RECYCLE CATALYTIC REFORMING PROCESS TO INCREASE AROMATICS YIELD

Abstract

The invention relates to a process and system arrangement to generate benzene, toluene and xylenes in a refinery. The process relies on recycling a C.sub.9+ aromatic bottoms stream from an aromatic recovery complex back to rejoining a hydrotreated naphtha stream as it enters a catalytic reformer. The aromatic bottoms can be further reacted through both the reformer and the subsequent aromatic recovery complex to transform to higher value compounds, thereby reducing waste or reducing bottoms' presence in gasoline pools.

Claims

1. A method for recovery of benzene, toluene and xylene, the method comprising: supplying to a naphtha reforming unit (NREF) a stream of hydrotreated naphtha; allowing the stream to flow through the NREF to generate reformate and hydrogen gas; supplying at least a portion of reformate from the NREF to an aromatics recovery complex (ARC); flowing the portion of reformate in the ARC through a reformate splitter to generate a C.sub.7+ stream; flowing the C.sub.7+ stream through a second splitter to generate a C.sub.8+ stream; flowing the C.sub.8+ stream through a clay tower to deolefinate the C.sub.8+ stream; flowing the deolefinated C.sub.8+ stream through a xylene re-run splitter to obtain a C.sub.8 stream and a C.sub.9+ stream; and recycling the C.sub.9+ stream back to enter the stream of hydrotreated naphtha to thereby reprocess the C.sub.9+ stream to recover benzene, toluene and xylene.

2. The method of claim 1, wherein the C.sub.9+ stream recycles to the stream of hydrotreated naphtha prior to entering the NREF.

3. The method of claim 1, wherein the C.sub.9+ stream recycles to the stream of hydrotreated naphtha within the NREF.

4. The method of claim 3, wherein the C.sub.9+ stream feeds into the NREF equally before each reactor unit contained therein.

5. The method of claim 1, wherein the NREF comprises a temperature and a catalyst suitable to provide sufficient energy to break an alkyl carbon-carbon bond.

6. The method of claim 5, wherein the temperature of the NREF is from about 490° C. to about 520° C.

7. The method of claim 5, wherein the catalyst comprises an acidic catalyst.

8. The method of claim 5, wherein the catalyst is selected from the group consisting of a zeolite, a platinum compound, a palladium compound or combinations thereof.

9. The method of claim 5, wherein the catalyst is a zeolite with a framework selected from the group consisting of Faujasite (FAU), Beta (BEA), Mordenite (MOR), ZSM-5 (MFI) or combinations thereof.

10. The method of claim 1, further comprising: flowing the C.sub.8 stream to a para-xylene extraction unit to obtain a para-xylene stream and a xylene isomer stream; flowing the xylene isomer stream to a xylene isomerization unit coupled to a further splitter; and recycling the xylene isomer stream to the xylene re-run splitter, wherein further C.sub.9+ compounds join the C.sub.9+ stream.

11. The method of claim 1, wherein the NREF has a hydrogen/oil operating ratio of about 100 to about 2500 L/L.

12. The method of claim 11, wherein the hydrogen/oil operating ratio is about 100 to about 1000 L/L.

13. The method of claim 11, wherein the hydrogen/oil operating ratio is about 100 to about 750 L/L

14. The method of claim 1, wherein the NREF has an operating liquid hourly space velocity (LHSV) of about 0.5 to about 40 h.sup.−1.

15. The method of claim 14, wherein the NREF has an operating LHSV of about 0.5 to about 10 h.sup.−1.

16. The method of claim 14, wherein the NREF has an operating LHSV of about 0.5 to about 4 h.sup.−1.

17. The method of claim 1, wherein the NREF has an operating pressure of about 1 to about 50 bar.

18. The method of claim 17, wherein the NREF has an operating pressure of about 1 to about 20 bar.

19. The method of claim 1, wherein the NREF has an operating temperature of about 250 to about 560° C.

20. The method of claim 19, wherein the NREF has an operating temperature of about 450 to about 560° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 shows a schematic overview of a typical refinery arrangement of systems.

[0022] FIG. 2 shows a more detailed schematic of the various processing units present in a typical aromatics recovery complex.

[0023] FIG. 3 shows a schematic of an example of the present disclosure, wherein an aromatic bottoms stream of C.sub.9+ hydrocarbons from the aromatics recovery complex is recycled back to the hydrotreated naphtha feed into the catalytic reformer.

[0024] FIG. 4 shows in greater detail possible inputs for the aromatic bottoms C.sub.9+ hydrocarbons back into a fixed bed catalytic reformer.

[0025] FIG. 5 shows in greater detail possible inputs for the aromatic bottoms C.sub.9+ hydrocarbons back into a circulating catalytic reformer.

[0026] The embodiments set forth in the drawing are illustrative in nature and not intended to be limiting to the claims. Moreover, individual features of the drawing will be more fully apparent and understood in view of the detailed description.

DETAILED DESCRIPTION

[0027] As used herein, the term “aromatics” includes C.sub.6-C.sub.8 aromatics, such as, for example, benzene and xylenes, whereas “aromatic bottoms” refer to the heavier fraction of C.sub.9+ compounds, including but not limited to C.sub.9, C.sup.10, C.sub.11, C.sub.12, C.sub.13, C.sub.14, C.sub.15, and C.sub.16 compounds.

[0028] A typical refinery complex is presented in FIG. 1 and a closer schematic of an aromatics recovery complex (ARC) from such is depicted in FIG. 2. The crude oil feed is distilled in an atmospheric distillation unit (ADU) to recover a naphtha fraction boiling in the range 36-180° C., a diesel fraction boiling in the range 180-370° C. and an atmospheric residue fraction boiling at 370° C. and higher. The naphtha fraction is then hydrotreated in a naphtha hydrotreating unit (NHT) to reduce the sulfur and nitrogen content to less than 0.5 ppmw. In general, the operating conditions of a NHT include a temperature in the range of from about 260° C. to about 400° C.; a pressure in the range of from about 1 bar to about 50 bars; and an LHSV in the range of from about 0.5 h.sup.−1 to about 40 h.sup.−1.

[0029] The hydrotreated naphtha fraction is then sent to a catalytic reforming unit (NREF) to improve its quality, i.e., increase octane number to produce gasoline blending stream or feedstock for an aromatics recovery unit. Similarly, the diesel fraction is hydrotreated in a separate diesel hydrotreating unit (DHT) to desulfurize the diesel oil to obtain diesel fraction meeting the stringent specifications. The atmospheric residue fraction is either used as a fuel oil component or sent to other separation/conversion units to convert them from low value hydrocarbons to various fuel oil products.

[0030] The reformate fraction from the catalytic reforming unit can be used as gasoline blending component or sent to an aromatic recovery complex (ARC) to recover high value aromatics, i.e., benzene, toluene, and xylenes, commonly called BTX. FIG. 2 shows more detail of the processes present in an aromatic recovery complex (ARC). The reformate stream flowing from the catalytic reforming unit is split into two fractions: light (C.sub.5, C.sub.6) and heavy (C.sub.7+) reformate. The light reformate is sent to a benzene extraction unit to extract benzene present therein and recover near benzene free gasoline. The heavy reformate stream is then sent to a second splitter to recover C.sub.7 and a C.sub.8+ stream. The C.sub.7 toluene stream is sent to a gasoline pool or other interconversion processes and the C.sub.8+ stream is sent to a clay tower to remove olefins. The olefin-free effluent is then sent to a xylene re-run splitter/fractionator to send the C.sub.8 stream to a para-xylene extraction unit to recover para-xylene. Other xylenes are also recovered during this latter process and are further sent to a xylene isomerization unit to catalytically convert them to para-xylene. The successfully converted fraction is recycled back to para-xylene extraction unit for distillation. The heavy fraction from the xylene re-run unit is recovered as process reject stream or aromatic bottoms of C.sub.9+ hydrocarbons.

[0031] Toluene is recovered as a separate fraction, and then may be converted into higher value products, for example benzene in addition to or alternative to xylenes. One toluene conversion process involves the disproportionation of toluene to make benzene and xylenes. Another process involves the hydrodealkylation of toluene to make benzene. Both toluene disproportionation and toluene hydrodealkylation result in the formation of benzene. With the current and continued environmental regulations involving benzene, it is desirable that the toluene conversion not result in the formation of significant quantities of benzene.

[0032] One problem faced by refineries is how to most economically reduce the benzene content in the reformate products sent to the gasoline pool by improving the processes and apparatus of systems described above. In some refineries, the aromatic complex bottoms are added to the gasoline fraction. However, the aromatic complex bottoms deteriorate the gasoline quality and in the long run impact the engine performance negatively.

[0033] The present disclosure concerns the identification that recycling the aromatic bottoms of C.sub.9+ alkylaromatic compounds generated from the ARC (i.e. at the xylene re-run unit or from a transalkylation unit) back to the catalytic reformer (FIG. 3) presents an opportunity to further generate higher value compounds rather than waste or redistribution to gasoline pools. Particularly, as described herein, the NREF may operate at temperatures of about 490 to about 575° C. and utilize an acidic catalyst. Collectively, these two features provide sufficient energy and opportunity for a carbon-carbon alkyl bond to be severed and to fracture or cleave di- or multi-aromatic compounds in the C.sub.9+ stream into mono-aromatics. Generating such in the NREF allows higher value aromatics to flow to the aromatics recovery complex and be isolated/recovered therein rather than be discarded as would happen in the first pass through. It should therefore be apparent to one skilled in the art that such recycling or recirculation can continue to exhaustion.

[0034] The aromatic bottoms can be recycled to enter the catalytic reformer at one or multiple points. As identified in FIGS. 4 and 5, the NREF can possess multiple reactors and multiple furnaces. Accordingly, the C.sub.9+ stream of aromatic bottoms can enter the NREF at one or multiple points therein. One point of entry is to rejoin the hydrotreated naphtha stream emerging from the NHT prior to entry to the NREF. The only parameter that may be impacted by returning the aromatic bottoms to the NREF is the liquid hourly space velocity (“LHSV”) as the added line increases the feed into the respective reforming unit.

[0035] Further, as set forth in FIGS. 4 and 5, the hydrotreated naphtha stream can flow through three or more reactors, passing through a furnace before entering each reactor. The C.sub.9+ stream, in addition or in lieu of joining the hydrotreated naphtha at or before entry to the NREF, may be inserted prior to a stream feeding into a furnace within the NREF or upon exit form a reactor with the NREF. As further depicted in FIG. 5, the reactors are connected to a regenerator to turn over spent catalyst. There are several types of process configurations which differ how they regenerate the reforming catalyst. Catalyst regeneration, which involves combusting detrimental coke in the presence of oxygen, includes a semi-regenerative process, cyclic regeneration, and continuous regeneration. Semi-regeneration involves the entire unit, including all reactors in the series, to be shut-down for catalyst regeneration. Cyclic configurations utilize an additional “swing” reactor to permit one reactor at a time to be taken off-line for regeneration while the others remain in service. Continuous catalyst regeneration configurations provide for essentially uninterrupted operation by catalyst removal, regeneration and replacement.

[0036] Referring first to FIG. 1, a schematic of a conventional system for gasoline and aromatic production is shown. In the embodiment of FIG. 1, a refinery with an aromatic complex is presented. In a refining system, a crude oil inlet stream 10 is fluidly coupled to atmospheric distillation unit (ADU) 100, and crude oil from the crude oil inlet stream 10 is separated into naphtha stream 20, atmospheric residue stream 12, and diesel stream 11. Diesel stream 11 proceeds to diesel hydrotreating unit (DHT) (not shown), and naphtha stream 20 proceeds to naphtha hydrotreating unit (NHT) 200. A hydrotreated naphtha stream 30 exits NHT 200 and enters catalytic naphtha reforming unit (NREF) 300. A separated hydrogen stream 31 exits NREF 300, and a reformate stream 40 also exits NREF 300. A portion of reformate stream 40 enters aromatic complex (ARC) 400, and another portion of reformate stream 40 is separated by pool stream 41 to a gasoline pool. The ARC 400 separates the reformate into a pool stream 42 (e.g., C.sub.4-C.sub.10 non-aromatics), an aromatics stream (C.sub.6-C.sub.8 aromatics) 43, and an aromatic bottoms stream (C.sub.9+) 60.

[0037] The crude oil is distilled in ADU 100 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 12 boils at about 370° C. and higher. Naphtha stream 20 is hydrotreated in NHT 200 to reduce the sulfur and nitrogen content to less than about 0.5 ppmw, and the hydrotreated naphtha stream 30 is sent to NREF 300 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 11 is hydrotreated in DHT to desulfurize the diesel oil to obtain a diesel fraction meeting stringent specifications at ultra-low sulfur diesel (ULSD). An atmospheric residue fraction is either used as a fuel oil component or sent to other separation or conversion units to convert low value hydrocarbons to high value products. Reformate stream 40 from NREF 300 can be used as a gasoline blending component or sent to an aromatic complex, such as ARC 400, to recover high value aromatics, such as benzene, toluene, and xylenes (BTX).

[0038] Referring to FIG. 2, an overview of an ARC 400, is shown. The reformate stream 40 from the NREF 300 of FIG. 1 flows initially into a reformate splitter 1 to separate into a light C.sub.5 and C.sub.6 hydrocarbon stream 401 and a heavy C.sub.7+ stream 410. The C.sub.5 and C.sub.6 stream 401 feeds to a benzene extraction unit 2 to separate into C.sub.5 and C.sub.6 non-aromatic stream 402 for raffinate motor gasoline (MoGas) and a C6 aromatics stream 403 for benzene products. The C.sub.7+ stream 410 feeds to a splitter 3 to produce a C7 cut MoGas stream 411 and a C.sub.8+ hydrocarbon stream 420.

[0039] The C.sub.8+ stream 420 is run through a clay treater 4 and then streamed 430 to a xylene re-run unit 5 to separate C.sub.8+ hydrocarbons into a C.sub.8 hydrocarbon stream 431 and C.sub.9+ (heavy aromatic MoGas) hydrocarbon stream 60. The xylene-re-run unit 5 is a distillation column including trays and/or structured packing and/or random packing to fractionate mixed xylenes from heavier aromatics. The C.sub.8 hydrocarbon stream 431 proceeds to a para-xylene extraction unit 6 to recover para-xylene in a para-xylene product stream 433. The para-xylene extraction unit 6 also produces a C.sub.7 cut MoGas stream 432, which combines with C.sub.7 cut MoGas stream 411 to produce C.sub.7cut MoGas stream 412. Other xylenes are recovered and sent to xylene isomerization unit 7 by stream 434 to convert them to para-xylene. The isomerization unit 7 includes a catalyst, such as a zeolite, that assists in transforming ortho- and meta-xylenes to para-xylene. The isomerized xylenes are sent to a splitter column 8. The converted fraction is recycled back to para-xylene extraction unit 6 from splitter column 8 by way of streams 452 and 431. Splitter top stream 451 is recycled back to reformate splitter 1. The heavy fraction from the xylene rerun unit 5 is recovered as aromatic bottoms (shown as C.sub.9+ and Hvy Aro MoGas in FIG. 2 at stream 60).

[0040] Referring to FIG. 3, a schematic is shown of one aspect of the present disclosure, in which the aromatic bottoms stream 60 is recycled and fed back into the catalytic reforming unit 300. Aromatic bottoms relate to C.sub.9+ aromatics and may be a more complex mixture of compounds including di-aromatics. C.sub.9+ aromatics boil in the range of about 100° C. to about 450° C.

[0041] Aromatics bottoms at stream 60 are recycled to the NREF 300 for full extinction or partially if a bleed stream 250 is required. Recycled aromatics bottoms at stream 60 will not substantially change the operating conditions, as the stream 60 enters at a temperature in the naphtha and gasoline boiling range. The liquid hourly space velocity (“LHSV”) may be impacted, as there will be increased feed to the respective reforming unit.

[0042] Referring to FIG. 4, a more detailed view of the NREF is seen, with the aromatic bottom stream 60 flowing from the ARC back into the NREF. The bottoms stream 60 may enter the NREF at one, two or three points. The NREF features three reactors 310 320 330 and a furnace 350 or multiple furnaces placed in between. The multiple reactors may be used due to the endothermicity of the reaction and catalyst deactivation in each reactor. The effluents are heated to the reaction temperature by the furnace and send to the next reactor. The hydrotreated naphtha 30 enters from the NHT and passes through the heat exchanges 360 furnace 350 and into the first reactor 310. The reaction passes back through the furnace 350 and to the second reactor 320. The reactants passes back through the furnace 350 and into the third reactor 330 and then passes through the heat exchanger 360 and to a splitter 340 to separate light gases 31 and reformate 40, which flows to the ARC 400.

[0043] FIG. 5 shows a slightly different arrangement of the NREF, with independent furnaces 350 placed between the reactors 310 320 330. Also depicted are feeds for catalyst regeneration through feeding spent catalyst to a regenerator 360 and then back to each reactor. As with FIG. 4, an aromatic bottoms stream of C.sub.9+ hydrocarbons can enter the NREF prior to entry in the first reactor 310, the second reactor 320 or the third reactor 330.

[0044] According to an aspect, either alone or in combination with any other aspect, a method for recovery of benzene, toluene and xylene, includes: supplying to a naphtha reforming unit (NREF) a stream of hydrotreated naphtha; allowing the stream to flow through the NREF to generate reformate and hydrogen gas; supplying at least a portion of reformate from the NREF to an aromatics recovery complex (ARC); flowing the portion of reformate in the ARC through a reformate splitter to generate a C.sub.7+ stream; flowing the C.sub.7+ stream through a second splitter to generate a C.sub.8+ stream; flowing the C.sub.8+ stream through a clay tower to deolefinate the C.sub.8+ stream; flowing the deolefinated C.sub.8+ stream through a xylene re-run splitter to obtain a C.sub.8 stream and a C.sub.9+ stream; and recycling the C.sub.9+ stream back to enter the stream of hydrotreated naphtha to thereby reprocess the C.sub.9+ stream to recover benzene, toluene and xylene.

[0045] According to a second aspect, either alone or in combination with any other aspect, the C.sub.9+ stream recycles to the stream of hydrotreated naphtha prior to entering the NREF.

[0046] According to a third aspect, either alone or in combination with any other aspect, the C.sub.9+ stream recycles to the stream of hydrotreated naphtha within the NREF.

[0047] According to a fourth aspect, either alone or in combination with any other aspect, the C.sub.9+ stream feeds into the NREF equally before each reactor unit contained therein.

[0048] According to a fifth aspect, either alone or in combination with any other aspect, the NREF comprises a temperature and a catalyst suitable to provide sufficient energy to break an alkyl carbon-carbon bond.

[0049] According to a sixth aspect, either alone or in combination with any other aspect, the operating temperature of the NREF is from about 490° C. to about 520° C.

[0050] According to a seventh aspect, either alone or in combination with any other aspect, the catalyst of the NREF is an acidic catalyst.

[0051] According to an eighth aspect, either alone or in combination with any other aspect, the catalyst is selected from a zeolite, a platinum compound, a palladium compound or combinations thereof.

[0052] According to a ninth aspect, either alone or in combination with any other aspect, the catalyst is a zeolite with a framework selected from Faujasite (FAU) (zeolite Y, USY), Beta (*BEA), Mordenite (MOR), ZSM-5 (MFI) or combinations thereof.

[0053] According to a tenth aspect, either alone or in combination with any other aspect, the method may also include: flowing the C.sub.8 stream to a para-xylene extraction unit to obtain a para-xylene stream and a xylene isomer stream; flowing the xylene isomer stream to a xylene isomerization unit coupled to a further splitter; and recycling the xylene isomer stream to the xylene re-run splitter, wherein further C.sub.9+ compounds join the C.sub.9+ stream.

[0054] According to an eleventh aspect, either alone or in combination with any other aspect, the NREF has a hydrogen/oil operating ratio of about 100 to about 2500 L/L.

[0055] According to a twelfth aspect, either alone or in combination with any other aspect, the NREF has a hydrogen/oil operating ratio of about 100 to about 1000 L/L.

[0056] According to a thirteenth aspect, either alone or in combination with any other aspect, the NREF has a hydrogen/oil operating ratio of about 100 to about 750 L/L

[0057] According to a fourteenth aspect, either alone or in combination with any other aspect, the NREF has an operating LHSV of about 0.5 to about 40 h.sup.−1.

[0058] According to a fifteenth aspect, either alone or in combination with any other aspect, the NREF has an operating LHSV of about 0.5 to about 10 h.sup.−1.

[0059] According to a sixteenth aspect, either alone or in combination with any other aspect, the NREF has an operating LHSV of about 0.5 to about 4 h.sup.−1.

[0060] According to a seventeenth aspect, either alone or in combination with any other aspect, the NREF has an operating pressure of about 1 to about 50 bar.

[0061] According to an eighteenth aspect, either alone or in combination with any other aspect, the NREF has an operating pressure of about 1 to about 20 bar.

[0062] According to a nineteenth aspect, either alone or in combination with any other aspect, the NREF has an operating temperature of about 250 to about 560° C.

[0063] According to a twentieth aspect, either alone or in combination with any other aspect, the NREF has an operating temperature of about 450 to about 560° C.

EXAMPLES

[0064] One or more of the previously described features will be further illustrated in the following example simulations using Arab light crude oil. The reformer was arranged as follows:

TABLE-US-00001 Hydrogen/Oil L/L 625 LHSV h.sup.−1 4 Pressure Bar 3 Temperature ° C. 520
with a catalyst of Pt on alumina, that is chlorinated in the process. The naphtha hydrotreater was arranged as follows:

TABLE-US-00002 Hydrogen/Oil L/L 200 LHSV h.sup.−1 6 Pressure Bar 20 Temperature ° C. 300
with a catalyst of Co—Mo on alumina. By recycling, the LHSV for the reformer increased from 4 to 4.5 h.sup.−1.

[0065] The difference between the two arrangements depicted in FIGS. 1 (Comparative Example A) and 3 (Inventive Example 1) were assessed for notable difference obtained by returning the C.sub.9+ stream of aromatic bottoms back to the NREF. The details are presented in Table 1 below.

TABLE-US-00003 Comparative Inventive Stream Name Units Example A Example 1 10 Crude Oil KBPSD 400.0 400.0 60 ARC Bottoms KBPSD 7.9 7.0 20 Naphtha to hydrotreater KBPSD 67.0 67.0 11 Atmospheric Residue KBPSD 200.5 200.5 30 Hydrotreated Naphtha KBPSD 66.2 74.2 11 Diesel KBPSD 164.2 164.2 40 Reformate KBPSD 53.0 60.9 43 Aromatics (BTX) Mtons/D 4.2 4.8 *KBPSD—kilo barrels per stream day; The returning line of the aromatic bottoms to the NREF caused an 11% decline in the amount of ARC bottoms present, while allowing almost a 14% increase in BTX production. This also minimizes C.sub.9+ production, which in turn minimizes the heavy ends in the gasoline as C.sub.9+ is no longer available to be added to the gasoline. Further, with this scheme, existing refinery equipment may be used without any further need to install additional process units to process this heavy stream.

[0066] Throughout this disclosure, ranges are provided. It is envisioned that each discrete value encompassed by the ranges are also included. Additionally, the ranges which may be formed by each discrete value encompassed by the explicitly disclosed ranges are equally envisioned.