Role of Asphaltenes in Inhibiting Corrosion and Altering the Wettability of the Steel Surface
Abstract Asphaltenes (heptane insolubles) from a variety of crude oils have been identified previously as contributors to inhibition of internal corrosion of mild steel pipelines. However, the mech...
Asphaltene Deposition on Metallic Surfaces
Abstract The potential for asphaltene deposition in wellbores and flowlines is a major concern during design of oil production and transportation facilities, especially in deep‐water environments. Understanding the processes that control asphaltene deposition, especially the relationship between precipitation and deposition, can help to reduce the risk and cost. Stainless steel capillary tubes were used to study the influences of factors including temperature, degree of asphaltene instability, and precipitant molar volume on asphaltene deposition from mixtures of stock‐tank oils and n‐alkanes. Temperature varied from 20°C to 60°C. Pressure drop across the capillary tube was used to estimate the amount and distribution of deposit formation. Existing asphaltic particles in stock‐tank oil samples did not create deposits. Below the wax appearance temperature, intermittent pressure spikes indicated deposition of wax. Above the wax appearance temperature, deposition occurred gradually from near‐onset mixtures created by co‐injection of oil and n‐alkane precipitants. Asphaltenes flocculated by addition of higher molar volume n‐alkanes deposited more material than those flocculated by lower molar volume n‐alkanes. Examination of the deposited materials showed that they contained not only asphaltenes but also waxes. Much different depositional characteristics were observed for solutions of asphaltenes in an aromatic solvent than for the stock‐tank oil from which they were derived.
Chapter 10 Effects of Asphaltene Precipitation on the Size of Vanadium-, Nickel-, And Sulfur-Containing Compounds in Heavy Crude Oils and Residua
Publisher Summary This chapter addresses the question of whether the concept of asphaltenes is appropriate to use when discussing certain aspects of petroleum-chemistry characterization, process monitoring and design—where size is an important factor. Although asphaltene precipitation concentrates the metal compounds, it tends to increase the average molecular size of the metal-containing compounds through agglomeration. This can cause analysis difficulties when size-related properties, for example, catalyst pore-metal-containing molecule interactions are being considered. Although the asphaltene precipitation does concentrate the sulfur-containing compounds to some extent, there is little evidence that the precipitation increases the average size of these compounds through agglomeration. The asphaltene precipitation, however, does separate some sulfur-containing compounds from the resin fraction. This could cause analytical difficulties if not accounted for, because these sulfur containing compounds in the resin fraction can have similar structures to those of the asphaltenes.