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.___________________________________________________________________________

Synthesis, Structure, and Selected Properties of Aluminum-, Gallium-, and Indium-Based Metal-Organic Frameworks

“…Electrochemistry, mechanochemistry, spray drying [57], and ultrasonic methods [58] have also been employed. For the G13-MOFs mainly solvothermal syntheses in autoclaves under conventional heating have been reported but recently, albeit only for the formation of Al-MOFs, room temperature syntheses in water [59,60], and continuous synthesis were described (see Section 5.6.1) [61][62][63]. The solvothermal route has two significant advantages compared to other synthesis methods: (i) It is relatively simple and cost-effective to employ on the lab scale, (ii) it allows for the usage of poorly soluble starting materials, and (iii) variation of chemical and process parameters often leads to new crystalline compounds.…”

“…Hence synthesis methods compatible with industrial needs, that is, low reaction temperatures, low-cost and non-corrosive starting materials, and appropriate metal sources, have been developed [2,63]. Importantly, the use of alkaline metal salts of the linker molecules have been shown to allow the room temperature synthesis of Al-MIL-53 [60] and aluminum fumarate [59].…”

“…Due to the high reproducibility of the synthesis conditions, once the reaction conditions have been established, larger amounts of the product can be in principle obtained by simply running the system for a longer time. The archetypical Al-MIL-53 was obtained at 500 g scale with space-time yields of 1300 kg m −3 d −1 [63]. This required the implementation of HPLC pumps into the process which is run at 250 ∘ C. However, the generated autogenous pressure can be challenging for the synthesis at larger scale.…”

Towards scalable and controlled synthesis of metal–organic framework materials using continuous flow reactors

“…40 The groups of Rubio-Martinez et al 38 and Taddei showing massive expansion or contraction once water, or other guest molecule is removed from the pores, after the material has been prepared. 41 Bayliss et al produced MIL-53(Al) using the sodium salt of terephthalic acid and water as the solvent, 37 while Taddei et al used DMF as solvent in their continuous microwave reactor, giving much superior space-time yields. 39 Surface area data proved the high quality of the samples produced, being consistent with the expected structural flexibility of the material.…”

Methane Adsorption in Metal–Organic Frameworks Containing Nanographene Linkers: A Computational Study

“…The use of MOFs with the rht topology, based on a singular net for the combination of 3-and 24-connected nodes, removes any concern for catenation (interpenetration or interweaving of multiple frameworks) and makes them an ideal target in design of ultrahigh porosity. The desolvation and associated activation using supercritical CO 2 and solvent exchange and processing 19,43 is a particularly promising method that allows generation of MOFs with ultrahigh surface areas.…”