GB711818A - Separation of aromatics from gasoline or kerosene fractions - Google Patents

Abstract

A cyclic process for separating aromatics from a gasoline or kerosene fraction comprises introducing into a bed of silica gel during each cycle, liquid charge equivalent to 50 to 85 per cent of "equilibrium amount" to adsorb aromatics selectively, displacing adsorbed aromatics by introducing an aromatic hydrocarbon liquid desorbent boiling below 500 DEG F. and outside the range of the charge, in an amount of 0.05 to 0.14 gal./lb. silica gel and sufficient to cause the charge hydrocarbon content of the effluent from the silica gel during each cycle to decrease below 5, preferably below 3, per cent by volume, and directly re-using the wet silica gel to treat further charge in the next cycle. The "equilibrium amount" is the quantity of charge which contains aromatics necessary to saturate 1 lb. silica gel when equilibrium is reached at the operating temperature. Equilibrium curves which relate per cent aromatic in the liquid phase to volume of aromatic apparently adsorbed per lb. silica gel are given for mixtures of toluene or benzene, and n-heptane, and mixtures of aromatics and saturateds from 300 DEG to 400 DEG F. straight-run naphtha. The charge may first be diluted with saturated hydrocarbons, e.g. propane, butane, pentanes or cyclopentane, suitably in a ratio of 4 vols. naphtha: 1 diluent. Curves are given showing how the aromatic recovery falls sharply when the charge exceeds 85 per cent of the "equilibrium amount" for naphtha + isopentane diluent and for a catalytic reformate. The effect of varying the amount of desorbent on the aromatic recovery is also illustrated. The desorbent may be a single aromatic hydrocarbon or a mixture and may boil below or above the charge. For a charge boiling above benzene, benzene is suitable and for a naphtha boiling below xylene, xylene is suitable. In a modification of the process, immediately following the charge and prior to introducing the desorbent, a low boiling saturated p hydrocarbon is introduced in relatively small amount, generally 0.01 to 0.03 gal./lb. silica gel, which results in an improved separation. The effluent from each phase of the cycle, containing saturated and aromatics respectively together with desorbent, is separately fractionated to recover the desired products, the desorbent being recycled. Examples relate to straight-run naphtha with or without isopentane diluent, a catalytic gasoline fraction containing also olefins, and a catalytic reformate, the desorbent being benzene or commercial xylenes, and isopentane being used in one case as the intermediate treating liquid.ALSO:A cyclic process for separating aromatics from a gasoline or kerosene fraction comprises introducing into a bed of silica gel during each cycle, liquid charge equivalent to 50-85 per cent. of "equilibrium amount" to adsorb aromatics selectively, displacing adsorbed aromatics by introducing an aromatic hydrocarbon liquid desorbent boiling below 500 DEG F. and outside the range of the charge, in an amount of .05-.14 gal./lb. silica gel and sufficient to cause the charge hydrocarbon content of the effluent from the silica gel during each cycle to decrease below 5, preferably below 3 per cent. by volume, and directly re-using the wet silica gel to treat further charge in the next cycle. The "equilibrium amount" is the quantity of charge which contains aromatics necessary to saturate 1 lb. silica gel when equilibrium is reached at the operating temperature. Equilibrium curves which relate per cent. aromatic in the liquid phase to volume of aromatic apparently adsorbed per lb. silica gel are given for mixtures of toluene or benzene and n-heptane and mixtures of aromatics and saturateds from a 300-400 DEG F. straight run naphtha. The charge may first be diluted with saturated hydrocarbons, e.g. propane, butane, pentanes or cyclopentane, suitably in a ratio of 4 vols. naphtha: 1 diluent. Curves are given showing how the aromatic recovery falls sharply when the charge exceeds 85 per cent. of the "equilibrium amount" for naphtha + isopentane diluent and for a catalytic reformate. The effect of varying the amount of desorbent on the aromatic recovery is also illustrated. The desorbent may be a single aromatic hydrocarbon or a mixture and may boil below or above the charge. For a charge boiling above benzene, benzene is suitable and for a naphtha boiling below scylene, scylene is suitable. In a modification of the process, immediately following the charge and prior to introducing the desorbent, a low boiling saturated hydrocarbon is introduced in relativity small amount, generally .01-.03 gal./lb. silica gel, which results in an improved separation. The effluent from each phase of the cycle, containing saturateds and aromatics respectively together with desorbent, is separately fractionated to recover the desired products, the desorbent being recycled. Examples relate to straight run naphtha with or without isopentane diluent, a catalytic gasoline fraction containing also olefins, and a catalytic reformate, the desorbent being benzene or commercial scylenes, and isopentane being used in one case as the intermediate treating liquid.