Tuning CO2 reaction enthalpy via metal complexes for advanced amine technology

Abstract

Amine-based CO₂ capture technology suffers from great energy penalty drawbacks, hindering its industrial application. The large capture energy consumption primarily rests in the enthalpy irreversibility of the CO₂ capture process where the reaction heat released in CO₂-absorption is wasted but the same amount of CO₂ reaction enthalpy is supplied to liberate CO₂ in CO₂-desorption. The present study proposes a new method of metal-ion-mediated amine regeneration (MMAR) that employs the metal–amine complexes as an internal energy buffer to tune the CO₂ reaction enthalpy. Using Ni(II) metal ions, we performed experimental calorimetric measurements to provide direct evidence that Ni(II)-ion additives reduce the CO₂ reaction enthalpy over the cyclic CO₂ loading, i.e., from 89.1 kJ per mol CO₂ to 78.5 kJ per mol CO₂ in the benchmark MEA solvent (11.9% reduction), and further to 62.9 kJ per mol CO₂ in the blended MEA/AMP solvent (29.4% reduction) at a Ni(II) concentration of 0.3 M. The decreased reaction heat is primarily attributed to the change in the reaction pathway from carbamate to bicarbonate formation, as well as the chemical heat buffer of the Ni(II)-MEA complex for enthalpy recovery and its in situ utilization. The reduced CO₂ reaction heat contributed to a decreased regeneration energy from 128.3 kJ per mol to 101.5 kJ per mol CO₂ in the blended MEA/AMP system, a 20.9% energy reduction as compared to the reference MEA. A comprehensive experimental investigation also revealed that the Ni(II)-ion additive has a negligible effect on cyclic CO₂ capacity, absorption kinetics, and solvent viscosity, and more importantly, it has a marginal influence on solvent degradation. The new chemistry of the MMAR system is anticipated to provide the amine solvent system with tunable reaction enthalpy, enabling a better energy performance in amine-based CO₂ capture.