System and method for maintaining the activity of an ethylbenzene dehydrogenation catalyst

Abstract

A method and system for dehydrogenating ethylbenzene can include mixing a steam stream and an ethylbenzene stream to form a feed mixture. The ethylbenzene / steam feed mixture can then be fed into a dehydrogenation reactor containing an alkali metal promoted catalyst. A liquid selected from an alkali metal liquid, an alkali metal compound liquid, or a liquid solution containing an alkali metal can be injected into a feed stream (such as the steam stream, the ethylbenzene stream, or the ethylbenzene / steam feed mixture). After injection, the liquid vaporizes and disperses into the feed stream upstream of the dehydrogenation reactor. The liquid can remain liquid from a point upstream of the injection to the injection nozzle. The liquid is dispersed in liquid form through the injection nozzle to form liquid droplets dispersed in the feed stream, which evaporate and / or dissolve into the vapor feed stream.

Description

Technical Field

[0001] The embodiments disclosed herein generally relate to the dehydrogenation of alkyl aromatics to form vinyl aromatics, such as the dehydrogenation of ethylbenzene to form styrene. More specifically, the embodiments herein relate to methods and systems for maintaining the activity of a catalyst within a dehydrogenation reactor. Background Art

[0002] During the preparation of styrene by dehydrogenating ethylbenzene, an iron oxide catalyst deactivates. One of the main reasons for catalyst deactivation is the migration of the potassium promoter in the catalyst. It has been proposed to inject a small amount of a potassium solution together with a mixed ethylbenzene / water (steam) feed to prevent potassium migration and keep the catalyst in an active form for a longer time. Steam, methane, and inert gases have been proposed as carriers for transporting the solution into the EB feed. However, the heating and vaporization of a solution of potassium hydroxide or a potassium salt can cause salt precipitation and clog the delivery pipeline.

[0003] US6936743 teaches that the lifespan of a potassium- or chromium-stabilized dehydrogenation catalyst can be extended by injecting 0.1 to 10 ppm of a "catalyst life extender". The life extender mentioned is potassium acetate.

[0004] US5739071 teaches that the lifespan of an iron-based / alkali metal-stabilized catalyst can be extended by continuously injecting an alkali metal or an alkali metal compound (such as injecting about 0.01 to 100 ppm of an alkali metal or an alkali metal compound). The compounds mentioned include potassium hydroxide, potassium carbonate, and potassium oxide. Metals including potassium or sodium metals are also mentioned. The '071 patent teaches that inert nitrogen can be used to carry the vaporized alkali metal or alkali metal compound into the reactor feed stream.

[0005] US8648007 teaches that the injection of potassium salts must be carried out carefully, otherwise the potassium salts will deposit in the injection device. In the example, in order to inject a 10% potassium acetate solution, the temperature of the vaporization device needs to be between 200°C and 480°C.

[0006] US20060224029 discloses that Cs compounds can be used to extend the lifespan of an Fe-based dehydrogenation catalyst.

[0007] The heating and vaporization of a solution of potassium hydroxide or a potassium salt can cause salt precipitation and clog the delivery pipeline. As a solution to this problem, working solutions have been proposed in the patents mentioned above (such as the '007 patent). However, due to their very high melting points, potassium salts are difficult to volatilize. For example, KOH melts at 360°C, K2CO3 melts at 891°C, potassium acetate melts at 292°C, and K2SO4 melts at 1069°C. Therefore, if there is some operational failure or a compound other than potassium acetate is used, the system in the '007 patent may still be prone to clogging. Summary of the Invention

[0008] Methods and systems for injecting potassium (as a pure metal or dissolved hydroxide or dissolved salt) have now been developed to avoid plugging in the injection system. Compared with existing systems, the embodiments herein can directly inject molten potassium metal or a solution of potassium salt or potassium hydroxide into the EB feed, main steam line, or main EB / steam feed that is about to enter the reactor. The injection nozzle can be designed to limit heat transfer to the potassium or potassium solution such that the potassium or potassium solution does not boil until it passes through the nozzle and enters the heat stream of the steam, EB, or EB / steam. After injection, the potassium or potassium compound can evaporate and thoroughly mix with the feed stream in the process pipeline before they reach the catalyst bed, so that the potassium is fully dispersed throughout the catalyst bed. While previous practices focused on vaporizing the material before injecting it into the reactor feed, the embodiments herein take a different approach and intentionally do not vaporize the potassium, potassium compound, or potassium solution before injection.

[0009] In one aspect, embodiments disclosed herein relate to a method for dehydrogenating ethylbenzene. The method can include mixing a steam stream and an ethylbenzene stream to form an ethylbenzene / steam feed mixture. Then, the ethylbenzene / steam feed mixture can be fed into a dehydrogenation reactor containing an alkali metal-promoted catalyst to convert a portion of the ethylbenzene into styrene. A liquid selected from an alkali metal liquid, an alkali metal compound liquid, or a liquid solution containing an alkali metal can be injected into a feed stream including at least one of a steam stream, an ethylbenzene stream, or an ethylbenzene / steam feed mixture. After injection, the liquid vaporizes and disperses into the feed stream upstream of the dehydrogenation reactor. The liquid (alkali metal, alkali metal compound liquid, or liquid solution containing an alkali metal) can remain in a liquid state from a point upstream of the injection to the injection nozzle. The liquid is dispersed in a liquid form through the injection nozzle to form liquid droplets dispersed in the feed stream, after which the liquid evaporates and / or dissolves into the vaporous feed stream.

[0010] In another aspect, embodiments disclosed herein relate to a system for maintaining the activity of a catalyst in an ethylbenzene dehydrogenation reactor. The system can include a liquid alkali feed stream, which is heated or insulated as needed to keep a liquid alkali feed selected from at least one of an alkali metal, an alkali metal compound liquid, and a liquid solution containing an alkali metal in a liquid state. The system can also include an injection nozzle for injecting the liquid alkali feed as a liquid into a process feed stream selected from a steam stream, an ethylbenzene feed stream, and an ethylbenzene / steam feed stream to form an alkali-containing feed. The system further includes a dehydrogenation reactor containing an alkali metal-promoted catalyst and having an inlet for receiving the alkali-containing feed or a mixture containing the alkali-containing feed.

[0011] To keep the liquid feed in a liquid state, the caustic feed stream can be steam traced, insulated, or coolant traced upstream of the injection nozzle. The steam tracing, insulation, etc. can continue until reaching the injection nozzle, or as close as possible to the injection nozzle.

[0012] In some embodiments, the system can also include a water feed stream fluidly connected to the injection nozzle. In some embodiments, a control system can be provided to alternately feed the liquid caustic feed and the water feed stream to the injection nozzle.

[0013] In another aspect, the embodiments disclosed herein relate to a method for maintaining catalytic activity in a reactor. The method can include injecting a liquid containing a catalyst regeneration compound into a vapor feed stream containing an inert substance and / or a reactant upstream of the inlet of the reactor. The liquid can be vaporized and dispersed into the vapor feed stream within a flow conduit upstream of the reactor to form a vapor mixture containing the catalyst regeneration compound and at least one of the inert substance or the reactant. The catalyst contained within the reactor can be contacted with the vapor catalyst regeneration compound to enhance the activity of the catalyst within the reactor while the catalyst in the reactor simultaneously undergoes its intended reaction.

[0014] Other aspects and advantages will become apparent from the following description and the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a simplified process flow diagram of a system for dehydrogenating ethylbenzene to form styrene according to an embodiment herein.

[0016] Figure 2 is a simplified process flow diagram of a system for injecting a compound into a dehydrogenation process according to an embodiment herein.

[0017] Figure 3 presents illustrative results of simulations of injecting a compound into a flowing stream of a dehydrogenation process according to an embodiment herein. DETAILED DESCRIPTION

[0018] The embodiments disclosed herein generally relate to the dehydrogenation of alkyl aromatics (such as alkylbenzenes) to form vinyl aromatics, such as for the dehydrogenation of ethylbenzene to produce styrene. More specifically, the embodiments herein relate to methods and systems for maintaining the activity of a catalyst within a dehydrogenation reactor. Even more specifically, the embodiments herein relate to injecting a catalyst regeneration compound into a reaction system. For example, the embodiments herein can relate to injecting potassium or a potassium compound to maintain the activity of the catalyst within the dehydrogenation reactor.

[0019] The embodiments herein are described in connection with the dehydrogenation of ethylbenzene to form styrene. However, those skilled in the art can readily understand that the methods disclosed herein can be applied to the dehydrogenation of other alkyl aromatic hydrocarbons to form vinyl aromatic hydrocarbons (such as the dehydrogenation of cumene to form α-methylstyrene, the dehydrogenation of ethyltoluene to form vinyltoluene) and methods for many other vinyl aromatic compounds. Methods for the dehydrogenation of butane to form butadiene, as well as other conversion processes, such as the dealkylation of alkyl aromatic hydrocarbons, the synthesis of ammonia, the synthesis of maleic anhydride, and other conversion processes can also benefit from the embodiments herein.

[0020] Referring now to Figure 1 , a simplified flow diagram showing a typical configuration of a dehydrogenation reaction zone for a styrene plant is shown. Styrene monomer is produced by dehydrogenating an ethylbenzene (EB) feed, which is an endothermic reaction. A vaporized azeotropic mixture of ethylbenzene and water is fed via flow line 24 to the reaction zone, which may include two to four dehydrogenation reactors 26, 28. The effluent from each reactor 26 can be reheated using steam before entering the next reactor 26 or the final reactor 28. The steam used to reheat the reactor effluent is typically referred to as main steam (MS), which is provided by steam superheater 30 via flow line 32 and coils 38 and ultimately enters the inlet 34 of the first reactor 26 together with the vaporized EB / water mixture. The vaporized EB / water mixture can also be preheated in exchanger 36 by the effluent from the final reactor 28. Figure 1 is an exemplary dehydrogenation system, and other methods and systems for dehydrogenating ethylbenzene can also benefit from the embodiments herein.

[0021] As mentioned above, the catalysts contained in reactors 26, 28 may lose activity due to the migration of catalytic or cocatalytic components. It is desirable to inject compounds to help maintain or preserve the activity of the catalysts, thereby extending the catalyst life and the total operating time of the reaction system before necessary shutdowns and catalyst replacements. For example, a potassium-stabilized dehydrogenation catalyst can benefit from the introduction of potassium or potassium compounds into the reactor. The embodiments herein can provide potassium in a useful form such that there is little or no accumulation of potassium or potassium salts in the injection system or associated piping.

[0022] Accordingly, the methods and systems disclosed herein can be used to directly inject molten potassium metal or a solution of potassium salt or potassium hydroxide into the vaporized reactor feed stream via one or more injection systems 50. For example, the liquid metal or solution can be introduced via one or more injection systems 50 into the ethylbenzene (EB) feed 24 / 25, main steam line 40, or main EB / steam feed 42 that is about to enter reactor 26. In some embodiments, for example, molten, liquid potassium can be injected into the EB / steam stream.

[0023] Potassium metal melts at approximately 63.5 °C. Vapor-heated vessels can be used to store potassium metal, and vapor-heated or insulated pipes can keep the metal in liquid form and allow it to flow into a processing unit. For example, liquid potassium can be metered directly into the pipe containing the EB / vapor feed entering the dehydrogenation reactor, such as stream 42 as shown in Figure 1 Potassium boils at approximately 759 °C. Typically, the feed entering the dehydrogenation reactor is at a temperature in the range of 500 °C to about 650 °C. The process temperature of the EB / vapor is hot enough to keep potassium molten but not hot enough to make potassium boil.

[0024] Through a nozzle, potassium metal can be injected or atomized into, for example, an EB / vapor feed mixture using nitrogen or other suitable inert gas. Since potassium metal does not boil or vaporize in the pipe leading to the nozzle, no scale deposits that could clog the pipeline are left. The expected feed rate of potassium into the system can be, for example, 50 to 1000 g / h, depending on the reactor size and catalyst content, and thus the feed rate can be controlled with common components.

[0025] In other embodiments, a solution of potassium salt or potassium hydroxide can be injected into the EB / vapor stream upstream of reactor 26. The potassium salt dissolved in water would start to boil or may mostly vaporize in the pipe leading to the injection nozzle, resulting in deposits of potassium salt or potassium hydroxide precipitating inside the pipe and thus clogging the system. The boiling point of a 50 wt% aqueous solution of KOH is about 145 °C, which is much colder than the temperature of 500 °C to 650 °C of the feed entering the reactor. However, according to the embodiments herein, the potassium solution is injected into the reactor feed via an insulated pipe, thus keeping the potassium solution at a low enough temperature such that the solution does not boil and the nozzle does not scale.

[0026] Figure 2 A simplified flow diagram of a system 50 for injecting a potassium solution without boiling the solution is shown in. The main EB / vapor feed 8 travels through pipe 7 towards the reactor inlet 6. The potassium solution 1 is fed through an injection nozzle assembly, which can include a feed pipe 4, a nozzle 5, and a housing 2, as well as insulation 3. The insulation 3 surrounds the feed pipe 4 and keeps the temperature of the potassium solution inside the feed pipe 4 below its boiling point until it reaches the nozzle 5, where the liquid solution is atomized into the EB / vapor feed 8. Since the potassium solution is kept as a liquid inside the pipe 4 until it reaches the nozzle 5, nozzle scaling can be minimized or eliminated.

[0027] The type of insulation and the thickness of the insulation layer required to prevent the potassium solution from boiling will depend on the potassium salt or compound used, as well as the expected flow rate of the solution as it travels through the pipe to the injection nozzle. Solutions with higher boiling points and higher solution flow rates will require less insulation. The flow rate of the solution can be used to target the injection of potassium into the reactor feed at a concentration between 0.01 and 10 ppm by weight. In some embodiments, the solution feed line can be insulated. In other embodiments, for example, the solution feed line can be cooled via heat exchange with water or other cool or cold heat exchange media (such as via heat exchange tracing), where the heat exchange tracing can include a ring pipe or coiled pipe wrapped around the solution feed pipe. The ring pipe or coiled pipe can surround the solution feed line at least near the EB, steam, or EB / steam injection location (such as within at least a few feet) to resist any heat exchange with significantly hotter EB, steam, or EB / steam pipes and feeds.

[0028] As described above, as Figure 2 The system as shown in can be used to inject the potassium solution into the feed stream continuously or intermittently. A pipe 4 including a jacket 2 can also be used, where a heat exchange medium 3 circulates within the pipe to keep the potassium solution liquid until it reaches the injection nozzle 5. Based on the above discussion, those skilled in the art can also envision the jacket 2 being used to provide a heating medium 3, such as steam tracing, in the annular region to keep the potassium metal molten until it reaches the injection nozzle 5. Intermittent injection can include continuous water flushing to keep the solution or fluid moving through the pipe 4.

[0029] For both molten potassium injection and potassium solution injection, it is also important to ensure that the solution or potassium vaporizes and mixes with the reactor feed. Therefore, the injection angle of the nozzle can be configured to provide good distribution, as well as to atomize the injected metal or solution with an appropriate particle size to occur mixing and vaporization without accumulating on the walls of the EB / steam feed pipe.

[0030] In some embodiments, a single central injection nozzle 5 can be provided at the center of the EB / steam feed pipe. In other embodiments, multiple injection nozzles can be located circumferentially around the pipe, thus injecting towards the center of the feed line; this can be a good way to distribute potassium in the case where the diameter of the feed pipe is very large (several inches). However, in both embodiments, the injection nozzle should be oriented such that the salt solution or molten metal is as far away from the wall of the pipe as possible to minimize deposits and corrosion.

[0031] In some embodiments, it has been found advantageous to use rather dilute potassium salts or potassium hydroxide solutions. For example, solutions of 0.02 to 0.5 wt% can be used. Although it may seem counterintuitive since the boiling point of the solution may be lower than that of a concentrated solution, it has been found that having a lower solution viscosity will assist in spraying the solution into smaller droplets and make it more easily dispersible / vaporizable. Having a low solution concentration also means that pure water or substantially pure water can be continuously fed through the syringe to keep it clear and clean. In some embodiments, the potassium salt or potassium hydroxide can also be introduced intermittently to maintain catalyst activity. If the solution is rather dilute, this will hardly affect the process conditions. Additionally, a dilute solution may require a higher flow rate to introduce the same amount of potassium, and thus the insulation requirements for keeping the potassium solution below its boiling point can be reduced.

[0032] As described above, the embodiments herein relate to a method for dehydrogenating an alkylbenzene (such as ethylbenzene) while maintaining catalyst activity. The method can include mixing a steam stream and an ethylbenzene stream to form an alkylbenzene / steam feed mixture. The alkylbenzene / steam feed mixture can then be fed to a dehydrogenation reactor containing an alkali metal-promoted catalyst to dehydrogenate a portion of the alkylbenzene, such as dehydrogenating ethylbenzene to form styrene.

[0033] To maintain the activity of the alkali metal-promoted catalyst, the method according to the embodiments herein includes injecting a liquid selected from an alkali metal liquid, an alkali metal compound liquid, or a liquid solution containing an alkali metal into a feed stream including at least one of a steam stream, an alkylbenzene feed stream, or an alkylbenzene / steam feed mixture. The liquid is injected as a liquid into the feed stream, and the liquid vaporizes and disperses into the feed stream upstream of the dehydrogenation reactor.

[0034] In some embodiments, the alkali metal-promoted catalyst includes a potassium-promoted catalyst. In some embodiments, the alkali metal-promoted catalyst can include an iron-based dehydrogenation catalyst. Examples of a large number of suitable iron-based catalysts are described in US5739071, such as various catalysts including, for example, Fe2O3 promoted with potassium. Other catalyst systems can also benefit from the injection method disclosed herein, such as injecting vanadium or a vanadium compound into, for example, a maleic anhydride reactor.

[0035] In some embodiments, the alkali metal is injected as a liquid solution. The liquid solution can be, for example, an extremely dilute solution of an alkali metal compound or an alkali metal salt in water. For example, the liquid solution containing an alkali metal can be an aqueous solution containing 0.01 to 1.0 wt%, such as 0.02 to 0.5 wt% of the alkali metal in water.

[0036] The injection system of the present disclosure can be configured to maintain a liquid (i.e., an alkali metal, an alkali metal compound liquid, or a liquid solution containing an alkali metal) in a liquid state from a point upstream of the injection to the injection nozzle. The injection system can then be used to disperse the liquid through the injection nozzle and form liquid droplets dispersed in a feed stream, at which point the injected liquid can dissolve or evaporate into the vapor feed stream.

[0037] In various embodiments, the injection nozzle can be configured to disperse droplets of the liquid, where the droplets can have an initial particle size of 100 microns or less, 75 microns or less, or 50 microns or less. As can be appreciated, the particle size of the droplets can decrease when the liquid disperses and dissolves into the vapor or otherwise evaporates. Thus, the "initial" particle size refers to the size of the droplet particles as they are ejected from the injection nozzle.

[0038] In some embodiments, the injection nozzle can be centrally disposed within the feed stream (e.g., near the longitudinal axis of the feed stream conduit). In other embodiments, the liquid can be dispersed through two or more injection nozzles circumferentially positioned around the feed stream, where the nozzles are configured to co-flow with the feed (e.g., EB, steam, or EB / steam) and inject toward the center of the feed stream. Co-flow injection allows the liquid to be pulled downstream and fed into the reactor with a significantly larger steam / hydrocarbon mixture. Additionally, co-flow injection can be configured to avoid injecting the liquid directly onto the conduit wall, thereby minimizing the accumulation of liquid droplets on the transfer conduit.

[0039] In some embodiments, the maintenance or restoration of catalyst activity may require continuous injection of an alkali metal or an alkali metal compound. In other embodiments, the maintenance or restoration of catalyst activity may only require intermittent injection of an alkali metal or an alkali metal compound. In some embodiments, for example, the method of the present disclosure can include alternately injecting a liquid and a pure water stream through the injection nozzle. In other words, the method can include intermittently stopping the injection of the liquid and instead injecting pure water through the injection nozzle. The injection of water can be carried out in a similar manner, where the water is maintained in a liquid state until it reaches the injection nozzle that distributes the water. The intermittent presence of the pure water liquid stream can help keep the conduit wall and the injection nozzle clean, thereby removing any accumulation of alkali metal or alkali metal compound that may occur due to normal operation or malfunction.

[0040] In some embodiments, the method of injecting a liquid can include atomizing the liquid with an inert gas. For example, nitrogen, carbon dioxide, steam, argon, or other gases considered inert to the reaction system of interest can be used. The inert gas can be admixed with the liquid upstream of or within the dispensing nozzle, thereby enhancing the dispersion of the liquid into the vapor / hydrocarbon transfer conduit with the desired initial particle size.

[0041] After the droplets are dispersed into the vapor or vapor / hydrocarbon feed stream, the droplets can evaporate and disperse as vapor into the feed stream. Complete vaporization of the liquid upstream of the reactor inlet is desirable in order to distribute the alkali metal or alkali metal compound throughout the catalyst bed and to avoid the liquid settling only on the catalyst particles near the inlet. In some embodiments, for example, it has been found that the evaporation of the liquid can be completed within a distance of about 5 meters, 10 meters, or 15 meters, depending on atomization and initial particle size, stream temperature, initial liquid droplet size, and other factors readily recognizable by those skilled in the art. Thus, in various embodiments, the injection nozzle assembly and associated components can be located at an appropriate distance upstream of the reactor inlet, such as at least 5 meters upstream of the reactor inlet, at least 10 meters upstream of the reactor inlet, or at least 15 meters upstream of the reactor inlet. In some embodiments, the injection nozzle is located in the main ethylbenzene / vapor feed stream at a distance of about 5 to 10 meters upstream of the dehydrogenation reactor inlet.

[0042] In other embodiments, such as where the liquid can be injected into, for example, the main steam line 40, it is preferred that the liquid be vaporized and well-dispersed into the stream before any mixing, bending, or other section of the piping system. Introducing the liquid at too short a distance before such sections of the piping system can result in direct impingement of the atomized liquid, leading to undesirable accumulation, restricted flow, and / or blockage of the piping components. Thus, in various embodiments, the injection nozzle assembly and associated components can be located in a straight pipe section at an appropriate distance upstream of a bend, tee, or other piping component, such as at least 5 meters upstream of the piping component, at least 10 meters upstream of the piping component, or at least 15 meters upstream of the piping component.

[0043] Embodiments herein also relate to a system for maintaining the activity of a catalyst in a reactor. The system can include a liquid feed stream, such as a liquid alkali feed stream. The liquid alkali feed stream can be configured to maintain a liquid alkali feed selected from at least one of an alkali metal, a liquid alkali metal compound, and a liquid solution containing an alkali metal in a liquid state. The system can also include an injection nozzle for injecting the liquid alkali feed as a liquid into a process feed stream selected from a vapor stream, an alkylaromatic (ethylbenzene) feed stream, and an alkylaromatic (ethylbenzene) / vapor feed stream to form an alkali-containing feed upstream of the reactor. The system herein can also include a dehydrogenation reactor that contains an alkali metal-promoted catalyst and has an inlet for receiving the alkali-containing feed or a mixture containing the alkali-containing feed.

[0044] Systems according to embodiments herein can include an alkali feed stream that is steam traced, insulated, or coolant traced to maintain the alkali feed as a liquid upstream of the injection nozzle. In some embodiments, the injection nozzle can be disposed near the axial center of the process feed stream. In other embodiments, more than two injection nozzles can be circumferentially disposed around the process feed stream.

[0045] The systems herein can also include a water feed stream fluidly connected to the injection nozzle. A control system and associated valves can also be used to intermittently inject the liquid water feed stream in place of the alkali feed stream. For example, the control system can be configured to alternately feed the liquid alkali feed and the water feed stream to the injection nozzle.

[0046] Examples

[0047] The injection of an aqueous potassium hydroxide solution (1996 ppm KOH aqueous solution by weight) was simulated. The solution was simulated to be injected into the pipe carrying the main steam feed to the reactor, where the solution was injected with a droplet size of 75 microns. At a simulated main steam line temperature of 860 °C, it was determined that the droplets would evaporate during a travel of about 21.9 feet through the pipe. The simulated droplet sizes are as Figure 2 shown, where the particle trails are colored by particle residence time.

[0048] As described above, embodiments herein can provide for the maintenance of catalyst activity by injecting a liquid reagent into a vapor feed stream. Embodiments herein advantageously deliver the liquid reagent as a liquid to the vapor feed stream, thereby minimizing the accumulation of salts or metals within and around the injection system and associated piping.

[0049] Although ethylbenzene dehydrogenation has been described above, the injection systems disclosed herein can be used in other applications that require injecting small amounts of non-volatile components into a gas phase. For example, the systems herein can be used to inject small amounts of vanadium into the feed of a maleic anhydride reactor.

[0050] Although the present disclosure includes a limited number of embodiments, those skilled in the art who benefit from the present disclosure will understand that other embodiments can be designed without departing from the scope of the present disclosure. Therefore, the scope should be limited only by the appended claims.

Claims

1. A method for dehydrogenating ethylbenzene, the method comprising: Mixing a steam stream and an ethylbenzene stream to form an ethylbenzene / steam feed mixture; Feeding the ethylbenzene / steam feed mixture into a dehydrogenation reactor containing an alkali metal-promoted catalyst to convert a portion of the ethylbenzene to styrene; Injecting a liquid selected from an alkali metal liquid, an alkali metal compound liquid, or a liquid solution containing an alkali metal into a feed stream comprising at least one of the steam stream, the ethylbenzene stream, or the ethylbenzene / steam feed mixture, wherein the liquid vaporizes upstream of the dehydrogenation reactor and disperses into the feed stream; Maintaining the liquid in a liquid state from a point upstream of the injection to the injection nozzle; and Alternately injecting the liquid and pure water stream through the injection nozzle.

2. The method according to claim 1, wherein the alkali metal-promoted catalyst comprises a potassium-promoted catalyst.

3. The method according to claim 1, wherein the liquid solution containing an alkali metal comprises 0.02 to 0.5 wt% alkali metal in water.

4. The method according to claim 1, wherein injecting the liquid selected from the alkali metal liquid, the alkali metal compound liquid, or the liquid solution containing the alkali metal into the feed stream comprising at least one of the steam stream, the ethylbenzene stream, or the ethylbenzene / steam feed mixture comprises: Dispersing the liquid through the injection nozzle to form liquid droplets dispersed in the feed stream; And Evaporating the liquid into the feed stream.

5. The method according to claim 4, wherein the dispersed droplets have an initial particle size of less than 75 microns.

6. The method according to claim 4, wherein the injection nozzle is centrally disposed within the feed stream.

7. The method according to claim 4, comprising dispersing the liquid through two or more injection nozzles circumferentially positioned around the feed stream and configured to flow in parallel with the steam stream, the ethylbenzene stream, or the ethylbenzene / steam feed mixture and inject toward the center of the feed stream.

8. The method according to claim 4, wherein injecting the liquid selected from the alkali metal liquid, the alkali metal compound liquid, or the liquid solution containing the alkali metal into the feed stream comprising at least one of the steam stream, the ethylbenzene stream, or the ethylbenzene / steam feed mixture comprises atomizing the liquid with an inert gas.

9. The method according to claim 4, wherein evaporating the liquid into the feed stream comprises evaporating the dispersed droplets into the feed stream within a distance of 10 meters.

10. A system for maintaining the activity of a catalyst in an ethylbenzene dehydrogenation reactor, the system comprising: A liquid alkali feed configured to maintain a liquid alkali feed selected from at least one of an alkali metal, an alkali metal compound liquid, and a liquid solution containing an alkali metal in a liquid state; An injection nozzle for injecting the liquid alkali feed as a liquid into a process feed stream selected from a steam stream, an ethylbenzene feed stream, and an ethylbenzene / steam feed stream to form an alkali-containing feed; A water feed stream fluidly connected to the injection nozzle; A control system configured to alternately feed the liquid caustic feed and the water feed stream to the injection nozzle; and A dehydrogenation reactor containing an alkali metal promoted catalyst and having an inlet for receiving the alkali-containing feed or a mixture comprising the alkali-containing feed.

11. The system according to claim 10, wherein the liquid caustic feed is steam-traced, insulated, or coolant-traced to maintain the liquid caustic feed as a liquid upstream of the injection nozzle.

12. The system according to claim 10, wherein the injection nozzle is disposed near the axial center of the process feed stream.

13. The system according to claim 10, comprising more than two injection nozzles circumferentially disposed around the process feed stream.

14. The system according to claim 10, wherein the injection nozzle is configured to disperse the liquid caustic feed in the form of droplets having an initial particle size of less than 75 microns.

15. The system according to claim 10, further comprising an inert gas feed stream fluidly connected to the injection nozzle.

16. The system according to claim 10, wherein the injection nozzle is located in the main ethylbenzene / steam feed stream at a distance of 5 to 10 meters upstream of the dehydrogenation reactor.

17. The system according to claim 10, wherein the injection nozzle is configured to maintain the injection of liquid droplets within the central portion of the process feed stream.

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