Accelerated Synthesis of a Ni₂Cl₂(BTDD) Metal-Organic Framework in a Continuous Flow Reactor for Atmospheric Water Capture

Atmospheric water capture (AWC) has tremendous potential to address the global shortage of clean drinking water. The Ni2Cl2(BTDD) metal-organic framework (MOF) has shown optimal water sorption performance under low relative humidity conditions, but its potentially high production costs, stemming in part from its lengthy multiday synthesis, has hindered widespread implementation. As with most traditional MOF syntheses, the original synthesis of Ni2Cl2(BTDD) involves batch reactors that have intrinsic inefficiencies impacting productivity during scale-up. We report a continuous manufacturing process for Ni2Cl2(BTDD) that can achieve higher yields, reduced solvent use, and drastically faster crystallization times in comparison to the batch process. Optimization of the synthesis space in the flow reactor as a function of residence time, temperature, and solvent volume yields 50% and 40% reductions in methanol and hydrochloric acid consumption by volume, respectively, with a simultaneous 3-fold increase in productivity (defined in units of kgMOF m-3day-1). A computational fluid dynamics (CFD) model was developed to quantitate productivity enhancements in the flow reactor based on improved heat-transfer rates, larger surface-area to volume ratios, and effective residence times. This work adds critical facets to the growing body of research suggesting that the synthesis of MOFs in flow reactors offers unique opportunities to reduce production costs.