Size Exclusion Chromatography: Characterization of Heavy Petroleum Residues. Application to Resid Desulfurization Process

Abstract

Size exclusion chromatography (SEC) is still the only of the existing analytical methods that can easily and routinely provide information on relative asphaltene molecular weight distributions. However, molecular weight characterization still suffers from several physicochemical drawbacks such as association of molecular units, adsorption on column material and lack of appropriate standards, which are not always underlined in the petrochemical literature where SEC is used as a routine analytical tool. Thus, the resulting molecular weight distribution can be either overestimated or underestimated depending on the chosen experimental conditions: sample concentration, solvent, temperature, type of column packing. In order to ORDER REPRINTS further reduce these artefacts, the influence of the above operating parameters has been studied on Arabian petroleum asphaltenes. Our results show that the obtained bimodal profiles are mainly due to association-dissociation phenomena rather than the co-existence of two distinct molecular populations of low and high molecular weights. Based on these results, samples from pilot plants were studied. We will show that SEC enables to differentiate asphaltenes from different source rocks and to follow feed and effluent evolutions during hydroconversion process. Even though this technique should be only used on a relative basis to compare molecular weight distributions at given analytical conditions, it was revealed to be very useful for the understanding of main hydroconversion reaction pathways.

Characterisation of Asphaltenes and Modelling of Flocculation – State of the Art

“…For instance, size exclusion chromatography is used to determine the molar masses of asphaltenes, residues and effluents of hydroconversion processes. Merdrignac et al (2004) demonstrated that size exclusion chromatography, although unsuitable for absolute determination of molar masses for these compounds, can be used to compare the molar mass distributions under given analytical conditions. Light, X-ray and neutron scattering techniques (Ravey and Espinat, 1990;Espinat, 1991) have also used in the determination of molar masses.…”

“…As conversion proceeds therefore, the residues processed become less stable, sometimes precipitating to such a point that they block up the pipes and the exchangers. Studies conducted on asphaltenes to investigate the conversion mechanisms have been described in several publications: Merdrignac et al (2004), Bartholdy and Andersen (2000), Wiehe (1992 and1993). Many questions are still unanswered, however, since prediction of flocculation phenomena remains a challenge: -what is the maximum conversion rate possible for a given crude without destabilising the effluents?…”

Effect of hydrotreating conditions on Maya asphaltenes composition and structural parameters

“…Asphaltene content, asphaltene-to-resins ratio, the metal impurities level and the size of asphaltenes are critical properties for catalyst activity [6].…”

Asphaltene Cross-flow Membrane Ultrafiltration on a Preparative Scale and Feedstock Reconstitution Method

“…SEC was performed on a Waters Alliance 2695 system, using a refractive index detector described elsewhere (Merdrignac et al, 2004). The system was controlled using an Empower chromatography manager.…”