Theory of asphaltene precipitation in a hydrocarbon cyclone

Abstract

Asphaltenes are a variety of semi-polar hydrocarbon species found in many crude oils worldwide. They make up a significant weight of the bitumen (up to 19%) found in the Canadian oil sands deposits near Fort McMurray. This deposit is the largest known oil reservoir in the world. Using conventional technologies for extracting oil from these deposits involves mining the ore, water washing the bulk mineral from the bitumen and then solvent washing the remaining water and fine mineral from the bitumen. In this context, asphaltenes present both a challenge and an opportunity. They have a tendency to stabilize emulsions of water and fine mineral, and they can play an important role in froth cleaning. However, they contribute significantly to the viscosity of the bitumen and when they precipitate in the wrong place they can cause significant problem with plugging and blinding in process equipment. Asphaltenes are large polar molecules that form when the bonds between asphaltene groups and resin molecules within a bituminous oil matrix are broken. This bonding is the result of Van der Waals coupling, which normally creates a stable oil emulsion rather than a conventional solution. When this bonding is broken the asphaltene molecules are capable of mutual bonding or flocculation. This process will entrap mineral and water and is an important mechanism for the cleaning of bituminous froth. Asphaltenes are stabilized in petroleum by the attachment of smaller hydrocarbon resin units. Whenever these resins are detached from the asphaltene molecules the asphaltenes can precipitate. The commonly accepted agent for effecting this so-called precipitation is the introduction of a large surplus of paraffin molecules, which sequester the resins so as to prevent them from attachment to asphaltene molecules, thereby destabilizing the asphaltene emulsion. This destabilization leads to flocculation driven precipitation and may be interpreted as a blocking of a reuptake mechanism. This paper asserts that it is the essential mechanism governing the process of asphaltene precipitation in paraffinic froth cleaning. The significant consequence of this is that it should not be necessary to have a surplus of paraffin molecules above “a precipitation threshold” to initiate asphaltene flocculation sufficient to produce significant cleaning effects. It could also result from a combination of fluidic action coupled with significantly lower paraffinic molecular concentrations. This leads to a theory of the hydrocarbon cyclone, which distinguishes it from the ordinary hydrocyclone and one that promotes additional mechanisms other than the usual hydrocyclone modes based on centrifugal vortex driven forces. It supports an explanation for the ternary splitting capability of the hydrocarbon cyclone and deals with the roles played by resin and asphaltene molecules in the froth cleaning process.