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EP-4741044-A1 - NITRILE PRODUCTION METHOD WITH IMPROVED AMMONIA ABSORPTION EFFECT

EP4741044A1EP 4741044 A1EP4741044 A1EP 4741044A1EP-4741044-A1

Abstract

The present invention relates to a process for producing a nitrile with improved ammonia absorption effect. The process can atomize the spraying liquid, increase the contact area with ammonia, and improve mass transfer efficiency. The process for producing the nitrile comprises a step of subjecting a hydrocarbon feedstock to ammoxidation reaction to produce a reaction product containing nitrile (called as reaction step), and a step of feeding the reaction product into an absorption device through a gas inlet and spraying a spraying liquid onto the reaction product via a spraying device within the absorption device to cool the reaction product and form an absorption atmosphere (called as cooling step), wherein when measured at a vertical distance of 3000 mm above the gas inlet, the absorption atmosphere has an extinction coefficient of 0.004-0.02 m -1 .

Inventors

  • ZHAO, Le
  • WU, LIANGHUA

Assignees

  • China Petroleum & Chemical Corporation
  • Sinopec (Shangai) Research Institute of Petrochemical Technology Co., Ltd.

Dates

Publication Date
20260513
Application Date
20240508

Claims (17)

  1. A process for producing a nitrile, comprising a step of subjecting a hydrocarbon feedstock to an ammoxidation reaction to produce a reaction product containing nitrile (called as reaction step), and a step of feeding the reaction product into an absorption device through a gas inlet and spraying a spraying liquid onto the reaction product via a spraying device within the absorption device to cool the reaction product and form an absorption atmosphere (called as cooling step), wherein when measured at a vertical distance of 3000 mm above the gas inlet, the absorption atmosphere has an extinction coefficient of 0.004-0.02 m -1 (preferably 0.006-0.018 m -1 ).
  2. The producing process according to claim 1, wherein when measured at a vertical distance of 3000 mm above the gas inlet, the absorption atmosphere has a droplet average diameter, D 32 , of 400-2600 µm (preferably 600-2400 µm), and/or, when measured at a vertical distance of 3000 mm above the gas inlet, the absorption atmosphere has a droplet size distribution, D 10 of 150-1500 µm, D 50 of 700-3000 µm, and D 90 of 1400-3600 µm (preferably D 10 of 250-1400 µm, D 50 of 800-2800 µm, and D 90 of 1600-3500 µm).
  3. The producing process according to claim 1, wherein when measured at a vertical distance of 8500 mm above the gas inlet, the absorption atmosphere has an extinction coefficient of 0.001-0.004 m -1 (preferably 0.0015-0.0035 m -1 ), and/or, when measured at a vertical distance of 8500 mm above the gas inlet, the absorption atmosphere has a droplet average diameter D 32 of 200-1400 µm (preferably 400-1000 µm), and/or, when measured at a vertical distance of 8500 mm above the gas inlet, the absorption atmosphere has a droplet size distribution of D 10 of 100-1000 µm, D 50 of 300-1800 µm, and D 90 of 500-2200 µm (preferably D 10 of 200-600 µm, D 50 of 400-1400 µm, and D 90 of 600-1800 µm).
  4. The producing process according to claim 1, wherein the spraying device comprises a spraying liquid inlet, a first spraying pipe in fluid communication with the spraying liquid inlet, a plurality of second spraying pipes in fluid communication with the first spraying pipe and extending perpendicularly to the first spraying pipe along both sides thereof, a plurality of third spraying pipes in fluid communication with the second spraying pipes and extending perpendicularly to the second spraying pipes along both sides thereof, and a nozzle located at the end of the third spraying pipe and in fluid communication therewith.
  5. The producing process according to claim 4, wherein, on two adjacent second spraying pipes, the linear distance M between the end of any one third spraying pipe on one second spraying pipe and the end of any one third spraying pipe on any other adjacent second spraying pipe is not less than 320 mm (preferably not less than 350 mm), and/or, the nozzle is same as or different from each other and each independently have a spraying liquid ejection rate of 0.5-7.5 t/h (preferably 0.9-6.5 t/h), and/or, the nozzle is same as or different from each other and each independently have a spraying liquid ejection pressure at the nozzle outlet of 0.03-0.85 MPaG (preferably 0.04-0.65 MPaG), and/or, the spraying liquid input pressure at the spraying liquid inlet is controlled to be 0.06-1.00 MPaG (preferably 0.12-0.90 MPaG, more preferably 0.18-0.80 MPaG), and/or, the difference (absolute value) in the spraying liquid input pressures between the spraying liquid inlets of any two spraying devices is less than 0.024 MPa (preferably less than 0.018 MPa, more preferably less than 0.012 MPa).
  6. The producing process according to claim 1, wherein a plurality (e.g., 2-10, preferably 4-8) of the spraying devices are arranged in layers inside the absorption device along the central axis direction of the absorption device with a predetermined vertical spacing, and/or, the vertical spacing between two adjacent spraying devices (calculated as the vertical spacing of the spraying liquid inlets of the spraying devices) is 650-1350 mm (preferably 750-1200 mm).
  7. The producing process according to claim 4, wherein when a cross-section is obtained by cutting the absorption device at a direction perpendicular to the central axis of the absorption device, at least one (preferably all) selected from the first spraying pipe, the second spraying pipe, and the third spraying pipe of one of the plurality of spraying devices and at least one (preferably all) selected from the first spraying pipe, the second spraying pipe, and the third spraying pipe of any other of the plurality of spraying devices substantially coincide in the projection on the cross-section.
  8. The producing process according to claim 7, wherein all nozzles of the one spraying device and all nozzles of the any other spraying device substantially coincide in the projection on the cross-section, and/or, two nozzles with substantially coinciding projections have the same spray diameter, and/or, two nozzles with substantially coinciding projections have the same spraying liquid rotating direction.
  9. The producing process according to claim 1, wherein the vertical distance between the gas inlet and the spraying liquid inlet of the spraying device (when more than one spraying device are present, referring to the spraying device closest to the gas inlet) is 800-6000 mm (preferably 1000-5000 mm), and/or, the gas inlet has an inner diameter of 800-1900 mm (preferably 900-1700 mm), and/or, the reaction product has a linear velocity within the absorption device of 0.6-1.5 m/s (preferably 0.7-1.3 m/s), and/or, the flow ratio by weight of the spraying liquid to the reaction product is 15-25:1.
  10. The producing process according to claim 1, wherein within the internal space between the gas inlet and the spraying device (when more than one spraying device are present, referring to the spraying device closest to the gas inlet) of the absorption device, no mechanical member capable of substantially affecting the gas flow is arranged.
  11. The producing process according to claim 7, wherein the angle between the projections on the cross-section of the spraying liquid inlet of the one spraying device and that of the any other spraying device is 180°.
  12. The absorption device according to claim 11, wherein among all the spraying devices, the angle between the projections on the cross-section of the spraying liquid inlets of any two odd-numbered spraying devices is 0°, the angle between the projections on the cross-section of the spraying liquid inlets of any two even-numbered spraying devices is 0°, and the angle between the projection on the cross-section of the spraying liquid inlet of any odd-numbered spraying device and that of the spraying liquid inlet of any even-numbered spraying device is 180°.
  13. The absorption device according to claim 11, wherein the nozzle comprises a nozzle inlet, a rotating chamber, and a nozzle outlet, wherein the rotating chamber is configured such that the spraying liquid fed in through the nozzle inlet leaves the nozzle outlet in a rotating manner after passing through the rotating chamber.
  14. The absorption device according to claim 11, wherein on at least one (preferably all) of the second spraying pipes, two adjacent (preferably all) nozzles located at the same side of the second spraying pipe are configured such that the spraying liquid is ejected out with the same rotating direction.
  15. The absorption device according to claim 14, wherein all nozzles located at the facing sides of two side-by-side adjacent second spraying pipes are configured such that the spraying liquid is ejected out with opposite rotating direction.
  16. The absorption device according to claim 14, wherein on at least one (preferably all) of the second spraying pipes, at least one (preferably all) nozzle located on one side of the second spraying pipe is configured such that the spraying liquid is ejected out with a rotating direction A, while at least one (preferably all) nozzle located on the opposite side of the second spraying pipe is configured such that the spraying liquid is ejected out with a rotating direction B, wherein the rotating direction A is opposite to the rotating direction B.
  17. The absorption device according to claim 16, wherein among all the nozzles of the spraying device, the number of nozzles ejecting the spraying liquid with the rotating direction A is equal or substantially equal to the number of nozzles ejecting the spraying liquid with the rotating direction B.

Description

The present invention relates to the technical field of gas absorption, and more particularly, to a process for producing nitrile with improved ammonia absorption effect. BACKGROUND In the process route for producing corresponding nitriles by ammoniation or ammoxidation, in order to maximize the conversion of raw material gases such as hydrocarbons, the raw material gas ammonia is generally used in an excess amount, i.e., the molar ratio of ammonia to hydrocarbon raw material gas being greater than 1. For example, in ammoxidation of propylene, the ammonia ratio (molar ratio of ammonia to propylene) is 1.10-1.35, and in ammoxidation of aromatic hydrocarbons, the ammonia ratio (molar ratio of ammonia to aromatic hydrocarbons) is 4-8. Therefore, the reactor outlet tail gas necessarily contains unreacted ammonia. On one hand, as in acrylonitrile production processes, reaction gases such as acrylonitrile are prone to polymerization under alkaline conditions. On the other hand, the escape of even a small amount of unreacted ammonia can easily cause environmental pollution. Therefore, in ammonification or ammoxidation processes, it is desired to use an absorption device (generally called as an ammonia absorption column or quench column) to remove unreacted ammonia from the gas phase using acid or water, which process is very necessary. With the development of production technology, production loads are continuously increasing, and the trend towards large-scale of devices represents the future development direction. The higher the device load, the larger the equipment, including the absorption device. It is known that in the absorption device, the circulating liquid (spraying liquid) is distributed within the absorption device via a spraying device and contacted countercurrently with the ammonia-containing gas to be absorbed, achieving the purpose of removing residual ammonia from the gas phase. CN105425849 teaches removal of residual ammonia by adjusting the amount of acid added based on the pH value of the effluent from the absorption device. CN1199940 teaches to improve the mass transfer and heat transfer effect between gas and liquid phases by adding internal components at the bottom of the absorption device, which in fact addresses the issue of uniform distribution of the ammonia-containing gas phase. However, the absorption device is still inevitably subjected to ammonia breakthrough, i.e., a small amount of ammonia escape still existing, leading to product loss in subsequent refining and separation units or causing environmental pollution. In the ammonia absorption methods of the prior art, after long-term operation of the absorption device, the ammonia content in the absorption tail gas increases significantly compared with the initial period of the operation. SUMMARY OF THE INVENTION In an ammonia absorption column, the spraying liquid is delivered to nozzles by a pump. Due to the high pressure of the spraying liquid, it is fed into the nozzle cavity through a tangential inlet, resulting in a rotating motion. After passing through the specially structured nozzle, the spraying liquid is ejected through the nozzle at high speed, breaking up into numerous small mist droplets. Most of the droplets, influenced by their own gravity and the centrifugal force from the rotating motion, move downward in the column. These droplets contact counter-currently with the upward-flowing gas. At the same time, a very small portion of the droplets may be entrained by the gas and move upward in the column. Inside the column, multiple layers of spraying devices are arranged. Each spraying device contains dozens or even hundreds of nozzles uniformly distributed across the cross-section thereof. During operation of the device, under the influence of the gas flow, the area within the column occupied by the spraying devices is filled with numerous small liquid droplets. Liquid droplets can cause strong attenuation of both visible light and infrared signals. By measuring the extinction coefficient of the droplets inside the column using infrared spectral radiation method or forward scattering method, a comprehensive evaluation of droplet size, quantity, distribution, etc., can be made. Generally, larger droplets and fewer droplets result in less light absorption, higher light transmittance, and a smaller extinction coefficient; vice versa, the extinction coefficient is larger. The inventors of the present invention have found that this problem can be solved by setting the extinction coefficient of the absorption atmosphere within a specific numerical range. The present invention is completed based on this discovery. Specifically, the present invention relates to the following aspects. 1. A process for producing a nitrile, comprising a step of subjecting a hydrocarbon feedstock to ammoxidation reaction to produce a reaction product containing nitrile (called as reaction step), and a step of feeding the reaction product into an absorp