Continuous flow production of metal-organic frameworks

doi:10.1016/j.coche.2015.02.001

Current Opinion in Chemical Engineering

Volume 8, May 2015, Pages 55-59

https://doi.org/10.1016/j.coche.2015.02.001 Get rights and content

Highlights

•
We survey the methods for making metal organic frameworks at scale.
•
Many techniques are found to be bespoke to a particular MOF, contributing to the small number of MOFs available when compared to those known.
•
We highlight recent developments in flow chemistry, which is versatile and does not compromise MOF quality.

While thousands of metal-organic frameworks (MOFs) are known to exist, only a handful are produced commercially. The myriad of potential applications imply that many different MOFs will be required at large scale and versatile production methods could enable this expansion. Continuous flow chemistry is a versatile technique that is compatible with a broad range of laboratory syntheses, with many innovative heating and workup processes, and also with well-established scaled processing methods. With a general synthetic method defined, the state of the art sees a wide and expanding range of MOF materials becoming market-ready in the near future. Key challenges currently lie in increasing processing efficiency, particularly in product work-up.

Graphical abstract

The number of MOFs produced at scale is tiny when compared to the plethora of known structures (Czaja AU, Trukhan N, Mueller U: Chem Soc Rev 2009, 38:1284–1293).

Introduction

Metal-organic frameworks (MOFs) are porous, crystalline materials derived from organic linkers bound periodically by metal coordination centres. MOFs have unprecedented internal surface areas and uniform pores (see Figure 1). Pore size and shape can be tuned by varying the organic linkers, leading to a vast range of possibilities for designing materials with desired functionalities for a raft of potential industrial applications [1, 2, 3, 4, 5]. Two decades of research into MOFs has uncovered a large number of high performing materials in gas storage [6, 7, 8], automotive components [6, 9, 10, 11], carbon capture [12], gas separation [13], drug delivery [14], sensing [15], photoelectronics [16] and catalysis [17^•].

A crucial pre-requisite for accessing the potential applications of MOFs is the ability to routinely synthesise these materials in large quantities (kg scale or higher) with high efficiency. High volume production of MOFs has been slow to develop and whilst more than 4700 MOFs have been reported, only 7 are commercially available [18]. As a consequence, the cost of these materials has remained prohibitively high, and their enormous potential has yet to make a significant impact on prospective markets. Scaled-up production using traditional laboratory routes such as the classical solvothermal synthesis remains challenging due to extended long reaction times and the production of low quality materials. Furthermore, the wide variety of methods for preparing MOFs and the singular nature of some of the preparations provides an inherent risk of inflexibility for any prospective production process. Specifically, switching a bespoke production system to a different MOF material is likely to require significant re-tooling, or indeed a completely new production train.

Section snippets

MOF synthesis chemistry

The classical synthesis of MOFs involves mixing solutions of the metal salt and organic linker, placing the mixed solution in a sealed reaction vessel and heating it to promote the growth of insoluble frameworks that precipitate as fine crystals [19]. This synthesis method is known as solvothermal synthesis, the reaction takes place over days or hours. Earlier slow solvent evaporation methods take place over days or weeks, but may still be employed to produce very large single crystals. The

The remaining challenge

Flow chemistry and continuous flow manufacturing are poised to impact the future synthesis of metal organic frameworks. The reproducibility of reaction conditions and therefore product quality have proven to exceed those obtained by batch processing and importantly, flow has enabled, for the first time, access to a broader range of MOFs at commercially viable quantities via a unified synthesis platform. Remaining challenges in the field relate to the downstream processing of crude reaction

References and recommended reading

Papers of particular interest, published within the period of review, have been highlighted as:

• of special interest
•• of outstanding interest

Acknowledgements

MRH acknowledges FT 130100345 for funding. All authors acknowledge the CSIRO for funding support.

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Continuous flow production of metal-organic frameworks

Highlights

Graphical abstract

Introduction

Section snippets

MOF synthesis chemistry

The remaining challenge

References and recommended reading

Acknowledgements

Int J Hydrog Energy

Chem Soc Rev

Chem Soc Rev

Chem Soc Rev

Chem Soc Rev

Q Nat Chem

Mater Chem

Mol Simul

Chem Soc Rev

Chem Eng Tech

Am Chem Soc

Chem Rev

Energy Environ Sci

Am Chem Soc

Chem Rev

Chem Commun

ACS Catal

Chem Mater

Acta Cryst B

J Chem Ed

J Mater Chem

J Am Chem Soc

AIChE

Adv Mater

Nat Chem

Chem Commun