Extractive distillation tower, extractive distillation system comprising extractive distillation tower, and extractive distillation method

Abstract

The invention relates to an extractive distillation tower. The extractive distillation tower, from bottom to top, sequentially comprises a tower tray layer, an active layer, and a packing material layer; the packing material layer comprises a gas-liquid contact mass transfer element hereinafter called the first packing material; the active layer comprises a gas-liquid contact mass transfer element hereinafter called the second packing material, or comprises a packing material / tower tray composite body, said body being a gas-liquid contact mass transfer element hereinafter called the third packing material and a gas-liquid contact mass transfer element composite body hereinafter called the first 3D jet tower tray; the tower tray layer comprises a gas-liquid contact mass transfer element hereinafter called the second 3D jet tower tray; the extractive distillation tower further comprises an extraction solvent inlet, a raw material inlet, a tower top gas phase outlet, a tower bottom liquid phase outlet and an optional side stream inlet; the packing material layer is located above the extraction solvent inlet; the active layer is located between the extraction solvent inlet and the raw material inlet; and the tower tray layer is located below the raw material inlet. The present invention further relates to an extractive distillation system comprising the extractive distillation tower and an extractive distillation method using the extractive distillation system.

Description

Extractive distillation tower, extractive distillation system including the extractive distillation tower, and extractive distillation method Technical Field

[0001] The present invention relates to the field of petrochemical aromatics separation, and in particular to an extractive distillation tower, an extractive distillation system and a method. Background Art

[0002] Distillation is a conventional separation unit operation and also a high energy consumption link in the petrochemical field. Driven by the "dual carbon" goal, reducing the energy consumption of the distillation process is a research direction that has attracted much attention. The reason for the high energy consumption is that it is difficult to balance the contradiction between the separation efficiency, pressure drop, and operational flexibility of the mass transfer elements in the gas-liquid contact in the tower. Extractive distillation is a special type of distillation process that is widely used in the separation process of aromatics and a variety of fine chemicals. Since the mass ratio of solvent to raw material (referred to as solvent ratio) is usually not less than 1, and the solvent has a high boiling point and is not easy to vaporize, the liquid phase load in the extractive distillation tower is significantly increased compared with conventional distillation towers, and the liquid-gas ratio at different positions in the tower varies greatly. At present, extractive distillation towers generally use tower plates such as float valves and inclined holes as gas-liquid mass transfer elements, which have problems such as low plate efficiency and easy flooding.

[0003] Wu Jimin et al. (“Application of New Packing Tower Technology in Cyclohexene-Cyclohexane Extraction and Distillation Tower”, Chemical Industry and Engineering Progress, 2004, 23(8): 880-882) attempted to use a structured packing tower to achieve cyclohexane-cyclohexene-benzene extraction and distillation. The original design used Mellapak250 structured packing. As the processing volume increased, the packing efficiency dropped sharply and reached the flooding limit. After replacing it with the structured packing produced by Tianda Tianjiu, it was still necessary to add another tower in series to meet the separation requirements.

[0004] Chinese patent CN1477092A discloses an acrylic acid purification distillation tower with a large-pore sieve plate in the lower section and a parallel-current jet plate in the upper section. By changing the internal components of the tower, the polymerization tendency of acrylic acid is reduced and the loss is reduced. Chinese patent CN100465147C discloses a distillation tower for separating acrolein from 3-hydroxypropionaldehyde. The upper section of the distillation section adopts a new vertical sieve plate, the lower section adopts a jet packing plate, and the stripping section adopts a structured packing, which can effectively reduce the polymerization tendency of acrolein and thus reduce the loss. Chinese patent CN1194878A discloses a hollow composite packing plate for use in ordinary distillation processes. A layer of structured packing is placed in the space below the plate to achieve high throughput and high flexibility in the operation of the distillation tower. However, the combination method of these mass transfer elements is not suitable for extractive distillation towers, and cannot improve the separation efficiency of the extractive distillation tower or reduce the pressure drop of the entire tower.

[0005] Summary of the Invention

[0006] One of the objects of the present invention is to provide an extractive distillation tower having high separation efficiency, which can effectively reduce the pressure drop across the tower and the tower bottom temperature, thereby further reducing energy consumption; or, under the condition that the tower diameter remains unchanged, further increase the raw material processing capacity, which is conducive to capacity expansion and transformation; the extractive distillation tower of the present invention has improved anti-clogging and defoaming capabilities, effectively reducing the risk of flooding.

[0007] To achieve the above objectives, according to a first aspect of the present invention, there is provided an extractive distillation column, comprising, from bottom to top, a tray layer, a movable layer, and a packing layer; the packing layer comprises gas-liquid contact mass transfer elements referred to as first packing; the movable layer comprises gas-liquid contact mass transfer elements referred to as second packing, or comprises a packing tray complex, wherein the packing tray complex is a complex of gas-liquid contact mass transfer elements referred to as third packing and gas-liquid contact mass transfer elements referred to as first stereoscopic jet-type trays; the tray layer comprises gas-liquid contact mass transfer elements referred to as second stereoscopic jet-type trays, wherein the extractive distillation column further comprises an extractive solvent inlet, a feed inlet, a top gas phase outlet, a bottom liquid phase outlet, and an optional side inlet, wherein the feed inlet is below the extractive solvent inlet, the packing layer is located above the extractive solvent inlet, the movable layer is located between the extractive 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, which is called a "first packing"; the gas-liquid contact mass transfer element contained in the active layer is a packing, which is called a "second packing", or is a packing tower plate complex, and the packing tower plate complex contains a packing called a "third packing" and a three-dimensional spray-type tower plate called a "first three-dimensional spray-type tower plate" or is composed of them; the gas-liquid contact mass transfer element contained in the tower plate layer is a three-dimensional spray-type tower plate, which is called a "second three-dimensional spray-type tower plate".

[0008] According to a second aspect of the present invention, the present invention provides an extractive distillation system, which includes an extractive distillation tower according to the first aspect, a condenser and a reflux drum, wherein the extractive distillation tower includes a tower top gas phase outlet, a side line inlet, an extraction solvent inlet, a raw material inlet and a tower bottom liquid phase outlet, wherein the extractive distillation tower is the extractive distillation tower according to the first aspect of the present invention; the reflux drum includes a reflux drum inlet and an oil phase outlet; the tower top gas phase outlet of the extractive distillation tower is connected to the reflux drum inlet through the condenser; and the oil phase outlet of the reflux drum is formed as a raffinate oil product outlet.

[0009] According to a third aspect of the present invention, the present invention provides an extractive distillation method using the extractive distillation column according to the first aspect and the extractive distillation system according to the second aspect.

[0010] The technical solution of the present invention creatively designs gas-liquid mass transfer elements in sections, tailored to the gas-liquid mass transfer characteristics and load variations within each section of the tower, to achieve energy savings and cost reductions. The extractive distillation tower of the present invention boasts high separation efficiency, effectively reducing overall tower pressure drop and bottom temperature, further reducing energy consumption. Alternatively, while maintaining a constant tower diameter, it allows for increased raw material throughput, facilitating capacity expansion and renovation. The extractive distillation tower of the present invention also exhibits strong anti-clogging and defoaming capabilities, effectively reducing the risk of flooding.

[0011] Other features and advantages of the present invention will be described in detail with reference to the accompanying drawings and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following detailed description, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0013] FIG1 shows a schematic diagram of an extractive distillation column and an extractive distillation system in Example 1 of the present invention.

[0014] FIG2 shows a schematic diagram of the extractive distillation column in Example 2 of the present invention.

[0015] FIG3 shows a schematic diagram of the extractive distillation column and the extractive distillation system in Example 3 of the present invention.

[0016] FIG4 shows a schematic diagram of the extractive distillation system in Example 5 of the present invention.

[0017] FIG5 shows a schematic structural diagram of the Venturi separator used in Example 5 of the present invention.

[0018] Description of Reference Numerals

[0019] 101: Extractive distillation column; 102: Venturi separator; 103: Reflux drum; 104: Condenser; 105: Non-aromatic distillation column; 106: Air riser; 107: Liquid extraction pipe; 108: Sieve plate; 109: Downcomer; 110: Third packing; 111: First packing; 112: Three-dimensional jet tray; 113: Second packing;

[0020] 1: Raw material inlet; 2: Extraction solvent inlet; 3: Gas phase outlet at the top of the tower; 4: Gas phase outlet; 5: Reflux tank inlet; 6: Liquid phase inlet; 7: Oil phase outlet; 8: Liquid phase outlet; 9: Liquid phase outlet at the bottom of the tower; 10: Side line inlet; 11: Gas phase inlet; 12: Water phase outlet;

[0021] 13: vortex core tube; 14: Venturi tube; 15: liquid delivery pipe; 16: liquid collection tube; 17: top opening of the expanded section; 18: open tube;

[0022] 19: Non-aromatic hydrocarbon outlet; 20: Oil phase inlet; 21: First oil phase outlet; 22: Second oil phase outlet; 23: Solvent outlet. DETAILED DESCRIPTION

[0023] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0024] Any specific numerical value disclosed in this specification (including the endpoints of a numerical range) is not limited to the exact value of the numerical value, but should be understood to also include values ​​close to the exact value, such as all possible values ​​within the range of ±5% of the exact value. Moreover, for a disclosed numerical range, the values ​​between the endpoints of the range, between the endpoints and the specific points in the range, and between the specific points can be arbitrarily combined to form one or more new numerical ranges, and these new numerical ranges should also be considered to be specifically disclosed in this specification.

[0025] Unless otherwise specified, the terms used in this specification have the same meanings as commonly understood by those skilled in the art. If a term is defined in this specification and its definition is different from the common understanding in the art, the definition in this document shall prevail.

[0026] In this application, except for the contents explicitly stated, any matters or items not mentioned are directly applicable to those known in the art without any changes. Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the technical solutions or technical ideas formed thereby are considered part of the original disclosure or original description of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless a person skilled in the art considers that the combination is obviously unreasonable.

[0027] Unless explicitly stated otherwise, throughout the specification and claims, the term “comprise” or its synonyms such as “comprising” or “containing”, etc., will be understood to include stated elements or components but not to exclude other elements or components.

[0028] In the present invention, unless otherwise specified, it should be understood that expressions such as “length”, “angle”, “above”, “below”, “vertical”, “upright”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “tangential”, “front”, “back”, “left”, and “right” indicate directions or positional relationships. These directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate that the device or component must have a specific direction, be constructed and operate in a specific direction, and therefore should not be understood as limiting the present invention.

[0029] In the present specification, unless otherwise specified or limited, the terms "disposed," "connected," "connected," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed or detachable connections, or integration; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0030] According to a first aspect of the present invention, there is provided an extractive distillation tower, comprising, from bottom to top, a tray layer, a movable layer, and a packing layer; the gas-liquid contact mass transfer elements contained in the packing layer are packing, referred to as first packing; the gas-liquid contact mass transfer elements contained in the movable layer are packing, referred to as second packing, or are a packing tray complex, wherein the packing tray complex is a complex of packing, referred to as third packing, and a three-dimensional spray-type tray, referred to as a first three-dimensional spray-type tray; the gas-liquid contact mass transfer elements contained in the tray layer are three-dimensional spray-type trays, referred to as second three-dimensional spray-type trays; wherein the extractive distillation tower further comprises an extractive solvent inlet, a feed inlet, a top gas phase outlet, a bottom liquid phase outlet, and an optional side inlet, wherein the feed inlet is below the extractive solvent inlet, and the packing layer is located above the extractive solvent inlet; the movable layer is located between the extractive solvent inlet and the feed inlet; and the tray layer is located below the feed inlet.

[0031] For illustration, in the present application, the expression "active layer" is intended to mean that the gas-liquid contacting and mass transfer elements of this layer in the extractive distillation column can be changed according to the composition of the feedstock, for example, changing from packing to a packed tray complex or from a packed tray complex to packing, while the gas-liquid contacting and mass transfer elements of other layers remain unchanged.

[0032] According to an embodiment of the first aspect above, the theoretical mass transfer stages of the packing layer account for 10%-25% of the theoretical mass transfer stages of the entire tower, and the first packing is a structured packing. Preferably, the structured packing is selected from one or more of a perforated plate corrugated packing, a mesh corrugated packing, a plate mesh corrugated packing, a grid packing and a corrugated ring packing.

[0033] According to an embodiment of the first aspect above, the theoretical mass transfer stages of the tower plate layer account for 30%-45% of the theoretical mass transfer stages of the entire tower. Preferably, the opening rate of the second three-dimensional spray-type tower plate is 5%-30%, the overflow weir height is 5mm-40mm, and the plate spacing is 400mm or more.

[0034] According to an embodiment of the first aspect above, the theoretical number of mass transfer stages of the active layer accounts for 40%-60%, preferably 45%-55%, of the theoretical number of mass transfer stages of the entire tower. This is beneficial to improving the separation efficiency of the extractive distillation tower, effectively reducing the pressure drop of the entire tower and the bottom temperature, and further reducing energy consumption. Under the condition that the tower diameter remains unchanged, the processing capacity of raw materials is increased, which is conducive to capacity expansion and transformation.

[0035] According to an embodiment of the first aspect above, the extractive distillation tower is used to separate aromatic compounds and non-aromatic compounds in the raw material. When the mass fraction of the 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 a second packing); preferably, the structured packing is selected from one or more of a perforated plate corrugated packing, a mesh corrugated packing, a plate mesh corrugated packing, a grid packing and a corrugated ring packing; this embodiment is conducive to improving the separation efficiency of the extractive distillation tower, effectively reducing the pressure drop of the entire tower and the tower bottom temperature, and further reducing energy consumption; under the condition that the tower diameter remains unchanged, the raw material processing capacity is increased, which is conducive to capacity expansion and transformation. When the mass fraction of non-aromatic compounds in the raw material is lower than 50%, the gas-liquid contact mass transfer element of the active layer is a packed tray complex, which includes regular packing (called the third packing) and a three-dimensional jet-type tray (called the first three-dimensional jet-type tray). Preferably, the opening rate of the first three-dimensional jet-type tray is 5%-30%, the overflow weir height is 5mm-40mm, and the plate spacing is more than 400mm; the third packing is preferably a perforated corrugated packing; this embodiment is conducive to improving the separation efficiency of the extractive distillation tower, effectively reducing the pressure drop of the entire tower and the tower bottom temperature, and further reducing energy consumption; under the condition that the tower diameter remains unchanged, the raw material processing capacity is increased, which is conducive to capacity expansion and transformation.

[0036] Conventional extractive distillation towers generally adhere to the constant molar flow assumption in both the rectifying and stripping sections. Within extractive distillation towers, because the solvent is essentially nonvolatile and the solvent ratio is typically not less than 1, substances in the feedstock that strongly bind to the solvent gradually enter the solvent (liquid phase), causing the liquid phase molar flow ratio to increase from top to bottom while the ascending gas phase gradually decreases. The inventors of the present invention surprisingly discovered through research that the gas-liquid loads and gas-liquid compositions at different locations within an extractive distillation tower exhibit unique characteristics. By optimizing the design and assembly of tower components based on these characteristics, the shortcomings of prior art distillation towers, particularly extractive distillation towers, can be overcome. 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 extractive distillation column along with the extractive solvent, the additive content above the extractive solvent inlet is zero. The use of packing in this section of the mass transfer elements improves the separation efficiency of the extractive distillation column and reduces the pressure drop across the column, while also eliminating the risk of packing contamination and clogging. Between the extraction solvent inlet and the feedstock inlet, varying levels of extractable substances in the feedstock can result in a higher L / V ratio in this section than between the top of the extractive distillation column and the extraction solvent inlet. In this case, using packing or a composite structure of packed trays for the gas-liquid mass transfer elements can help improve separation efficiency and increase throughput. Below the feedstock inlet, both L and V values ​​increase further, slightly improving L / V. The use of three-dimensional jet trays in the mass transfer elements increases operational flexibility, allowing the liquid phase to fall back onto the trays as a clear liquid, effectively preventing flooding.

[0037] According to one embodiment of the present invention, the theoretical mass transfer number of the packing layer is 10%-25% of the theoretical mass transfer number of the whole tower, the first packing is a structured packing, and the structured packing is selected from one or more of a perforated plate corrugated packing, a mesh corrugated packing, a plate mesh corrugated packing, a grid packing and a wave ring packing; the theoretical mass transfer number of the tower plate layer accounts for 30%-45% of the theoretical mass transfer number of the whole tower, the opening rate of the second three-dimensional jet-type tower plate is 5%-30%, the overflow weir height is 5mm-40mm, and the plate spacing is 400mm or more. The above embodiment is conducive to improving the separation efficiency of the extractive distillation tower, effectively reducing the pressure drop of the whole tower and the tower bottom temperature, and further reducing energy consumption; under the condition that the tower diameter remains unchanged, the processing capacity of raw materials is increased, which is conducive to capacity expansion and transformation; the anti-blocking and defoaming capabilities of the extractive distillation tower are improved, and the risk of flooding is reduced.

[0038] According to a second aspect of the present invention, the present invention provides an extractive distillation system, comprising an extractive distillation tower, a condenser, and a reflux drum, wherein the extractive distillation tower comprises a tower top gas phase outlet, a side line inlet, an extractive solvent inlet, a feed inlet, and a tower bottom liquid phase outlet, wherein the extractive distillation tower is the extractive distillation tower described in the first aspect of the present invention; the reflux drum comprises a reflux drum inlet and an oil phase outlet; the tower top gas phase outlet of the extractive distillation tower is connected to the reflux drum inlet via the condenser; the oil phase outlet of the reflux drum is formed as a raffinate oil product outlet; and the tower bottom liquid phase outlet of the extractive distillation tower is formed as a rich solvent outlet. The term "rich solvent" refers to the extractive solvent that has undergone the extraction process in the extractive distillation tower and is enriched in extracts.

[0039] According to one embodiment of the second aspect, the extractive distillation tower is used to separate aromatic compounds and non-aromatic compounds from the feedstock, and the extractive distillation system further includes a non-aromatic separation device, the non-aromatic separation device including a vapor phase inlet and a non-aromatic outlet; the vapor phase inlet of the non-aromatic separation device is connected to the vapor phase outlet at the top of the extractive distillation tower, and the non-aromatic outlet of the non-aromatic separation device is connected to the reflux drum inlet via the condenser. Preferably, the non-aromatic separation device is a non-aromatic distillation tower or a Venturi separator.

[0040] According to a preferred embodiment, the non-aromatic hydrocarbon separation device is a non-aromatic hydrocarbon distillation tower, wherein the non-aromatic hydrocarbon distillation tower further includes an oil phase inlet and a solvent outlet; the solvent outlet is connected to the upper part of the extractive distillation tower, and returns the distilled extractive solvent to the extractive distillation tower; 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 tower, and the first oil phase outlet is used to return part of the non-aromatic hydrocarbons in the reflux tank to the non-aromatic hydrocarbon distillation tower for circulation; the second oil phase outlet is used to discharge the remaining non-aromatic hydrocarbons in the reflux tank from the reflux tank.

[0041] According to a preferred embodiment, the non-aromatic hydrocarbon separation device is a Venturi separator, wherein the Venturi separator includes a liquid phase collection pipe and a Venturi tube disposed within the liquid phase collection pipe, wherein the Venturi tube includes the following sections connected in sequence: an optional constant diameter section, a reduced diameter section, a throat, and an expanded diameter section, wherein 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), wherein an opening leading to the liquid phase collection pipe is provided on the side wall of the expanded diameter section of the Venturi tube or at the end of the expanded diameter section, so that the liquid phase leaves the Venturi tube and enters the liquid phase collection pipe under the action of centrifugal force. The gas phase outlet at the top of the extractive 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 line inlet of the extractive distillation column, and the gas phase outlet of the Venturi separator is connected to the reflux drum inlet through the condenser. Preferably, the reflux tank further comprises a water phase outlet, and preferably the water phase outlet of the reflux tank is communicated with the liquid phase inlet of the venturi separator.

[0042] According to a preferred embodiment, the Venturi separator is positioned upright, wherein the Venturi tube comprises, from bottom to top, an optional, interconnected constant diameter section, a reduced diameter section, a throat, and an expanded diameter section. A liquid phase injection port is provided on the tube wall of the reduced diameter section of the Venturi tube. Specifically, the liquid phase input from the liquid phase inlet of the Venturi separator is injected into the Venturi tube in the reduced diameter section, where it comes into contact and mixes with the gas spirally ascending in the Venturi tube. Because the gas flows at high speed in the reduced diameter section of the Venturi tube in a spiral manner, the angular velocity of the spirally ascending gas increases as the diameter of the reduced diameter section decreases. Therefore, when the liquid phase is injected into the Venturi tube in the reduced diameter section, it flows and mixes with the spirally ascending gas, causing increasingly intense liquid disturbance and more complete gas-liquid mixing. This results in faster and more complete mass transfer between the gas and liquid, and a better separation effect. The liquid phase injection port on the wall of the venturi tube can be at any position of the reduced diameter section. Preferably, the distance between the position of the liquid phase injection port and the throat is 1 / 10-2 / 3 of the length of the reduced diameter section. More preferably, the distance between the position of the liquid phase injection port and the throat is 1 / 8-1 / 2 of the length of the reduced diameter section.

[0043] 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 to accelerate the mixing of the gas and liquid. The injection flow rate and speed of the liquid phase can be adjusted by those skilled in the art according to actual needs and the gas flow rate and flow rate. The injection direction of the nozzle can be in 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 at an angle of less than 60°, more preferably at an angle of less than 30°, for example, at an angle of less than 15°, and more preferably in the same direction as the gas flow direction.

[0044] According to a preferred embodiment, the liquid phase collection pipe surrounds at least a portion of the Venturi tube's structure on its periphery, for example, at least the sidewall of the expanded diameter section of the Venturi tube or the opening at the end of the expanded diameter section. The liquid phase collection pipe extends downward, encompassing the expanded diameter section of the Venturi tube, and may even encompass the throat and reduced diameter section, or even the entire Venturi tube. Preferably, the Venturi separator comprises a vertically disposed liquid phase collection pipe and a Venturi tube disposed vertically within the liquid phase collection pipe. If the liquid phase collection pipe surrounds the entire venturi tube, then the liquid infusion pipe for conveying the liquid phase connected to the liquid phase injection port on the wall of the venturi tube needs to pass through the liquid phase collection pipe wall. At this time, the liquid phase inlet of the venturi separator is connected to the liquid phase injection port on the wall of the venturi tube via the liquid infusion pipe passing through the liquid phase collection pipe wall, wherein the angle between the liquid infusion pipe and the conical busbar of the reduced diameter section of the venturi tube located below the liquid infusion pipe can be 10-90°, preferably 30-80°, for example 40°, 50°, 60° or 70°.

[0045] According to a preferred embodiment, the top of the liquid phase collecting pipe is closed, but an open pipe is provided for discharging the gas phase of the venturi separator, the upper end outlet of the open pipe forms the gas phase outlet of the venturi separator, and the open pipe passes downward through the top of the liquid phase collecting pipe and extends to the end of the expanded diameter section of the venturi tube, and is optionally connected to the end of the expanded diameter section of the venturi tube. If an opening for the liquid phase to exit the Venturi tube is provided on the sidewall of the expanded section of the Venturi tube, the open tube is connected to the end of the expanded section of the Venturi tube, and optionally, an opening is further provided between the lower end of the open tube and the end of the expanded section of the Venturi tube to allow liquid that has not been completely discharged from the opening in the expanded section to be completely discharged therefrom. If the opening for the liquid phase to exit the Venturi tube is provided at the end of the expanded section of the Venturi tube, the lower end of the open tube is completely or partially separated from the end of the expanded section of the Venturi tube to form an opening for the liquid phase to exit the Venturi tube. In this case, the opening is a continuous or discontinuous annular opening, and the height of the opening can be adjusted by raising or lowering the open tube. The height of the opening can be varied within a certain range depending on the liquid phase flow rate, as long as it allows substantially all of the liquid phase to exit the Venturi tube under the action of centrifugal force and enter the liquid phase collection tube, while preventing a significant amount of gas from entering the liquid phase collection tube. For example, the height of the opening is less than 10 centimeters, such as less than 5 centimeters.

[0046] According to a preferred embodiment, the diameter of the open tube can be slightly larger than the diameter of the end opening of the expanded section, for example, the diameter of the open tube is less than 5% larger than the diameter of the end opening of the expanded section. Preferably, the diameter of the open tube is the same as the diameter of the end opening of the expanded section.

[0047] According to a preferred embodiment, the Venturi separator further includes a device for causing gas to enter the Venturi tube in a spiral flow pattern, or a device for causing gas to enter the Venturi tube tangentially, so that the gas flows upward in a spiral pattern within the Venturi tube. The device is positioned at the entrance of the reduced diameter section of the Venturi tube, or within the constant diameter section of the Venturi tube. The device for causing gas to generate a spiral flow within the Venturi tube can be a device commonly used in the art, such as a vortex core tube.

[0048] According to a preferred embodiment, the device for making the gas flow in a spiral manner in the venturi tube is a vortex core tube, and a spiral guide plate is provided inside the vortex core tube. The vortex core tube is vertically arranged at the entrance of the reduced diameter 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 is formed as the gas phase inlet of the venturi separator.

[0049] According to a preferred embodiment, the number of vortex core tubes can be selected based on actual needs (such as gas flow rate, etc.), and can be one or more. If multiple vortex core tubes are used, the multiple vortex core tubes can be arranged in parallel, so that the vortex shearing of the vortex core tubes enhances the mixing of the overhead gas phase and the solvent (such as water), thereby improving the solvent removal effect and further ensuring that the solvent content in the raffinate oil product does not exceed 2 μg / g.

[0050] According to a preferred embodiment, the diameter of the liquid phase collection pipe is larger than the maximum diameter of the venturi tube disposed therein. Those skilled in the art may select a diameter based on actual needs and site conditions. Preferably, the diameter of the liquid phase collection pipe is 30% larger than the maximum diameter of the venturi tube disposed therein, preferably 20% larger, for example 10% or 5% larger.

[0051] According to a preferred embodiment, a structure (thread structure) for guiding the spiral upward flow of gas is provided on the inner wall of the optional equal diameter section, reduced diameter section, throat and expanded diameter section of the venturi tube, so that the gas flow or gas-liquid flow can flow spirally upward or downward along the inner wall of the venturi tube. The structure can be selected from swirl blades or spiral guide vanes, which can increase the tangential velocity of the fluid, avoid the wall effect of the fluid, strengthen the contact between the gas and the liquid, and further improve the separation efficiency of the venturi separator. The spiral rise angle of the swirl blades or spiral guide vanes is It can be selected by those skilled in the art according to actual conditions and adjusted according to changes in the diameter of the Venturi tube.

[0052] According to a preferred embodiment, the swirl blade or spiral guide vane can be a single or multi-start thread structure with a number of thread starts n (n is a positive integer greater than or equal to 1). If the swirl blade or spiral 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), due to the helical angle of the multi-start thread structure Approximately the helix angle of a single-start thread structure Therefore, the multi-thread structure can better guide the fluid on the inner wall of the Venturi tube and significantly reduce the pressure loss of the Venturi separator.

[0053] According to a preferred embodiment, in the Venturi separator, the volume flow rate ratio of the gas phase to the liquid phase can vary in a wide range, for example, 70-2500:1, preferably 200-1100:1; the inlet gas velocity of the Venturi separator is 1m / s-40m / s, preferably 5m / s-35m / s; the pressure loss of the Venturi separator is less than 20kPa, for example, 0.1kPa-10kPa, preferably 0.2kPa-5kPa; the absolute pressure of the liquid phase at the liquid phase injection port is above 170kPa, preferably 180kPa-1500kPa, and preferably 250-1000kPa.

[0054] According to a preferred embodiment, in the Venturi separator, the bottom of the liquid phase collecting tube is connected to the liquid phase outlet of the Venturi separator through a liquid discharge pipe, wherein a liquid seal is provided at the bottom of the liquid phase collecting tube to prevent the gas in the Venturi separator from entering the liquid discharge pipe.

[0055] According to a third aspect of the present invention, the present invention provides an extractive distillation method using the extractive distillation column according to the first aspect of the present invention or the extractive distillation system according to the second aspect.

[0056] According to an embodiment of the third aspect above, if the extractive distillation method uses the above-mentioned extractive distillation system, then the method also includes the following steps: allowing the raw material to enter the extractive distillation tower to contact with the extractive solvent, performing extractive distillation, and obtaining a rich solvent in the bottom of the tower; and allowing the top gas phase to enter the reflux tank after cooling.

[0057] According to a preferred embodiment, if the extractive distillation method uses the above-mentioned extractive distillation system including a venturi separator, then the extractive distillation method further includes the following steps: allowing the gas phase at the top of the extractive distillation tower to enter the venturi separator and contact with the washing liquid to wash and remove the extraction solvent in the gas phase to obtain a washed gas phase and a washing liquid phase containing the extraction solvent; returning the washing liquid phase to the extractive distillation tower for recycling, condensing the washed gas phase and entering the reflux tank for separation to obtain a raffinate oil product and an aqueous phase, and returning the aqueous phase to the venturi separator as a washing liquid.

[0058] According to an embodiment of the third aspect above, the extractive distillation method is used to separate aromatic hydrocarbons from non-aromatic hydrocarbons.

[0059] According to one embodiment of the third aspect above, the washing liquid is an aqueous solution, more preferably water.

[0060] According to one embodiment of the third aspect, the extractive distillation tower has a bottom temperature of 120°C-180°C, a full-tower pressure drop of 40 kPa-65 kPa, and / or an overhead gas phase temperature of 80°C-130°C, a top pressure of 0.1 MPa-0.5 MPa, and a solvent ratio of 1-6:1. This embodiment improves solvent removal, ensuring that the solvent content in the raffinate oil product does not exceed 2 μg / g.

[0061] According to one embodiment of the third aspect, in the packing layer of the extractive distillation tower, the mass flow rate ratio of the liquid phase to the ascending gas phase in the extractive distillation tower is 0.1-1:1, preferably 0.1-0.5:1; and / or, in the active layer of the extractive distillation tower, the mass flow rate ratio of the liquid phase to the ascending gas phase in the extractive distillation tower is 3-9:1, preferably 5-7:1; and / or, in the tray layer of the extractive distillation tower, the mass flow rate ratio of the liquid phase to the ascending gas phase in the extractive distillation tower is 5-12:1, preferably 7-10:1.

[0062] According to one embodiment of the present invention, the inlet gas velocity of the venturi separator is 1m / s-30m / s, preferably 5m / s-27m / s; the pressure loss of the venturi separator is 0.2kPa-5kPa, preferably 1kPa-3kPa; the absolute pressure of the washing liquid at the liquid phase injection port is 180kPa-1500kPa; in the venturi separator, the mass flow rate ratio of the washing liquid to the top gas phase is (0.2-1.0):1, preferably (0.3-0.5):1. In the present invention, the inlet gas velocity of the venturi separator refers to the inlet gas velocity of the top gas phase entering the reduced diameter section of the venturi tube. The above embodiment is conducive to improving the removal effect of the solvent, so that the solvent content in the raffinate oil product does not exceed 2μg / g.

[0063] According to one embodiment of the present invention, the venturi separator has a liquid phase removal rate of 82% or greater, preferably 90% to 99.9%, and a liquid phase separation accuracy of 1 μm to 10 μm. The liquid phase removal rate is calculated as follows: the weight of the liquid phase entering the liquid phase collection tube divided by the total weight of the liquid phase injected into the venturi tube. This embodiment improves solvent removal, ensuring that the solvent content in the raffinate oil product does not exceed 2 μg / g.

[0064] According to one embodiment, the raw material is an aromatic hydrocarbon-containing raw material or a ketone-alcohol oil.

[0065] According to a preferred embodiment of the third aspect above, the extractive distillation system includes a venturi separator, wherein the top gas phase outlet of the extractive distillation tower is connected to the gas phase inlet of the venturi separator; the liquid phase outlet of the venturi separator is connected to the side line inlet of the extractive distillation tower, and the gas phase outlet of the venturi separator is connected to the reflux tank inlet through the condenser; the water phase outlet of the reflux tank is connected to the liquid phase inlet of the venturi separator. The above-mentioned embodiment introduces a Venturi separator into the extractive distillation system, so that the trace extraction solvent in the top gas phase is washed with water in the Venturi separator and then returned to the extractive distillation tower, and the remaining gas phase enters the reflux tank after condensation, and the oil phase in the reflux tank is produced as the raffinate oil product; since the trace extraction solvent containing water is returned to the extractive distillation tower, this improves the selectivity of the extraction solvent, and makes it unnecessary for non-aromatic hydrocarbons to reflux into the extractive distillation tower, avoiding the formation of two liquid phases in the extractive distillation tower, increasing the content of non-aromatic hydrocarbons in the raffinate oil, and further improving the quality and yield of the aromatic hydrocarbon product in the extract; at the same time, the above-mentioned embodiment makes the extractive distillation system occupy a small area, does not require additional heating, and reduces energy consumption. The above-described embodiment indirectly increases the water content of the extraction solvent within the extractive distillation column through the use of a Venturi separator, thereby improving the selectivity of the extraction solvent and enhancing the quality and yield of the aromatic hydrocarbon product in the bottom extract. This also prevents non-aromatic hydrocarbons from returning to the extractive distillation column, preventing the formation of two liquid phases within the extractive distillation column, and further enhancing the separation efficiency of the extractive distillation. Therefore, surprisingly, it has been discovered that the combination of the extractive distillation column and the Venturi separator, due to the inclusion of the Venturi separator in the extractive distillation system, produces a synergistic effect in extractive distillation methods, particularly methods for separating aromatic hydrocarbons.

[0066] The extractive distillation tower and extractive distillation system according to the present invention have high separation efficiency, effectively reduce the pressure drop of the entire tower and the tower bottom temperature, and further reduce energy consumption; under the condition of unchanged tower diameter, the processing capacity of raw materials is further increased, which is conducive to capacity expansion and transformation; the extractive distillation tower of the present invention has strong anti-blocking and defoaming capabilities, effectively reducing the risk of flooding.

[0067] Example

[0068] The present invention is further illustrated below by way of examples, but the present invention is not limited thereto.

[0069] The sulfolane used in the Examples and Comparative Examples was a chemical reagent purchased from Inokai Technology Co., Ltd. The structured packing used in Examples 1-6 of the present invention was Mellapak 250-well corrugated structured packing. 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 undergoing the extraction process, which contains no or very low concentrations of extract; the term "rich solvent" refers to the extraction solvent after undergoing the extraction process, which is rich in extract.

[0070] Example 1

[0071] In this embodiment, an aromatic extraction system as shown in Figure 1 is used, which includes an extractive distillation tower 101, a non-aromatic distillation tower 105, a condenser 104 and a reflux drum 103; the extractive distillation tower 101 includes a feed inlet 1, an extraction solvent inlet 2, a tower top gas phase outlet 3, a side line inlet 10 and a tower bottom liquid phase outlet 9; the non-aromatic distillation tower 105 includes a gas phase inlet 11, a non-aromatic outlet 19, an oil phase inlet 20 and a solvent outlet 23; the reflux drum 103 includes a reflux drum inlet 5, a first oil phase outlet 21 and a second oil phase outlet 22; the tower top gas phase outlet 3 of the extractive distillation tower 101 is connected to the gas phase inlet of the non-aromatic distillation tower 105, and the non-aromatic outlet 19 of the non-aromatic distillation tower 105 is connected to the reflux drum inlet 5 through the condenser 104; the rich solvent in the tower bottom is produced through the tower bottom liquid phase outlet 9; and the raffinate oil is produced through the second oil phase outlet 22.

[0072] As shown in Figure 1, the extractive distillation tower includes a tray layer, a movable layer and a packing layer from bottom to top; the gas-liquid contact mass transfer element of the movable layer is a packing tray complex, and the packing tray complex is a complex 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 tray, and the gas-liquid contact mass transfer element in the packing layer is a first packing, and the first packing is a perforated corrugated structured packing.

[0073] In the lower section of the extractive distillation tower, the gas phase in the tower bottom passes through the three-dimensional jet tray from bottom to top through the gas lifting holes 106 at a certain speed. The gas lifting holes on the tray are arranged in a certain distribution pattern, and a liquid lifting pipe 107 and a vertical sieve plate 108 are arranged above the gas lifting holes; the liquid phase falls from top to bottom into the three-dimensional jet tray through the downcomer 109, and the liquid on the tray is lifted by the gas through the gap between the liquid lifting pipe and the tray, and 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 basically falls back to the tray in the form of clear liquid, enters the downcomer along the flow channel, and falls to the next tray.

[0074] Between the raw material inlet 1 and the extraction solvent inlet 2, the bottom gas phase passes through the three-dimensional jet packing tray from bottom to top through the gas riser holes at a certain speed. A liquid lift pipe and a third packing 110 are provided above the gas riser holes. The liquid phase falls from top to bottom onto the three-dimensional jet packing tray through the downcomer. The liquid on the tray is lifted by the gas through the gap between the liquid lift pipe and the tray. High-speed turbulent mixing and mass transfer occur in the liquid lift pipe. The gas and liquid then flow into the packing in parallel 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 onto the tray in the form of a clear liquid, enters the downcomer along the flow channel, and falls to the next tray.

[0075] Above the extraction solvent inlet 2 , gas and liquid transfer in the first filler 111 .

[0076] Using the C6-C7 fraction of reformate as feedstock, containing 65% aromatics by mass, the extractive distillation column shown in Figure 1 was used to separate benzene and toluene. Sulfolane was used as the solvent, the solvent ratio was set at 4.3, and the reflux ratio was set at 0.3. The separation requirements were: the aromatics content in the raffinate product should not exceed 0.2%, and the aromatics content in the bottoms rich solvent stream after solvent removal should be 99.9%. The structural parameters and energy consumption of the extractive distillation column are shown in Table 1, and the operating conditions of the non-aromatic distillation column are shown in Table 2.

[0077] Example 2

[0078] The extractive distillation system and raw materials used in this example are the same as those used in Example 1, with the only difference being the active layer of the extractive distillation column;

[0079] As shown in FIG2 , the extractive distillation tower has a structured packing as the gas-liquid contact mass transfer element in the active layer of the extractive distillation tower;

[0080] In the tray layer of the extractive distillation tower, the gas phase in the bottom of the tower contacts and transfers mass with the liquid phase through the three-dimensional spray-type tray 112 at a certain speed; in the active layer and packing layer of the tower, the gas and liquid transfer mass in the first packing 111 and the second packing 113.

[0081] The extractive distillation column shown in Figure 2 is used to separate benzene and toluene in the raw material. The raw materials, solvents, solvent ratios, reflux ratios and separation requirements are the same as those in Example 1. The parameters and energy consumption of the extractive distillation column are shown in Table 1, and the operating conditions of the non-aromatic distillation column are shown in Table 2.

[0082] Example 3

[0083] Using reformate C6 fraction as a raw material, the benzene mass fraction in the raw material is 26.5%, and the benzene in the raw material is separated using the extractive distillation tower and extractive distillation system shown in Figure 3, wherein the system includes an extractive distillation tower 101, a condenser 104, and a reflux drum 103; the extractive distillation tower 101 includes a raw material inlet 1, an extractive solvent inlet 2, an overhead gas phase outlet 3, a side line inlet 10, and a bottom liquid phase outlet 9; the reflux drum 103 includes a reflux drum inlet 5, a first oil phase outlet 21, and a second oil phase outlet 22; the overhead gas phase outlet 3 of the extractive distillation tower 101 is connected to the reflux drum inlet 5 through the condenser 104; some non-aromatic hydrocarbons in the reflux drum are returned to the extractive distillation tower through the first oil phase outlet 21; the rich solvent in the bottom of the tower is extracted through the bottom liquid phase outlet 9; and the raffinate oil is extracted through the second oil phase outlet 22.

[0084] The extractive distillation column's active layer features a second packing element, which is structured packing. In the extractive distillation column's trays, the bottom gas phase contacts and transfers mass with the liquid phase at a constant velocity via three-dimensional jet trays 112. In the active and packing layers, gas and liquid transfer occurs between the first and second packing elements 111 and 113. The solvent is sulfolane, with a solvent ratio of 3.8 and a reflux ratio of 0.5. Separation requirements: the mass fraction of benzene in the raffinate product should not exceed 0.1%, and the mass fraction of benzene in the bottom rich solvent stream after solvent removal should be 99.9%. The extractive distillation column parameters and energy consumption are shown in Table 1.

[0085] Example 4

[0086] The extractive distillation tower of this embodiment is the same as that of Example 1, except that the theoretical number of stages of the packing layer, the movable layer and the tray layer is different from that of Example 1. The specific parameters and energy consumption are shown in Table 1.

[0087] Example 5

[0088] The extractive distillation column used in this embodiment is the same as the extractive distillation column used in Example 1, except that the non-aromatic hydrocarbon separation device in this embodiment is a Venturi separator, as follows:

[0089] The extractive distillation system shown in FIG4 and the venturi separator shown in FIG5 , the system includes an extractive distillation column 101, a venturi separator 102, a reflux tank 103 and a condenser 104;

[0090] The extractive distillation column 101 includes a raw material inlet 1, an extraction solvent inlet 2, a side line 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, a water phase outlet 12, and an oil phase outlet 7;

[0091] The top gas phase outlet 3 of the extractive distillation column 101 is connected to the gas phase inlet 11 of the venturi separator 102; the liquid phase outlet 8 of the venturi separator 102 is connected to the side line inlet 10 of the extractive distillation column 101, and the gas phase outlet 4 of the venturi separator 102 is connected to the inlet 5 of the reflux tank 103; the water phase outlet 12 of the reflux tank 103 is connected to the liquid phase inlet 6 of the venturi separator 102; the oil phase outlet 7 of the reflux tank 103 forms the raffinate oil product outlet of the system; the condenser 104 is arranged between the gas phase outlet 4 of the venturi separator 102 and the reflux tank inlet 5;

[0092] The venturi separator 102 includes a liquid phase collecting pipe 16 arranged vertically and a venturi tube 14 arranged vertically in the liquid phase collecting pipe 16, and the throat of the venturi tube 14 is provided with a liquid phase inlet 6; the venturi separator includes a venturi tube 14, a vortex core tube 13, a liquid infusion pipe 15 and a liquid phase collecting pipe 16; the gas phase outlet 4 of the venturi separator 102 is arranged at the top of the liquid phase collecting pipe 16; the liquid phase inlet 6 of the venturi separator 102 is connected to the throat of the venturi tube 14 through the liquid infusion pipe 15; the bottom inlet of the venturi tube is formed as 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; the venturi tube 14 includes an equal diameter section, a reduced diameter section and an expanded diameter section which are connected in sequence from bottom to top, and the liquid infusion section The pipe 15 passes through the wall of the liquid phase collecting pipe 16 and is connected to the reduced diameter section of the venturi tube 14, and is close to the throat of the venturi tube; the top of the liquid phase collecting pipe 16 is connected to an open pipe 18, and the top opening of the open pipe 18 forms the gas phase outlet 4 of the venturi separator 102, and the bottom opening of the open pipe 18 extends downward into the liquid phase collecting pipe 16, and there is a gap between the top opening 17 of the expanded diameter section of the venturi tube 14; the diameter of the open pipe 18 is the same as the diameter of the top opening of the expanded diameter section; the angle between the liquid infusion pipe 15 and the venturi tube 14 is 90°; the vortex core tube 13 is uprightly arranged in the equal diameter section of the venturi tube, and the bottom inlet of the vortex core tube 13 forms the gas phase inlet 11 of the venturi separator 102; the number of vortex core tubes is one.

[0093] The raw material containing aromatic hydrocarbons enters the extractive distillation tower 101 through the raw material inlet 1, and the solvent sulfolane enters the extractive distillation tower 101 through the extraction solvent inlet 2. The raw material containing aromatic hydrocarbons and sulfolane contact in the extractive distillation tower 101 to extract aromatic hydrocarbons; the top gas phase of the extractive distillation tower 101 is discharged from the top gas phase outlet 3, passes through the vortex core tube 13 of the venturi separator 102, forms an upward vortex gas phase, and enters the venturi tube 14; the water phase from the reflux tank 103 enters the venturi tube 14 through the liquid infusion pipe 15; the vortex gas phase and the washing The washing liquid contacts the washing liquid and undergoes water washing and removal, producing a washed gas phase and a solvent-containing washing liquid phase. The solvent-containing washing liquid phase gradually gathers outside the vortex and is discharged from the bottom opening of the open tube 18 of the liquid phase collection pipe 16. It then enters the liquid phase collection pipe 16 and, under the action of gravity, reaches the bottom liquid phase outlet 8 for discharge. The washed gas phase is discharged from the gas phase outlet 4, passes through the condenser 104, and enters the reflux tank 103 for treatment. The raffinate 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 extractive 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 extractive distillation system are shown in Table 1.

[0094] Using the C6-C7 fraction of reformate as feedstock, the extractive distillation system (Figure 3) separates benzene and toluene from the feedstock, containing 65% aromatics. The solvent is sulfolane, the solvent ratio is 4.3, and the reflux ratio is 0.3. The separation requirements are: the aromatics content in the raffinate product should not exceed 0.2%, and the aromatics content in the bottoms rich solvent stream after solvent removal should be 99.9%. The operating conditions for the aromatics extraction column are shown in Table 1, and the operating conditions for the Venturi separator are shown in Table 2.

[0095] Compared with Example 1, the use of the venturi separator instead of the non-aromatic distillation tower can save the energy consumption of the bottom reboiler of the non-aromatic distillation tower, thereby reducing the energy consumption of the entire process and reducing the floor space.

[0096] Example 6

[0097] The method of this embodiment is the same as that of Example 5, except that the inlet gas velocity at the venturi tube inlet is 40 m / s, and the absolute pressure of the scrubbing liquid at the liquid phase injection port is 180 kPa; the liquid phase removal rate at the top gas phase outlet of the venturi separator 102 is 95%. The specific operating conditions of the aromatics extraction tower are shown in Table 1, and the operating conditions of the venturi separator are shown in Table 2.

[0098] Example 7

[0099] The extractive distillation system, operating method, and raw materials used in this example are the same as those used in Example 3 (containing 26.5% benzene). The only difference is the active layer of the extractive distillation column. In this example, the gas-liquid contact mass transfer element of the active layer is a packed tray composite.

[0100] As shown in Figure 2, the extractive distillation tower has a gas-liquid contact mass transfer element in the active layer, which is a packed tray complex including three-dimensional jet packing trays and Mellapak250 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 bottom solvent-rich stream after desolventization is 99.9%.

[0101] The extractive distillation column shown in FIG2 is used to separate benzene and toluene from the raw material. The raw materials, solvents, solvent ratios, reflux ratios and separation requirements are the same as those in Example 3. The parameters and energy consumption of the extractive distillation column are shown in Table 1.

[0102] Comparative Example 1

[0103] In this comparative example, the raw materials, solvents, solvent ratios, reflux ratios, and separation requirements are the same as those in Example 1. The difference from Example 1 is that the extractive distillation tower uses conventional F1 float valve trays to separate benzene and toluene from the raw materials. The parameters and energy consumption of the extractive distillation tower are shown in Table 3.

[0104] Comparative Example 2

[0105] In this comparative example, the solvent, solvent ratio, reflux ratio, and separation requirements were the same as in Example 1. The difference from Example 1 was that the extractive distillation column used Mellapak 250 structured packing throughout to separate the benzene and toluene in the feedstock used in Example 1. Due to the high liquid load in the middle and lower sections of the column, the column was prone to flooding. The column parameters under normal operating conditions are shown in Table 3.

[0106] Comparative Example 3

[0107] In this comparative example, the solvent, solvent ratio, reflux ratio, and separation requirements were the same as in Example 1. The difference from Example 1 was that the extractive distillation column employed stereospray trays throughout to separate the benzene and toluene in the feedstock used in Example 1. The column parameters and energy consumption are shown in Table 3.

[0108] Comparative Example 4

[0109] In this comparative example, the solvent, solvent ratio, reflux ratio, and separation requirements were the same as those in Example 3. The difference from Example 3 was that the extractive distillation column used a conventional F1 float valve column to separate the benzene from the feedstock used in Example 3. The column parameters and energy consumption are shown in Table 3.

[0110] Comparative Example 5

[0111] In this comparative example, the solvent, solvent ratio, reflux ratio, and separation requirements were the same as those in Example 3. The difference from Example 3 was that the extractive distillation column was entirely packed with Mellapak 250 structured packing to separate the benzene from the feedstock used in Example 3. The column parameters and energy consumption are shown in Table 3.

[0112] Comparative Example 6

[0113] In this comparative example, the solvent, solvent ratio, reflux ratio, and separation requirements were the same as those in Example 3. The difference from Example 3 was that the extractive distillation column used stereospray trays throughout to separate the benzene from the feedstock used in Example 3. The column parameters and energy consumption are shown in Table 3.

[0114] Table 1.

[0115] Table 2.

[0116] Table 3.

[0117] According to the data in Tables 1 and 2, by comparing Example 1 with Comparative Example 1, it can be seen that since the separation efficiency of the floating valve trays of the packing layer and the movable layer of the extractive distillation tower in Comparative Example 1 is lower than that of the structured packing and packed tray composite of Example 1, the full-tower pressure drop of the extractive distillation tower in Comparative Example 1 is larger, and the energy consumption is higher.

[0118] Comparing Example 1 with Comparative Examples 1 and 2 reveals that due to the large L / V ratios in the middle and lower sections of the tower, the separation efficiency using only filler is significantly reduced, resulting in a lower separation efficiency than that achieved with conventional valve trays. Consequently, the full-tower pressure drop in Comparative Example 2 is greater than that in Comparative Example 1, far exceeding that in Example 1, resulting in higher energy consumption. Using the extractive distillation tower of the present invention reduces the full-tower pressure drop and lowers the bottom temperature, further reducing energy consumption.

[0119] Comparison of Example 1 and Comparative Example 3 reveals that because the valve trays in the upper and middle sections of the extractive distillation column have lower separation efficiency than the structured packing and packed tray composites of the present application, the overall pressure drop and energy consumption in Comparative Example 3 are relatively high. Using the extractive distillation column of the present application reduces overall pressure drop and lowers the bottom temperature, further reducing energy consumption.

[0120] By comparing Example 3 with Comparative Examples 4-6, it can be seen that compared with Example 3, when the extractive distillation tower adopts F1 float valve trays, or Mellapak250 structured packing, or three-dimensional spray trays, the full-tower pressure drop is large and the energy consumption is higher, which further illustrates the superiority of the present application in the process of extractive distillation separation of benzene; using the extractive distillation tower of the present invention, the full-tower pressure drop is low, the bottom temperature is low, and the energy consumption is further reduced.

[0121] By comparing Example 1 with Example 4, it can be seen that within the theoretical number of stages of the packing layer, active layer and tray layer of the present invention, the extractive distillation tower of the present application has a lower full-tower pressure drop and a lower bottom temperature, further reducing energy consumption.

[0122] By comparing Example 1 with Example 2, it can be seen that when the mass fraction of non-aromatic hydrocarbons in the raw material is lower than 50%, if the gas-liquid contact mass transfer element of the active layer is selected as a packed tower plate complex, compared with when the gas-liquid contact mass transfer element of the active layer is selected as a packing, the full-tower pressure drop of the extractive distillation tower is lower, the tower bottom temperature is lower, and energy consumption is further reduced.

[0123] By comparing Example 3 with Example 7, it can be seen that when the mass fraction of aromatic hydrocarbons in the feedstock is less than 50% (i.e., the mass fraction of non-aromatic hydrocarbons in the feedstock is greater than 50%), if the gas-liquid contact mass transfer element of the active layer is selected as a packing, compared with when the gas-liquid contact mass transfer element of the active layer is a packing tray complex, the full-tower pressure drop of the extractive distillation tower is lower, the bottom temperature is lower, and energy consumption is further reduced.

[0124] Test Example 1

[0125] The components of the raffinate oil products obtained in Example 1 and Examples 5 and 6 were analyzed. The aromatic content and solvent content of the raffinate oil were analyzed by ASTM D-6536 and GGBM-04-2005 standard methods. The product composition is shown in Table 4.

[0126] Table 4

[0127] According to the data in Table 4, by comparing Example 1 and Example 5, it can be seen that after the extractive distillation system of Example 5 introduces the venturi separator, the water-containing solvent recovered by the venturi separator is circulated to the extractive distillation tower, thereby increasing the water content of the extractive solvent in the extractive distillation tower, improving the selectivity of the extractive solvent, increasing the content of non-aromatic hydrocarbons in the residual oil and the effect of solvent removal, and further improving the quality and yield of the aromatic hydrocarbon product in the extract; moreover, the venturi separator occupies a small area and does not require additional heating, further reducing energy consumption. By comparing Example 5 with Example 6, it can be seen that under the absolute pressure range of the venturi tube inlet gas velocity and the washing liquid at the liquid phase injection port of the present invention, the liquid phase removal rate is higher and the solvent content in the residual oil product is lower. Therefore, a synergistic effect is produced in the extractive distillation tower and the venturi separator of the present invention.

[0128] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within 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 scope of protection of the present invention.

[0129] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0130] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. An extractive distillation tower, characterized in that: The extractive distillation tower comprises, from bottom to top, a tray layer, an active layer and a packing layer; the packing layer comprises a gas-liquid contact mass transfer element called a first packing; the active layer comprises a gas-liquid contact mass transfer element called a second packing, or comprises a packing tray complex, wherein the packing tray complex is a complex of a gas-liquid contact mass transfer element called a third packing and a gas-liquid contact mass transfer element called a first stereoscopic jet tray; the tray layer comprises a gas-liquid contact mass transfer element called a second stereoscopic jet tray, wherein the extractive distillation tower further comprises an extractive solvent inlet, a raw material inlet, a tower top gas phase outlet, a tower bottom liquid phase outlet and an optional side line inlet, wherein the raw material inlet is below the extractive solvent inlet, the packing layer is located above the extractive solvent inlet, the active layer is located between the extractive solvent inlet and the raw material inlet, and the tray layer is located below the raw material inlet.

2. The extractive distillation tower according to claim 1, characterized in that The theoretical mass transfer number of the packing layer is 10%-25% of the theoretical mass transfer number of the whole tower, and / or the theoretical mass transfer number of the plate layer is 30%-45% of the theoretical mass transfer number of the whole tower, and / or the theoretical mass transfer number of the active layer is 40%-60% of the theoretical mass transfer number of the whole tower.

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

4. The extractive distillation tower according to any one of claims 1 to 3, characterized in that: The extractive distillation tower is used to separate aromatic compounds and non-aromatic compounds in the raw material; When the mass fraction of the 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 a second packing, and the structured packing is selected from one or more of a perforated plate corrugated packing, a mesh corrugated packing, a plate mesh corrugated packing, a grid packing and a corrugated ring packing; When the mass fraction of non-aromatic compounds in the raw material is lower than 50%, the gas-liquid contact mass transfer element in the active layer is a packed tower plate complex, wherein the opening rate of the first three-dimensional injection type tower plate is 5%-30%, the overflow weir height is 5mm-40mm, and the plate spacing is more than 400mm; the third filler is a regular filler, preferably a perforated plate corrugated filler.

5. An extractive distillation system, characterized in that: The extractive distillation system comprises an extractive distillation tower, a condenser and a reflux tank according to any one of claims 1 to 4; the reflux tank comprises a reflux tank inlet and an oil phase outlet; the top gas phase outlet of the extractive distillation tower is connected to the reflux tank inlet through the condenser; the oil phase outlet of the reflux tank is formed as a raffinate oil product outlet.

6. The extractive distillation system according to claim 5, characterized in that: The extractive distillation system is used to separate aromatic compounds and non-aromatic compounds in the raw material, and the extractive distillation system also includes a non-aromatic separation device, and the non-aromatic separation device includes a gas phase inlet and a non-aromatic outlet, wherein the gas phase inlet of the non-aromatic separation device is connected to the top gas phase outlet of the extractive distillation tower, and the non-aromatic outlet of the non-aromatic separation device is connected to the reflux tank inlet through the condenser; preferably, the non-aromatic separation device is selected from a non-aromatic distillation tower or a venturi separator.

7. The extractive distillation system according to claim 6, 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 collecting pipe surrounding at least a part of the structure of the venturi tube, and a liquid phase injection port is provided below the throat of the venturi tube; the reflux tank also includes a water phase outlet; The top gas phase outlet of the extractive distillation tower is connected to the gas phase inlet of the venturi separator; the liquid phase outlet of the venturi separator is connected to the side line inlet of the extractive distillation tower, and the gas phase outlet of the venturi separator is connected to the reflux tank inlet through the condenser; the water phase outlet of the reflux tank is connected to the liquid phase inlet of the venturi separator.

8. The extractive distillation system according to claim 7, characterized in that: The gas phase outlet of the venturi separator is arranged at the top of the liquid phase collecting pipe; the liquid phase inlet of the venturi separator is connected with the liquid phase injection port of the venturi tube through a liquid infusion pipeline; the bottom inlet of the venturi tube is formed as the gas phase inlet of the venturi separator or is connected with the gas phase inlet of the venturi separator, and the gas phase outlet of the venturi separator is connected with the top outlet of the venturi tube.

9. The extractive distillation system according to claim 8, characterized in that: The venturi tube includes, from bottom to top, an optional equal-diameter section, a reduced-diameter section, a throat and an expanded-diameter section, and the liquid infusion pipeline optionally passes through the tube wall of the liquid phase collecting tube and is connected to the liquid injection port of the venturi tube; an open tube is connected to the top of the liquid phase collecting tube, and the top opening of the open tube forms the gas phase outlet of the venturi separator, and the bottom opening of the open tube passes downward through the top of the liquid phase collecting tube and extends into the liquid phase collecting tube, and there is a gap between the bottom opening of the open tube and the top opening of the expanded-diameter section of the venturi tube; preferably, the diameter of the open tube is greater than or equal to the diameter of the top opening of the expanded-diameter section.

10. The extractive distillation system according to claim 9, characterized in that: The venturi separator also includes a vortex core tube, the interior of which is provided with a spiral guide vane, the vortex core tube is arranged at the entrance 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 is formed as the gas phase inlet of the venturi separator or is connected to the gas phase inlet of the venturi separator.

11. The extractive distillation system according to claim 9, characterized in that: Structures for guiding the spiral upward flow of gas are provided on the inner walls of the optional equal-diameter section, reduced-diameter section, throat section and expanded-diameter section of the venturi tube; preferably, the structure is selected from swirl blades or spiral guide vanes.

12. An extractive distillation method using the extractive distillation column according to any one of claims 1 to 4 or the extractive distillation system according to any one of claims 5 to 11.

13. The extractive distillation method according to claim 12, characterized in that: The extractive distillation method uses the extractive distillation system and includes the following steps: allowing the raw material to enter the extractive distillation tower to contact with the extractive solvent, perform extractive distillation, and obtain solvent-rich material in the tower bottom; allowing the top gas phase to enter the reflux tank after cooling.

14. The extractive distillation method according to claim 13, characterized in that: The extractive distillation system includes a venturi separator, and the extractive distillation method also includes the following steps: allowing the gas phase at the top of the extractive distillation tower 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 a solvent.

15. The extractive distillation method according to claim 14, characterized in that: The washing liquid is selected from washing water, and the washing liquid phase is returned to the extractive distillation tower for recycling, and the gas phase after washing is condensed and enters the reflux tank for separation to obtain a raffinate oil product and an aqueous phase, and the aqueous phase is returned to the venturi separator as a washing liquid.

16. The extractive distillation method according to claim 15, characterized in that: In the Venturi separator, the mass flow rate ratio of the washing liquid to the top gas phase is (0.2-1.0):1, preferably (0.2-0.5):1; and / or the inlet gas velocity of the Venturi separator is 1m / s-30m / s, and / or the absolute pressure of the washing liquid at the liquid phase injection port is 180kPa-1500kPa.

17. The extractive distillation method according to claim 13, characterized in that: The extractive distillation tower has a bottom temperature of 120°C-180°C, and a full tower pressure drop of 40kPa-65kPa; and / or, a top gas phase temperature of 80°C-130°C, and a top tower pressure of 0.1MPa-0.5MPa; and / or, a solvent ratio of 1-6:

1.

18. The extractive distillation method according to claim 13, characterized in that: The raw material is an aromatic hydrocarbon-containing raw material or a ketone alcohol oil.

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