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 sequentially comprises a tower plate layer, a movable layer and a filler layer from bottom to top, the filler layer comprises a gas-liquid contact mass transfer element called a first filler; the movable layer comprises a gas-liquid contact mass transfer element called as a second filler, or comprises a filler tower plate composite body, and the filler tower plate composite body is a composite body of a gas-liquid contact mass transfer element called as a third filler and a gas-liquid contact mass transfer element called as a first three-dimensional jet tower plate; the tower plate layer comprises a gas-liquid contact mass transfer element called a second three-dimensional jet tower plate, 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 line inlet, and the filler layer is located above the extraction solvent inlet; the movable layer is positioned between the extraction solvent inlet and the raw material inlet; and the tower plate layer is positioned below the raw material inlet. The invention also relates to an extractive distillation system comprising the extractive distillation tower and an extractive distillation method using the extractive distillation system.

Description

Technical Field

[0001] The present invention relates to the field of petrochemical aromatic 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. 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 operating flexibility of the mass transfer elements in the gas-liquid contact in the tower. Extractive distillation is a special type of distillation process, which is widely used in the separation process of aromatics and various fine chemicals. Since the solvent-raw material mass ratio (referred to as the 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 is quite different. 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 packed tower technology in cyclohexene-cyclohexane extractive distillation tower”, Chemical Industry Progress, 2004, 23(8): 880-882) attempted to use a structured packed tower to achieve cyclohexane-cyclohexene-benzene extractive 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 a 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-hydroxypropanal. 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 regular 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 regular 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 extractive distillation towers or reduce the pressure drop of the entire tower. Summary of the invention

[0005] One of the purposes of the present invention is to provide an extractive distillation tower, which has high separation efficiency and can effectively reduce the pressure drop of the entire tower and the temperature of the tower bottom, thereby further reducing energy consumption; or, under the condition that the tower diameter remains unchanged, 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 improved anti-clogging ability and defoaming ability, and effectively reduces the risk of flooding.

[0006] To achieve the above object, according to a first aspect of the present invention, there is provided an extractive distillation tower, which 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 referred to as a first packing; the active layer comprises a gas-liquid contact mass transfer element referred to as 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 referred to as a third packing and a gas-liquid contact mass transfer element referred to as a first stereoscopic jet type tray; the tray layer comprises a gas-liquid contact mass transfer element referred to as a second stereoscopic jet type 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. Specifically, the gas-liquid contact mass transfer element contained in the packing layer is a packing, which is called "first packing"; the gas-liquid contact mass transfer element contained in the active layer is a packing, which is called "second packing", or is a packing tower plate complex, and the packing tower plate complex contains a packing called "third packing" and a three-dimensional jet-type tower plate called "first three-dimensional jet-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 jet-type tower plate, which is called "second three-dimensional jet-type tower plate".

[0007] According to a second aspect of the present invention, the present invention provides an extractive distillation system, which comprises an extractive distillation tower, a condenser and a reflux tank according to the first aspect above, wherein the extractive distillation tower comprises 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 tank comprises a reflux tank inlet and an oil phase outlet; the tower top gas phase outlet of the extractive distillation tower is connected to the reflux tank inlet through the condenser; and the oil phase outlet of the reflux tank is formed as a raffinate oil product outlet.

[0008] 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.

[0009] According to the technical solution of the present invention, the gas-liquid mass transfer elements are creatively designed in sections according to the gas-liquid mass transfer characteristics and load changes of each part in the tower, so as to achieve the purpose of energy saving and consumption reduction. The extractive distillation tower of the present invention has high separation efficiency, which can effectively reduce the pressure drop of the whole tower and the temperature of the tower bottom, thereby further reducing energy consumption; or, under the condition that the tower diameter remains unchanged, it allows the processing capacity of raw materials to be 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, which can effectively reduce the risk of flooding.

[0010] Other features and advantages of the present invention will be described in detail with the aid of the accompanying drawings and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 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 specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0012] Figure 1 A schematic diagram of the extractive distillation tower and the extractive distillation system in Example 1 of the present invention is shown.

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

[0014] Figure 3 A schematic diagram of the extractive distillation tower and the extractive distillation system in Example 3 of the present invention is shown.

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

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

[0017] Description of Reference Numerals

[0018] 101: extractive distillation tower; 102: venturi separator; 103: reflux tank; 104: condenser; 105: non-aromatic distillation tower; 106: gas riser; 107: liquid extraction pipe; 108: sieve plate; 109 downcomer; 110: third filler; 111: first filler; 112: three-dimensional jet type tray; 113: second filler;

[0019] 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;

[0020] 13: vortex core tube; 14: venturi tube; 15: liquid delivery pipeline; 16: liquid phase collection tube; 17: top opening of the expanded diameter section; 18: open tube;

[0021] 19: non-aromatic hydrocarbon outlet; 20: oil phase inlet; 21: first oil phase outlet; 22: second oil phase outlet; 23: solvent outlet. DETAILED DESCRIPTION

[0022] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present invention, and is not intended to limit the present invention.

[0023] Any specific numerical value (including the endpoint of the numerical range) disclosed in this specification is not limited to the exact value of the numerical value, but should be understood to also cover values ​​close to the exact value, such as all possible values ​​within the range of ±5% of the exact value. In addition, for the disclosed numerical range, the endpoint values ​​of the range, the endpoint values ​​and the specific point values ​​in the range, and the specific point values ​​can be arbitrarily combined to obtain one or more new numerical ranges, and these new numerical ranges should also be regarded as specifically disclosed in this specification.

[0024] 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.

[0025] 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 regarded as part of the original disclosure or original record of the present invention, and should not be regarded as new contents not disclosed or anticipated herein, unless a person skilled in the art considers that the combination is obviously unreasonable.

[0026] 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.

[0027] 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”, “right”, etc. indicate directions or positional relationships. They 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 a device or component must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0028] In the specification of the present invention, unless otherwise clearly specified and limited, the terms "disposed", "connected", "connected", "connected" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] According to a first aspect of the present invention, there is provided an extractive distillation tower, which comprises, from bottom to top, a plate layer, an active layer and a packing layer; the gas-liquid contact mass transfer element contained in the packing layer is a packing, referred to as a first packing; the gas-liquid contact mass transfer element contained in the active layer is a packing, referred to as a second packing, or is a packing plate complex, wherein the packing plate complex is a complex of a packing referred to as a third packing and a stereoscopic spray-type plate referred to as a first stereoscopic spray-type plate; the gas-liquid contact mass transfer element contained in the plate layer is a stereoscopic spray-type plate, referred to as a second stereoscopic spray-type plate; 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, and 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 plate layer is located below the raw material inlet.

[0030] As an 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 tower can be changed according to the composition of the raw materials, for example, from packing to packed tray complex or from packed tray complex to packing, while the gas-liquid contacting and mass transfer elements of other layers remain unchanged.

[0031] According to an implementation manner 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.

[0032] According to an implementation mode 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 above 400mm.

[0033] According to an implementation mode of the first aspect above, the theoretical mass transfer number of the active layer accounts for 40%-60%, preferably 45%-55%, of the theoretical mass transfer number of the whole tower, which is beneficial to improving the separation efficiency of the extractive distillation tower, effectively reducing the pressure drop of the whole tower and the bottom temperature, and further reducing energy consumption; under the condition of unchanged tower diameter, the processing capacity of raw materials is increased, which is beneficial to capacity expansion and transformation.

[0034] According to an implementation manner 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 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 a perforated plate corrugated packing, a mesh corrugated packing, a plate mesh corrugated packing, a grid packing and a corrugated ring packing; this implementation manner 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 processing capacity of the raw material 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 plate complex, which comprises regular packing (referred to as the third packing) and three-dimensional jet-type plates (referred to as the first three-dimensional jet-type plates). Preferably, the opening rate of the first three-dimensional jet-type plates is 5%-30%, the overflow weir height is 5mm-40mm, and the plate spacing is above 400mm; the third packing is preferably a perforated plate 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 temperature of the tower bottom, and further reducing energy consumption; under the condition that the tower diameter remains unchanged, the processing capacity of the raw materials is increased, which is conducive to capacity expansion and transformation.

[0035] Conventional extractive distillation towers basically follow the constant molar flow assumption in the rectifying section and the stripping section; in the extractive distillation tower, since the solvent is basically non-volatile and the solvent ratio is usually not less than 1, the substances in the raw material that have a strong binding force with the solvent gradually enter the solvent (liquid phase), resulting in the liquid phase molar flow ratio gradually increasing from top to bottom, while the rising gas phase gradually decreases. The inventors of the present invention surprisingly found through research that the gas-liquid load and gas-liquid composition at different positions in the extractive distillation tower have their own characteristics. According to these characteristics, the optimization design and combination of the tower internal components can overcome the shortcomings of the distillation tower in the prior art, especially the extractive distillation tower. Above the extraction solvent inlet, the ratio of the mass flow of the liquid phase to the gas phase (L / V) does not exceed 1, and because the auxiliary agents with high boiling points and high viscosity such as defoaming agents enter the extraction distillation tower together with the extraction solvent, the content of the auxiliary agents above the extraction solvent inlet is 0. The mass transfer element of this section adopts fillers, which can improve the separation efficiency of the extraction distillation tower and reduce the pressure drop of the whole tower. At the same time, there is no hidden danger of the fillers getting dirty or blocked; between the extraction solvent inlet and the raw material inlet, the different contents of the substances to be extracted in the raw materials will cause the L / V of this section to be higher than the L / V between the top of the extraction distillation tower and the extraction solvent inlet. At this time, the gas-liquid mass transfer element selects fillers or a composite structure of filler trays, which is helpful to improve the separation efficiency and increase the processing capacity. Below the raw material inlet, the values ​​of L and V are further increased, and L / V is slightly increased. The mass transfer element adopts a three-dimensional jet-type tray to increase the operating flexibility, so that the liquid phase falls back to the tray in the form of clear liquid, effectively avoiding flooding.

[0036] According to one embodiment of the present invention, the mass transfer theoretical number of the packing layer is 10%-25% of the mass transfer theoretical 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 mass transfer theoretical number of the tower plate layer accounts for 30%-45% of the mass transfer theoretical 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 more than 400mm. The above-mentioned 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 kettle temperature, and further reducing energy consumption; under the condition of unchanged tower diameter, 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.

[0037] According to a second aspect of the present invention, the present invention provides an extractive distillation system, the extractive distillation system comprising an extractive distillation tower, a condenser and a reflux tank, the extractive distillation tower comprising 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 described in the first aspect of the present invention; the reflux tank comprises a reflux tank inlet and an oil phase outlet; the tower 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; the tower bottom liquid phase outlet of the extractive distillation tower is formed as a rich solvent outlet. The term "rich solvent" refers to an extractive solvent that has undergone an extraction process in an extractive distillation tower and is rich in extracts.

[0038] According to an embodiment of the second aspect, the extractive distillation tower 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; the gas phase inlet of the non-aromatic separation device is connected to the gas 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 tank inlet through the condenser. Preferably, the non-aromatic separation device is a non-aromatic distillation tower or a venturi separator.

[0039] According to a preferred embodiment, the non-aromatic separation device is a non-aromatic distillation tower, wherein the non-aromatic distillation tower also includes an oil phase inlet and a solvent outlet; the solvent outlet is connected to the upper part of the extractive distillation tower, and the distilled extractive solvent is returned 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 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.

[0040] According to a preferred embodiment, the non-aromatic hydrocarbon separation device is a venturi separator, wherein the venturi separator comprises a liquid phase collection pipe and a venturi tube arranged in the liquid phase collection pipe, the venturi tube comprises the following sections connected in sequence: an optional equal diameter section, a reduced diameter section, a throat and an expanded diameter 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), 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 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. Preferably, the reflux drum further comprises a water phase outlet, and preferably the water phase outlet of the reflux drum is communicated with the liquid phase inlet of the venturi separator.

[0041] According to a preferred embodiment, the venturi separator is placed vertically, wherein the venturi tube includes, from bottom to top, an optional equal diameter section, a reduced diameter section, a throat section and an expanded diameter section which are connected in sequence. A liquid phase injection port is provided on the tube wall in the reduced diameter section of the venturi tube, that is, the liquid phase input from the liquid phase inlet of the venturi separator is injected into the venturi tube in the reduced diameter section of the venturi tube so as to contact and mix with the gas flowing spirally upward in the venturi tube. Since the gas flows at high speed in the reduced diameter section in a spiral manner in the venturi tube, as the diameter of the reduced diameter section becomes smaller and smaller, the angular velocity of the spiral upward flow of the gas becomes larger and larger. Therefore, when the liquid phase is injected into the venturi tube in the reduced diameter section, it flows and mixes with the gas flowing spirally upward, the disturbance degree of the liquid becomes more and more intense, and the gas-liquid mixing becomes more and more complete. Therefore, the mass transfer between the gas and the liquid is faster and more complete, and the separation effect is better. 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.

[0042] According to a preferred embodiment, a nozzle may be provided at the liquid phase injection port on the tube 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 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, less than 15°, and more preferably in the same direction as the gas flow direction.

[0043] According to a preferred embodiment, the liquid phase collecting pipe surrounds at least a part of the structure of the Venturi tube at the periphery of the Venturi tube, for example, at least surrounds the opening provided on the side wall of the expanded diameter section of the Venturi tube or at the end of the expanded diameter section. The liquid phase collecting pipe extends downward, and can surround the expanded diameter section of the Venturi tube, and can even surround the throat and the reduced diameter section, and can even surround the entire Venturi tube. Preferably, the Venturi separator includes a vertically arranged liquid phase collecting pipe and a Venturi tube vertically arranged in the liquid phase collecting pipe. If the liquid phase collection tube 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 tube 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 tube wall, wherein the angle between the liquid infusion pipe and the conical generatrix 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°.

[0044] According to a preferred embodiment, the top of the liquid phase collecting tube is closed, but an open tube for discharging the gas phase of the venturi separator is provided, the upper end outlet of the open tube forms the gas phase outlet of the venturi separator, and the open tube passes downward through the top of the liquid phase collecting tube 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 leave the Venturi tube is provided on the side wall of the expanded diameter section of the Venturi tube, then the open tube is connected to the end of the expanded diameter section of the Venturi tube, and optionally an opening is also provided between the lower end of the open tube and the end of the expanded diameter section of the Venturi tube for allowing the liquid that has not been completely discharged at the opening in the expanded diameter section to be completely discharged here, if the opening for the liquid phase to be discharged from the Venturi tube is provided at the end of the expanded diameter section of the Venturi tube, then the lower end of the open tube and the end of the expanded diameter section of the Venturi tube are completely or partially spaced apart to form an opening for the liquid to be discharged from the Venturi tube, at this time, the opening is a continuous or discontinuous annular opening, and the height of the opening can be adjusted by raising and lowering the open tube. The height of the opening can be changed within a certain range according to the liquid phase flow rate, as long as it can satisfy the requirement that almost all the liquid phase leaves the Venturi tube under the action of centrifugal force and enters the liquid phase collection tube, and can prevent 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 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.

[0046] According to a preferred embodiment, the venturi separator further comprises a device for causing the gas to enter the venturi tube in a spiral flow manner or a device for causing the gas to enter the venturi tube tangentially, so that the gas flows upward in a spiral form in the venturi tube. The device is arranged at the entrance of the reduced diameter section of the venturi tube, or is arranged in the equal diameter section of the venturi tube. The device for causing the gas to generate a spiral flow in the venturi tube can be a commonly used device in the art, such as a vortex core tube.

[0047] 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 vane is arranged 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 forms the gas phase inlet of the Venturi separator.

[0048] According to a preferred embodiment, the number of the vortex core tubes can be selected according to 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 shear of the vortex core tubes strengthens the mixing of the top gas phase and the solvent (such as water), thereby improving the removal effect of the solvent, and further making the solvent content in the raffinate oil product not exceed 2μg / g.

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

[0050] 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-adhering 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 angle of the swirl blade or spiral guide vane 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.

[0051] According to a preferred embodiment, the swirl blade or spiral guide vane may 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 helix 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.

[0052] 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, preferably 250-1000kPa.

[0053] 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.

[0054] 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.

[0055] According to an implementation mode of the third aspect, if the extractive distillation method uses the extractive distillation system, the method further comprises 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.

[0056] 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 also 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.

[0057] According to an implementation manner of the third aspect above, the extractive distillation method is used to separate aromatic hydrocarbons from non-aromatic hydrocarbons.

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

[0059] According to an implementation of the third aspect, the extractive distillation tower has a bottom temperature of 120°C-180°C, a full tower pressure drop of 40kPa-65kPa, and / or a top gas phase temperature of 80°C-130°C, a top tower pressure of 0.1MPa-0.5MPa, and a solvent ratio of 1-6:1. The above implementation is conducive to improving the solvent removal effect, so that the solvent content in the raffinate oil product does not exceed 2μg / g.

[0060] According to an embodiment of the third aspect, in the packing layer of the extractive distillation tower, the mass flow rate ratio of the liquid phase in the extractive distillation tower to the ascending gas phase 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 in the extractive distillation tower to the ascending gas phase is 3-9:1, preferably 5-7:1; and / or, in the plate layer of the extractive distillation tower, the mass flow rate ratio of the liquid phase in the extractive distillation tower to the ascending gas phase 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 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-mentioned 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.

[0062] According to one embodiment of the present invention, the liquid phase removal rate of the venturi separator is 82% or more, preferably 90%-99.9%, and the liquid phase separation accuracy is 1μm-10μm, wherein the above-mentioned liquid phase removal rate = the weight of the liquid phase entering the liquid phase collection tube / the total weight of the liquid phase injected into the venturi tube. The above-mentioned 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, the raw material is an aromatic hydrocarbon-containing raw material or a ketone alcohol oil.

[0064] 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 implementation mode, by introducing a Venturi separator into the extractive distillation system, allows the trace amount of extraction solvent in the gas phase at the top of the tower to be 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 amount of 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, thereby 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 implementation mode enables the extractive distillation system to have a small footprint, no additional heating is required, and energy consumption is reduced. The above-mentioned embodiment indirectly increases the water content of the extraction solvent in the extractive distillation tower by using a venturi separator, thereby improving the selectivity of the extraction solvent and improving the quality and yield of the aromatic hydrocarbon product in the bottom extract; at the same time, it avoids the return of non-aromatic hydrocarbons to the extractive distillation tower, avoids the formation of two liquid phases in the extractive distillation tower, and further improves the separation effect of the extractive distillation. Therefore, it is surprisingly found that the combination of the extractive distillation tower and the venturi separator produces a synergistic effect in the extractive distillation method, especially in the aromatic hydrocarbon separation method, because the venturi separator is included in the extractive distillation system.

[0065] The extractive distillation tower and the extractive distillation system according to the present invention have high separation efficiency, effectively reduce the pressure drop of the whole tower and the temperature of the tower bottom, and further reduce energy consumption; under the condition that the tower diameter remains unchanged, 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, and effectively reduces the risk of flooding.

[0066] Example

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

[0068] The sulfolane used in the examples and comparative examples is a chemical reagent purchased from Inokai Technology Co., Ltd. The structured packing used in Examples 1-6 of the present invention is Mellapak 250 orifice plate corrugated structured packing. Unless otherwise specified, the remaining reagents are obtained through commercial sources. In the following examples and comparative examples, the term "poor solvent" refers to the extraction solvent before undergoing the extraction process, which does not contain or contains a very low concentration of extract; the term "rich solvent" refers to the extraction solvent after undergoing the extraction process, which is rich in extract.

[0069] Example 1

[0070] In this embodiment, the Figure 1 The aromatic extraction system shown in the figure comprises an extractive distillation tower 101, a non-aromatic distillation tower 105, a condenser 104 and a reflux tank 103; the extractive distillation tower 101 comprises a raw material 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 comprises a gas phase inlet 11, a non-aromatic outlet 19, an oil phase inlet 20 and a solvent outlet 23; the reflux tank 103 comprises a reflux tank 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 tank inlet 5 through the condenser 104; the rich solvent in the tower bottom is produced through the tower bottom liquid phase outlet 9; the raffinate oil is produced through the second oil phase outlet 22.

[0071] like Figure 1 The extractive distillation tower shown in the figure comprises, from bottom to top, a plate layer, an active layer and a packing layer in sequence; the gas-liquid contact mass transfer element of the active layer is a packing plate complex, and the packing plate complex is a complex of a third packing and a first three-dimensional jet type plate; the third packing is a perforated plate corrugated structured packing; the gas-liquid contact mass transfer element in the plate layer is a three-dimensional jet plate, and the gas-liquid contact mass transfer element in the packing layer is a first packing, and the first packing is a perforated plate corrugated structured packing.

[0072] In the lower section of the extractive distillation tower, the gas phase in the tower bottom passes through the three-dimensional jet tower plate from bottom to top through the gas lifting holes 106 at a certain speed. The gas lifting holes on the tower plate are opened in a certain distribution form, 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 tower plate through the downcomer 109, and the liquid on the tower plate is lifted by the gas through the gap between the liquid lifting pipe and the tower plate, and high-speed turbulent mixing and mass transfer are carried out 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 tower plate in the form of clear liquid, enters the downcomer along the flow channel, and descends to the next tower plate.

[0073] Between the raw material inlet 1 and the extraction solvent inlet 2, the gas phase of the tower bottom passes through the three-dimensional jet packing tower plate from bottom to top through the gas riser hole at a certain speed. A liquid lifting pipe and a third packing 110 are arranged above the gas riser hole. 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 lifting pipe and the tower plate, and the high-speed turbulent mixing and mass transfer are carried out in the liquid lifting pipe. Then, the gas and liquid flow into the packing in parallel to further enhance the mass transfer and complete the gas-liquid separation. The gas continues to rise due to the pressure difference, and the liquid basically falls back to the tower plate in the form of clear liquid, enters the downcomer along the flow channel, and falls to the next tower plate;

[0074] Above the extraction solvent inlet 2 , gas and liquid transfer in the first filler 111 .

[0075] The reformed oil C6-C7 fraction is used as the raw material, and the aromatic mass fraction in the raw material is 65%. Figure 1 The extractive distillation tower shown in the figure separates benzene and toluene, the solvent is sulfolane, the solvent ratio is 4.3, and the reflux ratio is 0.3. The separation requirements are: the mass fraction of aromatics in the raffinate product does not exceed 0.2%, and the mass fraction of aromatics after the solvent is removed from the rich solvent stream in the bottom of the tower is 99.9%. The structural parameters and energy consumption of the extractive distillation tower are shown in Table 1, and the operating conditions of the non-aromatic distillation tower are shown in Table 2.

[0076] Example 2

[0077] The extractive distillation system and raw materials used in this example are the same as those used in Example 1, the only difference being that the active layers of the extractive distillation tower are different;

[0078] like Figure 2 The extractive distillation tower shown, wherein the gas-liquid contact mass transfer element of the active layer of the extractive distillation tower is a structured packing;

[0079] In the plate layer of the extractive distillation tower, the gas phase in the bottom of the tower contacts and transfers with the liquid phase through the three-dimensional jet-type plate 112 at a certain speed; in the active layer and the packing layer of the tower, the gas and liquid transfer in the first packing 111 and the second packing 113.

[0080] use Figure 2The extractive distillation tower shown separates 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 tower are shown in Table 1, and the operating conditions of the non-aromatic distillation tower are shown in Table 2.

[0081] Example 3

[0082] The reformed oil C6 fraction is used as the raw material, and the mass fraction of benzene in the raw material is 26.5%. Figure 3 The extractive distillation tower and the extractive distillation system shown are used to separate benzene in the raw material, wherein the system comprises an extractive distillation tower 101, a condenser 104 and a reflux tank 103; the extractive distillation tower 101 comprises a raw material inlet 1, an extractive solvent inlet 2, a tower top gas phase outlet 3, a side line inlet 10 and a tower bottom liquid phase outlet 9; the reflux tank 103 comprises a reflux tank 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 reflux tank inlet 5 through the condenser 104; part of the non-aromatic hydrocarbons in the reflux tank are returned to the extractive distillation tower through the first oil phase outlet 21; the rich solvent in the tower bottom is produced through the tower bottom liquid phase outlet 9; the raffinate oil is produced through the second oil phase outlet 22;

[0083] The gas-liquid contact mass transfer element of the active layer of the extractive distillation tower is the second packing, and the second packing is a structured packing; in the plate layer of the extractive distillation tower, the gas phase of the tower bottom contacts and transfers with the liquid phase at a certain speed through the three-dimensional jet type plate 112; in the active layer and packing layer of the tower, the gas and liquid transfer 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 oil product does not exceed 0.1%, and the mass fraction of benzene after the solvent is removed from the rich solvent flow in the tower bottom is 99.9%. The parameters and energy consumption of the extractive distillation tower are shown in Table 1.

[0084] Example 4

[0085] The extractive distillation tower of this embodiment is the same as that of Embodiment 1, except that the theoretical numbers of the packing layer, the active layer and the plate layer are different from those of Embodiment 1. The specific parameters and energy consumption are shown in Table 1.

[0086] Example 5

[0087] The extractive distillation tower used in this embodiment is the same as the extractive distillation tower used in Example 1, except that the non-aromatic separation device of this embodiment is a venturi separator, as follows:

[0088] like Figure 4 The extractive distillation system shown and Figure 5 The venturi separator shown, the system comprises an extractive distillation column 101, a venturi separator 102, a reflux drum 103 and a condenser 104;

[0089] The extractive distillation tower 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;

[0090] The gas phase outlet 3 at the top of the extractive distillation tower 101 is communicated with the gas phase inlet 11 of the venturi separator 102; the liquid phase outlet 8 of the venturi separator 102 is communicated with the side line inlet 10 of the extractive distillation tower 101, and the gas phase outlet 4 of the venturi separator 102 is communicated with the inlet 5 of the reflux tank 103; the water phase outlet 12 of the reflux tank 103 is communicated with the liquid phase inlet 6 of the venturi separator 102; the oil phase outlet 7 of the reflux tank 103 is formed as 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;

[0091] 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 a liquid phase inlet 6 is provided at the throat of the venturi tube 14; the venturi separator includes a venturi tube 14, a vortex core tube 13, a liquid infusion pipeline 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 pipeline 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 4 is connected to the venturi tube 14 ... venturi tube 14 through the liquid infusion pipeline 15; the liquid phase inlet 6 of the venturi tube 102 is connected to the venturi tube 14 through the liquid infusion pipeline 15; the liquid phase inlet 6 of the The pipeline 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 infusion pipeline 15 and the venturi tube 14 is 90°; the vortex core tube 13 is vertically 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.

[0092] Aromatic raw materials enter 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 aromatic raw materials and sulfolane contact in the extractive distillation tower 101 to extract aromatics; 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 to form 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 pipeline 15; the vortex gas phase and the washing The washing liquid is contacted, and the washing liquid is washed and removed to obtain the washed gas phase and the washing liquid phase containing the solvent. The washing liquid phase containing the solvent gradually gathers outside the vortex and is discharged from the bottom opening of the opening tube 18 of the liquid phase collecting pipe 16, enters the liquid phase collecting pipe 16, and reaches 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 treatment. 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 returns to the extractive distillation tower 101 for recycling. The liquid phase removal rate at the gas phase outlet of the top of the venturi separator 102 is 99.8%, and the specific operating conditions of the extractive distillation system are shown in Table 1.

[0093] The reformed oil C6-C7 fraction is used as the raw material, and the aromatic mass fraction in the raw material is 65%. Figure 3 The extractive distillation system shown in the figure separates benzene and toluene in the raw material, the solvent is sulfolane, the solvent ratio is 4.3, and the reflux ratio is 0.3. The separation requirements are: the mass fraction of aromatics in the raffinate product does not exceed 0.2%, and the mass fraction of aromatics after the solvent is removed from the rich solvent stream in the bottom of the tower is 99.9%. 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.

[0094] 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.

[0095] Example 6

[0096] The method of this embodiment is the same as that of Embodiment 5, except that the inlet gas velocity at the inlet of the venturi tube is 40 m / s, and the absolute pressure of the washing 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.

[0097] Example 7

[0098] The extractive distillation system, operation method and raw materials used in this embodiment are the same as those used in Example 3 (containing 26.5% benzene), with the only difference being the active layer of the extractive distillation tower. In this embodiment, the gas-liquid contact mass transfer element of the active layer is a packed tray composite.

[0099] like Figure 2 The extractive distillation tower shown in the figure has a gas-liquid contact mass transfer element of the active layer of the extractive distillation tower, which is a packed plate complex, including a three-dimensional jet packing plate and a Mellapak250 structured packing; the separation requirements are: the mass fraction of benzene in the raffinate oil product does not exceed 0.1%, and the mass fraction of benzene in the bottom solvent-rich flow after the solvent is removed is 99.9%.

[0100] use Figure 2 The extractive distillation tower shown separates 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 3. The parameters and energy consumption of the extractive distillation tower 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 those in Example 1. The difference from Example 1 is that the extractive distillation tower uses conventional F1 floating valve plates to separate benzene and toluene in the raw materials. The parameters and energy consumption of the extractive distillation tower 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 those in Example 1, except that the extractive distillation tower uses Mellapak 250 structured packing to separate benzene and toluene in the raw materials used in Example 1. Due to the large liquid phase load in the middle and lower sections of the tower, the tower is prone to flooding. The parameters of the tower 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 those in Example 1, except that the extractive distillation tower uses a stereo jet type tray to separate benzene and toluene in the raw material used in Example 1. The tower 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 those in Example 3, except that the extractive distillation tower uses a conventional F1 float valve tower to separate the benzene in the raw material used in Example 3. The tower 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 those in Example 3, except that the extractive distillation tower uses Mellapak 250 structured packing to separate benzene in the raw material used in Example 3. The tower 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 those in Example 3, except that the extractive distillation tower uses a stereo jet type tray to separate the benzene in the raw material used in Example 3. The tower parameters and energy consumption are shown in Table 3.

[0113] Table 1.

[0114]

[0115] Table 2.

[0116]

[0117] Table 3.

[0118]

[0119] According to the data in Table 1 and Table 2, by comparing Example 1 with Comparative Example 1, it can be seen that since the separation efficiency of the floating valve tower plate of the packing layer and the active layer of the extractive distillation tower in Comparative Example 1 is not as good as the structured packing and the packing tower plate complex of Example 1, the full tower pressure drop of the extractive distillation tower in Comparative Example 1 is large and the energy consumption is high.

[0120] By comparing Example 1 with Comparative Examples 1 and 2, it can be seen that due to the large L / V ratio of the middle and lower sections of the tower, the separation efficiency of using only the filler is significantly reduced, resulting in a separation efficiency that is not as good as that of the ordinary floating valve tray. Therefore, the full tower pressure drop of Comparative Example 2 is greater than that of Comparative Example 1, far exceeding that of Example 1, and the energy consumption is higher. Using the extractive distillation tower of the present invention, the full tower pressure drop is low, the tower bottom temperature is low, and the energy consumption is further reduced.

[0121] By comparing Example 1 with Comparative Example 3, it can be seen that since the separation efficiency of the floating valve trays in the upper and middle sections of the extractive distillation tower is not as good as that of the structured packing and the packing tray composite of the present application, the pressure drop of the whole tower is large and the energy consumption is high in Comparative Example 3. When the extractive distillation tower of the present application is used, the pressure drop of the whole tower is low, the temperature of the tower bottom is low, and the energy consumption is further reduced.

[0122] 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 floating valve tower plates, or Mellapak250 structured packing, or three-dimensional injection tower plates, the pressure drop of the whole tower is large and the energy consumption is higher, which further illustrates the superiority of the present application in the process of extractive distillation and separation of benzene; using the extractive distillation tower of the present invention, the pressure drop of the whole tower is low, the bottom temperature of the tower is low, and the energy consumption is further reduced.

[0123] By comparing Example 1 with Example 4, it can be seen that within the theoretical stage range of the packing layer, the active layer and the tower plate layer of the present invention, the full-tower pressure drop of the extractive distillation tower of the present application is lower, the tower bottom temperature is lower, and the energy consumption is further reduced.

[0124] 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 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 bottom temperature is lower, and the energy consumption is further reduced.

[0125] By comparing Example 3 with Example 7, it can be seen that when the mass fraction of aromatic hydrocarbons in the raw material is lower than 50% (that is, the mass fraction of non-aromatic hydrocarbons in the raw material is higher than 50%), if the gas-liquid contact mass transfer element of the active layer is selected as a filler, compared with when the gas-liquid contact mass transfer element of the active layer is a filler plate complex, the full-tower pressure drop of the extractive distillation tower is lower, the bottom temperature is lower, and the energy consumption is further reduced.

[0126] Test Example 1

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

[0128] Table 4

[0129]

[0130] 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, which increases the water content of the extractive solvent in the extractive distillation tower, improves the selectivity of the extractive solvent, increases the content of non-aromatic hydrocarbons in the raffinate oil and the effect of solvent removal, and further improves the quality and yield of aromatic hydrocarbon products 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 raffinate oil product is lower. Therefore, a synergistic effect is produced in the extractive distillation tower and the venturi separator of the present invention.

[0131] 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, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

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

[0133] In addition, 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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