A process for the production of acetic acid and vinyl acetate

Abstract

A process for the production of acetic acid and vinyl acetate, the process comprising: a) feeding water and methyl acetate into a first reaction space and obtaining acetic acid and methanol from the hydrolysis of methyl acetate; and, b) subjecting a crude vinyl acetate composition to distillation purification to obtain purified vinyl acetate; and, c) subjecting a water-based mixture obtained in step a), the water-based mixture comprising water and acetic acid, and at least a portion of the purified vinyl acetate obtained in step b) to solvent extraction and extracting acetic acid from the water-based mixture using the purified vinyl acetate as solvent.

Description

Technical Field

[0001] This invention relates to a method for preparing acetic acid and vinyl acetate. Background Technology

[0002] Acetic acid and vinyl acetate are important intermediate or starting products in various processes, especially in the production of polyvinyl acetate (PVAc).

[0003] Polyvinyl acetate (PVC) is a widely used synthetic polymer obtained through the polymerization of vinyl acetate monomers. PVC is renowned for its excellent adhesion properties, flexibility, and durability, making it a key component in adhesives, coatings, and various industrial and consumer product applications. Due to its non-toxic nature, PVC is widely used in the production of woodworking adhesives, paper adhesives, and as a binder for latex paints. Furthermore, its industrial applicability is further expanded by its use as a precursor for polyvinyl alcohol (PVA) through hydrolysis. Therefore, the efficient and low-cost production of vinyl acetate, as the main monomer of PVC, has significant commercial and technological implications, highlighting the importance of improving the synthesis methods of acetic acid and vinyl acetate.

[0004] Methyl acetate is generated as a byproduct in the saponification of polyvinyl acetate (PVC) to produce polyvinyl alcohol (PVA). While this methyl acetate can be treated as a separate, marketable product, it can also be advantageously reintegrated into the overall production cycle. This can be achieved by hydrolyzing the methyl acetate to convert it back into its constituent components: acetic acid and methanol. The recovered acetic acid can be recycled as a starting material for the production of vinyl acetate monomer (VAM), while the recovered methanol can be reused as a solvent in the PVA process. Therefore, methyl acetate is a circulating stream in the aforementioned processes. In the presence of an acidic or basic catalyst, methyl acetate undergoes hydrolysis to produce acetic acid and methanol. The efficient conversion of methyl acetate into these valuable products is crucial for optimizing industrial processes, reducing costs, and improving the sustainability of acetic acid production.

[0005] The synthesis of acetic acid from methyl acetate via hydrolysis involves the breaking of ester bonds in the presence of water. As mentioned above, this reaction can be acid-catalyzed or base-catalyzed.

[0006] Acid-catalyzed hydrolysis typically uses strong acids such as hydrochloric acid (HCl) or sulfuric acid (H₂SO₄) as catalysts. Acid-catalyzed hydrolysis involves preparing a reaction mixture by mixing methyl acetate (CH₃COOCH₃) with excess water in a reaction vessel. A few drops of concentrated acid, such as H₂SO₄ or HCl, are added to catalyze the reaction.

[0007] Alternatively, alkali-catalyzed hydrolysis (saponification) using a strong base such as sodium hydroxide (NaOH) is possible. Alkali-catalyzed hydrolysis involves preparing a reaction mixture by mixing methyl acetate with an aqueous solution of NaOH in a reaction vessel. After hydrolysis, sodium acetate (CH3COO) is obtained.- Na + It can be converted into acetic acid by adding a strong acid (such as HCl or H2SO4).

[0008] In both cases, the reaction mixture can be heated under reflux conditions. The reaction mixture is then cooled, and acetic acid is separated from methanol by distillation or extraction. Preferably, acetic acid is purified by vacuum distillation or organic solvent extraction. A common and significant drawback of both homogeneous hydrolysis processes is the difficulty in separating the dissolved catalyst from the product mixture. This separation typically requires additional, often complex and energy-intensive purification steps. To circumvent these problems, the industry has developed alternative methods, such as using heterogeneous catalysts that remain in a different phase from the reaction mixture.

[0009] Therefore, common methods for the hydrolysis of methyl acetate involve the use of heterogeneous catalysts, typically employing a fixed-bed reactor configuration. In this prior art method, ion exchange resins are commonly used as solid-phase catalysts. A feed stream containing methyl acetate and water passes through the resin bed, and the hydrolysis reaction occurs on the resin bed.

[0010] Industrially, the hydrolysis of methyl acetate can be carried out in a fixed-bed reactor, followed by several separation steps, including distillation, extractive distillation, and entrainer distillation. However, the yield of a fixed-bed reactor is limited by chemical equilibrium, meaning that the conversion of methyl acetate to acetic acid and methanol will only end at the equilibrium point. Since a large amount of methyl acetate and water fails to react in the fixed-bed reactor, a large amount of recirculated flow is required.

[0011] Therefore, this process has been improved by providing a modified distillation column, incorporating the reaction section within the column and filling it with catalyst in structured packing, bulk packing, or trays to convert carboxylic esters into the corresponding carboxylic acids and alcohols. The chemical reaction occurs in the reaction section of this column, containing a heterogeneous catalyst, such as KATAPAK™ structured packing filled with Amberlyst-type catalyst (this is just one commercially available type). The reactive distillation apparatus and process for hydrolyzing carboxylic esters to obtain carboxylic acids and alcohols are disclosed in EP 1 220 825 B1, which is incorporated herein by reference. In the reaction section of the reactive distillation column, reaction products such as carboxylic acids and alcohols can be separated from reactants such as carboxylic esters and water. This separation results in the chemical reaction never reaching equilibrium, thus achieving 100% yield.

[0012] A drawback of the prior art reactive distillation of methyl acetate hydrolysis is that all products and unconverted water are discharged from the bottom of the reactive distillation column and must be further separated in a subsequent separation column. The overhead product (also known as the overhead distillate) of this reactive distillation column is only a small discharge stream containing carboxylic acid esters, alcohols, and light-boiling impurities. Due to the residence time in the bottom and piping, reverse reactions may occur, making it difficult to produce methanol free of methyl acetate. The reverse or inverse reaction occurs when the reaction products carboxylic acid and methanol recombine to form carboxylic acid esters. Therefore, the purity of the product from the reactive distillation column described in EP 1 220 825 B1 is inherently limited because the carboxylic acid and alcohol require a long residence time in the bottom and subsequent heat exchangers before the carboxylic acid is finally separated from the alcohol in the subsequent separation unit.

[0013] There is an urgent need in industry to provide processes that can both save energy and produce high-quality products.

[0014] US7576236B2, incorporated herein by reference, describes an integrated process and system for the production of acetic acid and vinyl acetate, wherein a portion of the heat generated during acetic acid production is transferred to the vinyl acetate production and / or purification process. Acetic acid is produced via an exothermic carbonylation reaction. At least a portion of the heat generated by this reaction is removed and transferred to a heat transfer system, such as a vapor condensate loop. Acetic acid is then reacted with ethylene and oxygen in the presence of a catalyst to produce vinyl acetate. At least a portion of the heat transferred to the vapor condensate loop is provided to the vinyl acetate production process or the vinyl acetate purification process to facilitate these operations. This integration of heat from acetic acid production into the vinyl acetate system saves costs and energy. Furthermore, downstream separation towers after the reaction can directly or indirectly utilize all or part of the heat from the reaction. Since vinyl acetate monomer production units consume energy in separating acetic acid, water, and vinyl acetate, using vinyl acetate as a solvent to extract acetic acid (separating it from water) is an effective method to optimize overall process energy consumption by establishing a large loop.

[0015] EP2502655 B1, incorporated herein by reference, relates to a method and apparatus for obtaining acetic acid and methanol by reactive distillation hydrolysis of methyl acetate. The reactive distillation column is configured as a partitioned column, having a reaction space and a product space separated by partition walls. The reaction space includes a first rectification zone, a first reaction zone containing a hydrolysis catalyst, and a first stripping zone. The product space includes a second rectification zone and a second stripping zone. A feed containing water and methyl acetate enters the reaction space and is hydrolyzed to acetic acid and methanol. Products are discharged from different locations—a first top product from the reaction space, a bottom product from the bottom of the column, a second top product from the product space, and an intermediate product from the product space containing more than 99% methanol. The partitioned wall design allows for independent control of the reaction space and the product space, improving product purity and reducing energy consumption.

[0016] However, demand continues to grow for processes that not only produce high-quality products but also achieve more significant energy savings. The production of acetic acid and vinyl acetate are both important industrial chemicals, requiring energy consumption processes that impact overall efficiency and cost-effectiveness. While various methods have been developed and described to optimize these production pathways, shortcomings remain in energy efficiency. Many existing technologies rely on high-temperature, high-pressure conditions or involve complex separation steps, resulting in excessive energy consumption. Therefore, there is an urgent need to improve methods to enhance energy efficiency while maintaining or even improving product quality, thereby making industrial production more sustainable and economically viable. Summary of the Invention

[0017] Therefore, the purpose of this invention is to design a method for preparing acetic acid and vinyl acetate, which can avoid the shortcomings of the prior art and, in particular, can further improve the energy-saving effect.

[0018] Therefore, according to the present invention, a method for preparing acetic acid and vinyl acetate is provided, the method comprising:

[0019] a) Water and methyl acetate are introduced into the first reaction space, and acetic acid and methanol are obtained from the hydrolysis of methyl acetate; and,

[0020] b) The crude vinyl acetate composition is purified by distillation to obtain purified vinyl acetate; and,

[0021] c) The aqueous mixture obtained in step a), comprising water and acetic acid, and at least a portion of the purified vinyl acetate obtained in step b), is subjected to solvent extraction, and acetic acid is extracted from the aqueous mixture using the purified vinyl acetate as a solvent.

[0022] Each step of the method of the present invention may be performed in part according to the known methods described above with reference to the prior art.

[0023] The use of step c) is not yet integrated in the prior art because vinyl acetate is used to extract acetic acid, ensuring further energy savings. Therefore, this invention provides a particularly advantageous solution for integrated industrial plants that produce methyl acetate as a byproduct, such as those simultaneously producing polyvinyl alcohol (PVA) and vinyl acetate monomer (VAM). This invention efficiently converts this byproduct into valuable chemicals that can be directly reused within the plant: acetic acid as a feedstock for the VAM process and methanol as a solvent for the PVA process. The main problem with this loop is its enormous energy consumption. Embodiments of this invention address this problem by cleverly utilizing the excess vinyl acetate reflux (as a solvent) inherent in the purification section of the VAM plant. This internal vinyl acetate stream can be used as an extractant in a high-efficiency liquid-liquid extraction unit (such as a Sulzer Kühni stirred column (ECR)) to separate acetic acid from an aqueous mixture. By replacing the energy-intensive distillation step with a novel extraction process utilizing the internal stream, this method achieves a significant reduction in energy consumption, thereby significantly improving the overall process economy and sustainability.

[0024] Step a) may include feeding a feed containing water and methyl acetate, or water and methyl acetate separately, into a first reaction space. The reaction space may be configured as a single reactor (or tower) or expanded into multiple reactors (or towers) in series or parallel, depending on process requirements and optimization factors. In a single-reactor configuration, all necessary reaction conditions, such as temperature, pressure, and the presence of a catalyst, can be maintained within a single unit to ensure efficient conversion. Alternatively, when the reaction space is distributed across multiple reactors, each reactor can be optimized for specific reaction stages such as initial mixing, hydrolysis, intermediate treatment, or final conversion, thereby improving process efficiency, selectivity, and energy utilization. This flexibility in reactor design allows for better control of reaction kinetics and overall yield, adapting the process to various industrial installations. In particular, a pretreatment tower may be provided for the methyl acetate feed to prepare an azeotrope of methyl acetate and methanol. In this method, the pretreatment tower preferably has a minimum temperature.

[0025] The feed stream introduced into the first reaction space is not limited to water and methyl acetate. It can also be a mixture containing methanol, methyl acetate, acetic acid, and water, for example, from a circulating or upstream process stream. In a preferred embodiment of the method of the invention, in step a), methyl acetate is hydrolyzed to acetic acid and methanol at 30–250°C, preferably 50–150°C, more preferably 70–120°C, and / or atmospheric pressure to 15 bar, preferably 1–10 bar, more preferably 1–5 bar. Maintaining appropriate pressure improves efficiency while reducing equipment costs. The above temperature range achieves an optimal balance between reaction rate and operational safety, while optimizing conversion and minimizing side reactions. Therefore, this ensures efficient hydrolysis without excessive energy consumption or undesirable side reactions. Temperatures below these ranges result in slow reaction rates, while higher temperatures lead to unwanted byproduct formation and catalyst degradation.

[0026] In some embodiments, the first reaction space may be located in a partitioned-wall column, such that step a) is carried out in the partitioned-wall column, and / or as reactive distillation, and / or, before the aqueous mixture is fed to the solvent extraction in step c), for example, in the partitioned-wall column, methanol is separated from the aqueous mixture. In this method, the partitioned-wall column can be used to improve the efficiency of the separation process, reduce energy consumption, and increase product purity. A partitioned-wall column is a specialized distillation device with internal partitions that allow for the simultaneous separation of multiple components within a single column. This configuration enables the selective removal of at least one of methanol, acetic acid, unreacted methyl acetate, and water in different sections of the column, thereby minimizing the need for additional separation steps and auxiliary equipment. By integrating the partitioned-wall column into the process, overall thermal efficiency can be improved, and product recovery optimized. This not only results in additional energy savings but also enhances process sustainability while maintaining high product quality. In particular, step a) may be carried out as reactive distillation in a partitioned-wall column, preferably a top partitioned-wall column. Alternatively, methyl acetate may be hydrolyzed to acetic acid and methanol in the first reaction space.

[0027] In step a), water and methyl acetate can be contacted with the hydrolysis catalyst within the first reaction space, resulting in at least partial hydrolysis to acetic acid and methanol. The contact between water and methyl acetate and the hydrolysis catalyst facilitates the conversion of methyl acetate to acetic acid and methanol. Hydrolysis catalysts, such as homogeneous acid catalysts of sulfuric acid or heterogeneous solid acid catalysts such as ion exchange resins or zeolites, improve reaction efficiency and yield by promoting the breaking of ester bonds in methyl acetate. Selecting suitable catalysts and reaction conditions ensures high selectivity for acetic acid formation while minimizing byproduct generation, contributing to an energy-efficient and economically feasible production process.

[0028] In this invention, the hydrolysis catalyst used in this method is preferably selected from a variety of acidic cation exchange resins that have been previously used in such hydrolysis reactions. Preferred resins include cross-linked styrene sulfonic acid gels cross-linked with divinylbenzene at 4% and 8%, sulfonated phenolic condensation products, and macro-network resins such as highly cross-linked styrene sulfonic acid resins. Generally, catalyst particle sizes of 10–125 mesh can be used. A particularly preferred catalyst is 8% cross-linked gel-type cross-linked polystyrene sulfonic acid with a particle size of 20–50 mesh and a salt exchange capacity of 5 milliequivalents of acid per gram of dry resin.

[0029] This method may specifically include the recovery of methanol and acetic acid from methyl acetate, wherein methyl acetate is continuously hydrolyzed, and methanol and acetic acid are separated from the resulting mixture of methanol, acetic acid, water, and unreacted methyl acetate. Thus, the aqueous mixture may contain methyl acetate, water, optionally methanol and / or acetic acid, and is fed together with vinyl acetate to a solvent extractor.

[0030] In some embodiments of the invention, water may be added to the methyl acetate first. This water serves two functions: first, it aids in the separation of methyl acetate from methanol, which is typically associated with methyl acetate; and second, it provides reactants for the hydrolysis reaction. The hydrolysis specifically produces a mixture containing unreacted methyl acetate, methanol, acetic acid, and water. This mixture can be separated to separate acetic acid and methanol. Thus, this mixture can be sent directly to step c) as an aqueous mixture, or further purified, particularly by at least partially removing methanol, and then sent to step c) as an aqueous mixture.

[0031] In the method of the present invention, the feed stream in step a) may contain about 45 to 95% methyl acetate, preferably about 60 to 85%. The feed stream may also contain water, typically at a concentration of about 5 to 60%, preferably about 10 to 40%. In addition, the feed stream may also contain up to about 20% methanol, 15% acetic acid and 1–2% acetaldehyde.

[0032] The present invention may include a vinyl acetate synthesis process, wherein the crude vinyl acetate is obtained by contacting oxygen, acetic acid, and ethylene with an oxidation catalyst in a second reaction space, and by the oxidation reaction of acetic acid and ethylene. This includes feeding acetic acid and ethylene into the second reaction space, whereby vinyl acetate is formed. The acetic acid used in this step may be from various sources, including external supply, acetic acid produced in step a), and / or most preferably, purified products from step c) or thereafter (particularly directly from step c)). In particular, "after step c)" refers to indirect sources from step c), i.e., the vinyl acetate and acetic acid extract is separated by, for example, distillation (particularly distillation purification of step b). Therefore, the vinyl acetate and acetic acid extract can also be purified by distillation. Utilizing the acetic acid after step c) is particularly advantageous because it ensures the highest purity and reduces the presence of impurities or byproducts that may negatively affect catalyst performance and / or reaction selectivity in the vinyl acetate synthesis. By integrating the high-purity acetic acid stream from step c), the process improves overall efficiency, minimizes the required additional purification steps, and optimizes the production of vinyl acetate with improved yield and quality.

[0033] The second reaction space can also be configured as a single reactor (or tower) or expanded to multiple reactors (or towers) in series or parallel, depending on process requirements and optimization factors. In a single-reactor configuration, all necessary reaction conditions, such as temperature, pressure, and the presence of catalyst, can be maintained within a single unit to ensure efficient conversion. Alternatively, when the reaction space is distributed across multiple reactors, each reactor can be optimized for specific reaction stages, such as initial mixing, hydrolysis, intermediate treatment, or final conversion, thereby improving process efficiency, selectivity, and energy utilization. This reactor design flexibility allows for better control of reaction kinetics and overall yield, enabling the process to adapt to various industrial settings.

[0034] In a preferred embodiment, the reaction in the second reaction space involves contacting oxygen, acetic acid, and ethylene (preferably gaseous) with an oxidation catalyst within the second reaction space to promote the selective oxidation of acetic acid and ethylene to vinyl acetate. The reaction is typically promoted under controlled temperature and pressure conditions using an oxidation catalyst supported on a support such as silicon or alumina, typically with palladium and / or gold, to maximize conversion efficiency and selectivity. By ensuring the reactants are gaseous, mass transfer limitations are minimized, thereby improving reaction kinetics and product yield. The partial oxidation process efficiently converts reactants to vinyl acetate while minimizing the formation of unwanted byproducts, contributing to optimized and energy-efficient industrial production processes.

[0035] Acetic acid and ethylene are preferably at least partially oxidized to vinyl acetate at 100–200°C (more preferably 150–175°C) and / or at 5–20 bar (preferably 7–12 bar) pressure, and / or in a steam-heated tube reactor, to provide a crude vinyl acetate composition for step b). Maintaining moderate pressure improves efficiency while reducing equipment costs. The aforementioned temperatures, on the other hand, provide an optimal balance between reaction rate and operational safety. Therefore, these ranges can further optimize conversion and minimize side reactions without excessive energy consumption.

[0036] The preparation of (crude) vinyl acetate by reacting ethylene with acetic acid and oxygen or an oxygen-containing gas in the gas phase can be carried out on a fixed-bed catalyst, as described in the prior art. As mentioned above, the reaction can be carried out in the presence of a suitable catalyst, further examples including catalysts containing palladium, an alkali metal salt of acetate as a promoter, and optionally a co-promoter such as gold or cadmium supported on a catalyst support. A typical vinyl acetate production process, contained in US Pat. No. 6,696,596 and incorporated herein by reference, describes a gas-phase reaction with oxygen or an oxygen-containing gas over a fixed-bed catalyst. Another example, seen in US Pat. No. 6,040,474 and incorporated herein by reference, describes the production of acetic acid and / or vinyl acetate using two reaction zones, wherein a first reaction zone contains ethylene and / or ethane for oxidation to acetic acid, and a second reaction zone contains acetic acid and ethylene, with the product flowing through subsequent separation to produce vinyl acetate.

[0037] The production of vinyl acetate may be carried out in a reactor (with a second reaction space) in which a main reactant stream containing acetic acid, ethylene and molecular oxygen is contacted in the presence of a first catalyst to form a reactor effluent containing vinyl acetate, ethylene, oxygen, water, carbon dioxide and / or acetic acid.

[0038] The mixture used in the reaction preferably contains more than the stoichiometric amount of ethylene required by chemistry. Therefore, the ethylene conversion rate is relatively low (approximately 10%), and to maintain ethylene efficiency, unreacted ethylene can be recycled to the second reaction space. Crude vinyl acetate can then be separated from the gaseous reaction product mixture by a multi-step process, particularly including the distillation-based purification in step b).

[0039] In some embodiments, the crude vinyl acetate composition may contain up to 50 wt% water, acetic acid, and / or ethylene, and is then sent for distillation-based purification to obtain purified vinyl acetate. In step b), the crude vinyl acetate composition is preferably subjected to a purification process to remove unreacted components, byproducts, and impurities, ensuring that the final product has a high purity suitable for industrial applications. The purification process may involve extraction or other separation techniques in addition to distillation steps to achieve the desired purity level. However, it is preferred to use a vinyl acetate dehydration tower (only) to provide vinyl acetate for extraction.

[0040] In some embodiments of the method of the present invention, the acetic acid extract of the purified vinyl acetate in step c) can be separated from the aqueous mixture and sent to the distillation-based purification in step b) or to another purification and / or separation process, such as a distillation-based purification / separation step.

[0041] The distillation-based purification in step b) is preferably carried out in a distillation column or multiple distillation columns arranged in parallel and / or in series. The purified vinyl acetate is preferably obtained as the overhead distillate, and / or the (crude) acetic acid composition is obtained as the bottom effluent, particularly discharged from the reboiler of the distillation column as a bottom stream. Furthermore, the crude acetic acid composition may be recycled to the second reaction space, and / or the overhead distillate may be sent to a condenser to condense some or all of the overhead distillate. The condensed overhead distillate may contain water and vinyl acetate, wherein the water is separated from the vinyl acetate by phase separation to provide purified vinyl acetate. If the condensed overhead distillate contains a mixture of water and vinyl acetate, this mixture undergoes phase separation, wherein the water is effectively separated from the vinyl acetate. This purification step ensures that the vinyl acetate is free from moisture contamination, which is crucial for its subsequent use or further processing.

[0042] Acetic acid separated during the purification of crude vinyl acetate can be efficiently recycled to improve process sustainability and reduce feedstock consumption. The recycled acetic acid can then be reintroduced for the production of vinyl acetate. Preferably, the recycled acetic acid has a purity of at least 90%, more preferably at least 95%, to ensure optimal reaction efficiency and minimize impurity accumulation. By implementing acetic acid recycling, this method improves overall process efficiency, reduces production costs, and decreases waste generation, contributing to a more economical and environmentally sustainable production method for acetic acid and vinyl acetate.

[0043] The aqueous mixture can be obtained directly or indirectly from step a), with or without the removal of certain components, such as methanol. Therefore, the aqueous mixture may contain water, methanol, and acetic acid, or water and acetic acid. Specifically, the aqueous mixture contains 10–50 wt% acetic acid, preferably 15–50% acetic acid, more preferably 30–50 wt% acetic acid, and the remainder of the aqueous mixture, excluding impurities, comprises methanol, methyl acetate, and / or water, or is composed of methanol, methyl acetate, and / or water.

[0044] This solvent extraction can be carried out in a solvent extraction unit, preferably a liquid-liquid extraction unit such as a liquid-liquid extraction tower. Thus, (purified) vinyl acetate can be used as an extractant in combination with other organic solvents, but preferably as the main component, or (except for impurities) as the sole component of the extractant. Therefore, acetic acid can be efficiently extracted from an aqueous mixture using the extractant via liquid-liquid extraction. This extraction process minimizes the energy consumption of distillation steps while increasing acetic acid recovery. Preferably, liquid-liquid extraction is carried out in a stirred tower or a group of stirred towers, such as a Kühni stirred tower (ECR), to ensure good mass transfer between the aqueous mixture and the extractant (organic phase).

[0045] Alternatively, a counter-current stirred tower can be used, which may include a mixing section containing a stirring device, particularly connected to a shaft. The counter-current liquid-liquid extraction tower may comprise a common vessel with a single mixing section and one or two static sections, the mixing section possibly having a stirring device, and the static sections possibly having structured packing. The tower may also have optional collectors and / or distributors. In use, a first liquid feed stream (i.e., an aqueous mixture) may be fed into the tower through one inlet, and a second liquid feed stream (i.e., vinyl acetate) may be fed into the tower through another inlet. This liquid-liquid contact occurs between the two feed streams, forming a product stream (i.e., a vinyl acetate solution of acetic acid) and a byproduct stream (i.e., the remainder of the aqueous mixture). The product stream may be removed through one outlet, and the byproduct stream through another outlet. The corresponding tower has been described in WO2013120551 A1, which is incorporated herein by reference.

[0046] In this method, acetic acid and vinyl acetate can be used as both intermediates and end products, depending on the intended application. Acetic acid can be further processed to produce vinyl acetate via an oxidation reaction with ethylene and oxygen, serving as an intermediate. Conversely, vinyl acetate can be used directly as an end product or as an intermediate in the preparation of PVA, such as as a solvent or key monomer in the polymerization process to form polyvinyl acetate or other polymeric materials. In particular, excess vinyl acetate refluxed in the production unit can be used as a solvent to extract acetic acid from the aqueous phase solution (i.e., an aqueous mixture) of methyl acetate hydrolysis. This solvent extraction, preferably a non-distillation separation method to separate acetic acid between water and excess vinyl acetate reflux, can save a significant amount of energy, for example, 20–30%, compared to existing technologies, especially compared to the known process of EP2502655A1, because distillation is no longer used after reactive distillation, but instead, solvent extraction in step c) is employed. Since vinyl acetate is used as an extractant and further used or produced in the process, energy consumption is saved, particularly by minimizing impurities. This versatility and energy efficiency enhance the industrial relevance of the method, making it suitable for a wide range of downstream applications.

[0047] As described above, vinyl acetate can be used to produce polymers. Polymers are molecules with high relative molecular weights whose structure essentially comprises, in practice or conceptually, repeating units derived from molecules with lower relative molecular weights. Both natural and synthetic polymers are obtained through polymerization reactions of many small molecules called monomers. A polymer can be defined as containing more than 50 monomer units. An example of a polymer is polyvinyl acetate, which is obtained using vinyl acetate as a monomer. The degree of polymerization of polyvinyl acetate is typically between 100 and 5000, and its ester groups are sensitive to alkaline hydrolysis, slowly converting polyvinyl acetate into polyvinyl alcohol and acetic acid. Therefore, at least another portion of purified vinyl acetate can be fed to a polymerization reactor or a unit containing a polymerization reactor and subjected to polymerization or copolymerization, particularly polymerization to polyvinyl acetate or copolymerization with acrylic acid, acrylates, crotonic acid, vinyl laurate, vinyl chloride, and / or ethylene. Furthermore, polyvinyl alcohol can be produced by first converting vinyl acetate to polyvinyl acetate, typically via free radical polymerization in methanol, followed by hydrolysis of the polyvinyl acetate to polyvinyl alcohol. Specifically, polyvinyl acetate is hydrolyzed into polyvinyl alcohol via alkaline-catalyzed transesterification.

[0048] In a preferred embodiment of the method of the present invention, when an additional polymerization step is included, vinyl acetate can be removed as unreacted monomer from the crude polyvinyl acetate composition obtained from the polymerization reaction. At least a portion of the unreacted monomer can be sent to solvent extraction in step c). Preferably, vinyl acetate is completely removed from polyvinyl acetate, which may be important for subsequent processing of polyvinyl acetate to produce polyvinyl alcohol. Residual vinyl acetate from the saponification reaction in the preparation of polyvinyl alcohol from polyvinyl acetate can cause discoloration of polyvinyl alcohol.

[0049] To produce polyvinyl alcohol, vinyl acetate can be polymerized in stages in methanol across multiple polymerization zones. Other solvents, such as tert-butanol, can also be used. The effluent from the polymerization reactor specifically consists of polyvinyl acetate containing solvent and unreacted vinyl acetate. A stripping column can be used to remove the solvent and unreacted monomer. A stream of hot solvent vapor is fed from the bottom of the column to strip unreacted vinyl acetate from the polymer. The solvent stream containing vinyl acetate is discharged from the top of the stripping column, while the bottom liquid containing polyvinyl acetate and solvent, but substantially free of vinyl acetate, is sent to the saponification unit. The saponification used herein preferably refers to the base-catalyzed transesterification of polyvinyl acetate with an alcohol, typically methanol.

[0050] An alternative to this stripping tower is to use a devolatilization device with a flash zone to vaporize the solvent and unreacted monomers contained in the polymer at a temperature above the glass transition temperature but below the temperature at which polyvinyl acetate decomposes, thereby flashing the solvent and unreacted monomer vapors. The flashed monomer and solvent vapors can then be recycled back to the polymerization reactor.

[0051] An apparatus designed to implement the method of the present invention may include multiple reactors and / or towers interconnected by a network of inlet and outlet pipelines and circulation pipelines to optimize material flow and process efficiency. Preferably, the apparatus includes at least one solvent extraction unit for separating acetic acid from an aqueous mixture, a reactor dedicated to the production of vinyl acetate, and a distillation unit with at least one distillation tower to ensure product purification and by-product separation to provide purified vinyl acetate. Furthermore, the apparatus may include a polymerization unit for processing vinyl acetate into polyvinyl acetate or other polymeric materials, and multiple independent reactors (or one independent reactor) dedicated to acetic acid production (such as reactive distillation), which may be arranged in series or parallel to optimize production capacity. By integrating the method of the present invention, the apparatus ensures high efficiency, energy savings, and improved product purity, while providing flexibility in the production of intermediates and final products.

[0052] As described above, step a) obtaining acetic acid and methanol from methyl acetate hydrolysis can be carried out by reactive distillation, specifically in a reactive distillation column arranged as a partitioned wall column, comprising a top, a body, and a reboiler. The body is arranged between the top and the reboiler. The column also includes a first reaction space and a product space. The first reaction space contains at least a first rectification zone and a first reaction zone, in which a hydrolysis catalyst can be arranged. The first rectification zone is arranged between the top and the first reaction zone. The column further includes a first stripping zone, arranged between the reboiler and the first reaction zone. A feed containing water and methyl acetate can enter the reaction space and contact the hydrolysis catalyst, causing at least partial hydrolysis to acetic acid and methanol. The first top product can be discharged from the top of the reaction space. The bottom product can be discharged from the reboiler, and the second top product can be discharged from the top of the product space. An intermediate product can be discharged from the product space. The intermediate product is preferably discharged between the top and bottom of the partition wall. Further, this intermediate product containing at least 99% methanol can be discharged. In one embodiment, a first feed containing at least 50% water and a second feed containing at least 15% methyl acetate enter the reaction chamber and contact the hydrolysis catalyst, causing at least partial hydrolysis to acetic acid and methanol. Methanol is a lower boiling point component compared to water and acetic acid, and therefore exits the column as an intermediate product via an intermediate pipe. Acetic acid and water are higher boiling point components, and therefore are discharged from the reboiler via a reboiler pipe. Another known method for recovering acetic acid from methyl acetate is described in US5113015A, which is incorporated herein by reference. Attached Figure Description

[0053] Figure 1 A schematic diagram of an apparatus for carrying out the method according to a particularly advantageous embodiment of the present invention.

[0054] Figure 2 A schematic diagram of an apparatus for carrying out the method according to another particularly advantageous embodiment of the invention.

[0055] Figure Labels

[0056] 10 devices

[0057] 12 Solvent Extraction Units

[0058] 14 Distillation Unit

[0059] 16 Aggregation Units

[0060] 17 Water inlet pipeline

[0061] 18 Reactive Distillation Unit

[0062] 19 Methanol outlet pipeline

[0063] 20 Solvent lines

[0064] 21 Tower top outlet pipeline

[0065] 22 Organic phase outlet pipeline

[0066] 24 Liquid inlet pipeline

[0067] 25 Polymer Unit Pipelines

[0068] 26. Aqueous phase outlet pipeline

[0069] 27 Vinyl acetate outlet pipeline

[0070] 28 Vinyl acetate inlet pipeline

[0071] 29 Wastewater outlet pipeline

[0072] 30 Separator

[0073] 31a Oxygen Flow

[0074] 31b Acetic acid flow

[0075] 31c Ethylene Flow

[0076] 32 Reactors

[0077] 34 Absorption Tower Series

[0078] 35 Methyl acetate pipeline

[0079] 36 Distillation Column Series

[0080] 37. Polymer exports. Detailed Implementation

[0081] Figure 1 A detailed schematic diagram of an apparatus 10 for obtaining acetic acid and vinyl acetate according to the method of the present invention is provided.

[0082] The process begins in solvent extraction unit 12, where acetic acid is fed into the unit as part of an aqueous mixture via liquid inlet line 24. The aqueous mixture containing acetic acid undergoes liquid-liquid extraction in solvent extraction unit 12. In solvent extraction unit 12, purified vinyl acetate from distillation unit 14 is used to extract acetic acid. The acetic acid-rich organic phase is discharged through organic phase outlet line 22, and the aqueous phase exits through aqueous phase outlet line 26.

[0083] Organic phase outlet line 22 transfers the extraction mixture in organic phase form to distillation unit 14. Acetic acid stream 31b, ethylene stream 31c, and oxygen stream 31a react in separate reactor 32 and, after passing through a series of absorption towers 34, yield a crude vinyl acetate composition, which is supplied through vinyl acetate inlet line 28 for distillation purification.

[0084] Distillation unit 14 facilitates separation and obtains the overhead product via overhead outlet line 21. This overhead product is condensed, and water is separated from vinyl acetate via phase separation to obtain purified vinyl acetate, which is discharged via vinyl acetate outlet line 27. Phase separation is carried out in separator 30 to further purify the vinyl acetate, ensuring it is free of moisture contamination. Wastewater from this process is discharged via wastewater outlet line 29.

[0085] The purified vinyl acetate discharged through the vinyl acetate outlet line 27 can be recycled to the distillation unit 14 and sent to the solvent extraction unit 12 via the solvent line 20 as a solvent for liquid-liquid extraction.

[0086] Figure 2 It shows according to Figure 1 The advanced configuration of the apparatus 10 (i.e., having a structure similar to that described above) further includes a polymerization unit 16 and a separate reactive distillation unit 18.

[0087] After hydrolysis in the first reaction space, acetic acid and methanol are produced, along with excess unreacted water. Figure 1 Unlike other methods, hydrolysis continues completely in the reactive distillation unit 18. The reactive distillation unit 18 supplies the solvent extraction unit 12 with an aqueous mixture primarily composed of acetic acid and water via a liquid inlet line 24. Preferably, the reactive distillation unit 18 is a partitioned wall column (DWC) according to EP2502655A1, wherein water is fed in through a water inlet line 17, and methanol is simultaneously distilled and separated in the reactive distillation unit 18 (partitioned wall column) and discharged through a methanol outlet line 19.

[0088] Solvent extraction unit 12 uses excess reflux of purified vinyl acetate provided by distillation unit 14 to separate acetic acid. The acetic acid extract from the vinyl acetate is then sent to distillation unit 14 through organic phase outlet line 22. The stream from aqueous phase outlet line 26 can be (partially) recycled to reactive distillation unit 18 (divider column).

[0089] In distillation unit 14, the crude vinyl acetate composition supplied via vinyl acetate line 28 is purified. A portion of the resulting vinyl acetate is then fed into polymerization unit 16 via polymerization unit line 25 after passing through a series of distillation columns 36. The vinyl acetate can be polymerized into polyvinyl acetate or copolymerized with other monomers such as acrylic acid or ethylene. The polymer is discharged from polymerization unit 16 through polymer outlet 37, and the methyl acetate byproduct is sent to reactive distillation unit 18 (divider column) via methyl acetate line 35.

[0090] The inclusion of polymerization unit 16 highlights the unit's ability to produce intermediate and final polymer products, enhancing the versatility and efficiency of the production process.

[0091] While various embodiments have been described for illustrative purposes, the above description should not be construed as limiting the scope of protection. Accordingly, various modifications, adjustments, and substitutions can be made by those skilled in the art without departing from the concept and scope of this application.

Claims

1. A method for preparing acetic acid and vinyl acetate, the method comprising: a) Water and methyl acetate are introduced into the first reaction space, and acetic acid and methanol are obtained from the hydrolysis of methyl acetate; as well as, b) The crude vinyl acetate composition is purified by distillation to obtain purified vinyl acetate; and, c) The aqueous mixture obtained in step a), comprising water and acetic acid, and at least a portion of the purified vinyl acetate obtained in step b), is subjected to solvent extraction, and acetic acid is extracted from the aqueous mixture using the purified vinyl acetate as a solvent.

2. The method according to claim 1, characterized in that, Separate the purified vinyl acetate acetic acid extract obtained in step c) from the aqueous mixture, and return the extract to the distillation in step b) for further purification.

3. The method according to claim 1 or 2, characterized in that, The distillation purification in step b) is carried out in a distillation column, with the purified vinyl acetate as the top product.

4. The method according to claim 1 or 2, characterized in that, The distillation purification in step b) is carried out in a distillation column, with the crude acetic acid composition as the bottom product.

5. The method according to claim 4, characterized in that, The bottom product is discharged from the bottom of the distillation column.

6. The method according to claim 3, characterized in that, The overhead product is sent to a condenser, which condenses some or all of the overhead product.

7. The method according to claim 6, characterized in that, The condensed overhead distillate contains water and vinyl acetate, wherein the water is separated from the vinyl acetate by phase separation to provide the purified vinyl acetate.

8. The method according to claim 1, characterized in that, The solvent extraction in step c) is a liquid-liquid extraction.

9. The method according to claim 1, characterized in that, The solvent extraction in step c) is carried out in a stirred tower.

10. The method according to claim 9, characterized in that, The solvent extraction in step c) is carried out in a countercurrent stirred tower.

11. The method according to claim 9, characterized in that, The mixing tower includes a mixing section with a stirring device.

12. The method according to claim 1, characterized in that, In step a), methyl acetate is hydrolyzed into acetic acid and methanol at a temperature of 30–250 °C.

13. The method according to claim 12, characterized in that, In step a), methyl acetate is hydrolyzed into acetic acid and methanol at a temperature of 50–150 °C.

14. The method according to claim 13, characterized in that, In step a), methyl acetate is hydrolyzed into acetic acid and methanol at a temperature of 70–120 °C.

15. The method according to claim 1, characterized in that, In step a), methyl acetate is hydrolyzed to acetic acid and methanol at atmospheric pressure to 15 bar.

16. The method according to claim 15, characterized in that, In step a), methyl acetate is hydrolyzed to acetic acid and methanol under a pressure of 1–10 bar.

17. The method according to claim 16, characterized in that, In step a), methyl acetate is hydrolyzed to acetic acid and methanol under a pressure of 1–5 bar.

18. The method according to claim 1, characterized in that, The aqueous mixture contains 10–50 wt% acetic acid, and the balance of the aqueous mixture, excluding impurities, contains methanol, methyl acetate and / or water, or is composed of methanol, methyl acetate and / or water.

19. The method according to claim 18, characterized in that, The water-based mixture contains 15–50 wt% acetic acid.

20. The method according to claim 19, characterized in that, The water-based mixture contains 30–50 wt% acetic acid.

21. The method according to claim 1, characterized in that, The first reaction space is located in the adjacent tower, and step a) is carried out in the adjacent tower.

22. The method according to claim 21, characterized in that, After separating methanol from the aqueous mixture in the adjacent column, the aqueous mixture is sent to the solvent extraction in step c).

23. The method according to claim 2, characterized in that, In step a), the water and methyl acetate are contacted with the hydrolysis catalyst in the first reaction space, causing at least partial hydrolysis into acetic acid and methanol.

24. The method according to claim 21, characterized in that, Oxygen, acetic acid, and ethylene are contacted with an oxidation catalyst in the second reaction space, where acetic acid and ethylene are at least partially oxidized to crude vinyl acetate.

25. The method according to claim 1, characterized in that, The methyl acetate is hydrolyzed into acetic acid and methanol. The resulting mixture, after leaving the first reaction space, is sent to step c) for solvent extraction and separation.

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