Carbon capture is a family of technologies that separate carbon dioxide (CO₂) from gas mixtures produced by industrial facilities, power plants, or the atmosphere. Its principal climate-related purpose is to limit the release of this greenhouse gas or enable its removal from the air. Capture is only one stage of a larger system: the separated CO₂ must subsequently be transported, used, or durably stored. The complete storage chain is called carbon capture and storage (CCS), while systems incorporating use are commonly described as carbon capture, utilisation and storage (CCUS). (iea.org)
Scope and distinctions
Carbon capture is an engineered gas-separation process, distinct from biological carbon uptake through photosynthesis. It can intercept CO₂ generated by burning fossil fuels or by industrial reactions, and it can collect atmospheric CO₂ through direct air capture (DAC). These applications have different implications for the carbon cycle and climate change. Capturing fossil-derived CO₂ before its release reduces emissions but does not remove CO₂ already present in the atmosphere. Carbon dioxide removal requires atmospheric uptake followed by durable storage. (iea.org)
Capture also differs from storage and utilisation. Producing a concentrated CO₂ stream does not, by itself, establish a climate benefit. That benefit depends on the energy used, emissions throughout the supply chain, and the ultimate destination and retention time of the captured carbon. (iea.org)
Capture configurations
Post-combustion capture separates CO₂ from exhaust after fuel combustion. Because combustion in air produces nitrogen-rich flue gas, the equipment must extract CO₂ from a larger gas mixture. This configuration can be applied to existing power and industrial facilities without replacing their basic production process, although substantial equipment and energy integration may be required. (netl.doe.gov)
Pre-combustion capture separates CO₂ from fuel-derived gases before combustion. In gasification-based systems, fuel is converted into synthesis gas; subsequent reactions convert carbon monoxide into CO₂ while producing additional hydrogen. CO₂ is then separated, leaving a hydrogen-rich fuel. The elevated CO₂ partial pressure can make separation easier than in dilute flue gas. (netl.doe.gov)
Oxy-fuel combustion uses oxygen rather than ordinary air. Its exhaust consists predominantly of CO₂ and water vapour, with impurities requiring further treatment. Removing water produces a CO₂-rich stream. The configuration simplifies separation but introduces energy and equipment requirements for oxygen production, gas purification, and combustion control. (netl.doe.gov)
DAC instead processes ambient air. Unlike point-source capture, it can address emissions independently of where they originated. Permanent storage of air-captured CO₂ constitutes a removal pathway; using it in products does not necessarily provide durable removal. (iea.org)
Separation technologies
Liquid-based systems use absorption to transfer CO₂ into a solvent, through physical dissolution or chemical interaction. After capture, the solvent is regenerated to release concentrated CO₂ and reused. Amine-based systems are an established reference technology; research focuses on reducing regeneration energy, degradation, corrosion, and solvent losses. (netl.doe.gov)
Solid-based systems use adsorption on sorbent surfaces. Regeneration can involve heating, pressure-swing adsorption, vacuum, or electrical processes. Useful sorbents must combine CO₂ selectivity and capacity with rapid uptake, durability, and repeated regeneration. Their performance depends on both material properties and the design of contactors and operating cycles. (netl.doe.gov)
Membrane separation uses materials that preferentially transport particular gases, producing streams with different compositions. Other approaches include low-temperature separation, electrochemical capture, and hybrid systems combining several methods. Selecting a process is a chemical engineering problem involving gas composition, operating conditions, required purity, equipment size, and energy consumption. (netl.doe.gov)
Transport, storage, and use
Captured CO₂ is generally conditioned and compressed before off-site transport. Pipelines, ships, rail, and trucks can connect capture facilities with storage sites or users. Transport and storage therefore form essential infrastructure beyond the capture plant itself. (iea.org)
Geological carbon storage injects CO₂ into suitable deep rock formations, including saline formations and depleted oil and gas reservoirs. Retention mechanisms include sealing beneath impermeable rock, residual trapping in pores, dissolution in brine, and reactions forming carbonate minerals. Site assessment examines porosity, permeability, injectivity, depth, and containment integrity. Subsurface monitoring tracks the CO₂ plume and changes in rock or fluid properties to identify migration pathways. (netl.doe.gov)
CO₂ utilisation includes applications in chemicals, fuels, and building materials. Storage duration varies: carbon in a fuel is normally released during combustion, whereas mineral-based products can retain it much longer. Evaluation must account for the displaced product, conversion energy, CO₂ source, and retention period rather than treating every tonne used as a tonne permanently stored. (iea.org)
Performance and applications
Capture costs vary substantially with CO₂ concentration, process design, scale, and location. Highly concentrated industrial streams generally require less separation effort than dilute streams. Transport distance and storage availability add further costs beyond capture equipment. (iea.org)
Capture rate and net emissions reduction are different measures. Additional heat, electricity, compression, and material supply affect overall performance. Life-cycle assessment considers these burdens alongside the captured quantity and downstream carbon fate. (netl.doe.gov)
Applications include power generation, hydrogen production, cement manufacturing, and petrochemical processes. Bioenergy with carbon capture and storage combines biological atmospheric uptake with capture and permanent storage from biomass processing or energy production. Operational research addresses reliable capture under changing plant loads, lower regeneration requirements, impurity tolerance, corrosion, and longer capture-medium lifetimes. (netl.doe.gov)