Exploring the Structure–Solubility Relationship of Asphaltene Models in Toluene, Heptane, and Amphiphiles Using a Molecular Dynamic Atomistic Methodology

Abstract

The solubility parameters, δ, of several asphaltene models were calculated by mean of an atomistic NPT ensemble. Continental and archipelago models were explored. A relationship between the solubility parameter and the molecule structure was determined. In general, increase of the fused-rings number forming the aromatic core and the numbers of heteroatoms such as oxygen, nitrogen, and sulfur produces an increase of the solubility parameter, while increases of the numbers and length of the aliphatic chains yield a systematic decrease of this parameter. Molecules with large total carbon atom number at the tails, n(c), and small aromatic ring number, n(r), exhibit the biggest values of δ, while molecules with small n(c) and large n(r) show the smallest δ values. A good polynomial correlation δ = 5.967(n(r)/n(c)) - 3.062(n(r)/n(c))(2) + 0.507(n(r)/n(c))(3) + 16.593 with R(2) = 0.965 was found. The solubilities of the asphaltene models in toluene, heptane, and amphiphiles were studied using the Scatchard-Hildebrand and the Hansen sphere methodologies. Generally, there is a large affinity between the archipelago model and amphiphiles containing large aliphatic tails and no aromatic rings, while continental models show high affinity for amphiphiles containing an aromatic ring and small aliphatic chains.

Asphaltene solubility in common solvents: A molecular dynamics simulation study

“…This equation is similar to the equation reported previously in Aray et al [41] but of course with different coefficients. Figure 1 …”

“…The obtained results, as reported in Table 2, included density (g/cm 3 ), hydrogen to carbon ratio (H/C), molecular mass (g/mol), solubility parameters (MPa Table 2 (values in parentheses) have small deviations, a maximum of 5 % compared to those reported by Aray et al [41] Additionally, Table 2 shows that the total solubility parameter, d, systematically increases with the addition of an aromatic ring from M3 to RH4 asphaltene with fully-added aromatic rings.…”

“…[37] In this work, all 28 known asphaltene structures were used in the MD simulation. Among these structures, M3, R1, A2_2, R2, A2_1, M2, R3, ZJ, VI, A1, RH1, RH2, M1, RH3, and RH4 were given by Aray et al, [41] and the remaining 13 structures, N1, N2, N3, N4, N5, N6, N7, N8, N9, N10, N11, N12, and N13, were collected from Redelius, [16] Pacheco et al, [42] Mullins, [43] and Zajac et al [44] It should be noted that M3 structure does not possess the essential characteristics of an asphaltene molecular structure. Therefore, it is used as the basic structure [41] to investigate how aromatic rings and heteroatoms are added into structures from an asphaltene molecule, and how they would affect the solubility of asphaltenes in various solvents.…”

“…Therefore, the R 0 value of 5.3 MPa 0.5 , which is considered a proper value for asphaltenes in organic solvents, was used in this work. [41,46] Figure 3 depicts the average RED for all the asphaltene structural models, along with the ratio of hydrogen to carbon atoms (H/C) in an asphaltene molecule. The (H/C) ratio is an important parameter which indicates the aromaticity of an asphaltene molecule.…”

“…The aggregation of asphaltene molecules in the absence of solvent (only asphaltene in the simulation box) and in the presence of a solvent, (heptane, toluene, or isopropyl benzene) were simulated and the results were compared with previous simulation results of RED and RDF. [22,23,27,41] The radial distribution function (RDF), g(r), was calculated for a pair of asphaltene molecules in two cases: asphaltene only, and asphaltenes and a solvent. Analysis of the trajectory for full NVT simulation was performed to calculate the asphaltene-asphaltene RDF.…”