Asphaltenes Transport into Hydroconversion Catalysts at High Temperature: Role of the Alumina Nanoporous Texture

Abstract

This study deals with the role of the alumina nanoporous texture in the accessibility of the asphaltene molecules to the active sites of resid hydroconversion catalysts. We have proposed in this contribution to investigate the diffusion and adsorption process into the porosity of various monomodal and bimodal alumina supports. It consists of immersing catalytic supports, under the form of extrudates, into an asphaltene solution in toluene. Optical microscopy observations of a cut of the cylindrical extrudates were carried out to follow the asphaltene penetration as a function of the contact time. We aimed at reaching a good asphaltene mass balance, taking into account (i) the evolution of the asphaltene concentration in solution and (ii) the precise determination of the amount of asphaltenes deposited into the support. The influence, on the mass transfer and the penetration depth, of various parameters such as temperature, asphaltene concentration of the solution, asphaltene size polydispersity, and alumina porous texture was appraised. The novelty of this Article resides in the evaluation of diffusion and adsorption of asphaltenes at high temperature (250 °C). Finally, an endeavor for the process modeling is presented. The adsorption equilibrium was modeled according to the Langmuir-type isotherm. A model considering the radial diffusion in a cylinder (the extrudate) was used providing an average diffusion coefficient.

Distributed Properties of Asphaltene Nanoaggregates in Crude Oils: A Review

“…GPC ICP-HR-MS chromatograms of the V, Ni, and S species in an atmospheric residue feedstock (ATM, green line), vacuum residue (VAC, blue line), blend of 93 vol % ATM, and 7% VAC (physical blend, red line) and theoretically reconstructed blend of 93 vol % ATM and 7 vol % VAC (black dashed) . Reprinted from ref . Copyright 2020, with permission from Elsevier.…”

“…The penetration of asphaltenes into catalyst materials is extremely important in refinery processes such as catalytic hydroprocessing, because the large molecules and nanoaggregates diffuse more slowly than the lighter fractions of crude oil. Penetration of asphaltenes from solution into catalyst pellets has been measured at up to 250 °C without reaction, but the complex combination of adsorption and diffusion with potential dissociation of asphaltene nanoaggregates prevents any determination of the distribution of molecular or nanoaggregate size . Although significant dissociation of nanoaggregates might be expected at temperatures of 250 °C, the comparison of the penetration of low- and high-molecular weight fractions and the size of the asphaltenes remaining in solution after uptake by catalyst pellets both indicated significant persistence of nanoaggregates.…”

“…GPC ICP-HR-MS chromatograms of the V, Ni, and S species in the feed (black dashed line) and the product for different temperatures after having been hydrotreated at 375–385 °C and LHSV 0.2 h –1 . Reprinted from ref . Copyright 2020, with permission from Elsevier.…”

“…Penetration of asphaltenes from solution into catalyst pellets has been measured at up to 250 °C without reaction, but the complex combination of adsorption and diffusion with potential dissociation of asphaltene nanoaggregates prevents any determination of the distribution of molecular or nanoaggregate size. 79 Although significant dissociation of nanoaggregates might be expected at temperatures of 250 °C, the comparison of the penetration of low-and high-molecular weight fractions and the size of the asphaltenes remaining in solution after uptake by catalyst pellets both indicated significant persistence of nanoaggregates. Separation and characterization of the most persistent nanoaggregates, after hydroprocessing, would give insight into the composition and behavior of this important subfraction of the asphaltenes.…”

Quantitative imaging of carbon in heterogeneous refining catalysts

“…They are cylindrical extrudates, 6 to 8 mm long, with a 2 mm diameter and a single-mode pore size distribution centered at 14 nm. 29 Their texture characteristics, obtained from porosity characterization performed by nitrogen adsorption and mercury porosimetry techniques (according the American Society for Testing and Materials (ASTM) D3663-03 and D4284-03 methods) are given in Table 1.…”