Investigating precipitation kinetics of asphaltenes from crude oil

Abstract

The precipitation of asphaltenes from crude oil can lead to serious problems in oil production and processing, such as plugged pipelines and process equipment. To better understand the properties responsible for asphaltene precipitation, this research focused on investigating precipitation behaviour of different crude oils. n-Heptane was used as a precipitant to induce asphaltene instability before fractionation. Several techniques of characterization were used to investigate the properties of precipitated asphaltenes precipitated at different times and precipitant concentrations. Small angle X-ray scattering (SAXS), nuclear magnetic resonance (1H and 13C NMR), elemental analyzer (EA) and inductively coupled plasma mass spectrometry (ICP-MS) were then used to assess the properties of asphaltenes for different cuts such as size of nanoaggregates, structural parameters (aromaticity and number of carbon per alkyl side chain), heteroatoms and metal contents, respectively. The results showed that the asphaltene precipitation rate for all crude oils investigated was controlled both by thermodynamics and diffusion process ((δ asph δ solution) 2/µsolution). Except cut 1, the asphaltenes precipitated firstly had higher heteroatoms and metal contents but less number of carbons per alkyl side chain because more polar fractions could induce asphaltenes to precipitate easily. The nanoaggregate sizes and aromaticity for different cuts were similar. This understanding may help better predict the instability of asphaltenes under different operational conditions and develop proper remediation techniques.