Separation of normal paraffins from hydrocarbon mixtures using zeolitic molecular sieves

摘要

In a process for separating a normal paraffin from a normally liquid hydrocarbon mixture also containing branched-chain and/or cyclic hydrocarbons by contacting the mixture in the liquid phase with a solid absorbent which selectively absorbs normal paraffins, the absorbed paraffin is desorbed with a normal paraffin in the liquid phase which contains at least four carbon atoms per molecule and of lower molecular weight than the absorbed paraffin. Desorbed hydrocarbon is readily separated from any desorbing hydrocarbon by fractionation. The feed for separation may be a gasoline mixture, e.g. a reformate, and the normal paraffins separated may be subjected to isomerization or other treatment to improve the octane number. Traces of isobutane and lower boiling hydrocarbons are preferably removed prior to the separation by distillation. Absorption and desorption are both preferably carried out at 80-152 DEG C. and 13.5-68 atmospheres, the pressure being sufficient to maintain the hydrocarbons in the liquid phase. The desorbing hydrocarbon may be removed from the absorbent by reducing the pressure. Normal butane is the preferred desorbing hydrocarbon. Absorbents which may be used preferably have a pore size of about 5.1 and include the crystalline alumino-silicates of calcium, magnesium, barium, strontium, sodium and potassium. The calcium compound is preferably heated to remove water of hydration. In a preferred embodiment separation is carried out continuously by the use of two absorption zones, one being used for absorption while the other is desorbed.