Analysis of insolubles of petroleum vacuum residues using TLC-FID

The insolubles (generally termed as asphaltenes) were obtained from precipi tation of Jodhpur and Heera vacuum residue using n-hexane, n-heptane and et hyl acetate followed by reprecipitation of n-heptane and ethyl acetate solu ble fractions of above using n-pentane. In order to investigate the solvent extraction power of different solvents and the composition of different in solubles, a TLC-FID procedure was optimized using silica S III chromrods wi th dichloromethane (95%)-methanol (5%) mixture as developing solvent. In th is method, the problems usually encountered in column chromatography and so lvent extraction methods are overcome. The method is rapid and needs a smal l amount of samples. Three peaks were obtained, thus providing composition of different insolubles in terms of three different compound classes i.e. r esins, asphaltenes and preasphaltenes. JVR insolubles were found to consist more amount of asphaltenes and preasphaltenes in comparison to HVR insolub les. The content of asphaltenes and preasphaltenes in heptane insolubles ar e relatively higher than that in n-hexane and ethyl acetate insolubles. It is concluded that these insolubles are indeed dominated by resins that cann ot be extracted fully in different solvents such as n-hexane, n-heptane, et hyl acetate and n-pentane.