Vacuum generation with low pressure steam from oxidative dehydrogenation

Abstract

Methods and a reactor system for producing acetic acid in a selective oxidation (SO) reactor are provided. An example method includes providing a fresh feed stream to the SO reactor, wherein the fresh feed stream includes a light hydrocarbon feed stream, a carbon dioxide feed stream, and a steam feed stream. 5 Acetic acid is formed in the SO reactor. An acetic acid product stream is separated from a reactor effluent stream in a scrubber. A recycle gas stream is obtained from the scrubber. At least a portion of the recycle gas stream is combined into the fresh feed stream to the SO reactor.

Description

[0001] VACUUM GENERATION WITH LOW PRESSURE STEAM FROM OXIDATIVE DEHYDROGENATION

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to oxidative dehydrogenation and, more particularly, to vacuum generation using low-pressure steam from oxidative dehydrogenation.

[0004] BACKGROUND ART

[0005] Olefins like ethylene, propylene, and butylene, are basic building blocks for a variety of commercially valuable polymers. Since naturally occurring sources of olefins do not exist in commercial quantities, polymer producers rely on methods for converting the more abundant lower alkanes into olefins. The method of choice for today’s commercial scale producers is steam cracking, a highly endothermic process where steam-diluted alkanes are subjected very briefly to a temperature of at least 800°C. The fuel demand to produce the required temperatures and the need for equipment that can withstand that temperature add significantly to the overall cost. Also, the high temperature promotes the formation of coke which accumulates within the system, resulting in the need for costly periodic reactor shut-down for maintenance and coke removal.

[0006] Selective oxidation processes, such as oxidative dehydrogenation (ODH), are an alternative to steam cracking that are exothermic and produce little or no coke. In ODH, a lower alkane, such as ethane, is mixed with oxygen in the presence of a catalyst and optionally an inert diluent, such as carbon dioxide (CO2) or nitrogen (N2) or steam. The process can be performed at temperatures as low as 300°C, to produce the corresponding alkene.

[0007] SUMMARY OF INVENTION

[0008] An embodiment described herein provides a method of processing, where the method includes: separating oxygen (O2) from air in a pressure swing adsorption (PSA) process; feeding the O2 and ethane to an oxidative dehydrogenation (ODH) reactor comprising an ODH catalyst; dehydrogenating the ethane to ethylene in the ODH reactor using the 02, generating a heat; recovering the heat generated in the ODH reactor using a heat-transfer fluid, generating a hot heat-transfer fluid; generating high-pressure (HP) steam from the hot heat-transfer fluid, generating a cooled heat-transfer fluid; running a steam turbine using the HP steam, generating low-pressure (LP) steam; and generating vacuum using the LP steam.

[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] Figure 1 is a simplified block diagram of oxidative dehydrogenation (ODH) coupled with an air separation and vacuum generation.

[0012] Figure 2 is a block diagram of a ODH reactor system.

[0013] Figure 3 is a simplified process flow diagram of a process for vacuum generation using low-pressure steam from an ODH process.

[0014] Figure 4 is a process flow chart of simplified vacuum generation for ASPEN Plus® simulation.

[0015] DESCRIPTION OF EMBODIMENTS

[0016] Catalytic oxidative dehydrogenation (ODH) of alkanes into corresponding alkenes is an alternative to steam cracking. In contrast to steam cracking, ODH may operate at lower temperature, for example below 450°C, and generally does not produce coke. For ethylene production, ODH may provide selectivity of over 85% and a greater yield for ethylene than steam cracking. ODH may be performed in a reactor vessel having a catalyst for the conversion of an alkane to a corresponding alkene. Acetic acid may be generated in the conversion of the lower alkanes (e.g., ethane) into the corresponding alkenes (e.g., ethylene).

[0017] For the low temperature ODH reaction, the oxidant can be provided as air or oxygen. To enable the use of oxygen (O2), the ODH process may require an air separation unit installed at the front end of the process. Pressure swing adsorption (PSA) is a method of separating gases based on varying degrees of adsorption over adsorbent materials such as zeolites and activated carbon. In a PSA process, pressure conditions are altered between an adsorption regime and desorption regime for the target gas. O2 can be purified from air using various PSA techniques including vacuum swing adsorption (VSA) and vacuum PSA (VPSA) with using zeolitic molecular serves as the adsorbents. The use of vacuum or reduced pressure conditions in air separation for the purpose of an ODH process may require installing a dedicated vacuum pump and may result in the increased process cost. Embodiments described herein provide integrated methods and systems of vacuum generation using low-pressure (LT) steam (e.g., 450 kPa or less) from an ODH process. The exothermic nature of ODH allows the recovery of generated heat from the ODH process. The recovered heat can be used to generate a steam. The steam is introduced to a vacuum vessel, and when it is cooled it condenses to water, generating a vacuum in the vacuum vessel.

[0018] In various embodiments, air separation to provide O2 for the ODH process uses the vacuum generated by the methods. Further, in some embodiments, the methods use LT steam. While high-pressure (HT) steam can be used for running a steam turbine, for example, the resulting LT steam is considered a low grade with little to no value except heating streams in the process. The vacuum generation described herein can provide an alternative or additional usage of the LT steam from the ODH process and thus help improving the process efficiency and reducing cost.

[0019] In the following, the methods and systems of vacuum generation coupled with ODH are described referring to Figures 1 and 2. Figure 3 is an example process flow diagrams for the method of vacuum generation. An example heat and mass balance simulated using ASPEN Plus® is then described referring to Figure 4 and Table 1.

[0020] Figure 1 is a simplified block diagram of oxidative dehydrogenation (ODH) coupled with air separation and vacuum generation. In various embodiments, an ODH process 100 integrates three process stages: air separation 102, ODH reaction 104, and vacuum generation 106. In this example, air 108 is provided to the air separation 102 (e.g., a VPSA process) to separate an O2 gas 110. The O2 gas can be then used for the ODH reaction 104. In this disclosure, the O2 gas is a gas composition containing 95% O2 or greater. Accordingly, the O2 can contain some other gas components.

[0021] The ODH reaction 104 is a catalytic process that can be used to convert one or more alkanes into corresponding alkenes using the O2 gas 110. A feed gas 112 containing an alkane is provided for the ODH reaction 104. In various embodiments, the feed gas 112 contains an alkane having a number of carbons in the range of 2 to 6, for example, ethane. Because the reaction is exothermic, the heat can be recovered to generate steam from water. In some embodiments, the steam is low-pressure (LT) steam 114, e.g., about 450 kPa or less, which can be then sent to the vacuum generation 106. In other embodiments, the ODH reaction 104 can generate first high-pressure (HT) steam, e.g., about 4 MPa (about 580 psi) or greater, and the HT steam is used by a process, e.g., running a steam turbine, that results in the LT steam.

[0022] Vacuum 116 generated using the steam 114 can be used to assist the overall ODH process. Particularly, in various embodiments, the vacuum 116 can be used to perform the air separation 102. Further details of each stage of the air separation 102, the ODH reaction 104, and the vacuum generation 106 will be described below referring to Figure 2. Air Separation

[0023] Figure 2 is a block diagram of an ODH reactor system 200. It can be understood that each of the illustrated units and components may include one or more vessels and supporting equipment, such as valves, pumps, sensors, and associated control equipment, such as distributed control systems, and the like.

[0024] As described above, the first stage of the ODH process can be air separation to produce O2 that can be used for the ODH reaction. As illustrated in Figure 2, the air 108 can be first sent to a filter 202 to prevent any liquid or solid particulars from entering the next unit. The air 108 is then compressed using an air compressor 204. In some embodiments, the air 108 is an atmospheric air and contains about 78.1 % nitrogen (N2), about 21.0% O2, and other components, e.g., argon and CO2.

[0025] The air 108 can be sent to an air separation unit 206 to produce the O2 gas 110. A pressure swing adsorption (PSA) process can be used for the air separation. In various embodiments, the air 108 is introduced into a bed of a solid adsorbent that adsorbs N2 selectively to O2. While N2 is captured by the solid adsorbent, O2 can pass through the bed as the O2 gas 110. In Figure 2, in accordance with an embodiment, the air separation unit 206 is illustrated as a two-column PSA system having a first column 208 and a second column 210. Generally, more than one adsorbent column can be used in the PSA process to enable a continuous process with minimal downtime, where one column is used for adsorption while another is regenerated by desorption.

[0026] In Figure 2, the first column 208 is being used for adsorption and the second column 210 is being regenerated. When the first column 208 is saturated with the adsorbed N2 and needs regeneration, the flow of the air 108 can be switched from the first column 208 to the second column 210 such that the adsorption can continue using the second column 210 while the first column 208 can be regenerated. Regeneration can be performed by flowing a purge gas, reducing the pressure of the column, or both. Dotted lines entering the second column 210 and exiting the first column 208 indicate these gas flow patterns temporary separated from the gas flow patterns shown by solid lines. In some embodiments, although not specifically illustrated in Figure 2, the air separation unit 206 can have only one column or more than two columns.

[0027] For a typical PSA system that requires vacuum, a vacuum blower may be used to reduce the desorption pressure in the columns. It also reduces the required inlet pressure to the columns. In various embodiments, the vacuum 116 needed for the air separation is generated using low-pressure (LT) steam 114 from the ODH process. In various embodiments, any PSA process that separates O2 from air can be used including vacuum swing adsorption (VSA) and vacuum PSA (VPSA). In various embodiments, the PSA process is performed under near-ambient temperatures, e.g., between about 10°C and about 40°C. In another embodiment, the PSA process may be performed under cryogenic conditions.

[0028] In various embodiments, the columns (e.g., the first column 208 and the second column 210) are charged with an adsorbent for N2 adsorption from the air 108. Various molecular sieve materials can be used for the adsorbent. Examples of the N2 adsorbent include low silica X (LSX), zeolite 5A, ion-exchanged LSX (Li- LSX, AgLi-LSX, Ca-LSX), Engelhard titanosilicate (Na-ETS-10, Ag-ETS-10), and SSZ-13.

[0029] In some embodiments, the O2 gas 110 generated by the air separation has at least 95% O2 purity and less than 0.15% N2 and the remainder can be argon. The O2 gas 110 can be sent to an oxygen storage 212 for storage. Oxidative Dehydrogenation (ODH)

[0030] In various embodiments, as illustrated in Figure 2, the O2 gas 110 stored in the oxygen storage 212 can be sent to an oxygen compressor 214 and then a mixer 216, where it is mixed with the feed gas 112 (e.g., ethane) and optionally a diluent gas 218 to form a mixed feed gas 220. The diluent gas 218 can include, for example, CO2, N2, or steam. The diluent gas 218 may be added to lower the flammability of the gas mixture during the ODH reaction. In addition, the diluent gas 218 can also provide a quenching effect to absorb heat generated by the exothermic ODH reaction. In some embodiments, the mixing in the mixer 216 can be performed using a non-flammable liquid, such as water, and bubbling each gas component in the liquid.

[0031] The mixed feed gas 220 can be sent to a ODH reactor 222. In the illustrated embodiment, the ODH reactor 222 is a tubular reactor with an attached cooling jacket 224. The ODH reactor 222 can be a fixed bed reactor or a fluidized bed reactor. The ODH reaction takes place in the presence of oxygen provided from the O2 gas 110. Although Figure 2 illustrates a single feed line to provide the mixed feed gas 220 to the ODH reactor 222, there can be a combination of feed lines.

[0032] The ODH reactor 222 contains a catalyst (e.g., a fixed bed of catalyst) for the conversion of the alkane (e.g., ethane) to the corresponding alkene (ethylene). The ODH catalyst can be a metal oxide catalyst. In some embodiments, the ODH catalyst include an oxide containing molybdenum (Mo), vanadium (V), tellurium (Te), niobium (Nb), or mixture thereof. In some embodiments, the catalyst contains Mo, V, Te, and Nb, and with Mo:V molar ratio from 1:0.12 to 1 :0.49, Mo:Te molar ratio from 1 :0.01 to 1 :0.30, Mo:Nb molar ratio 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 oxides. The molar ratios of Mo, V, Te, Nb can be determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0033] The catalyst provides for the ODH reaction to at a temperature of less than 400°C. An example catalyst is a mixed metal oxide having the formula MoaVbTecNbdPdeOf, where a, b, c, d, e, and f subscripts are relative atomic amounts of the elements Mo, V, Te, Nb, Pd, O, respectively. When a=1 , then b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0, 0.00<e<0.10, and f is a number to satisfy the valence state of the catalyst. Various embodiments of the methods described herein do not necessarily rely on the type of ODH catalyst, and various catalyst formulations and process temperatures, e.g., moderate temperatures of 400°C to 500°C or high temperatures above 500°C.

[0034] The ODH reaction generates a product stream 226 containing the alkene (e.g., ethylene). In the embodiments where ethane is converted to ethylene, acetic acid is also generated and present in the product stream 226. Other components of the product stream 226 can include CO2, carbon monoxide (CO), oxygenates, and water.

[0035] The product stream 226 can then sent to a quenching tower QT 228 for quenching and removal of the acetic acid and other oxygenates from the product stream 226 as an effluent 230 using a water stream 232. A first refined product stream 234, as a gas stream, can exit the quenching tower 228. The first refined product stream 234 can contain the target alkene product, unconverted alkanes, unreacted oxygen, CO2, CO, and the diluent.

[0036] The first refined product stream 234 can further be processed by an absorber tower AR 236 to remove CO2 to form a second refined product stream 240. In various embodiments, the absorber tower 236 is an amine wash system, where the first refined product stream 234 is contacted with a lean amine, such as diethanolamine, monoethanolamine, or methyldiethanolamine, among others. The majority of CO2 present in first refined product stream 234 can be captured by reaction with the lean amine. A caustic tower may be located downstream for further polishing and removal of trace amounts of CO2 that may have past the absorber tower 236. The second refined product stream 240 can be sent for further purification and processing, for example, a product compressor 242 and then cryogenic separation to further purify the ethylene.

[0037] The process and system illustrated in Figure 2 are for example only, and other reactor configurations and different process flows are possible. Depending on the installation environment, not all of the units shown may be present. Further, additional units may be present, for example, additional reactors and compressors. In some embodiments, although not specifically illustrated, the ODH reaction 104 is performed using two or more ODH reactors, for example, using those positioned in series. In such embodiments, subsequent ODH reactors can receive a product stream from a previous reactor to further react the unreacted alkanes. The process parameters can also be selected and controlled for each reactor. In one embodiment, the reaction temperature can be increased stepwise for the subsequent ODH reactors in series.

[0038] Heat Transfer and High-Pressure (HP) Steam Generation

[0039] The heat generated by the oxidative dehydrogenation (ODH) reaction can be recovered to generate a steam that could be used to power equipment or for other applications. In Figure 2, a heat-transfer fluid 244 is provided from a fluid storage 246 into the cooling jacket 224. In various embodiments, the heat-transfer fluid 244 can be treated water (e.g., demineralized water, boiler feedwater, etc.), glycol (e.g., ethylene glycol, propylene glycol, etc.), molten salt, or other type of heat-transfer fluid. In various embodiments, molten salt is used for the heat-transfer fluid 244. For example, nitrate salts such as potassium nitrate, sodium nitrate, calcium nitrate, and chloride-based salts such as lithium chloride-potassium chloride mixture and sodium chloride-potassium chloride mixture can be used. With their superior heat capacity, molten salts can effectively remove the heat from the exothermic ODH reaction and help managing reaction runaway.

[0040] Non-molten salt examples of the heat-transfer fluid 244 include DOWTHERM® heat-transfer fluids (Dow Chemical Company, Midland, Mich. USA), which may have glycol or synthetic organic compounds generally. Other examples include DW-Therm HT products (Huber USA, Gary, N.C. USA), SYLTHERM® silicon fluids (e.g., SYLTHERM 800) (Dow Chemical Company, Midland, Mich. USA), and SantoLubes® products (e.g., OS-750 or OS-124) (SantoLubes LLC, Spartanburg, S.C. USA).

[0041] The heat-transfer fluid 244 absorbs the heat generated by the ODH reaction and cools the ODH reactor 222, resulting in a heated heat-transfer fluid 248. The heated heat-transfer fluid 248 can be first sent to a flow bypass conduit 250 to separate the heated heat-transfer fluid 248 into fractions. In some embodiments, a first fluid fraction 252 can be sent to a first heat exchanger 254 and a second fluid fraction 256 can be sent to a second heat exchanger 258. For example, the second fluid fraction 256 can account for about 20-80 wt% the total flow of the heated heattransfer fluid 248.

[0042] For steam generation, water 260 is provided to the first heat exchanger 254 and heated with the first fluid fraction 252, and heated water 262 is sent to a flash vessel 264, where the heated water 262 flashed into a steam 266. A cooled first fluid fraction 268 can be sent back to the fluid storage 246.

[0043] In various embodiments, the steam 266 is a saturated steam. The steam 266 can be further heated by passing through the second heat exchanger 258 using the second fluid fraction 256 and can form high-pressure (HP) steam 270. A cooled second fluid fraction 272 can be sent back to the fluid storage 246 for reuse. Accordingly, the ODH reactor system 200 can include a circulation system to circulate the heat-transfer fluid 244 among the fluid storage 246, the cooling jacket 224, and the heat exchangers (e.g., the first heat exchanger 254 and the second heat exchanger 258). In some embodiments, a T-junction 274 can be used to merge the cooled first fluid fraction 268 and the cooled second fluid fraction 272 before sending the merged fluid back to the fluid storage 246.

[0044] The HP steam 270 can have a pressure of about 4 MPa (about 580.2 psi) or greater. In some embodiments, the HP steam 270 is a very high-pressure (VHP) steam having a pressure of about 9 MPa (about 1305.3 psi) or greater. The HP steam 270 can have a temperature between 300°C and 450°C.

[0045] The temperatures and pressures of the steam 266 and the HP steam 270 depend on the configuration of the ODH reactor system 200, e.g., the number of reactors and process temperatures. Further, the process of heat recovery for steam generation can vary, for example, by varying the partition ratio of the first fluid fraction 252 and the second fluid fraction 256, and design and operation of the flash vessel 264.

[0046] The HP steam 270 generated at this stage can be used as a part of the ODH process or other applications in a plant. For example, it can be used to power turbines attached to compressors (e.g., the product compressor 242 in Figure 2). Low-Pressure (LP) Steam Generation

[0047] In various embodiments, the HP steam 270 is used first for an application other than vacuum generation. For example, in Figure 2, the HP steam 270 can be used to run a steam turbine 276 connected to the product compressor 242. After running the steam turbine 276, the HP steam 270 can be converted to a low- pressure (LP) steam 114. In various embodiments, the LP steam 114 has a pressure of about 450 kPa (about 65.3 psi) or less. In some embodiments, the pressure can be between about 100 kPa (about 14.5 psi) and 300 kPa (about 43.5 psi). In one embodiment, the pressure is about 344.7 kPa (about 50 psi). The LP steam 114 can have a temperature between 100°C and 150°C. In some embodiments, the LP steam 114 is a saturated steam. Generally, the quality of such a steam is so low that their applications are limited (e.g., heating purposes). In various embodiments, on the other hand, the LP steam 114 can be used for vacuum generation as a part of the ODH process as described below.

[0048] Vacuum Generation and Application

[0049] In Figure 2, the LP steam 114 is sent to a vacuum vessel 278. In various embodiments, the temperature of the vacuum vessel 178 is maintained at a temperature of about 25°C or lower. The LP steam 114 condenses in the vacuum vessel 278, generating vacuum 116 and a condensate 280. The condensate 280 can be discharged from the vacuum vessel 278 via a discharge port. In some embodiments, the pressure of the LP steam 114 can be reduced prior to entering the vacuum vessel 278, for example, using a regulator 282. The pressure of the LP steam 114, in one embodiment, can be reduced from about 344.7 kPa (about 50 psi) to about 100 kPa (about 14.5 psi).

[0050] In various embodiments, the vacuum 116 generated is used as a part of the ODH process. In the illustrated embodiment in Figure 2, it is used for the desorption step for the air separation. Accordingly, the vacuum vessel 278 can be connected to outlets of the first column 208 and the second column 210 with appropriate valves and gas regulators. As previously described, the two-column PSA system can enable continuous air separation by allowing adsorption using one column while regenerating the other column. The vacuum 116 can be applied to reduce the pressure of the column to be regenerated (e.g., the second column 210 in Figure 2) by operating the valves. In Figure 2, the first column 208 is being used for adsorption and thus the valve between the first column 208 and the vacuum vessel 278 is closed. Due to the reduced pressure, the adsorbed species (e.g., N2) in the second column 210 desorbs and be removed from the second column 210 along with residual gases in the second column. These gases (e.g., N2, CO2, and moisture) flow into the vacuum vessel 278 and can later be vented to atmosphere. In some embodiments, the flow can be directed vented to atmosphere without entering the vacuum vessel 278. While there is only one vessel for vacuum generation is illustrated in Figure 2, in some embodiments, there can be more than one vacuum vessel depending on the size of the columns of the PSA system.

[0051] In some embodiments, the ODH reactor system 200 also includes an alternative vacuum pump 284 that is connected to the outlets of the first column 208 and the second column 210 with appropriate valves and gas regulators. The alternative vacuum pump 284 can be a backup and allow performing the desorption step even when the vacuum vessel 278 is unavailable for vacuum generation, e.g., due to the lack of the LP steam 114.

[0052] Figure 3 is a simplified process flow diagram of a process for vacuum generation using low-pressure steam from an ODH process. In Figure 3, a process 300 starts with separating 302 oxygen (O2) from air in a pressure swing adsorption (PSA) process, followed by feeding 304 O2 and ethane to an oxidative dehydrogenation (ODH) reactor comprising an ODH catalyst. Subsequently, the process 300 proceeds to dehydrogenating 306 the ethane to ethylene in the ODH reactor using O2, which generates a heat. The heat generated in the ODH reactor is recovered 308 using a heat-transfer fluid, generating a hot heat-transfer fluid. Next, high-pressure (HP) steam is generated 310 from the hot heat-transfer fluid, generating a cooled heat-transfer fluid. A steam turbine is then run 312 using the HP steam, generating low-pressure (LP) steam. Vacuum is generated 314 using the LP steam.

[0053] Other than in the operating examples or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, etc. used in the specification and claims are to be understood as modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that can vary depending upon the desired properties, which the present disclosure desires to obtain. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0054] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0055] Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10; that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. Because the disclosed numerical ranges are continuous, they include every value between the minimum and maximum values. Unless expressly indicated otherwise, the various numerical ranges specified in this application are approximations.

[0056] As used herein, the term “alkane” refers to a saturated hydrocarbon. In many cases, an alkane consists of hydrogen and carbon atoms arranged in a linear structure in which all of the carbon-carbon bonds are single bonds. Alkanes have the general chemical formula CnH2n+2. In many embodiments of the disclosure, alkane refers to one or more of methane, ethane, propane, butane, pentane, hexane, octane, decane, and dodecane. In particular embodiments, alkane refers to ethane and propane.

[0057] As used herein, the term “alkene” refers to unsaturated hydrocarbons that contain at least one carbon-carbon double bond. In many embodiments, alkene refers to alpha olefins. In many embodiments of the disclosure, alkene refers to one or more of ethylene, propylene, 1 -butene, pentene, pentadiene, hexene, octene, decene, and dodecene. Further, as used herein, the term includes other compounds with carbon-carbon double bonds, such as butadiene, among others. In particular embodiments, alkene refers to ethylene and propylene and, in some embodiments, ethylene.

[0058] As used herein, the term “fixed bed reactor” refers to one or more reactors, in series or parallel, often including a cylindrical tube filled with catalyst pellets with reactants flowing through the bed and being converted into products. The catalyst in the reactor may have multiple configurations including, but not limited to, one large bed, several horizontal beds, several parallel packed tubes, and multiple beds in their own shells.

[0059] As used herein, the term “fluidized bed reactor” refers to one or more reactors, in series or parallel, often including a fluid (gas or liquid) which is passed through a solid granular catalyst, which can be shaped as tiny spheres, at high enough velocities to suspend the solid and cause it to behave as though it were a fluid.

[0060] EXAMPLES

[0061] ASPEN Plus® simulation was conducted to evaluate the process of vacuum generation. Heat and mass balances of the process were simulated based on the ideal equation of state and the properties of steam were obtained using STEAM NBS. Figure 4 is a process flow chart 400 of simplified vacuum generation for ASPEN Plus® simulation. In Figure 4, a cooling inflow 402 enters a heat exchanger 404 and discharges an outflow 406. The heat exchanger 404 is used to maintain the temperature of a vacuum vessel 408. A first low-pressure (LP) steam 410 (at 584.0 kPa) is processed to reduce its pressure, and a second LP steam 412 (at 100 kPa) is fed to the vacuum vessel 408. In this simulation, a residual gas inflow 414 was assumed to be negligible. Condensation in the vacuum vessel 408 creates a condensate 416 and a resulting vapor 420. The parameters and the simulated heat and mass balances are summarized below in Table 1.

[0062] Table 1 : Heat and Mass Balance Based on Aspen Plus® Simulation

[0063] As the result of the condensation, the second LP steam 412 shrinks in volume about 1 ,938 times, generating a vacuum pressure (the pressure of the resulting vapor 420) of 9.6 kPa (about 1.4 psi or 0.09 atm). The results demonstrate the ability of the LT steam to generating vacuum through condensation with relatively small energy input for cooling.

[0064] Implementations

[0065] An implementation described herein provides a method of oxidative dehydrogenation, where the method includes: separating oxygen (O2) from air in a pressure swing adsorption (PSA) process; feeding the O2 and ethane to an oxidative dehydrogenation (ODH) reactor including an ODH catalyst; dehydrogenating the ethane to ethylene in the ODH reactor using the O2, generating a heat; recovering the heat generated in the ODH reactor using a heattransfer fluid, generating a hot heat-transfer fluid; generating a high-pressure (HP) steam from the hot heat-transfer fluid, generating a cooled heat-transfer fluid; running a steam turbine using the HP steam, generating a low-pressure (LP) steam; and generating vacuum using the LP steam.

[0066] In an aspect, combinable with any other aspect, the PSA process includes: compressing the air; sending the compressed air to a PSA column including a molecular sieve; selectively adsorbing nitrogen (N2) in the air on the molecular sieve, generating the O2; and desorbing the N2 from the molecular sieve using the vacuum generated from the LP steam.

[0067] In an aspect, combinable with any other aspect, generating the vacuum includes: sending the LP steam into a vessel; and condensing the LP steam in the vessel, generating liquid water.

[0068] In an aspect, generating the vacuum further includes discharging the liquid water from the vessel through an outlet.

[0069] In an aspect, generating the vacuum further includes maintaining a temperature of the vessel at 25°C or lower during the condensing.

[0070] In an aspect, combinable with any other aspect, the method further includes reducing the pressure of the LP steam prior to generating the vacuum.

[0071] In an aspect, combinable with any other aspect, the heat-transfer fluid includes a molten salt.

[0072] In an aspect, combinable with any other aspect, recovering the heat includes sending the heat-transfer fluid into a heat-transfer jacket attached to the ODH reactor.

[0073] In an aspect, combinable with any other aspect, the method further includes sending the cooled heat-transfer fluid into a heat-transfer jacket attached to the ODH reactor while recovering the heat.

[0074] In an aspect, combinable with any other aspect, the method further includes powering a compressor using the steam turbine.

[0075] In an aspect, combinable with any other aspect, a pressure of the HP steam is 4 MPa or greater.

[0076] In an aspect, combinable with any other aspect, a pressure of the HP steam is between 4 MPa and 9 MPa.

[0077] In an aspect, combinable with any other aspect, a pressure of the LP steam is 450 kPa or less.

[0078] In an aspect, combinable with any other aspect, a pressure of the LP steam is between 100 kPa (14.5 psi) and 300 kPa (43.5 psi).

[0079] In an aspect, combinable with any other aspect, a temperature of the HP steam is between 300°C and 450°C.

[0080] In an aspect, combinable with any other aspect, a temperature of the LP steam is between 100°C and 150°C. In an aspect, combinable with any other aspect, the LP steam is a saturated steam.

[0081] Another implementation described herein provides a system of air separation, where the system includes: a pressure swing adsorption (PSA) column including a molecular sieve to selectively adsorb nitrogen (N2) from air and release an oxygen (O2); an oxidative dehydrogenation (ODH) reactor including an ODH catalyst reactor to dehydrogenate ethane using the O2; a heat exchanger coupled to the ODH reactor and configured to recover heat from the dehydrogenation by turning a heat-transfer fluid to a hot heat-transfer fluid; a steam generator coupled to the heat exchanger to generate a high-pressure (HP) steam using the hot heattransfer fluid and to discharge a cooled heat-transfer fluid; a steam turbine to receive the HP steam and discharge a low-pressure (LP) steam; and a vacuum generator to generate vacuum using the LP steam, the vacuum generator including a port connected to an outlet of the PSA column.

[0082] In an aspect, combinable with any other aspect, the vacuum generator includes a vessel to receive and condense the LP steam.

[0083] In an aspect, combinable with any other aspect, the system further includes a gas regulator between the steam turbine and the vacuum generator, configured to reduce the pressure of the LP steam.

[0084] In an aspect, combinable with any other aspect, the system further includes a steam drum to generate the HP steam using the hot heat-transfer fluid.

[0085] In an aspect, combinable with any other aspect, the heat exchanger includes a circulation system to receive the cooled heat-transfer fluid from the steam generator for circulation.

[0086] In an aspect, combinable with any other aspect, the reactor includes a fixed- bed reactor.

[0087] Another implementation described herein provides an ethylene production system including: an air separator to separate oxygen (O2) from air; an oxidative dehydrogenation (ODH) reactor including an ODH catalyst to dehydrogenate ethane using the O2 from the air separator to ethylene and discharge a product stream including the ethylene; a heat exchanger to recover heat from the ODH; a steam generator to generate a HP steam using the recovered heat; a heat engine to receive the HP steam and generate a LP steam having a pressure lower than the HP steam; and a vacuum vessel to receive the LP steam and generate vacuum by condensing the LP steam, the vacuum vessel including a vacuum port to apply the vacuum to the air separator.

[0088] In an aspect, combinable with any other aspect, the air separator includes a first and a second pressure swing adsorption (PSA) column, and wherein a gas outlet of each of the PSA columns is connected to the vacuum port.

[0089] In an aspect, combinable with any other aspect, the first and second PSA columns are charged with a molecular sieve to selectively adsorb nitrogen (N2) from air.

[0090] In an aspect, combinable with any other aspect, the vacuum vessel includes a discharge port to discharge a condensate generated from the LP steam.

Claims

CLAIMS1. A method of oxidative dehydrogenation, the method comprising: separating oxygen (O2) from air in a pressure swing adsorption (PSA) process; feeding the O2 and ethane to an oxidative dehydrogenation (ODH) reactor comprising an ODH catalyst; dehydrogenating the ethane to ethylene in the ODH reactor using the O2, generating a heat; recovering the heat generated in the ODH reactor using a heat-transfer fluid, generating a hot heat-transfer fluid; generating a high-pressure (HP) steam from the hot heat-transfer fluid, generating a cooled heat-transfer fluid; running a steam turbine using the HP steam, generating a low-pressure (LP) steam; and generating vacuum using the LP steam.

2. The method of claim 1 , wherein the PSA process comprises: compressing the air; sending the compressed air to a PSA column comprising a molecular sieve; selectively adsorbing nitrogen (N2) in the air on the molecular sieve, generating the O2; and desorbing the N2 from the molecular sieve using the vacuum generated from the LP steam.

3. The method of claim 1 , wherein generating the vacuum comprises: sending the LP steam into a vessel; and condensing the LP steam in the vessel, generating liquid water.

4. The method of claim 3, wherein generating the vacuum further comprises discharging the liquid water from the vessel through an outlet.

5. The method of claim 3, wherein generating the vacuum further comprises maintaining a temperature of the vessel at 25°C or lower during the condensing.

6. The method of claim 1 , further comprising reducing the pressure of the LP steam prior to generating the vacuum.

7. The method of claim 1 , wherein the heat-transfer fluid comprises a molten salt.

8. The method of claim 1, wherein recovering the heat comprises sending the heat-transfer fluid into a heat-transfer jacket attached to the ODH reactor.

9. The method of claim 1, further comprising sending the cooled heat-transfer fluid into a heat-transfer jacket attached to the ODH reactor while recovering the heat.

10. The method of claim 1, further comprising powering a compressor using the steam turbine.

11. The method of claim 1 , wherein a pressure of the HP steam is 4 MPa or greater.

12. The method of claim 1, wherein a pressure of the HP steam is between 4 MPa and 9 MPa.

13. The method of claim 1, wherein a pressure of the LP steam is 450 kPa or less.

14. The method of claim 1, wherein a pressure of the LP steam is between 100 kPa (14.5 psi) and 300 kPa (43.5 psi).

15. The method of claim 1, wherein a temperature of the HP steam is between 300°C and 450°C.

16. The method of claim 1, wherein a temperature of the LP steam is between 100°C and 150°C.

17. The method of claim 1, wherein the LP steam is a saturated steam.

18. A system of air separation, the system comprising: a pressure swing adsorption (PSA) column comprising a molecular sieve to selectively adsorb nitrogen (N2) from air and release an oxygen (O2); an oxidative dehydrogenation (ODH) reactor comprising an ODH catalyst reactor to dehydrogenate ethane using the O2; a heat exchanger coupled to the ODH reactor and configured to recover heat from the dehydrogenation by turning a heat-transfer fluid to a hot heat-transfer fluid; a steam generator coupled to the heat exchanger to generate a high- pressure (HP) steam using the hot heat-transfer fluid and to discharge a cooled heat-transfer fluid; a steam turbine to receive the HP steam and discharge a low-pressure (LP) steam; anda vacuum generator to generate vacuum using the LP steam, the vacuum generator comprising a port connected to an outlet of the PSA column.

19. The system of claim 18, wherein the vacuum generator comprises a vessel to receive and condense the LP steam.

20. The system of claim 18, further comprises a gas regulator between the steam turbine and the vacuum generator, configured to reduce the pressure of the LP steam.

21. The system of claim 18, further comprising a steam drum to generate the HP steam using the hot heat-transfer fluid.

22. The system of claim 18, wherein the heat exchanger comprises a circulation system to receive the cooled heat-transfer fluid from the steam generator for circulation.

23. The system of claim 18, wherein the reactor comprises a fixed-bed reactor.24 An ethylene production system comprising: an air separator to separate oxygen (O2) from air; an oxidative dehydrogenation (ODH) reactor comprising an ODH catalyst to dehydrogenate ethane using the O2 from the air separator to ethylene and discharge a product stream comprising the ethylene; a heat exchanger to recover heat from the ODH; a steam generator to generate a HP steam using the recovered heat; a heat engine to receive the HP steam and generate a LP steam having a pressure lower than the HP steam; and a vacuum vessel to receive the LP steam and generate vacuum by condensing the LP steam, the vacuum vessel comprising a vacuum port to apply the vacuum to the air separator.

25. The ethylene production system of claim 24, wherein the air separator comprises a first and a second pressure swing adsorption (PSA) column, and wherein a gas outlet of each of the PSA columns is connected to the vacuum port.

26. The ethylene production system of claim 25, wherein the first and second PSA columns are charged with a molecular sieve to selectively adsorb nitrogen (N2) from air.

27. The ethylene production system of claim 24, wherein the vacuum vessel comprises a discharge port to discharge a condensate generated from the LP steam.

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