Energy & Fuels, Vol.34, No.5, 5679-5688, 2020
Study of the Influence of Resins on the Asphaltene Aggregates by H-1 DOSY NMR
Aggregation and precipitation of asphaltenes are relevant concerns during the extraction and processing of petroleum because of the severe damage they cause to the equipment for crude oil transportation. Studies show that the presence of resins can contribute to smaller aggregate formation and thereby reduce the asphaltene precipitation. Herein, we showed the investigation of the influence of resins on the size of asphaltene aggregates by diffusion-ordered spectroscopy (DOSY). The asphaltenes were extracted from crude oil by precipitation with n-heptane. The resins were extracted from the maltene fraction, and their samples were analyzed by H-1 and C-13 nuclear magnetic resonance spectroscopy. Aromatic and aliphatic hydrogen and carbon contents were estimated, including their subdivisions. From these results, we estimated the aromaticity factor (f(a)), the number of naphthenic rings (R-N), the number of total rings (R-T), the average length of alkyl chains (N-alk), the aromatic condensation index (Phi), and the aromatic condensation degree (xi), which were used to determine the asphaltene architecture. The asphaltene chemical structures were suggested for each sample (asphaltene 1 was predominantly continental, while asphaltenes 2 and 3 were archipelago), and the relative diffusion of asphaltene aggregates and resins in toluene-d(8) was determined by DOSY. Asphaltenes, resins, and their mixtures were prepared in toluene-d(8) at concentrations ranging from 5 to 7 wt %. The aspthaltenes/resins mixture proportions were 7:1; 7:2; 7:3; 1:1; and 2:1 wt %. Generally, the relative diffusion values of the solutions increased because of the addition of resins (asphaltenes/resins 7:3 > 7:2 > 7:1 wt %), indicating that their presence favors the formation of smaller aggregates.