Advanced BioFuels USA

by Erik F. Ringle (National Renewable Energy Laboratory)  With Extensive Data, Broad Analyses, and Detailed Models, NREL Scientists and Collaborators Stake the Boundaries of Producing Chemicals and Fuels From Carbon Dioxide, Biomass, and Renewable Electricity — … In fact, growing supplies of renewable electricity open exciting new doors for making identical products at potentially a fraction of the climate cost.

It begins with the steady turn of a wind turbine or a solar panel baking in the mid-afternoon sun. A current flows through an electrochemical cell filled with carbon dioxide (CO2)—siphoned from the air or captured from an ethanol refinery, cement plant, or other industrial source.

Energized by ions and radicals created by the charge, the carbon atom in the gas unglues itself from its oxygen neighbors and looks for new companions to bond with. It quickly latches itself to other newly freed carbon, as well as hydrogen atoms that are generated in the cell.

The exact molecule the carbon helps form depends on the electrocatalyst in the cell and the voltage applied at the outset:

Formic acid used as a food additive
Carbon monoxide for making numerous other chemicals
Ethylene—a precursor in the global plastics market
And more.

It is an electrochemical reaction, an emerging pathway for upgrading CO₂ and even biomass-derived compounds into the many plastics, detergents, fuels, and compounds that undergird the modern economy.

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Instead of dredging up “fossil” carbon stored underground, such methods recycle “modern” carbon found in CO₂ or biomass. And rather than relying on carbon-intensive energy sources, they are powered by renewable, zero-emission electricity. The result could be a fuel and chemical production process that is significantly less carbon intensive.

Still, many questions remain about the costs, risks, and technical challenges of making chemicals and fuels from green electricity and recycled carbon.

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Paper 1: The Economics of Carbon Dioxide Utilization

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In an Energy and Environmental Science paper, “The Economic Outlook for Converting CO₂ and Electrons to Molecules,” NREL researchers Zhe Huang, Schaidle, Grim, and Ling Tao analyze the economics of electrochemical CO₂ utilization today and in the future. The paper considers numerous technology factors and cost drivers that might impact the feasibility of producing chemicals, fuels, and materials from CO₂ and renewable electricity at scale.

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According to their study, it could soon be as cost effective to make some of the most widely used chemicals out of CO₂ and green electricity as it is to make them using current petroleum-based methods. At the current rate of falling electricity prices and expected improvements in technology, it could even become cheaper in some cases.

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To make it easier to sift through the data behind their analysis, Schaidle, Grim, and their colleagues have published a powerful online visualization tool. It includes interactive charts on the economic feasibility and key cost drivers of producing chemical intermediates from CO₂ and electricity across five different conversion pathways.

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Paper 2: The Status of Electrochemical Conversion of Plentiful Biomass
According to the U.S. Department of Energy, biomass resources in the United States could be harnessed to produce up to 50 billion gallons of biofuel each year, more than enough to cover the entire U.S. demand for jet fuel.

But where the carbon in CO2 forms a simple chemical configuration—a gas with one part carbon, two parts oxygen—the renewable carbon in that plentiful biomass is integrated into fibrous networks of lignin and carbohydrates. That makes the starting point for making chemicals with biomass fundamentally different.

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In a second paper published in ACS Energy Letters, Schaidle, Grim, and a larger team of scientists—including Francisco W.S. Lucas and Adam Holewinski from the University of Colorado, Boulder—analyze over 82 reactions driven by the electrochemical synthesis of biomass intermediates. Those reactions have potential advantages, according to the paper.

“Conventional methods only have heat and pressure as their hammers,” Grim explained. “With electrochemistry and biomass intermediates, we have the ability to target specific chemical bonds or groups that can be otherwise difficult to access.”

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“If you want this technology to get closer to becoming market competitive, you have to have an electrochemical process that is overall more efficient,” Schaidle added. “It makes the best utilization of the carbon coming in and the best utilization of the electrons coming in. That is where a lot of the technology advancements need to happen.”

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Why convert CO₂ and not just capture it and put it underground?

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Supported by the U.S. Department of Energy Bioenergy Technologies Office, ARPA-E, and other energy programs, a range of targeted research projects are already helping push down the cost and increase the efficacy of such technologies. One NREL-led team, for instance, is exploring how to use electrochemistry to enable biorefineries to recycle waste CO₂—increasing fuel yields by as much as 40% and decarbonizing the production of ethanol, as well as lipids. READ MORE