Deep eutectic solvent pretreatment alters surface morphology and functionality of activated hydrochar resulting in enhanced carbon dioxide capture
Al Ibtida Sultana, Robert W. Cheatham, M. Toufiq Reza
Abstract
Loblolly pine (LP), an abundant forest residue, could be a cost-effective biomass where pretreatment of LP with deep eutectic solvents (DES), considered as prospective green solvents, was hypothesized to enhance CO 2 capture efficiency by improving surface functionality and porosity in porous carbons derived from pretreated biomass. Thus, the aim of this research study was to produce ultraporous activated hydrochars by pretreating LP using choline chloride-urea, methyl triphenyl phosphonium bromide-ethylene glycol and contrast it with activated hydrochars obtained from untreated LP to assess its performance in CO 2 capture. In this study, porous adsorbent synthesis comprised of pretreating LP and then utilizing it as biomass precursor to be hydrothermally carbonized at 260 °C followed by chemical activation at 800 °C using KOH:hydrochar (wt%/ wt%) 4:1. The adsorbent materials demonstrated to have excellent surface porosity including maximum of surface area, total pore, and micropore volume of 2820 m 2 /g, 1.63 cm 3 /g and 0.62 cm 3 /g respectively. DES pretreatment of biomass resulted in substantial improvement in favorable surface functionality of hydroxyl and ether (O-H and C-O) groups by a maximum of 34.8 %, reflecting a rise in CO 2 uptake capacity in the corresponding activated hydrochars by a maximum of 21.0 %, resulting in 6.31 mmol of CO 2 captured per adsorbent mass (gram) at 3 bar and 25 °C, while heat of adsorption was 18.4–24.0 kJ/mol. Employing statistical tool of principal component analysis (PCA), synergistic effect of improved microporosity and surface functionalities (O-H and C-O groups) was highlighted, with overriding factor in CO 2 uptake determined as surface hydroxyl groups of the adsorbent material.