In a process for separating one or more 3,3-, 3,4- and 4,4-dimethyl biphenyl isomers, a feed comprising the isomers is contacted with a zeolite adsorbent which contains one or more metal cations in the +1 or +2 oxidation states. Separation processes for each of the 3,3-, 3,4- and 4,4-dimethyl biphenyl isomers is provided.

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 herein is a process for producing para-xylene comprising the steps of: (a) contacting a feedstock comprising toluene with a first catalyst under effective vapor phase toluene disproportionation conditions to disproportionate said toluene and produce a first product comprising benzene, unreacted toluene and greater than equilibrium amounts of para-xylene; and (b) contacting a feedstock comprising C.sub.9+ aromatic hydrocarbons and benzene with a second catalyst in the presence of 0 wt. % or more of hydrogen having a 0 to 10 hydrogen/hydrocarbon molar ratio under effective C.sub.9+ transalkylation conditions to transalkylate said C.sub.9+ aromatic hydrocarbons and produce a second product comprising xylenes.

Disclosed herein is a process for producing para-xylene comprising the steps of: (a) contacting a feedstock comprising toluene with a first catalyst under effective vapor phase toluene disproportionation conditions to disproportionate said toluene and produce a first product comprising benzene, unreacted toluene and greater than equilibrium amounts of para-xylene; and (b) contacting a feedstock comprising C.sub.9+ aromatic hydrocarbons and benzene with a second catalyst in the presence of 0 wt. % or more of hydrogen having a 0 to 10 hydrogen/hydrocarbon molar ratio under effective C.sub.9+ transalkylation conditions to transalkylate said C.sub.9+ aromatic hydrocarbons and produce a second product comprising xylenes.

A process for producing xylene from C.sub.9+ aromatic hydrocarbons comprises contacting a first feedstock comprising C.sub.9+ aromatic hydrocarbons with a first catalyst in the presence of 0 wt. % or more of hydrogen under effective vapor phase dealkylation conditions to dealkylate part of the C.sub.9+ aromatic hydrocarbons and produce a first product comprising benzene, toluene and residual C.sub.9+ aromatic hydrocarbons. A second feedstock comprising C.sub.9+ aromatic hydrocarbons and benzene and/or toluene is contacted with a second catalyst under effective liquid phase C.sub.9+ transalkylation conditions to transalkylate at least part of the C.sub.9+ aromatic hydrocarbons and produce a second product comprising xylenes.

A process for producing xylene from C.sub.9+ aromatic hydrocarbons comprises contacting a first feedstock comprising C.sub.9+ aromatic hydrocarbons with a first catalyst in the presence of 0 wt. % or more of hydrogen under effective vapor phase dealkylation conditions to dealkylate part of the C.sub.9+ aromatic hydrocarbons and produce a first product comprising benzene, toluene and residual C.sub.9+ aromatic hydrocarbons. A second feedstock comprising C.sub.9+ aromatic hydrocarbons and benzene and/or toluene is contacted with a second catalyst under effective liquid phase C.sub.9+ transalkylation conditions to transalkylate at least part of the C.sub.9+ aromatic hydrocarbons and produce a second product comprising xylenes.

Asymmetric membrane structures are provided that are suitable for various types of separations, such as separations by reverse osmosis. Methods for making an asymmetric membrane structure are also provided. The membrane structure can include at least one polymer layer. Pyrolysis can be used to convert the polymer layer to a porous carbon structure with a higher ratio of carbon to hydrogen.

Asymmetric membrane structures are provided that are suitable for various types of separations, such as separations by reverse osmosis. Methods for making an asymmetric membrane structure are also provided. The membrane structure can include at least one polymer layer. Pyrolysis can be used to convert the polymer layer to a porous carbon structure with a higher ratio of carbon to hydrogen.

The present invention relates to a process and to a device for the separation of a feedstock comprising benzene, toluene and C8+ compounds, in which: a toluene column (C10) is fed directly with a C7+ cut resulting from the bottom of a stabilization column (C11) positioned downstream of a transalkylation unit (P4); a C7 cut is withdrawn at the top of the toluene column (C10) and a C8+ cut is withdrawn at the bottom; a benzene column (C9) is fed with the C7 cut resulting from the toluene column (C10); an essentially aromatic cut resulting from an aromatics extraction unit (P1) is injected into the toluene column (C10) separately above the feeding of the C7+ cut or into the benzene column (C9).