WO2026028087A1

WO2026028087A1 - Online regeneration of oxidative dehydrogenation catalyst by treatment in process stream

Info

Publication number: WO2026028087A1
Application number: PCT/IB2025/057646
Authority: WO
Inventors: Jared Taylor; Shahin Goodarznia; William CHIMSUNUM; Vasily Simanzhenkov
Original assignee: Nova Chemicals International SA
Current assignee: Nova Chemicals International SA
Priority date: 2024-07-31
Filing date: 2025-07-28
Publication date: 2026-02-05
Anticipated expiration: 2027-01-31

Abstract

A method of concurrently producing ethylene and regenerating a first oxidative dehydrogenation (ODH) catalyst that is at least partially deactivated is disclosed. The method includes contacting, in a first reactor, the first ODH catalyst with a first gaseous feed comprising ethane and oxygen under conditions such that conversion of oxygen in the first reactor is less than or equal to 90% to produce a first product stream comprising ethylene and to regenerate the first ODH catalyst, wherein the molar ratio of ethane to oxygen in the first gaseous feed is between 0.5 and 1.5.

Description

ONLINE REGENERATION OF OXIDATIVE DEHYDROGENATION CATALYST BY TREATMENT IN PROCESS STREAM

TECHNICAL FIELD

The invention generally relates to regenerating a catalyst. More specifically, the present disclosure relates to online regeneration of a catalyst used in an oxidative dehydrogenation (ODH) process.

BACKGROUND ART

Oxidative dehydrogenation (ODH) is one of several processes used to produce alkenes (olefins) from alkanes, with other processes being steam cracking and fluid catalytic cracking. Ethylene, for example, can be produced by the oxidative dehydrogenation of ethane. Conventional processes for the oxidative dehydrogenation of ethane to produce ethylene involve the use of catalysts.

The use of catalysts in the oxidative dehydrogenation process has at least one major drawback, namely catalyst deactivation. In some instances, in the context of commercial production in a plant, the oxidative dehydrogenation process deactivates the catalyst gradually. In such instances, the regeneration of the catalyst can be coordinated based on the plant’s manufacturing schedule. In other instances, however, unexpected process malfunctions deactivate the catalyst; and in such instances, the plant is likely to experience production losses due to the unexpected need to interrupt regular operation and put the reactor into offline catalyst regeneration mode. Offline regeneration, even though well established, is an undesirable operation that can result in loss of production and an increase in the likelihood of producing off-specification product for a certain period when production is being restarted.

SUMMARY OF INVENTION

The present disclosure provides a solution to at least one or more of the aforementioned problems associated with the deactivation of catalysts in the oxidative dehydrogenation of alkanes to produce olefins. In some embodiments, the solution involves an online catalyst regeneration process where reactant feed gas is contacted with partially deactivated catalyst, while ensuring one pass oxygen conversion is below a certain value for a predetermined regeneration period. Once the regeneration period has passed and the catalyst has been regenerated, the oxygen one pass conversion can be increased above the certain value. A benefit of this process is that it can allow for the regeneration of a catalyst used in the oxidative dehydrogenation of alkanes process while operating the catalytic reactor in production mode so as to minimize production losses.

In some embodiments, the method disclosed herein for concurrently producing ethylene and regenerating a first oxidative dehydrogenation (ODH) catalyst that is at least partially deactivated includes contacting, in a first reactor, the first ODH catalyst with a first gaseous feed comprising ethane and oxygen under conditions such that conversion of oxygen in the first reactor is less than or equal to 90% to produce a first product stream comprising ethylene and to regenerate the first ODH catalyst, wherein the molar ratio of ethane to oxygen in the first gaseous feed is between 0.5 and 1.5.

In some embodiments, the method further includes providing a second gaseous feed including the first product stream to a second reactor unit connected in series with the first reactor unit, and contacting the second gaseous feed with a second ODH catalyst in the second reactor under conditions such that the conversion of oxygen in the second reactor is greater than 90%, producing a second product stream comprising ethylene.

In some embodiments, the second gaseous feed further includes an interstage feed gas comprising one or both of oxygen and ethane. In some embodiments, the interstage feed gas further comprises ethane. In some embodiments, the interstage feed is at a temperature of 200°C to 250°C.

In some embodiments, the conversion of oxygen in the second reactor is greater than 99% or is 100%.

In some embodiments, the second gaseous feed comprises (1) effluent from the last in the series of the one or more additional reactors and (2) an inter-stage feed gas comprising ethane and oxygen.

In some embodiments, the conditions in the first reactor comprise one or more of the following: the first gaseous feed having a molar ratio of 8 to 25 mol. % oxygen, 8 to 25 mol. % ethane, and 65 to 84 mol. % nitrogen; a gas hourly space velocity (GHSV) in a range of 500 h-1 to 30000 h-1; a temperature in a range of 300°C to 450°C; and a pressure in a range of 20 psig to 120 psig.

In some embodiments, the conditions in the first reactor comprise one or more of the following: the first gaseous feed having a molar ratio of 10 to 20 mol. % ethane, 8 to 25 mol. % oxygen, 10 to 45 mol. % carbon dioxide, and 10 to 45 mol. % steam; a gas hourly space velocity (GHSV) in a range of 2500 to 2900 h-1; a temperature in a range of 300°C to 450°C; and a pressure in a range of 20 psig to 100 psig. In some embodiments, the regenerating in the first reactor is initiated when ethane conversion in ODH reaction in the first reactor deteriorates from a range of 45% to 55% to a range of 35% to 44%.

In some embodiments, the conditions in the first reactor that result in conversion of oxygen in the first reactor to be less than or equal to 90% are maintained for a regenerating period of at least 2 hours.

In some embodiments, the regenerating period is in a range of 2 hours to 60 hours.

The present disclosure also provides a system for concurrently producing ethylene and regenerating a partially deactivated oxidative dehydrogenation (ODH) catalyst, the system including: a first reactor configured to dehydrogenate ethane in the presence of oxygen to produce ethylene; a second reactor connected in series with the first reactor and configured to dehydrogenate ethane in the presence of oxygen to produce ethylene; and a channel scheme comprising a first channel and a second channel, the first channel configured to provide a first gaseous feed comprising ethane and oxygen to either the first reactor or the second reactor, and the second channel configured to provide a product stream from the first reactor to a second reactor three-way valve.

In some embodiments, the channel scheme is configured to provide the first gaseous feed to the first reactor, the first reactor comprises the partially deactivated catalyst and the channel scheme is configured to provide a first product stream from the first reactor to the second reactor.

In some embodiments, the system further includes a valve and a feedline for providing an interstage gaseous feed comprising ethane and oxygen to a transfer line, the transfer line in fluid communication with the first and the second reactor.

In some embodiments, the system further includes one or more additional reactors in series with and between the first reactor and the second reactor.

In some embodiments, when the channel scheme is configured to provide the first gaseous feed to the second reactor, the second reactor comprises the partially deactivated catalyst and the channel scheme is configured to provide a first product stream from the first reactor to the second reactor.

Aspects of the invention are discussed throughout this specification. Any aspects discussed with respect to one aspect of the invention applies to other aspects of the invention as well and vice versa. Each aspect described herein is understood to be an aspect of the invention that is applicable to other aspects of the invention. It is contemplated that any aspect discussed herein can be combined with other aspects discussed herein and/or implemented with respect to any method or system of the invention, and vice versa. Furthermore, systems of the invention can be used to achieve methods of the invention.

Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

BRIEF DESCRIPTION OF DRAWINGS

Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings.

Figure 1 depicts a schematic diagram of an example of a system for producing ethylene and regenerating a catalyst according to some embodiments of the present disclosure.

Figure 2 depicts a schematic diagram of a second example of a system for producing ethylene and regenerating a catalyst according to some embodiment of the present disclosure.

Figure 3 depicts a schematic diagram of third example of a system for producing ethylene and regenerating a catalyst according to some embodiments of the present disclosure.

Figure 4 depicts a schematic of a method for concurrently producing ethylene and regenerating a catalyst according to some embodiments of the present disclosure.

Figure 5 depicts PXRD pattern of Catalyst A prior to calcination and after calcination.

Figure 6 depicts PXRD pattern of formulated Catalyst A.

Figures 7A and 7B depict ethane conversion and ethylene selectivity data for Catalyst C regeneration experiments 1.

Figure 8 depicts ethane conversion and selectivty for Catalyst D during regeneration.

DESCRIPTION OF EMBODIMENTS

Disclosed is an online catalyst regeneration process that can be used for regenerating a catalyst in an oxidative dehydrogenation (ODH) process for producing alkenes by maintaining the flow of reactant feed gas (comprising alkane and oxygen) while ensuring one pass oxygen conversion on-stream. This online regeneration of catalyst can, as compared to conventional processes, reduce reactor downtime and/or provide for safer operations. For example, described herein is the regeneration of performance on stream of catalyst that has been subject to operating conditions that cause gradual or more immediate catalyst deactivation. In some aspects, the catalyst is MoaVbBicTaaOx, where x is at least the number of oxygen atoms that renders the catalyst electrically neutral. In some embodiments x is the number of oxygen atoms that renders the catalyst electrically neutral. In some embodiments, x is greater than the number of oxygen atoms that render the catalyst electrically neutral, for example, when oxygen-containing species are adsorbed or trapped by the catalyst. In some embodiments, the catalyst is a mixed metal oxide having a formula MoaVbBicOx, wherein a is 1.0, b is about 0.01 to about 0.5, c is about 0.005 to about 0.5, and wherein x is at least a number that satisfies the valence state of the catalyst.

Operating conditions that can degenerate the catalyst include long term operation and unexpected process upsets such as thermal runaway, which may be caused by unintended pressure increase, loss of cooling, and prolonged reducing environment from, for example, unintended over-conversion of reactor feed (that is, oxygen converted to a non-measurable level at less than about 95% of the catalyst bed length). In some aspects of the present disclosure, it was found that certain treatment conditions disclosed herein resulted in complete regeneration of catalytic activity with little to no impact on product selectivity. Regeneration of catalyst by operating under a modified process stream offers advantages for commercial operation, such as allowing for safer operating modes. The catalyst bed may be cycled between high ethane and high oxygen partial pressures over a period of days, regenerating the catalyst on-stream while still having high selectivity towards valuable ethylene and acetic acid products. In certain embodiments, ethane can be injected into an oxygen rich stream, which is an inherently safer design than oxygen being injected in an ethane stream. The injection of ethane into an oxygen rich stream can help to prevent localized explosive atmospheres being generated in the process.

These and other non-limiting aspects of the present invention are discussed in further detail in the following sections.

A. Definitions

The following includes definitions of various terms and phrases used throughout this specification. The terms “about” or “approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment the terms are defined to be within 10%, preferably, within 5%, more preferably, within 1%, and most preferably, within 0.5%.

For the purposes of this disclosure, “X, Y, and/or Z” can be construed as X only, Y only, Z only, or any combination of two or more items X, Y, and Z (e.g., XYZ, XY, XZ, YZ).

The terms “wt. %”, “vol. %” or “mol. %” refer to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume, or the total moles of material that includes the component. In a non-limiting example, 10 moles of component in 100 moles of the material is 10 mol. % of component.

The term “substantially” and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

The terms “inhibiting” or “reducing” or “preventing” or “avoiding” or any variation of these terms, when used in the claims and/or the specification, include any measurable decrease or complete inhibition to achieve a desired result.

The term “effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

The use of the words “a” or “an” when used in conjunction with the term “comprising,” “including,” “containing,” or “having” in the claims or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”

The words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

The process of the present disclosure can “comprise,” “consist essentially of,” or “consist of’ particular reactants, components, compositions, etc., disclosed throughout the specification.

The term “primarily” as that term is used in the specification and/or claims, means greater than any of 50 wt. %, 50 mol. %, and 50 vol. %. For example, “primarily” may include 50. 1 wt. % to 100 wt. % and all values and ranges there between, 50.1 mol.% to 100 mol.% and all values and ranges there between, or 50.1 vol. % to 100 vol. % and all values and ranges there between. A disclosure of a numerical range in the specification and/or claims, is a disclosure of any range or value within the disclosed range. For example, a disclosure of a range of 1 to 10 includes ranges 1 to 5, 5 to 10, 3 to 8, 5 to 6, and 5.5 to 6.4 and so on, and includes values 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1.1 2.2, 3.3, 4.9, 5.8, 6.7, and so on.

B. Systems for Online Regeneration of Catalyst and Production of Ethylene

Referring now to the drawings, and more particularly to Figure 1, shown there and designated by the reference numeral 10 is a schematic of a non-limiting example of a system, according to some embodiments of the present disclosure, that is adapted to produce an alkene, (such as ethylene) by oxidative dehydrogenation (ODH) of the corresponding alkane (such as ethane), and to regenerate a partially deactivated oxidative dehydrogenation catalyst.

As shown in Figure 1, system 10 for the ODH of alkanes comprises a first reactor R1 configured to receive a first gaseous feed 100 and to contact the first gaseous feed 100 with a first ODH catalyst 102 disposed in the first reactor Rl. The skilled person will be familiar with reactor units for the oxidative dehydrogenation of alkanes and any suitable ODH reactor may be used. Non-limiting examples of reactors that may be used with the methods and systems disclosed herein include fixed bed reactors, fluidized bed reactors, moving bed reactors, ebullated bed reactors. In some embodiments, the reactor may be a fixed bed reactor. In some embodiments, the reactor may be a fluidized bed reactor. In some embodiments, the reactor may be a moving bed reactor. The first gaseous feed 100 includes an alkane such as ethane (C2H5), oxygen (O2), and optionally a diluent. The first reactor Rl is configured to receive the first gaseous feed 100 through a first conduit 101, when the first conduit 101 is in fluid communication with a gaseous feed source (not shown) through a first reactor three-way valve 103. As used herein, the term “conduit” is intended to refer to an entrance to the reactor that can act as either an inlet that can either receive the first gaseous feed 100 or, under certain operational modes described later herein, can alternatively act as an outlet for a product stream exiting the reactor. The first reactor Rl also includes a second conduit 105. As with the first conduit 101, the second conduit 105 can operate as either an inlet to or outlet from the first reactor Rl, depending on the operational mode.

The system 10 also includes a second reactor R2 in series with the first reactor Rl. The second reactor R2 is configured to be in fluid communication with Rl through at least a transfer line 107. In the example depicted in Figure 1, the transfer line 107 connects the second conduit 105 with a third conduit 109. The third conduit 109 can operate as either an inlet to or outlet from the first reactor Rl, depending on the operational mode. In this way, the second reactor R2 is configured to receive the first product stream 104 and contact the first product stream 104 with a second ODH catalyst 106 disposed in the second reactor R2 to produce a second product stream 108. The second reactor R2 includes a fourth conduit 111 and a second reactor three-way valve 113 through which the second product stream 108 can exit.

The system 10 further includes a channel scheme 115, which includes a first channel 117 and a second channel 119. The first channel 117 is operatively connected to the first reactor three-way valve 103 such that, in certain operational modes described herein, the gaseous feed 100 can be diverted from entering the first reactor R1 and instead enter the second reactor R2 through the fourth conduit 111 (operating as an inlet). The second channel 119 is in fluid communication with the first reactor R1 and the second reactor three-way valve 113 such that, in operational modes where the second reactor R2 receives the first gaseous feed 100, the flow in the system is reversed (counterclockwise, in the system of Figure 1) and a product stream can exit the first reactor R1 through the first conduit 101 (operating as an outlet) and through the second reactor three-way valve 113. In effect, the described system configuration allows for the first gaseous feed 100 to be selectively and alternatively sent to the first reactor unit R1 or the second reactor unit R2.

In some embodiments, the system 10 may optionally (indicated by a dashed box) include an interstage gaseous feed source (not shown) for providing an interstage gaseous feed 120 that is introduced into the system 10 through a valve 121 and a feedline 123. The interstage gaseous feed 120 may include oxygen and/or an alkane such as ethane. In some embodiments, the interstage gaseous feed 120 is oxygen. In some embodiments, the interstage gaseous feed 120 is a mixture of ethane and oxygen. In some embodiments, the system 10 is configured such that the interstage gaseous feed 120 and/or the first product stream 104 can be received by the second reactor unit R2. In some embodiments, the system 10 is configured such that the interstage gaseous feed 120 and the first product stream 104 are combined before being received by the second reactor unit R2. In some embodiments, the system 10 is configured such that the interstage gaseous feed 120 and the first product stream 104 are provided separately to the second reactor R2.

In some embodiments, the systems disclosed herein can include at least one additional reactor positioned between, and in series with, the first reactor and the second reactor. The at least one additional reactor may be 1, 2, 3, 4, or more reactors. In some embodiments, the at least one additional reactor is one additional reactor. In some embodiments, such as the schematic shown in Figure 2 of a non-limiting example of a system 20, the at least one additional reactor is two additional reactors R3, R4. The system 20 of Figure 2 is similar to the system 10, with like numbers representing like features.

Each reactor unit of the at least one additional reactor unit is configured to receive a product stream from the immediately preceding reactor unit, and to contact the product stream with an ODH catalyst disposed therein, thereby producing a respective product stream. For the example shown in the schematic of Figure 2, the first reactor unit R1 is adapted to contact first gaseous feed 200 with the first ODH catalyst 202 and thereby produce the first product stream 204-a, which, in some embodiments, comprises ethylene, unconverted ethane, and unconverted oxygen. A first at least one additional reactor R3 is adapted to receive the first product stream 204-a and to contact the first product stream 204-a with a catalyst 210 disposed therein and thereby produce product stream 204-b, which, in some aspects, comprises ethylene (at a higher concentration than the first product stream 204-a), unconverted ethane, and unconverted oxygen. A second at least one reactor R4 is adapted to receive the product stream 204-b and to contact the product stream 204-b with a catalyst 212 and thereby produce a product stream 204-c, which, in some aspects, comprises ethylene (at a higher concentration than intermediate product stream 204-b), unconverted ethane, and unconverted oxygen. When the at least one additional reactor is present, the product streams (for example, product stream 204-a, 204-b, and 204-c) may collectively be referred to as the product stream 204 that is received by the second reactor R2. The following features in Figure 2, namely first conduit 201, first reactor three-way valve 203, second conduit 205, transfer line 207, second product stream 208, third conduit 209, fourth conduit 211, second reactor three-way valve 213, channel scheme 215, first channel 217, second channel 219 have the same operational features as first conduit 101, first reactor three-way valve 103; second conduit 105, transfer line 107; second product stream 108, third conduit 109, fourth conduit 111, second reactor three-way valve 113, channel scheme 115, first channel 117, second channel 119, respectively (and for easy reference, like numbers representing like features).

A simplified schematic of system 20 is shown in Figure 3, but includes an interstage three-way valve 221 operatively connected to an interstage gaseous feed source (not shown) and feed lines 223 and 225 for introducing an interstage gaseous feed 220 into the system 20. The feed lines 223 and 225 are operatively connected to the interstage three-way valve 221 such that the interstage gaseous feed 220 can be provided to a transfer line 207a or a transfer line 207b, depending on the operational mode. The interstage gaseous feed 220 may include oxygen and/or an alkane such as ethane. The interstage gaseous feed 220 may also include a diluent, such as for example steam, N2, or CO2. In some embodiments, the interstage gaseous feed 220 includes oxygen. In some embodiments, the interstage gaseous feed 220 includes a mixture of oxygen and ethane. In some embodiments, the system 20 is configured such that the interstage gaseous feed 220 and/or first product stream 204 can be received by the second reactor unit R2. In some embodiments, the system 20 is configured such that the interstage gaseous feed 220 and first product stream 204 can be combined before being received by the second reactor unit R2. In some embodiments, the system 20 is configured such that the interstage gaseous feed 220 and the first product stream 204 can be provided separately to the second reactor unit R2.

The skilled person will be familiar with oxidative dehydrogenation catalysts and any suitable catalyst may be used in the systems and methods disclosed herein. In some embodiments, the first catalyst 102/202 includes molybdenum (Mo), vanadium (V), bismuth (Bi), and optionally tantalum (Ta). In some embodiments, the catalyst 102/202 is a mixed metal oxide having a formula of MoaVbTacBidOx, wherein a is 1.0, b is about 0.01 to about 0.5, c is about 0.005 to about 0.1, and d is about 0.005 to about 0.2, and wherein x is at least a number that satisfies the valence state of the catalyst. In some embodiments, the catalyst is a mixed metal oxide having a formula MoaVbBicOx, wherein a is 1.0, b is about 0.01 to about 0.5, c is about 0.005 to about 0.5, and wherein x is at least a number that satisfies the valence state of the catalyst. As used herein, the expression “satisfies the valence state of the catalyst” is intended to refer to rendering the catalyst electrically neutral. The catalyst 106/206 can include the same catalyst as described above with respect to catalyst 102/202 or it can be different. Similarly, the catalyst used in any of the at least one additional reactors, when present, can be the same catalyst as the first catalyst 102/202, the second catalyst 106/206, or can be different.

C. Method for Online Regeneration of Catalyst

The present disclosure provides a method of concurrently producing ethylene and regenerating a first oxidative dehydrogenation (ODH) catalyst that is at least partially deactivated and can be implemented by the systems described herein. The method includes contacting, in a first reactor, a first gaseous feed comprising ethane and oxygen with the first ODH catalyst under conditions such that conversion of oxygen in the first reactor is less than or equal to 90% to produce a first product stream comprising ethylene and to regenerate the first ODH catalyst, wherein the molar ratio of ethane to oxygen in the first gaseous feed is between 0.5 and 1.5. Without being bound by any particular theory, it is believed that the more oxidizing environment provided by operating the first reactor at less than or equal to 90% oxygen conversion may help regenerate the oxide on the catalyst surface, while the presence of ethane may help to mitigate localized overheating of the catalyst surface during regeneration that otherwise might be detrimental to catalyst selectivity. The method can further include contacting a second gaseous feed including the first product stream with a second ODH catalyst in a second reactor, under conditions such that the conversion of oxygen in the second reactor is greater than 90%, to produce a second product stream comprising ethylene, wherein the first and second reactors are connected in series. The second gaseous stream can include additional oxygen, or additional oxygen and ethane. Without being bound by any particular theory, operating the second reactor unit at oxygen conversions above 90% can reduce the potential for oxygen-based fouling/degradation downstream and operating the second reactor unit at oxygen conversions of 100% may eliminate such downstream fouling/degradation. The online catalyst regeneration methods described herein may advantageously eliminate down time as compared to offline regeneration methods.

An exemplary method 300, according to some embodiments of the present disclosure, for concurrently producing ethylene and regenerating a first ODH catalyst that is at least partially deactivated will be described with reference to the method schematic in Figure 4 and the system schematic of Figure 1. In this exemplary embodiment, the first ODH catalyst 102 disposed in the first reactor R1 is least partially deactivated at the start of the method. As used herein, the expression “at least partially deactivated” refers to a decrease in catalyst performance with respect to activity and/or selectivity to value added products (specifically alkenes) in the ODH reaction, such that to maintain the same conversion, the process temperature and/or pressure need to be increased or the feed flow to the reactor decreased. The deactivation may be result of prolonged time on stream in the ODH reaction under reducing environments (for example oxygen conversion > 90%) or unexpected process upsets, such as thermal run away. Thermal runaway may be a result of unintended pressure increase, loss of cooling, or loss feed diluent (such as steam, N2, CO2).

The method of catalyst regeneration disclosed herein may be initiated when activity and/or selectivity of a catalyst decreases below a threshold value. In some embodiments, the regenerating of the first ODH catalyst in the first reactor unit is initiated when ethane conversion in the ODH reaction in the first reactor deteriorates from a range of 45% to 55% to a range of 35% to 44% during steady state operation, and thereby indicating that regeneration of the ODH catalyst is needed. Ethane conversion is used an indicator of catalyst activity.

The method 300 includes a step 310 of providing a first gaseous feed 100, which comprises an alkane, such as ethane (C2H5), and oxygen (O2), and optionally a diluent (for example, one or more of nitrogen, carbon dioxide, and steam) to the first reactor unit Rl. In some embodiments, the molar ratio of ethane to oxygen in the first gaseous feed is between 0.5 and 1.5. In some embodiments, the first gaseous feed is provided to Rl through the second conduit 105.

In step 320 the first ODH catalyst 102, which is at least partially deactivated, is contacted with the first gaseous feed 100 in the first reactor Rl under conditions such that conversion of oxygen in the first reactor unit is less than or equal to 90% to produce a first product stream 104 including ethylene and to regenerate the first ODH catalyst 102. In some embodiments, the molar ratio of ethane to oxygen in the first gaseous feed is between 0.5 and 1.5. Without being bound by any particular theory, the molar ratio of ethane to oxygen allows for catalyst regeneration to occur outside of the flammable envelope for ethane and oxygen. In some embodiments, the oxygen and ethane in the first gaseous feed are converted by reaction to form one or more of: ethylene, water, carbon monoxide, carbon dioxide, and acetic acid in the first product stream 104. The first product stream 104 also includes unreacted ethane. In some embodiments, the method 300 further includes a step 330 of contacting a second gaseous feed with the second ODH catalyst 106 in a second reactor unit R2, under conditions such that the conversion of oxygen in the second reactor is greater than 90%, to produce a second product stream comprising ethylene, wherein the first and second reactors are connected in series. In some embodiments, the conditions in the second reactor are such that the conversion of oxygen in the second reactor is greater than 95%. In some embodiments, the conditions in the second reactor are such that the conversion of oxygen in the second reactor is 100%. The second gaseous feed includes the first product stream 104.

In some embodiments, the method 300 can include a step 315 providing an interstage feed gas including oxygen. In some embodiments, the interstage feed gas further includes ethane. In some embodiments, the interstage feed gas further includes one or more of steam, nitrogen, and carbon dioxide as a diluent. Without being bound by any particular theory, providing one or both of oxygen and ethane to the second reactor may reduce the volume to diluent required in the first gaseous feed. In some embodiments, the second gaseous feed includes the interstage feed gas.

In some embodiments, the conditions in the first reactor Rl during catalyst regeneration includes one or more of the following: the gaseous feed having a molar ratio of 8 to 25 mol. % oxygen, 8 to 25 mol. % ethane, and 65 to 84 mol. % nitrogen; a gas hourly space velocity (GHSV) in a range of 500 h'¹ to 30000 h’¹; a temperature in a range of 300°C to 450°C; and a pressure in a range of 20 psig to 100 psig. In some embodiments, the conditions in the first reactor comprise one or more of the following: the gaseous feed having a molar ratio of 10 to 20 mol. % ethane, 8 to 25 mol. % oxygen, 10 to 45 mol. % carbon dioxide, and 10 to 45 mol. % steam; a gas hourly space velocity (GHSV) in a range of 2500 to 2900 h'¹ or any value or range therein, including ranges of 2500 to 2550 h’¹, 2550 to 2600 h’¹, 2600 to 2650 hr ¹, 2650 to 2700 h’¹, 2700 to 2750 hr ¹, 2750 to 2800 h’¹, 2800 to 2850 h’ 2850 to 2900 h’¹, 2550 to 2850 h’¹, 2600 to 2800 h’¹, and 2650 to 2750 h’¹; a temperature in a range of 300°C to 450°C, or any value or range therein, including ranges of 300°C to 325°C, 325°C to 350°C, 350°C to 375°C, 375°C to 400°C, 400°C to 425°C, 425°C to 450°C, 325°C to 425°C, and 350°C to 400°C; and a pressure in a range of 20 psig to 100 psig, or any value or range therein, including ranges of 20 psig to 30 psig, 30 psig to 40 psig, 40 psig to 50 psig, 50 psig to 60 psig, 60 psig to 70 psig, 70 psig to 80 psig, 80 psig to 90 psig, 90 psig to 100 psig, 30 psig to 90 psig, 40 psig to 80 psig, and 50 psig to 70 psig.

In some embodiments, the conditions in the first reactor unit R1 that result in conversion of oxygen in the first reactor to be less than or equal to 90%, or any value or range therein, including ranges of 10 to 20%, 20 to 30%, 30 to 40%, 40 to 50%, 50 to 60%, 60 to 70%, 70 to 80%, 80 to 90%, 10 to 80%, 20 to 70%, and 30 to 60% are maintained for a regenerating period of at least 2 hours.

In some embodiments, the regenerating period is in a range of 2 hours to 60 hours, or any value or range therein, including ranges of 2 hours to 4 hours, 4 hours to 6 hours, 6 hours to 8 hours, 8 hours to 10 hours, 10 hours to 12 hours, 12 hours to 14 hours, 14 hours to 16 hours, 16 hours to 18 hours, 18 hours to 20 hours, 20 hours to 22 hours, 22 hours to 24 hours, 24 hours to 26 hours, 26 hours to 28 hours, 28 hours to 30 hours, 30 hours to 32 hours, 32 hours to 34 hours, 34 hours to 36 hours, 36 hours to 38 hours, 38 hours to 40 hours, 40 hours to 42 hours, 42 hours to 44 hours, 44 hours to 46 hours, 46 hours to 48 hours, 48 hours to 50 hours, 50 hours to 52 hours, 52 hours to 54 hours, 54 hours to 56 hours, 56 hours to 58 hours, 58 hours to 60 hours, 4 hours to 58 hours, 6 hours to 56 hours, 8 hours to 54 hours, 10 hours to 52 hours, 12 hours to 54 hours, 14 hours to 52 hours, 16 hours to 50 hours, 18 hours to 48 hours, 20 hours to 46 hours, 22 hours to 44 hours, 24 hours to 42 hours, 26 hours to 40 hours, 28 hours to 38 hours, and 30 hours to 36 hours.

In some embodiments, the conditions in the second reactor R2 under are such that the conversion of oxygen in the second reactor is in a range of 90 to 100%, or any value or range therein, including ranges of 90 to 91%, 91 to 92%, 92 to 93%, 93 to 94%, 94 to 95%, 95 to 96%, 96 to 97%, 97 to 98%, 98 to 99%, 99 to 100%, 91 to 99 %, 92 to 98%, 93 to 97%, and 94 to 96% to produce a second product stream 108 that includes ethylene. In some embodiments, oxygen and ethane are converted by reaction, to form one or more of: water, carbon monoxide, carbon dioxide, and acetic acid.

In some embodiments, interstage feed is at a temperature of 200°C to 250°C, or any value or range therein, including ranges of 200°C to 205°C, 205°C to 210°C, 210°C to 215°C, 215°C to 220°C, 220°C to 225°C, 225°C to 230°C, 230°C to 235°C, 235°C to 240°C, 240°C to 245°C, 245°C to 250°C, 205°C to 245°C, 210°C to 240°C, 215°C to 235°C, and 220°C to 230°C.

In embodiments of the method 300 described above, the channel scheme 115, including first channel 117 and second channel 119 are not in use. That is, the first reactor three-way valve 103 is in an operational position to provide the first gaseous feed 100 to the first reactor unit R1 and the first conduit 101 is operable as an inlet. Similarly, the second reactor three-way valve 113 is in an operable position to receive the second product stream from the second reactor unit R2 through the fourth conduit 111 (operable as an outlet) and the second product stream 108 exits the second reactor three-way valve.

When the first ODH catalyst achieves suitable activity and selectivity, the catalyst may be considered regenerated and the method includes a step 340 of increasing the oxygen conversion in the first reactor up to 100%, as is typical of an ODH reaction. Increasing the oxygen conversion in R1 back to 100% before decreasing oxygen conversion in R2 (for example, to regenerate the ODH catalyst in R2) will also remove excess oxygen from the system.

When the second ODH catalyst in the second reactor R2 becomes at least partially deactivated, the method 300 can be similarly implemented to regenerate the second ODH catalyst, such as the second ODH catalyst 106. Specifically, the first gaseous feed 100 can be provided to the second reactor R2 containing the at least partially deactivated catalyst 106 via first channel 117 for the example system shown in Figure 1. In this embodiment of the method, the first reactor three-way valve 103 is in an operational position such that the gaseous feed 100 is not provided to the first reactor unit R1 but instead is provided to the second reactor unit R2 through the fourth conduit 111, which is operating as an inlet.

In the method for regenerating the catalyst in R2, the second ODH catalyst 106 is contacted with the first gaseous feed 100 under conditions such that conversion of oxygen in the second reactor R2 is less than or equal to 90% to produce a product stream including ethylene and to regenerate the second ODH catalyst 106, wherein the molar ratio of ethane to oxygen in the first gaseous feed is between 0.5 and 1.5. The product stream also includes unreacted ethane. The method of regenerating the catalyst in the second reactor R2 of system 10 may further include a step of contacting a second gaseous feed with the first ODH catalyst in the first reactor Rl, under conditions such that the conversion of oxygen in the first reactor is greater than 90%, to produce a second product stream comprising ethylene. The second gaseous feed includes the product stream from R2. In some embodiments, the method includes a step of providing an interstage feed gas including one or both of oxygen and ethane. In some embodiments, the interstage gas feed further includes one or more of steam, nitrogen, and carbon dioxide as a diluent. In some embodiments, the interstage feed gas further includes oxygen. In some embodiments, interstage feed is at a temperature of 200°C to 250°C, or any value or range therein, including ranges of 200°C to 205°C, 205°C to 210°C, 210°C to 215°C, 215°C to 220°C, 220°C to 225°C, 225°C to 230°C, 230°C to 235°C, 235°C to 240°C, 240°C to 245°C, 245°C to 250°C, 205°C to 245°C, 210°C to 240°C, 215 °C to 235°C, and 220°C to 230°C.

The regeneration conditions for the second reactor unit R2 can be any of the regeneration conditions described for the first reactor unit Rl in the method 300. In some embodiments, the regeneration conditions in the second unit R2 comprise one or more of the following: the gaseous feed having a molar ratio of 8 to 25 mol. % oxygen, 8 to 25 mol. % ethane, and 65 to 84 mol. % nitrogen; a gas hourly space velocity (GHSV) in a range of 500 h'¹ to 30000 h’¹; a temperature in a range of 300°C to 450°C; and a pressure in a range of 20 psig to 100 psig. In some embodiments, the conditions in the second reactor comprise one or more of the following: the gaseous feed having a molar ratio of 10 to 20 mol. % ethane, 8 to 25 mol. % oxygen, 10 to 45 mol. % carbon dioxide, and 10 to 45 mol. % steam; a gas hourly space velocity (GHSV) in a range of 2500 to 2900 h'¹ or any value or range therein, including ranges of 2500 to 2550 h’¹, 2550 to 2600 h’¹, 2600 to 2650 hr ¹, 2650 to 2700 h’¹, 2700 to 2750 hr ¹, 2750 to 2800 h’¹, 2800 to 2850 h’¹, 2850 to 2900 h’¹, 2550 to 2850 h’¹, 2600 to 2800 h’¹, and 2650 to 2750 h’¹; a temperature in a range of 300°C to 450°C, or any value or range therein, including ranges of 300°C to 325°C, 325°C to 350°C, 350°C to 375°C, 375°C to 400°C, 400°C to 425°C, 425°C to 450°C, 325°C to 425°C, and 350°C to 400°C; and a pressure in a range of 20 psig to 100 psig, or any value or range therein, including ranges of 20 psig to 30 psig, 30 psig to 40 psig, 40 psig to 50 psig, 50 psig to 60 psig, 60 psig to 70 psig, 70 psig to 80 psig, 80 psig to 90 psig, 90 psig to 100 psig, 30 psig to 90 psig, 40 psig to 80 psig, and 50 psig to 70 psig.

In some embodiments, the regenerating in the second reactor unit R2 is initiated when ethane conversion in the ODH reaction in the second reactor deteriorates from a range of 45% to 55 % to a range of35%to 44%, and thereby indicating that regeneration of the ODH catalyst is needed.

In some embodiments, the conditions in the second reactor unit R2 that result in conversion of oxygen in the first reactor to be less than or equal to 90%, or any value or range therein, including ranges of 10 to 20%, 20 to 30%, 30 to 40%, 40 to 50%, 50 to 60%, 60 to 70%, 70 to 80%, 80 to 90%, 10 to 80%, 20 to 70%, and 30 to 60% are maintained for a regenerating period of at least 2 hours.

In some embodiments, the regenerating period is in a range of 2 hours to 60 hours, or any value or range therein, including ranges of 2 hours to 4 hours, 4 hours to 6 hours, 6 hours to 8 hours, 8 hours to 10 hours, 10 hours to 12 hours, 12 hours to 14 hours, 14 hours to 16 hours, 16 hours to 18 hours, 18 hours to 20 hours, 20 hours to 22 hours, 22 hours to 24 hours, 24 hours to 26 hours, 26 hours to 28 hours, 28 hours to 30 hours, 30 hours to 32 hours, 32 hours to 34 hours, 34 hours to 36 hours, 36 hours to 38 hours, 38 hours to 40 hours, 40 hours to 42 hours, 42 hours to 44 hours, 44 hours to 46 hours, 46 hours to 48 hours, 48 hours to 50 hours, 50 hours to 52 hours, 52 hours to 54 hours, 54 hours to 56 hours, 56 hours to 58 hours, 58 hours to 60 hours, 4 hours to 58 hours, 6 hours to 56 hours, 8 hours to 54 hours, 10 hours to 52 hours, 12 hours to 54 hours, 14 hours to 52 hours, 16 hours to 50 hours, 18 hours to 48 hours, 20 hours to 46 hours, 22 hours to 44 hours, 24 hours to 42 hours, 26 hours to 40 hours, 28 hours to 38 hours, and 30 hours to 36 hours. In the depicted example, at block 302, the first ODH catalyst is regenerated in the first reactor as a result of processing in the first reactor.

The regeneration of the catalyst in R2 can include contacting the second gaseous feed, with the first ODH catalyst in the first reactor unit R1 under conditions such that the conversion of oxygen in the second reactor is in a range for 90 to 100%, or any value or range therein, including ranges of 90 to 91%, 91 to 92%, 92 to 93%, 93 to 94%, 94 to 95%, 95 to 96%, 96 to 97%, 97 to 98%, 98 to 99%, 99 to 100%, 91 to 99 %, 92 to 98%, 93 to 97%, and 94 to 96% to produce a second product stream that includes ethylene. The second product stream exits the first reactor R1 through the first conduit 101 (operating as an outlet), through the second channel 119, and through the second reactor three-way valve, which is in an operational position to receive the second product stream through the second channel 119.

When the second ODH catalyst achieves suitable activity and selectivity, the catalyst may be considered regenerated and the oxygen conversion in the second reactor unit can be increased up to 100%, as typical of an ODH reaction. Increasing the oxygen conversion in R2 back to 100% before decreasing oxygen conversion in R1 (such as, for example, when the R1 catalyst is at least partially deactivated) will also remove excess oxygen from the system. In some embodiments, such as for example in Figures 2 and 3, the ODH system will include at least one additional reactor. In these embodiments, the at least one additional reactor can be operated at oxygen conversion of 90% during the regeneration of the first or the second ODH catalyst, such that only the final reactor in the system is operating at greater than 90% oxygen conversion during the regeneration period.

In embodiments where the at least one additional reactor unit is present without an interstage feed, each reactor of the at least one additional reactor may be operated at different temperatures to manage oxygen concentration.

In some embodiments, the at least one additional reactor unit and the interstage gaseous feed will be present. In these embodiments, when the first reactor unit R1 is being regenerated the interstage gaseous feed 220 may be introduced after the last of the at least one additional reactor unit and before R2 via transfer line 223. Conversely, when the second reactor unit R2 is being regenerated, the interstage feed gas, when present, may be introduced after the last of the at least one additional reactor unit and before R1.

By alternating the online catalyst regeneration method 300 between R1 and R2 (that is, by operating the reactor containing the at least partially deactivated catalyst at oxygen conversion less than or equal to 90% and the other reactor at oxygen conversion greater than 90%), the catalyst in the respective reactors can be alternately regenerated, thereby reducing or even eliminating downtime for offline catalyst regeneration.

While the systems and methods disclosed herein were described in the context of oxidative dehydrogenation of ethane to produce, amongst other things, ethylene, the disclosed systems and methods may be suitable for ODH of other alkanes.

As part of the disclosure of the present disclosure, specific examples are included below. The examples are for illustrative purposes only and are not intended to limit the disclosure. Those of ordinary skill in the art will readily recognize parameters that can be changed or modified to yield essentially the same results.

D. Examples

(1) Catalyst A Synthetic Procedure

The molybdenum(VI) oxide (MoOs) vanadium(V) oxide (V2O5), and oxalic acid dihydrate were purchased from Sigma-Aldrich. Bismuth hydroxide (Bi(OH)3) was purchased from Alfa Aesar. The tantalum pentoxide hydrate (Ta2C>5 XH2O) was purchased from Bass Tech International. All water used was distilled deionized water. Power X-ray diffraction (PXRD) experiments were performed using a PANalytical Empyrean powder X-ray diffractometer equipped with a monochromated Cu Ka X-ray source. Data was acquired between 3 - 80° 20 at a scan rate of l°/min. Data was analyzed using PANalytical HighScore software Version 4.8.

The following is the procedure that was followed.

The sample was prepared with solid reagents listed in Table 1. The solid reagents were added to a blender and mixed for 1 minute to blend and pulverize. The solid mixture was then transferred to a 40 mb glass bottle, after which 8.0 mb of the distilled water solvent was used to rinse the grinder and transfer the residual solids to the bottle. The sample was stirred lightly with a glass stir rod to form a thick orange slurry and another 2.8 mb of water was then used to rinse sample stuck to the stir rod back into the bottle. The vial was then placed in a glass lined steel autoclave, and water was filled around the vial to the level of the slurry to help with heat transfer and to maintain a humid atmosphere in the vessel (approximately 20 mb of water). The autoclave was then sealed and placed in an oven to heat from room temperature to 180°C over a period of 12 hours, held at 180°C for 48 hours, then turned off to cool back to ambient over a period of 3 - 4 hours. After reaction, the sample was a deep purple hard solid. The sample was scraped from the bottle onto filter paper in a vacuum filtration set-up and was washed with distilled water, with the filtrate being a deep blue color. The sample was washed until the filtrate from the sample was nearly colorless, then was left to dry on the filter paper to obtain 29.4870 of shiny purple-black powdered solid. Most of the sample (24.6823 g) was then calcined in a tubular autoclave under N2 flow (3.9 cm/min linear velocity at STP) for 8 hours at 80°C, after which it was heated to 600°C over a period of 6 hours, held at 600°C for 2 hours, then the furnace was turned off and the samples cooled back to ambient conditions over approximately 12 hours. After calcination, the sample was a deep purple-black powder. The mass of the solid samples before and after calcining is given in Table 2.

TABLE 1

Amounts of Reagents Used for Hydrothermal Synthesis of Catalyst A TABLE 2

Mass of Samples Before and After Calcination in N2

Powder X-ray diffraction (PXRD) analysis was conducted on the sample before and after calcination (Figure 4). By PXRD, both samples were characterized as a doped molybdenum vanadium oxide phase known in academic literature as Ml. Before calcination, the sample was characterized with a minor impurity of MoOs, which converted into the desired phase after calcination.

(2) Catalyst A Formulation and Shaping Procedure

The formulation procedure for the catalyst is outlined below. The a-alumina was purchased from Fisher Scientific. The polyethylene glycol) 1000, Mowiol 8-88, graphite flakes and poly(acrylic acid) were purchased from Sigma-Aldrich. All reagents were used as is without any further purification. All water that was used was distilled deionized water.

The calcined sample of Catalyst A (10.0671 g) was added along with a-alumina (10.0771 g), poly(acrylic acid) (0.0199 g) and water (100 mL) and stirred overnight in a beaker to disperse. This mixture was then vacuum filtered and left to dry. The filter cake was then transferred back into the beaker along with polyethylene glycol) 1000 (0.3912 g), Mowiol 8-88 (0.6008 g), poly(acrylic acid)(0.0163 g) and water (90 mL), and stirred while heating at 85°C until the water had evaporated. The sample was then placed in an oven at 90°C overnight to dry completely. After drying, the sample was lightly pulverized using a mortar and pestle, sieved to obtain particles between 250 pm and 500 pm in size. 1 wt.% of graphite flakes were then added to the sieved particles and the mixture was shaken in a closed container to disperse. The graphite coated particles were then pelleted using a Dott Bonapace model CPR-6 automatic pellet press to obtain cylindrical pellets with approximately 5 mm length and 3 mm diameter. The pellets were then placed in a quartz boat and heated first under dry air (1.8 cm/min linear velocity at STP) at a rate of 1 .0°C/min to 400°C, held at 400°C for 1 hour, then heating was stopped and the furnace was left to cool back to ambient conditions over approximately 12 hours. Following the air treatment, the atmosphere was then purged with dry nitrogen (3.9 cm/min linear velocity at STP) for 8 hours, then under the same nitrogen flow, heated at a rate of 1 ,6°C/min to 600°C, held at 600°C for 2 hours, then heating was stopped and the furnace was left to cool back to ambient conditions over approximately 12 hours. After the calcination/sintering procedure, the pellets mass was reduced by 5.28%. PXRD was collected on the sample following this procedure and showed that the sample was a mixture of the catalytically active Ml phase and a-alumina (Figure 5).

(3) Catalyst C Preparation Procedure

The molybdenum(VI) oxide (MoOs), vanadium(V) oxide (V2O5), and bismuth hydroxide (Bi(0H)3) were purchased from Fisher Scientific Canada. The tantalum pentoxide hydrate (Ta2O5 XH2O) was purchased from BassTech International. All water used was distilled deionized water.

Catalyst C was prepared at larger scale with slight modification to the procedure. All components listed in Table 3 were added to a PTFE lined 2 L steel Parr autoclave and stirred with an overhead stirrer. After approximately 45 minutes, the stirrer was removed and the vessel was sealed and placed in a programmable oven to heat from room temperature to 180°C over a period of 12 hours, held at 180°C for 48 hours, then the power was turned off and the oven cooled back to room temperature over a period of 3 - 4 hours. After cooling, the vessel was vented, then the sample was transferred into a 3 L beaker and stirred with 1 L of water overnight (approximately 16 hours) using an overhead stirrer. The next day, the sample was recovered by vacuum filtration, leaving a purple-black solid and a deep blue filtrate. The solid was washed with a further 3.5 L of water in approximately 500 mb portions until the filtrate was clear and almost colorless. This solid was then dried in an oven at 90°C for 16 hours to obtain 813.97 g of purple-black solid.

TABLE 3

Amounts of Reagents Used for Hydrothermal Synthesis of Catalyst C

The solid was then transferred to a quartz boat and was calcined in a tubular autoclave under N2 flow (3.9 cm/min linear velocity at STP) for 8 hours at 80°C, after which it was heated to 600°C over a period 6 hours, held at 600°C for 2 hours, then the furnace was turned off and the samples cooled back to ambient conditions over approximately 12 hours. (4) Catalyst C Formulation and Shaping Procedure

The alpha-alumina (a-AhCh) and bismuth hydroxide (Bi(0H)3) were purchased from Fisher Scientific Canada. All water was distilled deionized water. Granulation was performed using an Eirich EL- 1 Laboratory Mixer unit fitted with a Z-type rotor. All mixing steps during granulation were performed with a rotor tip speed of 25 m/s.

For granulation, alpha-alumina (260 g), bismuth hydroxide (30 g) and calcined catalyst C (300 g) were added to the bowl of the mixer unit and were blended for 2 minutes to form a homogenous mixture. After the dry blending step, water (160 mL) was added steadily over 2 minutes while still blending, then the wet mixture was allowed to blend for a further 2 minutes to form microgranules. The mixture was then dried in an oven overnight (approximately 16 hours) at 90°C, then sieved to obtain 180 - 500 pm granules. Approximately 1 wt.% graphite was then added to the sieved granules and the mixture was shaken in a closed container to blend. The graphite coated granules were then pelleted using a Dott Bonapace model CPR-6 automatic pellet press to obtain cylindrical pellets with approximately 5 mm length and 3 mm diameter. The pellets were then placed in a quartz boat and heated first under dry air (1.8 cm/min linear velocity at STP) at a rate of 1.0°C/min to 400°C, held at 400°C for 1 hour, then heating was stopped and the furnace was left to cool back to ambient conditions over approximately 12 hours. Following the air treatment, the atmosphere was then purged with dry nitrogen (3.9 cm/min linear velocity at STP) for 8 hours, then under the same nitrogen flow, heated at a rate of 1 ,6°C/min to 600°C, then heating was stopped and the furnace was left to cool back to ambient conditions over approximately 12 hours.

(5) Catalyst D Preparation Procedure

Catalyst D synthesis was carried out using a 300 mL stainless-steel Parr autoclave without stirring during heating. The oxides/hydroxides listed in Table 4 were blended in a blender before addition of oxalic acid and water. The solids were added to a 40 mL hypovial along with a stir bar, then water was used in portions to rinse the blender and transfer to the hypovial. The hypovial was stirred for approximately 30 minutes, forming an orange slurry which gently foamed for the first 20 minutes or so. The hypovial was then placed in a 300 mL steel Parr autoclave and water was filled around the vial for heat transfer and to maintain a humid atmosphere. The autoclave was then sealed and placed in a programmable oven to heat to 180°C over 12 hours, held at 180°C for 48 hours, then heating was stopped and the autoclave was left to cool back to room temperature. After the heating cycle, the autoclave was transferred to a fume hood and vented. After heating, the hypovial contained a hard deep- purple solid, which was transferred to a Buchner funnel on a vacuum flask, then the solid was rinsed with water until the fdtrate ran clear and colorless from an initial deep blue color. The solid was then transferred to an oven to dry at 90°C overnight, after which 26.8753 g of solid was obtained.

TABLE 4

Amounts of Reagents Used for Hydrothermal Synthesis of Catalyst D

(6) Catalyst D Formulation and Pelleting Procedure

Catalyst formulation and pelleting was conducted on a small scale using a blender to mix catalyst material and inert carrier into larger granules with water. To the blender, Catalyst D (13.1881 g) was added and the blender was pulsed to break up larger chunks of catalyst into fine dust. Next, alpha alumina (13. 1822 g) was added, and again the blender was pulsed multiple times to generate a homogenous dust. Water (10 m ) was then added and was blended, which ended up forming a thixotropic paste. The paste was transferred into a beaker and dried in an over overnight at 90°C.

After drying, the hard solid was gently pulverized using a mortar and pestle, then was sieved to obtain particle sizes between 180 - 500 pm (~19 g obtained). Graphite (~1 wt.%) was then added to the sieved granules as a lubricant and the mixture was shaken in a closed container to coat the granules with graphite. The sieved particles were then fed into an automatic pellet press (Dott Bonapace CPR-6) to obtain pressed cylindrical pellets with approximate dimensions of 3 mm diameter and 4.5 mm length.

(7) Catalytic Testing

Catalyst Samples A and C were tested for catalytic activity on a microreactor unit (MRU). For catalytic testing, the sample pellets were pulverized using a mortar and pestle, and particle sizes of 425 - 710 pm were sieved out for loading into the tubular reactor. Approximately 4 g of sample was placed in the reactor under a target gas flow rate of 150 seem (WHSV = 3.57 h'¹) and a target pressure of 23 psig. The target gas feed composition was 20 mol. % ethane, 10 mol. % oxygen and 70 mol. % nitrogen for all testing. Gas composition was determined by gas chromatography (GC) using an Agilent 6890N Gas Chromatograph, and analyzed using Chrom Perfect - Analysis, Version 6.1.10 for data evaluation.

For the MRU1 experiments, the mol.% ethane conversion temperature is determined at the WHSV of 3.57 h’¹, and a gas hourly space velocity (GHSV) in the range of 2000 to 5000 h'¹. The gaseous product exiting the catalyst bed is directed to vent during runs. When the gaseous product is to be analyzed, it is momentarily redirected to a gas chromatography unit to determine the percent of ethane, ethylene, O2, CO2, CO, and, optionally, acetic acid. The gas exiting the reactor was analyzed by gas chromatography. Conversion (C) of the ethane feed gas was calculated as a volume flow rate change of ethane in the product compared to feed ethane mass flow rate using the following formula:

In Eq. 1, X is the molar concentration of the corresponding compound in the gaseous effluent exiting the reactor at corresponding temperature. For all the experiments disclosed herein, acetic acid molar concentration was assumed to be 0 mol. %, since it could not be measured at the time.

Furthermore, the gas exiting the reactor was analyzed by GC to determine catalyst or catalyst material selectivity to ethylene (i.e., the percentage on a molar basis of ethane that forms ethylene). Selectivity to ethylene (SEthyiene) was determined using the following equation:

In the above equation 2, SEthyiene is the selectivity to ethylene and X is the molar concentration of the corresponding compound in the gaseous effluent exiting the reactor at corresponding temperature. For all the experiments described herein, acetic acid molar concentration was assumed to be 0 mol. %, since it could not be measured.

Steam was injected into the reactor using a syringe pump fdled with deionized water. The outlet of the syringe was situated directly prior to and above the reactor furnace, and was packed with glass wool to ensure a steady stream of water into the gas stream (rather than dropwise).

Catalyst Sample C experiment 2 was tested for catalytic activity under varying conditions on a second microreactor. For catalytic testing, a string of formulated cylindrical catalyst pellets of 3 mm diameter and 5 mm length were loaded into a tubular reactor. Approximately 2.2 g of pellets were placed in the reactor and the sample was exposed to varying gas flow rates between 64 and 232 seem, corresponding to gas hourly space velocity (GHSV) of 2122 h'¹ to 7700 h'¹. Pressures varied between 24 and 67 psig. Gas chromatography was collected using the same equipment as the first microreactor above.

In order to close the mass balance for ODH experiments on the second microreactor based on GC analysis of noncondensable product from the reactor, an assumption was made that all non-condensable gaseous products behave as ideal gases. The ideal gas equation of state is accurate in prediction of gas mixture behavior at operating pressure close to 1 atm- absolute. In the ODH experiments the product gas samples were collected and injected to a lab GC at operating pressure close to 1 atm absolute pressure, therefore the ideal gas behavior assumption is expected to generate an accurate prediction of the gas mixture behavior. The bulk chemical reactions in Table 5 were assumed in order to calculate formed amounts of condensable products. The reactions in Table 5 were used for the purpose of stoichiometrically-balanced mass balance calculations and not to represent the actual chemical reactions occurring in the ODH reaction.

TABLE 5

Bulk Chemical Reactions Assumed for Mass Balance Methodology

Based on reactions shown in Table 5, the following method was programmed and used in MS Excel. A GRG Nonlinear solving method was used with the objective of setting the absolute deviation of estimated and measured oxygen from the reactor to zero by modifying the acetic acid output in the solver.

In step 1, the total molar flow of C2 (ethane) into the reactor is calculated using Equation 3 :

F2Total = 100000*FTotal* (CEthane + 0.5*CcO2) / 22.4 Eq. 3 wherein F2Totai is the total molar flow of C2 into the reactor, [mmol/min]; Fiotai is the total feed flow to reactor (including all diluents), [seem]; CEthane is the molar fraction of ethane in total feed; Cco2 is the molar fraction of CO2 in total feed; and 22.4 is the molar volume at STP, [1/mol] .

In step 2, the molar flow of all reactive compounds in product effluent from the reactor is calculated excluding inert diluents.

The total molar flow of acetic acid in the product, [mmol/min] (FAAOUI) is estimated by Equation 4:

FAAOUI = y (first estimate: y = 1 [mmol/min]) Eq. 4

The total molar flows of C2 in non-condensable compounds in the reactor product is calculated using Equation 5 :

F2outx ⁼ F2Total * (Cxout/( SCxout)) * ((F2Total - PAAout) / F2Total) Eq. 5 wherein F2outx is the total molar flow of C2 of x, [mmol/min]; Cxout is the molar fraction of x in the reactor product; and x is Ethane, Ethylene, CO2, or CO.

The total molar flow of O2 from the reactor is calculated using the following algorithm:

If F20UTC-2 - (100000*F_Totai*(0.5*Cco2) / 22.4)) > 0 then use Equation 6:

Fo2out = ( I 00000*F_Total*(0.5 * Co2) / 22.4)) - 0.5 * F₂outetha-e - 3.5 * F2OUTCO2- 2.5* F2out-0 - 1 .5 * FoutAAout Eq. 6

If F20UTC02 - (100000*F_Totai*(0.5*Cco2) / 22.4)) < 0 then use Equation 7:

Fo2out = ( 100000*F_Total* (0.5 *Co2) / 22.4)) - 0.5 * F2outethane + ABS(3.5 * F2OUTCO-) - 2.5* F2out- o ■ 1.5* FoutAAout Eq. 7

The total molar flow of H2O from the reactor is calculated using Equation 8:

FffiOoutx = FH2O + F2outetha-e - 3 * F2OUTCO2- 3 *F2out-0 - FAAout Eq. 8

In step 3, the molar fractions of all reactive compounds in the product effluent from the reactor are calculated on the dry (water free) basis, using FAAOUI from step X04.

The molar fraction of acetic acid in the product is calculated using Equation 9:

CAAoutcalc ⁼ FAAout /( FAAout + SFxout + Fo2out) Eq. 9 The molar fraction of C2 in ethane, ethylene, CO2 and CO in the product is calculated using Equation 10:

Cxoutcalc ⁼ F2outx /( FAAout + SFxout + Fo2out) Eq. 10

The molar fraction of oxygen in the product is calculated using Equation 11 :

Co2outcalc ⁼ Fo2out /( FAAout + SFxout + Fo2out) Eq. 11

In step 4, the absolute deviation of estimated and measured O2 in the non-condensable product from the reactor is calculated using Equation 12:

D02 = Co2outcalc - (C02 / (CEthane +CEthylne + 0.5*CcO2 + 0.5CcO + C02) * -1 - CAAoutcalc))

Eq. 12

Step 5 is the decision point, if D02 is less than 1 O'⁴ proceed to step 6. If D02 is not less than 10'⁴, return to step 2 and repeat. On the repeated steps, FAAout = y (wherein y = new estimate [mmol/min]) is changed, and the steps are repeated to determine whether D02 is closer to the target in step 410.

In step 6, ethane conversion is calculated using Equation 13: and selectivity toward each product is calculated using Equation 14: wherein CxoutCalc ⁼ CEthyleneoutCalc, CAAoutCalc, 0.5 * Cc02outCalc Or 0.5 * CcOOutcalc .

(8) Catalyst A Regeneration Experiment

In this experiment, 3.9992 g of crushed and sieved Catalyst A pellets were placed on stream at a flow rate of 152 seem, a pressure of 23 psig, with a gas composition of 19.86 mol. % ethane, 10.35 mol. % oxygen and 69.80% nitrogen. Temperature was increased in the reactor until ethane conversion of approximately 50% was achieved, and the sample was left under these conditions to equilibrate for 114 h. The initial catalyst performance was 50.8% ethane conversion and 89.7% ethylene selectivity at 405°C. The catalyst was run for over 1000 hours under these conditions with final performance of 46.5% ethane conversion and 89.3% ethylene selectivity at 405°C after 1032 hours on stream, showing gradual deactivation over this time.

This catalyst was then further deactivated by increasing the reaction temperature to 428°C for 0.5 hours to achieve an oxygen conversion of 100% and ethane conversion of 58.9%, which exposed the outlet of the catalyst bed to highly reducing conditions. Following the 0.5 hours of full oxygen conversion, the catalyst had a performance of 45.1% ethane conversion and 88.5% ethylene selectivity at 405°C, showing that it had partially degraded from the oxygen depleted conditions. This catalyst was then left on stream overnight at 405 °C (approximately 15 hours) and the next day the performance was 46.3% ethane conversion and 88.9% ethylene selectivity, showing that the catalyst can self-regenerate under the process gas stream after short periods under oxygen depleted conditions.

This catalyst was again deactivated by increasing the reaction temperature to 428°C for 6 hours to achieve an oxygen conversion of 100% and ethane conversion of 59.3%. Following the 6 hours of full oxygen conversion, the catalyst had a performance of 43.3% ethane conversion and 87.3% ethylene selectivity at 405°C, showing that it had further degraded from the longer exposure to oxygen depleted conditions. This catalyst was then left on stream overnight (approximately 15 hours) at 405°C and the next day the performance had recovered slightly to 43.8% ethane conversion and 87.8% ethylene selectivity. The flow rate of the process gas was then increased to 228 seem for 16 hours at 405°C, then brought back down to 152 seem, with some change in the performance - 44.2% ethane conversion and 87.5% ethylene selectivity. Longer exposure to high flow rates (3 days) did not improve the performance further.

Select GC data for Catalyst A before and after various conditions are listed in Table 6.

TABLE 6

Select Catalytic Data for Catalyst A through Deactivation and Regeneration Procedures

All measurements were taken under a 23 psig mixture of 19.86 mol. % ethane, 10.35 mol. % oxygen and 69.80 mol.% nitrogen with a flow rate of 152 seem. (9) Catalyst C Regeneration Experiment 1

In this experiment, 3.9988 g of Catalyst C was placed on stream at a flow rate of 153 seem, a pressure of 23 psig, with a gas composition of 20.14 mol. % ethane, 10.15 mol. % oxygen and 69.71 mol. % nitrogen. Temperature was increased in the reactor until ethane conversion of approximately 50% was achieved, and the sample was left under these conditions to equilibrate for 8 h. The initial catalyst performance was 50.0% ethane conversion and 92.3% ethylene selectivity at 395°C. This was considered as baseline conditions.

The sample was then cooled to 370°C and the gas composition was changed to 69.50 mol.% ethane, 9.55 mol.% oxygen and 20.95 mol. % nitrogen. Temperature was then increased to achieve oxygen conversion of approximately 95% (375 °C) and the sample was left under these conditions for 120 hours. After, the sample was switched back to baseline conditions, and catalyst performance was 41.1% ethane conversion and 93.1% ethylene selectivity, showing that the reducing conditions resulted in 8.9% loss in ethane conversion.

A regeneration experiment was then attempted whereby the gas composition in the reactor was changed to 11.00 mol. % oxygen, 11.00 mol. % ethane and 78.00 mol. % nitrogen at 153 seem flow and pressure of 23 psig at 400°C. The sample was left under these conditions for 4 hours and the activity and selectivity was monitored over this time by GC analysis (Figure 6). The sample activity was noted to be gradually increasing over the 4 hour period, while the sample was still converting over 50% of the ethane with ethylene selectivity over 90%. After 4 hours, the sample was changed back to baseline conditions and ethane conversion was 44.9% and ethylene selectivity was 92.8%, showing that the 4 hour treatment under modified process conditions resulted in 3.8% recovery in sample activity with little change in selectivity.

The regeneration experiment was then restarted on the same sample for another 16 hours at 400°C under 11.00 mol. % oxygen, 11.00 mol. % ethane and 78.00 mol. % nitrogen at 153 seem flow and pressure of 23 psig. After changing back to baseline conditions, the sample had 46.8% ethane conversion and 92.7% ethylene selectivity, showing that a further 16 hours of treatment under the modified process conditions resulted in further sample regeneration of 1.9% ethane conversion with no impact to selectivity (Figure 7).

Select GC data for Catalyst B before and after various treatment conditions are listed in Table 7. TABLE 7

Sequential Baseline Catalytic Data for Catalyst C regeneration Experiment 1 through Deactivation and Regeneration Procedures

All measurements were taken under a 23 psig mixture of 20.14 mol. % ethane, 10.15 mol. % oxygen and 69.71 mol. % nitrogen with a flow rate of 153 seem.

(10) Catalyst C Regeneration Experiment 2

This regeneration experiment was conducted on whole catalyst pellets using the second microreactor. The mode of operation for this unit is similar to the first microreactor used for the experiments above, except there is an option for the use of steam as a diluent during normal operation. For this experiment, a string of catalyst pellets was loaded into reactor. These pellets were not pulverized and sieved as with first microreactor experiments above. Testing of the product stream was the same as for first microreactor, using the same gas chromatograph equipment.

Here, catalyst pellets were used for long term testing under variable conditions for 29 days, moving to a baseline condition periodically to check if catalyst performance had deviated over that time. The baseline conditions were 52.4 / 10.1 / 37.5 mol.% of ethane / oxygen / steam at 385°C, 50 psig and GHSV = 7700 h'¹. Over the initial 29 days, baseline performance of the catalyst remained consistent. After 29 days, the catalyst was operated under more extreme conditions, under the same process conditions as the baseline, but at 440°C operation temperature. The catalyst was operated at higher temperature conditions for 4 hours. After returning to baseline conditions, catalyst performance had degraded, with loss in both activity and product selectivity. After this, the catalyst was set to a regeneration in a 13.85 / 10.78 / 38.08 / 37.29 mol. % mixture of ethane / oxygen / carbon dioxide / steam at 350°C, 23 psig and GHSV = 2701 h'¹. This regeneration condition was used for 3 days, after which the conditions were changed back to baseline. After returning to baseline conditions, it was found that the catalyst activity had improved beyond the original baseline, with a slight loss in selectivity to acetic acid (Table 8), albeit with a higher ethane conversion.

TABLE 8

Sequential Baseline Catalytic Data for Catalyst C Regeneration Experiment 2 Through Deactivation and Regeneration Procedures

All measurements were taken under a 50 psig mixture of 52.4 mol. % ethane, 10.1 mol. % oxygen and 37.5 mol. % steam with GHSV of 7700 H ¹.

(11) Catalyst D Regeneration

Catalyst D was left on stream for more than 1000 hours. The process gas was changed to an oxygen rich 11: 11:78 mixture of ethane: oxygen: nitrogen at 330°C and was left under these conditions for three days with periodic sampling. Over this time, the ethane conversion increased from an initial 65.0% to 66.8%, while combined selectivity to ethylene and acetic acid remained constant at 91.2% (see Figure 8). After running under the oxygen rich conditions for three days, the gas stream was switched back to the initial conditions. It was found that the online regeneration procedure caused partial regeneration of catalyst, as the activity increased from 51.5% to 52.3% with no change in selectivity. Table 9 shows activity and selectivity of MoVaBibOx catalyst before and after the on-stream regeneration. Note that both ethane and oxygen conversion increase while selectivity to value added products remain constant, showing that the catalyst has become more active after the regeneration process without impacting the value added products. TABLE 9

Activity of Catalyst D Before and After on-Stream Regeneration

In the context of the present disclosure, at least the following embodiments are described.

Embodiment A. A method of concurrently producing ethylene and regenerating a first oxidative dehydrogenation (ODH) catalyst that is at least partially deactivated, the method comprising contacting, in a first reactor, the first ODH catalyst with a first gaseous feed comprising ethane and oxygen under conditions such that conversion of oxygen in the first reactor is less than or equal to 90% to produce a first product stream comprising ethylene and to regenerate the first ODH catalyst, wherein the molar ratio of ethane to oxygen in the first gaseous feed is between 0.5 and 1.5.

Embodiment B. The method according to embodiment A, further comprising providing a second gaseous feed comprising the first product stream to a second reactor unit connected in series with the first reactor unit, and contacting the second gaseous feed with a second ODH catalyst in the second reactor under conditions such that the conversion of oxygen in the second reactor is greater than 90%, producing a second product stream comprising ethylene.

Embodiment C. The method according to Embodiment 2, wherein the second gaseous feed further comprises an interstage feed gas comprising one or both of oxygen and ethane.

Embodiment D. The method according to Embodiment C, wherein the interstage feed gas further comprises ethane.

Embodiment E. The method according to Embodiment D, wherein the interstage feed is at a temperature of 200°C to 250°C.

Embodiment F. The method of any one of Embodiments B, C, D, or E, wherein conversion of oxygen in the second reactor is greater than 99% or is 100%. Embodiment G. The method according to any one of Embodiments B, C, D, E, or F, wherein one or more additional reactors are in series with and between the first reactor and the second reactor.

Embodiment H. The method according to Embodiment G, wherein the second gaseous feed comprises effluent from the last in the series of the one or more additional reactors.

Embodiment I. The method according to Embodiment G, wherein the second gaseous feed comprises (1) effluent from the last in the series of the one or more additional reactors and (2) an inter-stage feed gas comprising ethane and oxygen.

Embodiment J. The method according to any one of Embodiments A, B, C, D, E, F, G, H, or I, wherein the first ODH catalyst and/or the second ODH catalyst each individually comprise molybdenum (Mo), vanadium (V), tantalum (Ta), and bismuth (Bi), or oxides thereof.

Embodiment K. The method according to Embodiment J, wherein the first ODH catalyst and the second ODH catalyst are each individually a mixed metal oxide having a formula of MoaVbTacBidOx, wherein a is 1.0, b is about 0.01 to about 0.5, c is about 0.005 to about 0.1, and d is about 0.005 to about 0.2, and wherein x is at least a number that satisfies the valence state of the catalyst.

Embodiment L. The method of any one of Embodiments A, B, C, D, E, F, G, H, I, J, or K, wherein the conditions in the first reactor comprise one or more of the following: the first gaseous feed having a molar ratio of 8 to 25 mol. % oxygen, 8 to 25 mol. % ethane, and 65 to 84 mol. % nitrogen; a gas hourly space velocity (GHSV) in a range of 500 h'¹ to 30000 h’¹; a temperature in a range of 300°C to 450°C; and a pressure in a range of 20 psig to 120 Psig-

Embodiment M. The method according to any one of Embodiments A, B, C, D, E, F, G, H, I, J, or K, wherein the conditions in the first reactor comprise one or more of the following: the first gaseous feed having a molar ratio of 10 to 20 mol. % ethane, 8 to 25 mol. % oxygen, 10 to 45 mol. % carbon dioxide, and 10 to 45 mol. % steam; a gas hourly space velocity (GHSV) in a range of 2500 to 2900 h’¹; a temperature in a range of 300°C to 450°C; and a pressure in a range of 20 psig to 100 psig.

Embodiment N. The method according to any one of Embodiments A, B, C, D, E, F, G, H, I, J, K, L, or M, wherein the regenerating in the first reactor is initiated when ethane conversion in ODH reaction in the first reactor deteriorates from a range of 45% to 55% to a range of 35% to 44%. Embodiment O. The method of any one of Embodiments A, B, C, D, E, F, G, H, I, J, K, L, M, or N, wherein the conditions in the first reactor that result in conversion of oxygen in the first reactor to be less than or equal to 90% are maintained for a regenerating period of at least 2 hours.

Embodiment P. The method of Embodiment O, wherein the regenerating period is in a range of 2 hours to 60 hours.

Embodiment Q. The method of any one of Embodiments A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, or P, wherein the first gaseous feed further comprises a diluent.

Embodiment R. The method of Embodiment Q, wherein the diluent comprises one or more of nitrogen, carbon dioxide, and steam.

Embodiment S. A system for concurrently producing ethylene and regenerating a partially deactivated oxidative dehydrogenation (ODH) catalyst, the system comprising: a first reactor configured to dehydrogenate ethane in the presence of oxygen to produce ethylene; a second reactor connected in series with the first reactor and configured to dehydrogenate ethane in the presence of oxygen to produce ethylene; and a channel scheme comprising a first channel and a second channel, the first channel configured to provide a first gaseous feed comprising ethane and oxygen to either the first reactor or the second reactor, and the second channel configured to provide a product stream from the first reactor to a second reactor three-way valve.

Embodiment T. The system of Embodiment S, wherein when the channel scheme is configured to provide the first gaseous feed to the first reactor, the first reactor comprises the partially deactivated catalyst and the channel scheme is configured to provide a first product stream from the first reactor to the second reactor.

Embodiment U. The system of Embodiment T, comprising a valve and a feedline for providing an interstage gaseous feed comprising ethane and oxygen to a transfer line, the transfer line in fluid communication with the first and the second reactor.

Embodiment V. The system of any one of Embodiments S, T, or U, further comprising: one or more additional reactors in series with and between the first reactor and the second reactor.

Embodiment W. The system of any one of Embodiments S, T, U, or V, wherein when the channel scheme is configured to provide the first gaseous feed to the second reactor, the second reactor comprises the partially deactivated catalyst and the channel scheme is configured to provide a first product stream from the first reactor to the second reactor. Embodiment X. The system of any one of Embodiments S, T, U, V, or W, wherein the partially deactivated ODH catalyst comprises molybdenum (Mo), vanadium (V), tantalum (Ta), and bismuth (Bi), or oxides thereof.

Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein can be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Claims

1. A method of concurrently producing ethylene and regenerating a first oxidative dehydrogenation (ODH) catalyst that is at least partially deactivated, the method comprising contacting, in a first reactor, the first ODH catalyst with a first gaseous feed comprising ethane and oxygen under conditions such that conversion of oxygen in the first reactor is less than or equal to 90% to produce a first product stream comprising ethylene and to regenerate the first ODH catalyst, wherein the molar ratio of ethane to oxygen in the first gaseous feed is between 0.5 and 1.5.

2. The method of claim 1, further comprising providing a second gaseous feed comprising the first product stream to a second reactor connected in series with the first reactor, and contacting the second gaseous feed with a second ODH catalyst in the second reactor under conditions such that the conversion of oxygen in the second reactor is greater than 90%, producing a second product stream comprising ethylene.

3. The method of claim 2, wherein the second gaseous feed further comprises an interstage feed gas comprising one or both of oxygen and ethane.

4. The method of claim 3, wherein the interstage feed gas further comprises ethane.

5. The method of claim 4, wherein the interstage feed is at a temperature of 200°C to 250°C.

6. The method of any of claims 2 to 5, wherein conversion of oxygen in the second reactor is greater than 99% or is 100%.

7. The method of claim 2, wherein one or more additional reactors are in series with and between the first reactor and the second reactor.

8. The method of claim 7, wherein the second gaseous feed comprises effluent from the last in the series of the one or more additional reactors.

9. The method of claim 7, wherein the second gaseous feed comprises (1) effluent from the last in the series of the one or more additional reactors and (2) an inter-stage feed gas comprising ethane and oxygen.

10. The method of any one of claims 1 to 9, wherein the first ODH catalyst and/or the second ODH catalyst each individually comprise molybdenum (Mo), vanadium (V), tantalum (Ta), and bismuth (Bi), or oxides thereof.

11. The method of claim 10, wherein the first ODH catalyst and the second ODH catalyst are each individually a mixed metal oxide having a formula of MoaVbTacBidOx, wherein a is 1.0, b is about 0.01 to about 0.5, c is about 0.005 to about 0.1, and d is about 0.005 to about 0.2, and wherein x is at least a number that satisfies the valence state of the catalyst.

12. The method of any one of claims 1 to 11, wherein the conditions in the first reactor comprise one or more of the following: the first gaseous feed having a molar ratio of 8 to 25 mol. % oxygen, 8 to 25 mol. % ethane, and 65 to 84 mol. % nitrogen; a gas hourly space velocity (GHSV) in a range of 500 h'¹ to 30000 h’¹; a temperature in a range of 300°C to 450°C; and a pressure in a range of 20 psig to 120 psig.

13. The method of any one of claims 1 to 11, wherein the conditions in the first reactor comprise one or more of the following: the first gaseous feed having a molar ratio of 10 to 20 mol. % ethane, 8 to 25 mol. % oxygen, 10 to 45 mol. % carbon dioxide, and 10 to 45 mol. % steam; a gas hourly space velocity (GHSV) in a range of 2500 to 2900 h’¹; a temperature in a range of 300°C to 450°C; and a pressure in a range of 20 psig to 100 psig.

14. The method of any one of claims 1 to 13, wherein the regenerating in the first reactor is initiated when ethane conversion in ODH reaction in the first reactor deteriorates from a range of 45% to 55% to a range of 35% to 44%.

15. The method of any one of claims 1 to 14, wherein the conditions in the first reactor that result in conversion of oxygen in the first reactor to be less than or equal to 90% are maintained for a regenerating period of at least 2 hours.

16. The method of claim 15, wherein the regenerating period is in a range of 2 hours to 60 hours.

17. The method of any of claims 1 to 16, wherein the first gaseous feed further comprises a diluent.

18. The method of claim 17, wherein the diluent comprises one or more of nitrogen, carbon dioxide, and steam.

19. A system for concurrently producing ethylene and regenerating a partially deactivated oxidative dehydrogenation (ODH) catalyst, the system comprising: a first reactor configured to dehydrogenate ethane in the presence of oxygen to produce ethylene; a second reactor connected in series with the first reactor and configured to dehydrogenate ethane in the presence of oxygen to produce ethylene; and a channel scheme comprising a first channel and a second channel, the first channel configured to provide a first gaseous feed comprising ethane and oxygen to either the first reactor or the second reactor, and the second channel configured to provide a product stream from the first reactor to a second reactor three-way valve.

20. The system of claim 19, wherein when the channel scheme is configured to provide the first gaseous feed to the first reactor, the first reactor comprises the partially deactivated catalyst and the channel scheme is configured to provide a first product stream from the first reactor to the second reactor.

21. The system of claim 20, comprising a valve and a feedline for providing an interstage gaseous feed comprising ethane and oxygen to a transfer line, the transfer line in fluid communication with the first and the second reactor.

22. The system of claim 19, further comprising one or more additional reactors in series with and between the first reactor and the second reactor.

23. The system of claim 19, wherein when the channel scheme is configured to provide the first gaseous feed to the second reactor, the second reactor comprises the partially deactivated catalyst and the channel scheme is configured to provide a first product stream from the first reactor to the second reactor.

24. The system of any one of claims 19 to 24, wherein the partially deactivated ODH catalyst comprises molybdenum (Mo), vanadium (V), tantalum (Ta), and bismuth (Bi), or oxides thereof.