INFLUENCE OF THE STRUCTURE OF LOW MOLECULAR WEIGHT NITROGENOUS BASES IN HEAVY OIL ON THE COMPOSITION AND AGGREGATIVE STABILITY OF ASPHALTENES

The influence of the structure of low molecular weight nitrogenous bases in heavy oil on the composition and aggregative stability of asphaltenes has been studied. The objects of investigation were asphaltenes of heavy oil from the Usinsk field, as well as asphaltenes of model petroleum systems with nitrogen content 1.0-3.0 wt%, obtained by mixing the original oil with quinoline and pyridine. IR spectroscopy and elemental analysis were used to determine the composition and structure of asphaltenes. The colloidal stability of asphaltenes was analysed by spectrophotometry. It is shown that the introduction of nitrogenous bases into heavy oil leads to a decrease in hydrogen content with an increase in the proportion of nitrogen, which points to the incorporation of pyridine and quinoline molecules into the supramolecular structure of asphaltenes. The main reason for the incorporation of nitrogenous bases into asphaltene aggregates is the π-stacking interactions of aromatic rings. The colloidal stability of asphaltenes, assessed as the time of sedimentation onset, is determined to increase by a factor of 1.5, with an increase in pyridine content, and the degree of sedimentation inhibition can reach 90 % with respect to asphaltenes in the original oil. On the contrary, the presence of quinoline in asphaltenes causes a several-fold decrease in the time of their aggregation onset, but it also promotes detention of a part of aggregates in the colloid state, which results in a decrease in the amount of precipitate in comparison with original oil.