PNNL researchers announce waste-to-hydrogen conversion process

Pacific Northwest National Laboratory| Pacific Northwest National Laboratory).

A research team at the Department of Energy’s Pacific Northwest National Laboratory has developed a system capable of converting waste from sewage, food crops, algae and other renewable carbon sources into hydrogen fuel.

PNNL’s electrocatalytic oxidation fuel recovery system turns waste carbon from farms, sewage and other sources To produce hydrogen, you can also convert high-grade bio-based fuels into fuels. Researchers stated that while progress has been made in converting waste to useful fuel, it was not possible to complete the cycle using clean energy.

PNNL said the key to making it all work is a catalyst that combines billions of An electric current to accelerate the energy and immeasurable metal particles Conversion at room temperatures and pressure

“The currently used methods of treating biocrude requires high-pressure hydrogen, which is usually generated from natural gas,” said Juan A. Lopez-Ruiz, PNNL chemical engineer and project lead. “Our system can generate that hydrogen itself while simultaneously treating the wastewater at near atmospheric conditions using excess renewable electricity, making it inexpensive to operate and potentially carbon neutral.”

The system was tested using wastewater from an industrial-scale biomass transformation process. It worked for nearly 200 hours without any interruptions. PNNL stated that the only problem was that researchers ran out of wastewater samples. Lopez-Ruiz stated that the patent-pending system fixes several problems that have hindered attempts to make biomass economically sustainable.

“We know how to turn biomass into fuel,” Lopez-Ruiz said. “But we still struggle to make the process energy efficient, economical and environmentally sustainable—especially for small, distributed scales. This system is powered by electricity, which can be generated from renewable sources. It also generates heat and fuel to keep the system running. It has the potential to complete the energy recovery cycle.”

A new flow cell developed by PNNL can convert waste carbon from farms, sewage, and other sources into high-quality bio-based products more quickly. In this animation, the flow cell receives biocrude and wastewater from a hydrothermal liquefaction process. The system then removes the carbon from the wastewater, which allows for the reuse of clean water. The system even produces hydrogen, a valuable fuel, which can be captured to reduce the cost of the entire operation. Pacific Northwest National Laboratory).| Pacific Northwest National Laboratory)

Lab researchers said one effective process for converting wet waste carbon to fuel is called hydrothermal liquefaction (HTL). This process compresses the fossil fuel-production time and converts wet biomass into a biocrude oil with more energy in hours than it takes millennia. However, researchers found that the wastewater produced by the process needs to be treated further to get added value from what could otherwise be a liability.

“We realized that same (electro)chemical reaction that removed the organic molecules from wastewater could be also used to directly upgrade the biocrude at room temperature and atmospheric pressure as well,” Lopez-Ruiz said.

As part of PNNL’s new process, unrefined biocrude and wastewater can be fed into the system directly from an HTL output stream or other wet waste. The PNNL process also includes a flow cell where wastewater and biocrude are able to flow through the cell and encounter an electric current. A membrane divides the cell in half.

The positively charged part, known as an anode contains a thin titanium foil covered with nanoparticles ruthenium dioxide. The waste stream is subject to a catalytic transformation, where biocrude is converted into useful oils and paraffin. The chemical conversion of nitrogen-containing and oxygen-containing compounds into nitrogen and oxygen gases takes place simultaneously. The system can then return the wastewater to the HTL process.

On the negatively charged half of the flow cell, called a cathode, a different reaction takes place that can either hydrogenate organic molecules (such as the ones in treated biocrude) or generate hydrogen gas—an emerging energy source that the flow cell developers see as a potential source of fuel.

Researchers said the process’ speed was a bonus. They found that the electrochemical system at atmospheric conditions yielded conversion rates more than 100x higher than the thermal system at intermediate hydro pressures and temperatures. These findings were published In the Journal of Applied Catalysis B: Environment in November 2020.

You can read more on PNNL’s electrocatalytic oxidation fuel recovery system here. Southern California Gas Company agreed to part of the research.