Date of Award
Doctor of Philosophy (PhD)
Thies, Mark C
Ogale , Amod A
Bruce , David A
Kitchens , Christopher L
Walker , Terry H
Petroleum pitches are carbonaceous materials that serve as precursors for advanced carbon products. Because of their highly graphitic nature, such pitches are of particular interest for producing high thermal conductivity carbon fibers for thermal management applications, such as microelectronics packaging for hybrid and plug-in vehicles.
Even though the properties of the final carbon products are impacted by the molecular composition of the starting pitch precursor, a fundamental understanding of this relationship has yet to be established. To this end, dense-gas extraction (DGE), a fractionation technique that allows for the production of pitches of controlled composition for both analytical and rheological characterization, was investigated.
A continuous-flow apparatus, consisting of two countercurrent-flow packed columns, was designed and constructed for this study. Supercritical toluene, pentane, and methanol were all investigated as extractive solvents. An oligomeric petroleum pitch, M-50, was used as the feed pitch. The effect of column temperature gradient and pressure, solvent-to-pitch (S/P) ratio, solvent composition, and feed location was shown to play a significant role in pitch yield, oligomeric composition, mesophase content, and physical properties of the fractions obtained herein. In addition, co-solvent interactions between pitch molecules, the existence of reflux in the presence of a column temperature gradient, and the presence of thermal polymerization reactions were all demonstrated to have a significant effect on the purity of the fractions isolated. For example, in isolating dimer-rich pitches, an improvement in purity from 81 to 99 mol% was achieved by changing the extractive solvent from toluene (Tc = 319 °C) to pentane (Tc = 197 °C) - toluene mixtures, and operating the DGE column as a stripper/rectifier (vs. stripper only) at a positive temperature gradient (270 Top, 240 °C Bottom) and a S/P ratio greater than 15.
Pitches of narrow molecular weight distribution were isolated from the oligomeric feed pitch (M-50) on a continuous basis and characterized by MALDI mass spectrometry. In particular, monomer- and dimer-rich pitches with purities greater than 96 mol%, and trimer-rich pitches of 60 mol% purity, were obtained at overall product yields of 50% for the monomer, 14% for the dimer, and 5% for the trimer, at pitch flow rates ranging from 5 to 50 g/h. The softening point of pure monomer was found to be 40 °C, of pure dimer 215 °C, and of a trimer-rich cut 285 °C. By combining DGE with our analytical characterization techniques, we have been able to obtain the first reliable estimate of the molecular composition of M-50 pitch: 50 wt% monomer, 27 wt% dimer, and 23 wt% trimer and heavier species.
Cervo, Eduardo, "Isolating Petroleum Pitch Oligomers via Multistage Supercritical Extraction" (2010). All Dissertations. 553.