Study finds diesel derived by pyrolysis of plastic grocery bags suitable for blending with petroleum diesel
High-density polyethylene (HDPE) grocery bags can be successfully pyrolyzed to alternative diesel fuel, according to a new study by a team from the Illinois Sustainable Technology Center (ISTC) at the University of Illinois, Urbana-Champaign and the United States Department of Agriculture (USDA) Agricultural Research Service ARS.
Pyrolysis of the waste plastic grocery bags followed by distillation resulted in a liquid hydrocarbon mixture with an average structure consisting mostly of saturated aliphatic paraffinic hydrogens (96.8%), followed by aliphatic olefinic hydrogens (2.6%) and aromatic hydrogens (0.6%) that corresponded to the boiling range of conventional petroleum diesel fuel (#1 diesel 190–290 °C and #2 diesel 290–340 °C). Nearly all fuel properties—with the exception of density—were within ASTM D975 and EN 590 diesel specifications, according to the study published in the journal Fuel Processing Technology.
Notably, the derived cetane number (73.4) and lubricity (198 μm, 60 °C, ASTM D6890) represented significant enhancements over those of conventional petroleum diesel fuel. Other fuel properties included a kinematic viscosity (40 °C) of 2.96 mm2/s, cloud point of 4.7 °C, flash point of 81.5 °C, and energy content of 46.16 MJ/kg.—Sharma et al.
Gross product yield from the pyrolysis was 74% crude oil fraction, 17% solid residue; and 6% gases. The oil fraction broke down into 17-23% gasoline-range product; 35-42% diesel #1; 19-25% diesel #2; and 14-24% vacuum gas oil.
Americans throw away about 100 billion plastic shopping bags each year, according to the Worldwatch Institute. The US Environmental Protection Agency reports that only about 13% are recycled. The rest of the bags end up in landfills or escape to the wild, blowing across the landscape and entering waterways.
Previous studies have used pyrolysis to convert plastic bags into crude oil. The ISTC-lead team took the research further, however, by fractionating the crude oil into different petroleum products and testing the diesel fractions to see if they complied with national standards for ultra-low-sulfur diesel and biodiesel fuels.
The researchers said they were able to blend up to 30% of their plastic-derived diesel into regular diesel with no compatibility problems.
The Illinois Hazardous Waste Research Fund and the Environmental Research and Education Foundation supported this study.
Brajendra K. Sharma, Bryan R. Moser, Karl E. Vermillion, Kenneth M. Doll, Nandakishore Rajagopalan (2014) “Production, characterization and fuel properties of alternative diesel fuel from pyrolysis of waste plastic grocery bags,” Fuel Processing Technology, Volume 122, Pages 79-90 doi: 10.1016/j.fuproc.2014.01.019