Batch-screening guided continuous flow synthesis of the metal-organic framework HKUST-1 in a millifluidic droplet reactor

Metal-organic frameworks (MOFs) are a class of crystalline and porous adsorbents, with wide-ranging applications in gas separations, membrane materials as well as sensors. Commonly used batch synthesis techniques for MOF production are limited by low productivity, high operating costs, and slow crystallization timescales, severely impeding the large-scale manufacturing of these materials. However, batch synthesis is a useful and easy technique to screen multiple reaction parameters to find an optimal chemistry. Therefore, in this study, we have used the batch process and screened a multidimensional reaction space consisting of 45 sample variations based on the crystallinity, yield, and instantaneous precipitation, which could lead to tube clogging under flow conditions. We have found one optimized reaction chemistry, that could be used in flow conditions, which in this study is a novel millifluidic droplet-based reactor for the continuous synthesis of HKUST-1 crystals. The biphasic flow in the millifluidic reactor consisted of droplets of the reactant solution, dispersed in a continuous phase of silicone oil. We investigate the differences in the quality and quantity of HKUST-1 synthesized via the continuous and batch techniques. Moreover, we have demonstrated that the HKUST-1 samples prepared via the continuous synthesis in a droplet based millifluidic reactor, at an ultra-low residence time exhibit excellent physical properties comparable to that obtained for the samples prepared by the traditional batch process. A clean, easy-to-install, and reusable millifluidic reactor presented in this work may pave the path for an economically viable, large-scale synthesis of HKUST-1.