Brewster Angle Microscopy of Langmuir Films of Athabasca Bitumens, n‑C5 Asphaltenes, and SAGD Bitumen during Pressure-Area Hysteresis Yujuan Hua and Chandra W. Angle* CanmetENERGY/CanmetE ́ NERGIE, Natural Resources Canada/Ressources Naturelles Canada, Devon, Alberta T9G 1A8, Canada ABSTRACT: Bitumen films formed on water surfaces have negative consequences, both environmental and economic. CanmetENERGY has placed considerable research emphasis on understanding the structures of the bitumen films on water as a necessary step before optimization of bitumen extraction. The detailed structures of the adsorbed molecules and, espe- cially, the role of asphaltene molecules at the interfaces are still under scrutiny and debate. In the present study, we compared bitumen and asphaltene films as they were compressed and expanded under various surface pressures in order to achieve a clearer understanding of bitumen film structures. We used a customized NIMA Langmuir trough interfaced to a Brewster angle microscope (BAM) and CCD camera (Nanofilm_ep3BAM, Accurion, previously Nanofilm Gmbh) to study images of bitumen films at the air/water interface. The bitumen film appeared uniform with high reflectivity at a surface pressure of 18 mN·m -1 and exhibited a coarse pebblelike interface with reduced reflectivity in the liquid condensed (LC) phase at higher pressures (18-35 mN·m -1 ). During the first cycle of compression asphaltene films showed well-defined phase transitions and a uniformly smooth interface in the LC phase between 9 and 35 mN·m -1 . However, folding or buckling occurred at surface pressures from 35 to 44 mN·m -1 . On expansion, asphaltene films appeared to break into islands. The hysteresis of the pressure-area isotherm was much larger for asphaltenes than for bitumen. In both compression and expansion cycles, BAM images for bitumen films appeared to be more reproducible than those of the asphaltene films at the same surface pressures. Films for low-°API SAGD bitumen were almost identical to those for surface-mined bitumen. Films formed from partially deasphalted surface- mined bitumens showed higher compressibility and lower rigidity than the original bitumen. The BAM images illustrated significant differences between the partially deasphalted and original bitumen films. Other components in bitumen also played important roles in determining the interfacial properties of bitumen films. ■ INTRODUCTION An understanding of the interfacial behaviors of bitumen and crude oil films is important for recovery of valuable bitumen product discharged into tailings ponds and for remediation of oil spills. A certain percentage of the bitumen extracted from Athabasca oil sands is entrained in tailings underflow and, when deposited in tailings ponds, forms films that not only pose hazards to wildlife, but also represent an economic loss. Technologies for reduction and removal are therefore needed to ensure environmental sustainability in bitumen production. An understanding of the structures, physicochemical properties, and behaviors of bitumen films at the air/water interfaces is useful, not only for the development of techniques for removal and cleanup of oil sand tailings waters, but also for improving separations in clean bitumen extraction processes. Our study was designed to address both processes as part of the federal government research mandate for efficient production of clean energy from oil sand resources. The present study focuses on an understanding of the structures of Langmuir films of Athabasca oil sand bitumen (AOSB) as well as those of partially deasphalted AOSB (as occurs in upgrading), in comparisons with standard n-pentane (n-C5) precipitated asphaltenes of AOSB as reference. In addition, films for bitumen that was extracted from ∼400 m below the surface by a SAGD (steam assisted gravity drainage) process were compared to those of surface-mined bitumen. We have previously studied the mechanisms for the high stability of produced SAGD emulsions and methods for its destabilization. 1 Athabasca surface-mined and SAGD bitumens are highly viscous low-°API crude oils from northern Alberta, Canada. 2-4 Steam reduces the viscosity and increases the flow of bitumen in horizontal pipes. The surface-mined bitumen was extracted by tumbling the oil sands ores with hot caustic water, followed by gravity separation and froth treatments. 2-4 Previous studies on pressure/area isotherms of planar films at air/water interfaces have encompassed light 5 and heavy 6 oil, bitumen, 7-9 various asphaltenes, 7-17 maltenes, 7-9 and resin com- ponents that were either studied independently or mixed, 18,19 Received: October 23, 2012 Revised: November 22, 2012 Published: November 26, 2012 Article pubs.acs.org/Langmuir © 2012 American Chemical Society 244 dx.doi.org/10.1021/la304205t | Langmuir 2013, 29, 244-263