Studies on precipitation performance of Emphasis

Authors: C A Nwadinigwe I V Anigbogu O T Ujam

Publish Date: 2014/11/30

Volume: 5, Issue: 4, Pages: 403-407

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Abstract

Asphaltenes behave like blood cholesterol in that they deposit on the walls of crude oil transportation pipes thereby narrowing the internal diameters thus posing great dangers This study was designed to remove asphaltenes from light crudes by solvent precipitation and to investigate the comparative performance of nheptane single solvent and npentane/nheptane mixed solvent in this regard Each of three Nigerian crudes Bonny Export Bodo and Mogho crudes were first distilled at 350 °C to obtain the atmospheric residuum Asphaltenes were precipitated from each residuum at different stirring times with single nheptane and mixed npentane + nheptane solvents The precipitated asphaltenes were characterized with FTIR UV–visible spectrophotometers while the maltenes were fractionated to obtain the various fractions Results show that the asphaltenes were made up of saturated cyclic aliphatic hydrocarbons and unsaturated substituted aromatic hydrocarbon Also aromatics to saturates ratio and resins to asphaltenes ratio was higher in Bonny Export and lower in Mogho crude thus indicating that Bonny Export has the lowest asphaltene precipitation risk while Mogho crude has the highest risk The results also showed that resins stabilize asphaltenes in crude as addition of resins to the different crudes reduced the quantity of asphaltene precipitatedCrude oil is a multicomponent mixture consisting of naturally occurring hydrocarbons together with organic compounds of sulphur nitrogen and oxygen as well as trace amounts of metallic porphyrins such as those of vanadium nickel and iron The origin of crude oil can have a significant effect on its composition As a result crude oils widely vary in volatility density viscosity and color Crude oil may also contain dissolved inorganic gases such as nitrogen carbondioxide and hydrogen sulphide at high pressure and temperature conditionsThe conventional methods of physical fractionation used in the petroleum industry are based on physicochemical characteristics and include distillation extraction with solvents and adsorption by surface active substances The fractionation by extraction with nonpolar solvents of similar nature but of different boiling points is a separation analogous to fractional distillation which yields basically complex fractions first by boiling point ranges and consequently by molecular weight ranges Dehkisia et al 2004 Hoiberg 1965 Suelves et al 2003 The amount of fractions separated depends on the extent of dilution temperature and the nature of the solvents as well as the equilibrium of the system Hong and Watkinson 2004 SPEIght 1980Asphaltenes are important constituents in crude oil They are usually defined as a fraction of crude oil soluble in aromatic solvents such as toluene or benzene and insoluble in paraffinic solvents such as npentane or nheptane Asphaltenes contribute significantly to the high viscosity and the coking tendency of heavy oils and bitumen They cause solid deposits that obstruct flow in petroleum production systems Auflem 2002 Asphaltene can selfassociate and/or precipitate but the selfassociation and precipitation is mediated by other solubility fractions particularly resins SPEIght 1999 Hence asphaltenes and resins have often been lumped together as residue in crude oil causing reduction in crude oil production as they block the pores of reservoir rocks and can plug the wellbore tubing flowlines separators pumps tanks and other equipment and as a result cause barrier to the flow of oil Leontaritis and Mansori 1987The separation of residues into two fractions asphaltenes and maltenes is brought about by means of low molecular weight paraffinic hydrocarbons which have been recognized as possessing selective solvency for hydrocarbon systems and is known as solvent deasphalting The precipitation of insolubles from petroleum is known to follow a complex mechanism involving solubility equilibria adsorption and aggregation Thus the amounts and nature of insolubles precipitated by different hydrocarbon solvents will be different Ethyl acetate has been used to eliminate both resins and asphaltenes from the oil in one step and thus improving the quality of deasphalted oil Catellanos et al 1983

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