GB714614A - Improvements in or relating to the segregation of polynuclear aromatic hydrocarbons - Google Patents

Abstract

Aromatic hydrocarbons are separated from a petroleum fraction boiling above about 400 DEG F. by first adsorbing the fraction substantially completely in silica gel, desorbing non-aromatics, then desorbing the remaining aromatics, fractionating the latter into a plurality of fractions each of which is adsorbed on activated alumina and thereafter desorbed. The initial fraction may be a gas oil or "cycle oil" obtained in the catalytic cracking thereof. It is preferably diluted with a C3-C10 paraffin, e.g. heptane, and passed through a fixed bed of silica gel of a height not less than 15 times the diameter. Desorption is preferably effected with the same paraffin until all non-aromatics are removed. Desorption with a polar solvent, e.g. water, aldehydes, ketones, alcohols, ethers or pyridines, then yields an aromatic fraction which is vacuum distilled to yield 6-10 fractions each concentrated in a particular type of polynuclear aromatic, and to remove solvent. Preferably each fraction is then passed down a separate treating column consisting of a number of superposed alumina beds with interconnections to permit fluid flow, substantially all the aromatics being adsorbed in the upper portion. A normal paraffin is then passed down sufficient to wash part of the aromatics through to the lower part of the column. The aromatics are distributed along the column according to their structure, and each alumina bed is separately desorbed with a polar solvent and the product steam stripped to remove the solvent. Examples illustrate the treatment of a virgin gas oil and catalytic cycle oil boiling at about 400-1000 DEG F. to separate fractions including those consisting of substantially pure benzene type, naphthalene type, phenanthrene type, pyrene type, crysenes, benzphenanthrenes and benzanthracenes, and five fused benzene ring type hydrocarbons.ALSO:Aromatic hydrocarbons are separated from a petroleum fraction boiling above about 400 DEG F. by first adsorbing the fraction substantially completely on silica gel, desorbing non-aromatics, then desorbing the remaining aromatics, fractionating the latter into a plurality of fractions each of which is adsorbed on activated alumina and thereafter desorbed. The initial fraction may be a gas oil or "cycle oil" obtained in the catalytic fracking thereof. It is preferably diluted with a C3-C10 paraffin, e.g. heptane, and passed through a fixed bed of silica gel of a height not less than 15 times the diameter. Desorption is preferably effected with the same paraffin until all non-aromatics are removed. Desorption with a polar solvent, e.g. water, aldehydes, ketones, alcohols, ethers or pyridines, then yields an aromatic fraction which is vacuum distilled to yield 6-10 fractions each concentrated in a particular type of polynuclear aromatic, and to remove solvent. Preferably each fraction is then passed down a separate treating column consisting of a number of superposed alumina beds with interconnections to permit fluid flow, substantially all the aromatics being adsorbed in the upper portion. A normal paraffin is then passed down sufficient to wash part of the aromatics through to the lower part of the column. The aromatics are distributed along the column according to their structure, and each alumina bed is separately desorbed with a polar solvent and the product steam stripped to remove the solvent. Examples illustrate the treatment of a virgin gas oil and catalytic cycle oil boiling at about 400-1000 DEG F. to separate fractions including those consisting of substantially pure benzene type, naphthalene type, phenanthrene type, pyrene type, crysenes, benzphenanthrenes and benzanthracenes, and five fused benzene ring type hydrocarbons.