Carbon capture and conversion promoted by deep eutectic solvent and produced water

The development of efficient CO₂ capture routes to tackle the unprecedently high concentrations of this gas in the atmosphere is one of the world’s top-priority technological targets.¹ Recently, CO₂ absorption in deep eutectic solvents (DESs) has attracted scientific attention because of their adaptability compared to traditional ionic liquids and aqueous amine solutions.² Materials that can catalyse the conversion of carbon dioxide CO₂ into chemicals are gaining increasing attention.³ In oil and gas industry, the produced water is a term used for the water associated with oil during the extraction process. Sodium, chloride, calcium, magnesium, strontium, sulfate, bromide, potassium, iodide and bicarbonate are found abundantly in produced water with high salinity. Here, we describe the combined use of produced water aqueous solution of DES to effectively absorb and convert CO₂ into carbonates, demonstrated by solution and solid state NMR. In the reference experiment performed with DES solution in distilled water, only carbon capture is observed. At a first step, ¹³C NMR in solution proves the nucleophilic attack of CO₂ by DES. As CO₂ flow is maintained, HCO₃^- formation begins in a second step as the characteristic carbon NMR signal is detected. HCO₃^- increases and carbamate decreases during the course of reaction. Provided that the CO₂ flow is maintained, physiosobed is detected around 124ppm in the ¹³C NMR spectrum in solution. At the end, physiosobed CO₂ increases, HCO₃^- concentration reaches equilibrium and carbamate is no longer detected in the ¹³C NMR spectrum in solution. In the experiment performed with DES solution in produced water, both carbon capture and conversion is observed, as carbonate formation can be detected through the analysis of the precipitate formed by ¹³C solid state NMR.

References

[1] A. M. de Castro, L. A. Neves, M. C. Corvo, E. J. Cabrita, J. G. Crespo, Separation and Purification Technology, 2022, 280, 119921.

[2] A. A. Manafpour, F. Feyzi, Mehran Rezaee, Scientific Reports, 2024, 14, 19744.

[3] Koki Yagihara, Jialing Ni, Anqing Wang, Hajime Ohno, Yasuhiro Fukushima, Green Chem., 2025, 27, 1679.

Acknowledgments

PETROBRAS, Firjan-SENAI.