TWO STAGE HYDRODEARYLATION SYSTEMS TO CONVERT HEAVY AROMATICS INTO GASOLINE BLENDING COMPONENTS AND CHEMICAL GRADE AROMATICS

Abstract

Systems and methods include an aromatics complex (ARC), the ARC in fluid communication with a naphtha reforming unit (NREF) and operable to receive a reformate stream produced by the NREF, and the ARC further operable to separate the reformate stream into a gasoline pool stream, an aromatics stream, and an aromatic bottoms stream; and a hydrodearylation unit operable to receive heavy, non-condensed, alkyl-bridged, multi-aromatic compounds from the aromatic bottoms stream, the hydrodearylation unit further operable to hydrogenate and hydrocrack the heavy, non-condensed, alkyl-bridged, multi-aromatic compounds to produce a stream suitable for recycle to the NREF or the reformate stream, where the hydrodearylation unit is further operable to receive hydrogen produced in the NREF.

Claims

1. A system for oil separation and upgrading, the system comprising: an inlet stream comprising crude oil; an atmospheric distillation unit (ADU), the ADU in fluid communication with the inlet stream, and operable to separate the inlet stream into an ADU tops stream and an ADU middle stream, the ADU tops stream comprising naphtha, and the ADU middle stream comprising diesel; a naphtha hydrotreating unit (NHT), the NHT in fluid communication with the ADU and operable to treat with hydrogen the naphtha in the ADU tops stream; a naphtha reforming unit (NREF), the NREF in fluid communication with the NHT and operable to reform a hydrotreated naphtha stream produced by the NHT, and the NREF further operable to produce separate hydrogen and reformate streams; an aromatics complex (ARC), the ARC in fluid communication with the NREF and operable to receive the reformate stream produced by the NREF, and the ARC further operable to separate the reformate stream into a gasoline pool stream, an aromatics stream, and an aromatic bottoms stream; and a hydrodearylation unit operable to receive heavy, non-condensed, alkyl-bridged, multi-aromatic compounds from the aromatic bottoms stream, the hydrodearylation unit further operable to hydrogenate and hydrocrack the heavy, non-condensed, alkyl-bridged, multi-aromatic compounds to produce a stream suitable for recycle to the NREF or the reformate stream, where the hydrodearylation unit is further operable to receive hydrogen produced in the NREF.

2. The system according to claim 1, where the hydrodearylation unit comprises a hydrogenation unit and a light hydrocracking unit, and where the hydrogenation unit is operable to receive hydrogen produced in the NREF.

3. The system according to claim 2, further comprising a fractionator fluidly disposed between the ARC and the hydrodearylation unit, the fractionator operable to separate the heavy, non-condensed, alkyl-bridged, multi-aromatic compounds from the aromatic bottoms stream from compounds with a boiling point of about 180° C. or less.

4. The system according to claim 3, where the fractionator comprises an atmospheric distillation unit.

5. The system according to claim 1, where the aromatic bottoms stream comprises aromatic compounds with boiling points in a range of about 100° C. to about 450° C.

6. The system according to claim 1, where the stream suitable for recycle to the NREF or the reformate stream comprises at least one component selected from the group consisting of: mono-aromatics; naphthenic mono-aromatics; mono-naphthenics; di-naphthenics; paraffins; naphthenic di-aromatics; di-aromatics; tri-/tetra-aromatics; and combinations of the same.

7. The system according to claim 6, where the mono-aromatics comprise benzene, toluene, xylenes, and ethyl benzene.

8. The system according to claim 1, where the hydrodearylation unit produces a gas stream separate from the stream suitable for recycle to the NREF or the reformate stream, the gas stream comprising at least one component selected from the group consisting of: fuel gas, liquefied petroleum gas, ethylene, propylene, butylene, and combinations of the same.

9. The system according to claim 1, where the hydrodearylation unit is a dual catalyst hydrodearylation unit comprising at least 2 different catalysts.

10. The system according to claim 2, where at least one of the hydrogenation unit and light hydrocracking unit include a catalyst selected from the group consisting of: a noble metal, a non-noble metal, a zeolite, and a solid acid catalyst.

11. The system according to claim 10, where the hydrogenation unit includes a catalyst comprising platinum and where the light hydrocracking unit includes a catalyst comprising ZSM-5 zeolite with an alumina-only binder and no active phase metals.

12. The system according to claim 10, where the hydrogenation unit and light hydrocracking unit use different catalysts.

13. The system according to claim 1, where the heavy, non-condensed, alkyl-bridged, multi-aromatic compounds from the aromatic bottoms stream comprise at least two benzene rings connected by an alkyl bridge group having at least two carbons, and the benzene rings are connected to different carbons of the alkyl bridge group.

14. The system according to claim 1, where the hydrodearylation unit is operable at pressures between about 10 bar and about 100 bar.

15. The system according to claim 1, where the hydrodearylation unit is operable at pressures between about 15 bar and about 70 bar.

16. The system according to claim 1, where the hydrodearylation unit is operable at temperatures between about 150° C. and about 450° C.

17. The system according to claim 1, where the hydrodearylation unit is operable at temperatures between about 200° C. and about 400° C.

18. The system according to claim 1, where the hydrodearylation unit produces a bleed stream containing naphthenes and aromatics to be directed towards fuel pools suitable for diesel and jet fuel.

19. The system according to claim 1, wherein benzene content of the gasoline pool stream is less than about 3% by volume.

20. The system according to claim 1, wherein benzene content of the gasoline pool stream is less than about 1% by volume.

21. The system according to claim 4, where a portion of the stream suitable for recycle to the NREF or the reformate stream is recycled to the fractionator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following descriptions, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the disclosure and are therefore not to be considered limiting of the disclosure's scope as it can admit to other equally effective embodiments.

[0030] FIG. 1A is a schematic of a conventional system for gasoline and aromatic production.

[0031] FIG. 1B is a schematic of a conventional aromatics separation and recovery complex.

[0032] FIG. 2A is a schematic showing two-stage hydrodearylation of an aromatic bottoms stream for gasoline blending component and BTX production.

[0033] FIG. 2B is a schematic showing two-stage hydrodearylation of an aromatic bottoms stream, first fractionated, for gasoline blending component and BTX production.

[0034] FIGS. 3A-3C show schematics with material balances for certain example two-stage hydrodearylation processes.

DETAILED DESCRIPTION

[0035] So that the manner in which the features and advantages of the embodiments of systems and methods for catalytic hydrodearylation and aromatics recovery, may be understood in more detail, a more particular description of the embodiments of the present disclosure briefly summarized previously may be had by reference to the embodiments thereof, which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the disclosure and are therefore not to be considered limiting of the present disclosure's scope, as it may include other effective embodiments as well.

[0036] Referring first to FIG. 1A, a schematic of a conventional system for gasoline and aromatic production is shown. In the embodiment of FIG. 1A, a refinery with an aromatic complex is presented. In refining system 100, a crude oil inlet stream 102 is fluidly coupled to atmospheric distillation unit (ADU) 10, and crude oil from the crude oil inlet stream 102 is separated into naphtha stream 104, atmospheric residue stream 105, and diesel stream 106. Diesel stream 106 proceeds to diesel hydrotreating unit (DHT) 30, and naphtha stream 104 proceeds to naphtha hydrotreating unit (NHT) 20. A hydrotreated naphtha stream 108 exits NHT 20 and enters catalytic naphtha reforming unit (NREF) 40. A separated hydrogen stream 110 exits NREF 40, and a reformate stream 112 also exits NREF 40. A portion of reformate stream 112 enters aromatic complex (ARC) 50, and another portion of reformate stream 112 is separated by gasoline pool stream 114 to a gasoline pool. ARC 50 separates the reformate stream 112 into gasoline pool stream 116, aromatics stream 118, and aromatic bottoms 120.

[0037] The hydrotreated naphtha stream is reformed in a reforming unit to produce a gasoline reformate product stream. In general, the operating conditions for a reforming unit include a temperature in the range of from about 260° C. to about 560° C., and in certain embodiments from about 450° C. to about 560° C.; a pressure in the range of from about 1 bar to about 50 bars, and in certain embodiments from about 1 bar to about 20 bars; and a LHSV in the range of from about 0.5 h.sup.−1 to about 40 h.sup.−1, and in certain embodiments from about 0.5 h.sup.−1 to about 2 h.sup.−1. The reformate is sent to the gasoline pool to be blended with other gasoline components to meet the required specifications.

[0038] The crude oil is distilled in ADU 10 to recover naphtha, which boils in the range of about 36° C. to about 180° C., and diesel, which boils in the range of about 180° C. to about 370° C. An atmospheric residue fraction in atmospheric residue stream 105 boils at about 370° C. and greater. Naphtha stream 104 is hydrotreated in NHT 20 to reduce the sulfur and nitrogen content to less than about 0.5 ppmw, and the hydrotreated naphtha stream 108 is sent to NREF 40 to improve its quality, or in other words increase the octane number to produce gasoline blending stream or feedstock for an aromatics recovery unit. Diesel stream 106 is hydrotreated in DHT 30 to desulfurize the diesel oil to obtain a diesel fraction meeting stringent specifications at ultra-low sulfur diesel (ULSD) stream 121, such as, for example, less than 10 ppm sulfur. An atmospheric residue fraction is either used as a fuel oil component or sent to other separation or conversion units to convert lesser value hydrocarbons to products having greater value. Reformate stream 112 from NREF 40 can be used as a gasoline blending component or sent to an aromatic complex, such as ARC 50, to recover valuable aromatics, such as benzene, toluene and xylenes.

[0039] Referring now to FIG. 1B, a schematic of a prior art aromatics separation complex 122, such as, for example, ARC 50 of FIG. 1, is shown. Reformate stream 124 from a catalytic reforming unit, such as, for example, NREF 40 of FIG. 1, is split into two fractions: light reformate stream 128 with C.sub.5-C.sub.6 hydrocarbons, and heavy reformate stream 130 with C.sub.7+ hydrocarbons. A reformate splitter 126 separates reformate stream 124. The light reformate stream 128 is sent to a benzene extraction unit 132 to extract the benzene as benzene product in stream 138, and to recover substantially benzene-free gasoline in raffinate motor gasoline (mogas) stream 136. The heavy reformate stream 130 is sent to a splitter 134 which produces a C.sub.7 cut mogas stream 140 and a C.sub.8+ hydrocarbon stream 142.

[0040] Still referring to FIG. 1B, a xylene rerun unit 144 separates C.sub.8+ hydrocarbons into C.sub.8 hydrocarbon stream 146 and C.sub.9+ (heavy aromatic mogas) hydrocarbon stream 148. C.sub.8 hydrocarbon stream 146 proceeds to p-xylene extraction unit 150 to recover p-xylene in p-xylene product stream 154. P-xylene extraction unit 150 also produces a C.sub.7 cut mogas stream 152, which combines with C.sub.7 cut mogas stream 140 to produce C.sub.7 cut mogas stream 168. Other xylenes are recovered and sent to xylene isomerization unit 158 by stream 156 to convert them to p-xylene. The isomerized xylenes are sent to splitter column 162. The converted fraction is recycled back to p-xylene extraction unit 150 from splitter column 162 by way of streams 164 and 146. Splitter top stream 166 is recycled back to reformate splitter 126. The heavy fraction from the xylene rerun unit 144 is recovered as process reject or aromatic bottoms (shown as C.sub.9+ and Hvy Aro MoGas in FIG. 1B at stream 148). Stream 148 in FIG. 1B (similar to aromatic bottoms 120 in FIG. 1) can comprise heavy, non-condensed multi-aromatics such as di-aromatics.

[0041] Referring now to FIG. 2A, a schematic is provided showing two-stage hydrodearylation of an aromatic bottoms stream (for example, stream 148 of FIG. 1B) for gasoline blending component and BTX production. In crude oil separation and upgrading system 200, crude oil stream 202 is optionally combined with a hydrocarbon recycle stream 203 to form hydrocarbon feed stream 204, which feeds ADU 206. ADU 206 separates hydrocarbons from hydrocarbon feed stream 204 into naphtha stream 208, atmospheric residue stream 209, and diesel stream 210. Diesel stream 210 can be fed to a DHT (not pictured) for processing to produce ULSD. Naphtha stream 208 is fed to NHT 212 for processing. A hydrotreated naphtha stream 214 is fed to NREF 216. NREF 216 produces a hydrogen stream 218 and a reformate stream 220. A portion of reformate stream 220 proceeds to a gasoline pool by way of stream 222, and a portion of reformate stream 220 is fed to ARC 224. ARC 224 produces aromatics, for example, benzene and xylenes, at stream 226 and aromatic bottoms at stream 228. A portion of hydrocarbons from ARC 224 proceed to the gasoline pool by way of stream 230.

[0042] As described herein, the term “aromatics” includes C.sub.6-C.sub.8 aromatics, such as, for example, benzene and xylenes, for example, streams 138, 154 in FIG. 1B, whereas “aromatic bottoms” include the heavier fraction, for example, stream 148 in FIG. 1B (C.sub.9+). Aromatic bottoms relate to C.sub.9+ aromatics and may be a more complex mixture of compounds including di-aromatics, both condensed and non-condensed. C.sub.9+ aromatics boil in the range of about 100° C. to about 350° C.

[0043] Aromatic bottoms produced at stream 228 proceed to a two-stage hydrodearylation unit 232. In a hydrogenation unit 234, the aromatic bottoms are first combined with hydrogen from stream 236. Hydrogen in stream 236 can be supplied from NREF 216 via stream 238 in addition to or alternative to fresh hydrogen from make-up stream 240. The hydrogenated aromatic bottoms proceed via line 242 to a second stage for light hydrocracking in light hydrocracking unit 244. Light hydrocracking unit 244 produces a gas phase product stream 246, a two-stage hydrodearylated bottoms stream 248, and an optional bleed stream 250. Two-stage hydrodearylated bottoms stream 248 can be recycled to NREF 216, or all of two-stage hydrodearylated bottoms stream 248 or a portion of two-stage hydrodearylated bottoms stream 248 can be sent to be combined with reformate stream 220 via stream 252. In the embodiments of FIGS. 2A and 2B, the respective hydrogenation and light hydrocracking units are represented as separate units; however, in certain embodiments both hydrogenation and light hydrocracking of a heavy aromatic bottoms stream can occur in a single unit in different zones, for example, a single unit with different zones having different catalysts and reaction conditions for light hydrocracking and hydrogenation.

[0044] FIG. 2B is a schematic showing two-stage hydrodearylation of an aromatic bottoms stream, first fractionated, for gasoline blending component and BTX production. In crude oil separation and upgrading system 300, crude oil stream 302 is optionally combined with a hydrocarbon recycle stream 303 to form hydrocarbon feed stream 304, which feeds ADU 306. ADU 306 separates hydrocarbons from hydrocarbon feed stream 304 into naphtha stream 308, atmospheric residue stream 309, and diesel stream 310. Diesel stream 310 can be fed to a DHT (not pictured) for processing to produce ULSD. Naphtha stream 308 is fed to NHT 312 for processing. A hydrotreated naphtha stream 314 is fed to NREF 316. NREF 316 produces a hydrogen stream 318 and a reformate stream 320. A portion of reformate stream 320 proceeds to a gasoline pool by way of stream 322, and a portion of reformate stream 320 is fed to ARC 324. ARC 324 produces aromatics, for example, benzene and xylenes, at stream 326 and aromatic bottoms at stream 328. A portion of hydrocarbons from ARC 324 goes to the gasoline pool by way of stream 330.

[0045] As described herein, the term “aromatics” includes C.sub.6-C.sub.8 aromatics, such as, for example, benzene and xylenes, for example, streams 138, 154 in FIG. 1B, whereas “aromatic bottoms” include the heavier fraction, for example, stream 148 in FIG. 1B (C.sub.9+). Aromatic bottoms relate to C.sub.9+ aromatics and may be a more complex mixture of compounds including di-aromatics, both condensed and non-condensed. C.sub.9+ aromatics boil in the range of about 100° C. to about 350° C.

[0046] Aromatic bottoms produced at stream 328 proceed first to an atmospheric distillation unit (ADU) 329 (also referred to as a fractionator) prior to proceeding to a two-stage hydrodearylation unit 332. In ADU 329 aromatic bottoms are separated into different hydrocarbon components by boiling point. Those components boiling in the gasoline and naphtha range at about 180° C. and less are sent directly to a gasoline blending pool via stream 331, and the components boiling at about 180° C. and greater are sent to two-stage hydrodearylation unit 332, which includes hydrogenation and lesser pressure hydrocracking, along with dual catalyst use. The bottoms fraction boiling above the gasoline range, above about 180° C., requires treatment according to two-stage hydrodearylation unit 332. However, the aromatic bottoms fraction from ARC 324 does not necessarily have to be fractionated and can be treated directly in-line with the system and process represented by FIG. 2A.

[0047] In FIG. 2B, the heavy 180° C.+ fraction from ADU 329 is sent to two-stage hydrodearylation unit 332 for hydrogenation and light hydrocracking of the aromatic rings, with hydrodearylation also being undertaken, during which mono-naphthenes, paraffins, and BTX are produced. In a first hydrogenation unit 334, the aromatic bottoms are combined with hydrogen from stream 336. Hydrogen in stream 336 can be supplied from NREF 316 via stream 338 in addition to or alternative to fresh hydrogen from make-up stream 340. The hydrogenated aromatic bottoms proceed via line 342 to a second stage for light hydrocracking in light hydrocracking unit 344. Light hydrocracking unit 344 produces a gas phase product stream 346, a two-stage hydrodearylated bottoms stream 348, and an optional bleed stream 350. Two-stage hydrodearylated bottoms stream 348 can be recycled to NREF 316, or all of two-stage hydrodearylated bottoms stream 348 or a portion of two-stage hydrodearylated bottoms stream 348 can be sent to be combined with reformate stream 320 via stream 352.

[0048] Two-stage hydrodearylated bottoms stream 348, the product stream, is rich in naphthenes, paraffins, and mono-aromatics, and when recycled back to NREF 316 for dehydrogenation of de-alkylated rings, this produces additional BTX and gasoline blending components. Any bottoms products containing naphthenes and aromatics in minor proportion in light hydrocracking unit 344 may be directed to a diesel, jet fuel, or kerosene pool as a blending component via stream 350. In some embodiments, not pictured, a final two-stage hydrodearylated product stream, such as two-stage hydrodearylated bottoms stream 348, is recycled back to a fractionator unit downstream of the aromatics complex, such as ADU 329, for further processing and a greater conversion of the aromatic bottoms products.

[0049] FIGS. 3A-3C show schematics with material balances for certain example two-stage hydrodearylation processes. In FIGS. 3A-3C, the following abbreviations apply: MA=mono-aromatics; NMA=naphthenic mono-aromatics; MN=mono-naphthenics; DN=di-naphthenics; P=paraffins; NDA=naphthenic di-aromatics; DA=di-aromatics; TrA=tri-/tetra-aromatics. Similarly labeled units and streams are the same as those in previous figures.

EXAMPLES

[0050] In Example 1, 11.4775 kg of an aromatic bottoms fraction was distilled using a lab scale true boiling point distillation column with 15 or more theoretical plates using ASTM method D2917. 9.411 kg (82 W %) of a gasoline fraction boiling in the range of 36° C. to 180° C. was obtained, and 2.066 Kg (18 W %) of a residue stream boiling above 180° C. was obtained. The gasoline fraction was analyzed for its content and octane numbers.

TABLE-US-00001 TABLE 1 Properties of aromatic bottoms feed stream of Example 1. Feedstock Aromatic Tops Gasoline Bottoms Diesel Property Unit Bottoms IBP 180° C.− 180° C.+ Density g/cc 0.8838 0.8762 0.9181 Octane Number — NA 110 NA ASTM D2799 Cetane Index — NA NA 12 IBP ° C. 153 67 167  5 W % ° C. 162 73 176 10 W % ° C. 163 73 181 30 W % ° C. 167 76 192 50 W % ° C. 172 77 199 70 W % ° C. 176 79 209 90 W % ° C. 191 81 317 95 W % ° C. 207 81 333 FBP ° C. 333 83 422 Paraffins wt. % 0.00 n/a n/a Mono-aromatics wt. % 94.1 n/a n/a Naphtheno wt. % 0.9 n/a n/a Mono-aromatics Di-aromatics wt. % 3.7 n/a n/a Naphtheno wt. % 0.9 n/a n/a di-aromatics Tri+ Aromatics wt. % 0.3 n/a n/a n/a = not applicable

[0051] In Example 2, a non-fractionated aromatic bottoms stream was contacted with a commercially available Pt-containing hydrogenation catalyst, and a hydrocracking catalyst (H-ZSM-5 (MFI structure), SAR=23, 29 wt. % zeolite, 71 wt. % alumina-only binder) with no active phase metals in a pilot plant under the conditions as given in Table 2.

TABLE-US-00002 TABLE 2 Aromatic bottoms two-stage hydrodearylation (hydrogenation and light hydrocracking) conditions. Run Temperature Pressure LHSV # ° C. Bar hr.sup.−1 1 200 15 1.3 2 200 25 1.3 3 250 25 1.3 4 250 15 1.3 5 250 6 1.3 6 300 15 1.3 7 300 25 1.3 8 300 30 1.3 9 300 50 1.3 10 300 60 1.3 11 300 70 1.3 12 300 80 1.3 13 300 90 1.3 14 300 100 1.3 15 350 25 1.3 16 350 15 1.3 17 400 15 1.3 18 400 25 1.3

[0052] In this example, there was one reactor having the two different catalysts (for hydrogenation and light hydrocracking) stacked. However, in other embodiments there can be two separate reactors, each having its own catalyst type (for example, FIG. 2A). Separate reactors can operate at individual temperatures and pressures to provide more flexibility in product compositions. Suitable reactor types include a fixed-bed reactor, a slurry-bed reactor, an ebullated bed reactor, a continuously-stirred tank reactor, a moving-bed reactor, and combinations of the same.

[0053] The hydrogenation catalyst performs hydrodearylation and also hydrogenates di-aromatics to mono-naphthenic aromatics. Hydrogenation of mono-aromatics to naphthenes can also take place. One targeted reaction is hydrogenation of a single ring in condensed di-aromatics to single mono-aromatics containing a naphthenic ring. Then, a lesser-pressure hydrocracking catalyst can open the naphthenic ring of the mono-naphthenic aromatics to yield, for example, mono-aromatics and paraffins.

[0054] Feed and product compositions were analyzed by gas chromatography (GC), as well as 2D-GC, and certain results are shown in FIGS. 3A-3C. A substantial conversion of aromatics into paraffins and naphthenes can be observed showing the advantageous extent of the two-stage hydrodearylation process. Additionally, non-condensed and condensed di-aromatic content is reduced with hydrodearylation of the alkyl-bridged, non-condensed, di-aromatics resulting in mono-aromatics and mono-naphthenes. Increased levels of BTX are also obtained. The products can be recycled back as gasoline blending components to improve gasoline volume and quality. Further breakdown of the liquid product mono-aromatic species showed xylene and ethyl benzene formation, with a greater selectivity for C.sub.8 mono-aromatics than for toluene and benzene.

[0055] When subjecting the aromatic bottoms stream to the two-stage hydrodearylation (hydrogenation/light hydrocracking) process in Run 5, for example, there is benzene, toluene and C.sub.8 production of 8 kg (about 0.1 wt. % of the aromatic bottoms stream), 21 kg (about 0.1 wt. % of the aromatic bottoms stream), and 129 kg (about 0.9 wt. % of the aromatic bottoms stream), respectively.

[0056] Changing the operating conditions results in the hydrogenated/hydrocracked product stream yielding benzene, toluene, and C.sub.8 production of: 0 kg, 13 kg, and 1,115 kg (about 7.8 wt. % of the aromatic bottoms reject stream), respectively, for Run 9 (FIG. 3A). In Run 9, about 513 kg of H.sub.2 was added to hydrogenation unit 234, which as noted previously can be supplied from a NREF or from fresh make-up hydrogen.

[0057] For Run 15 (FIG. 3B) the operating conditions result in the hydrogenated/hydrocracked product stream yielding benzene, toluene, and C.sub.8 production of: 50 kg (about 0.3 wt. % of the aromatic bottoms stream), 222 kg (about 1.5 wt. % of the aromatic bottoms stream), and 847 kg (about 5.8 wt. % of the aromatic bottoms stream), respectively. In Run 15, about 342 kg of H.sub.2 was added to hydrogenation unit 234.

[0058] For Run 17 (FIG. 3C) the operating conditions result in the hydrogenated/hydrocracked product stream yielding benzene, toluene, and C.sub.8 production of: 112 kg (about 0.7 wt. % of the aromatic bottoms stream), 1065 kg (about 7.2 wt. % of the aromatic bottoms stream), and 1489 kg (about 10.0 wt. % of the aromatic bottoms stream), respectively. In Run 17, about 110 kg of H.sub.2 was added to hydrogenation unit 234. As shown, less hydrogen is required at increasing temperature and decreasing pressure.

[0059] Two-stage hydrodearylation with hydrogenation and lesser-pressure hydrocracking allows for processing of heavy aromatics streams with a dual catalyst system, and hydrodearylation is effected on alkyl-bridged di-aromatics. Products can be recycled back to a reformate unit to dehydrogenate naphthenes, to improve gasoline volume and quality, and also to increase BTX production. Suitable aromatic bottoms streams can be those comprising aromatic compounds with boiling points in a range of about 100° C. to about 450° C. In some embodiments, benzene content of gasoline pool streams is less than about 3% by volume. In some embodiments, benzene content of gasoline pool streams is less than about 1% by volume.

[0060] In certain embodiments of the systems and methods, an aromatic bottoms stream comprises greater than about 50 wt. % or greater than about 70 wt. % single-ring aromatics having alkyl groups containing three or more carbon atoms. In some embodiments, an aromatics bottom stream has between about 20 wt. % to about 95 wt. % single-ring aromatics having alkyl groups containing three or more carbon atoms. In some embodiments, the hydrogenation catalyst includes one or more noble metal catalyst. The noble metal catalyst can include Pt or Pd or a mixture thereof. In some embodiments, hydrogenation and/or light hydrocracking catalysts include at least one zeolite. The zeolite can include, for example, a USY framework or modified USY framework.

[0061] In some embodiments, the framework of modified USY contains Ti, Zr, or Hf or a mixture thereof. In some embodiments, a catalyst support includes alumina, silica-alumina, titania or a combination thereof. Zeolite content of a catalyst for use can be between about 1 wt. % to about 80 wt. %.

[0062] In some embodiments, the light hydrocracking catalyst includes a solid acid catalyst. The light hydrocracking catalyst can include an amorphous or crystalline catalyst. The solid acid catalyst can include a Lewis acid, a Brønsted acid, or a mixture thereof. The light hydrocracking catalyst can include a zeolite. The light hydrocracking catalyst can include a zeolite of structure MFI, FAU, MOR, BEA, or combinations thereof. The light hydrocracking catalyst support can include alumina, silica-alumina, titania, or combination thereof. The light hydrocracking catalyst weight percent of zeolite can be between about 1 wt. % to about 80 wt. %.

[0063] In some embodiments, active phase metals can be used and include Ni, Mo, W, or mixtures thereof. Active phase metals are applied as catalysts for hydrogenation of aromatic molecules. They are useful components of hydrocracking catalysts. In addition to hydrogenation, they enhance hydrogen transfer reactions. In the Examples described here, active phase metals were not applied, because cracking naphthenes with an acidic support was desired, however, in other embodiments active phase metals can be used.

[0064] In some embodiments here, alkyl-bridged, non-condensed, alkyl multi-aromatic compounds for hydrodearylation include at least two benzene rings connected by an alkyl bridge group having at least two carbons, and the benzene rings are connected to different carbons of the alkyl bridge group. In some embodiments, hydrodearylation generates mono-aromatics in addition to or alternative to mono-naphthenes.

[0065] In some embodiments, an aromatic bottoms stream is hydrogenated/hydrocracked to form naphthenes and/or naphtheno-aromatics and/or paraffins. In other embodiments, the aromatic bottoms stream is contacted with a hydrogenation and light hydrocracking dual catalyst, and is subjected to pressures of about 10 bar to about 100 bar, preferably about 15 bar to about 70 bar. Different catalysts can be in separate hydrogenation/light hydrocracking units (shown in FIGS. 2A, 2B), which provides unique temperature and pressure control of the separate units, but in other embodiments separate catalysts can be layered in one common unit for both hydrogenation and light hydrocracking (not pictured). In some embodiments, the pressure of a light hydrocracking unit is less than the pressure of a hydrogenation unit.

[0066] In some embodiments, the aromatic bottoms stream is contacted with the hydrogenation and/or hydrocracking dual catalyst (different catalysts in 2 separate units) and is subjected to temperatures of between about 150° C. to about 450° C., preferably about 200° C. to about 400° C. Hydrogenation reactions are thermodynamically controlled and are favorable at lesser temperatures than hydrocracking, and hydrogenation also is a function of the hydrogen partial pressures.

[0067] In some embodiments, a final two-stage hydrodearylated product stream is recycled back to a naphtha reforming unit (NREF). In some embodiments, a final two-stage hydrodearylated product stream is recycled back to a fractionator unit downstream of the aromatics complex. In some embodiments, a product stream is recycled back to the reformate stream, downstream of the NREF unit. In some embodiments, a bleed stream containing naphthenes in major proportions (more than about 50 wt. %, or more than about 70 wt. %, or preferably more than about 90 wt. %) in addition to or alternative to aromatics in minor proportions (less than about 50 wt. %, or less than about 70 wt. %, or preferably less than about 90 wt. %) from the product stream of hydrodearylation is directed towards fuel pools suitable for diesel or jet fuel. In some embodiments, a portion of a product stream comprises toluene (C.sub.7) and mono-aromatics containing two additional carbon atoms (for example, C.sub.8 xylenes and ethyl benzene).

[0068] The singular forms “a,” “an,” and “the” include plural referents, unless the context clearly dictates otherwise. The term “about” when used with respect to a value or range refers to values including plus and minus 5% of the given value or range.

[0069] One of ordinary skill in the art will understand that standard components such as pumps, compressors, temperature and pressure sensors, valves, and other components not shown in the drawings would be used in applications of the systems and methods of the present disclosure.

[0070] In the drawings and specification, there have been disclosed example embodiments of the present disclosure, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The embodiments of the present disclosure have been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the disclosure as described in the foregoing specification, and such modifications and changes are to be considered equivalents and part of this disclosure.