Effect of Surface Chemistry and Roughness on the High-Temperature Deposition of a Model Asphaltene

Abstract

Fouling of processing units because of asphaltene deposition is a common phenomenon that interrupts the operation of oil refineries. In this study, the deposition behavior of a model archipelago asphaltene was investigated in the temperature range of 150 o C to 350 o C. For a fixed surface chemistry, the differences in deposit chemistry with fouling temperature is a function of the thermochemical properties of the model asphaltene. Under static high pressure and high temperature fouling conditions, both surface roughness and chemistry play an important role in asphaltene deposition. Rough surfaces are shown to develop larger deposits because of less restrictive physical barriers to inhibit deposit growth. Passivating the surface with an alumina chemistry significantly reduces the impact of surface roughness, as well as the total amount of deposition. This beneficial effect of using a protective alumina chemistry is attributed to its high thermal stability and low diffusivity that inhibit the uncontrolled formation of thiolate and sulfide deposits that are found on unpassivated steels. Instead, alumina modifies the surface reaction to a self-limiting chemisorption and oxidation process that produces thin sulfate deposits at the surface. With further consideration to the reactive species present in solution, the findings of this study may be extended to determine suitable surface conditions that mitigate asphaltene fouling.

Low-Temperature Pack Aluminization Process on Pipeline Steel To Inhibit Asphaltene Deposition

“…The absence of the peak corresponding to sulfide (~161.5 eV) indicates that no metal sulfide is formed during the fouling experiment, similar to the previously studied ALD alumina passivated steel. 11 It is noteworthy that based on the XPS survey, the concentration of Fe on the top surface in all conditions is below 1 at. %, indicating enrichment of aluminum and the presence of an alumina passivating layer after aluminization.…”

“…[7][8] Though these oxides are more commonly used in their equilibrium corundum form, recent studies have shown their protective action even in a native amorphous form. [9][10][11] Such protective oxides can be introduced onto the surface of ferrous alloys by coating, [12][13][14] alloying the surface, 15 or changing the base composition of the alloy. [16][17] In a previous study, it was shown that an atomic layer deposition (ALD) coating of alumina on steel surfaces significantly reduces asphaltene deposition at elevated temperatures from 150 °C to 350 °C.…”

“…[16][17] In a previous study, it was shown that an atomic layer deposition (ALD) coating of alumina on steel surfaces significantly reduces asphaltene deposition at elevated temperatures from 150 °C to 350 °C. 11 The alumina surface chemistry, even in the amorphous form, was shown to alter the reaction pathway between the asphaltene and the surface from a corrosive sulfidation reaction to a self-limiting chemisorption and oxidation process. For the alumina coating to serve as an effective diffusion barrier against the inward diffusion of S at elevated temperatures, the coating must be both continuous and greater than a critical thickness of 5 nm.…”

“…For the alumina coating to serve as an effective diffusion barrier against the inward diffusion of S at elevated temperatures, the coating must be both continuous and greater than a critical thickness of 5 nm. 11 Despite the demonstrated benefits of ALD to produce anti-fouling alumina coatings on steel, it is crucial to bear in mind that typical film growth rates using ALD are very slow and, therefore intractable for most industrialscale applications. 18 Additionally, the application of a distinct coating creates an interface, which can be easily subjected to defects.…”

“…However, given the massive scale of refining equipment and material cost restrictions, this approach is not commonly pursued. It is known that protective surface oxides like chromia and alumina can significantly improve the corrosion and fouling resistance of ferrous alloys. , Though these oxides are more commonly used in their equilibrium corundum form, recent studies have shown their protective action even in a native amorphous form. − Such protective oxides can be introduced onto the surface of ferrous alloys by coating, − alloying the surface, or changing the base composition of the alloy. , …”