Dense-Gas Fractionation and MALDI Characterization of Carbonaceous Pitches

Abstract

The combination of multistage, dense-gas extraction (DGE) and matrix-assisted, laser desorption/ionization (MALDI) mass spectrometry (MS) was investigated for the fractionation and characterization of an oligomeric model pitch synthesized via the thermal polymerization of anthracene. Our approach was shown to be effective both for elucidating the molecular properties of the anthracene pitch and for generating narrow molecular weight (MW), oligomeric cuts that can serve as MW standards. DGE was used to fractionate 10-to 15-g charges of anthracene pitch into relatively pure, gram-and decigram-sized cuts containing 99+% monomers, 90+% dimers, and 80+% trimers, respectively. The multistage, semi-batch DGE process was carried out in two steps with toluene being used as the dense-gas solvent at both subcritical and supercritical conditions. In the first step, lower-MW species were stripped off as the overhead; for the second step, the remaining residue was extracted, yielding the desired oligomeric cuts as overhead. Computer process simulation was used to guide the experimental work and demonstrated the effect of column temperature gradient on the liquid reflux ratio and, as a result, product purity. MALDI-MS played a critical role in guiding the selection of DGE operating conditions, yielding absolute MW information on the fractions that were produced.

Clustering of polycyclic aromatic hydrocarbons in matrix‐assisted laser desorption/ionization and laser desorption mass spectrometry

“…+ ). Because of their structures, they represent suitable models for complex natural systems such as heavy oils, asphaltenes, or pitches 11–13. It is therefore interesting to clarify the mechanism regulating their desorption/photoionization process.…”

Laser desorption/ionization determination of molecular weight distributions of polyaromatic carbonaceous compounds and their aggregates

“…The refinement and upgrading of mass spectrometry (MS) techniques have provided a considerable impulse to the determination of the composition, molecular weight distribution (MWD) and structure of carbonaceous species 6–19. In particular, laser desorption/ionization mass spectrometry (LDI–MS) has currently achieved a mass resolution capable of discerning chemical composition and structure in complex carbonaceous mixtures, especially when applied in combination with chromatographic separation 13–15. The present article is focussed on the application of LDI–MS techniques to the characterization of specific classes of carbonaceous molecules, namely polycondensed hydrocarbons and heavy oil fractions (asphaltenes).…”

Control of the Molecular Weight Distribution of Petroleum Pitches via Dense‐Gas Extraction

“…To this end, our group [7,8] is investigating the use of dense-gas extraction (DGE) for the fractionation of petroleum pitches. Although the DGE concept is not new [9,10], its application to petroleum pitches with the goal of controlling MWD, is.…”