Meet The Solvent That Captures Up To 99.8% Of CO2 Emissions

Hidden in a fold of Norway’s western coast about an hour north of Bergen, you’ll find the Technology Centre Mongstad. This renowned carbon dioxide (CO₂) capture test facility, camouflaged by its industrial neighbors, is easy to miss. If you visited last year, you might not have noticed the flurry of activity surrounding testing of a new amine-based solvent. After all, the test was quiet, almost unremarkable. But like the facility itself, the test was hiding a significant advancement. In fact, the substance was absorbing 99.8% of the CO₂ emissions.

That solvent, known as KS-21™, is the culmination of nearly a decade of meticulous research by engineers at Mitsubishi Heavy Industries. Improving CO₂ capture efficiency from a hair over 90% to almost 100% changes the math for thermal fuel combustion, creating major implications for the energy transition – it accelerates emissions reduction for hard-to-abate industries and potentially transforms low-carbon or carbon-neutral emitters to net carbon negative.

“The results from our testing with KS-21™ suggest it’s possible to have a net zero or even net-negative process.” – Jerrad Thomas, Business Development Manager, Mitsubishi Heavy Industries America

The importance of CO₂ capture

While the idea of removing carbon dioxide from exhaust has been around since at least the 1970s, advances in CO₂ capture have made it an increasingly important component of the energy transition in recent years. The International Energy Agency’s Sustainable Development Scenario now envisions carbon dioxide capture, utilization and sequestration (CCUS) accounting for nearly 15% of the emissions reduction needed to bring the energy sector to net zero by 2070. As of 2021, existing CCUS facilities around the world had the capacity to capture more than 40 million tons of CO₂ each year.

The technology is particularly promising for regions and industries that so far lack economically viable alternatives for reducing CO₂ emissions. Consider traditionally hard-to-abate industries such as concrete, steel and heavy transportation, which have made only modest progress toward emissions-reduction goals due to the challenges involved in developing, testing and implementing new, less CO₂-intensive processes. Carbon dioxide_{capture offers those industries a way to reduce emissions with modifications to their existing infrastructure, buying them time to develop more substantial solutions.}

A better solvent

The process of removing CO₂ follows a law of diminishing returns, explains Jerrad Thomas, Business Development Manager at Mitsubishi Heavy Industries America. Seventy percent of today’s global post-combustion CO₂ capture capacity relies on the company’s technology. “It’s like gardening. If I were getting my garden ready for planting, pulling out one big boulder might remove 90% of the stone,” he says. “Without the proper tools, it would take a lot more time and energy to remove every last pebble. Imagine, then, that you’re trying to remove more than 90% of the CO₂ in an exhaust stream. MHI’s new solvent is the best tool for the job.”

Solvent-based solutions push exhaust gases through a structure called an absorber. Put simply, the solvent absorbs, or pulls, CO₂ out of the exhaust. That process is reversible: The solvent is then pumped from the absorber to a regenerator, where it’s heated to release the CO₂, then cooled and returned to the absorber.

^{Watch: How CO2 capture works.}

Traditional solvents are susceptible to heating losses, which can occur through either vaporization or thermal degradation of the solvent. “Throughout MHI’s 30-plus years in the industry, we’ve been looking for ways to reduce solvent losses,” says Thomas. The search whittled a list of more than 200 candidates down to KS-1™, the best-in-class solvent MHI introduced in the 1990s. Further refinements in the 2010s eventually produced a solvent that engineers suspected might be even better. The test results in Norway in 2021 proved them right.

The specific (and proprietary) characteristics of MHI’s KS-21™ enable the compound to absorb CO₂ more effectively than other solvents. It also degrades at a higher temperature than most solvents currently in use, says Thomas, and it has a lower vapor pressure, both resulting in reduced losses. This combination makes KS-21™ more efficient: Higher regeneration temperatures can be used to release the CO₂, and since the solvent resists thermal and vaporization losses, it doesn’t need to be replenished as frequently.

“Most people still don’t truly understand how important this breakthrough is for the future of CO2 capture and the decarbonization effort globally.”

KS-21™, which is now commercially available, does not necessitate large design changes relative to a typical amine-based CO₂ capture process. The capital investment is comparable to existing solutions due to similar equipment sizing, but developers can take advantage of the significant variable operating expense efficiencies.

Opening a new frontier

The arrival of KS-21™ could help companies hit key emissions-reduction milestones sooner. Companies basing their net zero targets on 90% capture – the industry standard – have to find ways to offset the remaining 10% of CO₂ emissions elsewhere in their operations. Boosting their CO₂ capture to almost 100% offers the potential to make these companies net-negative carbon emitters.

For example, Drax, a bioenergy company in the U.K., already has contracted to use KS-21™ as part of its plan to become carbon negative by 2030. “The results from our testing with KS-21™ suggest it’s possible to have a net zero or even net-negative process,” Thomas says.

For companies looking to address their historic emissions, this boost in technical capability could shorten the path. Here’s how: Some companies may be able to reduce the CO₂ in exiting gases to levels below the concentrations of CO₂ in the outside air, with the remarkable result that the fuel combustion process itself could be net zero or even net negative. Likewise, biomass facilities that replenish the carbon sinks they use as fuel could go from carbon neutral to net reducers of carbon emissions.

Other green technologies may be sexier or more visible than a new solvent that boosts CO₂-capture efficiency. But every percentage point counts – especially as we approach net zero and find that the low-hanging fruit has been picked. “I think most people still don’t truly understand how important this breakthrough is for the future of CO₂ capture and the decarbonization effort globally,” says Thomas.

In one respect, there was nothing notable in the air around that Norwegian facility during the testing of KS-21™. But that in itself was an enormous achievement.

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