Isolation of 3-methylhexane, trans-1,2-dimethylcyclopentane, and trans-1,3-dimethylcyclopentane from petroleum

Abstract

The fraction of a midcontinent pctroleum boiling between 90° and 92° C, from which thc aromatic hydrocarbons previously had been removed, was substantially resolved into its constituent hydrocarbons. Alternation of atmospheric distillation and azeotropic distillation with methyl alcohol separated the material boiling between 90° and 91.2° C into a paraffinic concentrate, containing approximately 75 percent of 2-methylhexane, and a naphthenic concentrate. From the naphthenic concentrate, trans-l,3-dimethylcyclopentane was isolated by crystallization from liquid ethane. A similar procedure separated the material boiling between 91.2° and 92° C into a naphthenic and a paraffinic concentrate. From the naphthenic concentrate, trans-l,2-dimethylcyclopentane was isolated by crystallization from liquid propane plus methane. From the paraffinic concentrate, 3-methylhexane was obtained in the residue from distillations at reduced pressure (215 mm Hg).The boiling point, refractive index, freezing point, density, carbon-hydrogen ratio, and critical solution temperature in aniline were determIned for the three hydrocarbons. Referred to the content of n-heptane as unity, the relative amounts of the three hydrocarbons in this petroleum were estimated to be as follows: trans-l,3-dimethylcyclopentane, 0.21; 3-methylhexane, 0.25; trans-l,2-dimethylcyclopentane, 0.31. CONTENTS Page

Separation of hydrocarbons by azeotropic distillation

“…Part I of figure 8 shows the separation obtained in the azeotropic distillation, with methyl alcohol (boiling point 66 0 C), of a substantially constant-boiling (92 0 C) fraction of paraffin and naphthene hydrocarbons [16].…”