Effect of Chemical Inhibitors on Asphaltene Precipitation and Morphology Using Ultra-Small-Angle X-ray Scattering

This paper presents time-resolved ultra-small-angle X-ray scattering (USAXS) results of the effect of chemical inhibitors, dodecylphenol (DDPh) and nonylphenol formaldehyde resin-1600 (NPFR), on the kinetic precipitation of asphaltenes. With length scale ranges probed between 1 nm and 5 mu m, USAXS provides a unique means to simultaneously characterize insoluble asphaltene clusters with length scales of >50 nm and soluble clusters with length scales of <50 nm. Both inhibitors tested were observed to reduce the insoluble asphaltene growth rate at 500 and 5000 ppm (mg/kg) inhibitor concentrations, with DDPh displaying a relatively larger reduction. Further, both of the chemical inhibitors tested modified the morphology of insoluble asphaltenes, and the most effective inhibitor, DDPh, also reduced the size of soluble asphaltene clusters. The asphaltene sample used in this study initially precipitated as a fractal cluster that transitioned to a second liquid or solid phase with a rough surface. These insoluble particles further flocculate into larger mass fractals and are commonly visualized with optical microscopy. The chemical inhibitors slowed the rate of transition to a new phase, and the fractal geometry of the insoluble particles persisted for longer times. Consequently, USAXS is a new tool that can be used to better understand the impact of chemical inhibitors on the structure and dynamic aggregation of asphaltenes over broad length scales.