Patent Publication Number: US-10759723-B2

Title: Methods and systems of upgrading heavy aromatics stream to petrochemical feedstock

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is divisional application of U.S. application Ser. No. 16/388,563, filed Apr. 18, 2019, which itself is a continuation-in-part application of U.S. application Ser. No. 16/032,642, filed on Jul. 11, 2018 and issued as U.S. Pat. No. 10,294,172 on May 21, 2019, which is a continuation application of U.S. application Ser. No. 15/435,039, filed on Feb. 16, 2017 and issued as U.S. Pat. No. 10,053,401 on Aug. 21, 2018. 
    
    
     TECHNICAL FIELD 
     The disclosure relates to methods and systems of upgrading heavy aromatics stream to petrochemical feedstock, and more specifically to a combination of a hydrodearylation unit and a transalkylation unit in an aromatics recovery complex. 
     BACKGROUND 
     In an aromatics complex, a variety of process units are used to convert naphtha or pyrolysis gasoline into benzene, toluene and mixed xylenes, which are basic petrochemical intermediates used for the production of various other chemical products. In order to maximize the production of benzene, toluene and mixed xylenes, the feed to an aromatics complex is generally limited from C 6  up to C 11  compounds. In most aromatic complexes, the mixed xylenes are processed within the complex to produce the particular isomer—para-xylene, which can be processed downstream to produce terephthalic acid. This terephthalic acid is used to make polyesters, such as polyethylene terephthalate. In order to increase the production of benzene and para-xylene, the toluene and C 9  and C 10  aromatics are processed within the complex through a toluene, C 9 , C 10  transalkylation/toluene disproportionation (TA/TDP) process unit to produce benzene and xylenes. Any remaining toluene, C 9 , and C 10  aromatics are recycled to extinction. Compounds heavier than C 10  are generally not processed in the TA/TDP unit, as they tend to cause rapid deactivation of the catalysts used at the higher temperatures used in these units, often greater than 400° C. 
     When para-xylene is recovered from mixed xylenes by a selective adsorption process unit in the complex, the C 8  feed to the selective adsorption unit is processed to eliminate olefins and alkenyl aromatics such as styrene in the feed. Olefinic material can react and occlude the pores of the zeolite adsorbent. The olefinic material is removed by passing a C 8+  stream across a clay or acidic catalyst to react olefins and alkenyl aromatics with another (typically aromatic) molecule, forming heavier compounds (C 16+ ). These heavier compounds are typically removed from the mixed xylenes by fractionation. The heavy compounds cannot be processed in the TA/TDP unit due to their tendency to deactivate the catalyst and are generally removed from the complex as lower value fuels blend stock. As many of the heavy alkyl aromatic compounds fractionate with the fractions containing greater than 10 carbon atoms, they are not typically sent as feedstock to the transalkylation unit, and instead are sent to gasoline blending or used as fuel oil. 
     SUMMARY 
     A need has been recognized for the characterization and recovery of higher value light aromatics in the range from C 6  to C 10  from certain heavy compounds before processing aromatic streams through specialized product production units, such as the TA/TDP unit. Embodiments disclosed here include characterization of the products formed during the treatment of aromatics streams during processing of hydrocarbons. Certain embodiments include processes for recovery of alkyl mono-aromatic compounds. An embodiment of the process for recovery of alkyl mono-aromatic compounds includes the steps of (a) supplying a feed stream containing C 9+  compounds from an aromatic complex to a separator to produce a first product stream containing C 9  and C 10  compounds and a second product stream containing one or more of heavy alkyl aromatic compounds and alkyl-bridged non-condensed alkyl multi-aromatic compounds; (b) supplying the first product stream containing C 9  and C 10  compounds to a transalkylation/toluene disproportionation process unit to yield a third product stream enriched in C 8  compounds; (c) allowing a hydrogen stream and the second product stream to react in presence of a catalyst under specific reaction conditions in a hydrodearylation reactor to yield a fourth product stream containing one or more alkyl mono-aromatic compounds and a fifth product stream containing C 11+  compounds; and (d) supplying the fourth product stream to the toluene transalkylation/toluene disproportionation process unit to produce alkyl mono-aromatic compounds. In an embodiment, the fourth product stream and the first product stream containing C 9  and C 10  compounds are mixed to form a feed stream for the toluene transalkylation/toluene disproportionation process unit. The feed stream can be from a xylene rerun column of an aromatic recovery process. The feed stream can be undiluted by a solvent. A portion of the hydrogen stream may be supplied to a catalyst bed in the hydrodearylation reactor to quench the catalyst bed. The process can further include supplying the fourth product stream containing one or more alkyl mono-aromatic compounds to a separator to recover a benzene-containing stream; and supplying the benzene-containing stream to the toluene transalkylation/toluene disproportionation process unit to produce alkyl mono-aromatic compounds. The process can further include recovering a C 8  stream from the separator; and supplying the C 8  stream to a para-xylene unit to produce para-xylene. The process can further include recovering a C 9+  stream from the separator; and supplying the C 9+  stream to the toluene transalkylation/toluene disproportionation process unit to produce alkyl mono-aromatic compounds. The process can further include supplying the fourth product stream containing one or more alkyl mono-aromatic compounds to a separator to recover a toluene-containing stream; and supplying the toluene-containing stream to the toluene transalkylation/toluene disproportionation process unit to produce alkyl mono-aromatic compounds. 
     The catalyst in the hydrodearylation reactor can include a support made of one or more of silica, alumina, titania, and a combination thereof. The catalyst in the hydrodearylation reactor can further include an acidic component being at least one member of the group consisting of amorphous silica-alumina, zeolite, and combinations thereof. The zeolite can be one or more of or derived from FAU, *BEA, MOR, MFI, or MWW framework types, wherein each of these codes correspond to a zeolite structure present in the database of zeolite structures as maintained by the Structure Commission of the International Zeolite Association. The catalyst in the hydrodearylation reactor can include an IUPAC Group 6-10 metal that is at least one member of the group consisting of iron, cobalt, nickel, molybdenum, tungsten, and combinations thereof. The IUPAC Group 8-10 metal can be present ranging from 2 to 20 percent by weight of the catalyst and the IUPAC Group 6 metal can be present ranging from 1 to 25 percent by weight of the catalyst. The conditions in the hydrodearylation reactor can include an operating temperature in the range of about 200 to 450° C., or about 250 to 450° C. and an operating hydrogen partial pressure in the range of about 5 bar gauge to 100 bar gauge. One of the alkyl mono-aromatic compounds produced by the toluene transalkylation/toluene disproportionation is a para-xylene. 
     Certain embodiments include systems for recovery of alkyl mono-aromatic compounds. An embodiment of a system for conversion of alkyl-bridged non-condensed alkyl multi-aromatic compounds to alkyl mono-aromatic compounds includes the following components: (i) a first separator adapted to receive a feed stream containing one or more of heavy alkyl aromatic compounds and one or more alkyl-bridged non-condensed alkyl multi-aromatic compounds having at least two benzene rings connected by an alkyl bridge group with at least two carbons and the benzene rings being connected to different carbons of the alkyl bridge group, and produces a first product stream containing C 9  and C 10  compounds and a second product stream containing one or more of heavy alkyl aromatic compounds and alkyl-bridged non-condensed alkyl multi-aromatic compounds; (ii) a hydrodearylation reactor fluidly coupled to the first separator and adapted to receive a hydrogen stream and the second product stream and to produce a third product stream in presence of a catalyst, the third product stream containing one or more alkyl mono-aromatic compounds; and (iii) a second separator fluidly coupled to the hydrodearylation reactor and adapted to receive the third product stream and to produce a benzene-containing stream, a toluene-containing stream, a C 8 -rich stream, and a bottoms C 9+  stream. The system can also include a transalkylation unit fluidly coupled to the second separator and adapted to receive the first product stream and one or more of the benzene-containing stream, the toluene-containing stream, and the bottoms C 9+  stream, and to produce alkyl mono-aromatic compounds. The system can also include a para-xylene unit fluidly coupled to the second separator and adapted to receive the C 8 -rich stream and to produce a para-xylene-rich stream. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings. Embodiments are illustrated by way of example and not by way of limitation in accompanying drawings. 
         FIG. 1  is a schematic representation of certain components of an aromatics processing system that upgrades fuel oil to a petrochemical feedstock, according to an exemplary embodiment. 
         FIG. 2  is a schematic representation of certain components of an aromatics processing system that upgrades fuel oil to a petrochemical feedstock, according to an exemplary embodiment. 
         FIG. 3  is a schematic representation of certain components of an aromatics processing system that upgrades fuel oil to a petrochemical feedstock, according to an exemplary embodiment. 
         FIG. 4  is a schematic representation of certain components of an aromatics processing system that upgrades fuel oil to a petrochemical feedstock, according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure describes various embodiments related to processes, devices, and systems for conversion of alkyl-bridged non-condensed alkyl aromatic compounds to alkyl mono-aromatic compounds. Further embodiments are described and disclosed. 
     In the following description, numerous details are set forth in order to provide a thorough understanding of the various embodiments. In other instances, well-known processes, devices, and systems may not have been described in particular detail in order not to unnecessarily obscure the various embodiments. Additionally, illustrations of the various embodiments may omit certain features or details in order to not obscure the various embodiments. Here, reference is made to the accompanying drawings that form a part of this disclosure. The drawings may provide an illustration of some of the various embodiments in which the subject matter of the present disclosure may be practiced. Other embodiments may be utilized, and logical changes may be made without departing from the scope of this disclosure. Therefore, the following detailed description is not to be taken in a limiting sense. 
     The description may use the phrases “in some embodiments,” “in various embodiments,” “in an embodiment,” or “in embodiments,” which may each refer to one or more of the same or different embodiments. Furthermore, the terms “comprising,” “including,” “having,” and the like, as used with respect to embodiments of the present disclosure, are synonymous. 
     As used in this disclosure, the term “hydrodearylation” refers to a process for cleaving of the alkyl bridge of non-condensed alkyl-bridged multi-aromatics or heavy alkyl aromatic compounds to form alkyl mono-aromatics, in the presence a catalyst and hydrogen. 
     As used in this disclosure, the term “stream” (and variations of this term, such as hydrocarbon stream, feed stream, product stream, and the like) may include one or more of various hydrocarbon compounds, such as straight chain, branched or cyclical alkanes, alkenes, alkadienes, alkynes, alkyl aromatics, alkenyl aromatics, condensed and non-condensed di-, tri- and tetra-aromatics, and gases such as hydrogen and methane, C 2+  hydrocarbons and further may include various impurities. 
     As used in this disclosure, the term “zone” refers to an area including one or more equipment, or one or more sub-zones. Equipment may include one or more reactors or reactor vessels, heaters, heat exchangers, pipes, pumps, compressors, and controllers. Additionally, an equipment, such as reactor, dryer, or vessels, further may include one or more zones. 
     As used in this disclosure, the term “rich” means an amount of at least 30% or greater, by mole percentage of a compound or class of compounds in a stream. Certain streams rich in a compound or class of compounds can contain about 50% or greater, by mole percentage of the particular compound or class of compounds in the streams. In certain cases, mole percentage may be replaced by weight percentage, in accordance with standard industry usage. 
     As used in this disclosure, the term “mixed xylenes” refers to a mixture containing one or more C 8  aromatics, including any one of the three isomers of di-methylbenzene and ethylbenzene. As used in this disclosure, the term “conversion” refers to the conversion of compounds containing multiple aromatic rings or mono-aromatic compounds with heavy (C4+) alkyl groups boiling above 210° C. to mono-aromatic compounds with a lighter alkyl groups boiling below 210° C. 
     During hydrocarbon processing, compounds composed of an aromatic ring with one or more coupled alkyl groups containing three or more carbon molecules per alkyl group are formed. Formation of these compounds may be from processes used by petroleum refiners and petrochemical producers to produce aromatic compounds from non-aromatic hydrocarbons, such as catalytic reforming. As many of these heavy alkyl aromatic compounds fractionate with the fractions containing greater than 10 carbon atoms, they are not typically sent as feedstock to the transalkylation unit, and instead are sent to gasoline blending or used as fuel oil. The methods and systems disclosed here result in upgrading a low-value fuel oil to petrochemical feed. 
     Provided here is an embodiment of a process to fractionate an effluent stream of a xylene re-run column and supply it as a feed stream to a hydrodearylation unit. In an embodiment, this stream is either subsequently processed or used to upgrade the fuel oil components (heavy fraction) to petrochemical feedstock. Methods and system disclosed here create value by processing a reject/bottoms stream from an aromatic complex and by upgrading a significant proportion of fuel oil into petrochemical feedstock. In an embodiment, the C 9+  stream from a xylene re-run column is fractionated to remove C 9  and C 10 , leaving a C 11+  stream, which is considered as a low-value fuel oil stream. The C 9  and C 10  stream is directed to a TA/TDP process unit to yield increased quantities of C 8  that can be further processed downstream to yield para-xylene. The C 11+  fuel oil stream is subjected to hydrodearylation and the hydrodearylated liquid products sent for processing in a transalkylation unit. The unconverted C 11+  (mainly condensed diaromatics) stream is directed as fuel oil. 
     Disclosed here is a process for recovery of alkyl mono-aromatic compounds that includes the following steps. A feed stream containing C 9+  compounds from an aromatic complex is supplied to a separator to produce a first product stream containing C 9  and C 10  compounds and a second product stream containing one or more of heavy alkyl aromatic compounds and alkyl-bridged non-condensed alkyl multi-aromatic compounds. In an embodiment, the feed stream is from a xylene rerun column of an aromatic recovery process. In certain embodiments, the feed stream is undiluted by solvents and is directly supplied to the separator. In an embodiment, the second product stream contains C 11+  compounds. This first product stream containing C 9  and C 10  compounds is supplied to a TA/TDP process unit to yield a third product stream enriched in C 8  compounds. The second product stream and a hydrogen stream are supplied to a hydrodearylation reactor to react in presence of a catalyst under specific reaction conditions to yield a fourth product stream containing C 9  and C 10  compounds and a fifth product stream containing unconverted C 11+  compounds. The fourth product stream is supplied further to a TA/TDP process unit to supply and produce alkyl mono-aromatic compounds. In certain embodiments, the C 8  content in the fourth product stream increases following the processing in the TA/TDP process unit. In certain embodiments, the fifth product stream containing unconverted C 11+  compounds can be recycled to the hydrodearylation reactor. In certain embodiments, the fourth product stream and the first product stream containing C9 and C10 compounds are mixed to form a feed stream for the TA/TDP process unit. In certain embodiments, the alkyl mono-aromatic compounds produced by the TA/TDP process unit is para-xylene. In certain embodiments, the hydrodearylated products are supplied to a separator to recover a benzene-containing stream. And this benzene-containing stream can be directed to an appropriate part of the TA/TPD process unit. In certain embodiments, the hydrodearylated products are supplied to a separator to recover a toluene-containing stream. And this toluene-containing stream can be directed to an appropriate part of the TA/TPD process unit. 
     In an embodiment, the feedstock to the hydrodearylation reactor (either whole or fractionated) is mixed with an excess of hydrogen gas in a mixing zone. A portion of the hydrogen gas is mixed with the feedstock to produce a hydrogen-enriched liquid hydrocarbon feedstock. This hydrogen-enriched liquid hydrocarbon feedstock and undissolved hydrogen is supplied to a flashing zone in which at least a portion of undissolved hydrogen is flashed, and the hydrogen is recovered and recycled. The hydrogen-enriched liquid hydrocarbon feedstock from the flashing zone is supplied as a feed stream to the hydrodearylation reactor. The hydrodearylated liquid product stream that is recovered from the hydrodearylation reactor is further processed as provided here. 
     In certain embodiments, the hydrogen stream is combined with the second product stream before being supplied to the hydrodearylation reactor. In certain embodiments, the hydrogen stream includes a recycled hydrogen stream and a makeup hydrogen stream. In certain embodiments, the hydrogen stream comprises at least 70% hydrogen by weight. The catalyst can be presented as a catalyst bed in the reactor. In certain embodiments, a portion of the hydrogen stream is fed to the catalyst bed in the reactor to quench the catalyst bed. In certain embodiments, the catalyst bed is comprised of two or more catalyst beds. The catalyst can include a support that is at least one member of the group consisting of silica, alumina, titania, and combinations thereof, and further includes an acidic component that is at least one member of the group consisting of amorphous silica-alumina, zeolite, and combinations thereof. The zeolite can be one or more of or derived from FAU, *BEA, MOR, MFI, or MWW framework types, wherein each of these codes correspond to a zeolite structure present in the database of zeolite structures as maintained by the Structure Commission of the International Zeolite Association. In certain embodiments, the catalyst includes an IUPAC Group 8-10 metal and an IUPAC Group 6 metal. In certain embodiments, the catalyst includes an IUPAC Group 8-10 metal that is at least one member of the group consisting of iron, cobalt, and nickel, and combinations thereof. The catalyst includes an IUPAC Group 6 metal that is at least one member of the group consisting of molybdenum and tungsten, and combinations thereof. In certain embodiments, the IUPAC Group 8-10 metal is 2 to 20 percent by weight of the catalyst and the IUPAC Group 6 metal is 1 to 25 percent by weight of the catalyst. In certain embodiments, the catalyst is comprised of nickel, molybdenum, ultrastable Y-type zeolite, and silica-alumina support. 
     In certain embodiments, the specific reaction conditions include an operating temperature of the reactor during the hydrodearylation reaction that is in the range of 200 to 450° C. In certain embodiments, the specific reaction conditions include an operating temperature of the reactor during the hydrodearylation reaction that is in the range of 250 to 350° C. In certain embodiments, the specific reaction conditions include an operating temperature of the reactor during the hydrodearylation reaction that is in the range of 300 to 350° C. The specific reaction conditions can include a hydrogen partial pressure of the reactor during the hydrodearylation reaction that is in the range of 5 to 100 bar gauge. In certain embodiments, the specific reaction conditions can include a hydrogen partial pressure of the reactor during the hydrodearylation reaction that is in the range of 50 to 100 bar gauge. In certain embodiments, the specific reaction conditions can include a hydrogen partial pressure of the reactor during the hydrodearylation reaction that is in the range of 5 to 80 bar gauge. In certain embodiments, the specific reaction conditions can include a hydrogen partial pressure of the reactor during the hydrodearylation reaction that is in the range of 5 to 30 bar gauge. The hydrogen partial pressure of the reactor during the hydrodearylation reaction can be maintained at less than 20 bar gauge. The specific reaction conditions can include a feed rate of the hydrogen stream that is in the range of 100 to 1000 standard liter per liter of feedstock. The specific reaction conditions can include a feed rate of the hydrogen stream that is in the range of 100 to 300 standard liter per liter of feedstock. 
     In an embodiment, a system is provided for conversion of alkyl-bridged non-condensed alkyl multi-aromatic compounds to alkyl mono-aromatic compounds. The system includes (i) a first separator that receives a feed stream containing one or more of heavy alkyl aromatic compounds and one or more alkyl-bridged non-condensed alkyl multi-aromatic compounds having at least two benzene rings connected by an alkyl bridge group with at least two carbons and the benzene rings that is connected to different carbons of the alkyl bridge group, and produces a first product stream containing C 9  and C 10  compounds and a second product stream containing one or more of heavy alkyl aromatic compounds and alkyl-bridged non-condensed alkyl multi-aromatic compounds; (ii) a hydrodearylation reactor fluidly coupled to the first separator and adapted to receive a hydrogen stream and the second product stream and to produce a third product stream in presence of a catalyst, and the third product stream containing one or more alkyl mono-aromatic compounds; (iii) a second separator fluidly coupled to the hydrodearylation reactor and adapted to receive the third product stream and to produce a benzene-containing stream, a toluene-containing stream, a C 8 -rich stream, and a bottoms C 9+  stream. In certain embodiments, the system further includes a transalkylation unit that is adapted to receive the toluene-containing stream and the bottoms C 9+  stream and to produce alkyl mono-aromatic compounds. In order to increase the production of benzene and para-xylene, the toluene and C 9  and C 10  aromatics are processed within the complex through a toluene, C 9 , C 10  transalkylation/toluene disproportionation (TA/TDP) process unit to produce benzene and xylenes. Any remaining toluene, C 9 , and C 10  aromatics are recycled to extinction. In certain embodiments, the second product stream is a C 11+  stream. In certain embodiments, the alkyl mono-aromatic compounds produced by the transalkylation unit includes para-xylene. 
     A typical refinery with an aromatic complex contains the following units: an atmospheric distillation unit, a diesel hydrotreating unit, an atmospheric residue unit, a naphtha hydrotreating unit, a naphtha reforming unit and an aromatics complex. The whole crude oil is distilled in an atmospheric distillation column to recover a naphtha fraction (compounds with a boiling point ranging from 36° C. to 180° C.), diesel fraction (compounds with a boiling point ranging from 180° C. to 370° C.) and atmospheric residue fraction (compounds with a boiling point at 370° C. or higher). The naphtha fraction is hydrotreated in a naphtha hydrotreating unit to reduce the sulfur and nitrogen content to less than 0.5 part per million by weight and the hydrotreated naphtha fraction is sent to a catalytic reforming unit to improve its quality, such as, an increase in the octane number to produce gasoline blending stream or feedstock for an aromatics recovery unit. Similarly, the diesel fraction is hydrotreated in a separate hydrotreating unit to desulfurize the diesel oil to obtain diesel fraction meeting the stringent specifications of sulfur content that is less than 10 parts per million. The atmospheric residue fraction is either used a fuel oil component or sent to other separation/conversion units to convert low value hydrocarbons to high value products. The reformate fraction from the catalytic reforming unit can be used as gasoline blending component or sent to an aromatic complex to recover high value aromatics, such as, benzene, toluene, and xylenes. The reformate fraction from catalytic reforming unit is split into two fractions: light and heavy reformate. The light reformate is sent to a benzene extraction unit to extract the benzene and recover gasoline that is substantially free of benzene. The heavy reformate stream is sent to a para-xylene (p-xylene) extraction unit to recover p-xylene. Other xylenes that are recovered from the p-xylene unit are sent to a xylene isomerization unit to convert them to p-xylene. The converted fraction is recycled to the p-xylene extraction unit. The heavy fraction from the p-xylene extraction unit is recovered as a process reject or bottoms stream. The aromatics bottoms fraction from an aromatic recovery complex is processed in two ways. One, the aromatics bottoms fraction is fractionated into a 180−° C. fraction ((compounds with a boiling point less than 180° C.) and sent to a gasoline pool as blending components, and a 180+° C. fraction sent to a hydrodearylation unit. Alternatively, the aromatics bottoms fraction is sent directly to a hydrodearylation unit to recover light alkyl mono-aromatic compounds from heavy alkyl aromatic and alkyl-bridged non-condensed alkyl aromatic compounds. A typical system for aromatic transalkylation to ethylbenzene and xylenes includes the following components: a first transalkylation reactor, a series of separators, a second transalkylation reactor, a stabilizer, and a p-xylene production unit. The feed stream to the first transalkylation reactor is a mixture of a C 9+  alkyl aromatics mixture and benzene. This feed stream in brought into contact with a zeolite catalyst in the first transalkylation reactor. The effluent stream from this transalkylation reactor is directed to a separation column. This effluent stream may be combined with effluent streams from the second transalkylation reactor before entry into a separation column. There are three exit streams from the separation column: an overhead stream containing benzene, a bottoms stream of C 8+  aromatics including ethylbenzene and xylenes, and a side-cut stream containing toluene. The overhead stream is recycled to the first transalkylation reactor. The bottoms stream is supplied to a second separation column. An overhead stream containing ethylbenzene and xylenes from the second separation column is directed to a para-xylene unit to produce a para-xylene product stream and a bottoms stream of C 9+  alkylaromatics. The side-cut stream from the separation column is recycled to a second transalkylation unit with or without the recovery of toluene. This side-cut stream from the separation column can be combined with bottoms stream from second separation column to form a combined stream that is supplied to a third separation column. This separation column separates the combined stream into a bottoms stream of C 11+  alkylaromatics (“heavies”) and an overhead stream of C 9 , C 10  alkylaromatics, and lighter compounds (including C 7  alkylaromatics) directed to a second transalkylation unit. Hydrogen is also supplied to the second transalkylation unit. Here, in the second transalkylation unit, the overhead stream and hydrogen are brought in contact with a transalkylation catalyst, and the effluent stream is directed to a stabilizer column. Two streams exit the stabilizer column: an overhead stream of light end hydrocarbons (generally comprising at least ethane) and a bottom stream of a second transalkylation product. 
     As previously described, the aromatic bottoms stream from an aromatic recovery complex can be directly supplied to a hydrodearylation unit and a hydrodearylated liquid product stream can be recovered for further processing. In an embodiment  100  as described in  FIG. 1 , the aromatic bottoms stream  104  from an aromatic recovery complex 102 is sent to a separator  106 . In an embodiment, this separator  106  can be a separation unit including a distillation column with 5 or more theoretical trays. In an embodiment, the separator  106  can be a flash vessel or a stripper. Two streams exit the separator  106 : an overhead stream  108  containing C 9  and C 10  compounds and a bottoms stream  110  containing C 11+  compounds. In an embodiment, the overhead stream  108  contains about 50-99 wt. % of the C 9  and C 10  compounds. In another embodiment, the overhead stream  108  contains about 60-99 wt. % of the C 9  and C 10  compounds. In an embodiment, the overhead stream  108  contains about 80-99 wt. % of the C 9  and C 10  compounds. For example, simulated distillation data indicated that the overhead stream  108  contains about 90-99 wt. % of the C 9  and C 10  compounds. And this data aligned with the two-dimensional gas chromatography data obtained in this instance, which revealed the stream  104  as containing about 91 wt. % of the C 9  and C 10  compounds. The C 9+  feed from a refinery can be “heavy” with a different composition. In other instances, the C 9  and C 10  compounds made up about 68 wt. % of the feed as determined by two-dimensional gas chromatography. The bottoms stream  110  containing C 11+  compounds is directed to a hydrodearylation unit  112  for processing into a hydrodearylated liquid product stream  114 . In an embodiment, the bottoms stream  110  contains about 5-99 wt. % of C 11+  compounds. In another embodiment, the bottoms stream  110  contains about 30-99 wt. % of C 11+  compounds. In an embodiment, the bottoms stream  110  contains about 80-99 wt. % of C 11+  compounds. In an embodiment, the hydrodearylated liquid product stream  114  contains greater than 10 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  114  contains greater than 20 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  114  contains greater than 40 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  114  contains about 50 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  114  contains about 70 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  114  contains about 90 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  114  contains less than 70 wt. % of di-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  114  contains less than 50 wt. % of di-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  114  contains less than 40 wt. % of di-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  114  contains less than 20 wt. % of di-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  114  contains less than 10 wt. % of di-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  114  contains less than 1 wt. % of di-aromatic compounds. The overhead stream  108  containing C 9  and C 10  compounds is combined with the hydrodearylated liquid product stream  114  leaving the hydrodearylation unit, and this combined stream  116  is supplied to a transalkylation reactor for further processing. 
     In another embodiment, the aromatic bottoms stream from an aromatic recovery complex is sent to a separator. In an embodiment, this separator can be a separation unit including a distillation column with 5 or more theoretical trays. In an embodiment, the separator can be a flash vessel or a stripper. In an embodiment  200  as described in  FIG. 2 , the aromatic bottoms stream  204  from an aromatic recovery complex 202 is sent to a first separator  206 . Two streams exit the first separator  206 : an overhead stream  208  containing C 9  and C 10  compounds and a bottoms stream  210  containing C 11+  compounds. In an embodiment, the overhead stream  208  contains about 50-99 wt. % of the C 9  and C 10  compounds. In another embodiment, the overhead stream  208  contains about 60-99 wt. % of the C 9  and C 10  compounds. In an embodiment, the overhead stream  208  contains about 80-99 wt. % of the C 9  and C 10  compounds. In an embodiment, the overhead stream  208  contains about 90-99 wt. % of the C 9  and C 10  compounds. The bottoms stream  210  containing C 11+  compounds is directed to a hydrodearylation unit  212  for processing a hydrodearylated liquid product stream  214 . In an embodiment, the bottoms stream  210  contains about 5-99 wt. % of C 11+  compounds. In another embodiment, the bottoms stream  210  contains about 30-99 wt. % of C 11+  compounds. In an embodiment, the bottoms stream  210  contains about 80-99 wt. % of C 11+  compounds. The hydrodearylated liquid product stream  214  is supplied to a second separator  216 . In an embodiment, the hydrodearylated liquid product stream  214  contains about 10 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  214  contains about 20 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  214  contains about 40 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  214  contains about 50 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  214  contains about 70 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  214  contains about 90 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  214  contains less than 70 wt. % of di-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  214  contains less than 40 wt. % of di-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  214  contains less than 20 wt. % of di-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  214  contains less than 10 wt. % of di-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  214  contains less than 1 wt. % of di-aromatic compounds. The hydrodearylated liquid product stream  214  is supplied to a second separator  216 . Four streams exit the second separator  216 : a benzene-containing stream  218 , a toluene-containing stream  220 , a C 8−  containing stream  222 , and a bottoms C 9+  stream  224 . In an embodiment, the benzene-containing stream  218  contains less than 30 wt. % of benzene. In another embodiment, the benzene-containing stream  218  contains less than 20 wt. % of benzene. In another embodiment, the benzene-containing stream  218  contains less than 10 wt. % of benzene. In another embodiment, the benzene-containing stream  218  contains less than 5 wt. % of benzene. The toluene-containing stream  220  can be directed to a transalkylation reactor as a feed stream. In the transalkylation reactor, the toluene is combined with a C 9+  stream to produce alkyl mono-aromatic compounds. In an embodiment, the toluene-containing stream  220  contains less than 30 wt. % of toluene. In another embodiment, the toluene-containing stream  220  contains less than 20 wt. % of toluene. In another embodiment, the toluene-containing stream  220  contains less than 15 wt. % of toluene. In another embodiment, the toluene-containing stream  220  contains less than 10 wt. % of toluene. The C 8 -containing stream  222  is directed to the p-xylene production unit. In an embodiment, the C 8 -containing stream  222  contains less than 30 wt. % of C 8  compounds, such as xylene and ethylbenzene. In another embodiment, the C 8 -containing stream  222  contains less than 20 wt. % of these C 8  compounds. In another embodiment, the C 8 -containing stream  222  contains less than 10 wt. % of these C 8  compounds. The C 9+  stream  224  can be supplied as part of a feed stream  226  to a transalkylation unit. In an embodiment, the C 9+  stream  224  is combined with the overhead stream  208  containing C 9  and C 10  compounds and supplied as part of a feed stream  226  to the transalkylation unit. 
     In an embodiment  300  as described in  FIG. 3 , the aromatic bottoms stream from an aromatic recovery complex is sent to a first separator  302 . Two streams exit the first separator  302 : an overhead stream  304  containing C 9  and C 10  compounds and a bottoms stream  306  containing C 11+  compounds. In an embodiment, the overhead stream  304  contains about 50-99 wt. % of the C 9  and C 10  compounds. In another embodiment, the overhead stream  304  contains about 60-99 wt. % of the C 9  and C 10  compounds. In an embodiment, the overhead stream  304  contains about 80-99 wt. % of the C 9  and C 10  compounds. For example, simulated distillation data indicated that the overhead stream  304  contains about 90-99 wt. % of the C 9  and C 10  compounds. 
     In an embodiment, the overhead stream  304  containing C 9  and C 10  compounds can be supplied as part of a feed stream  320  to a transalkylation unit. The bottoms stream  306  containing C 11+  compounds is directed to a hydrodearylation unit  308  for processing into a hydrodearylated liquid product stream  310 . In an embodiment, the bottoms stream  306  contains about 5-99 wt. % of C 11+  compounds. In another embodiment, the bottoms stream  306  contains about 30-99 wt. % of C 11+  compounds. In an embodiment, the bottoms stream  306  contains about 80-99 wt. % of C 11+  compounds. The hydrodearylated liquid product stream  310  is sent to a second separator  312 . In an embodiment, the hydrodearylated liquid product stream  310  contains about 10 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  310  contains about 20 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  310  contains about 40 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  310  contains about 50 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  310  contains about 70 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  310  contains about 90 wt. % of alkyl mono-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  310  contains less than 70 wt. % of di-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  310  contains less than 40 wt. % of di-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  310  contains less than 20 wt. % of di-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  310  contains less than 10 wt. % of di-aromatic compounds. In an embodiment, the hydrodearylated liquid product stream  310  contains less than 1 wt. % of di-aromatic compounds. 
     Four streams exit the second separator  312 : a benzene-containing stream  314 , a first toluene-containing stream  316 , a first C 8 -containing stream  318 , and a bottoms C 9+  stream. In an embodiment, the benzene-containing stream  314  contains less than 30 wt. % of benzene. In another embodiment, the benzene-containing stream  314  contains less than 20 wt. % of benzene. In another embodiment, the benzene-containing stream  314  contains less than 10 wt. % of benzene. In another embodiment, the benzene-containing stream  314  contains less than 5 wt. % of benzene. In an embodiment, the first toluene-containing stream  316  contains less than 30 wt. % of toluene. In another embodiment, the first toluene-containing stream  316  contains less than 20 wt. % of toluene. In another embodiment, the first toluene-containing stream  316  contains less than 15 wt. % of toluene. In another embodiment, the first toluene-containing stream  316  contains less than 10 wt. % of toluene. 
     In an embodiment, the first C 8 -containing stream  318  contains less than 30 wt. % of C 8  compounds, such as xylene and ethylbenzene. In another embodiment, the first C 8 -containing stream  318  contains less than 20 wt. % of these C 8  compounds. In another embodiment, the first C 8 -containing stream  318  contains less than 10 wt. % of these C 8  compounds. 
     In an embodiment, the bottoms C 9+  stream is supplied as part of a feed stream  320  to a transalkylation unit. The benzene-containing stream  314  is sent to a third separator  322 . Two streams exit the third separator  322 : a benzene-enriched stream  324  that is directed to a transalkylation reactor, and a second toluene-containing stream  326  that is directed to a fourth separator  328 , either as a separate feed stream or as a mixture with the first toluene-containing stream  316 . The first toluene-containing stream  316  can be supplied independently to the fourth separator  328 . Two streams exit the fourth separator  328 : a toluene-enriched stream  330  that is directed to a transalkylation reactor, and a second C 8 -containing stream  332  that is directed to a fifth separator  334 , either as a separate feed stream or as a mixture with the first C 8 -rich stream  318 . The first C 8 -rich stream  318  can be supplied independently to the fifth separator  334 . Two streams exit the fifth separator  334 : a C 8 -rich stream  336  that is directed to a p-xylene production unit, and a C 9+ -containing stream  338  that is directed to the transalkylation unit, either as a separate feed stream or as a mixture with the bottoms C 9+  stream  320 . In an embodiment, the C 9+ -containing stream  338  is combined with the overhead stream  304  containing C 9  and C 10  compounds from the first separator  302  and supplied as a feed stream  340  to the transalkylation unit. In another embodiment, the overhead stream  304  containing C 9  and C 10  compounds from the first separator  302 , the bottoms C 9+  stream  320  from the second separator  312 , and the C 9+ -containing stream  338  from the fifth separator  334  are combined and supplied as a feed stream  340  to a transalkylation unit. In another embodiment, each of these streams can be separately supplied to the first transalkylation unit. 
     Described here is a method and a system used for aromatic transalkylation to ethylbenzene and xylenes. In an embodiment  400  as described in  FIG. 4 , the aromatic bottoms stream from an aromatic recovery complex is sent to a hydrodearylation unit  402 . The hydrodearylated liquid product stream  404 , exiting from the hydrodearylation unit  402 , may also contain benzene, toluene and C 8  compounds, along with C 9+  alkyl aromatics. The hydrodearylated liquid product stream  404  is mixed with a benzene-containing stream  406  to form a feed stream  408 . The feed stream  408  is supplied to a transalkylation reactor  410  either with or without an additional hydrogen stream  412 . The feed stream  408  in the presence of a catalyst is converted to a first product stream  414  containing benzene, C 8+  aromatics including ethylbenzene and xylenes, and toluene. The first product stream  414  from the transalkylation reactor is directed to a first separation column  416 . The first product stream  414  is separated into three fractions: a first overhead stream  418  containing benzene, a first bottoms stream  420  containing C 8+  aromatics including ethylbenzene and xylenes, and a side-cut stream  422  containing toluene. The overhead stream  418  is recycled to the first transalkylation unit after benzene is removed via stream  424 . The first bottoms stream  420  of C 8+  aromatics, including ethylbenzene and xylenes, from the first separation column  416  is directed to a second separation column  426 . Two streams are recovered from this second separation column  426 : a second overhead stream  428  of ethylbenzene and xylenes, which is directed to a para-xylene unit  430  to produce a para-xylene-rich stream  432 , and a second bottoms stream  434  of C 9+  alkylaromatics. The side-cut stream  422  from the first separation column  416  is supplied as part of a feed stream  436  to a third separation column  438  after additional toluene is added or removed (not shown in  FIG. 4 ). Toluene is normally recycled to extinction by reacting with C 9  and C 10  to produce benzene and C 8 . If there is a decrease or lack of toluene in the system, make-up toluene may be required. If there is a decrease or lack of C 9 /C 10 , the amount of toluene can be proportionately reduced to make the stoichiometry. Certain market conditions may influence the removal of toluene from the system. The side-cut stream  422  is mixed with the second bottoms stream  434  of C 9+  alkylaromatics to form a combined feed stream  436  that is supplied to the third separation column  438 . Two streams are recovered from this third separation column  438 : a third bottoms stream  440  of C 11+  alkylaromatics and an overhead stream  442  of C 9  and C 10  alkylaromatics and lighter compounds (including C 7  alkylaromatics) directed to the transalkylation unit  410 . In certain embodiments, the unconverted products can be recycled to the hydrodearylation unit  402  (not shown in  FIG. 4 ). 
     Described here are processes and systems to fractionate the reject/bottoms stream of a xylene re-run column and to upgrade the fuel oil components (heavy fraction) to petrochemical feedstock. Also described are embodiments to upgrade the as-received reject/bottoms stream from the xylene re-run column. The C 9+  stream from a xylene re-run column is fractionated to remove C 9  and C 10 , leaving a C 11+  stream, which is considered as a low-value fuel oil stream. The C 9  and C 10  stream is directed to a TA/TDP process unit to be processed to yield increased quantities of C8 that can be further processed downstream to yield para-xylene. The C 11+  fuel oil stream is subjected to hydrodearylation. The unconverted C 11+  (mainly condensed diaromatics) stream is directed as fuel oil (approximately 25 wt. % of the original fuel oil stream). The methods and systems disclosed here allow a low-value fuel oil stream to be upgraded into petrochemical feedstock. Approximately 75% of the fuel oil is converted to isomer grade mixed xylenes. 
     EXAMPLES 
     A couple of methods and systems for integration of a hydrodearylation process with a transalkylation process are illustrated here. While the particular example provided below is for a stream containing C 9+  compounds, the methods and systems for integration of a hydrodearylation process with a transalkylation process can utilize a C 11+  feed. 
     Example 1 
     About 7.97 kilograms of an aromatic bottoms fraction, derived from a non-fractionated C 9+  feed, was distilled using a lab-scale true boiling point distillation column with 15 or more theoretical plate using the ASTM D2892 method. The feed stream contains about 83 weight percent (wt. %) of a gasoline fraction (compounds with a boiling point ranging from 36° C. to 180° C.) and about 17 wt. % of a residue fraction (compounds with a boiling point above 180° C.). 
     Properties and composition of the feed stream are shown in Tables 1 and 2. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Feedstock Aromatics 
                 Gasoline 
                 Residue 
               
               
                 Property 
                 Bottoms 
                 Fraction 
                 Fraction 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Density 
                 0.8834 
                 0.8762 
                 0.9181 
               
               
                 Octane Number 
                 Not applicable 
                 108 
                 Not applicable 
               
               
                 ASTM D2799 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Boiling Point, ° C. 
                 Boiling 
                 Boiling 
               
               
                   
                   
                 (Feedstock 
                 Point, ° C. 
                 Point, ° C. 
               
               
                   
                   
                 Aromatics 
                 (Gasoline 
                 (Residue 
               
               
                   
                 Property 
                 Bottoms) 
                 Fraction) 
                 Fraction) 
               
               
                   
                   
               
             
            
               
                   
                 Initial 
                 153 
                 154 
                 163 
               
               
                   
                 Boiling Point 
               
               
                   
                 10 wt. % 
                 163 
                 164 
                 190 
               
               
                   
                 30 wt. % 
                 166 
                 166 
                 202 
               
               
                   
                 50 wt. % 
                 172 
                 171 
                 231 
               
               
                   
                 70 wt. % 
                 175 
                 174 
                 289 
               
               
                   
                 90 wt. % 
                 191 
                 183 
                 324 
               
               
                   
                 Final 
                 337 
                 204 
                 359 
               
               
                   
                 Boiling point 
               
               
                   
                   
               
            
           
         
       
     
     In an example of a hydrodearylation process, a feedstock consisting of a non-fractionated xylene rerun column bottoms stream with the above described properties was treated in a hydrodearylation reaction zone containing a catalyst having nickel and molybdenum with ultrastable Y-type (USY) zeolite on a silica-alumina support operated at hydrodearylation conditions including a temperature ranging from 280 to 340° C., at a hydrogen partial pressure of 15 or 30 bar, a liquid hourly space velocity of 1.7 hr −1 . Feed and hydrodearylated liquid product compositions, as analyzed by two-dimensional gas chromatography, are provided in Table 3. 
                                                             TABLE 3               Run   Temperature   Pressure   MA   NMA   MN   DN   P   NDA   DA   TrA       #   ° C.   Bar   Wt. %   Wt. %   Wt. %   Wt. %   Wt. %   Wt. %   Wt. %   Wt. %                                                                            Feed   0   0   92.28   1.82   0.15   0.12   0.37   0.59   4.34   0.33       1   340   30   91.67   2.91   2.1   0.43   0.94   0.43   1.38   0.15       3   320   30   92.95   3.04   1.56   0.33   0.37   0.45   1.16   0.13       5   300   30   92.98   3.13   1.33   0.29   0.34   0.51   1.3   0.13       7   280   30   93.2   3.1   0.95   0.23   0.3   0.54   1.55   0.14       15   340   15   93.47   2.38   0.46   0.17   0.55   0.59   2.13   0.26       17   320   15   93.69   2.15   0.34   0.1   0.4   0.72   2.34   0.26       19   300   15   93.73   2.1   0.29   0.08   0.35   0.71   2.46   0.29       21   280   15   93.63   2.09   0.27   0.08   0.33   0.77   2.54   0.28                    
Key for Table 2—MA: Mono Aromatics; NMA: Naphtheno Mono Aromatics; MN: Mono-Naphthenes; DN: Di-naphthenes; P: Paraffins; NDA: Naphtheno Di Aromatics; DA: Diaromatics; and TrA: Tri Aromatics
 
     For example, subjecting the feed to hydrodearylation conditions in the presence of the catalyst and hydrogen at 320° C. and 30 bar, there is an approximately 75% reduction in diaromatic content. The decrease in the diaromatic content demonstrates that hydrodearylation has occurred and the low-value heavy components of the stream have been upgraded to higher value components. The technology also takes a low-value fuel oil from an aromatic bottoms/reject stream from an aromatic complex and upgrades the fuel oil to petrochemical feedstock. 
     Ranges may be expressed herein as from about one particular value and to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range. Where the range of values is described or referenced here, the interval encompasses each intervening value between the upper limit and the lower limit as well as the upper limit and the lower limit and includes smaller ranges of the interval subject to any specific exclusion provided. Where a method comprising two or more defined steps is recited or referenced herein, the defined steps can be carried out in any order or simultaneously except where the context excludes that possibility. While various embodiments have been described in detail for the purpose of illustration, they are not to be construed as limiting, but are intended to cover all the changes and modifications within the spirit and scope thereof.