Dense-gas fractionation of mixtures of petroleum macromolecules

Abstract

Dense-gas extraction (DGE) was used to fractionate a petroleum pitch feedstock of broad molecular weight distribution (MWD) into selected oligomeric constituents. The DGE process was carried out in a semibatch mode using the solvent toluene (T c = 318.6 • C, P c = 41.1 bar) and a pitch charge of 10-15 g. A packed column with reflux produced the equivalent of several equilibrium stages. The apparatus was operated at near and supercritical temperatures, with the stillpot at 320 • C and the column temperature increasing linearly up to the reflux condenser temperature of 360 • C. Operating pressures were determined by the conditions required to extract a given oligomer and varied from 44 to 84 bar. Using a monomer-rich petroleum pitch feed (MW n = 299, PDI = 1.10), a dimer-rich extract with a purity approaching 90% (MW n = 521, PDI = 1.07) was obtained, with the remaining residue (MW n = 883, PDI = 1.24) consisting of 95% trimer and higher oligomers. MALDI-TOF mass spectrometry was used to determine the MWD of the feed pitch and pitch fractions, with a unique matrix being used to enhance the response of higher MW species. The combination of DGE for separation and MALDI for accurate MW information is a powerful new technique for the molecular characterization of insoluble, high MW fossil fuels.

Mesophase evolution in heat-treated solid petroleum pitches

“…7, 2012 a mild formation of radical cations of polycyclic aromatic molecules, preventing unwanted fragmentation. 33,[37][38][39]41 According to Edwards et al, 33 the content of the matrix/pitch used in their study did not significantly affect the results. Thus, we chose the ratio 1:5 (analyte:matrix), the lowest studied.…”

“…These results are in accordance with those previously reported by Edwards and Thies. 38,39,41 The results from Marzec 45 also showed a bimodal distribution of masses for coal, with regions between m/z 130-600 and 1300-3500.…”

“…Former studies [36][37][38][39][40] suggest that when compounds, to be identified by MALDI, present problems with solubility, miscibility or segregation during crystallization, a matrix should be mixed with the analyte in the solid state with subsequent application, directly or in suspension, in the cell equipment (sample holder). Therefore, there were employed two different methods for sample preparation without solvents.…”

The Molecular Design of High-Performance Carbon Materials

“…For the solid-state analysis of M-50 pitch, the pitch and TCNQ were mixed using a grinding mill (Thermo Electron Corp., model Wig-L-Bug). The sample was then transferred to the MALDI target-plate cell using our water-spotting method [2,8]. For the solvent-based sample preparation of monomer-rich and dimer-rich fractions, a fine powder of TCNQ was prepared using a grinding mill.…”

“…The conventional technique for analytical-scale pitch separation, gel permeation chromatography (GPC), suffers from a number of disadvantages, including poor peak resolution and the incomplete solubility of higher mol wt pitches in even aggressive mobile-phase solvents [1,[6][7]. Thies and co-workers [8][9][10] have recently developed a technique, known as dense-gas extraction (DGE), for separating pitches into fractions of relatively narrow mol wt. Such fractions can serve as standards for additional characterization work; in addition, we are investigating their large-scale production via DGE as "designer" pitches whose molecular compositions are tailored for a given, final carbon product application [11].…”