ZIF-7 Synthesis Analysis

Separation constitutes approximately 60% of the energy expenditures in the petrochemical industry.  Enhancing this process is one way we can progress toward a more sustainable energy consumption model; separation membranes represent such a solution.  For instance, Metal Organic Framework membranes, or MOFs, can utilize the porosity of their metallic ion-organic molecule coordination for separation.  MOFs incorporate a large range of materials, yet zeolitic imidazolate frameworks (ZIFs), are of particular interest, specifically ZIF-7 and ZIF-8.  ZIFs are chemically and thermally stable and have desirable “window” sizes for olefin and paraffin separation.  Initial studies of ZIF powders showed very strong selectivity.  Unfortunately, these results were not reflected in the actual application of ZIF membranes, an issue commonly attributed to the flexibility of the pore sizes.  More recently, ZIF-8 was synthesized in water – as opposed to the traditional DMF – with excellent consequent separation, indicating that the issue may lie within microstructure or the activation process.  This was further exemplified in a study which synthesized ZIF-78 in DMF but used a progressive solvent exchange process to switch to methanol, eventually producing a high-performing ZIF membrane.  We plan to use a similar process to synthesize ZIF-7 in an effort to enhance its performance.