Patent GB-718909-A (GB)
Title: Improvements in or relating to a process for separating aromatic hydrocarbons
IPC: C10G21/16
Filed: 1951-11-21
Abstract: Aromatic hydrocarbons are separated from a mixture with non-aromatics by introducing the mixture into a counterflow multistage extraction system near the middle, introducing diethylene glycol containing approximately 0.5 per cent or more by weight of water into one end, withdrawing aromatic-free raffinate at the same end, and aromatic-rich extract at the other, stripping the extract to separate the aromatics, returning part thereof to the and other end, withdrawing the remainder and separating any olefins therein. Individual aromatic hydrocarbons may be isolated by fractionation. Benzene, toluene, and xylenes may be separated from paraffins and naphthenes while olefins, though not completely separated, are redistributed so that they are removable from the aromatics by rectification. Advantageously a feed containing at least 10 per cent of, for example, benzene, and not above 3 per cent of olefins is used. Gasoline or naphtha may be fractionated to concentrate C6 and C7 hydrocarbons or reformed, especially hydroformed or "platformed" fractions, may be used.  The extraction is preferably effected below 60 DEG  C., pressure being atmospheric or sufficient to maintain all phases liquid, with diethylene glycol containing 0.5-10 per cent of water.  The extract is fed to the column of a stripping still heated by a steam coil, with steam injection if desired.  The stripped hydrocarbons are condensed and a portion fed back to the extractor, the remainder passing to the column of a topping still where light ends including olefins tractor, the remainder passing to the column of a are removed. Bottoms pass to a finishing still.  Diagrams are given for the two-phase system benzene: petroleum naphtha: glycol solvent showing benzene solubility in the solvent-layer as a function of benzene concentration in the hydrocarbon layer, and variation of the separation factor as a function of the benzene concentration. The vapour pressures of glycol-water mixtures at different temperatures are also given.  In examples, benzene-rich products of "platforming" gasoline fractions are treated and 97 per cent or higher benzene recovered.  Specification 456,958, [Group III], and U.S.A. Specification 2,404,902 are referred to.ALSO:Aromatic hydrocarbons are separated from a mixture with non-aromatics by introducing the mixture into a counterflow p  multistage extraction system near the middle, introducing diethylene glycol containing approximately 0.5 per cent. or more by weight of water into one end, withdrawing aromatic-free raffinate at the same end, and aromatic-rich extract at the other, stripping the extract to separate the aromatics, returning part thereof to the said other end, withdrawing the remainder and separating any olefins therein. Benzene, toluene, and xylenes may be separated from paraffins and napthenes while olefins, though not completely separated, are redistributed so that they are removable from the aromatics by rectification.  Advantageously a feed containing at least 10 per cent. of, for example, benzene and not above 3 per cent. of olefins is used.  Gasoline or naphtha may be fractionated to concentrate C6 and C7 hydrocarbons or reformed, especially hydroformed or "platformed" fractions, may be used.  The extraction is preferably effected below 60 DEG C., pressure being atmospheric or sufficient to maintain all phases liquid, with diethylene glycol containing 0.5-10 per cent., of water.  The extract is fed to the column of a stripping still heated by a steam coil, with steam injection if desired.  The stripped hydrocarbons are condensed and a portion fed back to the extractor, the remainder passing to the column of a topping still where light ends including olefins are removed.  Bottoms pass to a finishing still.  Diagrams are given for the two-phase system benzene: petroleum naphtha: glycol solvent showing benzene solubility in the solvent layer as a function of benzene concentration in the hydrocarbon layer, and variation of the separation factor as a function of the benzene concentration.  The vapour pressures of glycol-water mixtures at different temperatures are also given.  In Examples, benzene-rich products of "platforming" gasoline fractions are treated and 97 per cent. or higher benzene recovered. Specification 456,958, and U.S.A. Specification 2,404,902 are referred to.