Effect of precipitating environment on asphaltene precipitation: Precipitant, concentration, and temperature

摘要

The objective of this work was to investigate the effect of precipitating environment on asphaltene precipitation such as, precipitant (n-alkanes: C5, C7, C9, C12, C14), asphaltene concentration, and temperature. A combination of gravimetric and spectroscopic techniques was used for the detection and quantification of asphaltene precipitation. By measuring the absorbance of the supernatant fluid with UV-vis spectrometer after centrifugation, the contents of precipitated asphaltenes were obtained by difference method. We found that at high n-alkane concentrations (>70% by volume), the precipitated asphaltenes decrease with increasing the carbon number of n-alkanes, while at low n-alkane concentrations (<50% by volume), the sequence of precipitated asphaltenes is C14 >C5 > C12 > C9 > C7. As asphaltene concentration increases the yield of precipitated asphaltenes increase, especially variation of asphaltene states from nano-aggregates to clusters lead to more serious precipitation. The stability of asphaltenes decreases with temperature elevating when the volume ratios of n-heptane/toluene are 4:6, 5:5, or 6:4. However, at higher ratio of n-heptane/toluene (7:3) the opposite effect occurs. Based on the view that the property of precipitated asphaltenes is diverse when diluting with different concentration of n-heptane, this bizarre phenomenon was investigated from the perspective of difference in asphaltene property. To verify this opposite effects, three sub-fractions of asphaltenes (SA1, SA2, and SA3) were extracted to investigate temperature effects.The experimental results show that SA3 (more soluble) become more stable at higher temperature while SA1 and SA2 (less soluble) were both destabilized with increasing temperature. (C) 2016 Elsevier B.V. All rights reserved.