Recovery of light olefins from dry hydrocarbon gases in petroleum refining and petrochemical manufacturing processes for alkylate production.

Abstract

A method and system for treating an olefin-containing stream is disclosed. The disclosed method and system are particularly suitable for treating off-gas streams in oil refineries or petrochemical processes, such as fluid catalytic cracking (FCC) units, cokers, steam crackers, etc. The stream is treated in an absorber tower to reject lighter stream components and to absorb ethylene and / or propylene in a solvent. The solvent is typically isobutane. The enriched solvent stream from the absorber tower is fed to an alkylation reactor, which reacts the dissolved olefins with the isobutane solvent to produce an alkylate product.

Description

Detailed Description of the Invention

[0001] [Field of the Invention] This application relates to methods and systems for recovering light olefins from petroleum refining and petrochemical manufacturing processes, and more specifically, for absorbing light olefins into a feed stream for an alkylation reaction.

[0002] [Introduction] Petrochemical and petroleum refining operations often involve processes that convert high-boiling and high-molecular-weight hydrocarbons into various products that are lighter, lower-boiling, and more valuable (i.e., "crack"). For example, fluid catalytic cracking (FCC) is widely used in refineries to convert heavy petroleum components into high-value fuels. FCC and other cracking processes produce a variety of products ranging from light gases to heavy oils. Processes and procedures within the refinery are used to separate the various FCC products based on their boiling point ranges, and products such as petroleum naphtha, gasoline, diesel, kerosene, jet fuel, and fuel oil are manufactured.

[0003] The stream containing the lightest components from an FCC unit is called offgas. The offgas stream typically contains ethane, ethylene, methane, and hydrogen, along with impurities such as carbon monoxide, carbon dioxide, and hydrogen sulfide. The offgas stream is considered to have low value because the only valuable component is ethylene, and it is generally costly to separate ethylene from the offgas stream. Therefore, refineries typically send the offgas stream to a fuel gas system, thereby recovering some value from the offgas stream by burning it to generate heat for in-refinery processes. However, the ethylene contained in the offgas stream would be more beneficial if it were used for higher-order purposes rather than being burned as fuel gas.

[0004] [Summary] Disclosed herein is a method for processing an olefin-containing stream. The olefin-containing stream comprises one or more olefins selected from the group consisting of ethylene and propylene, and one or more light components selected from the group consisting of hydrogen (H2), carbon monoxide (CO), and methane. The method comprises providing the olefin-containing stream to an absorption tower; separating one or more olefins from one or more light components by contacting the olefin-containing stream with a solvent that is an alkylation precursor in the absorption tower to provide an olefin-enriched solvent stream, thereby absorbing at least a portion of the one or more olefins into the solvent; providing the olefin-enriched solvent stream to an alkylation reactor; and reacting one or more olefins with the solvent in the alkylation reactor to produce alkylates. According to some embodiments, the solvent is isobutane. According to some embodiments, the olefin-containing stream is off-gas from a fluid catalytic cracking (FCC) process. According to some embodiments, the olefin-containing stream further contains one or more impurities selected from the group consisting of carbon dioxide, water, and hydrogen sulfide, and the method further includes pre-treating the olefin-containing stream to remove one or more impurities. According to some embodiments, the pre-treating includes washing the olefin-containing stream with an amine. According to some embodiments, the pre-treating includes contacting the olefin-containing stream with a caustic substance. According to some embodiments, the reaction of one or more olefins with a solvent in an alkylation reactor to produce an alkylate includes dimerizing one or more olefins to form a dimer, and reacting the dimer with a solvent to produce an alkylate. According to some embodiments, the alkylation reactor comprises a fixed catalyst bed having a solid acid alkylation catalyst. According to some embodiments, the reaction of one or more olefins with a solvent in an alkylation reactor to produce an alkylate includes producing an alkylate-containingAccording to some embodiments, the method further includes providing the alkylation reactor effluent to one or more separation columns, recovering a lean solvent from one or more separation columns, and recovering enriched alkylate products from one or more separation columns. According to some embodiments, the method further includes recirculating at least a portion of the lean solvent to an absorption column. According to some embodiments, the method further includes recirculating at least a portion of the lean solvent to the alkylation reactor.

[0005] Also disclosed herein is a system for processing an olefin-containing stream. The olefin-containing stream comprises one or more olefins selected from the group consisting of ethylene and propylene, and one or more light components selected from the group consisting of hydrogen (H2), carbon monoxide (CO), and methane. The system comprises an absorption tower and an alkylation reactor. The absorption tower is configured to separate one or more olefins from one or more light components by contacting the olefin-containing stream with a solvent that is an alkylation precursor, thereby absorbing at least a portion of the one or more olefins into the solvent, in order to provide an olefin-enriched solvent stream. The alkylation reactor is configured to receive the olefin-enriched solvent stream and react one or more olefins with the solvent to produce alkylates. According to some embodiments, the solvent is isobutane. According to some embodiments, the olefin-containing stream is off-gas from a fluid catalytic cracking (FCC) process. According to some embodiments, the system further comprises an amine washer upstream of the absorption tower, the amine washer is configured to remove one or more impurities selected from the group consisting of carbon dioxide and hydrogen sulfide from the olefin-containing stream. According to some embodiments, the system further comprises a caustic contact vessel upstream of the absorption tower, the caustic contact vessel being configured to contact the olefin-containing stream with a caustic substance to remove one or more impurities selected from the group consisting of carbon dioxide and hydrogen sulfide from the olefin-containing stream. According to some embodiments, the alkylation reactor comprises a stationary catalyst bed having a solid acid alkylation catalyst. According to some embodiments, the alkylation reactor is configured to supply the alkylation reactor effluent stream containing alkylates to one or more separation towers, the one or more separation towers being configured to separate the alkylation reactor effluent stream into a lean solvent stream and an enriched alkylate product stream. According to some embodiments, the system is configured to recirculate the lean solvent stream to one or more of the absorption tower and the alkylation reactor. [Brief explanation of the drawing]

[0006] [Figure 1] This shows a system for processing olefin-containing flows. [Modes for carrying out the invention]

[0007] [Detailed explanation] This disclosure provides a method and system for absorbing C2 and / or C3 olefins (i.e., ethylene and / or propylene) from off-gas flows of petroleum refining / petrochemical processes. Generally, C2+ hydrocarbons (including small amounts of C4 / C5) are absorbed, while C1 and hydrogen are excluded. The disclosed method and system are primarily described in the context of treating FCC off-gas. However, it should be understood that the method and system may be used to treat off-gas (and other C2 / C3 olefin-containing flows) generated by other processes, such as coking equipment, ethylene and propylene recovery equipment, and steam crackers. Generally, the method and system can be used for any ethylene and / or propylene-containing flow.

[0008] The disclosed method and system involves absorbing C2 and / or C3 olefins into a supply stream, which is then supplied to an alkylation reactor to produce alkylate products. Alkylates are the cleanest gasoline blend stream produced in refineries and are an ideal and clean fuel component due to their high octane, low vapor pressure, and low toxicity. Alkylates have been blended into gasoline for decades to improve octane, i.e., the anti-knock properties of gasoline. In addition, due to stringent state and federal regulations on gasoline production methods and properties, alkylates have become one of the most important and high-value blend stocks in the gasoline pool. The disclosed method and system provides a substantially improved processing value of off-gas streams by converting C2 and / or C3 olefins in an off-gas stream into high-value alkylate products, rather than sending the olefins into the refinery's fuel gas system.

[0009] Figure 1 shows a system 100 for absorbing C2 / C3 olefins from a flow and providing the C2 / C3 olefins as part of a feed stream for an alkylation reaction. In the illustrated system 100, the olefin-containing flow is supplied to the system via line 102. In the illustrated system, the olefin-containing flow is, for example, an off-gas flow from an FCC plant. As described above, such an off-gas flow may contain ethylene and / or propylene, ethane, methane, and hydrogen, along with impurities such as carbon monoxide, carbon dioxide, and hydrogen sulfide. A typical off-gas flow may have a pressure of, for example, about 120 psig.

[0010] In the illustrated system 100, the off-gas flow is pressurized in a compressor 104 to liquefy some of its components. For example, the off-gas flow may be pressurized to a pressure of about 180 psig to about 250 psig. The discharge pressure of the compressor 104 may be set so that the off-gas flow can pass through the pretreatment area 106 and enter the absorption / demethane tower (A / D tower) 108, which operates at a pressure of about 135 psig, as described below. According to one embodiment, the discharge pressure of the compressor 104 may be set to about 230 psig.

[0011] The compressed flow 110 may be supplied to a pretreatment area 106. The purpose of the pretreatment area 106 is to remove various impurities from the flow and prepare it for use in the downstream A / D tower 108. According to some embodiments, the pretreatment area 106 may include an amine system for removing large amounts of carbon dioxide (CO2) and / or H2S, a caustic wash for finally removing CO2 / H2S, and / or a dryer for removing moisture. Such apparatuses and processes are well known to those skilled in the art. For example, the amine wash system may include contacting the compressed olefin-containing flow with an amine such as monoethanolamine, diethanolamine, methyldiethanolamine, or diglycolamine to absorb CO2 and / or H2S from the olefin-containing flow. A typical amine gas treatment process includes an absorber unit and a regenerator unit, along with auxiliary equipment. In the absorber, the downward-flowing amine solution absorbs H2S and CO2 from the upward-flowing olefin-containing stream to produce a sweetened olefin-containing stream (i.e., an olefin-containing stream without H2S and CO2) as a product, and also produces a rich amine solution rich in the absorbed acidic gases (H2S and CO2). The resulting "rich" amine is then led to a regenerator (a stripper equipped with a reboiler) to produce a regenerated amine, or "lean" amine, which is recycled for reuse in the absorber. The stripped overhead gas stream from the regenerator, which is concentrated H2S and CO2, may be led to an acidic gas treatment. Following amine washing, the olefin-containing stream may be contacted with a caustic agent in a container for further sweetening. The olefin-containing stream may be dried by contacting an adsorbent bed composed of molecular sieve material. In the illustrated embodiment, the caustic material is sodium hydroxide or another caustic material well known in the art, and is supplied to the pretreatment area 106 via line 112. Acidic gas, spent caustic agent, and water are discharged from the pretreatment area 106 via lines 114, 116, and 118, respectively.It should be understood that, depending on the specific implementation and the composition of the off-gas flow, various different pretreatment processes may be performed to purify the off-gas flow. According to some embodiments, the pretreated off-gas flow may be cooled before being supplied to the A / D tower 108. For example, the compressed off-gas flow may be cooled to about 35°F.

[0012] In the illustrated embodiment, the pre-treated off-gas flow is supplied to the A / D tower 108 via line 120. The pre-treated off-gas flow in line 120 may contain ethylene and / or propylene and other components. These other components include hydrogen (H2), carbon monoxide (CO), methane, ethane, propane, n- and / or i-butane, butene, pentene, and pentane. The specific composition of the pre-treated off-gas flow in line 120 will depend on the composition of the source flow (i.e., flow 102) and the operating parameters of upstream equipment such as the compressor 104 and the pre-treatment area 106. Ideally, the pre-treated off-gas flow in line 120 is preferably rich in olefins (i.e., ethylene and / or propylene).

[0013] The A / D column 108 is an absorption column that serves two purposes: 1) to remove lighter components such as H2, CO, and methane from the off-gas stream while absorbing olefins (i.e., ethylene and / or propylene) into the solvent; and 2) to provide the olefins to the alkylation reactor as a feed stream particularly suitable for the alkylation reaction. As mentioned above, heavier components (such as C2 + paraffin) will also be absorbed. In the A / D column, the pretreated off-gas stream is brought into contact with the solvent, which is also the reactant in the downstream alkylation reactor. In other words, the solvent is itself an alkylation precursor. According to some embodiments, the solvent is isobutane, but it may also be other compounds such as isopentane. In system 100, lean isobutane is supplied to the A / D column 108 via line 122. The isobutane is contacted with the pre-treated off-gas in an A / D column to produce an enriched solvent stream 124 rich in olefins and heavier components from the off-gas, which is then supplied to the alkylation reactor 128, as described below. Lighter components that are not absorbed, such as H2 and CO, are discharged from the A / D column via line 126 and may undergo further treatment, such as pressure swing adsorption (PSA).

[0014] According to some embodiments, the A / D column 108 may consist of a single pressure-operated column for contacting (multiple) olefins with an isobutane solvent. Parameters that can vary considerably to improve olefin absorption include the presence or absence of trays, the number of trays, the operating temperature and operating pressure range, and the solvent-to-olefin ratio. According to some embodiments, the A / D column has about 20 theoretical stages (which may be conventional trays or an equal amount of packing) with a solvent-to-feed ratio of 2.45 wt / wt. According to some embodiments, the solvent may be cooled using an overhead condenser and fed to the top of the column as reflux. According to some embodiments, for example, the temperature profile may be about -30°F at the top stage and about 0°F at the bottom stage. According to some embodiments, a pre-treated off-gas feed may enter the bottom of the column at a vapor fraction of about 0.80. The A / D column may or may not have a reboiler. According to some embodiments, the net liquid bottom flow 124 may be sent to a feed / effluent heat exchanger and / or a solvent / effluent heat exchanger (not shown) to heat the flow (for example, to a temperature of about 60°C) before being sent to the alkylation reactor. According to some embodiments, the overhead flow may be partially condensed and sent to a reflux drum (not shown). Uncondensed material may be discharged from the drum as a net overhead vapor flow 126, or it may be sent to a PSA unit for further purification. This flow consists mostly of molecules lighter than ethylene. According to some embodiments, the goal is to recover approximately 90% of the ethylene from the A / D column 108.

[0015] A solvent-enriched stream 124 is supplied to one or more alkylation reactors 128. As described above, the solvent-enriched stream is enriched with ethylene and / or propylene, as well as heavier components. The solvent is typically isobutane, which functions both as a solvent and as a reagent in the alkylation reaction. The alkylation reactor converts the absorbed olefins and isobutane to alkylates. U.S. Patent No. 9,079,815 discloses an example of converting ethylene and isobutane to alkylates. According to some embodiments, the alkylation reactor converts olefins and isobutane to alkylates using solid acid alkylation technology. A particularly preferred alkylation reactor technology is the K-SAAT alkylation technology (KBR, Houston, Texas). This alkylation process uses a fixed-bed catalyst, typically a non-precious metal-supported zeolite material. An example of a preferred catalyst is the ExSact catalyst (KBR, Houston, Texas). When ethylene is converted to an alkylate, two molecules of ethylene first dimerize, that is, react with each other, to form butylene. Butylene then reacts with isobutane to form the alkylate isooctane. The amount of isobutane in the system can be controlled so that the reaction equilibrium moves toward the product, as described below.

[0016] The stoichiometric amounts of the reagents (i.e., olefins and isobutanes) supplied to the alkylation reactors 128 are controlled based on a component analysis of the flow 124. For example, according to some embodiments, it is desirable that the molar ratio of isobutane to propylene is about 10:1 and the molar ratio of isobutane to ethylene is about 5:1. Therefore, in order to maintain the correct stoichiometric amounts in the alkylation reactors 128, the composition of the supply flow is measurable, and the amount of isobutane in the system is adjustable (as will be described in more detail below).

[0017] The effluent 130 from the (multiple) alkylation reactors 128 may contain about 10% to 12% alkylate products, for example, the remainder being mainly isobutane. The reactor effluent 130 may be supplied to a further purification process, collectively shown in Figure 1 as a gas plant 132. The gas plant 132 may comprise, for example, one or more separation columns. According to some embodiments, the gas plant has a separation column configured to recover lean isobutane and recirculate the lean isobutane (or a portion thereof) to an A / D column via line 122. According to some embodiments, a portion of the recovered lean isobutane may be recirculated to the (multiple) alkylation reactors via line 134. According to some embodiments, n-butane may be taken out as a side flow from the separation column. The gas plant may have other separation columns for separating other components, such as ethane, propane, and other off-gas products.

[0018] As described above, a portion of the recovered lean solvent (isobutane) may be recycled to the alkylation reactor 128 via line 134. This is beneficial for several reasons. Firstly, according to some embodiments, it is desirable to recycle as little isobutane as possible to the A / D column 108, because using a large amount of isobutane requires a larger column and consumes more energy. Also, as described above, the equilibrium of the alkylation reaction can be controlled by controlling the amount of isobutane supplied to the alkylation reactor. Thus, the isobutane recirculation stream 134 provides a means for controlling the alkylation reaction.

[0019] As shown in Figure 1, make-up isobutane can be supplied to system 100 at various points. For example, make-up isobutane may be supplied to A / D column 108 via line 136. According to some embodiments, make-up isobutane may be mixed with pre-treated off-gas in line 120 (via line 138) before the pre-treated off-gas enters A / D column 108. For example, the pre-treated off-gas may be pre-contacted with make-up isobutane using a static mixer or bubbler before the mixture is supplied to the A / D column. Make-up isobutane may also be added directly to alkylation reactor 128 via line 140 and / or to components of gas plant 132 via line 142.

[0020] While specific embodiments of the present invention have been shown and described, it should be understood that the above discussion is not intended to limit the invention to these embodiments. It will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, the present invention is intended to encompass alternatives, modifications and equivalents that may fall within the spirit and scope of the invention as defined in the claims.

Claims

1. Ethylene and hydrogen (H ２ A method for treating an olefin-containing stream comprising one or more light components selected from the group consisting of carbon monoxide (CO) and methane, The olefin-containing stream having a vapor fraction of 0.80 is supplied to the absorption tower, To provide an ethylene-enriched solvent flow, the olefin-containing flow is brought into contact with a hydrocarbon solvent that is an alkylation precursor within the absorption tower, which operates at a pressure of approximately 930 kPa and in a temperature range from -34.4°C at the top of the absorption tower to -17.8°C at the bottom of the absorption tower, thereby separating the ethylene from the one or more light components by absorbing at least a portion of the ethylene into the hydrocarbon solvent. The ethylene-enriched solvent stream is supplied to the alkylation reactor, The alkylation reactor reacts the ethylene with the hydrocarbon solvent in the alkylation reactor to produce an alkylate and excess hydrocarbon solvent outflow from the alkylation reactor, The alkylation reactor effluent is separated into alkylate product and lean solvent stream, The first portion of the lean solvent stream is recirculated to the alkylation reactor, and the amount of the first portion is controlled to maintain a predetermined ratio of olefin to hydrocarbon solvent in the alkylation reactor, thereby maintaining an alkylation equilibrium that preferentially produces isooctane products when ethylene is reacted with the hydrocarbon solvent. The second portion of the lean solvent flow is recirculated to the absorption tower, Methods that include...

2. The method according to claim 1, The method wherein the hydrocarbon solvent is isobutane.

3. The method according to claim 1, The olefin-containing stream is an off-gas from a fluid catalytic cracking (FCC) process, in this method.

4. The method according to claim 1, The olefin-containing stream further contains one or more impurities selected from the group consisting of carbon dioxide, water, and hydrogen sulfide. The method further comprises pre-treating the olefin-containing stream to remove the one or more impurities.

5. The method according to claim 4, The pretreatment method includes washing the olefin-containing stream with an amine.

6. The method according to claim 4, The pretreatment method includes contacting the olefin-containing stream with a caustic substance.

7. The method according to claim 1, Reacting the ethylene with the hydrocarbon solvent in the alkylation reactor to produce the alkylate is, Dimerizing one or more of the aforementioned olefins to form a dimer, The process involves reacting the dimer with the hydrocarbon solvent to produce the alkylate, Methods that include...

8. The method according to claim 1, The alkylation reactor comprises a stationary catalyst bed having a solid acid alkylation catalyst.

9. The method according to Claim 1, A method wherein the amount of the first portion of the lean solvent stream that is recycled to the alkylation reactor is determined based on the determined composition of the alkylation reactor effluent.

10. A system for processing olefin-containing flow, The olefin-containing stream is One or more olefins selected from the group consisting of ethylene and propylene, Hydrogen (H ２ ), one or more light components selected from the group consisting of carbon monoxide (CO) and methane, Includes, The aforementioned system, An absorption tower having a hydrocarbon solvent that is an alkylation precursor, configured to separate one or more olefins from one or more light components by bringing the olefin-containing stream into contact with the hydrocarbon solvent at a pressure of about 930 kPa and in a temperature range from -34.4°C at the top of the absorption tower to -17.8°C at the bottom of the absorption tower, thereby absorbing at least a portion of one or more olefins into the hydrocarbon solvent, in order to provide an olefin-enriched solvent stream, An alkylation reactor configured to receive the olefin-enriched solvent stream and react one or more olefins with the hydrocarbon solvent to produce an alkylate, One or more separation columns configured to receive the alkylation reactor effluent flow containing the alkylate and to separate the alkylation reactor effluent flow into a lean solvent flow and an enriched alkylate product flow, A first recirculation line configured to recirculate a first portion of the lean solvent flow back to the absorption tower, A second recirculation line is configured to recirculate the second portion of the lean solvent flow back to the alkylation reactor, A system equipped with these features.

11. The system according to claim 10, The system wherein the hydrocarbon solvent is isobutane.

12. The system according to claim 10, The olefin-containing stream is an off-gas from a fluid catalytic cracking (FCC) process in the system.

13. The system according to claim 10, An amine washer is further provided upstream of the absorption tower. The amine washer is configured to remove one or more impurities selected from the group consisting of carbon dioxide and hydrogen sulfide from the olefin-containing stream.

14. The system according to claim 10, A caustic contact container is further provided upstream of the absorption tower. The caustic contact container is configured to bring the olefin-containing stream into contact with a caustic substance and remove one or more impurities selected from the group consisting of carbon dioxide and hydrogen sulfide from the olefin-containing stream.

15. The system according to claim 10, The alkylation reactor is a system comprising a stationary catalyst bed having a solid acid alkylation catalyst.

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