CN114516776A - Method and apparatus for producing ethylene and propylene - Google Patents
Method and apparatus for producing ethylene and propylene Download PDFInfo
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- CN114516776A CN114516776A CN202011302054.5A CN202011302054A CN114516776A CN 114516776 A CN114516776 A CN 114516776A CN 202011302054 A CN202011302054 A CN 202011302054A CN 114516776 A CN114516776 A CN 114516776A
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- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 title claims abstract description 77
- 239000005977 Ethylene Substances 0.000 title claims abstract description 77
- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 title claims abstract description 75
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 title claims abstract description 75
- 238000000034 method Methods 0.000 title claims abstract description 53
- 239000000463 material Substances 0.000 claims abstract description 213
- 238000004523 catalytic cracking Methods 0.000 claims abstract description 98
- 239000002994 raw material Substances 0.000 claims abstract description 54
- 238000004230 steam cracking Methods 0.000 claims abstract description 38
- 238000009835 boiling Methods 0.000 claims abstract description 17
- 150000004945 aromatic hydrocarbons Chemical class 0.000 claims abstract description 13
- 238000004064 recycling Methods 0.000 claims abstract description 8
- 238000006243 chemical reaction Methods 0.000 claims description 63
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 50
- 229910052799 carbon Inorganic materials 0.000 claims description 50
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical compound CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 claims description 28
- 238000005984 hydrogenation reaction Methods 0.000 claims description 25
- 239000002808 molecular sieve Substances 0.000 claims description 17
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 claims description 17
- 239000003054 catalyst Substances 0.000 claims description 8
- 238000010992 reflux Methods 0.000 claims description 3
- 230000002378 acidificating effect Effects 0.000 claims description 2
- 238000005265 energy consumption Methods 0.000 abstract description 5
- 238000004519 manufacturing process Methods 0.000 abstract description 3
- 150000001336 alkenes Chemical class 0.000 description 43
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 description 35
- 239000000047 product Substances 0.000 description 15
- VQTUBCCKSQIDNK-UHFFFAOYSA-N Isobutene Chemical compound CC(C)=C VQTUBCCKSQIDNK-UHFFFAOYSA-N 0.000 description 13
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 11
- 239000001257 hydrogen Substances 0.000 description 11
- 229910052739 hydrogen Inorganic materials 0.000 description 11
- HQQADJVZYDDRJT-UHFFFAOYSA-N ethene;prop-1-ene Chemical group C=C.CC=C HQQADJVZYDDRJT-UHFFFAOYSA-N 0.000 description 8
- 238000000926 separation method Methods 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 6
- 238000010586 diagram Methods 0.000 description 6
- NNPPMTNAJDCUHE-UHFFFAOYSA-N isobutane Chemical compound CC(C)C NNPPMTNAJDCUHE-UHFFFAOYSA-N 0.000 description 6
- IAQRGUVFOMOMEM-UHFFFAOYSA-N butene Natural products CC=CC IAQRGUVFOMOMEM-UHFFFAOYSA-N 0.000 description 4
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 description 3
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 3
- 238000005336 cracking Methods 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 239000001282 iso-butane Substances 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- KAKZBPTYRLMSJV-UHFFFAOYSA-N Butadiene Chemical compound C=CC=C KAKZBPTYRLMSJV-UHFFFAOYSA-N 0.000 description 2
- CZXDHMZKNAOPHQ-VOTSOKGWSA-N [(5e)-10-propyltrideca-5,9-dienyl] acetate Chemical compound CCCC(CCC)=CCC\C=C\CCCCOC(C)=O CZXDHMZKNAOPHQ-VOTSOKGWSA-N 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 125000000383 tetramethylene group Chemical group [H]C([H])([*:1])C([H])([H])C([H])([H])C([H])([H])[*:2] 0.000 description 2
- CTQNGGLPUBDAKN-UHFFFAOYSA-N O-Xylene Chemical compound CC1=CC=CC=C1C CTQNGGLPUBDAKN-UHFFFAOYSA-N 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 125000003118 aryl group Chemical group 0.000 description 1
- 239000001273 butane Substances 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 150000001993 dienes Chemical class 0.000 description 1
- XNMQEEKYCVKGBD-UHFFFAOYSA-N dimethylacetylene Natural products CC#CC XNMQEEKYCVKGBD-UHFFFAOYSA-N 0.000 description 1
- -1 ethylene, propylene Chemical group 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 238000006317 isomerization reaction Methods 0.000 description 1
- OFBQJSOFQDEBGM-UHFFFAOYSA-N n-pentane Natural products CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 239000000376 reactant Substances 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
- 239000008096 xylene Substances 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C4/00—Preparation of hydrocarbons from hydrocarbons containing a larger number of carbon atoms
- C07C4/02—Preparation of hydrocarbons from hydrocarbons containing a larger number of carbon atoms by cracking a single hydrocarbon or a mixture of individually defined hydrocarbons or a normally gaseous hydrocarbon fraction
- C07C4/06—Catalytic processes
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C4/00—Preparation of hydrocarbons from hydrocarbons containing a larger number of carbon atoms
- C07C4/02—Preparation of hydrocarbons from hydrocarbons containing a larger number of carbon atoms by cracking a single hydrocarbon or a mixture of individually defined hydrocarbons or a normally gaseous hydrocarbon fraction
- C07C4/04—Thermal processes
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C2529/00—Catalysts comprising molecular sieves
- C07C2529/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites, pillared clays
- C07C2529/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
- C07C2529/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
Abstract
The invention discloses a method for producing ethylene and propylene, which comprises the following steps: s1, carrying out catalytic cracking treatment on a raw material containing carbon-tetrahydrocarbon to respectively obtain a material flow I containing ethylene and propylene, a material flow II containing unreacted raw materials and a material flow III containing aromatic hydrocarbon; s2, optionally, circulating at least part of the material flow II together with the raw material to perform catalytic cracking treatment; s3, separating at least part of the material flow II to respectively obtain a material flow IV with a boiling point lower than the division point and a material flow V with a boiling point higher than the division point; s4, optionally, recycling at least part of the material flow IV to the step S1 for catalytic cracking treatment; s5, carrying out steam cracking treatment on the material flow V to obtain a material flow VI containing ethylene and propylene. By utilizing the method of the invention, the contradiction between energy consumption/investment and yield in the traditional method can be solved: the scale of the device is reduced, the energy consumption of the device is reduced, and the overall yield of ethylene and propylene based on fresh raw materials is not reduced or even improved.
Description
Technical Field
The present invention relates to a process for producing ethylene and propylene, and in particular to a process for producing ethylene and propylene from a feedstock comprising carbon tetrahydrocarbons.
Background
The main purpose of industrial steam cracking is to prepare low molecular olefins such as ethylene, propylene and butadiene as byproducts, and light aromatics such as benzene, toluene and xylene, and also to generate a small amount of heavy aromatics. Steam cracking is an endothermic reaction, typically carried out in a tubular furnace: the raw material and the steam are preheated and then enter a furnace tube of a heating furnace, are heated to 750-plus-900 ℃ for cracking, enter a quenching boiler, are rapidly cooled, and then enter a quencher and a cryogenic separation device below minus 100 ℃ to obtain various cracked products in sequence. Steam cracking is the main process for producing low molecular olefins such as ethylene and propylene.
The olefin catalytic cracking technology is a method for obtaining light molecular olefins of propylene and ethylene by using various mixed C4-C6 olefins as raw materials and catalytically cracking the olefins contained in the raw materials usually in the presence of a molecular sieve catalyst. Currently, representative olefin catalytic cracking processes mainly include: a Propylur process, an OCP process, an Omega process, an OCC process, a Superflex process and the like. Wherein, the total conversion rate of olefin in the Propylur process can reach 85%, the yield of propylene per pass is 40 mol%, the yield of ethylene is 10 mol% (relative to the total amount of olefin in the feed), the total conversion rate of olefin in the Omega process is more than 75%, and the conversion rate of olefin per pass in the OCC process is more than 60%.
In the conventional process, in order to increase the overall conversion, the unreacted material is recycled to the reactor, the unreacted mixed carbon four cannot be easily separated, the n-butane and the unreacted olefin material are recycled to the reactor, and in some cases, in order to achieve a considerable olefin yield, the recycle ratio (material recycled to the reactor/fresh material) is more than 2 or even 3. With this design, if the butane (especially n-butane) concentration in the feed is high, the economics will be greatly affected because too much inert components are recycled back to the reactor.
In order to completely dry and press the materials, the unreacted materials are discharged and used as the feeding materials for steam cracking after full hydrogenation, so that the normal butane in the raw materials can be utilized, but the method has the following problems: the unreacted C4 contains some isomeric hydrocarbons, such as isobutane and isobutene, because C four olefins can undergo isomerization reaction under the conditions of the claims to obtain a balanced composition, the balanced composition necessarily contains a large amount of isobutene, the isobutene can be changed into isobutane after being fully hydrogenated, the isobutane is an inferior steam cracking raw material, a large amount of methane and a very low ethylene yield can be obtained after cracking, meanwhile, the isobutene is a high-quality olefin catalytic cracking raw material, and the ethylene propylene yield is not different from that of normal olefins, so that the hydrogenation of the isobutene is huge waste of resources.
Disclosure of Invention
The invention aims to solve the technical problem that when the existing olefin catalytic technology is utilized to treat mixed carbon-containing four materials with high n-butane concentration, the single-pass conversion rate of the existing olefin catalytic cracking technology is not high enough, and unreacted materials need to be recycled in order to improve the total conversion rate; and the n-butane hardly participates in the reaction, and the circulation can cause the accumulation of the n-butane in the system, so that the whole device is greatly expanded in scale, and the energy consumption is higher.
In order to solve the technical problems, the invention provides a method for producing ethylene and propylene, which is characterized in that unreacted carbon four raw materials are divided into a division point at minus 6.8 +/-0.5 ℃, substances with a boiling point lower than the temperature are returned to a reaction unit, so that n-butane contained in the materials cannot return to a reactor, most of other unreacted butylene discharged out of a system is 2-butylene along with the n-butane, the unreacted butylene is completely changed into n-butane after full hydrogenation, and the n-butane is a high-quality steam cracking raw material and has very high diene yield and high attached yield after steam cracking. By utilizing the method of the invention, the contradiction between energy consumption/investment and yield in the traditional method can be solved: the device scale is reduced, the device energy consumption is reduced, and meanwhile, the whole ethylene propylene yield based on the fresh raw materials is not reduced or even improved.
In one aspect, the present invention provides a process for producing ethylene and propylene, comprising the steps of:
s1, carrying out catalytic cracking treatment on a raw material containing carbon-tetrahydrocarbon to respectively obtain a material flow I containing ethylene and propylene, a material flow II containing unreacted raw materials and a material flow III containing aromatic hydrocarbon;
s2, optionally, circulating at least part of the material flow II together with the raw material to perform catalytic cracking treatment;
s3, separating at least part of the material flow II to respectively obtain a material flow IV with a boiling point lower than the division point and a material flow V with a boiling point higher than the division point; the temperature of the division point is-6.8 +/-0.5 ℃;
s4, optionally, recycling at least part of the material flow IV to the step S1 for catalytic cracking treatment;
s5, carrying out steam cracking treatment on the material flow V to obtain a material flow VI containing ethylene and propylene.
According to some embodiments of the invention, the feedstock comprises carbon tetraolefins and n-butane.
According to a preferred embodiment of the invention, the n-butane content in the starting material is not less than 6% by weight, preferably not less than 15% by weight, more preferably not less than 25% by weight.
According to a preferred embodiment of the invention, the content of carbonitridienes in the feedstock is not less than 20 wt.%, preferably not less than 30 wt.%, more preferably not less than 40 wt.%.
According to the present invention, the catalytic cracking treatment in step S1 is not particularly limited, and can be appropriately selected by those skilled in the art according to the actual circumstances.
According to some embodiments of the present invention, the catalytic cracking process is performed in the presence of a catalyst in step S1, and the kind of the catalyst can be appropriately selected by those skilled in the art according to actual conditions.
According to a preferred embodiment of the invention, the catalyst is an acidic molecular sieve, more preferably comprises at least one of SAPO-34, ZSM-5, Y-type molecular sieves, and most preferably is a ZSM-5 molecular sieve.
According to a preferred embodiment of the present invention, the reaction temperature of the catalytic cracking treatment is 500-.
According to a preferred embodiment of the invention, the reaction pressure of the catalytic cracking treatment is between-0.05 and 0.5MPa, such as-0.1 MPa, 0MPa, 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa and any value in between, preferably between 0 and 0.3 MPa.
According to a preferred embodiment of the invention, the catalytic cracking treatment has a volume space velocity of from 5 to 35h-1For example, 6h-1、7h-1、8h-1、9h-1、10h-1、11h-1、12h-1、13h-1、14h-1、15h-1、16h-1、17h-1、18h-1、19h-1And any value in between, preferably 10-20h-1。
According to a preferred embodiment of the present invention, in step S1, the feedstock containing the tetracarbon is subjected to a catalytic cracking treatment, and the resulting reactants are subjected to a separation treatment, resulting in a stream I containing ethylene and propylene, a stream II containing unreacted feedstock, and a stream III containing aromatic hydrocarbons.
According to the embodiment of the invention, the separation can adopt the conventional rectification method in the field, such as the rectification separation of the material containing ethylene and propylene and C4, the separation of the material containing aromatic hydrocarbon and C4-C5, and the like.
According to the present invention, the separation method and process conditions in the above steps are not particularly limited, and those skilled in the art can appropriately select the method and process conditions according to actual circumstances.
According to some preferred embodiments of the present invention, the mass ratio of unreacted feed in stream II recycled in step S2 to fresh feed in step S1 is not higher than 5:1, preferably not higher than 3:1, more preferably not higher than 2:1, most preferably not higher than 1.2: 1.
According to some preferred embodiments of the present invention, at least part of the stream II is rectified by the rectifying tower in step S3, with a cut point of-6.8 ± 0.5 ℃, the fraction below the cut point obtained at the top of the tower is stream IV, and the fraction above the cut point obtained at the bottom of the tower is stream V.
According to a preferred embodiment of the invention, at least 80 wt.%, preferably at least 90 wt.%, more preferably at least 95 wt.% of the components having a boiling point below the cut-off point in the stream entering the rectification column are recovered at the top of the column.
The rectification column used according to the invention can be a rectification column known to the person skilled in the art, the method of operation being a matter of course self-selecting by the person skilled in the art.
According to a preferred embodiment of the invention, the rectification column comprises at least 60 layers, preferably at least 80 layers, more preferably at least 100 layers of theoretical trays.
According to a preferred embodiment of the present invention, the reflux ratio of the rectification column is not less than 3.0, preferably not less than 5.0, more preferably not less than 8.0.
According to a preferred embodiment of the invention, the column pressure of the rectification column is between 0.2 and 0.8MPa, preferably between 0.25 and 0.6MPa, more preferably between 0.3 and 0.55 MPa.
According to a preferred embodiment of the present invention, at least 60 wt%, preferably at least 80 wt%, more preferably at least 90 wt%, most preferably at least 95 wt% of stream IV in step S4 is recycled to step S1 for catalytic cracking treatment.
According to a preferred embodiment of the invention, the method further comprises: before steam cracking treatment is carried out on the material flow V, the material flow V is subjected to hydrotreating, namely, the material flow V is subjected to hydrotreating firstly, and then is subjected to steam cracking treatment, so that a material flow VI containing ethylene and propylene is obtained.
In the present invention, the olefins in the stream are saturated by hydrotreating and according to a preferred embodiment of the present invention, after hydrotreating, the olefin content in the saturated stream is not higher than 15 wt%, preferably not higher than 10 wt%, more preferably not higher than 5 wt%, most preferably not higher than 1 wt%.
The particular method of hydrotreating, e.g., process conditions, selected catalyst, etc., will be readily selected by those skilled in the art as appropriate for the particular application, provided that the olefin content of the saturated stream is within the above-described ranges.
According to a preferred embodiment of the invention, stream V is subjected to a steam cracking treatment, obtaining a stream VI comprising ethylene and propylene.
The particular method of steam cracking treatment, such as process conditions, selected catalyst, etc., can be selected by one skilled in the art according to the present invention, as appropriate.
According to a preferred embodiment of the present invention, the stream VI comprising ethylene and propylene obtained in step S5 is combined with the stream I comprising ethylene and propylene obtained in step S1 to obtain a stream enriched in ethylene and propylene.
In another aspect, the present invention provides a system for producing ethylene and propylene, comprising:
the catalytic cracking unit is used for carrying out catalytic cracking treatment on the raw material containing the carbon-tetrahydrocarbon to respectively obtain a material flow I containing ethylene and propylene, a material flow II containing unreacted raw materials and a material flow III containing aromatic hydrocarbon;
the rectifying tower is used for receiving at least part of the material flow II from the catalytic cracking unit and separating the material flow II to respectively obtain a material flow IV with the boiling point lower than the division point and a material flow V with the boiling point higher than the division point; the temperature of the division point is-6.8 +/-0.5 ℃;
optionally a hydrogenation unit for receiving and hydrotreating the stream V coming from the rectification column;
and the steam cracking unit is used for receiving the stream V from the rectifying tower and/or the product from the hydrogenation unit and carrying out steam cracking treatment on the stream V and/or the product to obtain a stream VI containing ethylene and propylene.
According to some embodiments of the invention, the catalytic cracking unit comprises a feedstock inlet, a stream I outlet, a stream II outlet, and a stream III outlet; and the material flow II outlet is connected with the raw material inlet and is used for recycling at least part of the material flow II together with the raw material to carry out catalytic cracking treatment.
According to some embodiments of the invention, the rectification column used according to the invention may be a rectification column known to the person skilled in the art, the method of operation being a matter of choice for the person skilled in the art.
According to a preferred embodiment of the invention, the rectification column comprises at least 60 layers, preferably at least 80 layers, more preferably at least 100 layers of theoretical trays.
According to a preferred embodiment of the present invention, the reflux ratio of the rectification column is not less than 3.0, preferably not less than 5.0, more preferably not less than 8.0.
According to a preferred embodiment of the invention, the column pressure of the rectification column is between 0.2 and 0.8MPa, preferably between 0.25 and 0.6MPa, more preferably between 0.3 and 0.55 MPa.
According to the preferred embodiment of the invention, the fraction obtained at the top of the rectifying tower and below the division point is the material flow IV, and the fraction obtained at the bottom of the rectifying tower and above the division point is the material flow V.
According to a preferred embodiment of the invention, the top of the rectification column is connected to a catalytic cracking unit for recycling at least part of the stream IV to the catalytic cracking unit for treatment.
The process flow of the system for producing ethylene and propylene by using the invention is as follows:
feeding a raw material containing carbon tetrahydrocarbon into a catalytic cracking unit to obtain a material flow I containing ethylene and propylene, a material flow II containing unreacted raw materials and a material flow III containing aromatic hydrocarbon; preferably, part of the stream II is recycled to the inlet of the catalytic cracking unit and is subjected to catalytic cracking treatment together with the raw material; at least part of the material flow II enters a rectifying tower for separation treatment, the material flow IV with the boiling point lower than the division point is obtained at the tower top, and the material flow V with the boiling point higher than the division point is obtained at the tower bottom; recycling at least part of the material flow IV to the inlet of the catalytic cracking unit, carrying out catalytic cracking treatment together with the raw material, and discharging the rest material flow IV; preferably, the stream V enters a hydrogenation unit for hydrogenation treatment and then enters a steam cracking unit for steam cracking treatment to obtain a stream VI containing ethylene and propylene; and combining the stream I and the stream VI to obtain a stream rich in ethylene and propylene.
Drawings
FIG. 1 is a process flow diagram of one embodiment of the present invention;
in fig. 1, 0 is a mixed carbon four stream, 1 is a catalytic cracking product containing ethylene propylene, 2 is discharged unreacted raw material, 3 is an aromatic hydrocarbon-rich catalytic cracking product, 4 is a light carbon four material rich in isobutylene, 5 is a heavy carbon four material rich in n-butane and 2-butene, 6 is a light carbon four material recycled to the reaction unit, 7 is unreacted raw material recycled to the reaction unit, 8 is discharged light carbon four, 9 is a heavy carbon four after full hydrogenation, 10 is a material rich in ethylene propylene after steam cracking, 11 is a combined material of 1 and 10, and is rich in ethylene propylene;
FIG. 2 is a process flow diagram of a prior art process;
in FIG. 2, 0 is a mixed C-C stream, 1 is a catalytically cracked product containing ethylene and propylene, 2 is discharged unreacted raw material, 3 is an aromatic-rich catalytically cracked product, and 7 is unreacted raw material recycled to the reaction unit
FIG. 3 is a process flow diagram of a prior art method;
in fig. 3, 0 is a mixed carbon-four stream, 1 is a catalytic cracking product containing ethylene and propylene, 2 is an discharged unreacted raw material, 3 is a catalytic cracking product rich in aromatic hydrocarbons, 7 is an unreacted raw material recycled to the reaction unit, 9 is a discharged unreacted raw material after full hydrogenation, 10 is a material rich in ethylene and propylene after steam cracking, and 11 is a combined material of 1 and 10 and is rich in ethylene and propylene.
Detailed Description
The present invention is further illustrated by the following examples, which are not to be construed as limiting the invention in any way. In the embodiment of the invention,% is mass percentage.
FIG. 1 is a process flow diagram of a preferred embodiment of the present invention, and as shown in FIG. 1, the system for producing ethylene and propylene of the present invention comprises a catalytic cracking unit, a rectifying tower, a hydrogenation unit and a steam cracking unit; feeding the mixed C-C material flow 0 (raw material) into a catalytic cracking unit to obtain a catalytic cracking product 1 (material flow I) containing ethylene and propylene, an unreacted raw material 2 (partial material flow II) and a catalytic cracking product 3 (material flow III) rich in aromatic hydrocarbon; the unreacted raw material 7 (part of the material flow II) is recycled to the inlet of the catalytic cracking unit and is subjected to catalytic cracking treatment together with the raw material; the unreacted raw material 2 enters a rectifying tower for treatment, a light carbon four material 4 (a material flow IV with the boiling point lower than-6.8 ℃) rich in isobutene is obtained at the top of the tower, and a heavy carbon four material 5 (a material flow V with the boiling point higher than-6.8 ℃) rich in normal butane and 2-butylene is obtained at the bottom of the tower; the light carbon four material 4 is divided into light carbon four 6 and light carbon four 8, the material flow 6 is circulated back to the inlet of the catalytic cracking unit and is subjected to catalytic cracking treatment together with the raw material, and the light carbon four 8 is discharged; the heavy carbon four raw material 5 (material flow V) enters a hydrogenation unit for hydrogenation treatment to obtain heavy carbon four 9, and then enters a steam cracking unit for steam cracking treatment to obtain a material 10 rich in ethylene and propylene; stream 1 and stream 10 are combined to yield stream 11 enriched in ethylene and propylene.
Fig. 2 is a process flow diagram of a prior art method for producing ethylene propylene, as shown in fig. 2, the plant comprising only a catalytic cracking unit. And (3) feeding the mixed C-C material flow 0 (raw material) into a catalytic cracking unit to obtain a catalytic cracking product 1 containing ethylene and propylene, an discharged unreacted raw material 2, a catalytic cracking product 3 rich in aromatic hydrocarbon and an unreacted raw material 7, circulating the unreacted raw material 7 back to the reaction unit, and discharging the material flow 2.
FIG. 3 is a process flow diagram of another prior art process for producing ethylene propylene, as shown in FIG. 3, without the inclusion of a rectification column. Feeding the mixed C-C material flow 0 (raw material) into a catalytic cracking unit to obtain a catalytic cracking product 1 containing ethylene and propylene, an unreacted raw material 2 and a catalytic cracking product 3 rich in aromatic hydrocarbon; part of the unreacted raw material 7 is circulated back to the inlet of the catalytic cracking unit and is subjected to catalytic cracking treatment together with the raw material; the unreacted raw material 2 enters a hydrogenation unit for hydrogenation treatment to obtain heavy carbon IV 9, and then enters a steam cracking unit for steam cracking treatment to obtain a material 10 rich in ethylene and propylene; stream 1 and stream 10 are combined to yield stream 11 enriched in ethylene and propylene.
Example 1
The flow shown in fig. 1 is adopted: the material flow 0 comprises 40 percent of C4 olefin and 60 percent of n-butane, the total flow is 1000kg/h, the material flows 1, 2, 3 and 7 are obtained by a catalytic cracking reaction unit, a ZSM5 molecular sieve is adopted for the catalytic cracking reaction, the reaction temperature is 560 ℃, the reaction pressure is 50kPa, and the space velocity is 20h-1. The mass flow ratio of stream 7 (essentially all unreacted feed) to stream 0 was 4.97 and the flow of stream 1 was 344kg/h containing 76kg/h ethylene and 229kg/h propylene. The flow rate of the material flow 2 is 633kg/h, the material flow is sent into a rectifying tower a with the theoretical number of trays being 100 layers, a light carbon four material flow 4 is obtained at the tower top and is divided into circulationA material flow 6 and a discharged material 8, wherein the material flow 6 accounts for 90% of the material flow 4 by mass; the tower bottom obtains heavy carbon four material flow 5, the flow rate of the heavy carbon four material flow is 616kg/h, the heavy carbon four material flow enters a steam cracking unit after full hydrogenation (the hydrogen consumption is 0.6kg/h), and material flow 10 is obtained, the ethylene content in the material flow 10 is 252kg/h, and the propylene content is 105 kg/h. Stream 1 and stream 10 are combined to give stream 11, the total amount of ethylene being 328kg/h and the total amount of propylene being 334 kg/h. Wherein the total feed to the olefin catalytic cracking unit is 5986 kg/h.
Example 2
The flow shown in fig. 1 is adopted: the material flow 0 comprises 40 percent of C4 olefin and 60 percent of n-butane, the total flow is 1000kg/h, the material flows 1, 2, 3 and 7 are obtained by a catalytic cracking reaction unit, a ZSM5 molecular sieve is adopted for the catalytic cracking reaction, the reaction temperature is 560 ℃, the reaction pressure is 50kPa, and the space velocity is 20h-1. The mass flow ratio of stream 7 (essentially all unreacted feed) to stream 0 was 2.97 and the flow of stream 1 was 335kg/h containing 74kg/h ethylene and 223kg/h propylene. The flow rate of the material flow 2 is 652kg/h, the material flow is sent into a rectifying tower a with the theoretical number of trays being 100 layers, a light carbon four material flow 4 is obtained at the top of the tower and is divided into a circulating material flow 6 and an external discharge material 8, wherein the material flow 6 accounts for 90 percent of the mass ratio of the material flow 4; the tower bottom obtains heavy carbon four material flow 5, the flow rate of the heavy carbon four material flow is 625kg/h, after full hydrogenation (the hydrogen consumption is 0.9kg/h), the heavy carbon four material flow enters a steam cracking unit to obtain material flow 10, the ethylene content in the material flow 10 is 256kg/h, and the propylene content is 106 kg/h. Stream 1 and stream 10 are combined to give stream 11, the total amount of ethylene being 330kg/h and the total amount of propylene being 329 kg/h. Wherein the total feed to the olefin catalytic cracking unit was 3994 kg/h.
Example 3
The flow shown in fig. 1 is adopted: the material flow 0 comprises 40 percent of C4 olefin and 60 percent of n-butane, the total flow is 1000kg/h, the catalytic cracking reaction unit obtains the material flows 1, 2, 3 and 7, a ZSM5 molecular sieve is adopted for the catalytic cracking reaction, the reaction temperature is 560 ℃, the reaction pressure is 50kPa, and the space velocity is 20h-1. The mass flow ratio of stream 7 (essentially all unreacted feed) to stream 0 was 0.99 and the flow of stream 1 was 308kg/h containing 68kg/h ethylene and 205kg/h propylene. The flow rate of the material flow 2 is 710kg/h, and the theoretical number of the tower trays is 100The rectifying tower a obtains a light carbon four material flow 4 at the tower top, and the light carbon four material flow is divided into a circulating material flow 6 and a discharged material 8, wherein the material flow 6 accounts for 90 percent of the mass ratio of the material flow 4; the tower bottom obtains heavy carbon four material flow 5, the flow rate of which is 652kg/h, and the heavy carbon four material flow enters a steam cracking unit after full hydrogenation (the hydrogen consumption is 2.1kg/h) to obtain material flow 10, wherein the ethylene content in the material flow 10 is 267kg/h, and the propylene content is 111 kg/h. Stream 1 and stream 10 are combined to give stream 11, the total amount of ethylene being 335kg/h and the total amount of propylene being 316 kg/h. Wherein the total feed to the olefin catalytic cracking unit was 2052 kg/h.
Example 4
The flow shown in fig. 1 is adopted: the material flow 0 comprises 40 percent of C4 olefin and 60 percent of n-butane, the total flow is 1000kg/h, the material flows 1, 2, 3 and 7 are obtained by a catalytic cracking reaction unit, a ZSM5 molecular sieve is adopted for the catalytic cracking reaction, the reaction temperature is 560 ℃, the reaction pressure is 50kPa, and the space velocity is 20h-1. The mass flow ratio of stream 7 (essentially all unreacted feed) to stream 0 was 0.09 and the flow of stream 1 was 263kg/h containing 58kg/h of ethylene and 175kg/h of propylene. The flow rate of the material flow 2 is 803kg/h, the material flow is sent into a rectifying tower a with 100 theoretical trays, a light carbon four material flow 4 is obtained at the top of the tower and is divided into a circulating material flow 6 and an external discharge material 8, wherein the material flow 6 accounts for 90 percent of the mass ratio of the material flow 4; the tower bottom obtains heavy carbon four-material flow 5 with the flow rate of 696kg/h, and the heavy carbon four-material flow enters a steam cracking unit after full hydrogenation (the hydrogen consumption is 3.9kg/h) to obtain material flow 10, wherein the ethylene content in the material flow 10 is 286kg/h, and the propylene content is 118 kg/h. Stream 1 and stream 10 are combined to give stream 11, with a total ethylene content of 344kg/h and a total propylene content of 293 kg/h. Wherein the total feed to the olefin catalytic cracking unit is 1186 kg/h.
Example 5
The flow shown in fig. 1 is adopted: the material flow 0 comprises 70 percent of C4 olefin and 30 percent of n-butane, the total flow is 1000kg/h, the material flows 1, 2, 3 and 7 are obtained by a catalytic cracking reaction unit, a ZSM5 molecular sieve is adopted for the catalytic cracking reaction, the reaction temperature is 560 ℃, the reaction pressure is 50kPa, and the space velocity is 20h-1. The mass flow ratio of stream 7 (essentially all unreacted feed) to stream 0 was 2.99, and the flow of stream 1 was 603kg/h, containing 134kg/h ethylene and 402k propyleneg/h. The flow rate of the material flow 2 is 355kg/h, the material flow is sent into a rectifying tower a with the theoretical number of trays being 100 layers, a light carbon four material flow 4 is obtained at the top of the tower and is divided into a circulating material flow 6 and an external discharge material 8, wherein the material flow 6 accounts for 90 percent of the mass ratio of the material flow 4; the tower bottom obtains heavy carbon four material flow 5, the flow rate of the heavy carbon four material flow is 326kg/h, the heavy carbon four material flow enters a steam cracking unit after full hydrogenation (the hydrogen consumption is 1.2kg/h), and material flow 10 is obtained, the ethylene content in the material flow 10 is 133kg/h, and the propylene content is 55 kg/h. Stream 1 and stream 10 are combined to give stream 11, the total amount of ethylene being 267kg/h and the total amount of propylene being 457 kg/h. Wherein the total feed to the olefin catalytic cracking unit is 4018 kg/h.
Example 6
The flow shown in fig. 1 is adopted: the material flow 0 comprises 70 percent of C4 olefin and 30 percent of n-butane, the total flow is 1000kg/h, the material flows 1, 2, 3 and 7 are obtained by a catalytic cracking reaction unit, a ZSM5 molecular sieve is adopted for the catalytic cracking reaction, the reaction temperature is 560 ℃, the reaction pressure is 50kPa, and the space velocity is 20h-1. The mass flow ratio of stream 7 (essentially all unreacted feed) to stream 0 was 0.99 and the flow of stream 1 was 559kg/h containing 124kg/h ethylene and 372kg/h propylene. The flow rate of the material flow 2 is 448kg/h, the material flow is sent into a rectifying tower a with the theoretical number of trays being 100 layers, a light carbon four material flow 4 is obtained at the top of the tower and is divided into a circulating material flow 6 and an external discharge material 8, wherein the material flow 6 accounts for 90 percent of the mass ratio of the material flow 4; the tower bottom obtains heavy carbon four material flow 5, the flow rate of the heavy carbon four material flow is 370kg/h, the heavy carbon four material flow enters a steam cracking unit after full hydrogenation (the hydrogen consumption is 2.9kg/h), and material flow 10 is obtained, the ethylene content in the material flow 10 is 152kg/h, and the propylene content is 63 kg/h. Stream 1 and stream 10 are combined to give stream 11, the total amount of ethylene being 276kg/h and the total amount of propylene being 435 kg/h. Wherein the total feed to the olefin catalytic cracking unit was 2070 kg/h.
Example 7
The flow shown in fig. 1 is adopted: the material flow 0 comprises 70 percent of C4 olefin and 30 percent of n-butane, the total flow is 1000kg/h, the material flows 1, 2, 3 and 7 are obtained by a catalytic cracking reaction unit, a ZSM5 molecular sieve is adopted for the catalytic cracking reaction, the reaction temperature is 560 ℃, the reaction pressure is 50kPa, and the space velocity is 20h-1. The ratio of the mass flow of stream 7 (essentially all unreacted feed) to that of stream 0 was 0.10,the flow rate of stream 1 was 465kg/h, containing 103kg/h of ethylene and 309kg/h of propylene. The flow rate of the material flow 2 is 648kg/h, the material flow is sent into a rectifying tower a with the theoretical number of trays being 100 layers, a light carbon four material flow 4 is obtained at the tower top and is divided into a circulating material flow 6 and an external discharge material 8, wherein the material flow 6 accounts for 90 percent of the mass ratio of the material flow 4; the tower bottom obtains a heavy carbon four-material flow 5, the flow rate of the heavy carbon four-material flow is 464kg/h, the heavy carbon four-material flow enters a steam cracking unit after full hydrogenation (the hydrogen consumption is 6.5kg/h), and a material flow 10 is obtained, wherein the ethylene content in the material flow 10 is 190kg/h, and the propylene content is 79 kg/h. Stream 1 and stream 10 are combined to give stream 11, the total amount of ethylene being 293kg/h and the total amount of propylene being 388 kg/h. Wherein the total feed to the olefin catalytic cracking unit was 1262 kg/h.
Comparative example 1
The flow shown in fig. 2 is adopted: the material flow 0 comprises 40 percent of C4 olefin and 60 percent of n-butane, the total flow is 1000kg/h, the catalytic cracking reaction unit obtains the material flows 1, 2, 3 and 7, a ZSM5 molecular sieve is adopted for the catalytic cracking reaction, the reaction temperature is 560 ℃, the reaction pressure is 50kPa, and the space velocity is 20h-1. The mass flow ratio of stream 7 (essentially all unreacted feed) to stream 0 was 2.97 and the flow of stream 1 was 315kg/h containing 70kg/h ethylene and 210kg/h propylene. The total feed to the olefin catalytic cracking unit was 3973 kg/h.
Comparative example 2
The flow shown in fig. 2 is adopted: the material flow 0 comprises 70 percent of C4 olefin and 30 percent of n-butane, the total flow is 1000kg/h, the material flows 1, 2, 3 and 7 are obtained by a catalytic cracking reaction unit, a ZSM5 molecular sieve is adopted for the catalytic cracking reaction, the reaction temperature is 560 ℃, the reaction pressure is 50kPa, and the space velocity is 20h-1. The mass flow ratio of stream 7 (essentially all unreacted feed) to stream 0 was 2.99 and the flow of stream 1 was 582kg/h containing 129kg/h ethylene and 387kg/h propylene. The total feed to the olefin catalytic cracking unit was 3992 kg/h.
Comparative example 3
The flow shown in fig. 3 is adopted: the material flow 0 comprises 40 percent of C4 olefin and 60 percent of n-butane, the total flow is 1000kg/h, the material flows 1, 2, 3 and 7 are obtained by a catalytic cracking reaction unit, a ZSM5 molecular sieve is adopted for the catalytic cracking reaction, the reaction temperature is 560 ℃, the reaction pressure is 50kPa,space velocity of 20h-1. The mass flow ratio of stream 7 (essentially all unreacted feed) to stream 0 was 2.97 and the flow of stream 1 was 316kg/h with 70kg/h ethylene and 210kg/h propylene. The flow rate of the material flow 2 is 649kg/h, after full hydrogenation (hydrogen consumption is 2.1kg/h), the material flow enters a steam cracking unit to obtain a material flow 10, the ethylene content in the material flow 10 is 227kg/h, and the propylene content is 117 kg/h. Stream 1 and stream 10 are combined to give stream 11 with a total amount of ethylene of 297kg/h and a total amount of propylene of 327 kg/h. Wherein the total feed to the olefin catalytic cracking unit is 3975 kg/h.
Comparative example 4
The flow shown in fig. 3 is adopted: the material flow 0 comprises 70 percent of C4 olefin and 30 percent of n-butane, the total flow is 1000kg/h, the material flows 1, 2, 3 and 7 are obtained by a catalytic cracking reaction unit, a ZSM5 molecular sieve is adopted for the catalytic cracking reaction, the reaction temperature is 560 ℃, the reaction pressure is 50kPa, and the space velocity is 20h-1. The mass flow ratio of stream 7 (essentially all unreacted feed) to stream 0 was 2.99 and the flow of stream 1 was 582kg/h containing 129kg/h ethylene and 387kg/h propylene. The flow rate of the material flow 2 is 353kg/h, after full hydrogenation (hydrogen consumption is 2.3kg/h), the material flow enters a steam cracking unit to obtain a material flow 10, the ethylene content in the material flow 10 is 124kg/h, and the propylene content is 64 kg/h. Stream 1 and stream 10 are combined to give stream 11, the total amount of ethylene being 253kg/h and the total amount of propylene being 451 kg/h. Wherein the total feed to the olefin catalytic cracking unit was 3992 kg/h.
TABLE 1 results of examples 1 to 4 and comparative examples 1 and 3
TABLE 2 results of examples 5 to 7 and comparative examples 2 and 4
It is clear from the above two tables that the ethylene propylene yield is advantageous and the feed to the catalytic cracking unit can be greatly reduced by using the example of the present invention, for example, the scale of the catalytic cracking unit in example 3 is only 51% of that in example 2, while the feed to the steam cracking unit is increased by only 4%, although the hydrogen consumption is increased by a large amount, the absolute value of the hydrogen consumption is still at a very low level.
Any numerical value mentioned in this specification, if there is only a two unit interval between any lowest value and any highest value, includes all values from the lowest value to the highest value incremented by one unit at a time. For example, if it is stated that the amount of a component, or a value of a process variable such as temperature, pressure, time, etc., is 50 to 90, it is meant in this specification that values of 51 to 89, 52 to 88 … …, and 69 to 71, and 70 to 71, etc., are specifically enumerated. For non-integer values, units of 0.1, 0.01, 0.001, or 0.0001 may be considered as appropriate. These are only some specifically named examples. In a similar manner, all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be disclosed in this application.
It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not constitute any limitation to the present invention. The present invention has been described with reference to exemplary embodiments, but the words which have been used herein are words of description and illustration, rather than words of limitation. The invention can be modified, as prescribed, within the scope of the claims and without departing from the scope and spirit of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather extends to all other methods and applications having the same functionality.
Claims (11)
1. A process for producing ethylene and propylene comprising the steps of:
s1, carrying out catalytic cracking treatment on a raw material containing carbon-tetrahydrocarbon to respectively obtain a material flow I containing ethylene and propylene, a material flow II containing unreacted raw materials and a material flow III containing aromatic hydrocarbon;
s2, optionally, circulating at least part of the material flow II together with the raw material to perform catalytic cracking treatment;
s3, separating at least part of the material flow II to respectively obtain a material flow IV with a boiling point lower than the division point and a material flow V with a boiling point higher than the division point; the temperature of the division point is-6.8 +/-0.5 ℃;
s4, optionally, recycling at least part of the material flow IV to the step S1 for catalytic cracking treatment;
s5, carrying out steam cracking treatment on the material flow V to obtain a material flow VI containing ethylene and propylene.
2. The method of claim 1, wherein the feedstock comprises carbon tetraolefins and n-butane; and/or the n-butane content in the feedstock is not less than 6 wt%, preferably not less than 15 w%, more preferably not less than 25 w%; and/or the content of carbon tetraolefin in the feedstock is not less than 20 wt%, preferably not less than 30 wt%, more preferably not less than 40 wt%.
3. The method according to claim 1 or 2, characterized in that the catalytic cracking treatment is performed in step S1 in the presence of a catalyst, preferably the catalyst is an acidic molecular sieve, more preferably comprises at least one of SAPO-34, ZSM-5, Y-type molecular sieves; and/or the presence of a gas in the gas,
the reaction conditions of the catalytic cracking treatment include: the reaction temperature is 500-600 ℃, preferably 540-590 ℃; the reaction pressure is-0.05 to 0.5MPa, preferably 0 to 0.3 MPa; the volume space velocity is 5-35h-1Preferably 10-20h-1。
4. The process according to any of claims 1 to 3, characterized in that the mass ratio of unreacted feedstock in stream II recycled in step S2 to fresh feedstock in step S1 is not higher than 5:1, preferably not higher than 3:1, more preferably not higher than 2: 1.
5. The process according to any one of claims 1 to 4, wherein at least part of stream II is subjected to rectification in step S3 by means of a rectification column, with a cut point of-6.8 ± 0.5 ℃, a fraction below the cut point obtained at the top of the column being stream IV and a fraction above the cut point obtained at the bottom of the column being stream V; preferably, at least 80 wt%, preferably at least 90 wt%, more preferably at least 95 wt% of the components in the stream entering the rectification column having boiling points below the cut point are recovered overhead.
6. The method according to any one of claims 1 to 5, wherein the rectification column comprises at least 60 layers, preferably at least 80 layers, more preferably at least 100 layers of theoretical trays; and/or the reflux ratio of the rectification column is not less than 3.0, preferably not less than 5.0, more preferably not less than 8.0; and/or the column pressure of the rectifying column is 0.2-0.8MPa, preferably 0.25-0.6MPa, more preferably 0.3-0.55 MPa.
7. Process according to any one of claims 1 to 6, characterized in that at least 60 wt.%, preferably at least 80 wt.%, more preferably at least 90 wt.% of stream IV in step S4 is recycled to step S1 for catalytic cracking treatment.
8. The method according to any one of claims 1-7, further comprising: stream V is hydrotreated before being subjected to steam cracking treatment.
9. A system for producing ethylene and propylene, comprising:
the catalytic cracking unit is used for carrying out catalytic cracking treatment on the raw material containing the carbon-tetrahydrocarbon to respectively obtain a material flow I containing ethylene and propylene, a material flow II containing unreacted raw materials and a material flow III containing aromatic hydrocarbon;
the rectifying tower is used for receiving at least part of the material flow II from the catalytic cracking unit and separating the material flow II to respectively obtain a material flow IV with the boiling point lower than the division point and a material flow V with the boiling point higher than the division point; the temperature of the division point is-6.8 +/-0.5 ℃;
optionally a hydrogenation unit for receiving and hydrotreating the stream V coming from the rectification column;
and the steam cracking unit is used for receiving the stream V from the rectifying tower and/or the product from the hydrogenation unit and carrying out steam cracking treatment on the stream V and/or the product to obtain a stream VI containing ethylene and propylene.
10. The system of claim 9, wherein the catalytic cracking unit comprises a feedstock inlet, a stream I outlet, a stream II outlet, and a stream III outlet; and the material flow II outlet is connected with the raw material inlet and is used for recycling at least part of the material flow II together with the raw material to carry out catalytic cracking treatment.
11. The system as claimed in claim 9 or 10, wherein the fraction obtained at the top of the rectifying tower and lower than the division point is a material flow IV, and the fraction obtained at the bottom of the rectifying tower and higher than the division point is a material flow V; preferably, the top of the rectification column is connected to a catalytic cracking unit for recycling at least part of the stream IV to the catalytic cracking unit for treatment.
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