Investigating the capability of CO2 absorption via arginine and histidine amino acid salt solutions at high pressures

Abstract

As global energy consumption rises, CO₂ emissions have become a critical concern, prompting extensive research into capture technologies. Conventional aqueous amine solvents face challenges due to the high energy required for regeneration, limiting large-scale applications. To overcome this, novel phase-change solvents, particularly water–amino acid systems, have been proposed to reduce regeneration energy. This study investigated the CO₂ absorption performance of amino acid salts synthesized from arginine and histidine with potassium hydroxide in aqueous N,N-dimethylformamide (DMF). CO₂ absorption capacity was measured under pressures between 5 and 30 bar, reflecting operational conditions of gas sweetening units, and at varying DMF concentrations. Results showed that higher pressure and DMF content enhanced absorption capacity, attributed to simultaneous increases in physical and chemical absorption. Phase analysis using 13C NMR revealed CO₂-related carbon bonds in the solid phase but not in the upper liquid phase, indicating that the liquid phase can be directly recovered without regeneration. Since most CO₂ resides in the solid phase, regenerating only this fraction significantly reduces energy demand. Among the tested solvents, arginine-based solutions displayed the highest absorption capacity, while histidine-based solutions showed the lowest, a trend linked to differences in amine group numbers. Absorption stability was assessed over three absorption–regeneration cycles. Across all amino acid salts, capacity declined only 6–8 % after three cycles, confirming their potential for efficient and energy-saving CO₂ capture.