SEPARATION OF PETROLEUM-HYDROCARBONS USING DEALUMINATED MORDENITE MOLECULAR-SIEVE .2. ALKYLNAPHTHALENES AND ALKYLPHENANTHRENES

A pentane solution of a crude oil fraction containing diaromatic and triaromatic hydrocarbons was subjected to a liquid chromatographic technique using dealuminated mordenite molecular sieves as the stationary phase and pentane as the mobile phase. Two fractions were obtained: one containing hydrocarbons not retained by the sieves that were eluted from the column and the other from acid digestion of the sieves and recovery of the liberated hydrocarbons. The hydrocarbons in each fraction were analysed using GC-MS techniques. Mass chromatograms showing dimethylnaphthalenes, trimethylnaphthalenes, tetramethylnaphthalenes, methylphenanthrenes and dimethylphenanthrenes revealed significant differences between the two fractions. Alkylnaphthalenes with substituents in both positions 1 and 4 were invariably excluded from the molecular sieve. Some alkylnaphthalenes with substituents in positions 1, 3 and 7 were weakly sorbed by the sieves whereas other isomers were strongly sorbed. Analysis of methylphenanthrenes and dimethylphenanthrenes showed that compounds with substituents in position 9 or 10 were excluded from the sieve channels. Some inhibition to sorption was displayed by compounds with substituents in position 4 whilst phenanthrenes substituted in position 2 appeared to be readily sorbed. The technique is useful for separating some alkylnaphthalene and alkylphenanthrene isomers that are difficult to separate using other, more conventional chromatographic techniques.