Multistage Fractionation of Petroleum Pitches with Supercritical Solvents

摘要

Two multistage separation techniques have been used to fractionate isotropic petroleum pitches: (1) a stagewise fractionation technique employing sequential, single-stage extractions with supercritical toluene, and (2) dense-gas fractionation with a packed column and reflux, with either supercritical pentane or toluene being used as the extractive solvent. With the stagewise technique, each stage was operated in a region of liquid-liquid equilibrium (LLE) at a temperature of 614 K and a solvent-to-pitch ratio of 2.0, and the pressure was sequentially reduced so as to precipitate out ～5 wt % of the feed pitch in each stage. Five single-stage flashes could be carried out in the LLE region at pressures ranging from 138 to 52 bar, and five pitch fractions comprising the heaviest third of the pitch were obtained. In contrast, with dense-gas fractionation multiple fractions of the lightest third of the feed pitch were obtained. In this case, the column was operated in the vapor-liquid equilibrium (VLE) region at temperatures about 20 K above the critical temperature of the solvent and pressures ranging from less than 20 to about 50 bar. The limited characterizations of the fractions that have been made to date indicate that both techniques are separating out fractions in terms of their molecular weight.