Reverse Combustion and its prospects

February 13, 2017 |

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Because burning fuels in an internal combustion engine produces CO2 and water as its byproducts, the idea of reverse combustion has been hanging around the halls of science for a long, long time. That is, recombining CO2 and water back into an energy carrier — a fuel. It’s a simple concept, but over the years it has proven to be difficult science.

A few months back, we reported on an advance from Oak Ridge National Laboratory with a 63 percent reaction efficiency that the research team suggested could be used to store excess electricity generated from variable power sources such as wind and solar.

How does that work? Well, the reaction is not a perpetual energy machine, and the reaction needs lots of power to run it. In fact, critics have noted that because the reaction is only 20% energy efficient. That is, you need 5 units of energy to make 1 unit of ethanol, measured by energy content. Accordingly, reviewers have said that the process is unlikely ever to be used to power vehicles, or anything else — it would be far more efficient, and emissions-friendly, to simply feed the electricity to an electric motor.

That’s why Oak Ridge pointed our attention to potential sources of power that are wasted — for example, excess wind or solar power not needed on the grid at any given moment. And there’s a point there — as cleantechnica observes, “overgeneration can cause reliability problems” and curtailment is the usual solution. But this same article points out that independent system operators, or ISOs, are becoming more adept at trading energy and spreading the load across the grid — for example, there’s the Energy Imbalance Market which permits the California Independent System Operator, Pacificorp and NV Energy to trade energy to address imbalance. That system serves more than 35 million customers in 8 states, and will add more utilities in 2017 — and that’s most likely to be the prevalent solution for some time in energy markets.

But before we write off the technology — let’s look at the Oak Ridge reaction again to examine the value — as we survey the latest in reverse combustion systems.

Because, the Oak Ridge gang was onto something when they pointed towards energy storage. Eliminate the cost of the incoming power, and that’s where there’s value in the system. So, we would not ourselves be looking at wind, solar or hydro — but rather at small, remote sources of biogas and fossil methane. For these, the methane is usually flared into CO2. That’s a concentrated CO2 source and a power source that is currently gone to waste. Couple that with water, and you really have something.

But, this brings us to another possibility among waste sources. What about waste heat? That’s energy, although not in the kind generally used for power generation or to make fuel.


An area of R&D that would be useful to look into is thermoelectricity. Even today, there are automotive thermoelectric generators — which are solid state devices that convert heat to electrical energy. They use the Seebeck effect – and you can read about it here.

Worth noting that 40 percent of internal combustion engine energy is lost to waste heat — a primary reason they are less efficient than electric motors.

Bottom line, a thermoelectic device uses temperature differences between two ends of a system to create a voltage. The problem is that they are costly, heavy and operate at around 5% efficiency when used in vehicles. The resulting weight-add to the vehicle hasn’t been worth the benefit.

Discoveries such as the Oak Ridge systems do create more options for thermoelectric system designers, looking at sources of waste heat and converting those into electricity that can be stored, collected and transported as fuel.

Capturing wasted photos at the farm

Which brings up another area for R&D, and that is the 47% of solar energy that is not photosynthetically active. Naturally, we don’t put solar panels in fields to compete with crops, but half of the energy that rains on fields is generally absorbed by the earth as heat * the major exception being green light, which is reflected). And of the radiation that strikes plants, 30 percent of that is lost because the plants can’t absorb it — either there’s too much coming in, or the photos miss the chloroplasts that absorb them.

One of these days someone is going to come up with a living system that shunts excess photons to a photovoltaic cell — and that will be an excellent source of energy that can power a farm and store excess energy in the form of a fuel.

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.

South Korean researchers develop new way to produce biofuel from CO2

In South Korea, researchers at 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.

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.

Liquid Light raises $15M and a lot of eyebrows as it advances towards making $$ out of waste CO2.

Liquid Light has been subsequently acquired by Avantium. In this article, we explore the value in the technology that clearly others are seeing too.

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.

Electrofuels — subject of ARPA-E research, and our 8-Slide Guide takes you through much of it.

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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