Reversible CO2 absorption and release by fatty acid salt aqueous solutions: From industrial capture to agricultural applications

Post-combustion CO2 capture from the flue gas is one of the key technology options to limit global climate change, providing the prospect of permanently lowering the greenhouse gas CO2 concentration, but the efficient use of captured CO2 remains a challenge. In agriculture, the concentration of CO2 in the air is far below the 0.1–1 % CO2 concentration required for plant growth. Therefore, increasing the CO2 concentration around plants can significantly increase crop yields. If a reversible reaction is constructed to absorb CO2 in an industrial flue gas environment and release CO2 under ambient temperature and pressure for improved photosynthesis in plant growth, a bridge may be built linking industrial capture with agricultural application. In this work, we prepared an environment-friendly aqueous system of sodium ricinoleate (NaRcn) to achieve reversible CO2 absorption and release. The carboxylate group of the NaRcn becomes protonated upon the absorption of CO2 in aqueous solutions to yield ricinoleic acid, which is marginally soluble in water, but dissolved in the emulsion formed by the unreacted NaRcn. Effective CO2 release can be achieved by the shift of the absorption equilibrium caused by pressure changes under ambient temperature and pressure. The absorbed CO2 in the NaRcn solutions was applied around the cotton leaves as a CO2 fertilizer, which significantly increased plant growth and biomass formation, indicating potential applications as a fertilizer in agriculture.