Methane made from CO2 and renewable hydrogen offers a new path toward cheaper carbon capture.
In their ongoing effort to make carbon capture more affordable, researchers at the Department of Energy’s Pacific Northwest National Laboratory have developed a method to convert captured carbon dioxide (CO2) into methane, the primary component of natural gas.
By streamlining a longstanding process in which CO2 is converted to methane, the researchers’ new method reduces the materials needed to run the reaction, the energy needed to fuel it and, ultimately, the selling price of the gas.
A key chemical player known as EEMPA makes the process possible. EEMPA is a PNNL-developed solvent that snatches CO2 from power plant flue gas, binding the greenhouse gas so it can be converted into useful chemicals.
Earlier this year, PNNL researchers revealed that using EEMPA in power plants could slash the price of carbon capture to 19 percent lower than standard industry costs—the lowest documented price of carbon capture. Now, in a study published on August 21, 2021, in the journal ChemSusChem, the team reveals a new incentive—in cheaper natural gas—to further drive down costs.
When compared to the conventional method of methane conversion, the new process requires an initial investment that costs 32 percent less. Operation and maintenance costs are 35 percent cheaper, bringing the selling price of synthetic natural gas down by 12 percent.
Methane’s role in carbon capture
Different methods for converting CO2 into methane have long been known. However, most processes rely on high temperatures and are often too expensive for widespread commercial use.
In addition to geologic production, methane can be produced from renewable or recycled CO2 sources, and can be used as fuel itself or as an H2 energy carrier. Though it is a greenhouse gas and requires careful supply chain management, methane has many applications, ranging from household use to industrial processes, said lead author and PNNL chemist Jotheeswari Kothandaraman.
“Right now a large fraction of the natural gas used in the U.S. has to be pumped out of the ground,” said Kothandaraman, “and demand is expected to increase over time, even under climate change mitigation pathways. The methane produced by this process—made using waste CO2 and renewably sourced hydrogen—could offer an alternative for utilities and consumers looking for natural gas with a renewable component and a lower carbon footprint.”
Calculating costs and capturing carbon
To explore the use of EEMPA in converting CO2 to methane, Kothandaraman and her fellow authors studied the reaction’s molecular underpinnings, then assessed the cost of running the process at scale in a 550-megawatt power plant.
Conventionally, plant operators can capture CO2 by using special solvents that douse flue gas before it’s emitted from plant chimneys. But these traditional solvents have relatively high water content, making methane conversion difficult.
Using EEMPA instead reduces the energy needed to fuel such a reaction. The savings stem partly from EEMPA’s ability to make CO2 dissolve more easily, which means less pressure is needed to run the conversion.
The authors’ assessment identified further cost savings, in that CO2 captured by EEMPA can be converted to methane on site. Traditionally, CO2 is stripped from water-rich solvents and sent off site to be converted or stored underground. Under the new method, captured CO2 can be mixed with renewable hydrogen and a catalyst in a simple chamber, then heated to half the pressure used in conventional methods to make methane.
The reaction is efficient, the authors said, converting over 90 percent of captured CO2 to methane, though the ultimate greenhouse gas footprint depends on what the methane is used to do. And EEMPA captures over 95 percent of CO2 emitted in flue gas. The new process gives off excess heat, too, providing steam for power generation.
Making more from CO2
The chemical process highlighted in the paper represents one path among many, said Kothandaraman, where captured CO2 can be used as a feedstock to produce other valuable chemicals.
PNNL researchers are developing technologies to capture CO2 from industrial emissions and from the atmosphere. Here, manager of the Carbon Management and Fossil Energy Market Sector, Casie Davidson, explains CO2 mitigation technologies and how they might deploy at scale. Credit: Presentation by Casie Davidson | Pacific Northwest National Laboratory
“I’ll be glad when I can make this process work for methanol as efficiently as it does for methane now,” she said. “That’s my long-term goal.” Methanol has many more applications than methane, said Kothandaraman, who has sought to uncover the catalytic reactions that could produce methanol from CO2 for roughly a decade. Creating plastics from captured CO2 is another route the team plans to explore.
“It’s important that we not only capture CO2, but find valuable ways to use it,” said Ron Kent, Advanced Technologies Development Manager at SoCalGas, “and this study offers a cost-effective pathway toward making something valuable out of waste CO2.”
Reference: “Integrated Capture and Conversion of CO2 Using a Water-lean, Post-Combustion CO2 Capture Solvent” by David Heldebrant, Jotheeswari Kothandaraman, Johnny Saavedra Lopez, Yuan Jiang, Eric D. Walter, Sarah D. Burton and Robert A. Dagle, 21 August 2021, ChemSusChem.
This study was supported by SoCalGas and the Department of Energy’s Technology Commercialization Fund and Office of Science.
In addition to Kothandaraman, authors include PNNL scientists Johnny Saavedra Lopez, Yuan Jiang, Eric D. Walter, Sarah D. Burton, Robert A. Dagle and David J. Heldebrant, who holds a joint appointment at Washington State University.
It would help if you told the readers what EEMPA stands for, and which catalyst is used for CO2 to methane conversion.
CO2 does not contain hydrogen, so you need to add hydrogen (H2) to make methane CH4, and you need energy to do it in the well known Fischer-Tropsch process. If all the ingredients do not contain fossil carbon, you get fossil free hydrocarbons including methane, but if you capture the CO2 from the exhaust gas from burning fossil methane (out of the ground) as appears to be the case in this example, then the CO2 is not fossil free and so the methane will not be either.
How is converting CO2 to Methane a good thing? Methane is a worse greenhouse gas than CO2.
Being a symmetrical molecule with no permanent dipole moment, carbon dioxide is NOT a greenhouse gas. It’s IR spectrum overlaps that of H2O. Unsymmetrical Carbon Monoxide IS a greenhouse gas. Why don’t you focus your synthesis efforts on Carbon Monoxide, where it will do some good?
Even though the synthesis process is more energy efficient than older processes it still requires energy input to create the more energy intensive molecule, methane. A efficiency gain of 30% makes sense economically but at this point the situation is so dire we need something closer to 100%.
The lead author pointed out that the hydrogen could be derived from electrolytic hydrogen. That is an energy intensive process that currently doesn’t economically compete with hydrogen generated from steam reformation of methane, which results in the emission of CO2 into the atmosphere. Assumptions that the hydrogen will be from electrolysis driven by renewable energy is a major assumption in this process. Also, if the methane, or its eventual synthetic compounds are burned then the carbon will likely go into the atmosphere again.
The article would have been better if the journalist sought the opinion of someone who would have pointed out such drawbacks.
Remember, CO2 is the basic food of all life on earth. In the 1960’s, there was a challenge by an English group that they could use the American press to convince Americans that CO2 is poison.
Converting CO2 to other useful products is one thing. Capturing it at the source or directly from the atmosphere to reach some Net-zero goal Is a waste of carbon fuel energy to get it done. It’s not about cost or efficiency, it’s about the amount in the end. The technology is unable to remove and store permanently enough oxidized carbon to leave even one part-per-million in the ground by 2050. We are not being told that in our misguided efforts to lower Earth’s temperature.
This does not make sense to me and sounds like a perpetual motion machine. You burn methane to produce energy then capture the CO2. Then you use energy to create hydrogen to turn the CO2 back into methane. Anyone see the problem here? Ultimately it takes more energy to turn the CO2 into methane than was gained in burning the methane to begin with. Why not just skip all of those steps and just use renewable energy to begin with. In the worst case, use renewable energy to create hydrogen then use the hydrogen directly to create energy when renewable is not available, i.e. when the sun goes down. IMHO something like an iron-air battery or molten metal battery might be more efficient.
If this is being used to create methane for transportation fuel then again, I don’t see the point unless you are extracting the CO2 from the air. Sources of CO2 need to be replaced by renewables. It would be idiotic at best to extract CO2 from a fossil fuel power plant.
Building infrastructure to capture carbon is just stupid for the sole purpose of getting carbon out of the atmosphere. You will always end up releasing more carbon to the atmosphere than if you have done nothing.
A better approach is preserving natural carbon sinks like trees. Reducing the amount of wildfires and deforestation would be cheaper and far more effective.
Making methane from CO2 only makes sense from an economic standpoint, everything else is bullsh*t.
Wouldn’t it be nice if scientists were researching ways to reduce carbon emissions, rather than ways to keep fossil fuel infrastructure relevant?
Wouldn’t it be nice if reporting challenged some of this bs, instead of greenwashing? Why is the actual efficiency of the new process never mentioned? (35% more efficient than what?) Maybe because it would highlight how ridiculous this is?
“the ultimate greenhouse gas footprint depends on what the methane is used to do…”
It’s either burnt, releasing the CO2 again, or leaks and is 85 times worse. What else would we do, bury it back in the ground?
Won’t the co2 just return after the methane has been burned? Only difference is now you will have lots of energy use from people working at the capture plant.
If we would just put houses underground, we wouldn’t need all that energy in the first place.
Interesting but that’s more like carbon recycling, calling it “carbon capture” is misleading. Feasibility and leakage must be considered, and the cost of producing green (not blue) H2, before declaring it a new technology.
This would be the same methane that is currently “flared off” from oil drilling rigs because burning it into CO2 is less polluting than just releasing it as waste. Why don’t we start with capturing that methane instead of finding new ways to create it from scratch?
Someone mentioned how the CO2 spectrum matches H2o… there for not a green house gas. This assertion is incorrect. H2O is a green house gas, and a temperature sink depending upon it’s physical state. When H2O is a gas, it the worst offender of runaway greenhouse effect. The more h2o that stays latent in the atmosphere the greater the multiplier. CO2 is just a trigger.