EA040398B1 - OXIDATIVE DEHYDROGENATION OF ETHANE - Google Patents

Description

Technical field

This invention relates to a process for the oxidative dehydrogenation of ethane (ODD).

State of the art

It is known that ethane is dehydrogenated under oxidizing conditions during the oxidative dehydrogenation (oxydehydrogenation; ODH) process. Examples of ethane ODH processes, including catalysts and other process conditions, are described in, for example, US7091377, WO2003064035, US20040147393, WO2010096909 and US20100256432. Mixed metal oxide catalysts containing molybdenum (Mo), vanadium (V), niobium (Nb) and, optionally, tellurium (Te) as metals can be used as ethane oxydehydrogenation catalysts.

Additionally, carbon dioxide is known to be used as a diluent in such ethane ODH processes. Feeding a diluent containing carbon dioxide to the ethane ODH step is disclosed, for example, in US20160326070. In addition to ethylene and water, the effluent from this ethane FDH step also contains unreacted ethane and carbon dioxide. It is desirable to recycle both the unreacted ethane and the carbon dioxide diluent to the ethane FDH step. However, the disadvantage of the method in US 20160326070 (see Fig. 1-5) is that carbon dioxide and unreacted ethane are separated from the effluent after ethane ODH in two different stages. After the removal of water from the effluent after the ethane ODH obtained from the process shown in FIG. 1 in US20160326070, the carbon dioxide is removed, for example by purification, and returned to the reactor. Finally, in the separation step of this process, ethane is separated from ethylene in the deethanizer and ethane is recycled to the reactor separately from carbon dioxide.

It is an object of the present invention to provide an ethane ODH process which includes feeding carbon dioxide as a diluent to the ethane ODH stage, in which unreacted ethane and carbon dioxide diluent can be recycled to the ethane ODH stage and the ethylene product can be recovered in such a manner, which is technically advantageous, simple, efficient and affordable. Such a technically feasible method will preferably lead to a reduction in energy consumption and/or a reduction in capital costs.

The essence of the invention

Surprisingly, it has been found that the above object can be achieved by co-separating unreacted ethane and carbon dioxide diluent, and at the same time recovering the ethylene product by a step which includes separation by complexation and which includes contacting at least a portion of a stream containing the specified ethane, carbon dioxide and ethylene, with a liquid solvent containing a complexing agent, and at this stage a stream containing ethylene is formed, and a stream containing unreacted ethane and carbon dioxide, the latter stream subsequently being recycled to the ethane ODH stage.

Accordingly, the present invention relates to a process for the oxidative dehydrogenation of ethane, comprising the steps of:

(a) subjecting the ethane-containing stream to oxidative dehydrogenation conditions, comprising contacting ethane with oxygen in the presence of a mixed metal oxide-containing catalyst, wherein a diluent containing carbon dioxide is fed to step (a), after which an ethylene-containing effluent is formed , optionally acetic acid, unreacted ethane, water, carbon dioxide, optionally unreacted oxygen, optionally carbon monoxide, and optionally acetylene;

(b) removing water from at least a portion of the effluent stream obtained in step (a), resulting in a stream containing ethylene, unreacted ethane, carbon dioxide, optionally unreacted oxygen, optionally carbon monoxide and optionally acetylene, and a stream containing water and optionally acetic acid;

(c) optionally removing unreacted oxygen and/or carbon monoxide and/or acetylene from at least a portion of the stream containing ethylene, unreacted ethane, carbon dioxide, optionally unreacted oxygen, optionally carbon monoxide and optionally acetylene obtained in step (b) ), resulting in a stream containing ethylene, unreacted ethane and carbon dioxide;

(d) removing ethylene from at least a portion of the stream containing ethylene, unreacted ethane and carbon dioxide obtained in step (b) or (c) using a complexation separation process that includes contacting at least a portion of said a liquid solvent stream containing a complexing agent, resulting in a stream containing ethylene and a stream containing unreacted ethane and carbon dioxide;

(e) recycling at least a portion of the stream containing unreacted ethane and carbon dioxide obtained in step (d) to step (a).

Brief description of graphic materials

In FIG. 1 shows an embodiment of the invention covering steps (a) to (e) of the method of the invention.

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In FIG. 2 shows an embodiment of the invention relating to step (d) of the method according to the invention.

Detailed description of the invention

The method of the present invention includes steps (a) to (e), with step (c) being an optional step. These steps and optional additional steps are described in more detail below.

Therefore, the method according to this invention includes steps (a) and (b), an optional step (c) and steps (d) and (e). Said method may include one or more intermediate steps between steps (a) and (b), between steps (b) and (c), between steps (c) and (d) and between steps (d) and (e). Additionally, said method may include one or more additional steps preceding step (a) and/or following step (e).

While the process of this invention and the composition or stream used in said process are described using the terms comprising or comprising one or more of the various steps and components described, respectively, they may also consist essentially of or consist of said one or more of the various steps described. and components, respectively.

In the context of this invention, in the event that a composition or stream contains two or more components, the total amount of these selected components should not exceed 100 vol.% or 100 wt.%.

As used herein, substantially absent means that the formulation or stream does not contain any detectable amount of the component in question.

Additionally, reference in this specification to fresh ethane is to ethane that does not contain unreacted ethane. Reference in this specification to unreacted ethane is made to ethane that was subjected to the oxidative dehydrogenation conditions in step (a) of the process of this invention, but which did not react.

Stage (a).

Step (a) of the process includes exposing the ethane-containing stream to oxidative dehydrogenation (ODH) conditions, including contacting ethane with oxygen (O ₂ ) in the presence of a mixed metal oxide catalyst, wherein a diluent containing carbon dioxide is fed to step ( a), resulting in an effluent containing ethylene, optionally acetic acid, unreacted ethane, water, carbon dioxide, optionally unreacted oxygen, optionally carbon monoxide, and optionally acetylene.

In step (a) ODH of ethane, ethylene is produced by oxidative dehydrogenation of ethane. Ethylene is formed first. However, at the same stage, ethylene can be oxidized to acetic acid. Additionally, at the same stage, ethylene can be dehydrogenated to acetylene (ethyne). Ethane can also be directly converted to acetic acid or acetylene. Additionally, carbon monoxide (CO) and carbon dioxide (CO2) can be formed at the same stage, for example by burning ethane and/or ethylene and/or acetic acid and/or acetylene.

In step (a) of the EDH of ethane, ethane, oxygen (O2) and carbon dioxide (CO2) can be fed into the reactor. These components may be fed into the reactor together or separately. That is, the reactor may be fed with one or more feed streams, preferably gas streams, containing one or more of said components. For example, a single feed stream containing oxygen, ethane and carbon dioxide may be fed to the reactor. Alternatively, two or more feed streams, preferably gas streams, may be fed to the reactor, and these feed streams may form a combined stream within the reactor. For example, one feed stream containing oxygen, another feed stream containing ethane, and another feed stream containing carbon dioxide may be fed into the reactor separately. In step (a), ethane ODH, ethane, oxygen and carbon dioxide are fed into the reactor, preferably in the gas phase.

Preferably in step (a) ODH of ethane, ie during contact of ethane with oxygen in the presence of a catalyst, the temperature is from 300 to 500°C. More preferably said temperature is 310 to 450°C, more preferably 320 to 420°C, most preferably 330 to 420°C.

Additionally, in step (a) ODH of ethane, i.e., during the contact of ethane with oxygen in the presence of a catalyst, typical pressures are 0.1-30 or 0.1-20 bar abs. (i.e. bar absolute pressure). Additionally, said pressure is preferably 0.1 to 15 bar abs, more preferably 1 to 10 bar abs, most preferably 3 to 10 bar abs. The indicated pressure refers to the total pressure.

In addition to oxygen and ethane, carbon dioxide is also fed to stage (a) of the ODH of ethane as a diluent. One or more additional diluents selected from the group consisting of noble gases, nitrogen (N2), steam (H ₂ O) and methane, preferably nitrogen and methane, may be fed to step (a) of the ethane ODH. However, since in this process carbon dioxide is already supplied as a diluent to step (a) of the EDH of ethane, there is no need to add any further diluent. Therefore, no additional diluent, in particular steam, is preferably fed to step (a) of the ethane ODH. Some methane may enter step (a) as an impurity

- 2 040398 when supplying ethane to stage (a). Additionally, some nitrogen may enter step (a) as an impurity when oxygen is supplied to step (a). In these cases, methane and nitrogen act as an additional diluent, in addition to carbon dioxide.

Typically, the proportion of the total feed stream in step (a) that is diluent is in the range of 5 to 90% by volume, preferably 25 to 75% by volume. Preferably, in the case of an isothermal type reactor, the proportion of the total feed stream in step (a) which is diluent is in the range of 5 to 90% by volume, preferably 25 to 75% by volume, and more preferably 40 to 60% by volume. %. Additionally, in the case of an adiabatic type reactor, the proportion of the total feed stream in step (a) that is diluent is preferably in the range of 50 to 95% by volume, preferably 60 to 90% by volume, and more preferably 70 to 85 about.%.

Preferably, the diluent supplied to step (a) contains from 1 to 100% by volume, more preferably from 5 to 100% by volume, more preferably from 10 to 100% by volume, more preferably from 20 to 100% by volume, more preferably 40 to 100% by volume, more preferably 60 to 100% by volume, more preferably 80 to 100% by volume, more preferably 90 to 100% by volume, more preferably 95 to 100% by volume and most preferably from 99 to 100 vol.% carbon dioxide, the remainder consists of one or more other diluents selected from the group consisting of noble gases, nitrogen (N ₂ ), steam (H ₂ O) and methane, preferably nitrogen and methane. Diluents other than carbon dioxide may be used in any desired ratio relative to each other. If one or more of said additional diluents other than carbon dioxide are supplied to step (a), the upper limit of the proportion of carbon dioxide in the diluent may be 20% by volume, preferably 40% by volume, more preferably 60% by volume, more preferably 80% by volume, more preferably 90% by volume, more preferably 95% by volume and most preferably 99% by volume.

Oxygen supplied to stage (a) ODH ethane, is an oxidizing agent, which leads to the oxidative dehydrogenation of ethane. Said oxygen may be from any source such as, for example, air. Suitable ranges for the molar ratio of oxygen to ethane include ranges below, at and above the stoichiometric molar ratio (which is 0.5 for the ODH reaction of ethane); preferably 0.01 to 1.1, more preferably 0.01 to 1, more preferably 0.05 to 0.8, most preferably 0.05 to 0.7. In one embodiment, the molar ratio of oxygen to ethane is 0.05 to 0.5, more preferably 0.05 to 0.47, most preferably 0.1 to 0.45. Additionally, in another embodiment of the invention, the molar ratio of oxygen to ethane is from 0.5 to 1.1, more preferably from 0.53 to 1, most preferably from 0.55 to 0.9. The specified ratio of oxygen to ethane is the ratio before contacting oxygen and ethane with the catalyst. That is, the ratio of oxygen to ethane indicated is the ratio of oxygen feed to ethane feed. Obviously, after contact with the catalyst, at least part of the oxygen and ethane is consumed. Additionally, the specified ethane in the specified molar ratio of oxygen to ethane includes both fresh ethane and recycled (unreacted) ethane.

Preferably, pure or substantially pure oxygen (O ₂ ) is used as the oxidizing agent in step (a) of the process of the present invention. Reference in this specification to pure or substantially pure oxygen is to oxygen which may contain a relatively small amount of one or more contaminants, including, for example, nitrogen (N ₂ ), the latter being at most 1% by volume, preferably not more than 7000 volume parts per million (vol. ppm), more preferably not more than 5000 vol. ppm, more preferably not more than 3000 vol. ppm, more preferably not more than 1000 vol. ppm, more preferably not more than 500 vol. ppm, more preferably not more than 300 vol. ppm, more preferably not more than 200 vol. ppm, more preferably not more than 100 vol. ppm, more preferably not more than 50 vol. ppm, more preferably not more than 30 vol. ppm, most preferably not more than 10 vol. ppm

Alternatively, however, it is also possible to use air or oxygen-enriched air as the oxidant in step (a). Such air or oxygen-enriched air will still contain nitrogen (N2) in an amount greater than 1 to 78 vol.% (air), preferably 1 to 50 vol.%, more preferably 1 to 30 vol.%, more preferably 1 to 20% by volume, more preferably 1 to 10% by volume, most preferably 1 to 5% by volume. This nitrogen will act as an additional diluent, in addition to carbon dioxide, and enter the stream containing unreacted ethane and carbon dioxide obtained from the separation step using complexation (d) according to this method; at least a portion of the stream is recycled to step (a) of the EDH of ethane in the process.

In order to prevent nitrogen accumulation in this process, nitrogen can be removed from the aforementioned stream obtained in step (d) before being recycled from step (e), for example, by labour-intensive cryogenic distillation. Additionally, this accumulation can be prevented by purging a portion of the stream containing unreacted ethane and carbon dioxide obtained in step (d) before recycling, as further described below. However, when blowing out a part

- 3 040398 of the specified stream part of the unreacted ethane is lost and is not returned to stage (a). Therefore, since carbon dioxide is used as the diluent, which is recycled in the process, the above-described pure or substantially pure oxygen is preferably used as the oxidant in step (a) of the process of the present invention. However, if, when oxygen is supplied to step (a), it still contains a relatively small amount of nitrogen, such a small amount of nitrogen can still be purged before recirculation from step (e) along with additional carbon dioxide resulting from the formation of carbon dioxide in step (a) and optionally in step (c).

In step (a), the ethane ODH catalyst is a mixed metal oxide catalyst. Preferably the ODH catalyst is a heterogeneous catalyst. Additionally, the ODH catalyst is preferably a mixed metal oxide catalyst containing molybdenum, vanadium, niobium and optionally tellurium as metals, which catalyst may have the following formula:

MofVaTebNb _c On where:

a, b, c and n are the ratio of the molar amount of the element in question to the molar amount of molybdenum (Mo);

a (for V) is 0.01 to 1, preferably 0.05 to 0.60, more preferably 0.10 to 0.40, more preferably 0.20 to 0.35, most preferably 0, 25 to 0.30;

b (for Te) is 0 or >0 to 1, preferably 0.01 to 0.40, more preferably 0.05 to 0.30, more preferably 0.05 to 0.20, most preferably 0 .09 to 0.15;

c (for Nb) is >0 to 1, preferably 0.01 to 0.40, more preferably 0.05 to 0.30, more preferably 0.10 to 0.25, most preferably 0.14 up to 0.20; and n (for O) is a number determined by the valency and repeatability of elements other than oxygen.

The amount of catalyst in step (a) ODH of ethane is not significant. Preferably, a catalytically effective amount of catalyst is used, that is, an amount sufficient to promote the ethane oxydehydrogenation reaction.

The FGD reactor that can be used in step (a) of the FGD of ethane can be any reactor, including fixed bed and fluidized bed reactors. Preferably the reactor is a fixed bed reactor.

Examples of oxydehydrogenation processes, including catalysts and process parameters, are disclosed, for example, in the aforementioned US7091377, WO2003064035, US20040147393, WO2010096909 and US20100256432, the contents of which are incorporated herein by reference.

Step (a) of the EDH of ethane produces water that enters the finished product stream in addition to the desired ethylene product. Additionally, as mentioned above, in step (a), acetic acid, acetylene, carbon monoxide and carbon dioxide can be generated. Additionally, carbon dioxide is fed as a diluent to step (a). Additionally, some of the ethane in step (a) remains unreacted and it may happen that not all of the oxygen is reacted in step (a). That is, step (a) of the ODH of ethane produces an effluent containing ethylene, optionally acetic acid, unreacted ethane, water, carbon dioxide, optionally unreacted oxygen, optionally carbon monoxide, and optionally acetylene.

Stage (b).

Step (b) of the process includes removing water from at least a portion of the effluent stream obtained in step (a), resulting in a stream containing ethylene, unreacted ethane, carbon dioxide, optionally unreacted oxygen, optionally carbon monoxide, and optionally acetylene, and a stream containing water and optionally acetic acid.

In the water removal step (b), the water is preferably removed by condensation. Water from the effluent obtained in step (a) may be condensed by cooling said effluent to a lower temperature, such as room temperature, after which the condensed water may be separated, resulting in a liquid stream containing the condensed water.

In the water removal step (b), the temperature may be from 10 to 150°C, for example from 20 to 80°C. In said step (b), the temperature is preferably at least 10°C or at least 20°C or at least 30°C. Additionally, in said step (b), the temperature is preferably not more than 150°C, or not more than 120°C, or not more than 100°C, or not more than 80°C, or not more than 60°C.

Additionally, in the water removal step (b), typical pressures are 0.01-30 or 0.01-20 bar abs. (i.e. bar absolute pressure). Additionally, said pressure is preferably 0.1 to 15 bar abs, more preferably 1 to 10 bar abs, most preferably 3 to 10 bar abs. The indicated pressure refers to the total pressure.

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In the event that the feed stream to the water removal step (b) additionally contains acetic acid, said acetic acid can be removed together with water from said stream in the water removal step (b), preferably together with water condensed from said stream. During or after the water removal step (b), additional water may be added to facilitate the removal of any amount of acetic acid.

Therefore, the water removal step (b) produces a stream containing ethylene, unreacted ethane, carbon dioxide, optionally unreacted oxygen, optionally carbon monoxide and optionally acetylene, and a stream containing water and optionally acetic acid. The latter stream may be a liquid stream containing condensed water and optionally acetic acid.

Optional step (c).

An optional step (c) of this process includes optionally removing unreacted oxygen and/or carbon monoxide and/or acetylene from at least a portion of the stream containing ethylene, unreacted ethane, carbon dioxide, optionally unreacted oxygen, optionally carbon monoxide and optionally acetylene, obtained in step (b), resulting in a stream containing ethylene, unreacted ethane and carbon dioxide.

In the event that the stream containing ethylene, unreacted ethane and carbon dioxide obtained in step (b) additionally contains unreacted oxygen and/or carbon monoxide and/or acetylene, these additional components can be removed in an optional step (c) before step separation by complexation (d). Alternatively, these additional components can be removed during and/or after the separation step using complexation (d), as further described below. However, it is preferred to remove these additional components prior to the complexation step (d) in order to avoid any difficulty in removing them during and/or after the complexation separation. For example, acetylene may form a strong bond with the complexing agent in step (d). Therefore, removing any amount of acetylene in optional step (c) successfully avoids the potential problems associated with the presence of acetylene in step (d). Similarly, in addition to the desired ethylene product in step (d), carbon monoxide can also be complexed with the complexing agent. Carbon monoxide forms stable complexes with Cu(I) which may be present in the complexing agent used in step (d). Finally, oxygen can oxidize a metal, such as Cu(I), from a metal salt or metal complex that can be used as a complexing agent in step (d). Therefore, it is also preferred to remove any unreacted oxygen and/or carbon monoxide prior to the separation step by complexation (d).

In optional step (c) of this process, any amount of acetylene may be removed by any known method. For example, acetylene can be removed by selective hydrogenation or an absorption process that uses acetone or dimethylformamide. Hydrogen (H2) is a hydrogenating agent that can be used to hydrogenate acetylene to ethylene. Additionally, it is preferable to use a selective acetylene hydrogenation catalyst that is more capable of catalyzing the hydrogenation of acetylene to ethylene than the hydrogenation of ethylene to ethane.

Additionally, in optional step (c) of this process, any unreacted oxygen and/or carbon monoxide may also be removed by any known method. For example, unreacted oxygen and carbon monoxide can be removed by catalytic oxidation of carbon monoxide to carbon dioxide, which preferably uses an oxidation catalyst containing platinum or palladium (see, for example, the aforementioned US20160326070). Accordingly, in the case where both acetylene and unreacted oxygen and carbon monoxide are removed in optional step (c), this can be done by first performing the selective hydrogenation of acetylene with hydrogen as the hydrogenation agent described above, and then the above-described oxidation of carbon monoxide to carbon dioxide, so that any residual hydrogen can react with oxygen to form water.

Alternatively, in optional step (c), unreacted oxygen and carbon monoxide may first be removed by distillation, such as cryogenic distillation, followed by the selective hydrogenation of acetylene using hydrogen as the hydrogenating agent as described above. Additionally, the above-described selective hydrogenation of acetylene using hydrogen as the hydrogenation agent can be performed first, followed by distillation to remove unreacted oxygen, carbon monoxide, and any residual hydrogen.

However, in the cases described above, the use of multiple steps to remove unreacted oxygen, carbon monoxide and acetylene before the separation step by complexation (d) is laborious. It has been found that in one embodiment of the optional step (c) of this process, when the stream containing ethylene, unreacted ethane and carbon dioxide obtained in step (b) further contains unreacted oxygen, carbon monoxide and optionally acetylene, these additional components are advantageously removed in a single step by oxidation of carbon monoxide and any amount of acetylene to form carbon dioxide. Therefore, in said preferred embodiment, optional step (c) includes optionally removing unreacted oxygen, carbon monoxide, and optionally acetylene from at least a portion of the stream containing ethylene, unreacted ethane, carbon dioxide, unreacted oxygen, carbon monoxide, and optionally acetylene obtained in step (b), wherein carbon monoxide and optionally acetylene are oxidized to carbon dioxide, which leads to the formation of a stream containing ethylene, unreacted ethane and carbon dioxide. As with any oxidation of hydrocarbons such as acetylene, in this preferred embodiment, water is formed when acetylene is present.

In said preferred embodiment of optional step (c), unreacted oxygen can be successfully used to oxidize both carbon monoxide and acetylene to carbon dioxide. There is no need to add an additional oxidizing agent or any other chemical such as hydrogen that can be used as a hydrogenating agent for the hydrogenation of acetylene as described above. Additionally, in said preferred embodiment of the invention, there is also no need to use a laborious distillation step (cryogenic) to remove unreacted oxygen, carbon monoxide and any amount of hydrogen.

In said preferred embodiment of optional step (c), the temperature may vary widely and is typically between 20 and 500°C and may be between 50 and 500°C or between 100 and 400°C. Preferably in said step (c) the temperature is in the range of 100 to 400°C, more preferably 150 to 300°C, more preferably 170 to 260°C, most preferably 200 to 260°C. In said step (c), the temperature may be at least 20°C, or at least 50°C, or at least higher than 100°C, or at least 110°C, at least higher than 110°C. C, or at least 120°C or at least higher than 120°C, or at least 130°C or at least higher than 130°C, or at least 140°C or at least higher than 140 °C, or at least 150°C, or at least higher than 150°C, or at least 160°C, or at least higher than 160°C, or at least 170°C, or at least higher than 170°C, or at least 180°C, or at least higher than 180°C, or at least 190°C, or at least higher than 190°C, or at least 200°C, or at least higher than 200°C, or at least 210°C, or at least 220°C, or at least 230°C, or at least 240°C. Additionally, in said step (c), the temperature may be at most 500°C, or at most 400°C, or at most 350°C, or at most 340°C, or at most 330°C, or at most 320°C. , or not more than 310°С, or not more than 300°С, or not more than 290°С, or not more than 280°С, or not more than 270°С, or not more than 260°С, or not more than 250°С.

Additionally, in said preferred embodiment of optional step (c), typical pressures are 0.1-30 or 0.1-20 bar abs. (i.e. bar absolute pressure). Additionally, said pressure is preferably 0.1 to 15 bar abs, more preferably 1 to 8 bar abs, most preferably 2 to 7 bar abs. The indicated pressure refers to the total pressure.

Additionally, in said preferred embodiment of optional step (c), additional oxygen may be supplied to said step (c). Such additional oxygen is added in addition to oxygen from the stream containing ethylene, unreacted ethane, carbon dioxide, unreacted oxygen, carbon monoxide and optionally acetylene, which is fed to the specified stage (c). Such additional oxygen may be required when the stream does not contain sufficient unreacted oxygen to oxidize all of the carbon monoxide and any acetylene from the same stream to carbon dioxide. Such additional oxygen can be added directly or indirectly to step (c), in particular at any time before and/or during step (c).

In said preferred embodiment of optional step (c), oxygen, carbon monoxide and optionally acetylene are removed from the stream containing ethylene, unreacted ethane, carbon dioxide, unreacted oxygen, carbon monoxide and optionally acetylene by oxidizing carbon monoxide and any amount of acetylene to carbon dioxide. . That is, unreacted oxygen from this stream is used to oxidize carbon monoxide and any amount of acetylene to carbon dioxide. As stated above, additional oxygen may be supplied to completely convert all of the carbon monoxide and acetylene (if present) to carbon dioxide. Such oxidation may also be referred to as combustion. Therefore, said step (c) results in a stream containing ethylene, unreacted ethane and carbon dioxide.

It is also envisaged that in the case where acetylene is produced in step (a) of the ODH of ethane, the removal of such acetylene may be part of said preferred embodiment of the optional step (c), after the water removal step (b) but before the step described above. oxidation, in particular by hydrogenation of acetylene to ethylene, as described above.

Accordingly, in a preferred embodiment of optional step (c), oxygen can be removed to such an extent that the stream obtained in said step (c) does not contain oxygen or contains a residual amount of oxygen that is not more than 10,000 ppm (v/v) of oxygen. . ppm), or not more than 1000 vol. ppm, or not more than 500 vol. ppm, or not more than 100 vol. ppm, or not more than 50 vol. ppm, or not more than 10 vol. ppm, or not more than 2 vol. ppm, or not more than 1 vol. ppm from the total volume of the flow obtained at the specified stage (c). Additionally, accordingly, in a preferred embodiment of the optional step (c), carbon monoxide and any amount of acetylene can be removed to such an extent that the stream obtained in the specified step (c) does not contain carbon monoxide and acetylene or contains a residual amount of carbon monoxide and acetylene, which is not more than 15 vol.% or not more than 10 vol.%, or not more than 5 vol.%, or not more than 1 vol.%, or not more than 500 parts per million by volume (vol. ppm) , or not more than 100 vol. ppm, or not more than 50 vol. ppm, or not more than 10 vol. ppm, or not more than 2 vol. ppm, or not more than 1 vol. ppm from the total volume of the flow obtained at the specified stage (c).

Said preferred embodiment of optional step (c) may be carried out in the presence of a catalyst, preferably an oxidation catalyst. Accordingly, said oxidation catalyst catalyzes the oxidation of carbon monoxide and any amount of acetylene to carbon dioxide. In particular, said oxidation catalyst preferably catalyzes the conversion of carbon monoxide and any amount of acetylene and oxygen to carbon dioxide by oxidizing carbon monoxide and any amount of acetylene to carbon dioxide.

In said preferred embodiment of optional step (c), any oxidation catalyst that catalyzes the oxidation of carbon monoxide to carbon dioxide can be used. For example, in said step (c), one of the carbon monoxide oxidation catalysts described in EP499402A1, US4956330, EP306945A1, EP421169A1, US5157204 and US5446232, the contents of which are incorporated herein by reference, can be used. Preferably said catalyst also catalyzes the oxidation of any amount of acetylene to carbon dioxide.

Preferably, the above oxidation catalyst, which can be used in said preferred embodiment of optional step (c), contains a transition metal. More preferably, said catalyst contains one or more metals selected from the group consisting of nickel (Ni), copper (Cu), zinc (Zn), palladium (Pd), silver (Ag), platinum (Pt), gold (Au) , iron (Fe), manganese (Mn), cerium (Ce), tin (Sn), ruthenium (Ru) and chromium (Cr), more preferably one or more metals selected from the group consisting of nickel, copper, zinc, platinum and ruthenium, even more preferably one or more metals selected from the group consisting of nickel, copper and zinc. Most preferably said catalyst contains copper and/or platinum. Accordingly, said catalyst contains copper or platinum, more preferably copper. For example, said catalyst may contain copper and zinc. In particular, said catalyst may be a metal oxide catalyst, which may be a partially reduced metal oxide catalyst, the metal(s) being described(s) above; for example, a catalyst containing copper oxide and optionally zinc oxide. The catalyst may be a supported catalyst in which one or more of these metals are supported, or an unsupported catalyst. In the case where the catalyst is a supported catalyst, the support may be any support such as alumina, titanium dioxide, silicon dioxide, zirconia or silicon carbide, preferably alumina. Additionally, the supported catalyst may be in any form, including tablets and extrudates, or it may be supported.

In some cases, in said preferred embodiment of optional step (c), it may not be possible or desirable to completely remove oxygen, carbon monoxide and optionally acetylene by oxidizing carbon monoxide and optionally acetylene to carbon dioxide with unreacted oxygen and any additional oxygen as described. higher. If so, and if after said oxidation it is desired to remove any remaining oxygen and/or carbon monoxide and/or acetylene, then, as part of said preferred embodiment of optional step (c), further treatment may be carried out to remove said components. Such post-treatment to remove components may include passing the stream through an absorber containing a sorbent (adsorbent and/or absorbent) that is capable of selectively absorbing any remaining oxygen, carbon monoxide and acetylene.

Stage (d).

Step (d) of the process includes removing ethylene from at least a portion of the stream containing ethylene, unreacted ethane and carbon dioxide obtained in step (b) or (c) by a complexation separation process that includes contacting at least at least a portion of said stream with a liquid solvent containing a complexing agent, resulting in a stream containing ethylene and a stream containing unreacted ethane and carbon dioxide.

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In step (d) of this process, at least a portion of the stream containing ethylene, unreacted ethane and carbon dioxide obtained in step (b) or (c) is subjected to a separation process using complexation. In such a complexation separation process, olefins (ethylene) can be selectively removed from neo-olefins (unreacted ethane). In the present invention, ethylene is not only successfully separated from unreacted ethane by complexation separation, but also from carbon dioxide diluent, which may be present in a relatively large amount and which also needs to be recycled, as well as unreacted ethane. When fed to step (d) of this process, the amount of carbon dioxide based on the total amount of ethylene, unreacted ethane and carbon dioxide can be from 1 to 99% by volume, preferably from 5 to 95% by volume, more preferably from 10 to 90% by volume. , more preferably 20 to 85% by volume, more preferably 30 to 80% by volume, more preferably 40 to 75% by volume, most preferably 50 to 70% by volume. Additionally, the specified amount of carbon dioxide may be at least 1 vol.% or at least 5 vol.%, or at least 10 vol.%, or at least 20 vol.%, or at least 30 vol.% , or at least 40 vol.%, or at least 50 vol.%. Additionally, the specified amount of carbon dioxide may be not more than 99 vol.% or not more than 95 vol.%, or not more than 90 vol.%, or not more than 85 vol.%, or not more than 80 vol.%, or not more than 75 vol.%, or not more than 70 vol.%.

In the present invention, the aforementioned complexing separation process comprises contacting at least a portion of the stream containing ethylene, unreacted ethane and carbon dioxide obtained in step (b) or (c) with a liquid solvent containing a complexing agent. The complexing agent is dissolved in said liquid solvent. That is, the separation method by complexation in step (d) of this method includes the so-called separation by complexation and absorption. In such separation by complexation and absorption, ethylene preferably forms a complex compound with a complexing agent that is dissolved in the liquid solvent.

Generally, olefin complexing uses a complexing agent to selectively form a reversible complex, preferably a π complex, with the olefins:

Olefin + Complexing agent Complex compound Olefin-Agent.

The reversibility of the complexation reaction allows the binding and release of the olefin by shifting the direction of the equilibrium of the reaction. The forward complexation reaction is favored by higher olefin partial pressure and lower temperature, while the reverse desorption reaction is favored by lower olefin partial pressure and higher temperature. Therefore, the complexation/desorption cycle can be created by changing the pressure, temperature, or both.

Preferably in the present invention, the separation step by complexation (d) comprises the following cycle of sub-steps:

(d1) contacting at least a portion of the stream containing ethylene, unreacted ethane and carbon dioxide obtained in step (b) or (c) with a liquid solvent containing a complexing agent, resulting in a stream containing unreacted ethane and carbon dioxide, at least part of which is returned from step (e) to step (a), and a liquid stream containing a solvent, a complexing agent and an ethylene complex; and (d2) desorbing the ethylene complex from at least a portion of the liquid stream containing the solvent, the complexing agent and the ethylene complex compound obtained in step (d1), resulting in a stream containing stripped ethylene and a liquid stream containing solvent and complexing agent; and (d3) recycling at least a portion of the liquid stream containing the solvent and complexing agent obtained in step (d2) to step (d1).

In step (d) of the process, a suitable complexing agent is an agent that selectively and reversibly complexes with ethylene and does not or substantially does not complex with unreacted ethane and carbon dioxide. The complexing agent may be in the form of a metal salt or metal complex that is soluble in the liquid solvent. Salts or compounds of silver (I) or copper (I) may be used, either alone or in combination with another metal, namely aluminium. The complexing agent is preferably a metal salt, which preferably further contains a silver (I) ion or a copper (I) ion, more preferably a silver (I) ion. Optionally, a mixture of complexing agents may be used, for example a mixture of copper and silver salts.

Suitable salts containing silver(I) ions include silver nitrate, silver tetrafluoroborate, silver hexafluorosilicate, silver hydroxytrifluoroborate, silver trifluoroacetate, silver perchlorate, silver triflate (CF ₃ SO ₂ OAg ⁺ ), and silver (V) hexafluoroantimonate (SbF6-Ag ⁺ ). Suitable salts containing copper (I) ions include copper nitrate; copper halides, namely copper chloride; copper sulfate;

- 8 040398 copper sulfonate; copper carboxylates; copper salts with fluorocarboxylic acids, namely copper trifluoroacetate and copper perfluoroacetate; fluorinated copper acetylacetonate; copper hexafluoroacetylacetonate; copper dodecylbenzenesulfonate; copper and aluminum halides, namely aluminum and copper tetrachloride;

CuAlCH ₃ Cl ₃ ; CuAlC2H ₅ Cl ₃ ; aluminum and copper cyanotrichloride. Silver nitrate is the most preferred complexing agent.

The concentration of the complexing agent in the liquid solvent should be such that substantially all of the complexing agent is dissolved in that solvent, which depends on the (maximum) solubility of said agent in said solvent. For example, silver nitrate has a solubility (in water) of 10.9 moles (75.4% by weight) at 35°C. Typically, the concentration of the complexing agent may be 1 to 10 moles, more preferably 1 to 8 moles, more preferably 1 to 6 moles, more preferably 2 to 5 moles, most preferably 2.5 to 4 moles.

Any suitable liquid solvent or mixture of liquid solvents can be used in step (d) to dissolve the complexing agent. In this specification, reference is made to liquid solvent to a solvent that is in a liquid state at a temperature of 25° C. and a pressure of 1 atmosphere. Preferably, said liquid solvent is water, an organic solvent, an ionic liquid, or a mixture thereof. Water is the most preferred.

Water can be used as a solvent for silver or copper salts, while hydrocarbon solvents, namely aromatic solvents, can be used for salts that contain organic ligands. Water is the preferred solvent because ethane and other neo-olefins, namely nitrogen, are extremely sparingly soluble in aqueous solutions. In contrast, ethane has a higher solubility in hydrocarbon solvents. Olefins, namely ethylene, have sufficient solubility in water so that mass transfer to the dissolved complexing agent occurs at an acceptable rate.

As mentioned above, the liquid solvent which is intended to dissolve the complexing agent may be an ionic liquid. As defined by Wasserscheid and Keim in Angewandte Chemie, 2000, 112, pp. 3926-3945, ionic liquids are salts that melt at a relatively low temperature. Therefore, ionic liquids are already liquid at relatively low temperatures. In addition, they are generally non-flammable and do not have a measurable vapor pressure. In this description, the ionic liquid means a salt that has a melting point or melting range below 100°C.

Ionic liquids are formed from positive ions and negative ions (cations and anions, respectively), but are generally charge neutral. The positive and negative ions are predominantly univalent, but multivalent anions and/or cations are also possible, which have up to five, preferably up to four, particularly preferably up to three, and particularly preferably up to two electrical charges. The charges inside the corresponding ions are either localized or delocalized.

When an ionic liquid is used to dissolve a complexing agent in the present invention, said ionic liquid may contain a cation which is an N,N'-dialkylimidazolium ion or an N-alkylpyridinium ion, preferably an N,N'dialkylimidazolium ion.

The alkyl groups in the above N,N'-dialkylimidazolium ion and N-alkylpyridinium ion may be C ₁ -C ₁₀ alkyl groups, preferably C 1 C ₄ alkyl groups. Examples of suitable C ₁ -C ₁₀ alkyl groups are methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, t-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, 2,4,4-trimethylpentyl and decyl . Preferably the cation in the ionic liquid is an N,N'-dialkylimidazolium ion, preferably an N,N'-dialkylimidazolium ion, where the alkyl groups are C ₁ -C ₁₀ alkyl groups as described above, preferably C 1 -C ₄ alkyl groups as described above.

A particularly preferred N,N'-dialkylimidazolium ion is 1-butyl-3methylimidazolium ion (BMIM ion). Another particularly preferred N,N'-dialkylimidazolium ion is 1,3-dimethylimidazolium ion (DMIM ion). Another particularly preferred N,N'dialkylimidazolium ion is 1-ethyl-3-methylimidazolium ion (EMIM ion).

When an ionic liquid is used to dissolve a complexing agent in the present invention, said ionic liquid may contain an anion selected from the group consisting of tetrafluoroborate ion (BF4 ^- ), alkoxyphosphonate ions, alkylsulfonate ions, hexafluorophosphate ion (PF6 ^- ) and amide ions. More preferably, said anion is selected from the group consisting of tetrafluoroborate ion, alkoxyphosphonate ions and amide ions. Most preferably said anion is the tetrafluoroborate ion.

The above alkoxyphosphonate ion has the formula RO-PH(=O)O ^- where R is an alkyl group, preferably a C ₁ -C ₁₀ alkyl group, more preferably a C 1 -C ₄ alkyl group. Examples of suitable C ₁ -C ₁₀ alkyl groups are methyl, ethyl, propyl, isopropyl, nbutyl, sec-butyl, t-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, 2,4,4-trimethylpentyl and decyl . A particularly preferred alkoxyphosphonate ion is the methoxyphosphonate ion.

- 9 040398

The above alkylsulfonate ion has the formula RS(=O)2O ^- where R is an alkyl group, preferably a Ci-Cio alkyl group, more preferably a C^Cg alkyl group. Examples of suitable Cl-ClO-alkyl groups are methyl, ethyl, propyl, isopropyl, nbutyl, sec-butyl, t-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, 2,4,4-trimethylpentyl and decyl.

The above amide ion has the formula R-N--R, where R and R' may be the same or different, and are preferably electron-withdrawing substituents. Typically, electron-withdrawing substituents are substituents that withdraw electrons from an electron-rich site in the molecule, in this case from an electron-rich nitrogen atom in said amide ion. Preferably R and R' are selected from the group consisting of cyano and alkanesulfonyl.

A particularly preferred amide ion is the dicyanamide ion, ie the ion of the formula RN ^- -R', where R and R' are cyano.

Said alkanesulfonyl substituent on said amide ion has the formula RS(=O) ₂ - where R is an alkyl group, preferably a C ₁ -C ₁₂ alkyl group, more preferably a C ₁ -C ₄ alkyl group, such as methyl, ethyl or n-butyl. Said alkyl groups may be linear or branched. Additionally, said alkyl group may be substituted with one or more halogen atoms. Said alkanesulfonyl substituent is preferably a trihalomethanesulfonyl substituent which has the formula CX ₃ S(=O) ₂ - where X is a halogen atom selected from the group consisting of fluorine, chlorine, bromine and iodine. More preferably, said halogen atom is fluorine. Most preferably said trihalomethanesulfonyl substituent is trifluoromethanesulfonyl (CF ₃ -S(=O) ₂ -).

In the case where an ionic liquid is used to dissolve the complexing agent in the present invention, the ionic liquid preferably contains the N,N'-dialkylimidazolium ion described above as a cation and a tetrafluoroborate ion as an anion. Preferably said N,N'-dialkylimidazolium ion is 1-butyl-3-methylimidazolium ion or 1-ethyl-3methylimidazolium ion, more preferably 1-butyl-3-methylimidazolium ion.

Suitable ionic liquids that can be used to dissolve the complexing agent are generally described in Potential of Silver-Based Room-Temperature Ionic Liquids for Ethylene/Ethane Separation, Galan Sanchez et al., Ind. Eng. Chem. Res., 2009, 48, pages 10650-10656, in particular in Table 1 of the said article, the disclosure of which is incorporated herein by reference. Additional suitable ionic liquids are described in Olefin Paraffin Separation Using Ionic Liquids, Goodrich, Cat. Rev., 2015, 28, pages 9-13, the disclosure of which is hereby incorporated by reference. Additional suitable ionic liquids are disclosed in WO201108664, WO200359483, WO200198239 and GB2383328, the disclosures of which are incorporated herein by reference.

Additionally, it is contemplated that in the complexation separation step (d) of this method, an ionic liquid is used as the liquid solvent containing the complexing agent. In such a case, the ionic liquid is both said liquid solvent and said complexing agent at the same time. Preferably, such an ionic liquid contains a silver (I) ion or a copper (I) ion, more preferably a silver (I) ion. Additionally, the anion in such an ionic liquid may be an anion as described above. Examples of such ionic liquids that can be used in this way are silver (I) bis(trifluoromethanesulfonyl)amide, which has the formula [(CF ₃ -S(=O) ₂ -) ₂ N] ^- Ag ⁺ (Ag[NTf ₂ ]), and tris(perfluoroethyl)silver (I) trifluorophosphate having the formula [(CF ₃ CF2) ₃ F ₃ P] ^- Ag ⁺ (Ag[FAP]). These and other suitable ionic liquids containing silver(I) ions are described in Liquid silver tris(perfluoroethyl) trifluoro phosphate salts as new media for propene/propane separation, Pliquette et al., Phys. Chem. Chem. Phys., 2016, 18, pages 28242-28253. However, for these ionic liquids, it is still preferable to add an additional liquid solvent, such as another ionic liquid that does not contain a metal ion as a cation, in order to liquefy and/or dilute the ionic liquid containing the metal ion.

In addition to the complexing agent, the liquid solvent may contain a modifier or a mixture of modifiers, namely an acid, a salt that does not complex olefins, an oxidizing agent, or a functional organic compound. Such a modifier may be used to increase the solubility and/or stability of the complexing agent in the solvent. Suitable examples of acid modifiers are nitric acid (HNO ₃ ) and fluoroboric acid (HBF 4 ). Additionally, such an acid modifier, especially nitric acid, can reduce the physical solubility of carbon dioxide in the liquid solvent, which advantageously facilitates the separation of carbon dioxide from ethylene in the separation step by complexation (d). In the case where an ionic liquid is used to dissolve the complexing agent in the present invention, it is preferred that the anion of the acid modifier (eg, HBF ₄ ) correspond to the anion of the ionic liquid.

- 10 040398

Silver nitrate is the most preferred complexing agent in the practice of this invention. Silver nitrate has a high solubility and is very stable in water. Additionally, any elemental silver that may be formed can be readily converted to silver nitrate with a small amount of nitric acid. Therefore, in step (d) of the present invention, an aqueous solution is preferably used which contains silver nitrate as a complexing agent. This aqueous solution preferably further contains nitric acid as a modifier.

In the aforementioned complexing step (d1), at least a portion of the stream containing ethylene, unreacted ethane and carbon dioxide obtained in step (b) or (c) is contacted with a liquid solvent containing a complexing agent. The partial pressure of ethylene in said step (r1) may be from 0.5 to 30 bar, more preferably from 1 to 20 bar, most preferably from 2 to 10 bar. The partial pressure of ethylene in step (d1) may be at least about the same as the partial pressure of ethylene in the stream containing ethylene, unreacted ethane and carbon dioxide obtained in step (b) or (c) or higher. Preferably, the ethylene partial pressure is increased before step (d1), for example by compression in a compressor. Additionally, the temperature of the liquid solvent supplied to said step (r1) is preferably below 50°C, more preferably below 40°C, and may be from -20 to 75°C, more preferably from 0 to 50°C, most preferably from 10 to 40°C. In step (d1), excessive temperature rise can be avoided by internal cooling.

Step (d1) may be carried out in a countercurrent column. Preferably, at least a portion of the stream containing ethylene, unreacted ethane and carbon dioxide obtained in step (b) or (c) is fed to the bottom of said column, and the liquid solvent containing the complexing agent is fed to the top of said column . Said column may contain packing or trays, preferably packing. The recovery of ethylene in the complexation step (r1) is preferably greater than 95%, more preferably greater than 98%.

In the aforementioned desorption step (d2), the ethylene complex is desorbed from at least a portion of the liquid stream containing the solvent, the complexing agent and the ethylene complex compound obtained in step (d1). In the present invention, desorption in step (d2) can be affected by lowering the partial pressure of ethylene or by increasing the temperature, or both. A combination of lowering the partial pressure of ethylene and raising the temperature is preferred. The total pressure in said step (r2) may be from 1 mbar to 5 bar, more preferably from 1 mbar to 3 bar, most preferably from 0.5 to 1.5 bar. Additionally, the temperature of the liquid stream supplied to said step (r2) may be from 55 to 130°C, more preferably from 65 to 130°C, most preferably from 80 to 120°C. Preferably, the temperature of said liquid stream is raised before being fed to step (d2), for example by heating. The ethylene recovery in the desorption step (r2) is preferably greater than 95%, more preferably greater than 98%. The liquid stream containing the solvent and the complexing agent obtained in the desorption step (r2) is returned to the complexation step (r1), preferably after cooling.

In the above complexation step (d1), a portion of the unreacted ethane and carbon dioxide is physically absorbed (dissolved) in the liquid solvent rather than complexed with the complexing agent (herein referred to as absorbed unreacted ethane and carbon dioxide). In the case where the liquid stream obtained in step (d1) contains a solvent, a complexing agent, an ethylene complex compound, absorbed unreacted ethane and carbon dioxide, it is preferable to separate said unreacted ethane and carbon dioxide from said liquid stream before feeding it to the desorption step. (d2). In such a case, the absorbed unreacted ethane and carbon dioxide are preferably removed from at least a portion of said liquid stream by contact with a stream containing ethylene, resulting in a stream containing ethylene, unreacted ethane and carbon dioxide, at least a portion which is fed to step (d1), and a liquid stream containing a solvent, a complexing agent and a complex compound of ethylene, at least part of which is fed to step (d2). Preferably, in said desorption step, the ethylene partial pressure and temperature are substantially unchanged to avoid premature desorption prior to step (d2).

The above purification step can be carried out in a countercurrent column. Preferably, at least a portion of the liquid stream obtained in step (d1) is fed to the top of said column, and the ethylene-containing purge stream is fed to the bottom of said column.

If acetylene is generated in step (a) of ethane ODH and not removed in optional step (c), acetylene may be present in the feed to the complexation separation step (d). As mentioned above, acetylene can form a strong bond with the complexing agent in step (d). Alkynes that contain an active hydrogen can form silver or copper alkynyl compounds, which have limited solubility in aqueous solution and

- 11 040398 do not decompose during desorption, so they can accumulate before precipitation. This leads to the consumption of the complexing agent, which can interfere with the flow and create a safety hazard. These deposits are sensitive to detonation, especially when dry, and precautions must be taken to eliminate them effectively. One way to solve this problem is to keep the concentration of silver acetylenide at a safe level using silver permanganate as an oxidizing agent. A small side stream may be withdrawn from the stripper and heated to, for example, 75° C. under partial vacuum. Solid silver permanganate is added to destroy the acetylide, which forms carbon dioxide and a free silver ion. The resulting manganese dioxide precipitates and is filtered from the solution. This leads to the reduction of silver without the addition of a foreign ion. The data and processing of silver acetylenides is given in US Pat. No. 4,174,353, the disclosure of which is incorporated herein by reference.

If carbon monoxide is generated in step (a) of ethane ODH and not removed in optional step (c), carbon monoxide may be present in the feed to the complexation step (d). As mentioned above, together with the desired ethylene product, carbon monoxide can also be complexed with the complexing agent in step (d). Carbon monoxide forms stable complexes with Cu(I) which may be present in the complexing agent used in step (d). In the latter case, such a carbon monoxide complex is not removed in the aforementioned stripping step, but will be stripped along with ethylene in the aforementioned stripping step (r2), resulting in a stream containing both ethylene and carbon monoxide.

If not all of the oxygen is reacted in step (a) of ethane ODH and unreacted oxygen is not removed in optional step (c), oxygen may be present in the feed to the complexation separation step (d). As mentioned above, oxygen can oxidize a metal, such as Cu(I), from a metal salt or metal complex that can be used as a complexing agent in step (d). Any oxygen can be removed in the aforementioned complexing step (r1) as part of the stream containing unreacted ethane and carbon dioxide.

Additionally, hydrogen (H ₂ ) may be present in the feed to the separation step by complexation (d). Hydrogen can cause gradual reduction of Ag(I) to metallic silver. It is preferable to exclude such reduction of silver in order to prevent the loss of silver through the formation of colloidal particles and deposition on the surface. The addition of small amounts of hydrogen peroxide, combined with maintaining the level of nitric acid in solution, can make the dissolved silver resistant to precipitation. More detailed information about this method is given in US patent No. 4174353, the disclosure of which is incorporated herein by reference.

Stage (d).

Step (e) of this process includes recycling at least a portion of the stream containing unreacted ethane and carbon dioxide obtained in step (d) to step (a).

The recycle stream containing unreacted ethane and carbon dioxide obtained in step (d) may contain from 5 to 90% by volume of carbon dioxide, more preferably from 10 to 80% by volume, most preferably from 20 to 70% by volume. Additionally, said recycle stream may contain from 10 to 95% by volume of unreacted ethane, more preferably from 20 to 90% by volume, most preferably from 30 to 80% by volume. Additionally, said recycle stream may contain methane, nitrogen, carbon monoxide and/or oxygen. Accordingly, the amount of methane is less than 20% by volume, more preferably less than 10% by volume, more preferably less than 5% by volume. Additionally, the total amount of nitrogen, carbon monoxide and/or oxygen is preferably less than 10% by volume, more preferably less than 5% by volume, more preferably less than 3% by volume. The specified methane can get when submitting fresh ethane to stage (a) ODH ethane. Additionally, said nitrogen may be supplied by supplying fresh oxygen to step (a) of the ODH of ethane.

Preferably, before returning the ethane to step (a) ODH, the aforementioned stream containing unreacted ethane and carbon dioxide obtained in step (d) is divided into at least two substreams, with at least one separated substream being returned to stage (a ) and at least one separated substream is not returned to step (a). The unreturned substream(s) are removed from the process (purged) and hence may be discarded. The proportion (1) of the separated substream(s) returned to step (a) to (2) the total stream before separation is preferably 80 to 99.9% by volume, more preferably 85 to 99% by volume, more preferably 90 to 98% by volume, most preferably 90 to 95% by volume. Additionally, said proportion may be at least 80 vol.% or at least 85 vol.%, or at least 90 vol.%, or at least 95 vol.%, or at least 97 vol.%, or at least 98 vol.%, or at least 99 vol.%, or not less than 99.5 vol.%. Additionally, the specified proportion may be not more than 99.9 vol.%, or not more than 99.7 vol.%, or not more than 99.5 vol.%, or not more than 99.3 vol.%, or not more than 99 vol. .%, or not more than 98 vol.%, or not more than 95 vol.%. Advantageously, in the event that additional carbon dioxide is produced in step (a) of ethane ODH and possibly in optional step (c), such additional carbon dioxide can be removed by separating the recycle stream prior to recycling so that the amount diluent based on carbon dioxide supplied to stage (a) ODH ethane, can be maintained constant.

An additional advantage in the above case of separation before recirculation is that, simultaneously with the removal of additional carbon dioxide produced in step (a) and optionally in step (c), the accumulation of certain components according to this invention is successfully prevented by blowing through part recycle stream before recirculation. These additional components that can be successfully removed by blowing include, for example, methane from a feed containing fresh ethane, and nitrogen from a feed containing oxygen, as mentioned above. Therefore, this separation and purging procedure has the additional advantage that the fresh ethane-containing feedstock fed to step (a) may contain a certain amount of methane impurities, preferably up to 5 vol.% or up to 3 vol.%, or up to 2 vol.%, or up to 1 vol.%, or up to 5000 volume parts per million (vol. ppm), or up to 2000 vol. ppm, or up to 1000 vol. ppm, or up to 500 vol. ppm Similarly, the oxygen containing feedstock supplied to step (a) may contain a certain amount of nitrogen impurities, preferably up to 5 vol.% or up to 3 vol.%, or up to 2 vol.%, or up to 1 vol.%, or up to 5000 volume parts per million (vol. ppm), or up to 2000 vol. ppm, or up to 1000 vol. ppm, or up to 500 vol. ppm By purging a portion of the recycle stream in step (a), the levels of these components in step (a) can also be successfully stabilized.

Optional additional steps.

Optionally, any propane is removed from the ethane-containing stream in a pre-separation step before being fed to step (a), for example by distillation. Therefore, in the case where propane is in the feed containing ethane, it is preferable that in the step preceding step (a) of this method, the stream containing ethane and propane is fed into the distillation column to obtain a stream containing propane and a stream, containing ethane. The last stream containing ethane, containing no or substantially no propane, is fed to step (a) of the process. Since propane is absent or substantially absent in said step (a), no propylene is formed or practically no propylene is formed from propane by means of FGD in step (a). This successfully prevents the laborious post-separation step of removing propylene from the ethylene recovered in step (d), since both propylene and ethylene can complex with the complexing agent used in step (d). The pre-separation step, which consists in removing propane from the stream containing ethane, before supplying ethane to the EGR stage, is disclosed in the application WO2017072086, the disclosure of which is incorporated herein by reference.

Additionally, in the event that the ethylene-containing stream obtained in step (d) further contains one or more contaminants selected from the group consisting of propylene, carbon monoxide, oxygen, carbon dioxide and water, this or these contaminants may be removed in one or more additional steps. However, such additional purification is not always necessary. In some cases, the raw ethylene stream may be sent without further purification to a plant where the ethylene is further converted. In the event that said contaminants are to be removed, this can be done by any method known to the person skilled in the art. Propylene can be removed by distillation. The carbon monoxide can be removed by conversion (oxidation) to carbon dioxide, for example using copper oxide as an oxidation catalyst, and then removing the carbon dioxide. Oxygen can be removed by using it as an oxidizing agent, for example, in the oxidation of metallic copper. Carbon dioxide can be removed by washing with caustic alkali. The water can be removed by drying, for example using molecular sieves.

Figures 1 and 2.

The method of this invention is further illustrated in FIG. 1 and 2.

In FIG. 1 shows an embodiment of the invention, covering steps (a)-(e) of the method according to the invention. In FIG. 1 stream 1 containing fresh ethane and some propane and methane is fed to distillation column 2 where it is separated into an overhead stream 3 containing fresh ethane and methane and a bottom stream 4 containing propane. Said stream 3, stream 6 containing oxygen, and recycle stream 17b containing carbon dioxide (diluent), unreacted ethane and some methane are fed to an oxidative dehydrogenation (ODH) unit 5 containing an ethane ODH catalyst containing a mixed metal oxide, and operating under the conditions of ODH, in which ethane is converted to ethylene in accordance with the above stage (a) of the method according to this invention. The product stream 7 exiting the FGD unit 5 contains water, methane, ethane, ethylene, oxygen, carbon monoxide, acetylene, carbon dioxide and acetic acid. Said stream 7 is fed into the water condenser 8. In the water condensation unit 8, water and any acetic acid are removed by condensation with stream 10 in accordance with step (b) above, by

Claims (12)

soba op this invention. Optionally, additional water is supplied to the water removal unit 8 via stream 9. The stream 11 coming from the water condensation unit 8, which contains methane, ethane, ethylene, oxygen, carbon monoxide, acetylene and carbon dioxide, is fed to the reactor 12 for gas purification. In the gas purification reactor 12, oxygen, acetylene and carbon monoxide are removed in accordance with step (c) of the method of the invention described above. In particular, carbon monoxide and acetylene are oxidized to carbon dioxide using the above-described oxidation catalyst, in particular an oxidation catalyst that contains copper. Optionally, additional oxygen is supplied to the gas purification reactor 12 via stream 13. The product stream 14 coming from the gas purification reactor 12 contains methane, ethane, ethylene and carbon dioxide. Stream 14 is fed to unit 15 for separation by complexation. In the complexation separation unit 15, the complexation separation method is applied in accordance with the above-described step (d) of the method of the present invention. The apparatus 15 for separating by complexation is further described below with reference to FIG. 2. The stream 18 exiting the complexation separation unit 15 contains ethylene. The stream 17 exiting the complexation separation unit 15 contains carbon dioxide (diluent), (unreacted) ethane and some methane. Said stream 17 is divided into a recycle substream 17b, which is fed to the FGD unit 5, and a substream 17a, which is removed from the process by blowing. This purge prevents the accumulation of methane (found in fresh ethane feed stream 1 and stream 3), additional carbon dioxide (which is produced in ethane FGD unit 5 and gas scrubbing reactor 12), and any nitrogen (which may be in feed stream 12). fresh oxygen 6). In FIG. 2 shows an embodiment of the invention with respect to step (d) of the method comprising steps (a)-(e) shown in FIG. 1. In FIG. 2, the stream 14 containing methane, ethane, ethylene and carbon dioxide, which comes from the gas purification reactor 12, is fed to the bottom of the absorber 15a, which is part of the complexation separation unit 15. Before this stream 14 is fed into the absorber 15a, it is compressed in a compressor (not shown in FIGS. 1 or 2). In absorber 15a, said stream 14 is contacted with a liquid solvent containing a complexing agent according to step (d1) above, this liquid solvent being supplied to the top of absorber 15a by stream 16. The partial pressure of ethylene in absorber 15a may be about 4 bar , and the temperature of the liquid stream 16 supplied to the absorber 15a may be about 30°C. The overhead stream 17 exiting absorber 15a contains carbon dioxide, ethane and methane. The bottom stream 19 exiting absorber 15a is a liquid stream containing solvent, complexing agent, ethylene complex and absorbed methane, ethane and carbon dioxide, which stream is fed to the top of stripper 15b which is also part of plant 15 for separation by complexation. In the stripper 15b, said absorbed methane, ethane and carbon dioxide are stripped off by contacting the ethylene containing stream 18b described above, which stream 18b is fed to the bottom of the stripper 15b. The partial pressure of ethylene in stripper 15b may be about 4 bar and the temperature of the liquid stream 19 fed to stripper 15b may be about 30°C. The top stream 20 from stripper 15b contains ethylene, methane, ethane and carbon dioxide and is compressed in a compressor (not shown in FIG. 2) and then fed to absorber 15a via stream 14. Bottom stream 21 from stripper 15b is a liquid stream which contains solvent, complexing agent and ethylene complexing compound and is fed to stripper 15c which is also part of the complexing separation unit 15. In stripper 15c, ethylene is stripped in accordance with step (d2) described above. The total pressure in stripper 15c may be about 500 mbar and the temperature of the liquid stream 21 fed to stripper 15c may be about 80°C. The overhead stream 18 leaving stripper 15c contains stripped ethylene and is split into two substreams 18a and 18b. Substream 18b is compressed in a compressor (not shown in FIG. 2) and then fed to stripper 15b. Substream 18a may be further purified. The bottom stream 16 exiting stripper 15c is a liquid stream which contains solvent and complexing agent and is returned to absorber 15a according to step (d3) above. CLAIM 1. The method of oxidative dehydrogenation of ethane, including the steps: (a) exposing the stream containing ethane to oxidative dehydrogenation conditions, comprising contacting ethane with oxygen in the presence of a catalyst containing a mixed metal oxide containing molybdenum, vanadium and niobium at a temperature of from 300 to 500 ° C, and step (a) is fed a diluent containing carbon dioxide, resulting in an effluent containing ethylene, unreacted ethane, water, carbon dioxide, unreacted oxygen, carbon monoxide and acetylene; - 14 040398 (b) removing water from at least part of the effluent stream obtained in step (a), resulting in a stream containing ethylene, unreacted ethane, carbon dioxide, unreacted oxygen, carbon monoxide and acetylene, and the stream containing water; (c) removing unreacted oxygen, carbon monoxide and acetylene from at least a portion of the stream containing ethylene, unreacted ethane, carbon dioxide, unreacted oxygen, carbon monoxide and acetylene obtained in step (b) by oxidizing carbon monoxide and acetylene to carbon dioxide using unreacted oxygen and an oxidation catalyst containing a transition metal, resulting in a stream containing ethylene, unreacted ethane and carbon dioxide; (d) removing ethylene from at least a portion of the stream containing ethylene, unreacted ethane and carbon dioxide obtained in step (c) by a complexation separation process which comprises contacting at least a portion of said stream with a liquid solvent containing a complexing agent, resulting in a stream containing ethylene, and a stream containing unreacted ethane and carbon dioxide; (e) recycling at least a portion of the stream containing unreacted ethane and carbon dioxide obtained in step (d) to step (a). 2. The method according to claim 1, characterized in that the catalyst in step (a) additionally contains tellurium. 3. Process according to claim 1 or 2, characterized in that the effluent from step (a) and the water-containing stream from step (b) additionally contain acetic acid. 4. Method according to claim 1, 2 or 3, characterized in that step (d) includes: (d1) contacting at least a portion of the stream containing ethylene, unreacted ethane and carbon dioxide obtained in step (c) with a liquid solvent containing a complexing agent, resulting in a stream containing unreacted ethane and carbon dioxide, at least a portion of which is returned from step (d) to step (a), and a liquid stream containing a solvent, a complexing agent and an ethylene complex; and (d2) desorbing the ethylene complex from at least a portion of the liquid stream containing the solvent, the complexing agent and the ethylene complex compound obtained in step (d1), resulting in a stream containing stripped ethylene and a liquid stream containing solvent and complexing agent; and (d3) recycling at least a portion of the liquid stream containing the solvent and complexing agent obtained in step (d2) to step (d1). 5. The method according to claim 4, characterized in that the liquid stream obtained in step (d1) contains a solvent, a complexing agent, an ethylene complex compound and absorbed unreacted ethane and carbon dioxide, in which the absorbed unreacted ethane and carbon dioxide are distilled from, at least part of said liquid stream by contacting with a stream containing ethylene, resulting in a stream containing ethylene, unreacted ethane and carbon dioxide, at least part of which is fed to step (d1), and a liquid stream containing solvent , a complexing agent and a complex compound of ethylene, at least part of which is fed to step (d2). 6. The method according to any one of the preceding claims, characterized in that the starting material supplied to step (d) contains an amount of carbon dioxide based on the total amount of ethylene, unreacted ethane and carbon dioxide, which is from 1 to 99 vol.%, preferably from 5 to 95% by volume, more preferably 10 to 90% by volume, more preferably 20 to 85% by volume, more preferably 30 to 80% by volume, more preferably 40 to 75% by volume, most preferably from 50 to 70 vol.%. 7. The method according to any one of the preceding claims, characterized in that the complexing agent in step (d) is a metal salt. 8. The method according to claim 7, characterized in that the metal salt contains a silver (I) ion or a copper (I) ion, preferably a silver (I) ion. 9. The method according to claim 8, characterized in that the metal salt is silver nitrate. 10. A method according to any one of the preceding claims, characterized in that the liquid solvent in step (d) is water, an organic solvent, an ionic liquid or a mixture thereof, preferably water. 11. The method according to any of the preceding claims, characterized in that before step (e) the stream containing unreacted ethane and carbon dioxide obtained in step (d) is divided into at least two substreams, and at least one separated substream is returned to step (a), and at least one separated substream is not returned to step (a). 12. The method according to claim 11, characterized in that the proportion of (i) the separated(s) substream(s) returned to stage (a) to (ii) the total stream before separation is from 80 to 99.9 vol.% , more preferably 85 to 99% by volume, more preferably 90 to 98% by volume, most preferably 90 to 95% by volume. -