An integrated reaction distillation system for producing butyl acrylate from crude acetic acid-containing acrylic acid

Abstract

The application provides an integrated reaction distillation system for producing butyl acrylate by using crude acetic acid containing acetic acid, which comprises an esterification dehydration unit, a reaction distillation unit and a main product refining unit; the esterification dehydration unit comprises a first esterification reactor, a second esterification reactor, an azeotropic dehydration tower and a dehydration tower reflux tank connected with the overhead outlet of the azeotropic dehydration tower; the reaction distillation unit comprises a reaction distillation tower filled with a solid acid catalyst; the reaction distillation tower is provided with a first feed inlet, an overhead outlet and a tower bottom outlet; the reaction distillation tower is also connected with an acetic acid supplement pipeline; the main product refining unit is connected with the tower bottom outlet of the reaction distillation tower; the acetic acid supplement pipeline is used to supplement acetic acid into the reaction distillation tower, so that butanol in an oil phase containing butanol and butyl acrylate reacts with acetic acid under the action of the solid acid catalyst to generate butyl acrylate and water. The application can directly process acetic acid containing raw materials in the traditional continuous esterification process and by-product butyl acrylate with high purity.

Description

Technical Field

[0001] This invention relates to a butyl acrylate production system, specifically an integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid, belonging to the field of acrylate production technology. Background Technology

[0002] Butyl acrylate is an important organic chemical intermediate. Its industrial production typically uses acrylic acid and n-butanol as raw materials, and is obtained through esterification under the action of an acid catalyst. In actual industrial production, the crude acrylic acid used as raw material often originates from the catalytic oxidation process of propylene, which inevitably contains a certain amount of acetic acid impurities, with the mass fraction of acetic acid usually ranging from 0.5% to 5%.

[0003] When crude acrylic acid containing acetic acid is used directly as a raw material for esterification, acetic acid will undergo a competitive esterification side reaction with n-butanol, generating butyl acetate as a byproduct in the system. The formation of butyl acetate itself is not unacceptable; the deeper problem lies in the fact that butyl acetate and n-butanol form a minimum azeotrope with a boiling point of approximately 117.2°C under normal pressure. This azeotropic characteristic makes it impossible to effectively separate butyl acetate and n-butanol under conventional distillation operations, resulting in a large amount of n-butanol being carried over into the byproduct stream. This causes both raw material loss and significant difficulties for subsequent refining processes.

[0004] To address the aforementioned challenge of azeotropic separation between butanol and butyl acetate, existing technologies typically employ extractive distillation or pressurized distillation. Extractive distillation requires a large amount of extractant, and the solvent recovery and regeneration processes increase the process length, introducing new solvent losses and waste disposal issues. While pressurized distillation can alter the azeotropic composition by changing the pressure, its operating pressure is significantly higher than atmospheric pressure, placing high demands on the equipment's pressure resistance. Furthermore, high-pressure operation leads to a substantial increase in steam consumption, resulting in high energy costs. Both of these approaches suffer from complex processes, high equipment investment, and high energy consumption, making them difficult to implement economically and efficiently for industrial application. Summary of the Invention

[0005] Based on the above background, the purpose of this invention is to provide an integrated reactive distillation system for producing butyl acrylate using crude acrylic acid containing acetic acid. This system breaks the azeotropic thermodynamic equilibrium between butanol and butyl acetate in situ through chemical reaction, thus solving the technical problems in the prior art where the by-product butyl acetate forms an azeotrope with the raw material butanol during the esterification of crude acrylic acid containing acetic acid to produce butyl acrylate, resulting in difficult separation, high energy consumption, and complex process.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] An integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid includes:

[0008] The esterification and dehydration unit includes a first esterification reactor, a second esterification reactor, an azeotropic dehydration tower, and a dehydration tower reflux tank connected in sequence to the top outlet of the azeotropic dehydration tower; the dehydration tower reflux tank is provided with an oil phase outlet;

[0009] The reactive distillation unit includes a reactive distillation column internally packed with a solid acid catalyst. The reactive distillation column is provided with a first feed inlet, a top outlet, and a bottom outlet. The reactive distillation column is also connected to an acetic acid replenishment pipeline. The first feed inlet is connected to the oil phase outlet of the dehydration tower reflux tank. The first feed inlet is used to receive an oil phase containing butanol and butyl acetate.

[0010] The main product refining unit is connected to the bottom outlet of the reactive distillation column, and the main product refining unit is equipped with a butyl acrylate discharge outlet.

[0011] The integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid is configured to: supplement acetic acid into the reactive distillation column through the acetic acid replenishment pipeline, so that the butanol in the oil phase containing butanol and butyl acetate undergoes an esterification reaction with the acetic acid under the action of the solid acid catalyst to produce butyl acetate and water.

[0012] Preferably, the reactive distillation column is also provided with a side-stream outlet. The integrated reactive distillation system for producing butyl acrylate from acetic acid-containing crude acrylic acid also includes a by-product purification unit. The by-product purification unit includes a water washing tower and a resin adsorption tower connected in sequence. The feed inlet of the water washing tower is connected to the side-stream outlet of the reactive distillation column. The water washing tower is configured to wash the material from the side-stream outlet with washing water, and the resin adsorption tower is configured to adsorb the washed material.

[0013] Preferably, the operating conditions of the water washing tower are: temperature 25~40℃, water-oil mass ratio 1:10~1:25; the resin adsorption tower is filled with alkaline adsorption resin, and the operating conditions of the resin adsorption tower are: temperature 20~50℃, liquid hourly space velocity 1~5h. -1 .

[0014] Preferably, the operating conditions of the reactive distillation column are: bottom temperature 90~125℃ and operating pressure 30~60 kPaA.

[0015] Preferably, the main product refining unit includes a light-light product removal tower, a washing tower, an alcohol recovery tower, and a product refining tower connected in sequence; the light-light product removal tower is provided with a second feed inlet, and the bottom outlet of the reactive distillation tower is connected to the second feed inlet; the outlet of the second esterification reactor is connected to the second feed inlet.

[0016] Preferably, a first connecting pipeline is provided between the top outlet of the light alkali removal tower and the feed inlet of the washing tower, and the first connecting pipeline is provided with a liquid alkali addition interface.

[0017] Preferably, the main product refining unit also includes a wastewater tower, which is provided with a third feed inlet; the bottom outlet of the light-weight removal tower and the bottom outlet of the washing tower are both connected to the third feed inlet.

[0018] Preferably, a circulation pipeline connects the top outlet of the alcohol recovery tower and the feed inlet of the azeotropic dehydration tower.

[0019] Preferably, the solid acid catalyst is selected from at least one of strong acid ion exchange resins, heteropoly acids, or solid superacids.

[0020] Preferably, an online monitoring module is installed on the pipeline connecting the oil phase outlet of the dehydration tower reflux tank and the first feed inlet of the reactive distillation column, and a regulating valve is installed on the acetic acid replenishment pipeline; the integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid is configured such that: the online monitoring module monitors the concentration of butanol in the oil phase containing butanol and butyl acetate in real time, and controls the opening of the regulating valve based on the monitoring results to adjust the amount of acetic acid replenished into the reactive distillation column.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] This invention discloses an integrated reactive distillation system for producing butyl acrylate from acetic acid-containing crude acrylic acid. By actively adding acetic acid within the reactive distillation column and utilizing a solid acid catalyst to convert butanol in the oil phase into butyl acetate in situ, the system eliminates the conditions for the presence of an azeotrope between butanol and butyl acetate, thus eliminating the need for extractive distillation and pressurized distillation, significantly simplifying the process. The reactive distillation column of this invention couples the catalytic reaction and distillation separation within the same equipment, effectively reducing equipment investment and operating energy consumption. Furthermore, the invention refines butyl acetate into a high-purity commercial-grade byproduct through a byproduct refining unit, achieving high-value utilization of the byproduct and improving the overall economic efficiency of the system. Finally, the invention enhances the system's regulatory capabilities and better addresses fluctuations in raw material composition through closed-loop control linked to an online monitoring module and regulating valves. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the process flow of an integrated reactive distillation system for producing butyl acrylate using crude acrylic acid containing acetic acid, according to the present invention.

[0025] In the diagram: R1, first esterification reactor; R2, second esterification reactor; C1, azeotropic dehydration tower; D1, dehydration tower reflux tank; C61, reactive distillation tower; C62, water washing tower; C63, resin adsorption tower; C21, light component removal tower; C22, washing tower; C3, wastewater tower; C4, alcohol recovery tower; C5, product refining tower. Detailed Implementation

[0026] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0027] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art. Unless otherwise specified, the components or equipment in the following embodiments are general standard parts or components known to those skilled in the art, and their structures and principles can be learned by those skilled in the art through technical manuals or conventional experimental methods.

[0028] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In this detailed description, numerous specific details are set forth to facilitate explanation and provide a thorough understanding of the embodiments of the present invention. However, one or more embodiments may be practiced by those skilled in the art without these specific details.

[0029] like Figure 1 As shown, an embodiment of the present invention discloses an integrated reactive distillation system for producing butyl acrylate using crude acrylic acid containing acetic acid, including an esterification and dehydration unit, a reactive distillation unit, a by-product purification unit, and a main product purification unit, with each unit connected in an orderly manner through material pipelines.

[0030] The esterification and dehydration unit, serving as the raw material processing and main reaction area, includes a first esterification reactor R1, a second esterification reactor R2, an azeotropic dehydration tower C1, and a dehydration tower reflux tank D1 connected in series with the top outlet of the azeotropic dehydration tower C1. The raw material, crude acrylic acid, contains acetic acid, typically with a mass fraction ranging from 0.5% to 5%. The raw material, n-butanol, is supplied externally. Both raw material streams first enter the first esterification reactor R1, where a preliminary esterification reaction occurs under the action of an acid catalyst. Acrylic acid reacts with n-butanol to produce butyl acrylate and water. Simultaneously, the acetic acid carried in the raw material undergoes a competitive esterification reaction with n-butanol, producing butyl acetate and water. The effluent from the first esterification reactor R1 enters the second esterification reactor R2, where the reaction time is further extended to achieve a higher conversion rate and reduce the amount of unreacted acrylic acid remaining in the final product stream.

[0031] Part of the feed from the second esterification reactor R2 enters the azeotropic dehydration tower C1. In tower C1, n-butanol is used as an azeotropic entrainer. Through n-butanol-water azeotropic distillation, the water generated in the esterification reaction is separated and removed from the reactants, thereby disrupting the thermodynamic equilibrium of the esterification reaction and propelling it towards the formation of butyl acrylate. The overhead vapor from tower C1 consists of n-butanol-water azeotrope and butyl acetate. After condensation, this vapor enters the dehydration tower reflux tank D1, where natural liquid-liquid stratification occurs. The lower layer is an aqueous phase, mainly composed of water, which is discharged from the system for wastewater treatment. The upper layer is an oil phase, mainly composed of n-butanol and butyl acetate, with small amounts of water and butyl acrylate. The oil phase outlet of the dehydration tower reflux tank D1 is connected to the reactive distillation unit, sending the oil phase rich in n-butanol and butyl acetate downstream for further processing. Since the oil phase is enriched with both n-butanol and butyl acetate, a binary azeotropic system, if conventional distillation methods are used to directly separate the oil phase, the azeotropic equilibrium will limit the effective separation of the two components. Therefore, this invention introduces a reactive distillation unit.

[0032] The core equipment of the reactive distillation unit is the reactive distillation column C61. Inside the reactive distillation column C61, a solid acid catalyst is packed. The solid acid catalyst is preferably at least one of a strong acid ion exchange resin, a heteropoly acid, or a solid superacid. Strong acid ion exchange resins are one of the mature solid acid catalysts in industry. Their surface-dense sulfonic acid groups provide ample proton acid sites for esterification reactions, exhibiting excellent catalytic activity in the esterification of acetic acid and n-butanol. Heteropoly acids possess extremely strong proton acidity and a large specific surface area, resulting in high catalytic activity. Solid superacids can efficiently catalyze esterification reactions at relatively low temperatures. The above-mentioned solid acid catalysts are packed into the catalytic reaction section of the reactive distillation column C61 in the form of structured catalytic packing or bulk packing. This allows the catalyst to serve both as an active site for the chemical reaction and as a separation packing for gas-liquid mass transfer, thus combining chemical reaction and distillation separation within a single unit.

[0033] The reactive distillation column C61 is equipped with a first feed inlet, a top outlet, a side feed outlet, and a bottom outlet, and is connected to an acetic acid replenishment line. The oil phase outlet of the dehydration tower reflux tank D1 is connected to the first feed inlet of the reactive distillation column C61 via a pipeline, continuously feeding an oil phase stream containing n-butanol and butyl acetate into the reactive distillation column C61. Acetic acid is replenished from the outside into the reactive distillation column C61 via the acetic acid replenishment line. The amount of acetic acid replenished is controlled at a stoichiometric ratio of 1.0 to 1.5 times the molar amount of n-butanol in the oil phase stream to ensure sufficient conversion of n-butanol while avoiding excessive acetic acid that would increase the load on subsequent separation processes.

[0034] To achieve dynamic control of acetic acid replenishment, an online monitoring module is installed on the pipeline between the oil phase outlet of the dehydration tower reflux tank D1 and the first feed inlet of the reactive distillation column C61. A regulating valve is installed on the acetic acid replenishment pipeline. The online monitoring module continuously monitors the concentration of n-butanol in the oil phase stream entering the reactive distillation column C61 in real time and transmits the concentration signal to the control system. The control system calculates the required acetic acid replenishment based on the real-time n-butanol concentration and correspondingly outputs control commands to drive the regulating valve to adjust its opening, thereby regulating the acetic acid replenishment flow rate. When the n-butanol concentration in the oil phase increases, the control system commands the regulating valve to open wider, and the acetic acid replenishment increases accordingly; when the n-butanol concentration decreases, the control system commands the regulating valve to close wider, and the acetic acid replenishment decreases accordingly. This closed-loop control mechanism, formed by the online monitoring and regulating valve linkage, improves the system's adaptability to fluctuations in the upstream feed composition, ensuring the continuous and stable operation of the reactive distillation column C61 with a near-optimal stoichiometric ratio.

[0035] Inside the reactive distillation column C61, acetic acid and n-butanol in the oil phase contact and undergo esterification at the active sites of the solid acid catalyst, producing butyl acetate and water. This in-situ esterification reaction continuously consumes n-butanol, causing its concentration in the reaction system to decrease, thermodynamically disrupting the azeotropic equilibrium between n-butanol and butyl acetate. As n-butanol is continuously consumed and converted, the n-butanol-butyl acetate azeotropic system, which was originally bound by azeotropic equilibrium and could not be separated, gradually evolves into a pure butyl acetate system. Butyl acetate can thus be freely separated and enriched by distillation under conditions without azeotropic constraints. Simultaneously, the water produced in the reaction has a significant boiling point difference with butyl acetate, allowing for good separation under distillation operation. Water, due to its higher boiling point, tends to concentrate towards the bottom of the column, while butyl acetate is concentrated in the upper middle part of the column and collected as a crude butyl acetate stream from the side outlet.

[0036] The operating pressure of reactive distillation column C61 is maintained at a reduced pressure of 30–60 kPaA, and the reboiler temperature is controlled within the range of 90–125 °C. The purpose of reduced pressure operation is to lower the boiling point temperature of the system, ensuring that the overall operating temperature within the column remains below the upper limit of the polymerization inhibition temperature of acrylic monomers. This suppresses the risk of free radical polymerization of butyl acrylate within the column due to high temperatures, preventing polymer blockage of the catalyst packing and trays. Controlling the upper limit of the reboiler temperature to 125 °C further strengthens the prevention of thermal polymerization. Within the operating pressure range of 30–60 kPaA, the relative volatility of butyl acetate, n-butanol, and acetic acid can be maintained within a reasonable range conducive to distillation separation, thereby ensuring the mass transfer efficiency of the reactive distillation coupling process.

[0037] The by-product refining unit is used to refine the crude butyl acetate stream from the side stream of the reactive distillation column C61 into a high-purity butyl acetate by-product. The by-product refining unit includes a water washing column C62 and a resin adsorption column C63 connected in sequence. The feed inlet of the water washing column C62 is connected to the side stream outlet of the reactive distillation column C61 via a pipeline.

[0038] After being drawn from the side stream of reactive distillation column C61, the crude butyl acetate stream first enters the washing column C62. The operating temperature of washing column C62 is maintained within the range of 25–40°C, and the mass ratio of washing water to crude butyl acetate stream (i.e., water-to-oil mass ratio) is controlled within the range of 1:10–1:25. The washing water and the material undergo countercurrent contact washing within washing column C62. Under these operating conditions, due to the strong hydrophilicity of acetic acid, its solubility in water is much greater than its solubility in butyl acetate. The residual acetic acid in the crude butyl acetate stream is preferentially extracted and transferred to the aqueous phase by the washing water, thus achieving the purpose of deacidification. Controlling the water-to-oil mass ratio within the range of 1:10–1:25 is the result of seeking the optimal balance between the deacidification effect and the washing loss of butyl acetate product. If the water-to-oil ratio is lower than 1:25, the washing water volume is insufficient, the removal of acetic acid is incomplete, and the residual acid content is difficult to meet product specifications. If the water-to-oil ratio is higher than 1:10, excessive water will increase the dissolution loss of butyl acetate and increase the subsequent wastewater treatment volume, leading to increased energy consumption. Controlling the operating temperature at 25~40℃ maintains a large liquid-liquid density difference between butyl acetate and water, which is beneficial for sufficient stratification and countercurrent contact between the two phases in the tower. It also prevents excessively high temperatures from increasing the solubility of butyl acetate in the aqueous phase, thereby reducing product loss. The butyl acetate stream after countercurrent washing and deacidification in water washing tower C62 is drawn from the top or side stream of water washing tower C62 and enters resin adsorption tower C63 for purification.

[0039] The C63 resin adsorption tower is filled with alkaline adsorption resin. The surface functional groups of the alkaline adsorption resin preferentially adsorb trace amounts of acidic components and moisture, further reducing the content of acidic impurities and moisture in the material to extremely low levels. The operating temperature of the C63 resin adsorption tower is controlled within the range of 20~50℃, and the liquid hourly space velocity (LHSV) of the material is controlled within the range of 1~5 h⁻¹. -1 Within the range. The liquid time-space velocity should be controlled between 1 and 5 h. -1 The optimal range was determined by comprehensively considering the adsorption kinetics of the alkaline adsorption resin and the adsorption capacity utilization of the resin bed. This range is suitable when the liquid hourly space velocity (LISH) is below 1 h⁻¹. -1 At this point, the residence time of the material in the resin bed is already sufficient, and further reducing the hourly space velocity (HSV) contributes less to improving the purity of the final product and will cause an unnecessary reduction in throughput; when the HSV is higher than 5 h... -1In some cases, the residence time of the material in the resin bed is too short, the adsorption and mass transfer process cannot proceed sufficiently, the removal rate of acidic impurities and moisture decreases significantly, and product quality is difficult to guarantee. After deep purification in resin adsorption tower C63, high-purity butyl acetate byproduct is obtained and discharged from the bottom of resin adsorption tower C63, which is the final commercial-grade butyl acetate product. The above byproduct purification route realizes the high-value utilization of butyl acetate, which is regarded as waste or low-value material in traditional processes, and creates additional economic benefits while digesting by-reaction products.

[0040] The main product refining unit receives material from the bottom of reactive distillation column C61 and combines it with the output from the second esterification reactor R2 for refining and separation, ultimately obtaining high-purity butyl acrylate as the main product. The main product refining unit includes sequentially connected light-light product removal column C21, washing column C22, alcohol recovery column C4, and product refining column C5, as well as a wastewater column C3 connected to the bottom outlets of both light-light product removal column C21 and washing column C22.

[0041] The light component removal column C21 has a second feed inlet. The bottom outlet of the reactive distillation column C61 is connected to this second feed inlet, as is the outlet of the second esterification reactor R2. The two streams are combined before entering the light component removal column C21. The bottom product of the reactive distillation column C61 mainly consists of butyl acrylate and small amounts of residual acrylic acid, acetic acid, water, and high-boiling-point heavy components. The outlet product of the second esterification reactor R2 mainly consists of butyl acrylate, unreacted acrylic acid, n-butanol, butyl acetate, and water generated during the reaction. The two streams are combined before entering the light component removal column C21. The light component removal column C21 separates the light components (water, n-butanol, butyl acetate, and some acetic acid, etc.) with boiling points lower than butyl acrylate from the top of the column, while retaining butyl acrylate and high-boiling-point heavy components in the bottom. The bottom material of the light-light removal tower C21 is mainly a water-containing heavy phase, which contains a small amount of dissolved organic matter. The bottom outlet of the light-light removal tower C21 is connected to the third feed port of the wastewater tower C3 through a pipeline, and the bottom material of the tower is sent to the wastewater tower C3 for centralized treatment.

[0042] The top discharge of the light component removal tower C21 is a vapor or liquid stream rich in light components, which is sent to the washing tower C22 via a first connecting pipeline. A liquid alkali inlet is provided on the first connecting pipeline connecting the top outlet of the light component removal tower C21 and the feed inlet of the washing tower C22. Liquid alkali is added online through this inlet, ensuring thorough mixing and contact with the top material of the light component removal tower C21. The addition of liquid alkali causes the residual acrylic acid in the material to neutralize with sodium hydroxide to form sodium acrylate, and the residual acetic acid to neutralize with sodium hydroxide to form sodium acetate. These acidic components are converted into their corresponding sodium salts and dissolved in the aqueous phase, achieving a significant chemical difference from the butyl acrylate in the oil phase. This reduces the content of residual acidic impurities in the butyl acrylate product and lessens the burden on subsequent distillation separation. The mixture after neutralization with liquid alkali enters the washing tower C22, where the oil and water phases are fully separated. The aqueous phase containing salts such as sodium acrylate and sodium acetate is discharged as the heavy phase at the bottom of the tower. This aqueous phase is connected to the third feed port of the wastewater tower C3 through the bottom outlet of the washing tower C22 and enters the wastewater tower C3 for unified treatment. The organic oil phase, from which acidic impurities have been removed, is drawn from the top of the washing tower C22 or the light phase outlet and enters the alcohol recovery tower C4.

[0043] The third inlet of wastewater tower C3 simultaneously receives two streams of wastewater from the bottom of light-weight product stripping tower C21 and the bottom of washing tower C22. Within wastewater tower C3, organic components (mainly n-butanol, butyl acetate, and a small amount of butyl acrylate) are stripped from the aqueous phase through steam stripping distillation, recovering valuable organic components. Simultaneously, the organic content in the wastewater is reduced to a level meeting emission standards before being discharged from the tower bottoms. The light-weight components stripped from wastewater tower C3 can be incorporated into the corresponding upstream recovery processes for recycling, depending on their composition.

[0044] The deacidified organic material from washing tower C22 enters alcohol recovery tower C4. Alcohol recovery tower C4 separates and recovers the higher concentration of n-butanol from butyl acrylate. In alcohol recovery tower C4, n-butanol, as a relatively light component, distills off from the top, and the overhead stream is a light component rich in n-butanol. A circulation pipeline connects the top outlet of alcohol recovery tower C4 to the feed inlet of azeotropic dehydration tower C1. Through this circulation pipeline, the n-butanol-rich stream recovered from the top of alcohol recovery tower C4 is directly recycled back to azeotropic dehydration tower C1, where it re-participates in the azeotropic dehydration process as an azeotropic entrainer. This achieves the recycling of n-butanol feedstock within the entire integrated system, effectively reducing the system's need for external replenishment of fresh n-butanol, and lowering feedstock consumption quotas and production costs. The bottom material of alcohol recovery tower C4 is mainly high-purity butyl acrylate, in which the content of n-butanol has been greatly reduced, but it may still contain a small amount of high-boiling-point heavy components (dibutyl acrylate, acrylic acid dimer, etc.). The bottom material of this tower enters the product refining tower C5 for final refining.

[0045] Product refining column C5 receives material from the bottom of alcohol recovery column C4 and separates butyl acrylate from high-boiling-point heavy components through precision distillation. In product refining column C5, butyl acrylate, as the target product, is collected from the top of the column, while the high-boiling-point heavy components are enriched in the bottom of the column and drawn off, sent to the heavy component processing system for further processing or incineration. The butyl acrylate product collected from the top of product refining column C5 has a purity of 99.5% or higher, meeting the commercial specifications for superior grade products, and is drawn off from the system as the final main product.

[0046] In summary, during the conventional butyl acrylate production process, butyl acetate is inevitably produced during the esterification of crude acrylic acid containing acetic acid and n-butanol. Butyl acetate and n-butanol form an azeotropic enrichment at the top of the azeotropic dehydration tower C1, resulting in the oil phase in the dehydration tower reflux tank D1 containing large amounts of both n-butanol and butyl acetate. The boiling points of the azeotropic system composed of n-butanol and butyl acetate are not significantly different from those of pure n-butanol and pure butyl acetate, making effective separation impossible through conventional distillation. This invention does not attempt to separate the two through physical means, but rather by adding acetic acid to the reactive distillation tower C61, using a chemical reaction to consume n-butanol in situ and convert it into more butyl acetate, thereby eliminating n-butanol from the system. Once the concentration of n-butanol decreases to a critical level below the azeotropic point, the thermodynamic equilibrium of the n-butanol-butyl acetate azeotropic system is disrupted, and the distillation separation of butyl acetate is no longer constrained by the azeotropic process, allowing for free enrichment and purification through distillation.

[0047] Within reactive distillation column C61, the esterification reaction of acetic acid and n-butanol, and the distillation separation of butyl acetate and water, occur simultaneously in the same unit, exhibiting a significant enhancing effect. Specifically, the esterification reaction of acetic acid and n-butanol is a reversible exothermic reaction with a thermodynamic equilibrium constant of approximately 4–7 at room temperature. This thermodynamically equilibrium-limited reaction system would struggle to achieve a conversion rate exceeding the equilibrium conversion rate in a pure reactor. In reactive distillation column C61, the distillation process effectively removes the products (butyl acetate and water) from the reaction zone. Butyl acetate, with a higher boiling point than acetic acid and n-butanol, tends to migrate downwards and be collected via a side stream. The relative volatility of water is favorable for separation under reduced pressure, resulting in a significant density difference between the water and organic phases. This water is continuously removed from the reaction equilibrium during distillation. The timely removal of these products causes the reaction equilibrium to continuously shift towards the formation of butyl acetate, thereby achieving a n-butanol conversion rate higher than the equilibrium conversion rate and effectively reducing the residual amount of n-butanol in the system. Conversely, the heat of reaction provided by the esterification reaction also provides part of the driving force for distillation separation, reducing the external heat requirement of the reboiler and thus reducing operating energy consumption.

[0048] This invention integrates four functional units—esterification dehydration, reactive distillation, by-product purification, and main product purification—into a single integrated system, creating a multi-layered synergistic relationship in material flow and energy utilization among the units. The oil phase stream containing n-butanol and butyl acetate generated by the esterification dehydration unit is directly and continuously fed into the reactive distillation unit for processing without any intermediate storage buffer, avoiding material loss due to intermediate storage and the risk of thermal polymerization of acrylic acid monomers during storage. The bottom product of the reactive distillation unit is combined with the product from the second esterification reactor R2 and enters the light product removal tower C21, achieving the combined processing of two main streams with similar compositions, reducing the number of equipment units and lowering overall fixed investment. The n-butanol-rich stream recovered by the alcohol recovery tower C4 is directly returned to the azeotropic dehydration tower C1 via a circulation pipeline, creating a closed-loop material circulation of n-butanol within the entire system, reducing the total consumption of n-butanol at the system level. Wastewater tower C3 centrally collects the wastewater from the bottom of light-duty removal tower C21 and the bottom of washing tower C22 for unified treatment, avoiding the need to set up multiple independent wastewater treatment facilities and realizing the intensive utilization of wastewater treatment resources.

[0049] Furthermore, because the acetic acid content in the crude acrylic acid feedstock fluctuates within a wide range of 0.5% to 5%, the concentration of n-butanol in the oil phase of the dehydration tower reflux tank D1 dynamically changes with the composition of the feedstock. If acetic acid is added at a fixed flow rate, when the acetic acid content in the feedstock is low, the concentration of n-butanol in the oil phase is relatively low, and the fixed amount of added acetic acid will result in excess. The excess acetic acid will enter the main product refining unit, increasing the processing load of the light-light removal tower C21 and the washing tower C22, and may affect the purity of the main product butyl acrylate. Conversely, when the acetic acid content in the feedstock is high, the concentration of n-butanol in the oil phase is relatively high, and the fixed amount of added acetic acid may be insufficient, leading to incomplete n-butanol conversion. After entering the main product refining unit, n-butanol will still accumulate at the top of the light-light removal tower C21, and some n-butanol will enter the washing tower C22 and the alcohol recovery tower C4 with the overhead stream, increasing the processing load of the alcohol recovery tower C4. Therefore, the online monitoring module of this invention continuously detects the concentration of n-butanol in the oil phase in real time. Combined with the dynamic control of the acetic acid replenishment flow rate by the regulating valve, it can detect changes and respond immediately when the raw material composition fluctuates, maintaining the acetic acid replenishment amount within the optimal range of 1.0 to 1.5 times the stoichiometry. This ensures that the reactive distillation column C61 operates continuously and stably under optimal conditions, guaranteeing the quality stability of the main product butyl acrylate and the by-product butyl acetate.

[0050] In contrast, using the same raw materials and esterification conditions as this embodiment, but without a reactive distillation column and acetic acid replenishment pipeline, existing technology directly feeds the oil phase from the dehydration tower reflux tank into a conventional distillation column for separation, attempting to force the separation of n-butanol and butyl acetate in the oil phase by increasing the number of theoretical plates and the reflux ratio. The conventional distillation column operates at atmospheric pressure, with the reflux ratio increased to 15 (far exceeding the normal reflux ratio range for distillation operations), and the number of theoretical plates increased to 60. Even so, because n-butanol and butyl acetate have a minimum azeotropic boiling point of approximately 117.2°C at atmospheric pressure, the mass fraction of n-butanol in the overhead distillate of the conventional distillation column remains near the azeotropic composition (approximately 32%), failing to effectively separate n-butanol and butyl acetate. In the overhead distillate, n-butanol and butyl acetate coexist in a near-azeotropic composition; n-butanol cannot be recovered to the main process, and butyl acetate cannot be purified into a qualified by-product. Table 1 shows a comparison of the performance indicators of this embodiment with those of existing technologies.

[0051] Table 1. Comparison of performance indicators between this embodiment and existing technologies.

[0052]

[0053] In Table 1, the comprehensive steam consumption of the reboiler is normalized to a baseline value of 1.00 based on this embodiment; the relative reduction in the n-butanol consumption quota is based on this embodiment, with positive values ​​indicating better than the baseline and negative values ​​indicating worse than the baseline.

[0054] As can be seen, in this embodiment, by adding acetic acid in the reactive distillation column and using a solid acid catalyst to convert n-butanol to butyl acetate in situ, the system recovery rate of n-butanol is increased to 96.2%, the purity of the main product reaches 99.7%, the purity of the by-product reaches 99.2%, and the steam consumption of the reboiler is reduced to about 24% of that in the prior art.

[0055] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. An integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid, characterized in that: The integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid includes: The esterification and dehydration unit includes a first esterification reactor, a second esterification reactor, an azeotropic dehydration tower, and a dehydration tower reflux tank connected in sequence to the top outlet of the azeotropic dehydration tower; the dehydration tower reflux tank is provided with an oil phase outlet; The reactive distillation unit includes a reactive distillation column internally packed with a solid acid catalyst. The reactive distillation column is provided with a first feed inlet, a top outlet, and a bottom outlet. The reactive distillation column is also connected to an acetic acid replenishment pipeline. The first feed inlet is connected to the oil phase outlet of the dehydration tower reflux tank. The first feed inlet is used to receive an oil phase containing butanol and butyl acetate. The main product refining unit is connected to the bottom outlet of the reactive distillation column, and the main product refining unit is equipped with a butyl acrylate discharge outlet. The integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid is configured to: supplement acetic acid into the reactive distillation column through the acetic acid replenishment pipeline, so that the butanol in the oil phase containing butanol and butyl acetate undergoes an esterification reaction with the acetic acid under the action of the solid acid catalyst to produce butyl acetate and water.

2. The integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid according to claim 1, characterized in that: The reactive distillation column is also equipped with a side-stream outlet. This integrated reactive distillation system for producing butyl acrylate from acetic acid-containing crude acrylic acid also includes a by-product purification unit. The by-product purification unit includes a water washing tower and a resin adsorption tower connected in sequence. The feed inlet of the water washing tower is connected to the side-stream outlet of the reactive distillation column. The water washing tower is configured to wash the material from the side-stream outlet with washing water, and the resin adsorption tower is configured to adsorb the washed material.

3. The integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid according to claim 2, characterized in that: The operating conditions of the water washing tower are: temperature 25~40℃, water-oil mass ratio 1:10~1:25; the resin adsorption tower is filled with alkaline adsorption resin, and the operating conditions of the resin adsorption tower are: temperature 20~50℃, liquid hourly space velocity 1~5h. -1 .

4. The integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid according to claim 1, characterized in that: The operating conditions of the reactive distillation column are: bottom temperature 90~125℃, operating pressure 30~60KpaA.

5. The integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid according to claim 1, characterized in that: The main product refining unit includes a light-light product removal tower, a washing tower, an alcohol recovery tower, and a product refining tower connected in sequence; the light-light product removal tower is provided with a second feed inlet, and the bottom outlet of the reactive distillation tower is connected to the second feed inlet; the outlet of the second esterification reactor is connected to the second feed inlet.

6. The integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid according to claim 5, characterized in that: A first connecting pipeline connects the top outlet of the light alkali removal tower to the feed inlet of the washing tower, and the first connecting pipeline is equipped with a liquid alkali addition interface.

7. An integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid, as described in claim 5, is characterized in that: The main product refining unit also includes a wastewater tower, which is provided with a third feed inlet; the bottom outlet of the light-weight removal tower and the bottom outlet of the washing tower are both connected to the third feed inlet.

8. An integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid, as described in claim 5, is characterized in that: A circulation pipeline connects the top outlet of the alcohol recovery tower to the feed inlet of the azeotropic dehydration tower.

9. An integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid, as described in claim 1, is characterized in that: The solid acid catalyst is selected from at least one of strong acid ion exchange resins, heteropoly acids, or solid superacids.

10. An integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid, as described in claim 1, characterized in that: An online monitoring module is installed on the pipeline connecting the oil phase outlet of the dehydration tower reflux tank and the first feed inlet of the reactive distillation column, and a regulating valve is installed on the acetic acid replenishment pipeline; the integrated reactive distillation system for producing butyl acrylate from crude acrylic acid containing acetic acid is configured such that: the online monitoring module monitors the concentration of butanol in the oil phase containing butanol and butyl acetate in real time, and controls the opening of the regulating valve based on the monitoring results to adjust the amount of acetic acid replenished into the reactive distillation column.

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