Dual-functionalized amines as single-component water-lean CO2 absorbents with low-viscosity and high-capacity: The synergistic effect of alkoxy and silyl groups

Abstract

Water-lean CO2 absorbents are promising alternatives to conventional aqueous alkanolamine-based solvents due to the potential benefits of reduced energy input and improved capacity. However, the exponential increase in viscosity with CO2 loading prohibits their industrial deployment by weakening internal mass and heat transfer as well as deteriorating or even blocking pipeline transportation. In this work, a series of alkoxy-silyl dual-functionalized amines have been devised as single-component CO2 absorbents in order to achieve enhanced flowability and efficiency under water-lean conditions. These nonaqueous amines were proved to be highly flowable (8–27 cP at 25 °C, 3–9 cP at 40 °C) under their maximum gravimetric capacity (11–17 wt% at 25 °C, 9–14 wt% at 40 °C), which is comparable to fully loaded 30 wt% MEA (11 cP at 25 °C, 4 cP at 40 °C). The synergistic effect of alkoxy and silyl groups on viscosity and capacity was systematically investigated by means of 13C NMR, in situ FTIR, DSC, VLE and DFT calculation, indicating that the reversible formation of carbamic acid through dual-stabilization, i.e. alkoxy-proton hydrogen bonding and silyl-oxygen complexation, should play the key role in improving both flowability and reaction stoichiometry. Meanwhile, these novel absorbents could be easily regenerated by desorption at 70 °C, and they could maintain structural integrity for at least 2 days under aerobic heating at 80 °C within closed system under CO2-loaded state. Furthermore, the intrinsic CO2-philic nature of both alkoxy and silyl functionalities would offer significant physical absorption under high pressures (20 and 30 bar). Hence, with remarkable flowability, enhanced capacity and easy reversibility, such dual-functionalized amines should certainly represent competitive candidates for further scale up and practical application.