Fractionation of alkylcarboxylate mixtures

A process for separating an alkyl carboxylate mixture according to degree of unsaturation, said process comprising the steps of

• (a) contacting a solution of said mixture in solvent with surface aluminated silica gel adsorbent to selectively adsorb alkyl carboxylate of higher degree of unsaturation and to leave in solution in solvent a fraction of said mixture enriched in content of alkyl carboxylate of lesser degree of unsaturation,
• (b) removing solution of fraction enriched in content of alkyl carboxylate of lesser degree of unsaturation from contact with adsorbent which has selectively adsorbed alkyl carboxylate of higher degree of unsaturation,
• (c) contacting adsorbent which has selectively adsorbed alkyl carboxylate of higher degree of unsaturation with solvent to cause desorption of adsorbed alkyl carboxylate and provide solution in solvent of fraction enriched in content of alkyl carboxylate of higher degree of unsaturation,
• (d) removing solution of fraction enriched in content of alkyl carboxylate of higher degree of unsaturation from contact with adsorbent;
• the alkyl carboxylate in said mixture having the formula ##STR6## in which R is aliphatic chain which contains from 5 to 25 carbon atoms and in which R.sub.1 is alkyl chain containing from 1 to 4 carbon atoms;
• the solvent in step (a) and the solvent in step (c) having the same composition or different compositions and being characterized by a solubility parameter (on a 25.degree. C. basis) ranging from about 7.0 to about 15.0, a solubility parameter dispersion component (on a 25.degree. C. basis) ranging from about 7.0 to about 9.0, a solubility parameter polar component (on a 25.degree. C. basis) ranging from 0 to about 6.0 and a solubility parameter hydrogen bonding component (on a 25.degree. C. basis) ranging from 0 to about 11.5;
• said adsorbent being derived from silica gel having a surface area of at least about 100 square meters per gram;
• said adsorbent being further characterized by a ratio of surface-silicon atoms to aluminum atoms ranging from about 3:1 to about 20:1, a moisture content less than about 10% by weight, and a particle size ranging from about 200 mesh to about 20 mesh;
• said adsorbent having cation substituents selected from the group consisting of cation substituents capable of forming .pi. complexes and cation substituents not capable of forming .pi. complexes and combinations of these;
• the solvent in step (a) and the solvent in step (c) and the ratio of surface-silicon atoms to aluminum atoms in the adsorbent and the level of cation substituents capable of forming .pi. complexes being selected to provide selectivity in step (a) and desorption in step (c).