Instability, precipitation and fouling in heavy oil systems

Asphaltenes are the most polar, highest molecular mass species found in crude oils and bitumens. Depending on the nature of the surrounding species, the temperature and pressure, asphaltene may be dissolved, or may flocculate resulting in precipitation.; Asphaltene precipitation during oil production and processing is a very serious problem in many areas throughout the world. To avoid precipitation, much research has been directed to the solubility of asphaltenes in petroleum liquids as a function of temperature, pressure and composition. Bitumen from oil sands deposits contains about 13.5% asphaltenes, and during its processing is mixed with low molecular mass diluents, which can lead to precipitation and to fouling of processing equipment.; In this work, the effects of diluent composition on asphaltene precipitation from Cold Lake vacuum residue (VR) and Athabasca atmospheric tower bottoms (ATB) were determined using the hot filtration method at 60-85°C. The selected diluents include pure n-alkanes (heptane, decane and dodecane), a tube oil basestock---paraflex (PFX), a heavy vacuum gas oil (HVGO) and a resin enriched fraction (REF) recovered from Cold Lake vacuum residue by supercritical fluid extraction and fractionation. The latter three complex diluents were tested alone and in blends, in order to cover a range of saturates from 56 to 99.4wt%, aromatics from 0.6 to 25wt%, and resins from 0 to 19wt%. For pure n-alkanes, the amount of asphaltene precipitation at a given diluent/residue ratio decreases as the molecular mass of n-alkanes increases. With the increase of diluent-to-residue ratios R, the amount of precipitated asphaltene, W, increases sharply at first and then levels off. Similar behaviour can be found for the mixtures of both feedstocks with the aliphatic diluent PFX. With more aromatic diluents such as pure HVGO or blends of HVGO/PFX=1, the increases in W with R are modest or slight within the range of experiment. The addition of the resin and aromatic-rich REF has a strong inhibition effect on asphaltene precipitation. For selected mixtures, the temperature effect on precipitation was investigated in the range of 60°C to 300°C. The results indicate that for the mixtures used in this work the solubility of asphaltenes increases monotonically with temperature. (Abstract shortened by UMI.)...