Asphaltene cracking in catalytic hydrotreating of heavy oils. 2. Study of changes in asphaltene structure during catalytic hydroprocessing

Abstract

Characteristics in catalytic conversion of asphaltenes In petroleum heavy residues were studied in the hydrotreating process. A Boscan crude, an Athabasca bitumen, and a Khafji vacuum residue were tested as typical feedstocks. Various analyses were made to obtain the properties of asphaltenes before and after the reaction, e.g., changes of heteroatoms such as sulfur and metals, and decreases of molecular weight. The characteristic changes of asphaltene molecules were also investigated by electron spin resonance (ESR) and X-ray analyses. The association and coordination of vanadyl in asphaltenes were studied by the temperature dependence on the ESR spectra, and the sizes of the stacked crystallites and the aggregated asphaltene micelles were measured with X-ray diffraction and small-angle scattering. In the asphaltene cracking mechanism, it was clarified that the main reactions were the destruction of asphaltene micelles caused by vanadium removal and the depolymerization of asphaltene molecules by removal of heteroatoms such as sulfur.

Asphaltene characterization as function of time on-stream during hydroprocessing of Maya crude

“…This kind of information gives more tools to development of upgrading technology and catalysts for higher heteroatoms content feedstocks [5].…”

Chemical derivatization of Athabasca oil sand asphaltene for analysis of hydroxyl and carboxyl groups via nuclear magnetic resonance spectroscopy

“…10 2 ±2 £ 10 4 amu [5,12,19]. Further complications arise from geochemical variances, which can alter the MWs of samples from different locations in oil or tar sands deposits.…”

“…[7±11]. For example, high number average molecular weights (MWs) of the order of thousands of amu for asphaltene solutions have been interpreted in terms of molecular association complexes [1,10,12,13]. This behavior is analogous to that of amphiphilic molecules, such as surfactants which form inverse micelles in apolar and low dielectric constant solvents [14], hemi-micelles with minerals and clays [15], and microemulsions with hydrocarbons in water [16].…”

“…1% nitrogen, 4% oxygen, and 8% sulfurÐthus appreciable numbers of heteroatom groups [1,6,17,19±21]. Characterization of polar groups is important in understanding chemical processes involved in the formation, oxidation, degradation, re®ning, environmental impact, and modi®ca-tion of natural fuels [1±3, 12,22,23]. It is the aim of this research to determine the number and types of oxygen containing acidic groups, namely, hydroxyl and carboxyl via chemical derivatization reactions, viz.…”

The extraction of bitumen from western oil sands: Volume 2. Final report

“…proposed that small amounts of sulfur compounds in vacuum residua may be converted by thermal reactions. Aliphatic and cyclic sulfides have been reported to be present in bitumens (267,268) and may be present in the PR Spring bitumen-derived heavy oil. These saturated sulfides may undergo thermal C-S bond hydrogenolysis in the absence of hydrogenation and/or hydrogenolysis activity.…”