NETL researchers developed an improved method for gasifying post-consumer plastic and biomass waste to generate clean hydrogen-rich syngas while reducing tar as an undesirable byproduct.

The U.S. Department of Energy (DOE) reports that “biomass gasification is a mature technology pathway that uses a controlled process involving heat, steam and oxygen to convert biomass to hydrogen and other products, without combustion.”

DOE anticipates that biomass gasification could be deployed in the near-term. However, traditional processes to reach the high temperatures required for conversion — heat exchangers or a heat transferring medium —results in the production of high levels of tar and char, which complicates separation processes, clogs pipelines and limits the hydrogen yield.

The new NETL approach uses microwave heating to supply the energy needed to maintain the temperature required for gasification and an earth-abundant catalyst to improve the process. The result is an increase in hydrogen yields and a reduction of tar yields to under 2%.

“NETL has demonstrated microwave-assisted gasifier design for mixed plastics and biomass, which reported hydrogen selectivity approximately 10 times higher compared to the reaction observed in a conventional thermal reactor without a catalyst,” NETL’s Dushyant Shekhawat said.

The work was the subject of a report authored by NETL published in Energy Conversion and management.

According to the U.S. Energy Information Administration, biomass consists of materials like paper, cardboard, food waste, grass clippings, leaves, wood and leather products. Plastics and other synthetic materials made from petroleum are nonbiomass materials.

The need for efficient management of post-consumer plastic and biomass waste has increased because of a dramatic increase in their use in everyday products.

According to the Organization for Economic Co-operation and Development Global Plastics, plastic use is expected to rise from 459 million metric tons in 2019 to 977 million metric tons by 2050 — an increase of 113%. The United Nations Environment Programme reports that plastic pollution can alter habitats and natural processes, reducing ecosystems’ ability to adapt to climate change, directly affecting millions of people’s livelihoods, food production capabilities and social well-being.  

In addition to using microwaves to provide heat, the NETL research used the catalytic effect of magnetite, an ore that is a good oxygen carrier, as a catalyst to transform plastics and corn stover — the leaves, stalks, and cobs of corn left in a field after harvest — to create gas composed of more hydrogen and less tar. The research was explained in a report in the International Journal of Hydrogen Energy.

“Plastic pollution is an environmental hazard because it threatens wildlife and human health,” Pranjali Muley, one of the authors of the report said. “Even though this issue has been realized for decades, more than 80% of the plastic waste eventually goes to landfill or is mismanaged because there are inefficient plastic recycling or incineration processes. Gasification of assorted plastic waste is an attractive alternative route to upcycling the waste to syngas, and many studies have shown that gasification of plastic mixed with biomass is more sustainable and environmentally friendly with high energy efficiency.”

NETL is a U.S. Department of Energy national laboratory that drives innovation and delivers solutions for an environmentally sustainable and prosperous energy future. By using its world-class talent and research facilities, NETL is ensuring affordable, abundant, and reliable energy that drives a robust economy and national security, while developing technologies to manage carbon across the full life cycle, enabling environmental sustainability for all Americans.