Methods and systems for producing ethylene and acetic acid and methods and systems for producing target compounds using ethylene and acetic acid

Abstract

The invention relates to a process (100) for producing ethylene and acetic acid, in which ethane and oxygen in a feed mixture (1) are subjected to oxidative catalytic dehydrogenation (110) to obtain a product mixture (2) comprising ethylene, acetic acid and other components. The ethylene content of the feed mixture (1) is between 0.25 mol.% and 30 mol.%. At least a portion of the ethylene content of the oxidative catalytic dehydrogenation feed mixture (1) is contained in the product stream (2) and recycled to the oxidative catalytic dehydrogenation (110). The product mixture (2) or a part of the product mixture (2) is subjected to a primary treatment (120 to 170) from which a subsequent mixture (5) is obtained, which is devoid of carbon dioxide and water in comparison to the product mixture (2). The subsequent mixture (5), or a portion of the subsequent mixture (5), is fed as a cryogenic separation feed to cryogenic separation (180, 190) including demethanation (180) and ethane-ethylene separation (190). At least a portion of the cryogenic separation feed is fed as a demethanation feed to the demethanation (180), and in the demethanation (180), the heavy fraction (6) and the light fraction (7) are formed as an overhead fraction, where the heavy fraction (6) or a portion of the heavy fraction (6) is fed to the ethane-ethylene separation (190), and where the light fraction (7) or a portion of the light fraction (7) is recycled to the oxidative dehydrogenation (110). The invention also relates to a system for preparing ethylene and acetic acid, and a method and a system for preparing a target compound by using ethylene and acetic acid.

Description

[0001] The present invention relates to a method and an apparatus for preparing ethylene and acetic acid, and to a method and an apparatus for preparing a target compound using ethylene and acetic acid, as described in the preambles of the corresponding independent patent claims. Background Art

[0002] The oxidative dehydrogenation (ODH) of alkanes having 2 to 4 carbon atoms is known in principle. In the ODH, the above alkanes react with oxygen to form the corresponding olefins and water, among other things. The present invention relates to the oxidative dehydrogenation of ethane to ethylene, also referred to below as ODHE. Therefore, when reference is made below to "oxidative catalytic dehydrogenation", this is to be understood in particular as the oxidative catalytic dehydrogenation of ethane.

[0003] ODHE can have advantages over established processes for producing olefins, such as steam cracking. Due to the exothermic nature of the reactions involved and the virtually irreversible formation of water, there are no thermodynamic equilibrium limitations. ODHE can be carried out at relatively low reaction temperatures. In principle, the catalyst used does not need to be regenerated, as the presence of oxygen enables or causes in-situ regeneration. Finally, compared to steam cracking, less worthless by-products, such as coke, are formed.

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

[0005] US2002 / 082445 A1 discloses a method for oxidizing C2 to C4 alkanes to produce corresponding olefins and corresponding carboxylic acids, the method comprising contacting alkanes, oxygen-containing molecular gas and corresponding olefins and optionally water in an oxidation reaction zone in the presence of at least one catalyst, the catalyst having an activity for oxidizing alkanes to corresponding olefins and carboxylic acids to produce a product stream comprising olefins, carboxylic acids and water. In the method, the molar ratio of olefins produced in the oxidation reaction zone to carboxylic acids is adjusted to or maintained at a predetermined value by controlling one or more factors of the concentration of olefins and optional water in the oxidation reaction zone and the pressure, temperature and residence time of the optional oxidation reaction zone. This oxidation method can be used in an integrated process, for example, for the production of vinyl acetate or ethyl acetate.

[0006] In particular, MoVNb-based catalyst systems have proven promising for ODHE, for example as described in "Oxidative dehydrogenation of ethane and propane: How far from commercial implementation?", Catal. Today, 2007, 127, 113-131 (F. Cavani et al.). Catalyst systems comprising additional Te can also be used. When "MoVNb-based catalyst system" or "MoVTeNb-based catalyst system" is mentioned herein, this means a catalyst system comprising the mentioned elements as mixed oxides, also denoted as MoVNbO x or MoVTeNbO x Te in brackets indicates that Te is optional. The present invention uses such a catalyst system.

[0007] In ODHE, especially when MoVNb(Te)O is used under industrially relevant reaction conditions xWhen using catalysts of the type described, large amounts of acetic acid are formed as a by-product. Therefore, for the economic operation of the plant, the coproduction and further use of ethylene and acetic acid are generally unavoidable and necessary when using catalysts of the type described. In this case, it is generally desirable to preferably form ethylene in technical applications, or it is undesirable to form acetic acid in conventional processes. However, in integrated petrochemical complexes, it is often precisely these two valuable products that are required. There are important technical processes that require ethylene and acetic acid as reactants, as described below. Therefore, it is necessary to find methods for producing ethylene and acetic acid, in particular in the ratios required for the respective processes.

[0008] Against this background, it was an object of the present invention to advantageously configure the production of ethylene and acetic acid using ethane oxidative dehydrogenation and in particular also to improve process products produced from ethylene and acetic acid. Summary of the invention

[0009] The above objects are achieved by a method and an apparatus having the features of the respective independent patent claims. Preferred embodiments of the invention are subject matter of the dependent patent claims and of the following description.

[0010] A process for producing ethylene and acetic acid is proposed, wherein ethane and oxygen in a feed mixture are subjected to oxidative catalytic dehydrogenation using a catalyst comprising at least molybdenum, vanadium and niobium and optionally tellurium as mixed oxides to obtain a product mixture comprising ethylene, acetic acid and other components. For the corresponding catalysts that can be used in the present invention, in particular the catalysts diluted with corresponding diluent materials or on suitable, in particular inert supports, reference is made to the above description. The corresponding catalysts are in particular free of sulfur or sulfur substances or have a content of less than 100 ppm (microweight fraction), in particular less than 10 ppm (weight), more in particular less than 1 ppm (weight) of sulfur or sulfur substances. In the present invention, the feed mixture has an ethylene content of 0.25 mol.% to 30 mol.%, in particular 0.5 mol.% to 25 mol.%, more in particular 1 mol.% to 20 mol.%, wherein the content can generally, regardless of the respective lower limit, be in particular less than 25 mol.%, more in particular less than 20 mol.%, even more in particular less than 15 mol.%.

[0011] As described below, the proposed process is based on the surprising finding that by using appropriate proportions of ethylene in the feed stream for the oxidative catalytic dehydrogenation, the proportion of acetic acid in the product stream can be significantly increased when using appropriate catalysts. In particular, the ratio of ethylene to acetic acid in the product stream can thereby be adjusted in a targeted manner so that it corresponds to the requirements of at least one downstream process or to the average requirements of several downstream processes. In this case, the setting can correspond to the actual requirements to a large extent; minor deviations or fluctuations can be compensated by suitable intermediate storage facilities (tanks), such as are usually present in the corresponding complex, whether for ethylene or for acetic acid.

[0012] In the present invention, at least a portion of the ethylene content of the feed mixture of the oxidative catalytic dehydrogenation is contained in the product stream of the oxidative catalytic dehydrogenation and recycled to the oxidative catalytic dehydrogenation. In this way, the ethylene content can be adjusted as required without using externally supplied ethylene.

[0013] The ethylene content in the feed mixture can be increased or adjusted by making various adjustments to the plant operation, in particular in the form of changing operating parameters and / or removing a partial stream in a separation section of the corresponding plant and adding this partial stream to the feed mixture. In particular, the operating adjustments made are such that only the ethylene content in the feed mixture is significantly increased, while the contents of other components (in particular ethane) remain approximately the same or decrease.

[0014] In the proposed method, the product mixture or a part of the product mixture is subjected to a primary treatment, from which a subsequent mixture is obtained which is deficient in carbon dioxide and water compared to the product mixture.

[0015] The subsequent mixture or a portion of the subsequent mixture is supplied to the cryogenic separation as a cryogenic separation feed, enabling demethanization and in particular ethane-ethylene separation. At least a portion of the cryogenic separation feed is supplied to the demethanization as a demethanization feed, and a heavy fraction and a light fraction are formed in the demethanization, the light fraction being a top fraction. Compared to the subsequent mixture, the heavy fraction is rich in compounds or hydrocarbons with two carbon atoms (C2 compounds, in particular the sum of ethane and ethylene), and lacks components with a boiling point lower than ethylene; whereas, compared to the subsequent mixture, the light fraction lacks compounds with two carbon atoms and is rich in components with a boiling point lower than ethylene. The light fraction may particularly contain a large amount of ethylene.

[0016] The proposed process may comprise feeding the heavy fraction or a portion of the heavy fraction to ethane-ethylene separation. In any case, however, the process involves recycling the light fraction or a portion of the light fraction to the oxidative dehydrogenation.

[0017] In the proposed method, the desired amount of ethylene is discharged together with the so-called C1 fraction (composed of compounds having a boiling point lower than ethylene) via the top stream of the improved demethanization. As an additional advantage, even in the case where the top temperature of this improved demethanization is relatively high, the liquid reflux containing ethylene can be additionally ensured. In addition, in the product stream of the catalytic oxidative dehydrogenation, the proportion of the C1 fraction or compounds having a boiling point lower than ethylene is generally low. In particular, it is expected that no methane will be produced or only a small amount of methane (for example, a certain proportion of methane produced by using ethane in the catalytic oxidative dehydrogenation) will be produced. Therefore, a large amount of carbon monoxide and ethylene (as the main C2 compound) remain in the top stream of the improved demethanization. Then, carbon monoxide is also returned to the catalytic oxidative dehydrogenation and is at least partially converted into carbon dioxide. Since the top mass flow of the corresponding improved demethanization is now significantly increased, a higher oxygen inlet concentration in the feed stream of the improved demethanization is also allowed, and critical enrichment of oxygen in the top stream will not occur. In a corresponding embodiment, the reaching of explosive components (ie, oxygen concentrations above the oxygen limit concentration, SGK) in the top stream of the modified demethanizer can still be effectively prevented by dilution with C2 compounds, in particular ethylene.

[0018] In one embodiment of the invention, a proportion of 1% to 35% of the ethylene (particularly by mass or volume) contained in the product stream of the oxidative catalytic dehydrogenation is recycled to the oxidative catalytic dehydrogenation. In particular, the lower limit of the proportion may also be 1%, 2% or 4% and the upper limit may be 35%, 30%, 20%, 10% and 5%. These values ​​have proven to be particularly advantageous, as shown below.

[0019] The removal of the ethylene stream or of the mixed stream comprising ethane and ethylene for recycling can in principle be carried out at different points in the process ("removal point"). Thus, the embodiments explained below (but not exhaustively) can be used, the process proposed here includes removal at the top of (also including) the improved demethanization.

[0020] In an embodiment of the invention, the recycled ethylene can be recycled to the oxidative catalytic dehydrogenation together with the ethane contained in the product mixture, in particular without being separated from each other. This makes it possible in particular to recycle the corresponding mixed fractions and avoid the need for complete separation.

[0021] Other components of the product mixture of the oxidative catalytic dehydrogenation may particularly include unconverted ethane, particularly including carbon monoxide and carbon dioxide and water with a boiling point lower than that of ethylene. The subsequent mixture is formed by primary treatment using the product mixture or a portion of the product mixture as described above, and the content of carbon dioxide and water is reduced compared to the product mixture. The subsequent mixture comprises at least a portion of ethane, ethylene and a compound with a boiling point lower than that of ethylene from the product mixture.

[0022] The primary treatment may in particular comprise condensation separation, formation of a water-acetic acid fraction, and carbon dioxide removal and drying. In addition, in particular compression and raw gas treatment (as described below) are also part of the primary treatment. An acetic acid fraction of any purity can be obtained from the water-acetic acid fraction, in particular in an acetic acid treatment plant. The corresponding process steps of the primary treatment can be designed in a standard manner and in particular represent the "hot" part of the corresponding separation train.

[0023] One embodiment of the present invention may in particular include a raw gas treatment in the primary treatment, which is particularly represented by the catalytic removal of acetylene, and carbon dioxide removal, particularly in the form of amine washing, and in particular adsorption drying. A portion of the gas mixture obtained from the raw gas treatment can be carried out upstream of the carbon dioxide removal and drying of the primary treatment and recycled to the oxidative catalytic dehydrogenation. In this embodiment, carbon dioxide is still contained in the corresponding gas mixture, and in the oxidative catalytic dehydrogenation, in particular at the catalyst used herein and typical reaction temperatures, carbon dioxide can be considered to be inert to a certain extent. The advantage of this article is that the burden of carbon dioxide removal is particularly reduced because the amount of gas to be treated is less.

[0024] Within the scope of the present invention, different embodiments can be provided for the cryogenic separation comprising demethanization and ethane-ethylene separation as described above, which particularly concern the sequence of these steps.

[0025] In one embodiment, at least a portion of the cryogenic separation feed can be fed to the demethanizer as a demethanizer feed in the form of a material composition that is unchanged compared to the subsequent mixture formed in the primary treatment, but also optionally after hydrogenation or another catalytic reaction, in particular for the removal of acetylene. The demethanizer can be carried out in a conventional manner, but in the proposed process, it is modified or manipulated so that the head fraction or light fraction (the two terms are used herein synonymously) has a certain ethylene content.

[0026] The ethylene content may be in particular (the following figures are all expressed in mole percentage or volume percentage) from 1% to 90%, further in particular from 5% to 75%, for example from 10% to 50%. As a further component, in a list which is not necessarily exhaustive, in particular the carbon monoxide content is up to 75%, in particular up to 50%, more in particular up to 25%, for example up to 10%, but the methane content is little or absent, i.e. the methane content is in particular up to 15%, more in particular up to 10%, even more in particular up to 5%, for example up to 2%. Ethane may also be present, the corresponding content of ethane ranging from 0% to 50%, in particular from 0% to 30%, more in particular from 0% to 20%. It goes without saying that the values ​​mentioned for each content may add up to up to 100%. The oxygen content is in particular below the SLC, in particular below 5%, 2.5%, 1% or 0.5%.

[0027] This top fraction is therefore recycled to the oxidative dehydrogenation in the process. At least ethane can also be recycled to the oxidative dehydrogenation from the demethanized bottom fraction or heavy fraction (the two terms are used herein synonymously). In particular, in this case, a C2 splitter of known type, i.e. at least partial separation of ethane and ethylene, can also be inserted. The ethane-rich fraction obtained herein can then be recycled, in particular, to the oxidative dehydrogenation.

[0028] In an alternative embodiment, the order of demethanization and ethane-ethylene separation is reversed. In this case, at least a portion of the cryogenic separation feed (in particular a cryogenic separation feed whose material composition has not been changed compared to the subsequent mixture formed in the primary treatment) can be supplied to the ethane-ethylene separation as ethane-ethylene separation feed, but can also be supplied to the ethane-ethylene separation optionally after hydrogenation or another catalytic reaction (in particular for removing acetylene). Therein, a heavy fraction and a light fraction can be formed in the ethane-ethylene separation, the heavy fraction being enriched in ethane and lacking in ethylene and components with a boiling point lower than ethylene compared to the subsequent mixture in the primary treatment, and the light fraction being lacking in ethane and enriched in ethylene and components with a boiling point lower than ethylene compared to the subsequent mixture in the primary treatment, wherein the light fraction or a portion of the light fraction is supplied to the demethanization as demethanization feed. The corresponding embodiments enable advantageous effects to be achieved, in particular by adjusting the feed of the corresponding ethane-ethylene separation or adjusting the removal of the component mixture.

[0029] Thus, in a corresponding embodiment, the demethanized top fraction may comprise a portion of the ethylene contained in the subsequent mixture formed in the primary treatment, in particular within the range already mentioned, wherein at least a portion of the top fraction may be recycled to the oxidative catalytic dehydrogenation to provide at least a portion of the ethylene content of the feed mixture.

[0030] Also provide the removal (for example, from the partial bottom stream of demethanization) of the mixed stream comprising ethane and ethylene outside ethane-ethylene separation, and then mix this mixed stream to the ethane stream of common recycling from the ethane-ethylene separation bottom.Alternatively, the mixed stream and / or the recycled ethane stream can be expanded before mixing, for example, heated with the process gas to be cooled.Under such operating mode, changing the ethylene circulation rate advantageously does not need to make any changes to the top and bottom specifications of ethane-ethylene separation.Mainly the change of ethane-ethylene separation load (inlet gas amount) and the moderate change of inlet gas composition.

[0031] In other embodiments, one or more other fractions selected from the top fraction formed in the ethane-ethylene separation and the bottom fraction formed in the ethane-ethylene separation can be at least partially or each of the one or more fractions can be at least partially recycled to the oxidative dehydrogenation. The respective fractions or recycled parts of the respective fractions can be combined with each other in any suitable manner and in any ratio.

[0032] In this case, one or at least one of a plurality of other fractions (for example, the top fraction formed in the demethanization and the bottom fraction formed in the demethanization) is advantageously formed or each is formed into one or more fractions comprising ethane and ethylene. These are mixed fractions produced in the above manner, and other components may also be included, depending on where they are formed, such as oxygen and / or carbon monoxide. If the partial gas mixture is removed from the primary treatment as described above, it may still particularly comprise carbon dioxide, so. However, the corresponding pure fraction (ethane and / or ethylene fraction) may also be recycled in a corresponding manner.

[0033] In particular, it is also possible to withdraw a side stream comprising ethane and ethylene from the ethane-ethylene separation, which side stream is at least partly recycled to the oxydehydrogenation.

[0034] In this case, in an embodiment of the invention, it is also possible to increase the ethylene slip at the bottom of the ethane-ethylene separation by partially reducing the reboiler power. In particular, this makes it possible to achieve a higher desired ethylene content in the reaction feed without further extraction and mixing processes and to save on possible additional heat exchanger passages for heating the ethylene-containing extraction stream.

[0035] A particular variant in this context is when the light gas leak is used in the bottoms of the ethane-ethylene separation upstream of the demethanization, since in this case, in addition to ethylene, the proportion of components with a boiling point lower than ethylene (in particular carbon monoxide and optionally methane) in the feed mixture is at least slightly increased.

[0036] In one embodiment of the invention, in particular, ethylene can be removed at the top of the ethane-ethylene separation or at any point in the optional available open ethylene refrigeration loop (in which the ethane-ethylene separation is integrated). The determination of the sampling point depends on the desired aggregation state and the pressure and temperature level of the ethylene stream. Similarly, at similar pressure and temperature levels, the other reaction feed streams are added as much as possible in a single-phase manner.

[0037] Thus, a portion of the ethylene contained in the product mixture can be transferred to an open refrigerant circuit, wherein at least a portion of the ethylene can be discharged from the open refrigeration circuit and recycled to the oxidative catalytic dehydrogenation to provide at least a portion of the ethylene content of the feed mixture.

[0038] The recycling alternative explained above can be carried out in particular in connection with the raw gas treatment already mentioned as part of the primary treatment, that is to say, the mentioned primary treatment step can in particular comprise at least a partial reaction of the acetylene and oxygen contained in the product mixture. However, other embodiments of the present invention can also comprise a hydrogenation downstream of the demethanization and upstream of the ethane-ethylene separation and downstream of the ethane-ethylene separation. In the latter case, i.e. in the case of hydrogenation, in particular in the case of the so-called tail-end hydrogenation, unlike the raw gas treatment, oxygen is generally not removed, so that oxygen can enter the recycled gas mixture, in particular in the light gas fraction of the demethanization. In all embodiments, it is advantageous to carry out this recycling without recirculating any acetylene. Those skilled in the art select the corresponding alternative in an appropriate manner.

[0039] In an embodiment of the invention, at least one material stream that is recycled to the oxidative catalytic dehydrogenation to provide at least a portion of the ethylene content of the feed mixture, or any other material stream, may be treated, in particular to separate hydrocarbons having three or more carbon atoms, so as to thereby separate heavier components from the reaction feed of the catalytic oxidative dehydrogenation and from the recycle stream. If desired, this treatment may also be carried out in particular with the fresh feed.

[0040] In the case of ethylene feed, the formation of carbon monoxide and carbon dioxide is expected to increase in the oxidative catalytic dehydrogenation. Here, the existing product purification of the corresponding plant for the oxidative catalytic dehydrogenation can be advantageously used, which can include demethanization and carbon dioxide removal in particular.

[0041] In addition, other purification steps may also be used in the method, such as trace removal or raw gas treatment and / or selective hydrogenation of hydrocarbons with two carbon atoms. The acetic acid fraction may be prepared by known methods and, if desired, may be obtained in a highly concentrated aqueous solution or in pure form. Thereby providing acetic acid for the corresponding downstream processes. An ethylene fraction may also be provided as required, which is at least partially used in these downstream processes. However, depending on the availability on site, additional ethylene or ethylene-containing streams or ethylene-rich streams from other sources (e.g., steam crackers) may also be used.

[0042] The invention also relates to a method for preparing a target compound using ethylene and acetic acid, wherein at least a portion of the ethylene and acetic acid is provided using a method according to any of the preceding claims. In this case, reference is made to the above description with regard to advantages and embodiments of providing ethylene and acetic acid.

[0043] By using embodiments of the present invention, particularly advantageous ethylene to acetic acid ratios of less than 5:1, less than 3:1, less than 2:1, or less than 1.5:1 (not accounting for recycled ethylene) can be achieved for downstream processes. In particular, the ratio is at least 0.8:1 to 1:1.

[0044] The target compound of the corresponding process can be in particular vinyl acetate monomer, ethyl acetate, ethylene-vinyl acetate or polyethylene terephthalate. As described below, in such processes, the ratio of ethylene to acetic acid is particularly desired, and embodiments of the present invention can advantageously provide this ratio.

[0045] The invention also relates to a device designed to carry out the method as described above. Therefore, explicit reference is also made to the above description regarding the corresponding device.

[0046] Embodiments of the present invention will be described below with particular reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A method according to an embodiment of the present invention is shown in the form of a schematic flow chart. DETAILED DESCRIPTION

[0048] If various aspects of the method are mentioned below, their explanation also applies to the corresponding device and its implementation. This also applies to method steps and device components. Method steps and device components with the same or similar functions and / or technical implementations are represented by the same reference numerals.

[0049] Figure 1The method shown in corresponds to an embodiment of the present invention and is marked as a whole with 100. In the method 100, the required reactants ethane C2H6 and oxygen O2 (here marked as a whole with 1) are supplied to the catalytic oxidative dehydrogenation 110. The circulation flow explained below can also be used to provide the corresponding material flow. In addition, if necessary, water vapor H2O can be supplied to the catalytic oxidative dehydrogenation 110 as a diluent. The water required for this can be at least partially from the raffinate water phase of the acetic acid purification 130 explained below, as shown by the dotted arrow.

[0050] In the catalytic oxidative dehydrogenation 110, a product mixture 2 is formed, which is subjected to condensation separation 120. In the condensation separation 120, a condensed fraction 3 is formed, which mainly contains water and acetic acid. The condensed fraction 3 is subjected to the above-mentioned acetic acid treatment 130, wherein a water fraction H2O mainly containing water and an acetic acid fraction AcOH mainly containing acetic acid are formed.

[0051] Downstream of the condensation separation 120, the product mixture 2 (now indicated by 4) is present in the form of lacking water and acetic acid. The product mixture 2 is then subjected to compression 140, optional feed gas treatment 150, carbon dioxide removal 160 and drying 170 in sequence. Steps 120 to 170 are referred to as "primary treatment" in the previous text. Downstream there is a component mixture marked as 5, which is also referred to as a subsequent mixture in the previous text. The subsequent mixture contains at least a portion of ethane, ethylene and compounds with a boiling point lower than ethylene from the product mixture 4. Compared with the product mixture 4, the subsequent mixture contains very small amounts of carbon dioxide and water, or is substantially free of these components.

[0052] Then, using at least a portion of the subsequent mixture 5 formed in the primary treatment, another component mixture is formed in the demethanizer 180, which is deficient in compounds having a boiling point lower than that of ethylene and is enriched in ethane and ethylene compared to the subsequent mixture 5. In this case, in the demethanizer 180, the top fraction 7 and the other component mixture are formed as the bottom fraction 6, which is specifically taken from the bottom of the column used in the demethanizer 180.

[0053] Finally, at least a portion of the bottom fraction 6 in an ethane-ethylene separation 190 (also referred to as a C2 splitter) is used to form an ethylene fraction C2H4 that is enriched in ethylene and deficient in ethane compared to the bottom fraction 6, and an ethane fraction C2H6 that is enriched in ethane and deficient in ethylene compared to the bottom fraction 6 of the demethanizer 180, as is typically seen in ethane-ethylene separation.

[0054] A1, A2, B, C, D and E show the circulation flow according to the embodiment of the present invention. Each circulation flow can (optionally deviate from Figure 1) alone or combined in any way with other streams.

[0055] In this case, A1 represents the ethane fraction from ethane-ethylene separation, which is returned to the oxidative catalytic dehydrogenation 110 for further reaction of the raw ethane. As shown in A2, this can be combined with the material stream 9 extracted via an intermediate withdrawal outlet of the ethane-ethylene separation 190, such as a distillation column used in the ethane-ethylene separation 190, the material stream 9 having a certain ethylene content, which can be adjusted in particular via the withdrawal point, and A2 can be returned to the oxidative catalytic dehydrogenation 110 together with this material stream 9. In general, whenever a combination of different material streams is described before recycling to the oxidative catalytic dehydrogenation 110, separate recycling is also a possible alternative.

[0056] Material stream B represents a portion of the ethylene fraction from ethane-ethylene separation 190, which can be recycled to oxidative catalytic dehydrogenation 110, in particular as an alternative or in addition to the embodiment marked A2. In this case, it can be combined with the top fraction 7 shown as C from demethanizer 180. In this case, in particular compared to conventional demethanizer, demethanizer 180 can be operated in such a way that, in addition to components with a boiling point lower than ethylene, a portion of the ethylene also enters the top fraction 7. However, as shown in D, a portion of the bottom fraction 9 comprising ethane and ethylene from demethanizer 8 can also be recycled. As in the other cases, any combination of the corresponding material streams can be performed before recycling.

[0057] Material stream E represents a portion of the gas mixture obtained from the raw gas treatment 150 , which is discharged from the primary treatments 120 to 170 upstream of the carbon dioxide removal 160 and the drying 170 and is returned to the oxidative catalytic dehydrogenation 110 .

[0058] Before explaining the specific aspects of the present invention and its embodiments, the principles and other aspects of the present invention are explained again below for classification.

[0059] As mentioned above, especially when using MoVNbTeO under industrially relevant reaction conditions x In the case of oxidative catalytic dehydrogenation with the catalyst, acetic acid is produced as a co-product in addition to ethylene. In this case, under industrially relevant conditions, the ratio of ethylene to acetic acid usually reaches about 5 to 10 mol / mol. However, the demand for acetic acid is often limited to specific downstream products (e.g. vinyl acetate monomer). Acetic acid can be separated off as a component of the aqueous condensate phase (typical acetic acid content in the condensate: 1 wt.% to 30 wt.%, 3 wt.% to 25 wt.% or 5 wt.% to 20 wt.%) and can usually be processed into separate valuable products by appropriate treatment.

[0060] The use of MoVNbTeO can be tuned in particular by adjusting the partial pressure of water in the reactants x The ratio of ethylene to acetic acid in the product stream of the oxidative catalytic dehydrogenation of the catalyst is adjusted, in particular, by adjusting the water partial pressure, space velocity and operating pressure in the reactor outlet stream, but can only be adjusted within certain limits (for example, see WO 2018 / 115416 A1, EP 3519377 B1 and WO2019 / 243480 A1). However, the present invention allows other conditions to be freely adjusted within the specified range. In order to ensure stable catalyst performance, a minimum water content is advantageous (for example, see WO 2018 / 115418 A1, EP 3558910 B1 and WO2019 / 243480 A1). With the help of a specially designed reactor design and combined with optimized operating conditions (such as space velocity) and / or linear velocity, an increase in ethylene production can be achieved (see US10,017,432 B2 and US 9,963,412 B2). However, even so, the acetic acid content in the product is still too high to be discarded. Therefore, the use of acetic acid as a product is indispensable, and a large amount of acetic acid needs to be provided according to demand.

[0061] Due to the co-production, the use of oxidative catalytic dehydrogenation is mainly limited to small and medium-sized plants and requires appropriate utilization of the produced acetic acid. On the other hand, in contrast to steam crackers, oxidative catalytic dehydrogenation produces (essentially) only ethylene and acetic acid as products. Therefore, appropriate utilization of other product fractions in the fractionation section and the corresponding equipment is no longer necessary. The present invention now specifically utilizes the formation of acetic acid during oxidative catalytic dehydrogenation and advantageously provides two co-products.

[0062] Apparatus for oxidative catalytic dehydrogenation generally comprises Figure 1 The basic process steps already described in , which can be arranged in a suitable manner. In addition to the oxidative catalytic dehydrogenation, condensation separation 120, acetic acid treatment 130, compression 140 and carbon dioxide removal 160 (in particular amine washing and possible alkali washing for fine cleaning) as well as ethane-ethylene separation 190 can also be carried out. In addition, if necessary, other process steps can be used at suitable locations, such as demethanization 180, as well as trace removal or feed gas treatment (hydrogen and oxygen can also be added, see, for example WO 2020 / 187572 A1), and selective hydrogenation of hydrocarbons with two carbon atoms. Separation of hydrocarbons with two and three carbon atoms can also be used, which can generally be arranged upstream of the catalytic oxidative dehydrogenation in order to separate heavier components from the ODHE feed mixture.

[0063] Of particular importance in the context of the present invention is the preparation of acetic acid. As mentioned at the outset, acetic acid is a component of the condensed phase. According to the prior art, it is very advantageous to extract acetic acid from the condensed phase. Suitable extractants are organic solvents, in particular ether solvents (e.g. methyl tert-butyl ether) or ester solvents (e.g. ethyl acetate). The acetic acid is then separated from the organic extract phase obtained in this way by distillation and the extractant is recovered for further extraction cycles. If necessary, the acetic acid obtained in this way can be subjected to a fine distillation again until the desired purity (e.g. glacial acetic acid) is reached. The aqueous raffinate phase produced during the extraction step can also be subjected to a distillation treatment in order to recover the extractant contained in the raffinate phase or to obtain wastewater that is as little polluted as possible. By means of the acetic acid treatment, acetic acid can be obtained in particular with a purity of greater than 95%, greater than 98% or greater than 99% and / or with a purity of at least 99.8% of the quality of glacial acetic acid and can be used in subsequent processes.

[0064] The preparation of acetic acid by other processes is basically known and technically mature (C. LeBerre, P. Serp, P. Kalck, GP Torrence, "Acetic acid", in "Ullmann's Encyclopedia of Industrial Chemistry (2014 edition)". In this case, the traditional and particularly important route of the reaction of methanol with carbon monoxide is used. The liquid phase oxidation of butane, naphtha or acetaldehyde, etc. is also known. The cited article also mentions a process for the catalytic oxidation of ethylene, with particular emphasis on the influence of the addition of Pd to the catalyst.

[0065] Oxidation processes starting from ethane using suitable mixed metal oxide catalysts (based on Mo, V and / or Nb) have also been developed and commercialized. In this case, special modifiers need to be used. For example, US 5,907,056 proposes AP, B, Hf, Te and As modifiers and assumes that only ethane is used as a raw material for oxidative catalytic dehydrogenation. The examples in this document achieve a maximum ethane yield of about 66% when the ratio of ethylene to acetic acid is between about 1:1 and 5:1. Only entries 7 and 8 in Table 3 of this document achieve a ratio of ethylene to acetic acid of about 1.9:1 and 5:1, respectively, but a P modified catalyst is used. Although US 6,258,992 A discloses a feed stream that may contain olefins (such as ethylene) in addition to alkanes, the catalyst disclosed therein must also contain sulfur substances. The examples in this document are limited to yields less than 20% (starting from pure ethane) and the resulting ethylene to acetic acid ratio is between 1:1 and 1:7. According to other applications, for example according to EP 1,140,355 B1, other promoters are added, in particular the (expensive) noble metal Pd, in order to increase the selectivity relative to acetic acid. However, the examples in this document are limited to paraffins as feed streams for oxidative catalytic dehydrogenation, and in addition to ethane, propane is also studied. US 6,030,920 A also includes the addition of Pd to MoVNbO x The invention relates to a catalyst and is specifically limited to reactions with ethane as feed stream for the corresponding selective oxidation.

[0066] In this case, processes requiring ethylene and acetic acid as reactants require the two reactants to be carried out in a defined ratio. This ratio of ethylene to acetic acid (on a molar basis) is, for example, 3:1 to 1:1 for the production of vinyl acetate monomer, 3:1 to 1:1 for the production of ethyl acetate, and 12:1 to 8:1 for the production of ethylene vinyl acetate. Ethylene vinyl acetate can be obtained by reacting vinyl acetate monomer with ethylene, which indicates that the ratio of ethylene to acetic acid is very high, or this ratio is also determined by the degree of copolymerization of ethylene and vinyl acetate monomers.

[0067] Another process is the preparation of polyethylene terephthalate via terephthalic acid, which requires a ratio of ethylene to acetic acid of 14:1 to 11:1 and acetic acid as solvent. In principle, acetic acid can be recycled in this case, but due to the harsh reaction conditions during the catalytic oxidation of p-xylene (typically at 175° C. to 225° C. and atmospheric oxygen at 15 bara to 30 bara), large solvent losses occur. Up to 0.05 tons of acetic acid are lost for every ton of polyethylene terephthalate produced.

[0068] However, as mentioned above, the conventional catalytic oxidative dehydrogenation of ethane with ethane as starting material can only provide a certain ratio of ethylene and acetic acid, and this ratio can only be influenced to a limited extent by the selection of the process conditions, in particular the water content in the reaction feed, the space velocity and the operating pressure, and, if necessary, a special reactor design. In particular, the high acetic acid content required in the downstream products vinyl acetate monomer or ethyl acetate cannot be achieved in this way. This means that more ethylene must be produced than is actually required, which is not always desirable, in particular if there is no further demand for ethylene at the corresponding location or in the corresponding compound. Alternatively, according to the prior art, acetic acid can be purchased or prepared using other methods, but this requires additional work.

[0069] In principle, it is possible to increase the acetic acid content to a ratio of ethylene to acetic acid significantly less than 5:1 (preferably 3:1 or less). However, this is not possible without significantly increasing the pressure design of the reactor and reducing the plant capacity to meet the increased safety requirements due to the increased oxygen demand and the significantly increased pressure. This means that a molar product ratio of ethylene to acetic acid significantly less than 5:1 cannot be achieved with a reactor design that can easily adjust ethylene to acetic acid in the range of about 5:1 to 10:1. Overall, this results in significantly higher complexity and thus significantly higher costs, making the economic feasibility questionable.

[0070] Thus, the present invention discloses a solution that allows the ethylene to acetic acid ratio to be adjusted flexibly as required, in particular in response to an increased demand for acetic acid, with a single technically proven reactor design. Embodiments of the present invention can be used in addition to known measures, such as varying the water content in the reaction feed of the oxidative catalytic dehydrogenation, the space velocity, the linear velocity or the operating pressure, and in addition to these measures, a simple adjustment to different desired ethylene to acetic acid ratios is also possible, in particular by adjusting the ethylene recycle to adapt it to otherwise identical plant requirements and operating conditions.

[0071] The percentage of recycled ethylene ("R_C2H4") to the total amount of recycled hydrocarbons having two carbon atoms ("R_G"), i.e. the sum of ethane and ethylene (in mol or kmol), hereinafter also referred to as PRE value, can be expressed as follows:

[0072] PRE=n(R_C2H4) / n(R_G)×100%.

[0073] Theoretical assumption: all ethane in the product mixture that is not converted in the oxidative catalytic dehydrogenation ("P_C2H6") is recycled to the oxidative catalytic dehydrogenation (technical losses, e.g. residues in purge streams or in other process streams are negligible) and that the circulating liquid does not contain any other components, such as small amounts of higher hydrocarbons and / or carbon monoxide, the following applies, where "R_C2H6" denotes the recycled ethane:

[0074] n(R_G)=n(R_C2H6)+n(R_C2H4)=n(P_C2H6)+n(R_C2H4)

[0075] Assuming that the typical ethane yield of oxidative catalytic dehydrogenation is 50% (the usual value in the technology is in the range of about 40% to 60%), the numerical results are shown in Table 1. In this case, the value of n(P_C2H4) only considers the ethylene formed in the oxidative catalytic dehydrogenation of ethane, but does not include unconverted ethylene. Therefore, this value is only used for orientation and cannot be measured separately in reality. However, according to the present invention, n(R_C2H4) is always less than n(P_C2H4).

[0076] The value of n(F_C2HG6) represents the ethane content of the feed mixture.

[0077] Table 1:

[0078]

[0079]

[0080] Due to the presence of small amounts of other components, such as higher hydrocarbons and / or carbon monoxide, the actual PRE values ​​are actually lower. Since ethylene is also used as a valuable product and it is particularly desirable to achieve a ratio of ethylene to acetic acid based on demand, particularly advantageous PRE values ​​are within the above range. In this way, in particular for downstream processes of oxidative catalytic dehydrogenation (i.e. without taking into account recycled ethylene), the above advantageous ratios of ethylene to acetic acid can be achieved.

[0081] In a test facility, the reaction of ethane and ethane-ethylene feedstocks under oxidative catalytic dehydrogenation conditions was investigated. The corresponding test reactor was designed as a double tube with a usable length of 0.9 m and an inner diameter of the reaction chamber of 10 mm. Heating or cooling was carried out with the aid of a thermal oil bath, which was pumped in through the outside of the reactor and thus heated or simultaneously cooled the interior / reaction zone (the reaction was exothermic). Due to the very good heat transfer properties, the oil bath temperature corresponded to the inlet temperature of the gas into the catalyst bed (also confirmed by measurements) and was therefore the reaction temperature. The test conditions and the results obtained are shown in Table 2.

[0082] It can be seen that when ethylene is present in the reaction feed, the selectivity shifts significantly towards acetic acid.

[0083] Table 2: Test conditions and results of ethane and ethane-ethylene mixture oxidation reactions

[0084]

[0085] The present invention, in its embodiments, is particularly capable of optimizing and adjusting the ethylene and acetic acid capacities on an as-needed basis, beyond the usual limits when using pure ethane feed. The ratio of ethylene to acetic acid can be adjusted flexibly, especially in the case of high acetic acid content. In particular, this can also exceed the ratio that can be achieved by simply changing the process parameters of the oxidative catalytic dehydrogenation.

[0086] Thus, the present invention advantageously enables the use of catalytic oxidative dehydrogenation even for higher acetic acid capacities, regardless of the specific ethylene requirements. This eliminates the limitations previously imposed by co-production, since the ratio of ethylene to acetic acid can be freely adjusted within a wide range without requiring a special reactor design (e.g., adapted space velocity or line velocity). Instead, prior art reactor designs can continue to be used.

[0087] In embodiments of the present invention, the ratio of ethylene to acetic acid can be quickly and flexibly adapted to changing requirements. By combining certain process steps (e.g., condensation separation and fractionation sections), product purification can be achieved with only a small amount of additional work. In particular, no additional acetic acid preparation or purchase process is required. No additional feed is required to prepare acetic acid. In addition, no expensive noble metal additives (especially Pd) are required to increase acetic acid selectivity. The catalyst is a conventional catalyst, in particular a mixed metal oxide catalyst.

[0088] According to an embodiment, the implementation of an ethane-ethylene splitter or C2 splitter requires less workload because the ethylene does not need to be completely separated. In general, the workload required is lower than that of a steam cracker, and no significant amount of by-products are formed (e.g., no or little methane is formed, and only trace amounts of higher hydrocarbons). Therefore, the overall process according to an embodiment of the present invention is highly selective for acetic acid and ethylene.

Claims

1. A method (100) for preparing ethylene and acetic acid, wherein: oxidative catalytic dehydrogenation (110) of ethane and oxygen in a feed mixture (1) using a catalyst comprising at least molybdenum, vanadium and niobium and optionally tellurium as mixed oxides to obtain a product mixture (2) comprising ethylene, acetic acid and other components, wherein the ethylene content of the feed mixture (1) is from 0.25 mol.% to 30 mol.%, and at least a portion of the ethylene content of the feed mixture (1) of the oxidative catalytic dehydrogenation is contained in the product stream (2) and is recycled to the oxidative catalytic dehydrogenation (110), - wherein the product mixture (2) or a portion of the product mixture (2) is subjected to a preliminary treatment (120 to 170), from which a subsequent mixture (5) is obtained, which is deficient in carbon dioxide and water compared to the product mixture (2), wherein the subsequent mixture (5) or a portion of the subsequent mixture (5) is fed as a cryogenic separation feed to a cryogenic separation (180, 190), the cryogenic separation (180, 190) comprising demethanization (180) and in particular comprising ethane-ethylene separation (190), wherein at least a portion of the cryogenically separated feed is supplied to the demethanizer (180) as a demethanizer feed, and in the demethanizer (180), a heavy fraction (6) and a light fraction (7) are formed as a top fraction, wherein, compared to the subsequent mixture (5), the heavy fraction (6) is enriched in hydrocarbons having two carbon atoms, in particular in the sum of ethane and ethylene, and is deficient in components having a boiling point lower than ethylene, - wherein, compared to the subsequent mixture (5), the light fraction (7) is deficient in hydrocarbons having two carbon atoms and is enriched in components having a boiling point lower than ethylene, and - wherein the light fraction (7) or a portion of the light fraction (7) is recycled to the oxidative dehydrogenation (110).

2. The method according to claim 1, wherein: In the light fraction (7), the ethylene content is 1% to 90%, the carbon monoxide content is up to 75%, the methane content is up to 25%, and the oxygen content is below the oxygen limit concentration, in particular less than 5%, wherein the percentages represent molar percentages or volume percentages.

3. The method (100) according to claim 1 or claim 2, wherein: A proportion of 1% to 35% of the ethylene contained in the product stream (2) of the oxidative catalytic dehydrogenation is recycled to the oxidative catalytic dehydrogenation (110).

4. The method (100) according to claim 3, wherein: The recycled ethylene is recycled to the oxidative catalytic dehydrogenation (110) together with the ethane contained in the product mixture (2) of the oxidative catalytic dehydrogenation.

5. The method (100) according to any one of the preceding claims, wherein: The other components of the product mixture (2) of the oxidative catalytic dehydrogenation in the oxidative catalytic dehydrogenation (110) include unconverted ethane, compounds having a boiling point lower than ethylene including carbon monoxide and carbon dioxide and water, and wherein the subsequent mixture (5) contains at least a portion of the ethane, the ethylene and the compounds having a boiling point lower than ethylene from the product mixture (2).

6. The method (100) according to claim 5, wherein: The primary treatment (120 to 170) comprises a raw gas treatment (150) and a carbon dioxide removal (160) and drying (170), wherein a portion of the gas mixture obtained from the raw gas treatment (150) is discharged from the primary treatment (120 to 170) upstream of the carbon dioxide removal (160) and drying (170) and is recycled to the oxidative catalytic dehydrogenation (110).

7. The method (100) of claim 1, wherein: At least a portion of the low-temperature separation feed is supplied to the ethane-ethylene separation (190) as an ethane-ethylene separation feed, wherein a heavy fraction (C2H6) and a light fraction (C2H6) are formed in the ethane-ethylene separation (190), the heavy fraction (C2H6) being rich in ethane and lacking in ethylene and components having a boiling point lower than ethylene compared to the subsequent mixture (5), the light fraction (C2H6) being lacking in ethane and rich in ethylene and components having a boiling point lower than ethylene compared to the subsequent mixture (5), and wherein the light fraction or a portion of the light fraction is supplied to the demethanizer (180) as a demethanizer feed.

8. The method (100) of claim 1, wherein: One or more fractions selected from the bottom fraction (6) formed in the demethanization (180), the top fraction (C2H4) formed in the ethane-ethylene separation (190) and the bottom fraction (C2H6) formed in the ethane-ethylene separation (190) are also at least partially or separately at least partially recycled to the oxidative dehydrogenation (110).

9. The method (100) according to claim 8, wherein: One or at least one of a plurality of fractions selected from the top fraction (7) formed in the demethanizer (180), the bottom fraction (6) formed in the demethanizer (180), the top fraction (C2H4) formed in the ethane-ethylene separation (190) and the bottom fraction (C2H6) formed in the ethane-ethylene separation (190) is formed or each is formed into a fraction containing ethane and ethylene.

10. A method according to any one of the preceding claims, wherein: A side stream (9) comprising ethane and ethylene is taken from the ethane-ethylene separation, said side stream (9) being at least partly recycled to the oxydehydrogenation (110).

11. The method (100) according to any one of the preceding claims, wherein: At least a portion of the ethylene contained in the product mixture (2) is transferred to an open refrigerant circuit, wherein at least a portion of the ethylene is discharged from the open refrigerant circuit and recycled to the oxidative catalytic dehydrogenation (110) to provide at least a portion of the ethylene share of the feed mixture (1).

12. The method (100) according to any one of the preceding claims, wherein: At least one material stream is treated which is recycled to the oxidative catalytic dehydrogenation (110) to provide at least a portion of the ethylene share of the feed mixture (1).

13. A method for preparing a target compound using ethylene and acetic acid, characterized in that: The ethylene and at least a portion of the acetic acid are provided using a process according to any one of the preceding claims.

14. A device configured to perform the method (100) according to any one of the preceding claims.

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