10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Molecular Content of the Critical Clusters of Lower n-Alkanes: Experimental Characterization Using Mass Spectrometric Detection and Small Angle X-ray Scattering
KEHINDE OGUNRONBI, Martina Lippe, Ruth Signorell, Barbara Wyslouzil, The Ohio State University
Abstract Number: 804 Working Group: Aerosol Physics
Abstract Understanding the vapor to liquid phase transition of n-alkanes is motivated by both technological and fundamental considerations. On the one hand, separation processes that recover natural gas liquid (NGL) from raw natural gas streams often involve expanding and cooling the natural gas stream across Joule-Thompson throttling valves, turbo-expanders, or supersonic nozzles. In all cases, vapor phase nucleation initiates condensation of the longer chain length alkanes. On the other hand, the simplicity of the interactions between n-alkane molecules makes them interesting candidates for both fundamental experimental and simulation studies.
In this work, we investigate the vapor-liquid nucleation of lower n-alkanes – pentane, hexane, and heptane – on the microsecond timescale in supersonic Laval nozzles and report the critical cluster sizes of droplets formed in the nozzles. We characterize the expanding gas mixture flow inside the nozzle using pressure trace measurements (PTM) and characterize the aerosols generated in the nozzle using small angle x-ray scattering (SAXS). Analyzing the SAXS and PTM data from different nozzles, characterized by different expansion rates, yields the supersaturation dependence of the nucleation rate, from which we determine the critical cluster sizes using the first nucleation theorem. The results from this conventional approach are compared with the results of directly characterizing the clusters in a uniform post-supersonic nozzle flow using mass spectrometric detection and soft single-photon by vacuum ultraviolet (VUV) light.