A multi-reactor reactive distillation device and process

Abstract

The present invention discloses a multi-kettle reactive distillation device, which includes a plurality of reaction kettles connected in series and a distillation column; a material adding unit is connected to the side wall of the first-stage reaction kettle; along the main material flow direction, the liquid-phase discharge port arranged at the upper part of the previous-stage reaction kettle is sequentially connected to the feed port of the next-stage reaction kettle; a gas-phase discharge port is arranged at the top of any stage of reaction kettle, the gas-phase discharge port at the top of the first-stage reaction kettle is connected to the bottom gas inlet of the second-stage reaction kettle, and the gas-phase discharge ports of the second-stage reaction kettle to the last-stage reaction kettle are respectively connected to the distillation column to perform rectifying separation on light components. The present invention also correspondingly provides a multi-kettle reactive distillation process. In the present invention, the structure of the heat exchange tube bundle enables high mass transfer and heat transfer efficiency in each stage of reaction kettle. The multi-stage reaction kettles with special structure heat exchange tube bundles built in, combined with the gradient viscosity and gradient temperature control that can be implemented industrially, can not only realize the reactive distillation of high-viscosity and easy-to-polymer systems, but also reduce steam consumption and wastewater discharge.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical production, and relates to a multi-kettle reactive distillation device and process. Background Art

[0002] Reactive distillation simultaneously completes reaction and distillation separation in the same system. Since the reaction process and the distillation process are carried out in the same equipment, compared with the traditional reaction unit in series with a separation unit, not only the process is simplified and equipment costs are saved; moreover, the reaction heat can be used to vaporize the liquid phase in the tower, thereby reducing the vaporization heat load; finally, since the product is continuously removed by distillation separation, the occurrence of side reactions is avoided, so the selectivity of the product is greatly improved, the product quality is improved, and the subsequent distillation operation cost is reduced.

[0003] Although reactive distillation has many advantages, when it is applied to materials with high viscosity and easy polymerization, it is very difficult to set up heat exchange tubes in the reaction kettle for heat transfer, and only the jacket heat transfer of the reaction kettle can be used. The jacket heat transfer area is small and cannot provide the heat required for vaporizing the reaction materials, making it difficult to achieve reactive distillation. Some processes first inject steam into the reactor to directly heat the materials, and at the same time, use the steam to entrain the light components to rise into the distillation tower to achieve the removal of light components from the high-viscosity system. Since the steam is both a heating medium and a stripping medium, the consumption is large, a large amount of wastewater is generated, causing secondary pollution and increasing the environmental protection cost.

[0004] Therefore, it is extremely necessary for those skilled in the art to provide a multi-kettle reactive distillation device and process with high mass and heat transfer efficiency and gradient viscosity control that can be industrially implemented for high-viscosity and easy-polymerization systems, which can not only achieve reactive distillation of high-viscosity and easy-polymerization systems, but also reduce steam consumption and wastewater discharge. Summary of the Invention

[0005] Aiming at the problems in the above-mentioned prior art, the purpose of the present invention is to provide a multi-kettle reactive distillation device and process with high mass and heat transfer efficiency and gradient viscosity control that can be industrially implemented, which can not only achieve reactive distillation of high-viscosity and easy-polymerization systems, but also reduce steam consumption and wastewater discharge.

[0006] One of the purposes of the present invention is to provide a multi-kettle reactive distillation device, and the technical solution adopted is as follows:

[0007] A multi-kettle reactive distillation device includes a multi-stage series of reaction kettles and a distillation tower;

[0008] The side wall of the first-stage reactor is connected to the material addition unit; along the main material flow direction, the liquid-phase discharge port arranged at the upper part of the previous-stage reactor is sequentially connected to the feed port of the next-stage reactor; a gas-phase discharge port is arranged at the top of any stage of the reactor, and the gas-phase discharge port at the top of the first-stage reactor is connected to the bottom gas inlet of the second-stage reactor, and the gas-phase discharge ports of the second-stage reactor to the last-stage reactor are respectively connected to the rectifying column to rectify and separate the light components.

[0009] Preferably, a jacket is provided on the outer wall of the first-stage reactor, and heat exchange tubes are built in any stage of the reactor for heating and vaporizing the materials in each stage of the reactor.

[0010] Further, the heat exchange tubes I in the first-stage reactor are arranged along the central axis of the first-stage reactor;

[0011] The whole of the heat exchange tubes I is below the liquid level in the reactor, and the top end of the heat exchange tubes I is at a distance of L1 from the liquid surface, and the bottom end penetrates through the bottom of the first-stage reactor and extends downward.

[0012] Further, except for the first-stage reactor, the heat exchange tubes II in any stage of the reactor are horizontally placed along the side wall of the reactor at the lower part of each stage of the reactor.

[0013] Further, the bottom end of the heat exchange tubes along their length direction penetrates through the side wall of the reactor of this stage and extends outward.

[0014] Further, the heat exchange tubes II are arranged in 1 or 2 layers in each stage of the reactor, and the heat exchange tubes II located on the same layer are evenly distributed along the circumference in the horizontal cross-section.

[0015] Further, the heat exchange tubes of the heat exchange tubes I and the heat exchange tubes II are both double-layer sleeves, including an outer tube and an inner tube placed inside the outer tube. The annulus between the outer tube and the inner tube is used for steam circulation, and the top of the inner tube along the tube length direction is communicated with the inside of the outer tube for the inner tube to circulate condensate;

[0016] A steam inlet is provided at the bottom of the outer tube along the tube length direction for introducing steam; a condensate outlet is provided at the bottom end of the double-layer sleeve along the tube length direction for the condensate after steam heat exchange and condensation to flow back and discharge.

[0017] Preferably, the reactors are set to be 3 to 4 stages in series.

[0018] Preferably, a feed pipeline for low-boiling reaction monomers is also connected to the bottom of at least one stage of the reactor.

[0019] Preferably, except for the first-stage reactor, a steam feed pipeline is also connected to the bottom of any stage of the reactor for heating and stripping the materials in the reactor.

[0020] Preferably, the rectification column is arranged above the second-stage reaction kettle; a gas-phase feed inlet is tangentially arranged along the side line at the bottom of the rectification column, and a liquid-phase reflux inlet communicated with the second-stage reaction kettle is also provided.

[0021] Preferably, the height from the bottom of the rectification column to the first tray is 1.8 - 2.5 m, and the upward flow rate of the gas-phase material is controlled to be less than 2 m / s.

[0022] The second object of the present invention is to provide a multi-kettle reactive distillation process, which comprises the following steps:

[0023] S1. The material is first heated and reacted in the first-stage reaction kettle. The liquid-phase discharge of the first-stage reaction kettle enters the second-stage reaction kettle for continuous heating and reaction. The gas-phase discharge of the first-stage reaction kettle enters the bottom of the second-stage reaction kettle as the stirring and stripping gas of the second-stage reaction kettle.

[0024] S2. The liquid-phase material continues to be heated and reacted in the second-stage reaction kettle. The light components in it vaporize and rise to enter the rectification column for separation. The liquid-phase discharge in the reaction enters the third-stage reaction kettle to complete the reaction.

[0025] S3. The liquid-phase material is heated for deep reaction in the third-stage reaction kettle. The gas-phase material of the third-stage reaction kettle enters the rectification column for separation. The liquid-phase discharge is directly discharged or enters the next-stage reaction kettle to continue repeating this step.

[0026] Preferably, the temperature of the material in the multi-stage reaction kettles along the main material flow direction is controlled to increase by 5 - 15 °C in sequence.

[0027] Preferably, a low-boiling-point reaction monomer is introduced into at least one of the multi-stage reaction kettles.

[0028] More preferably, the viscosity of the material in the first-stage reaction kettle is controlled below 50 cp, and the reaction conversion rate is controlled between 70 - 90% by using a low-boiling-point monomer; the viscosity of the material in the second-stage reaction kettle is controlled below 100 cp, and the reaction conversion rate is controlled between 90 - 100% by using a low-boiling-point monomer; the viscosity of the material in the third-stage reaction kettle is controlled below 200 cp, so that the reaction conversion rate reaches or is basically close to 100%.

[0029] Preferably, steam is introduced into any reaction kettle except the first-stage reaction kettle.

[0030] More preferably, the reaction kettles are set as 4 in series; among them, the addition amount of steam in the second-stage reaction kettle is 0.2 - 0.5% of the amount of the liquid material in the kettle; the addition amount of steam in the third-stage reaction kettle is 0.4 - 0.8% of the amount of the liquid material in the kettle; the addition amount of steam in the fourth-stage reaction kettle is 0.8 - 1.8% of the amount of the liquid material in the kettle.

[0031] The present invention can bring the following beneficial effects:

[0032] 1) In the device of the present invention, the material first enters the first-stage reactor for reaction, and then successively enters the subsequent stages of reactors until the reaction is completed. The light components in the process converge to the rectification kettle and are continuously separated through the rectification kettle, reducing the occurrence of side reactions and improving the reaction efficiency of the product. Thus, in the present invention, multiple reaction kettles share one rectification tower, realizing the synchronous progress of reaction and separation and improving the reaction efficiency.

[0033] 2) In the present invention, heat exchange tube bundles with special structures are respectively adopted in each stage of the reactor. On the one hand, efficient heat transfer on the outer wall of the heat exchange tubes is realized, reducing the heat transfer film thickness and viscosity and improving the heat transfer efficiency. On the other hand, self-circulation and mixing of the material in the kettle are realized, and with the assistance of stripping steam, uniform mixing of gas and liquid in the reactor is achieved. Thus, when the viscosity of the material in the kettle is less than 200 cp, gas-liquid complete mixing can be realized without a stirrer, and the phenomenon of heat exchange tube wall sticking can be avoided. In addition, the amount of stripping steam can be reduced, and the environmental protection cost can be lowered.

[0034] 3) In the process of the present invention, by connecting multiple reaction kettles in series and controlling the feed ratio of reaction monomers and the reaction temperature in a gradient manner, the reaction conversion rate and the material viscosity in each stage of the reactor are controlled, improving the reaction rectification efficiency.

[0035] In summary, the heat exchange tube bundle structure of the present invention enables high mass transfer and heat transfer efficiency in each stage of the reactor. The multi-stage reactor with a heat exchange tube bundle with a special structure inside, combined with the gradient viscosity and temperature control that can be implemented industrially, can not only realize the reaction rectification of high-viscosity and easy-to-polymerize systems, but also reduce steam consumption and wastewater discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a layout schematic diagram of the reaction rectification device of the present invention.

[0037] Figure 2 It is a structural schematic diagram when the heat exchange tube bundle II in the reactor of the present invention is set to 2 layers.

[0038] Figure 3 It is a structural schematic diagram of the heat exchange tube bundle II in the present invention.

[0039] Figure 4 It is a layout schematic diagram along the circumferential direction when the heat exchange tube bundle II in the present invention is located on the same layer.

[0040] Figure 5 It is a structural schematic diagram of the heat exchange tube bundle I in the present invention.

[0041] The meanings of the reference symbols in the drawings:

[0042] 1 - First - stage reactor, 10 - Material addition unit, 11 - Jacket, 12 - Heat - exchange tube bundle Ⅰ;

[0043] 2 - Second - stage reactor, 20 - Heat - exchange tube bundle Ⅱ, 121 / 200 - Outer tube, 122 / 201 - Inner tube;

[0044] 3 - Third - stage reactor; 4 - Fourth - stage reactor; 5 - Distillation column; 6 - Feed pipeline for low - boiling - point reaction monomers;

[0045] 7 - Steam feed pipeline, 70 - Steam distributor;

[0046] a - Liquid - phase discharge port, b - Feed port, c - Gas - phase discharge port, d - Inlet port;

[0047] e - Steam inlet, f - Condensate outlet, g - Gas - phase feed port, h - Liquid - phase reflux port. Detailed implementation mode

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation modes of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings and other implementation modes can be obtained.

[0049] To make the drawings concise, only the parts related to the present invention are schematically shown in each drawing, and they do not represent their actual structures as products.

[0050] According to an embodiment provided in this example, as Figure 1 shown, it is a multi - kettle reactive distillation device, including multiple serially connected reactors and a distillation column 5;

[0051] A material addition unit 10 is connected to the first-stage reactor 1; along the main material flow direction, the liquid-phase discharge port a provided at the upper part of the previous-stage reactor is sequentially connected to the feed port b of the next-stage reactor; a gas-phase discharge port c is provided at the top of any stage of the reactor 1, and the gas-phase discharge port c at the top of the first-stage reactor 1 is connected to the inlet port d at the bottom of the second-stage reactor 2, and the gas-phase discharge ports of the second-stage reactor 2 to the last-stage reactor are respectively connected to a distillation column to separate light components. Thus, multiple-stage reactors share one distillation column 5 to realize the synchronous progress of reaction and separation and improve the reaction efficiency. In particular, the gas-phase discharge of the first-stage reactor 1 directly enters the second-stage reactor instead of being directly connected to the distillation column 5 for distillation separation. On the one hand, it can play a role in stirring and stripping in the second-stage reactor 2 to promote the reaction, and on the other hand, it will not cause a large amount of unreacted low-boiling monomers in the first-stage reactor 1 to be carried out to the distillation column, reducing the reaction efficiency. Among them, the main material flow direction refers to the flow direction of the main reaction product.

[0052] In practical applications, the reactors are preferably set to 3 - 4 stages:

[0053] The side wall of the first-stage reactor 1 is connected to the material addition unit 10. Specifically, various reaction monomers (such as monomer one and monomer two) are respectively added to the first-stage reactor 1 through pipelines, and more than 70% of the reaction is completed therein; the liquid-phase discharge port a provided at the upper part of the first-stage reactor 1 is connected to the feed port b at the bottom of the second-stage reactor 2, so that the liquid-phase discharge of the first-stage reactor 1 enters the second-stage reactor 2 to continue the reaction, and the gas-phase discharge port c provided at the top is connected to the bottom inlet port d of the second-stage reactor 2, so that the gas-phase discharge enters the bottom of the second-stage reactor 2 as the stirring and stripping gas of the second-stage reactor 2;

[0054] The liquid-phase discharge port a provided at the upper part of the second-stage reactor 2 is connected to the feed port at the bottom of the third-stage reactor 3, so that the liquid-phase discharge can enter the third-stage reactor 3 to continue the deep reaction. The gas-phase discharge port c provided at the top of the second-stage reactor 2 is connected to the distillation column 5 for separation. The low-boiling light components in the distillation column 5 are separated from the top of the column, and the heavy components are refluxed from the bottom of the column to the second-stage reactor 2; in addition to continuing to complete the reaction, the second-stage reactor 2 also undertakes the function of the reboiler of the reactive distillation column 5, where the light components are vaporized and rise into the distillation column 5, and the liquid-phase discharge of the reaction enters the third-stage reactor 3 to make the material reaction complete;

[0055] The gas-phase discharge port c of the third-stage reactor 3 is connected to the distillation column 5 for light component purification. When the reactor is set to be 3 stages, the liquid-phase discharge of the third-stage reactor 3 is directly discharged; when the reactor is set to be 4 stages, the liquid-phase discharge of the third-stage reactor 3 enters the fourth-stage reactor 4 to continue stripping. The main function of the fourth-stage reactor 4 is to thoroughly strip the light components and reduce the light component content in the heavy components.

[0056] In addition, the rectifying column 5 is arranged above the second-stage reactor 2, so that a large amount of light components (especially small-molecule by-products of the reaction) in the second-stage reactor 2 are fully separated from the reaction system, improving the reaction and product purification efficiency. Since most of the reactions have been completed in the second-stage reactor 2 and the viscosity of the material is not too high yet, it can be used as a reboiler to vaporize and separate the material repeatedly.

[0057] As a preferred embodiment, a low-boiling reaction monomer feed pipe 6 is also connected to the bottom of at least one stage of the reactor. Specifically, it needs to be selectively set according to the actual working conditions. For the subsequent reactors where the reaction has basically been completed, there is no need to set up the low-boiling reaction monomer feed pipe 6 anymore. For example, when the reactors are set in series with 4 stages, the viscosity of the material in the first-stage reactor 1 is controlled below 50 cp. According to the viscosity change, the reaction conversion rate is controlled between 70-90% by controlling the feed and feed ratio of the reaction monomers. Generally, a low-boiling reaction monomer (monomer three) is selected to control the conversion rate. The viscosity of the material in the second-stage reactor 2 is controlled below 100 cp. The conversion rate is controlled between 90-100% by controlling the supplementary addition amount of the low-boiling reaction monomer (monomer three) according to the viscosity change. The third-stage reactor 3 is used for deep reaction, and the low-boiling reaction monomer (monomer three) is controlled according to the feed ratio of 100% conversion rate, and the viscosity of the material is controlled below 200 cp. There is no need to introduce the low-boiling reaction monomer into the fourth-stage reactor anymore.

[0058] As another preferred embodiment, except for the first-stage reactor 1, a steam feed pipe 7 is also connected to the bottom of any stage of the reactor for heating and stripping the reactants. More preferably, a steam distributor 70 is also provided on the steam feed pipe 7. More specifically, as shown in Figure 2 The steam distributor 70 is a straight pipe with a diameter of 50-200 mm. The side wall of the straight pipe is obliquely upwardly provided with pores. The angle α with the vertical direction is 30-45°. The aperture of the pores is 5-20 mm, and the pore spacing between adjacent pores is 10-50 mm, and the pore spacing between adjacent pores is not less than 2 times the aperture. The inclination range of the pores enables the steam to have not only an initial velocity upward along the axis, but also an initial velocity diffusing radially around. This kind of pore angle avoids the short circuit of the steam in the reactor, improves the distribution of the steam on the entire cross section of the reactor, and improves the stripping efficiency; the aperture size and pore spacing take into account both the effective dispersion of the steam and reduce the probability of being blocked by the liquid material due to too small an aperture. Thus, the dispersion stripping effect of the steam is improved.

[0059] On the basis of the above embodiments, a jacket 11 is provided on the outer wall of the first-stage reactor 1, and a heat exchange tube bundle is provided inside any stage of the reactor for heating and vaporizing the substances in the reactor.

[0060] Specifically, monomers 1 to 3 (depending on the reaction conditions, there can also be 2 reaction monomers or more reaction monomers) enter the first-stage reactor 1 from the bottom according to the required stoichiometric ratio and react under appropriate process conditions. The heat source required for the reaction is indirectly provided by the heat medium through the jacket 11, and the insufficient part of the heat supply of the jacket 11 is provided by the built-in heat exchange tube bundle I 12 placed in the first-stage reactor 1 from the lower part.

[0061] More preferably, the heat exchange tube bundle I 12 in the first-stage reactor 1 is arranged along the central axis of the first-stage reactor 1. The whole heat exchange tube bundle I 12 is below the liquid level, and the top end of the heat exchange tube bundle I 12 is at a distance L1 from the liquid surface. L1 is preferably (100 - 500) mm. The bottom end of the heat exchange tube bundle I 12 passes through the bottom of the first-stage reactor 1 and extends downward, facilitating the corresponding steam inlet e and condensate outlet f to be respectively arranged at the part where the heat exchange tube bundle I 12 extends downward from the bottom of the first-stage reactor 1. Specifically, both ends of the first-stage reactor 1 are of elliptical structure, and the middle part is of cylindrical structure. The bottom end of the heat exchange tube bundle I 12 passes through the bottom tangent of the first-stage reactor and extends downward.

[0062] Specifically, the built-in heat exchange tube bundle I 12 in the first-stage reactor 1 can form a high-temperature zone around the heat exchange tube bundle, accelerating the reaction while causing the surrounding materials to expand in volume and decrease in density, forming a special density distribution field and directional push flow in the reactor. In the vertical direction, a density distribution field with a small density at the bottom and a large density at the top will be formed in the reactor. In the radial direction, a density distribution field with a small density in the center and a large density at the reactor wall will be formed. Under this density field, an upward internal circulation flow will be formed (as shown by the arrow flow in the first-stage reactor in Figure 1 ). With the stirring effect of the evaporation gas on the materials, rapid mixing of the reaction materials can be achieved, and mass transfer and heat transfer in the reactor can be satisfied without stirring.

[0063] The heat exchange tube bundle Ⅱ20 in any reactor stage except the first-stage reactor 1 is horizontally placed at the lower part inside the reactor along the side wall of the reactor. The bottom end of the heat exchange tube bundle Ⅱ20 along its length direction penetrates through the side wall of this stage of the reactor and extends outwards, facilitating the corresponding steam inlet e and condensate outlet f to be respectively arranged at the part where the heat exchange tube bundle Ⅱ20 extends outwards from the side wall of this stage of the reactor 1. The horizontally placed heat exchange tube bundle Ⅱ20 plays a role in cutting and mixing the rising gas-liquid mixture, enabling more uniform mixing between the gas and the liquid. The rising gas-liquid flow becomes narrower in the flow channel and faster in speed between the heat exchange tubes of the heat exchange tube bundle Ⅱ20, and the gas-liquid flow passes through the outer surface of the heat exchange tube at a high speed, improving the heat exchange efficiency and simultaneously cleaning the heat exchange tube and thinning the adhesion layer on the outer surface of the heat exchange tube. Specifically, the heat exchange tube bundle Ⅱ20 forms a special density distribution field inside the reactor, that is, in the vertical direction, the material density and viscosity gradually increase from bottom to top, and in the radial cross-section, the material density and viscosity gradually increase from outside to inside. The volume expansion of the low-density material causes the material to form an internal circulation in the reactor with the outer circle from bottom to top and the inner circle from top to bottom (as shown by the arrow flow direction in Figure 2 ). Thus, the arrangement of the heat exchange tube bundle Ⅱ20 maximizes the heating and mass transfer efficiency of the steam, has a high vaporization efficiency of the material, and is not easy to form an adhesion layer on the heat transfer surface.

[0064] More preferably, the heat exchange tube bundle Ⅱ20 is arranged in 1 or 2 layers horizontally along the side wall inside the reactor. The heat exchange tube bundle Ⅱ20 on the same layer is circumferentially evenly distributed in the cross-section, and the number of the heat exchange tube bundle Ⅱ20 on any layer does not exceed 5 along the circumferential direction.

[0065] Specifically, the diameter D of the heat exchange tube bundle Ⅰ12 and the heat exchange tube bundle Ⅱ20 is controlled within the range of (500 - 1500) mm, and the total number of the heat exchange tube bundle Ⅱ20 can be between 2 and 10 according to the heat load. Combining Figure 5 as shown, the distance L2 between the relative heat exchange tube bundle Ⅱ20 on the same layer circumference is (300 - 1000) mm, the minimum distance L3 between adjacent heat exchange tube bundle Ⅱ20 is (100 - 500) mm, and the distance between the two layers of heat exchange tube bundle Ⅱ20 is (600 - 1500) mm. In practical applications, the total number of the heat exchange tube bundle Ⅱ20 in the third-stage reactor 3 and the fourth-stage reactor 4 is 2 - 6, and the number of the single layer horizontally arranged along the side wall of the reactor does not exceed 3.

[0066] Among them, combining Figure 3 、 4As shown, the heat exchange tubes of the heat exchange tube bundle I 12 and the heat exchange tube bundle II 20 are double-layer sleeves, including an outer tube 121 / 200 and an inner tube 122 / 201 disposed inside the outer tube 121 / 200. The annulus between the outer tube 121 / 200 and the inner tube 122 / 201 is used for steam circulation. The top of the inner tube 122 / 201 in the tube length direction is communicated with the inside of the outer tube 121 / 200 to allow condensate to flow through the inner tube 122 / 201;

[0067] A steam inlet e is provided at the bottom of the outer tube 121 / 200 in the tube length direction for introducing steam; a condensate outlet f is provided at the bottom end of the double-layer sleeve in the tube length direction for discharging the condensate after the steam is cooled by heat exchange.

[0068] Specifically, the outer tube 121 and the inner tube 122, the outer tube 200 and the inner tube 201 cooperate to form a double-layer sleeve. Steam is introduced into the outer tube 121 / 200 through the steam inlet e at the bottom of the double-layer sleeve. During the upward movement, the latent heat is released to heat the material outside the tube. The condensate is pushed by the steam to rise to the top and fall into the inner tube 122 / 201, flows out of the inner tube, and gathers together at the bottom end of the heat exchange tube bundle and is discharged from the system. That is, the annulus between the outer tube 121 / 200 and the inner tube 122 / 201 circulates steam, and the inner tube circulates condensate. The advantage of this heat exchange tube bundle is that the side in contact with the material through the partition wall is high-temperature steam, with a high heat transfer coefficient and high heat transfer efficiency, so as to maintain a high vaporization rate of the material outside the tube and avoid the phenomenon of wall sticking. More specifically, the outer diameter of the outer tube of the heat exchange tube is 40 mm - 80 mm, the inner diameter of the inner tube is 20 mm - 25 mm, and the distance between adjacent two heat exchange tubes is 20 mm - 50 mm. Combined Figure 5 As shown, the length L4 of the heat exchange tube is 1000 mm - 4000 mm.

[0069] In addition, both ends of any stage of the reaction kettle 1 are elliptical structures, and the middle part is a cylindrical structure; the aspect ratio of any stage of the reaction kettle is within the range of 1.2 - 2. If the aspect ratio is too low, it is not conducive to liquid sedimentation. If the aspect ratio is too high, it is not conducive to the removal and mixing of the gas phase. Except for the first-stage reaction kettle, the distance between the liquid level in each stage of the reaction kettle and the top of the reaction kettle is greater than 1.5 m. This buffer space can prevent high-viscosity liquid from being entrained into the distillation column.

[0070] Based on any of the above embodiments, a gas-phase feed port g is tangentially arranged along the side line at the bottom of the rectifying column 5; bottom side-line tangential feeding is adopted to reduce the entrainment of heavy components to the trays when light components enter the column. Moreover, a liquid-phase reflux port h communicating with the second-stage reactor 2 is provided at the bottom of the rectifying column 5. More preferably, the height from the bottom of the rectifying column 5 to the first tray is 1.8 - 2.5 m, and the upward gas velocity is less than 2 m / s; to ensure the complete sedimentation of the entrained heavy components. More preferably, any one of sieve trays, directed sieve trays (including valve trays) or floating valve trays is adopted for 50% of the separation trays in the lower part of the rectifying column 5, and the upper trays can be selected to have the same form as the lower trays or high-efficiency packing trays can be selected.

[0071] Except for the first-stage reactor, substances such as solvents, by-products, and stripping steam in each stage of the reactor enter the rectifying column and are separated in the rectifying column. The lowest-boiling fraction is produced at the top of the column, the slightly higher-boiling light fraction is produced in the middle of the column, and the heavy components are refluxed to the second-stage reactor.

[0072] Based on the above embodiments, according to another embodiment provided by the present invention, it is a multi-kettle reactive distillation process, including the following steps:

[0073] S1. The material is first heated and reacted in the first-stage reactor. The liquid-phase discharge of the first-stage reactor enters the second-stage reactor for continuous heating and reaction, and the gas-phase discharge enters the bottom of the second-stage reactor as the stirring and stripping gas of the second-stage reactor;

[0074] S2. The liquid-phase material continues to be heated and reacted in the second-stage reactor. The light components in it vaporize and rise into the rectifying column, and the liquid-phase discharge in the reaction enters the third-stage reactor for reaction;

[0075] S3. The liquid-phase material is heated and deeply reacted in the third-stage reactor. The gas-phase material of the third-stage reactor enters the rectifying column for separation, and the liquid-phase discharge is directly discharged or enters the next-stage reactor to continue repeating this step.

[0076] In this embodiment, after the reaction in the first-stage reactor 1, the liquid-phase heavy-component material generated in the reaction sequentially passes through the subsequent stages of reactors until the reaction is 100% completed; while the gas-phase discharge first enters the second-stage reactor 2 to promote the stirring and stripping of the materials in the kettle, and after improving the reaction efficiency, it enters the rectifying column 5 for light-component purification, and the liquid-phase material continues to react in the subsequent stages of reactors and, under the stripping action, the generated gas-phase discharge also enters the rectifying column to further reduce the light-component content in the heavy components and completely strip and separate the light components.

[0077] As a preferred embodiment, the temperature control in the multi-stage reactor increases sequentially by 5-15 °C; to slow down the increasing trend of viscosity caused by the increase in the average molecular weight of the material and improve the reaction efficiency. Specifically, in combination with the above embodiments, through the special settings of the heat exchange tube bundle I 12 and the heat exchange tube bundle II 20 in each stage of the reactor (not repeated here), the gas-liquid uniform mixing in the non-stirring state and the efficient vaporization of light components are realized. Furthermore, through reactive distillation, a high yield of reaction products and the separation of products and by-products are achieved.

[0078] As another preferred embodiment, a low-boiling monomer is introduced into at least one stage of the multi-stage reactor to increase the conversion rate of the reaction products. Specifically, it needs to be selectively set according to the actual working conditions. For the subsequent reactors that have reached 100% reaction, there is no need to introduce low-boiling monomers to promote the reaction.

[0079] In practical applications, the reactors are set to 3-4 stages in series. The viscosity of the material in the first-stage reactor 1 is controlled below 50 cp. According to the viscosity change, by controlling the feed ratio of each reaction monomer and selecting a low-boiling monomer (monomer three), the reaction conversion rate is controlled between 70-90%. The viscosity of the material in the second-stage reactor 2 is controlled below 100 cp. The conversion rate is controlled between 90-100% by controlling the supplementary amount of the low-boiling monomer (monomer three) according to the viscosity change. The third-stage reactor 3 is used for deep reaction, and the low-boiling monomer (monomer three) is controlled according to the feed ratio of 100% conversion rate, and the viscosity of the material is controlled below 200 cp. When the reactor is set to 4 stages, the liquid-phase discharge of the third-stage reactor 3 enters the fourth-stage reactor 4 for further stripping. The main function of the fourth-stage reactor 4 is to completely strip the light components and reduce the light component content in the heavy components. Since the reaction is completed in the first three stages of the reactor, there is no need to additionally introduce low-boiling monomers.

[0080] More preferably, the addition amount of stripping steam in the second-stage reactor 2 is 0.2-0.5% of the amount of liquid material in the reactor. The addition of stripping steam (or other gases) breaks the liquid-phase material circulating in the reactor together with the gas-phase material from the first-stage reactor 1 and the gas-phase vaporized in the reactor, achieving gas-liquid mixing on a smaller scale, desorbing the light components wrapped by the liquid, and thus reducing the viscosity of the reaction material. Additionally, control: the addition amount of stripping steam in the third-stage reactor 3 is 0.4-0.8% of the amount of liquid material in the reactor; the addition amount of stripping steam in the fourth-stage reactor 4 is 0.7-1.8% of the amount of liquid material in the reactor, further separating and purifying the by-product light components from the heavy components. The "%" here represents the mass ratio.

[0081] In the above embodiments, by connecting multiple reactors in series and controlling the gradient of the feed ratio and temperature of each reaction monomer, the control of the reaction conversion rate and the material viscosity is achieved.

[0082] Synthesis reaction of methyl methacrylate in Comparative Example 1

[0083] Although the viscosity of the reactant system is not high, it contains methyl acrylate, an easily polymerizable monomer;

[0084] Reaction monomers: methanol, water, methylacrylamide sulfate.

[0085] Reactive distillation apparatus

[0086] Same as Figure 1 , it includes four serially connected reaction kettles and a distillation column. The material enters the first-stage reaction kettle 1 for reaction and then sequentially enters the feed ports of the next-stage reaction kettles; gas-phase discharge ports are provided at the top of any reaction kettle. The gas-phase discharge port at the top of the first-stage reaction kettle is connected to the bottom gas inlet of the second-stage reaction kettle. The gas-phase discharge ports of the second-stage reaction kettle to the last-stage reaction kettle are respectively connected to the distillation column to perform rectification separation of light components; and low-boiling reaction monomers are introduced through the low-boiling monomer pipeline 6 in the first three reaction kettles to promote the reaction conversion rate, and steam is added through the steam pipeline 7 for steam stripping in the last three reaction kettles.

[0087] However, different from Figure 1 is that in this example, jacket heat exchange is carried out on the outer wall of the four-stage reaction kettles, and no internal heat exchange tubes are provided.

[0088] Methacrylic acid, water, and methanol are produced at the top of the distillation column, and the final liquid-phase discharge from the reaction kettle is a mixture of ammonium bisulfate, sulfuric acid, and H2O.

[0089] Reactive distillation process

[0090] The material first undergoes a heating reaction in the first-stage reactor. Monomer three is introduced, and the feed ratios and temperatures of the reaction monomers are adjusted to control the reaction conversion rate in the first-stage reactor at 90%. The gaseous material from the first-stage reactor enters the second-stage reactor for stirring and heating and stripping. The liquid material continues to complete the reaction in the second-stage reactor. The temperature of the second-stage reactor is monitored and controlled by a thermometer to be 10°C higher than that of the first-stage reactor. 1% steam (the ratio to the liquid material volume in this stage) is injected into the second-stage reactor to control the reaction conversion rate in the second-stage reactor at 95%. The light components therein vaporize and rise to enter the distillation column for separation. The liquid discharge from the reaction enters the third-stage reactor to complete the reaction. The liquid material undergoes a deep reaction in the third-stage reactor. The heating temperature is controlled to be 15°C higher than that of the second-stage reactor. 1% steam (the ratio to the liquid material volume in this stage) is injected into the third-stage reactor to make the reaction proceed completely. The light components therein vaporize and rise to enter the distillation column for separation. The liquid discharge after the reaction enters the fourth-stage reactor. The temperature of the fourth-stage reactor is controlled to be 15°C higher than that of the second-stage reactor. 1% steam (the ratio to the liquid material volume in this stage) is injected to completely strip the light components in the liquid material.

[0091] Reaction result

[0092] Reaction conversion rate: 99.5%. The steam consumption is 3.5% of the feed. The water content in the liquid-phase mixture discharged from the reaction is 26%. The residence time of the material in each stage of the reactor is 1 hour.

[0093] Synthesis of methyl methacrylate in Example 1

[0094] The reactant system and reaction monomers are the same as those in Comparative Example 1;

[0095] Reactive distillation device

[0096] Same as Figure 1 and includes four serially-connected reactors and a distillation column. The material enters the first-stage reactor 1 for reaction and then sequentially enters the feed ports of the next-stage reactors. Gas-phase discharge ports are provided at the top of any stage of the reactor. The gas-phase discharge port at the top of the first-stage reactor is connected to the bottom gas inlet of the second-stage reactor. The gas-phase discharge ports of the second-stage reactor to the fourth-stage reactor are respectively connected to the distillation column to perform rectification separation on the light components. And low-boiling reaction monomers are introduced through the low-boiling monomer pipeline 6 in the first three stages of the reactor to promote the reaction conversion rate, and steam is added through the steam pipeline 7 for stripping in the last three stages of the reactor.

[0097] However, different from Figure 1 this is that in this example, there is no heat exchange tube bundle Ⅰ12 in the first-stage reactor, and only jacket heating is used. Heat exchange tube bundles are provided in the second-stage reactor, the third-stage reactor, and the fourth-stage reactor as Figure 2The two-layer heat exchange tube bundle II 20 with a total of 4 units as shown. The spacing L2 between the relative heat exchange tube bundles II 20 in the same layer along the circumferential direction is 600 mm; the diameter D of the heat exchange tube bundle II 20 is 800 mm; the spacing between the two layers is 800 mm; the outer tube 200 of the heat exchange tube has a diameter of 60 mm, and the inner tube 201 has a diameter of 25 mm.

[0098] The top of the distillation column produces methacrylic acid, water, and methanol, and the final liquid discharge from the reaction kettle is a mixture of ammonium bisulfate, sulfuric acid, and H2O.

[0099] Reactive distillation process

[0100] It is basically the same as Example 1, except that: the reaction conversion rate of the first-stage reaction kettle is controlled at 85%; the reaction conversion rate of the second-stage reaction kettle is controlled at 95%, and 0.3% of steam is injected into the second-stage reaction kettle (the ratio to the liquid material amount in this stage kettle); the reaction in the third-stage reaction kettle is complete, and 0.6% of steam is injected into the third-stage reaction kettle (the ratio to the liquid material amount in this stage kettle); 0.7% of steam is injected into the fourth-stage reaction kettle (the ratio to the liquid material amount in this stage kettle).

[0101] Reaction result

[0102] Reaction conversion rate: 99.9%, and the steam consumption is 1.6% of the feed. The water content in the reaction effluent liquid mixture is 17%. The residence time of the material in each reaction kettle is 0.7 hours. It is superior to Comparative Example 1 in terms of residence time, stripping steam consumption, and water content in the effluent liquid.

[0103] Example 2

[0104] The reaction system, reactive distillation device, and corresponding process of this example are basically the same as those of Example 1. The differences are only as follows:

[0105] Reactive distillation device

[0106] 1. Cancel the setting of the fourth-stage reaction kettle, and correspondingly cancel the stripping step of the fourth-stage reaction kettle.

[0107] 2. Install a heat exchange tube bundle I 12 with a diameter D of 600 mm in the first-stage reaction kettle. The top of the heat exchange tube bundle I 12 is 500 mm away from the liquid surface.

[0108] Reactive distillation process

[0109] The reaction conversion rate of the first-stage reaction kettle is controlled at 95%; the reaction in the second-stage reaction kettle is complete, and 0.6% of steam is injected into the second-stage reaction kettle (the ratio to the liquid material amount in this stage kettle); 0.8% of steam is injected into the third-stage reaction kettle (the ratio to the liquid material amount in this stage kettle).

[0110] Reaction result:

[0111] Reaction conversion rate: 99.95%, and the stripping steam consumption is 1.4% of the feed. The water content in the liquid mixture discharged from the reaction is 17.3%. The residence time of the material in each reaction kettle is 0.8 hours.

[0112] Example 3

[0113] The reaction system, reactive distillation device and corresponding process of this example are basically the same as those of Example 1. The differences are only as follows:

[0114] Reactive distillation process

[0115] The reaction conversion rate of the first-stage reaction kettle is controlled at 90%; the reaction conversion rate of the second-stage reaction kettle is controlled at 95%, and 0.25% of steam (the ratio to the feed amount) is injected into the second-stage reaction kettle; the reaction in the third-stage reaction kettle is complete, and 0.6% of steam (the ratio to the feed amount) is injected into the third-stage reaction kettle; 0.7% of steam (the ratio to the feed amount) is injected into the fourth-stage reaction kettle.

[0116] Reaction results:

[0117] Reaction conversion rate: 99.94%, and the steam consumption is 1.55% of the feed. The water content in the liquid mixture discharged from the reaction is 17%. The residence time of the material in each reaction kettle is 0.7 hours.

[0118] Example 4

[0119] The reaction system, reactive distillation device and corresponding process of this example are basically the same as those of Example 1. The differences are only as follows:

[0120] Reactive distillation device

[0121] As Figure 1 shown, in addition to using jacket heating in the first-stage reaction kettle, there is also a heat exchange tube bundle Ⅰ12 with a diameter D of 600 mm built in; the top of the heat exchange tube bundle Ⅰ12 is 500 mm away from the liquid surface.

[0122] Reactive distillation process

[0123] The reaction conversion rate of the first-stage reaction kettle is controlled at 90%; the reaction conversion rate of the second-stage reaction kettle is controlled at 98%, and 0.3% of steam (the ratio to the liquid material amount in this stage of the kettle) is injected into the second-stage reaction kettle; the reaction in the third reaction kettle is complete, and 0.6% of steam (the ratio to the liquid material amount in this stage of the kettle) is injected into the third-stage reaction kettle; 0.7% of steam (the ratio to the liquid material amount in this stage of the kettle) is injected into the fourth-stage reaction kettle.

[0124] Reaction results

[0125] Reaction conversion rate: 99.98%, stripping steam consumption is 1.6% of the feed. The water content in the liquid mixture discharged from the reaction is 16.8%. The residence time of the material in each reaction kettle is 0.7 hours.

[0126] Comparative Example 2: Synthesis of bis(2,2,6,6-tetramethylpiperidinol) sebacate (high-viscosity system)

[0127] Reaction monomers: piperidinol, dimethyl sebacate, solvent n-heptane

[0128] Reactive distillation device

[0129] It includes a single reaction kettle (for esterification reaction), a distillation column. A jacket is provided on the outer wall of the kettle body of the single reaction kettle for jacket heat exchange. The gas phase outlet of the reaction kettle is directly connected to the distillation column. Methyl methacrylate, water, and methanol are produced at the top of the distillation column, and the final liquid phase discharge of the reaction kettle is the product of bis(2,2,6,6-tetramethylpiperidinol) sebacate.

[0130] Reactive distillation process

[0131] Reaction and distillation are carried out in batch operation. After the stirring in the single reaction kettle is completely reacted for 5 hours, and then vacuum distillation is carried out for 3 hours. After the by-products and solvents are distilled off, the liquid phase product is discharged and then enters the cooling water for flushing crystallization to recover the product.

[0132] Reaction results: Product yield: 90.5%. Product purity: 98%. Due to poor gas-liquid mass transfer effect, the reaction conversion rate is relatively low. Due to poor separation effect, the product purity is not high, affecting the downstream application of the product.

[0133] Example 5 Synthesis of bis(2,2,6,6-tetramethylpiperidinol) sebacate

[0134] The reactant system and reaction monomers are the same as those in Comparative Example 2:

[0135] Reactive distillation device

[0136] It includes three reaction kettles in series and a distillation column. The material enters the first-stage reaction kettle and then sequentially enters the feed ports of the next-stage reaction kettles; a gas phase discharge port is provided at the top of any reaction kettle. The gas phase discharge port at the top of the first-stage reaction kettle is connected to the bottom gas inlet of the second-stage reaction kettle. The gas phase discharge ports from the second-stage reaction kettle to the third-stage reaction kettle are respectively connected to the distillation column to carry out rectification separation of light components; and all three reaction kettles introduce low-boiling reaction monomers through the low-boiling monomer pipeline 6 to promote the reaction conversion rate, and steam stripping is carried out by adding steam through the steam pipeline 7 to the latter two reaction kettles.

[0137] Among them, one vertical heat exchange tube bundle Ⅰ12 is arranged on the center line in the first-stage reaction kettle; two layers of sixFigure 3 - 4 The heat exchange tube bundle Ⅱ 20 shown; the heat exchange tube bundle Ⅰ 12 in the first-stage reactor has a diameter of 800 mm, the distance from the top of the tube bundle to the liquid level L1 is 300 mm, the outer tube 121 of the heat exchange tube has a diameter of 60 mm, the inner tube 122 has a diameter of 25 mm, and the adjacent tube spacing is 30 mm.

[0138] The heat exchange tube bundle Ⅱ 20 in the second-stage reactor has a diameter of 600 mm, the distance from the bottom end of the tube bundle along its length direction to the tangent line of the bottom of the reactor is 100 mm, the outer tube 200 of the heat exchange tube has a diameter of 50 mm, the inner tube 201 has a diameter of 20 mm, and the adjacent tube spacing is 30 mm. The end spacing L2 between the relative heat exchange tube bundles on each layer is 500 mm, and the vertical spacing between two layers is 600 mm.

[0139] Reactive distillation process

[0140] The material is first heated and reacted in the first-stage reactor, introducing monomer three and adjusting the feed ratio and temperature of each reaction monomer to control the temperature in the first-stage reactor at 100 °C, the viscosity in the reactor at about 35 cp, and the reaction conversion rate at 80%; the gas phase (methanol and n-heptane) in the first-stage reactor is introduced into the bottom of the second-stage reactor, and the liquid phase is discharged into the second-stage reactor for continuous reaction; the temperature in the second reactor is controlled at about 110 °C, injecting 0.3% steam (the ratio to the liquid feed amount) to make the reaction in the second-stage reactor complete and the viscosity controlled at about 150 cp; the liquid phase discharged from the second-stage reactor enters the third-stage reactor for deep light component removal, and the gas phase (methanol, n-heptane, steam) enters the distillation column for separation. Methanol is produced at the top of the distillation column, n-heptane and water are produced in the middle of the column. After the n-heptane and water are phase-separated, part of the n-heptane returns to the second-stage reactor, and part of the n-heptane returns to the first-stage reactor (not shown in the figure), and the water enters the downstream recrystallization unit for reuse; the temperature in the third reactor is controlled at about 125 °C, injecting 0.8% steam (the ratio to the liquid feed amount) to control the viscosity in the reactor below 200 cp.

[0141] Reaction results: The reaction residence time is 4 hours, the product yield: 99.5%. The product purity is 99.8%.

[0142] Example 6

[0143] The reaction system, reactive distillation device and corresponding process of this example are basically the same as those of Example 5. The differences are only as follows:

[0144] In the reaction device: The heat exchange tube bundle Ⅰ 12 in the first-stage reactor has a diameter D of 1000 mm, the distance from the top of the tube bundle to the liquid level L1 is 300 mm, the outer tube 121 of the heat exchange tube has a diameter of 60 mm, the inner tube 122 has a diameter of 25 mm, and the adjacent tube spacing is 30 mm.

[0145] In the reactive distillation process: The reaction conversion rate of the first-stage reactor is controlled at 90%, the temperature inside the first-stage reactor is controlled at 105°C, and the viscosity is controlled at about 45 cp. The gas phase (methanol and n-heptane) of the first-stage reactor is introduced into the bottom of the second-stage reactor, and the liquid-phase discharge enters the second-stage reactor for further reaction; the temperature inside the second reactor is controlled at about 120°C, and the reaction in the second-stage reactor is completed. 0.3% steam is injected into the second-stage reactor, and the viscosity is controlled at about 150 cp. The liquid-phase discharge of the second-stage reactor enters the third-stage reactor for deep light component removal, and the gas phase (methanol, n-heptane, and steam) enters the distillation column for separation. Methanol is produced at the top of the distillation column, and heptane and water are produced in the middle of the column. After the heptane and water are phase-separated, part of the heptane is returned to the second-stage reactor, part of the heptane is returned to the first-stage reactor, and the water enters the downstream recrystallization unit for reuse; the temperature inside the third reactor is controlled at about 130°C, the viscosity of the third-stage reactor is controlled below 200 cp, and 0.8% steam is injected.

[0146] Reaction results:

[0147] The reaction residence time is 4 hours, the product yield is 99.3%, and the product purity is 99.8%.

[0148] It should be noted that the above embodiments can be freely combined according to needs. The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A multi-kettle reactive distillation device, characterized in that: It includes a multi-stage series of reaction kettles and a distillation column; The side wall of the first-stage reaction kettle is connected to a material addition unit; along the main material flow direction, the liquid-phase discharge port provided at the upper part of the previous-stage reaction kettle is sequentially connected to the feed port of the next-stage reaction kettle; a gas-phase discharge port is provided at the top of any stage of the reaction kettle, and the gas-phase discharge port at the top of the first-stage reaction kettle is connected to the bottom air inlet of the second-stage reaction kettle, and the gas-phase discharge ports of the second-stage reaction kettle to the last-stage reaction kettle are respectively connected to the distillation column to perform rectification separation on light components; Among them, the bottom of at least one stage of the reaction kettle is also connected to a low-boiling-point reaction monomer feed pipeline.

2. The multi-kettle reactive distillation device according to claim 1, characterized in that: A jacket is provided on the outer wall of the first-stage reaction kettle, and a heat exchange tube bundle is built in any stage of the reaction kettle for heating and vaporizing the materials in each stage of the kettle.

3. The multi-kettle reactive distillation device according to claim 2, characterized in that: The heat exchange tube bundle Ⅰ in the first-stage reaction kettle is arranged along the central axis of the first-stage reaction kettle; The whole of the heat exchange tube bundle Ⅰ is below the liquid level in the kettle, and the top of the heat exchange tube bundle Ⅰ is at a distance of L1 from the liquid surface, and the bottom end penetrates through the bottom of the first-stage reaction kettle and extends downward.

4. The multi-kettle reactive distillation device according to claim 2, characterized in that: Except for the first-stage reaction kettle, the heat exchange tube bundles Ⅱ in other stages of the reaction kettles are horizontally placed along the side walls of the kettles at the lower parts of each stage.

5. The multi-kettle reactive distillation device according to claim 4, characterized in that: The heat exchange tube bundles Ⅱ are arranged in one or two layers in each stage of the kettle, and the heat exchange tube bundles Ⅱ located on the same layer are evenly distributed along the circumference in the horizontal cross-section.

6. The multi-kettle reactive distillation device according to claim 2, characterized in that: The heat exchange tubes of the heat exchange tube bundle are all double-layer sleeves, including an outer tube and an inner tube placed inside the outer tube. The annulus between the outer tube and the inner tube is used for steam circulation, and the top of the inner tube along the tube length direction is communicated with the inside of the outer tube for the inner tube to circulate condensate; A steam inlet is provided at the bottom of the outer tube along the tube length direction for introducing steam; a condensate outlet is provided at the bottom end of the double-layer sleeve along the tube length direction for the condensate after steam heat exchange and condensation to flow back and discharge.

7. The multi-kettle reactive distillation device according to claim 1, characterized in that: The reaction kettles are set to be in series of 3 to 4 stages; and / or; Except for the first-stage reaction kettle, the bottoms of other stages of the reaction kettles are also connected to a steam feed pipeline.

8. The multi-kettle reactive distillation device according to claim 1, characterized in that: The distillation column is arranged above the second-stage reaction kettle; a gas-phase feed port is tangentially provided at the bottom of the distillation column along the side line, and a liquid-phase reflux port communicated with the second-stage reaction kettle is also provided; and / or; The distance from the bottom of the distillation column to the first tray is 1.8 - 2.5 m, and the upward flow velocity of the gas-phase material is controlled to be less than 2 m / s.

9. A multi-kettle reactive distillation process, characterized in that, It includes the following steps: S1. First, the material is heated and reacted in the first-stage reactor. The liquid-phase discharge of the first-stage reactor enters the second-stage reactor for continuous heating and reaction. The gas-phase discharge of the first-stage reactor enters the bottom of the second-stage reactor as the stirring and stripping gas of the second-stage reactor; S2. The liquid-phase material continues to be heated and reacted in the second-stage reactor. The light components therein vaporize and rise to enter the distillation column for separation. The liquid-phase discharge in the reaction enters the third-stage reactor to complete the reaction; S3. The liquid-phase material is heated and deeply reacted in the third-stage reactor. The gas-phase material of the third-stage reactor enters the above-mentioned distillation column for separation. The liquid-phase discharge is directly discharged or enters the next-stage reactor to continue repeating this step; Moreover, a low-boiling reaction monomer is introduced into at least one of the multi-stage reactors.

10. The multi-kettle reactive distillation process according to claim 9, wherein: In the multi-stage reactors along the main material flow direction, the temperature of the material in the kettles is controlled to increase by 5-15 °C in sequence; and / or; Steam is introduced into each reactor except the first-stage reactor respectively.

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