Snaring CO₂ before it floats into the atmosphere is a key component in slowing global warming. Creating incentives for the largest emitters to adopt carbon capture technology, however, is an important precursor. The high cost of commercial capture technology is a longstanding barrier to its widespread use.

PNNL scientists believe methanol can provide that incentive. It holds many uses as a fuel, solvent, and an important ingredient in plastics, paint, construction materials and car parts. Converting CO₂ into useful substances like methanol offers a path for industrial entities to capture and repurpose their carbon.

PNNL chemist David Heldebrant, who leads the research team behind the new technology, compares the system to recycling. Just as one can choose between single-use and recyclable materials, so too can one recycle carbon.

“That’s essentially what we’re trying to do here,” said Heldebrant. “Instead of extracting oil from the ground to make these chemicals, we’re trying to do it from CO₂ captured from the atmosphere or from coal plants, so it can be reconstituted into useful things. You’re keeping carbon alive, so to speak, so it’s not just ‘pull it out of the ground, use it once, and throw it away.’ We’re trying to recycle the CO₂, much like we try to recycle other things like glass, aluminum and plastics.”

As described in the journal Advanced Energy Materials, the new system is designed to fit into coal-, gas-, or biomass-fired power plants, as well as cement kilns and steel plants. Using a PNNL-developed capture solvent, the system snatches CO₂ molecules before they’re emitted, then converts them into useful, sellable substances.

A long line of dominoes must fall before carbon can be completely removed or entirely prevented from entering Earth’s atmosphere. This effort — getting capture and conversion technology out into the world — represents some of the first few crucial tiles.

Deploying this technology will reduce emissions, said Heldebrant. But it could also help stir the development of other carbon capture technology and establish a market for CO₂-containing materials. With such a market in place, carbon seized by anticipated direct air capture technologies could be better reconstituted into longer-lived materials.

The call for cheaper carbon capture

In April 2022, the Intergovernmental Panel on Climate Change issued its Working Group III report focused on mitigating climate change. Among the emissions-limiting measures outlined, carbon capture and storage was named as a necessary element in achieving net zero emissions, especially in sectors that are difficult to decarbonize, like steel and chemical production.

“Reducing emissions in industry will involve using materials more efficiently, reusing and recycling products and minimizing waste,” the IPCC stated in a news release issued alongside one of the report’s 2022 installments. “In order to reach net zero CO₂ emissions for the carbon needed in society (e.g., plastics, wood, aviation fuels, solvents, etc.),” the report reads, “it is important to close the use loops for carbon and carbon dioxide through increased circularity with mechanical and chemical recycling.”

PNNL’s research is focused on doing just that — in alignment with DOE’s Carbon Negative Shot. By using renewably sourced hydrogen in the conversion, the team can produce methanol with a lower carbon footprint than conventional methods that use natural gas as a feedstock. Methanol produced via CO₂ conversion could qualify for policy and market incentives intended to drive adoption of carbon reduction technologies.

Methanol is among the most highly produced chemicals in existence by volume. Known as a “platform material,” its uses are wide ranging. In addition to methanol, the team can convert CO₂ into formate (another commodity chemical), methane and other substances.

A significant amount of work remains to optimize and scale this process, and it may be several years before it is ready for commercial deployment. But, said Casie Davidson, manager for PNNL’s Carbon Management and Fossil Energy market sector, displacing conventional chemical commodities is only the beginning. “The team’s integrated approach opens up a world of new CO₂ conversion chemistry. There’s a sense that we’re standing on the threshold of an entirely new field of scalable, cost-effective carbon tech. It’s a very exciting time.”

Crumbling costs

Commercial systems soak up carbon from flue gas at roughly $46 per metric ton of CO₂, according to a DOE analysis. The PNNL team’s goal is to continually chip away at costs by making the capture process more efficient and economically competitive.

The team brought the cost of capture down to $47.10 per metric ton of CO₂ in 2021. A new study described in the Journal of Cleaner Production explores the cost of running the methanol system using different PNNL-developed capture solvents, and that figure has now dropped to just below $39 per metric ton of CO₂.

“We looked at three CO₂-binding solvents in this new study,” said chemical engineer Yuan Jiang, who led the assessment. “We found that they capture over 90 percent of the carbon that passes through them, and they do so for roughly 75 percent of the cost of traditional capture technology.”

Different systems can be used depending on the nature of the plant or kiln. But, no matter the setup, solvents are central. In these systems, solvents wash over CO₂-rich flue gas before it’s emitted, leaving behind CO₂ molecules now bound within that liquid.

Creating methanol from CO₂ is not new. But the ability to both capture carbon and then convert it into methanol in one continuously flowing system is. Capture and conversion has traditionally occurred as two distinct steps, separated by each process’s unique, often non-complementary chemistry.

“We’re finally making sure that one technology can do both steps and do them well,” said Heldebrant, adding that traditional conversion technology typically requires highly purified CO₂. The new system is the first to create methanol from “dirty” CO₂.

Dialing down tomorrow’s emissions

The process of capturing CO₂ and converting it to methanol is not CO₂-negative. The carbon in methanol is released when burned or sequestered when methanol is converted to substances with longer lifespans. But this technology does “set the stage,” Heldebrant said, for the important work of keeping carbon bound inside material and out of the atmosphere.

Other target materials include polyurethanes, which are found in adhesives, coatings, and foam insulation, and polyesters, which are widely used in fabrics for textiles. Once researchers finalize the chemistry behind converting CO₂ into materials that keep it out of the atmosphere for climate-relevant timescales, a wide web of capture systems could be poised to run such reactions.

In lieu of today’s smokestacks, Heldebrant envisions CO₂ refineries built into or alongside power plants, where CO₂-containing products can be made on site. “We are at a turning point,” Heldebrant and his coauthors wrote in a recent article published in the journal Chemical Science, “where we can continue to use 20th century, monolithic capture and conversion infrastructure or we can begin the transition to a new 21st century paradigm of integrated solvent-based carbon capture and conversion technologies.”

This technology is available for licensing. Please contact Sara Hunt, PNNL commercialization manager, to learn more.

This work was supported by the Department of Energy’s Technology Commercialization Fund, the Office of Fossil Energy and Carbon Management, and Southern California Gas. Part of the work was performed at EMSL, the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility at PNNL.

When the 350-400 degree Celsius fluid exiting the Earth’s crust through deep-sea hydrothermal vents mixes with sea water it creates large porous rocks often referred to as ‘chimneys’ or hydrothermal deposits. These chimneys are colonized by microbes that thrive in high-temperature environments. For decades, Reysenbach has collected chimneys from deep-sea hydrothermal vents across the world’s oceans, and her lab uses genetic fingerprinting and cultivation techniques to study the microbial diversity of the communities associated with these rocks.

In this new study, Reysenbach and the team were able to take advantage of advances in molecular biology techniques to sequence the entire genomes of the microbes in these communities to learn more about their diversity and interconnected ecosystems.

The team constructed genomes of 3,635 Bacteria and Archaea from 40 different rock communities. The amount of diversity was staggering and greatly expands what is known about how many different types of Bacteria and Archaea exist. The researchers discovered at least 500 new genera (the level of taxonomic organization above species) and have evidence for two new phyla (five levels up from species). “Phyla is way up on the taxonomic rank, so that’s really cool,” says Reysenbach.

The team also found evidence of microbial diversity hotspots. Samples from the deep-sea Brothers volcano located near New Zealand, for instance, were especially enriched with different kinds of microorganisms, many endemic to the volcano.

“That biodiversity was just so huge, off the charts,” says Reysenbach. “At one volcano there was so much new diversity that we hadn’t seen elsewhere before.” This finding may suggest that the increased complexity of the subsurface rocks of a volcano makes them more likely to house diverse microbial species compared to deep-sea hydrothermal vents.

Besides finding a jaw-dropping amount of microorganism biodiversity in these high-temperature ecosystems, the genomic data from this study also showed that many of these organisms depend on one another for survival. By analyzing the genomes, the researchers found that some microorganisms cannot metabolize all of the nutrients they need to survive so they rely on nutrients created by other species in a process known as a “metabolic handoff.”

“By looking at these genomes, we really got a much better understanding of what a lot of these microorganisms are doing and how they’re interacting,” says Reysenbach. “They’re communal; they share food with each other.”

This study has inspired a new phase of research for Reysenbach: gaining an in-depth understanding of the interactions between these deep-sea microorganisms. “For me the most exciting part is that I really want to be able to grow these things in the lab,” says Reysenbach. “I want to be able to see [a microorganism] under a microscope and understand if it needs somebody else to live with.”

The research, published recently in the journal Limnology and Oceanography Letters, compiles over 118 million readings of dissolved oxygen and temperature taken from over 125,000 locations in rivers across six continents and 93 countries and spanning over 100 years, from 1900 to 2018. Hypoxia, defined in this study as dissolved oxygen concentrations below 2 milligrams per liter, was detected in rivers and streams in 53 countries, with 12.6% of all locations exhibiting at least one hypoxic measurement.

“Hypoxia in coastal waters and lakes is widely recognized as a detrimental environmental issue, yet we have lacked a comparable understanding of hypoxia in rivers,” Blaszczak, with the University’s College of Agriculture, Biotechnology & Natural Resources, said. “While 12.6% might not seem like a huge percentage, previously it was generally thought that occurrences of hypoxia in rivers and streams were exceedingly rare. Having shown presence of hypoxia in one of every eight river locations with data is definitely a game changer in terms of how we need to think of and give attention to the issue of hypoxia in rivers and streams.”

Blaszczak says that advances in measuring hypoxia over the past 15 years or so using field-deployable dissolved oxygen sensor technology that allows for constant monitoring, such as every hour, has given researchers the tools to get a better handle on the presence of hypoxia. Previously, readings were taken manually using a handheld probe or by collecting water samples mostly during the day, when oxygen levels are naturally higher, due to photosynthesis occurring during daylight hours.

“Photosynthesis by algae produces oxygen that is released into the water column,” Blaszczak explains. “So, you’re not getting a true picture of hypoxia occurrence if you only measure during the day. Hypoxic conditions are much more likely to develop in the early morning hours, after the lack of photosynthesis all night. The newer technology allows for us to capture that data.”

In fact, the research showed a dramatic difference in results between using the older methods and the newer technology, due to the times of day measurements are taken.

“We find that if we only sampled during the day every day, between 8 a.m. and 5 p.m., it would under detect the number of river locations where we observe hypoxia by about 25%,” she said.

Blaszczak says that much of the data from the study is more recent, and taken using the newer technology.

“There wasn’t a lot of testing going on, especially before the 1950s,” she said. “Even all the way up to around 2005 or so, the data at a global scale is pretty scarce.”

Research shows natural and human influences

As expected, the data showed hypoxia in rivers was most present in warmer, smaller and lower-gradient, stiller waters, where oxygen isn’t being “stirred” into the water from turbulence. Blaszczak says the research found these conditions occur most often in rivers draining naturally occurring wetlands, as well as in rivers draining some urban areas, where human actions have created hypoxic conditions.

“We as people managing waters often influence these conditions — by extracting water, building dams and increasing the amount of organic matter released into rivers, for example,” she says. “We can set up these conditions of very low flows. Rivers surrounded by wetlands and urban areas had about the same probability of hypoxia occurrence. That shows that while it can occur naturally, we also can create these conditions that are conducive to hypoxia.”

Blaszczak says that hypoxia often isn’t recognized until it’s too late.

“You’ll see a report in the media of a fish kill that was caused by hypoxia — from very low flows from dams, a release of something into a river, or something else we can control,” she says. “If we can put out more sensors to monitor conditions, we can get early warning signals, and take action to mediate the problem, such as modifying the flow in some way.”

Blaszczak says newer sensor technology that provides constant monitoring is also important because the duration of hypoxic conditions affects the harm it might induce.

“Fish do have, in some cases, avoidance strategies. So, if it is only for a couple of hours, they can try to manage themselves, by staying up closer to the surface, for example,” she says. “But if it is more extended, then they have a harder time. And, there are other factors. The size of the organism may influence its ability to survive, and some organisms are not as mobile, so they can’t adjust to survive a more prolonged hypoxic event.”

Besides the harm hypoxia can cause to aquatic life, it can also stimulate production of the greenhouse gases methane and nitrous oxide.

“There’s just nothing good about hypoxia in rivers or other bodies of water,” Blaszczak says. “We can’t eliminate it completely, but we can certainly do a better job of monitoring it and take actions to prevent it, rather than to stimulate it.”

Taking a global view

On a more positive note, Blaszczak says that looking at data from 1950 to 2018, the research showed that, globally, there doesn’t seem to be an overall increase in hypoxic conditions in rivers. However, in certain locations, there are increases. And, in some locations, the presence is extreme, she says. The researchers put together a worldwide map that is featured in the research article, which color codes the number of hypoxia occurrences they found by region, with blue being rare occurrences and red being the highest presence of hypoxia.

“You’ll see that Florida is completely red, off the charts,” Blaszczak noted.

Much of the U.S. is in the yellow, or midrange. Blaszczak says that there is much more data available from the U.S. overall than other countries. She and a team of researchers compiled data from government-supported work and other published data to create the data set that spans all continents except Antarctica, but is dominated by data from North America. Each location had to have a geographic coordinate, at least one measurement of dissolved oxygen, a corresponding water temperature and a date-time stamp. Blaszczak then analyzed the data, as part of her research for her College’s Department of Natural Resources & Environmental Science and Experiment Station.

She embarked on leading the study after attending a workshop in September 2018 held in Switzerland and convened by Jim Heffernan and Tom Battin from Duke University. The workshop aimed to advance the global understanding of the dynamics of hypoxia in rivers and streams and was supported by the Swiss National Science Foundation and the U.S. National Science Foundation.

Moving forward, Blaszczak says more monitoring with newer technology is key to mitigating harmful effects of hypoxia in rivers.

“We need to further develop our capacity to identify when and where rivers are vulnerable to the development of hypoxic conditions, so that we can guide river management in the face of continuing climate and land-use change. Supporting ongoing monitoring and expanding monitoring to regions where data is sparse is essential,” she said.

Blaszczak is grateful for researchers and governments that provided data used in the study and for the co-authors of the study, including Lauren E. Koenig, Francine H. Mejia, Lluís Gómez-Gener, Christopher L. Dutton, Alice M. Carter, Nancy B. Grimm, Judson W. Harvey, Ashley M. Helton and Matthew J. Cohen.