Hydrothermal Co-liquefaction of Cellulose and Polypropylene using Co-solvents

• Hydrothermal co-liquefaction led to formation of energy-dense bio-crude and soild residue. • Glycerol and paraffin oil co-solvents enhanced the bio-crude yields and quality. • Maximum bio-crude yield (78.5 wt%) was obtained using glycerol co-solvent at 350 °C. • Selectivity to aliphatic hydrocarbons was more in the bio-crude using paraffin oil co-solvent. • Addition of glycerol decreased the carbon content and the HHV of the solid residues. Hydrothermal co-liquefaction of feedstocks that decompose in widely different temperature regimes is a promising strategy to convert thermally stable olefinic plastics at sub-critical conditions by utilizing the synergetic interactions between the intermediates generated from biopolymers and synthetic polymers. In this study, cellulose and polypropylene (PP) are co-liquefied, and the effects of temperature (300–350 °C), residence time (15–45 min), cellulose-to-PP mass ratio (25:75, 50:50 and 75:25 w%/w%) and co-solvents (glycerol, paraffin oil) on product yields and quality are thoroughly studied. Results suggest that water alone is inadequate to liquefy PP, while the incorporation of glycerol and paraffin oil greatly enhance the conversion and the bio-crude yield. Maximum bio-crude yield (78.6 wt.%) was obtained at 350 °C-30 min with cellulose:PP of 50:50 w%/w% using water:glycerol solvent. The selectivity to aliphatic hydrocarbons in the bio-crude was high (∼96.5 %) at 350 °C-15 min for a cellulose:PP ratio of 25:75 w%/w% in water-paraffin oil solvent.