engleski

Characterisation of asphaltenes by DOSY NMR spectroscpy

Crude oil and crude oil residues represent one of the most complex natural compound mixtures. They are consisted of thousands of components with different sizes and structures. Nowadays, one of the main goals in oil industry is to transfer heavy crude oil residues into lighter distillates. One of the main problem during refining process is associated with the presence of the asphaltenes, which are the heaviest and the most polar and least reactive molecules in crude oils. Asphaltenes cause many problems during production, such as blocking of production pipes, reduction in oil flow and catalyst deactivation. Asphaltenes are complex organic macromolecular mixtures containing condensed aromatic and saturated rings, aliphatic moieties and different heteroatoms. Despite of many efforts and variety of analytical methods used, the complex asphaltene structures are not completely elucidated. In this research, concentration dependent diffusion measurements have been performed in order to determine the lowest aggregation concentration of asphaltenes. Pseudo two- dimensional DOSY NMR technique was applied to separate asphaltene components according to their diffusion coefficients. Hydrodynamic radius and molecular weight of asphaltenes were estimated from diffusion coefficients by using Stokes-Einstein equation and Gierer-Wirtz model. Three different samples were analyzed: crude oil and samples from crude oil distillation, atmospheric and vacuum residues. Changes in diffusion coefficients reflect formation of different types of asphaltene agregates.

asphaltenes, DOSY NMR, characterization

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