AU2007345527B2

AU2007345527B2 - Method and system for recovering aromatics from a naphtha feedstock

Info

Publication number: AU2007345527B2
Application number: AU2007345527A
Authority: AU
Inventors: William George Rhodey
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-02-02
Filing date: 2007-02-02
Publication date: 2012-04-19
Anticipated expiration: 2027-02-02
Also published as: GB2460968A; GB0914144D0; CA2674212C; GB2460968B; CA2674212A1; WO2008092232A1; AU2007345527A1

Abstract

The present invention relates to a method and system for recovering aromatics from a naphtha feedstock obtained from a crude petroleum, natural gas condensate, or petrochemical feedstock. The method and system comprise the steps of recovering an aromatics fraction from the feedstock prior to reforming.

Description

WO 2008/092232 PCT/CA2007/000147 PROCESS AND SYSTEM FOR EXTRACTION OF A FEEDSTOCK FIELD The present invention relates to a process and system for extraction of chemical components from a 5 feedstock, such as a petroleum, natural gas condensate, or petrochemical feedstock. BACKGROUND In a conventional petroleum or petrochemical refinery process and system, crude feedstock is processed by 10 a crude distillation unit. The crude feedstock may comprise crude oil and/or feedstock having undergone partial processing ("intermediate refinery feedstock"). The crude distillation unit produces a naphtha fraction, together with a number of other fractions useful in production of refined 15 oil products, for example, gasoline, jet fuel, diesel, etc., and fractions useful for the production of specialty chemicals. The naphtha fraction is primarily composed of paraffins, olefins, naphthenes and aromatics. Paraffins are 20 alkane hydrocarbons of general formula CnH 2 n+ 2 , which may be substituted, and wherein n is a whole number; e.g., from 1 14. The term "paraffins" is also generally understood to include isoparaffins. Olefins are hydrocarbons having at least one carbon-carbon double bond, such as an alkenes of 25 general formula CnH 2 n, which may be substituted and wherein n is a whole number; e.g., from 2-14. The olefin fraction may also comprise alkynes of general formula CH 2 n- 2 , which may be substituted and wherein n is a whole number; e.g., from 2 14. When n is greater than 12, the fraction may be referred 30 to as distillates; e.g., jet fuel, diesel, etc. Higher n fractions may be useful for other purposes. Olefins WO 2008/092232 PCT/CA2007/000147 (including substituted olefins) where n=12-14 may be found in both the naphtha fraction and the distillates fraction. The naphthenes include cycloalkanes and alkyl substituted cycloalkanes. Many naphthenes are chemical precursors to 5 the aromatics. The aromatics found in a petroleum or petrochemical feedstock include a range of conjugated hydrocarbon rings and alkyl substituted conjugated hydrocarbon rings. Hydrocarbon fractions are often referred to as C, 10 fractions or C,* fractions with n being a whole number. It is to be understood that C,* includes the nth fraction (i.e., the Cn fraction) as well as higher n fractions. The whole range naphtha fraction from the crude distillation unit is processed in a naphtha splitter 15 producing an overhead stream (typically referred to as a Light Straight Run or LSR), and a bottoms stream of heavy naphtha. The LSR is rich in paraffins, and the heavy naphtha is rich in naphthenes and aromatics. The heavy naphtha bottoms stream is hydrotreated to remove sulphur and 20 other contaminants, obtaining a sweet naphtha, which is fed to a naphtha reformer where it may be combined with other intermediate sweet naphtha streams, for example, sweet natural gas condensates and hydrocracker naphtha. In the naphtha reformer, the naphtha components are reformulated 25 into components of a gasoline product. The naphtha reformer is usually a high severity reformer, which produces aromatics, including benzene, toluene and xylenes ("BTX"), as well as other aromatics that enable the reformate to have an octane quality sufficient to 30 meet gasoline octane specifications. Benzene, toluene and xylenes may all also be used in the production of 2 WO 2008/092232 PCT/CA2007/000147 petrochemical derivatives. Of the xylenes that may be used in the production of petrochemical derivatives, para- and ortho-xylene are worth particular mention, although meta xylenes may also be of value. 5 High severity reformers are run at high temperatures (e.g., inlet temperatures of about 900 degrees Fahrenheit - around 480 degrees Celsius - or greater) with commercially available catalyst, and have long residence times. The residence time is a factor of the number of 10 reactors and the amount of catalyst involved. High severity reformers typically involve four or five reactors in series. Also, at each reactor, heating to the noted inlet temperature is required in order to produce the desired gasoline products. High severity reformers are associated 15 with high operating costs and may result in a significant volume loss across reactors of high economic value gasoline components. Gasoline is a blend of LSR and reformate and other gasoline components obtained from the crude, such as butane, 20 alkylate, isopentane, methyl tertiary butyl ether, ethanol and catalytic cracker gasoline. The proper boiling point, octane number, and other gasoline specifications are met by the blend of the LSR, reformate and other gasoline components. 25 The benzene content of gasoline has been regulated to a low value in many nations including Canada and the United States. Refiners have chosen four methods to reduce benzene in the gasoline product in order to produce a gasoline having an octane quality sufficient to meet 30 gasoline octane specifications. Refiners have: (1) removed benzene precursors before the naphtha reformer to preclude 3 WO 2008/092232 PCT/CA2007/000147 or reduce benzene production in the reformer; (2) hydrotreated or saturated the benzene fraction of the reformate to convert the benzene to non-aromatics; (3) developed new reformer catalysts that selectively do not 5 react with the benzene precursors; and (4) removed benzene from the reformate or a fraction thereof by aromatics extraction. With the exception of the aromatics extraction method, each of these methods reduce the net amount of benzene available for benzene derivative production thereby 10 increasingly moving the industry to more expensive methods to produce benzene. Aromatics extraction is most commonly performed by solvent or extractive distillation. C 6 to C 8 aromatics are fractionated in a fractionation tower, usually into benzene 15 and a toluene/xylenes mixture. The raffinate stream obtained after extraction of these aromatics can be blended into gasoline. Additional benzene could be produced from the toluene and xylenes recovered by fractionation using hydrodealkylation and/or toluene disproportioning processes. 20 Producing benzene from these two processes introduces additional capital cost and volume loss of expensive feedstock. The term "raffinate" is used throughout this application. It will be understood by the skilled reader 25 that the composition of the raffinate will depend on the specific extraction process, and feedstock. Alternative sources of benzene, such as pyrolysis gasoline ("pygas"), catcracker gasoline, and Coker naphtha are also available, but obtaining benzene from these sources 30 involve high operating costs. Also, these sources, although 4 significant in volume, are not sufficient to satisfy the world benzene market. Another high cost process for producing benzene is the UOP/BP Cyclar process that uses propane and butane to make 5 benzene and other aromatics. There is a world scale unit at a British Petroleum (BP) refinery in the United Kingdom. This process has the limitation of not producing a significant portion of the aromatics as benzene, thus not adequately satisfying the world benzene market. A lower cost method to produce benzene directly in the refinery process would be beneficial. A process and system for extraction of chemical components from a feedstock, such as petroleum, natural gas condensate or petrochemical feedstock, that maximizes high 5 economic value streams at high volumetric yields would also be of benefit. Attempts have been made to modify the conventional refinery process, such as by fractionating feedstock and using different reformers on each fraction, see, for example, US D 6,051,128. SUMMARY According to one aspect of the present invention, there is provided a method of recovering aromatics comprising the steps of: 5 (a) providing a C 6 to C 11 hydrocarbon fraction; (b) recovering from the C 6 to C 11 hydrocarbon fraction an aromatics fraction, an aromatics precursors fraction and a raffinate fraction in an aromatics extraction unit; 0 (c) converting aromatics precursors in the aromatics precursors fraction to aromatics; and 5 3186838_1 (GHMatters) P81452.AU (d) recovering aromatics from step (c) in an aromatics extraction unit; wherein the C6 to C 11 hydrocarbon fraction provided 5 in step (a) is subjected to step (b) without having been subjected to a reforming or a dehydrogenation process. According to another aspect of the present invention, there is provided a method for producing a ) hydrogen-rich, carbon dioxide free, gas, the method comprising carrying out the method as defined in the above aspect, and recovering a gas phase produced in step (c). According to another aspect of the present 5 invention, there is provided a system for recovering aromatics from a naphtha feedstock, comprising: (a) a naphtha splitter for separating a C6* fraction from the naphtha feedstock; (b) a hydrotreater unit or a distillation unit for D separating a C 6 to C 11 hydrocarbon fraction from the C,* fraction; (c) an aromatics extraction unit for recovering from the C 6 to C 1 hydrocarbon fraction an aromatics fraction, an aromatics precursors fraction and a raffinate fraction; 5 (d) a dehydrogenation unit or a reformer for converting the aromatics precursors in the aromatics precursors fraction to aromatics; and (e) optionally a desulphurizing unit for removing sulfur from the naphtha feedstock prior to the separating of 0 the C 6 * fraction; wherein the hydrotreater unit or distillation unit for separating the C 6 to C 11 hydrocarbon fraction from the C 6 ' fraction, and the aromatic extraction unit, are operatively connected such that the C 6 to C 1 1 hydrocarbon fraction is not 5 subjected to a reformer or a dehydrogenation unit prior to the 5a 31O8638 1 (GHMalttrs) PS1452AU recovery of the aromatics fraction, the aromatics precursors fraction and the raffinate fraction. According to another aspect of the present invention there is provided a system for producing a hydrogen-rich, carbon dioxide free, gas, comprising a system as defined in the above aspect together with means for recovering a gas phase produced by the dehydrogenation unit or the low-severity reformer. ) According to another aspect of the present invention, there is provided a method of recovering aromatics from a naphtha feedstock comprising the steps of: (a) separating from the naphtha feedstock a C6 to C11 hydrocarbon fraction; (b) recovering from the C6 to C11 hydrocarbon fraction an aromatics fraction, an aromatics precursors fraction, and a raffinate fraction in an aromatics extraction unit; (c) converting aromatics precursors in the aromatics precursors fraction to aromatics; and (d) recovering aromatics from 5b I1AA'AA I MCHMtterI PRI4A AlJ WO 2008/092232 PCT/CA2007/000147 step (c) in the aromatics extraction unit. In one embodiment, the method further comprises recycling from step (d) any unreacted aromatics precursors back to step (c). According to another aspect of the present 5 invention, there is provided a method of recovering aromatics from a whole range naphtha feedstock comprising the steps of: (a) subjecting the whole range naphtha feedstock to a desulphurizing process; (b) separating from the desulphurized whole range naphtha feedstock obtained in 10 step (a) a C6 to C 11 hydrocarbon fraction; (c) recovering from the C6 to C 1 u hydrocarbon fraction an aromatics fraction, an aromatics precursors fraction and a raffinate fraction in an aromatics extraction unit; (d) converting aromatics precursors in the aromatics precursors fraction to 15 aromatics; and (e) recovering aromatics from step (d) in the aromatics extraction unit. In one embodiment, a dehydrogenation unit is used in step (d), and in another embodiment, a low severity reformer is used. The method may further comprise recycling from step (e) any unreacted 20 aromatics precursors to step (d). According to another aspect of the present invention, there is provided a method of recovering aromatics from a naphtha feedstock comprising the steps of: (a) separating from the naphtha feedstock a C6 to C 1 25 hydrocarbon fraction; (b) recovering from the C 6 to C 11 hydrocarbon fraction an aromatics fraction, an aromatics precursors fraction and a raffinate fraction in an aromatics extraction unit; (c) converting aromatics precursors in the aromatics precursors fraction to aromatics in a 30 dehydrogenation unit; and (d) recovering aromatics from step (c) in the aromatics extraction unit. In one embodiment, 6 WO 2008/092232 PCT/CA2007/000147 the method further comprises recycling from step (d) any unreacted aromatics precursors to step (c). According to yet another aspect of the present invention, there is provided a system for recovering 5 aromatics from crude feedstock, comprising: (a) separating from the crude feedstock in a crude distillation unit a whole range naphtha fraction; (b) subjecting the whole range naphtha feedstock to a desulphurizing process; (c) separating a C6* fraction from the desulphurized whole range 10 naphtha fraction obtained from step (b) in a naphtha splitter; (d) separating a C6 to C 11 hydrocarbon fraction from the C6* fraction; (e) recovering from the C6 to C 11 hydrocarbon fraction an aromatics fraction, an aromatics precursors fraction and a raffinate fraction in an aromatics 15 extraction unit; (f) converting aromatics precursors in the aromatics precursors fraction to aromatics; (g) recovering aromatics from step (f) in the aromatics extraction unit; and (h) optionally recycling from step (g) any unreacted aromatics precursors to step (f). In one embodiment, a 20 dehydrogenation unit is used in step (f), and in another embodiment, a low severity reformer is used. According to a further aspect of the present invention, there is provided a system for recovering aromatics from crude feedstock, comprising: (a) separating 25 from the crude feedstock in a crude distillation unit a whole range naphtha fraction; (b) separating a CG* fraction from the whole range naphtha fraction obtained from step (b) in a naphtha splitter; (c) separating a C 6 to C 1 u hydrocarbon fraction from the C6* fraction; (d) recovering from the C 6 to 30 C 11 hydrocarbon fraction an aromatics fraction, an aromatics precursors fraction and a raffinate fraction in an aromatics extraction unit; (e) converting aromatics precursors in the 7 WO 2008/092232 PCT/CA2007/000147 aromatics precursors fraction to aromatics in a dehydrogenation unit; (f) recovering aromatics from step (e) in the aromatics extraction unit; and (g) optionally recovering from step (f) any unreacted aromatics precursors 5 from step (e) and returning the unreacted aromatics precursors to the dehydrogenation unit for conversion to aromatics. According to a yet further embodiment of the invention, there is provided a method of recovering 10 aromatics from a naphtha feedstock comprising the steps of: (a) separating from the naphtha feedstock a C 6 to C 11 hydrocarbon fraction; (b) recovering from the C 6 to C 11 hydrocarbon fraction an aromatics fraction, a C 6 to C 11 aromatics precursors fraction and a raffinate fraction in an 15 aromatics extraction unit; (c) reforming the whole range of

C

6 to C 1 aromatics precursors in the aromatics precursors fraction in a conventional reformer; and (d) recovering aromatics from step (c) in the aromatics extraction unit. BRIEF DESCRIPTION OF THE DRAWINGS 20 Figure 1 illustrates a conventional refinery system for a crude feedstock. Figure 2 illustrates a refinery system according to an embodiment of the present invention. Figure 3 illustrates a refinery system according to another 25 embodiment of the present invention. DETAILED DESCRIPTION A function of a reformer is to reformulate molecules from non-aromatics (e.g., paraffins, including isoparaffins, and naphthenes) to aromatics such that 8 WO 2008/092232 PCT/CA2007/000147 gasoline octane quality specifications can be achieved. Typically, a reformer has four or five reactors in series with heaters between reactors to heat the effluent from each reactor to the reactor inlet temperature of the next 5 reactor. The predominant reactions in the reformer are endothermic requiring this inter stage heating. Typical catalysts for use in catalytic reformers are platinum and rhenium incorporated in a catalyst support medium, each metal and support medium playing a dominant part in 10 promoting different reactions to occur. Reactions that occur in the reformer include: (1) isomerization of paraffins to isoparaffins; (2) hydrocracking and demethylation of paraffins (including isoparaffins); (3) dehydrocyclization of paraffins 15 (including isoparaffins) to five membered rings; (4) isomerization of five membered rings to six membered rings; (5) dehydrogenation of six membered rings to aromatics; and (6) dealkylation, including demethylation, of aromatics. The reactions may also be described as converting naphthenes 20 to aromatics, and converting paraffins (including isoparaffins) to either cyclic members (e.g., naphthenes and aromatics) or to smaller paraffinic members. The reformate produced comprises aromatics including benzene, toluene and xylenes ("BTX") in various 25 concentrations, as well as other aromatics, depending on the naphtha feed composition, typically measured as the Naphthenes + Aromatics (N+A) percent. Hydrogen gas is produced as a by-product of aromatics production in the dehydrocyclization and dehydrogenation reactions, for 30 example. Hydrogen is consumed by hydrocracking and dealkylation (including demethylation) reactions. 9 WO 2008/092232 PCT/CA2007/000147 In the reformer, naphthenes react very quickly and efficiently (high conversion) while paraffins react slowly and with poorer yields of aromatics and also producing light components of Ci-C 4 molecules. The naphthenic reactions, 5 although resulting in conversion to higher density products, do not exhibit the high volume loss typical of paraffinic reactions. Temperature and residence time in the reactors are two parameters that determine the severity of the reactions. 10 These parameters may be controlled to produce the highest yield of aromatics. As indicated above, a conventional reformer normally comprises four or five reactors in series to attain the highest yield of aromatics in a typical operation. Most of the naphthenes are converted to 15 aromatics in the first two reactors, while the paraffinic reactions mainly occur in the last two or three reactors. Figure 1 illustrates a conventional refinery process. Crude feedstock (10) is processed in a crude distillation unit (20). The whole range naphtha stream 20 obtained (30) is processed in a naphtha splitter (40) to separate the LSR (50) from the heavy naphtha (60), which is further processed in a hydrotreater (70) to remove sulphur, and other components, such as nitrogen. The sweet naphtha stream produced (80), along with any other intermediate 25 refinery sweet naphtha feed streams (90) that may be added, are treated in high severity naphtha reformer (100) to obtain a reformate (110). A C 6 to Ce reformate stream (120) can also be recovered and further processed in an aromatics extraction unit (130). Aromatics (140) may be further 30 fractionated in a selective fractionation unit (150), usually into a benzene (160) fraction, and a toluene/xylenes 10 WO 2008/092232 PCT/CA2007/000147 mixture (170). The raffinate stream (180) obtained following aromatics extraction can be blended into gasoline. As described above, high severity naphtha reformers used in conventional practice involve high 5 temperatures and long residence times to obtain BTX and other aromatics meeting the gasoline octane specification. High severity reforming results in a significant volume loss across the reactors of the naphtha reformer and may crack some benzene precursors to lower value products. Also, and 10 as described above, the effluent from each reactor stage needs to be reheated for the next stage to produce sufficient aromatics. Reforming the aromatics achieves no benefit, as the aromatics are the desired product, and increases capital and operating costs, in part because of 15 the volume of material being heated at each stage. In the present invention, naturally occurring aromatics are recovered from a naphtha stream following processing in a naphtha splitter and prior to naphtha reforming. C 6 to Cn 1 aromatics and aromatic precursors may 20 be recovered as concentrated streams. Benzene and/or other aromatics, including toluene and xylenes, may then be recovered directly without reforming. Benzene precursors and/or other aromatics precursors may then be sent to a unit that converts aromatics precursors to aromatics, such as a 25 commercially available dehydrogenation unit, or a conventional or low severity reformer for conversion into benzene and/or other aromatics. A low severity reformer targets the naphthenic reactions. Compared to a high severity reformer, a low 30 severity reformer is operated at shorter residence times and lower temperatures. A low severity reformer may comprise 11 WO 2008/092232 PCT/CA2007/000147 only one or two reactors compared to the four or five of a conventional naphtha reformer. Also, each reactor of the low severity reformer may be operated at an inlet temperature of about 800 degrees Fahrenheit (about 425 5 degrees Celsius) or greater. The temperature of the low severity reformer will depend, in part, on the choice of catalyst and catalyst support, as would be understood by a person skilled in the art. The lower temperature and shorter residence time of a low severity reformer may reduce 10 the paraffinic reactions that may occur in a high severity reformer. The catalyst used in the low severity reformer may be selected to target the naphthenic reactions as opposed to the paraffinic reactions. Suitable catalysts or catalyst 15 systems would be known to the person skilled in the art, and include, for example, commercially available platinum and/or rhenium catalysts on a zeolite support. The pressure of the low severity reformer may also be selected to optimize aromatics production, usually 200 20 pounds per square inch gauge (PSIG) or lower. If more than one reactor is used in the low severity reformer, the reactors may be in series or parallel. Using reactors in series may further promote paraffinic reactions. To further reduce the possibility of 25 paraffinic reactions, the reactors may therefore be used in parallel. Figures 2 and 3 illustrate embodiments of the present invention. A crude feedstock (200) is treated in a crude distillation unit (210) to obtain a whole range 30 naphtha stream (220). The whole range naphtha stream (220) is further processed in a naphtha splitter (230). 12 WO 2008/092232 PCT/CA2007/000147 According to the embodiment of the invention shown in Figure 2, the whole range naphtha stream (220) is subjected to a preliminary desulphurizing (225). This initial desulphurizing step may be, for example, a 5 conventional caustic treating addition or the Minalk TM process to remove mercaptans from the light naphtha. The sweetened LSR could then be recovered as overheads (240) from the naphtha splitter (230) to be routed to gasoline blending, for example. 10 In the naphtha splitter (230), a LSR fraction comprising C 1 to CG hydrocarbons (240) may be separated from a heavy naphtha fraction comprising C6* hydrocarbons (250) The C1 to C6 fraction comprises mainly linear or branched hydrocarbons. This fraction may be further processed in, 15 for example, a debutanizer (not shown) to optionally recover: fuel gas, which may be used, for example, to fuel the process of the invention; butane; and a fraction comprising C 5 and C6 hydrocarbons that may be routed to the gasoline pool. Naphthenes and aromatics are concentrated in 20 the heavy C6* fraction. According to an invention embodiment, the naphtha splitter (230) may comprise a commercially available deisohexanizer or a commercially available demethylcyclopentanizer, or a tower designed for both services, which may be used to recover 25 methylcyclopentane (MCP). Use of the demethylcyclopentanizer recovers MCP, as part of the overheads, that may be routed to the gasoline pool, and the deisohexanizer may be used to route the MCP, as part of the bottoms, and ultimately to the low severity reformer or 30 other unit for converting aromatics precursors to aromatics. The CG* fraction (250) can be separated in a hydrotreater unit (260) into a C6 to C11 fraction (270) and a 13 WO 2008/092232 PCT/CA2007/000147 C12+ fraction (280) and sour fuel gas (not shown). The hydrotreater unit (260) is used to remove sulphur (i.e., hydrodesulfurization), and possibly nitrogen (i.e., hydrodenitrogenation), and may comprise a stabilizer plus a 5 fractionation tower or the stabilizer may be a combination stabilizer/fractionation unit. There are a number of commercially available hydrotreating units that may be used in this step. The hydrotreater unit (260) may also convert any olefins to paraffins, and the C 6 to C8 paraffins may then 10 be recovered (not shown) and, for example, used as feedstock for a steam cracker. The CrystaSulf TM process of CrystaTech or a known sour gas treatment process may also be used to remove sulphur from the sour fuel gas stream, which may then be used, for example, as fuel. The C12* fraction (280) 15 recovered may be used in the production of distillate, diesel or jet fuel, for example. According to the invention embodiment shown in Figure 2, having an initial desulphurizing step (225) may optimize the hydrotreater unit (260), such as by allowing a smaller unit, resulting in a 20 potential cost savings. In another invention embodiment, not shown in the Figures, the intial desulphurizing step is the only desulphurizing step employed in the process of the invention. In this embodiment the whole range naphtha (220) 25 is subjected to a desulphurizing step (225) (e.g., hydrotreating) before routing to the naphtha splitter (230). The sweetened LSR is then recovered, and the heavy naphtha then fractionated (e.g., by distillation) into a C 6 to C 11 fraction (270), which is then further treated in the manner 30 described herein. The C6 to C 11 fraction (270) may be subjected to aromatics extraction in an aromatics extraction unit (290). 14 The composition of C 6 's in the C 6 to C 11 fraction (270) will depend in part on whether or not the naphtha splitter (230) comprises a deisohexanizer or a demethylcyclopentanizer. If it does not include either unit (or any other fractionation 5 unit), the whole range of C 6 hydrocarbons will be present in the C 6 to C 11 fraction (270). If a deisohexanizer is used, the

C

6 's include benzene, cylcohexane and MCP in the C 6 to C 1 1 fraction (270), and if a demethycyclopentanizer is used, the

C

6 1 s include benzene and cyclohexane in the C 6 to C 11 fraction D (270). Any aromatics extraction unit (290) could be used, including, for example, an aromatics extractive distillation unit commercially available from GTC Technology, such as the GTC GT-BTX"' unit. The aromatics extraction unit (290) is used 5 to produce a stream of C 6 to C 1 1 aromatics (300), and a raffinate comprising C 6 to C 11 paraffins, isoparaffins, and naphthenes. The aromatics fraction (300) may be routed to a selective distillation unit (330) to selectively recover ) aromatics (340, 350, 360). For example, benzene could be selectively recovered in a benzene distillation unit; or, in another embodiment, a xylenes distillation unit could be used to recover a benzene fraction, a toluene fraction, and a xylenes fraction. The fraction (370) comprising any aromatics 5 remaining after selective distillation could be routed to the gasoline pool, for example. Where solvent is added in the aromatics extraction process, the aromatics fraction (300) recovered may first be routed to a solvent stripper (not shown) to recover the 0 solvent before the aromatics fraction is further 15 3188838 1 (GHMatters) P81452.AU WO 2008/092232 PCT/CA2007/000147 fractionated. Solvent recovered may be recycled to the aromatics extraction unit (290). According to another embodiment of the invention, benzene and xylenes are selectively concentrated prior to 5 aromatics extraction. A stream of C 6 's as overheads and C 8 ss as bottoms could be obtained, and these fractions could be combined and routed to the aromatics extraction unit to recover benzene and xylenes. The mid-stream C 7 1 s could then be combined with the raffinate from the aromatics extraction 10 unit. In the aromatics extraction process, aromatics precursors (320) are concentrated and separated from the remaining components of the raffinate, which remainder (310) may be routed to a gasoline pool for use in making gasoline, 15 and/or which may be further treated to remove C 6 to C 8 paraffins. The C 6 to C 8 paraffins may be used, for example, as feedstock for a steam cracker. Aromatic precursors may be routed to a low severity reformer (380), or a dehydrogenation or other unit, 20 as discussed above, which has the function of converting aromatics precursors to aromatics. The reformate/conversion product (390) comprising aromatics and any unreacted aromatic precursors may then be routed to the aromatics extraction unit (290) for further processing. 25 The aromatics precursors (320) recovered from the aromatics extraction unit (290) may also be concentrated into selected fractions (not shown). In this manner, selected fractions could be routed to the low severity reformer (or other unit for converting aromatics precursors 30 to aromatics), with non-selected precursors forming part of the raffinate (310), which could be sent to, for example, a 16 WO 2008/092232 PCT/CA2007/000147 conventional reformer. Also, the aromatics precursors fraction will normally include other hydrocarbons in addition to aromatics precursors, such as paraffins, which could also be selectively recovered. In an exemplary 5 embodiment, normal paraffins are recovered, and, for instance, routed to a steam cracker, or routed to distillate blending. In one embodiment it is C 6 to C 8 normal paraffins that are so recovered. CG and C 7 hydrocarbons have a boiling point of up 10 to about 220 degrees Fahrenheit (about 104 degrees Celsius).

C

8 hydrocarbons have a boiling range of about 220 to about 265 degrees Fahrenheit (about 104 to about 129 degrees Celsius). The C 9 to C 11 hydrocarbons have a boiling point of about 265 degrees Fahrenheit (about 129 degrees Celsius) or 15 greater. These fractions may therefore be separated by distillation, and then further separated into their paraffinic and naphthenic components by way of a further distillation. For instance, a C 6 fraction could be separated 20 using a commercially available fractionation unit (e.g., a dehexanizer) into a hexanes feedstock for use in, for instance, a steam cracker, and a fraction high in CG naphthenes for treatment in the low severity reformer (or other unit). Similarly, C 7 and Ca fractions could be 25 separated in commercially available fractionation units (e.g., a deheptanizer and deoctanizer, respectively) into heptane and C 7 naphthenes and into octane and C 8 naphthenes, respectively. The heptanes and octanes may be sent to a steam cracker, for example, and the C 7 and Ca naphthenes may 30 then be sent to the low severity reformer (or other unit). In another invention embodiment, instead of using a distillation process, a molecular sieve or sorbent may be 17 WO 2008/092232 PCT/CA2007/000147 used. Examples include adsorbents available from UOP, and, UOP's SorbexT or MaxEne processes. These processes utilize molecular adsorptive solvents or solids to selectively remove paraffins from hydrocarbons thereby separating into a 5 paraffin and non-paraffin stream (for example, naphthenes). By using a distillation or other separation process, C 6 to C 8 naphthenes may be selectively routed to the low severity reformer (380), or another unit for converting aromatics precursors to aromatics. By using a distillation or other 10 separation process, the concentration of aromatic precursors in stream (320) may be increased to, for example, about 75 80% v/v with the remaining components being mainly isoparaffins. It may be necessary for the aromatics precursors 15 stream (320) to be run through a sulphur guard bed (not shown) to remove traces of sulphur before reforming in the low severity reformer (380), or before treatment in another unit for converting aromatics precursors to aromatics. The precursor stream (320) may also be recycled (not shown) to 20 the hydrotreater unit (260) to remove sulphur and/or nitrogen and/or saturate olefins. The low severity reformer (or other unit) can be monitored for increasing concentrations of non-aromatics precursors. If increasing, a stream of the non-aromatics 25 precursors (not shown) could be separated from the aromatics precursors stream routed to the low severity reformer (or other unit). The non-aromatics precursors stream may then be, for instance, routed to the gasoline pool, used as feedstock for a steam cracker, or subjected to another 30 distillation or extraction process to remove paraffins and isoparaffins for the gasoline pool or as a feedstock for a steam cracker, etc. 18 WO 2008/092232 PCT/CA2007/000147 The reformate/conversion product (390) may be routed to the aromatics extraction unit (290) for extraction of aromatics. Any unreacted aromatic precursors (320) could be returned for further processing to the low severity 5 reformer (380) or other unit used for converting aromatics precursors to aromatics. High naphthenic concentrations may therefore be maintained in the low severity reformer or other unit. Also, by concentrating the feedstock in naphthenic content in this manner, the possibility of 10 paraffinic reactions may further be reduced. One or more additional feed streams (400) may optionally be added as supplemental feed to the naphtha splitter (230), and/or one or more additional feed streams (410, 420) may also be added and directed to the aromatics 15 extraction unit as a combined stream (430) with the C6 to C 1 fraction (270) and/or the reformate/conversion product (390). If the additional feed (410, 420) is first mixed with the reformate/conversion product (390), the mixed stream may optionally be split to concentrate selected 20 aromatics and/or aromatics precursors. By splitting the stream a stream concentrated in single double bond olefins and aromatics suitable for gasoline blending may also be obtained. The one or more additional feed streams (400, 410, 25 420) may be chosen from feedstocks having a high C 4 to C 8 content, with the majority of components in the C 5 to C 6 ranges. For example, streams with a high proportion of benzene precursors, such as methylcyclopentane and cyclohexanes, and toluene and xylenes precursors; feed 30 streams of olefinic material having high concentrations of aromatics and aromatic precursors; and feed streams having a high proportion of aromatics may be chosen. A stream low in 19 WO 2008/092232 PCT/CA2007/000147 sulphur, nitrogen and olefins may be routed directly to the naphtha splitter (230) or aromatics extraction unit (290); otherwise, the stream may first be subjected to, for example, a hydrotreating step, solvent extraction, caustic 5 soda treatment, etc. This initial step of concentrating the feedstock (400, 410, 420) may also increase the volume of aromatics produced. The one or more additional feed streams (400, 410, 420) may, for example, comprise one or more of a condensate 10 (e.g., a non-refinery intermediate stream) comprising aromatics and/or aromatic precursors; natural gasoline comprising aromatics and/or aromatic precursors; and a refinery reformate low in sulphur components but comprising aromatics and/or aromatic precursors. An example of an 15 additional feed is pygas. The pygas may be subjected to an initial liquid phase hydrogenation prior to aromatics extraction, to remove sulfur and to saturate any olefins containing two or more double bonds or triple bonds to single double bond olefins. A fraction that is concentrated 20 in single double bond olefins can then be recovered by, for example, distillation and sent to the gasoline pool, for example. A C 6 to C 8 aromatics fraction can also be obtained by, for example, distillation, and which fraction may then be routed to the aromatics extraction unit (290). Other 25 additional feedstreams would be known to a person skilled in the art. The skilled person will understand that where reference is made to, for example, a feedstream "low" in sulfur or other components, the concentration of the 30 components in the feedstream is sufficiently low to meet product specifications. 20 WO 2008/092232 PCT/CA2007/000147 Benzene, toluene and xylenes precursors may be simultaneously processed in the low severity reformer (380), or other unit for converting aromatics precursors to aromatics. BTX may then be recovered in the aromatics 5 extraction unit (290), or benzene, toluene and xylenes selectively recovered in a selective distillation unit (330), as described above. The process of the invention may also be optimized to selectively produce benzene, toluene or xylenes, or a 10 combination thereof, such as by optimizing severity of the low severity reformer and/or by optimizing feedstock variables of the low severity reformer or other unit for converting aromatics precursors to aromatics. For instance, the feedstock may be varied by selectively concentrating 15 benzene, toluene and/or xylenes precursors from the aromatics extraction unit by distillation or another extraction process using, for example, a molecular sieve or sorbant, as discussed above. Also, the constitution of the feedstock may be altered by adding condensate or other 20 refinery or petrochemical streams high in benzene, toluene and/or xylenes to the aromatics extraction unit, also as discussed above. The hydrogen produced (not shown) as a by-product of the reforming step may be recovered and used for the 25 hydrotreatment step, and/or may be recovered as a high economic value stream, such as hydrogen by using a known hydrogen purification process. The sulphur obtained from the various desulphurizing steps described herein may be collected and 30 may be combined. Sulphur obtained may be useful for the production of agricultural products, for example. 21 WO 2008/092232 PCT/CA2007/000147 Also, the skilled person will appreciate that other hydrocarbon streams may be selectively recovered at different stages of the process described above, including, for example, liquified petroleum gas (LPG), jet fuel, 5 diesel, vacuum gas oil (VGO), and other product streams not specifically mentioned above using methods known to one skilled in the art. Product streams may be subjected to further processing as would be apparent to the skilled person. 10 A low severity reformer for use in the present invention may be obtained using known reformer technology with reactors and operating parameters adjusted as described above as would be understood by a person skilled in the art. The process of the invention does not have to be 15 practiced in a refinery setting. It may be practiced as a "stand alone" process to produce aromatics such as benzene, xylenes and/or toluene, and/or to concentrate aromatics precursors of, for example, benzene, toluene and/or xylenes. The stand alone process may then be used to feed an existing 20 refinery. The naphtha splitter, hydrotreater unit, aromatics extraction unit, and low severity reformer or other unit for converting aromatics precursors to aromatics could constitute an "off site" plant. In a conventional refinery configuration, the 25 volume loss across a high severity reformer processing heavy naphtha is about 20 to 35% calculated based on N+2A (i.e., the concentration of Naphthenes plus twice the concentration of Aromatics in the feedstock). Volume losses by using a process of the present invention across the low severity 30 reformer are projected to be about 10%. The overall volume loss of about 5% is therefore expected to be lower than 22 WO 2008/092232 PCT/CA2007/000147 typical losses of the order of 15% to 25% using conventional process technology. By using a process according to the present invention a hydrogen production surplus may also be obtained 5 that is greater than in a conventional refinery scheme. In a conventional reformer the hydrogen stream volumetric yield is about 0.8 to 1.0 moles per mole of naphtha feed, and depends on the N+2A quality of the feedstock. By using a low severity reformer according to the present invention 2.5 10 to 3.5 moles hydrogen per mole of naphtha feed may be obtained, depending on the quality of the feedstock. Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it is readily 15 apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims. The citation of any publication, patent or patent 20 application is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication, patent or patent application by virtue of prior invention. It must be noted that as used in the specification 25 and the appended claims, the singular forms of "a", "and" "the" include plural reference unless the context clearly indicates otherwise. Unless defined otherwise all technical and scientific terms used herein have the same meaning as 23 commonly understood to one of ordinary skill and the art to which this invention belongs. In the claims which follow and in the preceding description of the invention, except where the context requires 5 otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments 10 of the invention. It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any 15 other country. 24 3186638_1 (GHMatters) P81452.AU

Claims

1. A method of recovering aromatics comprising the steps of: 5 (a) providing a C 6 to C 1 1 hydrocarbon fraction; (b) recovering from the C 6 to C 11 hydrocarbon fraction an aromatics fraction, an aromatics precursors fraction and a raffinate fraction in an aromatics extraction unit; (c) converting aromatics precursors in the aromatics 10 precursors fraction to aromatics; and (d) recovering aromatics from step (c) in an aromatics extraction unit; wherein the C 6 to C 11 hydrocarbon fraction provided in step (a) is subjected to step (b) without having been subjected 15 to a reforming or a dehydrogenation process.

2. The method according to claim 1, wherein the C 6 to C 11 hydrocarbon fraction is obtained by separation from a naphtha feedstock. 20

3. The method according to claim 1, wherein the C 6 to C 1 hydrocarbon fraction is obtained by separation from a C6* fraction of a naphtha feedstock. 25

4. The method according to claim 2 or 3, wherein the naphtha feedstock is a whole range naphtha feedstock.

5. The method according to claim 4, wherein the whole range naphtha feedstock is obtained by crude distillation of a 30 crude feedstock. 25

6. The method according to any one of claims 2 to 5, wherein the naphtha feedstock is a combined feedstock from crude oil and an additional feedstock from another source comprising aromatics, aromatics precursors, or a combination 5 thereof.

7. The method according to any one of claims 1 to 6, wherein the C 6 to C 11 hydrocarbon fraction is separated from the naphtha feedstock by distillation. 10

8. The method according to any one of claims 1 to 6, wherein the C 6 to C 11 hydrocarbon fraction is separated from the naphtha feedstock using a hydrotreater unit. 15

9. The method according to any one of claims 1 to 7, wherein the naphtha feedstock is desulphurized prior to separation of the C 6 to C 11 hydrocarbon fraction.

10. The method according to any one of claims 1 to 7, 20 wherein the C 6 to C 11 hydrocarbon fraction is desulphurized prior to step (b)

11. The method according to claim 9 or 10, wherein the desulphurizing process is the Minalk process, a caustic 25 treating addition, a hydrotreating process, or a combination thereof.

12. The method according to any one of claims 1 to 11, wherein a deisohexanizer or a demethylcyclopentanizer is also 30 used to obtain the C 6 to C 11 hydrocarbon fraction. 26

13. The method according to any one of claims 1 to 12 further comprising recovering from step (d) any unreacted aromatics precursors and returning them to step (c) for conversion to aromatics. 5

14. The method according to any one of claims 1 to 13, wherein benzene, toluene, xylenes, or a combination thereof, are recovered, and the aromatics precursors fraction comprises C 6 to C 8 naphthenes and paraf fins. 10

15. The method according to claim 14, wherein the aromatics precursors fraction is further fractionated by fractional distillation to selectively concentrate C6, C 7 , or C9 naphthenes, or a combination thereof, in the aromatics 15 precursors fraction, with C 6 , C 7 or C8 normal paraffins, or a combination thereof, being separately selectively recovered.

16. The method according to claim 14, wherein the aromatics precursors fraction is further fractionated by using 20 an extraction process comprising a molecular sieve or a sorbent to selectively concentrate C 6 , C 7 , or C 8 naphthenes, or a combination thereof, in the aromatics precursors fraction, with C 6 , C, or C 8 normal paraffins, or a combination thereof, being separately selectively recovered. 25

17. The method according to any one of claims 1 to 16, wherein step (c) is carried out in a dehydrogenation unit.

18. The method according to any one of claims 1 to 16, 30 wherein step (c) is carried out in a conventional reformer. 27

19. The method according to any one of claims 1 to 16, wherein step (c) is carried out in a low severity naphtha reformer. 5

20. The method according to claim 19, wherein the low severity naphtha reformer comprises a platinum catalyst, a rhenium catalyst, or a combination thereof.

21. The method according to any one of claims 1 to 20, 10 wherein an additional feedstock from another source comprising aromatics, aromatics precursors, or a combination thereof, and having a low sulphur content, is introduced to the aromatics extraction unit in step (b). 15

22. The method according to claim 21, wherein the additional feedstock is first treated (a) to remove sulphur, (b) to remove nitrogen, (c) to convert olefins to paraffins or isoparaffins, or (d) two or more of (a) to (c). 20

23. The method according to claim 21 or 22, wherein the additional feedstock is pyrolysis gasoline.

24. The method according to claim 23, wherein the pyrolysis gasoline is first hydrogenated, and then subjected to 25 a fractionation to recover an aromatics fraction, which is routed to the aromatics extraction unit, and a single double bond olefinic fraction, which is separately recovered.

25. A system for recovering aromatics from a naphtha 30 feedstock, comprising: 28 (a) a naphtha splitter for separating a C6' fraction from the naphtha feedstock; (b) a hydrotreater unit or a distillation unit for separating a C 6 to C 11 hydrocarbon fraction from the C 6 ' 5 fraction; (c) an aromatics extraction unit for recovering from the C 6 to C3u hydrocarbon fraction an aromatics fraction, an aromatics precursors fraction and a raffinate fraction; (d) a dehydrogenation unit or a reformer for 10 converting the aromatics precursors in the aromatics precursors fraction to aromatics; and (e) optionally a desulphurizing unit for removing sulfur from the naphtha feedstock prior to the separating of the C 6 * fraction; 15 wherein the hydrotreater unit or distillation unit for separating the C 6 to C 11 hydrocarbon fraction from the C6* fraction, and the aromatic extraction unit, are operatively connected such that the C 6 to C 11 hydrocarbon fraction is not subjected to a reformer or a dehydrogenation unit prior to the 20 recovery of the aromatics fraction, the aromatics precursors fraction and the raffinate fraction.

26. The system according to claim 25, wherein component (b) is a hydrotreater unit and the desulphurizing unit is a 25 caustic treating system.

27. The system according to claim 25, wherein component (b) is a distillation unit and the desulphurizing unit is a hydrotreater unit. 30 29

28. The system according to any one of claims 25 to 27, which further comprises a fractional distillation unit for removal of C 6 , C 7 or C 8 paraffins, or a combination thereof, from the aromatics precursor fraction, and for concentration of 5 C 6 , C 7 , or C 8 naphthenes, or a combination thereof, in the aromatics precursors fraction.

29. The system according to any one of claims 25 to 27, which further comprises a molecular sieve or sorbent for 10 removal of C 6 , C, or C 8 paraffins, or a combination thereof, from the aromatics precursor fraction, and for concentration of C 6 , C7, or C 8 naphthenes, or a combination thereof, in the aromatics precursors fraction. 15

30. The system according to any one of claims 25 to 29, wherein the naphtha splitter comprises a deisohexanizer or a demethylcyclopentanizer.

31. The system according to any one of claims 25 to 30, 20 wherein component (d) is a dehydrogenation unit.

32. The system according to any one of claims 25 to 30, wherein component (d) is a conventional reformer. 25

33. The system according to any one of claims 25 to 30, wherein component (d) is a low severity naphtha reformer.

34. Aromatics prepared according to the method of any one of claims 1 to 24. 30 30

35. A method of recovering aromatics, a system for recovering aromatics from a naphtha feedstock or aromatics prepared by the method, substantially as herein described with reference to the accompanying drawings. 5

36. A method for producing a hydrogen-rich, carbon dioxide free, gas, the method comprising carrying out the method as defined in claim 17, 19 or 20, and recovering a gas phase produced in step (c). 10

37. A system for producing a hydrogen-rich, carbon dioxide free, gas, comprising a system as defined in claim 31 or 33 together with means for recovering a gas phase produced by the dehydrogenation unit or the low-severity reformer. 15

38. Use of the system as defined in claim 31 or 33 for producing a hydrogen-rich, carbon dioxide free, gas. 31