Non-recyclable polypropylene manufacturing waste and biomass residues such as sawdust, rice straw and algae can be converted into energy-dense liquid fuel, according to a study published in Biotechnology for Biofuels and Bioproducts, Bioenegineer.org reported.
The research, led by Sukanya Hongthong and Surachai Wongcharee, examined co-hydrothermal liquefaction, a process that uses hot, pressurised water to convert mixed feedstocks into bio-crude. The experiments were conducted at 350 degrees Celsius under subcritical water conditions, using a catalyst derived from industrial waste.
The team combined polypropylene waste with three biomass feedstocks — sawdust, rice straw and the microalga Chlorella — to investigate whether plastic could improve the quality of bio-crude produced from biomass. Biomass-derived oil typically contains high levels of oxygen, which reduces its energy density.
The addition of polypropylene significantly improved the fuel characteristics of the resulting oil. The highest reported higher heating value reached 32.95 megajoules per kilogram, while the atomic oxygen-to-carbon ratio declined from 0.43 to 0.19.
These results indicate a reduction in oxygen content and an increase in hydrocarbon-like compounds, bringing the liquid fuel closer to fossil crude in terms of energy content. FTIR spectroscopy and Van Krevelen analysis also indicated increased hydrocarbon formation and fewer oxygen-containing functional groups following catalytic treatment.
The findings suggest that combining plastic manufacturing waste with biomass could offer a potential route to producing higher-energy liquid fuels while making use of difficult-to-recycle industrial plastics and agricultural residues.
