Controlling the oligomeric composition and char yield of pyrene pitches via continuous supercritical extraction. (15th January 2023)

• Record Type: Journal Article
• Authors: Lamie, W. Cabell; Tindall, Graham W.; Hoffman, Wesley P.; Thies, Mark C.
• Is Part Of: Fuel. Volume 332(2023)Part 1
• Publication Date: 2023-01-15
• Subjects: Pitch -- Pyrene -- Supercritical Extraction -- Toluene -- Oligomers -- Fractionation; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2022.126030
• Languages: English
• ISSNs: 0016-2361

Abstract

Graphical abstract: Highlights: Continuous supercritical extraction with toluene was used to extract oligomers from pyrene pitch. 90% pure mixture of dimers and trimers had a char yield of just under 50% Stripping unreacted monomer from the pitch produced a low-melting pitch with a char yield of 65%. Synergy between individual oligomers results in higher-than-expected char yields. Abstract: Continuous supercritical extraction (SCE) was investigated for its ability to control the oligomeric composition of a pyrene pitch generated by the catalytic polymerization of pyrene in the presence of AlCl3 . Key objectives of this work were the nearly complete removal of the starting monomer, generation of a well-defined pitch with a high char yield, and isolation of a fraction consisting exclusively of intermediate-sized oligomers. Following the design and construction of an SCE unit for processing up to 500 g/h of feed pyrene pitch with supercritical toluene (Tc = 319 °C, Pc = 41.1 bar), a 2-column setup was used to isolate ∼350 g of a fraction consisting of greater than 90 % isotropic dimer plus mesogenic trimer combined. Although the char yield of this oligomeric mixture was only moderate (i.e., 47.1 %), it still significantly exceeded the weighted average char yield (i.e., 30 %) of the individual monomers present, suggesting a synergistic interplay between the different species during charring. With the above results indicating that pyrene oligomers larger than trimer (i.e., X-mers) are needed to attain higher char yields, the focus of our next continuous SCE run was simply on removing as much unreacted monomer as possible, to the exclusion of all other oligomers. Using a one-column SCE setup, a ∼350 g fraction containing almost 90 % dimer and higher oligomers was isolated, and a respectable char yield of 65.2 % was obtained with this "monomer-depleted" pitch. Furthermore, the softening point was a relatively low 185 °C, quite respectable in terms of processability. In summary, these initial results indicate the potential of continuous SCE as a tool for controlling the properties of oligomeric pyrene pitches for selected applications.