A series of ammonium-based protic ionic liquids (APILs) namely ethanolammonium pentanoate ETOHAC5, ethanolammonium heptanoate ETOHAC7, triethanolammonium pentanoate TRIETOHAC5, triethanolammonium heptanoate TRIETOHAC7, tributylammonium pentanoate TBAC5 and tributylammonium heptanoate TBAC7 was synthesized via proton transfer. Their structural confirmation and physiochemical properties namely thermal stability, phase transition, density, heat capacity (Cp) and refractive index (RI) have been determined. Specifically, TRIETOHA APILs have crystallization peaks ranging from �31.67 to �1.00 °C, owing to their large density values. A comparison study revealed the low Cp values of APILs in comparison to monoethanolamine (MEA) which could be advantageous for APILs to be used in CO2 separation during recyclability processes. Additionally, the performance of APILs toward CO2 absorption was investigated by using a pressure drop technique under a pressure range of 1-20 bar at 298.15 K. It was observed that TBAC7 recorded the highest CO2 absorption capacity with the value of 0.74 mole fraction at 20 bar. Additionally, the regeneration of TBAC7 for CO2 absorption was studied. Analysis of the measured CO2 absorption data showed marginal reduction in the mole fraction of CO2 absorbed between fresh and recycled TBAC7 thus proving the promising potential of APILs as good liquid absorbents for CO2 removal. © 2023 The Royal Society of Chemistry