A new method to produce hydrogen from plastic waste

Image Credit: Adobe Stock/j-mel

A team of researchers from University of Massachusetts Lowell (UML), north of Boston, is working with U.S. Army researchers to develop a way to extract hydrogen from plastic waste that can be used as fuel for transportation as well as to produce electricity in fuel cells.

The process uses plasma technology to break down plastic waste – in this case, low-density polyethylene (LDPE) – into its chemical components; hydrogen is then produced efficiently in the process, while minimizing carbon dioxide emissions.

The researchers say their strategy could help address the challenge of disposing plastic waste, which is often incinerated or dumped in landfills, thereby cutting down greenhouse gas emissions while simultaneously providing a source of hydrogen. “Our plasma technology, when powered by renewable electricity from wind and solar, can lead to the sustainable upcycling of plastic waste and production of green hydrogen,” said UML mechanical and industrial engineering associate professor and research team member Juan Pablo Trelles.

In this project, the researchers use high-voltage electrical discharges inside a reactor chamber, which is held at atmospheric pressure conditions (no pressurization or vacuum is needed) and without external heating or cooling. The electrical discharge breaks down the air molecules inside the chamber, creating plasma – an electrically conducting gas consisting of highly energetic particles, free electrons and heavy particles (ions and neutral atoms and molecules).

“The electrons and highly reactive gas species in the plasma then collide with the LDPE, which is made up of hydrogen and carbon chains, breaking these chains and producing hydrogen and light hydrocarbons as gas products and carbon compounds as solid products,” said UML engineering Ph.D. student Benard Tabu, who is the lead researcher working in Trelles’ group.

The team’s reactor is different from reactors that use thermal plasma, which feature temperatures generally exceeding 12,000 degrees Celsius (more than 21,000 degrees Fahrenheit) and are being used in waste treatment plants around the world. Thermal reactors typically have low rates of hydrogen production, low energy efficiency and limited selectivity in the chemical reactions, according to Tabu.

“We are exploiting the use of non-thermal plasma, in which the gas is held at relatively low temperatures of less than 1,000 degrees, but the free electrons remain at very high energy levels to extract hydrogen from the waste materials,” Tabu said. “This can lead to potentially higher efficiency in the waste treatment process and can be implemented in compact, inexpensive installations.”

With their current system, the researchers estimate that from 1 metric ton of LDPE, they can produce up to 6 kilograms of hydrogen. In addition to LDPE, the team’s plasma technology can potentially be applied to processing other plastic wastes, as well as biomass waste from agriculture, food industry and cellulose from sawmill dust, and converting them into high-value chemicals and additives.

“We envision this technology to be the initial steps toward converting any solid organic waste into valuable products by direct use of renewable energy, leading to greater environmental and economic benefits,” Tabu said.