Piperazine-impregnated silica aerogel for direct air capture of CO2 for prevention of urea formation

Abstract

Direct air capture (DAC) of CO2 using solid sorbents is a promising negative emission technology to reduce global greenhouse gas emissions. Despite many advantages of alkyl-amine-based adsorbents, degradation caused by urea formation under a dry CO2 regeneration remains a challenge. Herein, we hypothesized that certain nitrogen-containing heterocyclic compounds can contribute toward suppressing urea formation by the ring structure and thus, selected piperazine (PZ) as a representative chemical. PZ was wet-impregnated onto a silica aerogel (PZ/silica) with controlled pore size and volume. The synthesized sorbents exhibited high CO2 sorption uptake and kinetics. In a cyclic test via temperature swing adsorption (adsorption: calibrated 200 ppm CO2; desorption: dry CO2), PZ/silica exhibited stable and high adsorption capacities (average 1.3 mmol/g over 24 cycles). The suppression of urea formation in PZ/silica under extended dry CO2 regeneration was demonstrated using an in-situ diffuse reflectance infrared Fourier transform spectroscopy, thereby proving the above hypothesis. PZ/silica showed good anti-oxidation performance of CO2 capture, 1.6 mmol CO2/g, after 12 h oxidation under 21% O2 balanced with N2. Besides, PZ/silica maintained a CO2 adsorption uptake of 0.79 mmol/g after the preliminary adsorption of H2O. This study proposes a novel way to synthesize DAC solid adsorbents using N-containing heterocyclic compounds.