Preparation method and equipment of butyric anhydride

Abstract

The invention relates to the technical field of chemical synthesis, and discloses a preparation method and equipment of butyric anhydride, and the preparation method comprises the following steps: butyric acid and acetic anhydride are subjected to a preliminary reaction in a reaction section of a rectifying tower at the reaction temperature of 70-145 DEG C; a product at the bottom of the reaction section is input into a tubular reactor for continuous reaction at the reaction temperature of 110-175 DEG C, and a product obtained through reaction in the tubular reactor is conveyed back to the rectifying tower for separation; and at least part of the butyric anhydride product obtained from the tower kettle of the rectifying tower is introduced into the shell pass of the tubular reactor for heat exchange, and the heat-exchanged material flows back to the tower kettle of the rectifying tower. The low-speed second-step reaction of butyric acid and acetic acid butyric anhydride is enhanced in the tubular reaction area with high temperature and high heat transfer efficiency, residues of acetic acid butyric anhydride and unreacted butyric acid are reduced, and meanwhile, the high-temperature butyric anhydride material in the tower kettle is utilized to perform heat exchange on the shell pass of the tubular reactor, so that recovery and reutilization of heat in the tower kettle are realized, and the production cost is reduced. And the overall energy consumption of the equipment is reduced.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, specifically to a method and equipment for preparing butyric anhydride. Background Technology

[0002] Butyric anhydride, also known as butyryl oxide, is a colorless and transparent liquid widely used in the preparation of cellulose acetate butyrate, butyrate esters, fragrances, and other products, making it an important basic chemical raw material. Currently, the main industrial method for preparing butyric anhydride is the transesterification reaction of butyric acid and acetic anhydride. Conventional processes typically use batch reactors. Once a certain conversion rate is reached, acetic anhydride, acetic acid, and butyric acid are sequentially distilled off, finally yielding the butyric anhydride product and discharging the residue. However, this process is slow, resulting in a long operating cycle. Furthermore, the use of batch distillation for separation makes it difficult to further improve product purity and yield, leading to problems such as low butyric anhydride product quality and high production costs.

[0003] From the perspective of reaction mechanism, the transesterification process of butyric acid and acetic anhydride is a two-step series reaction. The first step is the reaction of butyric acid with acetic anhydride to produce acetic butyric anhydride and acetic acid. This reaction is relatively fast and irreversible, as shown in equation (1). The second step is the further reaction of butyric acid with acetic butyric anhydride to produce acetic anhydride and acetic acid. This reaction is relatively slow and reversible, as shown in equation (2). (1) (H3CCO)2O + C3H7COOH → H3CCO-O-OCC3H7+ CH3COOH; (2) H3CCO-O-OCC3H7+ C3H7COOH → (OCC3H7)2O + CH3COOH; Because the boiling point distribution of reactants and products is reasonable, i.e., acetic acid < acetic anhydride < butyric acid < butyric anhydride, under reactive distillation conditions, the byproduct acetic acid can be continuously stripped from the top of the column, thereby shifting the equilibrium of step (2) toward the formation of butyric anhydride and improving the overall conversion rate. By coupling the reaction and separation processes within the same reactive distillation column, the reaction efficiency can be significantly improved and energy consumption reduced, making it a more ideal process direction at present.

[0004] Existing technologies have proposed separating acetic acid and the intermediate acetic butyric anhydride by incorporating baffles or secondary column structures within the distillation column, thereby improving the coupling efficiency between reaction and separation. However, since the reaction rate in the second step is significantly lower than that in the first step, a longer residence time and higher reaction temperature are still required to increase the conversion rate and reduce the intermediate concentration. As a result, the overall theoretical plate count of the device is higher, the heat input to the reboiler is greater, and both equipment investment and energy consumption are significantly increased, leading to lower system energy efficiency.

[0005] Therefore, existing reactive distillation processes still suffer from problems such as limited rate control steps, high energy consumption, large tower height, and high equipment investment. There is an urgent need for a new type of reaction equipment that can effectively enhance the second-step reaction, accelerate the reaction rate, and operate efficiently at higher temperatures, so as to further reduce system energy consumption and improve the yield and purity of butyric anhydride. Summary of the Invention

[0006] This invention provides a method and apparatus for preparing butyric anhydride, which solves the problems in the prior art where the second step of the reaction between butyric acid and acetic butyric anhydride to produce butyric anhydride has a low reaction rate, resulting in a limited overall reaction conversion rate. Higher yields can only be obtained at higher temperatures and longer residence times. At the same time, the coupling efficiency between the reaction and separation processes is not high, resulting in high energy consumption, tower height, and increased equipment investment.

[0007] In a first aspect, the present invention provides a method for preparing butyric anhydride, comprising: Butyric acid and acetic anhydride undergo a preliminary reaction in the reaction section of the distillation column at a temperature of 70℃-145℃. The product from the bottom of the reaction section is fed into a tubular reactor to continue the reaction at a temperature of 110℃-175℃. The product obtained from the reaction in the tubular reactor is then sent back to a distillation column for separation. The butyric anhydride product obtained from the bottom of the distillation column is introduced at least partially into the shell side of the tubular reactor for heat exchange, and the heat-exchanged material is refluxed back to the bottom of the distillation column.

[0008] The butyric anhydride preparation method of this invention achieves dynamic coupling of reaction and separation by forming a material circulation between a reactive distillation column and a tubular reactor. The product from the bottom of the reaction section of the distillation column is introduced into the tubular reactor for further reaction, and then the product is refluxed back to the distillation column for separation. This structural design enhances the second-step reaction of butyric acid and acetic acid butyric anhydride to produce butyric anhydride within the tubular reactor, prolonging the residence time of the reactants and suppressing backmixing of the byproduct acetic acid, thereby significantly improving the conversion efficiency of the rate-controlled step.

[0009] Furthermore, at least a portion of the butyric anhydride product obtained from the distillation column reboiler is introduced into the shell side of the tubular reactor for heat exchange. This allows for heat exchange between the high-temperature stream from the reboiler and the reaction stream within the reactor, improving the temperature stability of the tubular reactor without requiring additional energy consumption. In this invention, some heat from the reboiler is recovered and used to heat the tubular reactor, achieving energy self-circulation between the reboiler and the reactor. This reduces the load on the reboiler, contributing to lower overall energy consumption and improving the economic efficiency and stability of the process operation.

[0010] In one alternative embodiment, the pressure conditions inside the distillation column are 10 kPa to 70 kPa.

[0011] In one alternative embodiment, the reflux ratio of the distillation column is (0.5-9):1.

[0012] Preferably, the pressure conditions inside the distillation column are 10 kPa-50 kPa; Preferably, the reflux ratio of the distillation column is (4-7.5):1.

[0013] Unless otherwise specified, all pressures mentioned in this invention refer to absolute pressure, and the unit is kPa.

[0014] In one optional embodiment, the distillation column includes a rectification section located above the reaction section and a stripping section located below the reaction section. The product obtained from the continued reaction is transported back to the reaction section of the distillation column. The temperature conditions of the rectification section are 55℃-120℃, and the temperature conditions of the stripping section are 100℃-188℃.

[0015] In one alternative embodiment, the number of theoretical plates in the reaction section is 8-16.

[0016] In one alternative implementation, the number of theoretical plates in the rectification section is 6-12.

[0017] In one alternative implementation, the number of theoretical plates in the stripping section is 6-12.

[0018] In one alternative embodiment, the mass ratio of butyric acid to acetic anhydride is (1.5-4):1.

[0019] In one alternative implementation, a portion of the butyric anhydride product obtained from the bottom of the distillation column is introduced into the shell side of a tubular reactor for heat exchange, while the other portion is output and collected. Preferably, the mass flow rate ratio of butyric anhydride product entering the tubular reactor for heat exchange to butyric anhydride product collected at the output is (1.8-6):1.

[0020] Secondly, the present invention provides an apparatus for use in any of the preparation methods described in the present invention, comprising a distillation column and a tubular reactor, wherein the feed inlet and discharge outlet of the tubular reactor are respectively connected to the reaction section of the distillation column, and the reboiler of the distillation column is connected to the shell side of the tubular reactor for cross-heat exchange with the tubular reactor.

[0021] In one alternative embodiment, the diameter of the tubular reactor is 19mm-57mm.

[0022] In one alternative implementation, the tube length is 2.5m-4.5m.

[0023] In one alternative implementation, the tube arrangement angle is 30°-90°.

[0024] The equipment provided by this invention connects the inlet and outlet of the tubular reactor to the reaction section of the distillation column, respectively, so that the material in the reaction section can form a continuous circulation between the reaction environment inside the column and the high-temperature enhanced reaction environment of the tubular reactor, thereby significantly extending the residence time of the reactants and improving the conversion depth of key reaction steps.

[0025] The distillation column reboiler is connected to the shell side of the tubular reactor, allowing the high-temperature stream from the reboiler to exchange heat with the tubular reactor. This enables effective recovery and reuse of the reboiler heat, reduces the reboiler load, and improves the overall energy efficiency and operational stability of the system.

[0026] In one optional embodiment, the distillation column includes a rectification section disposed above the reaction section and a stripping section disposed below the reaction section, and the feed inlet and discharge outlet of the tubular reactor are respectively connected to the bottom of the reaction section.

[0027] This invention divides the distillation column structure into a rectification section above the reaction section and a stripping section below the reaction section. The feed and discharge ports of the tubular reactor are connected to the bottom of the reaction section, making the reaction zone the core node of the entire column system. This structural arrangement allows the reaction section to directly receive the high-temperature reaction stream from the tubular reactor, ensuring continuous conversion of the reactants within the optimal temperature gradient and material concentration environment. Simultaneously, the rectification section above the reaction section promptly removes low-boiling-point byproducts, reducing their adverse effects on reaction equilibrium, while the stripping section below further enriches heavy components and maintains stable material composition in the reaction section. The equipment of this invention ensures sufficient residence and circulation of reactants within the reaction section and enhances reaction kinetic efficiency through the selective separation provided by the upper and lower column sections, resulting in a closer coupling between the reaction and separation processes, thereby significantly improving the yield and purity of butyric anhydride.

[0028] In one alternative embodiment, the reboiler of the distillation column is connected to a discharge pipe for discharging butyric anhydride products; Preferably, the bottom of the distillation column is connected to the shell side of the tubular reactor via a heat exchange pipeline, and the discharge pipe is connected to the heat exchange pipeline.

[0029] The technical solution of this invention has the following advantages: The butyric anhydride preparation method of the present invention forms a cyclic coupling system of reaction and separation between the reaction section of the distillation column and the tubular reactor. The reaction section completes the first stage of the anhydride reaction, so that the material initially generates butyric anhydride at a suitable temperature. The material at the bottom of the reaction section further enters the tubular reactor to complete the second stage reaction at a higher temperature, thereby effectively improving the conversion rate of the difficult reaction step. The post-reaction stream is returned to the distillation column, so that the light components are removed in time and the heavy components are effectively enriched, which is conducive to promoting the reaction equilibrium to the target direction.

[0030] Simultaneously, the butyric anhydride product from the bottom of the reactor is used to heat the shell side of the tubular reactor, achieving heat recovery and self-circulation from the bottom of the reactor. This not only reduces the demand for external heat sources and lowers the reboiler load, but also improves the temperature stability within the tubular reactor, making the reaction conditions more uniform and reliable. Therefore, the method of this invention significantly improves the yield and purity of butyric anhydride, and enhances overall energy efficiency and the stability of the equipment operation.

[0031] This invention relates to an apparatus for preparing butyric anhydride. By directly connecting a tubular reactor to the reaction section of a distillation column, the reactants continuously circulate between the reaction environment within the column and the high-temperature intensified reaction zone of the tubular reactor, significantly increasing the residence time and conversion depth. Simultaneously, the interconnected structure between the distillation column reboiler and the shell side of the tubular reactor enables cross-heat exchange, allowing for efficient recovery of reboiler heat to maintain the reaction temperature in the tubular reactor. This reduces reboiler energy consumption and makes the reaction temperature more stable and reliable. Through this structural design, the apparatus achieves deep coupling of reaction and separation, improving the butyric anhydride production efficiency and product purity, and significantly enhancing overall energy efficiency and the economics of plant operation. Attached Figure Description

[0032] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the equipment assembly structure for preparing butyric anhydride according to the present invention.

[0034] Explanation of reference numerals in the attached figures: 1. Rectifying section; 11. First heat exchange pipeline; 12. Second heat exchange pipeline; 2. Reaction section; 21. Top of reaction section; 22. Bottom of reaction section; 3. Stripping section; 4. Shell and tube heat exchanger; 41. Liquid feed line; 42. Gas discharge line; 5. Butyric anhydride discharge pipe; 6. Acetic acid discharge pipe; 7. Condenser; 8. Reboiler. Detailed Implementation The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0035] The purity of butyric anhydride and acetic acid involved in the embodiments and comparative examples of this invention were all detected and analyzed using gas chromatography, wherein the gas chromatography was performed using a Shimadzu GC. The 2030 gas chromatograph was used for qualitative and quantitative analysis of the reaction products. The chromatographic detection conditions are shown in Table 1. Table 1: Chromatographic Detection Conditions

[0036] The correction factor is calculated using the following formula: In the formula: f i ′ : The relative correction factor for component i; f i ，f s ： Components i and standard objects S The absolute correction factor; W i , W s Components in the standard sample i and standard objects S The weight; A i , A s Components i and standard objects S The peak area; This invention uses acetic acid as the reference substance S, and performs quantitative analysis of other components using the relative correction factor of component i relative to acetic acid. The relative correction factors of each component used in this invention are shown in Table 2.

[0037] Table 2: Relative Correction Factors for Each Component

[0038] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0039] As shown in Figure 1, this embodiment provides a reaction apparatus for preparing butyric anhydride, including a distillation column and a tubular reactor. The tubular reactor in this invention adopts a tubular heat exchanger structure, hereinafter referred to as tubular heat exchanger 4. The inlet and outlet of the tubular heat exchanger 4 are respectively connected to the reaction section 2 of the distillation column.

[0040] The distillation column consists of a rectification section 1, a reaction section 2, and a stripping section 3 from top to bottom. The first feed inlet 21 at the top of the reaction section can be used to introduce acetic acid or anhydride feedstocks; the second feed inlet 22 at the bottom of the reaction section is used to supplement another stream of reactants.

[0041] The connection methods between the shell-and-tube heat exchanger 4 and the reaction section 2 include, but are not limited to, the following: The liquid feed line 41 and gas discharge line 42 of the shell-and-tube heat exchanger are both connected to the bottom 22 of the reaction section. Specifically, one end of the liquid feed line 41 connects to the bottom 22 of the reaction section, and the other end connects to the bottom inlet of the heat exchanger 4; one end of the gas discharge line 42 connects to the bottom 22 of the reaction section, and the other end connects to the top outlet of the heat exchanger 4. During operation, the liquid material at the bottom 22 of the reaction section enters the liquid feed line 41 through siphoning and flows into the shell-and-tube heat exchanger 4; the gas generated inside the shell-and-tube heat exchanger 4 returns to the bottom 22 of the reaction section via the gas discharge line 42, creating a circulation path for the reactants within the reaction zone and promoting heat transfer and renewal of the reactants.

[0042] The preferred structural parameters for the tubular reactor are: tube diameter of 19 mm to 57 mm, tube length of 2.5 m to 4.5 m, and tube arrangement angle of 30° to 90°. This size range ensures sufficient heat transfer area while maintaining good flow distribution, thereby improving reaction efficiency.

[0043] Preferably, the reboiler of the distillation column is connected to the shell side of the tubular reactor 4 via heat exchange pipes to achieve cross-heat exchange between the reboiler and the tubular reactor 4, thereby recovering reboiler heat and improving overall energy efficiency. Specifically, the reboiler outlet is connected to the shell side of the heat exchanger 4 via a first heat exchange pipe 11 and a second heat exchange pipe 12, and butyric anhydride product can be output and collected through the butyric anhydride outlet pipe 5 provided on the first heat exchange pipe 11.

[0044] A condenser 7 is installed at the top of the distillation column to condense and reflux the overhead gas, and discharge the overhead product acetic acid through the acetic acid discharge pipe 6. A reboiler 8 is installed in the bottom of the distillation column to provide the necessary heat of vaporization and maintain stable separation and reaction conditions of the materials in the column.

[0045] The structure described in this embodiment achieves simultaneous improvement in reaction enhancement, energy cascade utilization, and distillation stability through the cyclic connection between the distillation column and the tubular heat exchanger 4, the cross heat exchange between the column bottom and the tubular heat exchanger 4, and the synergistic effect of the column top condensation and column bottom reboiling system. It can be effectively applied to the continuous preparation process of butyric anhydride.

[0046] Example 1 This embodiment provides a method for preparing butyric anhydride, as detailed below: This embodiment uses, as follows: Figure 1 The reaction apparatus shown prepares butyric anhydride. The distillation column has a diameter of 800 mm. The column shell and reboiler 8 are both made of 904L stainless steel to meet the corrosion resistance requirements of the reaction medium. MellapakPlus 452.Y structured packing is used inside the column. The entire distillation column has 20 theoretical plates, corresponding to a total packing height of approximately 10 m. Specifically, the rectification section 1 has 6 theoretical plates, the reaction section 2 has 8 theoretical plates, and the stripping section 3 has 6 theoretical plates. The shell-and-tube heat exchanger 4 used for the circulating reaction adopts a shell-and-tube structure with an outer diameter of φ19 mm. Each tube is 2.5 m long, with a total of 70 tubes arranged at a 30° angle. The total heat exchange area of ​​this heat exchanger is 10.2 m². 2 .

[0047] The raw material, n-butyric acid, is continuously fed into the distillation column at a flow rate of 150 kg / h through the first inlet at the top 21 of the reaction section, while the raw material, acetic anhydride, is continuously fed into the distillation column at a flow rate of 100 kg / h through the second inlet at the bottom 22 of the reaction section, with a mass flow rate ratio of 1.5:1. The liquid phase material at the bottom 22 of the reaction section automatically flows into the tube side of the shell-and-tube heat exchanger 4 through the liquid feed line 41 under siphon action, with a flow rate of 77 kg / h entering the shell-and-tube heat exchanger 4. The gaseous phase material generated in the shell-and-tube heat exchanger 4 returns to the bottom 22 of the reaction section through the gas outlet line 42, realizing a circulating reaction between the column section and the shell-and-tube heat exchanger.

[0048] The liquid material from the bottom of the distillation column enters the shell side of the tubular heat exchanger 4 via the first heat exchange line 11 at a flow rate of 259 kg / h. After heat exchange, it flows back to the bottom of the distillation column via the second heat exchange line 12, forming a stable heat exchange cycle between the bottom and the shell side of the tubular heat exchanger. The reboiler 8 installed at the bottom of the column provides heat of evaporation to maintain the vaporization of the bottom material, allowing the reaction and separation processes to continue. The condenser 7 installed at the top of the column condenses the rising vapor phase into liquid and refluxes it into the column to maintain the separation efficiency of the rectification section and ensure the purity of the top distillate.

[0049] The distillation column operates at a pressure of 10 kPa and a reflux ratio of 4:1. The temperatures in rectification section 1 are 55-70℃, reaction section 2 is 70-100℃, stripping section 3 is 100-125℃, and the temperature in the shell-and-tube heat exchanger 4 is 110-115℃. It should be noted that the temperatures in each section of the distillation column represent temperature ranges from bottom to top, not fixed temperature points. Under stable operating conditions, a temperature gradient exists along the column height, with the highest temperature at the bottom and the lowest at the top, and the internal temperature of each section varies continuously. The temperature range of the shell-and-tube heat exchanger corresponds to the temperature range between when the material enters and exits the heat exchanger.

[0050] During the reactive distillation process, butyric anhydride generated after separation and reaction in the tubular heat exchanger 4 and various sections of the column is continuously discharged from the butyric anhydride outlet pipe 5 on the bottom side of the distillation column at a flow rate of 143 kg / hr. The mass flow rate ratio of butyric anhydride product entering the tubular reactor for heat exchange from the bottom of the column to the mass flow rate of butyric anhydride product collected at the output is 1.8:1. Acetic acid product condensed at the top of the distillation column is continuously discharged from the acetic acid outlet pipe 6.

[0051] In this embodiment, the reactive distillation column produces butyric anhydride with a purity of 99.8 wt% and acetic acid with a purity of 99.5 wt%. The reboiler load of the distillation column is 201 kW, and the condenser load is 186 kW.

[0052] Example 2 This embodiment provides a method for preparing butyric anhydride, as detailed below: This embodiment uses, as follows: Figure 1The reaction apparatus shown prepares butyric anhydride. The distillation column has a diameter of 700 mm. The column shell and reboiler 8 are both made of 904L stainless steel to meet the corrosion resistance requirements of the reaction medium. The column packing uses MellapakPlus 452.Y structured packing. The entire distillation column has 26 theoretical plates, corresponding to a total packing height of approximately 13 m. Specifically, the rectification section 1 has 8 theoretical plates, the reaction section 2 has 10 theoretical plates, and the stripping section 3 has 8 theoretical plates. The shell-and-tube heat exchanger 4 used for the circulating reaction adopts a shell-and-tube structure with an outer diameter of φ38 mm. Each tube is 3.5 m long, with a total of 35 tubes arranged at a 45° angle. The total heat exchange area of ​​this heat exchanger is 14.6 m². 2 .

[0053] The raw material, n-butyric acid, is continuously fed into the distillation column at a flow rate of 200 kg / h through the first inlet at the top 21 of the reaction section, while the raw material, acetic anhydride, is continuously fed into the distillation column at a flow rate of 80 kg / h through the second inlet at the bottom 22 of the reaction section, with a mass flow rate ratio of 2.5:1. The liquid phase material at the bottom 22 of the reaction section automatically flows into the tube side of the shell-and-tube heat exchanger 4 through the liquid feed line 41 under siphon action, with a flow rate of 103 kg / h entering the shell-and-tube heat exchanger 4. The gaseous phase material generated in the shell-and-tube heat exchanger 4 returns to the bottom 22 of the reaction section through the gas outlet line 42, realizing a circulating reaction between the column section and the shell-and-tube heat exchanger.

[0054] The liquid material from the bottom of the distillation column enters the shell side of the tubular heat exchanger 4 at a flow rate of 455 kg / h through the first heat exchange pipe 11. After heat exchange, it flows back to the bottom of the distillation column through the second heat exchange pipe 12, forming a stable heat exchange cycle between the bottom and the shell side of the tubular heat exchanger. The reboiler 8 installed at the bottom of the column provides heat of evaporation to maintain the vaporization of the bottom material, allowing the reaction and separation processes to continue. The condenser 7 installed at the top of the column condenses the rising vapor phase into liquid and refluxes it into the column to maintain the separation efficiency of the rectification section and ensure the purity of the top distillate.

[0055] The reactive distillation column operates at a pressure of 25 kPa and a reflux ratio of 6:1. The temperatures in rectification section 1 are 77-85℃, reaction section 2 is 85-115℃, stripping section 3 is 115-150℃, and the temperature in the shell-and-tube heat exchanger 4 is 135-140℃. It should be noted that the temperatures in each section of the distillation column represent temperature ranges from bottom to top, not fixed temperature points. Under stable operating conditions, a temperature gradient exists along the column height, with the highest temperature at the bottom and the lowest at the top, and the internal temperature of each section varies continuously. The temperature range of the shell-and-tube heat exchanger corresponds to the temperature range between when the material enters and exits the heat exchanger. During the reactive distillation process, butyric anhydride generated after separation and reaction in the tubular heat exchanger 4 and various sections of the column is continuously discharged from the butyric anhydride outlet pipe 5 on the bottom side of the distillation column at a flow rate of 161 kg / hr. The mass flow rate ratio of butyric anhydride product entering the tubular reactor for heat exchange from the bottom of the column to the mass flow rate of butyric anhydride product collected at the output is 2.8:1. Acetic acid product condensed at the top of the distillation column is continuously discharged from the acetic acid outlet pipe 6.

[0056] In this embodiment, the reactive distillation column produces butyric anhydride with a purity of 99.8 wt% and acetic acid with a purity of 99.9 wt%. The reboiler load of the distillation column is 260 kW, and the condenser load is 243 kW.

[0057] Example 3 This embodiment uses, as follows: Figure 1 The reaction apparatus shown prepares butyric anhydride. The distillation column has a diameter of 600 mm. The column shell and reboiler 8 are both made of 904L stainless steel to meet the corrosion resistance requirements of the reaction medium. The column packing uses MellapakPlus 452.Y structured packing. The entire distillation column has 40 theoretical plates, corresponding to a total packing height of approximately 20 m. Specifically, the rectification section 1 has 12 theoretical plates, the reaction section 2 has 16 theoretical plates, and the stripping section 3 has 12 theoretical plates. The shell-and-tube heat exchanger 4 used for the circulating reaction adopts a shell-and-tube structure with an outer diameter of φ57 mm. Each tube is 3 m long, with a total of 38 tubes arranged at a 90° angle. The total heat exchange area of ​​this heat exchanger is 30.6 m². 2 .

[0058] The raw material, n-butyric acid, is continuously fed into the distillation column at a flow rate of 300 kg / h through the first inlet at the top 21 of the reaction section, while the raw material, acetic anhydride, is continuously fed into the distillation column at a flow rate of 75 kg / h through the second inlet at the bottom 22 of the reaction section, with a mass flow rate ratio of 4:1. The liquid material at the bottom 22 of the reaction section flows automatically into the tube side of the shell-and-tube heat exchanger 4 via the liquid feed line 41 under siphon action, with a flow rate of 155 kg / h entering the shell-and-tube heat exchanger 4. The gaseous material generated within the shell-and-tube heat exchanger 4 returns to the bottom 22 of the reaction section via the gas discharge line 42, achieving a circulating reaction between the column section and the shell-and-tube heat exchanger.

[0059] The liquid material from the bottom of the distillation column enters the shell side of the tubular heat exchanger 4 at a flow rate of 1500 kg / h through the first heat exchange pipe 11. After heat exchange, it flows back to the bottom of the distillation column through the second heat exchange pipe 12, forming a stable heat exchange cycle between the bottom and the shell side of the tubular heat exchanger 4. The reboiler 8 installed at the bottom of the column provides heat of evaporation to maintain the vaporization of the bottom material, allowing the reaction and separation processes to continue. The condenser 7 installed at the top of the column is used to condense the rising gas phase into liquid and reflux it into the column to maintain the separation efficiency of the rectification section and ensure the purity of the top distillate.

[0060] The reactive distillation column operates at a pressure of 50 kPa and a reflux ratio of 7.5:1. The temperatures in rectification section 1 are 96-110℃, reaction section 2 is 110-130℃, stripping section 3 is 130-172℃, and the temperature in the shell-and-tube heat exchanger 4 is 155-159℃. It should be noted that the temperatures in each section of the distillation column represent temperature ranges from bottom to top, not fixed temperature points. Under stable operating conditions, a temperature gradient exists along the column height, with the highest temperature at the bottom and the lowest at the top. The internal temperature of each section varies continuously. The temperature range of the shell-and-tube heat exchanger corresponds to the temperature range between when the material enters and exits the heat exchanger. During the reactive distillation process, butyric anhydride generated after separation and reaction in the tubular heat exchanger 4 and various sections of the column is continuously discharged from the butyric anhydride outlet pipe 5 on the bottom side of the distillation column at a flow rate of 252 kg / hr. The mass flow rate ratio of butyric anhydride product entering the tubular reactor for heat exchange from the bottom of the column to the mass flow rate of butyric anhydride product collected at the output is 6:1. Acetic acid product condensed at the top of the distillation column is continuously discharged from the acetic acid outlet pipe 6.

[0061] In this embodiment, the reactive distillation column produces butyric anhydride with a purity of 99.9 wt% and acetic acid with a purity of 99.7 wt%. The reboiler load of the distillation column is 303 kW, and the condenser load is 288 kW.

[0062] Example 4 This embodiment uses, as follows: Figure 1The reaction apparatus shown prepares butyric anhydride. The distillation column has a diameter of 500 mm. The column shell and reboiler 8 are both made of 904L stainless steel to meet the corrosion resistance requirements of the reaction medium. MellapakPlus 452.Y structured packing is used inside the column. The entire distillation column has 20 theoretical plates, corresponding to a total packing height of approximately 10 m. Specifically, the rectification section 1 has 6 theoretical plates, the reaction section 2 has 8 theoretical plates, and the stripping section 3 has 6 theoretical plates. The shell-and-tube heat exchanger 4 used for the circulating reaction adopts a shell-and-tube structure with an outer diameter of φ19 mm. Each tube is 2.5 m long, with a total of 70 tubes arranged at a 30° angle. The total heat exchange area of ​​this heat exchanger is 10.2 m². 2 .

[0063] The raw material, n-butyric acid, is continuously fed into the distillation column at a flow rate of 150 kg / h through the first inlet at the top 21 of the reaction section, while the raw material, acetic anhydride, is continuously fed into the distillation column at a flow rate of 100 kg / h through the second inlet at the bottom 22 of the reaction section, with a mass flow rate ratio of 1.5:1. The liquid phase material at the bottom 22 of the reaction section automatically flows into the tube side of the shell-and-tube heat exchanger 4 through the liquid feed line 41 under siphon action, with a flow rate of 77 kg / h entering the shell-and-tube heat exchanger 4. The gaseous phase material generated in the shell-and-tube heat exchanger 4 returns to the bottom 22 of the reaction section through the gas outlet line 42, realizing a circulating reaction between the column section and the shell-and-tube heat exchanger.

[0064] The liquid material from the bottom of the distillation column enters the shell side of the tubular heat exchanger 4 via the first heat exchange line 11 at a flow rate of 259 kg / h. After heat exchange, it flows back to the bottom of the distillation column via the second heat exchange line 12, forming a stable heat exchange cycle between the bottom and the shell side of the tubular heat exchanger. The reboiler 8 installed at the bottom of the column provides heat of evaporation to maintain the vaporization of the bottom material, allowing the reaction and separation processes to continue. The condenser 7 installed at the top of the column condenses the rising vapor phase into liquid and refluxes it into the column to maintain the separation efficiency of the rectification section and ensure the purity of the top distillate.

[0065] The distillation column operates at a pressure of 70 kPa and a reflux ratio of 4:1. The temperatures in rectification section 1 are 106-120℃, reaction section 2 is 120-145℃, stripping section 3 is 145-188℃, and the temperature in the shell-and-tube heat exchanger 4 is 170-175℃. It should be noted that the temperatures in each section of the distillation column represent temperature ranges from bottom to top, not fixed temperature points. Under stable operating conditions, a temperature gradient exists along the column height, with the highest temperature at the bottom and the lowest at the top. The internal temperature of each section varies continuously. The temperature range of the shell-and-tube heat exchanger corresponds to the temperature range between when the material enters and exits the heat exchanger.

[0066] During the reactive distillation process, butyric anhydride, generated after separation and reaction in the tubular heat exchanger 4 and various sections of the column, is continuously discharged from the butyric anhydride discharge pipe 5 on the bottom side of the distillation column at a flow rate of 143 kg / hr. The ratio of the flow rate entering the tubular reactor from the bottom to the flow rate discharged from the bottom is 1.8:1. Acetic acid product condensed at the top of the distillation column is continuously discharged from the acetic acid discharge pipe 6.

[0067] In this embodiment, the reactive distillation column produces butyric anhydride with a purity of 99.7 wt% and acetic acid with a purity of 99.6 wt%. The reboiler load of the distillation column is 185 kW, and the condenser load is 171 kW.

[0068] Example 5 The difference between this embodiment and Embodiment 1 is that the reflux ratio of the distillation column is controlled to be 0.5:1 during the reactive distillation process.

[0069] Example 6 The difference between this embodiment and Embodiment 1 is that the reflux ratio of the distillation column is controlled at 9:1 during the reactive distillation process.

[0070] Comparative Example 1 This comparative example uses a partitioned column reactive distillation to produce butyric anhydride; details are as follows: The diameter of the adjacent column is 1200mm. The material of the column shell and reboiler is 904L. The packing material inside the column is MellapakPlus 452.Y structured packing. The total number of theoretical plates in the adjacent column is 81, the total packing height is 45m, the number of theoretical plates in the rectifying section is 18, the number of theoretical plates in the reaction section is 22, the number of theoretical plates in the stripping section is 16, the number of theoretical plates in the rectifying section of the secondary column is 38, and the number of theoretical plates in the common stripping section is 25. The cross-sectional area ratio of the secondary column to the main column is 0.4:1.

[0071] The feed flow rate of raw material n-butyric acid is 150 kg / h, which enters from the top of the reaction section, and the feed flow rate of raw material acetic anhydride is 100 kg / h, which enters from the bottom of the reaction section. The mass ratio of the feed materials is 1.5:1.

[0072] The reactive distillation column operates at a pressure of 10 kPa and a reflux ratio of 4:1. The temperatures are as follows: rectification section 55-70℃, reaction section 70-100℃, stripping section 100-118℃, and common stripping section 118-123℃. The main column reflux ratio is 2.8, and the auxiliary column reflux ratio is 3.4. It should be noted that the temperatures described above represent temperature ranges at different heights from bottom to top within each section, not fixed temperature points. Under stable operating conditions, the distillation column exhibits a temperature gradient along its height, with the highest temperature at the bottom and the lowest at the top. The internal temperature of each section varies continuously.

[0073] In this comparative example, butyric anhydride with a purity of 99.5 wt% was produced, of which acetic acid butyric anhydride concentration reached 0.5 wt%; acetic acid with a purity of 99.6 wt% was produced, with a reboiler load of 367 kW and a condenser load of 345 kW.

[0074] Comparative Example 2 The difference between this comparative example and Example 2 is that this comparative example does not use a shell-and-tube heat exchanger; the material inside the column relies solely on the heat transfer and material circulation within the distillation column itself to complete the reactive distillation process. The specific production preparation method is as follows: This comparative example uses a 700 mm diameter distillation column for reactive distillation. The column shell and reboiler 8 are both made of 904L stainless steel to meet the corrosion resistance requirements of the reaction medium. MellapakPlus 452.Y structured packing is used inside the column. The entire distillation column has 26 theoretical plates, corresponding to a total packing height of approximately 13 m. Specifically, the rectification section 1 has 8 theoretical plates, the reaction section 2 has 10 theoretical plates, and the stripping section 3 has 8 theoretical plates.

[0075] The raw material, n-butyric acid, is continuously fed into the distillation column through the first inlet at the top 21 of the reaction section at a flow rate of 200 kg / h, and the raw material, acetic anhydride, is continuously fed into the distillation column through the second inlet at the bottom 22 of the reaction section at a flow rate of 80 kg / h. The mass flow ratio of the two is 2.5:1.

[0076] The operating pressure of the reactive distillation column is 25 kPa, the reflux ratio is 6:1, the temperature of rectification section 1 is 77-85℃, the temperature of reaction section 2 is 85-115℃, and the temperature of stripping section 3 is 115-150℃.

[0077] Under the above conditions, the butyric anhydride product obtained in this comparative example has a purity of 93.7 wt%, with an acetic acid butyric anhydride content of 4.2 wt% and a butyric acid content of 2.1 wt%; the acetic acid distilled from the top of the column has a purity of 99.9 wt%. Under these conditions, the reboiler load is 372 kW and the condenser load is 364 kW.

[0078] Comparative Example 3 The difference between this comparative example and Example 3 is that the liquid material in the reboiler of the distillation column in this comparative example does not exchange heat with the shell side of the tubular heat exchanger 4. The tubular heat exchanger is only used as a circulating reaction unit in the reaction section, thus eliminating the shell-side heat exchange linkage between the reboiler and the tubular heat exchanger.

[0079] The raw material, n-butyric acid, is continuously fed into the distillation column at a flow rate of 300 kg / h through the first inlet at the top 21 of the reaction section, while the raw material, acetic anhydride, is continuously fed into the distillation column at a flow rate of 75 kg / h through the second inlet at the bottom 22 of the reaction section, with a mass flow rate ratio of 4:1. The liquid material at the bottom 22 of the reaction section flows automatically into the tube side of the shell-and-tube heat exchanger 4 via the liquid feed line 41 under siphon action, with a flow rate of 155 kg / h entering the shell-and-tube heat exchanger 4. The gaseous material generated in the reaction within the shell-and-tube heat exchanger 4 returns to the bottom 22 of the reaction section via the gas discharge line 42, forming an internal circulation reaction between the column section and the shell-and-tube heat exchanger.

[0080] In this comparative example, the bottom material is not used as the heat exchange medium. Instead, external steam is supplied to the shell side of the shell-and-tube heat exchanger 4. The steam flow rate entering the shell side is 112 kg / h to maintain the reaction temperature inside the shell-and-tube heat exchanger.

[0081] Under the above conditions, the butyric anhydride produced by the reactive distillation column has a purity of 99.9 wt%; the acetic acid produced has a purity of 99.7 wt%. The reboiler load of the distillation column is 366 kW, and the condenser load is 386 kW.

[0082] Test Example 1 This test case compared the embodiment and the comparative example, comparing the purity of butyric anhydride product, the purity of acetic acid by-product, and the energy consumption level of the distillation column, including indicators such as reboiler load and condenser load. The relevant test results are shown in Table 3.

[0083] Table 3: Performance Comparison Results of Each Example and Comparative Example

[0084] As can be seen from the results in Table 3, the embodiments of the present invention maintain high levels of both butyric anhydride purity and acetic acid purity. At the same time, the reboiler load and condenser load of the embodiments of the present invention are significantly lower than those of the comparative example, reflecting that while achieving high-purity products, the overall energy consumption is lower and the process operation is more efficient.

[0085] Comparative Example 1 uses a partitioned-wall column reactive distillation method for production. Although the partitioned-wall column structure can improve separation efficiency to some extent, and the purity of butyric anhydride and acetic acid is close to that of the embodiments of the present invention, it requires the coupled operation of multiple columns and complex reflux organization within the column, resulting in reboiler and condenser loads that are much higher than those of the embodiments of the present invention. It is evident that even with comparable product purity levels, the present invention significantly reduces heat energy requirements through the coupling of the tubular reactor and the column bottom heat exchange, and its operating energy consumption is significantly better than that of the partitioned-wall column process.

[0086] The main difference between Comparative Example 2 and Example 2 is that a tubular heat exchanger is not used; the material in the column relies solely on material circulation and heat transfer within the distillation column to maintain the reaction and separation process. Under these conditions, the butyric anhydride purity of Comparative Example 2 is only 93.7 wt%, significantly lower than that of the present invention, and accompanied by a significant increase in the residual amounts of acetic acid butyric anhydride and butyric acid; simultaneously, the reboiler load and condenser load are higher than those of Example 2. It is evident that without a tubular reactor to enhance the reaction step, the conversion of butyric acid to butyric anhydride is limited, the heat load is difficult to effectively distribute, leading to a decrease in product purity and an increase in energy consumption. The present invention enhances the two-stage reaction through a tubular reactor and optimizes the heat gradient through material circulation, achieving better results than relying solely on internal column circulation.

[0087] The difference between Comparative Example 3 and Example 3 is that while the tubular reactor is retained for recycling the bottom stream of the reaction section, the thermal coupling between the distillation column reboiler and the shell side of the tubular reactor is eliminated, and shell side heating is replaced by external steam. Although this structure still achieves a similar level of product purity as the Example 3, the reboiler load and condenser load are both higher than in Example 3. It is evident that the lack of internal thermal integration between the distillation column reboiler and the shell side of the tubular reactor leads to increased external steam demand and difficulty in recovering and utilizing the heat load of the column system, thus significantly increasing overall energy consumption.

[0088] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A process for the preparation of butyric anhydride, characterized in that: Comprising: Butyric acid, acetic anhydride in the reaction section of the rectifying column to carry out the preliminary reaction, the reaction temperature is 70-145℃; The product at the bottom of the reaction section is input into the tubular reactor to continue the reaction, the reaction temperature is 110-175℃, and the product obtained by the reaction of the tubular reactor is transported back to the rectifying column for separation; The butyric anhydride product obtained from the column bottom of the rectifying column is at least partially introduced into the shell side of the tubular reactor for heat exchange, and the material after heat exchange is refluxed to the column bottom of the rectifying column.

2. The process for the preparation of butyric anhydride according to claim 1, characterized in that: The pressure condition in the rectifying column is 10-70kpa; And / or, the reflux ratio of the rectifying column is (0.5-9):1; Preferably, the pressure condition in the rectifying column is 10-50kpa; Preferably, the reflux ratio of the rectifying column is (4-7.5):

1.

3. The preparation method of butyric anhydride according to claim 1 or 2, characterized in that: The rectifying column comprises a rectifying section arranged above the reaction section and a stripping section arranged below the reaction section, and the product obtained by the continued reaction is transported back to the reaction section of the rectifying column, wherein the temperature condition of the rectifying section is 55-120℃, and the temperature condition of the stripping section is 100-188℃.

4. The process for the preparation of butyric anhydride according to claim 3, characterized in that: The theoretical plate number of the reaction section is 8-16; And / or, the theoretical plate number of the rectifying section is 6-12; And / or, the theoretical plate number of the stripping section is 6-12.

5. A process for the preparation of butyric anhydride according to any one of claims 1 to 4, characterized in that: The mass ratio of butyric acid to acetic anhydride is (1.5-4):

1.

6. A process for the preparation of butyric anhydride according to any one of claims 1 to 5, characterized in that: Part of the butyric anhydride product obtained from the column bottom of the rectifying column is introduced into the shell side of the tubular reactor for heat exchange, and the other part is output for collection; Preferably, the mass flow ratio of the butyric anhydride product input into the tubular reactor for heat exchange to the butyric anhydride product output for collection is (1.8-6):

1.

7. An apparatus for preparing butyric anhydride, characterized by: Comprising a rectifying column and a tubular reactor, the feed inlet and the discharge outlet of the tubular reactor are respectively communicated with the reaction section of the rectifying column, the column bottom of the rectifying column is communicated with the shell side of the tubular reactor for cross heat exchange with the tubular reactor.

8. A plant for the production of butyric anhydride according to claim 7, characterized in that: The diameter of the column tube of the tubular reactor is 19-57mm; and / or, the length of the column tube is 2.5-4.5m; and / or, the tube arrangement angle of the column tube is 30-90°.

9. A plant for the production of butyric anhydride according to claim 8, characterized in that: The rectifying column comprises a rectifying section arranged above the reaction section and a stripping section arranged below the reaction section, and the feed inlet and the discharge outlet of the tubular reactor are respectively communicated with the bottom of the reaction section.

10. An apparatus for preparing butyric anhydride according to any one of claims 7 to 9, characterized in that: The column bottom of the rectifying column is connected with a discharge pipe for outputting butyric anhydride product; Preferably, the column bottom of the rectifying column is communicated with the shell side of the tubular reactor through a heat exchange pipeline, and the discharge pipe is connected on the heat exchange pipeline.

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