The International Maritime Organization has set a hard deadline: by 2050, the global shipping fleet must cut its CO₂ emissions by at least 50% compared to 2008 levels. That is regulation, not a suggestion. And it leaves the maritime sector with a difficult practical problem. How do you pull carbon dioxide out of engine exhaust on a ship, where space, weight, and energy are all in short supply?
For years, the answer has been the same one used in power plants and heavy industry: pump the exhaust through a solution of monoethanolamine (MEA). MEA works. It absorbs CO₂ reliably, the chemistry is well understood, and the supply chain already exists. But on a ship, MEA’s biggest flaw becomes impossible to ignore. The energy required to release the captured CO₂ and regenerate the solvent is enormous. A significant chunk of the ship’s fuel gets burned just to run the carbon capture process, which rather defeats the purpose.
A different approach: phase-change solvents
The basic idea behind a new generation of carbon capture solvents is straightforward: don’t heat the entire solvent volume. Design a system where the CO₂-rich portion separates into a dense liquid phase, so only that small fraction needs to be heated during regeneration.
That is what phase-change absorbents do. When they absorb CO₂, the solution splits into two layers. A CO₂-loaded phase sits at the bottom, and a lean phase floats above it. You draw off the small, CO₂-heavy layer, heat it to release the gas, cool it, and send it back. The lean phase barely needs to be touched.
Recent research tested this idea by combining a range of amines with different phase-separation promoters, organic solvents that trigger the splitting behaviour when CO₂ is absorbed. Seven amines and seven promoters were screened. Three combinations actually produced usable phase separation:
- DETA + n-butanol + water (DTNB)
- DETA + NMP + water (DTNP)
- DETA + DMSO + water (DTSO)
All three use diethylenetriamine (DETA) as the primary amine, and all three share the same mass ratio of 3 parts amine to 3 parts promoter to 4 parts water.
DETA already beats MEA before you add any tricks
Even without phase-change behaviour, DETA absorbs more CO₂ than MEA. At saturation, DETA holds 1.05 moles of CO₂ per mole of amine. MEA manages just 0.52. That is a 102% improvement in raw capacity, which means less solvent, smaller equipment, and less weight on a ship that has no space to spare.
But absorption capacity is only half the equation. The real question is whether the solvent can be regenerated without burning through fuel. That is where phase separation makes a difference.
DETA + DMSO + water comes out on top
Of the three phase-change systems that worked, one clearly outperformed the others. The combination of DETA with dimethyl sulfoxide (DMSO) and water, called DTSO, posted the best numbers across every metric that matters.
Absorption: 46% more CO₂ than MEA
Under conditions that simulate real ship engine exhaust (5 vol% CO₂ in nitrogen, at 40°C), DTSO absorbed 3.17 moles of CO₂ per kilogram of solvent. The standard 5 M MEA benchmark absorbed 2.17 mol/kg. A 46% gap is not trivial. A capture system built around DTSO could be noticeably smaller for the same throughput, or handle higher exhaust volumes in the same footprint.
DTSO also reached 95% loading faster than the other phase-change candidates. On a ship where exhaust gas flows continuously, faster kinetics mean a smaller absorption column.
Desorption: 12% more CO₂ released
Regeneration is where many promising solvents fall apart. They soak up CO₂ fine but refuse to let it go without excessive heat. DTSO does not have this problem. During desorption at 130°C, it released 2.13 mol CO₂/kg, compared to 1.90 for MEA.
Neither of the other two phase-change solvents beat MEA on desorption. DTNP released 1.48 mol/kg and DTNB just 1.28. DTSO was the only one to outperform MEA on both absorption and desorption.
Energy: the figure that actually matters
DTSO’s regeneration energy requirement is 6,178 kJ per mole of CO₂. MEA requires roughly 21,294 kJ/mol. That is a 71% reduction.
In practical terms, for every unit of fuel a ship burns to regenerate its carbon capture solvent with DTSO, it would need to burn three and a half times as much with conventional MEA. Over a long voyage, the fuel savings would be substantial.
Why DTSO performs so well
The energy savings come from two things happening at once.
First, phase separation means only the CO₂-rich phase gets heated. That is a much smaller volume than the total solvent in the system. Instead of boiling the whole tank, you are heating a fraction of it.
Second, the 130°C regeneration temperature speeds up CO₂ release. Less liquid to heat plus faster kinetics means shorter regeneration cycles and less run time for the heater.
The other two phase-change systems (DTNB and DTNP) also benefit from volume reduction, but their regeneration energies landed at 70% and 66% of MEA respectively. Better than baseline, but nowhere near the 29% that DTSO achieved.
The caveats
No solvent is perfect. A few problems sit between DTSO’s lab results and actual deployment on a ship.
DMSO costs more than the simple solvents used in conventional amine systems, and it raises toxicity concerns that would need proper handling procedures onboard.
Amine solutions corrode steel, and corrosion worsens at elevated temperatures. The 130°C regeneration temperature is standard for amine scrubbing, but over thousands of operating hours, material degradation becomes a real engineering headache.
Ship motion is another open question. Phase separation depends on gravity to split the liquid into two clean layers. On a vessel pitching and rolling in heavy seas, keeping that separation stable could be tricky. These systems have not been tested under realistic motion conditions yet.
And real ship exhaust contains SO₂ and NOₓ, which were left out of these experiments. In practice, those acidic gases react with amines to form heat-stable salts that gradually degrade solvent performance. Whether DTSO tolerates those contaminants well enough for long-term operation is unknown.
So what now
None of those problems are unsolvable. Corrosion-resistant alloys and linings already exist. DMSO prices drop with scale. Phase separators that compensate for ship motion can be engineered. Solvent management for contaminant gases is a solved problem from decades of power-plant experience.
The shipping industry does not have the luxury of waiting for a perfect solution. IMO regulations are tightening, and the current MEA-based approach burns too much fuel to scale to the levels being demanded. Phase-change solvents like DTSO offer a real, measurable improvement. They cut the energy penalty by more than two-thirds while also increasing capture capacity.
Shipping moves roughly 80% of global trade by volume and produces about 3% of worldwide CO₂ emissions. Incremental gains matter when the numbers are that large. What counts is getting something that works well enough onto actual vessels, not waiting for something flawless.
The chemistry checks out. The open questions are about engineering, cost, and logistics at sea. If those answers come back positive, and early signs suggest they will, phase-change CO₂ capture could become standard equipment on commercial ships within the next decade.
Frequently asked questions
What is MEA and why is it the standard for carbon capture?
Monoethanolamine (MEA) is a liquid amine that reacts with CO₂ to form a soluble compound. Power plants and industrial facilities have used it for decades. It absorbs CO₂ effectively, the chemistry is simple, and there is an established supply chain. The main problem is the amount of heat needed to strip the CO₂ back out so the solvent can be reused.
What is a phase-change solvent?
A phase-change solvent is an absorbent that splits into two separate liquid layers after it picks up CO₂. One layer is rich in CO₂ and the other is lean. Because only the small CO₂-rich layer needs to be heated during regeneration, far less energy is required compared to conventional solvents where the entire volume must be heated.
How much energy does DTSO save compared to MEA?
DTSO requires roughly 6,178 kJ to regenerate one mole of captured CO₂. MEA needs about 21,294 kJ for the same amount. That works out to a 71% reduction in regeneration energy, or put differently, DTSO uses only 29% of the energy that MEA does.
Why was DMSO chosen as the phase-separation promoter?
DMSO (dimethyl sulfoxide) was one of seven organic solvents tested as phase-separation promoters. It ended up performing best when combined with DETA and water. The DTSO blend absorbed more CO₂, released more during regeneration, and required less energy than the other candidates (n-butanol and NMP).
Can this actually work on a moving ship?
That remains to be proven. Phase separation depends on gravity to create two distinct liquid layers. Ship motion from waves could disrupt that separation. No one has tested these solvents under realistic sea conditions yet, so motion-compensated separator design is one of the engineering challenges that needs to be solved before deployment.
What about the SO₂ and NOₓ in real exhaust gas?
The experiments so far have used clean simulated exhaust containing only CO₂ and nitrogen. Real ship engine exhaust contains sulfur oxides and nitrogen oxides, which can react with amines to form heat-stable salts. These salts gradually reduce the solvent’s effectiveness. How DTSO handles these contaminants over long periods of operation is not yet known.
Is DMSO safe to use on ships?
DMSO is more expensive than conventional amine solvents and does have toxicity concerns, so proper handling procedures and spill containment would be essential. It is used in pharmaceutical and industrial applications already, but deploying it in the confined spaces of a ship’s engine room adds a layer of safety engineering that still needs to be addressed.
When could phase-change carbon capture appear on commercial ships?
If the remaining engineering challenges can be solved, phase-change CO₂ capture systems could start appearing on commercial vessels within the next decade. The chemistry is proven at lab scale. The work that remains is about building reliable hardware, confirming long-term solvent stability, and demonstrating the economics at full scale.