A rectification column structure for separating hexafluoropropylene oligomer isomers

Abstract

The present application relates to a rectifying tower structure for separating hexafluoropropylene oligomer isomers, comprising a tower body, an upper mass transfer zone, a lower mass transfer zone, a main feed inlet, a reflux feed inlet, and a gas-liquid distribution assembly arranged between the upper and lower mass transfer zones; the gas-liquid distribution assembly comprises a main liquid phase collection tray, a riser, and a main liquid phase descending channel with a liquid seal structure, the riser is correspondingly provided with a reflux liquid phase liquid supply assembly in communication with the reflux feed inlet and a plurality of sets of axial wetting areas with different liquid inlet heights. The present application guides the main liquid phase and the reflux liquid to different descending paths respectively, and passively adjusts the number of wetting areas with different liquid supply positions varying with the liquid level, so that the ascending gas phase is in stable countercurrent contact with the reflux liquid in the riser, achieving the effect of strengthening the local mass transfer of the reflux material and improving the mass transfer stability under different reflux loads while maintaining the normal rectification process.

Description

Technical Field

[0001] This invention relates to the field of chemical distillation, specifically to a distillation column structure for separating isomers of hexafluoropropylene oligomers. Background Technology

[0002] Hexafluoropropylene can undergo oligomerization under catalytic conditions to form a mixture of products including dimers D1 and D2 and trimers T1, T2, and T3. Since the boiling points of adjacent isomers are quite close—the boiling point difference between D1 and D2 is approximately 4–5 °C, and the boiling point difference between T1, T2, and T3 is approximately 2–6 °C—multi-stage distillation is typically required for separation, placing high demands on the gas-liquid mass transfer efficiency and operational stability of the distillation column.

[0003] In the continuous distillation of hexafluoropropylene oligomers, transition fractions containing both light and heavy target components can easily form between adjacent components. To improve the recovery rate of the target components, these transition fractions usually need to be returned to the fore-stage distillation process for re-separation. For example, in the separation of D2 and trimer, the transition fraction rich in D2 and containing a small amount of trimer can be refluxed to the D2 rectification section for further processing.

[0004] The conventional approach to handling the reflux material is to combine it with the main feed or the normally descending liquid phase within the column and then reintroduce it into the distillation process. However, since the flow rate and composition of the reflux material differ from the normal main reflux, direct mixing makes it difficult to establish suitable gas-liquid contact conditions for this small flow rate material. If a separate packing section or stripping structure is installed, it may increase the pressure drop and space required within the column, which is particularly detrimental to the operation of the vacuum distillation column.

[0005] The purpose of this invention is to design a distillation column structure for separating isomers of hexafluoropropylene oligomers, addressing the problems existing in the prior art. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention provides a distillation column structure for separating isomers of hexafluoropropylene oligomers, which can effectively solve at least one of the problems existing in the prior art.

[0007] This invention provides a distillation column structure for separating isomers of hexafluoropropylene oligomers, comprising a column body and an upper mass transfer zone and a lower mass transfer zone disposed within the column body, characterized in that: The tower body is provided with a main feed inlet and a reflux feed inlet, and the main feed inlet is connected to the lower mass transfer zone; A gas-liquid splitting assembly is provided between the upper mass transfer zone and the lower mass transfer zone, and the gas-liquid splitting assembly is located above the main feed inlet along the axial direction of the tower body. The gas-liquid separation assembly includes a main liquid phase collection plate, at least one air riser disposed on the main liquid phase collection plate, and a main liquid phase descending channel communicating with the main liquid phase collection plate. The air riser passes through the main liquid phase collection plate and forms an air riser channel communicating with the gas phase spaces on the upper and lower sides of the main liquid phase collection plate. The main liquid phase descending channel extends downward from the main liquid phase collection plate, and its liquid outlet is located below the air inlet at the lower end of the gas rising channel along the axial direction of the tower body. The lower end of the main liquid phase descending channel is provided with a liquid seal structure to prevent the gas phase from passing through the main liquid phase descending channel from bottom to top. The air riser is equipped with a reflux liquid phase supply component that is connected to the reflux feed inlet; The inner wall of the rising gas channel is provided with at least two sets of axially wetting regions that extend along the axial direction of the rising gas channel and are spaced apart from each other in the circumferential direction. The reflux liquid phase supply component is provided with at least two sets of supply channels that are respectively connected to different sets of axially wetting regions. The at least two sets of supply channels have liquid inlet positions with different heights, so that when the liquid level in the reflux liquid phase supply component reaches the height of the corresponding liquid inlet position, reflux liquid phase is supplied to the corresponding axially wetting region. This allows the reflux liquid phase input from the reflux inlet to flow downward along the axial wetting region in the liquid supply state, while the gas phase rising from the lower mass transfer zone flows upward along the rising gas channel and comes into countercurrent contact with the reflux liquid phase within the axial wetting region.

[0008] Preferably, a liquid distribution plate is provided inside the tower body and below the main feed inlet. The liquid distribution plate includes a base plate, an overflow groove provided on the base plate, and a distribution guide hood provided below the base plate. The lower end of the main liquid phase descending channel extends into the overflow tank and is located below the working liquid level of the overflow tank, so as to form a liquid seal structure through the liquid held in the overflow tank.

[0009] Preferably, the outer periphery of the main liquid phase collection tray is provided with a baffle extending upward along the axial direction of the tower body; The main liquid phase collection plate is provided with a downcomer, and the main liquid phase downcomer channel includes a downcomer hood formed by extending downward from the periphery of the downcomer.

[0010] Preferably, the air-lifting cylinder includes a cylinder body, and the reflux liquid phase supply assembly includes an annular liquid distribution groove disposed on the outer side of the upper end of the cylinder body and surrounding the cylinder body; The axial wetting area includes a liquid guiding groove disposed on the inner wall of the cylinder and extending along the axial direction of the cylinder. The upper ends of the liquid guiding grooves in different groups are located at different heights. Each liquid guiding groove has a liquid distribution hole at its upper end that connects the liquid guiding groove and the annular liquid distribution groove. Each liquid distribution hole constitutes a corresponding liquid supply channel.

[0011] Preferably, a liquid supply component is provided in the liquid supply channel at least at the lowest liquid inlet position, the liquid supply component being used to guide the reflux liquid phase in the reflux liquid phase supply assembly to the corresponding axial wetting area.

[0012] Preferably, a capillary liquid guiding layer is provided in the liquid guiding groove.

[0013] Preferably, the capillary liquid guiding layer is a metal mesh layer or a capillary textured lining layer.

[0014] Preferably, the liquid guiding grooves are provided in three groups, and each group of liquid guiding grooves is staggered around the circumference of the air riser so that the liquid guiding grooves are uniformly distributed around the circumference of the air riser.

[0015] Preferably, the lower end of the air lift cylinder is provided with a guide section, which forms a guide surface for guiding the reflux liquid phase descending along the inner wall of the air lift channel toward the radially outer side of the air lift cylinder; A gas collection isolation hood is coaxially arranged below the flow guide section. The gas collection isolation hood has an air inlet corresponding to the gas rising channel in the middle. The gas collection isolation hood and the flow guide section are spaced apart along the axial direction of the tower body so that the gas phase rising from the lower mass transfer zone enters the gas rising channel through the air inlet, and the return liquid phase flowing outward along the flow guide section is discharged downward along the radial outer side of the air inlet.

[0016] Preferably, a rain shield is provided above the air lift cylinder. The outer edge of the rain shield protrudes from the outer periphery of the air lift cylinder in the radial direction and forms an outlet gap between it and the upper end of the air lift cylinder to guide the main liquid phase that descends from the upper mass transfer zone to the upper part of the air lift cylinder to the main liquid phase collection tray outside the air lift cylinder.

[0017] Therefore, the present invention provides the following effects and / or advantages: In existing hexafluoropropylene oligomer distillation processes, the reflux material typically re-merges with the main feed or the normally descending liquid phase within the column before participating in distillation. This is not conducive to establishing independent gas-liquid contact conditions for small-flow reflux materials. To address this, this invention provides separate main feed and reflux feed inlets, with the gas-liquid splitter positioned above the main feed inlet. This allows the main feed to enter the lower mass transfer zone for normal distillation, while the reflux material enters the axial wetting zone within the rising gas channel via the reflux liquid phase supply assembly. This enables the main feed and reflux material to use different flow paths within the column, reducing premature mixing of the reflux material with the main feed stream, and utilizing the rising gas phase in the lower mass transfer zone for targeted counter-current mass transfer of the reflux material.

[0018] If the main liquid phase directly enters the rising gas channel, it will increase the local liquid load, while the ordinary descending channel may become a bypass path for the gas phase to rise. To address this, this invention collects the descending main liquid phase from the upper mass transfer zone using a main liquid phase collection tray, and positions the outlet of the main liquid phase descending channel below the inlet of the rising gas channel, allowing the main liquid phase to bypass the gas-liquid splitter and be directly transported to the bottom of the rising gas channel. Simultaneously, a liquid seal structure at the lower end of the main liquid phase descending channel prevents the gas phase from flowing in the opposite direction. This creates a gas-liquid flow path where the main liquid phase descends independently and the main gas phase rises through the rising gas channel, avoiding interference from the main liquid phase with the local mass transfer of the reflux material within the rising gas channel and reducing the impact of gas phase bypass on the mass transfer effect. The overflow trough of the liquid distribution tray can also be used to form a liquid seal, combining the liquid seal function with the subsequent collection and distribution of the main liquid phase, simplifying the internal structure of the tower.

[0019] When the reflux material flow rate changes, using a fixed wetting area can easily lead to insufficient wetting at low flow rates and excessively thick local liquid films at higher flow rates. To address this, this invention provides at least two sets of axial wetting regions within the gas riser channel, with corresponding liquid supply channels having different inlet heights. This ensures that when the liquid level in the reflux liquid phase supply assembly reaches the corresponding height, the corresponding axial wetting regions receive liquid sequentially. This allows for a gradual increase in the actual wetting area participating in mass transfer as the reflux liquid volume increases, translating more of the change in reflux liquid volume into a change in effective wetting area, thus improving the stability and adaptability of the liquid film under different reflux loads.

[0020] In the specific structure, an annular liquid distribution groove is set around the air-lifting cylinder, and liquid is supplied to different liquid guiding grooves through distribution holes at different heights. This allows for staged liquid supply directly by utilizing changes in the liquid level within the annular distribution groove, eliminating the need for an additional active control mechanism. Furthermore, a liquid supply component is installed at the lowest liquid inlet position, and a metal mesh layer or capillary textured lining layer is installed within the liquid guiding groove. This ensures uniform distribution of the reflux liquid phase, enhancing the liquid attraction and continuous wetting capabilities under low liquid level and low flow conditions. Multiple sets of liquid guiding grooves distributed circumferentially around the air-lifting cylinder help reduce gas-liquid imbalance caused by reflux liquid concentration on one side, resulting in more balanced gas-liquid contact within the air-lifting channel.

[0021] After the reflux liquid phase completes countercurrent mass transfer along the inner wall of the riser channel, it is easily re-entrained if it directly enters the rising main airflow. To address this, the present invention includes a guide section at the lower end of the riser to guide the descending reflux liquid phase radially outward, and a gas collection and isolation hood with a central air inlet is coaxially arranged below it. This allows the rising gas phase to enter the riser channel from the center, while the descending liquid phase exits radially outward along the air inlet opening. This enables the rising gas phase and the descending liquid phase after mass transfer to form a staggered flow at the bottom of the riser, reducing the probability of the reflux liquid being re-entrained by the main airflow.

[0022] If the upper end of the riser is directly open, the descending main liquid phase in the upper mass transfer zone may fall into the riser channel and mix with the reflux material. To address this, the present invention provides a protective hood with its outer edge protruding beyond the outer perimeter of the riser, and maintains an outlet gap between the protective hood and the riser, allowing the gas phase to discharge upwards, while the descending main liquid phase is guided to the main liquid phase collection tray outside the riser. Combined with the baffle on the outer perimeter of the main liquid phase collection tray, this further reduces the direct entry of the main liquid phase into the riser channel and the formation of wall flow along the tower wall, which helps maintain the stability of the reflux liquid phase composition and mass transfer state inside the riser channel.

[0023] In summary, this invention separates the main feed inlet and the reflux feed inlet, allowing the main feed and reflux materials to use different in-tower processing paths. Through the main liquid phase collection tray, the main liquid phase descending channel, and the liquid seal structure, the normal main liquid phase bypasses the reflux liquid mass transfer area in the rising gas channel, while simultaneously restricting the main gas phase from bypassing via the descending liquid path. By using supply channels at different heights and multiple sets of axial wetting zones, the reflux liquid can passively expand its wetting range with changes in liquid level, and the capillary liquid guiding structure improves wetting stability at low flow rates. Furthermore, the flow path isolation between the main gas phase, the reflux liquid phase, and the normal main liquid phase is achieved through the guide section at the bottom of the rising gas cylinder, the gas collection isolation hood, and the top anti-drenching hood. Thus, without the need for additional independent stripping equipment, a stable and adaptable local countercurrent mass transfer condition can be formed for the reflux material, while also considering normal gas-liquid flow in the distillation column and relatively low additional structural complexity. Attached Figure Description

[0024] Figure 1 This is a three-dimensional structural diagram of the present invention.

[0025] Figure 2 This is a schematic diagram of the overall structure of the present invention.

[0026] Figure 3 This is a partial cross-sectional view of the present invention.

[0027] Figure 4 This is a three-dimensional structural diagram highlighting the gas-liquid splitting component in this invention.

[0028] Figure 5 This is a cross-sectional view of the gas-liquid splitting component in this invention.

[0029] Figure 6 This is a three-dimensional structural diagram of the air lift cylinder in this invention.

[0030] Figure 7 This is a three-dimensional and cross-sectional structural diagram of the air-lift cylinder in this invention.

[0031] Figure 8 This is a schematic cross-sectional view of the first direction highlighting the air cylinder body in this invention.

[0032] Figure 9 This is a schematic cross-sectional view of the second direction highlighting the air cylinder body in this invention.

[0033] In the picture: 100. Tower body; 110. Condenser; 120. Reboiler; 121. Liquid phase circulation pipeline; 122. Gas phase return pipeline; 130. Upper mass transfer zone; 140. Gas-liquid splitting zone; 150. Lower mass transfer zone; 160. Reflux feed inlet; 170. Main feed inlet; 171. Bend; 200. Liquid distribution plate; 210. Base plate; 211. Liquid discharge opening; 220. Overflow trough; 221. Overflow plate; 230. Distribution guide hood; 300. Gas-liquid splitting assembly; 310. Main liquid phase collection plate; 311. Baffle; 31 2. Liquid outlet; 320. Air riser; 321. Air riser channel; 322. Cylinder body; 323. Liquid guide groove; 324. First liquid distribution hole; 325. Second liquid distribution hole; 326. Third liquid distribution hole; 327. Capillary liquid guiding layer; 330. Main liquid phase descending channel; 340. Flow guide section; 341. Flow guide surface; 350. Gas collection isolation cover; 351. Air inlet opening; 360. Rainproof structure; 361. Rainproof cover; 362. Support rod; 400. Return liquid phase supply assembly; 410. Annular liquid distribution groove; 420. Return liquid supply main pipe. Detailed Implementation

[0034] The distillation column structure and its working process of the present invention will be further described below with reference to a preferred embodiment. It should be understood that this embodiment is used to illustrate the structural composition of the present invention, the cooperation relationship between the parts, and the corresponding gas-liquid flow process, and is not intended to limit the scope of protection of the present invention.

[0035] like Figures 1-9 As shown, this embodiment provides a distillation column structure for separating isomers of hexafluoropropylene oligomers, particularly suitable for separating reflux material that needs to be returned to the column for further processing during the normal distillation of the main material. The distillation column includes a column body 100, with a condenser 110 connected to the top of the column body 100 and a reboiler 120 connected to the bottom of the column body 100. Inside the column body 100, an upper mass transfer zone 130, a gas-liquid splitting zone 140, and a lower mass transfer zone 150 are arranged axially from top to bottom.

[0036] A gas phase outlet is provided at the top of the tower body 100, and the gas phase outlet is connected to the condenser 110. The gas phase rising from the inside of the tower body 100 to the top of the tower enters the condenser 110 through the gas phase outlet and is condensed into liquid. At least part of the condensed liquid returns to the top of the tower body 100 to form the top reflux, and the remainder can be collected as the top product. After entering the tower body 100, the top reflux liquid flows downward through the upper mass transfer zone 130, where it comes into countercurrent contact with the upward-flowing gas phase inside the tower.

[0037] The bottom of the column body 100 forms a liquid containment space in the reboiler. A reboiler 120 is located outside the column body 100 and is connected to the bottom of the column body 100 via a liquid phase circulation line 121 and a gas phase return line 122. The reboiler liquid can enter the reboiler 120 through the liquid phase circulation line 121, where it is heated and at least partially vaporized. The resulting gas phase re-enters the bottom of the column body 100 through the gas phase return line 122 and flows upwards to continuously provide the rising gas phase required for distillation. The unvaporized liquid phase can be returned to the reboiler or, depending on process requirements, collected as bottom product.

[0038] The upper mass transfer zone 130 includes structured packing and a packing support for supporting the structured packing. The structured packing can be a corrosion-resistant structured packing suitable for fluorine-containing materials. The packing support is fixed inside the tower body 100 and located below the structured packing, so that the structured packing is stably maintained at a predetermined height. The main reflux liquid returning from the top condenser 110 flows downward through the structured packing, while the rising gas phase flows upward through the structured packing, and the two come into countercurrent contact on the mass transfer surface provided by the structured packing.

[0039] The lower mass transfer zone 150 also includes structured packing and a packing support located below the structured packing. The mixed liquid, redistributed by the liquid distribution plate 200, falls above the lower mass transfer zone 150 and enters the lower structured packing evenly; the gas phase generated by the reboiler 120 and entering from the bottom of the column passes upward through the lower structured packing and undergoes normal distillation mass transfer with the descending liquid phase.

[0040] The column body 100 is provided with a main feed inlet 170 and a reflux feed inlet 160. The main feed inlet 170 is located above the lower mass transfer zone 150 and is used to feed the bulk material to be refined into the column. One end of the main feed inlet 170 extending into the column body 100 is connected to a downwardly bent pipe, the lower end of which opens downwards and faces the liquid distribution plate 200 located below it. Thus, after the bulk material enters the column body 100 through the main feed inlet 170, it does not directly impact the packing or column wall as a transverse jet, but is discharged downwards along the bent pipe 171 and falls into the liquid distribution plate 200.

[0041] The reflux inlet 160 is used to input reflux material that requires further enhanced separation. For D2 distillation of hexafluoropropylene oligomers, this reflux material can be a transitional reflux liquid rich in D2 and containing a certain amount of heavier components. The reflux inlet 160 is not premixed outside the column with the main inlet 170, but is directly connected to the reflux liquid phase supply assembly 400 located in the gas-liquid separation zone 140, giving the reflux material a distinct in-column flow path from the bulk material.

[0042] A gas-liquid splitting assembly 300 is provided in the gas-liquid splitting region 140 between the upper mass transfer zone 130 and the lower mass transfer zone 150. The gas-liquid splitting assembly 300 is located above the main feed inlet 170 along the axial direction of the tower body 100. The gas-liquid splitting assembly 300 includes a main liquid phase collection plate 310 arranged laterally inside the tower body 100, a plurality of air risers 320 arranged on the main liquid phase collection plate 310, and a main liquid phase descending channel 330 communicating with the main liquid phase collection plate 310.

[0043] The main liquid phase collection tray 310 basically spans the internal cross-section of the tower body 100, and its outer periphery cooperates with the inner wall of the tower body 100 to receive the main liquid phase descending from the upper mass transfer zone 130. An upwardly extending baffle 311 is provided on the outer periphery of the main liquid phase collection tray 310. The baffle 311 fits tightly against the inner wall of the tower body 100. The baffle 311 can circumferentially limit the liquid collected on the main liquid phase collection tray 310, reducing the liquid from directly crossing the edge of the collection tray and forming wall flow along the inner wall of the tower body 100.

[0044] Multiple air risers 320 are evenly arranged on the main liquid phase collection tray 310. In this embodiment, seven air risers 320 are preferably arranged, with one air riser 320 located at the center of the main liquid phase collection tray 310, and the other six air risers 320 evenly spaced around the central air riser 320 circumferentially. This arrangement allows the gas phase passing through the main liquid phase collection tray 310 from bottom to top to be more evenly dispersed within the cross-sectional area of ​​the tower body 100. Of course, the number and arrangement of the air risers 320 can be changed accordingly for different tower diameters or different gas phase loads.

[0045] Each riser 320 penetrates the main liquid phase collection plate 310, and a riser channel 321 is formed inside the riser 320, connecting the upper and lower gas phase spaces of the main liquid phase collection plate 310. Apart from the necessary riser channel 321 and liquid descending structure, the main liquid phase collection plate 310 basically blocks the large-area direct connection between the upper and lower gas phase spaces, so that the rising gas phase generated in the lower mass transfer zone 150 mainly passes upward through each riser 320 and then through the gas-liquid splitting assembly 300.

[0046] A downcomer 312 is provided through one side of the main liquid phase collection tray 310, and a main liquid phase downcomer channel 330 is formed by extending downward from the periphery of the downcomer 312. In this embodiment, the main liquid phase downcomer channel 330 preferably adopts a downcomer hood structure that extends downward along the periphery of the downcomer 312. The main liquid phase downcomer channel 330 extends from the main liquid phase collection tray 310 to below the lower air inlet of the gas riser channel 321, so that the main liquid phase descending from the upper mass transfer zone 130 and collected by the main liquid phase collection tray 310 can be directly transported along the main liquid phase downcomer channel 330 to the bottom of the gas riser 320 without entering the gas riser 320 to participate in the local countercurrent mass transfer set for the return material.

[0047] A liquid distribution plate 200 is installed below the gas-liquid splitter assembly 300, and the liquid distribution plate 200 is located below the main feed inlet 170 and the bend at the end of the main feed inlet 170. The liquid distribution plate 200 is used to uniformly receive the main material, the main liquid phase returned from the upper mass transfer zone 130, and the recovered liquid phase discharged downward after local mass transfer in the air lift cylinder 320, and then reorganizes the above liquid phases and transports them to the lower mass transfer zone 150.

[0048] The liquid distribution tray 200 includes a base plate 210, an overflow groove 220 disposed on the base plate 210, and a distribution guide hood 230 disposed below the base plate 210. The base plate 210 is disposed generally laterally inside the tower body 100, and its peripheral edge is provided with a base edge that fits tightly against the inner wall of the tower body 100 to form a truncated structure. A liquid discharge opening 211 for downward liquid flow is formed through the center of the base plate 210. The distribution guide hood 230 is disposed directly below the liquid discharge opening 211 and has an overall funnel shape that gradually narrows in the downward direction.

[0049] In this embodiment, the distribution guide hood 230 forms two progressively smaller guide steps (not shown in the figure) along the height direction, so that the liquid falling from the liquid inlet 211 in the substrate 210 first passes through a larger primary guide area and then enters a smaller secondary guide area. This structure allows for the re-rectification of liquids collected from different directions onto the liquid distribution disk 200, causing the liquid to fall from the center of the liquid distribution disk 200 into the structured packing material above the lower mass transfer zone 150, and then re-spread on the packing material.

[0050] The lower end of the bend at the main feed inlet 170 is directly opposite the liquid distribution plate 200, so that the main material falls into the liquid distribution plate 200 first, instead of directly entering the lower structured packing. In this way, the main material can first collect with the main liquid phase transported down from the main liquid phase descending channel 330 and the recovered liquid phase descending after local mass transfer in the area where the liquid distribution plate 200 is located, and then be uniformly redistributed downwards through the middle of the liquid distribution plate 200, so as to reduce the uneven liquid distribution caused by liquid phases from different sources falling directly into local positions of the packing.

[0051] An overflow plate 221 is formed on one side of the upper surface of the substrate 210. Both ends of the overflow plate 221 extend to the inner wall of the column body 100, forming the aforementioned overflow trough 220 in conjunction with the inner wall of the column body 100. The lower end of the main liquid phase descending channel 330 is inserted into the overflow trough 220, with its lowest point lower than the top height of the overflow plate 221 and located below the normal operating liquid level of the overflow trough 220. During distillation column operation, a certain height of liquid is continuously maintained in the overflow trough 220, thereby immersing the lower end of the main liquid phase descending channel 330 in the liquid to form a liquid seal. The effective liquid column height of the liquid seal should be greater than the liquid column height required for the corresponding maximum gas phase pressure difference, with a safety margin.

[0052] Normally, the main liquid phase can enter the overflow tank 220 from top to bottom along the main liquid phase descending channel 330. However, the gas phase located below the main liquid phase descending channel 330 is blocked by a liquid seal and cannot rise in the opposite direction along the main liquid phase descending channel 330. Therefore, the main liquid phase descending channel 330 can enable the main liquid phase to be transported downward across the local mass transfer area of ​​the riser 320, while not becoming a bypass path for the lower gas phase to bypass the riser 320 upward.

[0053] Each air-lifting cylinder 320 includes a cylindrical body 322, with an air-lifting channel 321 formed inside the body 322. An annular liquid distribution groove 410 is provided around the upper outer side of the body 322. The upper end of the annular liquid distribution groove 410 is open to receive the return liquid phase conveyed by the return feed port 160. The annular liquid distribution groove 410 constitutes the main liquid holding space of the return liquid phase supply assembly 400 corresponding to the air-lifting cylinder 320.

[0054] The return feed inlet 160 is connected to the annular liquid distribution tank 410 corresponding to each air cylinder 320 through the return liquid supply main pipe 420, so that the return material can enter multiple annular liquid distribution tanks 410 respectively.

[0055] The inner wall of the air lift cylinder 320 is provided with multiple liquid guiding grooves 323 extending along its axial direction. The multiple liquid guiding grooves 323 are arranged at intervals around the circumference of the air lift cylinder 320, and each liquid guiding groove 323 forms an axial wetting area for the reflux liquid phase to flow downward.

[0056] In this embodiment, each air-lift cylinder 320 has eight liquid-guiding grooves 323 on its inner wall. The bottom heights of the eight liquid-guiding grooves 323 are kept at the same level, while the top heights are different, thus forming different liquid inlet positions. They are divided into three groups according to the height of the corresponding liquid inlet positions.

[0057] The first group includes two liquid guiding grooves 323, which are symmetrically arranged along one diameter of the air lifting cylinder 320. The upper ends of the two liquid guiding grooves 323 are respectively connected to the outer annular liquid distribution groove 410 through two first liquid distribution holes 324 located at the lowest position.

[0058] The second group also includes two liquid guiding grooves 323, which are symmetrically arranged along another diameter. The second liquid distribution hole 325 corresponding to the second group of liquid guiding grooves 323 is higher than the first liquid distribution hole 324. In this embodiment, the diameter of the second group is perpendicular to the diameter of the first group.

[0059] The third group includes four liquid guiding grooves 323, and the corresponding four third liquid distribution holes 326 are located at a position higher than the second liquid distribution holes 325. The four third group liquid guiding grooves 323 are respectively located in the circumferential area between the first group and the second group of liquid guiding grooves 323.

[0060] With the above configuration, the three sets of eight liquid distribution holes are arranged at approximately equal intervals around the air lift cylinder 320. In circumferential terms, the eight liquid guiding grooves 323 ensure a relatively even liquid film distribution around the air lift cylinder 320 when the entire wetted area is in operation.

[0061] The first liquid distribution hole 324, the second liquid distribution hole 325, and the third liquid distribution hole 326 all penetrate the cylinder wall of the air lifting cylinder 320, connecting the annular liquid distribution groove 410 with the corresponding liquid guiding groove 323. Since the different sets of liquid distribution holes are at different heights, the change in liquid level in the annular liquid distribution groove 410 can be directly converted into the change in the number of wetting areas actually put into operation.

[0062] When the flow rate of the reflux material is small, the liquid level in the annular liquid distribution tank 410 is at a low position. The reflux liquid mainly enters the first set of liquid guiding grooves 323 through the first liquid distribution hole 324 at the lowest position, so that the limited liquid volume is concentrated in the two axial wetting areas to form a relatively stable descending liquid film.

[0063] When the amount of return liquid entering the annular liquid distribution tank 410 increases, and the drainage capacity of the lowest-level first liquid distribution hole 324 is insufficient to maintain the liquid level in the tank at a low level, the liquid level in the annular liquid distribution tank 410 gradually rises. When the liquid level reaches the second liquid distribution hole 325, the second set of liquid guiding grooves 323 begins to receive liquid, increasing the number of wetting zones participating in countercurrent mass transfer from two to four.

[0064] When the amount of refluxed liquid is further increased and the liquid level in the annular liquid distribution groove 410 reaches the third liquid distribution hole 326, the third group of four liquid guiding grooves 323 are put into operation simultaneously, so that all eight liquid guiding grooves 323 form a descending liquid film.

[0065] Therefore, this embodiment can passively change the number of wetting areas actually participating in gas-liquid mass transfer by utilizing the liquid level change in the annular liquid distribution tank 410 caused by the change in the flow rate of the refluxed material. Reducing the number of working wetting areas under low liquid volume conditions can concentrate the limited liquid volume to form a stable liquid film; gradually increasing the wetting area under higher liquid volume conditions can reduce the situation where the increase in liquid volume is entirely converted into an increase in the original liquid film thickness.

[0066] To improve the continuous liquid supply capacity of the lowest-level wetting zone under low flow conditions, a liquid supply component (not shown in the figure) is provided at least within the first liquid distribution hole 324 at the lowest position. The liquid supply component can be a metal wire mesh with capillary action, a capillary suction strip, or other structures with liquid guiding capabilities; this embodiment uses a capillary suction strip as an example. Part of the liquid supply component remains in contact with the return liquid in the annular liquid distribution tank 410, while another part extends to the first set of liquid guiding grooves 323, so that even when the liquid level in the annular liquid distribution tank 410 is low or fluctuates, liquid can still be continuously supplied to the first set of liquid guiding grooves 323 through capillary action.

[0067] Each liquid guiding groove 323 is further provided with a capillary liquid guiding layer 327. In this embodiment, the capillary liquid guiding layer 327 is preferably a metal wire mesh layer resistant to corrosion by fluorine-containing media, and the metal wire mesh layer extends along the axial direction of the liquid guiding groove 323. The return liquid entering the liquid guiding groove 323 is jointly restricted by the geometric boundary of the liquid guiding groove 323 and the capillary effect of the metal wire mesh, and can continuously spread downward along the inner wall of the air lifting cylinder 320.

[0068] In another embodiment, the capillary liquid guiding layer 327 may also be a capillary textured liner provided in the liquid guiding groove 323, such as a fine groove surface, a microporous structure or other corrosion-resistant surface structure that can enhance the ability of liquid to spread axially.

[0069] The lower end of the air riser 320 is equipped with a gas-liquid isolation structure to allow the descending reflux liquid and the rising main gas phase to flow in a staggered manner.

[0070] Specifically, the lower end of the cylinder body 322 of the air lift 320 is connected to a guide section 340 that extends downward and radially outward. The guide section 340 can be configured as a funnel shape, with its inner surface continuous with the inner wall of the cylinder body 322, thereby forming a guide surface 341 that guides the liquid descending along the inner wall of the cylinder body 322 further downward and gradually radially outward.

[0071] A gas collecting isolation hood 350 is coaxially disposed directly below the flow guide section 340, and the gas collecting isolation hood 350 is fixed to the lower part of the flow guide section 340 by connecting ribs. The gas collecting isolation hood 350 can also adopt a trumpet-shaped structure, and an air inlet 351 corresponding to the gas rising channel 321 is provided in its middle. The gas collecting isolation hood 350 and the upper flow guide section 340 are kept at a distance along the axial direction of the tower body 100, and their opposing surfaces are preferably substantially parallel, thereby forming a liquid phase discharge gap around the central air inlet 351 between them.

[0072] The main gas phase moving upward from the lower mass transfer zone 150 is restricted and guided by the gas collection isolation hood 350, enters the interior of the riser 320 through the middle air inlet 351, and continues to move upward along the riser channel 321.

[0073] On the other hand, the reflux liquid that descends along the inner wall of the liquid guide groove 323 and the air lift cylinder 320 and completes local mass transfer reaches the lower end of the cylinder body 322, moves radially outward along the trumpet-shaped guide section 340, and is discharged downward from the annular area surrounding the central air inlet opening 351.

[0074] Therefore, a staggered flow state is formed at the bottom of the riser 320, where the main gas phase enters upward from the central region and the reflux liquid that has completed mass transfer is discharged downward from the outer region. This can reduce the situation where the descending liquid phase falls directly into the high-speed rising airflow and is re-entrained.

[0075] The recovered liquid phase discharged from the periphery of the riser 320 then falls downwards to the liquid distribution plate 200, where it is collected together with the main material falling from the bend in the main feed inlet 170 and the main liquid phase entering the liquid distribution plate 200 through the main liquid phase descent channel 330. After the liquid phases from the different sources are collected on the liquid distribution plate 200, they enter the distribution guide hood 230 through the liquid drop opening 211 in the middle of the substrate 210, and are then redistributed downwards along the middle of the tower body 100 to the structured packing in the lower mass transfer zone 150 by the distribution guide hood 230.

[0076] The upper end of the air riser 320 is equipped with a rainproof structure 360 ​​for isolating the normal main liquid phase in the upper part.

[0077] Specifically, an umbrella-shaped rain shield 361 is installed directly above each air cylinder 320. The rain shield 361 is fixed to the upper end of the air cylinder 320 by multiple support rods 362 and maintains a certain distance from the upper port of the air cylinder 320.

[0078] The outer edge of the rain shield 361 protrudes radially from the outer periphery of the annular liquid distribution tank 410, so that the normal main liquid phase or droplets descending from the upper mass transfer zone 130 to the top of the air riser 320 first fall onto the surface of the rain shield 361, and flow radially outward along the umbrella-shaped surface towards the air riser 320, and finally fall into the main liquid phase collection tray 310, instead of directly entering the air riser channel 321.

[0079] After the upward-facing gas phase inside the lift cylinder 320 reaches the upper end, it can be discharged from the lateral gas outlet gap formed between the rainproof cover 361 and the upper end of the lift cylinder 320, and further enter the upper mass transfer zone 130.

[0080] Therefore, the anti-drenching cover 361 at the top of the riser 320 cooperates with the main liquid phase collection plate 310 so that the liquid flowing downward inside the riser 320 is mainly supplied by the reflux liquid phase supply component 400 corresponding to the reflux feed port 160, while the normal main liquid phase from the top condensate reflux and the upper mass transfer zone 130 is mainly guided to the outside of the riser 320.

[0081] During normal operation of the distillation column, the liquid at the bottom of the column is heated by the external reboiler 120 to form a rising gas phase. The rising gas phase first enters the lower mass transfer zone 150 from the bottom of the column body 100, and then undergoes normal countercurrent distillation mass transfer with the downward flowing main material, main liquid phase and recovered liquid phase in the lower structured packing.

[0082] After completing the lower mass transfer process, the gas phase continues to rise and, after reaching the gas-liquid splitter assembly 300, enters each of the rising gas cylinders 320 under the guidance of the gas collection isolation hood 350.

[0083] At the same time, the return material enters the annular liquid distribution groove 410 on the outside of each air cylinder 320 through the return feed port 160, and enters the corresponding liquid guiding groove 323 through one or more sets of liquid distribution holes according to the actual liquid level. Under the action of the capillary liquid guiding layer 327, a downward liquid film is formed along the inner wall of the air cylinder 320.

[0084] Therefore, inside the riser 320, the rising main gas phase and the descending reflux liquid form an independent local countercurrent mass transfer process. For the separation of hexafluoropropylene oligomer D2, this local mass transfer process can be used to encourage the relatively volatile components in the reflux liquid to further enter the rising gas phase, while the relatively heavier components remain more in the descending liquid phase.

[0085] After completing local mass transfer, the reflux liquid phase is discharged to the outside through the guide section 340 at the bottom of the riser 320 and falls into the liquid distribution plate 200 below. The rising gas phase continues to rise along the riser 320 and enters the upper mass transfer zone 130 through the gas outlet gap below the rainproof cover 361.

[0086] After the gas phase enters the upper mass transfer zone 130, it continues to undergo normal distillation mass transfer with the descending reflux liquid from the top condenser 110 in the upper structured packing. Finally, the light components enriched in the top gas phase enter the condenser 110 through the top gas phase outlet. Part of the condensate is refluxed back to the upper mass transfer zone 130, and the other part is collected as product.

[0087] The main liquid phase descending from the upper mass transfer zone 130, upon reaching the gas-liquid splitter assembly 300, is guided by the rain shield 361 at the top of each lift cylinder 320 to the outside of the lift cylinder 320 and falls into the main liquid phase collection tray 310. The main liquid phase on the main liquid phase collection tray 310 is then directly transported through the downcomer 312 and the main liquid phase downcomer channel 330 to below the lower air inlet of the lift cylinder 320, and enters the overflow trough 220 of the liquid distribution tray 200. Since the lower end of the main liquid phase downcomer channel 330 is submerged below the working liquid surface of the overflow trough 220, a liquid seal can be continuously formed, preventing the lower gas phase from rising in the reverse direction along the main liquid phase downcomer channel 330.

[0088] Thus, the internal flow paths of the liquid and gas phases are formed within the column body 100, which are both complementary and distinct. The main material falls directly into the liquid distribution plate 200 through the bend at the end of the main feed inlet 170, and after redistribution, enters the lower mass transfer zone 150. The normal main liquid phase in the upper part is collected by the main liquid phase collection plate 310 and then directly transported to the bottom of the riser 320 through the main liquid phase descending channel 330 with a liquid seal, before entering the liquid distribution plate 200. The reflux material enters the reflux liquid phase supply assembly 400 outside the riser 320 through the independent reflux feed inlet 160, and descends along the axial wetted area in the riser channel 321, where it undergoes local countercurrent mass transfer with the main gas phase. After completing the mass transfer, the recovered liquid phase falls back into the liquid distribution plate 200. The liquid distribution plate 200 collects the main material, the recovered liquid phase, and the main liquid phase, and then allows them to fall again from the middle onto the structured packing in the lower mass transfer zone 150, thereby restoring the normal main distillation process.

[0089] Meanwhile, the main gas phase generated by the reboiler 120 at the bottom of the column undergoes normal mass transfer in the lower mass transfer zone 150, localized enhanced mass transfer for the reflux liquid phase inside the riser 320, and normal mass transfer in the upper mass transfer zone 130, before finally being condensed by the top condenser 110. Thus, without the need for a separate independent reflux stripping column or a large additional packed section, the existing rising gas phase in the distillation column can be used to implement locally enhanced mass transfer of the reflux material, and the passive staged wetting structure formed by different liquid supply positions at different heights can adapt to changes in the reflux liquid volume.

[0090] In other embodiments, the number of riser cylinders 320 and their arrangement on the main liquid phase collection tray 310 can be adjusted according to the tower body 100 diameter and gas phase load; two, three, or more sets of axial wetting areas can be provided, and the number and circumferential position of the liquid distribution holes corresponding to different sets can also be determined according to the reflux liquid volume and the required wetting area; different corrosion-resistant capillary materials can be used for the liquid supply components and the capillary liquid guiding layer 327; the guide section 340 and the gas collection isolation cover 350 can also adopt other mutually cooperating shapes that can achieve central air intake and peripheral liquid discharge. The above changes do not change the basic structural relationship of this embodiment, which involves the independent descent of the main liquid phase, the selective entry of the reflux liquid into the riser channel 321, and the countercurrent mass transfer of the main gas phase and the reflux liquid within the riser channel 321.

[0091] The main reflux liquid is the reflux liquid returned from the top condenser of the column, the reflux liquid phase is the fraction to be recovered returned from the subsequent separation unit, and the main feed inlet is the main material input from the bottom of the previous separation unit.

[0092] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

Claims

1. A distillation column structure for separating isomers of hexafluoropropylene oligomers, comprising a column body (100) and an upper mass transfer zone (130) and a lower mass transfer zone (150) disposed within the column body (100), characterized in that: The tower body (100) is provided with a main feed inlet (170) and a reflux feed inlet (160), and the main feed inlet (170) is connected to the lower mass transfer zone (150); A gas-liquid splitting assembly (300) is provided between the upper mass transfer zone (130) and the lower mass transfer zone (150), and the gas-liquid splitting assembly (300) is located above the main feed inlet (170) along the axial direction of the tower body (100); The gas-liquid splitting assembly (300) includes a main liquid phase collection plate (310), at least one air riser (320) disposed on the main liquid phase collection plate (310), and a main liquid phase descending channel (330) communicating with the main liquid phase collection plate (310). The air riser (320) penetrates the main liquid phase collection plate (310) and forms an air riser channel (321) communicating with the upper and lower gas phase spaces of the main liquid phase collection plate (310). The main liquid phase descending channel (330) extends downward from the main liquid phase collection plate (310), and its liquid outlet is located below the air inlet at the lower end of the gas rising channel (321) along the axial direction of the tower body (100). The lower end of the main liquid phase descending channel (330) is provided with a liquid seal structure to prevent the gas phase from passing through the main liquid phase descending channel (330) from bottom to top. The air riser (320) is equipped with a reflux liquid phase supply assembly (400) that is connected to the reflux feed port (160); The inner wall of the gas rising channel (321) is provided with at least two sets of axially wetting regions that extend along the axial direction of the gas rising channel (321) and are spaced apart from each other in the circumferential direction. The reflux liquid phase supply assembly (400) is provided with at least two sets of supply channels that are respectively connected to different sets of axially wetting regions. The at least two sets of supply channels have liquid inlet positions with different heights, so that when the liquid level in the reflux liquid phase supply assembly (400) reaches the height of the corresponding liquid inlet position, reflux liquid phase is supplied to the corresponding axially wetting region.

2. The distillation column structure for separating isomers of hexafluoropropylene oligomers according to claim 1, characterized in that: A liquid distribution plate (200) is provided inside the tower body (100) and below the main feed inlet (170). The liquid distribution plate (200) includes a base plate (210), an overflow groove (220) provided on the base plate (210), and a distribution guide hood (230) provided below the base plate (210). The lower end of the main liquid phase descending channel (330) extends into the overflow tank (220) and is located below the working liquid level of the overflow tank (220) so as to form a liquid seal structure through the liquid held in the overflow tank (220).

3. The distillation column structure for separating isomers of hexafluoropropylene oligomers according to claim 1, characterized in that: The outer periphery of the main liquid phase collection plate (310) is provided with a flange (311) that extends upward along the axial direction of the tower body (100); The main liquid phase collection plate (310) is provided with a downcomer (312) through it, and the main liquid phase downcomer channel (330) includes a downcomer hood formed by extending downward from the periphery of the downcomer (312).

4. The distillation column structure for separating isomers of hexafluoropropylene oligomers according to claim 1, characterized in that: The air-lift cylinder (320) includes a cylinder body (322), and the reflux liquid phase supply assembly (400) includes an annular liquid distribution groove (410) disposed on the outer side of the upper end of the cylinder body (322) and surrounding the cylinder body (322); The axial wetting area includes a liquid guiding groove (323) disposed on the inner wall of the cylinder (322) and extending axially along the cylinder (322); The upper ends of the liquid guiding grooves (323) in different groups are located at different heights. Each liquid guiding groove (323) has a liquid distribution hole that connects the liquid guiding groove (323) and the annular liquid distribution groove (410) at its upper end. Each liquid distribution hole constitutes the corresponding liquid supply channel.

5. A distillation column structure for separating isomers of hexafluoropropylene oligomers according to claim 4, characterized in that: A liquid supply component is provided in the liquid supply channel at least at the lowest liquid inlet position. The liquid supply component is used to guide the reflux liquid phase in the reflux liquid phase supply assembly (400) to the corresponding axial wetting area.

6. A distillation column structure for separating isomers of hexafluoropropylene oligomers according to claim 4, characterized in that: A capillary liquid guiding layer (327) is provided inside the liquid guiding groove (323).

7. A distillation column structure for separating isomers of hexafluoropropylene oligomers according to claim 6, characterized in that: The capillary liquid guiding layer (327) is a metal wire mesh layer or a capillary textured lining layer.

8. A distillation column structure for separating isomers of hexafluoropropylene oligomers according to claim 4, characterized in that: The liquid guiding groove (323) is provided in three groups, and each group of liquid guiding grooves (323) is arranged alternately around the air cylinder (320) so that each liquid guiding groove (323) is uniformly distributed around the air cylinder (320).

9. A distillation column structure for separating isomers of hexafluoropropylene oligomers according to claim 1, characterized in that: The lower end of the air lifting cylinder (320) is provided with a guide section (340), which forms a guide surface (341) for guiding the reflux liquid phase descending along the inner wall of the air lifting channel (321) to the radially outer side of the air lifting cylinder (320). A gas collecting isolation hood (350) is coaxially arranged below the flow guide (340). The gas collecting isolation hood (350) has an air inlet corresponding to the gas rising channel (321) in the middle. The gas collecting isolation hood (350) and the flow guide (340) are spaced apart along the axial direction of the tower body (100) so that the gas phase rising from the lower mass transfer zone (150) enters the gas rising channel (321) through the air inlet, and the reflux liquid phase flowing outward along the flow guide (340) is discharged downward along the radial outer side of the air inlet.

10. A distillation column structure for separating isomers of hexafluoropropylene oligomers according to claim 4, characterized in that: A rain shield (361) is provided above the air lift cylinder (320). The outer edge of the rain shield (361) protrudes from the outer periphery of the annular liquid distribution groove (410) along the radial direction of the air lift cylinder (320), and forms an outlet gap between the air lift cylinder (320) and the upper end of the air lift cylinder (320) to guide the main liquid phase that descends from the upper mass transfer zone (130) to the air lift cylinder (320) to the main liquid phase collection plate (310) outside the air lift cylinder (320).

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