An extractive distillation column, an extractive distillation system comprising the extractive distillation column and an extractive distillation method

Abstract

The present application relates to an extractive distillation column comprising, from bottom to top, a tray section, a movable section and a packing section; the packing section comprises gas-liquid contact mass transfer elements referred to as first packing; the movable section comprises gas-liquid contact mass transfer elements referred to as second packing, or comprises a packing-tray composite which is a composite of gas-liquid contact mass transfer elements referred to as third packing and gas-liquid contact mass transfer elements referred to as first stereo-spray tray; the tray section comprises gas-liquid contact mass transfer elements referred to as second stereo-spray tray, wherein the extractive distillation column further comprises an extractant inlet, a feedstock inlet, a top vapor outlet, a bottom liquid outlet and optionally a side inlet, and the packing section is located above the extractant inlet; the movable section is located between the extractant inlet and the feedstock inlet; the tray section is located below the feedstock inlet. The present application also relates to an extractive distillation system comprising the above extractive distillation column and an extractive distillation method using the extractive distillation system.

Description

Technical Field

[0001] This invention relates to the field of aromatic hydrocarbon separation in petrochemicals, specifically to an extraction distillation column, extraction distillation system, and method. Background Technology

[0002] Distillation is a conventional separation unit operation and also a high-energy-consuming process in the petrochemical industry. Driven by the "dual carbon" goal, reducing energy consumption in distillation processes has become a research focus. The high energy consumption stems from the difficulty in balancing the separation efficiency, pressure drop, and operational flexibility of the mass transfer elements in the gas-liquid contact section of the column. Extractive distillation is a special type of distillation process widely used in the separation of aromatics and various fine chemicals. Because the solvent-to-feed mass ratio (solvent ratio) is usually not less than 1, and the solvent has a high boiling point and is not easily vaporized, the liquid load in extractive distillation columns is significantly higher than in conventional distillation columns, resulting in a large difference in the liquid-to-gas ratio at different locations within the column. Currently, extractive distillation columns commonly use trays with floating valves or inclined holes as gas-liquid mass transfer elements, which suffer from low tray efficiency and a tendency to flooding.

[0003] Wu Jimin et al. (“Application of novel packed tower technology in cyclohexene-cyclohexane extractive distillation tower”, Chemical Industry and Engineering Progress, 2004, 23(8): 880-882) attempted to achieve extractive distillation of cyclohexane-cyclohexene-benzene using structured packed towers. The original design used Mellapak250 structured packing, but the packing efficiency dropped sharply after the throughput increased, reaching the flooding limit. When the structured packing was replaced with that produced by Tianda Tianjiu, it was still necessary to add a tower in series to meet the separation requirements.

[0004] Chinese patent CN1477092A discloses an acrylic acid purification distillation column with a large-pore sieve plate in the lower section and a co-flow spray tray in the upper section. By modifying the internal components of the column, the polymerization tendency of acrylic acid is reduced, thus lowering losses. Chinese patent CN100465147C discloses a distillation column for separating acrolein from 3-hydroxypropionaldehyde. The upper section of the rectification section uses a novel vertical sieve plate, the lower section uses a spray-packed tray, and the stripping section uses structured packing, which effectively reduces the polymerization tendency of acrolein, thereby reducing losses. Chinese patent CN1194878A discloses a hollow composite packed tray for use in ordinary distillation processes. A layer of structured packing is placed in the space below the tray to achieve high throughput and high flexibility in the distillation column operation. However, these combinations of mass transfer elements are not suitable for extractive distillation columns, failing to improve the separation efficiency or reduce the overall pressure drop. Summary of the Invention

[0005] One objective of this invention is to provide an extraction distillation column with high separation efficiency, which can effectively reduce the overall pressure drop and bottom temperature of the column, thereby further reducing energy consumption; or, under the condition of constant column diameter, further increase the feed throughput, which is beneficial for capacity expansion and renovation; the extraction distillation column of this invention has improved anti-clogging and defoaming capabilities, effectively reducing the risk of flooding.

[0006] To achieve the above objectives, according to a first aspect of the present invention, an extractive distillation column is provided, comprising, from bottom to top, a tray layer, a movable layer, and a packing layer; the packing layer includes a gas-liquid contact mass transfer element referred to as a first packing; the movable layer includes a gas-liquid contact mass transfer element referred to as a second packing, or includes a packing-tray composite, the packing-tray composite being a composite of a gas-liquid contact mass transfer element referred to as a third packing and a gas-liquid contact mass transfer element referred to as a first three-dimensional jet type tray; the tray layer includes a gas-liquid contact mass transfer element referred to as a second three-dimensional jet type tray, wherein the extractive distillation column further includes an extraction solvent inlet, a feed inlet, a top gas phase outlet, a bottom liquid phase outlet, and an optional side stream inlet, wherein the feed inlet is below the extraction solvent inlet, the packing layer is located above the extraction solvent inlet, the movable layer is located between the extraction solvent inlet and the feed inlet, and the tray layer is located below the feed inlet. Specifically, the gas-liquid contact mass transfer element contained in the packing layer is a packing material, referred to as the "first packing"; the gas-liquid contact mass transfer element contained in the active layer is a packing material, referred to as the "second packing", or a packed tray composite, the packed tray composite comprising a packing material referred to as the "third packing" and a three-dimensional jet tray referred to as the "first three-dimensional jet tray", or composed of the latter; the gas-liquid contact mass transfer element contained in the tray layer is a three-dimensional jet tray, referred to as the "second three-dimensional jet tray".

[0007] According to a second aspect of the present invention, an extraction distillation system is provided, the extraction distillation system comprising an extraction distillation column according to the first aspect described above, a condenser, and a reflux tank, wherein the extraction distillation column includes a top vapor phase outlet, a side stream inlet, an extraction solvent inlet, a feed inlet, and a bottom liquid phase outlet, wherein the extraction distillation column is the extraction distillation column according to the first aspect of the present invention; the reflux tank includes a reflux tank inlet and an oil phase outlet; the top vapor phase outlet of the extraction distillation column is connected to the reflux tank inlet through the condenser; and the oil phase outlet of the reflux tank is configured as a raffinate product outlet.

[0008] According to a third aspect of the present invention, the present invention provides an extraction distillation method using the extraction distillation column according to the first aspect and the extraction distillation system according to the second aspect.

[0009] According to the technical solution of this invention, the gas-liquid mass transfer elements are creatively designed in segments based on the gas-liquid mass transfer characteristics and load changes in each part of the tower, thereby achieving the purpose of energy saving and consumption reduction. The extraction distillation tower of this invention has high separation efficiency, which can effectively reduce the overall pressure drop and the temperature of the tower bottom, thereby further reducing energy consumption; or, under the condition of constant tower diameter, it allows for further increase in the raw material throughput, which is conducive to capacity expansion and transformation; the extraction distillation tower of this invention has strong anti-clogging and defoaming capabilities, which can effectively reduce the risk of flooding.

[0010] Other features and advantages of the invention will be described in detail with reference to the accompanying drawings and the following detailed description. Attached Figure Description

[0011] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0012] Figure 1 A schematic diagram of the extraction distillation column and extraction distillation system in Embodiment 1 of the present invention is shown.

[0013] Figure 2 A schematic diagram of the extraction distillation column in Embodiment 2 of the present invention is shown.

[0014] Figure 3 A schematic diagram of the extraction distillation column and extraction distillation system in Embodiment 3 of the present invention is shown.

[0015] Figure 4 A schematic diagram of the extraction distillation system in Embodiment 5 of the present invention is shown.

[0016] Figure 5 A schematic diagram of the structure of the Venturi separator used in Embodiment 5 of the present invention is shown.

[0017] Explanation of reference numerals in the attached figures

[0018] 101: Extractive distillation column; 102: Venturi separator; 103: Reflux tank; 104: Condenser; 105: Non-aromatic distillation column; 106: Gas riser; 107: Liquid riser; 108: Perforated sieve plate; 109: Downcomer; 110: Third packing; 111: First packing; 112: Three-dimensional jet tray; 113: Second packing;

[0019] 1: Raw material inlet; 2: Extraction solvent inlet; 3: Top vapor outlet; 4: Vapor outlet; 5: Reflux tank inlet; 6: Liquid inlet; 7: Oil outlet; 8: Liquid outlet; 9: Bottom liquid outlet; 10: Side stream inlet; 11: Vapor inlet; 12: Aqueous outlet;

[0020] 13: Vortex core tube; 14: Venturi tube; 15: Infusion pipeline; 16: Liquid phase collection tube; 17: Top opening of the expansion section; 18: Opening pipe;

[0021] 19: Non-aromatic hydrocarbon outlet; 20: Oil phase inlet; 21: First oil phase outlet; 22: Second oil phase outlet; 23: Solvent outlet. Detailed Implementation

[0022] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0023] Any specific numerical value (including the endpoints of a range) disclosed in this specification is not limited to its exact value, but should be understood to also include values ​​close to that exact value, such as all possible values ​​within ±5% of that exact value. Furthermore, with respect to the disclosed numerical range, one or more new numerical ranges can be obtained by arbitrarily combining the endpoint values ​​of the range, the endpoint values ​​with specific point values ​​within the range, and the specific point values ​​themselves; these new numerical ranges should also be considered as specifically disclosed in this specification.

[0024] Unless otherwise stated, the terms used in this specification have the same meaning as commonly understood by those skilled in the art. If a term is defined in this specification and its definition differs from the common understanding in the art, the definition herein shall prevail.

[0025] In this application, except where expressly stated, any matters or issues not mentioned are directly applicable to those known in the art without any modification. Furthermore, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the resulting technical solutions or ideas shall be considered part of the original disclosure or original record of this invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider the combination to be clearly unreasonable.

[0026] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its synonyms such as "including" or "containing" shall be understood to include the stated elements or components without excluding other elements or other components.

[0027] In this invention, unless otherwise stated, it should be understood that the expressions “length,” “angle,” “above,” “below,” “vertical,” “standing,” “horizontal,” “top,” “bottom,” “inner,” “outer,” “tangential,” “front,” “back,” “left,” and “right,” etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing this invention and simplifying the description. They do not mean that the indicating device or component must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this invention.

[0028] In this specification, unless otherwise explicitly stated and limited, the terms "set up," "connected," "linked," and "connected" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0029] According to a first aspect of the present invention, an extraction distillation column is provided, comprising, from bottom to top, a tray layer, a movable layer, and a packing layer; the packing layer includes a gas-liquid contact mass transfer element that is packing material, referred to as first packing material; the movable layer includes a gas-liquid contact mass transfer element that is packing material, referred to as second packing material, or a packing-tray composite, wherein the packing-tray composite is a composite of a packing material referred to as third packing material and a three-dimensional jetting tray referred to as first three-dimensional jetting tray; the tray layer includes a gas-liquid contact mass transfer element that is a three-dimensional jetting tray, referred to as second three-dimensional jetting tray; wherein the extraction distillation column further includes an extraction solvent inlet, a feed inlet, a top gas phase outlet, a bottom liquid phase outlet, and an optional side stream inlet, wherein the feed inlet is below the extraction solvent inlet, the packing layer is above the extraction solvent inlet; the movable layer is located between the extraction solvent inlet and the feed inlet; and the tray layer is located below the feed inlet.

[0030] For illustrative purposes, the term "active layer" in this application is intended to indicate that the gas-liquid contact mass transfer element of this layer in the extraction distillation column can be changed according to the different compositions of the raw materials, for example, from packing to a packed tray composite or from a packed tray composite to packing, while the gas-liquid contact mass transfer elements of other layers remain unchanged.

[0031] According to one embodiment of the first aspect above, the theoretical mass transfer order of the packing layer accounts for 10%-25% of the theoretical mass transfer order of the entire tower, and the first packing is a structured packing. Preferably, the structured packing is selected from one or more of perforated plate corrugated packing, mesh corrugated packing, plate mesh corrugated packing, grid packing and corrugated ring packing.

[0032] According to one embodiment of the first aspect above, the theoretical mass transfer stages of the tray layer account for 30%-45% of the total theoretical mass transfer stages of the tower. Preferably, the opening ratio of the second three-dimensional jet-type tray is 5%-30%, the overflow weir height is 5mm-40mm, and the tray spacing is 400mm or more.

[0033] According to one embodiment of the first aspect above, the theoretical mass transfer stages of the active layer account for 40%-60% of the total theoretical mass transfer stages of the column, preferably 45%-55%. This is beneficial to improving the separation efficiency of the extraction distillation column, effectively reducing the overall pressure drop and column bottom temperature, and further reducing energy consumption. Under the condition of constant column diameter, it increases the amount of raw material processed, which is beneficial to capacity expansion and transformation.

[0034] According to one embodiment of the first aspect above, the extraction distillation column is used to separate aromatic compounds and non-aromatic compounds from the raw material. When the mass fraction of non-aromatic compounds in the raw material is not less than 50%, the gas-liquid contact mass transfer element of the active layer is a structured packing (referred to as the second packing). Preferably, the structured packing is selected from one or more of perforated plate corrugated packing, mesh corrugated packing, plate mesh corrugated packing, grid packing, and corrugated ring packing. This embodiment is beneficial to improving the separation efficiency of the extraction distillation column, effectively reducing the overall pressure drop and bottom temperature of the column, and further reducing energy consumption. Under the condition of constant column diameter, it increases the raw material throughput, which is beneficial to capacity expansion and renovation. When the mass fraction of non-aromatic compounds in the feed is less than 50%, the gas-liquid contact mass transfer element of the active layer is a packed tray composite, which includes structured packing (referred to as the third packing) and a three-dimensional jetting tray (referred to as the first three-dimensional jetting tray). Preferably, the first three-dimensional jetting tray has an opening ratio of 5%-30%, an overflow weir height of 5mm-40mm, and a tray spacing of 400mm or more. The third packing is preferably perforated corrugated packing. This implementation method is beneficial to improving the separation efficiency of the extraction distillation column, effectively reducing the overall column pressure drop and column bottom temperature, and further reducing energy consumption. Under the condition of constant column diameter, it increases the feed throughput, which is beneficial to capacity expansion and renovation.

[0035] Conventional extractive distillation columns generally follow the constant molar flow assumption in the rectification and stripping sections. Within the extractive distillation column, because the solvent is essentially non-volatile and the solvent ratio is typically not less than 1, substances in the feed that have strong binding affinity to the solvent gradually enter the solvent (liquid phase), causing the liquid phase molar flow ratio to gradually increase from top to bottom, while the rising gas phase gradually decreases. The inventors of this invention have surprisingly discovered that the gas-liquid load and gas-liquid composition at different locations within the extractive distillation column have their own characteristics. Optimizing the design and combination of the column's internal components based on these characteristics can overcome the shortcomings of existing distillation columns, especially extractive distillation columns. Above the extraction solvent inlet, the liquid-to-gas mass flow ratio (L / V) does not exceed 1. Since high-boiling-point, high-viscosity additives such as defoamers enter the extraction distillation column along with the extraction solvent, the additive content above the extraction solvent inlet is zero. Packing is used for the mass transfer elements in this section, which improves the separation efficiency of the extraction distillation column, reduces the overall pressure drop, and eliminates the risk of packing fouling or clogging. Between the extraction solvent inlet and the feed inlet, the varying content of the extractable substance in the feed results in a higher L / V ratio than between the top of the extraction distillation column and the extraction solvent inlet. In this case, using packed or packed-plate composite structures for the gas-liquid mass transfer elements helps improve separation efficiency and increase throughput. Below the feed inlet, both L and V values ​​increase further, with a slight increase in L / V. Using three-dimensional jet-type trays for the mass transfer elements increases operational flexibility, allowing the liquid phase to fall back onto the trays as a clear liquid, effectively preventing flooding.

[0036] According to one embodiment of the present invention, the theoretical mass transfer order of the packing layer is 10%-25% of the theoretical mass transfer order of the entire column. The first packing is structured packing, selected from one or more of perforated plate corrugated packing, mesh corrugated packing, plate mesh corrugated packing, grid packing, and corrugated ring packing. The theoretical mass transfer order of the tray layer accounts for 30%-45% of the theoretical mass transfer order of the entire column. The second three-dimensional jet-type tray has an opening ratio of 5%-30%, an overflow weir height of 5mm-40mm, and a tray spacing of 400mm or more. The above embodiment is beneficial for improving the separation efficiency of the extraction distillation column, effectively reducing the overall pressure drop and bottom temperature, and further reducing energy consumption. Under the condition of constant column diameter, it increases the feed throughput, which is beneficial for capacity expansion and renovation. It also improves the anti-foaming and defoaming capabilities of the extraction distillation column and reduces the risk of flooding.

[0037] According to a second aspect of the present invention, an extractive distillation system is provided, comprising an extractive distillation column, a condenser, and a reflux tank. The extractive distillation column includes a top vapor outlet, a side stream inlet, an extractive solvent inlet, a feed inlet, and a bottom liquid outlet, wherein the extractive distillation column is the extractive distillation column described in the first aspect of the present invention. The reflux tank includes a reflux tank inlet and an oil phase outlet. The top vapor outlet of the extractive distillation column is connected to the reflux tank inlet via the condenser. The oil phase outlet of the reflux tank is configured as a residual oil product outlet. The bottom liquid phase outlet of the extractive distillation column is configured as a solvent-rich outlet. The term "solvent-rich" refers to the extractive solvent after undergoing the extraction process in the extractive distillation column, which is rich in extractants.

[0038] According to one embodiment of the second aspect above, the extraction distillation column is used to separate aromatic compounds and non-aromatic compounds from the raw material. The extraction distillation system further includes a non-aromatic separation device, which includes a gas phase inlet and a non-aromatic outlet. The gas phase inlet of the non-aromatic separation device is connected to the top gas phase outlet of the extraction distillation column, and the non-aromatic outlet of the non-aromatic separation device is connected to the inlet of the reflux tank through the condenser. Preferably, the non-aromatic separation device is a non-aromatic distillation column or a Venturi separator.

[0039] According to a preferred embodiment, the non-aromatic hydrocarbon separation device is a non-aromatic hydrocarbon distillation column, wherein the non-aromatic hydrocarbon distillation column further includes an oil phase inlet and a solvent outlet; the solvent outlet is connected to the upper part of the extraction distillation column, and the distilled extraction solvent is returned to the extraction distillation column; the oil phase outlet of the reflux tank includes a first oil phase outlet and a second oil phase outlet, the first oil phase outlet is connected to the oil phase inlet of the non-aromatic hydrocarbon distillation column, and the first oil phase outlet is used to return a portion of the non-aromatic hydrocarbons in the reflux tank to the non-aromatic hydrocarbon distillation column for circulation; the second oil phase outlet is used to discharge the remaining non-aromatic hydrocarbons from the reflux tank.

[0040] According to a preferred embodiment, the non-aromatic hydrocarbon separation device is a Venturi separator, wherein the Venturi separator includes a liquid phase collection tube and a Venturi tube disposed within the liquid phase collection tube. The Venturi tube includes the following sections connected in sequence: optionally a constant diameter section, a narrowing section, a throat, and an expanding section. The Venturi separator has a gas phase inlet, a liquid phase inlet, a liquid phase outlet, and a gas phase outlet (i.e., a non-aromatic hydrocarbon outlet). An opening leading to the liquid phase collection tube is provided on the side wall of the expanding section of the Venturi tube or at the end of the expanding section, so that the liquid phase leaves the Venturi tube and enters the liquid phase collection tube under the action of centrifugal force. The top gas phase outlet of the extraction distillation column is connected to the gas phase inlet of the Venturi separator; the liquid phase outlet of the Venturi separator is connected to the side inlet of the extraction distillation column; and the gas phase outlet of the Venturi separator is connected to the inlet of the reflux tank through the condenser. Preferably, the reflux tank further includes an aqueous phase outlet, and preferably the aqueous phase outlet of the reflux tank is connected to the liquid phase inlet of the Venturi separator.

[0041] According to a preferred embodiment, the Venturi separator is placed vertically, wherein the Venturi tube comprises, from bottom to top, an optional equal-diameter section, a narrowing section, a throat, and an expanding section connected in sequence. A liquid phase injection port is provided on the wall of the narrowing section of the Venturi tube; that is, the liquid phase input from the liquid phase inlet of the Venturi separator is injected into the narrowing section of the Venturi tube to contact and mix with the spirally rising gas within the Venturi tube. Because the gas flows at high speed in a spiral manner within the narrowing section of the Venturi tube, the angular velocity of the spirally rising gas increases as the diameter of the narrowing section decreases. Therefore, when the liquid phase is injected into the Venturi tube in the narrowing section, it flows and mixes with the spirally rising gas, resulting in increasingly intense liquid turbulence and more thorough gas-liquid mixing. Consequently, the mass transfer between the gas and liquid is faster and more complete, leading to better separation. The liquid injection port on the wall of the venturi tube can be located at any position in the narrowing section. Preferably, the distance between the position of the liquid injection port and the throat is 1 / 10 to 2 / 3 of the length of the narrowing section, and more preferably, the distance between the position of the liquid injection port and the throat is 1 / 8 to 1 / 2 of the length of the narrowing section.

[0042] According to a preferred embodiment, a nozzle can be provided at the liquid phase injection port on the wall of the venturi tube to spray the liquid phase into the gas in the venturi tube in the form of small droplets, thereby accelerating gas-liquid mixing. The injection flow rate and velocity of the liquid phase can be adjusted by those skilled in the art according to actual needs and gas flow rate and velocity. The injection direction of the nozzle can be any direction, preferably at an angle of less than 90° to the gas flow direction at the location of the liquid phase injection port, more preferably less than 60°, more preferably less than 30°, for example less than 15°, and more preferably in the same direction as the gas flow direction.

[0043] According to a preferred embodiment, the liquid collection tube surrounds at least a portion of the structure of the Venturi tube around its outer periphery, for example, at least surrounding the sidewall of the enlarged section of the Venturi tube or an opening at the end of the enlarged section. The liquid collection tube extends downward, potentially surrounding the enlarged section of the Venturi tube, or even the throat and narrowed section, or even the entire Venturi tube. Preferably, the Venturi separator comprises an upright liquid collection tube and a Venturi tube upright within the liquid collection tube. If the liquid phase collection tube surrounds the entire Venturi tube, then the liquid delivery pipe for transporting the liquid phase, which is connected to the liquid phase inlet on the wall of the Venturi tube, needs to pass through the wall of the liquid phase collection tube. In this case, the liquid phase inlet of the Venturi separator is connected to the liquid phase inlet on the wall of the Venturi tube via the delivery pipe that passes through the wall of the liquid phase collection tube. The angle between the delivery pipe and the generatrix of the conical section of the Venturi tube below the delivery pipe can be 10-90°, preferably 30-80°, for example 40°, 50°, 60° or 70°.

[0044] According to a preferred embodiment, the top of the liquid phase collection tube is closed, but it is provided with an opening tube for the gas phase discharge of the Venturi separator. The upper outlet of the opening tube forms the gas phase outlet of the Venturi separator. The opening tube passes downward through the top of the liquid phase collection tube and extends to the end of the enlarged section of the Venturi tube, optionally connecting to the end of the enlarged section of the Venturi tube. If an opening for liquid phase exiting the Venturi tube is provided on the side wall of the expanded section, the opening pipe is connected to the end of the expanded section. Optionally, an additional opening is provided between the lower end of the opening pipe and the end of the expanded section to allow liquid not completely discharged at the opening in the expanded section to be completely discharged there. If the opening for liquid phase exiting the Venturi tube is located at the end of the expanded section, the lower end of the opening pipe and the end of the expanded section are completely or partially spaced apart to form an opening for liquid exiting the Venturi tube. In this case, the opening is a continuous or intermittent annular opening, and the height of the opening can be adjusted by raising or lowering the opening pipe. The height of the opening can vary within a certain range according to the liquid flow rate, as long as it satisfies the requirement that almost all the liquid phase leaves the Venturi tube and enters the liquid phase collection tube under the action of centrifugal force, and prevents a significant amount of gas from entering the liquid phase collection tube. For example, the height of the opening is less than 10 cm, for example, less than 5 cm.

[0045] According to a preferred embodiment, the diameter of the open pipe can be slightly larger than the diameter of the end opening of the expansion section. For example, the diameter of the open pipe is less than 5% larger than the diameter of the end opening of the expansion section. Preferably, the diameter of the open pipe is the same as the diameter of the end opening of the expansion section.

[0046] According to a preferred embodiment, the Venturi separator further includes a device for causing gas to enter the Venturi tube in a helical flow manner or for causing gas to enter the Venturi tube tangentially, so that the gas flows upward in a helical manner within the Venturi tube. The device is disposed at the inlet of the reduced-diameter section of the Venturi tube or in the constant-diameter section of the Venturi tube. The device for causing the gas to flow helically within the Venturi tube can be a device commonly used in the art, such as a vortex core tube.

[0047] According to a preferred embodiment, the device for causing gas to flow in a spiral manner in a Venturi tube is a vortex core tube, the inside of which is provided with a spiral guide vane. The vortex core tube is vertically arranged at the inlet of the narrowed section of the Venturi tube or vertically arranged in the equal-diameter section of the Venturi tube, and the bottom inlet of the vortex core tube forms the gas phase inlet of the Venturi separator.

[0048] According to a preferred embodiment, the number of vortex core tubes can be selected according to actual needs (such as gas flow rate), and there can be one or more. If multiple vortex core tubes are used, they can be arranged in parallel, so that the vortex shearing through the vortex core tubes enhances the mixing of the gas phase at the top of the column with the solvent (such as water), thereby improving the solvent removal effect and further ensuring that the solvent content in the raffinate product does not exceed 2 μg / g.

[0049] According to a preferred embodiment, the diameter of the liquid phase collection tube is larger than the maximum diameter of the venturi tube disposed therein, and those skilled in the art can select the appropriate diameter based on actual needs and site conditions. Preferably, the diameter of the liquid phase collection tube is 30% larger than the maximum diameter of the venturi tube disposed therein, more preferably 20%, for example 10% or 5%.

[0050] According to a preferred embodiment, a structure (threaded structure) guiding the spiral upward flow of gas is provided on the inner wall of any selected equal-diameter section, reduced-diameter section, throat, and expanded-diameter section of the Venturi tube. This allows the gas flow or gas-liquid flow to spiral upward or downward along the inner wall of the Venturi tube. The structure can be selected from swirl vanes or spiral guide vanes, which can increase the tangential velocity of the fluid, avoid the fluid adhering to the wall effect, enhance the contact between the gas and liquid, and further improve the separation efficiency of the Venturi separator. The helix angle of the swirl vanes or spiral guide vanes... The appropriate method can be selected by those skilled in the art based on the actual situation, and can be adjusted according to changes in the diameter of the venturi tube.

[0051] According to a preferred embodiment, the swirl vane or helical guide vane can be a single- or multi-start thread structure with n threads (n is a positive integer greater than or equal to 1). If the swirl vane or helical guide vane is a multi-start thread structure, and the pitch of the multi-start thread structure (n>1) is the same as the pitch of the single-start thread structure (n=1), the helix angle of the multi-start thread structure will be... Approximately the helix angle of a single-start thread structure The multi-threaded structure is n times larger than that of the Venturi tube, thus it can better guide the fluid on the inner wall of the Venturi tube and significantly reduce the pressure loss of the Venturi separator.

[0052] According to a preferred embodiment, in the Venturi separator, the volumetric flow rate ratio of the gas phase to the liquid phase can vary within a wide range, for example, 70-2500:1, preferably 200-1100:1; the inlet gas velocity of the Venturi separator is 1 m / s-40 m / s, preferably 5 m / s-35 m / s; the pressure loss of the Venturi separator is below 20 kPa, for example, 0.1 kPa-10 kPa, preferably 0.2 kPa-5 kPa; the absolute pressure of the liquid phase at the liquid phase inlet is above 170 kPa, preferably 180 kPa-1500 kPa, preferably 250-1000 kPa.

[0053] According to a preferred embodiment, in the Venturi separator, the bottom of the liquid phase collection pipe is connected to the liquid phase outlet of the Venturi separator via a liquid discharge pipe, wherein a liquid seal is provided at the bottom of the liquid phase collection pipe to prevent gas in the Venturi separator from entering the liquid discharge pipe.

[0054] According to a third aspect of the present invention, the present invention provides an extraction distillation method using the extraction distillation column described in the first aspect of the present invention or the extraction distillation system described in the second aspect of the present invention.

[0055] According to one embodiment of the third aspect above, if the extraction distillation method uses the extraction distillation system described above, the method further includes the following steps: introducing the raw material into the extraction distillation column to contact the extraction solvent, performing extraction distillation, and obtaining a solvent-rich solution in the column bottom; and cooling the gas phase at the top of the column before it enters a reflux tank.

[0056] According to a preferred embodiment, if the extraction distillation method uses the above-described extraction distillation system including a Venturi separator, the extraction distillation method further includes the following steps: allowing the gas phase at the top of the extraction distillation column to enter the Venturi separator and contact with the washing liquid to wash away the extraction solvent in the gas phase, obtaining a washed gas phase and a washing liquid phase containing the extraction solvent; returning the washing liquid phase to the extraction distillation column for recycling; condensing the washed gas phase and separating it in the reflux tank to obtain a residual oil product and an aqueous phase; and returning the aqueous phase as washing liquid to the Venturi separator.

[0057] According to one embodiment of the third aspect above, the extraction distillation method is used for the separation of aromatic hydrocarbons and non-aromatic hydrocarbons.

[0058] According to one embodiment of the third aspect above, the washing liquid is an aqueous solution, more preferably water.

[0059] According to one embodiment of the third aspect above, the bottom temperature of the extraction distillation column is 120℃-180℃, and the overall pressure drop is 40kPa-65kPa; and / or, the temperature of the vapor phase at the top of the column is 80℃-130℃, and the pressure at the top of the column is 0.1MPa-0.5MPa; the solvent ratio is 1-6:1. The above embodiments are beneficial for improving the solvent removal effect, ensuring that the solvent content in the raffinate product does not exceed 2μg / g.

[0060] According to one embodiment of the third aspect above, in the packing layer of the extraction distillation column, the mass flow rate ratio of the liquid phase to the rising gas phase in the extraction distillation column is 0.1-1:1, preferably 0.1-0.5:1; and / or, in the moving layer of the extraction distillation column, the mass flow rate ratio of the liquid phase to the rising gas phase in the extraction distillation column is 3-9:1, preferably 5-7:1; and / or, in the tray layer of the extraction distillation column, the mass flow rate ratio of the liquid phase to the rising gas phase in the extraction distillation column is 5-12:1, preferably 7-10:1.

[0061] According to one embodiment of the present invention, the inlet gas velocity of the Venturi separator is 1 m / s-30 m / s, preferably 5 m / s-27 m / s; the pressure loss of the Venturi separator is 0.2 kPa-5 kPa, preferably 1 kPa-3 kPa; the absolute pressure of the washing liquid at the liquid phase inlet is 180 kPa-1500 kPa; and the mass flow rate ratio of the washing liquid to the overhead gas phase in the Venturi separator is (0.2-1.0):1, preferably (0.3-0.5):1. In this invention, the inlet gas velocity of the Venturi separator refers to the inlet gas velocity of the overhead gas phase entering the narrowed section of the Venturi tube. The above embodiment is beneficial to improving the solvent removal effect, ensuring that the solvent content in the raffinate product does not exceed 2 μg / g.

[0062] According to one embodiment of the present invention, the liquid phase removal rate of the Venturi separator is 82% or higher, preferably 90%-99.9%, and the liquid phase separation accuracy is 1μm-10μm, wherein the above-mentioned liquid phase removal rate = weight of liquid phase entering the liquid phase collection tube / total weight of liquid phase injected into the Venturi tube. The above embodiment is beneficial for improving the solvent removal effect, ensuring that the solvent content in the residual oil product does not exceed 2μg / g.

[0063] According to one embodiment, the raw material is an aromatic hydrocarbon-containing raw material or a ketol oil.

[0064] According to a preferred embodiment of the third aspect above, the extraction distillation system includes a Venturi separator, wherein the top gas phase outlet of the extraction distillation column is connected to the gas phase inlet of the Venturi separator; the liquid phase outlet of the Venturi separator is connected to the side inlet of the extraction distillation column; the gas phase outlet of the Venturi separator is connected to the inlet of the reflux tank through the condenser; and the aqueous phase outlet of the reflux tank is connected to the liquid phase inlet of the Venturi separator. The above-described implementation introduces a Venturi separator into the extraction distillation system. This allows trace amounts of extraction solvent in the overhead vapor phase to be washed with water in the Venturi separator before being returned to the extraction distillation column. The remaining vapor phase is condensed and enters a reflux tank, where the oil phase is collected as the raffinate product. Because the trace amounts of aqueous extraction solvent are returned to the extraction distillation column, the selectivity of the extraction solvent is improved. Furthermore, non-aromatic hydrocarbons do not need to be refluxed to the extraction distillation column, avoiding the formation of two liquid phases within the column. This increases the non-aromatic hydrocarbon content in the raffinate, further improving the quality and yield of aromatic hydrocarbon products in the extract. Simultaneously, this implementation results in a smaller footprint for the extraction distillation system, eliminates the need for additional heating, and reduces energy consumption. The above-described implementation indirectly increases the water content of the extraction solvent in the extractive distillation column by using a Venturi separator, thereby improving the selectivity of the extraction solvent and increasing the quality and yield of aromatic products in the bottom effluent. Simultaneously, it prevents non-aromatic hydrocarbons from returning to the extractive distillation column and avoids the formation of two liquid phases within the column, further improving the separation effect of extractive distillation. Therefore, it has been surprisingly found that the inclusion of a Venturi separator in the extractive distillation system produces a synergistic effect in extractive distillation methods, especially in aromatic separation methods.

[0065] The extraction distillation column and extraction distillation system of the present invention have high separation efficiency, effectively reduce the overall pressure drop and bottom temperature of the column, and further reduce energy consumption; under the condition of constant column diameter, the raw material throughput is further increased, which is conducive to capacity expansion and transformation; the extraction distillation column of the present invention has strong anti-clogging and defoaming capabilities, effectively reducing the risk of flooding.

[0066] Example

[0067] The present invention will be further illustrated by the following examples, but the present invention is not limited thereto.

[0068] The sulfolane used in the examples and comparative examples was a chemical reagent purchased from Innovent Biologics Inc. The structured packing material used in Examples 1-6 of this invention was Mellapak 250 well plate corrugated structured packing material. Unless otherwise specified, all other reagents were obtained commercially. In the following examples and comparative examples, the term "lean solvent" refers to the extraction solvent before the extraction process, which contains little or no extract; the term "rich solvent" refers to the extraction solvent after the extraction process, which is rich in extract.

[0069] Example 1

[0070] In this embodiment, the following is used: Figure 1 The aromatic hydrocarbon extraction system shown includes an extraction distillation column 101, a non-aromatic hydrocarbon distillation column 105, a condenser 104, and a reflux tank 103. The extraction distillation column 101 includes a feed inlet 1, an extraction solvent inlet 2, a top vapor phase outlet 3, a side stream inlet 10, and a bottom liquid phase outlet 9. The non-aromatic hydrocarbon distillation column 105 includes a vapor phase inlet 11, a non-aromatic hydrocarbon outlet 19, an oil phase inlet 20, and a solvent outlet 23. The reflux tank 103 includes a reflux tank inlet 5, a first oil phase outlet 21, and a second oil phase outlet 22. The top vapor phase outlet 3 of the extraction distillation column 101 is connected to the vapor phase inlet of the non-aromatic hydrocarbon distillation column 105, and the non-aromatic hydrocarbon outlet 19 of the non-aromatic hydrocarbon distillation column 105 is connected to the reflux tank inlet 5 through the condenser 104. The solvent-rich bottom is collected through the bottom liquid phase outlet 9, and the residual oil is collected through the second oil phase outlet 22.

[0071] like Figure 1 The extraction distillation column shown includes, from bottom to top, a tray layer, an active layer, and a packing layer. The gas-liquid contact mass transfer element in the active layer is a packed tray composite, which is a composite of a third packing and a first three-dimensional jet-type tray. The third packing is a perforated corrugated structured packing. The gas-liquid contact mass transfer element in the tray layer is a three-dimensional jet-type tray, and the gas-liquid contact mass transfer element in the packing layer is the first packing, which is a perforated corrugated structured packing.

[0072] In the lower section of the extraction distillation column, the gas phase in the column bottom passes through the riser hole 106 from bottom to top through the three-dimensional jet tray at a certain speed. The riser holes on the tray are opened in a certain distribution pattern. Above the riser holes, the liquid lifting pipe 107 and the vertical sieve plate 108 are installed. The liquid phase falls from top to bottom into the three-dimensional jet tray through the downcomer 109. The liquid on the tray is lifted by the gas through the gap between the liquid lifting pipe and the tray. It undergoes high-speed turbulent mixing and mass transfer in the liquid lifting pipe and the vertical sieve plate. The gas continues to rise due to the pressure difference, and the liquid falls back to the tray in the form of clear liquid. It enters the downcomer along the flow channel and descends to the next tray.

[0073] Between the raw material inlet 1 and the extraction solvent inlet 2, the gas phase in the bottom of the tower passes through the gas riser from bottom to top through the three-dimensional jet packing tower plate at a certain speed. A liquid riser and a third packing 110 are set above the gas riser. The liquid phase falls from top to bottom into the three-dimensional jet packing tower plate through the downcomer. The liquid on the tower plate is lifted by the gas through the gap between the liquid riser and the tower plate. It undergoes high-speed turbulent mixing and mass transfer in the liquid riser. Then, the gas and liquid flow into the packing to further enhance mass transfer and complete gas-liquid separation. The gas continues to rise due to the pressure difference, and the liquid falls back to the tower plate in the form of clear liquid. It enters the downcomer along the flow channel and descends to the next tower plate.

[0074] Above the extraction solvent inlet 2, gas-liquid mass transfer occurs in the first packing 111.

[0075] Using reformed oil C6-C7 fraction as feedstock, with an aromatic hydrocarbon mass fraction of 65%, the following process was employed: Figure 1 The extraction distillation column shown separates benzene and toluene using sulfolane as the solvent at a solvent ratio of 4.3 and a reflux ratio of 0.3. The separation requirements are: the mass fraction of aromatics in the raffinate product should not exceed 0.2%, and the mass fraction of aromatics in the solvent-rich stream from the bottom of the column after solvent removal should be 99.9%. The structural parameters and energy consumption of the extraction distillation column are shown in Table 1, and the operating conditions of the non-aromatic distillation column are shown in Table 2.

[0076] Example 2

[0077] The extraction distillation system and raw materials used in this embodiment are the same as those used in Example 1, the only difference being the different active layer of the extraction distillation column;

[0078] like Figure 2 The extraction distillation column shown has a structured packing material as the gas-liquid contact mass transfer element in the active layer.

[0079] In the tray layer of the extraction distillation column, the gas phase in the bottom of the column passes through the three-dimensional jet-type tray 112 at a certain velocity and comes into contact with the liquid phase for mass transfer; in the moving layer and the packing layer of the column, the gas and liquid transfer mass in the first packing 111 and the second packing 113.

[0080] use Figure 2The extraction distillation column shown separates benzene and toluene from the raw material. The raw material, solvent, solvent ratio, reflux ratio and separation requirements are the same as in Example 1. The parameters and energy consumption of the extraction distillation column are shown in Table 1, and the operating conditions of the non-aromatic distillation column are shown in Table 2.

[0081] Example 3

[0082] The feedstock is C6 fraction of reformed oil, with a benzene mass fraction of 26.5%. Figure 3 The extraction distillation column and extraction distillation system shown separate benzene from the feedstock. The system includes an extraction distillation column 101, a condenser 104, and a reflux tank 103. The extraction distillation column 101 includes a feedstock inlet 1, an extraction solvent inlet 2, a top vapor outlet 3, a side stream inlet 10, and a bottom liquid outlet 9. The reflux tank 103 includes a reflux tank inlet 5, a first oil phase outlet 21, and a second oil phase outlet 22. The top vapor outlet 3 of the extraction distillation column 101 is connected to the reflux tank inlet 5 via the condenser 104. A portion of the non-aromatic hydrocarbons in the reflux tank is returned to the extraction distillation column through the first oil phase outlet 21. The solvent-rich bottoms are collected through the bottom liquid outlet 9. The residual oil is collected through the second oil phase outlet 22.

[0083] The gas-liquid contact mass transfer element in the active layer of the extractive distillation column is the second packing, which is a structured packing. In the trays of the extractive distillation column, the gas phase in the bottom layer passes through the three-dimensional jet tray 112 at a certain velocity and contacts the liquid phase for mass transfer. In the active layer and the packed layer of the column, gas-liquid mass transfer occurs in the first packing 111 and the second packing 113. The solvent is sulfolane, the solvent ratio is 3.8, and the reflux ratio is 0.5. The separation requirements are: the mass fraction of benzene in the raffinate product does not exceed 0.1%, and the mass fraction of benzene in the solvent-rich stream in the bottom layer after solvent removal is 99.9%. The parameters and energy consumption of the extractive distillation column are shown in Table 1.

[0084] Example 4

[0085] The extraction distillation column in this embodiment is the same as that in Example 1, except that the theoretical number of packing layers, moving layers and tray layers is different from that in Example 1. Specific parameters and energy consumption are shown in Table 1.

[0086] Example 5

[0087] The extraction distillation column used in this embodiment is the same as that used in Example 1, except that the non-aromatic hydrocarbon separation device in this embodiment is a Venturi separator, as detailed below:

[0088] like Figure 4 The extraction distillation system shown and Figure 5 The Venturi separator shown includes an extraction distillation column 101, a Venturi separator 102, a reflux tank 103, and a condenser 104.

[0089] The extraction distillation column 101 includes a raw material inlet 1, an extraction solvent inlet 2, a side stream inlet 10, a bottom liquid phase outlet 9, and a top gas phase outlet 3; the Venturi separator 102 includes a gas phase inlet 11, a liquid phase inlet 6, a liquid phase outlet 8, and a gas phase outlet 4; the reflux tank 103 includes a reflux tank inlet 5, an aqueous phase outlet 12, and an oil phase outlet 7.

[0090] The vapor outlet 3 at the top of the extraction distillation column 101 is connected to the vapor inlet 11 of the Venturi separator 102; the liquid outlet 8 of the Venturi separator 102 is connected to the side inlet 10 of the extraction distillation column 101; the vapor outlet 4 of the Venturi separator 102 is connected to the inlet 5 of the reflux tank 103; the aqueous outlet 12 of the reflux tank 103 is connected to the liquid inlet 6 of the Venturi separator 102; the oil outlet 7 of the reflux tank 103 forms the residual oil product outlet of the system; the condenser 104 is located between the vapor outlet 4 of the Venturi separator 102 and the inlet 5 of the reflux tank.

[0091] The Venturi separator 102 includes a vertically arranged liquid collection tube 16 and a Venturi tube 14 vertically arranged inside the liquid collection tube 16. The throat of the Venturi tube 14 is provided with a liquid inlet 6. The Venturi separator includes the Venturi tube 14, a vortex core tube 13, a delivery pipe 15, and the liquid collection tube 16. The gas outlet 4 of the Venturi separator 102 is located at the top of the liquid collection tube 16. The liquid inlet 6 of the Venturi separator 102 is connected to the throat of the Venturi tube 14 through the delivery pipe 15. The bottom inlet of the Venturi tube forms the gas inlet of the Venturi separator, and the gas outlet of the Venturi separator is connected to the top outlet of the Venturi tube. The Venturi tube 14 includes, from bottom to top, a constant diameter section, a narrowing diameter section, and an expanding diameter section connected sequentially. Pipeline 15 passes through the wall of liquid collection pipe 16 and connects to the reduced diameter section of Venturi tube 14, and is close to the throat of Venturi tube; the top of liquid collection pipe 16 is connected to open pipe 18, the top opening of open pipe 18 forms the gas phase outlet 4 of Venturi separator 102, the bottom opening of open pipe 18 extends downward into liquid collection pipe 16, and is spaced from the top opening 17 of the expanded diameter section of Venturi tube 14; the diameter of open pipe 18 is the same as the diameter of the top opening of the expanded diameter section; the angle between infusion pipeline 15 and Venturi tube 14 is 90°; vortex core tube 13 is vertically installed in the equal diameter section of Venturi tube, and the bottom inlet of vortex core tube 13 forms the gas phase inlet 11 of Venturi separator 102; there is one vortex core tube.

[0092] Aromatic feedstock enters extraction distillation column 101 through feedstock inlet 1, and solvent sulfolane enters extraction distillation column 101 through extraction solvent inlet 2. Aromatic feedstock and sulfolane are contacted in extraction distillation column 101 for aromatic extraction. The overhead gas phase of extraction distillation column 101 is discharged from overhead gas phase outlet 3, and after passing through the vortex core tube 13 of Venturi separator 102, forms an upward vortex gas phase, which enters Venturi tube 14. Aqueous phase from reflux tank 103 enters Venturi tube 14 through liquid delivery pipe 15. The vortex gas phase and washing... The washing liquid comes into contact with the gas phase and is washed to remove the solvent, resulting in a washed gas phase and a washing liquid phase containing solvent. The washing liquid phase containing solvent gradually accumulates on the outside of the vortex and is discharged from the bottom opening of the liquid phase collection pipe 16 and the bottom liquid phase outlet 8 under the action of gravity. The washed gas phase is discharged from the gas phase outlet 4, passes through the condenser 104, and enters the reflux tank 103 for processing. The residual oil is discharged from the oil phase outlet 7 of the reflux tank 103. The liquid phase discharged from the liquid phase outlet 8 is returned to the extraction distillation column 101 for recycling. The liquid phase removal rate at the top gas phase outlet of the Venturi separator 102 is 99.8%. The specific operating conditions of the extraction distillation system are shown in Table 1.

[0093] Using reformed oil C6-C7 fraction as feedstock, with an aromatic hydrocarbon mass fraction of 65%, the following process was employed: Figure 3 The extraction distillation system shown separates benzene and toluene from the feedstock using sulfolane as solvent at a solvent ratio of 4.3 and a reflux ratio of 0.3. The separation requirements are: the mass fraction of aromatics in the raffinate product should not exceed 0.2%, and the mass fraction of aromatics in the solvent-rich stream from the bottom of the column should be 99.9% after solvent removal. Specific operating conditions for the aromatics extraction column are shown in Table 1, and operating conditions for the Venturi separator are shown in Table 2.

[0094] Compared with Example 1, using this Venturi separator instead of the non-aromatic distillation column can save energy consumption of the reboiler in the bottom of the non-aromatic distillation column, thereby reducing the overall energy consumption of the process and reducing the floor space required.

[0095] Example 6

[0096] The method in this embodiment is the same as that in embodiment 5, except that the inlet gas velocity at the venturi tube inlet is 40 m / s, the absolute pressure of the washing liquid at the liquid phase injection port is 180 kPa, the liquid phase removal rate at the gas phase outlet at the top of the venturi separator 102 is 95%, the specific operating conditions of the aromatic extraction tower are shown in Table 1, and the operating conditions of the venturi separator are shown in Table 2.

[0097] Example 7

[0098] The extraction distillation system, operating method, and raw materials used in this embodiment are the same as those used in Example 3, except that the active layer of the extraction distillation column is different. In this embodiment, the gas-liquid contact mass transfer element of the active layer is a packed tray composite.

[0099] like Figure 2 The extraction distillation column shown has a gas-liquid contact mass transfer element in the active layer that is a packed tray composite, comprising a three-dimensional jet packed tray and Mellapak 250 structured packing. The separation requirements are: the mass fraction of benzene in the raffinate product does not exceed 0.1%, and the mass fraction of benzene in the solvent-rich stream at the bottom of the column after solvent removal is 99.9%.

[0100] use Figure 2 The extraction distillation column shown separates benzene and toluene from the raw material. The raw material, solvent, solvent ratio, reflux ratio and separation requirements are the same as in Example 3. The parameters and energy consumption of the extraction distillation column are shown in Table 1.

[0101] Comparative Example 1

[0102] In this comparative example, the raw materials, solvents, solvent ratios, reflux ratios, and separation requirements are the same as in Example 1. The difference from Example 1 is that the extraction distillation column uses conventional F1 floating valve trays to separate benzene and toluene from the raw materials. The parameters and energy consumption of the extraction distillation column are shown in Table 3.

[0103] Comparative Example 2

[0104] In this comparative example, the solvent, solvent ratio, reflux ratio, and separation requirements are the same as in Example 1. The difference is that the entire extraction distillation column uses Mellapak 250 structured packing to separate benzene and toluene from the feedstock used in Example 1. Due to the high liquid load in the middle and lower sections of the column, it is prone to flooding. The parameters of the column under normal operating conditions are shown in Table 3.

[0105] Comparative Example 3

[0106] In this comparative example, the solvent, solvent ratio, reflux ratio, and separation requirements are the same as in Example 1. The difference is that the extraction distillation column uses a three-dimensional jet tray to separate benzene and toluene from the raw material used in Example 1. The column parameters and energy consumption are shown in Table 3.

[0107] Comparative Example 4

[0108] In this comparative example, the solvent, solvent ratio, reflux ratio, and separation requirements are the same as in Example 3. The difference is that the extraction distillation column uses a conventional F1 floating valve column to separate benzene from the feedstock used in Example 3. The column parameters and energy consumption are shown in Table 3.

[0109] Comparative Example 5

[0110] In this comparative example, the solvent, solvent ratio, reflux ratio, and separation requirements are the same as in Example 3. The difference is that the extraction distillation column uses Mellapak 250 structured packing throughout to separate benzene from the feedstock used in Example 3. The column parameters and energy consumption are shown in Table 3.

[0111] Comparative Example 6

[0112] In this comparative example, the solvent, solvent ratio, reflux ratio, and separation requirements are the same as in Example 3. The difference is that the extraction distillation column uses a three-dimensional jet-type tray to separate benzene from the feedstock used in Example 3. The column parameters and energy consumption are shown in Table 3.

[0113] Table 1.

[0114]

[0115] Table 2.

[0116]

[0117] Table 3.

[0118]

[0119] Based on the data in Tables 1 and 2, by comparing Example 1 with Comparative Example 1, it can be seen that the separation efficiency of the floating valve trays in the packing layer and moving layer of the extraction distillation column in Comparative Example 1 is not as good as that of the structured packing and packing tray composite in Example 1. Therefore, the overall pressure drop of the extraction distillation column in Comparative Example 1 is larger and the energy consumption is higher.

[0120] By comparing Example 1 with Comparative Examples 1 and 2, it can be seen that due to the large L / V ratio in the middle and lower sections of the column, the separation efficiency using only packing material decreases significantly, resulting in a lower separation efficiency than that of ordinary floating valve trays. Therefore, the overall pressure drop of Comparative Example 2 is greater than that of Comparative Example 1, far exceeding that of Example 1, and its energy consumption is higher. Using the extraction distillation column of the present invention, the overall pressure drop of the column is lower, the bottom temperature is lower, and energy consumption is further reduced.

[0121] By comparing Example 1 with Comparative Example 3, it can be seen that, due to the lower separation efficiency of the floating valve trays in the upper and middle sections of the extraction distillation column compared to the structured packing and packed tray composite of this application, the overall pressure drop and energy consumption are higher in Comparative Example 3. Using the extraction distillation column of this application, the overall pressure drop and reboiler temperature are lower, further reducing energy consumption.

[0122] By comparing Example 3 with Comparative Examples 4-6, it can be seen that, compared with Example 3, the pressure drop of the entire extraction distillation column is larger and the energy consumption is higher when the entire column is equipped with F1 floating valve trays, Mellapak 250 structured packing, or three-dimensional jet-type trays, which further illustrates the superiority of this application in the extraction distillation separation of benzene. Using the extraction distillation column of this invention, the overall pressure drop of the column is lower and the bottom temperature is lower, further reducing energy consumption.

[0123] By comparing Example 1 with Example 4, it can be seen that within the theoretical number of levels of the packing layer, moving layer and tray layer of the present invention, the extraction distillation column of this application has a lower overall pressure drop and a lower bottom temperature, further reducing energy consumption.

[0124] By comparing Example 1 and Example 2, it can be seen that when the mass fraction of non-aromatic hydrocarbons in the raw material is less than 50%, if the gas-liquid contact mass transfer element of the active layer is selected as a packed tray composite, the overall pressure drop of the extraction distillation column is lower and the bottom temperature is lower compared with the selection of packing as the gas-liquid contact mass transfer element of the active layer, thus further reducing energy consumption.

[0125] By comparing Examples 3 and 7, it can be seen that when the mass fraction of aromatics in the raw material is less than 50% (i.e., the mass fraction of non-aromatics in the raw material is greater than 50%), if the gas-liquid contact mass transfer element of the active layer is selected as a packing material, compared with the case where the gas-liquid contact mass transfer element of the active layer is a packing tray composite, the overall pressure drop of the extraction distillation column is lower and the bottom temperature is lower, further reducing energy consumption.

[0126] Test Example 1

[0127] The raffinate products obtained in Examples 1, 5, and 6 were analyzed for their components. The composition of the raffinate was determined by analyzing the aromatic content and solvent content using the standard methods of ASTM D-6536 and GGBM-04-2005. The product composition is shown in Table 4.

[0128] Table 4

[0129]

[0130] According to the data in Table 4, a comparison of Examples 1 and 5 shows that in Example 5, after introducing the Venturi separator, the aqueous solvent recovered by the Venturi separator is recycled back to the extraction distillation column, increasing the water content of the extraction solvent in the column, improving solvent selectivity, increasing the non-aromatic content in the raffinate, and enhancing solvent removal efficiency. This further improves the quality and yield of aromatic products in the extract. Moreover, the Venturi separator has a small footprint and requires no additional heating, further reducing energy consumption. A comparison of Examples 5 and 6 shows that, within the range of the Venturi tube inlet gas velocity and the absolute pressure of the washing liquid at the liquid phase injection port, the liquid phase removal rate is higher, and the solvent content in the raffinate product is lower. Therefore, the extraction distillation column and Venturi separator of this invention produce a synergistic effect.

[0131] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0132] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0133] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. An extraction distillation column, characterized in that, The extraction distillation column comprises, from bottom to top, a tray layer, a movable layer, and a packing layer; the packing layer contains a gas-liquid contact mass transfer element referred to as the first packing; the movable layer contains a gas-liquid contact mass transfer element referred to as the second packing, or contains a packing-tray composite, wherein the packing-tray composite is a combination of a gas-liquid contact mass transfer element referred to as the third packing and a gas-liquid contact mass transfer element referred to as the first three-dimensional jet type tray; the tray layer contains a gas-liquid contact mass transfer element referred to as the second three-dimensional jet type tray, wherein the extraction distillation column further includes an extraction solvent inlet, a feed inlet, a top gas phase outlet, a bottom liquid phase outlet, and an optional side stream inlet, wherein the feed inlet is below the extraction solvent inlet, the packing layer is located above the extraction solvent inlet, the movable layer is located between the extraction solvent inlet and the feed inlet, and the tray layer is located below the feed inlet.

2. The extraction distillation column according to claim 1, characterized in that, The theoretical mass transfer order of the packing layer is 10%-25% of the theoretical mass transfer order of the entire tower, and / or the theoretical mass transfer order of the tray layer accounts for 30%-45% of the theoretical mass transfer order of the entire tower, and / or the theoretical mass transfer order of the active layer is 40%-60% of the theoretical mass transfer order of the entire tower.

3. The extraction distillation column according to any one of claims 1-2, characterized in that, The first packing is structured packing, which is selected from one or more of perforated plate corrugated packing, mesh corrugated packing, grid packing and corrugated ring packing; and / or the second three-dimensional spray type tower plate has an opening ratio of 5%-30%, an overflow weir height of 5mm-40mm, and a plate spacing of 400mm or more.

4. The extraction distillation column according to any one of claims 1-2, characterized in that, The extraction distillation column is used to separate aromatic and non-aromatic compounds from the raw material. When the mass fraction of non-aromatic compounds in the raw material is not less than 50%, the gas-liquid contact mass transfer element in the active layer is a structured packing called the second packing, which is selected from one or more of the following: perforated plate corrugated packing, mesh corrugated packing, grid packing and corrugated ring packing. When the mass fraction of non-aromatic compounds in the raw material is less than 50%, the gas-liquid contact mass transfer element in the active layer is a packed tray composite, wherein the opening ratio of the first three-dimensional spray type tray is 5%-30%, the overflow weir height is 5mm-40mm, and the tray spacing is more than 400mm; the third packing is structured packing.

5. The extraction distillation column according to claim 4, characterized in that, The third packing material is a perforated plate corrugated packing material.

6. An extraction distillation system, characterized in that, The extraction distillation system includes an extraction distillation column, a condenser, and a reflux tank according to any one of claims 1-5; the reflux tank includes a reflux tank inlet and an oil phase outlet; the top gas phase outlet of the extraction distillation column is connected to the reflux tank inlet through the condenser; the oil phase outlet of the reflux tank is formed as a raffinate product outlet.

7. The extraction distillation system according to claim 6, characterized in that, The extraction distillation system is used to separate aromatic and non-aromatic compounds from the raw material. The extraction distillation system also includes a non-aromatic separation device, which includes a gas phase inlet and a non-aromatic outlet. The gas phase inlet of the non-aromatic separation device is connected to the top gas phase outlet of the extraction distillation column, and the non-aromatic outlet of the non-aromatic separation device is connected to the inlet of the reflux tank through the condenser.

8. The extraction distillation system according to claim 7, characterized in that, The non-aromatic hydrocarbon separation device is a Venturi separator, which includes a gas phase inlet, a liquid phase inlet, a liquid phase outlet, and a gas phase outlet. The Venturi separator includes a Venturi tube and a liquid phase collection pipe surrounding at least a portion of the structure of the Venturi tube, with a liquid phase injection port located below the throat of the Venturi tube. The reflux tank also includes an aqueous phase outlet. The top gas phase outlet of the extraction distillation column is connected to the gas phase inlet of the Venturi separator. The liquid phase outlet of the Venturi separator is connected to the side inlet of the extraction distillation column, and the gas phase outlet of the Venturi separator is connected to the inlet of the reflux tank via the condenser. The aqueous phase outlet of the reflux tank is connected to the liquid phase inlet of the Venturi separator.

9. The extraction distillation system according to claim 8, characterized in that, The gas phase outlet of the Venturi separator is located at the top of the liquid phase collection tube; the liquid phase inlet of the Venturi separator is connected to the liquid phase injection port of the Venturi tube through a liquid delivery pipe; the bottom inlet of the Venturi tube is formed as the gas phase inlet of the Venturi separator or is connected to the gas phase inlet of the Venturi separator; and the gas phase outlet of the Venturi separator is connected to the top outlet of the Venturi tube.

10. The extraction distillation system according to claim 9, characterized in that, The Venturi tube comprises, from bottom to top, a constant diameter section, a narrowing section, a throat, and an expanding section. The infusion conduit passes through the wall of the liquid phase collection tube and connects to the liquid inlet of the Venturi tube. The top of the liquid phase collection tube is connected to an open pipe, the top opening of which forms the gas phase outlet of the Venturi separator. The bottom opening of the open pipe extends downward through the top of the liquid phase collection tube and into the liquid phase collection tube, and is spaced from the top opening of the expanding section of the Venturi tube.

11. The extraction distillation system according to claim 10, characterized in that, The Venturi separator also includes a vortex core tube, the inside of which is provided with a spiral guide vane. The vortex core tube is located at the inlet of the reduced diameter section of the Venturi tube or in the equal diameter section of the Venturi tube, and the bottom inlet of the vortex core tube forms the gas phase inlet of the Venturi separator or is connected to the gas phase inlet of the Venturi separator.

12. The extraction distillation system according to claim 10, characterized in that, The Venturi tube has structures on its inner walls at the constant diameter section, narrow diameter section, throat, and wide diameter section that guide the spiral upward flow of gas.

13. The extraction distillation system according to claim 7, characterized in that, The non-aromatic hydrocarbon separation device is selected from a non-aromatic hydrocarbon distillation column or a Venturi separator.

14. The extraction distillation system according to claim 10, characterized in that, The diameter of the open pipe is greater than or equal to the diameter of the top opening of the expanded section.

15. The extraction distillation system according to claim 12, characterized in that, The structure is selected from swirl blades.

16. An extraction distillation method using the extraction distillation system according to any one of claims 6-15.

17. The extraction distillation method according to claim 16, characterized in that, The extraction distillation method uses the extraction distillation system and includes the following steps: the raw material is introduced into the extraction distillation column and brought into contact with the extraction solvent to perform extraction distillation, and a solvent-rich material is obtained in the column bottom; the vapor phase at the top of the column is cooled and then enters the reflux tank.

18. The extraction distillation method according to claim 17, characterized in that, The extraction distillation system includes a Venturi separator, and the extraction distillation method further includes the following steps: allowing the gas phase from the top of the extraction distillation column to enter the Venturi separator, contact with the washing liquid, and perform washing and removal treatment to obtain a washed gas phase and a washing liquid phase containing solvent.

19. The extraction distillation method according to claim 18, characterized in that, The washing liquid is selected from washing water, and the washing liquid phase is returned to the extraction distillation column for recycling. The washed gas phase is condensed and then enters the reflux tank for separation to obtain the raffinate oil product and the aqueous phase. The aqueous phase is returned to the Venturi separator as washing liquid.

20. The extraction distillation method according to claim 19, characterized in that, In the Venturi separator, the mass flow rate ratio of the washing liquid to the gas phase at the top of the extraction distillation column is (0.2-1.0):1; and / or, the inlet gas velocity of the Venturi separator is 1 m / s-30 m / s; and / or, the absolute pressure of the washing liquid at the liquid phase injection port is 180 kPa-1500 kPa.

21. The extraction distillation method according to claim 17, characterized in that, The bottom temperature of the extraction distillation column is 120℃-180℃, and the overall pressure drop is 40kPa-65kPa; and / or, the temperature of the gas phase at the top of the column is 80℃-130℃, and the pressure at the top of the column is 0.1MPa-0.5MPa; and / or, the solvent ratio is 1-6:

1.

22. The extraction distillation method according to claim 17, characterized in that, The raw material is an aromatic hydrocarbon-containing raw material or a ketol oil.

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