Method and system for preparing isobutene from tert-butyl alcohol

Abstract

The invention relates to a method and system for preparing isobutene from tert-butyl alcohol, and the method comprises the following steps: S1, hydrolyzing initial tert-butyl alcohol to obtain a first product containing water, isobutene and unreacted tert-butyl alcohol; s2, performing membrane permeation separation on the first product to obtain a water permeate and a retentate containing isobutene and unreacted tert-butyl alcohol; s3, performing flash evaporation separation on the retentate to obtain gas-phase isobutene and liquid-phase tert-butyl alcohol; circulating the liquid-phase tert-butyl alcohol and repeating the steps S1 to S3 until the total conversion rate of the initial tert-butyl alcohol reaches a preset value; rectifying the liquid-phase tert-butyl alcohol, all water permeates and all gas-phase isobutene obtained in the last-stage circulation to obtain high-purity isobutene, water-tert-butyl alcohol azeotrope and wastewater; the water-tert-butyl alcohol azeotrope is extracted from the side line of the rectifying stripping section and returns to S2 for recycling. Through cyclic coupling of hydrolysis, membrane permeation separation, flash separation and rectification, high-purity isobutene is obtained, the conversion rate of tert-butyl alcohol is high, and the discharge amount of wastewater is low.

Description

Technical Field

[0001] The present application relates to the technical field of isobutylene preparation, and in particular to a method and system for preparing isobutylene from tert-butyl alcohol. Background Art

[0002] Isobutylene is an important monomer in the synthesis of diisobutylene, butyl rubber, and polyisobutylene. It is also a basic organic chemical raw material for the production of various chemicals, including methyl methacrylate. The production of high-purity isobutylene by hydrolysis of tert-butyl alcohol offers advantages such as a simple process flow, minimal side reactions, and low investment.

[0003] Tertiary butyl alcohol is usually hydrolyzed in the presence of an acidic catalyst such as an acidic silica-alumina molecular sieve or a sulfonic acid resin to produce isobutylene and water. This reaction is controlled by thermodynamic equilibrium and is endothermic. The reaction equation is shown in Equation (1):

[0004]

[0005] During the hydrolysis of tert-butanol, water and isobutylene are continuously generated. The generated water and / or isobutylene affect the catalytic action of the catalyst, hindering the reaction from proceeding in the forward direction of generating water and isobutylene, making it difficult to achieve the desired conversion rate for the hydrolysis of tert-butanol. In addition, the currently discharged industrial wastewater contains tert-butanol that forms an azeotropic reaction with water, resulting in tert-butanol loss and environmental pollution. Summary of the Invention

[0006] The present application provides a method and system for preparing isobutylene from tert-butanol to solve the following technical problems: how to improve the reaction efficiency of preparing isobutylene from tert-butanol, the conversion rate of tert-butanol, and reduce wastewater discharge.

[0007] In a first aspect, an embodiment of the present application provides a method for preparing isobutylene from tert-butyl alcohol, the method comprising:

[0008] S1, hydrolyzing the initial tert-butanol raw material to obtain a first product containing water, isobutylene and unreacted tert-butanol;

[0009] S2. Subjecting the first product to membrane permeation separation to obtain a water permeate and a retentate containing isobutylene and unreacted tert-butyl alcohol;

[0010] S3, flash-distilling the retentate containing isobutylene and unreacted tert-butyl alcohol to obtain gaseous isobutylene and liquid tert-butyl alcohol, respectively;

[0011] S4, circulating the liquid phase tert-butanol and repeating steps S1 to S3 until the total conversion rate of the initial tert-butanol raw material reaches a preset value;

[0012] S5. The liquid-phase tert-butanol, all the water permeates, and all the gaseous isobutylene obtained by the final stage of the cycle are distilled to obtain high-purity isobutylene, a water-tert-butanol azeotrope, and wastewater, respectively; wherein the distillation comprises a rectifying section and a stripping section, the water-tert-butanol azeotrope is separated by extracting from the side line of the stripping section, and the water-tert-butanol azeotrope is returned to step S2 for recycling.

[0013] Optionally, the preset value of the total conversion rate of the initial tert-butanol raw material is ≥99.90%.

[0014] Optionally, the step of circulating the liquid phase tert-butanol and repeating steps S1 to S3 until the total conversion rate of the initial tert-butanol raw material reaches a preset value comprises:

[0015] The liquid phase tert-butanol is divided into a first circulation liquid phase tert-butanol and a second circulation liquid phase tert-butanol, and the steps S1 to S3 are circulated respectively and repeated until the total conversion rate of the initial tert-butanol raw material reaches a preset value; wherein the first circulation liquid phase tert-butanol is used to participate in the tert-butanol hydrolysis reaction of the current cycle, and the second circulation liquid phase tert-butanol is used to participate in the tert-butanol hydrolysis reaction of the next cycle or for distillation; wherein, in the single-stage cycle,

[0016] The flow rate of the first circulating liquid phase tert-butyl alcohol satisfies: 0≤L1≤4.0L0;

[0017] The flow rate of the second circulating liquid phase tert-butyl alcohol satisfies: (L3, 1.0L0) min ≤L2≤5.0L0;

[0018] L0 represents the flow rate of the initial tert-butanol raw material, kg / h, L1 represents the flow rate of the first circulating liquid phase tert-butanol, kg / h, L2 represents the flow rate of the second circulating liquid phase tert-butanol, kg / h, and L3 represents the flow rate of the liquid phase tert-butanol obtained in step S3 after this stage reaction, kg / h.

[0019] Optionally, the process parameters of the hydrolysis reaction include: an operating temperature of 55° C. to 125° C., and an operating pressure of 0.5 MPa to 2.4 MPa.

[0020] Optionally, the membrane osmotic separation includes a retentate zone and a permeate zone; wherein,

[0021] The process parameters of the retentate zone include: operating temperature of 55°C to 125°C, operating pressure of 0.5MPa to 2.4MPa;

[0022] The process parameters of the permeation zone include: operating temperature of 30°C to 120°C, absolute operating pressure of 1kPa to 90kPa;

[0023] The process parameters of the membrane used in the membrane osmotic separation include: membrane flux of 1.0 kg / (m 2 ·h)~300.0kg / (m 2 ·h), the membrane separation factor is 10.0~1000.0.

[0024] Optionally, the process parameters of the flash separation include: an operating temperature of 50° C. to 110° C., and an operating pressure of 0.15 MPa to 1.15 MPa.

[0025] Optionally, a distillation tower is used for the distillation, and the process parameters of the distillation include: a top operating temperature of the distillation tower is 5°C to 85°C, a bottom operating temperature of the distillation tower is 105°C to 166°C, and an operating pressure is 0.15MPa to 1.0MPa.

[0026] Optionally, the number of plates in the rectifying section is 12 to 32, and the number of plates in the stripping section is 12 to 36; wherein,

[0027] The feed positions of all the gaseous isobutylene are located below any tray between the 2nd tray and the 10th tray from the top to the bottom of the distillation section; and / or,

[0028] The extraction position of the water-tert-butanol azeotrope is located below any tray between the 5th and 11th trays from the top to the bottom of the stripping section; and / or

[0029] The feed positions of all the water permeates are located below any tray between the 17th tray and the 33rd tray from the top to the bottom of the stripping section.

[0030] Optionally, the extraction flow rate of the water-tert-butanol azeotrope is negatively correlated with the content of tert-butanol in the wastewater.

[0031] In a second aspect, an embodiment of the present application provides a system for preparing isobutylene from tert-butyl alcohol, the system being configured to implement the steps of any one of the methods described in the first aspect, the system comprising:

[0032] A multi-stage tert-butanol hydrolysis reaction assembly 1 is connected in sequence, and the tert-butanol hydrolysis reaction assembly 1 includes: a reactor 2, a membrane permeation separator 3 and a flash separator 4 connected in sequence, all of the flash separators 4 constitute a flash separator 4, and a partition is provided between every two flash separators 4;

[0033] The distillation tower 5 is respectively connected to the water permeate outlet of each stage of the membrane permeation separator 3 and the gas outlet of each stage of the flash separator 4; the distillation tower 5 includes a distillation section 51 and a stripping section 52, and a side line extraction line 6 is provided in the stripping section 52. The side line extraction line 6 is connected to the feed port of at least one membrane permeation separator 3.

[0034] Optionally, the multi-stage tert-butanol hydrolysis reaction assembly 1 includes: a first tert-butanol hydrolysis reaction assembly 101, comprising: a first reactor 201, a first membrane permeation separator 301 and a first flash separator 401 connected in sequence, wherein the liquid outlet of the first flash separator 401 is respectively connected to the feed port of the first reactor 201;

[0035] The second tert-butanol hydrolysis reaction assembly 102 includes: a second reactor 202, a second membrane permeation separator 302, and a second flash separator 402 connected in sequence, wherein the liquid outlet of the second flash separator 402 is respectively connected to the feed port of the second reactor 202, and the feed port of the second reactor 202 is also connected to the liquid outlet of the first flash separator 401;

[0036] The third tert-butanol hydrolysis reaction assembly 103 includes: a third reactor 203, a third membrane permeation separator 303 and a third flash separator 403 connected in sequence; the liquid outlet of the third flash separator 403 is respectively connected to the feed port of the third reactor 203 and the feed port of the distillation tower 5, and the feed port of the third reactor 203 is also connected to the liquid outlet of the second flash separator 402.

[0037] Optionally, the first flash separator 401, the second flash separator 402 and the third flash separator 403 are contained in a horizontal cylindrical separator 7; wherein, a partition is provided between each adjacent two flash separators 4, and the partition is used to prevent the liquids in the lower parts of each flash separator 4 from mixing with each other and to fully mix the gases in the upper parts of each flash separator 4.

[0038] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0039] The present invention provides a method for preparing isobutylene from tert-butanol. The initial tert-butanol raw material undergoes a hydrolysis reaction. The preparation of isobutylene from tert-butanol is controlled by thermodynamic equilibrium and is an endothermic reaction. Water and isobutylene are continuously generated during the hydrolysis of tert-butanol. The first product containing water, isobutylene, and unreacted tert-butanol is separated by membrane osmosis. The generated water is promptly removed from the reaction system to prevent excessive water from being adsorbed by the catalyst and covering the catalyst active center. In addition, the generated isobutylene is promptly removed from the reaction system to ensure that the reaction continues in the forward direction of the tert-butanol hydrolysis reaction, thereby significantly improving the reaction efficiency of the tert-butanol hydrolysis. The retentate containing isobutylene and unreacted tert-butanol is flash-distilled to obtain gaseous isobutylene and liquid tert-butanol, respectively. The liquid tert-butanol is circulated and steps S1 to S3 are repeated to ensure that the total conversion rate of the initial tert-butanol raw material reaches a preset value. The liquid tert-butanol, all water permeates, and all gaseous isobutylene obtained from the final cycle are rectified to obtain high-purity isobutylene, a water-tert-butanol azeotrope, and wastewater, respectively. The rectification includes a rectifying section and a stripping section, the water-tert-butanol azeotrope is extracted from the side of the stripping section, and the water-tert-butanol azeotrope is returned to step S2 for recycling, thereby improving the utilization rate of the tert-butanol. Therefore, through the highly coupled multi-stage reaction-multi-stage membrane separation-multi-stage flash separation-primary distillation separation, high-purity isobutylene is obtained, the total conversion rate of the initial tert-butanol raw material is improved, and the discharge of wastewater is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0041] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0042] Figure 1 A schematic flow chart of a method for preparing isobutylene from tert-butyl alcohol provided in an embodiment of the present application;

[0043] Figure 2 This is a schematic structural diagram of a system for preparing isobutylene from tert-butyl alcohol provided in an embodiment of the present application; wherein,

[0044] 1-tert-Butanol hydrolysis reaction assembly, 2-reactor, 3-membrane permeation separator, 4-flash separator, 5-distillation column, 51-distillation section, 52-stripping section, 6-side line extraction line, 101-first tert-Butanol hydrolysis reaction assembly, 201-first reactor, 301-first membrane permeation separator, 401-first flash separator, 102-second tert-Butanol hydrolysis reaction assembly, 202-second reactor, 302-second membrane permeation separator, 402- Second flash separator, 103-third tert-butanol hydrolysis reaction assembly, 203-third reactor, 303-third membrane permeation separator, 403-third flash separator, 404-first partition, 405-second partition, 7-horizontal cylindrical separator, 8-booster, 9-condenser, 1001-reflux tank, 1002-reflux pump, 11-reboiler, 1201-first circulation pump, 1202-second circulation pump, 1203-third circulation pump. DETAILED DESCRIPTION

[0045] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0046] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0047] In this application, unless otherwise specified, the directional words used, such as "upper" and "lower", refer specifically to the directions of the drawings in the accompanying drawings. In addition, in the description of the present application specification, the terms "including", "comprising", etc., mean "including but not limited to". In this article, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In this article, "at least one" refers to one or more, and "a plurality" refers to two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0048] It should be noted that, in this application, terms such as "upper," "lower," "left," "right," "front," "back," "top," "bottom," "inside," "outside," "vertical," "horizontal," "transverse," and "longitudinal" indicate positions or locations based on the positions or locations shown in the accompanying drawings. These terms are primarily intended to better describe this application and its embodiments and are not intended to limit the devices, elements, or components indicated to having a specific orientation, or to being constructed or operated in a specific orientation.

[0049] Furthermore, some of the above terms may be used to express other meanings besides indicating a position or location. For example, the term "on" may also be used to express a dependency or connection in certain circumstances. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0050] Furthermore, the terms "installed," "disposed," "provided with," "connected," and "connected" should be interpreted broadly. For example, they can refer to fixed connections, removable connections, or integral structures; mechanical connections or electrical connections; direct connections, indirect connections through an intermediary, or internal communication between two devices, elements, or components. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0051] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0052] In a first aspect, the present invention provides a method for preparing isobutylene from tert-butyl alcohol. Figure 1 This is a schematic diagram of a method for preparing isobutylene from tert-butyl alcohol provided in an embodiment of the present application; see Figure 1 , the method comprising:

[0053] S1, the initial tert-butyl alcohol raw material is subjected to a multi-stage hydrolysis reaction to obtain a first product containing water, isobutylene and unreacted tert-butyl alcohol; the initial tert-butyl alcohol raw material is subjected to a hydrolysis reaction, which is the starting step of the entire process. The reaction generates a first product containing water, isobutylene and unreacted tert-butyl alcohol. The degree of progress of this reaction affects the ratio of each component and the difficulty of processing in subsequent steps. The reaction of tert-butyl alcohol hydrolysis to generate isobutylene and water is a reversible reaction, and the reaction conditions (such as operating temperature, operating pressure, catalyst, etc.) have a significant impact on the equilibrium and rate of the reaction.

[0054] In some embodiments, the process parameters of the hydrolysis reaction include: an operating temperature of 55° C. to 125° C., and an operating pressure of 0.5 MPa to 2.4 MPa.

[0055] The operating temperature of the hydrolysis reaction can be 55°C to 125°C, at which the rate of the hydrolysis reaction can be ensured and the catalyst can maintain a high reaction activity over a long operating cycle. The operating pressure can be 0.5MPa to 2.4MPa, at which the tert-butyl alcohol hydrolysis reaction can be carried out in a liquid phase and is conducive to reducing the size of the reaction equipment. For example, the operating temperature of the hydrolysis reaction can be 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, etc.; the operating pressure can be 0.5MPa, 0.6MPa, 1.0MPa, 1.5MPa, 1.6MPa, 2.0MPa, 2.4MPa, etc. By controlling the processing parameters of hydrolysis reaction, making the per pass conversion of every grade of trimethyl carbinol hydrolysis reaction can be 40%~65%, do not pursue too high trimethyl carbinol per pass conversion, make reaction can be carried out under relatively relaxed condition (as aforementioned suitable operation temperature and working pressure range), help the long cycle stable operation of device.Though every grade of trimethyl carbinol per pass conversion is not very high, by the setting of multistage reactor and follow-up cyclic operation (as unreacted trimethyl carbinol is looped back to reactions step, side line extraction line is set, etc.), can improve the total conversion of trimethyl carbinol on the whole, reach preset value.This mode, when guaranteeing the stable operation of device, also can realize making full use of raw material, has taken into account the reliability of economic benefit and device, has reduced equipment and operating cost.

[0056] The catalyst used in the hydrolysis reaction can be one or more of a beta zeolite catalyst, a clay catalyst, and a macroporous cation exchange resin catalyst. The volumetric space velocity of the catalyst bed liquid can be 0.5h -1 ~12.0h -1 .

[0057] S2. Subjecting the first product to membrane permeation separation to obtain a water permeate and a retentate containing isobutylene and unreacted tert-butyl alcohol;

[0058] The first product is separated using a selectively permeable membrane, yielding a water permeate in the permeate zone and a retentate containing isobutylene and unreacted tert-butyl alcohol in the retentate zone. Membrane permeation separation, a separation method based on the principle of membrane selective permeation, offers advantages such as low energy consumption and simple operation. This step effectively separates water from the mixture, improving the efficiency of subsequent flash and distillation separations and reducing plant energy consumption. Membrane properties (such as selectivity, permeability, and stability) play a key role in separation effectiveness.

[0059] In some embodiments, the membrane osmotic separation comprises a retentate zone and a permeate zone; wherein,

[0060] The process parameters of the retentate zone include: operating temperature of 55°C to 125°C, operating pressure of 0.5MPa to 2.4MPa;

[0061] The process parameters of the permeation zone include: operating temperature of 30°C to 120°C, absolute operating pressure of 1kPa to 90kPa;

[0062] The process parameters of the membrane used in the membrane osmotic separation include: membrane flux of 1.0 kg / (m 2 ·h)~300.0kg / (m 2 ·h), the membrane separation factor is 10.0~1000.0.

[0063] The operating temperature of the membrane permeation zone can be 30℃~120℃, which can ensure that the phase of water permeate is gas phase and matches the operating temperature of the retentate zone of 55℃~125℃; the absolute operating pressure of the membrane permeation zone is 1kPa~90kPa, and the operating pressure of the retentate zone is 0.5MPa~2.4MPa, which can ensure the operating pressure difference on both sides of the membrane, enhance the driving force of the permeation process, and improve the membrane flux and separation efficiency. Membrane flux is one of the important indicators to measure membrane separation performance. Membrane flux can be

[0064] 1.0kg / (m 2 ·h)~300.0kg / (m 2h). Within this range, the equipment cost and operating cost of the membrane permeation separator can be taken into account, so that the device can be operated at a lower total equipment and operating cost. The membrane separation factor reflects the separation ability of the membrane for different substances. The membrane separation factor can be 10.0 to 1000.0. Within this range, the selectivity and life of the membrane can be ensured, and water can be effectively separated from other substances such as tert-butyl alcohol, thereby improving the purity of the permeate and retentate. For example, the operating temperature of the permeation zone may be 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, etc.; the absolute operating pressure of the permeation zone may be 1 kPa, 3 kPa, 5 kPa, 7 kPa, 9 kPa, 10 kPa, 15 kPa, 20 kPa, 25 kPa, 30 kPa, 35 kPa, 40 kPa, 45 kPa, 50 kPa, 60 kPa, 70 kPa, 80 kPa, 90 kPa, etc.; the membrane flux may be 1.0 kg / (m 2 ·h)、5.0kg / (m 2 ·h)、10.0kg / (m 2 ·h)、20.0kg / (m 2 ·h)、30.0kg / (m 2 ·h)、50.0kg / (m 2 ·h)、100.0kg / (m 2 ·h)、150.0kg / (m 2 ·h)、200.0kg / (m 2 ·h)、250.0kg / (m 2 ·h)、300.0kg / (m 2 h), etc.; the membrane separation factor may be 10.0, 20.0, 50.0, 100.0, 500.0, 1000.0, etc. After step S2 is implemented, the molar fraction of water in the water permeate may be 85% to 100%.

[0065] The permeable membrane can be an organic membrane, an inorganic membrane or an organic-inorganic composite membrane, among which the organic membrane includes polyvinyl alcohol membrane (PVA), polyetherimide, chitosan, alginic acid, nitrocellulose / polymethacrylate, maleimide acrylic acid copolymer, 4-ethylpyridine acrylonitrile copolymer, sulfonated polystyrene / PVA, etc.; the inorganic membrane includes ZSM-5 high silicon-aluminum ratio zeolite membrane, NaA low silicon-aluminum ratio zeolite membrane, etc.; the organic-inorganic composite membrane includes polyvinyl alcohol doped NaA composite membrane, polyvinyl alcohol doped magnetic Fe2O3 nanoparticle composite membrane, etc.

[0066] S3, flash-distilling the retentate containing isobutylene and unreacted tert-butyl alcohol to obtain gaseous isobutylene and liquid tert-butyl alcohol, respectively;

[0067] The retentate containing isobutylene and unreacted tert-butyl alcohol is subjected to flash separation. By reducing the operating pressure, most of the isobutylene is vaporized to form gaseous isobutylene, while the majority of the tert-butyl alcohol remains in the liquid phase. Flash separation is a simple and effective separation method that utilizes the difference in boiling points between isobutylene and tert-butyl alcohol at different operating pressures. Flash conditions (such as operating pressure and operating temperature) require precise control to ensure the most complete separation of isobutylene from the liquid phase while avoiding excessive vaporization of tert-butyl alcohol, thereby improving separation efficiency and product purity.

[0068] In some embodiments, the process parameters of the flash separation include: an operating temperature of 50° C. to 110° C., and an operating pressure of 0.15 MPa to 1.15 MPa.

[0069] The operating temperature of the flash separation can be 50°C to 110°C, and the operating pressure can be 0.15MPa to 1.15MPa. Under the above operating conditions, the retentate containing isobutylene and unreacted tert-butanol changes from a liquid phase to a gas-liquid mixed phase. The gaseous isobutylene and liquid tert-butanol can be effectively separated by flash evaporation, and the gaseous isobutylene contains as low a tert-butanol content as possible, and the liquid tert-butanol contains as low a isobutylene content as possible. For example, the operating temperature of the flash separation can be 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, etc.; the operating pressure can be 0.15MPa, 0.2MPa, 0.3MPa, 0.4MPa, 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa, 0.9MPa, 1.0MPa, 1.15MPa, etc.

[0070] S4, circulating the liquid phase tert-butanol and repeating steps S1 to S3 until the total conversion rate of the initial tert-butanol raw material reaches a preset value;

[0071] The liquid tert-butyl alcohol is recycled back to step S1 for further hydrolysis, S2 for further membrane permeation separation, and S3 for further flash separation or sent to a distillation column until the total conversion rate of the initial tert-butyl alcohol raw material reaches a preset value. This cyclic operation can improve the utilization rate of tert-butyl alcohol and reduce the waste of raw materials.

[0072] In some embodiments, the preset value of the total conversion rate of the initial tert-butanol feedstock is ≥99.90%.

[0073] When the preset value is set to ≥99.90%, it means that after a series of hydrolysis reactions, separation, and recycling operations, at least 99.90% of the initial tert-butyl alcohol feedstock can be converted into the target product isobutylene and water. This greatly improves the utilization rate of the raw material and reduces the waste of tert-butyl alcohol. Exemplary preset values ​​can be 99.90%, 99.91%, 99.92%, 99.93%, 99.94%, 99.95%, 99.96%, 99.97%, 99.98%, 99.99%, etc.

[0074] In some embodiments, the step of circulating the liquid tert-butanol and repeating steps S1 to S3 until the total conversion rate of the initial tert-butanol raw material reaches a preset value comprises:

[0075] The liquid phase tert-butanol is divided into a first circulation liquid phase tert-butanol and a second circulation liquid phase tert-butanol, and the steps S1 to S3 are circulated respectively and repeated until the total conversion rate of the initial tert-butanol raw material reaches a preset value; wherein the first circulation liquid phase tert-butanol is used to participate in the tert-butanol hydrolysis reaction of the current cycle, and the second circulation liquid phase tert-butanol is used to participate in the tert-butanol hydrolysis reaction of the next cycle or for distillation; wherein, in the single-stage cycle,

[0076] The flow rate of the first circulating liquid phase tert-butyl alcohol satisfies: 0≤L1≤4.0L0;

[0077] The flow rate of the second circulating liquid phase tert-butyl alcohol satisfies: (L3, 1.0L0) min ≤L2≤5.0L0;

[0078] L0 represents the flow rate of the initial tert-butanol raw material, kg / h, L1 represents the flow rate of the first circulating liquid phase tert-butanol, kg / h, L2 represents the flow rate of the second circulating liquid phase tert-butanol, kg / h, and L3 represents the flow rate of the liquid phase tert-butanol obtained in step S3 after this stage reaction, kg / h.

[0079] The liquid phase tert-butyl alcohol is divided into a first circulation liquid phase tert-butyl alcohol and a second circulation liquid phase tert-butyl alcohol, and steps S1 to S3 are circulated separately. This division method increases operational flexibility. By controlling the flow rates of the two circulations separately, the reaction and separation processes can be more finely regulated to achieve a preset total conversion rate. According to the actual conditions of the reaction and separation, the flow rate ratio of the two circulations can be adjusted so that the reaction is carried out under more suitable conditions, thereby improving reaction efficiency and conversion rate.

[0080] S5. The liquid-phase tert-butanol, all the water permeates, and all the gaseous isobutylene obtained by the final stage of the cycle are distilled to obtain high-purity isobutylene, a water-tert-butanol azeotrope, and wastewater, respectively; wherein the distillation comprises a rectifying section and a stripping section, the water-tert-butanol azeotrope is separated by extracting from the side line of the stripping section, and the water-tert-butanol azeotrope is returned to step S2 for recycling.

[0081] The liquid-phase tert-butyl alcohol obtained in the final cycle is primarily composed of unreacted tert-butyl alcohol, which may also contain small amounts of dissolved isobutylene and other impurities. The water permeate, primarily water, is separated from the mixture during the membrane permeation separation step and may contain trace amounts of tert-butyl alcohol and isobutylene. The gaseous isobutylene is primarily obtained through flash separation and may contain a small amount of tert-butyl alcohol vapor. These three materials, with different compositions and phases, are fed to different parts of the distillation column for further distillation and separation. This reduces the presence of components such as tert-butyl alcohol and water in the separated isobutylene product, reduces the presence of components such as tert-butyl alcohol and isobutylene in the separated wastewater, and reduces the presence of components such as isobutylene and water in the water-tert-butyl alcohol azeotrope extracted from the sideline of the stripping section.

[0082] The rectifying section, located above the feed inlet, primarily performs multiple partial condensations and vaporizations on the ascending gas phase, continuously increasing the concentration of volatile components (such as isobutylene) in the gas phase. The ascending gas phase contacts the descending liquid phase on the tower plates or packing, transferring heat and mass. Volatile isobutylene continuously vaporizes from the liquid phase into the gas phase, while less volatile components (such as water and tert-butyl alcohol) remain in the liquid phase and continue to flow downward. Through the rectifying section, high-purity isobutylene product can be obtained at the top of the tower. The stripping section, located below the feed inlet, primarily performs multiple partial vaporizations and condensations on the descending liquid phase to increase the concentration of less volatile components in the liquid phase. The descending liquid phase contacts the ascending gas phase on the tower plates or packing. Through mass and heat transfer, less volatile components such as water and tert-butyl alcohol in the gas phase continuously condense into the liquid phase, while more volatile isobutylene in the liquid phase continuously vaporizes into the gas phase. Water-tert-butyl alcohol azeotrope is extracted and separated from the stripping section side line, and this is because in this position, the concentration of water and the trimethyl carbinol has reached azeotropic composition, and the components such as iso-butylene, water carried are less.By the repeatedly mass transfer and heat transfer process of rectifying section, iso-butylene is enriched at cat head and distilled from cat head and condensed and collected in gaseous form, obtains highly purified iso-butylene product.Water and the trimethyl carbinol form azeotrope, and its boiling point and composition are relatively fixed and other components carried are less.The water-tert-butyl alcohol azeotrope extracted from the stripping section side line, recycles by returning step S2 (membrane permeation separation), has realized the recycling of resources, has reduced the waste of raw materials, and has simplified the complex process that water-tert-butyl alcohol azeotrope is separated, has reduced equipment and operating cost.

[0083] It is worth mentioning that under some working conditions, such as when the temperature of the tert-butanol hydrolysis reaction increases at the end of the reaction, trace or small amounts of isobutylene will undergo a superposition reaction to generate some side reaction products with higher boiling points, such as diisobutylene. In this case, in order to reduce the organic matter content in the wastewater discharge and ensure that the mass fraction of water in the wastewater discharge is not less than 99.95%, a second side line can be set near the bottom of the distillation section of the distillation tower to extract side reaction products such as diisobutylene from the second side line.

[0084] In some embodiments, the distillation is performed using the distillation tower, and the process parameters of the distillation include: the top operating temperature of the distillation tower is 5°C to 85°C, the bottom operating temperature of the distillation tower is 105°C to 166°C, and the operating pressure is 0.15MPa to 1.0MPa.

[0085] The top operating temperature of a distillation tower can range from 5°C to 85°C. The lower the top operating temperature, the higher the cost of condensing the overhead distillate into a liquid, but the lower the cost of sending the water permeate to the distillation tower for further separation. In actual operation, the optimal top operating temperature can be determined using conventional methods based on the principle of minimizing total operating costs. The bottom operating temperature of a distillation tower can range from 105°C to 166°C, which is beneficial for separating the water-tert-butyl alcohol azeotrope from the bottom wastewater. The top operating pressure of a distillation tower is the dew point pressure corresponding to the top operating temperature. For example, the top operating temperature of the distillation tower can be 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, etc.; the bottom operating temperature of the distillation tower 5 can be 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 166°C, etc.; the top operating pressure can be 0.15MPa, 0.2MPa, 0.3MPa, 0.4MPa, 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa, 0.9MPa, 1.0MPa, etc. In addition, the process parameters of the distillation also include: the reflux ratio can be 0.8 to 8.5.

[0086] In some embodiments, the number of plates in the rectifying section is 12 to 32, and the number of plates in the stripping section is 12 to 36; wherein,

[0087] The feed positions of all the gaseous isobutylene are located below any tray between the 2nd tray and the 10th tray from the top to the bottom of the distillation section; and / or,

[0088] The extraction position of the water-tert-butanol azeotrope is located below any tray between the 5th and 11th trays from the top to the bottom of the stripping section; and / or

[0089] The feed positions of all the water permeates are located below any tray between the 17th tray and the 33rd tray from the top to the bottom of the stripping section.

[0090] The main function of the rectifying section is to increase the volatile component (isobutylene) in the gas phase. The number of plates in the rectifying section can range from 12 to 32 to ensure the purification of isobutylene. The main task of the stripping section is to increase the concentration of the less volatile components (water and tert-butyl alcohol) in the liquid phase. The number of plates in the stripping section can range from 12 to 36 to fully concentrate water and tert-butyl alcohol and ensure the purity of the water-tert-butyl alcohol azeotrope. The feed position for all gaseous isobutylene is located below any tray between the 2nd and 10th trays (counted from top to bottom) of the rectifying section, which is beneficial to improving the purity of the isobutylene at the top of the tower and reducing energy consumption. The extraction position for the water-tert-butanol azeotrope is located below any tray between the 5th and 11th trays (counted from top to bottom) of the stripping section, ensuring that the amount of water and isobutylene components carried by the water-tert-butanol azeotrope is minimized. The feed position for all water permeate is located below any tray between the 17th and 33rd trays (counted from top to bottom) of the stripping section, thereby improving the separation efficiency of the rectifying column and reducing the consumption of thermal utilities for providing heat to the reboiler. For example, the number of plates in the rectifying section may be 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, etc.; the number of plates in the stripping section may be 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, etc.; the feed positions of all gaseous isobutylene are located at the 2nd, 3rd, 4th, and 5th plates from the top down of the rectifying section. , 5, 6, 7, 8, 9, and 10 tower plates; the extraction position of the water-tert-butanol azeotrope is located below any tower plate between the 5th, 6th, 7th, 8th, 9th, 10th, and 11th tower plates counting from top to bottom of the distillation section; the feeding position of all water permeates is located below any tower plate between the 17th, 18th, 19th, 30th, 31st, 32nd, and 33rd tower plates counting from top to bottom of the distillation section.

[0091] In some embodiments, the extraction flow rate of the water-tert-butanol azeotrope is negatively correlated with the content of tert-butanol in the wastewater.

[0092] The extraction flow rate of the water-tert-butanol azeotrope is negatively correlated with the content of tert-butanol in the wastewater. This can be understood as follows: the tert-butanol content in boiling water decreases as the side-drawn flow rate of the water-tert-butanol azeotrope increases. By increasing the side-drawn flow rate of the water-tert-butanol azeotrope, the tert-butanol content in the wastewater can be correspondingly reduced. Therefore, the side-drawn flow rate of the water-tert-butanol azeotrope can be regulated to achieve the recycling of tert-butanol, improve the reaction efficiency of tert-butanol, and reduce the waste of tert-butanol.

[0093] Furthermore, the method for preparing isobutylene from tert-butyl alcohol provided in the embodiments of the present application has the following features, including but not limited to:

[0094] (1) Using a selective permeable membrane to promptly remove water and / or isobutylene generated by the hydrolysis reaction is beneficial to the tert-butanol hydrolysis reaction from the perspective of chemical equilibrium. Since the tert-butanol hydrolysis reaction is an endothermic reaction controlled by thermodynamic equilibrium, the presence of excessive water and / or isobutylene will shift the equilibrium toward the reverse reaction, while timely removal of water and / or isobutylene from the reaction system will prompt the reaction to continue in the forward reaction direction. This not only improves the reaction efficiency and the conversion rate of tert-butanol, but also enables the reaction to proceed under relatively low temperature and pressure conditions, reducing dependence on harsh reaction conditions, and reducing energy consumption and equipment size. At the same time, it also avoids water covering the active center of the catalyst, ensuring the activity and stability of the catalyst, extending the service life of the catalyst, and further improving the reaction efficiency;

[0095] (2) Flash separation effectively separates the retentate containing isobutylene and unreacted tert-butyl alcohol into gaseous isobutylene and liquid tert-butyl alcohol. The difference in boiling points between the two allows for preliminary separation of isobutylene and tert-butyl alcohol. The gaseous isobutylene and liquid tert-butyl alcohol are then sent to different parts of the distillation tower, effectively reducing the energy consumption and tower diameter required for distillation tower separation, thereby reducing equipment and operating costs.

[0096] (3) A distillation process different from conventional processes is adopted. Through the rational design of the distillation section and the stripping section, the final circulating liquid phase tert-butyl alcohol, water permeate, and gaseous phase isobutylene are further distilled and separated to obtain high-purity isobutylene, water-tert-butyl alcohol azeotrope, and wastewater. The water-tert-butyl alcohol azeotrope is returned to the membrane permeation separation step for recycling, simplifying the process flow for treating the water-tert-butyl alcohol azeotrope, further improving the conversion rate of tert-butyl alcohol, and reducing raw material loss.

[0097] (4) The water permeate is mainly composed of water and is in the gas phase. Its feed position is located at the lower part of the distillation section, which can play an important role in stripping the liquid from top to bottom in the distillation column, thereby significantly reducing the heat utility consumption for providing heat to the reboiler;

[0098] (5) A highly coupled process of multi-stage reaction-multi-stage membrane separation-multi-stage flash separation-one-stage distillation separation is adopted. The water and isobutylene generated during the reaction are separated in time by membrane separation and flash separation, which can effectively reduce the accumulation of isobutylene and other products in the reaction system, and further reduce the amount of side reaction products such as diisobutylene. This not only increases the isobutylene yield, but also reduces the organic matter content in the wastewater. Correspondingly, it also further reduces the difficulty and cost of wastewater treatment.

[0099] In a second aspect, an embodiment of the present application provides a system for preparing isobutylene from tert-butyl alcohol, the system being configured to implement the steps of any one of the methods described in the first aspect, the system comprising:

[0100] A tert-butanol hydrolysis reaction assembly 1 is connected in multiple stages in sequence, and the tert-butanol hydrolysis reaction assembly 1 includes: a reactor 2, a membrane permeation separator 3 and a flash separator 4 connected in sequence.

[0101] The distillation tower 5 is respectively connected to the water permeate outlet of each stage of the membrane permeation separator 3 and the gas outlet of each stage of the flash separator 4; the distillation tower 5 includes a distillation section 51 and a stripping section 52, and a side line extraction line 6 is provided in the stripping section 52. The side line extraction line 6 is connected to the feed port of at least one membrane permeation separator 3.

[0102] Reactor 2 can be a tubular reactor, comprising a tube side and a shell side. The tube side includes reaction tubes, which contain a catalyst for the tert-butyl alcohol hydrolysis reaction. When viewed from above, the reaction tubes are evenly distributed across the entire cross-section of reactor 2 in an equilateral triangle or square arrangement. The reaction tube diameter ranges from 25 mm to 250 mm, and the center-to-center distance between adjacent reaction tubes is 1.1 to 1.3 times the diameter of the reaction tube. Steam, thermal oil, hot water, electricity, or other heating media is introduced into the shell side to maintain a constant reaction temperature within the reaction tubes of reactor 2. Reactor 2 can be operated alone or in parallel.

[0103] Membrane permeation separator 3 comprises a retentate zone, a permeate membrane, and a permeate zone. The reaction product contacts the permeate membrane during its flow within membrane permeation separator 3. The permeate membrane is hydrophilic, meaning that water dissolves in and diffuses through the membrane at a higher rate than components such as tert-butyl alcohol and isobutylene. Due to the pressure differential across the membrane, water preferentially diffuses through the membrane, ultimately yielding a permeate primarily composed of water in the permeate zone. A retentate primarily composed of tert-butyl alcohol and isobutylene is obtained in the retentate zone and is then discharged to flash separator 4. Membrane permeation separator 3 can be constructed in a tubular, plate-and-frame, spiral, or hollow fiber configuration.

[0104] In some embodiments, the first flash separator 401, the second flash separator 402 and the third flash separator 403 are contained in a horizontal cylindrical separator 7, wherein a partition is provided between each two adjacent flash separators 4, and the partition is used to prevent the liquids in the lower parts of the flash separators 4 from mixing with each other and to fully mix the gases in the upper parts of the flash separators 4.

[0105] Multiple flash separators 4 share a horizontal cylindrical separator 7, and a partition is set between each adjacent flash separator 4. The height of the partition is 70% to 85% of the diameter of the flash separator 4, which is used to isolate the liquid in the lower part of each flash separator 4 so that the liquid in the lower part of each flash separator 4 does not mix with each other, but the gas in the upper part of each flash separator 4 can be fully mixed. For example, Figure 2 As shown, the flash separator 4 includes a first flash separator 401, a second flash separator 402, and a third flash separator 403. These three flash separators share a horizontal cylindrical separator, wherein a partition is provided between each two adjacent flash separators. Specifically, a first partition 404 is provided between the first flash separator 401 and the second flash separator 402, and a second partition 405 is provided between the second flash separator 402 and the third flash separator 403.

[0106] The permeates separated by the membrane permeation separators 3 are collected together and then enter the inlet of the booster 8 as a mixed permeate. After being pressurized by the booster 8, the mixed permeate is sent to the lower part of the distillation tower 5 for further separation. Alternatively, after being pressurized by the booster 8, the mixed permeate can first enter the shell side of the reactor 2 to provide heat for the tert-butyl alcohol hydrolysis reaction before entering the distillation tower 5.

[0107] The supercharger can be operated in parallel or / and in series, and the type can be one or more of piston, screw, rotor, centrifugal, mixed flow, and steam jet compressors.

[0108] The distillation tower 5 comprises a rectifying section 51 and a stripping section 52, with the rectifying section 51 at the top and the stripping section 52 at the bottom, separated by the feed point of the rectifying feed. Under the action of the distillation tower 5, the isobutylene in the tower flows upward until it reaches the top and enters the condenser 9 from the top. Inside the condenser 9, it is cooled to 4.5°C to 45.0°C before entering the reflux tank 1001. After being pressurized by the reflux pump 1002, a portion of the isobutylene is returned to the top of the distillation tower 5 as reflux, while the remaining portion is output from the system as the isobutylene product. The mass fraction of isobutylene in the isobutylene product is ≥99.99%. If the isobutylene product contains other components, these can be further separated and removed using conventional methods such as distillation, adsorption, and extraction.

[0109] As shown in Table 1, tert-butyl alcohol and water form an azeotrope during the distillation process, and the azeotropic composition changes with pressure.

[0110] Table 1 Azeotropic composition and azeotropic temperature of water-tert-butanol azeotrope at different pressures

[0111]

[0112] These water-tert-butanol azeotropes are difficult to separate using conventional distillation towers. In the embodiment of the present application, a sideline extraction line 6 is provided within the stripping section 52 of the distillation tower 5 for extracting sideline materials including the water-tert-butanol azeotrope. After the sideline materials are extracted, they can be directly returned to any membrane permeation separator 3 or enter each membrane permeation separator 3 in equal proportions, thereby eliminating the complex process used by conventional methods to separate the water-tert-butanol azeotrope. After the sideline materials are extracted, wastewater with a water mass fraction of ≥99.95% can be obtained at the bottom of the distillation tower 5. When the wastewater discharged from the bottom of the tower contains other components, conventional distillation, adsorption, extraction, and other methods can be further used to separate and remove the other components.

[0113] A reboiler 11 is also provided at the bottom of the distillation tower 5 to provide heat for the separation of light and heavy components in the distillation tower 5. An alternative solution is that before the material at the bottom of the distillation tower 5 enters the reboiler 11 for heating, it can first enter the shell side of the reactor 2 to provide heat for the hydrolysis reaction before entering the reboiler 11.

[0114] In summary, through distillation, high-purity isobutylene, a side-line material containing a water-tert-butanol azeotrope, and wastewater are obtained at the top, side line, and bottom of the distillation tower 5, respectively. The high-purity isobutylene is exported as a product, and the side-line material is returned to at least one membrane separation permeator 3 to separate the water and then returned to the reaction system. The wastewater is reused in other devices or sent to a sewage treatment plant for further treatment.

[0115] In some embodiments, Figure 2 This is a schematic diagram of the structure of a system for preparing isobutylene from tert-butyl alcohol provided in an embodiment of the present application; see Figure 2 The multi-stage tert-butanol hydrolysis reaction assembly 1 includes: a first tert-butanol hydrolysis reaction assembly 101, including: a first reactor 201, a first membrane permeation separator 301 and a first flash separator 401 connected in sequence, and the liquid outlet of the first flash separator 401 is respectively connected to the feed port of the first reactor 201;

[0116] The second tert-butanol hydrolysis reaction assembly 102 includes: a second reactor 202, a second membrane permeation separator 302, and a second flash separator 402 connected in sequence, wherein the liquid outlet of the second flash separator 402 is respectively connected to the feed port of the second reactor 202, and the feed port of the second reactor 202 is also connected to the liquid outlet of the first flash separator 401;

[0117] The third tert-butanol hydrolysis reaction assembly 103 includes: a third reactor 203, a third membrane permeation separator 303 and a third flash separator 403 connected in sequence; the liquid outlet of the third flash separator 403 is respectively connected to the feed port of the third reactor 203 and the feed port of the distillation tower 5, and the feed port of the third reactor 203 is also connected to the liquid outlet of the second flash separator 402.

[0118] For example, for the production of high-purity isobutylene using a highly coupled process of three-stage reaction-three-stage membrane separation-three-stage flash separation-one-stage distillation separation, the tert-butanol raw material is first fed into the first reactor 201 to generate a first product, and the first product enters the first membrane permeation separator 301. The first membrane permeation separator 301 includes a first retentate zone, a first permeate membrane, and a first permeate zone, which is used to separate the first product into a first permeate and a first retentate, wherein the main component of the first permeate is water, which is fed to the distillation tower 5 for further separation, and the main components of the first retentate are tert-butanol and isobutylene, which are fed to the first flash separator 401 for flash evaporation. At a lower pressure, the first retentate is flashed into a first gas phase product and a first liquid phase product. The first gas phase product is a saturated gas containing more isobutylene and less tert-butanol, and is sent to the distillation tower 5 for further separation; the first liquid phase product is a saturated liquid containing more tert-butanol and less isobutylene, and is sent to the second reactor 202 to continue the tert-butanol hydrolysis reaction (part of the first liquid phase product can be returned to the inlet of the first reactor 201) to generate a second product. The second product enters the second membrane permeation separator 302, and the second membrane permeation separator 302 is used to separate the second product into a second permeate and a second retentate. Then the second retentate enters the second flash separator 402, and in the second flash separator 402, the second retentate enters the second flash separator 402. 02 is flashed into a second gas phase product and a second liquid phase product, and then the second liquid phase product is sent to the third reactor 203 to continue the tert-butanol hydrolysis reaction (part of the second liquid phase product can be returned to the inlet of the second reactor 202) to generate a third product, and the third product enters the third membrane permeation separator 303, and the third membrane permeation separator 303 is used to separate the third product into a third permeate and a third retentate, and then the third retentate enters the third flash separator 403, and is flashed into a third gas phase product and a third liquid phase product in the third flash separator 403, and then the third liquid phase product can be used as a distillation feed to enter the distillation tower 5 for further separation (part of the third liquid phase product can be returned to the inlet of the third reactor 203). The above process can timely discharge the water and isobutylene generated by the hydrolysis reaction of tert-butanol, so that the reaction continues to proceed in the positive reaction direction of tert-butanol hydrolysis, thereby greatly improving the reaction efficiency; the gas including the first gas phase product, the second gas phase product, and the third gas phase product can be fully mixed in the upper part of the flash separator 4 and then enter the distillation tower 5 as a mixed gas phase product for further separation, and the mixed permeate from the outlet of the booster also enters the distillation tower 5 for further separation.

[0119] For example, the first gas phase isobutylene from the first flash separator 401 is fully mixed with the second gas phase product and the third gas phase product at the top of the flash separator 4 and then sent to the distillation tower 5 for further separation; the first liquid phase tert-butanol is discharged from the bottom liquid outlet of the first flash separator 401 as the first liquid phase product and is pressurized by the first circulation pump 1201 and then separated into a first circulation material and a second circulation material. The first circulation material returns to the inlet of the first reactor 201, mixes with the tert-butanol raw material, and then enters the tube side of the first reactor 201 together; the second circulation material enters the inlet of the second reactor 202;

[0120] The second gaseous isobutylene from the second flash separator 402 is fully mixed with the first gaseous product and the third gaseous product at the top of the flash separator 4 and then sent to the distillation tower 5 for further separation; the second liquid tert-butyl alcohol is discharged from the bottom liquid outlet of the second flash separator 402 as the second liquid product and is pressurized by the second circulation pump 1202 to be divided into a third circulation material and a fourth circulation material. The third circulation material returns to the inlet of the second reactor 202 and is mixed with the second mixed material before entering the tube side of the second reactor 202 together; the fourth circulation material enters the inlet of the third reactor 203;

[0121] The third gas-phase isobutylene from the third flash separator 403 is fully mixed with the first gas-phase product and the second gas-phase product at the top of the flash separator 4 and then sent to the distillation tower 5 for further separation; the third liquid-phase tert-butanol is discharged from the bottom liquid outlet of the third flash separator 403 as the third liquid-phase product and is pressurized by the third circulation pump 1203 and is divided into a fifth circulation material and a distillation feed. The fifth circulation material returns to the inlet of the third reactor 203, mixes with the fourth circulation material, and then enters the pipe side of the third reactor 203 together; the distillation feed enters the distillation tower 5 for further separation.

[0122] In addition, the cross-circulation of the third tert-butyl alcohol hydrolysis reaction assembly 103 can be achieved by installing a flow control valve or a buffer tank in the cross-connected pipeline. A heavy component discharge port (second sideline extraction port) can also be added at the bottom of the distillation column to prevent the circulation and accumulation of byproducts such as diisobutylene.

[0123] The system for preparing isobutylene from tert-butanol is implemented based on the above-mentioned method for preparing isobutylene from tert-butanol. The specific steps of the method for preparing isobutylene from tert-butanol can be referred to the above-mentioned embodiments. Since the system for preparing isobutylene from tert-butanol adopts part or all of the technical solutions of the above-mentioned embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above-mentioned embodiments, which will not be described in detail here.

[0124] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods in the following examples where specific conditions are not specified are usually measured in accordance with national standards. If there are no corresponding national standards, then the methods are carried out in accordance with general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0125] Example 1

[0126] Isobutylene was produced using the apparatus and method disclosed herein using a water-containing tert-butyl alcohol feedstock at a temperature of 35°C, a pressure of 1.50 MPa.A, and a flow rate of 10,000.0 kg / h, wherein the mass fraction of tert-butyl alcohol was 95.8% and the mass fraction of water was 4.2%. Example 1 represents the initial stage of the apparatus operation. Specific operating parameters for the main equipment during the production process are shown in Table 2.

[0127] Table 2 Specific operating parameters of the main equipment in Example 1

[0128]

[0129]

[0130] The flow rates and compositions of the main logistics in Example 1 are shown in Tables 3, 4 and 5.

[0131] Table 3 Flow and composition of major logistics (I)

[0132]

[0133]

[0134] Table 4 Flow and composition of major logistics (II)

[0135]

[0136] Table 5 Flow and composition of major logistics (III)

[0137]

[0138] ① As can be seen from Table 2, the catalyst activity is relatively high at the initial stage of the device operation, and the first circulation material flow rate, the third circulation material flow rate, and the fifth circulation material flow rate in Example 1 are all 0.

[0139] ② It can also be seen from Table 2 that the tert-butanol conversion rates of the first reactor, the second reactor, and the third reactor are 58.2%, 59.3%, and 60.2%, respectively. The system and method disclosed in the embodiment of the present application do not pursue an excessively high single-pass conversion rate of tert-butanol, so that the reaction is carried out under mild conditions, which is conducive to the long-term stable operation of the device.

[0140] ③ It can be seen from Tables 3, 4 and 5 that after membrane separation and equilibrium flash separation, the molar fractions of tert-butanol in the first liquid phase product, the second liquid phase product and the third liquid phase product are 0.641856, 0.562780 and 0.584084, respectively, which are much higher than 0.237179, 0.189216 and 0.167305 of the first product, the second product and the third product, respectively. The purpose of timely discharge of water and isobutylene generated by each reaction is achieved, so that the reaction continues to proceed in the forward reaction direction of tert-butanol hydrolysis, thereby improving the reaction efficiency and reducing the energy consumption for distillation tower separation.

[0141] ④ As can be seen from Tables 3, 4, and 5, Example 1 ultimately produced 7251.2 kg / h of isobutylene product, with an isobutylene mass fraction of 0.999920. Example 1 also produced 1715.397 kg of wastewater, with a water mass fraction of 0.999525. This wastewater can be used for injection of other equipment or discharged to a sewage treatment plant for further treatment.

[0142] ⑤ It can also be seen from Table 3, Table 4, and Table 5 that in Example 1, isobutylene was produced according to the steps disclosed in this application, and the total conversion rate of tert-butyl alcohol was:

[0143] (1-mass flow rate of tert-butyl alcohol in wastewater / mass flow rate of tert-butyl alcohol in tert-butyl alcohol raw material)*100%

[0144] =(1-(2748.8*0.000475) / (10000.0*0.958000)*100%=99.986%.

[0145] ⑥ The total energy consumption of the device in Example 1 is 132.7 kgoe / t isobutylene product.

[0146] Example 2 to Example 4

[0147] The raw material composition, process flow, and operating conditions in Examples 2 to 4 were identical to those in Example 1. However, the device was at the end of its operating cycle, and the catalyst activity decreased compared to Example 1. The per-pass conversion of tert-butyl alcohol in Reactor 2 was lower than that in Example 1, and the total conversion of tert-butyl alcohol decreased. In the case of insufficient catalyst activity, the total conversion of tert-butyl alcohol could be increased to over 99.9% by adjusting the circulating material flow rate.

[0148] Example 2: The first circulation material flow rate was adjusted from 0 to 20,000 kg / h, and other conditions remained unchanged. The total conversion rate of tert-butanol increased from 98.672% to 99.981%, and the tert-butanol content in the wastewater decreased from 7,800 mg / kg to 512 mg / kg.

[0149] Example 3: The third circulation material flow rate was adjusted from 0 to 28000 kg / h, the total conversion rate of tert-butanol increased from 98.793% to 99.983%, and the tert-butanol content in the wastewater decreased from 7360 mg / kg to 624 mg / kg.

[0150] Example 4: The fifth circulation material flow rate was adjusted from 0 to 39000 kg / h, the total conversion rate of tert-butanol increased from 98.556% to 99.984%, and the tert-butanol content in the wastewater decreased from 8250 mg / kg to 667 mg / kg.

[0151] Example 5-Example 6

[0152] The raw material composition, process flow, operating conditions, and product specifications in Examples 5 and 6 are exactly the same as those in Example 1.

[0153] Example 5: The side stream flow rate was adjusted from 2331.0 kg / h to 1400.0 kg / h, with other conditions remaining unchanged. The tert-butyl alcohol content in the wastewater increased from 475 mg / kg to 1012 mg / kg, and the total energy consumption decreased from 132.7 kgoe / t of isobutylene product to 127.1 kgoe / t of isobutylene product.

[0154] Example 6: The side stream flow rate was adjusted from 2331.0 kg / h to 3250.0 kg / h, with other conditions remaining unchanged. The tert-butanol content in the wastewater decreased from 475 mg / kg to 212 mg / kg, and the total energy consumption increased from 132.7 kgoe / t of isobutylene product to 137.9 kgoe / t of isobutylene product.

[0155] Comparative Example 1

[0156] Comparative example 2 discloses a system for preparing polymer-grade isobutene by hydrolysis of tert-butyl alcohol, and its publication number is CN218393609U, and this system includes the equipment such as the tert-butyl alcohol treating tower, the first catalytic distillation tower, the second catalytic distillation tower, gas compressor, isobutylene heavy-removing tower, water washer, isobutylene light-removing tower connected in sequence, wherein water washer adopts deionized water to wash the intermediate material containing isobutylene, after the discharging of water washer bottom water washing water (process water at the bottom of the tower) and is communicated with the reflux port of the second catalytic distillation tower, the second catalytic distillation tower bottom is connected with alcohol-containing wastewater discharge pipeline.As seen, comparative example 1 increases alcohol-containing wastewater amount after being changed into alcohol-containing wastewater by outside deionized water, and the one is to increase deionized water consumption, and the 2nd is unfavorable for environmental protection. In addition comparative example 1 is communicated with the reflux port of the second catalytic distillation tower by water washer bottom water washing water, is equivalent to increasing reaction product concentration, is unfavorable for the tert-butyl alcohol hydrolysis reaction and is carried out to the positive reaction direction, reduces tert-butyl alcohol conversion and reaction efficiency.

[0157] In contrast, Example 1 of the present application adopts a highly coupled process of three-stage reaction-three-stage membrane separation-three-stage flash separation-one-stage distillation separation to produce high-purity isobutylene. It does not require desalted water from the outside, and the water and isobutylene generated by the hydrolysis of tert-butanol can be discharged in time before the next stage of reaction, thereby reducing the discharge of alcohol-containing wastewater and improving the conversion rate of tert-butanol.

[0158] One or more technical solutions in the embodiments of the present application may have at least the following technical effects or advantages:

[0159] (1) The embodiments of the present application provide a method and system for preparing isobutylene from tert-butanol that is efficient, energy-saving, and environmentally friendly. The method can discharge water generated by hydrolysis of tert-butanol in a timely manner, effectively separate the water-tert-butanol azeotrope, and recycle the separated tert-butanol, thereby reducing wastewater discharge, simplifying the process flow, and reducing equipment investment and energy consumption.

[0160] (2) High-purity isobutylene is produced by adopting a highly coupled process of multi-stage reaction-multi-stage membrane separation-multi-stage flash separation-one-stage distillation separation.

[0161] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A method for preparing isobutylene from tert-butyl alcohol, the method comprising: S1, hydrolyzing the initial tert-butanol raw material to obtain a first product containing water, isobutylene and unreacted tert-butanol; S2. Subjecting the first product to membrane permeation separation to obtain a water permeate and a retentate containing isobutylene and unreacted tert-butyl alcohol; S3, flash-distilling the retentate containing isobutylene and unreacted tert-butyl alcohol to obtain gaseous isobutylene and liquid tert-butyl alcohol, respectively; S4, circulating the liquid phase tert-butanol and repeating steps S1 to S3 until the total conversion rate of the initial tert-butanol raw material reaches a preset value; S5. The liquid-phase tert-butanol, all the water permeates, and all the gaseous isobutylene obtained from the final stage of the cycle are distilled to obtain high-purity isobutylene, a water-tert-butanol azeotrope, and wastewater, respectively; wherein the distillation comprises a rectifying section and a stripping section, the water-tert-butanol azeotrope is obtained by being extracted from the side line of the stripping section, and the water-tert-butanol azeotrope is returned to step S2 for recycling.

2. The method according to claim 1, characterized in that The preset value of the total conversion rate of the initial tert-butanol raw material is ≥99.90%.

3. The method according to claim 1, characterized in that The step of circulating the liquid phase tert-butanol and repeating steps S1 to S3 until the total conversion rate of the initial tert-butanol raw material reaches a preset value comprises: The liquid phase tert-butanol is divided into a first circulation liquid phase tert-butanol and a second circulation liquid phase tert-butanol, and the steps S1 to S3 are circulated respectively and repeated until the total conversion rate of the initial tert-butanol raw material reaches a preset value; wherein the first circulation liquid phase tert-butanol is used to participate in the tert-butanol hydrolysis reaction of the current cycle, and the second circulation liquid phase tert-butanol is used to participate in the tert-butanol hydrolysis reaction of the next cycle or for distillation; wherein, in the single-stage cycle, The flow rate of the first circulating liquid phase tert-butyl alcohol satisfies: 0≤L1≤4.0L0; The flow rate of the second circulating liquid phase tert-butyl alcohol satisfies: (L3, 1.0L0) min ≤L2≤5.0L0; L0 represents the flow rate of the initial tert-butanol raw material, kg / h, L1 represents the flow rate of the first circulating liquid phase tert-butanol, kg / h, L2 represents the flow rate of the second circulating liquid phase tert-butanol, kg / h, and L3 represents the flow rate of the liquid phase tert-butanol obtained in step S3 of this cycle, kg / h.

4. The method according to claim 1, wherein The process parameters of the hydrolysis reaction include: an operating temperature of 55° C. to 125° C., and an operating pressure of 0.5 MPa to 2.4 MPa.

5. The method according to claim 1, wherein The membrane permeation separation comprises a retentate zone and a permeate zone; wherein, The process parameters of the retentate zone include: operating temperature of 55°C to 125°C, operating pressure of 0.5MPa to 2.4MPa; The process parameters of the permeation zone include: operating temperature of 30°C to 120°C, absolute operating pressure of 1kPa to 90kPa; The process parameters of the membrane used in the membrane osmotic separation include: membrane flux of 1.0 kg / (m 2 ·h)~300.0kg / (m 2 ·h), the membrane separation factor is 10.0~1000.

0.

6. The method according to claim 1, wherein The process parameters of the flash separation include: an operating temperature of 50° C. to 110° C., and an operating pressure of 0.15 MPa to 1.15 MPa.

7. The method according to claim 1, characterized in that A distillation tower is used for the distillation. The process parameters of the distillation include: a top operating temperature of the distillation tower is 5° C. to 85° C., a bottom operating temperature of the distillation tower is 105° C. to 166° C., and an operating pressure of 0.15 MPa to 1.0 MPa.

8. The method according to claim 1, characterized in that The number of plates in the rectifying section is 12 to 32, and the number of plates in the stripping section is 12 to 36; wherein, The feed positions of all the gaseous isobutylene are located below any tray between the 2nd tray and the 10th tray from the top to the bottom of the distillation section; and / or, The extraction position of the water-tert-butanol azeotrope is located below any tray between the 5th and 11th trays from the top to the bottom of the stripping section; and / or The feed positions of all the water permeates are located below any tray between the 17th tray and the 33rd tray from the top to the bottom of the stripping section.

9. The method according to claim 1, characterized in that The extraction flow rate of the water-tert-butanol azeotrope is negatively correlated with the content of tert-butanol in the wastewater.

10. A system for preparing isobutylene from tert-butyl alcohol, the system being used to implement the method according to any one of claims 1 to 9, the system comprising: A multi-stage sequentially connected tert-butanol hydrolysis reaction assembly (1), comprising: a reactor (2), a membrane permeation separator (3), and a flash separator (4) connected in sequence; A distillation tower (5) is connected to the water permeate outlet of each stage of the membrane permeation separator (3) and the gas outlet of each stage of the flash separator (4); the distillation tower (5) includes a distillation section (51) and a stripping section (52); a side line extraction line (6) is provided in the stripping section (52), and the side line extraction line (6) is connected to the feed port of at least one membrane permeation separator (3).

11. The system according to claim 10, wherein: The multi-stage tert-butyl alcohol hydrolysis reaction assembly (1) comprises: The first tert-butyl alcohol hydrolysis reaction assembly (101) comprises: a first reactor (201), a first membrane permeation separator (301), and a first flash separator (401) connected in sequence, wherein the liquid outlet of the first flash separator (401) is respectively connected to the feed port of the first reactor (201); The second tert-butanol hydrolysis reaction assembly (102) comprises: a second reactor (202), a second membrane permeation separator (302), and a second flash separator (402) connected in sequence, wherein the liquid outlet of the second flash separator (402) is respectively connected to the feed inlet of the second reactor (202), and the feed inlet of the second reactor (202) is also connected to the liquid outlet of the first flash separator (401); The third tert-butanol hydrolysis reaction component (103) comprises: a third reactor (203), a third membrane permeation separator (303) and a third flash separator (403) connected in sequence; the liquid outlet of the third flash separator (403) is respectively connected to the feed inlet of the third reactor (203) and the feed inlet of the distillation tower (5), and the feed inlet of the third reactor (203) is connected to the liquid outlet of the second flash separator (402).

12. The system according to claim 11, wherein: The first flash separator (401), the second flash separator (402) and the third flash separator (403) are contained in a horizontal cylindrical separator (7); wherein a partition is provided between each two adjacent flash separators (4), and the partition is used to prevent the liquids in the lower parts of the flash separators (4) from mixing with each other and to fully mix the gases in the upper parts of the flash separators (4).

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