Theoretical and experimental studies on the separation of cinnamyl acetate and cinnamaldehyde by adsorption onto a β-cyclodextrin polyurethane polymer

Abstract

In order to isolate cinnamyl acetate (CAc) and cinnamaldehyde (CA), which coexist in cinnamon oil, a crosslinked polymer of β-cyclodextrin polyurethane (CDPU) was synthesized via a facile route and investigated as a selective adsorbent. The successful crosslinking was confirmed by FTIR, TG-DSC, XRD, SEM and N₂ adsorption–desorption analysis. The adsorption mechanism was investigated through a series of instrumental analyses and theoretical calculations, indicating that the combination of non-covalent interactions (e.g., hydrogen bonding, hydrophobic interactions) accounts for the superior affinity of CAc to CDPU, compared with CA. The adsorption behaviors of CAc and CA on CDPU were performed in the static adsorption mode, in which CDPU exhibited a selective adsorption property to CAc. The adsorption kinetics and isotherms in a single component system agreed well with the pseudo-second-order kinetic model and Freundlich isotherm model, respectively. It is noteworthy that the equilibrium adsorption amount was enhanced in the presence of the co-solute, presumably resulting from the cooperative effect arising from Lewis acid–base and π–π stacking interactions between the adsorbed CAc and CA molecules. Due to the stronger adsorption affinity of CAc to CDPU, adsorption enhancement of CAc in the presence of CA is greater than that of CA in the presence of CAc, resulting in higher CAc/CA selectivity with increasing concentrations of the equimolar mixture of CAc and CA. Additionally, CDPU could be easily regenerated and maintained high adsorption capacities and separation efficiency even after six adsorption/desorption cycles.