Adsorptive Separation of Furfural/5-Hydroxymethylfurfural in MAF-5 with Ellipsoidal Pores
Yu Zhao, Jun Xu, Jing Wang, Jinglan Wu, Meizhen Gao, Bin Zheng, Hong Xu, Qi Shi, Jinxiang Dong
Abstract
The objective of this work is to study the adsorptive separation of the biomass-derived furfural (Fur) and 5-hydroxymethylfurfural (5-HMF). Because Fur and 5-HMF have similar ellipsoidal shapes, the diffusion of the larger 5-HMF may be blocked by the elliptical window of adsorbents. Thus, two zeolitic imidazolate framework (ZIF) materials with the identical chemical composition, MAF-6 and MAF-5, were used as spherical and ellipsoidal pore adsorbents, respectively. In the dynamic column adsorption of a binary-component system (Fur/5-HMF, 5/5 wt %) in an aqueous solution, the adsorption amounts of Fur on MAF-6 display a 13% decrease compared with the single-component system, whereas the adsorption amounts of Fur on MAF-5 are identical to those obtained in the single-component system and the amounts of adsorbed 5-HMF are almost negligible. Thus, the Fur/5-HMF selectivity is only 6.4 for MAF-6, whereas the selectivity reached 115.8 for MAF-5. The results show that the narrow elliptical window/ellipsoidal tile of MAF-5 enhanced separation selectivity compared with the larger circular window/spherical cage of MAF-6. In addition, the general rate model and density functional theory calculations further verify that the elliptical window of MAF-5 exhibits a strong mass-transfer barrier that must be overcome for the diffusion of the larger 5-HMF molecules.