Sustainable coffee‐based CO2 adsorbents: toward a greener production via hydrothermal carbonization

Abstract

AbstractActivated carbons for adsorption of CO2 under flue gas conditions were prepared by means of hydrothermal carbonization (HTC) and subsequent CO2 activation of spent coffee grounds. The HTC of the samples consisted of their heating at moderate temperature with a high water content in autoclave. A preliminary screening concluded that 1:2 biomass/water ratio (spent coffee grounds as received) and no chemicals added during HTC with further activation in CO2 at 800°C for 1 h are suitable conditions to produce the CO2 adsorbents. In addition, the response surface methodology (RSM) successfully evaluated the combined effect of HTC temperature and dwell time, to maximize the CO2 capture capacity within the experimental region. Both the lowest temperature and dwell time (120°C, 3 h) resulted in the maximum CO2 capture capacity (2.95 wt.%). Two activated carbons (ACs) were then produced: one via hydrothermal carbonization optimized by means of response surface methodology (RSM) followed by CO2 activation (HC‐Co) and the other one by single‐step CO2 activation as described in the Group's patent ES2526259 (AC‐Co). Analysis of the features and performances of the two ACs revealed superior chemical and textural characteristics on HC‐Co for CO2 adsorption under post‐combustion capture conditions; HTC process is the sole responsible of this enhancement. Moreover, the proposed methodology to produce CO2 adsorbents from spent coffee grounds represents a more energy‐efficient approach. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.