(191d) Separation and Purification of Bioderived Furanic Molecules with Metal-Organic Frameworks

Furanics are important “platform chemical” precursors to polymers, pharmaceuticals, and fine chemicals, and can also be used as biofuels. Conversion of sugars or other feedstocks to furanics often leads to complex product mixtures in which the components are typically heat sensitive, have similar physicochemical properties, and form azeotropes, thus making conventional separation processes such as distillation unfavorable. Such “high-resolution” separations (wherein the molecules possess very similar characteristics) require approaches based upon precisely tailored nanoporous materials as separating agents. In particular, this work introduces the use of metal-organic framework (MOFs) materials to purify furanic products from liquid mixtures generated during processing of lignocellulosic feedstocks. MOFs are a group of newly explored nanoporous materials consisting of metal ions/clusters coordinated to organic linker molecules. Based upon their structural properties as well as preliminary experiments, two classes of MOFs (i.e., UiO and ZIF) are identified as potential adsorbents with high selectivity, capacity, and reusability. Our present focus is on developing two new separation processes for the purification of furfural and 2,5-dimethylfuran (DMF) respectively. A suite of characterization and modeling techniques including single-component adsorption, ideal adsorbed solution theory (IAST) calculations, multicomponent vapor/liquid mixture breakthrough experiments, and pulsed-field-gradient nuclear magnetic resonance (PFG-NMR) are used to build the key structure-property (i.e., adsorption/diffusion) relations. A recent advance (Chiang et al, ACS Sus Chem Eng, 6, 7931-7939, 2018) is the purification of DMF from n-butanol (BuOH) wherein the separation is limited by an azeotrope formation at 90% DMF at 1 bar and elevated temperature. Our current investigation shows that ZIF-8 (with high DMF/BuOH selectivity at low DMF content) and defect-engineered UiO-66 (with high BuOH/DMF at low BuOH content) adsorbents, when used in series, can upgrade dilute DMF feeds from 10 wt% to purified (99%+) DMF and also generate a high-purity (>95%) n-BuOH recycle. Finally, we will discuss the design and optimization of a simulated moving-bed (SMB) adsorptive separation process using ZIF-8 and UiO-66 adsorbents for DMF separation and BuOH recycle from a multicomponent feed mixture feed.