Biofuels beyond corn: The pathway from CO2, water and electricity to liquid fuels

July 4, 2017 |

Much of the angst over ethanol’s expansion comes from stakeholders’ worries over corn and land use. Justified or not, there’s worry over cost, food security. environmental impact, grower adoption, supply chain. And so on and so on. It would be fair to regard these questions as the most perplexing for the replacement of fossil fuels by biofuels.

Accordingly, researchers attract extravagant amounts of attention when they find ways to make ethanol from other inputs. There’s been the cellulosic wave, then waste — and alongside there has been steady progress in what are known as the electrofuels. These are fuels made directly from CO2, water and either sunlight or electricity. Generally if a microorganism is involved, there’s sunlight in the picture (not always); inorganic catalysts (generally, metal-based, and expensive) have used electricity to power the conversion.

“The eye on the prize is to create better catalysts that have game-changing potential by taking carbon dioxide as a feedstock and converting it into much more valuable products using renewable electricity or sunlight directly,” says Thomas Jaramillo, an associate professor of chemical engineering at Stanford and of photon science at the SLAC National Accelerator Laboratory.

The issues?

One, the conversion mechanism. We reported on the slow productivity rates with some of the most promising microorganisms, here. There are the struggles to build an investor-affordable reactor for micro-organisms, which has caused delays for Joule.

With the inorganic catalysts, it’s been selectivity. As Jaramillo nots, “Copper is one of the few catalysts that can produce ethanol at room temperature,” he said. “You just feed it electricity, water and carbon dioxide, and it makes ethanol. The problem is that it also makes 15 other compounds simultaneously, including lower-value products like methane and carbon monoxide. Separating those products would be an expensive process and require a lot of energy.”

So it’s good news this past week when Stanford University scientists reported on a promising technology to make renewable ethanol from water, carbon dioxide and electricity delivered through a copper catalyst.

“Copper (100), (111) and (751) look virtually identical but have major differences in the way their atoms are arranged on the surface,” said Christopher Hahn, an associate staff scientist at SLAC and co-lead lead author of the study.

To compare electrocatalytic performance, the researchers placed the three large electrodes in water, exposed them to carbon dioxide gas and applied a potential to generate an electric current.

The results were clear. When the team applied a specific voltage, the electrodes made of copper (751) were far more selective to liquid products, such as ethanol and propanol, than those made of copper (100) or (111).

Ethanol from thin air advances with catalyst breakthrough

At ORNL, a yield breakthrough

We reported last October that researchers from Oak Ridge National Laboratory have come up with a highly-efficient process to make liquid fuels directly from carbon dioxide and water, with a yield of 63 percent. Typically, this type of electrochemical reaction results in a mix of several different products in small amounts. And let’s add this: the process relies on low-cost materials, and operates at room temperature in water — so there’s a distinct hope that the process will scale cost-effectively.

The catalyst’s novelty lies in its nanoscale structure, consisting of copper nanoparticles embedded in carbon spikes. This nano-texturing approach avoids the use of expensive or rare metals such as platinum that limit the economic viability of many catalysts. ORNL researchers developed a catalyst made of copper nanoparticles (seen as spheres) embedded in carbon nanospikes that can convert carbon dioxide into ethanol.

“We discovered somewhat by accident that this material worked,” said ORNL’s Adam Rondinone, lead author of the team’s study published in ChemistrySelect. “We were trying to study the first step of a proposed reaction when we realized that the catalyst was doing the entire reaction on its own.”

It appears that the spiky textured surface of the catalysts provides ample reactive sites to facilitate the carbon dioxide-to-ethanol conversion. “They are like 50-nanometer lightning rods that concentrate electrochemical reactivity at the tip of the spike,” Rondinone said.

Wind and solar. The ORNL research team proposed that the process could be used to store excess electricity generated from variable power sources such as wind and solar. The intermittent nature of wind and solar energy production has been a well-known barrier to using these forms of renewable energy to provide base load to the electrical grid.

Something nearer-term? Think biogas from dairy operations. We suggested in “Bossie the Climate Warrior” earlier this month that methane emissions can be flared to convert methane to CO2, and herein combined with on-site water to make ethanol. That’s a second value stream for a dairy farmer who, at best, right now is generally looking at burning methane to produce power or compressing it for CNG vehicles. Here’s a higher value use.

Ethanol from carbon monoxide

It’s not quite the same as CO2, but carbon monoxide is found in abundance, and aggregated, at steel mills , and we reported earlier this year that Stanford scientists found a new, highly efficient way to produce liquid ethanol from carbon monoxide gas.

“Most materials are incapable of reducing carbon monoxide and exclusively react with water,” Kanan said. “Copper is the only exception, but conventional copper is very inefficient.” In the Nature experiment, Kanan and Li used a cathode made of oxide-derived copper. When a small voltage was applied, the results were dramatic.

“The oxide-derived copper produced ethanol and acetate with 57 percent faradaic efficiency,” Kanan said. “That means 57 percent of the electric current went into producing these two compounds from carbon monoxide. We’re excited because this represents a more than 10-fold increase in efficiency over conventional copper catalysts. Our models suggest that the nanocrystalline network in the oxide-derived copper was critical for achieving these results.”

For the Nature study, Kanan and Li built an electrochemical cell – a device consisting of two electrodes placed in water saturated with carbon monoxide gas. When a voltage is applied across the electrodes of a conventional cell, a current flows and water is converted to oxygen gas at one electrode (the anode) and hydrogen gas at the other electrode (the cathode). The challenge was to find a cathode that would reduce carbon monoxide to ethanol instead of reducing water to hydrogen.

Why not just use electricity for EVs?

So, here’s one limitation and concern. It’s not a perpetual energy machine. The process consumes energy in the form of electric power, so why not just use the electricity to power electric vehicles?

In the end, the battle is over energy storage.

The simplest way to see the battle is that electric vehicles have a very efficient motor and a lousy energy storage system. Liquid fuels have much less efficiency in the motor, but very dense energy storage. The longer you wish to travel or the bigger the load you need to haul, the more you like combustion.

That’s why people get very tempted by fuel cells. These power an electric motor, but use on-board hydrogen instead of electric batteries to carry the power.

Nirvana would of course be a fuel cell-like system that converted liquids instead of compressed hydrogen gas into electrons to power a motor. That would be so much lighter than an electric battery and so much faster to refuel — that we’d all put the EV vs biofuels battle behind us, and use both.

For now, the primary application of electrofuels will be in heavy-duty situations — so, diesel and jet fuel are big prizes — or in cases where there is excess electricity available, or whether the of social cost CO2 emissions are worth more than the costs of running the process.  Hence a scenario proposed by ORNL with excess energy from wind or solar energy production.

“A process like this would allow you to consume extra electricity when it’s available to make and store as ethanol,” Rondinone said. “This could help to balance a grid supplied by intermittent renewable sources.”

Reacting CO2 with hydrogen, as an alternative to water

Last November, we reported that researchers at South Korea’s UNIST uncovered new ways to make biofuel from carbon dioxide (CO2), the most troublesome greenhouse gas. In their paper published in the journal Applied Catalysis B: Environmental, the team presented direct CO2 conversion to liquid transportation fuels by reacting with renewable hydrogen (H2) generated by solar water splitting.

This new delafossite-based catalyst, composed of inexpensive, earth-abundant copper and steel is used in a reaction between CO2 emissions of industrial plants and H2 generated from solar hydrogen plant to produce diesel.

Making ethylene from CO2, water and electricity

For those who wonder if ethanol (or any fuel) has enough value to justify investment, there’s the alternative of renewable chemicals. Last July, we reported that a team from Ruhr-Universität Bochumsaid that how plasma-treated copper can be used as a catalyst to perform highly selective conversion of the greenhouse gas carbon dioxide into ethylene. PhD student Hemma Mistry from the Institute for Experimental Physics IV in Bochum used copper films treated with oxygen or hydrogen plasmas as catalysts. Through these plasma treatments, she altered the properties of the copper surface, rendering it rougher or less rough, for example, and oxidizing the material. The researcher varied the plasma parameters systematically until she hit on the optimal surface properties.

Other systems that use energy, water and CO2 to make a fuel

Joule’s quest for fuels from CO2, sunlight and water

We reported here that the EPA has favorably reviewed the company’s Microbial Commercial Activity Notice for Joule’s first commercial ethanol-producing catalyst. This clears the catalyst for commercial use at the company’s demonstration plant in New Mexico, the company says.

Boosting Ethanol’s Value via CO2 use: The Digest’s Multi-Slide Guide to White Dog Labs

White Dog will be on stage at ABLC 2017 with an update on how they can boost ethanol plant efficiency by utilizing waste CO2.

PHYCO2, MSU “breakthrough” grows algae 24/7 without sunlight

We reported last year here that PHYCO2 disclosed “a technology breakthrough” in Phase I of the multi-year trial with Michigan State University (MSU).  The technology partnership set out to capture manmade carbon dioxide (a greenhouse gas emission (GHG)) and create renewable alternative energy feedstock.  Phase I proved the technology can capture significant amounts of CO2 for high-density algae cultivation with the PHYCO2 Patented algae photo bioreactor.

Solar Fuels: Making hydrocarbon fuels directly from CO2 and sunlight

In this review, we looked at companies such as Algenol and Joule.

A Hoover for atmospheric CO2

In western Canada we reported that a technology is under development whose developers say can reduce the cost of recovering CO2 directly from the atmosphere to $150-$200 per ton in the 2010s, and ultimately they believe to $100 per ton.

All I need is the Air that I Breathed. Microbial Dairies using CO2, sunlight and water. 

We looked at a variety of technologies in this review.

Fuel From Thin Air? The skinny on making gasoline from air and water

Back in 2012, Robert Rapier reported for us on a U.K.-based company called Air Fuel Synthesis (AFS) reported it was producing gasoline from raw materials reportedly being literally air and water.

Electrofuels update: Patent granted for CO2-to-gasoline process

In 2015, we reported that the US Patent and Trademark Office issued patent number 9,217,161 for a process to ferment biomass or gases directly to hydrocarbons like hexane and octane.  The process belongs to the electrofuels family — technologies involving microorganisms that could use hydrogen or electricity to convert carbon dioxide to liquid fuels.

Can electrofuels and electrosugars save the day?

In this review, we looked at the potential to make sugars as well as fuels from electricity generated by microbes.

Doing it in the Dark: Fuel from thin air, and beyond light

Here we looked at a range of “fuel from thin air” microvarmints including a research team from Shota Atsumi’s lab at the University of California, Davis that engineered Synechococcus elongatus PCC 7942, a strain of photosynthetic cyanobacteria, to grow without the need for light.

Is it the perfect energy solution? Where solar, carbon capture and bio collide

Last year we speculated, “one of these days your personal transportation system might look like this. A solar or wind energy facility generates renewable electricity, which is converted into a solar fuel using electrofuel technology that converts CO2 and water to a fuel using electricity (rather than photosynthesis) to power the operation. That fuel is then used in a Microbial fuel cell that is loaded on your vehicle, which translates the fuel back into an electric current for an electric motor.”

Microbial Hybrids: Connecting solar energy and electric vehicles via biobatteries

In this review we noted “There are more than a dozen technologies somewhere in development with a dizzying array of acronyms. Microbial fuel cells, microbial electrolysis cells, microbial methanogenesis cells, microbial reverse electrodialysis electrolysis cells, microbial struvite production cells, and microbial desalination cells among them. To those in the field, known as MFCs, MECs, MMCs, MRECs, MSCs and MDCs.” And we reviewed the state of the state of the art.

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