Purification of Metal-Organic Framework Materials

Purification of Porous Materials NU 2009-007 Inventors Omar Farha Joseph Hupp Abstract Northwestern researchers developed a solvent-based density-discrimination process particularly suited for metal-organic framework isolation and purification. A tremendous development in the area of functional, nanostructured materials is the emergence of structurally well defined, permanently microporous metal-organic framework materials (MOFs) which are generally synthesized via one-pot solvo-thermal methods. This invention provides a process for rapidly purifying MOF materials under conditions commonly encountered in their synthesis. Pure MOF products are separated and isolated by exploiting solvent / MOF density differences. Parent solvent CH2BrCl readily suspends crude MOF mixtures due to its high density (1.99 g/cm3). Addition of a second less dense miscible solvent affords the appropriate solution properties where the MOF mixture separates into suspended and settled fractions, enabling separation. Powder x-ray diffraction (PXRD) data can be employed for both fractions and compared to candidate PXRD patterns for product validation. Once conditions are established, MOF separation typically occurs rapidly, important for process scale-up. The process has been demonstrated effective in the following common MOF preparation problems: (1) isolation of a desired crystalline MOF from a mixture containing a second compound comprising the same organic-strut and/or metal-ion building blocks, (2) separation of a desired mixed-strut material from a second crystalline MOF containing only a single type of strut, and (3) separation of a non-interpenetrating MOF from an otherwise identical material consisting of catenated networks. Isolation of even minor components (e.g. 15%) of mixed phases have been realized. The process should also prove applicable to separating MOFs from linear coordination polymers or insoluble metal salts. Applications Gas storage Chemical separations Selective catalysis Advantages Scalable Broadly applicable Rapid product isolation and purification IP Status A patent application has been filed.