WO2017137866A1 - Methods and systems for generating light olefins using a cyclic reactor configuration - Google Patents

Abstract

Methods and systems for generating light olefins using a cyclic reactor configuration are provided. Methods can include heating a feedstream including hydrocarbons in a first heating unit and introducing the feedstream to a first reactor train including a first catalyst until the first catalyst becomes deactivated. Methods can further include heating a first regeneration stream including a regeneration gas in the first heating unit and introducing the first regeneration stream to the first reactor train until the first catalyst becomes activated. Methods can further include heating the feedstream in a second heating unit and introducing the feedstream to a second reactor train including a second catalyst while introducing the first regeneration stream to the first reactor train.

Description

METHODS AND SYSTEMS FOR GENERATING LIGHT OLEFINS USING A

CYCLIC REACTOR CONFIGURATION CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/294,472, filed February 12, 2016, which is hereby incorporated by reference in its entirety.

FIELD

[0002] The disclosed subject matter relates to methods and systems for generating light olefins using a cyclic reactor configuration where at least one reactor is operating while catalyst in at least one other reactor is being regenerated.

BACKGROUND

[0003] Catalytic cracking can be used to convert various hydrocarbons into more desirable products, such as light products and gasoline. Such hydrocarbons can come from natural gas condensates, petroleum distillates, coal tar distillates and/or peat, and can contain light naphtha, heavy naphtha, straight run naphtha, full range naphtha, delayed coker naphtha, coker fuel oil and/or gas oils, e.g., light coker gas oil and heavy coker gas oil.

[0004] For example, catalytic cracking can be used to produce light olefins, such as ethylene and propylene. However, catalytic cracking can require high temperatures (e.g., above 600°C), which can often lead to catalyst deactivation due to coke formation on the catalyst. Thus, the combination of high temperatures and catalyst deactivation can require a process that continuously regenerates catalysts, such as a fluidized catalytic cracking (FCC) process. However, FCC mandates a balance of heat between the catalyst regeneration and the riser (or reactor) in order to operate effectively. Specifically, the combustion of coke is used to heat the catalytic cracking reaction, and therefore the yield of coke must be large enough to supply the required heat to the riser. [0005] Certain techniques for catalyst regeneration are known in the art. For example, U.S. Patent No. 4, 133,743 discloses a continuous process for converting hydrocarbons, e.g., by catalytic cracking, using a series of moving bed reactors to continuously regenerate catalysts. Similarly, U.S. Patent No. 5,336,829 discloses a process for the continuous dehydrogenation of paraffinic and olefinic hydrocarbons, using two or more moving bed reactors arranged in series. U.S. Patent Publication No. 2006/0213811 discloses a process for the catalytic reforming of naphtha using multiple moving bed reactors arranged in series or parallel. U.S. Patent No. 8,324,441 discloses a process for the cracking of pentane to form light olefins, which uses multiple moving bed reactors to continuously draw deactivated catalyst from the reactors to the regenerators.

[0006] U.S. Patent No. 8,389,789 discloses a process for the catalytic cracking of olefinic hydrocarbons including feeding a hydrocarbon feedstock to multiple fixed bed reactors arranged in parallel. One or more reactors can be taken off-line when the catalyst is deactivated and a regeneration gas can be heated and diverted to the off-line reactors to regenerate the catalysts. U.S. Patent No. 5,417,843 discloses a process for the catalytic reforming of two hydrocarbon streams, which includes feeding the hydrocarbon streams to parallel first stage reforming zones, each including multiple fixed bed reactors arranged in series, and then to parallel second stage reforming zones, each including one or more moving bed reactors. The second stage reforming zones share a common catalyst regenerator.

[0007] U.S. Patent No. 4,406,777 discloses techniques for regenerating catalysts in a multiple reactor system, which can be used for catalytic cracking. The reactors can be fixed bed reactors containing catalysts, and are operated in series. Periodically, the last reactor can be taken off-line for regeneration, and then becomes the first reactor in series, such that the feedstock passes through the reactor with the freshest catalyst first. U.S. Patent No. 8,409,853 discloses a system for the continuous enzymatic treatment of lipid-containing compositions including multiple fixed bed reactors arranged in series. One or more reactors can be taken off-line, e.g., to replenish the enzyme, without interrupting flow.

[0008] However, there remains a need for improved techniques for generating light olefins by the catalytic cracking of hydrocarbons.

SUMMARY OF THE DISCLOSED SUBJECT MATTER

[0009] The disclosed subject matter provides techniques for generating light olefins using a cyclic reactor configuration, where at least one reactor is operating while catalyst in at least one other reactor is being regenerated.

[0010] In certain embodiments, an exemplary method of generating olefins by the catalytic cracking of hydrocarbons using a cyclic reactor configuration can include heating a feedstream including the hydrocarbons in a first heating unit and introducing the feedstream to a first reactor train including a first catalyst until the first catalyst is deactivated. The method can further include heating a first regeneration stream including a regeneration gas in the first heating unit and introducing the first regeneration stream to the first reactor train until the first catalyst is activated. The method can further include heating the feedstream in a second heating unit and introducing the feedstream to a second reactor train including a second catalyst while introducing the first regeneration stream to the first reactor train.

[0011] In certain embodiments, the hydrocarbons can include light naphtha. Alternatively or additionally, the hydrocarbons can include heavy naphtha, kerosene, and/or diesel. The hydrocarbons can have a boiling point of less than about 350°C. Water or a diluent can be combined with the feedstream. The first reactor train and the second reactor train can each include from one to seven fixed bed reactors. The first heating unit and the second heating unit can each include at least one heat exchanger and at least one fired heater. The regeneration gas can include air. In certain embodiments, introducing the feedstream to the first reactor train can generate a first product stream including greater than about 44 wt-% of combined ethylene and propylene. Introducing the feedstream to the second reactor train can generate a second product stream including greater than about 44 wt-% of combined ethylene and propylene. In certain embodiments, the method can further include separating paraffins and C₅ and heavier olefins, if any, from the first product stream and the second product stream and combining the paraffins and C₅ and heavier olefins with the feedstream.

[0012] In certain embodiments, the method can further include introducing the feedstream to the second reactor train until the second catalyst is deactivated. The method can further include heating a second regeneration stream containing a second regeneration gas in the second heating unit and introducing the second regeneration stream to the second reactor train while introducing the feedstream to the first reactor train and until the second catalyst is activated.

[0013] The presently disclosed subject matter also provides systems for generating light olefins by the catalytic cracking of hydrocarbons using a cyclic reactor configuration. In certain embodiments, the system can include a first heating unit, coupled to a first reactor train, and a second heating unit, coupled to a second reactor train. The system can further include a first air line, coupled to the first heating unit, and a second air line, coupled to the second heating unit. The system can further include a feed line, coupled to both of the first heating unit and the second heating unit, for providing a feedstream, and a valve, coupled to the feed line, for directing the feedstream to one of the first heating unit and the second heating unit.

[0014] In certain embodiments, the first reactor train and the second reactor train can each include from one to seven fixed bed reactors. The first heating unit and the second heating unit can each include at least one heat exchanger and at least one fired heater. The system can further include a separation unit, coupled to the first reactor train and the second reactor train, for separating olefins and unconverted hydrocarbons from product lines from each of the reactor trains. The system can further include a recycle line for recycling unconverted hydrocarbons to the feed line.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 depicts a method of generating light olefins using a cyclic reactor configuration according to one exemplary embodiment of the disclosed subject matter.

[0016] FIG. 2 depicts a system for generating light olefins using a cyclic reactor configuration according to one exemplary embodiment of the disclosed subject matter.

[0017] FIG. 3 provides a graphical representation of the catalytic activity of the six catalysts of Example 3 over six hours in a fixed bed reactor.

DETAILED DESCRIPTION

[0018] The presently disclosed subject matter provides techniques for generating light olefins using a cyclic reactor configuration. For example, multiple reactors can be operated cyclically such that at least one reactor is operating while catalyst in at least one other reactor is being regenerated. The cyclic reactor configuration can be used to generate light olefins, e.g., ethylene and propylene, by the catalytic cracking of hydrocarbons.

[0019] Methods for generating light olefins can include alternating a feedstream containing hydrocarbons between two reactor trains containing a catalyst, such that one reactor is operating at all times. The catalyst within the non-operating reactor can be regenerated while the feedstream is provided to the operating reactor. For the purpose of illustration and not limitation, FIG. 1 is a schematic representation of a method according to a non-limiting embodiment of the disclosed subject matter.

[0020] In certain embodiments, the method 100 can include heating a feedstream including hydrocarbons in a first heating unit 101. The feedstream can contain any hydrocarbon feedstock suitable for catalytic cracking. For example, the feedstream can contain light naphtha, heavy naphtha, kerosene, diesel, or a combination thereof. In certain embodiments, the feedstream contains light naphtha. In certain embodiments, the feedstream can include paraffins. In particular embodiments, the feedstream can have a boiling point of less than about 350°C. The feedstream can be combined with a recycle stream from the reactor trains, such that it further includes unconverted hydrocarbons, e.g., paraffins and heavier olefins. In certain embodiments, the feedstream can further include water.

[0021] In certain embodiments, the feedstream can be preheated prior to heating in the first heating unit. For example, the feedstream can be preheated by indirect heat exchange, e.g., with a product stream from the catalytic cracking. Additionally or alternatively, the feedstream can be pressurized. For example, the feedstream can be pressurized to a pressure of up to about 10 bar.

[0022] As used herein, the term "about" or "approximately" means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, "about" can mean a range of up to 20%, up to 10%, up to 5%, and or up to 1% of a given value.

[0023] In certain embodiments, the feedstream can be heated in the first heating unit to a temperature from about 450°C to about 900°C, or from about 530°C to about 800°C, or from about 580°C to about 750°C. In a particular embodiment, the feedstream can be heated to a temperature of about 650°C. The first heating unit can include at least one heat exchanger and at least one fired heater.

[0024] In certain embodiments, the feedstream can be combined with water and/or a diluent. The water and/or diluent can be combined with the feedstream prior to heating the feedstream. For example, the diluent can be dry gas. By way of example, and not limitation, the dry gas can include greater than about 70 vol-% methane. The dry gas can further include additional components, such as hydrogen, ethane, and/or propane. The feedstream can optionally be combined with water in the form of steam. In certain alternative embodiments, the feedstream is not combined with water. Where the feedstream is combined with water, the ratio between the water and the feedstream can be up to about 10: 1. For example, the water to feedstream ratio can range from about 0: 1 to about 10: 1, or from about 0.1 : 1 to about 2: 1, or from about 0.3: 1 to about 1.5: 1.

[0025] The method 100 can further include introducing the feedstream to a first reactor train containing a first catalyst until the first catalyst becomes deactivated 102. For example, the feedstream can be introduced to a first catalyst within a first reactor train. In certain embodiments, the reactor train can include from one to seven fixed bed reactors, which can be arranged in series and/or parallel within the reactor train.

[0026] Catalysts for use in the presently disclosed subject matter can be any catalyst suitable for the catalytic cracking of hydrocarbons. In certain embodiments, the catalyst includes a zeolite catalyst. For example, the catalyst can include one or more zeolite based solid acid catalysts having medium pore size (i.e., zeolites with a 10-membered ring) and/or large pore size (i.e., zeolites with a 12-membered ring). Examples of zeolite catalysts having medium pore size include MFI, MEL, MTT, MRE, MWW, FER, CGS, SVR and STW. Examples of zeolites having large pore size include MOR, FAU, BOG, MTW, MAZ, OFF, BEA, MEI, LTL and GME. In particular embodiments, the zeolite catalyst can be a ZSM-5 catalyst. The silica to alumina ratio of the zeolite catalyst can range from about 2 to pure siliceous zeolites (i.e., greater than about 1000). As known in the art, the zeolite catalysts can undergo post treatment. For example, the zeolite catalysts can be treated to introduce mesoporosity and/or macroporosity. As a further example, the zeolite catalysts can be treated to change the silica to alumina ratio, e.g., by demetallation, such as by dealumination (acid leaching), desilication (base treatment), or steaming. In certain embodiments, various chemicals can also be used to enhance the stability, activity and selectivity. For example, the addition of phosphorous, alkaline, alkaline earth metals, transition metals and rare earth metals can be used to improve catalyst performance.

[0027] In certain embodiments, the feedstream can be introduced to a mixture of one or more catalysts. For example, the reactor train can include a mixture of two, or a mixture of three catalysts. In certain embodiments, multiple catalysts can be combined in a single reactor. In other embodiments, multiple reactors in a reactor train can include different catalysts.

[0028] The feedstream can undergo catalytic cracking. For example, the catalytic cracking can generate a product stream including light olefins, e.g., ethylene and propylene. In certain embodiments, the reaction can take place at a temperature from about 450°C to about 900°C, or from about 530°C to about 800°C, or from about 580°C to about 750°C. The reaction can take place in a vacuum. Alternatively, the reaction can take place at a pressure of up to about 10 bar. The weight hourly space velocity (WHSV) of the reaction can be from about 1 h^"1 to about 15 h^"1, or from about 2 h^"1 to about 10 h^"1, or from about 4 h^"1 to about 9 h^"1, or about 6 h^"1.

[0029] Introducing the feedstream to a first reactor train can generate a first product stream. For example, the first product stream can contain light olefins, e.g., ethylene and propylene. The first product stream can further contain other components, including but not limited to heavier olefins (e.g., C₅ and heavier olefins), paraffins, and aromatics. In particular embodiments, the first product stream can have a combined yield of ethylene and propylene that is greater than about 40 wt-%, greater than about 44 wt-%, greater than about 47 wt-%, greater than about 50 wt-%, or greater than about 52 wt-%.

[0030] Over time, catalytic cracking can cause coke (carbonaceous) deposits to form on the catalyst, leading to catalyst deactivation. For example, the catalyst can be considered deactivated when the conversion and/or yield of the reaction have declined by a certain percentage. For example, the catalyst can be considered deactivated when conversion and/or yield have declined by about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, or about 90%.

[0031] The activity of the catalyst can be reactivated or regenerated using a regeneration gas. For example, the regeneration gas can contain oxygen, and the oxygen can react with and remove the coke deposits from the catalyst, e.g., via combustion. Therefore, in certain embodiments, the method 100 can include heating a first regeneration stream including a regeneration gas in the first heating unit 103 and introducing the first regeneration stream to the first reactor train until the first catalyst is activated 104. The regeneration gas can be heated to a suitable temperature to control catalyst reactivation. For example, the regeneration gas can be heated to a temperature from about 350°C to about 550°C.

[0032] By way of example, the catalyst can be considered activated when its activity is restored to a certain percentage of its initial activity. Thus, the regeneration gas can be introduced to the first catalyst until its activity is restored to that certain percentage. For example, the activity of the first catalyst can be restored to greater than about 70%, greater than about 80%, greater than about 90%, greater than about 95%, or greater than about 99% of its initial activity.

[0033] In certain embodiments, the regeneration gas can include air, for example, atmospheric air. The flow of air can be controlled to limit the temperature of the regeneration, i.e., the temperature within the reactor train. In certain embodiments, the temperature of the air and combustion products exiting the reactor train is less than 850°C, and preferably between 500°C and 750°C. The air and combustion products can be cooled, e.g., to below 50°C, using one or more heat exchangers and/or fin fans. In certain embodiments, the cooled air and combustion products can be transferred to a gas-liquid separator to separate the gas from any water produced during combustion. In alternative embodiments, the air and combustion products can be combined with the product stream from the operating reactor train and transferred to a separation unit with the product stream.

[0034] While the first catalyst is being regenerated with the regeneration gas, it can be desirable to continue to react the feedstream in a second reactor to maintain continuous output of a product stream. Therefore, the method 100 can include heating the feedstream in a second heating unit 105 and introducing the feedstream to a second reactor train containing a second catalyst while introducing the first regeneration stream to the first reactor train 106. Using this method, two reactors can be operated in a cyclic configuration, such that the first reactor is used for the catalytic cracking of hydrocarbons (i.e., the first reactor is in "operation mode"), while the catalyst of the second reactor is activated (i.e., the second reactor is in "regeneration mode"). In certain embodiments, the first reactor can remain in operating mode for up to 1 hour, up to 6 hours, up to 12 hours, up to 24 hours, up to 2 days, up to 4 days, or up to 5 days until the catalyst is deactivated. Once the catalyst of the first reactor has been deactivated and the catalyst of the second reactor has been activated, the modes of the reactors can be switched, such that the first reactor is in regeneration mode and the second reactor is in operation mode. In this manner, the method can be used to continuously generate a product stream from the feedstream using a cyclic reactor configuration.

[0035] The methods for heating the feedstream in the second heating unit and introducing the feedstream to a second reactor train can be the same as discussed above in connection with the first heating unit, first catalyst, and first reactor train. For example, as in the first heating unit, the feedstream can be heated in the second heating unit to a temperature from about 450°C to about 900°C, or from about 530°C to about 800°C, or from about 580°C to about 750°C. The feedstream can be heated to the same or a different temperature in the second heating unit as compared to the first heating unit.

[0036] In certain embodiments, the feedstream can be introduced to the second catalyst in a second reactor train. The second catalyst can be any catalyst suitable for the catalytic cracking of hydrocarbons, for example, the catalysts described above. In certain embodiments, the first catalyst and the second catalyst can be the same. The second reactor train can include from one to seven fixed bed reactors, which can be arranged in series and/or parallel. The reactors within the second reactor train can all contain the same catalyst. Alternatively, the various reactors within the second reactor train can contain different catalysts. The reaction parameters, e.g., temperature, pressure, and WHSV, can be within the same ranges disclosed above in connection with the first reactor train. However, the temperature, pressure, and WHSV need not be the same in both the first reactor train and second reactor train.

[0037] Introducing the feedstream to the second reactor train can generate a second product stream. For example, the second product stream can contain light olefins, e.g., ethylene and propylene. The second product stream can further contain other components, including but not limited to heavier olefins (e.g., C₅ and heavier olefins), paraffins, and aromatic s. In particular embodiments, the second product stream can have a combined yield of ethylene and propylene that is greater than about 40 wt-%, greater than about 44 wt-%, greater than about 47 wt-%, greater than about 50 wt-%, or greater than about 52 wt-%.

[0038] In certain embodiments, the feedstream can be introduced to the second catalyst until the second catalyst is deactivated. For example, the second catalyst can be considered deactivated when conversion and/or yield have declined by about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, or about 90%.

[0039] The method 100 can further include heating a second regeneration stream in the second heating unit 107 and introducing the second regeneration stream to the second reactor train while introducing the feedstream to the first reactor train and until the second catalyst is activated 108. In this manner, the second catalyst can be regenerated while the feedstream is introduced to the first catalyst, as described above. The second regeneration stream can include air, for example, atmospheric air.

[0040] The presently disclosed subject matter further provides systems for generating light olefins using a cyclic reactor configuration, for example, by the catalytic cracking of hydrocarbons. An exemplary system having a cyclic reactor configuration can include two parallel reactor trains, each containing catalysts, and a valve for switching the flow of a feedstream between the reactor trains in order to alternate the reactor trains between operation mode and regeneration mode.

[0041] For the purpose of illustration and not limitation, FIG. 2 is a schematic representation of a system according to a non-limiting embodiment of the disclosed subject matter. The system 200 can include a feed line 201 for supplying a feedstream. The feedstream can include the hydrocarbon feedstock, as described above.

[0042] In particular embodiments, the feed line 201 can be coupled to a pump 202 for pressurizing the feedstream. Additionally, the pump can be coupled to a heat exchanger 204, e.g., via a transfer line 203, for pre-heating the feedstream. The heat exchanger for use in the presently disclosed subject matter can be any type suitable for heating gaseous or liquid streams. For example, but not by way of limitation, such heat exchangers include shell and tube heat exchangers, plate heat exchangers, plate and shell heat exchangers, adiabatic wheel heat exchangers, and plate fin heat exchangers.

[0043] "Coupled" as used herein refers to the connection of a system component to another system component by any suitable means known in the art. The type of coupling used to connect two or more system components can depend on the scale and operability of the system. For example, and not by way of limitation, coupling of two or more components of a system can include one or more joints, fittings, valves, transfer lines or sealing elements. Non-limiting examples of joints include threaded joints, soldered joints, welded joints, compression joints and mechanical joints. Non-limiting examples of fittings include coupling fittings, reducing coupling fittings, union fittings, tee fittings, cross fittings and flange fittings. Non-limiting examples of valves include gate valves, globe valves, ball valves, butterfly valves and check valves. Non-limiting examples of transfer lines include pipes, hose, tubing, and ducting, which can be made of any suitable material, including stainless steel, carbon steel, cast iron, ductile iron, non-ferrous metals and alloys, for example including aluminum, copper, and/or nickel, and non-metallic materials, e.g., concrete and plastic.

[0044] The system can further include a splitter 206, coupled to the heat exchanger 204, e.g., via a transfer line 205. A person having ordinary skill in the art will appreciate that the pump 202 and heat exchanger are optional components of the system, and thus in alternate embodiments, the feed line 201 can be directly coupled to one of the heat exchanger or the splitter.

[0045] The splitter 206 can be coupled to one or more valves 207, which can be used to divert the feedstream to one or more reactor trains. For example, the system 200 can include a first heating unit 213 and a second heating unit 223, which can in turn be coupled to a first reactor train 215 and a second reactor train 225, respectively. The valve can shift the flow of the feedstream to one or more of the first heating unit and the second heating unit.

[0046] The heating units 213, 223 for use in the presently disclosed subject matter can include any suitable equipment for heating gaseous or liquid streams. In certain embodiments, the first heating unit and/or second heating unit can include a fired heater. The first heating unit and/or the second heating unit can further include at least one heat exchanger. The first heating unit can be coupled to the first reactor train 215, e.g., via a transfer line 214. Similarly, the second heating unit can be coupled to the second reactor train 225, e.g., via a transfer line 224. [0047] Each of the first reactor train 215 and the second reactor train 225 can include from one to seven reactors. The first reactor train and the second reactor train can include the same or a different number of reactors. The reactors within the reactor trains can be arranged in series, in parallel, or in a combination of both. For example, but not limitation, the reactors can be fixed bed reactors. In alternative embodiments, the reactor trains can include multiple moving bed reactors rather than fixed bed reactors.

[0048] One or more air lines 212, 222 can be coupled to each of the first heating unit 213 and the second heating unit 223. In alternative embodiments, the air lines can be coupled directly to the first reactor train 215 and the second reactor train 225. The air lines can include one or more valves for controlling the flow of air to the heating units and/or the reactor trains. In certain embodiments, transfer lines (not shown) can be coupled to each of the first reactor train and the second reactor train for removing air and combustion products from the reactor trains. The transfer lines can be coupled to one or more heat exchangers and/or fin fans for cooling the air and combustion products.

[0049] In certain embodiments, one or more product lines 216, 226 can be coupled to the first reactor train 215 and the second reactor train 225. The product lines can transfer one or more product streams from the reactor trains. The product lines can be coupled to a mixer 230 for combining the product streams in the product lines.

[0050] In particular embodiments, the mixer 230 can be coupled to the heat exchanger 204, e.g., via a transfer line 231, to provide indirect heat exchange between the product stream and the feedstream. Thus, the product stream can be used to pre-heat the feedstream. Another transfer line 232 can transfer the product stream from the heat exchanger.

[0051] In certain embodiments, the product stream can be transferred to a separation unit 233 via the transfer line 232. The separation unit can separate the products stream into its various components. In certain embodiments, the separation unit can separate olefins, e.g., ethylene and propylene, from the product stream. For example, the separation unit can include one or more flash drums. Additionally or alternatively, the separation unit can include one or more distillation columns. The one or more distillation columns can be stage or packed columns, and can include plates, trays and/or packing material. The separation unit can further include additional components for product separation, as known in the art.

[0052] The separation unit 233 can separate the product stream into various components. For example, the separation unit can be used to separate light gases (e.g., hydrogen, methane, and ethane) and/or liquefied petroleum gas (i.e., propane and butane) from the product stream containing ethylene and/or propylene. Additionally or alternatively, the separation unit can be used to separate C₄ to C₈ paraffins and olefins, as well as aromatics and heavier products, from the product stream containing ethylene and/or propylene. Additionally, the separation unit can be used to remove water from the product stream, e.g., by condensation.

[0053] In certain embodiments, the separation unit 233 can be used to recover unconverted hydrocarbons from the product stream. The unconverted hydrocarbons can include any materials from the feedstream that were not converted to light olefins in the reactor trains. The unconverted hydrocarbons can also include certain intermediate materials formed during catalytic cracking. For example, the unconverted hydrocarbons can include paraffins and/or heavier olefins (e.g., C₅ and heavier olefins). A recycle line 234 can be coupled to the separation unit for transferring unconverted hydrocarbons to the feed line 201.

[0054] The presently disclosed systems can further include additional components and accessories including, but not limited to, one or more gas exhaust lines, cyclones, product discharge lines, reaction zones, heating elements and one or more measurement accessories. The one or more measurement accessories can be any suitable measurement accessory known to one of ordinary skill in the art including, but not limited to, pH meters, flow monitors, pressure indicators, pressure transmitters, thermowells, temperature-indicating controllers, gas detectors, analyzers and viscometers. The components and accessories can be placed at various locations within the system.

[0055] The methods and systems of the presently disclosed subject matter can provide advantages over certain existing technologies. Exemplary advantages include increased olefins yield from the catalytic cracking of hydrocarbons and efficient catalyst regeneration while maintaining continuous product output.

[0056] The following examples provide techniques for generating light olefins in accordance with the disclosed subject matter. However, the following examples are merely illustrative of the presently disclosed subject matter and should not be considered as a limitation in any way.

Example 1; Catalytic cracking in a fixed bed reactor compared to a fluidized bed reactor.

[0057] In this Example, a naphtha feedstream was cracked catalytically in both a fixed bed reactor and a pilot plant containing a fluidized bed reactor to compare the conversion and yields of each reactor type. The fixed bed reactor is representative of the reactors used in the cyclic reactor configuration of the disclosed subject matter. Table 1 provides the composition of the feedstream, which contained light straight run naphtha.

Table 1. Feedstream com osition

[0058] The naphtha feedstream was cracked catalytically in both a fixed bed reactor and a fluidized bed pilot plant. The residence time in the fixed bed reactor was 10 minutes. However, the residence time in the fluidized bed pilot plant was less than one minute, due to the constraints of a fluidized bed reactor. Table 2 provides the reaction conditions, as well as the yields of each reactor.

Table 2. Reaction Conditions and Yields

[0059] Compared to the fluidized bed reactor, the fixed bed reactor increased the olefins yield by about 10%, having a combined yield of ethylene and propylene of greater than 44 wt-%. Additionally, the fixed bed reactor showed an increased conversion compared to the fluidized bed reactor. These results show that a fixed bed reactor can be a suitable alternative to a fluidized bed reactor for the catalytic cracking of hydrocarbons, and indeed, the cyclic process of the disclosed subject matter can provide improved yield and conversion compared to a fluidized bed process. Example 2: Catalytic cracking in a fixed bed reactor compared to a fluidized bed reactor.

[0060] In this Example, the naphtha feedstream described in Example 1 was cracked catalytically in a fixed bed reactor and a lab- scale fluidized bed reactor to compare the conversion and yields of each reactor type. Table 3 provides the reaction conditions, as well as the yields of each reactor.

Table 3. Reaction Conditions and Yields

[0061] Compared to the fluidized bed reactor, the fixed bed reactor increased the olefins yield by about 16%, having a combined yield of ethylene and propylene of greater than 44 wt-%. Additionally, the fixed bed reactor showed an increased conversion compared to the fluidized bed reactor. These results show that the cyclic process of the disclosed subject matter, which uses fixed bed reactors, can provide improved yield and conversion compared to a fluidized bed process.

Example 3: Catalyst stability in a fixed bed reactor.

[0062] In this Example, the stabilities of six different catalysts were compared during catalytic cracking in a fixed bed reactor. The catalysts were based on ZSM-5, which was modified by post-treatment and impregnated with phosphorous. The catalysts were: (1) parent ZSM-5; (2) alkaline treated ZSM-5; (3) titanium impregnated/exchanged ZSM-5; (4) phosphorous exchanged/impregnated ZSM-5; (5) alkaline treated ZSM-5, which was exchanged/impregnated with phosphorous; and (6) titanium impregnated/exchanged ZSM-5, which was exchanged/impregnated phosphorous. The stability of each catalyst was monitored over six hours. The combined yield of ethylene and propylene over the six hours is shown in FIG. 3. Three catalysts maintained activity and selectivity, while the other three showed steady deactivation. This data suggests that the three catalysts that maintained activity can be used effectively in a fixed bed reactor in a cyclic configuration for the catalytic cracking of hydrocarbons, and can be cyclically regenerated using the methods and systems disclosed herein.

* * *

[0063] In addition to the various embodiments depicted and claimed, the disclosed subject matter is also directed to other embodiments having other combinations of the features disclosed and claimed herein. As such, the particular features presented herein can be combined with each other in other manners within the scope of the disclosed subject matter such that the disclosed subject matter includes any suitable combination of the features disclosed herein. The foregoing description of specific embodiments of the disclosed subject matter has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosed subject matter to those embodiments disclosed.

[0064] It will be apparent to those skilled in the art that various modifications and variations can be made in the systems and methods of the disclosed subject matter without departing from the spirit or scope of the disclosed subject matter. Thus, it is intended that the disclosed subject matter include modifications and variations that are within the scope of the appended claims and their equivalents.

Claims

1. A method for generating light olefins by the catalytic cracking of hydrocarbons using a cyclic reactor configuration, the method comprising: heating a feedstream comprising the hydrocarbons in a first heating unit; introducing the feedstream to a first reactor train comprising a first catalyst until the first catalyst becomes deactivated; heating a first regeneration stream comprising a regeneration gas in the first heating unit; introducing the first regeneration stream to the first reactor train until the first catalyst becomes activated; and heating the feedstream in a second heating unit and introducing the feedstream to a second reactor train comprising a second catalyst while introducing the first regeneration stream to the first reactor train.

2. The method of claim 1, wherein the hydrocarbons comprise light naphtha.

3. The method of claim 1, wherein the hydrocarbons comprise heavy naphtha, kerosene, and/or diesel.

4. The method of claim 1, wherein the hydrocarbons have a boiling point of less than about 350°C.

5. The method of claim 1, further comprising combining one of water or a diluent with the feedstream.

6. The method of claim 1, wherein the first reactor train and the second reactor train each comprise from one to seven fixed bed reactors.

7. The method of claim 1, wherein the first heating unit and the second heating unit each comprise at least one heat exchanger and at least one fired heater.

8. The method of claim 1, wherein the regeneration gas comprises air.

9. The method of claim 1, wherein the introducing the feedstream to a first reactor train comprises generating a first product stream comprising greater than about 44 wt-% of combined ethylene and propylene.

10. The method of claim 9, wherein the introducing the feedstream to a second reactor train comprises generating a second product stream comprising greater than about 44 wt-% of combined ethylene and propylene.

11. The method of claim 10, further comprising separating paraffins and C₅ and heavier olefins, if any, from the first product stream and the second product stream and combining the paraffins and C₅ and heavier olefins with the feedstream.

12. The method of claim 1, further comprising: introducing the feedstream to the second reactor train until the second catalyst becomes deactivated; and heating a second regeneration stream comprising a second regeneration gas in the second heating unit and introducing the second regeneration stream to the second reactor train while introducing the feedstream to the first reactor train and until the second catalyst becomes activated.

13. A system for generating light olefins by the catalytic cracking of hydrocarbons using a cyclic reactor configuration, the system comprising: a first heating unit, coupled to a first reactor train; a second heating unit, coupled to a second reactor train; a first air line, coupled to the first heating unit; a second air line, coupled to the second heating unit; a feed line, coupled to both of the first heating unit and the second heating unit, for providing a feedstream; and a valve, coupled to the feed line, for directing the feedstream to one of the first heating unit and the second heating unit.

14. The system of claim 13, wherein the first reactor train and the second reactor train each comprise from one to seven fixed bed reactors.

15. The system of claim 13, wherein the first heating unit and the second heating unit each comprise at least one heat exchanger and at least one fired heater.

16. The system of claim 13, further comprising a separation unit, coupled to the first reactor train and the second reactor train, for separating olefins and unconverted hydrocarbons from a first product line from the first reactor train and a second product line from the second reactor train.

17. The system of claim 16, further comprising a recycle line, coupled to the separation unit and the feed line, for recycling unconverted hydrocarbons.