By Niu Song and Jian Yanjun, CCS Shanghai Rules & Research Institute

With the advancement of the temperature control goals under the Paris Agreement, the International Maritime Organization (IMO) has formulated a phased emission reduction roadmap, targeting a 20% to 30% reduction in international shipping greenhouse gas emissions by 2030 compared to 2008 levels, a 70% to 80% reduction by 2040, and the achievement of net-zero emissions around 2050. Faced with these increasingly stringent requirements, the emission reduction potential of traditional energy-saving measures (such as high-efficiency propellers and low-resistance hull designs) is approaching a bottleneck, while new alternative fuels (methanol, ammonia, hydrogen) face practical obstacles including insufficient infrastructure and high retrofitting costs. Against this backdrop, onboard carbon capture technology has emerged as an innovative solution to meet the industry's rigorous demands. Characterized by its "immediate reduction" capability, it serves as a critical pathway to achieve deep decarbonization for the existing fleet while remaining compatible with current power systems, and is now transitioning from technical R&D and pilot projects to commercial application.

As an emission reduction solution that does not require modifications to existing ship power systems and is compatible with carbon-based fuels, onboard carbon capture technology is not only a key technical measure for the global shipping industry to address deep decarbonization requirements but also an indispensable transitional technology from the era of fossil fuels to net-zero emissions. Its significance extends beyond environmental benefits; based on supporting carbon emission reduction, driving industrial upgrading, ensuring energy security, and maintaining supply chain stability, it is poised to reconstruct the global shipping value chain.

I. Current Status of Onboard Carbon Capture Technology Development

Carbon capture technology involves separating and capturing carbon dioxide from exhaust emissions, followed by utilization or storage to prevent its release into the atmosphere, thereby achieving carbon dioxide emission reduction. As a critical transitional solution for the shipping industry to achieve its "dual carbon" goals, onboard carbon capture technology faces unique challenges. Constrained by factors such as complex exhaust gas composition, low CO2 concentration, limited onboard space, restricted energy availability, and harsh operating environments, the practical application of Onboard Carbon Capture Systems (OCCS) presents hurdles in terms of safety, reliability, and economy. Nevertheless, numerous enterprises have initiated demonstration installations of OCCS, focusing on resolving technical bottlenecks and adapting to industry scenarios. Through technological innovation, they are driving the industrial implementation of OCCS to address the challenges of the industry's green transition.

Based on the principle of post-combustion CO2 capture, this approach does not alter the ship's original fuel combustion or power mode and requires minimal modifications to existing power systems, making it the most widely applied carbon capture technology currently. Concurrently, with the advancement of cracking hydrogen production technology, pre-combustion carbon capture technologies—such as pre-combustion decarbonization (solid carbon) for LNG—have garnered significant attention from the shipping industry, with relevant research and systems having already obtained Approval in Principle (AIP).

1. Technical Routes and Current Status

(1) Tower-based Carbon Capture Technology

The principle of tower-based carbon capture technology involves utilizing amine-based decarbonizers to undergo reversible chemical reactions with CO2 within a tower apparatus (absorption at low temperatures, desorption at high temperatures). The process flow primarily includes exhaust gas pre-treatment, absorption in the absorber, desorption in the desorber, compression and liquefaction, storage of captured liquid CO2, and resource reuse or storage. The main challenges of tower-based carbon capture technology lie in the system's complex equipment structure, large space occupation, high energy consumption, safety risks associated with decarbonizers (such as corrosion and toxicity), and difficulties in the disposal of liquid CO2.

Currently, tower-based carbon capture technology has been successfully installed and operated on 82,000 DWT bulk carrier newbuilding (0.5 t/h) and a 14,000 TEU container ship (1.65 t/h).

(2) High-Speed Rotating Carbon Capture Technology

The principle of high-speed rotating carbon capture technology is consistent with that of tower-based technology, utilizing amine-based absorbents to undergo reversible chemical reactions with CO2 to achieve capture and separation (absorption at low temperatures, desorption at high temperatures). The key difference is that instead of a tower structure, the absorption and desorption processes occur within a high-speed rotating apparatus. This utilizes a high-gravity field generated by rapid rotation to intensify gas-liquid mass transfer. Through centrifugal force, the equipment volume is reduced while the contact area and time between gas and liquid are increased, thereby significantly enhancing absorption and separation efficiency.

The main challenges of high-speed rotating carbon capture technology include: 1. Mechanical reliability: The lifespan of rotating components is relatively short. 2. Ship environmental adaptability: Frequent rolling and vibrations can cause fluctuations in mass transfer efficiency. 3. High investment costs: The investment and maintenance for precision equipment such as rotating beds, high-speed motors, and control systems are higher than those for traditional processes. 4. Risks associated with rotating beds: Due to the high internal pressure within the rotating bed, seal failure could potentially lead to solvent ejection causing injury.

Figure 2 Schematic Diagram of Amine-based Absorption Onboard Carbon Capture System (High-Speed Rotating)

Currently, the "OceanGuard" carbon capture system, adopting high-speed rotating carbon capture technology, has been retrofitted and put into operation on a 57,000 DWT bulk carrier (0.042 t/h).

(3) Cryogenic Desublimation Carbon Capture Technology

The principle of cryogenic desublimation carbon capture technology leverages CO2's property of directly transitioning from gas to solid at specific temperature and pressure conditions. It uses a refrigeration system (desublimation reactor) to cool exhaust gas to -100°C~-140°C, collects solid CO2, then melts and compresses it into liquid for storage via a post-treatment unit (melting heater). Key challenges include: 1. High energy consumption of the refrigeration system. 2. Equipment stability at low temperatures: material embrittlement and difficulties in cold energy matching. 3. Frequent defrosting: dry ice easily causes system blockages. 4. Precision control & storage complexity: requires accurate temperature control; captured CO2 purity is low, and storage/unloading demands specialized equipment. 5. Poor ship compatibility: conflicts with limited space, weight constraints, and vessel motion/vibration.

Figure 3 Schematic Diagram of Carbon Dioxide Phase Transition

(4) Membrane Separation Carbon Capture Technology

The principle of membrane separation carbon capture technology utilizes the selective permeability of membrane materials. Based on the differences in the dissolution-diffusion rates of gas molecules within the membrane, it enables carbon dioxide in ship exhaust gas to preferentially pass through, thereby separating it from other gases. This technology features a simple process flow that does not require desorption; its main energy consumption is attributed to the permeate gas compression module. The system is lightweight and easy to arrange, with design architectures typically categorized into single-stage and multi-stage membrane separation. Single-stage membrane separation offers a simple structure with a captured CO2 purity of approximately 70% to 80%. Multi-stage membrane separation generally employs 2-3 stages of membrane modules and permeate gas compression modules, achieving a CO2 capture rate exceeding 85% with a purity of up to 98%.

The main challenges of membrane separation carbon capture technology include: 1. Membrane performance degradation: Influenced by the marine environment and impurities (such as SO2 and particulate matter) in ship exhaust gas, requiring regular chemical cleaning to maintain performance. 2. Accelerated aging: Long-term exposure to high temperatures and vibration environments can accelerate membrane aging, affecting its service life. 3. Trade-off between capture rate and purity: There is an imbalance between the CO2 capture rate and purity; increasing the capture rate tends to reduce purity, necessitating further system optimization.

Currently, membrane separation carbon capture technology has seen pilot applications in the FPSO sector; the Catcher FPSO in the North Sea utilizes UOP Separex  hollow fiber membranes, achieving a carbon dioxide capture rate exceeding 90%.

(5) Adsorption Carbon Capture Technology

The principle of adsorption carbon capture technology utilizes the selective and reversible adsorption capabilities of sorbents (such as activated carbon and zeolites) for carbon dioxide. Under specific conditions, the sorbent selectively adsorbs CO？ from flue gas, separating it from ship exhaust through physical action or chemical reactions, and then desorbs the CO？ by altering certain conditions (such as temperature and pressure). The adsorption capacity of the sorbent primarily depends on its surface area, operating pressure, temperature difference, and material type. The process flow mainly includes exhaust gas pre-treatment, CO2 adsorption in the exhaust gas (adsorption bed), sorbent desorption, and storage after CO2 compression and liquefaction.

The main challenges of adsorption carbon capture technology include: 1. Limited adsorption capacity: there is a need to develop new high-capacity sorbents to enhance adsorption capacity. 2. Limited sorbent lifespan: surface modification technologies are required to enhance sulfur and moisture resistance to prolong service life. 3. Accelerated corrosion in marine environments: adsorption equipment operating in long-term marine salt spray environments faces accelerated corrosion, leading to system aging, which necessitates special anti-corrosion treatment. 4. The additional loading of adsorption materials results in significant weight and volume, causing a loss of ship cargo hold capacity and/or deadweight tonnage.

Sorbent Particles

Figure 5 Schematic Diagram of Adsorption Working Principle

Currently, leveraging advantages such as compact equipment and zero risk of liquid leakage, adsorption carbon capture technology has taken the lead in achieving commercialization in the FPSO sector (AGOGO FPSO, 2023), while its application on merchant vessels has also entered the demonstration and verification phase.

(6) LNG Reforming for Hydrogen Production with Pre-combustion Decarbonization

The technical principle of LNG reforming for hydrogen production with pre-combustion decarbonization primarily involves thermal catalytic decomposition. This process involves the non-oxidative decomposition of LNG (primarily methane) into carbon and hydrogen under high-temperature conditions with the aid of a catalyst, following the reaction: CHC→ C(s) + 2H2. The generated solid carbon powder can be stored in dedicated spaces and unloaded when the vessel calls at a port, achieving a carbon capture rate of over 95%. The hydrogen produced from pyrolysis can be burned in a mixture with LNG or used to generate electricity via hydrogen fuel cells.

The main challenges for its practical shipboard application include: 1. Carbon deposition covers the catalyst surface, leading to decreased activity and necessitating frequent regeneration or replacement. 2. The high-temperature reaction (approximately 600-900°C) consumes significant energy. 3. Equipment such as reactors, cooling systems, and carbon storage tanks occupies ship space and increases vessel weight. 4. There are risks associated with high-temperature environments, hydrogen leakage, and carbon powder self-ignition.

Figure 6 Schematic Diagram of Marine Pre-combustion Decarbonization for LNG

Based on the above analysis, tower-based carbon capture is currently the most mature technology and is suitable for most medium-to-large-sized vessels. High-speed rotating carbon capture technology, with its high efficiency and compact characteristics, serves as an ideal choice for ships with limited space. LNG reforming for hydrogen production with pre-combustion decarbonization offers a unique low-carbon transition pathway for LNG-powered ships; meanwhile, innovative technologies such as membrane separation and adsorption methods provide new options for small-to-medium-sized vessels as well as certain specific scenarios.

With the continuous development of onboard carbon capture technology, the integration of multiple technologies (such as cold energy + waste heat power generation), the cascade utilization of waste heat/cold energy, and the development of new high-efficiency absorbents/catalysts will continuously improve system energy efficiency, reduce carbon dioxide emissions, and drive onboard carbon capture technology from demonstration applications toward large-scale practical shipboard implementation.

II. Future Development Trends

At the current stage, the onboard carbon capture industry chain has entered a period of rapid growth. However, for its widespread commercial promotion, four major hurdles—technical, economic, infrastructure, and policy—must still be overcome. The most urgent tasks include perfecting the standard system, accelerating the construction of port facilities, and expanding channels for the subsequent storage and utilization of CO2.

1.Technology Development Direction

Future onboard carbon capture technology will advance toward the goals of "high efficiency, compactness, low energy consumption, and low cost." The development of new high-efficiency decarbonizers will improve capture efficiency and reduce regeneration energy consumption; advanced reactor technologies such as high-gravity rotating beds will further minimize equipment volume; and the development of membrane materials will further reduce equipment weight and the impact on ship layout, making them suitable for more vessel types.

Simultaneously, the integrated innovation of various energy-saving technologies will become a key direction. For instance, combining OCCS with onboard waste heat and cold energy recovery can significantly reduce the energy consumption of CO2 capture and liquefaction. Furthermore, the chemical utilization and storage of post-capture CO2 can achieve resource recycling, effectively lowering storage costs. Finally, integration with digital and intelligent technologies—by monitoring ship operating conditions and recoverable energy in real-time to dynamically adjust system operation—will enhance system flexibility and resilience, achieving a dynamic balance and optimal matching between CO2 capture efficiency and energy consumption.

2. Innovation in Service Models

In April 2025, the MEPC 83 meeting officially approved the development plan for the OCCS regulatory framework. Concurrently, with continuous breakthroughs in onboard carbon capture technology, it is expected to enter a period of large-scale promotion around 2030, establishing itself as one of the primary technologies for deep decarbonization in the shipping industry. Future service models will also shift from simple OCCS installation toward comprehensive carbon management services. Shipowners can utilize OCCS through leasing or hosting models, where professional service providers are responsible for equipment maintenance and carbon unloading, thereby reducing the pressure of initial investment.

Furthermore, port operators will construct supporting carbon unloading facilities and charge service fees based on volume. Energy and chemical enterprises will undertake subsequent transportation, utilization, and storage, bridging the final link of the industrial chain. This will form a new "Shipowner—Port—Chemical" collaborative ecosystem for carbon management.

3. Policy and Standard Improvement

The IMO has specifically established an OCCS Correspondence Group, focusing on formulating technical standards for onboard carbon capture technology, developing guidelines for testing, inspection, and certification, analyzing the impact of current legal barriers on the use of OCCS and the transfer of carbon transport, and promoting the access of recognized/certified receiving facilities. Simultaneously, various countries will further strengthen cooperation in infrastructure construction, planning global CO2 transportation networks and utilization/storage bases to create an integrated "Capture-Transport-Unloading-Utilization/Storage" network. Furthermore, the collaborative development of the carbon capture industry chain will see upstream and downstream enterprises cooperating to form a closed-loop industrial ecosystem of "Technology R&D—Equipment Manufacturing—Operational Services—Utilization/Storage." This will accelerate the establishment of a unified global OCCS technical standard and certification system, facilitating the cross-border promotion of this technology.

4. Future Application Scenarios

Regarding the future application scenarios for OCCS, first is the retrofitting of existing ships. For existing vessels struggling to meet emission requirements, onboard carbon capture systems will be the primary technology to help them gradually reduce CO2 emissions. Second is LNG/LPG-powered vessels, particularly LNG carriers. The coupled utilization of cold energy from LNG/LPG fuel with OCCS, along with waste heat recovery technologies, can significantly reduce the energy consumption of CO2 capture and compression. Third is vessels navigating routes with convenient CO2 unloading capabilities. These ships can unload the CO2 captured by OCCS in a timely manner, reducing the time the vessel spends "sailing under load," which is equivalent to indirectly improving the operational efficiency and emission reduction effect of OCCS. Finally, there is the development of emerging industries for the resource utilization/storage of CO2 (geological storage, chemical storage and resource utilization). In addition to geological and oceanic storage, "storage" specifically mentions chemical storage—utilizing CO2 to produce chemical products or mineralized building materials. This not only enables the long-term storage of captured CO2 but also allows for the production of low-carbon (or even zero-emission) chemicals.

III. Conclusion

As a "bridge technology" for decarbonization in the shipping industry, onboard carbon capture technology offers irreplaceable advantages in terms of compatibility with existing ship power systems and the rapid achievement of emission reduction targets. Currently, the technology has transitioned from the R&D phase to the stage of practical ship verification and demonstration applications. Technological breakthroughs and project practices in China, Europe, and various Asian countries have laid a solid foundation for large-scale promotion. Despite challenges such as space constraints, high costs, and insufficient infrastructure, with technological iteration, policy support, and the improvement of market mechanisms, onboard carbon capture technology is expected to enter a phase of large-scale application around 2030, becoming one of the primary pillars for the shipping industry to achieve IMO emission reduction goals.

In the future, the deep integration of technological innovation, service model innovation, and policy innovation will drive onboard carbon capture technology from an "optional solution" to a "mandatory requirement." By coupling multiple technologies to enhance emission reduction efficiency and economic viability, coordinating the entire industrial chain to improve infrastructure, and leveraging carbon market linkages to unlock commercial value, onboard carbon capture technology will not only help the shipping industry achieve net-zero and even negative carbon emissions but also foster new industrial ecosystems and economic growth points, providing solid technical support for global climate governance.