Patent Application
20150166435
The technical field generally relates to apparatuses and methods for processing hydrocarbons, and more particularly relates to methods and apparatuses that produce aromatics.
Aromatics, particularly benzene, toluene, ethylbenzene, and the xylenes (ortho, meta, and para isomers), which are commonly referred to as “BTEX” or more simply “BTX,” are extremely useful chemicals in the petrochemical industry. They represent the building blocks for materials such as polystyrene, styrene-butadiene rubber, polyethylene terephthalate, polyester, phthalic anhydride, solvents, polyurethane, benzoic acid, and numerous other components. Conventionally, BTEX is obtained for the petrochemical industry by separation and processing of fossil-fuel petroleum fractions, for example, in catalytic reforming or cracking refinery process units, followed by BTX recovery units.
Typically, integrated refining-petrochemical complexes separate a crude feedstock into a “straight run” or desired fraction of naphtha, such as C6-C10 naphtha, i.e., naphtha containing hydrocarbons having carbon chain lengths of six to ten, and a heavier fraction containing longer chain hydrocarbons such as heavy oils and residues. The naphtha stream typically undergoes reforming to produce a reformate with an increased aromatic content. The heavier fraction is typically cracked, such as by a fluid catalytic cracking (FCC) unit to form a “heart cut” or desired fraction of hydrocarbons, such as C6-C10 FCC hydrocarbons.
Conventionally, the naphtha stream and the FCC stream are processed to form selected aromatics. For example, a conventional process cracks the heavier fraction to form the FCC hydrocarbon stream and combines the FCC hydrocarbon stream with the straight run naphtha. Then, the combined stream is passed through a reforming unit to form a reformate. The reformate is processed in an aromatics complex to produce selected aromatic products, such as benzene and para-xylene.
Because aromatics are the building blocks of so many materials, there is a need to increase production of desired aromatics from integrated refining-petrochemical complexes. Typically, reforming units are used to produce aromatics from straight run naphtha, however such reforming units may convert existing aromatics in streams combined with straight run naphtha to other less desired compounds. Thus, there is a need to increase aromatics production without decreasing the value of other streams produced in the integrated refining-petroleum complexes, such as gasoline blends.
Accordingly, it is desirable to provide methods and apparatuses for processing hydrocarbons that produce aromatics. It is also desirable to provide methods and apparatuses for processing hydrocarbons that enable an increase in the production of aromatics through extracting of aromatics in a stream that bypasses a reforming unit. Also, it is desirable to provide such methods and apparatuses that operate economically. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
Methods and apparatuses for processing hydrocarbons are provided. In an exemplary embodiment, a method for processing hydrocarbons includes fractionating a feed stock to form a C6-C10 naphtha stream and a C11+ hydrocarbon stream. The method reforms the C6-C10 naphtha stream. Further, the method cracks the C11+ hydrocarbon stream to form a stream of C6-C10 hydrocarbons and extracts aromatics from the stream of C6-C10 hydrocarbons to form an extract stream. The method includes combining the C6-C10 naphtha stream and the extract stream containing the aromatics. Also, the method includes processing the C6-C10 naphtha stream and the extract stream in an aromatics complex to form selected aromatic products. Further, the embodiment may include reforming raffinate streams.
In another embodiment, a method for processing hydrocarbons includes fractionating a hydrocarbon stream in a fractionation unit and forming a first fraction and a second fraction. The method introduces the first fraction to a reforming unit and reforms the first fraction to form a reformate stream. The method includes feeding the reformate stream to an aromatics processing zone and producing a benzene product and a para-xylene product. Further, the method introduces the second fraction into a fluid catalytic cracking (FCC) unit and cracks the second fraction to form a cracked stream of hydrocarbons. The method includes feeding the cracked stream to an aromatic extraction unit and extracting aromatics from the cracked stream in an extract stream. The method further includes bypassing the reforming unit with the extract stream and introducing the extract stream to the aromatics processing zone, wherein the extract stream is processed in the aromatic processing zone to produce the benzene product and the para-xylene product.
In another embodiment, an apparatus for processing hydrocarbons is provided. The apparatus includes a fractionation unit configured to form a C6-C10 naphtha stream and a C11+ hydrocarbon stream from a feed stock. The apparatus further includes a cracking unit configured to crack the C11+hydrocarbon stream to form a stream of C6-C10 hydrocarbons and a first aromatic extraction unit configured to extract a first aromatic stream from the stream of C6-C10 hydrocarbons. Also, the apparatus includes a reforming unit configured to reform the C6-C10 naphtha stream and form a reformate and a second aromatic extraction unit configured to extract a second aromatic stream from the reformate. The apparatus is provided with an aromatics processing unit configured to produce a benzene product and a para-xylene product from the first aromatic stream and the second aromatic stream.
Embodiments of methods and apparatuses for processing hydrocarbons will hereinafter be described in conjunction with the following drawing figures wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the methods or apparatuses for processing hydrocarbons. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.
Various embodiments of methods and apparatuses for processing hydrocarbons with enhanced production of valuable product streams are described herein. For example, embodiments herein provide for the enhanced production of aromatics, such as for example benzene, toluene, and xylene (BTX). The embodiments produce additional aromatics from FCC C6-C10 hydrocarbon streams as compared to conventional processing. Exemplary embodiments utilize aromatics recovery from the FCC C6-C10 hydrocarbon stream and avoid reforming those aromatics. In one embodiment, an extract stream including aromatics is removed from the FCC C6-C10 hydrocarbon stream and fed to an aromatics complex including fractionation and isomerization units to produce streams of desired aromatic species. In another embodiment, a portion of the extract stream including aromatics is removed from the FCC C6-C10 hydrocarbon stream and fed to the naphtha reformer. In another embodiment, the extraction of aromatics from the FCC C6-C10 hydrocarbon stream forms a raffinate comprising primarily paraffins and olefins that is fed to the naphtha reformer and an extract that is fed to an aromatics complex.
Referring to
In the exemplary embodiment, the stream 212 is processed by a residue hydrotreating unit 220 that removes sulfur, nitrogen, organometallics, and asphaltenes from the stream 212 to form a hydrotreated stream 222. The residue hydrotreating unit 220 may use a fixed-bed catalytic hydrotreating process with catalysts employed to facilitate demetallization and desulfurization. The exemplary hydrotreated stream 222 is fed to a fluid catalytic cracking (FCC) unit 226. In an exemplary embodiment, the FCC unit 226 is run under severe FCC conditions. An exemplary fluid catalytic cracking unit 226 is operated to form a selected fraction of hydrocarbons, such as hydrocarbons having carbon chain lengths of from six to ten, i.e., C6-C10 hydrocarbons. As a result, a cracked stream 228, for example an FCC C6-C10 hydrocarbon stream 228, is formed by the FCC unit 226. Under severe FCC processing, the aromatic content of the cracked stream may be as high as about 50 weight percent (wt %) to about 70 wt %. Other fractions formed by the FCC unit 226 are not illustrated but may include a C5− stream or streams and a C11+ stream or streams.
The cracked stream 228 is fed to a selective hydrotreating unit 230, in an embodiment. The selective hydrotreating unit 230 saturates diolefins in the cracked stream 228. Further, the selective hydrotreating unit 230 converts mercaptans in the cracked stream 228 to disulfide compounds. Exemplary selective hydrotreating conditions include a temperature of about 250° C. to about 350° C. and a pressure of about 1000 kilopascals (kPa) to about 4000 kPa. As a result of the selective hydrotreating process, a hydrotreated stream 232 is formed with a reduced diolefin and mercaptan content.
In
As shown in
The resulting hydrotreated stream 252 contains paraffins, olefins and naphthenes and is fed to a reforming unit 256 for their conversion into aromatics. An exemplary reforming unit 256 is a catalytic reforming unit with continuous catalyst regeneration (CCR). The reforming unit 256 may be operated at a temperature of from about 495° C. to about 560° C. Compounds in the hydrotreated stream 252 are reformed to produce a reformate stream 260. Specifically, naphthenes are dehydrogenated to form aromatics, normal paraffins are isomerized to form isoparaffins, and paraffins are dehydrocyclized, i.e., dehydrogenated and aromatized, to form aromatics. Further, the aromatics present in the hydrotreated stream 252 can undergo demethylation and dealkylation reactions.
In the exemplary embodiment, the reformate stream 260 is fed to an aromatics complex 261, and specifically to a reformate splitter distillation column 262 therein. The reformate splitter distillation column 262 functions to separate or “split” the reformate stream 260 by distilling the reformate stream 260 into a heavier higher boiling fraction as stream 264 and a lighter, lower boiling fraction as stream 266. The reformate splitter distillation column 262 may be configured such that, for example, the heavier fraction in stream 264 includes primarily, such as greater than about 80%, greater than about 90%, or greater than about 95%, hydrocarbons having eight or more carbon atoms (C8+). The lighter fraction in stream 266 may include primarily (such as greater than about 80%, greater than about 90%, or greater than about 95%) hydrocarbons having seven or fewer carbon atoms (C7−).
The lighter fraction 266 is passed from the reformate splitter distillation column 262 to an extractive distillation process unit 270 for removing non-aromatic compounds from the lighter fraction 266. In one particular embodiment, extractive distillation process unit 270 may employ a sulfolane solvent to separate aromatic compounds from non-aromatic compounds. Other extraction methods, such as liquid-liquid solvent extraction are also well-known and practiced for separation of non-aromatic compounds from aromatic compounds, and their use in place of, or in addition to, extractive distillation process unit 270 is contemplated herein. Extractive distillation process unit 270 produces a raffinate stream 274 that includes primarily, such as greater than about 80%, greater than about 90%, or greater than about 95%, non-aromatic C7− hydrocarbons and an extract stream 272 that includes primarily, such as greater than about 80%, greater than about 90%, or greater than about 95%, benzene and toluene. In
In
A fractionation process is performed on the streams 272 and 282 in the benzene distillation column 286 and benzene, having a lower boiling point than toluene, is removed from benzene distillation column 286 as a product stream 310. Toluene, having a higher boiling point than benzene, is removed from distillation column 286 as stream 312. Stream 312 may further include heavier aromatic hydrocarbons such as various xylene isomers. Stream 312 is fed to the toluene distillation column 288.
In the toluene distillation column 288, toluene is separated from heavier components, i.e., components having lower boiling points than toluene, and is removed as stream 314, such as overhead stream 314. The heavier aromatic hydrocarbons are removed as stream 316, such as bottom stream 316. As shown, the toluene rich stream 314 is fed to the Tatoray process unit 300. The Tatoray process unit 300 converts toluene into benzene and xylenes in a toluene disproportionation process. Further, the Tatoray process unit 300 converts a mixture of toluene and aromatic hydrocarbons having nine carbon atoms (C9) into xylenes in a transalkylation process. Hydrogen is fed to the Tatoray process unit 300 so that the disproportionation and transalkylation processes are conducted in a hydrogen atmosphere to minimize coke formation. As shown, a stream 318 of benzene, toluene and xylenes exits the Tatoray process unit 300 and is recycled to the benzene distillation column 286 for further processing.
Stream 316, including a mixture of xylenes, exits the toluene distillation column 288 and is fed to a para-xylene separation unit 294. Separation of para-xylene from the other xylenes in the para-xylene separation unit 294 results in the formation of an extract stream 319 containing para-xylene. A raffinate stream 320 is fed to the xylene isomerization unit 296 which reestablishes an equilibrium mixture of isomers via xylene isomerization and conversion of ethyl benzene to benzene or xylenes. The isomerized effluent 322 formed by the xylene isomerization unit 296 is fed to the light distillation unit 298, which forms a stream 324, such as overhead stream 324, primarily containing benzene, toluene, and ethylbenzene, and a stream 326, such as bottom stream 326, containing C8+ aromatics including primarily ortho-, meta-, para-xylenes. Stream 326 is combined with the C8+ fraction 264 from the reformate splitter distillation column 262 and is fed to the xylene distillation column 292. As shown, the xylene distillation column 292 further receives a bottom raffinate stream 328 from the para-xylene separation unit 294.
The xylene distillation column 292 separates a stream 336, such as an overhead stream 336, containing xylenes. Stream 336 is combined with the heavier aromatic hydrocarbons in stream 316 from the toluene distillation column 288 and is fed to the para-xylene separation unit 294. A stream 340, such as a bottom stream 340, including heavier components is removed from the xylene distillation column 292 and is fed to the heavy aromatic distillation column 290. The heavy aromatic distillation column 290 removes any lighter aromatics present in stream 340 as a stream 344, such as overhead stream 344. Stream 344 is combined with the toluene in stream 314 and is fed to the Tatoray process unit 300. Heavy aromatics are removed from the process in a stream 350, such as a bottom stream 350.
In the exemplary embodiment of
While the extract stream 242 removed from the aromatics extraction unit 240 is described above as being fed to the aromatics complex via line 276, in other embodiments the extract stream 242, or a portion of the extract stream 242 may be combined with the naphtha stream 210 upstream of the reforming unit 256 via line 354. As shown, line 354 delivers aromatics from extract stream 242 to the naphtha stream 210 upstream of the naphtha hydrotreating unit 250. In comparison, the line 360 delivers the desulfurized stream 238 of FCC C6-C10 hydrocarbon without having aromatics extracted therefrom. As a result, a method or apparatus using line 360 would not obtain as high a yield of aromatics.
Referring to
In the exemplary embodiment of
As with the exemplary embodiment illustrated in
The apparatus 200 of
As described herein, methods and apparatuses for processing hydrocarbons have been provided. In an exemplary embodiment, a method and apparatus extracts aromatics from a cracked hydrocarbon stream, extracts aromatics from a naphtha reformate and processes the aromatics to form selected aromatic product streams. Aromatics extracted from the cracked hydrocarbon stream do not pass through a naphtha reforming unit and avoid dealkylation therein.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the claimed subject matter in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment or embodiments. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope set forth in the appended claims.
