GB826089A - A process for the separation of normal hydrocarbons from mixtures by selective adsorption - Google Patents

Abstract

Normal hydrocarbons of at least 4 carbon atoms are separated from hydrocarbon mixtures containing them by selective adsorption on a particulate mass of a solid zeolite molecular sieve of maximum pore diameter 5-6 , followed by desorption and reuse, each desorption being a partial one carried out so that the amount of normal C4+ hydrocarbons left in the molecular sieve is one-half to nine-tenths of the total capacity under the conditions employed. Normal paraffins up to eicosane can be separated; the process may be used to upgrade gasolines such as catalytic reformates by removing, at least partially, normal hydrocarbons, the concentration of normal hydrocarbons in the effluent preferably being reduced to below 10%. The sieve may be a natural zeolite, such as chabazite or gmelinite, or a synthetic zeolite such as that of formula BaAl2Si4O12, or H2O or sieve MS-5A (Linde Air Products Company), which is a sodium/calcium aluminosilicate. They may be used alone or held in shape by the addition of 10 to 20% of clay. They may be continuously circulated between adsorption and desorption zones using fluidized or other techniques or in a single zone alternately adsorbing and desorbing with a fixed or moving bed. Adsorption is performed in the vapour phase at 250-600 DEG C. at atmospheric pressure to 70 kg./cm.2. Liquid hourly space velocities of up to 20 v./v./hr. are used. Desorption methods include heating or lowering the pressure but preferred is sweeping with an inert gas, e.g. hydrogen, nitrogen, methane, propane, helium, argon or flue gas (scrubbed to remove reactive impurities). When using a single zone the sweeping gas may be alternated with the feed flow or may be applied continuously adding pulses of hydrocarbon feed, if desired increasing the flow of sweeping gas during desorption. The adsorption and desorption steps are correlated so that during adsorption the amount of hydrocarbons adsorbed is about the same as the amount desorbed during the previous desorption. The effluents during adsorption and desorption may be collected separately by passing the effluent alternately through separate collecting devices, e.g. condensers and receivers, or by passing both continuously through two collecting zones adapted to collect the effluents separately, e.g. a relatively warm condenser for the branched hydrocarbons followed by a cold condenser for branched hydrocarbons carried through and the normal hydrocarbons. Absorption or adsorption collecting methods can also be applied.