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Direct air capture of CO2 via aqueous-phase absorption and crystalline-phase release using concentrated solar power


Using negative emissions technologies for the net removal of greenhouse gases from the atmosphere could provide a pathway to limit global temperature rises. Direct air capture of carbon dioxide offers the prospect of permanently lowering the atmospheric CO2 concentration, providing that economical and energy-efficient technologies can be developed and deployed on a large scale. Here, we report an approach to direct air capture, at the laboratory scale, using mostly off-the-shelf materials and equipment. First, CO2 absorption is achieved with readily available and environmentally friendly aqueous amino acid solutions (glycine and sarcosine) using a household humidifier. The CO2-loaded solutions are then reacted with a simple guanidine compound, which crystallizes as a very insoluble carbonate salt and regenerates the amino acid sorbent. Finally, effective CO2 release and near-quantitative regeneration of the guanidine compound are achieved by relatively mild heating of the carbonate crystals using concentrated solar power.

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This research was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division.

Author information

F.M.B. performed and analysed the CO2 absorption and sorbent regeneration experiments, and the potentiometric titration measurements. N.J.W. optimized and scaled up the synthesis of PyBIG, optimized the CO2 absorption and sorbent regeneration with PyBIG, and performed the solubility measurements. C.A.S. designed and synthesized the PyBIG compound. M.K.K. performed and analysed the DSC and TGA measurements. R.C. led the project, conceptualized the study, performed the measurements with concentrated solar power and wrote the manuscript. All authors contributed to discussions and manuscript reviews.

Competing interests

A US patent application (no. 15/813,557), currently pending, has been filed, with R.C., C.A.S. and N.J.W. as inventors, covering the DAC system described in this manuscript.

Correspondence to Radu Custelcean.

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Supplementary Information

Supplementary Figures 1–12, Supplementary Tables 1–3 and Supplementary Methods

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Fig. 1: CO2 capture from ambient air with PyBIG.
Fig. 2
Fig. 3: Representative CO2-loading curves for aqueous amino acid solutions.
Fig. 4: Amino acid regeneration.