Waste carbon from farms, wastewater and other sources can be more easily processed into high-quality bio-based fuels with a new PNNL-developed flow cell. In this animation, the flow cell receives biosour and wastewater from a hydrothermal liquefaction process. It then removes carbon from the wastewater, allowing clean water to be reused. The system even generates hydrogen, a valuable fuel that can be captured, reducing the cost of the entire operation. Credit: Sarah Levine Pacific Northwest National Laboratory

Patented process removes biofuel contaminants from wastewater using an additive-free process that generates hydrogen to feed its own work

The holy grail of biofuel researchers is to create a self-sustaining process that converts waste from sewage, food crops, algae and other renewable carbon sources into fuels, while keeping waste carbon out of our environment and water. Although much progress has been made in converting such waste into usable fuel, completing the clean energy cycle has proved difficult to crack.

A team of researchers at the Pacific Department of Energy’s Northwest National Laboratory (PNNL) has already developed a system that does just that. The PNNL electrocatalytic oxidation recovery system converts what was once considered non-recoverable, dilute “waste” carbon into valuable chemicals while producing useful hydrogen. Because renewable energy is used, the process is carbon-neutral or even possibly negative.

The key to making everything work is an elegantly designed catalyst that combines billions of infinitesimal metal particles and electric current to accelerate energy conversion at room temperature and pressure.

Juan A. Lopez Ruiz PNNL

Juan A. Lopez-Ruiz, a chemical engineer at PNNL, is leading a research team that recently developed a new flow cell reactor that facilitates the path to renewable fuel. Credit: Andrea Starr Pacific Northwest National Laboratory

“The methods currently used to treat bio-raw materials require high-pressure hydrogen, which is usually generated from natural gas,” said Juan A. Lopez-Ruiz, PNNL chemical engineer and project manager. “Our system can generate this hydrogen on its own, while treating wastewater in near-weather conditions, using excess energy from renewable sources, making it cheap to operate and potentially carbon-neutral.

Hungry system

The research team tested the system in a laboratory using a sample of wastewater from a biomass conversion process on an industrial scale for over 200 hours of continuous operation without losing any efficiency in the process. The only limitation was that the wastewater sample of the research team had expired.

“It’s a starvation system,” Lopez-Ruiz said. “The speed of the process is proportional to how much waste carbon you are trying to convert. It could work endlessly if you had the wastewater to keep traveling through it.

The patented system solves several problems that hamper biomass efforts to become an economically viable source of renewable energy, according to Lopez-Ruiz.

“We know how to turn biomass into fuel,” Lopez-Ruiz said. “But we are still struggling to make the process energy efficient, economical and environmentally sustainable – especially on a small, distributed scale. This system runs on electricity, which can come from renewable sources. And it generates its own heat and fuel to keep it running. It has the potential to complete the energy recovery cycle. “

“As the electricity grid begins to shift its energy sources towards integrating more renewable energy sources,” he added, “it is becoming increasingly sensible to rely on electricity for our energy needs. We have developed a process that uses electricity to convert carbon compounds in wastewater into useful products, while removing impurities such as nitrogen and sulfur compounds.

Closing the energy gap

Hydrothermal liquefaction (HTL) is a very effective method for converting wet waste carbon into fuel. This process essentially shortens the time required for the production of natural fossil fuels by turning wet biomass into energy-dense biosurf oil for hours, not millennia. However, the process is incomplete in the sense that wastewater generated as part of the process requires additional treatment to add value to what would otherwise be an obligation.

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

This is where the new PNNL process comes into play. Unrefined bio-raw and wastewater can be fed into the system directly from HTL effluent or other wet waste. The PNNL process consists of a so-called flow cell, where wastewater and biocurs flow through the cell and encounter a charged environment created by an electric current. The cell itself is divided in half by a membrane.

PNNL flow cell bioreactor

A new flow cell bioreactor developed at Pacific Northwest National Laboratory can purify wastewater (see here) and generate hydrogen to fuel the process. Credit: Andrea Starr Pacific Northwest National Laboratory

The positively charged half, called the anode, contains a thin titanium film coated with ruthenium oxide nanoparticles. Here, the waste stream undergoes catalytic conversion, as the biosow product is converted into useful oils and paraffin. At the same time, water-soluble pollutants, such as oxygen and nitrogen-containing compounds, undergo a chemical conversion that converts them to nitrogen and oxygen gases, normal components of the atmosphere. Wastewater leaving the system with contaminants removed can be returned to the HTL process.

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

“We see the hydrogen by-product generated by the process as a net plus. When collected and fed into the system as fuel, it can keep the system running with less energy, potentially making it more carbon-efficient and carbon-neutral than current biomass conversion operations, ”said Lopez-Ruiz. .

The rate of chemical conversion provides an additional benefit to the system.

“We’ve compared speeds – that’s how quickly we can remove oxygen from organic molecules with our system, as opposed to energy-intensive thermal removal,” Lopez-Ruiz said. “We have obtained more than 100 times higher conversion rates with the electrochemical system in atmospheric conditions than with the thermal system at intermediate hydrogen pressures and temperatures.” These findings are published in Journal of Applied Catalysis B: Environmental in November 2020

Reducing the use of rare earth metals

One significant disadvantage of many commercial technologies is their dependence on rare earth metals, sometimes called platinum group metals. The global supply chain for these elements relies mainly on outdated extraction technologies that are energy-intensive, use huge amounts of water and generate hazardous waste. According to the Department of Energy, which has made domestic procurement a top priority, imports account for 100 percent of the United States’ supply of 14 of the 35 critical materials and more than half of the other 17.

The system addresses this problem by including a unique method for depositing nanoparticles of metals responsible for chemical conversion. These particles have a large surface that requires less metal to do its job. “We have found that the use of metal nanoparticles, unlike metal thin films and foils, reduces the metal content and improves electrochemical characteristics,” said Lopez-Ruiz. These findings were recently published in Journal of Applied Catalysis B: Environmental. The new catalyst requires 1000 times less precious metal, in this case ruthenium, than is usually needed for such processes. In particular, the laboratory-scale flow reactor uses an electrode with about 5 to 15 milligrams of ruthenium, compared to about 10 grams of platinum for a comparable reactor.

For these useless carbon compounds

The research team also showed that the PNNL process can handle the treatment of small water-soluble carbon compounds – by-products found in the wastewater stream from current HTL processes – as well as many other industrial processes. There are about a dozen of these damn difficult-to-handle small-carbon compounds in wastewater streams at low concentrations. So far, there has been no cost-effective technology to deal with them. These short circuit carbon compounds, such as propane[{” attribute=””>acid and butanoic acid, undergo transformation to fuels, such as ethane, propane, hexane, and hydrogen, during the newly developed process.

A preliminary cost analysis showed the electricity cost required to run the system can be fully offset by running the operation at low voltage, using the propane or butane to generate heat and selling the excess hydrogen generated. These findings were published in the July 2020 issue of the Journal of Applied Electrochemistry.

Battelle, which manages and operates PNNL for the federal government, has applied for a United States patent for the electrochemical process. CogniTek Management Systems (CogniTek), a global company that brings energy products and technology solutions to market, has licensed the technology from PNNL. CogniTek will be integrating the PNNL wastewater treatment technology into patented biomass processing systems that CogniTek and its strategic partners are developing and commercializing. Their goal is the production of biofuels, such as biodiesel and bio jet fuels. In addition to the commercialization agreement, PNNL and CogniTek will collaborate to scale up the wastewater treatment reactor from laboratory scale to demonstration scale.

“We at CogniTek are excited by the opportunity to extend the PNNL technology, in combination with our core patents and patent pending decarbonization technology,” said CogniTek Chief Executive Officer Michael Gurin.

The technology, dubbed Clean Sustainable Electrochemical Treatment—or CleanSET, is available for license by other companies or municipalities interested in developing it for industry-specific uses in municipal wastewater treatment plants, dairy farms, breweries, chemical manufacturers and food and beverage producers. To learn more about how this technology works, or to schedule a meeting with a technology commercialization manager, visit PNNL’s Available Technologies site.

In addition to Lopez-Ruiz, the PNNL research team included Yang Qiu, Evan Andrews, Oliver Gutiérrez and Jamie Holladay. The research was supported by the Department of Energy’s Advanced Manufacturing Office and the Chemical Transformation Initiative, a Laboratory Directed Research and Development Program at PNNL. Portions of the research were conducted as part of a Cooperative Research and Development Agreement with Southern California Gas Company.

References: “Anodic electrocatalytic conversion of carboxylic acids on thin films of RuO2, IrO2, and Pt” by Yang Qiu, Juan A. Lopez-Ruiz, Udishnu Sanyal, Evan Andrews, Oliver Y. Gutiérrez and Jamie D. Holladay, 25 June 2020, Applied Catalysis B: Environmental.
DOI: 10.1016/j.apcatb.2020.119277

“Electrocatalytic valorization into H2 and hydrocarbons of an aqueous stream derived from hydrothermal liquefaction” by Juan A. Lopez-Ruiz, Yang Qiu, Evan Andrews, Oliver Y. Gutiérrez and Jamie D. Holladay, 9 July 2020, Journal of Applied Electrochemistry.
DOI: 10.1007/s10800-020-01452-x

“Electrocatalytic decarboxylation of carboxylic acids over RuO2 and Pt nanoparticles” by Yang Qiu, Juan A. Lopez-Ruiza, Guomin Zhu, Mark H. Engelhard, Oliver Y. Gutiérrez and Jamie D. Holladay, 1 January 2022, Applied Catalysis B: Environmental.
DOI: 10.1016/j.apcatb.2021.121060

Patent-Pending Technology Converts “Waste” Carbon Into Valuable Chemicals and Useful Elements

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