Alkyl-demethylation of C2+-hydrocarbyl substituted aromatic hydrocarbons can be utilized to treat one or more of a heavy naphtha reformate stream, a hydrotreated SCN stream, a C8 aromatic hydrocarbon isomerization feed stream, a C9+ aromatic hydrocarbon transalkylation feed stream, and similar hydrocarbon streams to produce additional quantity of xylene products.

Alkyl-demethylation of C2+-hydrocarbyl substituted aromatic hydrocarbons can be utilized to treat one or more of a heavy naphtha reformate stream, a hydrotreated SCN stream, a C8 aromatic hydrocarbon isomerization feed stream, a C9+ aromatic hydrocarbon transalkylation feed stream, and similar hydrocarbon streams to produce additional quantity of xylene products.

Para-xylene production processes are disclosed, with such processes being integrated with extractive distillation or other separation to effectively separate, for example to remove and recover, ethylbenzene and other components that co-boil with the isomers of xylene. This allows for xylene isomerization, downstream of the separation of para-xylene from its other isomers, to be operated under milder conditions (e.g., liquid phase, absence of added hydrogen) without the need for ethylbenzene conversion. The associated decreased yields of byproducts such as light gases and non-aromatic hydrocarbons, together with the generation of purified ethylbenzene having value for styrene monomer production, can significantly improve overall process economics.

Para-xylene production processes are disclosed, with such processes being integrated with extractive distillation or other separation to effectively separate, for example to remove and recover, ethylbenzene and other components that co-boil with the isomers of xylene. This allows for xylene isomerization, downstream of the separation of para-xylene from its other isomers, to be operated under milder conditions (e.g., liquid phase, absence of added hydrogen) without the need for ethylbenzene conversion. The associated decreased yields of byproducts such as light gases and non-aromatic hydrocarbons, together with the generation of purified ethylbenzene having value for styrene monomer production, can significantly improve overall process economics.

Disclosed is a method for providing improved hydrogenation activity by pretreating a catalyst in a three-step manner before selective hydrogenation of unsaturated hydrocarbons in an aromatic fraction in the presence of an oxide-type bimetallic (particularly nickel-molybdenum) supported catalyst.

A catalyst system is disclosed for producing para-xylene from a C.sub.8 hydrocarbon mixture comprising ethylbenzene and at least one xylene isomer other than para-xylene. The catalyst system comprises a first catalyst bed and a second catalyst bed. The first catalyst bed comprises a first zeolite and a rhenium hydrogenation component. The first zeolite has a constraint index from 1 to 12, an average crystal size from 0.1 to 1 micron and has been selectivated to have an ortho-xylene sorption time of greater than 1200 minutes based on its capacity to sorb 30% of the equilibrium capacity of ortho-xylene at 120? C. and an ortho-xylene partial pressure of 4.5?0.8 mm of mercury. The second catalyst bed comprises a second zeolite and a rhenium hydrogenation component. The second zeolite has a constraint index ranging from 1 to 12 and an average crystal size of less than 0.1 micron.

A catalyst system is disclosed for producing para-xylene from a C.sub.8 hydrocarbon mixture comprising ethylbenzene and at least one xylene isomer other than para-xylene. The catalyst system comprises a first catalyst bed and a second catalyst bed. The first catalyst bed comprises a first zeolite and a rhenium hydrogenation component. The first zeolite has a constraint index from 1 to 12, an average crystal size from 0.1 to 1 micron and has been selectivated to have an ortho-xylene sorption time of greater than 1200 minutes based on its capacity to sorb 30% of the equilibrium capacity of ortho-xylene at 120? C. and an ortho-xylene partial pressure of 4.5?0.8 mm of mercury. The second catalyst bed comprises a second zeolite and a rhenium hydrogenation component. The second zeolite has a constraint index ranging from 1 to 12 and an average crystal size of less than 0.1 micron.

Disclosed is a method for providing improved hydrogenation activity by pretreating a catalyst in a three-step manner before selective hydrogenation of unsaturated hydrocarbons in an aromatic fraction in the presence of an oxide-type bimetallic (particularly nickel-molybdenum) supported catalyst.

An alkylaromatics isomerisation catalyst, which catalyst comprises at least 50 wt % of an inorganic binder; at least 0.01 wt % of a Group VIII metal and 1-9 wt % ZSM-12 zeolite wherein the silica to alumina molar ratio (SAR) of the ZSM-12 zeolite is in the range of from 60 to 200, and a process for the isomerisation of alkylaromatics to provide a reaction mixture, said process comprising contacting a hydrocarbon stream comprising alkylaromatics with such catalyst.

An alkylaromatics isomerisation catalyst, which catalyst comprises at least 50 wt % of an inorganic binder; at least 0.01 wt % of a Group VIII metal and 1-9 wt % ZSM-12 zeolite wherein the silica to alumina molar ratio (SAR) of the ZSM-12 zeolite is in the range of from 60 to 200, and a process for the isomerisation of alkylaromatics to provide a reaction mixture, said process comprising contacting a hydrocarbon stream comprising alkylaromatics with such catalyst.