The CO2 capturing ability of cellulose dissolved in NaOH(aq) at low temperature

Abstract

Herein, we explore the intrinsic ability of cellulose dissolved in NaOH(aq) to reversibly capture CO₂. The stability of cellulose solutions differed significantly when adding CO₂ prior to or after the dissolution of cellulose. ATR-IR spectroscopy on cellulose regenerated from the solutions, using ethanol, revealed the formation of a new carbonate species likely to be cellulose carbonate. To elucidate the interaction of cellulose with CO₂ at the molecular level, a ¹³C NMR spectrum was recorded on methyl α-D-glucopyranoside (MeO-Glcp), a model compound, dissolved in NaOH(aq), which showed a difference in chemical shift when CO₂ was added prior to or after the dissolution of MeO-Glcp, without a change in pH. The uptake of CO₂ was found to be more than twice as high when CO₂ was added to a solution after the dissolution of MeO-Glcp. Altogether, a mechanism for the observed CO₂ capture is proposed, involving the formation of an intermediate cellulose carbonate upon the reaction of a cellulose alkoxide with CO₂. The intermediate was observed as a captured carbonate structure only in regenerated samples, while its corresponding NMR peak in solution was absent. The reason for this is plausibly a rather fast hydrolysis of the carbonate intermediate by water, leading to the formation of CO₃²⁻, and thus increased capture of CO₂. The potential of using carbohydrates as CO₂ capturing agents in NaOH(aq) is shown to be simple and resource-effective in terms of the capture and regeneration of CO₂.