Ksenia I. Smyshlyaeva

Since 2020, 0.5% limits on the sulfur content of marine fuels have been in effect worldwide. One way to achieve this value is to mix the residual sulfur and distillate low sulfur components. The main problem with this method is the possibility of sedimentation instability of the compounded residual marine fuel due to sedimentation of asphaltenes. In this paper, the application of the UNIFAC group solution model for calculating the solubility of asphaltenes in hydrocarbons is considered. This model makes it possible to represent organic compounds as a set of functional groups (ACH, AC, CH₂, CH₃), the qualitative and quantitative composition of which determines the thermodynamic properties of the solution. According to the asphaltene composition, average molecular weight (450–2500 mol/L) and group theories of solutions, a method for predicting the sedimentation stability of compounded residual marine fuels was proposed. The effect of the heat of fusion, temperature of fusion, molecular weight, and group composition on the solubility of asphaltenes in marine fuel has been evaluated. The comparison of the model approach with the data obtained experimentally is carried out. The results obtained make it possible to predict the sedimentation stability of the fuel system depending on the structure and composition of asphaltenes.

The effects of asphaltenes from two heavy oil residues on the sedimentation stability of residual marine fuels were assessed and compared. As base components of residual marine fuels, the vacuum residue (VacRes) and visbreaking residue (VisRes) were taken. The heptane-insoluble fractions (HI-fractions), including asphaltenes, isolated from vacuum residue and visbreaking residue, were analyzed to determine the elemental composition (XRF) and cluster parameters (XRD). The results of the analysis of the parameters of the asphaltene cluster (HI-fraction) for vacuum residue and visbreaking residue showed that d_γ – 6.1 and 5.9 Å, L_c – 26.72 and 20.78 Å, and L_a – 7.68 and 7.20 Å. The sedimentation stability of residual marine fuel was determined according to the ISO 10307-1-2009 (TSA) method and described using ternary phase diagrams. The ratio of stable compositions to the total number of possible compositions (with a step of 10 wt%) was 65/66 or 98.5% for residual marine fuel comprising a mixture VacRes/ULSD/LCGO (vacuum residue/ultra-low sulphur diesel/light catalytic gas oil). Meanwhile, the ratio of stable compositions to the total number of possible compositions was 38/66 or 57.6% for residual marine fuel comprising a mixture VisRes/ULSD/LCGO (visbreaking residue/ultra-low sulphur diesel/light catalytic gas oil).