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CN-117736764-B - Method and system for preparing olefin by dehydrogenating low-carbon alkane

CN117736764BCN 117736764 BCN117736764 BCN 117736764BCN-117736764-B

Abstract

The invention relates to the technical field of petrochemical industry, in particular to a method and a system for preparing olefin by dehydrogenating low-carbon alkane. The method comprises (1) introducing light alkane into a moving bed reaction zone filled with dehydrogenation catalyst for dehydrogenation reaction to obtain dehydrogenation product, separating the dehydrogenation product to obtain hydrogen, alkene and alkane, and (2) introducing the catalyst to be regenerated flowing out from the bottom of the moving bed reaction zone into a regenerator for regeneration treatment to obtain regenerated catalyst, and recycling the regenerated catalyst back into the moving bed reaction zone for dehydrogenation reaction. The method provided by the invention can improve the conversion rate of low-carbon alkane, realize continuous circulation of the catalyst and prolong the operation period of the device.

Inventors

  • ZHANG JINXING
  • WANG JIEGUANG
  • LIU CHANGCHENG
  • MA CHONG
  • ZHANG XINKUAN
  • REN JIANQIANG

Assignees

  • 中国石油化工股份有限公司
  • 中石化石油化工科学研究院有限公司

Dates

Publication Date
20260505
Application Date
20220914

Claims (20)

  1. 1. A method for preparing olefin by dehydrogenating low-carbon alkane, which is characterized by comprising the following steps: (1) Introducing low-carbon alkane into a moving bed reaction zone filled with a dehydrogenation catalyst for dehydrogenation reaction to obtain a dehydrogenation product, and separating the dehydrogenation product to obtain hydrogen, alkene and alkane; (2) Introducing a spent catalyst flowing out of the bottom of the moving bed reaction zone into a regenerator for regeneration treatment to obtain a regenerated catalyst, and recycling the regenerated catalyst back to the moving bed reaction zone to participate in the dehydrogenation reaction; The regenerator comprises a buffer zone, a primary burning zone, a secondary burning zone, an oxychlorination zone, a drying zone and a cooling zone which are sequentially communicated along the flow direction of the spent catalyst, wherein the gases of the primary burning zone and the secondary burning zone are respectively and independently circulated; Introducing air and a part of the chlorine-containing gas discharged from the oxychlorination zone as a gas I into the one-stage coking zone, and introducing air and another part of the chlorine-containing gas discharged from the oxychlorination zone as a gas II into the two-stage coking zone so that the oxygen content of the regenerated gas in the one-stage coking zone is 0.5 to 1% by volume, the chlorine content of the regenerated gas in the one-stage coking zone is 0.0003 to 0.3% by volume, and the oxygen content of the regenerated gas in the two-stage coking zone is 2 to 6% by volume, and the chlorine content of the regenerated gas in the two-stage coking zone is 0.0003 to 0.3% by volume.
  2. 2. The method of claim 1, wherein a portion of the regeneration gas exiting the one-stage char zone is recycled back into the one-stage char zone after being mixed with the gas I as a first recycle gas.
  3. 3. The method according to claim 2, wherein the amount of the first recycle gas and/or the gas I introduced is controlled such that the chlorine content of the regeneration gas in the one-stage char zone is 0.0003-0.2 vol%.
  4. 4. The process according to claim 1 or 2, wherein the regeneration gas exiting the secondary coking zone is recycled back into the secondary coking zone after mixing with the gas II as a second recycle gas.
  5. 5. The method according to claim 4, wherein the introduction amounts of the second recycle gas and the gas II are controlled so that the chlorine content of the regeneration gas in the two-stage coking zone is 0.0003 to 0.2 vol%.
  6. 6. A process according to any one of claims 1 to 3, wherein the gas I is a part of the chlorine-containing gas exiting the oxychlorination zone and the gas II is another part of the chlorine-containing gas exiting the oxychlorination zone.
  7. 7. A process according to any one of claims 1 to 3, wherein in step (1) a portion of the hydrogen obtained after separation is recycled back to the moving bed reaction zone to participate in the dehydrogenation reaction.
  8. 8. A process according to any one of claims 1 to 3, wherein in step (1) the lower alkane is a C 3 -C 5 alkane.
  9. 9. The method of claim 8, wherein in step (1), the lower alkane is selected from at least one of refinery by-products, shale gas, oilfield associated gas.
  10. 10. A process according to any one of claims 1 to 3, wherein in step (1), the dehydrogenation reaction conditions comprise at least a temperature of 550 to 700 ℃, a pressure of 0.01 to 0.5MPa, a hydrogen-hydrocarbon volume ratio of 0.2 to 2:1, and a volume space velocity of 0.1 to 10h -1 .
  11. 11. The process according to claim 10, wherein in the step (1), the dehydrogenation reaction is carried out under conditions including at least a temperature of 600 to 650 ℃, a pressure of 0.01 to 0.2MPa, a hydrogen-hydrocarbon volume ratio of 0.4 to 0.7:1, and a volume space velocity of 0.3 to 8h -1 .
  12. 12. A process according to any one of claims 1 to 3, wherein in step (1), the dehydrogenation catalyst comprises a support which is an alumina support and an active component which contains a platinum group metal element, a group IVA metal element, an alkali metal element and a chlorine element.
  13. 13. The method of claim 12, wherein the support is theta alumina.
  14. 14. The method of claim 12, wherein the alkali metal element is potassium element.
  15. 15. The method according to claim 12, wherein in the step (1), the active component contains 0.1 to 1 mass% of the platinum group metal element, 0.1 to 1 mass% of the group IVA metal element, 0.5 to 2 mass% of the alkali metal element, and 0.4 to 2 mass% of the chlorine element, based on the total mass of the carrier.
  16. 16. The method according to claim 15, wherein in step (1), the active component contains 0.1 to 1 mass% of platinum element, 0.1 to 1 mass% of tin element, 0.5 to 2 mass% of potassium element, and 0.5 to 1.5 mass% of the chlorine element, based on the total mass of the carrier.
  17. 17. A method according to any one of claims 1 to 3, wherein in step (2), the carbon content in the spent catalyst is 1 to 5 mass%.
  18. 18. The method according to claim 17, wherein the carbon content in the spent catalyst is 1-3 mass%.
  19. 19. A process according to any one of claims 1 to 3, wherein in step (2) the conditions of the one-stage coking zone comprise at least an inlet temperature of the regeneration gas of from 350 to 600 ℃ and a pressure of from 0.1 to 1.0MPa.
  20. 20. The method of claim 19, wherein the conditions of the one-stage char zone comprise at least an inlet temperature of the regeneration gas of 400-500 ℃.

Description

Method and system for preparing olefin by dehydrogenating low-carbon alkane Technical Field The invention relates to the technical field of petrochemical industry, in particular to a method and a system for preparing olefin by dehydrogenating low-carbon alkane. Background Propylene is an important organic chemical raw material and is used for producing products such as polypropylene, acrylonitrile, butanol, octanol, propylene oxide, isopropanol and the like. The traditional propylene mainly comes from byproducts of ethylene preparation by steam cracking, the isobutene almost comes from refinery gas and cracked C 4 fraction, and along with the increasing demand of the petrochemical industry for propylene and isobutene, the traditional propylene and isobutene sources cannot meet the market demand. Along with the maturity of shale gas exploitation technology, a large amount of high-quality and low-cost processes for preparing propylene and isobutene by directly catalyzing and dehydrogenating propane and butane and alkane are provided for the market, and the process is accepted by the market more and more due to the economical and environment-friendly technology. The process for preparing the low-carbon alkane by the low-carbon alkane dehydrogenation mainly comprises a moving bed process and a fixed bed process, wherein the design of a reaction system of the fixed bed process is relatively simple, but the switching operation is very frequent due to the frequent regeneration of the catalyst, and the requirements on a control system, a valve and equipment are higher. The moving bed process can realize continuous regeneration and circulation of the catalyst, so that the catalyst is kept in a higher active state, the activity of the catalyst can be obviously improved, and the yield of propylene can be ensured. The existing continuous regeneration process of the propane dehydrogenation catalyst is characterized in that a pressure conversion and atmosphere replacement system is arranged at the bottom of a moving bed reaction zone, a pressure conversion and flow control system is arranged at the bottom of a regenerator, catalyst blanking is a pulse type discontinuous process, and metal fatigue at the joint of the regenerator is easy to cause cracking of the inner network of the regenerator. CN112569872a discloses a moving bed system for the dehydrogenation of light alkanes to produce light alkanes. The technical scheme includes that the device comprises a raw material pretreatment unit, a fuel separation unit, a moving bed reaction unit, a hydrogen separation unit, a product purification unit, a product separation and purification unit and a catalyst regeneration unit which are sequentially connected through pipelines, wherein the moving bed reaction unit comprises a plurality of reaction pipelines which are arranged in parallel, and a heating furnace and a reactor are arranged on the reaction pipelines. CN1100852C discloses a method and apparatus for regenerating hydrocarbon conversion catalyst, the catalyst to be regenerated passes through the burning zone, oxychlorination zone, predrying zone and roasting zone of the regenerator in turn from top to bottom, the added predrying zone can use the regenerated recycle gas after dechlorination and drying to predrying the catalyst after oxychlorination, thereby reducing the dry gas consumption of the roasting zone, the oxygen-containing gas entering the roasting zone is determined by the oxygen consumption required by burning, the gas entering the roasting zone can all enter the oxychlorination zone, then enter the regenerated gas circulation loop, oxygen is supplied for burning, the calcining zone of the regenerator has no redundant oxygen-containing gas to be exhausted, thus eliminating the purifying measure of the exhaust gas of the calcining zone. CN110452085A discloses a countercurrent moving bed C3/C4 alkane dehydrogenation process, wherein the flow direction of a catalyst between reactors is opposite to the flow direction of a reactant flow, the method comprises the steps that mixed hydrogen and C3/C4 alkane feed flow through a heat-combined heat exchanger and a heating furnace, enter a first-stage reactor and sequentially flow through a second-stage reactor and a last-stage reactor in series to form a reactant flow, the catalyst is regenerated through a regenerator and enters the last-stage reactor, sequentially flow through the second-stage reactor and the first-stage reactor in series to form a catalyst flow, and a hydrogen permeable membrane separator is arranged at the outlet of each-stage reactor. Compared with the existing industrialized propane dehydrogenation process, the method can improve the single-pass conversion rate of the C3/C4 alkane, reduce the reaction temperature, improve the selectivity, save energy, reduce carbon deposition on the catalyst, prolong the service life of the catalyst and reduce the investment of devices. Disclosure of Invention Th