Purification of 2,5-Dimethylfuran from n-Butanol Using Defect-Engineered Metal–Organic Frameworks

The removal of n -butanol (BuOH) from 2,5-dimethylfuran (2,5-DMF) is an important issue in the sustainable production of 2,5-DMF from fructose in biphasic organic solvents such as BuOH. The formation of an azeotrope (at 90 mol % 2,5-DMF) renders conventional distillation ineffective for producing pure 2,5-DMF. Here we describe a highly butanol-selective adsorption process based upon zirconium terephthalate (UiO-66) metal organic frameworks. In particular, defects created by monoacid modulators lead to increased surface polarity and pore volume, leading to enhanced butanol selectivity and capacity. The adsorption behavior of 2,5-DMF and BuOH in pristine (nonmodulated), benzoic acid-modulated (BA) and formic acid-modulated (FA) UiO-66 MOFs, as well as the structural and textural characteristics of these materials, are investigated in detail via a suite of characterization methods. Unary adsorption isotherms show a tunable increase in the BuOH adsorption selectivity in the order UiO-66 < BA-UiO-66 < FA-UiO-66. Binary vapor breakthrough measurements then show that the FA-UiO-66 adsorbent achieves excellent BuOH/2,5-DMF selectivity (∼13) and adsorption capacity (∼6 mmol/g), allowing a 99+% pure 2,5-DMF breakthrough product and a BuOH-rich (60–96%) recycle stream. Detailed analysis of binary breakthrough data at different 2,5-DMF compositions and comparison with ideal adsorbed solution theory predictions, show that the increased selectivity is due to selective interactions of BuOH with the polar defect regions in the UiO-66 framework. Finally, liquid-phase breakthrough measurements with a 90 mol % 2,5-DMF feed and pelletized FA-UiO-66 demonstrates a high liquid–solid equilibrium selectivity (8) that is thermodynamically consistent with its vapor–solid equilibrium selectivity.