Harnessing High-Density-Polyethylene-Derived Liquid as a Model Solvent for the Co-Liquefaction of Low-Rank Coals: Toward Sustainable Mesophase Pitch for Making High-Quality Carbon Fibers from Waste Plastics

Wenjia Wang (), Adam Gallacher, Karissa Jolley, Mitchell G. Nelson and Eric Eddings
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Wenjia Wang: Department of Chemical Engineering, The University of Utah, Salt Lake City, UT 84112, USA
Adam Gallacher: Department of Chemical Engineering, The University of Utah, Salt Lake City, UT 84112, USA
Karissa Jolley: Department of Chemical Engineering, The University of Utah, Salt Lake City, UT 84112, USA
Mitchell G. Nelson: Department of Chemical Engineering, The University of Utah, Salt Lake City, UT 84112, USA
Eric Eddings: Department of Chemical Engineering, The University of Utah, Salt Lake City, UT 84112, USA

Sustainability, 2025, vol. 17, issue 11, 1-18

Abstract: The accumulation of polyolefin waste, particularly high-density polyethylene (HDPE), presents a growing environmental challenge due to limited recycling options and poor end-of-life recovery. This study explores a strategy to convert HDPE into mesophase pitch (MP), a valuable carbon precursor, by integrating polyolefin recycling with the mild solvolysis liquefaction (MSL) of low-rank coals. HDPE was first hydrogenolyzed into a hydrogen-rich aromatic liquid (HDPE-liquid), which was then used as the liquefaction solvent. Under identical conditions (400 °C, 60 min), Utah Sufco coal co-liquefied with HDPE-liquid produced tar that formed mesophase pitch with a higher mesophase content (84.5% vs. 78.6%) and a lower softening point (~302 °C vs. >350 °C) compared to pitch from conventional tetralin (THN). The approach was extended to Illinois #6 and Powder River Basin coals, increasing the mesophase content from 12.4% to 32.6% and 17.8% to 62.1%, respectively. These improvements are attributed to differences in tar composition: HDPE-derived tars had lower terminal methyl (Hγ) contents, reducing cross-linking during thermal upgrading. This work demonstrates that HDPE-derived liquids can act as functional solvents for coal liquefaction, enabling an effective route to recycle polyolefin waste into durable carbon products, while also reducing reliance on fossil-based solvents for mesophase pitch production.

Keywords: waste plastics; coal; mesophase pitch; thermochemical liquefaction; reaction engineering (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2025
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