Direct coal liquefaction (DCL) stands as a promising process in the realm of energy production. This process is characterized by its ability to break down the complex macromolecular structure of coal using a solvent under moderate conditions.[1] Direct liquefaction aims to yield liquid fuels with a targeted hydrogen-to-carbon ratio, which is achieved through hydrogenation reactions. Conversely, inadequate hydrogen availability can lead to the formation of undesirable residues.[2-4] The co-liquefaction of coal with other feed materials have been examined extensively. Co-liquefaction involves the simultaneous treatment of various carbonaceous materials, including coal, biomass, and plastic waste, within a shared solvent or reaction medium.[5] This innovative process capitalizes on the synergistic properties of diverse feedstocks, aiming to increase overall conversion efficiencies and generate valuable liquid products. Central to the success of co-liquefaction is an understanding of the intricate interactions between the heterogeneous components during the thermochemical conversion process.
The main driving force of the work presented in this investigation is the use of various wastes such as coal fines and plastics, and a solvent that has limited use in liquefaction processes, i.e. benzene. Co-liquefaction experiments were conducted utilizing a vitrinite-rich medium rank C bituminous coal typically utilized in coal-to-liquid processes and an inertinite-rich medium rank C bituminous discard coal fraction along with polypropylene (PP) and low-density polyethylene (LDPE) as feed materials at 450°C. Using tetralin, a hydrogen-donor solvent, and benzene, a hydrogen-poor solvent, allowed for a comprehensive assessment of liquefaction efficiency and the quantity and quality of derived products, comparing aromatic solvents with differing hydrogen-donor capabilities. 
Tetralin co-liquefaction experiments involving the vitrinite-rich coal exhibited the highest carbon conversion values when co-processed with PP and LDPE, reaching 83.3 and 80.8%, respectively. Overall conversion during tetralin liquefaction involving the inertinite-rich coal was lower, attributed to the differences in maceral composition between the coals. The co-liquefaction of the inertinite-rich coal with PP and LDPE showcased conversion values of 76.4 and 72.5%, respectively. Remarkably, experiments involving LDPE revealed significantly higher conversion values compared to predicted values, indicating synergistic effects between coal and plastic materials, influencing the product yields and overall conversion. Molecular structure disparities in the feed materials notably impacted conversion outcomes. 
GC-MS analysis of the liquid fractions derived from the co-liquefaction experiments of LDPE using benzene as the solvent revealed high yields of alkanes and alkenes, indicative of benzene's hydrogen-donor properties. ¹H NMR analysis of the liquid yields derived from the co-liquefaction using benzene revealed an abundant presence of tetralin and its derivatives, with LDPE derived liquids exhibiting higher aliphatic-to-aromatic proton ratios compared to PP. Remarkably, experiments conducted using benzene demonstrated a high presence of aliphatic protons in the liquid fraction. Alongside the formation of biphenyl, as determined using GC-MS, the results indicate that dehydrogenation of benzene occurred. Moreover, polypropylene and low-density polyethylene were found to facilitate hydrogen transfer in the co-liquefaction process, effectively converting inertinite-rich discarded coal into liquid products when co-processed. Additionally, solid residue chars derived from inertinite-rich coal blends exhibited higher gasification reactivities during CO₂ gasification experiments when compared to those containing vitrinite-rich coal. The results from this study indicate the potential of utilizing inertinite-rich coal fines and plastics such as PP and LDPE in co-liquefaction processes and subsequent gasification of residue chars.

In this investigation, polypropylene (PP) and low-density polyethylene (LDPE) were used in liquefaction experiments using tetralin and benzene as solvents. The temperature of the reaction vessel was increased to 450°C at 10 °C/min, with an isothermal reaction time of 60 minutes. This study investigated the influence of feed material and choice of solvent on conversion values and liquid yield composition during liquefaction experiments. Results showed that differences in the molecular structure of polypropylene and low-density polyethylene significantly affected conversion. Tetralin liquefaction yielded conversion values of 97.0% for PP and 23.8% for LDPE, while benzene liquefaction yielded conversion values of 98.5% for PP and 97.5% for LDPE at 450°C. Benzene liquefaction of PP and LDPE produced liquid fractions comprising alkanes and alkenes. Furthermore, it was found that benzene acted as a hydrogen-donor solvent, which was supported by the presence of biphenyl in the liquid fraction derived from benzene liquefaction. Overall, PP and LDPE demonstrated potential for high conversion to liquid products in liquefaction experiments conducted at 425–450°C.