Apparatus and process for separating acrylonitrile

Abstract

The application provides an acrylonitrile separation device and a separation process, the separation device uses multi-overflow trays with different overflow numbers for the extraction section and the stripping section of a large-diameter recovery tower, improves the liquid phase processing capacity of the recovery tower, reduces the tower pressure drop, and is provided with a plurality of high-efficiency fixed valves on the mass transfer zone of the multi-overflow tray, thereby increasing the gas-liquid contact area and contact time and further improving the separation efficiency of unit mass transfer; moreover, the high-efficiency fixed valve can effectively prevent tray plugging and prolong the operation cycle of the recovery tower; the acrylonitrile separation process provides specific proportions of solvent water and water-rich water and specific recovery tower parameters, and in combination with the acrylonitrile separation device provided by the application, solves the problem of uneven gas-liquid distribution in a large-scale recovery tower, improves the separation efficiency of the tower, makes the oxazole content in the oil phase at the top of the tower below 20 ppm, the total content of other impurities except water less than 250 ppm, simultaneously reduces the whole-tower pressure drop and the risk of tray plugging, and reduces the energy consumption of the device.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of acrylonitrile production, and further relates to an acrylonitrile separation device and a separation process. BACKGROUND

[0002] Acrylonitrile is an important organic synthetic material, and is a main raw material for producing acrylon fiber, ABS resin, carbon fiber, acrylamide and other high polymer materials. Acetonitrile, hydrocyanic acid and other products are by-products generated during the production of acrylonitrile, and are also high-value chemical products. In the past decade, with the rapid development of domestic economy, as the market demand for acrylonitrile continues to increase, the incremental technology of acrylonitrile production device has gradually improved, and it has become a trend for the development of acrylonitrile technology to build large-scale acrylonitrile devices, improve device capacity, improve acrylonitrile product quality and increase product competitiveness. This also puts forward higher separation requirements for the separation system in large-scale acrylonitrile production devices.

[0003] In the acrylonitrile separation system, the recovery tower is the most critical separation process. The function of the recovery tower is to separate and remove acetonitrile, oxazole, propyl aldehyde, acetone and other trace impurities in the feed liquid containing hydrocyanic acid, acrylonitrile and acetonitrile by using extraction distillation method, to obtain a high-purity acrylonitrile and hydrocyanic acid mixture, and to further separate the acrylonitrile and hydrocyanic acid products in the subsequent equipment.

[0004] However, the existing recovery tower often has the following problems: 1. The separation efficiency of the tower is low, and it cannot meet the product quality requirements in the new standard: the oxazole content in the acrylonitrile product obtained by the existing acrylonitrile recovery tower process is generally required to be ≤200ppm, and through process optimization and adjustment, the oxazole content in the acrylonitrile product can be ≤80ppm, but the new standard requires the oxazole content to be ≤30ppm. In addition, the new standard requires the acetone content to be reduced from 80ppm to 50ppm, and the existing technology cannot meet the above requirements; 2. With the large-scale development of acrylonitrile devices, large-diameter recovery towers have the problems of poor gas-liquid distribution, large pressure drop, poor gas-liquid mass transfer efficiency, low separation efficiency of the tower and large energy consumption of the device; 3. During the separation operation, the material in the recovery tower is easy to polymerize and block the tray, affecting the operation cycle of the tower.

[0005] Therefore, how to solve the problems of uneven gas-liquid distribution, low separation efficiency and easy blocking of the tray in the large-scale recovery tower has become an important problem for the large-scale development of acrylonitrile devices.

[0006] Chinese Patent Document 106892843A discloses a method for controlling impurities in a recovery column, including overhead and sidestream impurities. The method controls overhead and sidestream impurities by utilizing the flow rate of an aqueous solvent added to the distillation column and the distillation column temperature. The ratio of the aqueous solvent flow rate to the flow rate of a mixture comprising acrylonitrile and acetonitrile in the recovery column is controlled to be approximately 1:2 to 1:1.6, or the ratio of the sidestream flow rate to the flow rate of the mixture comprising acrylonitrile and acetonitrile is controlled to be approximately 1:1.25 to 1:1.7. Furthermore, the recovery column has a pressure drop of approximately 16 psid or less. The recovery tower temperature is controlled by maintaining the top portion of the middle section at approximately 65-85°C, the bottom portion at approximately 100-120°C, and the top portion at approximately 55-85°C. There is a temperature difference of approximately 0-20°C between the top and bottom portions of the top region of the recovery tower. The bottom portion of the recovery tower has a temperature of approximately 105-125°C, and there is a temperature difference of approximately 5-15°C between the top and bottom portions of the bottom section of the recovery tower. This method improves the separation efficiency of the recovery tower and reduces the impurity content at the top of the tower by controlling the process parameters of the recovery tower. However, this method does not change the gas-liquid mass transfer and phase equilibrium and only stabilizes the operation of the recovery tower, with limited improvement in separation efficiency.

[0007] Chinese patent document CN113861503A discloses a monomer recovery device and method for carbon fiber precursor production. This device uses feed rate and concentration to control the steam flow in the reboiler, enabling temperature feedforward control. This allows for precise temperature control of the recovery tower, improving the tower's recovery efficiency. This method only reduces production fluctuations caused by manual operation and fails to fundamentally improve the recovery tower's separation efficiency. Summary of the Invention

[0008] To address the problems of low separation efficiency and tray clogging caused by uneven mass transfer in existing large-diameter recovery towers, the present invention aims to provide an acrylonitrile separation device and a matching separation process. The separation device uses multiple overflow trays with different overflow numbers according to the different diameters of the extraction section and the stripping section of the recovery tower, thereby improving the liquid phase processing capacity of the recovery tower. Multiple high-efficiency solid valves are provided in the mass transfer area of ​​the multiple overflow trays, thereby increasing the gas-liquid contact area and contact time, further improving the separation efficiency of the unit mass transfer, and reducing the tower pressure drop. The high-efficiency solid valves can also effectively prevent tray clogging, thereby extending the operating cycle of the recovery tower. The acrylonitrile separation process provides a specific solvent water and rich water ratio as a separation process parameter. Combined with the acrylonitrile separation device provided by the present invention, the problem of uneven gas-liquid distribution in large-scale recovery towers is solved, the tower separation efficiency is improved, the oxazole content in the oil phase at the top of the tower is less than 20 ppm, and the total content of other impurities other than water is less than 250 ppm. At the same time, the pressure drop of the entire tower and the risk of tray clogging are reduced, thereby reducing the energy consumption of the device.

[0009] In order to achieve the above object, the present invention provides the following technical solutions:

[0010] An acrylonitrile separation device comprises: a recovery tower, the recovery tower comprises a tower body and a tower kettle connected in an upper and lower manner, the tower body is divided from bottom to top into a stripping section tower body and an extraction section tower body of different diameters; the diameter of the extraction section tower body is smaller than the diameter of the stripping section tower body; a plurality of first multi-overflow tower trays are provided in the extraction section tower body, and the plurality of first multi-overflow tower trays are evenly spaced along the vertical direction; a plurality of second multi-overflow tower trays are provided in the stripping section tower body, and the plurality of second multi-overflow tower trays are evenly spaced along the vertical direction; the plate surfaces of the first multi-overflow tower trays and the plate surfaces of the second multi-overflow tower trays are both provided with Multiple independent and parallel liquid receiving plate areas, multiple mass transfer areas and multiple downcomer areas, the liquid receiving plate area is provided on one side of any mass transfer area, and the downcomer area is provided on the other side; the number of mass transfer areas of the first multiple overflow tower plates is less than the number of mass transfer areas of the second multiple overflow tower plates; the mass transfer area is provided with multiple air holes and multiple high-efficiency solid valves, the high-efficiency solid valve includes at least three support plates and a solid valve baffle, and the solid valve baffle is provided with an exhaust hole; one end of the support plate is connected to the mass transfer area, and the other end of the support plate is connected to the solid valve baffle, and an air outlet is formed between two adjacent support plates.

[0011] In some embodiments, the fixed valve baffle is arranged parallel to the mass transfer area; or, the fixed valve baffle is arranged to be inclined downward from one end away from the liquid receiving disk area to one end close to the liquid receiving disk area, and the angle α between the fixed valve baffle and the horizontal direction is 5-60°.

[0012] In some embodiments, a plurality of overflow weirs are provided on the plate surface of the first multi-overflow tower tray and the plate surface of the second multi-overflow tower tray. The overflow weir is arranged between the mass transfer zone and the downcomer zone. The overflow weir is used to make the liquid in the mass transfer zone overflow evenly to the downcomer zone; the height of the overflow weir is 20-80 mm.

[0013] In some embodiments, the ratio of the diameter of the tower body, the width of the downcomer area and the liquid receiving plate area is: (8-30):1:(0.6-1.2); the diameter ratio of the stripping section tower body to the extraction section tower body is 1.1-2; the width of the mass transfer zone on the first multi-overflow tower plate is 100-1800 mm; the width of the mass transfer zone on the second multi-overflow tower plate is 400-2000 mm.

[0014] In some embodiments, the porosity of the mass transfer zone is 6-15%; and the high-efficiency solid valves are arranged in a triangle or a quadrilateral on the mass transfer zone.

[0015] In some embodiments, a rich water feed inlet is provided at the bottom of the extraction section tower body, and a rich gas outlet is provided at the top of the extraction section tower body; the stripping section tower body is provided with a crude acetonitrile outlet; the acrylonitrile separation device is further provided with a phase separator and an acetonitrile tower, the phase separator is provided with a rich material inlet, an oil phase outlet and a water phase outlet, the rich material inlet and the water phase outlet are respectively connected to the rich gas outlet and the rich water feed inlet, the oil phase outlet is connected to a subsequent device, the phase separator is used to separate the oil phase containing acrylonitrile in the rich gas and the water phase containing hydrocyanic acid; the inlet of the acetonitrile tower is connected to the crude acetonitrile outlet.

[0016] In some embodiments, the stripping section tower body is further provided with a lean water outlet and a liquid collector for collecting lean water, the liquid collector is arranged at the bottom of the stripping section tower body, the lean water outlet is arranged on the side wall near the bottom of the stripping section tower body, and the lean water outlet is connected to the outlet of the liquid collector; the tower kettle is provided with a lean water return port; the acrylonitrile separation device is further provided with a lean water buffer tank, the inlet and outlet of the lean water buffer tank are respectively connected to the lean water outlet and the lean water return port.

[0017] In some embodiments, the stripping section tower body, the phase separator and the lean water buffer tank are all provided with a sodium carbonate feed port; the acrylonitrile separation device is further provided with a sodium carbonate supply pipeline, which is respectively connected to the sodium carbonate feed ports of the stripping section tower body, the phase separator and the lean water buffer tank, and is used to input sodium carbonate for adjusting the pH into the stripping section tower body, the phase separator and the lean water buffer tank, respectively.

[0018] The present invention also provides an acrylonitrile separation process, which uses the acrylonitrile separation device described above and comprises the following steps:

[0019] Rich water containing impurities such as acrylonitrile, acetonitrile, hydrocyanic acid and oxazole enters the extraction section tower body, mixes with solvent water entering from the top of the extraction section tower body to form an acrylonitrile-water azeotrope, and performs extractive distillation to separate acrylonitrile, hydrocyanic acid and acetonitrile, while removing impurities such as oxazole from the rich water. The rich water containing acetonitrile enters the stripping section tower body downward, and rich gas containing acrylonitrile, hydrocyanic acid and water is discharged from the rich gas outlet at the top of the extraction section tower body. The rich water containing acetonitrile is distilled and purified in the stripping section tower body to obtain crude acetonitrile, and a liquid phase containing a small amount of organic matter is obtained in the tower bottom. The mass ratio of the rich water to the solvent water is 1:(5.5-9). The gas velocity through the gas outlet is controlled to be 6-20 m / s.

[0020] In some embodiments, the top temperature of the tower body is controlled to be 65-75°C, and the top pressure of the tower body is controlled to be 0.005-0.008 MPaG; the temperature of the tower bottom is controlled to be 110-118°C, and the pressure of the tower bottom is controlled to be 0.05-0.07 MPaG; the pressure drop of the recovery tower is controlled to be 40-65 kPa; the pH of the lean water in the tower bottom and the pH in the lean water buffer tank are controlled to be 6-8, and the pH in the phase separator is controlled to be 6-7.5.

[0021] Compared with the prior art, the production system and method of high-purity acrylonitrile provided by the present invention have the following beneficial effects:

[0022] 1. The present invention adopts multiple overflow trays with different overflow numbers for the different tower diameters of the extraction section and the stripping section of the recovery tower, which can effectively shorten the liquid phase process, reduce the liquid level gradient of the tray, make the liquid level thickness in the mass transfer area uniform, the gas-liquid flow uniform, the mass transfer on the entire tray uniform, and reduce the pressure drop. The larger the tower diameter and the more overflow numbers, the more obvious the effect; the liquid phase processing capacity of the recovery tower is improved, and the tray operation is more stable;

[0023] 2. In the existing recovery tower, the extraction section tower body and the stripping section tower body generally use tower plates with the same overflow number. For example, the entire tower uses two overflow tower plates or four overflow tower plates. The gas-liquid load in the stripping section tower body is large. In order to ensure the separation efficiency of the stripping section tower plates, it is usually necessary to increase the diameter of the stripping section tower plates, thereby increasing the equipment cost. However, in this application, the overflow number of the tower plates in the stripping section is increased, and excellent separation efficiency can be obtained without increasing the size of the tower plates, thereby reducing the tower diameter of the stripping section tower body and reducing equipment investment. Moreover, as the scale of the recovery tower continues to increase, the overflow number of the tower plates in the extraction section and the stripping section is increased at the same time, which can effectively reduce the diameter of the entire tower and reduce equipment investment.

[0024] 3. The recovery tower of the present invention adopts a mixed configuration of trays with different overflow numbers, which can reduce the pressure drop of the large-diameter recovery tower, reduce the tower bottom temperature, further save the steam consumption of the tower bottom reboiler, reduce the energy consumption of the recovery tower process, and reduce the risk of polymerization in the tower;

[0025] 4. The present invention is equipped with multiple high-efficiency fixed valves on the mass transfer area of ​​the tower tray. By controlling the length of the support plate to adjust the angle of the exhaust hole, the flow direction of the gas phase is consistent with the flow direction of the overflow liquid. The tower tray overflow weir and the tower tray opening rate are set to a specific height to increase the gas-liquid contact area and contact time, thereby improving the separation efficiency of the unit mass transfer. The oxazole content in the material extracted from the top of the recovery tower is ≤20ppm;

[0026] 5. The high-efficiency fixed valve provided by the present invention can also effectively prevent the blockage of multiple overflow trays, reduce the pressure drop of the trays and the temperature of the tower bottom, reduce the polymerization of materials, and extend the operation cycle;

[0027] 6. The present invention provides different sodium carbonate feed ports on different tower bodies of the recovery tower, and controls the amount of sodium carbonate added to the different sodium carbonate feed ports, thereby controlling the pH value at different locations in the recovery tower, reducing the risk of product polymerization in the tower, reducing the content of polymers in the tower kettle, the first tower tray, and the lean water in the lean water buffer tank, and reducing product losses. By controlling the pH adjustment range at different locations in the recovery tower to be different, the removal efficiency of impurities in the tower is effectively improved, the separation efficiency of the recovery tower is further improved, and equipment corrosion is reduced.

[0028] 7. The acrylonitrile separation device provided by the present invention has a specific crude acetonitrile discharge position and number of discharge trays at the crude acetonitrile outlet on the stripping section tower body, which facilitates the discharge of crude acetonitrile and improves the separation efficiency of the tower. At the same time, the separated crude acetonitrile is sent to the acetonitrile tower for further purification to prepare high-purity acetonitrile;

[0029] 8. The present invention provides an acrylonitrile separation process, which sets a specific ratio of solvent water to rich water and specific recovery tower parameters to improve the separation efficiency of the recovery tower, thereby ensuring that product quality requirements are met while also achieving energy conservation.

[0030] 9. The separation process matched with the acrylonitrile separation device provided by the present invention makes the oxazole content in the top oil phase below 20 ppm, and the total content of other impurities except water is less than 250 ppm. Combined with the subsequent traditional acrylonitrile refining process, the acrylonitrile purity is above 99.7 wt%, which can meet the current market demand for high-purity acrylonitrile raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The preferred embodiments will be described below in a clear and understandable manner with reference to the accompanying drawings to further illustrate the above-mentioned characteristics, technical features, advantages and implementation methods of the present invention.

[0032] Figure 1 A schematic structural diagram of the acrylonitrile separation device provided by the present invention;

[0033] Figure 2 A schematic structural diagram of a high-efficiency fixed valve provided by the present invention;

[0034] Figure 3 A cross-sectional view of the high-efficiency fixed valve provided by the present invention;

[0035] Figure 4 This is a schematic diagram of the planar layout of the four overflow tray structure;

[0036] Figure 5 The schematic diagram of the arrangement of five-layer four-overflow trays is shown in the axial section of the tower body;

[0037] Figure 6 This is a schematic diagram of the planar layout of the six overflow tray structure;

[0038] Figure 7 The schematic diagram of the arrangement of three-layer six overflow trays is shown in the axial section of the tower body;

[0039] Figure 8 Shown is a schematic diagram of the planar layout of the eight overflow tray structure;

[0040] Figure 9 The schematic diagram of the arrangement of three layers of eight overflow trays is shown as an axial cross-section of the tower body.

[0041] Description of Figure Numbers:

[0042] 1—extraction tower body; 101—first multi-overflow tray; 102—rich water feed inlet; 103—solvent water inlet; 104—rich gas outlet;

[0043] 2—stripping section tower body; 201—second overflow tray; 202—crude acetonitrile outlet; 203—lean water outlet;

[0044] 3—high-efficiency fixed valve; 301—fixed valve baffle; 302—exhaust hole; 303—air outlet; 304—first support plate; 305—second support plate; 306—third support plate; 307—exhaust hole inclined baffle;

[0045] 4—phase separator; 401—rich material inlet; 402—oil phase outlet; 403—water phase outlet; 404—lean water return port;

[0046] 5—acetonitrile tower; 6—lean water buffer tank; 7—sodium carbonate feed port;

[0047] 8—Liquid collector; 9—Sodium carbonate supply pipeline. DETAILED DESCRIPTION

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific embodiments of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings and other embodiments can be obtained based on these drawings without inventive work.

[0049] To simplify the drawings, only portions relevant to the invention are schematically depicted in each figure; they do not represent the actual structure of the product. Furthermore, to simplify the drawings and facilitate understanding, in some figures, only one component with the same structure or function is schematically depicted or labeled. In this document, "one" not only means "only one" but also "more than one."

[0050] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0051] It should be noted that, unless otherwise specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they can refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on the specific circumstances.

[0052] In addition, in the description of the present invention, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0053] Example 1

[0054] like Figure 1 - Figure 3 As shown, the present invention provides an acrylonitrile separation device, comprising:

[0055] The recovery tower includes a tower body and a tower kettle connected upper and lower. The tower body is divided into a stripping section tower body 2 and an extraction section tower body 1 with different diameters from bottom to top. The diameter of the extraction section tower body 1 is smaller than that of the stripping section tower body 2.

[0056] The recovery tower also includes a trapezoidal tower body. Since the diameter of the extraction section tower body 1 is smaller than that of the stripping section tower body 2, they can be connected through the trapezoidal tower body, that is, the tower body is divided into the stripping section tower body 2, the trapezoidal tower body and the extraction section tower body 1 from bottom to top.

[0057] Preferably, the diameter ratio of the stripping section tower body 2 to the extraction section tower body 1 is 1.1-2.

[0058] Furthermore, a plurality of first multi-overflow trays 101 are provided in the extraction section tower body 1, and the plurality of first multi-overflow trays 101 are evenly spaced apart in the vertical direction.

[0059] A plurality of second multi-overflow trays 201 are provided in the stripping section tower body 2, and the plurality of second multi-overflow trays 201 are evenly spaced apart in the vertical direction.

[0060] The plate surface of the first multi-overflow tower plate 101 and the plate surface of the second multi-overflow tower plate 201 are both provided with multiple liquid receiving plate areas, multiple mass transfer areas and multiple downcomer areas that are independent of each other and parallel to each other. A liquid receiving plate area is provided on one side of any mass transfer area, and a downcomer area is provided on the other side.

[0061] The mass transfer zone is an effective area for gas-liquid mass transfer, while the downcomer zone is a channel for liquid to flow downward. The mass transfer zone maintains a certain liquid layer on the tower tray, ensuring sufficient gas-liquid contact. The receiving tray area on one tower tray corresponds to the downcomer area on the upper tray, and the downcomer area on that tray corresponds to the receiving tray area on the lower tray. Liquid flowing down from the downcomer area on the upper tray reaches the receiving tray area on that tray and overflows into the mass transfer zone, where it undergoes mass transfer with the rising gas phase, achieving gas-liquid separation. The liquid then overflows into the downcomer area and flows out of the downcomer area to the receiving tray area on the lower tray.

[0062] The number of mass transfer zones of the first multiple overflow tray 101 is smaller than the number of mass transfer zones of the second multiple overflow tray 201 .

[0063] For a recovery tower with a large diameter, the extraction section 1 at the top and the stripping section 2 at the bottom have different diameters. Compared to using multiple overflow trays with the same overflow number uniformly within the tower body, the present invention provides multiple overflow trays with different overflow numbers within the extraction section 1 and stripping section 2, respectively, based on different tower diameters (the diameter of the tower body, for convenience, simply referred to as the tower diameter below). This effectively shortens the liquid phase flow, reduces the tray liquid level gradient, and ensures uniform liquid surface thickness and gas-liquid flow in the mass transfer zone, uniform mass transfer across the entire tray, and reduced pressure drop. The larger the tower diameter and the greater the overflow number, the more pronounced the effect.

[0064] Furthermore, the mass transfer area of ​​the first multi-overflow tower plate 101 and the mass transfer area of ​​the second multi-overflow tower plate 201 are both provided with multiple air holes and multiple high-efficiency fixed valves 3. The high-efficiency fixed valve 3 includes at least three support plates and a fixed valve baffle 301. The fixed valve baffle 301 is provided with an exhaust hole 302.

[0065] One end of the support plate is connected to the mass transfer area, and the other end of the support plate is connected to the fixed valve baffle 301. An air outlet 303 is formed between two adjacent support plates.

[0066] In some embodiments, as Figure 2 and Figure 3 As shown, the fixed valve baffle 301 is arranged parallel to the mass transfer area; alternatively, the fixed valve baffle 301 is arranged to be tilted downward from the end away from the liquid receiving pan to the end closer to the liquid receiving pan, and the angle α between the fixed valve baffle 301 and the horizontal direction is 5-60°. The above tilting can be achieved by adjusting the lengths of the multiple support plates.

[0067] Furthermore, on the first multi-overflow tray 101, if the fixed valve baffle 301 is tilted, the angle α between the fixed valve baffle 301 and the horizontal direction is preferably 10-28°. On the second multi-overflow tray 201, if the fixed valve baffle 301 is tilted, the angle α between the fixed valve baffle 301 and the horizontal direction is preferably 15-30°.

[0068] For example, the high-efficiency fixed valve 3 is provided with three support plates, specifically including: a first support plate 304, a second support plate 305 and a third support plate 306. Figure 2 and Figure 3 As shown, the width of the first support plate 304 and the width of the second support plate 305 are both smaller than the width of the third support plate 306. Preferably, the width of the third support plate 306 is 1-3 times the width of the first support plate 304 and the width of the second support plate 305 respectively.

[0069] The lengths of the first support plate 304, the second support plate 305, and the third support plate 306 are adjusted so that the fixed valve baffle 301 is parallel to the mass transfer area, or the fixed valve baffle 301 is tilted at a certain angle toward the liquid receiving disk area, that is, the fixed valve baffle 301 is tilted downward from the end away from the liquid receiving disk area to the end close to the liquid receiving disk area, and the angle α between the fixed valve baffle 301 and the horizontal direction is 5-60°, and the optimal angle α is 10-28°. The inclination of the fixed valve baffle 301 toward the liquid receiving disk area can align the gas flow direction with the liquid flow direction, prolong the gas-liquid contact time, and improve the separation efficiency.

[0070] In some embodiments, the upper surface of the fixed valve baffle 301 is further provided with an exhaust hole inclined baffle 307 located above the exhaust hole 302. One end of the exhaust hole inclined baffle 307 is connected to the fixed valve baffle 301, and there is a gap between the other end and the exhaust hole 302 for air flow to pass through. The function of the exhaust hole inclined baffle 307 is to make the exhaust direction of the exhaust hole 302 blow laterally.

[0071] More preferably, the inclined exhaust hole baffle 307 is tilted upward from one end away from the liquid receiving pan area to one end close to the liquid receiving pan area, that is, the inclined exhaust hole baffle 307 allows the exhaust gas of the exhaust hole 302 to be blown toward the liquid receiving pan area.

[0072] The air flow rises through the mass transfer zone and is discharged through the air outlet 303 of the high-efficiency solid valve 3 to transfer mass with the liquid phase. At this time, part of the air flow squeezes the solid valve baffle 301, and there will be some vortex areas at the center of the solid valve baffle 301. The gas flow state is poor. The setting of the exhaust hole 302 can release this part of the gas, improve the flow direction of the air flow, and enhance the guiding effect of the high-efficiency solid valve 3.

[0073] The high-efficiency fixed valves 3 are arranged in a triangle or quadrilateral on the mass transfer area, and the opening rate of the tower plate is controlled to be 6-15%. The fixed valve baffles 301 correspond one-to-one with the air holes on the mass transfer area, and the gas velocity through the air outlet 303 is controlled to be 6-20m / s, which can effectively prevent the air outlet 303 from being blocked and reduce the pressure drop of the tower plate.

[0074] In some embodiments, multiple overflow weirs are provided on the plate surface of the first multi-overflow tower tray 101 and the plate surface of the second multi-overflow tower tray 201. The overflow weir is arranged between the mass transfer zone and the downcomer zone. The overflow weir is used to make the liquid in the mass transfer zone overflow evenly to the downcomer zone.

[0075] The height of the overflow weir is 20-80 mm, preferably 40-60 mm. The overflow weir can also prevent the rising gas from flowing into the downcomer area. The number of overflow weirs needs to be determined according to the number of mass transfer zones.

[0076] In summary, by setting a specific overflow weir height, the opening ratio of the tower tray and the angle α of the fixed valve baffle 301, the gas-liquid contact time on the tower tray can be made 0.2-1s, thereby improving the gas-liquid mass transfer efficiency and enhancing the separation effect.

[0077] In some embodiments, downcomers are provided in the downcomer area on the plate surface of the first multi-overflow tower tray 101 and the plate surface of the second multi-overflow tower tray 201. The downcomers are in a downward straight cylindrical structure or a structure that is wide at the top and narrow at the bottom. The width of the downcomer area is 200-2000 mm. The downcomers are preferably of a suspended structure. The distance between the bottom of the downcomer and the liquid receiving tray area of ​​the next tower tray is 20-120 mm (for convenience of expression, the distance between the bottom of the downcomer and the liquid receiving tray area of ​​the next tower tray is referred to as the bottom gap).

[0078] The liquid receiving tray areas on the plate surface of the first multi-overflow tray 101 and the plate surface of the second multi-overflow tray 201 are both flat or grooved, and the width of the liquid receiving tray areas is 200-1600 mm.

[0079] The overflow intensity of the first multi-overflow tray 101 and the second multi-overflow tray 201 is 20-100m 3 / h / m.

[0080] In some embodiments, 20-40 first multi-overflow trays 101 are provided in the extraction stage tower body 1, and the distance between two adjacent layers of the first multi-overflow trays 101 is 400-800 mm.

[0081] The width of the mass transfer zones on the first multi-overflow tray 101 is 100-1800 mm, preferably 500-1400 mm. More preferably, the number of mass transfer zones is consistent with the overflow flow number, which refers to the number of liquid divisions on the tray, and is numerically equal to the number of overflow weirs.

[0082] Furthermore, the ratio of the diameter of the extraction section tower body 1, the width of the downcomer region and the liquid receiving plate region is: (8-30):1:(0.6-1.2).

[0083] 50 to 80 second multi-overflow trays 201 are provided in the stripping section tower body 2, and the distance between two adjacent layers of the second multi-overflow trays 201 is 400 to 800 mm.

[0084] The width of the mass transfer zone on the second multi-overflow tray 201 is 400-2000 mm, preferably 600-1600 mm. More preferably, the number of mass transfer zones is consistent with the overflow flow rate.

[0085] Furthermore, the ratio of the diameter of the stripping section tower body 2, the width of the downcomer area and the liquid receiving plate area is: (8-30):1:(0.6-1.2).

[0086] It should be noted that the existing multi-overflow tower trays include four overflow tower trays, six overflow tower trays and eight overflow tower trays, among which the four overflow tower trays are provided with four mass transfer zones, the six overflow tower trays are provided with six mass transfer zones, and the eight overflow tower trays are provided with eight mass transfer zones. In the present invention, the tower diameters of the extraction section tower body 1 and the stripping section tower body 2 are different. Therefore, multi-overflow tower trays with different overflow numbers (number of mass transfer zones) are respectively arranged in the extraction section tower body 1 and the stripping section tower body 2. When the tower diameter is 4-8m, four overflow tower trays can be used; when the tower diameter is 6-10m, six overflow tower trays can be used; when the tower diameter is 9-15m, eight overflow tower trays can be used.

[0087] like Figure 4-9 As shown, Figure 4 The figure shows a typical schematic diagram of the structural plan layout of a four-overflow tray, where A and E represent the downcomer area, B and D represent the mass transfer area, and C represents the liquid receiving tray area. Figure 5 Shown is a schematic diagram of the arrangement of five layers of four overflow trays in the axial cross section of the tower body.

[0088] Figure 6 The figure shows a typical six-overflow tray structural plan layout diagram, where A and E represent the downcomer area, B, D and F represent the mass transfer area, and C and G represent the liquid receiving tray area. Figure 7 Shown is a schematic diagram of the arrangement of three-layer six overflow trays in the axial cross section of the tower body.

[0089] Figure 8 The figure shows a typical eight-tray structure plan layout diagram, where A, E, and I represent the downcomer area, B, D, F, and H represent the mass transfer area, and C and G represent the receiving tray area. Figure 9 Shown is a schematic diagram of the arrangement of three layers of eight overflow trays in the axial cross section of the tower body.

[0090] Example 2

[0091] Based on Example 1, a rich water feed port 102 is provided at the bottom of the extraction section tower body 1, and a solvent water inlet 103 and a rich gas outlet 104 are provided at the top of the extraction section tower body 1. More preferably, the rich water feed port 102 is provided on the trapezoidal tower body.

[0092] In some embodiments, the rich water is extractively distilled in the extraction section tower body 1, and the rich gas containing acrylonitrile and hydrocyanic acid is discharged through the rich gas outlet 104, while the rich water containing acetonitrile enters the stripping section tower body 2 from the bottom of the extraction section tower body 1. Specifically, the rich water flows down from the downcomer area of ​​the first multi-overflow tower tray 101 and enters the liquid receiving tray area of ​​the second multi-overflow tower tray 201 at the top of the stripping section tower body 2 through the drainage pipe.

[0093] The stripping section tower body 2 is provided with a crude acetonitrile outlet 202 and a lean water outlet 203. Specifically, the crude acetonitrile outlet 202 is preferably arranged on the middle section of the stripping section tower body 2, and the lean water outlet 203 is arranged on the side wall near the bottom of the stripping section tower body 2.

[0094] Preferably, the crude acetonitrile outlet 202 is arranged on the stripping section tower body 2 corresponding to 30-45 second multi-overflow tower trays 201 below the rich water feed inlet 102, and the number of extraction plates is 1-5 second multi-overflow tower trays 201.

[0095] The tower bottom is provided with a lean water return port 404.

[0096] The acrylonitrile separation device further includes a phase separator 4 , an acetonitrile tower 5 and a lean water buffer tank 6 .

[0097] Phase separator 4 is equipped with a rich gas inlet 401, an oil phase outlet 402, and a water phase outlet 403. Rich gas inlet 401 is connected to the rich gas outlet 104 of extraction stage 1, water phase outlet 403 is connected to the rich water feed inlet 102, and oil phase outlet 402 is connected to a subsequent purification device. Phase separator 4 is used to separate the oil phase containing acrylonitrile from the rich gas from the water phase containing hydrocyanic acid. The water phase returns to the extraction stage 1 and enters the stripping stage 2 along with the rich water.

[0098] The inlet of the acetonitrile tower 5 is connected to the crude acetonitrile outlet 202 , and the crude acetonitrile obtained by distillation and purification in the stripping section tower body 2 is discharged into the acetonitrile tower 5 from the crude acetonitrile outlet 202 .

[0099] The inlet of the lean water buffer tank 6 is connected to the lean water outlet 203. The lean water from the bottom of the stripping section tower body 2 is discharged from the lean water outlet 203 and enters the lean water buffer tank 6 for storage. The outlet of the lean water buffer tank 6 is connected to the lean water return port 404. A portion of the lean water in the lean water buffer tank 6 is introduced into the tower kettle after pH adjustment to form stripping steam, and the other portion of the lean water can be used for system heat recovery and sent to the subsequent system.

[0100] In some embodiments, the acrylonitrile separation device is further provided with a sodium carbonate supply pipeline 9. Specifically, the stripping section tower body 2, the phase separator 4 and the lean water buffer tank 6 are all provided with a sodium carbonate feed port 7. The sodium carbonate supply pipeline is respectively connected to the sodium carbonate feed port 7 of the stripping section tower body 2, the phase separator 4 and the lean water buffer tank 6. The sodium carbonate supply pipeline inputs sodium carbonate into the stripping section tower body 2, the phase separator 4 and the lean water buffer tank 6 respectively to adjust the pH of the liquid phase.

[0101] Furthermore, the sodium carbonate feed port 7 on the stripping section tower body 2 is preferably arranged at the stripping section tower body 2 corresponding to the 2nd to 10th second multi-overflow trays from bottom to top in the stripping section tower body 2.

[0102] If the pH in the recovery tower system is high, acrylonitrile and hydrocyanic acid are likely to polymerize within the tower, clogging the tower trays. If the pH is low, some of the already formed polymers of acetone cyanohydrin, acrolein cyanohydrin, hydrocyanic acid, and acrylonitrile, as well as related impurities, are likely to decompose, breaking down into small molecular impurities that enter the subsequent distillation system, increasing the difficulty of impurity removal in the subsequent system and easily leading to excessive levels of oxazole and hydrocyanic acid in the product. Sodium carbonate is added to phase separator 4 to control the pH of the aqueous phase returning to the extraction stage 1 within phase separator 4 to 6-7.5. This allows the impurities to form high-boiling-point substances under weak acid or alkaline conditions and be discharged from the bottom of the recovery tower.

[0103] Sodium carbonate is added to the stripping section tower body 2 to adjust the pH of the lean water to 6-8, and sodium carbonate is added to the lean water buffer tank 6 to control the pH of the lean water returned to the tower kettle to 6-8. This can prevent excessive acidity or alkalinity in the recovery tower, prevent the polymerization or hydrolysis of organic matter such as acrylonitrile, reduce the risk of tower plate clogging, and improve separation efficiency.

[0104] In some embodiments, a plurality of liquid collectors 8 for collecting lean water are further provided at the bottom of the stripping section tower body 2. The inlet of the liquid collector 8 is connected to the downcomer of the first second multi-overflow tower tray 201 at the bottom of the stripping section tower body 2. The number of the liquid collectors 8 is half the number of the overflow weirs of the second multi-overflow tower tray 201.

[0105] Furthermore, the outlet of the liquid collector 8 is connected to the lean water outlet 203 via a liquid collecting pipe, so that the lean water accumulated in the liquid collector 8 is sent to the lean water buffer tank 6 .

[0106] In some embodiments, the tower bottom is provided with a reboiler, which is used to heat the lean water to generate rising stripping steam.

[0107] The device is also provided with a rich water flow meter for detecting the flow of rich water entering the recovery tower, and a steam flow meter for detecting the flow of stripping steam.

[0108] A sensitive plate is installed in the tower body. The temperature of the sensitive plate, rich water flow and stripping steam flow form a cascade adjustment to control the temperature of the sensitive plate and ensure the rapid stability of the recovery tower.

[0109] Example 3

[0110] The present invention also provides an acrylonitrile separation process, which uses the acrylonitrile separation device provided in the above embodiments 1 and 2, such as Figure 1 As shown, the steps are as follows:

[0111] Rich water (acidic first material) containing impurities such as acrylonitrile, acetonitrile, hydrocyanic acid, oxazole, acrolein, acetone cyanohydrin, and acrolein cyanohydrin enters the extraction section tower body 1 from the rich water feed port 102 on the trapezoidal tower body. Solvent water (a second material) enters the extraction section tower body 1 from the solvent water inlet 103. An acrylonitrile-water azeotrope is formed in the extraction section tower body 1. Extractive distillation is performed to separate acrylonitrile, hydrocyanic acid, and acetonitrile, while removing impurities such as oxazole from the rich water. The rich water containing acetonitrile and unremoved impurities such as oxazole flows downward into the stripping section tower body 2. Rich gas (a third material) containing acrylonitrile, hydrocyanic acid, and water is discharged from the rich gas outlet 104, cooled, and then enters the phase separator 4 for oil-water separation. The aqueous phase returns to the extraction section tower body 1 from the rich water feed port 102, and the oil phase (an eighth material, containing acrylonitrile and hydrocyanic acid) is sent to the subsequent device for further distillation and purification from the oil phase outlet 402.

[0112] Rich water containing acetonitrile and impurities such as unremoved oxazole flows from extraction section 1 into stripping section 2, where it undergoes distillation and purification. The lean water in the bottom of the tower is heated in a reboiler until vaporized, providing stripping steam for stripping section 2. Crude acetonitrile (the fourth material) is withdrawn from the crude acetonitrile outlet 202 in the middle sideline of stripping section 2. A liquid phase containing a small amount of organic matter (the fifth material) is obtained from the bottom of the tower and discharged to the wastewater concentration unit.

[0113] Lean water (the sixth material) is extracted from the liquid collector 8 and enters the lean water buffer tank 6. Part of the lean water returns to the tower kettle (the seventh material) through the lean water return port 404, and the other part of the lean water can be used for system heat recovery and sent to the subsequent system (the ninth material).

[0114] In some embodiments, the top temperature of the tower body is controlled to be 65-75° C., and the top pressure of the tower body is controlled to be 0.005-0.008 MPaG.

[0115] The temperature of the tower bottom is controlled at 110-118°C and the pressure of the tower bottom is controlled at 0.05-0.07MPaG.

[0116] Control the pressure drop of the recovery tower to 40-65kPa.

[0117] The empty tower gas velocity is controlled at 0.5-2m / s. The empty tower gas velocity here refers to the gas phase flow rate calculated when there are no internal components in the tower when the steam generated by the tower kettle is present.

[0118] The mass ratio of rich water to solvent water is controlled to be 1:(5.5-9), preferably 1:(6.5-7.5).

[0119] The air velocity passing through the air outlet 303 is controlled to be 6-20 m / s.

[0120] Under the above control conditions, in the oil phase in the phase separator 4, the oxazole content is 0-20 ppm, the acetone content is 0-100 ppm, the acetonitrile content is 0-100 ppm, and the acrolein content is 0-40 ppm.

[0121] The crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 has an acrylonitrile content of 0 to 1300 ppm, a hydrocyanic acid content of 0 to 1000 ppm, and a polymer content of 0 to 200 ppm.

[0122] The effects of the high-purity acrylonitrile production system and production method provided in Examples 1-3 are described below with reference to specific examples.

[0123] Example 4

[0124] like Figure 1 As shown, the recovery tower includes an extraction section tower body 1 and a stripping section tower body 2.

[0125] The diameter of the extraction section tower body 1 is 6800mm. 29 first multi-overflow trays 101 are set in the extraction section tower body 1. The spacing between two adjacent first multi-overflow trays 101 is 500mm. The first multi-overflow tray 101 adopts four overflow trays. Figure 4 .

[0126] Specifically: the width of the downcomer zone A is 680 mm, the width of the mass transfer zones B and D is 840 mm, the liquid receiving plate zone C is grooved and has a width of 685 mm, and the width of the downcomer zone E is 705 mm.

[0127] Set the overflow intensity of the tray to 43.2m 3 / m / h. The downcomer is a suspended structure with a bottom clearance of 50mm. Multiple high-efficiency fixed valves 3 are installed in mass transfer zones B and D. The lengths of the three support plates are adjusted so that the fixed valve baffle 301 is tilted downward from the end away from the liquid receiving pan to the end closer to the liquid receiving pan. The angle α between the fixed valve baffle 301 and the horizontal is 13°-15°. Multiple high-efficiency fixed valves 3 are arranged in a triangular pattern in the mass transfer zone.

[0128] The opening rate of the tower tray is controlled to be 10.2%, and the gas velocity through the gas outlet 303 is controlled to be 10.2-13.9 m / s.

[0129] The height of the overflow weir is set to 50 mm, at which point the gas-liquid contact time is 0.2-1 s.

[0130] The diameter of the stripping section tower body 2 is 9100 mm. 62 second multi-overflow trays 201 are arranged in the stripping section tower body 2. The spacing between two adjacent second multi-overflow trays 201 is 600 mm. The second multi-overflow tray 201 adopts six overflow trays. Figure 6 .

[0131] Specifically: the width of the downcomer area A is 520 mm, the width of the mass transfer areas B, D, and F is 1055 mm, the liquid receiving plate area C is grooved and has a width of 360 mm, the width of the downcomer E is 370 mm, and the liquid receiving plate area G is grooved and has a width of 365 mm.

[0132] Set the overflow intensity of the tray to 62.5m 3 / m / h. The downcomer is a suspended structure with a 50mm bottom clearance. Multiple high-efficiency fixed valves 3 are installed in mass transfer zones B, D, and F. The lengths of the three support plates are adjusted so that the fixed valve baffle 301 is tilted downward from the end facing away from the liquid receiving pan to the end facing closer to the liquid receiving pan, with an included angle α of 16-19°. Multiple high-efficiency fixed valves 3 are arranged in a triangular pattern in the mass transfer zone.

[0133] The opening rate of the tower tray is controlled to be 8.8%, and the gas velocity through the gas outlet 303 is controlled to be 11.3-16.1 m / s.

[0134] The height of the overflow weir is set to 50 mm, at which point the gas-liquid contact time meets the design requirements.

[0135] Rich water (the first material) containing impurities such as acrylonitrile, acetonitrile, hydrocyanic acid, oxazole, and acrolein enters the extraction section tower body 1 from the rich water feed inlet 102 (the 62nd second overflow tray 201 from bottom to top in the stripping section tower body 2) provided on the trapezoidal tower body, and solvent water (the second material) enters the extraction section tower body 1 from the solvent water inlet 103 (the 91st tray from bottom to top in the recovery tower, i.e., the 29th first overflow tray 101 from bottom to top in the extraction section tower body 1). In the tower body 1, an azeotrope of acrylonitrile and water is formed, and extractive distillation is performed to separate acrylonitrile, hydrocyanic acid and acetonitrile, and at the same time, oxazole in the rich water is removed. The liquid phase containing acetonitrile flows downward into the stripping tower body 2, and the rich gas (the third material) containing acrylonitrile, hydrocyanic acid and water is discharged from the rich gas outlet 104 at the top of the tower. After cooling, it enters the phase separator 4 for oil-water separation. The aqueous phase returns to the extraction tower body 1, and the oil phase (the eighth material) is sent to the subsequent device for further distillation and purification.

[0136] The liquid phase containing acetonitrile is distilled and purified in the stripping section tower body 2. The lean water in the tower bottom is heated by a reboiler to generate steam that moves upward. The steam is extracted at the 31st or 32nd second multi-overflow tower tray 201 to obtain crude acetonitrile (the fourth material) and sent to the acetonitrile tower 5.

[0137] Lean water (the sixth material) is drawn from the liquid collector 8 of the stripping section tower 2 and enters the lean water buffer tank 6. A portion of the lean water returns to the tower bottom (the seventh material) through the lean water return port 404. The remaining lean water (the ninth material) is used for system heat recovery and then sent to subsequent equipment. The liquid phase (the fifth material) containing a small amount of organic matter obtained in the tower bottom is sent to the subsequent wastewater concentration unit.

[0138] Sodium carbonate is added to the sixth second multi-overflow tray 201 from bottom to top in the stripping section tower body 2 to control the pH of the lean water to 6.5-7.5; sodium carbonate is added to the phase separator 4 to control the pH of the aqueous phase in the phase separator 4 to 6.5-7; sodium carbonate is added to the lean water buffer tank 6 to control the pH of the lean water returning to the tower bottom to 6.8-7.3.

[0139] The temperature of the 48th tower plate is controlled to be 86-88℃ through cascade regulation of the sensitive plate temperature, rich water flow rate and tower kettle reboiler steam flow rate, and the mass ratio of rich water to solvent water is controlled to be 1:8.5.

[0140] The top temperature of the tower body is controlled to be 71.2°C and the top pressure is controlled to be 0.007MPaG.

[0141] The temperature of the tower bottom is controlled to be 114.8℃ and the pressure of the tower bottom is controlled to be 0.063MPaG.

[0142] The pressure drop of the entire recovery tower is controlled to be 56kpa.

[0143] The heat load of the reboiler is controlled to be 188927kw.

[0144] Under the above conditions, the content of oxazole in the oil phase of the phase separator 4 was 6 ppm, the content of acetonitrile was 22 ppm, the content of acetone was 7 ppm, and the content of acrolein was 6 ppm.

[0145] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 is 624 ppm, the content of hydrocyanic acid is 555 ppm, and the content of polymer is 112 ppm.

[0146] Example 5

[0147] The difference from Example 4 is that the lengths of the support plates of the high-efficiency solid valves 3 in the extraction section tower body 1 and the stripping section tower body 2 are adjusted respectively so that the angle α in the extraction section tower body 1 is 22°-25°, and the angle α in the stripping section tower body 2 is 26°-29°.

[0148] The rest is the same as example 4, under this condition, the content of oxazole in the oil phase of phase separator 4 is 8 ppm, the content of acetonitrile is 28 ppm, the content of acetone is 9 ppm, and the content of propylene aldehyde is 11 ppm.

[0149] The content of acrylonitrile in the crude acetonitrile material (the fourth material) extracted from the side line of the stripping section tower body 2 is 636 ppm, the content of hydrocyanic acid is 573 ppm, and the content of polymer is 117 ppm.

[0150] Example 6

[0151] The difference from example 4 is that the length of the support plate of high-efficiency solid valve 3 in extraction section tower body 1 and stripping section tower body 2 is adjusted respectively, so that the included angle α in extraction section tower body 1 is 5°-8°, and the included angle α in stripping section tower body 2 is 7°-10°.

[0152] The rest is the same as example 4, under this condition, the content of oxazole in the oil phase of phase separator 4 is 14 ppm, the content of acetonitrile is 38 ppm, the content of acetone is 16 ppm, and the content of propylene aldehyde is 12 ppm.

[0153] The content of acrylonitrile in the crude acetonitrile material (the fourth material) extracted from the side line of the stripping section tower body 2 is 741 ppm, the content of hydrocyanic acid is 667 ppm, and the content of polymer is 121 ppm.

[0154] Example 7

[0155] The difference from example 4 is that the length of the support plate of high-efficiency solid valve 3 in extraction section tower body 1 and stripping section tower body 2 is adjusted respectively, so that the included angle α in extraction section tower body 1 is 51°-54°, and the included angle α in stripping section tower body 2 is 48°-52°.

[0156] The rest is the same as example 4, under this condition, the content of oxazole in the oil phase of phase separator 4 is 26 ppm, the content of acetonitrile is 81 ppm, the content of acetone is 19 ppm, and the content of propylene aldehyde is 13 ppm.

[0157] The content of acrylonitrile in the crude acetonitrile material (the fourth material) extracted from the side line of the stripping section tower body 2 is 826 ppm, the content of hydrocyanic acid is 717 ppm, and the content of polymer is 128 ppm.

[0158] Example 8

[0159] The difference from example 4 is that the mass ratio of water-rich to solvent water is controlled to be 1:7.5, the temperature of the tower kettle is controlled to be 114.7℃, the pressure of the tower kettle is controlled to be 0.061MPaG, the pressure drop of the whole tower of the recovery tower is controlled to be 54kpa, and the heat load of the reboiler is controlled to be 182314kw.

[0160] The rest were the same as in Example 4. Under these conditions, the content of oxazole in the oil phase of the phase separator 4 was 8 ppm, the content of acetonitrile was 31 ppm, the content of acetone was 10 ppm, and the content of acrolein was 11 ppm.

[0161] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 was 668 ppm, the content of hydrocyanic acid was 627 pm, and the content of polymer was 111 ppm.

[0162] Example 9

[0163] The difference from Example 4 is that the mass ratio of rich water to solvent water is controlled to 1:6.5, the temperature of the tower bottom is controlled to 114.7°C, the pressure of the tower bottom is 0.060 MPaG, the pressure drop of the entire recovery tower is 53 kPa, and the heat load of the reboiler is 175892 kW.

[0164] The rest were the same as in Example 4. Under these conditions, the content of oxazole in the oil phase of the phase separator 4 was 13 ppm, the content of acetonitrile was 33 ppm, the content of acetone was 14 ppm, and the content of acrolein was 14 ppm.

[0165] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 is 852ppm, the content of hydrocyanic acid is 788pm, and the content of polymer is 147ppm.

[0166] Example 10

[0167] The difference from Example 4 is that the mass ratio of rich water to solvent water is controlled to 1:5.5, the temperature of the tower bottom is controlled to 114.5°C, the pressure of the tower bottom is 0.059 MPaG, the pressure drop of the entire recovery tower is 52 kPa, and the heat load of the reboiler is 170615 kW.

[0168] The rest were the same as in Example 4. Under these conditions, the content of oxazole in the oil phase of the phase separator 4 was 18 ppm, the content of acetonitrile was 53 ppm, the content of acetone was 25 ppm, and the content of acrolein was 18 ppm.

[0169] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 was 1021 ppm, the content of hydrocyanic acid was 977 pm, and the content of polymer was 168 ppm.

[0170] Comparative Example 1

[0171] The difference from Example 4 is that the high-efficiency solid valve 3 in the extraction section tower body 1 and the stripping section tower body 2 are replaced with a traditional float valve, the tower top temperature is controlled to 71.2°C, the tower top pressure is 0.007 MPaG, the tower bottom temperature is 115.0°C, the tower bottom pressure is 0.069 MPaG, the pressure drop of the recovery tower is 62 kPa, and the heat load of the reboiler is 191430 kW.

[0172] The rest were the same as in Example 4. Under these conditions, the content of oxazole in the oil phase of the phase separator 4 was 43 ppm, the content of acetonitrile was 61 ppm, the content of acetone was 17 ppm, and the content of acrolein was 11 ppm.

[0173] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 was 1328 ppm, the content of hydrocyanic acid was 1076 pm, and the content of polymer was 228 ppm.

[0174] Comparative Example 2

[0175] The difference from Example 4 is that the second multi-overflow tray 201 in the stripping section tower body 2 adopts four overflow trays, and the structure is shown in FIG. Figure 4 Specifically, the width of downcomer zone A is 910 mm, the width of mass transfer zones B and D is 1120 mm, the receiving tray zone C is grooved and 920 mm wide, and the width of downcomer E is 940 mm. The overflow rate of the tray is set at 88.9 m³ / m³ / h, the downcomers are suspended, and the bottom clearance of the downcomers is 50 mm.

[0176] The temperature of the top of the tower is controlled to be 71.2℃, the pressure of the top of the tower is 0.007MPaG, the temperature of the bottom of the tower is 115.3℃, the pressure of the bottom of the tower is 0.074MPaG, the pressure drop of the entire recovery tower is 67kpa, and the heat load of the reboiler is 193706kw.

[0177] The rest were the same as in Example 4. Under these conditions, the content of oxazole in the oil phase of the phase separator 4 was 44 ppm, the content of acetonitrile was 87 ppm, the content of acetone was 21 ppm, and the content of acrolein was 13 ppm.

[0178] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 was 1203 ppm, the content of hydrocyanic acid was 931 pm, and the content of polymer was 315 ppm.

[0179] Comparative Example 3

[0180] The difference from Example 4 is that the lengths of the support plates of the high-efficiency solid valve 3 in the extraction section tower body 1 and the stripping section tower body 2 are respectively adjusted so that the angle α in the extraction section tower body 1 and the angle α in the stripping section tower body 2 are both 0°, that is, the solid valve baffle 301 is parallel to the mass transfer zone.

[0181] The pressure drop of the entire recovery tower is controlled to be 62kpa.

[0182] The rest were the same as in Example 4. Under these conditions, the content of oxazole in the oil phase of the phase separator 4 was 29 ppm, the content of acetonitrile was 76 ppm, the content of acetone was 19 ppm, and the content of acrolein was 14 ppm.

[0183] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 was 871 ppm, the content of hydrocyanic acid was 709 pm, and the content of polymer was 185 ppm.

[0184] Example 11

[0185] like Figure 1 As shown, the recovery tower includes an extraction section tower body 1 and a stripping section tower body 2.

[0186] The diameter of the extraction section tower body 1 is 8200mm. 30 first multi-overflow trays 101 are set in the extraction section tower body 1. The spacing between two adjacent first multi-overflow trays 101 is 500mm. The first multi-overflow tray 101 adopts six overflow trays. Figure 6 .

[0187] Specifically: the width of the downcomer area A is 500 mm, the width of the mass transfer areas B, D and F is 895 mm, the liquid receiving plate area C is grooved and has a width of 355 mm, the width of the downcomer area E is 360 mm, and the liquid receiving plate area G is grooved and has a width of 390 mm.

[0188] Set the overflow intensity of the tray to 41.4m 3 / m / h. The downcomer is a suspended structure with a bottom clearance of 50mm. Multiple high-efficiency fixed valves 3 are installed in mass transfer zones B, D, and F. The lengths of the three support plates are adjusted so that the fixed valve baffle 301 is tilted downward from the end away from the liquid receiving pan to the end closer to the liquid receiving pan. The angle α between the fixed valve baffle 301 and the horizontal is 14°-16°. Multiple high-efficiency fixed valves 3 are arranged in a triangular pattern in the mass transfer zone.

[0189] The opening rate of the tower plate is controlled to be 10.8%, and the gas velocity through the gas outlet 303 is controlled to be 11.3-13.5 m / s.

[0190] The height of the overflow weir is set to 50 mm, at which point the gas-liquid contact time meets the design requirements.

[0191] The diameter of the stripping section tower body 2 is 11000mm. 65 second overflow trays 201 are arranged in the stripping section tower body 2. The spacing between two adjacent second overflow trays 201 is 600mm. The second overflow tray 201 adopts eight overflow trays. Figure 8 .

[0192] Specifically: the width of the downcomer zone A is 510 mm, the width of the mass transfer zones B, D, F and H is 890 mm, the liquid receiving plate zones C and G are grooved and have a width of 420 mm, the width of the downcomer E is 395 mm, and the width of the downcomer I is 380 mm.

[0193] Set the overflow intensity of the tray to 90.3m 3 / m / h. The downcomer is a suspended structure with a 50mm bottom clearance. Multiple high-efficiency fixed valves 3 are installed in mass transfer zones B, D, F, and H. The lengths of the three support plates are adjusted so that the fixed valve baffle 301 is tilted downward from the end facing away from the liquid receiving pan to the end facing closer to the liquid receiving pan, with an angle α of 17°-20°. Multiple high-efficiency fixed valves 3 are arranged in a triangular pattern in the mass transfer zone.

[0194] The opening rate of the tower tray is controlled to be 9.0%, and the gas velocity through the gas outlet 303 is controlled to be 12.2-16.4 m / s.

[0195] The height of the overflow weir is set to 50 mm, at which point the gas-liquid contact time meets the design requirements.

[0196] Rich water (the first material) containing impurities such as acrylonitrile, acetonitrile, hydrocyanic acid, oxazole, and acrolein enters the extraction section tower body 1 from the rich water feed inlet 102 (the 65th second overflow tray 201 from bottom to top in the stripping section tower body 2) provided on the trapezoidal tower body, and solvent water (the second material) enters the extraction section tower body 1 from the solvent water inlet 103 (the 95th tray from bottom to top in the recovery tower, i.e., the 30th first overflow tray 101 from bottom to top in the extraction section tower body 1). In the tower body 1, an azeotrope of acrylonitrile and water is formed, and extractive distillation is performed to separate acrylonitrile, hydrocyanic acid and acetonitrile, and at the same time, oxazole in the rich water is removed. The liquid phase containing acetonitrile flows downward into the stripping tower body 2, and the rich gas (the third material) containing acrylonitrile, hydrocyanic acid and water is discharged from the rich gas outlet 104 at the top of the tower. After cooling, it enters the phase separator 4 for oil-water separation. The aqueous phase returns to the extraction tower body 1, and the oil phase (the eighth material) is sent to the subsequent device for further distillation and purification.

[0197] The liquid phase containing acetonitrile is distilled and purified in the stripping section tower body 2. The lean water in the tower bottom is heated by a reboiler to generate steam that moves upward. The steam is extracted at the 32nd or 33rd second multi-overflow tray 201 to obtain crude acetonitrile (the fourth material) and sent to the acetonitrile tower 5.

[0198] Lean water (the sixth material) is drawn from the liquid collector 8 of the stripping section tower 2 and enters the lean water buffer tank 6. A portion of the lean water returns to the tower bottom (the seventh material) through the lean water return port 404. The remaining lean water (the ninth material) is used for system heat recovery and then sent to subsequent equipment. The liquid phase (the fifth material) containing a small amount of organic matter obtained in the tower bottom is sent to the subsequent wastewater concentration unit.

[0199] Sodium carbonate is added to the sixth second multi-overflow tray 201 from bottom to top in the stripping section tower body 2 to control the pH of the lean water to 6.5-7.5; sodium carbonate is added to the phase separator 4 to control the pH of the aqueous phase in the phase separator 4 to 6.5-7; sodium carbonate is added to the lean water buffer tank 6 to control the pH of the lean water returning to the tower bottom to 6.8-7.3.

[0200] The temperature of the 48th tower plate is controlled at 86-88°C by cascade adjustment of the sensitive plate temperature, rich water flow rate and tower kettle reboiler steam flow rate, and the mass ratio of rich water to solvent water is controlled at 1:8.5.

[0201] The top temperature of the tower body is controlled to be 71.2°C and the top pressure is controlled to be 0.007MPaG.

[0202] The temperature of the tower bottom is controlled to be 114.8℃ and the pressure of the tower bottom is controlled to be 0.069MPaG.

[0203] The pressure drop of the entire recovery tower is controlled to be 62kpa.

[0204] The heat load of the reboiler is controlled to be 288613kw.

[0205] Under the above conditions, the content of oxazole in the oil phase of the phase separator 4 was 7 ppm, the content of acetonitrile was 23 ppm, the content of acetone was 8 ppm, and the content of acrolein was 7 ppm.

[0206] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 is 627 ppm, the content of hydrocyanic acid is 561 ppm, and the content of polymer is 118 ppm.

[0207] Example 12

[0208] The difference from Example 11 is that the lengths of the support plates of the high-efficiency solid valves 3 in the extraction section tower body 1 and the stripping section tower body 2 are adjusted respectively so that the angle α in the extraction section tower body 1 is 21°-24°, and the angle α in the stripping section tower body 2 is 25°-28°.

[0209] The rest were the same as in Example 11. Under the above conditions, the content of oxazole in the oil phase of the phase separator 4 was 10 ppm, the content of acetonitrile was 26 ppm, the content of acetone was 10 ppm, and the content of acrolein was 12 ppm.

[0210] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 is 643 ppm, the content of hydrocyanic acid is 592 ppm, and the content of polymer is 121 ppm.

[0211] Example 13

[0212] The difference from Example 11 is that the lengths of the support plates of the high-efficiency solid valves 3 in the extraction section tower body 1 and the stripping section tower body 2 are adjusted respectively so that the angle α in the extraction section tower body 1 is 7°-9°, and the angle α in the stripping section tower body 2 is 8°-10°.

[0213] The rest were the same as in Example 11. Under the above conditions, the content of oxazole in the oil phase of the phase separator 4 was 15 ppm, the content of acetonitrile was 29 ppm, the content of acetone was 15 ppm, and the content of acrolein was 14 ppm.

[0214] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 is 757 ppm, the content of hydrocyanic acid is 671 ppm, and the content of polymer is 132 ppm.

[0215] Example 14

[0216] The difference from Example 11 is that the lengths of the support plates of the high-efficiency solid valves 3 in the extraction section tower body 1 and the stripping section tower body 2 are adjusted respectively so that the angle α in the extraction section tower body 1 is 45°-48°, and the angle α in the stripping section tower body 2 is 50°-54°.

[0217] The rest were the same as in Example 11. Under the above conditions, the content of oxazole in the oil phase of the phase separator 4 was 17 ppm, the content of acetonitrile was 31 ppm, the content of acetone was 17 ppm, and the content of acrolein was 15 ppm.

[0218] The crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 has an acrylonitrile content of 761 ppm, a hydrocyanic acid content of 691 ppm, and a polymer content of 135 ppm.

[0219] Example 15

[0220] The difference from Example 11 is that the mass ratio of rich water to solvent water is controlled to be 1:7.5, the top temperature of the tower body is controlled to be 71.2°C, the temperature of the tower bottom is 114.7°C, the pressure of the tower bottom is 0.068 MPaG, the pressure drop of the entire recovery tower is 61 kPa, and the heat load of the reboiler is 274182 kW.

[0221] The rest were the same as in Example 11. Under these conditions, the content of oxazole in the oil phase of the phase separator 4 was 9 ppm, the content of acetonitrile was 29 ppm, the content of acetone was 10 ppm, and the content of acrolein was 9 ppm.

[0222] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 was 651 ppm, the content of hydrocyanic acid was 611 pm, and the content of polymer was 109 ppm.

[0223] Example 16

[0224] The difference from Example 11 is that the mass ratio of rich water to solvent water is controlled to be 1:6.5, the top temperature of the tower body is controlled to be 71.2°C, the temperature of the tower bottom is controlled to be 114.6°C, and the heat load of the reboiler is controlled to be 265956kw.

[0225] The rest were the same as in Example 11. Under these conditions, the content of oxazole in the oil phase of the phase separator 4 was 16 ppm, the content of acetonitrile was 350 ppm, the content of acetone was 15 ppm, and the content of acrolein was 14 ppm.

[0226] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 was 862 ppm, the content of hydrocyanic acid was 802 pm, and the content of polymer was 151 ppm.

[0227] Example 17

[0228] The difference from Example 11 is that the mass ratio of rich water to solvent water is controlled to 1:5.5, the top temperature of the tower body is controlled to 71.2°C, the pressure drop of the recovery tower is 61kPa, and the heat load of the reboiler is 257977kw.

[0229] The rest were the same as in Example 11. Under these conditions, the content of oxazole in the oil phase of the phase separator 4 was 20 ppm, the content of acetonitrile was 55 ppm, the content of acetone was 45 ppm, and the content of acrolein was 21 ppm.

[0230] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 was 1188 ppm, the content of hydrocyanic acid was 965 pm, and the content of polymer was 197 ppm.

[0231] Example 18

[0232] The difference from Example 11 is that the height of the overflow weir of the first multi-overflow tower tray 101 and the overflow weir of the second multi-overflow tower tray 201 are both set to 60 mm, the pressure of the tower bottom is controlled to 0.065 MPaG, and the heat load of the reboiler is 289901 kW.

[0233] The rest were the same as in Example 11. Under these conditions, the content of oxazole in the oil phase of the phase separator 4 was 6 ppm, the content of acetonitrile was 21 ppm, the content of acetone was 9 ppm, and the content of acrolein was 7 ppm.

[0234] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 was 597 ppm, the content of hydrocyanic acid was 523 pm, and the content of polymer was 112 ppm.

[0235] Example 19

[0236] The difference from Example 11 is that the height of the overflow weir of the first multi-overflow tower tray 101 and the overflow weir of the second multi-overflow tower tray 201 are both set to 30 mm, the top temperature of the tower body is controlled to 71.2°C, the temperature of the tower bottom is 114.6°C, the pressure of the tower bottom is 0.063 MPaG, the pressure drop of the entire recovery tower is 56 kPa, and the heat load of the reboiler is 282840 kW.

[0237] The rest were the same as in Example 11. Under these conditions, the content of oxazole in the oil phase of the phase separator 4 was 19 ppm, the content of acetonitrile was 47 ppm, the content of acetone was 39 ppm, and the content of acrolein was 17 ppm.

[0238] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 was 812 ppm, the content of hydrocyanic acid was 719 pm, and the content of polymer was 146 ppm.

[0239] Example 20

[0240] The difference from Example 11 is that the height of the overflow weir of the first multi-overflow tower tray 101 and the overflow weir of the second multi-overflow tower tray 201 are both set to 80 mm, the temperature of the tower kettle is controlled to 115.2°C, the pressure of the tower kettle is 0.071 MPaG, the pressure drop of the entire recovery tower is 64 kPa, and the heat load of the reboiler is 299478 kW.

[0241] The rest were the same as in Example 11. Under these conditions, the content of oxazole in the oil phase of the phase separator 4 was 18 ppm, the content of acetonitrile was 37 ppm, the content of acetone was 11 ppm, and the content of acrolein was 10 ppm.

[0242] The content of acrylonitrile in the crude acetonitrile material (fourth material) extracted from the side line of the stripping section tower body 2 was 592 ppm, the content of hydrocyanic acid was 573 pm, and the content of polymer was 125 ppm.

[0243] The above are only preferred embodiments of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An acrylonitrile separation device, characterized in that: include: A recovery tower, comprising a tower body and a tower kettle connected in an upper and lower manner, wherein the tower body is divided from bottom to top into a stripping section tower body and an extraction section tower body of different diameters; The diameter of the extraction section tower body is smaller than the diameter of the stripping section tower body; The extraction section tower body is provided with a plurality of first multi-overflow trays, and the plurality of first multi-overflow trays are evenly spaced in the vertical direction; A plurality of second multi-overflow trays are provided in the stripping section tower body, and the plurality of second multi-overflow trays are evenly spaced in the vertical direction; The first multi-overflow tray and the second multi-overflow tray are both provided with a plurality of liquid receiving tray areas, a plurality of mass transfer areas and a plurality of downcomer areas that are independent and parallel to each other, and the liquid receiving tray area is provided on one side of any mass transfer area and the downcomer area is provided on the other side; The number of mass transfer zones of the first multi-flood tray is smaller than the number of mass transfer zones of the second multi-flood tray; The mass transfer area is provided with a plurality of air holes and a plurality of high-efficiency fixed valves, the high-efficiency fixed valves include at least three support plates and a fixed valve baffle, and the fixed valve baffle is provided with an exhaust hole; One end of the support plate is connected to the mass transfer area, and the other end of the support plate is connected to the fixed valve baffle, and an air outlet is formed between two adjacent support plates.

2. The acrylonitrile separation device according to claim 1, characterized in that The fixed valve baffle is arranged in parallel with the mass transfer zone; or, The fixed valve baffle is tilted downward from one end away from the liquid receiving disc area to one end close to the liquid receiving disc area, and an angle α between the fixed valve baffle and the horizontal direction is 5-60°.

3. The acrylonitrile separation device according to claim 2, characterized in that A plurality of overflow weirs are provided on the deck of the first multi-overflow tray and the deck of the second multi-overflow tray, and the overflow weirs are arranged between the mass transfer zone and the downcomer zone, and are used to uniformly overflow the liquid in the mass transfer zone into the downcomer zone; The height of the overflow weir is 20-80 mm.

4. The acrylonitrile separation device according to claim 1, characterized in that The ratio of the diameter of the tower body, the width of the downcomer area and the width of the liquid receiving plate area is: (8-30):1:(0.6-1.2); The diameter ratio of the stripping section tower body to the extraction section tower body is 1.1-2; The width of the mass transfer zone on the first multi-flow tray is 100-1800 mm; The width of the mass transfer zone on the second multi-overflow tray is 400-2000 mm.

5. The acrylonitrile separation device according to claim 2, characterized in that: The porosity of the mass transfer zone is 6-15%; The high-efficiency solid valves are arranged in a triangle or a quadrilateral on the mass transfer area.

6. The acrylonitrile separation device according to claim 1, characterized in that The bottom of the extraction section tower body is provided with a rich water feed inlet, and the top of the extraction section tower body is provided with a rich gas outlet; The stripping section tower body is provided with a crude acetonitrile outlet; The acrylonitrile separation device is further provided with a phase separator and an acetonitrile tower. The phase separator is provided with a rich material inlet, an oil phase outlet and a water phase outlet, the rich material inlet and the water phase outlet are respectively connected to the rich gas outlet and the rich water feed inlet, the oil phase outlet is connected to a subsequent device, and the phase separator is used to separate the oil phase containing acrylonitrile and the water phase containing hydrocyanic acid in the rich gas; The inlet of the acetonitrile column is connected to the crude acetonitrile outlet.

7. The acrylonitrile separation device according to claim 6, characterized in that The stripping section tower body is further provided with a lean water outlet and a liquid collector for collecting lean water, the liquid collector is arranged at the bottom of the stripping section tower body, the lean water outlet is arranged on the side wall close to the bottom of the stripping section tower body, and the lean water outlet is connected to the outlet of the liquid collector; The tower kettle is provided with a lean water return port; The acrylonitrile separation device is further provided with a lean water buffer tank, the inlet and outlet of the lean water buffer tank are respectively connected to the lean water outlet and the lean water return port.

8. The acrylonitrile separation device according to claim 7, characterized in that The stripping section tower body, the phase separator and the lean water buffer tank are all provided with a sodium carbonate feed port; The acrylonitrile separation device is further provided with a sodium carbonate supply pipeline, which is respectively connected to the sodium carbonate feed ports of the stripping section tower body, the phase separator and the lean water buffer tank, and is used to supply sodium carbonate for adjusting the pH to the stripping section tower body, the phase separator and the lean water buffer tank respectively.

9. An acrylonitrile separation process using the acrylonitrile separation device according to any one of claims 1 to 8, characterized in that: The steps include: Rich water containing impurities such as acrylonitrile, acetonitrile, hydrocyanic acid, and oxazole enters the extraction section tower body, mixes with solvent water entering from the top of the extraction section tower body to form an acrylonitrile-water azeotrope, and performs extractive distillation to separate acrylonitrile, hydrocyanic acid, and acetonitrile, while removing impurities such as oxazole from the rich water. The rich water containing acetonitrile flows downwardly into the stripping section tower body, and rich gas containing acrylonitrile, hydrocyanic acid, and water is discharged from the rich gas outlet at the top of the extraction section tower body. The rich water containing acetonitrile is distilled and purified in the stripping section tower to obtain crude acetonitrile, and the tower bottom obtains a liquid phase containing a small amount of organic matter; The mass ratio of the rich water to the solvent water is 1:(5.5-9); The air velocity passing through the air outlet is controlled to be 6-20 m / s.

10. The acrylonitrile separation process according to claim 9, characterized in that: The tower top temperature of the tower body is controlled to be 65-75° C., and the tower top pressure of the tower body is controlled to be 0.005-0.008 MPaG; The temperature of the tower kettle is controlled to be 110-118°C, and the pressure of the tower kettle is controlled to be 0.05-0.07 MPaG; Control the pressure drop of the recovery tower to 40-65kPa; The pH of the lean water in the tower kettle and the pH in the lean water buffer tank are both controlled to be 6-8, and the pH in the phase separator is controlled to be 6-7.5.

Images