GB576592A - Separation of hydrocarbons - Google Patents

Abstract

Olefins are separated from mixtures with more saturated hydrocarbons by extracting with a preferential solvent consisting of a carboxylic acid anhydride, a carboxylic ester of a keto alcohol or a polycarbonyl compound wherein the carbon atoms of the carbonyl groups are adjacent or separated by one or more carbon atoms which are devoid of hydroxy groups and with the carbon atoms of the carbonyl groups form an unbroken acyclic carbon chain, and separating the undissolved hydrocarbons from the liquid solution of the olefins. The separation of narrow boiling mixtures predominating in C4 hydrocarbons, of ethylene from ethane, propylene from propane, n-butylene from a butane, pentadienes from amylenes, and pentadienes or amylenes from iso- or n-pentane is referred to. Solvents specified are anhydrides such as acetic, propionic, butyric, butyric-acetic, acetic-propionic, n- and iso-valeric, acetic-isovaleric, di-acetyl, di- and tetra-halo-diacetyls, acetyl propionyl, acetyl acetone, halo-acetyl acetones, methyl propyl diketone, propionyl acetone, acetonyl acetone, dipropionyl acetyl isobutyryl, methyl acetyl acetone, butyryl acetone, propionyl butyryl, isobutyryl acetone, acetyl isovaleryl, methyl acetyl propionyl methane, ethyl acetyl acetone, pentan- and heptan-triones, formates and acetates of hydroxy acetone, diacetone alcohol, esters of keto acids such as methyl and ethyl aceto-acetates and levulinates, and esters of polybasic acids such as diethyl oxalate, malonate, succinate, and maleate, methyl ethyl oxalate, and dimethyl malonate. The mixture to be separated may be extracted while in vapour or liquid phase. In ordinary extraction, the temperature is preferably below the boiling point of the solvent, but above the condensation temperature of the most readily condensible constituent of the mixture which is extracted as a vapour. Extractive distillation is preferably operated at superatmospheric pressure. The solubilities of butadiene and butylene at 20 DEG C. in several of the specified solvents are given. In an example, acetic anhydride is fed to the top of a column kept at about 20 DEG C., a vapour mixture of 40 per cent butadiene and 60 per cent butylenes being fed near the centre. Bottom reflux is provided, and the fat solvent at the bottom yields over 98 per cent pure butadiene.