Multistage separation and molecular composition of interfacial active materials in Bohai heavy oil

Key words:  heavy oil  multistage chromatographic separation  interfacial active material  ESI-FT-ICR MS  molecular composition

Abstract:

Bohai heavy oil was separated into three fractions of φ₁-Ⅱ, φ₂ -Ⅰand φ₂-Ⅱ by hydrated silica gel column with different water content. The interfacial activity of these fractions decreased in the following order:φ₁-Ⅱ, φ₂-Ⅱ, φ₂ -Ⅰ. The interfacial activity of isolated interfacial material is in accordance with the amount of water loaded onto the silica gel. Molecular composition of oil components were characterized by negative ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT- ICR) mass spectrometry (MS). It is found that the composition of heteroatoms in oil components is relatively complex. Class species such as N₁,N₁O₁,N₁O₂,N₁O3 ,N₁O₄,N₂,O₁,O₁S₁,O₂,O₂S₁,O₃,O₃S₁,O₄,O₄S₁,O₄,O₅S₁ are identified with high resolution FT- ICR MS. The most interface-active species within Bohai heavy oil are the O1~5S₁, N₁O3~4 and O₅ species, mainly in φ₁-Ⅱ; the next are the lower order O2~4 and N₁O1~2 species, and the weakest are N1~2 and O₁ species, mainly in φ₂ -Ⅰ. The O₂~4 and N₁O1~2 species exist three oil fractions and show significant differences. The O₂~4 and N₁O₁ species with owest carbon number/lower DBE in most interface-active compounds φ₁-Ⅱ. While in φ₂-Ⅱ, the O₂~4 and N₁O₁ species have lower carbon number ranges but highest DBE, which present similiar characteristic of asphaltenic species. However for N₁O₂ species in three oil fractions, the carbon number and DBE decrease as the interfacial activity increases.