Asphaltene Precipitation from Athabasca Bitumen Using an Aromatic Diluent: A Comparison to Standardn-Alkane Liquid Precipitants at Different Temperatures

Abstract

Asphaltenes are precipitated from Athabasca bitumen upon the addition of liquid precipitants. The asphaltene onset and the amount of precipitated asphaltenes using different equivalents of added liquid precipitant are determined. The deasphalting power of an aromatic solvent with structural similarities to toluene, namely, α,α,α-trifluorotoluene (BTF), is investigated, and the results are compared to using n-pentane (n-C5), n-hexane (n-C6), and n-heptane (n-C7) as liquid precipitants. A correlation between maximum asphaltene precipitation and the surface tension of the pure liquid precipitants studied is observed. Increasing the temperature results in increasing the volume fraction of liquid precipitant at the asphaltene onset and a decrease in the amount of maximum asphaltene precipitation. Composition elemental analyses show a small increase in the relative amounts of sulfur atoms in asphaltenes with increasing precipitation temperatures. The appearances of asphaltenes precipitated at different temperatures are compared before and after thorough washing with excess liquid precipitant. Asphaltene precipitation experiments are time-consuming and have motivated us to introduce an empirical function to describe asphaltene yields between asphaltene onset and maximum asphaltene precipitation requiring less experimental data. Our results provide useful tools for future studies of gradient asphaltene precipitation; processes that are of current interest with the development of new(er) techniques for bitumen extraction.

Effect of Temperature on Asphaltenes Precipitation: Direct and Indirect Analyses and Phase Equilibrium Study

“…However, it has been reported in the literature that precipitant physicochemical properties could affect the asphaltenes precipitation yield as follows: at high concentrations of paraffins, short-chain n -alkanes behave as stronger precipitants than long ones, while at low precipitant concentrations, longer chain length alkanes (ranging from 7 to 10 carbon molecules) increase the asphaltene precipitation onset to a maximum . The precipitation onset, or flocculation point, , could be defined as the minimum amount of precipitant that is responsible for asphaltenes aggregation and destabilization start point.…”

“…Maqbool et al have demonstrated that at higher temperatures the mass of asphaltene precipitated is smaller, but the precipitation onset time is shorter, due to the effect of viscosity on the aggregation of asphaltenes . On the contrary, Bjoroy et al stated that the increase in temperature leads to higher asphaltene onset values, although there is a consensus about the decrease in the precipitation yields …”

“…13 On the contrary, Bjoroy et al stated that the increase in temperature leads to higher asphaltene onset values, although there is a consensus about the decrease in the precipitation yields. 12 Recently, Yang et al proposed that one subfraction of asphaltene (the heavy part of asphaltenes) became more insoluble with the increase in temperature, increasing the precipitation. On the contrary, a second subfraction (the light part, which contains lower average molecular weights, less aromatic, and a lesser content of heteroatoms than the heavy one) became more soluble and precipitated less at higher temperatures.…”

“…4 Also, it is interesting to mention that although asphaltene precipitation is recognized as a slow kinetic process, most of the phase equilibria studies were made by considering a typical time of 24 h for equilibration. Reproductible results in asphaltene precipitation yields have been found at times above 16 h, 12 with minor kinetic effects at higher precipitant concentrations. 13 From this, it could be noted that there is a lack of studies that involve the effects of temperature on asphaltene precipitation by using both direct and indirect methods.…”

Comprehensive Characterization of Asphaltenes by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Precipitated under Different n-Alkanes Solvents

“…Their definition is, therefore, not directly related to their chemical composition, but simply to their solubility. Due to a complex chemical composition, aggregation tendency, low solubility and high boiling points, the challenges to characterize asphaltenes at the molecular level are great and their actual composition is still a matter of debate. − It is generally accepted, however, that asphaltenes are highly aromatic compounds, with several heteroatoms in their composition and few and small alkyl chains. − Asphaltenes from crude oils are often precipitated using n -heptane, ,, and eventually other alkanes, − but the chemical composition of these precipitates have never been compared via FT-ICR MS petroleomic approaches. Gu and collaborators, using mostly physicochemical assays and bulk spectroscopy analysis, have compared asphaltenes precipitated by using three different n -alkanes, concluding on highest aromaticity and MW for n -heptane precipitation when compared to propane and n -pentane.…”