Oxidative dehydrogenation (ODH) reactor

Abstract

A system and method including providing ethane and oxygen through an inlet plenum of an ODH multi-tubular reactor to give a reaction mixture flowing through the first pass of the tube side to an intermediate plenum at the opposite longitudinal end of the ODH reactor, introducing additional oxygen into the intermediate plenum to mix with the reaction mixture via a mixer, flowing the reaction mixture having the additional oxygen from the intermediate plenum through a second pass of the tube side to an outlet plenum at the same longitudinal end as the inlet plenum, dehydrogenating ethane to ethylene in the reaction mixture in the first pass and in the second pass via ODH catalyst on the tube side, flowing a coolant through the shell side to remove heat from the reaction mixture, and discharging the reaction mixture from the outlet plenum as an effluent of the ODH reactor.

Description

[0001] OXIDATIVE DEHYDROGENATION (ODH) REACTOR

[0002] TECHNICAL FIELD

[0003] This disclosure relates to an oxidative dehydrogenation (ODH) reactor.

[0004] BACKGROUND ART

[0005] Catalytic oxidative dehydrogenation of alkanes into corresponding alkenes is an alternative to steam cracking. In contrast to steam cracking, oxidative dehydrogenation (ODH) may operate at lower temperature and generally does not produce coke. For ethylene production, ODH can provide a greater yield for ethylene than does steam cracking. The ODH may be performed in a reactor vessel having catalyst for the conversion of an alkane to a corresponding alkene. Acetic acid as a byproduct may be generated in the conversion of the lower alkanes (e.g., ethane) into the corresponding alkenes (e.g., ethylene). The product alkene and byproduct acetic acid may each be recovered from the ODH reactor effluent.

[0006] SUMMARY OF INVENTION

[0007] An aspect relates to a method of operating an oxidative dehydrogenation (ODH) reactor system, the method including providing feed including ethane and oxygen through an inlet plenum of an ODH reactor to give a reaction mixture flowing through a first pass of a tube side of the ODH reactor to an intermediate plenum of the ODH reactor, wherein the intermediate plenum is at an opposite longitudinal end of the ODH reactor relative to the inlet plenum, and wherein the ODH reactor is a multi-tubular reactor having the tube side and a shell side. The method includes introducing additional oxygen into the reaction mixture in the intermediate plenum, and mixing the additional oxygen with the reaction mixture via a mixer in the intermediate plenum. The method includes flowing the reaction mixture having the additional oxygen from the intermediate plenum through a second pass of the tube side to an outlet plenum of the ODH reactor, wherein flow direction through the second pass is opposite of flow direction through the first pass, and wherein the outlet plenum is at same longitudinal end of the ODH reactor as the inlet plenum. The method includes dehydrogenating ethane to ethylene in the reaction mixture in the first pass and in the second pass via ODH catalyst on the tube side, and flowing a coolant through the shell side, thereby removing heat from the reaction mixture and the ODH catalyst. The method includes discharging the reaction mixture from the outlet plenum as an effluent of the ODH reactor.

[0008] Yet another aspect is an ODH reactor system having an ODH reactor that is a multi-tubular fixed-bed reactor including: a tube side have ODH catalyst to dehydrogenate ethane into ethylene; an inlet plenum to receive feed including ethane and oxygen to introduce the feed to a first pass of the tube side; the first pass of the tube side to receive the feed from the inlet plenum to give a reaction mixture on the first pass of the tube side; an intermediate plenum to receive the reaction mixture from the first pass and receive additional oxygen introduced into the intermediate plenum from external of the ODH reactor, wherein the intermediate plenum is at an opposite longitudinal end of the ODH reactor relative to the inlet plenum; a mixer in the intermediate plenum to mix the additional oxygen with the reaction mixture, wherein the mixer includes a static mixer or packing, or both; a second pass of the tube side to receive the reaction mixture with the additional oxygen from the intermediate plenum, wherein flow direction through the second pass is opposite of flow direction through the first pass; an outlet plenum to receive the reaction mixture from the second pass and discharge the reaction mixture as a product mixture that is effluent from the ODH reactor, wherein the outlet plenum is at same longitudinal end of the ODH reactor as the inlet plenum; and a shell side to receive coolant to remove heat from the reaction mixture and the ODH catalyst.

[0009] The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.

[0010] BRIEF DESCRIPTION OF DRAWINGS

[0011] FIG. 1 and FIG. 1A are a diagram of an example of an oxidative dehydrogenation (ODH) single-pass (one-pass) multi-tubular fixed-bed reactor.

[0012] FIG. 2 is a diagram of an ODH two-pass multi-tubular fixed-bed reactor.

[0013] FIG. 3 is a diagram of an ODH reactor system having the ODH two-pass multi-tubular fixed-bed reactor of FIG. 2.

[0014] FIG. 4 is a block flow diagram of a method of operating an ODH reactor system having an ODH two-pass multi-tubular reactor.

[0015] FIG. 5 is a diagram of an ODH two-pass fixed-bed reactor.

[0016] FIG. 6A is a diagram of an ODH two-pass fixed-bed reactor and accompanying cross-sectional view. FIG. 6B is a diagram of an ODH fixed-bed reactor with catalyst beds in series and accompanying cross-sectional view.

[0017] FIG. 60 is a diagram of an ODH fixed-bed reactor with catalyst beds in parallel and accompanying cross-sectional view.

[0018] Like reference numbers and designations in the various drawings indicate like elements.

[0019] DESCRIPTION OF EMBODIMENTS

[0020] Embodiments of the present techniques relate to an oxidative dehydrogenation (ODH) multi-tubular reactor (e.g., shell-and-tube reactor) that dehydrogenates ethane into ethylene in presence of oxygen. The ODH multitubular reactor may be a two-pass reactor on the tube side to facilitate intermediate introduction of oxygen into the reactor (between the first pass and the second pass) to promote ethane / oxygen conversion and operational stability. An advantage may be that due to the intermediate addition of oxygen between the first pass and the second pass, less oxygen is included in the feed and thus the amount of diluent in the feed to give the feed outside of flammability limits may be beneficially reduced. This may beneficially lead to reduction of reactor size and associated equipment in the ODH reactor system. In implementations, a majority of oxygen gas introduced in the feed to the first pass may typically be consumed in the ODH reaction in the first pass. Therefore, the intermediate addition of oxygen inter-pass (between the first pass and the second pass) may provide oxygen for the ethane dehydrogenation to proceed adequately through the second pass. A mixer as static internal(s) (e.g., static mixer, packing, etc.) may be situated between the first pass and the second pass to promote mixing of the added oxygen with the reaction mixture from the first pass. The mixer may also be configured as a flame arrester to account for auto-ignition due to the intermediate addition of oxygen.

[0021] In operation, a feed including ethane and oxygen may be provided through an inlet plenum of the ODH two-pass multi-tubular reactor to give a reaction mixture flowing through the first pass of the ODH reactor tube side to an intermediate plenum of the ODH reactor. The intermediate plenum may be between the first pass and the second pass and at a longitudinal end portion of the ODH reactor opposite the inlet plenum. Oxygen is introduced into the intermediate plenum and combines with the reaction mixture discharging from the first pass. In the intermediate plenum, the reaction mixture from the first pass with the added oxygen flows through a mixer (having static internals) in the intermediate plenum. The reaction mixture with the added oxygen as mixed flows from the intermediate plenum through the second pass of the tube side to an outlet plenum of the ODH reactor. An ODH reactor effluent having product ethylene may discharge from the reactor from the outlet plenum.

[0022] The ODH multi-tubular reactor dehydrogenates ethane to ethylene in the reaction mixture in the first pass and in the second pass via ODH catalyst on the tube side. As indicated, the final reaction mixture may discharge from the outlet plenum as the ODH reactor effluent having product ethylene. Ethylene may be separated (recovered) from the ODH reactor effluent to give the product ethylene.

[0023] The ODH reaction of ethane / oxygen to ethylene / water is generally exothermic. For operational stability, the ODH reaction may be performed with the feed and reaction mixture compositions above the ethane upper flammable limit (UFL).

[0024] A challenge with an ODH one-pass (single-pass) multi-tubular reactor may be achieving high ethane conversion (e.g., above 50%) through the single pass and high oxygen conversion (e.g., near 100%) towards desired carbon-base product (ethylene) through the single pass without encountering unstable excess reaction. To address this operational challenge, two ODH multi-tubular reactors (each being one pass) may be disposed operationally in series and oxygen gas added interstage between the two reactors. However, such an approach may generally be more capital expenditure and operating cost (due to inclusion of the second reactor and the inter-stage equipment) compared to the present ODH two-pass multitubular reactor (e.g., FIG. 2) that accomplishes intermediate addition of oxygen to the reaction mixture. Certain implementations herein do not employ addition of oxygen gas to the reaction mixture flowing from a first ODH reactor to a second ODH reactor for two ODH reactors operationally in series.

[0025] Other approaches to achieve high one pass ethane / oxygen conversion with an ODH multi-tubular reactor may include to include oxygen in the feed to the conventional inlet of the reactor and inject additional oxygen (e.g., via a concentric O2 injector) into the middle of the tube bundle directly into the tubes or into tubes not part of a tube bundle. Static mixers can be employed inside the tubes. Unfortunately, the employment of injectors to inject oxygen directly into the tubes can generally increase the size of the ODH reactor resulting in increased capital expenditure. The technique may employ multiple injectors in the middle of (or throughout) the tube bundle (tube assembly) or in the middle of (or throughout) tubes not part of a tube bundle. Regrettably, the orifices on the tubes for the injection of oxygen gas may be prone to fouling and becoming plugged resulting in costly operational downtime of the ODH reactor. Further, the presence of orifice fittings and / or static mixers in the tubes can inhibit ease of uniform ODH catalyst loading and unloading for the tubes in ODH catalyst replacement. Conversely, the presence of a static mixer and / or packing (e.g., fixed packing) in the intermediate plenum of the present two-pass ODH reactor (e.g., FIG. 2) generally does not affect catalyst loading / unloading and can be configured in the larger volume of the intermediate plenum to be more robust and resistant to fouling or becoming plugged. Certain implementations herein with a one-pass ODH reactor and / or two- pass ODH reactor (e.g., FIG. 2) do not inject oxygen gas directly into tubes in a pass of the tube bundle.

[0026] In present embodiments, the ODH reactor may dehydrogenate ethane to ethylene via an ODH catalyst in presence of oxygen. The dehydrogenation of ethane to ethylene may be a reaction of ethane with oxygen via the ODH catalyst to give the ethylene. The ODH reactor may be a multi-tubular fixed-bed reactor having ODH catalyst on the tube side for the ODH reaction, and in which coolant (e.g., molten salt or oil) flows on the shell side to remove the heat of reaction from the tube side.

[0027] The feed (process feed) to the ODH reactor may include ethane and oxygen conveyed in a conduit to the ODH reactor. The feed may also include diluent to place the feed outside of flammability limits. The diluent can be, for example, nitrogen gas (N2), carbon dioxide gas (CO2), water (steam), helium, argon, or methane, or any combinations thereof. In implementations, steam or vaporized water can be an attractive diluent, for example, due to the relative simplicity of the separation of the water from the ODH reactor effluent. The feed is introduced to the ODH reactor to give a reaction mixture flowing on the tube side of the ODH reactor. If the diluent in the feed includes water, the water in the reactor effluent may include both unreacted diluent water and water generated in the ODH reaction in the ODH reactor.

[0028] Components in addition to ethylene that form in the ODH reactor may include acetic acid, carbon dioxide, carbon monoxide, and water. Thus, an ODH plant having the ODH reactor may produce ethylene as product and acetic acid as coproduct. Carbon monoxide and carbon dioxide may undesirably form in the ODH reactor and discharge in the reactor effluent with the ethylene and acetic acid.

[0029] The ODH reactor may generate ethylene (C2H4) as the main product and acetic acid (CH3COOH) as a value-added coproduct. The ODH reactor may generate carbon monoxide (CO), carbon dioxide (CO2), and water (H2O). The reactions or reaction mechanisms in the ODH reactor characterized as reactions of ethane (C2H6) and oxygen (O2) can be explained at least in part as follows:

[0030] C2H6 + 0.5 O2 C2H4 + H2O

[0031] C2H6 + 1.5 O2 CH3COOH + H2O

[0032] C2H6 + 2.5 O2 2 CO + 3 H2O

[0033] C2H6 + 3.5 O2 2 CO2 + 3 H2O

[0034] The product effluent from the ODH reactor system may include ethylene, acetic acid, carbon dioxide, carbon monoxide, water, and unreacted ethane. Again, in addition to dilution steam (if employed) as water in the ODH reactor effluent, the effluent may also include water (as water vapor or steam) formed in the ODH reactor.

[0035] The processing of the effluent may include condensing the water and acetic acid to remove the acetic acid and water from the ODH reactor effluent. The water and acetic acid may be condensed, for example, via a heat exchanger utilizing a cooling medium (e.g., cooling water, air, etc.). In some implementations, a flash drum vessel or quench tower vessel may facilitate separation of the liquid as condensed from the effluent.

[0036] In implementations, the condensed water and the condensed acetic acid as a mixture from the ODH reactor effluent may be processed in an acetic acid unit (e.g., having an extractor column vessel, solvent recovery column vessel, and water stripper column vessel) to separate the co-product acetic acid and liquid water. In implementations, the water may be recycled for use in the ODH plant. For instance, the water discharging from the acetic acid unit may be recycled (as recycle water) for scrubbing process gas in the effluent processing and / or as water for the dilution steam in the ODH reactor feed preparation, and so on.

[0037] After the condensed water and condensed acetic acid are removed from the effluent, the remaining portion of the effluent as gas can include ethylene, CO, CO2, and ethane. This gas may be scrubbed (e.g., with liquid water) in a scrubber column vessel to remove residual acetic acid vapor and residual water vapor from the gas. The gas may be subjected to separations to remove CO and CO2. The gas may be sent through a C2 splitter (ethane / ethylene splitter) (a distillation column vessel having distillation trays) to separate the ethane from the gas to give the product ethylene.

[0038] As for the ODH reactor system, ODH catalyst (e.g., as a fixed bed) may be disposed inside the tubes of the ODH reactor (whether one pass as in FIG. 1 or two pass as in FIG. 2). The term “ODH catalyst” as used herein may be catalyst known for ODH of ethane. The ODH catalyst may give an ODH reaction that dehydrogenates ethane to ethylene and in which acetic acid as a byproduct may be formed. A low-temperature ODH catalyst may be beneficial. One non-limiting example of an ODH catalyst that may be utilized in an ODH reactor is a low- temperature ODH catalyst that includes molybdenum (Mo), vanadium (V), tellurium (Te), niobium (Nb), and oxygen (O), wherein the molar ratio of molybdenum to vanadium is from 1 :0.12 to 1:0.49, the molar ratio of molybdenum to tellurium is from 1:0.01 to 1:0.30, the molar ratio of molybdenum to niobium is from 1 :0.01 to 1:0.30, and oxygen is present at least in an amount to satisfy the valency of any present metal elements. The molar ratios of molybdenum, vanadium, tellurium, niobium can be determined by inductively coupled plasma mass spectrometry (ICP- MS). Another non-limiting example of an ODH catalyst that may be utilized in an ODH reactor is a catalyst that includes molybdenum (Mo); vanadium (V); bismuth (Bi); tantalum (Ta) or niobium (Nb), or both; and oxygen (O), wherein the molar ratio of molybdenum to vanadium is from 1:0.01 to 1 :0.5, the molar ratio of molybdenum to bismuth is from 1:0.005 to 1:0.2, the molar ratio of molybdenum to tantalum, if present, or to niobium, if present, is from 1:0.005 to 1 :0.1 , and oxygen is present at least in an amount to satisfy the valency of any present metal elements to render the catalyst electrically neutral. The catalyst may be labeled as low temperature ODH catalyst in providing for the ODH reaction at less than 550°C, less than 500°C, less than 450°C, less than 425°C, less than 400°C, or less than 375°C, or in the ranges, for example, of 300°C to 550°C, 300°C to 500°C, 300°C to 450°C, 275°C to 425°C, 275°C to 550°C, 250°C to 550°C, or 250°C to 400°C, and the like.

[0039] FIG. 1 is an example of an ODH single-pass (one-pass) multi-tubular fixed- bed reactor 100 that is a vessel. The vessel is typically a cylindrical vessel having elliptical or semi-elliptical heads. The vessel may have a vertical orientation (as depicted) or a horizontal orientation. The ODH multi-tubular fixed-bed reactor 100 has a shell 102 and a tube bundle, which may be similar to a shell-and-tube heat exchanger, except that the tubes 104 have a fixed bed of catalyst. The tube bundle is multiple tubes 104 generally aligned in parallel.

[0040] As a general representation for clarity, the tubes 104 are depicted as few in number and large in diameter. The tubes 104 will instead typically have a smaller diameter than depicted relative to the diameter of the reactor vessel or shell 102. The number of tubes 104 in the tube bundle of the ODH multi-tubular fixed-bed reactor 100 can range in the thousands, such as 10,000 to 50,000, e.g., 30,000 tubes 204 as a particular non-limiting example).

[0041] The ODH multi-tubular fixed-bed reactor 100 (single-pass) includes a tube side and a shell side. The tube side may be the process side (for conversion in a flowing reaction mixture of process feed into product). The shell side may be the utility side (for flow of a heat transfer fluid). The shell side can be similar in effect to a vessel jacket, but may be similar or analogous to a shell side of a shell-and-tube heat exchanger.

[0042] In the tube bundle, the tubes 104 may be supported and held in place as parallel by a tube sheet 103 (e.g., a plate). The tube sheet 103 may be a circular plate that is perforated so that the tubes 104 fit through the perforated openings. In operation, the tubes 104 receive and discharge fluid through the perforated openings.

[0043] A tube sheet 103 is typically disposed at each longitudinal end of the tube bundle. In other words, one tube sheet 103 may be disposed at one end of the tube bundle, and a second tube sheet 103 may be disposed at the other end of the tube bundle. There may be also be transverse baffles 216 or support plates having perforations for the tubes 104 dispose along the tube bundle.

[0044] The shell 102 wall may be the vessel wall. The volume of the shell 102 around the longitudinal length of the tubes 104 may be characterized as the shell side of the reactor 100. Again, the shell side may be for flow of heat transfer fluid around the tubes 104.

[0045] The volume inside the tubes 104 may be characterized as the tube side of the reactor 100. Additionally, the longitudinal end portions of the vessel may be considered as the tube side. In particular, the longitudinal end portions of the vessel in which the process feed 106 is introduced to the tubes 104 and the ODH reactor effluent 108 (process product) is discharged from the tubes 104, respectively, may be characterized as or associated with the tube side of the reactor 100.

[0046] In other words, an inlet plenum 105 (a volume region as an inlet header) and an outlet plenum 107 (a volume region as an outlet header) are associated with the tube side and isolated from the shell side by the two tube sheets 103, respectively. In operation, the feed 106 enters the reactor 100 through a reactor inlet nozzle, the inlet plenum 105, and the inlet tube sheet 103 into the tubes 104 to give a reaction mixture flowing through the tubes 104. The reaction mixture flowing through the tubes 104 discharges from the tubes 104 through the outlet tube sheet 103, the outlet plenum 107, and a reactor outlet nozzle, as the effluent 108 from the reactor 102.

[0047] The tubes 104 can be filled (at least partially) with ODH catalyst 112. See FIG. 1A that is an exploded view of a tube 104 having a tube wall 110 and ODH catalyst 112 disposed in the tube 104. The ODH catalyst 112 may be a fixed bed of ODH catalyst in the tubes 104. The ODH catalyst 112 may facilitate conversion of the feed 106 into the product effluent 108 discharged from the reactor. In operation, the provision (supply) of the feed 106 to the tube side may give a reaction mixture flowing through the tubes 104 and in which reaction(s) in the reaction mixture are promoted (enabled, advanced) by the catalyst 112. As discussed, the process feed 106 may enter the vessel through a vessel inlet (e.g., inlet nozzle) to the tube side. The process product effluent 108 may discharge from the vessel through a vessel outlet (e.g., outlet nozzle) from the tube side.

[0048] The process feed 106 enters a bottom portion of the vessel. The reactor effluent 108 (process product) discharges from a top portion of the vessel. However, the reactor 100 can be configured for the process feed 106 to enter the top portion of the vessel and the effluent 108 to discharge from the bottom portion of the vessel.

[0049] A heat transfer fluid 114 may enter the vessel (to the shell side) through a vessel inlet (e.g., inlet nozzle) to flow through the shell side around the tubes 104. For implementations of the reaction on the tube side as exothermic (as is typical for ODH), the heat transfer fluid 114 may be a cooling medium (coolant) and in which the heat transfer fluid 114 removes the heat of reaction. For instances of the reaction on the tube side as endothermic or in which heat may be beneficial such as for maintenance purposes or in abnormal operation, the heat transfer fluid 114 may be a heating medium to provide heat for the endothermic reaction or to provide the heat for maintenance.

[0050] The heat transfer fluid 114 provided to the reactor 100 and that enters the shell side may be labeled as heat-transfer fluid supply. The heat transfer fluid 114 may flow around the tubes 104. Therefore, the heat transfer fluid 114 may be subjected to heat exchange with the process reaction mixture and catalyst 112 on the tube side. The shell side may include baffle(s) 116 to generate more turbulent flow of the heat transfer fluid 114 to improve (increase) heat transfer between the heat transfer fluid 114 and the tube side.

[0051] The heat transfer fluid 118 may discharge from the reactor 100 from the shell side, such as through a vessel outlet (e.g., outlet nozzle). The heat transfer fluid 118 that discharges from the reactor 100 from the shell side may be labeled as heat-transfer fluid return sent (as return) to a heat-transfer fluid supply system. The composition of the heat transfer fluid 118 that discharges from the reactor 100 may be the same as the composition of the heat transfer fluid 114 supplied to the reactor 100. The discharged heat-transfer fluid 118 may have the same composition but a different temperature than the supplied heat-transfer fluid 114 due to the heat exchange with the reaction mixture (and ODH catalyst 112) on the tube side.

[0052] The flow of the heat transfer fluid 114 through the shell side is in a co-current flow direction with the flow of the reaction mixture on the tube side. However, the flow of the heat transfer fluid 114 through the shell side can instead be in a counter current flow direction with the flow of the reaction mixture on the tube side. For instance, in the illustrated implementation, the reactor 100 can instead be configured with the inlet for the heat transfer fluid 114 supply on the upper portion of the vessel and the outlet for the heat transfer fluid 118 return on the lower portion of the vessel.

[0053] The heat transfer fluid 114 may typically be a coolant because the ODH reaction is exothermic. The shell 102 via the coolant may maintain the reaction mixture and ODH catalyst 112 on the tube side at a specified temperature (isotherm temperature). The temperature of the reaction mixture and / or ODH catalyst 112 may be related to the catalyst 112 bed average temperature, catalyst 112 bed peak temperature, coolant temperature through the shell 102, and the like. In implementations, the heat transfer fluid 114 can be maintained at a specified temperature to give desired temperatures for the reaction mixture and the catalyst 112. The temperature of at least one of the heat transfer fluid (e.g., coolant), the reaction mixture, or the ODH catalyst 112 may be maintain at a specified temperature via flowing the coolant through the shell 102.

[0054] Again, for an ODH reactor, the heat transfer fluid 114 may typically be a coolant because the reactions on the tube side are generally exothermic. Heat transfer occurs from the reaction mixture and catalyst 112 on the tube side through the tube wall 110 to the heat transfer fluid 114 flowing through the shell side. The heat transfer fluid 114 as coolant for an ODH reactor can be, for example, steam, water (including pressurized or supercritical water), oil, or molten salt, and so forth. Molten salt may be selected as the coolant due to relatively high stability of the molten salt and due to relatively high heat-transfer coefficient values provided by molten salt at the temperature (e.g., 300-500°C) of operation of the ODH reactor. Water (critical point is 374°C and 22,064 kPa) or very high-pressure steam [(e.g., 1500 pounds per square inch gauge (psig) or greater] employed as the heat transfer fluid 114 would give relatively high pressure on the shell side leading to thicker walls of the shell (vessel).

[0055] The diameter (e.g., inside diameter) of the tubes 104 for an ODH multitubular reactor (whether single pass as in FIG. 1 or two pass as in FIG. 2) may be specified to give adequate velocity of the reaction mixture through the tubes 104 to advance a sufficient Reynolds number (Re) to give a satisfactory heat transfer coefficient. The flow hydraulics of the reaction mixture in the tubes 104 can affect heat transfer from the reaction mixture and ODH catalyst 112 to the coolant on the shell side. For typical operating conditions and capacities of an ODH reactor (whether single pass as in FIG. 1 or two pass as in FIG. 2), the tube 104 diameter (e.g., inside diameter) for an ODH reactor may be specified, for example, in the ranges of 0.75 inch to 2.0 inch, 0.75 inch to 1.5 inch, or 0.75 inch to 1.25 inch. Diameters less than 0.75 inch can give difficulty in loading catalyst 112 to the tubes 104 (filling or placing the catalyst 112 into the tubes 104) in implementations. However, tube 104 diameters (for an ODH reactor) less than 0.75 inch can be accommodated in certain implementations. In examples, tube 104 diameters (for an ODH reactor) greater than 1.25 inch or greater than 1.5 inch can give inadequate velocity of the reaction mixture through the tubes 104 leading to poor heat transfer. However, tube 104 diameters (for an ODH reactor) greater than 1.5 inch can be accommodated in certain implementations.

[0056] The reactor vessel may be a pressure vessel designed and configured (e.g., with adequate wall thickness) to be subjected to an internal pressure up to a specified pressure (design pressure) greater than ambient pressure (atmospheric pressure). A pressure vessel may be rated to hold a fluid up to the design pressure. In operation, the operating pressure in a pressure vessel may generally be maintained less than the design pressure. A pressure vessel may be constructed per a formal standard or code, such as the American Society of Mechanical Engineers (ASME) Boiler & Pressure Vessel Code (BPVC) or the European Union (EU) Pressure Equipment Directive (PED). For an ODH reactor as a multi-tubular fixed-bed reactor, the reactor vessel and the tubes may be metal, such as steel (e.g., stainless steel).

[0057] Two or more ODH single-pass (one-pass) multi-tubular fixed-bed reactors 100 may be employed (in series and / or parallel) in an ODH reactor system of an ODH plant that converts ethane to produce ethylene. Such a configuration may be employed to inject intermediate (inter-stage) oxygen gas to the reaction mixture. However, such an approach may generally be more capital intensive and with increased operating cost (due to inclusion of the second reactor and the inter-stage equipment) compared to the present ODH two-pass multi-tubular reactor (e.g., FIG. 2) that accomplishes intermediate addition of oxygen to the reaction mixture.

[0058] For the ODH one-pass multi-tubular reactor of FIG. 1, or other ODH one- pass multi-tubular reactors, injectors on the tubes to inject intermediate oxygen gas directly into the tubes into the reactor mixture may be employed. Yet, the employment of injectors to inject oxygen directly into the tubes can generally increase the size of the ODH reactor resulting in increased capital expenditure. Moreover, the orifices on the tubes of the injectors for the injection of oxygen gas may be prone to fouling and becoming plugged resulting in undesired operational downtime of the ODH reactor. For the intermediate injection of oxygen gas directly into the tubes, static mixers may be situated in the tubes. However, the presence of the static mixer and / or injector orifice fittings in the tubes can inhibit ease of uniform catalyst loading / unloading for the tubes in ODH catalyst replacement. Conversely, the presence of a static mixer and / or packing in the intermediate plenum of the present two-pass ODH reactor (e.g., FIG. 2) generally does not affect catalyst loading / unloading and can be configured in the larger volume of the intermediate plenum to be more robust and resistant to fouling or becoming plugged.

[0059] FIG. 2 is an ODH two-pass multi-tubular fixed-bed reactor 200 that is a vessel (e.g., a pressure vessel). The reactor vessel and the tubes may be metal, such as steel (e.g., stainless steel). The number of tubes can range in the thousands (e.g., 30,000 tubes, with 15,000 tubes in the first pass 202 and another 15,000 in the second pass 204). The number of tubes in the first pass 202 may be, for example, in the range of 5,000 to 25,000. The number of tubes in the first pass 202 may be, for example, in the range of 5,000 to 25,000.

[0060] The ODH multi-tubular reactor 200 is 2-pass (two pass, double pass) on the tube side in having a first set of tubes as the first pass 202, and a second set of tubes as the second pass 204. The reactor 200 has a tube bundle in which the first pass 202 is through a first part (e.g., about half) of the tube bundle, and the second pass 204 is through the other part (e.g., the other half) of the tube bundle, as indicated by dividing line 205. In other embodiments, the first pass 202 may be a first tube bundle and the second pass 204 may be a second tube bundle. The ODH multi-tubular reactor 200 is a fixed-bed reactor in having a first fixed bed of ODH catalyst in the tubes in the first pass 202 and a second fixed bed of ODH catalyst in the tubes in the second pass 204.

[0061] The ODH multi-tubular fixed-bed reactor 200 (two-pass) includes a tube side and a shell side. The tube side may be the process side (for conversion of ethane in a flowing reaction mixture into ethylene). The tube side includes the first pass 202 of tubes and the second pass 204 of tubes. The shell side may be the utility side (for flow of a coolant). The shell side can be similar in effect to a vessel jacket, and / or may be similar or analogous to a shell side of a shell-and-tube heat exchanger.

[0062] The ODH multi-tubular fixed-bed reactor 200 has the shell 206 and the tube bundle, which may be similar to a shell-and-tube heat exchanger, except that the tubes in the tube bundle have a fixed-bed of catalyst. The tube bundle is multiple tubes generally aligned in parallel. The tube bundle its tubes may run longitudinally generally parallel with the longitudinal centerline of the reactor vessel. In the tube bundle, the tubes may be supported and held in place as parallel by a tube sheet 208 (e.g., a plate). The tube sheet 208 may be a circular plate that is perforated so that the tubes fit through the perforated openings. In operation, the tubes receive and discharge fluid through the perforated openings.

[0063] A tube sheet 208 is typically disposed at each longitudinal end of the tube bundle. In other words, one tube sheet 208 may be disposed at one end of the tube bundle, and a second tube sheet 208 may be disposed at the other end of the tube bundle. There may be also be transverse baffles or support plates having perforations for the tubes dispose along the tube bundle.

[0064] The shell 206 wall may be the vessel wall. The volume of the shell 206 around the longitudinal length of the tubes may be characterized as the shell side of the reactor 200. Again, the shell side may be for flow of heat transfer fluid (e.g., coolant) around the tubes of both passes 202, 204.

[0065] As discussed with respect to FIG. 1 , the volume inside the tubes may be characterized as the tube side of the reactor 200. Additionally, the longitudinal end portions of the vessel may be considered or characterized as (or associated with) the tube side of the reactor 200.

[0066] The inlet plenum 210 (a volume region as an inlet header) of the reactor 200 at a longitudinal end portion of the reactor receives the process feed 212 in operation for introduction of the feed 212 into the tubes of the first pass 202 to give a reaction mixture 214 flowing through the tubes of the first pass 202. A dividing plate 213 may be situated to separate (isolate) the inlet plenum 210 from the outlet plenum 215.

[0067] The reaction mixture 214 discharges as a first-pass product reaction mixture 216 from the tubes of the first pass 202 into an intermediate plenum 218 (a volume region as an intermediate header) of the reactor 200. The intermediate plenum 218 may be at a longitudinal end portion of the reactor 200 opposite the inlet plenum 210.

[0068] The first-pass product reaction mixture 216 from the first pass 202 combines with oxygen gas (O2) 220 to flow through a mixer 222 in the intermediate plenum 216 to give an intermediate reaction mixture 224 introduced to the inlet of the second pass 204 of tubes. The oxygen gas 220 is fed through an inlet nozzle of the reactor vessel into the intermediate plenum 216. In some implementations, water 225 (e.g., liquid water or steam) can be added to the intermediate plenum 218. The water 225 may cool the contents (reaction mixture 216 and intermediate reaction mixture 224) in the intermediate plenum 218 to avoid possibility of auto-ignition in the intermediate plenum 218 if such is an issue. The water 225 (if employed) may be injected through a reactorvessel inlet nozzle (not shown) into the inlet plenum 218. For the water 225 as liquid water, the liquid water may evaporate to further advance the cooling of the contents in the intermediate plenum 218.

[0069] The intermediate reaction mixture 224 that flows into the second pass 204 from the intermediate plenum 218 has more oxygen than the first-pass product reaction mixture 216 that discharged from the first pass 202 due to the addition of the oxygen 220 into the intermediate plenum 218. The intermediate reaction mixture 224 exiting from the intermediate plenum 218 flows through the tubes of the second pass 204 in a direction opposite the flow direction of the reaction mixture 214 through the tubes of the first pass 202.

[0070] The tubes of the first pass 202 can be filled (at least partially) with a first ODH catalyst. The first ODH catalyst may be a fixed-bed of catalyst in the tubes of the first pass 202. The tubes of the second pass 204 can be filled (at least partially) with a second ODH catalyst. The second ODH catalyst may be a fixed- bed of catalyst in the tubes of the second pass 204. The first and second ODH catalyst may facilitate the ODH reaction in the tubes and associated conversion of ethane into ethylene in the tubes. The first ODH catalyst and the second ODH catalyst may be the same (e.g., same source, same type, generally the same composition, etc.). On the other hand, the first ODH catalyst and the second ODH catalyst can be different with respect to each other. As discussed, the ODH catalyst (first and second) may facilitate or promote the ODH reaction conversion of ethane / O2 (dehydrogenation of ethane) into ethylene / H2O. ODH catalyst that can give an ODH reaction that dehydrogenates ethane to ethylene and forms acetic acid as a byproduct may be applicable to the present techniques. A low- temperature ODH catalyst may be beneficial. The catalyst may be low temperature in providing for the ODH reaction at less than 450°C, less than 425°C, or less than 400°C. The temperature of the effluent 226 as discharged may be, for example, in the ranges of 300°C to 450°C, or 275°C to 425°C, commensurate with the operating temperature (e.g., 300°C to 450°C, or 275°C to 425°C) of the reactor 102 vessel.

[0071] The final reaction mixture (second-pass product reaction mixture) discharges from the second pass tubes through the outlet plenum 215 as the ODH reactor effluent 226. The effluent 226 has the product ethylene and other components generated in the ODH reaction, as well as unreacted ethane. The outlet plenum 215 may be at the same longitudinal end portion of the reactor 200 as the inlet plenum 210. The outlet plenum 215 may be separated from (isolated from) the inlet plenum by a dividing plate 213, as mentioned. As discussed, the effluent 226 may be processed to isolate (recover) ethylene as product for distribution to users.

[0072] A heat transfer fluid 228 may enter the reactor vessel (into the shell side) through a vessel inlet (e.g., inlet nozzle) to flow through the shell 206 side around the tubes in the first pass 202 and the second pass 202. The representation of the dividing line 205 for the tube side is generally not a division of the shell 206.

[0073] The heat transfer fluid 228 on the shell side may be subjected to heat exchange with the process reaction mixture and ODH catalyst on the tube side. As the ODH reaction is exothermic, the heat transfer fluid 228 is a cooling medium (coolant), such as molten salt, oil, etc. The heat transfer fluid 228 as coolant on the shell side removes the heat of reaction of the ODH reaction on the tube side. The technique may include flowing the coolant through the shell side to maintain the reaction mixture (and ODH catalyst) on the tube side at a specified temperature. The technique may include maintaining temperature of at least one of the heat transfer fluid 228, the reaction mixture 214, 224, or the ODH catalyst at a specified temperature via flowing the heat transfer fluid 228 (e.g., coolant) through the shell 206 at a specified temperature, such as in the ranges of 300°C to 550°C, 300°C to 500°C, 300°C to 475°C, 300°C to 450°C, 300°C to 425°C, 300°C to 400°C, 350°C to 500°C, 350°C to 450°C, 325°C to 425°C, 275°C to 425°C, or 250°C to 400°C, and the like. The temperature of the reaction mixture 214, 224 and / or ODH catalysts may be congruent with or related to each catalyst-bed average temperature, each catalyst-bed peak temperature, coolant 228 temperature through the shell, coolant 230 as discharged, and the like. In some implementations, the coolant 228 (or coolant 230) temperature can be controlled at the aforementioned specified temperature ranges to give a desired temperature for the reaction mixture 214, 224 and / or the ODH catalysts. The heat transfer fluid 230 may discharge from the reactor 200 from the shell side, such as through a vessel outlet (e.g., outlet nozzle). The composition of the heat transfer fluid 230 that discharges from the reactor 200 may be generally the same as the composition of the heat transfer fluid 228 supplied to the reactor 200. The discharged heat-transfer fluid 230 may have a different temperature than the supplied heat-transfer fluid 228 due to the heat exchange with the reaction mixture (and ODH catalyst) on the tube side. For the heat transfer fluid as coolant, the discharged heat-transfer fluid 230 (as return) may have a greater temperature (increased temperature) than the supplied heat-transfer fluid 228.

[0074] The mixer 222 may be static internals in the intermediate plenum 218. The static internals may be, for instance, metal (e.g., stainless steel, nickel alloy, etc.) or ceramic, and the like. In implementations, the mixer 222 has no moving parts, or has no parts configured to move to promote mixing via movement. The mixer 222 may fill or substantially fill a vertical (longitudinal) cross section of the intermediate plenum 218, such that most or all of the first-pass product reaction mixture 216 with added oxygen gas 220 flows through the mixer 222. In certain implementations, the mixer 222 as static components may fill a majority (greater than 50%) or substantially all of the intermediate plenum 218 volume. The static internals may provide surface area for mixing and may cause turbulence to promote mixing. Again, the static internals may be generally non-moving elements. The static internals may be, for example, plates, baffles, or fixed helical-shaped objects, and so on.

[0075] In implementations, the static internals are a static mixer or multiple static mixers. The mixer 222 may be a static mixer (or akin to a static mixer) such as commonly employed in-line in a conduit (e.g., pipe). The mixer 222 may be multiple static mixers disposed in parallel and / or series. The static internals or static mixer (or multiple static mixers) can be situated in a conduit or conduits (pipes, tubes, etc.) in the intermediate plenum 218. A static mixer may be a precision-engineered device for the continuous mixing of fluid materials, including without moving components. The static internals (e.g., ceramic or metal such as stainless steel, nickel alloy, etc.) of the mixer 222 including as a static mixer(s) may be a plate type, baffles (a series of baffles), and / or have a helical shape (e.g., rectangular plates twisted around at 180° so that they make a double-helix shape), and so forth. The static internals may be packing, such as generally spherical (e.g., metal or ceramic balls) or irregular shaped objects, packed or fixed in the intermediate plenum 218. The static internals may be packing fixed in the intermediate plenum 218, such as packing utilized in absorber, stripper, or distillation columns. The mixer 222 may be a packed bed with packing as static internals in the intermediate plenum 218. In implementations, the packing may generally be inert to the ODH reaction mixture at the operating conditions (e.g., operating temperature) of the reactor 200. The material of construction of the packing may be, for example, ceramic or metal such as stainless steel, nickel alloy, etc. The packing may be random (dumped) packing, such as Raschig rings, Lessing rings, Pall rings, saddle rings (Berl saddles or INTALOX® saddles, Bialecki ring, Dixon ring, Tri-Packs (spherical), solid spheres, porous spheres, irregular shapes, and so forth. The packing may be structured (systematically arranged) packing that may involve discs, honeycomb-shaped internals, knitted wires, corrugated structure packing, gauze shape packing, crimped packing, etc.

[0076] In addition to providing for mixing of the reaction mixture 216 with the oxygen gas 220, the mixer 222 can be a flame arrester (also spelled flame arrestor). A flame arrester may allow flow but prevent flame transmission. The mixer 222 additionally as a flame arrestor, for example, may stop propagation of flame resulting from auto-ignition of the reaction mixture 216 (with presence of increased amount of oxygen by addition of the oxygen 220). While the mixer 222 via mixing may reduce probability of auto-ignition by reducing occurrence of local regions of high oxygen concentration, the mixer 222 may also be configured as a flame arrester to arrest auto-ignition or an auto-ignition flame if such does occur. The mixer 222 if configured as a flame arrestor may stop propagation of a flame resulting from ignition of the reaction mixture 216 other than auto-ignition. Flame arresters may be passive, mechanical devices. They may be typically installed, for instance on vessels (e.g., on a storage tank nozzle), containers, or a vapor piping system, and the like. A function may be to allow gases to pass through during normal operating conditions, but stop a flame to prevent fire propagation under in abnormal operations of the protected system. A flame arrester (which may include deflagration arrester, flame trap, detonation arrester, etc.) is typically fitted to openings of enclosures, or to pipe work, and is intended to allow flow but prevent flame transmission and combustion by extinguishing the flame. A flame arrester may stop or confine a fire, prevent ignition including auto-ignition, and stop propagation of a flame. A flame arrester may function at least in part by absorbing the heat from a flame front thus dropping the burning gas / air mixture below its autoignition temperature (consequently, the flame may extinguish. The heat may be absorbed through channels (passages) of the mixer 222 as a flame arrestor. In implementations, these channels may be chosen and measured as the maximum experimental safe gap (MESG) of the gas for the particular application. These passages can be crimped metal, ribbon, wire mesh, plate with holes, random packing, and the like. The static internals in the mixer 222 for performing as a flame arrester can be spiral wound or crimped-metal (ribbon flame cell elements) to inhibit flame propagation by absorbing and dissipating heat.

[0077] The ODH two-pass multi-tubular reactor 200 can have more plenums than the three depicted plenums 210, 215, and 218. For instance, the first pass 202 can be split (divided) longitudinally into two sections, and with a plenum between the two sections to receive addition of O2 into the reaction mixture 214 flowing through the first pass 202. This additional O2 would not be directly injected into the tubes such as into the side of the tubes through the tube wall (so to avoid such complexity), but instead added (fed) to the plenum between the two vertical sections of the first pass 202. In this configuration, the first pass 202 of tubes (first pass 202 of the tube side) would include two vertical sections of tubes separated by a plenum that receives O2 intermediate the two vertical sections. The second pass 204 could be likewise configured. Other configurations of the ODH reactor 200 are applicable for incorporating more than three plenums for the tube side, including plenums to receive additional O2.

[0078] Certain embodiments of an ODH reactor system include multiple (e.g., two) ODH two-pass multi-tubular reactors 200 disposed operationally in parallel. The system can include a heat exchanger (e.g., shell-and-tube heat exchanger, plate-fin type heat exchanger, etc.) to cool a combined stream of the effluent 226 from each reactor 200 with a cooling medium (e.g., cooling water, air, feed 212 to one or more of the reactors 200, etc.) to condense acetic acid and water in the combined stream of the effluents 226. In implementations, the cooled combined stream of reactor effluents 226 can discharge from the heat exchanger, for example, to a flash vessel (flash drum) in which the condensed acetic acid and condensed water can be removed via (discharged from) a bottom outlet of the flash vessel. In implementations, this condensed liquid as discharged can be processed to recover the acetic acid as product (coproduct). The remaining portion (gas with any water vapor and / or acetic acid vapor) in the flash vessel can discharge overhead from the flash vessel for further processing to recover the product ethylene. The gas discharging overhead from the flash vessel may include, for example, ethylene, carbon dioxide, carbon monoxide, unreacted ethane, etc.

[0079] FIG. 3 is an ODH reactor system 300 having the ODH two-pass multi-tubular reactor 200 of FIG. 2. The ODH two-pass multi-tubular reactor 200 vessel may have an effluent outlet for discharge of the effluent 226 from the reactor 200. As depicted in FIG. 2, the effluent outlet may be a vessel outlet nozzle. This vessel outlet nozzle for the effluent 226 may be coupled to an effluent discharge conduit for flow of the discharged effluent 226 from the reactor 200. The temperature of the effluent 226 as discharged may be, for example, in the range of 300°C to 500°C commensurate with the operating temperature (e.g., 300°C to 500°C) of the ODH two-pass multi-tubular reactor 200 vessel. Other temperature ranges are applicable, as discussed.

[0080] The ODH reactor system 300 includes a heat exchanger 302 disposed along the effluent discharge conduit. In operation, the heat exchanger 302 cools the effluent 226 with water 304 as a cooling medium. For example, the effluent exchanger 302 may cool the effluent 226 to a temperature in the range of 150°C to 350°C (or in the range of 200°C to 300°C). The effluent 226 may be cooled, for example, by an amount in a range of 50°C to 350°C across the heat exchanger 302. The water 304 (e.g. as BFW from a BFW pump) may be heated in the heat exchanger 302 with heat from the effluent 226 to vaporize the water 304 in the heat exchanger to give the discharged stream 306 as steam. On the other hand, the heat exchanger 302 may heat (pre-heat) the water 304 to give heated water 304 as stream 306 that vaporizes (flashes) after exiting the heat exchanger 302 into the steam.

[0081] The water 304 as cooling medium may be heated with heat from the effluent 226 to [a] vaporize the water 304 into steam in the heat exchanger 302 or [b] for the heated water 304 to vaporize (flash) downstream, for example, in a flash vessel or steam drum. The heat exchanger 302 (as effluent cooler and steam generation heat exchanger) may be, for example, a shell-and-tube heat exchanger or a fin- type heat exchanger (e.g., with a finned-tube bundle), and so on. The water 304 may be, for example, demineralized water, steam condensate, or boiler feedwater (BFW), and the like. Boiler feedwater may be treated demineralized water.

[0082] In the depicted implementation, the heat exchanger 302 is a steamgeneration heat exchanger to heat the water 304 (e.g., liquid water) with the effluent 226 as a heating medium to: [1] vaporize the water 304 in the heat exchanger 302 to generate steam from the water 304 to give the discharged stream 306 as steam; or [2] heat (pre-heat) and not vaporize the water 304 to give the discharged stream 306 as heated water 304 for downstream vaporization of the water into the steam. Thus, the heat exchanger 302 may be characterized as a steam-generation heat exchanger.

[0083] In the latter configuration [2], the steam-generation heat exchanger 302 may act as a preheater (e.g., BFW preheater). The steam generation system may include additional equipment, such as a vessel (e.g., flash vessel), a pump (e.g., boiler feedwater pump), etc. In embodiments, the heat exchanger 302 may heat (pre-heat, not vaporize) the water 324 for vaporization of the water 304 into steam, for example, in a steam drum. In those embodiments, the heat exchanger 302 may receive water 304 from the steam drum or from a boiler feedwater (BFW) pump, and discharge heated (pre-heated) water 304 (generally not steam) as stream 306 to, for example, the steam drum.

[0084] The steam generated (in configurations [1] or [2]) may discharge into a steam header (or sub-header) conduit or through a conduit to a user, and so on. Higher-pressure steam may generally be more valuable than lower pressure steam. Higher-pressure steam, such as greater than 600 psig or greater than 1500 psig, may typically be more valuable than lower pressure steam, such as less than 600 psig or less than 150 psig. The pressure of the steam generated via the steamgeneration heat exchanger 302 may be a function of the temperature of the effluent 226 driven by the operating temperature (ODH reaction temperature) of the ODH reactor 200.

[0085] The effluent 226 (as cooled by the heat exchanger 302) may discharge from the heat exchanger 302 to downstream processing. The downstream processing of the effluent 226 may isolate product ethylene and byproduct (coproduct) acetic acid. The effluent 226 may flow from the heat exchanger 302 through a feed heat exchanger 308 (e.g., a cross exchanger) in route to the downstream processing. The ODH reactor system 300 may include the feed heat exchanger 308 that heats the feed 212 flowing to the ODH reactor 200. The feed heat exchanger 308 may be, for example a shell-and-tube heat exchanger or a plate-fin heat exchanger. In implementations, the feed heat exchanger 308 may be a cross exchanger, and in which the feed 212 is heated with the effluent 226. Thus, the effluent 226 operationally between the heat exchanger 302 and the downstream processing may be utilized to heat the feed 212 in the feed heat exchanger 308. In other implementations, the feed heat exchanger 308 may utilize steam instead of the effluent 226 as the heating medium.

[0086] FIG. 4 is a method of 400 operating an ODH reactor system with an ODH two-pass multi-tubular reactor (e.g., see FIG. 2) having a tube side and a shell side. The ODH multi-tubular reactor is a two-pass reactor on the tube side. The reactor may be a fixed bed reactor in having a fixed bed of ODH catalyst in the tubes of the first pass and a fixed bed of ODH catalyst in the tubes of the second pass. The tube side is generally the inside volume of the tubes. As discussed, the longitudinal end portions (e.g., as inlet plenum, intermediate plenum, and outlet plenum) of the reactor can be characterized as or associated with the tube side (e.g., as tube-side headers).

[0087] At block 402, the method includes providing feed including ethane and oxygen (oxygen gas O2) through an inlet plenum of the ODH two-pass multi-tubular reactor to give a reaction mixture flowing through the first pass of the reactor. In implementations, the feed may include diluent, such as steam, nitrogen (N2) gas, carbon dioxide (CO2) gas, methane, helium, or argon, or any combinations thereof. The inlet plenum is at a longitudinal end portion of the ODH two-pass multi-tubular reactor.

[0088] At block 404, the method includes flowing the reaction mixture through the first pass of the tube side of the ODH two-pass multi-tubular reactor to an intermediate plenum of the reactor. The ODH reaction occurs in the tubes of the first pass. The intermediate plenum is at an opposite longitudinal end of the reactor relative to the inlet plenum.

[0089] At block 406, the method includes adding (introducing) additional oxygen gas into the reaction mixture in the intermediate plenum. This oxygen injected from external of the reactor directly into the intermediate plenum may be labeled as additional oxygen in that this oxygen is in addition to the oxygen in the feed that flowed through the first pass to the intermediate plenum. Much of the oxygen that flowed in the reaction mixture through the first pass may be consumed (converted) in the ODH reaction in the first pass.

[0090] At block 408, the method includes mixing the additional oxygen with the reaction mixture via a mixer in the intermediate plenum. As discussed, the mixer may be static internals. The mixer may be a static mixer(s), packing, etc. The mixer may promote mixing of the added oxygen with the reaction mixture from the first pass. The mixer may also be configured as a flame arrester. The mixing via the mixer may reduce local spots (volume regions) of high concentration of O2 in the intermediate plenum and thus reduce, limit, or eliminate any tendency of autoignition in the intermediate plenum. The flame arresting properties could also prevent autoignition or stop an autoignition flame. If desired, liquid water from external of the ODH two-pass multi-tubular reactor may be injected directly into the intermediate plenum to evaporate in the intermediate plenum to cool the reaction mixture and additional oxygen in the intermediate plenum.

[0091] At block 410, the method includes flowing the reaction mixture having the additional oxygen from the intermediate plenum through the second pass of the tube side to an outlet plenum of the ODH two-pass multi-tubular reactor. The flow direction through the second pass is opposite of flow direction through the first pass. The outlet plenum is at the same longitudinal end of the reactor as the inlet plenum.

[0092] At block 412, the method includes dehydrogenating ethane to ethylene in the reaction mixture in the first pass and in the second pass via ODH catalyst on the tube side. The ODH reaction occurs in the tubes of the first pass and in the tubes of the second pass. The ODH reaction is promoted via the ODH catalyst on the tube side. A primary reaction may be C2H6 + 0.5 O2 — > C2H4 + H2O, which is the conversion of ethane / oxygen to ethylene / water with the ethylene as a desired product. The coproduct acetic acid may also be produced in the ODH reaction via the reaction C2H6 + 1.5 O2 - CH3COOH + H2O. Carbon monoxide and carbon dioxide may also be generated (typically undesired) by the following reaction equations C2H6 + 2.5 O2 — > 2 CO + 3 H2O, and C2H6 + 3.5 O2 — > 2 CO2 + 3 H2O.

[0093] At block 414, the method includes flowing a coolant through the shell side, and maintaining the coolant at a specified temperature and / or the reaction mixture in the tubes on the tube side (in both passes) at a specified temperature. The method may include maintaining temperature of at least one of the coolant, the reaction mixture, or the ODH catalyst at a specified temperature via flowing the coolant through the shell side. The specified temperature may be, for example, in the ranges of 300°C to 550°C, 300°C to 500°C, 350°C to 500°C, 350°C to 450°C, 325°C to 425°C, 300°C to 475°C, 300°C to 450°C, 300°C to 425°C, 300°C to 400°C, 275°C to 425°C, or 250°C to 400°C, and the like. The coolant flows around and adjacent the tubes to receive heat from the reaction mixture in the tubes through the tube wall of the tubes.

[0094] The coolant may be, for example, molten salt, or oil or other high- temperature heat transfer fluid. The molten salt can include, for example, potassium nitrate, sodium nitrate, potassium nitrite, and / or sodium nitrite. Examples include ASD molten salt available from Durferrit GmbH having headquarters in Mannheim, Germany, and HITEC® heat transfer medium available from Coastal Chemical Co., LLC having headquarters in Houston, Texas, USA, and the like. The HITEC heat transfer medium is a mixture of inorganic salts of potassium nitrate, sodium nitrite, and sodium nitrate. The oil or other high-temperature transfer fluid if utilized as coolant, for example, may be SYLTHERM® 800 (stabilized heat transfer fluid) or DOWTHERM® A (organic heat transfer fluid) available from The Dow Chemical Company, officially Dow Inc., having headquarters in Midland, Michigan, USA, or THERMINOL® VP-1 [mixture of diphenyl oxide (DPO) and biphenyl] or THERMINOL 75 (synthetic heat transfer fluid) available from Eastman Chemical Company having headquarters in Kingsport, Tennessee, USA, or SANTOLUBES® OS-750 or SANTOLUBES OS- 124 available from SANTOLUBES LLC having headquarters in Spartanburg, South Carolina, USA.

[0095] At block 416, the method includes discharging the reaction mixture from the outlet plenum as an effluent of the ODH two-pass multi-tubular reactor. The method may include flowing the effluent through a heat exchanger to heat boiler feedwater with the effluent to generate steam. The method may include flowing the effluent through a heat exchanger that is a cross-exchanger to heat the feed with the effluent.

[0096] The method may include flowing the effluent from the heat exchanger that heats boiler feedwater to the cross-exchanger (as a second heat exchanger) that heats the feed with the effluent. As discussed, the effluent from the ODH two-pass multi-tubular fixed-bed reactor may include at least ethylene, acetic acid, carbon monoxide, carbon dioxide, water, and unreacted ethane. The effluent may be processed to isolate product ethylene and byproduct (coproduct) acetic acid for distribution from the ODH plant to users.

[0097] An embodiment is a multi-tubular fixed-bed reactor comprising: a tube side having catalyst to facilitate reaction of a reactant into a product; an inlet plenum to receive feed comprising the reactant; a first pass of the tube side to receive the feed from the inlet plenum as a reaction mixture flowing through the first pass; an intermediate plenum to receive the reaction mixture from the first pass and receive an additional component introduced at the intermediate plenum, wherein the intermediate plenum is at an opposite longitudinal end of the multi-tubular fixed-bed reactor relative to the inlet plenum; a mixer in the intermediate plenum to mix the component with the reaction mixture; a second pass of the tube side to receive the reaction mixture from the intermediate plenum, wherein flow direction through the second pass is opposite of flow direction through the first pass; an outlet plenum to receive the reaction mixture from the second pass and discharge the reaction mixture as effluent from the multi-tubular fixed-be reactor, wherein the outlet plenum is at a same longitudinal end of the multi-tubular fixed-bed reactor as the inlet plenum; and a shell side to receive a heat transfer fluid to maintain the reaction mixture on the tube side at a specified temperature, or maintain the heat transfer fluid at a specified temperature to give a desire temperature of the reaction mixture. Features may be wherein the mixer comprises a static mixer or packing, or both, that act as a flame arrester, wherein the mixer comprises the static mixer comprising a metal static mixer, and / or wherein the mixer comprises the packing comprising inert packing.

[0098] An embodiment is method of operating an ODH reactor system, including providing feed including ethane and oxygen through an inlet plenum of an ODH reactor to give a reaction mixture flowing through a first pass of a tube side of the ODH reactor to an intermediate plenum of the ODH reactor, wherein the intermediate plenum is at an opposite longitudinal end of the ODH reactor relative to the inlet plenum, and wherein the ODH reactor is a multi-tubular reactor having the tube side and a shell side. In implementations, the feed includes diluent including steam, nitrogen (N2) gas, carbon dioxide (CO2) gas, methane, helium, or argon, or any combinations thereof. The method includes introducing additional oxygen into the reaction mixture in the intermediate plenum, mixing the additional oxygen with the reaction mixture via a mixer in the intermediate plenum, flowing the reaction mixture having the additional oxygen from the intermediate plenum through a second pass of the tube side to an outlet plenum of the ODH reactor, wherein flow direction through the second pass is opposite of flow direction through the first pass, and wherein the outlet plenum is at the same longitudinal end of the ODH reactor as the inlet plenum. The mixer may include static internals that promote the mixing, and the mixer may be configured as a flame arrestor. The mixer may include a static mixer or packing, or both. The mixer may act as a flame arrestor. The method may include injecting water from external of the ODH reactor into the intermediate plenum.

[0099] The method includes dehydrogenating ethane to ethylene in the reaction mixture in the first pass and in the second pass via ODH catalyst on the tube side, flowing a coolant (e.g., molten salt) through the shell side (thereby removing heat from the reaction mixture and the ODH catalyst), and discharging the reaction mixture from the outlet plenum as an effluent of the ODH reactor. The method may include maintaining temperature of at least one of the coolant, the reaction mixture, or the ODH catalyst at a specified temperature (e.g., in a range of 350°C to 500°C) via flowing the coolant through the shell. The method may include flowing the effluent through a heat exchanger to heat boiler feedwater with the effluent to generate steam. The method may include flowing the effluent through a heat exchanger that is a cross-exchanger to heat the feed with the effluent. The method may include flowing the effluent through a first heat exchanger to heat boiler feedwater with the effluent to generate steam, and flowing the effluent from the first heat exchanger through a second heat exchanger that is a cross-exchanger to heat the feed with the effluent.

[0100] Another embodiment is an ODH reactor system having an ODH reactor that is a multi-tubular fixed-bed reactor including a tube side having ODH catalyst to dehydrogenate ethane into ethylene, an inlet plenum to receive feed including ethane and oxygen to introduce the feed to a first pass of the tube side, the first pass of the tube side to receive the feed from the inlet plenum to give a reaction mixture on the first pass of the tube side. In implementations, the feed includes diluent including steam, nitrogen (N2) gas, carbon dioxide (CO2) gas, methane, helium, or argon, or any combinations thereof. The ODH reactor has an intermediate plenum to receive the reaction mixture from the first pass and receive additional oxygen introduced into the intermediate plenum from external of the ODH reactor, wherein the intermediate plenum is at an opposite longitudinal end of the ODH reactor relative to the inlet plenum. The ODH reactor includes a mixer in the intermediate plenum to mix the additional oxygen with the reaction mixture, wherein the mixer includes a static mixer or packing, or both. In implementations, the mixer is configured to act as a flame arrester.

[0101] The ODH reactor includes second pass of the tube side to receive the reaction mixture with the additional oxygen from the intermediate plenum, wherein flow direction through the second pass is opposite of flow direction through the first pass. The ODH reactor includes an outlet plenum to receive the reaction mixture from the second pass and discharge the reaction mixture as a product mixture that is effluent from the ODH reactor, wherein the outlet plenum is at the same longitudinal end of the ODH reactor as the inlet plenum. The ODH reactor includes a shell side to receive coolant (e.g., molten salt) to remove heat from the reaction mixture and the ODH catalyst. In implementations, the ODH catalyst includes low- temperature ODH catalyst configured for dehydrogenation of ethane into ethylene at a temperature in a range of 250°C to 550°C. The ODH reactor system may include a heat exchanger to receive the effluent to heat boiler feedwater with the effluent to generate steam. The ODH reactor system may include a heat exchanger that is a cross-exchanger to receive the effluent to heat the feed. The ODH reactor system may include a first heat exchanger to receive the effluent to heat boiler feedwater with the effluent to generate steam, and a second heat exchanger that is a cross-exchanger to receive the effluent from the first heat exchanger to heat the feed.

[0102] EXAMPLES

[0103] Example 1

[0104] A simulation was generated using gPROMS software (version 2.2.0.55228). FIG. 5 illustrates reactor 500 that was modeled by the simulation. The kinetic model equation for the simulated reactor 500 was developed from catalyst experimentation on the following catalyst active phase formulation: 45 weight percent of active phase Mo1.0V0.37Te0.23Nb0.14O4.97 (from ICP-MS analysis) mixed with a balance (55 weight percent) of Versal 250 alumina. To simulate the reactor coolant, properties of oil coolant taken from past experiments were used. The feed (stream 1) included ethane, carbon dioxide, and oxygen. The feed (stream 1) was flowed through the first catalyst bed (section 1). The stream then exited the first catalyst bed (section 1) and entered a static mixer. Interstage oxygen (stream 2) was flowed to the static mixer. The stream (previously stream 1) mixed with the interstage oxygen (stream 2) in the static mixer. The mixture flowed from the static mixer through the second catalyst bed (section 2). The product (stream 3) exited the second catalyst bed (section 2). The oil coolant surrounds each catalyst bed (sections 1 and 2) to provide cooling. Table 1 provides operating conditions of the reactor 500. Table 2 provides a mass balance of the simulation for the reactor 500. The reactor 500 in Example 1 is shown to output 0.47 mol.% of oxygen in the product (stream 3). In other implementations, the oxygen content of the product (stream 3) can be lower (for example, less than 0.1 mol.%) by adjusting parameters (such as operating conditions) and / or specifications of the reactor (such as including additional reactor tubes).

[0105] Table 1 : Reactor Operating Conditions

[0106] Table 2: Mass Balance

[0107] Example 2

[0108] A comparative case study was performed to compare various reactor setups. FIG. 6A illustrates reactor 600A, which was the same as the reactor 500 for Example 1 (shown in FIG. 5). FIG. 6B illustrates reactor 600B which includes two catalyst beds in series. FIG. 60 illustrates reactor 6000 which includes two catalyst beds in parallel. FIGS. 6A, 6B, and 6C also illustrate cross-sections of reactors 600A, 600B, and 6000, respectively. For each of the reactors 600A, 600B, and 600C, the total volume of the combined catalyst beds (sections 1 and 2) was the same (3,687 cubic centimeters (cm3)), meaning the three comparative reactor configurations (600A, 600B, 600C) would exhibit the same catalyst performance (indexed by ethane conversion and selectivity toward carbon-based products) at the same reactor operating conditions (reactor temperature, inlet pressure, and gas hourly space velocity (GHSV)). The following parameters were applied:

[0109] • The catalyst bed length for reactor 600A was 549 centimeters (cm), and the catalyst bed lengths for reactors 600B and 6000 were adjusted to achieve the same total volume of catalyst bed (3,687 cm3).

[0110] • For all reactors 600A, 600B, and 600C, the inside diameter of each reactor tube was 2.43 cm.

[0111] • For all reactors 600A, 600B, and 600C, the thickness of each reactor tube was 0.21 cm.

[0112] • For all reactors 600A, 600B, and 6000, the distance between the outside wall of each reactor tube to the inside wall for the coolant jacket was 0.5 cm. • For reactor 600A, the distance between the outside wall of the reactor tube of section 1 to the outside wall of the reactor tube of section 2 was 0.5 cm.

[0113] • The outside diameter of the oxygen injector for reactor 600C was 0.6 cm.

[0114] • The thickness of the oxygen injector for reactor 600C was 0.21 cm.

[0115] • For all reactors 600A, 600B, and 600C, two tube sheets were provided for each jacketed reactor.

[0116] • For all reactors 600A, 600B, and 600C, the thickness of each tube sheet was 5.08 cm.

[0117] • For all reactors 600A, 600B, and 600C, the diameter of each tube sheet was identical to the outside diameter of the corresponding coolant jacket.

[0118] • For all reactors 600A, 600B, and 600C, stainless steel class 316 alloy with a density of 8.07 grams per centimeter cubed (g / cm3) was used for the material of construction.

[0119] • Stainless steel class 316 alloy with a density of 4.84 g / cm3was used for the material of construction for the mixers of reactors 600A and 600B and for the oxygen injector of reactor 600C.

[0120] For reactor 600B, the feed flowed through the first catalyst bed (section 1). The first catalyst bed (section 1) was surrounded by a first coolant jacket. The stream then exited the first catalyst bed (section 1) and entered a mixer. Interstage oxygen was flowed to the mixer. The stream (previously stream 1) mixed with the interstage oxygen in the mixer. The mixture flowed from the mixer through the second catalyst bed (section 2). The second catalyst bed (section 2) was surrounded by a second coolant jacket. The product exited the second catalyst bed (section 2).

[0121] For reactor 600C, the feed was distributed to the first catalyst bed (section 1) and to the second catalyst bed (section 2). The first catalyst bed (section 1) and the second catalyst bed (section 2) was surrounded by a coolant jacket. Oxygen was flowed to an oxygen injector disposed between the catalyst beds (sections 1 and 2). The oxygen flowed from the oxygen injector and into the catalyst beds (sections 1 and 2). The oxygen mixed with the feed in the catalyst beds (sections 1 and 2). Product streams exited the catalyst beds (sections 1 and 2). As shown in the cross-section C-C of FIG. 6C, the reactor 600C had the form of several concentric cylinders, with the innermost cylinder being the oxygen injector, the intermediate cylinder housing the catalyst beds, and the outermost cylinder being the coolant jacket.

[0122] Table 3 provides the mass of metal used in the reactors 600A, 600B, and 600C. The relative increase in mass of reactors 600B and 600C in comparison to reactor 600A is also shown in Table 3. The data provided in Table 3 shows that reactor 600A uses the least amount of metal, which directly results in a reduction in capital costs in comparison to the configurations for reactors 600B and 600C. As shown in Table 3, reactor 600B uses 36% more metal in comparison to reactor 600A. For reactor 600A, the static mixer can be replaced with an inert packed bed, which could still provide adequate mixing functionality and further reduce the cost of the setup of reactor 600A. The reactors 600A, 600B, and 600C for Example 2 include single reactor tubes with cooling jackets. If scaled for commercial use, each coolant jacket could encompass multiple reactor tubes (for example, up to 50,000 reactor tubes). In such scaled-up cases, the difference in comparative capital costs between the reactor setups for 600A, 600B, and 600C would also scale proportionally.

[0123] Table 3: Mass of Metal used in Reactor Setups

[0124] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure.

[0125] INDUSTRIAL APPLICABILITY

[0126] Systems and methods for oxidative dehydrogenation of alkanes, such as the oxidative dehydrogenation of ethane to ethylene.

Claims

CLAIMS1. A method of operating an oxidative dehydrogenation (ODH) reactor system, the method comprising: providing feed comprising ethane and oxygen through an inlet plenum of an ODH reactor to give a reaction mixture flowing through a first pass of a tube side of the ODH reactor to an intermediate plenum of the ODH reactor, wherein the intermediate plenum is at an opposite longitudinal end of the ODH reactor relative to the inlet plenum, and wherein the ODH reactor is a multi-tubular reactor having the tube side and a shell side; introducing additional oxygen into the reaction mixture in the intermediate plenum; mixing the additional oxygen with the reaction mixture via a mixer in the intermediate plenum; flowing the reaction mixture having the additional oxygen from the intermediate plenum through a second pass of the tube side to an outlet plenum of the ODH reactor, wherein flow direction through the second pass is opposite of flow direction through the first pass, and wherein the outlet plenum is at same longitudinal end of the ODH reactor as the inlet plenum; dehydrogenating ethane to ethylene in the reaction mixture in the first pass and in the second pass via ODH catalyst on the tube side; flowing a coolant through the shell side, thereby removing heat from the reaction mixture and the ODH catalyst; and discharging the reaction mixture from the outlet plenum as an effluent of the ODH reactor.

2. The method of claim 1 , wherein the mixer comprises static internals that promote the mixing.

3. The method of claim 2, wherein mixer is configured as a flame arrestor.

4. The method of claim 1 , wherein the mixer comprises a static mixer or packing, or both, and wherein the mixer acts as a flame arrestor.

5. The method of claim 1 , maintaining temperature of at least one of the coolant, the reaction mixture, or the ODH catalyst at a specified temperature via flowing the coolant through the shell.

6. The method of claim 5, wherein the specified temperature is in a range of350°C to 500°C.

7. The method of claim 1, wherein the coolant comprises molten salt.

8. The method of claim 1, wherein the feed comprises diluent comprising steam, nitrogen (N2) gas, carbon dioxide (CO2) gas, methane, helium, or argon, or any combinations thereof.

9. The method of claim 1, comprising injecting water from external of the ODH reactor into the intermediate plenum.

10. The method of claim 1, comprising flowing the effluent through a heat exchanger to heat boiler feedwater with the effluent to generate steam.

11. The method of claim 10, comprising flowing the effluent from the heat exchanger through a second heat exchanger that is a cross-exchanger to heat the feed with the effluent.

12. The method of claim 1, comprising flowing the effluent through a heat exchanger that is a cross-exchanger to heat the feed with the effluent.

13. An oxidative dehydrogenation (ODH) reactor system, comprising: an ODH reactor that is a multi-tubular fixed-bed reactor comprising: a tube side comprising ODH catalyst to dehydrogenate ethane into ethylene; an inlet plenum to receive feed comprising ethane and oxygen to introduce the feed to a first pass of the tube side; the first pass of the tube side to receive the feed from the inlet plenum to give a reaction mixture on the first pass of the tube side; an intermediate plenum to receive the reaction mixture from the first pass and receive additional oxygen introduced into the intermediate plenum from external of the ODH reactor, wherein the intermediate plenum is at an opposite longitudinal end of the ODH reactor relative to the inlet plenum; a mixer in the intermediate plenum to mix the additional oxygen with the reaction mixture, wherein the mixer comprises a static mixer or packing, or both; a second pass of the tube side to receive the reaction mixture with the additional oxygen from the intermediate plenum, wherein flow direction through the second pass is opposite of flow direction through the first pass; an outlet plenum to receive the reaction mixture from the second pass and discharge the reaction mixture as a product mixture that is effluent fromthe ODH reactor, wherein the outlet plenum is at same longitudinal end of the ODH reactor as the inlet plenum; and a shell side to receive coolant to remove heat from the reaction mixture and the ODH catalyst.

14. The system of claim 13, wherein the ODH catalyst comprises low- temperature ODH catalyst configured for dehydrogenation of ethane into ethylene at a temperature in a range of 250°C to 550°C.

15. The system of claim 13, wherein the coolant comprises molten salt.

16. The system of claim 13, wherein the feed comprises diluent comprising steam, nitrogen (N2) gas, carbon dioxide (CO2) gas, methane, helium, or argon, or any combinations thereof.

17. The system of claim 13, comprising a heat exchanger to receive the effluent to heat boiler feedwater with the effluent to generate steam.

18. The system of claim 17, comprising a second heat exchanger that is a cross- exchanger to receive the effluent from the heat exchanger to heat the feed.

19. The system of claim 13, comprising a heat exchanger that is a crossexchanger to receive the effluent to heat the feed.

20. The system of claim 13, wherein the mixer acts as a flame arrester.

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