400
Volume space velocity/h^-1	0.8	0.6	0.8	0.6
Content of C₂-C₆ n-alkanes in the product, wt%	58	78	48	74

Preparation of ethylene by steam cracking
Reaction temperature/°C	880	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3	0.3
Water-to-oil ratio by weight	0.4	0.4	0.4	0.4
Yield of ethylene, wt%	34.4	40.0	32.7	37.9
Yield of propylene, wt%	16.6	13.5	17.5	14.0
Yield of butadiene, wt%	3.8	3.5	3.7	3.6
Processing benefit per ton oil, CNY/ton	Reference-20	Reference-30	Reference-50	Reference-70

No.	Comparative Example 5	Comparative Example 6	Comparative Example 7	Comparative Example 8
Hydroconversion
Raw material	Raw material1	Raw material6	Raw material7	Raw material1
Catalyst	Cat-A7	Cat-A1	Cat-Al	Cat-A1
Reaction temperature/°C	330	420	400	250
Reaction pressure/MPa	3.0	3.0	3.0	3.0
Volume ratio of hydrogen to oil	600	400	400	400
Volume space velocity/h^-1	1.0	0.6	1.0	0.8
Content of C₂-C₆ n-alkanes in the product, wt%	45	43	38	18

Preparation of ethylene by steam cracking
Reaction temperature/°C	880	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3	0.3
Water-to-oil ratio by weight	0.4	0.4	0.4	0.4
Yield of ethylene, wt%	31.4	30.8	27.5	26.6
Yield of propylene, wt%	18.5	18.6	18.9	19.1
Yield of butadiene, wt%	3.8	3.8	4.2	3.3
Processing benefit per ton oil, CNY/ton	Reference-40	Reference-30	Reference-50	-120

No.	Comparative Example 9	Comparative Example 10	Comparative Example 11	Comparative Example 12
Hydroconversion
Raw material	Raw material1	Raw material1	Raw material1	Raw material1
Catalyst	Cat-A1	Cat-A1	Cat-A1	Solid acid catalyst
Reaction temperature/°C	200	400	400	400
Reaction pressure/MPa	3.0	3.0	3.0	3.0
Volume ratio of hydrogen to oil	400	20	5	400
Volume space velocity/h^-1	0.8	0.8	0.8	0.8
Content of C₂-C₆ n-alkanes in the product, wt%	18	24	22	42

Preparation of ethylene by steam cracking
Reaction temperature/°C	880	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3	0.3
Water-to-oil ratio by weight	0.4	0.4	0.4	0.4
Yield of ethylene, wt%	26.6	29.2	28.5	30.6
Yield of propylene, wt%	19.1	18.7	18.8	18.9
Yield of butadiene, wt%	3.3	3.2	3.2	3.9
Processing benefit per ton oil, CNY/ton	-120	-110	-100	-30

By comparison, it could be seen that the process according to the present invention could effectively convert a low-quality ethylene raw material into a high-quality ethylene raw material, where the hydrocarbon stream after the hydro-conversion could greatly improve the yield of ethylene and the yield of triene of the ethylene device. Moreover, the process procedures according to the present invention was simple with low difficulty of operation, thus had very good economic benefit.

Second Series of Examples

In the following Examples and Comparative Examples, the yield was calculated as the mass percent of the output compared to the feed amount. The processing benefit per ton oil denoted the gain per 1 ton of feedstock processed, calculated as (price of ethylene product-price of feedstock and hydrogen-energy consumption of processing)/processing capacity, taking the benefit obtained by using the feedstock without hydroconversion directly as the ethylene raw material as the reference of the processing benefit per ton oil.
In the following Examples and Comparative Examples, each hydroconversion catalyst was represented by Cat-A with a number, such as Cat-A1, Cat-A2, Cat-A3, etc. The hydroconversion catalysts were prepared by a conventional saturation impregnation process for active metal, and the physicochemical properties of the obtained catalyst were shown in Table 1
The catalysts of Cat-A1 to Cat-A3 were prepared by the process comprising:

The catalysts of Cat-A4 to Cat-A6 were prepared by the process comprising:

The catalyst of Cat-A7 was prepared by the process comprising:

(1) selecting mordenite with a SiO₂/Al₂O₃ molar ratio of 15, mechanically mixing the mordenite with a binder, molding, drying at 120°C for 10 hours, and calcinating at 500°C for 4 hours, to prepare the catalyst.

Table 1

Catalyst	Cat-A1	Cat-A2	Cat-A3	Cat-A4	Cat-A5	Cat-A6	Cat-A7
Pore volume, cm³/g	0.35	1.45	0.25	0.35	0.45	0.25	0.35
Specific surface area, m²/g	300	200	400	300	200	400	300

Content, wt%, based on the weight of the support
Mordenite	55	40	70				55
ZSM-5				55	40	70
Alumina	19	25	17	19	25	17	45

Active metal content in the catalyst, wt%
MoO₃	20	25	10	20	25	10	0
NiO	6	10	3	6	10	3	0

Table 2

Raw material	Raw material 1	Raw material 2	Raw material 3	Raw material 4	Raw material 5	Raw material 6	Raw material 7	Raw material 8
C₄ iso-alkane content, wt%	1	2	0.5	1	0.4	80	1	1
C₄ n-alkane content, wt%	2	3	1.5	2	0.6	11	2	2
C₅-C₆ n-alkanes content, wt%	16	28	10	42	3	2	16	16
C₅-C₆ iso-alkanes content, wt%	78	65	85	50	95	7	78	78
C₇₊ Hydrocarbons and Cyclic Hydrocarbon content, wt%	3	2	3	5	1	0	3	3
Sulfur content, wt%	600	200	1000	6000	30	500	150	3000
Initial boiling point, °C	24	25	22	25	23	16	24	24
End boiling point, °C	64	66	63	67	62	45	64	64

Example 1

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 47 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 2

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A2;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 38 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 3

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A3;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 31 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 4

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A4;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 59 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 5

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A5;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 53 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 6

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A6;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 46 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 7

The process shown in Fig.2 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A4;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was separated by the fractionation column to provide C₂ and C₃ hydrocarbons to be used as ethylene raw material, while the remaining stream (called as the C₄-C₆ recycling stream) was cracked. The process conditions and conversion results in this Example are shown in Table 3.

Example 8

The process shown in Fig.2 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A5;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was separated by the fractionation column to provide C₂ and C₃ hydrocarbons to be used as ethylene raw material, and the C₄-C₆ hydrocarbons were recycled for cracking. The process conditions and conversion results in this Example are shown in Table 3.

Example 9

The process shown in Fig.2 was used, comprising:

Example 10

The process shown in Fig.1 was used, comprising:

(1) the raw material 2 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 39 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 11

The process shown in Fig.1 was used, comprising:

(1) the raw material 3 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A4;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 36 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 12

The process shown in Fig.1 was used, comprising:

In this Example, about 28 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes.

Example 13

The process shown in Fig.1 was used, comprising:

(1) the raw material 7 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

Example 14

The process shown in Fig.1 was used, comprising:

(1) the raw material 8 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

Comparative Example 1

The process shown in Fig.1 was used, comprising:

(1) the raw material 4 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

Comparative Example 2

The process shown in Fig.1 was used, comprising:

(1) the raw material 4 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A4;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

Comparative Example 3

The process shown in Fig.1 was used, comprising:

(1) the raw material 5 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

Comparative Example 4

The process shown in Fig.1 was used, comprising:

(1) the raw material 5 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A4;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

Comparative Example 5

The process shown in Fig.1 was used, comprising:

(1) the raw material 6 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

Comparative Example 6

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A7;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

Table 3 Conversion Results

No.	Example 1	Example 2	Example 3
Hydroconversion
Raw material	Raw material 1	Raw material 1	Raw material 1
Catalyst	Cat-A1	Cat-A2	Cat-A3
Reaction temperature/°C	415	395	385
Reaction pressure/MPa	4	4	4
Volume ratio of hydrogen to oil	800	600	700
Volume space velocity/h^-1	1	0.6	1
Content of C₂-C₆ n-alkanes in the product, wt%	63	54	47
Sulfur Content in Product, mg/kg	100	150	200

Preparation of ethylene by steam cracking
Supplemental Sulfur for Cracking the raw material, mg/kg	50	0	0
Reaction temperature/°C	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3
Water-to-oil ratio by weight	0.4	0.4	0.4
Yield of ethylene, wt%	36.9	33.2	31.6
Yield of propylene, wt%	15.7	17.4	17.8
Yield of butadiene, wt%	3.5	3.8	3.8
Processing benefit per ton oil, CNY/ton	Reference+160	Reference+180	Reference+140

No.	Example 4	Example 5	Example 6
Hydroconversion
Raw material	Raw material 1	Raw material 1	Raw material 1
Catalyst	Cat-A4	Cat-A5	Cat-A6
Reaction temperature/°C	405	410	400
Reaction pressure/MPa	4	4	4
Volume ratio of hydrogen to oil	600	400	600
Volume space velocity/h^-1	0.6	0.6	1
Content of C₂-C₆ n-alkanes in the product, wt%	75	69	62
Sulfur Content in Product, mg/kg	120	140	180

Preparation of ethylene by steam cracking
Supplemental Sulfur for Cracking the raw material, mg/kg	30	10	0
Reaction temperature/°C	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3
Water-to-oil ratio by weight	0.4	0.4	0.4
Yield of ethylene, wt%	39.3	38.4	36.6
Yield of propylene, wt%	13.9	14.5	15.7
Yield of butadiene, wt%	3.5	3.6	3.5
Processing benefit per ton oil, CNY/ton	Reference+150	Reference+170	Reference+160

Continued Table 3 Conversion Results

No.	Example 7	Example 8	Example 9
Hydroconversion
Raw material	Raw material 1	Raw material 1	Raw material 1
Catalyst	Cat-A4	Cat-A5	Cat-A6
Reaction temperature/°C	405	400	393
Reaction pressure/MPa	4	4	4
Volume ratio of hydrogen to oil	400	400	400
Volume space velocity/h^-1	0.8	0.8	0.8
Content of C₂-C₆ n-alkanes in the product, wt%	89	90	91
Sulfur Content in Product, mg/kg	110	160	190

Preparation of ethylene by steam cracking
Supplemental Sulfur for Cracking the raw material, mg/kg	40	0	0
Reaction temperature/°C	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3
Water-to-oil ratio by weight	0.4	0.4	0.4
Yield of ethylene, wt%	45.3	45.8	46.4
Yield of propylene, wt%	10.5	10.2	10
Yield of butadiene, wt%	4.1	4.1	4
Processing benefit per ton oil, CNY/ton	Reference+80	Reference+60	Reference+160

No.	Example 10	Example 11	Example 12
Hydroconversion
Raw material	Raw material 2	Raw material 3	Raw material 1
Catalyst	Cat-A1	Cat-A4	Cat-A1
Reaction temperature/°C	400	400	380
Reaction pressure/MPa	4	4	5
Volume ratio of hydrogen to oil	400	400	400
Volume space velocity/h^-1	1	0.8	0.6
Content of C₂-C₆ n-alkanes in the product, wt%	55	52	44
Sulfur Content in Product, mg/kg	50	300	150

Preparation of ethylene by
steam cracking
Supplemental Sulfur for Cracking the raw material, mg/kg	100	0	0
Reaction temperature/°C	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3
Water-to-oil ratio by weight	0.4	0.4	0.4
Yield of ethylene, wt%	33.9	32.1	31.3
Yield of propylene, wt%	17.3	17.5	18.1
Yield of butadiene, wt%	3.7	3.9	3.9
Processing benefit per ton oil, CNY/ton	Reference+60	Reference+50	Reference+50

Continued Table 3 Conversion Results

No.	Example 13	Example 14
Hydroconversion
Raw material	Raw material 1	Raw material 1
Catalyst	Cat-A1	Cat-A1
Reaction temperature/°C	415	415
Reaction pressure/MPa	4	4
Volume ratio of hydrogen to oil	800	800
Volume space velocity/h^-1	1	1
Content of C₂-C₆ n-alkanes in the product, wt%	62	63
Sulfur Content in Product, mg/kg	40	800

Preparation of ethylene by steam cracking
Supplemental Sulfur for Cracking the raw material, mg/kg	110	0
Reaction temperature/°C	880	880
Reaction pressure/MPa	0.3	0.3
Water-to-oil ratio by weight	0.4	0.4
Yield of ethylene, wt%	36.5	36.1
Yield of propylene, wt%	15.7	15.8
Yield of butadiene, wt%	3.5	3.5
Processing benefit per ton oil, CNY/ton	Reference+100	Reference+90

Continued Table 3 Conversion Results

No.	Comparative Example 1	Comparative Example 2	Comparative Example 3
Hydroconversion
Raw material	Raw material 4	Raw material 4	Raw material 5
Catalyst	Cat-A1	Cat-A4	Cat-A1
Reaction temperature/°C	415	405	415
Reaction pressure/MPa	4.0	4.0	4.0
Volume ratio of hydrogen to oil	800	600	800
Volume space velocity/h^-1	1.0	0.6	1.0
Content of C₂-C₆ n-alkanes in the product, wt%	56	68	38
Sulfur Content in Product, mg/kg	1400	1500	5

Preparation of ethylene by steam cracking
Supplemental Sulfur for Cracking the raw material, mg/kg	0	0	145
Reaction temperature/°C	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3
Water-to-oil ratio by weight	0.4	0.4	0.4
Yield of ethylene, wt%	33.2	37.2	30.1
Yield of propylene, wt%	17.6	14.6	18.7
Yield of butadiene, wt%	3.7	3.4	4.0
Processing benefit per ton oil, CNY/ton	Reference-40	Reference-60	Reference-70

No.	Comparative Example 4	Comparative Example 5	Comparative Example 6
Hydroconversion
Raw material	Raw material 5	Raw material 6	Raw material 1
Catalyst	Cat-A4	Cat-A1	Cat-A7
Reaction temperature/°C	405	420	415
Reaction pressure/MPa	4.0	3.0	4
Volume ratio of hydrogen to oil	600	600	800
Volume space velocity/h^-1	0.6	0.6	1.0
Content of C₂-C₆ n-alkanes in the product, wt%	46	44	19
Sulfur Content in Product, mg/kg	7	500	100

Preparation of ethylene by steam cracking
Supplemental Sulfur for Cracking the raw material, mg/kg	143	0	50
Reaction temperature/°C	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3
Water-to-oil ratio by weight	0.4	0.4	0.4
Yield of ethylene, wt%	32.0	31.2	24.5
Yield of propylene, wt%	17.8	18.6	19.3
Yield of butadiene, wt%	3.9	3.8	3.3
Processing benefit per ton oil, CNY/ton	Reference-90	Reference-25	Reference-150

Through comparison, it could be seen that by using the process of the present invention, sulfides in the sulfur-containing raw material could be effectively converted into hydrogen sulfide and selectively retained in the conversion product. When the conversion product is used as ethylene raw material, the amount of sulfur injection can be reduced or even eliminated, enabling high-value utilization of a valueless component.

Third Series of Examples

In the following Examples and Comparative Examples, the yield was calculated as the mass percent of the output compared to the feed amount. The processing benefit per ton oil denoted the gain per 1 ton of feedstock processed, calculated as (price of ethylene product-price of feedstock and hydrogen-energy consumption of processing)/processing capacity, taking the benefit obtained by using the feedstock without hydroconversion directly as the ethylene raw material as the reference of the processing benefit per ton oil.
In the following Examples and Comparative Examples, each hydroconversion catalyst was represented by Cat-A, Cat-B, Cat-C with a number, such as Cat- A1, Cat-A2, Cat-A3, and the like. The hydroconversion catalyst was prepared by a conventional saturation impregnation process for active metal, and the physicochemical properties of the obtained catalyst were shown in Table 1.
The catalyst of Cat-A was prepared by the process comprising:

The catalyst of Cat-B was prepared by the process comprising:

The catalyst of Cat-C was prepared by the process comprising:

(1) selecting ZSM-35 molecular sieve with a SiO₂/Al₂O₃ molar ratio of 20, mechanically mixing the ZSM-35 with a binder, molding, drying at 120°C for 10 hours, and calcinating at 500°C for 4 hours, to prepare a catalyst support.
(2) impregnating the catalyst support obtained in step (1) with a solution containing active components, drying at 120°C for 10 hours, and calcinating at 500°C for 4 hours, to prepare the hydroconversion catalyst.

The catalyst of Cat-D was prepared by the process comprising:

(1) selecting SAPO-34 molecular sieve with a SiO₂/Al₂O₃ molar ratio of 0.5, mechanically mixing the SAPO-34 with a binder, molding, drying at 120°C for 10 hours, and calcinating at 500°C for 4 hours, to prepare a catalyst support.
(2) impregnating the catalyst support obtained in step (1) with a solution containing active components, drying at 120°C for 10 hours, and calcinating at 500°C for 4 hours, to prepare the hydroconversion catalyst.

The catalyst of Cat -E was prepared by the process comprising:

(1) selecting Y molecular sieve with a SiO₂/Al₂O₃ molar ratio of 15, mechanically mixing the Y molecular sieve with a binder, molding, drying at 120°C for 10 hours, and calcinating at 500°C for 4 hours, to prepare a catalyst support.
(2) impregnating the catalyst support obtained in step (1) with a solution containing active components, drying at 120°C for 10 hours, and calcinating at 500°C for 4 hours, to prepare the hydroconversion catalyst.

Table 1

Catalyst	Cat-A1	Cat-A2	Cat-A3	Cat-B1	Cat-B2	Cat-B3	Cat-A4
Pore volume, cm³/g	0.35	0.45	0.25	0.35	0.45	0.25	0.35
Specific surface area, m²/g	300	200	400	300	200	400	300

Content, wt%, based on the weight of the support
Mordenite	55	40	70
ZSM-5				55	40	70	55
Alumina	19	25	17	19	25	17	44

Active metal content in the catalyst, wt%
MoO₃	20	25	10	20	25	10
NiO	6	10	3	6	10	3
Pt							1

Continued Table 1

Catalyst	Cat-C	Cat-D	Cat-E
Pore volume, cm³/g	0.35	0.35	0.35
Specific surface area, m²/g	300	300	300

Content, wt%, based on the weight of the support
SAPO-14	55
ZSM-35		55
Y			55
Alumina	19	19	19

Active metal content in the catalyst, wt%
MoO₃	20	20	20
NiO	6	6	6

Table 2

Raw material	Raw material 1	Raw material 2	Raw material 3	Raw material 4	Raw material 5	Raw material 6
C₄ iso-alkane content, wt%	1	2	0.5	1	0.4	80
C₄ n-alkane content, wt%	2	3	1.5	2	0.6	11
C₅-C₆ n-alkanes content, wt%	16	28	10	42	3	2
C₅-C₆ iso-alkanes content, wt%	78	65	85	50	95	7
C₇₊ Hydrocarbons and Cyclic Hydrocarbon content, wt%	3	2	3	5	1	0
Initial boiling point, °C	24	25	22	25	23	16
End boiling point, °C	64	66	63	67	62	45

Example 1

The process shown in Fig.1 was used, comprising:

In this Example, about 33 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 0.9:1.

Example 2

The process shown in Fig.1 was used, comprising:

In this Example, about 37 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 1.4:1.

Example 3

The process shown in Fig.1 was used, comprising:

In this Example, about 42 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 2.1:1.

Example 4

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-B1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 62 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 5:1.

Example 5

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-B2;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 57 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 4.4:1.

Example 6

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-B3;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 52 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 3.9:1.

Example 7

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded, along the flowing direction of the raw material, successively with hydroconversion catalysts Cat-B1 and Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 48 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 3.2:1.

Example 8

The process shown in Fig.1 was used, comprising:

In this Example, about 44 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 2.3:1.

Example 9

The process shown in Fig.1 was used, comprising:

In this Example, about 40 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 2.5:1.

Example 10

The process shown in Fig.1 was used, comprising:

In this Example, about 38 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 1.8:1.

Example 11

The process shown in Fig.1 was used, comprising:

In this Example, about 36 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 1.3:1.

Example 12

The process shown in Fig.1 was used, comprising:

In this Example, about 42 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 2.2:1.

Example 13

The process shown in Fig.1 was used, comprising:

(1) the raw material 3 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-B1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 56 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 4.1:1.

Example 14

The process shown in Fig.1 was used, comprising:

In this Example, about 25 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 0.7:1.

Example 15

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-C;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 28 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 0.8:1.

Example 16

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-D;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

In this Example, about 26 wt% of the total amount of C₅-C₆ iso-alkanes were converted into C₂-C₆ n-alkanes. The weight ratio of C₂-C₃ hydrocarbons to C₄-C₆ n-alkanes in the reaction effluent was 0.7:1.

Comparative Example 1

The process shown in Fig.1 was used, comprising:

Comparative Example 2

The process shown in Fig.1 was used, comprising:

(1) the raw material 4 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-B1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

Comparative Example 3

The process shown in Fig.1 was used, comprising:

Comparative Example 4

The process shown in Fig.1 was used, comprising:

(1) the raw material 5 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-B1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

Comparative Example 5

The process shown in Fig.1 was used, comprising:

Comparative Example 6

The process shown in Fig.1 was used, comprising:

Comparative Example 7

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-E;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was directly used as ethylene raw material. The process conditions and conversion results in this Example are shown in Table 3.

Comparative Example 8

The process shown in Fig.1 was used, comprising:

(1) the raw material 1 and hydrogen were mixed and sequentially fed into the hydroconversion reaction zone; which hydroconversion reaction zone was loaded with hydroconversion catalyst Cat-A1;
(2) the reaction effluent from the hydroconversion reaction zone in step (1) was subjected to gas-liquid separation, to obtain a hydrogen-rich gas and a liquid-phase stream. The hydrogen-rich gas was recycled, and the liquid-phase stream was separated into n- and iso-alkanes, from which the n-alkanes were used as ethylene raw materials, and the iso-alkanes were recycled to the hydroconversion reaction zone. The process conditions and conversion results in this Example are shown in Table 3.

Table 3 Conversion Results

No.	Example 1	Example 2	Example 3
Hydroconversion
Raw material	Raw material 1	Raw material 1	Raw material 1
Catalyst	Cat-A1	Cat-A2	Cat-A3
Reaction temperature/°C	400	400	405
Reaction pressure/MPa	4	4	4
Volume ratio of hydrogen to oil	600	500	600
Volume space velocity/h^-1	1.2	0.8	1
Content of C₂-C₆ n-alkanes in the product, wt%	49	53	58

Preparation of ethylene by steam cracking
Reaction temperature/°C	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3
Mass ratio of water to oil	0.4	0.4	0.4
Yield of ethylene, wt%	32.8	33.2	35.4
Yield of propylene, wt%	17.7	17.4	16.6
Yield of butadiene, wt%	3.8	3.8	3.7
Processing benefit per ton oil, CNY/ton	Reference+190	Reference+170	Reference+160

No.	Example 4	Example 5	Example 6
Hydroconversion
Raw material	Raw material 1	Raw material 1	Raw material 1
Catalyst	Cat-B1	Cat-B2	Cat-B3
Reaction temperature/°C	420	410	410
Reaction pressure/MPa	4	4	4
Volume ratio of hydrogen to oil	500	400	400
Volume space velocity/h-1	0.8	1	0.8
Content of product C2-C6 n-alkanes, wt%	78	73	68

Preparation of ethylene by steam cracking
Reaction temperature/°C	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3
Mass ratio of water to oil	0.4	0.4	0.4
Yield of ethylene, wt%	40.2	39.5	37.9
Yield of propylene, wt%	13.5	13.8	14.5
Yield of butadiene, wt%	3.3	3.4	3.6
Processing benefit per ton oil, CNY/ton	Reference+190	Reference+180	Reference+160

Continued Table 3 Conversion Results

No.	Example 7	Example 8	Example 9	Example 10	Example 11
Hydroconversion
Raw material	Raw material 1	Raw material 1	Raw material 1	Raw material 1	Raw material 1
Catalyst	Cat-B1/Cat-A1	Cat-B1/Cat-A1	Cat-B1/Cat-A1	Cat-B1/Cat-A1	Cat-B1/Cat-A1
Weight ratio of catalyst A to catalyst B	1:5	1: 2	1:1	2,1	5:1
Reaction temperature/°C	405	400	400	390	390
Reaction pressure/MPa	4	4	4	4	4
Volume ratio of hydrogen to oil	400	500	600	500	600
Volume space velocity/h^-1	0.8	0.8	0.8	0.8	0.6
Content of C₂-C₆ n-alkanes in the product, wt%	64	60	56	54	52

Preparation of ethylene by steam cracking
Reaction temperature/°C	880	880	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3	0.3	0.3
Mass ratio of water to oil	0.4	0.4	0.4	0.4	0.4
Yield of ethylene, wt%	37.2	36.1	34.6	33.8	33.2
Yield of propylene, wt%	15.7	16.4	16.8	17.7	17.9
Yield of butadiene, wt%	3.5	3.6	3.7	3.8	3.9
Processing benefit per ton oil, CNY/ton	Reference+ 160	Reference +170	Referen ce+190	Reference+ 170	Reference+ 150

No.	Example 12	Example 13	Example 14	Example 15	Example 16
Hydroconversion
Raw material	Raw material 2	Raw material 3	Raw material 1	Raw material 1	Raw material 1
Catalyst	Cat-A1	Cat-A4	Cat-A1	Cat-C 1	Cat-D1
Reaction temperature/°C	400	405	380	400	400
Reaction pressure/MPa	4	4	4	4	4
Volume ratio of hydrogen to oil	400	400	400	600	600
Volume space velocity/h-1	0.8	0.8	1.1	1.2	1.2
Content of product C2-C6 n-alkanes, wt%	58	72	41	44	42

Preparation of ethylene by steam cracking
Reaction temperature/°C	880	880	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3	0.3	0.3
Mass ratio of water to oil	0.4	0.4	0.4	0.4	0.4
Yield of ethylene, wt%	35.2	39.2	29.8	31.2	30.5
Yield of propylene, wt%	16.6	13.8	19.2	18.6	19.3
Yield of butadiene, wt%	3.8	3.4	4	3.9	4
Processing benefit per ton oil, CNY/ton	Reference+ 70	Reference +80	Referen ce+50	Reference+ 60	Reference+ 50

Continued Table 3 Conversion Results

No.	Comparative Example 1	Comparative Example 2	Comparative Example 3	Comparative Example 4
Hydroconversion
Raw material	Raw material 4	Raw material 4	Raw material 5	Raw material 5
Catalyst	Cat-A1	Cat-A4	Cat-A1	Cat-A4
Reaction temperature/°C	400	420	400	420
Reaction pressure/MPa	4	4	4	4
Volume ratio of hydrogen to oil	600	500	600	500
Volume space velocity/h^-1	1.2	0.8	1.2	0.8
Content of C₂-C₆ n-alkanes in the product, wt%	45	75	43	72

Preparation of ethylene by steam cracking
Reaction temperature/°C	880	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3	0.3
Mass ratio of water to oil	0.4	0.4	0.4	0.4
Yield of ethylene, wt%	31.7	39.8	30.8	38.9
Yield of propylene, wt%	18.6	13.7	18.7	14
Yield of butadiene, wt%	3.9	3.4	4	3.5
Processing benefit per ton oil, CNY/ton	Reference-30	Reference-50	Reference-50	Reference-70

No.	Comparative Example 5	Comparative Example 6	Comparative Example 7	Comparative Example 8
Hydroconversion
Raw material	Raw material 1	Raw material 6	Raw material 1	Raw material 1
Catalyst	Cat-A7	Cat-A1	Cat-E	Cat-A1
Reaction temperature/°C	330	410	420	400
Reaction pressure/MPa	4	4	4	4
Volume ratio of hydrogen to oil	600	400	400	600
Volume space velocity/h^-1	1	0.6	0.6	1.2
Content of C₂-C₆ n-alkanes in the product, wt%	44	36	24	47

Preparation of ethylene by steam cracking
Reaction temperature/°C	880	880	880	880
Reaction pressure/MPa	0.3	0.3	0.3	0.3
Mass ratio of water to oil	0.4	0.4	0.4	0.4
Yield of ethylene, wt%	31.6	28.4	26.5	32.1
Yield of propylene, wt%	18.5	20.1	20.3	17.8
Yield of butadiene, wt%	3.8	4.1	4.3	3.8
Processing benefit per ton oil, CNY/ton	Reference-50	Reference-40	Reference-100	Reference-20

By comparison, the process according to the present invention could realize selective conversion of iso-alkanes, could flexibly adjust the ratio of C₂-C₃ alkanes to C₄-C₆ n-alkanes in the conversion product, in turn realized flexible adjustment of the structure of the ethylene product and improved the flexibility of the ethylene device product.

Claims

A process for improving the quality of a hydrocarbon stream, comprising the steps of:
1) providing a hydrocarbon stream containing C₅-C₆ iso-alkanes, wherein the content of the C₅-C₆ iso-alkanes in the hydrocarbon stream is 60-90 wt% (preferably 70-80 wt%), based on the total weight of the hydrocarbon stream being 100 wt%,

2) converting at least a part (e.g., 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) of the C₅-C₆ iso-alkanes in the presence of a catalyst and hydrogen by a conversion reaction into C₂-C₆ n-alkanes, to obtain a conversion product, wherein the catalyst comprises a molecular sieve and a non-noble metal hydrogenation-active metal component,

3) steam cracking the conversion product to obtain a cracking product comprising ethylene.
The process according to claim 1, wherein the hydrocarbon stream has a sulfur content of 50-5000 mg/kg (preferably 200-1000 mg/kg), based on the total weight of the hydrocarbon stream.
The process according to claim 1, wherein the hydrocarbon stream comprises C₇₊ hydrocarbons in an amount of 0-10 wt% (preferably 0.5-5 wt%), C₅-C₆ n-alkanes in an amount of 10-30 wt% (preferably 15-25 wt%), C_4- hydrocarbons in an amount of 0-10 wt% (preferably 2-5 wt%), and cyclic hydrocarbons in an amount of 1-10 wt% (preferably 2-5 wt%), based on the total weight of the hydrocarbon stream being 100 wt%.
The process according to claim 1, wherein the conversion product comprises C₂-C₃ alkanes and C₄-C₆ n-alkanes (preferably C₅-C₆ n-alkanes), and the weight ratio of the C₂-C₃ alkanes to the C₄-C₆ n-alkanes (preferably C₅-C₆ n-alkanes) is 0.5:1 to 8:1 (preferably 0.9:1 to 5:1).
The process according to claim 1, wherein the conversion product comprises C₇₊ hydrocarbons in an amount of not more than 5 wt% (preferably not more than 1 wt%), C₅-C₆ iso-alkanes in an amount of 0-50 wt% (preferably 10-40 wt%), C₂-C₆ n-alkanes in an amount of 40-90 wt% (preferably 50-80 wt%), and cyclic hydrocarbons in an amount of not more than 3 wt% (preferably not more than 1 wt%), based on the total weight of the conversion product being 100 wt%.
The process according to claim 1, wherein the molecular sieve is one or more selected from the group consisting of mordenite, ZSM molecular sieves, SAPO molecular sieves, and EU-1 molecular sieves, more preferably one or more selected from the group consisting of mordenite and ZSM molecular sieves, particularly preferably one or more selected from the group consisting 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 one or more selected from the group consisting of mordenite and ZSM-5 molecular sieve (particularly preferably, the weight ratio of mordenite to ZSM-5 molecular sieve is 0-100:100-0, preferably 10-50:50-10).
The process according to claim 1, wherein the non-noble metal hydrogenation-active metal component is one or more selected from the group consisting of non-noble metals of Group VIB of the Periodic Table and non-noble metals of Group VIII of the Periodic Table, preferably, the non-noble metal of Group VIB is one or more selected from the group consisting of molybdenum and tungsten (particularly preferably molybdenum), and the non-noble metal of Group VIII is one or more selected from the group consisting of cobalt and nickel (particularly preferably nickel).
The process according to claim 7, wherein based on the weight of the catalyst, the non-noble metal of Group VIB (calculated as oxide) is present in an amount of 5.0-30.0 wt% (preferably 10-20 wt%), and the non-noble metal of Group VIII (calculated as oxide) is present in an amount of 0.5-15.0 wt% (preferably 3-10 wt%).
The process according to claim 1, wherein based on the weight of the catalyst, the molecular sieve is present in an amount of 30-80 wt% (preferably 40-70 wt%).
The process according to claim 1, wherein the conversion reaction is carried out under the reaction conditions of: 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 300-500°C (preferably 350-450°C), a liquid hourly volume space velocity of 0.1-15.0 h^-1 (preferably 0.5-5.0 h^-1), and a hydrogen-to-oil volume ratio of 50:1-2500:1 (preferably 100:1-2000:1 or 100:1-1000:1).
The process according to claim 1, wherein the step 3) comprises the steps of:
3-A-1) separating the conversion product (called as a first separation) to obtain a separated stream with C₂+ hydrocarbons as the main part (such as representing 95 wt% or more, 98 wt% or more, 99 wt% or more, or essentially 100 wt% of the total amount),

3-A-2) steam cracking the separated stream to obtain a cracked product comprising ethylene.
The process according to claim 11, wherein the first separation is operated under conditions comprising a pressure of 0.5-10.0 MPaG (preferably 2.0-8.0 MPaG or 2.0-5.0 MPaG) and a temperature of 40-70 °C.
The process according to claim 1, wherein the step 3) comprises the steps of:
3-B-1) separating the conversion product (called as a first separation) to obtain a separated stream with C₂+ hydrocarbons as the main part (such as representing 95 wt% or more, 98 wt% or more, 99 wt% or more, or essentially 100 wt% of the total amount),

3-B-2) separating the separated stream (called as a second separation) to obtain a higher-carbon stream comprising C₄+ hydrocarbons as the main part (such as 90 wt% or more, 95 wt% or more, 98 wt% or more, 99 wt% or more, or substantially 100 wt% of the total amount) and a lower-carbon stream comprising C₂-C₃ hydrocarbons as the main part (such as 90 wt% or more, 95 wt% or more, 98 wt% or more, 99 wt% or more, or substantially 100 wt% of the total amount),

3-B-3) optionally, recycling the higher-carbon stream as a hydrocarbon stream back to step 2) for the conversion reaction,

3-B-4) steam cracking the lower-carbon stream to obtain a cracked product comprising ethylene.
The process according to claim 13, wherein the first separation is operated under conditions comprising a pressure of 0.5-10.0 MPaG (preferably 2.0-8.0 MPaG or 2.0-5.0 MPaG) and a temperature of 40-70 °C, and the second separation is operated under conditions comprising a pressure of 0.5-1.5 MPaG and a temperature of 30-60 °C.
The process according to claim 1, wherein the operating conditions for the steam cracking comprise: a reaction temperature of 750-900°C, a reaction pressure of 0.1-0.5 MPaG, a water-to-oil ratio by weight of 0.2-0.6, and a system sulfur content of 100-200 mg/kg.