EA040909B1 - METHOD FOR THE PRODUCTION OF ETHYLENE OXIDE - Google Patents

Description

Field of invention

The invention relates to a method for the production of ethylene oxide.

State of the art

Ethylene oxide is used as a chemical intermediate, mainly in the production of ethylene glycols, but also in the production of ethoxylates, ethanolamines, solvents and glycol ethers. It can be obtained by direct oxidation of ethylene. There are several ways to obtain the original ethylene material. For example, a method for producing ethylene by oxidative dehydrogenation (oxydehydrogenation; ODH) of ethane is known. The ethane ODH process and the ethylene oxide production process mentioned above have in common that both use oxygen.

WO 2012101069 discloses a process in which the aforementioned ethane ODH and ethylene oxide production processes are combined. WO 2012101069 discloses a process for producing ethylene oxide, comprising the following steps: producing ethylene by creating conditions for oxydehydrogenation of a stream containing ethane, resulting in a stream containing ethylene and unreacted ethane; obtaining ethylene oxide by creating conditions for the oxidation of ethylene and unreacted ethane from a stream containing ethylene and unreacted ethane, resulting in a stream containing ethylene oxide, unreacted ethylene and unreacted ethane; and recovering ethylene oxide from the stream containing ethylene oxide, unreacted ethylene and unreacted ethane.

In addition, in a particular embodiment of WO 2012101069, the stream containing unreacted ethylene and unreacted ethane is separated from the aforementioned stream containing ethylene oxide, unreacted ethylene and unreacted ethane, then the stream containing unreacted ethylene and unreacted ethane is separated into a stream containing unreacted ethylene , which is returned to the ethylene oxide production stage, and a stream containing unreacted ethane, which is returned to the ethylene production stage. Thus, in this embodiment of WO 2012101069, unreacted ethylene is returned to the ethylene oxide production stage and unreacted ethane is returned to the ethane ODH stage.

The above embodiment is illustrated in FIG. 3 in WO 2012101069. In said FIG. 3, stream 11 containing unreacted ethylene and ethane is divided into two substreams 11a and 11b. Substream 11a is returned to ethylene oxide production unit 5. Substream 11b is fed to ethylene/ethane separation unit 12. Stream 13 containing unreacted ethylene and stream 14 containing unreacted ethane are returned to ethylene oxide plant 5 and ethylene plant 2, respectively. In addition, as described in WO 2012101069, a third stream can be separated in the ethylene/ethane separation unit 12, namely an overhead purge stream containing non-condensable components such as oxygen and/or argon.

It is an object of the present invention to provide a simplified integrated process for the production of ethylene oxide from ethane, comprising ODH of ethane followed by oxidation of ethylene, which process can be technically feasible, efficient and inexpensive. Such a technically feasible process will preferably result in lower energy consumption and/or lower capital costs.

The essence of the invention

Surprisingly, it has been found that the above objective can be achieved with an integrated process combining an ethane ODH step and a subsequent ethylene oxide production step, with both ethylene and ethane from the stream containing ethylene oxide, ethylene, ethane and water obtained from the ethylene oxide production step. , return to the ODH stage of ethane. For example, it has been found that with the present fully integrated process, the risks associated with the use of an oxidizing agent (eg, oxygen) required in both the ethane ODH step and the ethylene oxide step can be reduced. For further explanation and discussion of other advantages, see the Benefits of the Present Invention section below.

Accordingly, the present invention relates to a process for the production of ethylene oxide, comprising the following steps:

(a) obtaining ethylene by creating conditions for oxydehydrogenation of the stream containing ethane, resulting in the formation of a stream containing ethylene, ethane, water and acetic acid;

(b) separating at least a portion of the stream obtained in step (a) into a stream containing ethylene and ethane and a stream containing water and acetic acid;

(c) obtaining ethylene oxide by causing the oxidation of ethylene and ethane from the stream containing ethylene and ethane obtained in step (b), resulting in a stream containing ethylene oxide, ethylene, ethane and water;

(d) separating at least a portion of the stream obtained in step (c) into a stream containing ethylene and ethane and a stream containing ethylene oxide and water;

(e) returning to step (a) ethylene and ethane from the stream containing ethylene and ethane obtained in step (d), wherein steps (a) and (c) produce carbon dioxide, which is removed in an additional step between steps (b ) and (c) and/or between steps (d) and (e).

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In addition, the present invention relates to a method for the production of monoethylene glycol, in which at least part of the ethylene oxide obtained in the above process is converted into monoethylene glycol.

Brief description of graphic materials

The figure illustrates an embodiment of the invention.

Detailed description of the invention

The method according to the invention includes steps (a)-(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). In addition, said method may include one or more additional steps preceding step (a) and/or following step (e).

While the process of the present invention and the composition or stream used in said process are described in terms of comprising, 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 several different steps and components described, respectively.

In the context of the present invention, when a composition or stream contains two or more components, these components should be chosen so that their total amount does not exceed 100 vol.% or 100 wt.%.

In the present description, it is assumed that the expression is essentially absent means that there is no detectable amount of the component in question in the composition or stream.

In addition, in the present description, it is assumed that the term fresh ethane refers to ethane that does not contain unreacted ethane. In the present description, it is assumed that the term unreacted ethane refers to ethane that was under the conditions of oxidative dehydrogenation in step (a) of the method of the present invention, but was not converted. In addition, in the present description, it is assumed that the term unreacted ethylene refers to ethylene that was under oxidizing conditions in step (c) of the method of the present invention, but was not converted.

Stage (a).

Step (a) of the process of the present invention includes the production of ethylene by allowing the oxidative dehydrogenation of a stream containing ethane, resulting in a stream containing ethylene, ethane, water and acetic acid. This step is also called the ethane ODH step. Since in step (e) of the present process ethylene and ethane are recycled to step (a), in step (a) the stream containing ethylene and ethane is subjected to oxidative dehydrogenation conditions, resulting in a stream containing ethylene, ethane, water and acetic acid. acid. Step (a) may include contacting the stream containing ethylene and ethane with oxygen (O2). Furthermore, said contacting can be carried out in the presence of a catalyst containing a mixed metal oxide. Such a catalyst is further described below.

In step (a) ODH of ethane, ethylene is produced by oxidative dehydrogenation of ethane. In step (a), part of the ethylene generated in step (a) and the ethylene recycled in step (e) to step (a) is oxidized to acetic acid. In step (a), ethylene can also be dehydrogenated to acetylene (ethyne). Ethane can also be directly converted to acetic acid or acetylene. In step (a), carbon dioxide (CO2) and carbon monoxide (CO) are formed, for example from the combustion of ethane and/or ethylene and/or acetic acid and/or acetylene.

In step (a) ODH of ethane, ethane, ethylene and oxygen (O2) may be fed to the reactor. These components can be fed into the reactor together or separately. In other words, the reactor may be fed with one or more feed streams, preferably gas streams, containing one or more of these components. For example, a single feed stream containing oxygen, ethane and ethylene can be fed to the reactor. Alternatively, two or more feed streams, preferably gas streams, may be fed into the reactor, wherein the feed streams may form a combined stream within the reactor. For example, one feed stream containing oxygen, another feed stream containing fresh ethane, and another feed stream containing unreacted ethane and unreacted ethylene, the latter of which in step (e) is returned to step (a) of the present process, can be fed into the reactor separately. In step (a) ODH of ethane, ethane, ethylene and oxygen are typically fed into the reactor in the gas phase.

In the present invention, the weight ratio of ethylene to ethane when fed to step (a) ODH of ethane may be in the range of 0.1:1 to 2:1, preferably 0.2:1 to 1.5:1, more preferably 0 .3:1 to 1.3:1. When determining said mass ratio, the following is assumed: a) said ethylene includes unreacted ethylene, which in step (e) is returned to step (a); and b) said ethane includes fresh ethane which is fed to step (a) and unreacted ethane which is returned to step (a) in step (e). Said fresh ethane and said unreacted ethane and unreacted ethylene (ie recycled ethane and ethylene) may be fed into the reactor used in step (a) through the same inlet or through two different inlets. Said weight ratio may be at least 0.1:1, preferably at least 0.2:1, more preferably at least 0.3:1, more preferably at least 0.4:1, more preferably at least 0.5:1, more preferably at least 0.6:1. Further, said weight ratio may be at most 2:1, preferably at most 1.8:1, more preferably at most 1.6:1, more preferably at most 1.5:1, more preferably at most 1.3 :1, more preferably not more than 1.1:1, more preferably not more than 1:1, more preferably not more than 0.9:1.

The ethane conversion in step (a) can vary widely and can range from 10% to 70%, typically 15% to 60%.

Preferably, in step (a) the ODH of ethane, i. e. during the contact of ethylene and 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.

In addition, in step (a) the ODH of ethane, i.e. during contact of ethylene and ethane with oxygen in the presence of a catalyst, typical pressures are 1.1-30, or 1.1-20, or 1.1-15 bar abs. (i.e. bar absolute pressure). In the present invention, said pressure is preferably above 10 bar abs, more preferably 10 to 20 bar abs, most preferably 11 to 18 bar abs. The indicated pressure refers to the total pressure.

The ethane ODH step (a) may be fed with one or more diluents selected from the group consisting of inert gases, nitrogen (N2), steam (H2O) and methane, preferably steam and/or methane, most preferably methane. Some nitrogen and/or inert gases can be supplied to stage (a) as an impurity in the oxygen supplied to stage (a). In such a case, they act as (additional) diluents. In the case of supplying water vapor as a diluent, it can be supplied in the manner disclosed in WO 2017198762, the content of which is incorporated herein by reference. The use of methane as a diluent (also referred to as ballast gas in the description) in both step (a) and step (b) of the present process is further described below.

The oxygen supplied to step (a) ODH of ethane is the oxidizing agent. Said oxygen may be from any source such as, for example, air. The molar ratio of oxygen to ethylene and ethane is usually 0.01 to 1.1, more preferably 0.01 to 1, more preferably 0.05 to 0.8, more preferably 0.05 to 0.7, more preferably 0.1 to 0.6, more preferably 0.2 to 0.55, most preferably 0.25 to 0.5. The specified ratio of oxygen to ethylene and ethane is the ratio before oxygen, ethylene and ethane come into contact with the catalyst. In other words, the specified ratio of oxygen to ethylene and ethane is the ratio of oxygen in the feed to ethylene and ethane in the feed. Obviously, after contact with the catalyst, at least part of the oxygen, ethylene and ethane is consumed. In addition, the specified ethane in the specified molar ratio of oxygen to ethylene and ethane includes both fresh ethane and recycled (unreacted) ethane.

Preferably, pure or substantially pure oxygen (O2) is used as the oxidizing agent in step (a) of the process of the present invention. As used herein, pure or substantially pure oxygen refers to oxygen which may contain a relatively small amount of one or more contaminants, including, for example, nitrogen (N2) and/or argon, which may be at most 1% by volume, preferably at most 7000 parts per million by volume (ppmv), more preferably 5000 ppmv maximum, more preferably 3000 ppmv maximum, more preferably 1000 ppmv maximum, more preferably 500 ppmv maximum, more preferably 300 ppmv maximum, more preferably 200 ppmv maximum, more preferably 100 maximum ppmv, more preferably a maximum of 50 ppmv, more preferably a maximum of 30 ppmv, most preferably a maximum of 10 ppmv.

Step (a) can be carried out in the presence of an ethane ODH catalyst, preferably in the presence of a mixed metal oxide catalyst. Preferably, the ODH catalyst is a heterogeneous catalyst. Further preferably, the ODH catalyst is a mixed metal oxide catalyst containing molybdenum, vanadium, niobium and optionally tellurium as metals, the catalyst having the following formula:

MoiVaTebNbcOn 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 0.05 to 0.20 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 that is determined by the valency and frequency of occurrence 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, i. e. an amount sufficient to promote the desired reaction(s).

The ODH reactor that can be used in step (a) ODH of ethane can be any reactor, including fixed bed reactors and fluidized bed reactors. A suitable reactor is a fixed bed reactor.

Examples of oxydehydrogenation processes, including catalysts and process conditions, are disclosed, for example, in the aforementioned US Pat.

Step (b).

Step (b) of the present process includes separating at least a portion of the stream obtained in step (a) into a stream containing ethylene and ethane and a stream containing water and acetic acid.

Step (b) may be carried out by condensation. Water and acetic acid in the stream obtained in step (a) may be condensed by cooling said stream to a lower temperature, such as room temperature, after which the condensed water and acetic acid may be separated, resulting in a liquid stream containing condensed water and acetic acid. Additional water may be added during or after step (b) to assist in the removal of acetic acid.

In step (b), the temperature may be from 10 to 150°C, for example from 20 to 80°C. Preferably, in said step (b), the temperature is at least 10°C, or at least 20°C, or at least 30°C. Further preferably, in said step (b), the temperature is at most 150°C, or at most 120°C, or at most 100°C, or at most 80°C, or at most 60°C.

In addition, in step (b) the typical pressure is 1.1-30 or 1.1-20 bar abs (ie bar absolute). Further preferably, said pressure is 1 to 18 bar abs, more preferably 3 to 16 bar abs, most preferably 5 to 15 bar abs. The indicated pressure refers to the total pressure.

Thus, in step (b), a stream containing ethylene and ethane and a stream containing water and acetic acid are formed. The latter stream may be a liquid stream containing condensed water and acetic acid.

Stage (c).

Step (c) of the process of the present invention comprises producing ethylene oxide by conditioning ethylene and ethane to be oxidized from the ethylene and ethane containing stream obtained in step (b) or in the additional carbon dioxide removal step described below, which is carried out between steps (b) and (c) resulting in a stream containing ethylene oxide, ethylene, ethane and water. Preferably, at least a portion of said stream is fed to step (c). Preferably, ethylene and ethane from said stream are not separated from each other before being fed to step (c). In addition, it is preferable that the specified stream is completely fed to stage (c).

In addition, in step (c) of the present process, ethylene and ethane from the ethylene and ethane containing stream that is formed in step (d) or in the additional carbon dioxide removal step described below between steps (d) and (e) may be in oxidation conditions. This is further described below in Step (e).

Step (c) of producing ethylene oxide may include bringing ethylene and ethane into contact with oxygen (O ₂ ). Said oxygen supplied to step (c) is an oxidizing agent and may be in the form of high purity oxygen, preferably greater than 90% purity, preferably greater than 95%, more preferably greater than 99% and most preferably greater than 99.4%. . Suitable reaction pressures in step (c) for producing ethylene oxide are 1.1-30 bar, more preferably 3-25 bar, most preferably 5-20 bar. Suitable reaction temperatures in this step are 100400°C, more preferably 200-300°C.

In the present invention, the weight ratio of ethylene to ethane fed to step (c) of producing ethylene oxide may be in the range of 0.1 to 10, preferably 0.3 to 8, more preferably 0.5 to 6. the ratio may be at least 0.1, preferably at least 0.3, more preferably at least 0.5, more preferably at least 0.7, more preferably at least 1.0. In addition, said weight ratio may be at most 10, preferably at most 8, more preferably at most 6, more preferably at most 5, more preferably at most 4.

Furthermore, it is preferred that said contacting of ethylene and ethane with oxygen in step (c) is carried out in the presence of a catalyst, preferably a catalyst containing silver. A typical reactor for the ethylene oxide production step consists of a set of tubes filled with catalyst. The reactor tubes may be surrounded by a coolant which removes the heat of reaction and makes it possible to control the temperature.

In the case of using a silver-containing catalyst in step (c) of producing ethylene oxide, the silver in the silver-containing catalyst is preferably in the form of silver oxide. Preferred is a catalyst containing particles in which silver is deposited on a carrier.

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Suitable support materials include refractory materials such as alumina, magnesium oxide, zirconia, silica, and mixtures thereof. The catalyst may also contain a promoter component, such as rhenium, tungsten, molybdenum, chromium, nitrate or nitrite forming compounds, and combinations thereof. Preferably, the catalyst is a granular catalyst, eg in the form of a fixed catalyst bed, or a powdered catalyst, eg in the form of a fluidized catalyst bed.

As described herein, the nature of the ethylene oxidation catalyst, if present, is not critical to obtaining the benefits of the present invention. The amount of ethylene oxidation catalyst is irrelevant. If a catalyst is used, it is preferable to use a catalytically effective amount, i.e. an amount sufficient to accelerate the oxidation reaction of ethylene. Although the specific amount of catalyst is not critical to the invention, preference may be given to using the catalyst in such an amount that the gas hourly space velocity (GHSV) is from 100 to 50,000 h' ¹ , preferably from 500 to 20,000 h' ¹ , more preferably from 1000 to 10000 h ^-1 , most preferably from 2000 to 4000 h ^-1 .

As used herein, GHSV, or Gas Hourly Space Velocity, is a unit volume of gas at normal temperature and pressure (0°C, 1 atmosphere, i.e., 101.3 kPa) passing through a unit volume of catalyst per hour.

Examples of ethylene oxidation processes, including catalysts and other process conditions, are disclosed, for example, in US 20090281345 and GB 1314613, the contents of which are incorporated herein by reference. All of these ethylene oxidation processes are suitable for ethylene oxidation step (c) in the process of the present invention.

Typically, a ballast gas (also referred to as a diluent in the present specification) is added during the production of ethylene oxide. The oxidation of ethylene requires an oxidizing agent such as high purity oxygen. Since an oxidizing agent is required, it is important to control the safe functioning of the reaction mixture. Nitrogen, argon, methane or ethane can be used as such ballast gas. Thus, one of the functions of the ballast gas is to control this safe operation.

In the present invention, both ethylene and ethane from the stream containing ethylene and ethane obtained in step (b) are fed to step (c) for producing ethylene oxide. Thus, in the process of the present invention, unreacted ethane from ethane ODH step (a) can advantageously be used as ballast gas in step (c) of ethylene oxidation, so that no or less additional ballast gas is required. As a result, the ethylene oxidation process is simpler and more efficient than in the case of a non-integrated process. If the amount of ethane in the stream obtained in step (b) is insufficient, step (c) may be fed with one or more additional gases selected from the group consisting of nitrogen, methane and ethane. Preferably, methane is supplied as additional ballast gas. The use of methane as a diluent (herein also referred to as ballast gas) in both step (a) and step (b) of the present process is further described below.

The amount of ethylene fed to step (c) of producing ethylene oxide may be from 1 to 50 wt.%, preferably from 3 to 30 wt.%, more preferably from 4 to 20 wt.%, most preferably from 5 to 15 wt.% , based on the total mass of raw materials supplied to stage (c). The amount of ethane fed to stage (c) of producing ethylene oxide may be from 1 to 50 wt.%, preferably from 1 to 30 wt.%, more preferably from 2 to 25 wt.%, most preferably from 3 to 20 wt.% based on the total mass of raw materials supplied to stage (c).

In the process of the present invention, a moderator such as a chlorohydrocarbon such as monochloroethane (ethyl chloride), vinyl chloride or dichloroethane may be supplied in the ethylene oxide production step to control the performance of the catalyst. The most suitable is the use of ethyl chloride.

Retarders that can be preferably used in the ethylene oxide production step of the process of the present invention are also disclosed in the aforementioned GB 1314613, the contents of which are incorporated herein by reference. GB 1314613 discloses the use in the production of ethylene oxide from ethylene of an inhibitor (ie moderator) selected from ethylene dichloride, vinyl chloride, dichlorobenzene, monochlorobenzene, dichloromethane and chlorinated phenyls, chlorinated biphenyls and chlorinated polyphenyls.

As described herein, the nature of the moderator, if any, is not essential to obtaining the benefits of the present invention. The amount of such a moderator in the reaction mixture may be from 1 ppmv to 2 vol%, preferably from 1 to 1000 ppmv. The minimum amount of moderator in the reaction mixture may be 0.1, 0.2, 0.5, 1, 2, 5, 10, or 50 ppmv. The maximum amount of moderator in the reaction mixture can be 2.1 vol.%, 1000, 800, 600, 400, 200 or 150 ppmv.

A suitable range of retarder amount for the above group of specific inhibitors (i.e., retarders) that can be used in the ethylene oxide production step of the process

- 5 040909 according to the present invention, is also disclosed in the above-mentioned GB 1314613, the contents of which are incorporated herein by reference.

Advantageously, it is not necessary to remove any carbon monoxide and/or any acetylene present in the feed to step (c). In step (c) oxidizing ethylene, carbon monoxide may be oxidized to carbon dioxide, which in turn may be removed in accordance with the present invention, as further described below. Similarly, in step (c), acetylene can be oxidized to carbon dioxide. For example, the amount of acetylene in the feed to step (c) may be up to and including 1000 ppmv, preferably a maximum of 500 ppmv, more preferably a maximum of 200 ppmv, based on the total weight of the feed. Therefore, advantageously, since it is not necessary to remove any carbon monoxide and/or any acetylene, the additional gas purification reactor can be omitted in the process of the present invention.

Alternatively, at least a portion of the feed to step (c), or at least a portion of the feed to the additional carbon dioxide removal step described below, which takes place between steps (b) and (c), may be treated, resulting in which carbon monoxide and/or acetylene is oxidized to carbon dioxide. Preferably, said oxidation is carried out in the presence of an oxidation catalyst, preferably an oxidation catalyst which contains a transition metal. Preferably, said oxidation catalyst contains one or more metals selected from the group consisting of nickel, copper, zinc, palladium, silver, platinum, gold, iron, manganese, cerium, tin, ruthenium and chromium. Further preferably, said oxidation catalyst contains copper and/or platinum, preferably copper or platinum, more preferably copper. The temperature during said oxidative treatment may be from 50 to 500°C, for example from 100 to 400°C. Preferably, said temperature is in the range of 100 to 400°C, more preferably 150 to 300°C, most preferably 200 to 260°C.

The above oxidative treatment may be carried out in a separate reactor prior to step (c) or in the additional carbon dioxide removal step described below between steps (b) and (c). Alternatively, said treatment may be carried out inside the reactor used in step (c), namely in its initial section, while the actual step (c) is carried out in the next section of the same said reactor.

Step (d).

Step (d) of the present process includes separating at least a portion of the stream containing ethylene oxide, ethylene, ethane and water obtained in step (c) into a stream containing ethylene and ethane and a stream containing ethylene oxide and water.

Ethylene oxide can be easily removed from the stream obtained in step (c) using techniques known to those skilled in the art. Step (b) can be carried out in the same manner as step (b) as described above, for example by condensation, taking into account the different boiling point of the ethylene oxide recovered in step (d). The preferences and implementation options described for step (b) also apply to step (d).

Optional components that may also be present in the stream comprising ethylene oxide, ethylene, ethane and water obtained in step (c), which also includes carbon dioxide, are: additional ballast gas, moderator and unreacted oxygen (O ₂ ). Carbon dioxide is generated in step (c), which can also use additional ballast gas and moderator as described above. In addition, in step (c), oxygen can be used as an oxidizing agent. In this case, step (d) forms a stream containing ethylene, ethane, carbon dioxide, optionally additional ballast gas, optionally a moderator and optionally oxygen, and a stream containing ethylene oxide and water.

Stage (e).

In the process of the present invention, step (e) includes returning to step (a) ethylene and ethane from the ethylene and ethane containing stream obtained in step (d) or in the additional carbon dioxide removal step described below between steps (d) and (e). ). In the process of the present invention, it is preferred that the ethylene from said stream is not recycled directly to step (c) or to the additional carbon dioxide removal step mentioned below between steps (b) and (c), but is recycled only indirectly via step (a). Accordingly, at least a portion of said stream is returned to step (a). Preferably, ethylene and ethane from said stream are not separated from each other before being returned to step (a). In addition, it is preferable that said thread is completely returned to step (a).

In addition, in the process of the present invention, ethylene and ethane from the ethylene and ethane containing stream obtained in step (d) or in the additional carbon dioxide removal step between steps (d) and (e) described below can be recycled to step ( c) or to the following additional carbon dioxide removal step between steps (b) and (c).

In the absence of an additional carbon dioxide removal step between steps (b) and (c), ethylene and ethane can be returned to step (c) from the ethylene and ethane containing stream obtained in step

- 6 040909 additional removal of carbon dioxide between steps (d) and (e). In said case, a portion of said stream is returned to step (c). Furthermore, in this case, it is preferable that ethylene and ethane from said stream are not separated from each other before being recycled to step (c).

In the absence of an additional carbon dioxide removal step between steps (d) and (e), ethylene and ethane from the ethylene and ethane containing stream obtained in step (d) may be returned to the additional carbon dioxide removal step between steps (b) and (c) or to step (c). In this case, a portion of said stream is returned to an additional carbon dioxide removal step between steps (b) and (c) or to step (c). Furthermore, in this case it is preferable that ethylene and ethane from said stream are not separated from each other before being recycled to an additional carbon dioxide removal step between steps (b) and (c) or to step (c).

In the case where there is both an additional carbon dioxide removal step between steps (b) and (c) and an additional carbon dioxide removal step between steps (d) and (e), ethylene and ethane from the ethylene and ethane containing stream obtained in an additional carbon dioxide removal step between steps (d) and (e), may be returned to step (c). In this case, a part of said stream is returned to step (c). In addition, in this case it is preferable that ethylene and ethane from said stream are not separated from each other before returning to step (c).

Returning a portion of the stream containing ethylene and ethane obtained in step (d) or the additional carbon dioxide removal step between steps (d) and (e) described below to step (c) or the additional carbon dioxide removal step described below between steps ( b) and (c), as described above, can be carried out by dividing said stream into streams (i) and (ii), with stream (i) returning to step (a) and stream (ii) returning to step (c ) or an additional carbon dioxide removal step between steps (b) and (c).

When returning ethylene and ethane in step (e) as described above, the ethylene and ethane containing stream that is returned in step (e) may contain the moderator used in step (c) as described above. The amount of moderator in said stream may vary from 1 ppmv to 2 vol%, preferably from 1 to 1000 ppmv. The minimum amount of moderator in the specified flow can be 0.1, 0.2, 0.5, 1, 2, 5, 10, or 50 ppmv. The maximum amount of moderator in the specified stream can be 2.1 vol.%, 1000, 800, 600, 400, 200 or 150 ppmv.

Removal of carbon dioxide.

In the present invention, carbon dioxide is generated in step (a) of ethane ODH and step (c) of producing ethylene oxide. Moreover, in the present invention, said carbon dioxide is removed in an additional step between steps (b) and (c) and/or between steps (d) and (e). In the present invention, there may be one carbon dioxide removal step, namely between steps (b) and (c) or between steps (d) and (e). In addition, in the present invention, there may be two steps for removing carbon dioxide, namely between steps (b) and (c) and between steps (d) and (e). In the present invention, it is preferred that the carbon dioxide removal step is between steps (b) and (c). More preferably, the present invention has one carbon dioxide removal step, and said step is between steps (b) and (c). Thus, in this more preferred case, there is no carbon dioxide removal step between steps (d) and (e).

In the case where carbon dioxide is removed in the present invention in an additional step between steps (b) and (c), the stream obtained in step (a) contains ethylene, ethane, water, acetic acid and carbon dioxide, and at least part this stream is separated in step (b) into a stream containing ethylene, ethane and carbon dioxide and a stream containing water and acetic acid. In addition, said additional step between steps (b) and (c) includes the removal of carbon dioxide from at least a portion of the stream containing ethylene, ethane and carbon dioxide obtained in step (b), resulting in a stream containing ethylene and ethane. In addition, in step (c) ethylene oxide is obtained from the last stream containing ethylene and ethane, creating conditions for the oxidation of ethylene and ethane.

In the ODH embodiment of ethane, as shown in FIG. 3 of the aforementioned WO 2012101069, carbon dioxide is not removed between the ethane and ethylene oxide ODH steps, so that the carbon dioxide can be directed to the ethylene oxide step. According to the present invention, in the aforementioned additional carbon dioxide removal step between steps (b) and (c), carbon dioxide is preferably prevented from entering step (c) of producing ethylene oxide. It is well known that the presence of carbon dioxide during the production of ethylene oxide, which is carried out in step (c) of the process of the present invention, reduces the activity and/or selectivity (to ethylene oxide) of the catalyst used in this step.

According to the present invention, in the case where carbon dioxide is removed in an additional step between steps (d) and (e), the stream obtained in step (c) contains ethylene oxide, ethylene, ethane, water and carbon dioxide, and at least part this stream is separated in step (d) into a stream containing ethylene, ethane and carbon dioxide and a stream containing ethylene oxide and water. In addition, said additional step between steps (d) and (e) includes removing carbon dioxide from at least a portion of the stream containing ethylene, ethane and carbon dioxide obtained in step (d), resulting in a stream containing ethylene and ethane. Next, in step (e), ethylene and ethane from this stream containing

- 7 040909 ethylene and ethane are returned to step (a).

In the above additional carbon dioxide removal step or steps, carbon dioxide can be removed by any of the well known techniques. A suitable carbon dioxide scavenging agent to be fed to such a step may be an aqueous solution of a base such as sodium hydroxide and/or an amine. After such removal of carbon dioxide, the stream from which carbon dioxide has been removed may be dried to remove any residual water before being fed to the next step.

Methane as a diluent in steps (a) and (c).

In the present invention, most preferably, methane is used as a diluent in both step (a) and step (c) and the methane from the stream obtained in step (c) is returned to step (a).

In the above case, the method of the present invention includes the following steps:

(a) obtaining ethylene by creating oxidative dehydrogenation conditions for a stream containing ethane, ethylene and methane, resulting in a stream containing ethylene, ethane, methane, water and acetic acid;

(b) separating at least a portion of the stream obtained in step (a) into a stream containing ethylene, ethane and methane and a stream containing water and acetic acid;

(c) obtaining ethylene oxide by causing the oxidation of ethylene, ethane and methane from the stream containing ethylene, ethane and methane obtained in step (b), resulting in a stream containing ethylene oxide, ethylene, ethane, methane and water;

(d) separating at least a portion of the stream obtained in step (c) into a stream containing ethylene, ethane and methane and a stream containing ethylene oxide and water;

(e) returning ethylene, ethane and methane from the ethylene, ethane and methane containing stream obtained in step (d) to step (a), wherein steps (a) and (c) produce carbon dioxide, which is removed in an additional step between steps (b) and (c) and/or between steps (d) and (e).

Moreover, in the above case, some of the methane may be lost in the separation steps (b) and (d) and in the carbon dioxide removal step(s). In this case, the relative amount of methane can be kept constant by supplying a make-up stream containing methane to the process of the present invention. Such a make-up stream can be fed to step (a) and/or step (c), preferably step (c).

advantages of the invention.

Thus, in the present invention, it is preferably not necessary to separate ethane from ethylene at all before returning to step (a), since both ethylene and ethane are returned to step (a). In contrast, in the ethane ODH embodiment of the above described process disclosed in WO 2012101069, ethylene and ethane must be separated to allow ethylene to be directly returned to the ethylene oxidation stage, while ethane is returned to the ethane ODH stage. This additional step of separating ethylene and ethane, which is successfully eliminated in the method of the present invention, is inconvenient because it requires an ethylene/ethane separation apparatus in which ethylene and ethane are separated by cryogenic distillation, resulting in high energy and capital costs.

In addition, in the method of the present invention, in step (e) at least a portion of the stream containing ethylene, ethane, carbon dioxide, optionally additional ballast gas, optionally a moderator and optionally oxygen obtained in step (d), can be returned to step (a), i. e. without any intermediate separation/processing steps between said steps (d) and (a). In addition to the absence of an ethane-ethylene separation step, as discussed above, this provides the following additional benefits.

The advantage is that unreacted oxygen does not need to be removed from the above stream before it is returned to step (a), since such oxygen can still be used as an oxidizing agent in step (a), as described above. In addition, since the present invention does not require cryogenic distillation to separate ethane and ethylene, there can be no safety risk caused by the presence of oxygen in cryogenic distillation. This risk can be reduced by the laborious removal of unreacted oxygen prior to said cryogenic distillation step. Thus, in the present method, such a safety hazard is successfully eliminated and, therefore, there is no need for the above-described removal of oxygen.

In addition, in the present invention, it is preferably not necessary to directly supply oxygen to step (a), but oxygen can be supplied indirectly through supply to step (c) and recirculation in step (e) to step (a). Therefore, in the present invention, there should be only one oxygen supply point, namely, in step (c) of oxidizing ethylene, especially in the case where the oxygen conversion in said step (c) is kept relatively low. Such a single oxygen supply point may be located anywhere between steps (a) and (c), but preferably, oxygen from said oxygen supply point is supplied directly to step (c). Having a single oxygen supply point in an integrated process is an advantage as it reduces the risk associated with oxygen handling and reduces equipment costs.

The foregoing differs from the ethane ODH embodiment shown in FIG. 3 of the aforementioned WO 2012101069, where oxygen is supplied separately for the ODH of ethane and the production of ethylene oxide, through two different feed points, in streams 15 and 4, respectively. In the process shown in FIG. 3, part of the oxygen that was not converted during the production of ethylene oxide is recycled back to the ethylene oxide plant via streams 9a and 11a. The rest of the unreacted oxygen is fed to the ethylene/ethane separation unit 12, where the oxygen is removed as a non-condensable gas in the overhead bleed (which can be a safety hazard). This means that oxygen is not present in the stream returned to the ethane ODH plant, which creates the need for an additional oxygen supply point for the ethane ODH plant. The loss of oxygen feed in the purge stream and the need for an additional oxygen supply point, as described above, are successfully eliminated in the present invention. Since there is no such loss of oxygen feed in the present invention, there is no need to maximize the oxygen conversion in step (c) to reduce said oxygen loss, and this is advantageous because the relatively high conversion results in an unfavorable decrease in ethylene oxide selectivity.

In addition, it is an advantage that no need to remove carbon dioxide from the above stream containing ethylene, ethane, carbon dioxide, optionally, additional ballast gas, optionally, moderator and optionally oxygen obtained in stage (d), before recycling to stage (a ). In addition, the carbon dioxide generated from both ethane ODH and ethylene oxide production can still be removed together, in a single additional carbon dioxide removal step between steps (b) and (c), while at the same time making it possible to also avoid the negative effect of carbon dioxide on the ethylene oxidation reaction, as described above.

It is also an advantage that additional ballast gas (e.g. methane) does not need to be removed from the above stream before it is returned to step (a), since such additional ballast gas can still be used as a diluent in step (a), as described above. The relatively large amount of such additional ballast gas in step (a) of the ethane ODH further helps to maintain a low oxygen concentration in the ethane ODH reactor, and this effectively reduces ignition risks.

Finally, as mentioned above, in the case where a moderator is used in the ethylene oxide production step in the present invention, such moderator is also returned to step (a). Surprisingly, it has been found that such moderator, recycled to step (a), advantageously does not interfere with the ODH reaction of ethane in step (a).

Therefore, the process of the present invention does not require any intermediate separation/treatment steps after the removal of the ethylene oxide product and water in step (d) and before returning to step (e). The elimination of the aforementioned ethane/ethylene separation step is a significant advantage as it results in significant process simplification with fewer separation processes and equipment, as well as significant cost savings such as savings in compression, cooling, etc.

In addition, it has surprisingly been found that ethylene, which is recycled to step (a) of ethane ODH in the process of the present invention, is predominantly converted to acetic acid (and, to a lesser extent, to oxides of carbon), which is another valuable product besides ethylene oxide. The aforementioned WO 2012101069 focuses only on the production of ethylene oxide and does not disclose the co-production of ethylene oxide and acetic acid in one integrated process. In addition, in the method of the present invention, acetic acid is easily recovered in step (b) of removing water. This is not an additional step since WO 2012101069 also uses such a water removal step.

In general, in an integrated process according to the invention, a single cycle can be successfully implemented by supplying additional ballast gas (make-up stream) and oxygen at only one point in the entire process, preferably in the feed to the ethylene oxide production stage, and supplying fresh ethane to the ethane ODH stage, and returning the effluent from said ethylene oxide production step, after removing only ethylene oxide and water from it, and without separating ethane, ethylene and any other components, completely to stage (a) ODH ethane, and at this stage (a) it is possible to still use additional ballast gas and (unreacted) oxygen, with the valuable acetic acid being formed as a valuable by-product, and the carbon dioxide produced in the reaction steps (a) and (c) can still be removed together in a single step between steps (b) and (c), without adversely affecting the moderator on the ethane ODH reaction in step (a).

Production of monoethylene glycol.

Preferably, at least a portion of the ethylene oxide is converted to monoethylene glycol (MEG), which is a useful liquid product. Thus, the present invention also relates to a method for the production of monoethylene glycol, comprising the following steps: obtaining

- 9 040909 ethylene oxide by the method of the present invention, as described above; and converting at least a portion of the ethylene oxide to monoethylene glycol.

The conversion of ethylene oxide to MEG can be accomplished using any MEG production process that uses ethylene oxide. Typically, ethylene oxide is hydrolysed with water to MEG. Optionally, ethylene oxide is first converted with carbon dioxide to ethylene carbonate, which is then hydrolyzed to MEG and carbon dioxide. Water is supplied to the MEG zone in the form of a raw material containing water, preferably in the form of pure water or steam. The MEG product is obtained from the MEG zone as an effluent containing MEG. Suitable methods for the production of ethylene oxide and MEG are described, for example, in US 2008139853, US 2009234144, US 2004225138, US 20044224841 and US 2008182999, the descriptions of which are incorporated herein by reference.

The invention is further illustrated in the figure as described below.

In the process flow diagram shown in the figure, stream 1 containing fresh ethane is fed into ethane ODH unit 2. Return stream 15 containing ethylene, ethane, methane, carbon dioxide and oxygen is also fed to ethane unit 2 ODH. Stream 3 containing ethylene, ethane, methane, water, acetic acid and carbon dioxide from ethane ODH unit 2 is sent to a water removal unit 4 in which water and acetic acid are removed in stream 5. Stream 6 containing ethylene, ethane , methane and carbon dioxide coming from the water removal plant 4, optionally combined with the following substream 15a, are sent to the carbon dioxide removal unit 7, where carbon dioxide is removed in stream 8. Optionally, stream 6, optionally combined with the below substream 15a, is separated, and substream 6a is fed directly to the ethylene oxide production unit 10.

A stream 9 containing ethylene, ethane and methane from the carbon dioxide removal unit 7, optionally combined with the substream 15b mentioned below, and a stream 11 containing oxygen are fed to the ethylene oxide production unit 10. In addition, the ethylene oxide production unit 10 is fed with a make-up stream containing methane (not shown in the figure). Stream 12 containing ethylene oxide, ethylene, ethane, methane, carbon dioxide, water and oxygen from the ethylene oxide production unit 10 is sent to the ethylene oxide separation unit 13. Ethylene oxide and water are removed by stream 14. In addition, stream 15 containing ethylene, ethane, methane, carbon dioxide and oxygen is returned to ethane ODH unit 2. Optionally, stream 15 is split and substream 15a and/or substream 15b is returned to carbon dioxide removal unit 7 and ethylene oxide production unit 10, respectively.

Claims (10)

CLAIM 1. Method for the production of ethylene oxide, including the following steps: (a) obtaining ethylene by creating oxydehydrogenation conditions for a stream containing ethane, resulting in a stream containing ethylene, ethane, water, acetic acid and carbon dioxide; (b) separating at least a portion of the stream obtained in step (a) into a stream containing ethylene, ethane and carbon dioxide and a stream containing water and acetic acid; (c) obtaining ethylene oxide by causing the oxidation of ethylene and ethane from the stream containing ethylene and ethane obtained in step (b), resulting in the formation of a stream containing ethylene oxide, ethylene, ethane, water and carbon dioxide; (d) separating at least a portion of the stream obtained in step (c) into a stream containing ethylene, ethane and carbon dioxide and a stream containing ethylene oxide and water; (e) returning to step (a) ethylene and ethane from the stream containing ethylene and ethane obtained in step (d), wherein steps (a) and (c) produce carbon dioxide, which is removed in an additional step between steps (b ) and (c) and/or between steps (d) and (e). 2. Process according to claim 1, wherein the weight ratio of ethylene to ethane fed to step (a) is in the range of 0.1:1 to 2:1, preferably 0.2:1 to 1.5:1 , more preferably from 0.3:1 to 1.3:1. 3. The method according to claim 1 or 2, characterized in that the weight ratio of ethylene to ethane supplied to step (c) is in the range from 0.1 to 10, preferably from 0.3 to 8, more preferably from 0, 5 to 6. 4. Process according to any one of the preceding claims, characterized in that at least a portion of the ethylene and ethane containing stream obtained in step (d) is returned to step (a). 5. The method according to claim 4, characterized in that the stream containing ethylene and ethane obtained in step (d) is completely returned to step (a). 6. Process according to any one of the preceding claims, characterized in that in step (c) a moderator is used and the moderator is present in the stream containing ethylene and ethane, which is returned in step (e), preferably in an amount of from 1 ppm by volume (ppmv) up to 2 vol.%, more preferably from 1 to 1000 ppmv. - 10 040909 7. A method according to any one of the preceding claims, characterized in that the carbon dioxide is removed between steps (b) and (c), preferably in a single carbon dioxide removal step which is between steps (b) and (c). 8. A process according to any one of the preceding claims, wherein methane is used as a diluent in both step (a) and step (c) and the methane from the stream obtained in step (c) is returned to step (a). 9. The method according to claim 8, which includes the steps: (a) obtaining ethylene by creating oxidative dehydrogenation conditions for a stream containing ethane, ethylene and methane, resulting in a stream containing ethylene, ethane, methane, water, acetic acid and carbon dioxide; (b) separating at least a portion of the stream obtained in step (a) into a stream containing ethylene, ethane, methane and carbon dioxide and a stream containing water and acetic acid; (c) producing ethylene oxide by allowing ethylene, ethane and methane to be oxidized from the ethylene, ethane and methane containing stream obtained in step (b), resulting in a stream containing ethylene oxide, ethylene, ethane, methane, water and dioxide carbon; (d) separating at least a portion of the stream obtained in step (c) into a stream containing ethylene, ethane, methane and carbon dioxide and a stream containing ethylene oxide and water; (e) returning ethylene, ethane and methane from the ethylene, ethane and methane containing stream obtained in step (d) to step (a), wherein steps (a) and (c) produce carbon dioxide, which is removed in an additional step between steps (b) and (c) and/or between steps (d) and (e). 10. Method for the production of monoethylene glycol, including the steps of obtaining ethylene oxide by the method according to any one of the preceding paragraphs; and converting at least a portion of the ethylene oxide to monoethylene glycol.