Measuring Asphaltene Deposition Onset from Crude Oils Using Surface Plasmon Resonance

We present a surface plasmon resonance(SPR) sensor for crude oils that can be used to directly measure asphaltenedeposition onset. Surface plasmon resonancedescribes a condition in which light incident onto a highly conductive metallic film couples into resonant charge oscillations of the metal. The SPR condition is highly sensitive to slight perturbations in the dielectric environment in the immediate vicinity of the thin-film, less than 1 μm away at visible frequencies. Here, we show that shifts in the peak surface plasmon resonantwavelength can be used to measure the onset of deposition of asphaltenesfrom a titration experiment. Initially, the SPR peak wavelength of the neat crude oil is measured. Next, the gradual addition of n- heptanedilutes the crude oil and produces a lower SPR peak wavelength, which results from the lower refractive index of the mixture. When the amount of added n- heptaneapproaches the deposition onset point, asphaltenesprecipitate and are deposited onto the thin-film surf...