Carbon utilization versus storage
Carbon utilization and carbon storage are two pathways after CO2 is captured. Both remove or manage CO2, but they serve different purposes and timelines.
Carbon storage (sequestration)
- Purpose: permanently isolate CO2 from the atmosphere.
- Common methods: geological storage in depleted oil and gas reservoirs or deep saline aquifers, and mineralization where CO2 reacts with minerals to form stable carbonates.
- Timescale: intended to keep CO2 out of the atmosphere for decades to millennia.
Carbon utilization (CCU)
- Purpose: convert captured CO2 into commercial products or feedstocks.
- Examples: synthesizing fuels (e-fuels), chemicals, building materials (e.g., concrete cures), or using CO2 in enhanced oil recovery.
- Timescale: utilization often results in products that can re-release CO2 when used or burned, unless permanently mineralized. The climate benefit depends on the product's lifecycle.
Key differences
- Permanence: storage aims for long-term sequestration; utilization may be temporary unless CO2 is locked into durable materials.
- Value creation: utilization creates marketable products, potentially offsetting capture costs. Storage typically requires policy incentives like carbon credits to cover costs.
- Applicability: utilization can be attractive where the CO2 can displace more carbon-intensive feedstocks; storage is essential for deep emission reductions and negative emissions when combined with bioenergy or DAC.
Considerations for climate impact
Not all utilization provides a net climate benefit. The overall impact depends on the product lifecycle, energy used in conversion, and whether the CO2 is eventually released. Permanent mineralization and long-lived building materials provide clearer climate benefits, while fuel synthesis needs careful assessment to ensure lifecycle emissions are lower than alternatives.
Conclusion
Both storage and utilization are important tools. Storage offers durable removals; utilization offers economic value and pathways to circular carbon, but its climate benefits depend on durability and lifecycle emissions.