METHOD AND APPARATUS FOR THE PRODUCTION OF VINYL ACETATE

Description

[0001] The present invention relates to a process and a plant for producing vinyl acetate according to the preambles of the corresponding independent patent claims. Background of the invention

[0002] The oxidative dehydrogenation (ODH) of paraffins with two to four carbon atoms is generally known. In ODH, the paraffins are reacted with oxygen to form, among other things, the respective olefins and water. The present invention relates in particular to the oxidative dehydrogenation of ethane to ethylene, hereinafter also referred to as ODHE.

[0003] ODH(E) can be advantageous over more established processes for producing olefins, such as steam cracking or catalytic dehydrogenation. Due to the exothermic nature of the reactions involved and the virtually irreversible formation of water, there is no thermodynamic equilibrium limitation. ODH(E) can be carried out at comparatively low reaction temperatures. Regeneration of the catalysts used is generally not required, as the presence of oxygen enables or causes in-situ regeneration. Finally, in contrast to steam cracking, smaller amounts of valueless byproducts such as coke are formed.

[0004] For further details regarding ODH(E) please refer to relevant literature, for example Ivars, F. and Löpez Nieto, JM, Light Alkanes Oxidation: Targets Reached and Current Challenges, in: Duprez, D. and Cavani, F. (eds.), Handbook of Advanced Methods and Processes in Oxidation Catalysis: From Laboratory to Industry, London 2014: Imperial College Press, pages 767-834, or Gärtner, CA et al., Oxidative Dehydrogenation of Ethane: Common Principles and Mechanistic Aspects, ChemCatChem, Vol. 5, No. 11, 2013, pages 3196 to 3217, and X. Li, E. Iglesia, Kinetics and Mechanism of Ethane Oxidation to Acetic Acid on Catalysts Based on Mo-V-Nb Oxides, J. Phys. Chem. C, 2008, 112, 15001-15008.

[0005] In particular, MoVNb-based catalyst systems have proven promising for ODH(E), as mentioned, for example, in F. Cavani et al., "Oxidative dehydrogenation of ethane and propane: How far from commercial implementation?", Catal. Today, 2007, 127, 113-131. Catalyst systems additionally containing Te can also be used. Reference here to a "MoVNb-based catalyst system" or a "MoVTeNb-based catalyst system" refers to a catalyst system that contains the aforementioned elements as a mixed oxide, also expressed as MoVNbO x or MoVTeNbO x , respectively. Te in parentheses indicates its optional presence. The invention is used in particular with such catalyst systems.

[0006] In ODH, particularly when using MoVNb(Te)O x -based catalysts under industrially relevant reaction conditions, significant amounts of the respective carboxylic acids of the paraffins used, especially acetic acid in the case of ODHE, are formed as byproducts. Therefore, for economical plant operation, coproduction of olefins and carboxylic acids is generally unavoidable when using the described catalyst type; preferential formation of olefins is usually desirable in industrial applications.

[0007] Depending on the reaction conditions and the catalysts used, in addition to the already mentioned by-products (acetic acid, for example, can also be another valuable product), certain amounts of carbon monoxide and carbon dioxide are also produced as undesirable by-products in ODH(E). Current improvement and optimization approaches are partly aimed at minimizing the proportion of these carbon oxides. Currently, the proportion of carbon oxides can be reduced to less than 5%.

[0008] Recently, commercial concepts have become known based on the earlier, more theoretical approaches and laboratory-scale work, which are based in particular on the aforementioned mixed oxide catalysts. For example, reference can be made to EP 3 519 377 B1 (WO 2018 / 115416 A1), WO 2018 / 115418 A1, WO 2018 / 082945 A1, US 10,730,810 B2 (WO 2018 / 115494 A1), EP 3 700 663 B1 (WO 2019 / 081682 A1), WO 2019 / 243480 A1, US 10,730,811 B2 (WO 2018 / 115414 A1), WO 2020 / 187572 A1 of the applicant and WO 2018 / 153831 A1, WO 2018 / 019761 A1 WO 2018 / 019760 A1, WO 2017 / 198762 A1, WO 2017 / 144584 A1, WO 2020 / 074750 A1, US 9,963,412 B2, US 10,017,432 B2 by other applicants. These concepts have in common that air or oxygen is always used as the oxidizing agent, and only minor amounts of carbon oxides are present in the product stream.

[0009] With regard to subsequent process steps, a high purity of the ethylene product (e.g., so-called "polymer grade," especially greater than 99.9%) is typically desired in ODHE. Therefore, appropriate purification steps downstream of the actual ODHE and the removal of trace components, especially residual oxygen from the ODHE, as well as carbon monoxide and the resulting acetylene compounds, must be considered.

[0010] For the removal of acetylene from a process gas in ethylene plants (steam crackers), for example, isothermal crude gas hydrogenation (after drying, before a known C2 / C3 separation, i.e., deethanization), isothermal C2 hydrogenation (after C2 / C3 separation, before C1 / C2 separation, i.e., demethanization), or adiabatic tail-end hydrogenation (usually after C1 / C2 separation and before or after C2 splitter) are generally used. For steam cracking processes and these known processing and separation steps, reference is made to specialist literature such as the article "Ethylene" in Ullmann's Encyclopedia of Industrial Chemistry, online edition, 2009, DOI 10.2002 / 14356007.a10_045.pub3.

[0011] In established steam cracker technology, all of these hydrogenations take place in the absence of molecular oxygen and at carbon monoxide concentrations of significantly less than 1% (typically less than 2,500 ppm, especially less than 1,500 ppm). While originally Ni-based catalysts were primarily used for this purpose, nowadays noble metal catalysts (particularly Pd-based ones) are used for such concepts, which can also be doped with other metals such as Ag, Ce, and others. The use of Rh, Ir, Ru, Pt, and Au-based systems has also been reported, particularly in the scientific literature.

[0012] The presence of (relatively) high carbon monoxide levels, as is the case with ODH(E), therefore usually requires different approaches. For example, combined removal of carbon monoxide and oxygen directly at the outlet of an ODHE reactor has been described in US 2010 / 0256432 A1 and WO 2017 / 144584 A1.

[0013] EP 3 708 557 A1 and EP 3 708 558 A1 describe a process and suitable catalysts that enable at least partial removal of acetylene and / or oxygen from the product gas of an ODHE. Catalysts containing copper oxide or ruthenium are advantageously used. This acetylene and / or oxygen removal can be followed by carbon dioxide removal.A corresponding process can comprise subjecting a corresponding process gas or a gas mixture formed using at least a portion of the process gas, in the order specified here, partially or completely to condensate separation, compression, at least partial removal of oxygen and one or more of the acetylenes, and one or more stages of carbon dioxide removal, wherein the at least partial removal of the oxygen and the acetylene(s) takes place simultaneously and by a catalytic reaction using a catalyst containing copper oxide or ruthenium, and at least in the form of a hydrogenation.

[0014] According to WO 2018 / 153831 A1, oxygen, carbon monoxide, and optionally acetylene are removed from the product stream of an ODHE. This generally discloses the use of an oxidation catalyst, which may contain, in particular, the metals Ni, Cu, Zn, Pd, Ag, Pt, Au, Fe, Mn, Ce, Sn, Ru, and Cr as constituents. Cu and / or Pt-based systems are preferably used, but in particular Cu-based systems. In the previously cited WO 2017 / 144584A1, the same applicant describes a concept for oxygen removal as a downstream bed in the ODH main reactor, i.e., upstream of the process condensate separation, wherein this downstream bed is heated / cooled with a separate coolant stream. The catalyst of this downstream bed can, on the one hand, have the same composition as the ODH catalyst or be modified with other elements such as Sb, but preferably Cu.

[0015] In addition to the requirement for high product purity of the ethylene product, downstream cryogenic plant components also require quantitative carbon dioxide removal. Carbon dioxide can also be relatively easily removed from the product mixture due to its high interaction with suitable solvents or scrubbing liquids, especially at concentrations encountered in ODHE. Known carbon dioxide removal processes, particularly appropriate scrubbing (e.g., amine scrubbing), can be used. The loaded scrubbing liquid is then regenerated in a separate column, releasing very pure carbon dioxide through desorption.

[0016] If subsequent steps require the absence or only a very low residual concentration of carbon dioxide (e.g. due to catalyst inhibition or poisoning), the residual carbon dioxide content after an amine wash can be further reduced as required by an optional caustic wash as a fine cleaning step.

[0017] With certain exceptions, the corresponding wash liquids can also react with oxygen, which can lead to adverse aging or damage to the detergents over time, requiring a continuous purge and makeup flow or leading to an undesirable shortening of the service life of these wash liquids. Therefore, the removal of oxygen upstream of a corresponding wash is advantageous from this perspective.

[0018] According to the state of the art, water removal is typically carried out using regenerative dryers based on molecular sieves and, in addition to achieving the product specification, is also essential with regard to subsequent cryogenic process steps in order to avoid blockages due to ice deposition.

[0019] Typically, as part of a suitable process control in an ODHE process, methane contained in the product stream (e.g., particularly originating from the ODHE's ethane feed stream) must also be removed. This typically involves a C1 / C2 separation ("demethanizer" or demethanization) of a known type, which requires appropriate cryogenic conditions. Such a demethanizer simultaneously removes carbon monoxide from the product stream. Thus, a C1-minus fraction is formed, which contains methane and / or carbon monoxide as its essential components. Generally, a "C1-minus fraction" is understood here to be a fraction that predominantly or exclusively contains methane and components with lower boiling points than methane, such as, in particular, carbon monoxide and oxygen. Accordingly, a "C2-plus fraction" is a fraction that predominantly or exclusively contains components with higher boiling points than methane.The term "predominantly or exclusively" or "rich" refers to a proportion of at least 75%, 80%, 85%, 90%, 95%, or 99% by volume, mass, or molar. Corresponding numerical values ​​also apply when a "predominant portion" is mentioned, for example, in relation to any product or subsequent stream. A "predominant portion" refers in particular to more than 50%, more than 66%, more than 75%, or more than 90% (relative to a partial volume of a total volume or a partial amount of a total amount, and the like). If a fraction is designated by the name of the main component contained ("ethane fraction," "ethylene fraction," and the like), it does not necessarily have to consist exclusively of this component, but can also predominantly contain this component or be rich in it in the sense explained.

[0020] Traces of oxygen still present in the demethanizer inlet stream also enter this C1-minus fraction. Therefore, the goal is usually to limit the oxygen content in the demethanizer inlet stream and thus avoid the potential formation of an explosive atmosphere at the top of a column used in this process (see also WO 2018 / 082945 A1). For example, EP 3 456 703 A1 describes a demethanizer in the separation section of an ODHE plant, which is (also) combined with pressure swing adsorption in the top stream for this purpose.

[0021] Finally, unconverted ethane must be separated from ethylene, which is done using a C2 splitter, which is also operated under cryogenic conditions. This splitter must be designed and operated in such a way that ethane in the ethylene is removed virtually quantitatively, while simultaneously ensuring that the ethane stream returned to the ODHE contains as little or no ethylene as possible.

[0022] A major application for vinyl acetate (VAM) is its polymerization into polyvinyl acetate (PVAc) or other copolymers. Vinyl acetate thus represents an important intermediate in the chemical industry.

[0023] The current production process starts with ethylene and acetic acid and is described, for example, in the article "Vinyl Esters" in Ullmann's Encyclopedia of Industrial Chemistry, online edition, 2019, DOI 10.1002 / 14356007.a27_419.pub2. These are converted in an exothermic reaction with the addition of oxygen in a gas-phase process. Fixed-bed reactors with Pd catalysts are typically used. A particularly noteworthy side reaction is the oxidative conversion of ethylene to carbon dioxide. Ethylene and acetic acid are preferably used in a ratio of 2 to 3:1, and oxygen is added in a ratio of up to 0.5 equivalents relative to acetic acid. Typical reaction conditions are 120 °C to 180 °C at a pressure of 5 bar to 12 bar.Typically, an inert gas such as carbon dioxide (e.g., 10 to 30%), nitrogen, or argon is added to better control the reaction heat and ignition range. However, it is also possible to synthesize vinyl acetate without the addition of carbon dioxide or with a significantly lower proportion of carbon dioxide than previously mentioned.

[0024] Contaminants in the vinyl acetate synthesis feedstream, particularly acetylene and carbon monoxide, have a negative impact on vinyl acetate synthesis. Ideally, the feed for vinyl acetate synthesis is free of these compounds or contains them only in extremely low concentrations. A suitable ethylene feed for vinyl acetate synthesis can therefore be provided, according to the state of the art, in particular as highly purified ethylene (e.g., "polymer grade") from corresponding processes such as steam cracking and a downstream purification and separation section.

[0025] The actual synthesis of vinyl acetate is then followed by a downstream processing step, which in particular comprises phase separation (separation of the gas phase and liquid crude product) and advantageously also a scrubbing step, which serves in particular to increase the efficiency of vinyl acetate yield by means of extraction with acetic acid, but which also forms the basis for the recovery of ethylene and, if necessary, carbon dioxide as feedstocks for the synthesis of vinyl acetate. Usually, a separate absorptive carbon dioxide removal step is then carried out in this stream or a substream in order to adjust the carbon dioxide content. The aforementioned article in Ullmann's Encyclopedia of Industrial Chemistry specifically mentions a regenerative potassium carbonate solution for this purpose. Various distillative solutions are used for the subsequent purification of the vinyl acetate crude product, which are described in detail in the aforementioned article.The processing (phase separation, washing, absorptive removal of carbon dioxide and distillation) usually takes place at a lower pressure than the synthesis of vinyl acetate.

[0026] In principle, approaches to the process-engineering integration of ODHE and vinyl acetate synthesis are known. These appear advantageous, as ODHE typically yields acetic acid as a by-product, and vinyl acetate synthesis, in turn, starts from ethylene and acetic acid.

[0027] The present invention aims to demonstrate improved and more effective possibilities for the process-engineering integration of ODHE and vinyl acetate synthesis. Disclosure of the invention

[0028] The above-mentioned object is achieved by the measures specified in the respective independent patent claims. Preferred embodiments are the subject of the dependent patent claims and the following description.

[0029] In the following, known processes which comprise a process-engineering integration of vinyl acetate synthesis and ODHE will first be explained in order to demonstrate the advantages and features of the present invention.

[0030] If pressure values ​​are given below in bar, they are absolute pressures unless otherwise stated. Pressure differences are expressed in bar.

[0031] WO 2018 / 114747 A1 discloses, among other things, a carbon dioxide removal process and a C2 splitter downstream of the vinyl acetate synthesis and carbon dioxide removal, with recirculation of ethylene to the vinyl acetate synthesis and of ethane to the ODHE. However, at least one partial stream from the ODHE—which therefore also contains carbon dioxide due to the process—is always introduced into the vinyl acetate synthesis. Only a bypass of the vinyl acetate synthesis allows the direct transfer of a partial stream from the ODHE to the carbon dioxide removal process. Such a configuration means that only a limited variation of the carbon dioxide content is possible. Undesirable changes can occur, particularly in the case of changes in the conversion and product distribution behavior of the ODHE. In particular, complete separation of the carbon dioxide in the inlet stream of the vinyl acetate synthesis and / or enrichment to very low residual carbon dioxide contents is therefore not possible.Furthermore, there is no information on the advantageous implementation of the respective pressure levels of the individual reaction and separation steps, nor on the corresponding necessary compression of the process streams and, in particular, the recycle streams. In particular, this document suggests a decreasing pressure gradient, with carbon dioxide removal thus taking place at a lower pressure than vinyl acetate synthesis.

[0032] WO 2018 / 114752 A1 also discloses an integration of ODHE and vinyl acetate synthesis. The focus here is on the use of vapor permeation to separate water from the ODHE outlet stream. Embodiments of the further process control are otherwise closely based on the aforementioned document and, here too, do not disclose any further solutions within the meaning of the present invention. Neither of the two aforementioned documents addresses the presence of methane in the process streams (in particular resulting from methane in the ODHE feed), and thus, no approaches for methane separation are disclosed.

[0033] In particular, these documents do not address the influence of trace components, especially carbon monoxide and acetylene, on vinyl acetate synthesis. No solution for removing these trace components is proposed.

[0034] The aforementioned documents cite WO 1998 / 005620 A1, which describes a sequential connection of ODHE and vinyl acetate synthesis. However, this document also focuses particularly on the separation and, if necessary, recirculation of acetic acid and / or vinyl acetate or correspondingly enriched substreams. This document does not disclose specific details on carbon dioxide removal. Typically, the ODHE outlet stream is fed to vinyl acetate synthesis without carbon dioxide removal. Thus, no removal, depletion, or adjustment of the carbon dioxide content in the vinyl acetate synthesis inlet stream takes place. This document also does not address the presence of methane in the process streams and therefore does not contain any approach to methane separation in an integrated process.

[0035] According to a variant disclosed in WO 1998 / 005620 A1, carbon monoxide can be oxidized to carbon dioxide in ODHE. However, this requires a catalyst that produces an ODHE product stream with very low carbon monoxide contents. As previously discussed, typical ODHE catalysts, particularly MoVNb-based catalyst systems, do not (yet) meet this requirement. Thus, this approach does not provide a solution for sufficient carbon monoxide removal in the sense of integrating ODHE and vinyl acetate synthesis. According to another variant, a Pd-containing catalyst is used in vinyl acetate synthesis, which also converts carbon monoxide in a suitable reaction. As described in the document, however, this design is limited to Pd-based catalysts.Even though the catalysts used today for vinyl acetate synthesis are typically Pd-based, the additional carbon dioxide removal and coupling of the reaction steps in vinyl acetate synthesis result in a significant limitation in the process parameters, e.g., in the case of changes in the composition of the inlet stream, since the behavior of carbon monoxide removal and vinyl acetate synthesis cannot be influenced and adjusted independently of each other.

[0036] WO 2000 / 069802 A1 is also cited in the above-mentioned documents and describes the sequential integration of an ODHE and a vinyl acetate synthesis, in particular with MoVNb-based catalysts for the ODHE and in particular Pd-based catalysts for the vinyl acetate synthesis. In this document, carbon dioxide removal is provided either only in the gas stream downstream of the ODHE, i.e., upstream of the vinyl acetate synthesis (located Figure 1) or the carbon dioxide contained in the gas stream after the ODHE is completely transferred to the vinyl acetate synthesis and carbon dioxide removal only takes place downstream of the vinyl acetate synthesis ( Figure 2 ). This document also does not address the presence of methane in the process streams and thus does not contain any approach to methane separation in an integrated process. This document does not disclose any solutions for the removal of traces of, for example, carbon monoxide, acetylene, and / or oxygen. A corresponding intermediate step is explicitly excluded according to the claim. Therefore, no suitable technical solution for the task of carbon monoxide removal is disclosed. Rather, the document aims at an embodiment of the ODHE in which no carbon monoxide is produced, which, as previously stated, does not correspond to the state of the art even today.

[0037] WO 2001 / 090042 A1 also describes the integration of an ODHE and a vinyl acetate synthesis. Pd-doped catalysts of the type Mo a Pd b X c Y d are used for the ODHE. Carbon dioxide removal together with "inerts" from a recycle stream of the vinyl acetate synthesis to the ODHE is only hinted at in a sketch without further explanation. A schematic drawing outlines a carbon monoxide removal upstream of the vinyl acetate synthesis, but without demonstrating advantageous solutions. According to the description, no carbon monoxide is produced in the ODHE or only in an amount of less than 100 ppm, which does not correspond to the behavior under technically relevant conditions (see above). There are no details regarding acetylene in the product stream of the ODHE or its removal upstream of the vinyl acetate synthesis.

[0038] Further documents which also disclose or indicate corresponding combinations, but not the measures proposed according to the invention, are, for example, US 2005 / 0148791 A1, US 5,066,365 A, US 2014 / 066650 A1 and US 2002 / 058849 A1.

[0039] Independently of the aforementioned documents, WO 2019 / 175732 A1 also describes a linking of an ODHE using various catalysts (including MoVTeNbOx-based systems) with a vinyl acetate synthesis. Carbon monoxide oxidation and acetylene removal take place directly in the gas phase portion of the ODHE outlet stream using at least one metal or a corresponding metal oxide selected from groups 11, 4, 7, or 9, the lanthanides or actinides – explicitly mentioning Cu, Ag, Au, or combinations thereof. However, detailed explanations only cover metals from group 11 and the optional use of CeO2 or ZrO2 as promoters. Metals or their oxides from groups 8 (in particular Ru) and 10 (in particular Ni, Pd, Pt), however, are not mentioned anywhere in the application as suitable for this purpose.The application does not address the advantageous positioning—particularly with regard to the pressure level—of the claimed oxidation of carbon monoxide. A more detailed integration of the two processes is not disclosed. Regarding carbon dioxide removal, this document contains only very general references to an unspecified "inert removal unit." However, this does not involve selective carbon dioxide removal and does not allow for the demand-based adjustment of a proportion of an individual or all inert components in the feed stream of vinyl acetate synthesis, in particular not for the demand-based adjustment of the carbon dioxide content. Rather, a joint, i.e., non-selective removal of all inert components in a single step is proposed. As is known to the person skilled in the art, such removal is not possible according to the prior art, in particular by means of absorptive scrubbing.According to special designs, oxygen and acetylene are practically completely absent in the feed stream of the vinyl acetate synthesis.

[0040] Carbon dioxide is conventionally removed, in particular, by absorption (e.g., regenerable amine washes and non-regenerable caustic washes). Carbon dioxide can be removed relatively easily from the product mixture due to its high interaction with suitable solvents or scrubbing liquids. Known processes for carbon dioxide removal, in particular corresponding washes (e.g., amine washes), can also be used within the scope of the invention. The loaded scrubbing agent in amine washes is then regenerated in a separate column, with essentially pure carbon dioxide being released by desorption and being available as a relatively pure stream for further use. Further fine purification and reduction of the carbon dioxide content is possible by caustic wash. Carbon dioxide can therefore be separated off as required and recovered in the associated regeneration as an almost pure substance.Due to the solubility increasing with pressure, absorptive carbon dioxide removal preferably takes place, and in particular also within the scope of the present invention, at elevated pressure, i.e. more than 5 bar, in particular more than 10 bar and in particular more than 15 bar.

[0041] Within the scope of an advantageous separation and purification sequence, cryogenic and non-cryogenic distillation processes can also be used in particular within the scope of the present invention, wherein a demethanizer and a C2 splitter are used according to the invention.

[0042] In a so-called demethanizer, a lighter fraction (C1minus fraction) is formed as the overhead stream, while a heavier fraction (C2plus fraction) is obtained as the bottoms stream. The C1minus fraction is particularly enriched in methane and / or carbon monoxide, while the bottoms fraction is depleted in these components or free of these components. The term "enriched" here refers to any increased content, but in particular a content increased by at least a factor of 2, 5, 10, 100 or more, of one or more components, relative to a starting mixture before enrichment. Accordingly, the term "depleted" here refers to any reduced content, but in particular a content reduced by at least a factor of 2, 5, 10, 100 or more, of one or more components, relative to a starting mixture before depletion.

[0043] In the case of an ODHE, the bottoms fraction therefore predominantly or exclusively contains ethane and ethylene. A demethanizer is typically operated, and in particular also within the scope of the present invention, in a pressure range between 10 bar and 50 bar, preferably 15 bar and 40 bar, particularly preferably between 20 bar and 35 bar. In particular, the head temperature must be set correspondingly low to ensure a liquid reflux. Typical temperatures here are below -50 °C, in particular below -70 °C, and more particularly below -80 °C.

[0044] EP 3 339 277 A1 describes the demethanizer of an ODHE process. For example, EP 3 456 703 A1 describes an ODHE process that initially comprises a demethanizer in the separation section. The overhead stream formed here, comprising in particular methane, is fed to a pressure swing adsorption (PSA) system to recover the ethylene contained in this stream and return it to the separation section of the ODHE plant.

[0045] Furthermore, the separation of ethylene and unreacted ethane in a so-called C2 splitter is required. Ethylene is typically obtained in a purity of more than 98%, preferably more than 99%, particularly preferably more than 99.5%. Ethane is recycled as reaction feed in both steam cracking and ODHE processes, i.e., for example, recycled back into the ODHE reactor. In order to minimize any loss of ethylene, this fraction is also usually obtained in high purity. A C2 splitter is typically, and in particular also in the context of the present invention, operated in a pressure range between 5 bar and 50 bar, preferably 7 bar and 40 bar, particularly preferably between 8 bar and 35 bar. Here, too, depending on the pressure used, a relatively low head temperature is required, i.e. typically less than -5 °C, in particular less than -20 °C, and more particularly less than -50 °C.

[0046] Further separation and purification steps (as a non-exhaustive list) include phase separations, in particular by means of separators and decanters, reactive, in particular catalytic removal of oxygen and trace compounds (in particular carbon monoxide and acetylene), in particular with the addition of hydrogen and / or oxygen, adsorptive purification and drying processes, which can use regenerable and non-regenerable adsorbents depending on the material and intended use, and pressure swing adsorption (PSA) and membrane processes, which can also be used within the scope of the present invention. Features and advantages of the invention

[0047] The object of the present invention already stated above can be concretized in particular in a first aspect in the creation of a process control which enables a particularly efficient integration of ODHE and vinyl acetate synthesis and thus a use of the product mixture of the ODHE for the vinyl acetate synthesis.

[0048] The starting point is based on the state of the art as follows: A "conventional" ODHE produces, in addition to ethylene, acetic acid as a by-product. The ratio of ethylene to acetic acid can be adjusted as required within certain limits. A minimum oxygen content must usually be ensured at the outlet of the ODHE reactor to avoid catalyst damage. However, this residual oxygen content is minimized as far as possible according to the state of the art and is usually at least 0.41 mol% in the entire ODHE outlet stream (i.e., in the moist process gas stream before condensate separation), but at most less than 1.5 mol%, less than 0.8 mol%, or less than 0.6 mol%. Downstream, oxygen removal measures can then be provided, as described, for example, in the documents already mentioned (e.g., US2010 / 0256432 A1). Ethylene is usually provided as a pure product and is separated from other hydrocarbons, particularly, for example,Ethane and methane are released. Methane can be introduced, in particular, as a component of the ODHE feed stream. Vinyl acetate synthesis requires ethylene and acetic acid as reactants, typically in a ratio of 3:1 to 1:1. Furthermore, oxygen must be added as a reactant for vinyl acetate synthesis.

[0049] However, for a further integration of the two processes, the following aspects in particular must be taken into account, for which the present invention, particularly in its embodiments, provides advantageous solutions: In addition to ethylene and acetic acid, other by-products are also produced in the ODHE, in particular acetylene and carbon monoxide in addition to carbon dioxide, which must be removed by suitable process steps. Acetylene and carbon monoxide in particular have a negative impact on subsequent process steps, including the vinyl acetate synthesis in this case. In vinyl acetate synthesis, a suitable diluent is usually added, which then has to be removed from the product mixture of the vinyl acetate synthesis. Carbon dioxide is often used for this task, and additional carbon dioxide is also produced as a by-product in the vinyl acetate synthesis. Accordingly, the product stream from the vinyl acetate synthesis must also be subjected to carbon dioxide purification. However, the inlet stream of the vinyl acetate synthesis can also contain no or only small amounts of carbon dioxide.In particular, process-optimized carbon dioxide processing is not yet part of available technologies or developments. Rather, carbon dioxide is typically removed through isolated purification steps and not utilized within an integrated overall process. In particular, the compression of gas streams requires considerable effort in terms of the required complex equipment (compressors, often multi-stage) and operating costs (energy consumption for compression). Sequentially connecting independent ODHE and vinyl acetate synthesis processes requires multiple compression and expansion steps throughout the process chain. However, even known approaches to process integration of ODHE and vinyl acetate synthesis do not offer an optimized approach for selecting suitable process configurations and optimized pressure levels.

[0050] As mentioned, a carboxylic acid is formed as a by-product or co-product in the ODH, acetic acid in the case of ethane used in the ODH (i.e., in the ODHE). Adjusting the ethylene to acetic acid ratio is possible by suitable measures, as described in WO 2018 / 115418 A1, WO 2018 / 115416 A1, and WO 2019 / 243480 A1, such as the choice of catalyst or the reaction conditions, in particular the adjustment of the water partial pressure in the process gas stream of the ODHE (see in particular WO 2018 / 115416 A1).

[0051] Within the scope of the present invention, a ratio of ethylene to acetic acid between 1:1 and 10:1, in particular between 2:1 and 5:1, and more particularly between 2.5:1 and 4:1, is particularly desirable. This acetic acid, together with water of reaction, can be separated relatively easily from a corresponding product mixture of the oxidative dehydrogenation by condensation and / or water washing. Thus, the product stream is separated into a condensate phase and a gas phase.

[0052] By suitable processes known to those skilled in the art, it is then also possible, if necessary, to enrich the acetic acid from the condensate phase and recover it as a separate valuable product, which can be fed into the vinyl acetate synthesis. The gas phase from the ODHE product stream then contains, in particular, ethylene, but also other components such as unreacted ethane, methane (particularly from the ODHE feed), and in particular, carbon monoxide and carbon dioxide, as well as small amounts of acetylene (less than approximately 300 to 400 ppmv) as byproducts.

[0053] In the context of the present invention, the oxidative dehydrogenation is advantageously carried out at a pressure level of 1 bar to 10 bar, in particular 2 bar to 6 bar, and the vinyl acetate production is advantageously carried out at a pressure level of 2 bar to 50 bar, in particular 5 bar to 15 bar.

[0054] Building on these principles, the present invention discloses, in one main aspect, an optimized solution for efficient carbon dioxide removal from an integrated ODHE and vinyl acetate synthesis. This solution, in particular, enables the carbon dioxide content in the inlet stream of the vinyl acetate synthesis to be easily adjusted as needed. The invention cleverly utilizes the following facts: 1. In vinyl acetate synthesis, a certain proportion of carbon dioxide can be used as a diluent in the reaction feed for vinyl acetate synthesis, meaning that carbon dioxide can pass through the vinyl acetate synthesis or is even desired in certain proportions. The carbon dioxide content in the feed for vinyl acetate synthesis can be 0 to 30%, in particular 0 to 15%, and more particularly 0 to 5%. 2. In vinyl acetate synthesis, (further) carbon dioxide is formed as a by-product anyway. 3. Due to its strong interaction with suitable solvents or scrubbing liquids, carbon dioxide can be removed relatively easily from the product mixture. In particular, known processes for carbon dioxide removal, in particular appropriate scrubs (e.g. amine scrubs), can be used. Carbon dioxide can therefore be separated off as required and recovered in the associated regeneration as an almost pure substance.Such carbon dioxide removal can be performed at a suitable point in the process. Further fine purification and reduction of the carbon dioxide content is, as already mentioned, possible in principle through a subsequent caustic wash.

[0055] In addition, the invention discloses, particularly in corresponding advantageous embodiments, an advantageous selection of the pressure levels of the corresponding process steps. As explained below, if necessary, further necessary process steps such as demethanizers and / or C2 splitters are also advantageously included and taken into account. In principle, reaction and process steps can also be arranged at a suitable point within the overall process to remove by-products or trace compounds. In particular, the process according to the invention can include necessary purification steps for removing traces, in particular carbon monoxide, acetylene, and / or oxygen.

[0056] In a corresponding group of embodiments or a further aspect, which will be explained below, the present invention addresses the problem that the product stream of the ODHE, as mentioned above, contains, in addition to ethylene and components such as ethane and carbon dioxide, and in particular also carbon monoxide and acetylene (typically in a content of less than 300 to 400 vppm). This particularly applies to a gas phase of the product stream of an ODHE after condensation.

[0057] The aforementioned object of the invention is achieved in that the respective gas phase product streams of an ODHE and a vinyl acetate synthesis are each at least partially subjected to a joint carbon dioxide removal. This carbon dioxide removal is preferably carried out as an absorptive and regenerative scrubbing. In order to achieve the most efficient carbon dioxide removal possible, an elevated pressure is advantageously selected for the carbon dioxide removal. In the context of the present invention, the carbon dioxide removal therefore preferably takes place at a higher pressure level than the ODHE and the vinyl acetate synthesis. The respective gas phase product streams of these steps (i.e. the ODHE and the vinyl acetate synthesis) can therefore be fed to a joint compression and then to the joint carbon dioxide removal according to the invention. The joint compression can be carried out in one or more stages.Accordingly, the merging of both partial flows can also only take place after a suitable compression stage, ie that initially in one or more first compression stages only the product flow of one of the two steps is compressed and then in one or more second compression stages the further joint compression takes place.

[0058] The carbon dioxide removed in an absorptive scrub can then be recovered as a carbon dioxide fraction during scrubbing regeneration and fed in suitable proportions to the vinyl acetate synthesis feed stream to enable dilution with carbon dioxide as needed. A particular advantage here is that the carbon dioxide concentration at the vinyl acetate synthesis inlet can be adjusted over a very wide range, independent of the carbon dioxide content in the ODHE product stream. This embodiment therefore represents a particularly advantageous variant.

[0059] In principle, a partial stream of the ODHE product mixture can also be fed into the vinyl acetate synthesis upstream of the carbon dioxide removal process. Such a process is known from WO 2018 / 114747 A1. However, since such a partial stream has a specific composition, particularly with regard to carbon dioxide, ethane, and possibly methane (see further details below), and also contains carbon monoxide and acetylene, which are known poisons for vinyl acetate synthesis catalysts, such a process does not appear advantageous or is only possible for a small proportion of the total vinyl acetate synthesis feed stream. Furthermore, fluctuations in the process gas composition are to be expected as a result of fluctuations in the operation of the ODHE and / or vinyl acetate synthesis, which in turn can be expected to result in further undesirable feedback to the vinyl acetate synthesis.

[0060] To achieve the stated objectives, the invention proposes a process for producing vinyl acetate, in which, in one or more first process steps, ethane and oxygen are subjected to oxidative catalytic dehydrogenation (ODHE) to obtain a first product mixture containing ethane, ethylene, water, acetic acid and carbon dioxide, and in which, in one or more second process steps, ethylene and acetic acid are subjected to catalytic vinyl acetate synthesis to obtain a gaseous second product mixture containing ethylene, vinyl acetate and carbon dioxide, wherein at least a portion of the ethylene and at least a portion of the acetic acid which are subjected to the catalytic conversion in the one or more second process steps are formed by at least a portion of the ethylene and at least a portion of the acetic acid from the first product mixture.

[0061] According to the invention, as already stated above in other words, a first subsequent mixture containing ethane, ethylene, and carbon dioxide is formed using at least a portion of the first product mixture, and a second subsequent mixture containing ethylene and carbon dioxide is formed using at least a portion of the second product mixture. The formation of the first subsequent mixture comprises subjecting at least a portion of the first product mixture to a condensative separation of water and acetic acid to obtain a condensate fraction containing water and acetic acid, and subjecting the first subsequent mixture to a condensative separation of water and acetic acid, and forming at least a portion of the acetic acid, which is subjected to the catalytic vinyl acetate synthesis in the one or more second process steps, from at least a portion of the acetic acid from the condensate fraction.

[0062] It is further provided that a third subsequent mixture containing ethane, ethylene and carbon dioxide is formed using at least a portion of the first subsequent mixture and using at least a portion of the second subsequent mixture, more precisely by combining at least a predominant portion of the first subsequent mixture and the second subsequent mixture, wherein the formation of the second subsequent mixture comprises subjecting at least a portion of the second product mixture to a vinyl acetate separation to obtain a vinyl acetate-containing precursor fraction and the second subsequent mixture.

[0063] It is also provided that at least a portion of the third subsequent mixture is subjected to one or more third process steps, wherein the one or more third process steps comprise a joint carbon dioxide removal, wherein in the one or more third process steps a fourth subsequent mixture containing ethane and ethylene and a carbon dioxide fraction are formed, and wherein at least a portion of the fourth subsequent mixture is subjected to a separation in which an ethane fraction and an ethylene fraction are formed.

[0064] At least a portion of the ethylene which is subjected to the catalytic vinyl acetate synthesis in the one or more second process steps is formed by at least a portion of the ethylene from the ethylene fraction, and / or at least a portion of the ethane which is subjected to the oxidative catalytic dehydrogenation in the one or more first process steps is formed by at least a portion of the ethane from the ethane fraction.

[0065] Further details and advantages of the measures proposed according to the invention have already been explained in detail. An inlet stream into the vinyl acetate synthesis can, in particular, have a carbon dioxide content of between 0 and 30%, and the third process step, or at least one of the third process steps, can be carried out in a pressure range that is higher, and in particular at least 1 bar, 2 bar, 5 bar, or 10 bar higher, than the pressure range in which the first and second process steps are carried out.

[0066] In principle, the corresponding product stream after the joint carbon dioxide removal according to the invention (i.e., the fourth subsequent mixture downstream of the third process step(s), or a corresponding portion thereof) can be fed directly to the vinyl acetate synthesis (i.e., to the one or more second process steps). In particular, any ethane and / or methane still present act as inert diluents in the vinyl acetate synthesis.

[0067] However, in practice, such an embodiment is hampered by the presence of carbon monoxide and / or acetylene in the gas stream, which can act as catalyst poisons in vinyl acetate synthesis if not previously removed. Therefore, within the framework of an integrated process, further purification, as described below, is advantageous. This can take place upstream or downstream of the carbon dioxide removal, i.e., upstream or downstream of the third process step(s). In the former case, which represents the case according to the invention, the formation of the first subsequent mixture comprises the at least partial removal of carbon monoxide and / or acetylene, and in the latter case, the fourth subsequent mixture is subjected to at least partial removal of carbon monoxide and / or acetylene.

[0068] However, for the additional separation steps mentioned below, depending on the selected temperature levels, in addition to the carbon dioxide removal according to the invention, drying may also be required beforehand in order to avoid blockages caused by freezing of water or carbon dioxide.

[0069] As also explained above in other words, the carbon dioxide removal advantageously comprises a regenerative adsorptive carbon dioxide removal, in which a scrubbing liquid is used which is loaded with carbon dioxide during the regenerative absorptive carbon dioxide removal, and from which the carbon dioxide is expelled while obtaining the carbon dioxide fraction. At least a portion of the carbon dioxide fraction can be passed as a diluent through the one or more second process steps, i.e., the vinyl acetate synthesis, as also explained above.

[0070] The formation of the first downstream mixture comprises, as mentioned, subjecting at least a portion of the first product mixture to a condensative separation of water and acetic acid (hereinafter also referred to as "condensate separation") to obtain a (liquid) condensate fraction containing water and acetic acid, and subjecting the first downstream mixture to a condensate separation of water and acetic acid (hereinafter also referred to as "condensate separation"). At least a portion of the acetic acid subjected to the one or more second process steps of the catalytic vinyl acetate synthesis is, as also mentioned, formed by at least a portion of the acetic acid from the condensate fraction. The latter can be formed in particular in a condensate separation (also referred to as acetic acid purification) downstream of the condensate separation. Reference can also be made to the above explanations regarding this aspect of an embodiment of the present invention.

[0071] In one embodiment of the present invention, the formation of the third secondary mixture may comprise subjecting at least a portion of the first secondary mixture and at least a portion of the second secondary mixture to joint compression. As already explained in this regard, a multi-stage compressor of a known type may be used, for example, to which at least a portion of the first secondary mixture can be supplied upstream of a first compressor stage and at least a portion of the second secondary mixture can be supplied upstream of a second compressor stage, wherein the second compressor stage can be arranged upstream or downstream of the first compressor stage.

[0072] In the process proposed according to the invention, the formation of the second downstream mixture comprises subjecting at least a portion of the second product mixture to obtain a vinyl acetate-containing precursor fraction and the second downstream mixture to a vinyl acetate separation, as also already mentioned. In the vinyl acetate separation, a portion of the acetic acid from the aforementioned condensate fraction can be used as an absorbent.

[0073] Within the scope of the present invention, at least a portion of the precursor fraction can be subjected to vinyl acetate purification, in which a vinyl acetate fraction, a by-product fraction, and an acetic acid fraction can be formed. In particular, at least a portion of the acetic acid subjected to the catalytic vinyl acetate synthesis in the one or more second process steps can be formed by at least a portion of the acetic acid from the acetic acid fraction from the vinyl acetate purification.

[0074] As already mentioned, at least a portion of the fourth subsequent mixture is subjected to a separation in which an ethane fraction and an ethylene fraction are formed. The separation comprises, in particular, a drying process of a type known per se and described above, followed by a demethanization according to the invention, and a C2 separation in a C2 splitter. However, other separation sequences and separation arrangements are also usable. For details, reference is made to the above explanations. At least a portion of the ethylene subjected to the catalytic vinyl acetate synthesis in the one or more second process steps is formed by at least a portion of the ethylene from the ethylene fraction, and / or at least a portion of the ethane subjected to the oxidative catalytic dehydrogenation in the one or more first process steps is formed by at least a portion of the ethane from the ethane fraction.Further details on this aspect have also been explained previously.

[0075] In a preferred embodiment of the invention, a C2 splitter can be integrated into the process and, in particular, the feed stream of the vinyl acetate synthesis can be depleted of ethane or ethane can be quantitatively removed from this stream. In particular, an embodiment in which the ethylene fraction from the C2 splitter still contains a certain proportion of ethane is particularly advantageous in order to minimize the expenditure (equipment / investment costs / operating costs) for this separation. In particular, the ethane content in the stream for vinyl acetate synthesis, i.e. the ethylene fraction which in this case is fed into the one or more second process steps for vinyl acetate synthesis without further separation processing, can be between 0 and 20 mol%, in particular between 0.01 and 10 mol%, furthermore in particular between 0.5 and 5 mol% ethane.A gas phase from the vinyl acetate synthesis, which contains ethane and unreacted ethylene, can also be recycled at a suitable point upstream of the C2 splitter.

[0076] Through the joint carbon dioxide removal according to the invention, a certain concentration of ethane can build up in the circuit via the vinyl acetate synthesis due to the recirculation, whereby the C2 splitter provided according to the described embodiment, however, effects a continuous discharge of ethane and avoids excessive ethane dilution. In this way, optimal ethane dilution in this stream can also be achieved. The ethane stream from the C2 splitter (the described ethane fraction) is advantageously at least partially recycled to the ODHE and, in contrast, preferably contains the lowest possible proportion of ethylene; however, quantitative removal of ethylene is not absolutely necessary here either. The ethylene content can, for example, be between 0 and 20 mol%, in particular between 0.01 and 10 mol%, more particularly between 0.5 and 5 mol%.

[0077] Within the scope of the present invention, a C2 splitter can advantageously be operated at relatively low pressures starting from approximately 5 bar (see also the above statements). For industrial implementation, a pressure slightly above vinyl acetate synthesis is particularly advantageous. "Slightly above" is understood here to mean a pressure difference of up to 15 bar, preferably up to 10 bar, and particularly preferably up to 5 bar.

[0078] The demethanizer provided in one embodiment of the invention can be used or configured in particular for the at least partial removal of methane, but also carbon monoxide, from the process gas stream, i.e., from the fourth downstream mixture or a further downstream mixture thereof, in order, for example, to avoid or limit enrichment in a cycle via vinyl acetate synthesis. The demethanizer can be arranged at a suitable point in the process and, in particular, upstream of a C2 splitter or downstream of a C2 splitter in the overhead stream. The overhead stream of a demethanizer can contain not only methane but also carbon monoxide and oxygen, provided these are not removed in an upstream trace removal process—e.g., in a crude gas treatment process explained below. As previously described, ensuring liquid reflux (condensation of the C1minus fraction) requires correspondingly low temperatures.Nevertheless, a demethanizer can also be advantageously operated within the scope of the present invention at a pressure slightly above that of vinyl acetate synthesis if a correspondingly low head temperature is set.

[0079] In a particularly advantageous embodiment of the present invention, however, complete or at least predominant removal of carbon monoxide takes place upstream of the demethanizer in a crude gas treatment process (also referred to elsewhere as trace removal) or in any type of process step. Complete removal of methane from the process stream in the demethanizer is not required; rather, depletion is sufficient, i.e., a reduction of the mass of methane contained in the process stream by at least 90%, preferably at least 50%, and particularly preferably at least 25%. The remaining methane content can be separated relatively easily from the product stream of vinyl acetate synthesis after vinyl acetate synthesis.The essential task of the demethanizer is therefore to reduce the methane content upstream of the vinyl acetate synthesis to a level suitable for vinyl acetate synthesis and / or to prevent methane accumulation in any possible cycle. In contrast to the typically desired provision of a pure ethylene product, however, a quantitative or near-quantitative removal of methane from the ethylene feed of the vinyl acetate synthesis is not required. This represents a further particular advantage of the present invention over conventional separation and purification sequences. This particular advantage is only made possible by the upstream carbon monoxide removal (crude gas treatment).

[0080] Aspects of embodiments of the invention, which can be combined in any way with all of the embodiments explained and with one another, therefore comprise in particular that at least methane and / or carbon monoxide are at least partially removed from the process stream by means of a demethanizer and / or that the carbon dioxide removal takes place at a higher pressure level than the ODHE and the vinyl acetate synthesis, and wherein a single-stage or multi-stage compression takes place upstream of the carbon dioxide removal. Such aspects further comprise in particular an additional removal of traces, in particular of carbon monoxide and / or acetylene. The trace removal can be provided in any way. Removal of carbon monoxide and / or acetylene can take place before or after compression and before carbon dioxide removal.In particular, in all embodiments of the process according to the invention, the outlet stream from an ODHE reactor (moist process gas, i.e., the first product mixture) can contain more than 0.40 mol%, in particular more than 0.6 mol%, or more than 1.5 mol% oxygen. After removal of carbon monoxide, the oxygen content can be, in particular, more than 0.01 mol%, more than 0.05 mol%, or more than 0.20 mol%, but in particular always less than 0.4 mol%. The oxidative dehydrogenation can, in particular, be operated such that ethylene and acetic acid are produced in the first product mixture in a ratio of between 1:1 and 10:1, in particular in a ratio of 2:1 to 5:1, and further in particular in a ratio of 2.5:1 to 4:1.

[0081] In a group of embodiments which has already been mentioned above and will now be explained further, the present invention therefore addresses the problem that the product stream of the ODHE, as mentioned above, contains, in addition to ethylene and components such as ethane and carbon dioxide, in particular also carbon monoxide and acetylene (typically in a content of less than 300 to 400 vppm).

[0082] This particularly concerns a gas phase of the product stream of the ODHE, i.e. the first product mixture, after condensation.

[0083] As mentioned, acetylene and carbon monoxide, in particular, must be removed as completely as possible from the vinyl acetate synthesis feedstream, as both are potential catalyst poisons for vinyl acetate synthesis. Existing approaches do not provide an advantageous solution for removing these traces within the framework of an integrated process. The present invention therefore discloses, in embodiments, an optimized solution for trace removal (in particular of acetylene and / or carbon monoxide) in an integrated arrangement of ODHE and vinyl acetate synthesis. In a first embodiment (with a "raw gas treatment," see above), the invention cleverly utilizes the following facts: 1. Oxidative removal of acetylene and possibly carbon monoxide in the gas phase of the ODHE outlet stream is known. 2. The ODHE requires a residual oxygen content at the reactor outlet. The gas phase of the ODHE outlet stream therefore contains a certain amount of oxygen. 3. At the same time, oxygen is added for vinyl acetate synthesis, as described above.

[0084] A joint catalytic conversion of oxygen and acetylene in the gas phase of an outlet stream from an ODHE over suitable catalysts in such a crude gas treatment is described, as previously explained, for example, in WO 2020 / 187572 A1 and WO 2018 / 153831 A1. However, the aim here is to remove both oxygen and acetylene almost quantitatively in order to achieve the desired ethylene quality in further product purification, particularly by fractionation, without additional measures, and to avoid the accumulation of oxygen in certain fractions, particularly in a C1-minus fraction. Carbon monoxide can also be at least partially converted in this process.

[0085] If necessary, in an integration of an ODHE and a vinyl acetate synthesis in a non-inventive embodiment, complete oxygen removal may not be provided before the product mixture of the ODHE (previously also referred to as the "first product mixture") is fed to the vinyl acetate synthesis as a source of ethylene and acetic acid. Remaining oxygen can then be transferred to the vinyl acetate synthesis, where it serves as a reactant. Thus, an increased oxygen content can initially be permitted at the ODHE outlet, which is particularly advantageous for the operation of the ODHE, which requires a minimum oxygen content in the outlet stream.

[0086] An increased oxygen content can, in particular, achieve greater tolerance of the ODHE to any operating fluctuations and an overall longer catalyst service life. If required, additional oxygen and / or hydrogen can also be fed in before or during the raw gas treatment (cf. WO 2020 / 187572 A1). A particular advantage here is that the oxygen content at the inlet of the raw gas treatment also represents an additional degree of freedom. In addition to the oxygen from the outlet of the ODHE, additional oxygen can be fed in as needed before the raw gas treatment, thus achieving optimal performance of this raw gas treatment for acetylene and / or carbon monoxide removal. Accordingly, the further feed of oxygen into the vinyl acetate synthesis feed can be reduced. In principle, catalysts known to those skilled in the art can be used in the raw gas treatment.

[0087] In particular, the catalysts described in WO 2020 / 187572 A1 and WO 2018 / 153831 A1 are used. Therefore, reference is made here to these two documents and the further explanations contained therein. In particular, catalysts containing copper oxide or catalysts containing at least one of the elements copper, manganese, zinc, nickel, platinum, palladium, rhodium, and / or ruthenium can be used in the raw gas treatment. According to the invention, such a raw gas treatment can be arranged before or after compression of the gas phase of the ODHE outlet stream, or at a suitable pressure level between two compression stages. In other words, the component mixture previously referred to as the "first product mixture" is fed to the raw gas treatment.

[0088] Ethane and possibly methane contained in the gas phase of the ODHE can also be fed into the vinyl acetate synthesis without separation, where they serve as an inert or diluent medium. In some embodiments, further process steps can then be included, which, as explained below, in addition to carbon dioxide removal, as previously discussed in detail, can include, in a suitable configuration, in particular, drying, an optional demethanizer, and / or a C2 splitter.

[0089] Unconverted ethylene can then be fully or partially recycled for vinyl acetate synthesis. In addition to ethylene, this residual gas stream may also contain other components, particularly carbon dioxide, ethane, and / or methane. If the raw gas treatment does not achieve sufficient carbon monoxide removal or is operated in such a way that only acetylene is adequately removed, any remaining carbon monoxide in the process stream can be removed after the raw gas treatment in a demethanizer, if required, which also functions to at least partially remove methane. If the residual gas stream from the vinyl acetate synthesis contains no proportions of acetylene and / or carbon monoxide, the recycling described above can be carried out without involving the raw gas treatment.

[0090] However, if the residual gas stream from the vinyl acetate synthesis also contains proportions of, in particular, acetylene and / or possibly carbon monoxide, in one embodiment of the present invention the raw gas treatment can also advantageously be included in the recycling process described above. For this purpose, the residual gas stream from the vinyl acetate synthesis is at least partially fed into the gas phase of the ODHE outlet stream. In this way, the residual gas stream from a vinyl acetate synthesis will then also be subjected to a common raw gas treatment after separation of condensable components. Thus, no additional purification stages are required in the residual gas stream from the vinyl acetate synthesis. In these cases too, the raw gas treatment can be arranged according to the invention before or after compression of the gas phase of the ODHE outlet stream, or even at a suitable pressure level between two compressor stages.At least a partial feed-in of the residual gas stream from the vinyl acetate synthesis takes place at a suitable point upstream of the raw gas treatment.

[0091] In a further embodiment ("tailend hydrogenation"), the invention cleverly utilizes the following facts: 1. The removal of acetylene from ethylene-rich process streams via a so-called tail-end hydrogenation is known. 2. Carbon monoxide can be removed in a demethanizer via the C1-minus fraction. 3. Oxygen removal is also possible via the C1-minus fraction in a demethanizer. 4. Alternatively, a standalone oxidative conversion of CO with oxygen is also known.

[0092] First, the gas phase of the outlet stream of an ODHE and the residual gas stream from a vinyl acetate synthesis are at least partially combined. The combined gas mixture then undergoes suitable process steps, which—similar to those already described for raw gas treatment and explained in detail below—can, in a suitable arrangement, include, in particular, carbon dioxide removal, drying, a demethanizer, and / or a C2 splitter. The demethanizer, in particular, serves to remove carbon monoxide contained in the combined gas mixture. At the same time, any existing proportions of methane and / or oxygen are removed. In this embodiment, the removal of carbon monoxide and carbon dioxide is advantageous, since these two compounds have a negative influence on the activity and / or selectivity in the subsequent tail-end hydrogenation.According to the invention, the removal of acetylene then takes place in a downstream tail-end hydrogenation, which can alternatively be located either upstream or downstream of a C2 splitter. In this way, traces of carbon monoxide and / or acetylene can also be removed in an optimized process chain, and no additional purification steps in the residual gas stream of the VAM synthesis are necessary for this task(s). In principle, catalysts known to those skilled in the art can be used in the tail-end hydrogenation. In particular, catalysts containing at least one of the elements Ni, Pd, Rh, Ir, Ru, Pt, Ce, Ag, and Au can be used.

[0093] A plant for producing vinyl acetate is also the subject of the present invention. For the features of such a plant, reference is expressly made to the corresponding independent patent claim.

[0094] For features and advantages of the system proposed according to the invention and advantageous embodiments thereof, reference is expressly made to the above statements regarding the method according to the invention and advantageous embodiments thereof. In particular, the system proposed according to the invention and corresponding embodiments are designed to carry out corresponding method variants. Examples of implementation

[0095] The invention is further explained below with reference to examples which correspond to embodiments of the invention and the associated figures.

[0096] The Figures 1 to 4 illustrate methods and systems, based on which features of embodiments according to the invention are explained, in the form of schematic process diagrams, wherein Figure 2 refers to a variant not according to the invention.

[0097] If reference is made below to aspects of a process, these explanations apply equally to corresponding systems and their configurations. The same applies to process steps and system components. Process steps and system components with the same or comparable function and / or technical implementation are indicated with identical reference symbols.

[0098] The Figure 1The process illustrated is designated overall by 100. In the process 100, the required reactants ethane C 2 H 6 and oxygen O 2 are fed to an ODHE (previously designated as one or more first process steps or process components 10). Depending on the ethane source and any upstream purification steps, the ethane stream C 2 H 6 can also contain certain proportions of, for example, methane and / or higher hydrocarbons. In addition, if required, steam H 2 O can be fed in as a diluent. The water required for this can in particular also originate at least partially from the raffinate water phase of an optional acetic acid purification or condensate separation 50, as illustrated by a dashed arrow.

[0099] In the ODHE, i.e. in the one or more first process steps or process components 10, a product mixture is formed which was previously referred to as the first product mixture and is indicated here by 11. After cooling and condensation (not shown), a phase separation or separation 40 of a condensate fraction 41, i.e. an aqueous phase which may contain acetic acid, takes place. This can be fed to the aforementioned acetic acid purification or condensate separation 50. The remaining gas phase, which essentially contains unreacted ethane as well as ethylene and carbon dioxide as well as certain proportions of carbon monoxide and possibly other trace compounds, previously also referred to as the first subsequent mixture, is then compressed to a required pressure level in a compression stage 45 and fed to a carbon dioxide removal stage, which here is part of one or more process steps orcorresponding plant components, which were previously referred to as third process steps or plant components 30.

[0100] A recycle stream 22 from a vinyl acetate synthesis, which may be part of one or more process steps or corresponding plant components, previously referred to as second process steps or plant components 20, is fed in, followed by a scrubbing stage 60 corresponding to the pressure level before compression 45 or before a corresponding compressor stage. The recycle stream 22 was previously also referred to as the second downstream mixture.

[0101] According to the embodiment illustrated here, both the gaseous portion of the product of the ODHE (first subsequent mixture 12) and the gaseous residual stream from the vinyl acetate synthesis (second subsequent mixture 22) are subjected to joint carbon dioxide removal in the third process step(s) or steps.

[0102] Plant components 30 are subjected to this process. A material stream fed therein and resulting from the combination of the first and second downstream mixtures (12 and 22) was previously also referred to as the third downstream mixture 31. Carbon dioxide removal comprises, in particular, an absorptive scrub. A carbon dioxide fraction 33 obtained during the regeneration of the loaded absorbent (not explicitly shown) can, if desired, be partially fed to the vinyl acetate synthesis as a diluent in an amount that is tailored to requirements and can be easily adjusted at any time in the form of a material stream 34. Depending on the requirements, carbon dioxide removal can also comprise an optional caustic scrub (not explicitly shown), which serves to further reduce the carbon dioxide content in the remaining gas stream or fourth downstream mixture 32 with a carbon dioxide content already reduced in the absorptive scrub.

[0103] After drying 80, this material stream 32, previously also referred to as the fourth subsequent mixture, is fed to further distillation process steps and a further separation. These distillation process steps include, in particular, a C2 splitter or C2 separation 90, which separates the process stream, in particular, into a fraction at least enriched in ethane (abbreviated to "ethane fraction") C2H6 and a fraction at least enriched in ethylene (abbreviated to "ethylene fraction") C2H4. Furthermore, an optional demethanizer 85 can also be included in the process arrangement. This optional demethanizer 85 serves to remove light components as a C1minus fraction, which can particularly contain the components methane, carbon monoxide, and oxygen. The optional demethanizer 85 can optionally be configured as in Figure 1shown upstream of the C2 splitter 90, or downstream of a corresponding C2 splitter in the ethylene-enriched fraction or ethylene fraction C2H4. The fraction or ethane fraction C2H6 at least enriched in ethane is in turn fed to the ODHE or to the one or more first process steps 10 as a feed stream. The fraction or ethylene fraction C2H4 at least enriched in ethylene is fed to the vinyl acetate synthesis or to the one or more second process steps 20 as a feed stream. Optionally, a partial stream of this C2H4 fraction can also be branched off and made available as a reactant stream for other processes (not explicitly shown).

[0104] Further feed streams of the vinyl acetate synthesis or the one or more second process steps 20 include, in particular, a supply of oxygen O 2 , a provision of acetic acid, in particular from the aforementioned acetic acid purification or condensate separation 50, as well as the already mentioned demand-based provision of carbon dioxide from the carbon dioxide removal 30 or the one or more third process steps. In addition, an acetic acid fraction from a vinyl acetate processing 70, which may in particular include distillation processes, can also be recycled in the form of a material stream 73, and optionally also from an additional external source, such as designated by C 2 H 4 O 2 .

[0105] The outlet stream from the vinyl acetate synthesis or the one or more second process steps 20 is then subjected to the previously described scrubbing 60, which, on the one hand, generates a gas stream which, as described, is fed to the compression 45 as a second subsequent mixture 22 and which, in particular, contains unreacted ethylene and carbon dioxide. Additional carbon dioxide is formed as a by-product of the vinyl acetate synthesis. Other volatile constituents may also be present, e.g., oxygen or constituents from the ethylene-enriched fraction or ethylene fraction C2H4 from the C2 splitter, in particular ethane. An acetic acid stream is also fed to the scrubbing 60 as a scrubbing agent, which can originate either from the acetic acid purification or condensate separation 50 and / or the previously mentioned, in particular distillative, vinyl acetate purification 70 and / or from an additional external source.This scrubbing agent is then used to remove the reaction product vinyl acetate from the (second) product mixture of the vinyl acetate synthesis or of the one or more second process steps 20 and feed it to the aforementioned, particularly distillative, vinyl acetate purification 70. In process step 70, the desired end product vinyl acetate is then obtained in the form of a vinyl acetate fraction 71 in the required purity. A by-product fraction 72 is also obtained, which contains, in particular, water, but also other by-products of the vinyl acetate synthesis.

[0106] The process 100 may also include, if required, further optional purification steps to remove trace compounds and optional purge streams to prevent the accumulation of undesirable trace compounds in recycle streams. These are described in Figure 1 not explicitly shown. It is referred to the Figures 3 and 4 referred to.

[0107] In Figure 2Another process or system is illustrated in the form of a schematic flow chart and is designated as 200. The explanations for Figure 1 Deviations and additions are explained below.

[0108] A gas phase remaining in the vinyl acetate separation 60, which is also designated 22 here, is first subjected to further compression 45a and then fed to carbon dioxide removal or to corresponding process steps or plant components 30. As before, the carbon dioxide removal comprises, in particular, an absorptive scrubbing step. The carbon dioxide stream 33 obtained in the regeneration of the loaded absorbent (not explicitly shown) can, as described above—if desired—be partially fed to the vinyl acetate synthesis or to the process step(s) or plant components 20 in the form of a material stream 34 as a diluent in an amount that is appropriate to requirements and can be easily adjusted at any time.Depending on requirements, carbon dioxide removal may also include an optional caustic scrub (not explicitly shown), which serves to further reduce the carbon dioxide content in the gas stream, which has already been reduced in the absorptive scrub. After drying 80, this stream is fed to further distillation process steps and further separation. These distillation process steps include, in particular, a C2 splitter 90 and an optional demethanizer 85, as already described in . Figure 1 executed.

[0109] In contrast to the Figure 1In the embodiment shown, the first product mixture 11 or a corresponding subsequent mixture 22 is not combined with the second product mixture 21 or the corresponding subsequent mixture 22 before both are fed to the process step(s) or plant component 30, i.e., the carbon dioxide removal. Instead, a subsequent mixture 12a is fed after compression 45 into a trace component removal 210, which may in particular comprise acetylene hydrogenation, carbon monoxide elimination, and / or oxygen removal, and into which a material stream 211, for example comprising additional hydrogen and / or oxygen, can be fed. A subsequent mixture formed here, designated 31, is fed to the process step(s) or plant component 20, i.e., the vinyl acetate synthesis, and a product mixture formed here is treated as explained.

[0110] In Figure 3Another process or system is illustrated in the form of a schematic flow chart and is designated as 300. The explanations to the Figures 1 and 2 and the procedure or Annex 100 or 200. Deviations and additions are explained below.

[0111] The further compression 45a from Figure 2 is not applicable here, and comparable with Figure 2 the first and second subsequent mixtures 12, 22 are combined before or in the compression 45. The formation of a third subsequent mixture 31 also includes the Figure 2 This can be done in particular as described in Figure 3shown schematically and, as previously explained, implemented as a crude gas treatment. In this way, the carbon monoxide and / or acetylene contents can be reduced to a level that is non-critical for the vinyl acetate synthesis in the process step(s) or plant components 20. A partial stream 31a, shown in dashed lines, can be branched off upstream of the process step(s) or plant components 30 and fed directly to the vinyl acetate synthesis, and the ethane and carbon dioxide contained therein serve as the desired and, in practice, necessary diluent. The further fractionation essentially corresponds to the process control according to Figure 2However, due to the positioning of trace gas removal 210, a significant reduction in the oxygen content in the fourth downstream mixture 32 can now be achieved. This can, in particular, prevent excessive oxygen enrichment in the overhead stream of the optional demethanizer 85 and the potential formation of a dangerous explosive atmosphere in this area.

[0112] In Figure 4 Another process or system is illustrated in the form of a schematic flow chart and is designated as 400. The explanations to the Figures 1 to 3 and the procedure or Annex 100 to 300. Deviations and additions are explained below.

[0113] The raw gas removal 210 from Figure 3is omitted. Accordingly, routing a partial stream 31a upstream of the carbon dioxide removal or the process steps or plant components 30 directly to the vinyl acetate synthesis or the process steps or plant components 20 is not technically feasible due to the expected carbon monoxide and acetylene contents at this point. The removal of carbon monoxide and traces of oxygen then takes place by means of the demethanizer 85, which must therefore necessarily be provided in this embodiment of the invention. Due to the already mentioned possible formation of a dangerous explosive atmosphere in the region of the overhead stream of the demethanizer 85, special additional aspects must be observed in the technical design in this area in accordance with the relevant regulations and procedures known to those skilled in the art within the framework of technical explosion protection.

[0114] In this embodiment of the invention, the feed stream of the C2 splitter 90 is then subjected to a tailend hydrogenation 410, which selectively hydrogenates acetylene to ethylene with the addition of the required hydrogen. Both the demethanizer 85 and the tailend hydrogenation 410 can be operated independently of one another, optionally as in Figure 4 shown upstream of the 90 or downstream of the C2 splitter 90 in the ethylene-enriched fraction C 2 H 4 . However, in any case, the demethanizer 85 must be arranged upstream of the tailend hydrogenation 410, since carbon monoxide and oxygen each have a negative influence in the tailend hydrogenation 410.

Claims

1. Process for producing vinyl acetate, in which in one or more first process steps (10), ethane and oxygen are subjected to oxidative catalytic dehydrogenation to obtain a first product mixture (11) containing ethane, ethylene, water, acetic acid and carbon dioxide, and in which in one or more second process steps (20), ethylene and acetic acid are subjected to catalytic vinyl acetate synthesis to obtain a gaseous second product mixture (21) containing ethylene, vinyl acetate and carbon dioxide, at least a portion of the ethylene and at least a portion of the acetic acid, which are subjected to the catalytic conversion in the one or more second process steps (20), being formed by at least a portion of the ethylene and at least a portion of the acetic acid from the first product mixture (11), characterized in that - using at least a portion of the first product mixture (11), a first resultant mixture (12) containing ethane, ethylene and carbon dioxide is formed, the formation of the first resultant mixture (12) comprising an at least partial removal of oxygen, carbon monoxide and / or acetylene, and further comprising subjecting at least a portion of the first product mixture (11) to condensative separation (40) of water and acetic acid to obtain the first resultant mixture (12) and a condensate fraction (41) containing water and acetic acid, and at least a portion of the acetic acid, which is subjected to the catalytic vinyl acetate synthesis in the one or more second process steps (20), being formed by at least a portion of the acetic acid from the condensate fraction (41), - in that, using at least a portion of the second product mixture (21), a second resultant mixture (22) containing ethylene and carbon dioxide is formed, the formation of the second resultant mixture (22) comprising subjecting at least a portion of the second product mixture (21) to vinyl acetate separation (60) to obtain the second resultant mixture (22) and a precursor fraction (61) containing vinyl acetate, - in that, by combining at least a predominant portion of both the first resultant mixture (12) and the second resultant mixture (22), a third resultant mixture (31) containing ethane, ethylene and carbon dioxide is formed, - in that at least a portion of the third resultant mixture (31) is subjected to one or more third process steps (30), the one or more third process steps (30) comprising carbon dioxide removal, a carbon dioxide fraction (33) and a fourth resultant mixture (32) containing ethane and ethylene being formed in the one or more third process steps (30), and at least a portion of the fourth resultant mixture (32) being subjected to a separation (85, 90) in which an ethane fraction and an ethylene fraction are formed, - in that at least a portion of the ethylene, which is subjected to the catalytic vinyl acetate synthesis in the one or more second process steps (20), is formed by at least a portion of the ethylene from the ethylene fraction, and / or at least a portion of the ethane, which is subjected to the oxidative catalytic dehydrogenation in the one or more first process steps (20), is formed by at least a portion of the ethane from the ethane fraction, and - in that at least a portion of the fourth resultant mixture and / or at least a portion of the ethylene fraction is subjected to demethanization (85).

2. Process according to claim 1, in which the carbon dioxide removal comprises regenerative adsorptive carbon dioxide removal, in which a scrubbing liquid is used which is loaded with carbon dioxide during the regenerative absorptive carbon dioxide removal, and from which the carbon dioxide is stripped to obtain the carbon dioxide fraction (33).

3. Process according to either of the preceding claims, in which at least a portion of the carbon dioxide fraction (33) is passed through the one or more second process steps (20) as a diluent.

4. Process according to any of the preceding claims, in which the formation of the third resultant mixture (31) comprises subjecting at least a portion of the first resultant mixture (12) and at least a portion of the second resultant mixture (22) to a common compression (45).

5. Process according to any of the preceding claims, in which a portion of the acetic acid from the condensate fraction (41) is used as an absorbent in the vinyl acetate separation (60).

6. Process according to any of the preceding claims, in which at least a portion of the precursor fraction (61) is subjected to vinyl acetate purification (70), in which a vinyl acetate fraction (71), a by-product fraction (72) and an acetic acid fraction (73) are formed.

7. Process according to any of the preceding claims, in which the ethylene fraction is formed as an ethylene fraction containing up to 20 mol.% ethane and / or the ethane fraction is formed as an ethane fraction containing up to 20 mol% ethylene.

8. Plant for producing vinyl acetate, comprising one or more first plant units (10) which is or are designed to subject ethane and oxygen to oxidative catalytic conversion to obtain a first product mixture (11) containing ethane, ethylene, water, acetic acid and carbon dioxide, and comprising one or more second plant units (20) which is or are designed to subject ethylene and acetic acid to catalytic vinyl acetate synthesis to obtain a gaseous second product mixture (21) containing ethylene, vinyl acetate and carbon dioxide, the plant being designed to form at least a portion of the ethylene and at least a portion of the acetic acid, which are subjected to the catalytic conversion in the one or more plant components (20), using at least a portion of the ethylene and at least a portion of the acetic acid from the first product mixture (11), characterized in that - the plant is designed to form a first resultant mixture (12) containing ethane, ethylene and carbon dioxide using at least a portion of the first product mixture (11), the formation of the first resultant mixture (12) comprising an at least partial removal of oxygen, carbon monoxide and / or acetylene, and further comprising subjecting at least a portion of the first product mixture (11) to condensative separation (40) of water and acetic acid to obtain the first resultant mixture (12) and a condensate fraction (41) containing water and acetic acid, and at least a portion of the acetic acid, which is subjected to the catalytic vinyl acetate synthesis in the one or more second process steps (20), being formed by at least a portion of the acetic acid from the condensate fraction (41), - in that the plant is designed to form a second resultant mixture (22) containing ethylene and carbon dioxide using at least a portion of the second product mixture (21), the formation of the second resultant mixture (22) comprising subjecting at least a portion of the second product mixture (21) to vinyl acetate separation (61) to obtain the second resultant mixture (22) and a precursor fraction (61) containing vinyl acetate, - in that the plant is designed to form a third resultant mixture (31) containing ethane, ethylene and carbon dioxide by combining at least a predominant portion of the first resultant mixture (12) and of the second resultant mixture (22), - in that the plant has one or more third plant components (30) which is or are designed to subject at least a portion of the third resultant mixture (31) to carbon dioxide removal, and which is or are designed to form a carbon dioxide fraction (33) and a fourth resultant mixture (32) containing ethane and ethylene, at least a portion of the fourth resultant mixture (32) being subjected to a separation (85, 90) in which an ethane fraction and an ethylene fraction are formed, - in that the plant is designed to form at least a portion of the ethylene, which is subjected to the catalytic vinyl acetate synthesis in the one or more second process steps (20), using at least a portion of the ethylene from the ethylene fraction, and / or to form at least a portion of the ethane, which is subjected to the oxidative catalytic dehydrogenation in the one or more first process steps (20), using at least a portion of the ethane from the ethane fraction, and - in that the plant is designed to subject at least a portion of the fourth resultant mixture and / or at least a portion of the ethylene fraction to demethanization (85).