Synthesis of metal–organic frameworks by continuous flow

Abstract

A continuous flow process for the synthesis of a metal–organic framework using only water as the reaction medium and requiring only short residence times is described. This affords a new route to scale-up of materials incorporating many of the principles of Green Chemistry. The process is demonstrated by the synthesis MIL-53(Al) via continuous flow reaction requiring only 5–6 minutes with a space time yield of 1300 kg m⁻³ d⁻¹. We have demonstrated the synthesis of 500 g of MIL-53(Al) using this process, which can be scaled-up further by simply feeding further solutions of metal salt and ligand through the reactor. The product has a higher surface area and a better colour than a commercially produced sample of this MOF. In addition, a new and effective method for the extraction of terephthalic acid from within the pores of MIL-53(Al) using supercritical ethanol has been developed, representing a new methodology for activation and removal of substrates from porous hosts.