Analysis of insolubles of petroleum vacuum residues using TLC-FID

The insolubles (generally termed as asphaltenes) were obtained from precipitation of Jodhpur and Heera vacuum residue using n-hexane, n-heptane and ethyl acetate followed by reprecipitation of n-heptane and ethyl acetate soluble fractions of above using n-pentane. In order to investigate the solvent extraction power of different solvents and the composition of different insolubles, a TLC-FID procedure was optimized using silica S III chromrods with dichloromethane (95%)-methanol (5%) mixture as developing solvent. In this method, the problems usually encountered in column chromatography and solvent extraction methods are overcome. The method is rapid and needs a small amount of samples. Three peaks were obtained, thus providing composition of different insolubles in terms of three different compound classes i.e. resins, asphaltenes and preasphaltenes. JVR insolubles were found to consist more amount of asphaltenes and preasphaltenes in comparison to HVR insolubles. The content of asphaltenes and preasphaltenes in heptane insolubles are relatively higher than that in n-hexane and ethyl acetate insolubles. It is concluded that these insolubles are indeed dominated by resins that cannot be extracted fully in different solvents such as n-hexane, n-heptane, ethyl acetate and n-pentane.