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

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 in the temperature range of 150 to 350 degrees C was investigated. 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.