Emerging concepts in intermediate carbon dioxide emplacement to support carbon dioxide removal
Substantial upscaling of carbon dioxide capture is possible in the coming decades but existing solutions for storage are projected to be limited in annual capacity by as much as 2–10 GtCO2 per year until mid-century. Temporary storage of CO2 in a solid or liquid state could prove useful for filling this gap in capacity, until more permanent and ideally lucrative CO2 sequestration options come online. There are several concepts for reversible solid-state and chemical CO2 storage, but their advantages and limitations have yet to be reviewed in this context. This article focuses on the physical and chemical aspects of CO2 storage via liquid and solid chemical carriers and sorbents, and gives an overview of the energetics around their use, as well as prospects for their future development. Exciting opportunities for coupling capture and medium to high maturity multi-year storage technologies could support carbon removal in the coming decades. Highlights of the analysis are the remarkable storage capacity of oxalic acid and formic acid (CO2-density of 1857 kg m−3 and 1152 kg m−3, compared with condensed liquid CO2 at 993–1096 kg m−3, respectively), the relative scalability and compatibility of carbonate salts for stationary storage with direct air capture, and the potential promise of multiple carriers for CO2 transportation. Solid sorbents do not achieve such ultra-high storage capacities, but could improve storage over compressed gas tanks on a capacity and energetics basis.