Recovery of benzene and benzene derivatives from gasoline fractions and refinery streams

Abstract

A process for the separation of the aromatic compounds benzene, toluene and xylene from an aromatics-containing reformate gasoline and pyrolysis gasoline or a coke-oven light oil or an aromatics-containing refinery stream, in which the aromatics are separated by an extractive distillation uses a novel solvent combination made up of the compounds n,n′-diformyl piperazine or 2,2-bis-(cyanoethyl)ether in a combination with n-formyl morpholine as a second solvent for extractive distillation so that the solvent combination obtained shows a higher selectivity with regard to the aromatics to be extracted so that a lower solvent load is required. The aromatics-containing feed mixture is first submitted to a pre-distillation so that the obtained fraction has a narrow boiling point range. This fraction is then submitted to an extractive distillation in a first column, in which an aromatics-lean head product of predominantly paraffinic hydrocarbons is obtained as well as an aromatics-enriched bottom product. The bottom product is passed to a second column in which an aromatics-rich raffinate is obtained by reducing the pressure or increasing the temperature so that the extracting solvent combination obtained as bottom product can be recycled into the process.

What is claimed is: 
     
         1 . A method of utilizing a mixture of n-formyl morpholine and n,n′-diformyl piperazine in any composition desired, wherein it is employed in an extractive distillation of an aromatics-rich hydrocarbon mixture. 
     
     
         2 . A method of utilizing a mixture of n-formyl morpholine and 2,2′-bis-(cyanoethyl)ether in any composition desired, wherein it is employed in an extractive distillation of an aromatics-rich hydrocarbon mixture. 
     
     
         3 . In an extractive distillation process, exposing an aromatics-rich hydrocarbon mixture to a solvent mixture comprising n-formyl morpholine and n,n′-diformyl piperazine, each solvent being present in the mixture in any desired proportion to maximize the selectivity of the solvent mixture. 
     
     
         4 . In an extractive distillation process, exposing an aromatics-rich hydrocarbon mixture to a solvent mixture comprising n-formyl morpholine and 2,2′-bis-(cyanoethyl), each solvent being present in the mixture in any desired proportion to maximize the selectivity of the solvent mixture.