(668b) Topological Effects on Separation of Alkane Isomers in Metal-Organic Frameworks

The separation of linear and branched alkanes from mixtures is an important industrial process, particularly for enriching the octane rating of gasoline. These separations are commonly done using distillation; however, adsorption offers a less energy-intensive alternative. Metal-organic frameworks (MOFs) are nanoporous, crystalline materials made from inorganic nodes connected via organic linkers. Owing to the large number of nodes, linkers, and functional groups that can be combined to make a unique MOF, there are a virtually unlimited number of possible MOFs. Computational screening can be used to choose materials tailored for a specific application, such as alkane separations.

Nodes and linkers can also be connected in different topologies, or connection networks. In some cases the same set of nodes and linkers may be able to form multiple MOFs with different topologies. These polymorphs are made from the same chemical building blocks but may have radically different pore structures that can affect the adsorption of guest molecules. In this work, we examine the adsorption of C1-C6 hydrocarbons in a large set of topologically-diverse MOFs including many families of polymorphs. We will describe structure-performance relationships in this set of MOFs as they relate to the selective adsorption of linear and branched alkane isomers. We will discuss the influence of the topology on the adsorption capacity and selectivity for separating branched isomers of these alkanes based on the shape and size of the MOF pores and suggest some novel materials that exhibit good selectivity for branched alkane separations.