NETL researchers are closing in on a more effective and less expensive way to combine a growing accumulation of plastic waste with coal and biomass for a steam gasification process that can produce hydrogen-rich syngas — a versatile gas that can be used as a fuel or as a building block for a range of chemicals that can help tackle critical energy challenges.

NETL’s findings were explained in a recent article in Fuel, a publication dedicated to the science and technology of fuel and energy.

Low-density polyethylene (LDPE) is a thermoplastic polymer used in packaging, bags, containers and other applications. High-density polyethylene (HDPE) is derived from petroleum and is commonly used in food and beverage containers, cleaning product bottles, and pipes. HDPEs and LDPEs account for most discarded plastics because of their widespread single-use applications.

According to a team of NETL researchers led by Ping Wang, steam gasification — a thermochemical process that converts carbonaceous materials like biomass or coal into syngas and hydrogen with high hydrogen yield and improved syngas quality — provides a promising pathway for transforming leftover plastics and other materials into valuable products.

Traditional approaches to gasify plastic waste present specific problems. For example, the low melting points of plastics make them prone to agglomeration — when particles stick together — leading to clogging and flow obstruction in gasifiers. Plastics also require energy-intensive size reduction processes like shredding, crushing and grinding to achieve uniform particle sizes, which are essential for maintaining consistent reaction kinetics and increase operational costs. Tar formation from the high volatile content of plastics can also reduce process efficiency.

NETL researchers say they believe gasification of plastic waste using coal refuse in the process can overcome a range of barriers facing effective plastic gasification because coal waste contains varying amounts of alkali and alkali earth metals, which can catalyze char gasification and tar cracking.

“Plastic waste management is increasingly becoming a global concern and must be urgently addressed,” Wang said. “According to one estimate, 6.3 billion tons of plastic waste were generated in the last six decades, out of which, 60% accumulated in the landfills and natural environment. The inadequate management of waste plastic in landfills causes serious environmental problems, such as groundwater contamination and sanitary-related issues.”

She said the plastics problems also lead to the loss of valuable and natural resources because most plastics are made from oil and gas. By adopting steam gasification to convert waste plastic into hydrogen and syngas, the energy content in the plastic can be recovered.

“Co-gasification of plastics with other feedstocks, such as coal and biomass, also offers a flexible approach that allows feedstock proportions to be adjusted to achieve desired product distribution,” she said. “For example, adjusting the blend ratio and temperature can optimize syngas yield and efficiency.”

According to the NETL research, coal-related wastes present an attractive cofeedstock option because they can potentially mitigate environmental impacts while reducing disposal and management costs.

“Our findings demonstrate the flexibility of cogasification, allowing precise tuning of syngas characteristics for specific downstream applications,” Wang said. “Further optimization of the co-gasification process could enhance the economic viability of gasification in waste-to-energy processes.”

NETL is a U.S. Department of Energy (DOE) national laboratory dedicated to advancing the nation's energy future by creating innovative solutions that strengthen the security, affordability and reliability of energy systems and natural resources. With laboratories in Albany, Oregon; Morgantown, West Virginia; and Pittsburgh, Pennsylvania, NETL creates advanced energy technologies that support DOE’s mission while fostering collaborations that will lead to a resilient and abundant energy future for the nation.